industrial perspectives for bioethanol

Transcrição

INDUSTRIAL
PERSPECTIVES
FOR BIOETHANOL
DIRETORIA EXECUTIVA
Mauricio Prates de Campos Filho
Diretor Executivo
Nelson Antonio Pereira Camacho
Diretor para Assuntos Administrativos e Financeiros
Saul Gonçalves d’Ávila
Diretor para Assuntos Científicos e Tecnológicos
INDUSTRIAL
PERSPECTIVES
FOR BIOETHANOL
Eduardo P. Carvalho Isaias C. Macedo José Luiz Olivério
Pedro Wongtschowski Francisco I. Pellegrini Flávio C. Cavalcanti
Anderson F. Cunha Silvia K. Missawa Gonçalo A. G. Pereira
Silvio R. Andrietta Maria da Graça Stupiello Andrietta
Adrie J. J. Straathof Çagri Efe Luuk A. M. van der Wielen
Peter M. M. Nossin Telma T. Franco Carlos Eduardo Vaz Rossell
H. J. Veringa P. Alderliesten
Edited by
Telma Teixeira Franco
Coleção UNI E M P Inovação
INDUSTRIAL PERSPECTIVES FOR BIOETHANOL
ISBN 85-98951-06-4
Av. Paulista, 2.200 - 16 o andar
Tel. (11) 2178-0466
Fax. (11) 3283-3386
[email protected]
www.uniemp.org.br
01310-300 São Paulo - SP
Produzido no Brasil
2006
LIST OF CONTENTS
Preface
Telma T. Franco
9
Section 1
Industrial Perspectives for Bioethanol:
a Brazilian approach
11
Chapter 1
Ethanol from Sugar Cane in Brazil:
the Industrial Technology Perspectives
Eduardo P. Carvalho and Isaias C. Macedo
13
Chapter 2
Technological evolution of the Brazilian
sugar and alcohol sector:
Dedini’s contribution
José Luiz Olivério
19
Chapter 3
Insertion of bioethanol into a new paradigm
for the Brazilian chemical industry
Pedro Wongtschowski, Francisco I. Pellegrini
and Flávio C. Cavalcanti
33
Section 2
BioTechnology and Engineering Science integration
for Chemical and Fuel Industries
57
Chapter 4
Industrial Potential of Yeast Biotechnology
in the Production of Bioethanol in Brazil:
the Example of Conditional Flocculation
Anderson F. Cunha, Silvia K. Missawa
and Gonçalo A. G. Pereira
59
Chapter 5
Optimization and Limits of Ethanol Production
Silvio R. Andrietta
and Maria da Graça Stupiello Andrietta
77
Chapter 6
Innovation and sustainability through
industrial biotechnology
Adrie J. J. Straathof, Çagri Efe,
Luuk A. M. van der Wielen,
Peter M. M. Nossin and Telma T. Franco
91
Chapter 7
Advances of the Brazilian production of chemicals
and other products from biomass
Telma T. Franco
107
Section 3
Role of Bioethanol in the Energy Landscape
121
Chapter 8
Conversion of lignocellulose biomass (bagasse and straw)
from the sugar-alcohol industry into bioethanol
Carlos Eduardo Vaz Rossell
123
Chapter 9
Advanced techniques for generation of energy
from biomass and waste
H. J. Veringa and P. Alderliesten
143
Preface
Telma T. Franco
The sixth volume of Uniemp collection is dedicated to the Industrial
perspectives of Bioethanol. It is organized in three sections, the Brazilian approach to the industrial perspectives for Bioethanol; the biotechnology and engineering science integration for chemical and fuel
Industries and finally, the role of Bioethanol in the energy landscape.
Each of these sections aims to cover different views of experts from
academic, industrial and governmental areas.
The Brazilian industrial perspectives for Bioethanol is covered in
three chapters. Different views of the industrial sector are described,
namely that of the sugar cane producers, of the equipment manufacture
and the view of the chemical industry. The first chapter was written by
the president of the São Paulo Sugarcane Association, Eduardo Pereira
de Carvalho with a collaboration of Isaías Macedo; the second was written
by the director of Oxiteno, Pedro Wongtschowski, with the collaboration
of Francisco I. Pellegrini and Flávio C. Cavalcanti and the third chapter
was written by the Senior Operational Vice President, Dedini S/A Indústrias de Base, José Luiz Olivério.
Carvalho and collaborator address the current perspectives of the
sugarcane producers. The text describes their current context, some
technological achievements and evolution, discusses medium and longterm future technologies and points out the potential and feasible new
products from Bioethanol and sugarcane.
Pedro Wongtschowski and collaborators, from Oxiteno, discuss the
insertion of Bioethanol for the Brazilian chemical industry, the competitiveness of Bioethanol as fuel and raw material for the chemical industry.
10
Jose Luis Olivério discusses a model to explain the development of
the sugar cane industry. The model is divided in five stages that refer to
five different aspects: the capacity of equipment, the overall yield, the
sugar cane energy, the improvement of the use of sugarcane products
and byproducts and the view of a sugar and alcohol mill as energy-andfood- producing unit.
The integration of biotechnology and engineering sciences for changes in chemical and fuel industries is addressed by four experts. Fundamental aspects of molecular biology and an application case are outlined
by Gonçalo Amarante Guimaraes Pereira & collaborators, from Unicamp.
A simple case describes how a microorganism can be modified to satisfy
the needs of an industrial technological process.
Engineering aspects of fermentation are discussed by Silvio Andrietta and Maria da Graça Stupiello Andrieta, from Unicamp. The possibilities for optimizing ethanol production, the limiting factors for ethanol
productivity and yields and the environmental impact and restrictions
are discussed.
Future possibilities for industrial plant are addressed by Adrie J.J.
Straathof, Çaðri Efe and Luuk A.M. van der Wielen (Delft University of
Technology) Peter M.M. Nossin (DSM Corporate Technology) and Telma
T. Franco (Unicamp), with emphasis on the integration of hydrolysis
and fermentation to Bioethanol.
The seventh chapter and the last of this section is written by Telma
T. Franco (Unicamp), who reviews the advances of the Brazilian production of chemicals and other products from biomass.
The role of Bioethanol in the energy landscape is covered by two
chapters.
Carlos Eduardo Vaz Rossell, from the Energy group of NIPE, explores
the complexity of the sugarcane bagasse and of straw. Their chemical
composition and morphological aspects are discussed.
H. J. Veringa and P. Alderliesten, from the Energy research Centre
of the Netherlands, emphasize the conversion process and equipments
for the generation of energy from biomass and waste.
Section 1
Industrial Perspectives
for Bioethanol:
a Brazilian approach
Ethanol from Sugar Cane in Brazil:
the Industrial Technology Perspectives
Eduardo Pereira de Carvalho
Isaias C. Macedo
Introduction
The establishment of the ethanol program in Brazil has required
extensive technology development in production, logistics and end utilization in the last 30 years. It is expected that in the next 10 – 20 years
a much more efficient use of the sugar cane biomass will increase significantly the range of products and their value. Energy (both power and
liquid fuels) may become the most important fraction of the sales. Technologies in development (worldwide) may be the key for this transformation: the hydrolysis of biomass (bagasse and trash), as well as
many different fermentation technologies; and the biomass gasification,
leading to power or fuel synthesis. Sugar cane appears as an ideal feedstock for the future “bio-refineries”, for its relatively low cost, large
availability and an interesting mix of 1/3 sucrose, 2/3 pre-processed
ligno-cellulosic material.
The context today
In 2005, 380 M t sugar cane were processed in 310 sugar mills in
Brazil (41 new are being built), yielding 26 M t sugar and 15.7 M m3
ethanol. Brazil is the world’s largest producer of sugar cane (33.9%),
sugar (18.5%) and ethanol (36.4%). It is also the largest exporter of sugar
and ethanol.
14
Ethanol corresponds to 40.6% of the fuel for light vehicles (total
fleet: 19.2 M vehicles). Flex-fuel cars correspond to more than 70% of the
sales of new units (end of 2005), and all the gasoline is blended with
20% ethanol.
Ethanol production and use in Brazil has been considered an important example of the introduction of renewable energy sources, with a
large scale of production. Complete process integration was obtained,
at the sugar mills: flexibility, better sugar quality and reduced losses. It
required extensive technology development in production, logistics and
end utilization in the last 30 years. It also required specific legislation,
initial subsidies and a great deal of negotiation among producers, automakers, government officials and the “competition”: the oil industry.
Highlights in technology evolution
From 1980 to 1990 some achievements were important:
·
·
·
··
·
·
Introduction of cane varieties developed for Brazil; stillage use
in ferti-irrigation; biological controls in cane production and improvement in agricultural operations (cultivation, harvesting)
Development of the “4 roll” milling system; microbiology for
large scale “open” fermentations; production flexibility: synergy ethanol/
sugar; and increased energy production (self-sufficiency)
Ethanol specifications; engine (E-100) developments; blending,
storage and transportation systems
From 1990 to 2000 the developments included:
Optimization of cane harvesting, loading and transportation;
mapping of the sugar cane genome; plant transformations; harvesting
mechanization
Selling of surplus power; advances in industrial automation;
better technical management systems (agriculture and industry)
The Flex-fuel engines
Net results for the 1975-2000 period, in S. Paulo, indicate increases
of 33% (t cane/ha); 8% (sugar % cane); 14% conversion: (sugars in cane)
ETHANOL FROM SUGAR CANE IN BRAZIL: THE INDUSTRIAL TECHNOLOGY...
15
to (ethanol); and also 130% in fermentation productivity, m3 ethanol /
(m3 reactor . day)
For the Brazilian Center South, averages in 2003/4 were
··
·
Sugar cane productivity: 84.3 t / ha
Sugar % cane: 14.6
Industrial conversion: 86%
A frequently asked question relates to the possibilities of yet large
advances for the next years. Can we say that the sugar cane agro-industry
in Brazil has a “mature technology” status, with worldwide lowest costs
and high product quality? Are we looking for continuous, small improvements, from now on?
Technologies for the future
Some of the most promising advances for the next years may be:
·
·
··
·
Technology evolution: (precision agriculture, separation processes, integrated harvesting / loading / transportation systems, industrial automation)
By- products: surplus electricity (already started); ethanol from
bagasse and trash (5 – 10 years?)
Sucrose derived products (being implemented)
Medium – long term perspectives for sugar cane genetically modified varieties
Medium-long term: the “bio-refineries” with full utilization of
sucrose and wastes (bagasse and trash)
The full utilization of biomass wastes is being considered for its
very large potential, for energy or materials production. As an example,
sugar cane in Brazil (2005: 60 M t sucrose; 120 M t ligno-cellulosic
material) could yield (using 30% surplus bagasse + 50% trash could) 48
M dry t of biomass wastes, with a very low recovery cost (~1 €/GJ).
Average (world) costs for biomass today (wastes, energy farms) are
2 - 3 • /GJ; plans for 1.5 • /GJ, future.
16
It is clear that the sugar cane industry can invest in the full utilization of 2/3 of its raw material (the “wastes”, today) to promote a large
diversification, in the same scale as ethanol is a diversification (in Brazil).
Two processes (with many variations) may be the key to the “bio-refineries” in the future; both are in development today:
·
·
Biomass (hydrolysis) —— > sugars, (ethanol, other): commercial
~ 2010 to 2020
Biomass (gasification) —— > power or synthesis fuels (ethanol,
DME, gasoline, diesel); commercial ~ 2015 to 2025.
Both need more efficient, cheaper technologies and cheaper biomass.
Biomass gasification brings two important concepts: power generation with BIG-CC cycles; and more recently fuel synthesis. Both need
significant cost reduction to compete with oil at $30. /bbl, or with “conventional” electric energy. Needed R&D includes: biomass feeding systems; gasification for medium Heating Value gas, using air; gas cleaning;
turbines for low HV gas; synthesis reactors (example, liquid phase reactors for DME synthesis).
Biomass hydrolysis, yielding sugars from ligno-cellulosic materials,
has strong R&D efforts in pilot plant phase (some pre-commercial) aiming
at cost reduction; it could lead to a wide range (and large scale) applications worldwide. Future pre-treatments would be mostly physical (steam
explosion, Liquid Hot Water); hydrolysis/fermentation processes could
be coupled, and use the 5 and 6 Carbon sugars (for ethanol). Future
processes could reach 52% of energy recovery from biomass (in ethanol)
against 35% today. The research programs include demonstration of pretreatment physical processes; biomass feeding; microorganisms and
enzymes for CBP (and simpler) processes.
Other uses of sucrose (or sugars from hydrolysis)
There has been significant expansion in the last 15 years, worldwide,
with some products reaching 1 M t / year.
ETHANOL FROM SUGAR CANE IN BRAZIL: THE INDUSTRIAL TECHNOLOGY...
17
·
·
··
·
·
They represented 23% of the global sweetener market (2002):
fructose, glucose, and polyols.
Organic acids (citric, gluconic, lactic, ascorbic): 0.7 M t / year
(1998)
Amino-acids (MSG, lysine, threonine): ~1.5 M t / year
Polyols: 1.4 M t / year (48% sorbitol, 2001); glycerol (from all
sources) was 0.8 M t / year (2000).
Enzymes: smaller volumes, high added value; from all sources,
US$ 1500. M / year, expected to double till 2008.
Plastics: still as a promise: PLA, PHAs, 3-GT; 10 M t / year could
be used only for packaging, substituting for oil derived plastics.
The sugar industry in Brazil has some commercial production: Llysine; MSG; yeast extracts; citric acid; and sorbitol. Plastics (PHB) are
in pre-commercial stage.
Possibilities for “larger scale” products (~1 M t/year) and specialties
(10 – 50k t/year) are being evaluated in many sugar mills.
Ethanol based products have been established in Brazil; they were
discontinued in the 90’s, and are being re-evaluated. From 1980 to 1990
more than 30 products used up to 0.5 M m3 ethanol / year; in 1993 the
installed capacity for 14 products was larger than 100000 t / year.
The analyses for the development of sucrose derived products in
Brazil consider:
·
·
Materials and auxiliary systems have relatively low cost (sugar,
energy, effluent treatment and disposal)
An “average size” sugar mill, with 1/3 of its cane, could produce
~ 70,000. t / year of a new sucrose derived product; it would probably be
self-sufficient in energy, and in many cases the mill’s effluent / disposal
systems would be used
Technologies for “new” products are in many cases available
(though not always the “best”) for licensing or buying.
Commercializing the product is a difficult point for most sugar
mills; adequate partnerships and associations may be necessary in some
cases, especially if exportation is considered (the most usual situation).
·
·
18
Comments
It is expected that in the next 10 – 20 years a much more efficient
use of the sugar cane biomass will increase significantly the range of
products and their value. Energy (both power and liquid fuels) will become the most important fraction of the sales.
Some technologies in advanced development stage (worldwide) may
be the key for this transformation: the hydrolysis of biomass (bagasse
and trash), as well as many different fermentation technologies; and
the biomass gasification, leading to power or fuel synthesis.
Sugar cane appears as an ideal feedstock for the future “biorefineries”, for its relatively low cost, large availability and an interesting
mix of 1/3 sucrose, 2/3 pre-processed ligno-cellulosic material.
Eduardo Pereira de Carvalho
UNICA
Isaias C. Macedo
NIPE, UNICAMP
Technological evolution of the Brazilian sugar
and alcohol sector: Dedini’s contribution
Abstract
During the past 30 years, the sugarcane production in Brazil, increased
from less than 100 million metric tonnes to more than 400 million tonnes
today. This expansion was necessitated by the expansion in the bioethanol
and cane sugar demand, both locally and globally. This paper describes and
discusses the various stages of the evolution of the industry, as well as the
next trends, supported by technological advances, in particular those emanating from Dedini’s significant expertise.
La evolución tecnología en la industria del azúcar y del alcohol
en Brasil: la contribución de Dedini Durante los últimos 30 años la producción de caña de azúcar en Brasil aumentó de una cifra por debajo de
100 millones de toneladas métricas a más de 400 millones de toneladas en
la actualidad. Dicha incremento fue el resultado del aumento en la demanda
por bioetanol y caña de azúcar, tanto local como global. En este trabajo se
describen y analizan las varias etapas de la evolución en la industria, así
como también las tendencias futuras respaldadas por los avances tecnológicos, en particular aquellos procedentes de la valiosa experiencia de Dedini.
Die technologische Evolution des brasilianischen Zucker- und
Alkoholsektors: Dedinis Beitrag In den letzten 30 Jahren hat sich die
Zuckerrohrproduktion in Brasilien von unter 100 Millionen Tonnen auf
heutige über 400 Millionen Tonnen erhöht. Diese Expansion wurde durch
die lokale und globale Steigerung der Bioethanol- und Rohrzuckernach-
20
frage notwendig. Dieses Referat beschreibt und diskutiert die verschiedenen Stadien der Evolution dieses Industriezweigs sowie die nächsten
Trends, die, von technologischen Fortschritten unterstützt, insbesondere
aus dem beträchtlichen Wissensschatz von Dedini entspringen.
Introduction
The Brazilian sugar and alcohol industry is the most competitive
in the world, matched by high productivity, better yields and low costs.
The industry well demonstrates how Brazilian technological capabilities
can respond quickly and effectively to the most diverse market stimuli
and demands, by offering quality products, that have been developed
with its own technology or, when acquired abroad, is well capable of
embracing new technology, as well as expanding the know-how to produce the technology locally and thereby minimize imports. The catalyst
responsible for such development has been the expansion that the industry has experienced over the last 30 years, spurred on by increase in
ethanol production, followed later by sugar production and, more recently, focus on maximizing the use of sugarcane. Over this period, combination of experience and accumulation of new knowledge has been successfully applied to improving not only productivity on, but also innovations
in the development of new equipment and processes or systems as well
as the establishment of optimized plants. We believe that such evolution
is due to the integration and interaction of four stakeholders in the process: namely the equipment manufacturers, the technology institutes and
R&D centers, industry consultants and the mills/distilleries. Dedini, as
a leading company in the supply of parts, components, equipment, systems and complete plants, throughout its history and nowadays, has
contributed significantly to the advances in the industry through the
introduction of pioneering solutions and products.
Model of technological evolution – the 5 big stages
It is our understanding that such development in the industrial area
may be explained by Figure 1, where the 5 big stages of the technological
TECHNOLOGICAL EVOLUTION OF THE BAZILIAN SUGAR AND ALCOHOL SECTOR...
21
evolution in the past few decades are highlighted: 1) increase of equipment capacities; 2) increase of overall yields; 3) greater use of sugarcane
energy: 4) greater use of sugarcane products and byproducts; 5) sugar
and alcohol mill defined as an energy-and-food producing unit.
Figure 1. Sugar and alcohol sector - model of industrial technological evolution - 5 big stages
Figure 2. The sugar and alcohol mill defined as an energy-and-food producing unit
22
Increase of equipment capacities
With the implementation of PROALCOHOL programme, priority was
first given to the development of capacity increase. Such priority was justified by the need to raise sugarcane processing to obtain bigger production
volumes (a PROALCOHOL requirement), allied to the lack of resources for
investment in plants expansion. As a consequence, the existing equipment
were used to their limits and upgraded by means of the development of
the materials used, fittings, components and design modifications to
achieve better performances. Item 1 of Figure 3 shows this first stage.
Figure 3. Results obtained by the technological evolution with emphasis
on Dedini products
Increase of overall yields
Both at individual process level and overall plant efficiency, there
have been significant advances in productivity. This has been made possi-
23
ble with an important contribution of the technology developed by the
equipment manufacturers, who can offer solutions for maximizing
alcohol and sugar production. The examples are presented in items 2
and 4 of Figure 3.
Greater use of sugarcane energy
The concept of sugarcane use has evolved during this period of
time, from exclusive juice supplier to juice and energy supplier, by using
the byproducts bagasse and stillage (effluent from alcohol production)
as energy inputs. Regarding energy optimization, besides improvements
in maximizing the production of energy at the mill, there has also been
a concerted effort to minimize its consumption during sugar and alcohol
production. This has resulted in energy surplus available to be sold to
the grid for profit. A whole set of equipment and engineering solutions
has been developed to allow such better use of the cane energy, as can
be seen in items 3 and 4 of Figure 3.
Greater use of sugarcane products and by-products
At the early stages of PROALCOHOL programme, sugarcane was
only used as feedstock for sugar and alcohol production. But significant
advances in technology and process conversion has made it possible
today for a modern mill to produce different types of sugar and alcohol,
yeasts for cattle feed, huge energy surplus in the form of bagasse,
electricity or heat supplied to third parties, stillage as fertilizer and feedstock for the production of biogas/biomethane, and biodegradable plastics, among others. Those technologies are available from the equipment
manufacturers.
The sugar and alcohol mill defined as an energy- and- food
producing unit
Some entrepreneurs of the industry conceive the agricultural (+) industrial integrated unit not only as a sugar and alcohol producing unit
but as energy and food too. Figure 2 is self-explanatory and shows this 5th
24
stage of technological evolution. It should be emphasized that the representation is simplified, since the number of by- and co-products from agricultural and industrial activities are much higher. The equipment industry meets the requirements of the mills by supplying the plants and machinery required for such diversified production with Brazilian technology.
Results of the technological evolution
The advances in technological developments, from the beginning
of PROALCOHOL up to now, has served to improve industry performance
while at the same time reduced costs. Figure 3 highlights this evolution
and presents the respective state of-the-art of the technology that is
available in the marketplace for sugarcane processing, as well as Dedini’s
technologies and equipment that make possible such performance. The
contribution of this development is also reflected in costs reduction, as
shown in Figure 4, making Brazilian ethanol industry very competitive,
particularly in light of the current high price of crude oil. With these
results, Brazilian bioethanol is already competitive with fossil fuels.
The next great leap
In addition to the environmental benefit for the use of ethanol or
ethanol-gasoline blends, the comparatively low current Brazilian bioethanol production cost of around US$ 30 per barrel compared with over
U$60/barrel for crude oil currently, has not only increased local demand
but globally too. These developments in paralel with the growing demand
of bioenergy has clearly set up opportunities for equipment manufacturers involved in this sector, to penetrate the market. With this in mind,
we will present the new technologies that we understand have the higher
potential to contribute to this new stage of accelerated development.
New technologies - the 3 BIOs revolution
Dedini’s vision is that the technological evolution will be focused
on the optimum use of the resources that are available in sugarcane
agribusiness, and new technologies will be developed with this purpose.
25
Currently, a number of new developments are underway. We highlight 3
new technologies - the 3 BIOs - due to the revolutionary impact that
they will have on the sugarcane industry: (a) production of bioelectricity
from the use of bagasse, straw, and co-products, such as stillage; (b)
bioethanol production from bagasse and straw; (c) biodiesel production
integrated to the sugar and alcohol mill. Emphasis is given to the use of
straw (i.e., tops, leaves and straw), since it contains about 1/3 of the
cane energy (in rough numbers, the remaining 1/3 is found in juice, and
the other 1/3 in bagasse).
Figure 4. Technological evolution: anhydrous bioethanol cost reduction - Brazil
Bioelectricity production - the 1st BIO
The energy content of the sugarcane produced in Brazil annually
is quite significant, in the same order of magnitude of the Brazilian
yearly production of oil, as shown in Figure 5. It was based on the annual
volume of cane processed for sugar and alcohol production (produced
during the milling season, 6 – 8 months), measured in kcal and compared
to the annual production of oil (12 months), also expressed in kcal. By
way of information, 386.2 million metric tons of sugarcane were processed by the sugar and alcohol industry during the 2004/05 season. Figure
26
5 shows the average daily production of oil (barrels/day), but the energy
calculation was based on the total oil produced in the respective year.
Bagasse is extensively used today in mills as a source of energy for
the industrial process. The efficiency however has been low, but this
can be improved significantly with available technology. Further, biogas,
which is produced from the anaerobic biodigestion of stillage can be
used for energy purposes too. The new development is to exploit energy
contained in cane crop residues. Technical hurdles and economic rationale for its exploitation has already begun, but the issue of collecting
and transporting these residues to the factories, and the underlying
costs associated withal those operations has yet to be fully developed.
Today, several Brazilian mills, mainly in the State of São Paulo, have
already been using crop residues as fuel. Technology is now available
to make use of these residues in boilers. We confidently feel that the
transference costs will be recovered several fold from the subsequent
energy produced. Surplus cogeneration of power from these residues
(as well as bagasse and biogas) adds to the overall profitability of the
enterprise (see figure 6). It should be emphasized that the technology is
already available to the industrial sector, and that the solutions and
equipment for energy optimization that are shown in the “mill features”
are part of Dedini’s products line.
Figure 5. Comparative total yearly energy content: sugarcane x oil - Brazil
27
Figure 6. Sugar and alcohol mill for maximum production of bioelectricity.
Bioethanol production from bagasse and straw - the 2nd BIO
Bioethanol production from lignocellulosic materials is increasingly
receiving research interest worldwide. In this direction, Dedini has developed the DHR-Dedini Hidrólise Rápida (Dedini Rapid Hydrolysis) - a
hydrolysis process that converts the cellulosic matter of bagasse into
sugars that, when fermented and distilled, result in bioethanol production. DHR revolutionary continuous process reduces hydrolysis reaction
time, enabling high yields, few unit operations, minimum investment,
reduced energy consumption and low operating costs. The process was
developed in the late 80s in laboratory and in pilot scale, and its technicaleconomic feasibility has since been confirmed quite satisfactorily. In 2003,
a Semi-Industrial Plant of 5,000 liters of ethanol/day started operations
in São Luiz Mill, Pirassununga, Brazil, of Dedini Agro Group, through a
joint venture between Dedini, COPERSUCAR and FAPESP (Research Support Foundation of the State of São Paulo). The Unit is currently in the
stage of continuous operation, with the purpose of completing the engineering parameters for production on industrial scale. Figure 7 presents
two pictures of the Semi-Industrial Plant. When its full potential is attained,
28
DHR will have a huge impact to the industry. We confidently feel that ,
it will: • almost double the current production of bioethanol per hectare
of harvested cane, with the use of the surplus bagasse and straw; and •
bring down the costs of bioethanol production. Figure 8 shows the impact
of the DHR process on the overall productivity of the bioethanol mill.
Figure 7. The semi-industrial plant - 5,000 I/day - DHR process
Figure 8. DHR - impact on production and productivity.
29
Biodiesel production integrated to the sugar and alcohol mill
– the 3rd BIO
As noted earlier in the 5th stage of the technological evolution, the
mill is conceived not only as a sugar-and-alcohol producing unit but of
energy and food too. More recently, this 5th stage of technological evolution embraced the integration of biodiesel production in sugar and
alcohol plants. This integration makes it possible to maximize the use
of available resources while helping to keep biodiesel production cost to
a minimum. It is important to note that the Brazilian Biodiesel Program
was approved by the Government and entered into force in 2004/2005.
Biodiesel is a natural substitute for diesel oil, using renewable feedstocks
like vegetable oils, animal fats and re-used cooking oil reacting with
ethanol or methanol in the presence of acid or basic catalyst. If the ethyl
route with bioethanol is used, the biodiesel produced will be 100% renewable. The biodiesel/sugar and alcohol mill integration concept was introduced by Dedini into the market in 2004, and has become reality, with
Dedini closing the first pioneering sale in the world of an integrated biodiesel plant for Barralcool Mill in Barra do Bugres, Mato Grosso, Brazil,
in November/2005. The plant has capacity for 50,000 tons/year of biodiesel, and a series of advanced and innovative features, such as, the
use of a number of different types of vegetable oils (such as oils from
soya, sunflower, peanuts, cotton seed, etc.) and animal fats as feedstock
in the same plant, which operates with flexibility in the ethyl or methyl
route. As Barralcool Mill has already pioneered the bioelectricity production in Mato Grosso State, this mill will be the first in the world to produce bioethanol, bioelectricity and biodiesel. The stages of full integration
of biodiesel production in a sugar and alcohol mill are shown in Figure
9. The Barralcool Mill is already in the first stage, that means, partial
industrial integration. The 2nd and 3rd stages are the next implementation phases of this new concept. The 2nd stage already has supporting
technology for successful implementation. The 3rd one is in the initial
stage of development and will have a great impact in additional cost
reduction of biodiesel, as well as bioethanol. Figure 9 shows the 3 BIOs
as products of the same sugar and alcohol mill: bioelectricity, bioethanol
and biodiesel.
30
Figure 9. Biodiesel production integrated to the sugar and alcohol mill the 3 evolution stages
Conclusions
Figure 3 well demonstrates the significant technological advances
in the sugar and alcohol sector in Brazil which has informed its development and made it the key player in the global industry. The advances
31
have not been restricted just to the processing sector. Sugarcane production has expanded from less than 100 million of tons at the beginning of PROALCOHOL programme, to around 400 million tonnes today.
Arguably, Dedini has been and continues to be one of the leading players
contributing to the success of the industry. Figure 10 presents Dedini’s
contribution to the sugar and alcohol mills, with reference to the supplies
made, which represent the biggest sales volume in the world. Among
other facts, the following must be pointed out: • Dedini’s market share
in equipment already installed in Brazilian mills (Historical Market Share)
is higher than 80%; • more than 80% of all bioethanol produced in Brazil
- which numerically correspond to around 30% of the world ethanol –
use Dedini distilleries and equipment. Finally, it must be pointed out that
Dedini accepts the challenge to contribute even further to the competitiveness of the sugarcane industry, by fully meeting the demand for
technology, equipment and complete plants, and making it possible to
raise even more the high performance of yields, productivity and costs.
Figure 10. Dedini’s contribution to the sugarcane industry
Senior Operational Vice President, Dedini S/A Indústrias de Base.
Tel: +55 19 3403 3006 Fax: +55 19 3421 3642 E-mail:
[email protected] Web: www.dedini.com.
32
References
COPERSUCAR, Área Central de Planejamento e Economia. PROÁLCOOL –
Fundamentos e Perspectivas, São Paulo; ed. COPERSUCAR, 2nd edition 1989,
122 p., Brasil.
Goldenberg, J., Coelho, S.T. and Lucon, O.(2002) – Ethanol Learning Curve –
The Brazilian Experience, Elsevier, Biomass and Energy, 26, pg 301-304.
Olivério, J. L. – “Desenvolvendo Integralmente o Potencial de Geração com as
Tecnologias Existentes”, In: 2nd Sugarcane and Energy International Seminar,
2002, Ribeirão Preto, INEE-Instituto Nacional de Eficiência Energética, Brazil.
Olivério, J. L. – “Produção de Álcool a Partir do Bagaço: o Processo DHR”. In: II
International Conference – Fuel Ethanol Internationalization, 2002, São Paulo,
DATAGRO, Brazil.
Olivério, J. L. – “Evolução Tecnológica do Setor Sucroalcooleiro: a Visão da
Indústria de Equipamentos”, In: 8th STAB National Congress, November 2002,
Recife, PE, Brazil.
Olivério, J. L. and Hilst, A.P. – “DHR-Dedini Hidrólise Rápida (Dedini Rapid
Hydrolysis) – Revolutionary Process for Producing Alcohol from Sugar Cane
Bagasse”, Proceedings XXV ISSCT Congress, 2005, Guatemala, pg. 320-327.
Olivério, J. L. and Hilst, A.P. – “DHR-Dedini Hidrólise Rápida (Dedini Rapid
Hydrolysis) – Revolutionary Process for Producing Alcohol from Sugar Cane
Bagasse”, International Sugar Journal, March 2004, ner 1263, pg. 168-172.
Olivério, J.L. – “A Indústria Brasileira das Produtoras de Biocombustíveis:,
Bioetanol e Biodiesel”, 1st Brazil-Germany Biofuels
Fórum, November 2004, São Paulo, Brazil.
Acknowledgments:
This article was firstly published in the International Sugar Journal 2006,
vol. 108 (1287): 120-129, and it is now here published with their
authorization.
Insertion of Bioethanol into a new paradigm
for the Brazilian Chemical Industry
Pedro Wongtschowski
Francisco I. Pellegrini
Flávio do Couto Bezerra Cavalcanti
CONTENTS
INTRODUCTION
General
Bioethanol as Fuel
Commercial Bioethanol as raw material
Integrated production of chemicals
··
··
·
COMPETITIVENESS OF BIOETHANOL AS FUEL
Competitiveness of conventional production
Production cost of bioethanol
Price composition of bioethanol producer price
The economic attractiveness of conventional bioethanol
·
·
·
·
Competitiveness with full utilization of sugarcane
Hydrolysis of lignocellulosic materials
· Production cost of bioethanol – Full utilization
· Economic attractiveness of Bioethanol – Full utilization
·
ETHANOL AS RAW MATERIAL FOR THE CHEMICAL INDUSTRY
Non-Integrated Production of Ethylene
Integrated Production of Ethylene
··
34
Conventional ethanol
· Full
utilization of sugarcane
· Conclusions
·
The Tree of Bioethanol Derivatives
· · Ethylene
Traditional Derivatives – Acetic Acid and Ethyl
· AcetatePotential
Derivatives – n-Butanol, Methyl Ethyl
·
·
Ketone, Ethylene Oxide, Monoethylene Glycol
Bioethanol as coadjuvant raw material
The Tree of Bioethanol Derivatives revisited
INTRODUCTION
General
All of the ethanol produced in Brazil is bioethanol, in the sense that
it is produced by aerobic fermentation (with Saccharomyces cerevisiae)
of musts containing mainly sugars with six carbon atoms, such as glucose and fructose obtained after inversion (hydrolysis) of sucrose in
slightly acid medium at low temperatures, the sucrose being obtained
from milled cane stalks.
The use of bioethanol as a renewable raw material as required for
its insertion into a new paradigm for the chemical industry, depends
fundamentally on three aspects: producer price (identified here as the
price paid to sugar mills and/or distilleries); availability and reliability,
in that order.
Whenever the producer price is higher than production cost, the production becomes feasible and ensures product availability in amounts
that can be considered unlimited in the short and medium terms, given
the availability of agriculturable land with appropriate climate, in Brazil.
In other words, it is possible to say that bioethanol is an abundant raw
material or that it can at least be produced in relative abundance, provided its production is required and remunerated by the market.
INSERTION OF BIOETHANOL INTO A NEW PARADIGM FOR THE BRAZILIAN...
35
The reliability of bioethanol supply, on its turn, is connected to the
reliability of the economic appeal of its production that, as seen below,
is also influenced by agribusiness exogenous factors such as the international price of crude oil and the tax burden. Although these factors are
decisive, they will interfere only indirectly on the economic appeal of bioethanol production, whose technical reliability can be undoubtedly ensured.
For now, it is enough to mention that there is great hope that the
bioethanol production will maintain its economical appeal for a long
time, ensuring its supply at least in the fuel market context. As mentioned
before, the use of bioethanol as raw material will depend on other factors.
Let us analyze the status of bioethanol in two different scenarios,
one based on the conventional production of bioethanol and the other
based on full utilization of sugarcane. Also, let us state from the beginning that the lower its production cost, the higher the probability of
its availability to the fuel market.
The use of bioethanol as raw material for the chemical industry, in
non-integrated plants, will naturally depend on the price paid to the
bioethanol producers, by the market, and on the economical feasibility
of this operation at market prices of the end products, many of which
are also influenced by the international price of crude oil.
Finally, we will also analyze the competitiveness of integrated production of chemicals where, instead of purchasing bioethanol at the
market, the producer of chemicals buys sugarcane from a supplier and
bioethanol remains as an intermediate link in the process chain.
Concerning integrated production of bioethanol, two different scenarios are possible, one conventional and the other with full utilization
of the sugarcane, with expectation of advantages for the latter.
Bioethanol as Fuel
The market price of bioethanol, which is directly correlated to the
bioethanol producer price, is defined by mechanisms intrinsic to the
domestic fuel market that, on its turn, is influenced by the global fuel
market and, to a lesser extent, by the price of sugar on the global markets.
The key parameter in the fuel market is the international price of crude
36
oil; therefore, to a great extent, the price of commercial bioethanol and
the bioethanol producer price become directly influenced by the international price of crude oil.
Whenever international prices are high, the domestic market pays
more for automotive fuels, including bioethanol, either used alone or
mixed with gasoline, and the producer gets higher prices for the bioethanol that is made available in distilleries. Conversely, when international
prices of crude oil are low, producers will pay less for the bioethanol in
the distillery.
A progressive decrease in international prices of crude oil might make
the production of bioethanol unfeasible, for the fuel market, if the price
of bioethanol received by the producer were lower than its production cost.
This is what really happens, although the current mechanism of price
fixation for sugarcane (the raw material for bioethanol production) is
connected to the prices of sugar and alcohol, which to a certain extent are
related to the international price of crude oil. Thus, a reduction in price
of crude oil promotes a reduction in price of sugarcane, although not in
the same proportion, somehow protecting bioethanol producers and
strengthening their business. As expected, the crucial questions posed
refer to the future performance of the international price of crude oil.
Given that, since the crises occurred in the 1970s, the international
prices of crude oil do not show any direct correlation with its production
costs and often are multiples of them, a climate of total uncertainty
concerning the future performance of these prices will always prevail.
Speculations concerning the occurrence, on the medium term, of
the so-called production peak of crude oil suggest that, as a function of
a tendency toward relative scarcity, the international price of crude oil
will never return to the levels shown in the 1990s and in the beginning
of this century, around $ 25 per barrel, unless technological breakthroughs were to occur concerning either exploitation and production
of crude oil or consumption of automotive fuels.
Even in such case, crude oil suppliers would, as they are today, be
in the comfortable position of, at the least menacing signs, being able
to reduce considerably the prices of crude oil by merely reducing their
profits, without necessarily incurring in losses.
37
Currently, for a crude oil production cost in the order of $10 per barrel,
which is considered reasonable as an indication of the average global
cost, the production cost is in the order of $ 75 per ton or approximately
$ 2.0 per million Btu, indicating the extreme competitiveness of the crude
oil and fuel derivatives industry, besides establishing the parameter which
industries using alternative fuels will have to compete with.
If we consider a minimum sales price of crude oil that ensures remuneration for investments and payment of royalties on production, the
minimum global average price of crude oil would be in the order of $ 3.0
per million Btu, requiring fuel derivatives to be sold for approximately
$ 3.5 per million Btu.
Therefore, any producer of an alternative fuel whose production
cost is higher than $3.5 per million Btu is really in an uncomfortable
position. An international price of crude oil of $ 60 per barrel, such as
the current one, increases sales prices of fuel derivatives to approximately
$ 15.2 per million Btu, placing alternative fuel producers in a circumstantially more comfortable position.
Commercial bioethanol as raw material for the chemical industry
Since most bioethanol goes to the automotive fuel market, both in
its pure form and mixed with gasoline, its use as raw material in the
chemical industry depends, as mentioned above, on its market price as
established by a mechanism of direct competition with gasoline, based
on their respective heat powers and combustion efficiencies in Ottocycle engines.
On the other hand, the price of gasoline at fuel stations is directly
correlated with the international price of crude oil, although through
variable correlation coefficients, since the factors intervening in the establishment of these coefficients (such as the corresponding tax burden)
vary as a function of the balance established in the Brazilian social and
political scenarios and of the use of administered prices as parameters
of macroeconomic adjustments.
This shows that the international price of crude oil is the parameter
fixing the limits of competitiveness of the commercial bioethanol, as
38
raw material for the chemical industry since, on one hand, it establishes
a floor price for commercial bioethanol due to its energetic equivalence
to gasoline and, on the other hand, establishes a ceiling price for chemicals that can be produced both from bioethanol and crude oil derivatives.
Establishing the floor price of commercial bioethanol and the ceiling
price of each chemical that can be produced both from bioethanol and
from crude oil derivatives, as a function of the international price of
crude oil, becomes then the main objective of any technical and
economical analysis intended to determine the feasibility of bioethanol
use as raw material for the chemical industry.
For each specific application of bioethanol as raw material it is
possible to identify an alternative standard process where the raw materials are crude oil derivatives and/or natural gas derivatives and compare it with the alcohol-chemistry process, and also determine a critical
price for crude oil, above which the alcohol-chemistry process, besides
being competitive with the alternative standard process, shows to be
economically attractive according to a specific profitability criterion.
Integrated production of chemicals
As an alternative to commercial bioethanol, integrated production
of chemicals from sugarcane has been suggested, where bioethanol appears
only as an intermediate product. In this case, if we disregard the opportunity cost represented by the simple sale of bioethanol to the fuel market,
it would be possible to expect that one of the restrictions imposed by crude
oil price, that is, the price floor of the raw material, would be eliminated.
However, even when we consider integrated production of chemicals
from sugarcane, the price of bioethanol in the fuel market, together
with the price of sugar in the international market, continue to affect
the feasibility of using bioethanol, now an intermediate, as raw material
for the production of chemicals. This is due to the fact that sugarcane
price is directly correlated to bioethanol producer price through the bioethanol market price, as well as to sugar producer price through the
international market price of sugar.
39
Therefore, the integrated production of chemicals that use sugarcane
as a raw material experiences (i) a direct restriction by the international
price of crude oil, that continues to fix the ceiling price of chemicals
that can be produced both from bioethanol and crude oil derivatives; (ii)
an indirect restriction by the international price of crude oil that affects
the market price of bioethanol and, as a consequence, the price of sugarcane and (iii) a direct restriction by the international market price of
sugar, which also affects the price of sugarcane.
Moreover, the prevailing pricing rule to establish the price of sugarcane, whose parameters necessarily reflect conjunctural aspects, can be
changed unpredictably. Under certain circumstances, a substantial
change in price of sugarcane can render an operation to be implemented,
or even an ongoing operation of integrated production of a given chemical, unfeasible.
When purchasing sugarcane or, more specifically, when buying cane
stalks from the supplier, the integrated producer of chemicals is acquiring
not only the sucrose paid for, according to the rule that established the
price of sugarcane, but also the whole amount of lignocellulosic material
associated with the stalk, that is, the bagasse, which, in principle, the
supplier will provide at no cost.
Therefore, if the integrated producer has access to appropriate technologies for bagasse processing aimed to its conversion into additional
sugars, even if the parameters of fixation of sugarcane price are kept
unchanged, the integrated producer will notice that the effective price
of the raw material is lower than the price of cane stalk.
The more additional sugars can be produced from bagasse, the
higher the cost reduction of raw material. The feasibility of bagasse conversion into additional sugars directly induces us to the feasibility of
using also the tops and straw remaining on the sugarcane plantation
after mechanized harvesting.
Of course a substantial fraction of the tops and straw produced
during the harvest can be conveyed to the industrial unit, as an additional
raw material for the conversion unit that converts bagasse into additional
sugars, further reducing the apparent price of the raw material. For estimate purposes, it is worth mentioning that the amount of biomass pre-
40
sent in integral sugarcane (stalk + tops and straw) is, on the Brazilian
average, equally distributed among sucrose, dry fibers from bagasse
and dry fibers from tops and straw. This means that the total biomass
produced by a given sugarcane plantation in one crop equals three times
the total amount of sucrose used to produce sugar and alcohol by
conventional operations.
Therefore, full utilization of sugarcane using any technique for conversion of lignocellulosic materials is the means integrated producers can
use to reduce the apparent price of his raw material and become more
competitive vis-à-vis producers who use crude oil derivatives as raw material.
COMPETITIVENESS OF BIOETHANOL AS FUEL
Competitiveness of conventional production
· Production cost of bioethanol
Given the technical and economical parameters currently prevailing
in the sugar and alcohol sector, Brazil is the region with the lowest production cost of ethanol in the world, even when using the conventional
technology, since
– Both in Southeastern and Northeastern Brazil, the crop season is
long (about 8 months);
– The average agricultural productivity, in the five-cut schedule is
high, in the order of 80 ton/ha per year;
– The dry biomass content in the plant itself is high, in the order of
36% (w/w);
– Finally, the species used are highly resistant to pests, so no incidents of this kind were noticed in the recent past.
If we consider that (a) cane stalk has an average sucrose content of
14.6% (w/w); (b) approximately 98% (w/w) of sucrose are recovered in
the milling process; (c) the yield of bioethanol equals 45% the sucrose
41
yield in the fermentation and distillation processes, the conclusion is
that, according to the conventional process, 64.2 kg of bioethanol are
produced per ton of cane stalk fed to the distillery; this means that 15.6
tons of cane stalk are required to produce one ton of bioethanol. Knowing
that, besides the cane stalk, there is a $ 43 cost to produce one ton of
bioethanol, its total production cost can be easily estimated using the
equation below.
Production cost of bioethanol = 15.6 x price of cane stalk +
43.0 (I)
Where the price of cane stalks and the production costs of bioethanol
are expressed as $ per ton. This equation is generally valid regardless the
price of crude oil, since its angular coefficient (15.6) is not affected by
the price of crude oil and its already small linear coefficient (43.0) almost
does not change with the price of crude oil. In other words, equation (I)
above provides a fair estimate of bioethanol production costs.
For example, in the current scenario – beginning of 2006 –, with
the cane stalk supply price equal to $ 15 per ton, which still does not
mirror the unexpected increases both in the bioethanol producer price
and the international price of sugar, which in the last 3 years rose from
an average $ 200 per ton to $ 400 per ton, using equation (I) above, we
have a total production cost for bioethanol in the order of $ 277 per ton.
This corresponds to a production cost of approximately $ 10.3 per
million Btu, an intermediate situation between the minimum sales price
and the current average price of fuel derivatives, respectively $ 3.5 per
million Btu and $ 15.2 per million Btu.
Since the current bioethanol producer price is approximately $ 620
per ton, which is incompatible with the international price of crude oil,
it can be seen that the production of bioethanol is today an abnormally
appealing operation, given the current price of cane stalk, with a unit gross
profit in the order of $ 340 per ton for a unit investment of $ 300 per ton
bioethanol/year and a gross profit/investment ratio in the order of 1:1.
However, the adjustment of the cane stalk price to the current international market sugar price, that reflects directly on the domestic market
42
sugar price, could be concerning both for bioethanol producers and
integrated producers in terms of the price of sugarcane, that is fixed as
a function of the bioethanol producer price and sugar producer price.
Supposing we applied the correlation to estimate the price of sugarcane as a function of the bioethanol producer price ($ 620 per ton) and
sugar producer price ($ 400 per ton), the price obtained for sugarcane
would be approximately $ 26 per ton and the production costs of bioethanol would rise to approximately $ 440 per ton.
Bioethanol producers would face a reduction in the unit gross profit
from approximately $ 340 per ton to approximately $ 180 per ton, as
well as a reduction in the gross profit/investment ratio to something
around 0.6:1, which is closer to the historic average of the sector.
This sharp increase in the international price of sugar, a phenomenon that has occurred before, is supposedly a reflex of a slight transient reduction in the global stocks of this product, associated with a
perception of the increase in bioethanol demand and production. Since
both products come from the same raw material (sugarcane), it would
be possible to infer that a fraction of sugarcane larger than the currently
used would be diverted to bioethanol production, causing a relative scarcity of sugar.
In reality, the global demand for sugar grows vegetatively and the
growth of this demand is easily met by major producers through gradual
increases in the production capacity, either by using idle capacity or
diverting less sucrose to produce ethanol, since most industrial units
are designed to simultaneously produce sugar and bioethanol and, in
some cases, present flexibility beyond the 50-50 ratio in the distribution
of sucrose between sugar production and bioethanol production.
It is also possible to interpret this increase in the international
price of sugar as an attempt from producers to keep it aligned with the
so called parity criterion that correlates the bioethanol and sugar
producer prices, taking into account that to produce and sell one ton of
bioethanol, the producer will not produce and sell 2.2 tons of sugar.
Historically, in the last few years, the price of sugar has been equivalent
to 150% the parity price of sugar in relation to bioethanol; so, it would
be possible to express the price of sugar by the following equation:
43
Sugar producer price = 1.5 x bioethanol producer price / 2.2
(II)
Where the sugar producer price and the bioethanol producer price
are expressed as $ per ton. Coincidentally or not, for a bioethanol producer
price equal to $ 620 per ton we can estimate a sugar producer price,
according to the correlation with the parity price, in the order of $ 420
per ton, for a current price in the order of $ 400 per ton.
Based on this, the conclusion is that the abnormality does not lie
in the international price of sugar, but in the bioethanol producer price,
that is abnormally high compared with its historical correlation with
international prices of crude oil.
A return to normality is expected for the near future, with a decrease
in bioethanol and sugar producer prices, without unexpected rises that
could cause temporary or permanent increases in cane stalk prices.
· Formation of bioethanol producer price
The possibility of using bioethanol directly as an automotive fuel
in “dual fuel” engines, as well as in engines adapted to use a mixture of
gasoline and ethanol provides a mechanism to form the bioethanol
producer price based on its market price at fuel stations, connected to
the price of gasoline at these same fuel stations.
Based on the ratio between the combustion heats of bioethanol and
gasoline, as well as on the ratio between the efficiencies of Otto cycle
engines, when using bioethanol and gasoline, an equilibrium point is
established, to form the price of bioethanol at fuel stations, equal to 70%
the price of gasoline in these same stations, with both prices expressed
as volume or mass units.
Maximum price of bioethanol at fuel stations = 0.700 x price of
gasoline at fuel stations
(III)
In other words, whenever the price of bioethanol is higher than 70%
the price of gasoline at the fuel station, if there is a supply of gasoline
44
in the same sales point, consumers who own dual-fuel vehicles will immediately suspend the purchase of bioethanol and shift toward gasoline.
This is an effective mechanism to control the price of bioethanol.
On the other hand, the net bioethanol producer price delivered to
the door of the distillery keeps historically a variable proportion within
a narrow range in relation to the price of bioethanol at fuel stations,
51.5% being a good estimate of this proportion. This means that the
producer receives a net price for bioethanol in the distillery in the order
of 36% the price of gasoline at fuel stations.
Net bioethanol producer price = 0.361 x price of gasoline at
fuel stations
(IV)
Taking into account that the price of gasoline at Brazilian fuel stations expressed as dollar per ton keeps historically an average ratio of
24.1 with the international price of crude oil expressed as dollar per
barrel, it can be seen that the bioethanol producer price correlates with
the international price of crude oil according to equation (V) below.
Net bioethanol producer price = 8.717 x international price of
crude oil (V)
Where the price of bioethanol is expressed as $ per ton and the
international price of crude oil is expressed as $ per barrel. This correlation expresses approximately what was observed in the recent past and
is expected to occur in the short and medium terms, in the Brazilian
scenario of automotive fuels.
It is not expected that realization prices, equivalent to net sales
prices, for gasoline received by Brazilian refineries will be different from
international prices of this product; also not expected is a major reduction
in the tax burden charged on the price of gasoline; no significant structural change is foreseen in the automotive fuel sector; as a consequence,
it is possible to admit a high probability of validity of the correlation
expressed by equation (V) at least in the short- and medium terms.
It is exactly from equation (V) above that we infer that the bioethanol
45
producer price is at least approximately 18% higher than the price this product should present as a function of the international price of crude oil.
· The economic attractiveness of conventional bioethanol
Based on the correlations shown above, the conclusion is that exclusive production of bioethanol by the conventional process has great
economical attractiveness, characterized by a less than 4-year simple
payout period, when the price of crude oil is higher than $ 43 per barrel,
as can be seen from the following estimates:
– International price of crude oil:
– Bioethanol producer price:
– Sugar producer price:
– Cane stalk supplier price:
– Production cost of bioethanol:
– Unit gross profit:
– Unit total investment:
– Gross Profit / Investment Ratio:
$ 43 per barrel
$ 375 per ton
$ 256 per ton
$ 15.9 per ton
$ 291 per ton
$ 84 per ton
$ 300 per ton
28.0 % per year
It is worth emphasizing that the attractiveness of conventional production of bioethanol, as shown above, lies on the premise that the price
of gasoline at Brazilian fuel stations will keep, with the international
price of crude oil, a relationship higher than the relation prevailing among
international prices of gasoline, in different consumer markets, and the
international price of crude oil. This means that Brazilian gasoline is proportionally more expensive than gasoline sold in the different global markets.
In summary, supposing the validity of the premises on international
price of crude oil and the relationship between the price of gasoline at
fuel stations and the price of crude oil, the production of bioethanol, based
on extraction of sucrose from cane stalks and on the use of bagasse
fibers as fuel, is reliable and highly profitable.
Moreover, given the high probability that international prices of
crude oil will keep over the $ 43 per barrel and that the structure of the
price of Brazilian gasoline will be maintained, the probability of the
46
attractiveness of bioethanol production, even using the conventional
process, will be also maintained high.
However, it is worth emphasizing that the attractiveness of the
conventional production of bioethanol, for the fuel market, lies currently
on premises for which there are no guarantees of permanence in the
medium and long terms, except for the guarantee connected to the perception of relative scarcity of crude oil, the global demand for biofuels,
and the Brazilian government avidity for taxes.
Competitiveness through full utilization of sugarcane
· Hydrolysis of lignocellulosic materials
Recently, emphasis has been given to the possibility, published since
a long time in the technical and patent literature, of full utilization of sugarcane by applying the lignocellulosic hydrolysis technology to the dry
fibers contained in the bagasse and also in tops and straw, or more precisely, to be applied to the hemicellulose and cellulose contained in fibers
of bagasse and tops + straw, respectively around 35% and 40% (w/w).
In one of its most popular versions – the diluted acidic hydrolysis –
the lignocellulosic materials hydrolysis process can be performed in
stages. The first stage, known as pre-hydrolysis, is milder and aims to
convert hemicellulose into a solution of pentoses (sugars with 5 carbon
atoms). Subsequently, the remaining fiber, now containing essentially
lignin and cellulose, can be subjected to a second, more energetic stage,
also known as hydrolysis, that aims to convert cellulose into a solution
of hexoses (sugars with 6 carbon atoms).
Another version of the process is enzymatic hydrolysis that is very
encouraged by enzyme producers; similar to the starch enzyme hydrolysis
that is applied mainly in the US to produce ethanol from corn, it could
be applied to sugarcane lignocellulosic materials. However, due to the
characteristics of these lignocellulosic materials, the specific consumption of enzymes – a costly insum – is still very high, making the process
apparently unattractive from an economic perspective.
47
A third way that is also being developed is the so-called SSF (Simultaneous Saccharification and Fermentation) where genetically modified
microorganisms are used to simultaneously hydrolyze hemicellulose and
cellulose, converting them into their respective C5 and C6 sugars which
would then be converted into bioethanol by fermentation in the reaction
medium itself.
The tops and straws are burnt prior to manual harvesting; or, they
are left on the field during mechanical harvesting. Bagasse is entirely
burnt in sugar mills (to produce exclusively sugar) or in distilleries (to
produce exclusively ethanol) for steam and electric power generation.
As for distilleries, 25% of the amount of bagasse produced in sugar
mills would be more than enough to meet the demand of the distillery
for steam and electric power; this means that with a properly designed
distillery there would be a surplus of bagasse equal to 75% the total
amount of bagasse that was produced in the sugar mills, which reached
the distillery incorporated to the cane stalks.
In reality, since lignin represents about 25% (w/w) of fibers both
from bagasse and tops + straws, the potential increase in production of
sugars by hydrolysis of hemicellulose and cellulose, that represent
together 75% of fibers, equals 150% the production of sucrose; this means
that, ideally, for the same planted area, the production of bioethanol
could be multiplied by a factor of 2.5. However, supposing that hydrolysis
yields are lower than theoretical yields, we can achieve twice the
production of bioethanol for the same plantation area.
· Production cost of bioethanol – Full utilization
With full utilization of sugarcane, only 9.4 tons of integral sugarcane are required to produce one ton of bioethanol. Moreover, a reduction
in the other production costs from $ 43 to about $ 32 per ton of bioethanol
is noticed. Therefore, equation (V) is converted
Production cost of bioethanol = 9.4 x Price of integral sugarcane
+ 32.0 (VI)
48
For a price of integral sugarcane equal to that of cane stalk ($ 15
per ton), a new total production cost of bioethanol, in the order of $ 175
per ton of bioethanol is obtained. This means a reduction in the production cost in the order of $ 102 per ton of bioethanol, corresponding to
approximately 37%.
· Economic attractiveness of bioethanol - Full utilization
From the correlations developed above, the conclusion is that exclusive production of bioethanol by the process of full utilization of sugarcane has great economical attractiveness, characterized by a less than
4-year simple payout period, when the price of crude oil is higher than
$ 21 per barrel, as shown by the estimates below.
– Sugar producer price:
– Cane stalk supplier price:
– Production cost of bioethanol:
– Gross Profit / Investment ratio:
$ 21 per barrel
$ 183 per ton
$ 125 per ton
$ 7.8 per ton
$ 105 per ton
$ 84 per ton
$ 300 per ton
28.0 % per year
In short, assuming the same premises concerning the conventional
production of bioethanol are valid, we note that an improved production
using the lignocellulosic materials hydrolysis process remains as reliable
as the conventional production, although more competitive, as indicated
by the international price of crude oil, that ensures the simple 4-year
payout period, which is shorter for production with full utilization of
sugarcane than for conventional production.
Moreover, the improved process shows to be more robust in face of
a low probability tendency of alignment of the relationship between the
price of Brazilian gasoline and the international price of crude oil, with the
prevailing relationship among the prices of gasoline in different markets,
and the international price of crude oil. Similarly, the improved process
49
shows to be more robust than the conventional process in face of casual
drops in the international price of crude oil, which is also not probable.
ETHANOL AS RAW MATERIAL FOR THE CHEMICAL INDUSTRY
Non-integrated production of Ethylene
Concerning the possible use of ethanol as raw material for the chemical industry, it is enough to examine the economical feasibility of
Ethylene production, for Ethylene market prices, as defined by conventional production from naphtha produced from crude oil, since Ethylene
production is the most onerous operation in terms of bioethanol mass
yield, requiring the consumption of almost 1.7 tons of bioethanol per
ton of Ethylene to be produced.
In short, it is known that, usually, the international price of Ethylene
related to the international price of crude oil, through the price of naphtha, can be expressed, as $ per ton, with a factor that ranges from 17.0
and 19.0 multiplied by the international price of crude oil, expressed as $
per barrel. Assuming the range average value:
International price of Ethylene = 18.0 x international price of
crude oil (VII)
On the other hand, it is possible to estimate the total production cost
of Ethylene from bioethanol purchased at the market, using a simple
linear correlation with bioethanol and multiplying the price of bioethanol
by a factor of 1.676 and adding a factor of 60, the result being expressed
as $ per ton of Ethylene.
Production cost of Ethylene = 1.676 x price of bioethanol + 60
(VIII)
To simplify the comparison we can express the total production cost
of Ethylene from bioethanol as a direct linear function of the international
50
price of crude oil, taking into account the existing correlation between the
price of bioethanol (in $ per ton) and the international price of crude oil
(in $ per barrel):
Production cost of Ethylene = 14.612 x international price of
crude oil + 60 (IX)
Direct comparison between the production cost of Ethylene from
bioethanol purchased at the market, and the international price of Ethylene, both prices varying as a function of the international price of crude
oil, shows that for an investment index of $ 300 per ton of Ethylene per
year, one obtains a less than 4-year simple payout period if the price
of crude oil is higher than $ 42.5 per barrel. Under these conditions we
have:
– Production cost of Ethylene:
– International price of Ethylene:
$ 42.5 per barrel
$ 370 per ton
$ 681 per ton
$ 765 per ton
$ 84 per ton
$ 300 per ton
28.0 % per year
This means that if the correlations among prices of bioethanol, crude
oil and Ethylene are maintained, the non-integrated production of Ethylene from commercial bioethanol becomes feasible and economically
attractive with global crude oil prices over $ 42.5 per barrel. It is worth
noting that even if the conventional process is used, this price already
makes bioethanol production for the fuel market feasible, thus ensuring
its availability.
The risks assumed in the production of Ethylene from bioethanol are
the same incurred when the production of bioethanol itself is established,
that is, tendency to align the price of Brazilian gasoline to the price of
gasoline in different markets, in terms of its relation with the international price of crude oil, and drop in the international price of crude oil
51
itself, to values below $ 42.5 per barrel, although these are unlikely
events, at least on the short term.
Integrated production of Ethylene
· Conventional ethanol
In the integrated production of Ethylene from sugarcane by means
of the conventional process to produce ethanol, a less than 4-year simple
payout period is obtained for an international price of crude oil over $
52.2 per barrel. Under these conditions we have:
– Sugarcane supplier price:
$ 52.2 per barrel
$ 15.3 per ton
$ 713 per ton
$ 939 per ton
$ 226 per ton
$ 800 per ton
28.0 % per year
The requirement of an international price for crude oil, in this case,
higher than the one required in the case of non-integrated production of
Ethylene, reflects the need for a higher unit gross profit to ensure the
same profitability, at a higher investment index that includes, not only
the production of bioethanol but, also the production of Ethylene.
It can be seen that the requirement of a higher international price for
crude oil reduces the probability of maintaining the economic attractiveness of conventional integrated production of bioethanol because it
is lower the probability of maintaining the international price of crude
oil above $ 52.2 per barrel.
· Full utilization of sugarcane
In the case of integrated production of Ethylene from sugarcane,
with full utilization, a less than 4-year simple payout period is obtained
with an international price of crude oil over $ 25.3 per barrel. Under
these conditions we have:
52
– Sugar supplier price:
$ 25.3 per barrel
$ 7.4 per ton
$ 230 per ton
$ 455 per ton
$ 226 per ton
$ 800 per ton
28.0 % per year
The need for an international price of crude oil, in this case, lower
than the international price of crude oil using integrated production
without full utilization of sugarcane, reflects the reduction of the ratio
between the production cost of Ethylene and the crude oil price from
16.4 to 9.1 (with crude oil at $ 25.3 per barrel) and from 13.7 to 6.8 (with
crude oil at $ 52.2 per barrel). Most important, however, is to note that
being higher the probability of crude oil prices exceeding $ 25.3 per
barrel, higher is the probability of maintaining the economic attractiveness of integrated production of Ethylene with full utilization of sugarcane.
Conclusions
Therefore, we reach the conclusion that both versions of Ethylene production from sugarcane, namely the conventional processing and the process
based on full utilization, currently have an economic appeal. However, as
expected, the alternative more likely to maintain its economic attractiveness is the integrated production with full utilization of sugarcane.
This led to the ongoing effort, in Brazil and abroad, to make the industrial technology required for such full utilization commercially available.
The Tree of Bioethanol Derivatives
· Ethylene
The previous section showed the high probability of the economic
attractiveness of Ethylene production from bioethanol, both in nonintegrated and integrated models and in the latter case, in its two
versions, namely the conventional bioethanol production process and
53
the process that adopts full utilization of sugarcane. As expected, integrated production with full utilization of sugarcane is the most attractive
among all cases studied.
· Traditional derivatives: acetic acid, ethyl acetate and others
The same can be said about the production of other first generation
derivatives of bioethanol, such as acetic acid and ethyl acetate that can
be obtained by the so-called direct routes; acetic acid, via an old, well
known route with new clothing, that is, aerobic fermentation using Acetobacter, and ethyl acetate by catalytic dimerization of ethanol.
Moreover, considering that in Brazil the alcohol-based chemical
industry preceded the petrochemical industry by approximately 40 years,
it is worth mentioning, at least en passant, some products that have been
produced from bioethanol along the time.
The Brazilian chemical production of alcohol started its activities in the
1920s1 with the production, by Rhodia, of ethyl chloride, diethyl ether and
acetic acid, and grew due to the implementation, fomented by a fiscal incentive policy, of several industrial units, some of which operate to this day.
During the 1960s, Rhodia and Fongra started to produce acetic acid
derivatives from bioethanol in Brazil (currently Rhodia imports acetic
acid); later, Fongra was purchased by Hoechst to be deactivated in 1980;
Victor Sense (also deactivated in 1980) produced butanol and acetone;
Eletroteno (Solvay) and Union Carbide produced Ethylene.
Today, the units of Solvay and Union Carbide (currently DOW) operate with petrochemical Ethylene whose production started in Brazil in
1972, when Petroquímica União started operating, followed in 1978 by
COPENE (Companhia Petroquímica do Nordeste), starting the competition
between bioethanol and naphtha for the production of Ethylene.
Between 1965 and 1971, Coperbo – Companhia Pernambucana de
Borrachas – located in Cabo city, produced polybutadiene by polymerization of butadiene obtained from bioethanol. The Butadiene Unit remai1
For more information on this matter refer to Chemical industry – Risks and Opportunities (in Portuguese) by P. Wongtschowski, Edgard Blücher Ltda Publishers, 2nd ed., 2002.
54
ned deactivated from 1972 through the beginning of the 1980s and was
modified to produce Ethylene and acetic aldehyde from bioethanol; these
products were used by CAN – Companhia Alcoolquímica Nacional – a
company located next to Coperbo, to produce vinyl acetate monomer.
In 1969, in Igarassu city, also in Pernambuco state, Elekeiroz do
Nordeste started the production of 2-ethyl-hexanol from bioethanol via
a route that begins with the dehydrogenation of bioethanol to give acetic
aldehyde (that is also a precursor of acetic acid); acetic aldehyde is dimerized to give acetaldol which, on its turn, is dehydrated to give crotonaldehyde. Crotonaldehyde is then hydrogenated to give butyric aldehyde, a precursor of both n-butanol and 2-ethyl-hexanol. This was the
base for the extension of Elekeiroz’s product range that in 1977 already
produced, besides 2-ethyl-hexanol (also called octanol), butanol and
ethyl acetate; in 1986 the line was extended to include acetic aldehyde,
acetic acid and 2-ethyl-hexanoic acid. With the change in the incentive
policy, competition with Petroquímica became unfair and the Igarassu
Unit was closed in 1993.
Salgema was incorporated into Trikem in 1996 (today Braskem) and
for some time produced Ethylene from bioethanol as a permanent raw
material for its dichloroethane unit that is currently supplied with Ethylene from Braskem; CBE – The Brazilian Styrene Company – began to make
ethylbenzene from Ethylene produced from bioethanol, replaced later
by petrochemical Ethylene; CBE produced also ethyl chloride until 1996.
· Bioethanol as a coadjuvant raw material
Besides the derivatives produced by using exclusively bioethanol
as raw material, there are other important derivatives that use bioethanol
as a coadjuvant raw material. These derivatives will benefit directly
from any possible reduction in the market price of bioethanol; such
derivatives include the ethyl ethers of MEG/DEG/TEG (mono/di/tri ethylene glycol) produced by reacting ethanol with Ethylene oxide; ethyl
ethers of MPG/DPG/TPG (mono/di/tri propylene glycol) produced by
reacting ethanol with propene oxide, and ethyl acetate produced by
reacting acetic acid (in this case derived from methanol) with bioethanol.
55
The Tree of Bioethanol Derivatives revisited
Based on the above, we can redraw the Chemical Alcohol Tree based
on a criterion of competitiveness and profitability in order to contain:
– Ethylene and derivatives (openly competing with Ethylene from
naphtha):
(P-001)
· Ethylene
Ethylene oxide (P-002) and derivatives
· Polyethylenes
· PVC (P-004) (P-003)
· Styrene and Polystyrene (P-005 and P-006)
·
– Acetic acid and Acetates
Acetic acid (P-007)
· Ethyl
(P-008)
· Butyl acetate
acetate (P-009)
·
– Ethyl acetate (via direct route – P-008)
– Ethylene oxide (P-002 via direct route) and derivatives
– Methyl ethyl ketone (P-009)
– Propylene oxide ethers (P-010)
It can be seen that at least 10 important products and/or families in
the Brazilian chemical sector can be competitively produced from bioethanol, provided that the ongoing development efforts are completed and the
results obtained with the completion of these efforts correspond to expectations.
Pedro Wongtschowski, Francisco I. Pellegrini
and Flávio do Couto Bezerra Cavalcanti
OXITENO, São Paulo
Section 2
BioTechnology and Engineering
Science integration
for Chemical and Fuel Industries
Industrial Potential of Yeast Biotechnology
in the Production of Bioethanol in Brazil:
the Example of Conditional Flocculation
Anderson Ferreira da Cunha
Silvia Kazue Missawa
Gonçalo Amarante Guimarães Pereira
Introduction
The existence of life on earth as we know it is due fundamentally
to the reduction of CO2 levels primarily existing in the atmosphere, mainly
through the fixation of this compound into carbon chains. These longterm processes combine with geologic events, although they are basically
biological activities.
Man as a species has developed in this rather milder atmosphere,
although his social and economic progress, in the last hundred years,
has reversed the direction of carbon fixation and is now jeopardizing
biological maintenance of the atmosphere. Since the introduction of fossil
fuels (gasoline, diesel, etc.) utilization, we have systematically released
gigantic amounts of carbonic gas back to the atmosphere effectively
reversing millions of years of carbon fixation. This means that our social
progress is taking us back to our biological environmental starting point,
which will certainly have major consequences.
In recent years a number of research studies, as well as scientific
and social organizations, have pointed to this problem, although without
much success. The largest producers of CO2 even admit that this process
is occurring, but up to now, they have only considered it as something
that will occur in the remote future. Within this context, weather changes
60
that have occurred in the past few years, particularly floods and the
record number of hurricanes, have brought to light an unmistakable
demonstration that the consequences of fossil fuels are already here.
Therefore, there is no more time to wait, alternative and renewable energy
sources must be found.
The history of economic events show that during great crises, great
opportunities arise and the ability to capitalize during these times is
key to economic success. In the specific scenario of the fuel crisis a
huge opportunity has been created for countries that have ample land,
sun and water. This is undoubtedly the case of Brazil.
Although most of the developed world has reached a situation that
is considered critical, with dependence on imported petroleum and alarming and overwhelming natural phenomena linked to climate changes,
Brazil started take positive step to reduce this situation about 30 years
ago, for economical reasons. With the oil shortage that occurred in 1973
and 1979, oil prices rose from US$ 4.00 to US$ 40.00 per barrel. Between
1973 and 1974, fuel costs jumped from US$ 600 million to over US$ 2
billion. This gigantic impact on the balance of payments showed the
strategic vulnerability of Brazil, which at the time was importing nearly
80% of the oil consumed by the Country, and therefore was highly susceptible to an energy collapse.
In 1975, Brazil launched Proalcool, the Brazilian Program for
Alcohol Fuel. Sugarcane alcohol soon provided an ideal alternative fuel
for gasoline. In order to make this program feasible, the Brazilian government offered a financial plan that was supported by the World Bank,
which made it possible to increase the areas planted to sugarcane, build
new plants and develop and enlarge boiler shop industries (source:
UNICA, the Sao Paulo State Sugarcane Agribusiness Union –
www.unica.com.br).
Once available, this so-called green fuel was harnessed in two forms.
Initially, it was mixed with gasoline as anhydrous alcohol. This process
has increased the amount of alcohol in gasoline over time, i.e. the
gasoline distributed in Sao Paulo city changed from a 20% v/v mixture
in 1977 to 22% in 1980, which has been adopted all over the country
(Demetrius 1990). Also during this period the first cars that exclusively
INDUSTRIAL POTENTIAL OF YEAST BIOTECHNOLOGY IN THE PRODUCTION...
61
utilized hydrated alcohol were introduced, unfortunately, these vehicles
used poorly adapted gasoline motors and were not well received. Only
during the 1980s, after the second oil shortage did automobile manufacturers launched new models that were especially manufactured to
work with alcohol. Also during this time alcohol prices were kept favorable to gasoline, through governmental subsidies. The success of these
automobiles exceeded all predictions. In 1984, alcohol-powered cars represented 94.4% of the assembly line production in Brazil, which accounted for 19 out of 20 cars.
However, this huge increase in demand was not maintained and combined with increases in the Brazilian production of crude oil and the reduction in the world price of this commodity, there was limited interest in
maintaining the alcohol subsidies. Moreover, ethanol producers started
an irrational process of increasing prices, which led to a shortage of the
product, resulting in a lack of confidence in the consumer market. As a
combined consequence, the production of alcohol-powered cars fell from
88.4% in 1988 to 61% in 1989, to 19.9% in 1990 and finally to 0.3% in 1996.
However, in spite of the program’s limit adoption, the government
viewed this as strategically important to the country and kept alcohol
production at high levels. In 1991 a new federal law mandated the addition of 22% anhydrous alcohol to gasoline, which helped to promote the
production of ethanol for fuel purposes. Associated with this strategy,
environmental factors in cities like Sao Paulo, where air pollution had
reached alarming levels, could also be improved by the addition of alcohol
to gasoline.
More recently, the alcohol program has once again returned to the
spotlight, at first because a consistent and apparently irreversible increase in the international crude oil prices and due to the development
of the so-called FLEX engines that are capable of burning hydrated
alcohol/gasoline mixture at any proportion. Cars with these new motors
have given Brazilian consumers a choice in which fuel to use and thus
a relevant power to resist increases in gasoline prices.
Thus, given the global demand for alternative fuels, Brazil now presents itself as the country capable of leading the world. Brazil has a huge
production capacity and has developed new technologies for production,
62
distribution and utilization of ethanol, as well as demonstrating increased implementation of these technologies. For example, the sugar mill
extract process has increased the amount of sugar that can be processed
from sugarcane. The sugar extraction index, that was 89%, at the beginning of the Proalcool program, has reached 97% today. In parallel,
the sugarcane residues (bagasse) burning technology to produce energy
has been widely adopted, thus making approximately 95% of the sugar
mills self-sufficient in terms of electricity (van Haandel 2005), and in
some case providing excess electric that is redirected into the national
electrical networks.
However, there are still technological advances that remain to be
developed in order to maximize the inherently biological processes. In
the case of sugarcane, over the last few years an intensive research
effort has been developed to improve the plant. Genomics have been
used to in an attempt to understand the biochemical processes connected
to the plant’s physiology, and these have lead to potential features of
agronomic importance (Vettore et al. 2003; Vincentz et al. 2004). This
advancement has led to the recent creation of companies focused on the
use of biotechnology in the development of new cultivated varieties, as
in the case of Canavialis (www.canavialis.com.br). Curiously, this has
not happened in the case of Saccharomyces cerevisiea. Even though this
yeast is an essential part in fermentation, very little research has been
done to improve its efficiency and specificity. This lack of research presents huge opportunities for biotechnological improves. This issue will
be discussed in detail in the following items.
The Biochemistry of Ethanol Production
The ethanol production process in Brazil occurs almost exclusively
by fermentation of sugarcane juice by yeasts, mainly the Saccharomyces
cerevisiae species, an organism that, given its technological importance,
is widely used as an experimental model to understand eukaryotic cells
(Goffeau et al. 1996).
Biochemically, alcohol fermentation is the degradation of hexoses
into ethanol with the production of 2 ATP molecules in the process. In
63
the case of sugarcane juice, the fermentation process metabolizes the
disaccharide sucrose that is formed by one molecule of fructose and one
molecule of glucose. The first step is the hydrolysis of sucrose by invertase enzyme that is encoded by the SUC2 gene. Both glucose and fructose
enter the glycolytic pathway and are converted into pyruvate via a sequence of reactions (Figure 1). Pyruvate is then decarboxylated to form
acetaldehyde and this releases CO2 and causes intense bubbling when
the cells are grown in liquid medium. Later, the acetaldehyde molecule
is reduced to ethanol, and this reaction is catalyzed by the enzyme alcohol
dehydrogenase 1 (ADH1). The glucose depletion results in the end of
the fermentation phase. During this period the yeast cells vigorously
multiply, which is characterized by an exponential growth phase. From
the depletion point on the yeasts seem to enter a stationary phase, but
they actually continue to grow for a long period, and actually consume
the ethanol previously produced through respiration. This change from
fermentation metabolism into respiratory metabolism is called diauxic
shift, which involves intense genetic reprogramming (De Risi et al. 1997;
Lashkari et al. 1997), and is based on an increase in the transcription of
certain genes and repression of others.
To better understand these processes it is important to briefly mention how these genes are organized and how they work. Basically, the
genes that encode proteins are organized into two independent regions,
namely, a promoter region and a coding region. The promoter region is
responsible for the transcription regulation that defines when a gene
should be switched on or off. When the gene is switched on, in a portion
close to the coding region, a messenger RNA (mRNA) starts to form and
copies the information from the coding region, which will be translated
later into a protein by ribosomes. It is fundamental to note that these
regions of the gene act independently and may be interchangeable
through genetic engineering, for example, leading to the formation of
new genes with unique expression patterns (Lewin 1990).
In particular, the growth in a medium containing glucose leads to
the repression of a series of genes involved with respiration and the use
of alternative sources of carbon. The SUC2 gene is repressed under these
conditions, thus preventing the release of further amounts of glucose
64
and fructose stored in the sucrose molecule (Gancedo 1998). The ADH1
gene, on the other hand, is induced by this sugar.
The end of fermentation activates a set of genes required for respiration and leads to intense multiplication of mitochondria (Mahler et
al. 1975; Ulery et al. 1994). In particular, the absence of glucose in the
medium activates the transcription of ADH2 (alcohol dehydrogenase 2)
gene (Ciriacy 1979). The enzyme produced by the expression of this gene
oxidizes ethanol to acetaldehyde via the reverse of the ADH1 pathway;
acetaldehyde is then converted into acetate, which participates in the
later stages of the Krebs cycle that is the major aerobic respiration cycle
(Devlin 1997) (Figure 1).
Figure 1. Schematic diagram of the fermentation and respiration reactions. The dotted
arrows indicate the pathway that is activated after glucose depletion (ethanol oxidation).
PDC1, 5, 6: pyruvate decarboxylase; PDA1, PDB1, PDX1, LPD1, LAT1: enzymes form
the pyruvate dehydrogenase complex; ALD6: aldehyde dehydrogenase; ACS1: acetylCoA synthetase; ADH1: alcohol dehydrogenase 1; ADH2: alcohol dehydrogenase 2.
65
Industrial Production of Ethanol
An interesting question is: why do yeasts produce ethanol? This
would seem to be a waste if we consider it from the energetic perspective;
respiration produces a much higher amount of energy compared to fermentation. However, from the strategic perspective, this seems to have
been an effective evolutionary pathway. After all, only a few organisms
are able to live in high concentrations of ethanol, a compound that is
largely used as an antisepsis. While the yeast developed the ability to
produce high concentrations of ethanol, the species also developed a
system to resist this compound. Therefore, during theproduction of ethanol, the yeast can reduce significantly the competition from other organisms for the existing substrates and afterwards can consume the ethanol
that was produced; while waiting for new stocks of sugar to be made
available. If we look at the natural environments, this seems to be the
logical strategy used by yeasts in fruits like grapes. As fruits fall from
the vine, an environment is created that is similar to a fermentation
vat, where ethanol is rapidly produced in large amounts. When new
fruits fall from the vine this provides new stocks of sugar, and the entire
cycle begins again. This parallel shows that the industrial fermentation
of alcohol is just a scaled increase of a natural phenomenon. This process
is not a human invention, but rather a human discovery.
Industrially, the production of alcohol follows basically two processes: fed-batch and continuous fermentation, with the first being the
most used. In the fed-batch process, fermentation occurs in independent
vats, beginning with low concentrations of yeast cells and high concentrations of substrate. The whole mixture of must (mixture of sugarcane
juice and molasses), nutrients and yeast is added to the vat and after
approximately 8 hours, once the fermentation has ended, the entire
contents are removed and centrifuged. The “wine” – a name used in the
sugar mills industry to indicate the fermented sugarcane juice without
the yeast – is conveyed to the distillation towers, while the yeast milk,
that is, the yeast broth obtained by centrifugation, is subjected to a
decontamination treatment in the treatment vat consisting of a lowering
of the pH with concentrated sulfuric acid. The yeast is then returned to
66
the vat and a new load of must is added, to start a new fermentation cycle
(Wheals et al. 1999) (Figure 2).
Figure 2. The fed-batch process of ethanol production. The whole mixture of must,
nutrients and yeast is added to the vat and, once the fermentation has ended, the
whole contents are removed and centrifuged. The wine is distilled and the yeast milk is
returned to the vat, where a new load of must is added, starting a new fermentation
cycle.
To start the fermentation, the original yeast used by sugar mills is
usually multiplied under sterile conditions up to 50 liters and sent to a
pilot stage until it reaches the volume required to start the production.
This volume varies according to the size of the mill and can reach a
value of up to 600,000 liters (Zarpelon and Andrietta 1992, Wheals et
al. 1999).
An important observation that was only recently ascertained was
that, although the yeast is inoculated at high levels, in some sugar
mills it is rapidly replaced with wild yeast strains within a few fermen-
67
tation cycles and is then maintained until the end of the cropping season
(da Silva Filho et al. 2005). In many cases this replacement is not even
noted and there is no decrease in the productivity of the mill, possibly
because the invading yeasts are better adapted to the conditions of the
mill. Recently we have detected this fact in a large sugar mill in the
Campinas region that for many years had been inoculating a strain to
start the crop, and after a few weeks this strain was replaced with a
wild strain that increased the process. This fact demonstrates clearly
the low importance given to the fermentation agent, which is considered
an abiotic factor. These factors may actually open up new opportunities
for the development of new technological advances for improving the
yeast strains used.
The Yeast
This microorganism has been used in the production of bread and
beverages for centuries. Since the nineteenth century it became an important experimental model, to the extent that it was the first eukaryotic
organism to have its genome fully sequenced (Goffeau et al. 1996; Goffeau 1998), which tremendously simplified investigations to understand
its metabolism. Moreover, Saccharomyces cerevisiae is an organism that
can be easily genetically manipulated, which has led to a systematic deletion of all of its genes, either individually or in combination, in order
to analyze their functions and determine how their products interact
(Dujon 1998; Hauser et al. 1998). Full information is available for real
time searches at the site www.yeastgenome.org.
The effective production of ethanol requires that yeasts included in
the process have some essential characteristics such as: (1) ability to
ferment rapidly and, effectively produce ethanol; (2) a high tolerance to
ethanol; (3) a high osmotolerance (ability to ferment concentrated solutions of carbohydrates such as, for example, sugar molasses used in
many sugar mills to produce ethanol); (4) genetic stability; (5) cellular
viability and tolerance toward repeated fermentation cycles; (6) tolerance
to temperature variations; (7) a high competitive capacity. There are
several yeast species capable of producing ethanol on a large scale;
68
however, over 97% of processes involve the use of the species Saccharomyces cerevisiae (Stewart et al. 1987).
Therefore based on the knowledge we have of this organism, it is
possible to manipulate it genetically to adequate it even further to the
fermentation process. Several methods that have been used in the past
have been to employed classical methods such as: cross hybridizations,
selection and isolation of new strains.
The advent of molecular biology and the development of genetic
engineering techniques made it possible to manipulate genes to increase
the possibility of changing undesired characteristics or adding new desirable ones. Through transformation of an organism with modified genes,
it is now possible to make the organism express certain characteristics
that are not identified in natural populations. This means that it could
be possible to build strains with specific functions, for industrial uses.
Yeast flocculation and its use in alcohol fermentation processes
A phenomenon that plays an important role in industrial production
is yeast flocculation, that can be defined as the ability of certain strains
to aggregate and form multicell masses that will separate by
sedimentation or flotation (Stratford 1996; Stan and Despa 2000). This
feature has been employed successfully in the beer industry to facilitate
the removal of cells once the fermentation has ended (Stratford 1996).
This precedent makes us think about it could possibly be used in a similar
fashion in the ethanol production industry, since it would eliminate the
need for centrifugation, an expensive and complicated step in the process.
In fact, this idea has led to the development of industrial procedures
of alcohol production based on flocculating yeasts (Domingues et al. 2000,
Domingues et al. 2001, Kondo et al. 2002). However, it was shown that
continuous flocculation has a series of disadvantages and can lead to a
reduction in the overall production of ethanol, as well as to in-process
problems such as duct clogging (Stratford 1992, Verstrepen et al. 2003).
The physical and genetic mechanism of flocculation has been widely
studied in recent years (Verstrepen et al. 2003). It involves primarily the
interaction of surface proteins of a certain lecithin-like, sugar-binding
69
cell, with exposed sugar residues on surrounding cells. Thus, a cell producing a flocculation protein is capable of interacting with cells that do
not produce the protein, and interact with the exposed sugars of those
cells (Stratford and Carter 1993) (Figure 3).
Figure 3. Schematic diagram of flocculation mechanism showing that all cells have
sugar residues on their cell walls and that, after glucose (C6H12O6) depletion, flocculin
– the flocculation-related protein – is formed.
Several genes have been genetically identified as being responsible
for flocculation. Such genes express proteins called flocculins. The control
mechanism for flocculins and proteins encoded them is different and
has been intensely studied (Cormack 2004; Halme et al. 2004). The option
used by industry has been to control flocculation by using engineering
solutions. However, it seems that there is a huge potential for using
biotechnological techniques to develop strains more adequate to the
industrial process.
Based on this, we developed the following scenario: the ideal yeast
should be perfectly soluble in the medium while this medium would
include a fermentation substrate, i.e. sugar. The cells would be able to
efficiently exploit this substrate because they would multiply and reach
the maximum total contact surface. However, once the sugar was depleted, ideally we should have the opposite response, that is, the cells would
aggregate and be deposited on the bottom of the vat. This would prevent
ethanol consumption and the cells could be separate naturally, thus
eliminating the need for centrifugation.
To determine if this idea was viable we used laboratory strains of
S. cerevisiae, which are easily manipulated. At the same time we created
a hybrid gene containing the promoter region of the ADH2 gene asso-
70
ciated with the coding region of the FLO5 flocculation gene. From this
point on we had a desired effect. As mentioned before, the ADH2 gene
promoter is repressed by glucose, and induced when this sugar is depleted
from the medium. This mechanism selectively insures that the cells will
continue to produce ethanol while preventing its oxidization to acetaldehyde when there is a flow in the opposite direction (Figure 1). At this
point the flocculin encoded by the FLO5 gene is produced, and mobilized
to the cell surface thus leading to a synchronized sedimentation (Figure
4). Starting with this simple system we were able to achieve a situation
where we could sense the sugar levels in the medium, quench the fermentation at the appropriate moment and removing the yeast cells at that
point. In a broader sense, we developed intelligent yeast – or, at least,
smart yeast.
Figure 4. Expression of FLO5 gene under the control of the ADH2 gene promoter regulatory region.
1- Wild strain; 2- Wild strain with the flocculation gene controlled by glucose levels; 3Wild strain with constitutively activated flocculation gene. A. Culture medium with
glucose; B. Culture medium after glucose depletion. As shown in the figure, the strain
whose flocculation gene is controlled by glucose levels is deposited after carbohydrate
depletion.
71
This prototype worked perfectly in the laboratory, was patented
(INPI # 0001122), and was awarded a Honorable Mention in the 2000
issue of the National Contest of Brazilian Inventions. It was the only
laureate invention in the biotechnology area.
However, we know that a huge challenge is in front of us. As
mentioned before, in the fermentation vats there is strong competition
among microorganisms, and only the best-adapted strains reside in the
process. Thus, our invention has no potential to produce a default strain
that could be largely employed. On the contrary, we must be capable of
identifying specific strains from the different sugar mills and modify
them genetically so that they acquire the ability to flocculate according
to the schematic diagram shown above. Recently we achieved this in the
first industrial strains (Cunha et al. 2006) by integrating the flocculation
cassette into the arginine permease gene present in all isolates of the
species. This makes cells resistant to a drug called canavanine, allowing
the selection of the transforming agents. However, the production of
alcohol using these transforming agents is still unsatisfactory, and is
the object of intense investigation.
Additionally, our laboratory team is committed to developing strains
that are more resistant to ethanol and less capable of consume this
compound. Theoretically, this can be achieved by deleting a few alreadyidentified genes. This is an ongoing study and preliminary results are
not yet ready to be disclosed at this time. With these first steps accomplished we are hopeful that it is possible to achieve higher concentrations
of ethanol in the fermentation stage.
Conclusion
Based on all current information, it appears that the demand for
ethanol is no longer a national issue, but a global concern. This change
in scale suggests that future ethanol programs will need to have a lot more
stability than previous programs in order to meet future requirements.
Thus, the search for an increase in ethanol production and in the efficacy
of the process will dramatically increase and will be an opportunity for
Brazil to develop high tech solutions on its own. Innovative improve-
72
ments have already been made to fermentation engineering and the
automotive industry, particularly with the launching of FLEX fuel cars.
However, major advances in the biological process of fermentation, or
more specifically in the genetics of the yeast S. cerevisiae have yet to be
accomplished. This report presents the development of conditional flocculating yeasts that have the potential of eliminating the need for centrifugation from the industrial fermentation process. When this system is
available on the industrial scale, the possibility of having small alcohol/
sugar mills spread all over the country using the fed-batch production
process, will be feasible since the costly centrifugation step will be replaced with genetically modified “smart yeast”.
Anderson Ferreira da Cunha, Silvia Kazue Missawa
and Gonçalo Amarante Guimarães Pereira
Institute of Biology, Department of Genetics and Evolution
State University of Campinas - UNICAMP
Campinas, SP – Brazil
73
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Optimization and Limits
of Ethanol Production
Silvio Roberto Andrietta
Maria da Graça Stupiello Andrietta
1. Introduction
The use of alcohol to replace gasoline, once more a Brazilian reality,
is now a global reality. This biofuel is gaining importance in the world
market as a renewable fuel. This fact has multiple reasons, the main
one being the need for developed countries to reduce their dependence
on crude oil, given that the world’s largest reserves of this fossil fuel
are located in politically unstable regions. Climate changes observed in
recent years have called the attention of the global population to the
effects of global heating caused by burning fossil fuels. Within this scenario, Brazil is in a privileged position since it started a program to
produce alcohol (Proálcool) in 1970. In addition, the country has production growth potential, thanks to the availability of land for growing
sugarcane, the raw material used for alcohol production in Brazil. However, this scenario was not always favorable. Once Proalcool – the program
developed to boost alcohol production – was created, a production peak
occurred as a function of the installation of a large number of industrial
units. At that time there were signs that the price of crude oil would
progressively increase in the years to follow, a fact that was not confirmed. With the price of crude oil falling to a level of 15 American dollars
per barrel in the 1980s, the price of alcohol could not compete with the
price of gasoline, not even with all the existing productivity improvements. So, the government had to subsidize its production, making it
78
less commercially appealing, since its price depended on state positive
intervention. At the end of the 1980s and beginning of the 1990s a problem
of alcohol fuel shortage occurred in fuel stations, creating consumer
distrust. This brought the sales of alcohol-powered cars to near extinction. Eventually, alcohol consumption was dramatically reduced and
the supply became greater than demand. As a function of this new reality,
in the following years the production units invested in sugar mills,
increasing the production of sugar to the detriment of alcohol production.
With the increase in sugar supply, the price of this product in the global
market dropped significantly, having reached its minimum value in 2001,
which caused one of the greatest crises in the production sector.
At the beginning of the present century the marketing of ethanol
has benefited once more from the situation. The introduction of the
dual-fuel motor car by the main assembly plants plus the crude oil price
increase in the global market, associated with environmental appeals,
made alcohol viable again as a price-competitive fuel when compared
to gasoline, bringing investments back into the sector. However, the
1980 and 1990 decades were marked by a lack of investment in fermentation processes. Without investments, ethanol production stabilized
around 15 million liters per year. The sector reacted to this new reality,
and 75 new production units are predicted to be installed until 2015,
with an expected production of over 30,000,000 billion liters of alcohol.
2. Production Limits
Ethanol production in Brazil is not limited by lack of cultivable
land and labor for sugarcane production, but by market oscillations
and lack of definition, by the government, of an energy matrix for the
Country. The price of alcohol depends on different factors such as product
demand and price in the internal and external markets, and price of
crude oil. Because alcohol consumption by dual-fuel motor cars is 30%
higher than gasoline consumption, the price of alcohol should be at
most 70% the price of gasoline for the use of alcohol to become advantageous to consumers. With a strong Brazilian currency, the price of
gasoline has been kept stable in spite of its price increase in the global
OPTIMIZATION AND LIMITS OF ETHANOL PRODUCTION
79
market. This fact limits the price of alcohol in the internal market. On
the other hand, the demand for alcohol in the international market has
been increasing, levering its price upwards. Moreover, the possibility
for Brazil to produce more alcohol – and consequently, less sugar – to
supply the internal market increases the price of sugar in the global
market, making sugar more profitable than alcohol. Should this trend
be maintained, the amount of ethanol produced in the 2006 crop should
be smaller than planned, with likelihood of shortage to the extent that
sales of dual-fuel motor cars would be affected.
With the current installed capacity, ethanol could achieve an annual
production of over 20 million liters, diverting a larger amount of sugar
from sugarcane to ethanol production. However, this may not happen
because when sugar production is reduced, its price tends to increase
and the production becomes economically more interesting.
The combination of these factors will affect the production of alcohol
fuel by limiting it to profits linked to the sale of this product. To solve
this problem a progressive increase in sugarcane production will be
required in order to meet the demand, regulating the price of sugar in
the global market and allowing the alcohol production to increase by
using the excess amount of sugarcane. In addition, policies are required
that favor alcohol production by minimizing the period between the old
and a the news season crop and making it possible for small producers
with small working capital to obtain better prices with the sale of this
product, since they are forced to quickly sell their production in order to
meet their expenses. The increasing demand for alcohol in the external
market is another factor that can cause a shortage in the internal market
in case the price of gasoline is not significantly readjusted in the coming
years. If alcohol prices in the internal market are kept at a high level such
that the use of alcohol for dual-fuel motor cars becomes unfeasible, a
shrinkage in the market of these cars might occur, affecting their
commercialization in the future.
The market of crude oil and sugar is now and will continue to be
the limitation of alcohol production in the next years since the trend is
that the demand for this product will grow faster than supply in the
next few years.
80
3. Production Optimization
The productivity increase in sugar-alcohol industry is based on two
main items, namely, gains in agricultural production and gains in the
fermentation unit.
Gains in agricultural production have occurred since the implementation of the Alcohol Program in the 1970s. New varieties of sugarcane
produced by different research centers have improved agricultural productivity, increasing significantly the production of total reducing sugars
(TS) per acre. This is made possible thanks to studies that were aimed
at finding sugarcane varieties more resistant to different diseases, have
maturation cycles appropriate for early- and late season crops, adapt
themselves better to more rigorous environmental conditions, and reach
higher TS levels. Besides increasing the productivity and profitability
for production units, this improvement and selection task can promote
a 70% reduction in the cost of raw material in relation to the total production cost. Another strength is that these new varieties of sugarcane
can be cultivated in regions that were not indicated before for this type
of culture, such as Center Western Brazil.
On the other hand, although technological innovations were introduced in industry along the years in the extraction, juice treatment,
evaporation and distillation processes, efficacy and productivity gains
are low compared with those obtained by optimization of bioconversion
units. This is due to the fact that these units employ microorganisms to
convert fermentable sugars into ethanol in a totally no sterility environment from the microbiological perspective, without proper control of
the raw material employed, and often using rudimentary processes.
The evolution of alcohol fermentation in Brazil went through various
stages worth describing. Already in the 1960s, the fed-batch process
started being used in Brazil to produce aguardente (a spirit distilled from
sugarcane) and ethanol. Due to its satisfactory performance, this process
was chosen to equip the industrial units that were introduced when the
Alcohol Program was launched, totally replacing less productive methods
such as the cutting process and classical processes traditionally used to
ferment depleted molasses from sugar mills in the early 1960s. Even though
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the operating process was not suitable, given that it tried to maintain
the substrate in the medium at relatively low constant levels throughout
the filling, and since it aimed to prevent the supposed substrate inhibition
of the bioconversion agent (in this case, Saccharomyces cerevisiae yeast),
it was possible to achieve great productivity increase in the processes
thanks to the use of an effective system of cell separation and recirculation that increased the yeast concentration inside the bioreactors. In
the following years, the fed-batch process operation gradually improved
with the implementation of microbiological control laboratories and
became less susceptible to fermentation accidents. However, a more
adequate evaluation of its theoretical fundaments and changes in the
conduction of this process did not occur. Parallel studies on continuous
fermentation processes were started whose primary objective was to
increase the productivity of bioconversion processes, allowing the full
use of the installed equipment, which is impossible in the fed-batch
process. The first continuous fermentation processes were adaptations
of the already existing fed-batch process in the unit. These so-called
first generation processes presented serious operating problems, since
they did not take into account any engineering principle concerning the
in-process flow of material. Both the interconnections between bioreactors and their design were inappropriate, since they allowed in-process
material accumulation due to cell sedimentation inside the bioreactors.
These conception errors in the first processes led to a series of operating
problems that, on their turn, delayed the implementation of new continuous fermentation processes, providing them with undesirable features
such as low stability. During the second half of the 1980s the second
generation of continuous fermentation processes was introduced. These
processes were based on engineering principles that emphasized the
bioreactor design and how bioreactors were interconnected, but the
advances were limited to this. Although operating problems were significantly reduced, the processes continued to present problems, since they
had been intuitively conceived with no previous kinetic studies, which
led to errors that impaired the performance of these processes. In the
beginning of the 1990s the first continuous alcohol fermentation processes based on kinetic studies and greatly concerned with bioreactors
82
design and their interconnections were introduced. These so-called third
generation processes require good agitation in the bioreactors and a
design that allows proper cleansing of the parts that are not immersed
in the wine during the processing, besides preventing in-process accumulation of material inside the bioreactors. These new processes have
been used successfully in many distillation plants built from 1990 on,
without any relevant problems and with good stability. Such evolution
in the fermentation processes was responsible for an approximately 60%
increase in the bioconversion process productivity, from 6.0 g ethanol /
unit volume (liter) of bioreactor x h to values close to 10 g ethanol / unit
volume (liter) of bioreactor x h.
In spite of the advancement occurred during the last years, studies
aiming to improve bioconversion unit productivity have been performed
and several ways have been analyzed and evaluated with the clear
purpose of achieving productivity increase without negatively affecting
the process yield. The main studies include the selection of more productive yeast strains, effective application of kinetic concepts to fermentation
processes, and development of new processes.
In an attempt to find more productive yeast strains, natural selection
was the adopted way, since the use of genetically modified strains showed
limitations due to the characteristic of the process that operates in a
non-sterile manner, therefore with a mixed population of yeasts and
bacteria. Under these conditions, the genetically modified lineages introduced into the process were not capable of competing with native microorganisms present in the process, being quickly replaced. Desirable features
of lineages of industrial use are the following: high yield of ethanol and
cells, high conversion speed, high tolerance toward ethanol, and resistance toward temperatures around 35°C. Based on these features, several
research groups have been working with the purpose of selecting new
strains for industrial use from the fermentation processes themselves,
since yeasts isolated from the sugarcane juice / fermentation vat itself
“ecosystem” have great chances of success in vat environments. Currently, four strains isolated from industrial units are widely employed with
success in industrial processes.
With regard to conception and operation of fermentation processes,
83
an important tool for optimizing the operation and achieving maximum
productivity is the use of kinetic models to better understand the behavior
of the yeast lineages employed in the process. Although the fed-batch
process has been used for years, its operation was not optimized according to kinetic performance. Operations of this process in Brazilian distillation plants are a function of the amount of juice available. In such
distillation plants, the juice from the mill is sent to bioreactors under
the same flow conditions as it was generated, which implies poor flexibility to control the feeding flow. Under these conditions the substrate
concentration changes continuously inside the bioreactors, reaching up
to 120 g/liter. Recent studies showed that the filling speed is in direct
proportion to productivity, meaning that the faster bioreactors are fed,
the faster the fermentation. This fact shows that yeast cell inhibition
caused by high cell concentration in the beginning of the process – where
it can reach 90 g dry mass per liter – is much more significant than
substrate inhibition. In fact, substrate inhibition is not observed with
levels of up to 150 g/liter when treated sugarcane juice is used as raw
material. This fact allows us to state that it would be possible to use a
simple batch process without impairing the process productivity and
that the fed-batch process was adopted only due to the physical limitation
of having to instantly fill the bioreactors. In addition, other factors such
as foam formation and availability of heat exchangers to remove the
heat that was generated are important when making the decision to
adopt the process operation strategy. By using the knowledge of the
kinetics of the process, it is possible to simulate and optimize the operating conditions of these processes and increase their productivity without
affecting the production cost because of an increase in consumption of
inputs or due to yield decrease. Similarly, we found that continuous
processes operating with multiple bioreactors in series show much higher
productivity compared to single-bioreactor fermentation systems. This
occurs because product inhibition and substrate limitation are the factors
that interfere most in the fermentation speed. Thus, processes allowing
the formation of increasing gradients of product and decreasing gradients
of the substrate will favor this bioconversion. Tubular bioreactors would
be the most indicated in this case, but this does not occur because it is
84
physically impossible to maintain a pumped flow for this application,
since during ethanol production a large amount of carbon dioxide is
formed which, when released, would promote the mixture of reactants
materials. However, multiple perfect-mixture bioreactors in series behave
approximately like a tubular bioreactor, being therefore the most
appropriate configuration for this application. Technical and economical
viability studies performed in the beginning of the 1990s showed that
the most appropriate configuration would include four bioreactors in
series. Moreover, the conversion level, particularly in the first bioreactor,
is fundamentally important for the good performance of the system. In
the first bioreactor, conversion levels above 60% are not desirable since
they decrease the fermentation speed during the process, which becomes
less productive and may damage the yeast cells.
To achieve significant productivity increases in alcohol production
in installed plants that use all currently available technological resources,
it is necessary to develop new processes that consider totally revolutionary operating conditions. Within this context and based on fermentation kinetics, different processes using strategies that favor the increase
of productivity of the bioconversion process have been studied. Such
processes follow basically two lines, namely the decrease of product
inhibition by extracting it from the fermentation medium, and the increase of cell concentration inside the bioreactor with no need for recycling.
Extractive fermentation, that attempts in-process extraction of the
alcohol produced from the fermentation medium, aims to increase the
bioconversion speed by reducing the inhibiting effect of alcohol on the
yeast cells. The extraction can be performed in different ways, the most
studied being alcohol evaporation in a flash tank coupled to the bioreactor.
On the other hand, the aim is to increase the system’s conversion
speed by increasing the in-process cell concentration without need for
recycling. For this it is necessary that yeast cells be retained in the
bioreactor, which is possible by means of immobilization processes, with
or without support. Immobilization with support, besides implying higher
costs, eventually brings operating problems, since it requires changing
the bed due to the sizes of bioreactors. A simpler solution would be to use
85
self-immobilizing cells that would not require the use of a support. These
yeast strains have flocculating features and can be used in bioreactors,
forming stable beds through which the fermenting medium percolates.
These processes can reach productivities of over 25 g ethanol per
unit volume (liter) of bioreactor x h and may be considered fourth generation processes. Currently, the great challenge is to stabilize these processes so that they become competitive and safe to the extent of being
installed in industrial units. Based on the performance level currently
achieved by either fed-batch or continuous fermentation processes, fourth
generation processes will have to show that they are really interesting
from the economic perspective in order to be implemented. This will
require many laboratory and pilot scale studies until any one of those
processes deserves the necessary trust.
4. Impact of environmental restrictions on the fermentation
process
Studies performed before 2000 aimed only at productivity increase
and efficacy of bioconversion units. However, particularly in Sao Paulo
state, the new environmental rules – that should reach other Brazilian
states in a near future – have important limitations to operating conditions in ethanol production units. The first rule concerns the amount
of water impounded directly from rivers for use in industrial processes.
Before that, the cooling water used in bioreactors was collected directly
from rivers at a mean temperature of 26°C. Since direct water collection
from water springs is being limited by environmental agencies and will
be charged for in a very near future, alcohol production units are adapting
themselves to the new reality and closing the cooling water circuit. Water
cooling towers are installed in these systems and, depending on the
region, the water is supplied at 30°C. Since the desirable operating temperature in a bioreactor is 34°C, the heat exchanger areas increase, as
well as the flows of water and fermenting wine through the heat exchangers, requiring higher initial investment and higher energy consumption
to displace the reagent fluid and the cooling fluid. The increase in the
cooling water temperature makes operations at temperatures lower than
86
33°C economically impossible; therefore, it is necessary to work with
yeast strains that can resist operating temperatures close to 35°C. In
continuous processes the aim is to achieve decreasing temperature gradients during the fermentation stages. This type of operation becomes
interesting, since temperature becomes more prejudicial to the yeast
cell when associated with high concentration of ethanol. Since the ethanol concentration in the first bioreactor is relatively low, its temperature
can be a little higher. In the case of the last bioreactor, where the ethanol
concentration is higher, temperatures lower that 33°C are recommended.
The second restriction that has been applied to alcohol producers
is the amount of the acidic residue from distillation (vinhoto in Portuguese) that can be applied into the soil according to the potassium concentration existing in it. Such residue is a suitable fertilizer and in some
regions where rains concentrate during a few months of the year, as is
the case in Goias state, this is an important source of irrigation water
for sugarcane cultivation during the draught months. In regions where
rains are better distributed, this acidic residue is less important as source
of irrigation water and becomes a required fertilizer. However, since it is
not too concentrated, its transportation to remote regions makes its use
unfeasible, so a situation is generated where half of the cultivated area
of the production unit receives twice the required amount of potassium
from the acidic residue, while the other half is fertilized with commercial
potassium chloride. This situation should change in the next years since
the addition of potassium to soil will be restricted by the new environmental laws and the production units will have to adapt themselves to
the new rules. The first steps are already being taken and consist of
modifying the operating conditions in bioconversion units in order to
generate more concentrated acidic residue. For this, the units must work
with the highest possible levels of ethanol in the fermented wine, which
implies multiple changes in the raw material preparation process, which
must be capable to generate a feeding medium with concentrations of
substrates high enough to reach desirable ethanol concentrations. This
requires the installation of juice concentrators and brings the end of the
practice that is so common in production units, where the juice from the
first set of rollers is diverted to the sugar mill and the juice from the
87
second set of rollers, which is the result of combined soaking and is much
more diluted, is conveyed to the fermentation unit. The potassium concentration in the acidic residue depends also on the raw material used
in fermentation. When sugarcane juice only is used, where the ratio
between fermentable sugars and total soluble solids reaches values above
85%, the amount of potassium in the acidic residue is lower than when
molasses are used, when this ratio can reach up to 60% for the same
ethanol concentration in the fermented wine. Concerning the acidic residue of distillation, working with spent molasses as raw material from
the fermentation unit seems more interesting. However, the increase in
osmotic pressure and the presence of other inhibiting substances from
molasses in the fermentation medium will eventually reduce the conversion speed and impair the process productivity. One reasonable solution for this problem can be the use of acidic residue concentrators
that would solve the problem of potassium concentration in the residue
without great changes in the fermentation process; however, to have
this, a higher amount of energy would be consumed.
A definite solution should allow to the microorganisms work under
the limit conditions without a decrease in the yield of bioconversion
and from then on the acidic residue from distillation should be concentrated up to the potassium amount required to make the cost of its distribution competitive with the cost of the fertilizer to be acquired in the
market.
5. Final Comments
Since multiple factors point out to an increasing global demand for
alcohol, an increase in alcohol production is interesting. Brazil is one of
the countries with highest potential to increase this production. However,
the volume of investments directed to ethanol production is linked to
market factors, particularly the sugar and crude oil markets.
Productivity increases in production units lead necessarily to agricultural productivity increases; and, for the industry, to optimization of
the bioconversion unit. The great majority of installed industrial units
is outdated and could benefit from the existing technologies already
88
implemented in some industrial units. However, in order to achieve significant gains in productivity, it will be necessary to apply new technologies
that are being studied.
The environmental restrictions imposed on production units require
changes in the operating conditions of the bioconversion units, and the
use of new technologies to handle effluents of these units, as well as
the adjustment of fermentation processes to the new reality will be
indispensable.
Silvio Roberto Andrietta
Maria da Graça Stupiello Andrietta
Biotechnology and Process Division,
Biological and Agricultural Research Center,
University of Campinas (CPQBA/UNICAMP)
89
References
ANDRIETTA, S.R. Otimização de processos de fermentação alcoólica
em múltiplos estágios. STAB Açúcar, Álcool e Subprodutos, 1991;
10(2):32-37.
ANDRIETTA, S.R. Modelagem, simulação e controle de fermentação
alcoólica contínua em escala industrial. Campinas, SP, Brazil 1994, 178
pages. Thesis (Doctor’s Degree in Food Engineering) – Faculdade de
Engenharia de Alimentos, Universidade Estadual de Campinas.
ANDRIETTA SR, MAUGERI FILHO F. Optimum design of continuous
fermentation unit of an industrial plant alcohol production. Advances
in Bioprocess Engineering 1994;1:47-52.
FERREIRA E. Otimização de processos de fermentação alcoólica
operando em batelada-alimentada. Campinas, SP, Brazil 2005, 128 pages.
Thesis (Master’s Degree in Chemical Engineering). Faculdade de Engenharia Química, Universidade Estadual de Campinas.
MOURA AG, MODL J. Concentração de vinhaça. Tecnologia, equipamentos e sua integração energética numa destilaria. Presented at the STAB
International Symposium. Águas de São Pedro, SP, Brazil 2005.
SILVA FLH. Modelagem, Simulação e Controle de fermentação alcoólica contínua extrativa. Campinas, SP, Brazil 1997, 162 pages. Thesis
(Doctor’s Degree in Food Engineering). Faculdade de Engenharia de Alimentos, Universidade Estadual de Campinas.
TOSETTO GM, ANDRIETTA SR. Influência da matéria-prima no comportamento cinético de levedura na produção de etanol. Presented at the
VII Seminar on Enzymatic Hidrolysis of Biomass – SHEB, Maringa, PR,
Brazil 2002.
VIEGAS MC, ANDRIETTA MGS, ANDRIETTA SR. Use of tower reactors
for continuous ethanol production. Brazilian Journal of Chemical Engineering 2002;19(2):167-173.
Innovation and sustainability through
industrial biotechnology
Adrie J. J. Straathof
Çagri Efe
Peter M. M. Nossin
Telma T. Franco
Luuk A. M. van der Wielen
Abstract
Industrial biotechnology is expected to be a large contributor in the
transition from a fossil-resource based energy landscape towards a more
sustainable situation where biobased alternatives should have a substantial role. Two scenarios are presented here that show that on the basis
of current levels of technology, economic feasibility can be expected. Moreover, it is envisioned that complete redesign of the biobased production
of biofuels and chemicals can result in substantial innovation and a
further improved economic opportunities in this inevitable transition.
Introduction
Increasing wealth and a rapidly expanding human population create
an increasing demand on energy and raw materials. Fossils reserves
are steadily drained and environmental (e.g. “Katrina”) and political
(e.g. Iraque) disturbances impact price and security of delivery substantially. Furthermore, emission of CO2 from fossil resources has a substantial impact on climate change. Availability of sustainable, renewable
resources for energy and chemistry are of tremendous societal urgency.
92
Possible solutions may be offered by biobased, renewable resources, in
Dutch “Groene Grondstoffen”, which are essentially created from solar
energy and CO2. Aiming at lowering (towards zero) CO2 emissions and a
reduced dependency on fossil resources, such as crude oil, while meeting
the major technical challenges, new biobased, economic opportunities
will also be created, for the Dutch agro, energy and chemicals industries
as well as for the trade and transport sectors.
The Platform for Renewable Resources (in Dutch: Platform Groene
Grondstoffen PGG) is an advisory committee to the Dutch government
on biobased solutions for the energy and fuels sectors, directed at all
relevant economic sectors. For the Netherlands and under several constraints, a 30% replacement of fossil resources by biobased alternatives
in the year 2030 seems feasible. An important constraint is zero growth
in energy consumption relative to the level of 3000 PJ by the year 2000.
To achieve these goals, a combined package of measures to increase
energy efficiency and reduce consumption as well as to enable a largescale transfer towards biobased (and other) resources is necessary. This
includes issues such as biomass (or its derivatives) and improved use
of available agro-resources and residue streams. The following four main
application areas for biobased resources are distinguished, and estimates
of fossil replacement are given in brackets: transport fuels (60% or 324
PJ/a), chemicals and materials (25% or 140 PJ/a), electricity (25% or 203
PJ/a) and heat (17% or 65 Pj/a). PGG has identified groups of measures
(in Dutch: “transitiepaden”) to achieve this situation by 2030: (1) import;
(2) production of renewable resources; (3) coproduction of chemicals,
fuels and energy; (4) production of synthetic natural gas and (5)
innovative use of renewable resources.
Within the third theme, coproduction of chemicals, transport fuels
and energy, a wide range of conversion and fractionation (bioraffinage)
options are considered. These include bio and thermochemical conversion
towards fuels and chemicals, with the combined production of other
energy forms; i.e. electricity and heat. Not all underlying technologies
are mature, and particular their integration is not yet well established.
This is clearly a field which is seeing and will see major technological
development, and has substantial economic opportunities. A simplified
INNOVATION AND SUSTAINABILITY THROUGH INDUSTRIAL BIOTECHNOLOGY
93
and schematic version of the network of potential conversions towards
desired products is shown (Figure 1).
Figure 1: Schematical and condensed overview of fractionation and conversion
of biomass in desired industrial and consumer products.
Based on these numbers, the biofuels and the chemical sector are
expected to be key players in the transition to a sustainable future. The
scale of the global tendency to embrace biobased solutions in these
sectors will require (also) the large scale use lignocellulosic and other
residual agro streams. Therefore, the inventory of technological and
other innovation opportunities on the basis of specific case scenarios
seems timely and relevant, and is the purpose of this contribution.
Two scenario studies are presented. In the first one, ethanol production from lignocellulosic feedstock is described. In the second one,
the potential to produce acrylic acid from sugars is discussed.
Ethanol production from lignocellulosic feedstock
In recent years, there has been an increasing interest in utilizing
lignocellulosic biomass, which is the most abundant natural feedstock
94
for ethanol production. Almost 70% of cellulose biomass can be hydrolyzed into pentose and hexose sugars, which can later on be fermented
into ethanol.
This section summarizes a desk study on the application of the
current knowledge in the sugar-ethanol industry to investigate the feasibility of sugar and ethanol production from sugar cane in order to search
for alternative usages for the side products of the sugar production and
to improve the existing technology to get more sustainable and environmentally friendly processes.
Therefore a conventional sugar/ethanol plant with current technology (year 2005) was compared to a future plant (year 2015).
In the conventional plant (2005), 52% of the sucrose extracted from
sugar cane is crystallized into sugar and the remainder is fermented into
ethanol. Bagasse, the fiber remaining after extraction, is burnt to generate electricity. The vinasse, which is the organic and salt-rich stillage
from distillation; the filter cake, which is rich in coagulated proteins,
gums, organics, sulphate and phosphate salts; and the cogenerator ash,
which is mainly composed of the mineral portion of the bagasse, are
sent back to the fields to be used as fertilizer for the cane plantations.
The proposed 2015 plant is generated based on the current technology. However, in this future case, the cellulose and hemicellulose fractions of lignocellulose are hydrolyzed into hexose and pentose sugars
to be used as substrate for ethanol production. In addition, vinasse,
filter cake and the genetically modified yeast are combusted and streams
rich in organic materials are treated in a wastewater treatment plant.
The proposed plant location is Sao Paulo, a state of Brazil. The
proposed plants have a sugar cane processing capacity of 5 million tons/
year, which is within the range of the top ten largest existing plants.
The ethanol processing plants yield yeast, carbon dioxide, vinasse,
filter cake and bagasse as side products. Using the existing technologies,
the yeast output of the plants is minimized and the yeast produced is
combusted. The conventional plant utilizes bagasse as fuel for electricity
and steam generation for the process.
In the conventional plant, the main input streams to the plant are
sugar cane and recycled water. Minor raw materials are limestone, sul-
95
phur and sulphuric acid. In the future case, in addition to the inputs listed
for conventional plants, acidifying agents for pretreatment and cellulase
for cellulose hydrolysis are inputs of the process.
The design contains the following items, which are partly summarized in this text:
Basic assumptions, plant capacity and location, composition of
streams entering and leaving the process, block schemes and pure component properties.
Thermodynamic properties relating to the components in the
system.
Process and the flow scheme of the plants.
Process controls required.
Mass and energy balances.
Equipment designs.
Safety and HAZOP analysis.
Wastes generated.
Economical evaluation.
·
·
··
··
··
·
Description of the 2005 Plant
The streams entering and leaving the designed 2005 plant are given
in Figure 2.
Figure 2. Process yields calculated for the 2005 plant (flows are given per ton of sugar cane)
96
The sugar cane from fields is fed into a milling unit. Five roller
mills are used in series that contain three rollers and another pressure
roller.
Bagasse from the mills is sent to a bagasse handling unit where
the moisture content is reduced from 50 to 12 % and then it is sent to
cogeneration and boiler units where it is combusted as fuel for the generation of steam and electricity for plant use. Since water evaporates
during the combustion, its contribution to the heating value is negative.
The airflow into the cogenerator is preheated by flue gases and then the
flue gases are passed through the dewatering section to reduce the
moisture content of the bagasse.
The dark green juice from the mills is acid and turbid with a pH of
approximately 5.5; 35% of the juice is destined for ethanol production
and the remainder goes for sugar production. These proportions are
determined based on the assumption that 48% of the sucrose in the
juice is converted into ethanol and the rest into sugar crystals.
A sulphitation unit operation is used to bleach the juice. The required
sulphur dioxide is produced by burning elemental sulphur in sulphur
burners and absorbed by juice in a sulphitation tower.
Following sulphitation, overliming takes place to neutralize the juice
to pH 6-8. Lime milk, about 0.5 kg CaO per ton of cane, neutralizes the
natural acidity of the juice, forming insoluble lime salts. Heating the
limed juice (95°C or above) coagulates the albumin and some of the fats,
waxes and gums and the precipitate formed entraps the suspended solids
as well as finer particles.
The Ca(OH)2 is produced from CaCO3. The limestone is burned in a
calciner to produce CaO, which is later on blended with the juice from
the filters to prepare the lime milk. After sulphitation, during liming
and juice heating, polymeric flocculant is added to the juice in clarification units. Sedimentation is carried out in tray type clarifiers and a rotary
filter unit is used to recover the juice. The filter cake is sent back to the
fields as fertilizer.
The clarified juice is sent to a six-staged multi-effect evaporation
section to increase the sugar content of the juice to 68 % w/w. The condensates from the evaporators are sent to a cooling tower and recycled
97
as process water. The last vapor is condensed in vacuum generators and
removed as condensed water.
In the next step, the concentrated sugar solution is sent to vacuum
boiling pans. The crystallizer is fed with the crude sugar from the second
stage crystallizer to supply the seed for the crystallization of the sugar.
The molasses from the first pan is fed into the second pan and the molasses from the second pan is fed to the fermentors. The solid contents
of the molasses from the centrifuge vary between w/w 60-70%. The moisture content of the crystal sugar from the centrifuge is less than w/w
1%. The sugar recovery in each crystallizer is 60% and the total sugar
recovery is 84%. Crystalline sugar from the centrifuge is sent to driers.
Rotary granulators are used for drying.
The clarified juice is mixed with filtered juice from filters and molasses from crystallization. During the fermentation, sugar is converted
to ethanol with 92% of the theoretical yield, which corresponds to 0.460.47 g ethanol/g sugar. Fermentation is carried out in six vessels to
maintain a continuous operation and to prevent the need for extra storage
tanks for broth and recycle biomass. The biomass is recycled to maintain
high cell concentrations in the fermentors. The biomass is separated
from the broth using continuous disc type centrifuges and sent to a
biomass sterilization vessel, which is a stirred vessel for blending the
biomass with a pH 2 acid solution.
The carbon dioxide-rich gas from the fermentors is passed through
an ethanol scrubber column to prevent volatile organic emissions to the
atmosphere and to recover lost ethanol. This column is not only fed
with the gas from the fermenter, but, also with the carbon dioxide rich
vapor distillate from the beer column. The absorption water is recycled
from the evaporators and boiling pans. Carbon dioxide is released to
atmosphere.
The medium from the fermenter is mixed with the ethanol solution
from the ethanol scrubbers and sent downstream.
In a beer column, ethanol is separated from the wine (initially at
~8%) as a vapor (~40%). The product is removed as a vapor stream
from the sixth stage of the column. The carbon-dioxide rich distillate is
removed out the tower at a temperature of 20ºC to reduce the amount of
98
ethanol in the vapor. The bottoms, stillage, has most of the salts and
suspension solids, but most important of all is the significant amount
of glycerol, acetic acid and fusel oils in the bottoms. To recover the fusel
oil and glycerol, another side draw is installed on the column, one stage
above the reboiler, to separate most of the fusel oil and glycerol from
the vinasse. All of the vinasse (the stillage) used as fertilizer. In a rectification column, the product from the beer column is concentrated to
92.5 % and some impurities are removed. Bottoms are removed with the
side draw of the beer column outside the battery limit to be further
purified.
The final dehydration of ethanol is carried out in molecular sieve
absorption columns. These work in tandem. The columns are regenerated
by using hot nitrogen at 200ºC. The nitrogen is circulated in the system.
Description of the 2015 Plant
The streams entering and leaving the designed 2015 plant are given
in Figure 3.
Figure 3. Process yields calculated for the 2015 plant
(flows are given per ton of sugar cane)
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The 2015 case process is conceptually designed based on current
2005 technology. Like in the 2005 case, 48 % of the sucrose will be utilized for ethanol production and 52% will be isolated as sugar crystals.
On the other hand, in the future case, the bagasse, the lignocellulosic
portion of sugar cane, will be hydrolyzed to pentose and hexose sugars
and lignin. In addition, the organic waste generated in the process (i.e.
vinasse, filter cake, and microorganisms) will also be combusted in cogeneration units instead of sent to the fields untreated. The milling unit,
sugar section and ethanol recovery section have the same structure as
in the 2005 plant with some variations in equipment sizes.
The first step in bagasse hydrolysis is pretreatment. Acid-catalyzed
steam explosion is used. The liquid portion is removed from the fibers
via screw presses. Before detoxification, some of the hydrolysate is
bypassed to readjust its pH from 10 to 4.5. The fiber portion is transferred
to cellulose hydrolysis vessels. The wash water for the screw presses is
a portion of conditioned hydrolysates. The reason for this is to prevent
dilution of the hydrolysate and to avoid large reactor sizes due to the
dilution.
The acetic acid concentrations are 2-3 g/l and do not inhibit fermentation. By diluting the hydrolysate with molasses clarified juice and
filtrate from the filters, the concentration of all the inhibitory compounds
will be halved. The final concentration of lignin degradation products
going to fermentors after overliming is 1.4 g/l. Considering the high
cell concentrations, this will not inhibit fermentation thus, detoxification
is considered only during the overliming. Detoxification is carried out
by overliming to pH 10.
The suspension from the clarifiers is sent to a rotary filter and
dehydrated to 55% water. The filter cake is sent to the cogenerator due
to the presence of the organic material inside the cake. The filtrate is remixed with hydrolysate. As previously mentioned some portion of the
hydrolysate is utilized as wash water for the screw presses. The remaining portion is sent to hydrolysis vessels.
After pre-treatment the detoxified liquid fraction contains the pentose sugars and this stream is used to dilute the fibers to 20% solids.
The solid fraction from pretreatment contains the cellulase and the lignin
100
fraction. This solid fraction is exposed to cellulase to hydrolyze the
cellulose in the hexose sugars. The cellulose hydrolysis vessels are composed of two parallel vessel sets of four vessels in order to mimic plug
flow behavior and to prevent from being vessel volumes too large.
After cellulose hydrolysis, lignin residue is separated from the mixed
sugar solution and sent to the cogenerator as fuel. The liquid fraction
which contains sugars is sent to the fermentors to produce ethanol.
Similar to the 2005 plant, seven fermentors are utilized for fermentation.
The downstream processes have the same structure as in the conventional plant.
The waste streams generated in the process are the filter mud containing sugar cane organic ingredients, vinasse and water. The wastewater (condensates and vapors from evaporators, boiling pans, detoxification and dehydration) undergoes water treatment outside the battery
limit, but the costs are included.
The vinasse is concentrated and sent to the cogenerator as fuel.
The lignin residue, yeast and the filter mud are dehydrated using the
flue gasses from the cogenerator before being sent to furnace. Since the
generation of steam and electricity is not sufficient to meet the demands
of the plant, the generation of electricity is lowered and the generation
of steam is increased to meet the demands. The excess of demand for
electricity is supplied by purchasing from the grid.
The solids from the furnace (ash, gypsum and dirt) are sent to land
fills.
The acid solution from the yeast sterilization unit is neutralized using
lime and precipitated to be treated as land fill. The unit is outside the
battery limit, but the costs are included in the cash flows.
Economy of 2005 Plant
The results of an economical analysis of the 2005 plant reveal that
the required total capital investment is $102 million. The investment is
determined using the location factor of 0.4 for Brazil. This factor is
determined based on the social and economical comparison of Brazil
with the US and European countries. Based on this investment value,
101
the net present value of the investment is $166 million using a discount
rate of 4%. The sensitivity analysis shows that plant operation is profitable for a location factor of up to 0.7. The pay out periods is below 3.5
years up to a location factor of 0.7. This time period is acceptable for
chemical plants. The same analysis reveals that the maximum interest
rate for which investment can remain economical throughout the investment period is 26.5% for the location factor of 0.4. This value falls to
3.7% when the location factor is increased to 0.7. When compared to the
current US inflation rate (~3.2%), the plant still remains compatible
with the market.
A cash flow analysis reveals that the price of sugar cane is the
main yearly operational cost (87%). Therefore, the economic parameters
are highly sensitive to the price of sugar cane. The other cost factors do
not have major economic effects. The sensitivity analysis is carried out
on the net present value, pay out period, discounted cash flow rate of
return and rate of return values. Although the parameters are highly
sensitive to the price of sugar cane, the net present value of the investment is $106 million even when the price of sugar cane is 20% higher
than current prices.
The parameters also are highly sensitive to revenues (ethanol and
sugar). The sensitivity to electricity is lower, but still higher than the
sensitivities to minor operating costs like utilities, labor etc.
The production costs of ethanol are higher than the current reported
production costs ($190/ton). However, the minimum production costs,
excluding everything except the sugar cane, are approximately $140/
ton. Therefore, more insight into details of the plant should be obtained.
The overall conclusion is that the 2005 plant is economical and
favorable for investment even for investment costs of up to $170 million.
Economy of 2015 Plant
The calculated investment requirement for the 2015 plant is $133
million after including the location factor of 0.4 for Brazil. The net present
value of the 2015 plant is $370 million, which is more than double the
present value of the 2005 plant. The reason for this is that when ligno-
102
cellulose hydrolysis is included in the design the investments do not
change significantly, while the revenues are almost doubled. The payout
period for the 2015 plant is 1.4, which means the plant recovers the
investment in less then 2 years. The analysis shows that the plant remains profitable as long as the location factor is increased up to 1. The
discounted cash flow analysis reveals that the plant investment can
stand interest rates of up to 38% and 7.3% for location factors of 0.4 and
0.9, respectively.
Like in the 2005 plant, the costs of sugar cane and the selling prices
of ethanol and sugar are the major factors that can negatively affect the
economic parameters. However, even a negative deviation of 30% in the
price of sugar cane from the current prices yields a net present value of
$150 million, which proves to be a profitable investment. In the 2015
plant, the economic parameters are not as sensitive to sugar cane and
sugar prices as to ethanol prices. Still there are major effects. The
variations of ±30% in ethanol and sugar prices yielded ±60% variations
in the net present value of the investments. The sensitivity to cellulase
prices is not as high as the sensitivity to sugar cane and product prices.
Variations of ±30% in cellulase price yielded ±6% in net present value
of the investment. None of the cost factors (i.e. labor, fixed cost etc.)
have major effects on the economic parameters. Variations in fixed costs
affected the parameters most, but still the sensitivity is ±6% for variations of ±30%.
The costs of ethanol production (~$167/ton) are significantly lower
than the production costs in the 2005 plant.
In conclusion, this analysis shows that it is highly attractive to
focus on ethanol production from lignocellulosic feedstocks.
Feasibility of fermentative acrylic acid production from sugars
As mentioned above, renewable materials such as sugars are interesting alternative carbon sources for the production of fuels and chemicals, in particular considering the potential of modern biotechnological
methods. Acrylic acid is one of the target chemical products that is occasionally discussed in this context (Danner and Braun, 1999; Carole et
103
al., 2004; Willke and Vorlop, 2004). The potential of biotechnological
routes to produce acrylic acid were recently reviewed (Straathof et al.,
2005) and this study is summarized here.
Acrylic acid (also known as 2-propenoic acid) is a commodity chemical with an estimated annual production capacity of 4.2 million metric
ton, which ranks it about 25th in the list of organic chemical products.
The major utilization of acrylic acid, its salt and esters, is in polymeric
flocculants, dispersants, coatings, paints, adhesives and binders for leather, paper and textile. Acrylic acid is conventionally produced from
petrochemicals. Currently most of the commercial acrylic acid is produced
by partial oxidation of propene. In the so-called single-step process, the
yield is at most 50-60%, resulting in large amounts of waste. A two-step
process via acrolein is preferred, achieving about 90% yield overall. There
is a requirement for efficient one-step processes starting from cheap
carbon sources. Unfortunately, petrochemical carbon sources are not
renewable. This implies that their use adds to global CO2 emissions and
that they should become scarcer and more expensive in the future. Fermentative production of acrylic acid from sugars might be an interesting
alternative.
A major hurdle for the development of an industrial fermentative
process for production of acrylic acid from sugars is the toxicity of acrylic
acid to potential host organisms. However, by analogy to other fermentative carboxylic acids, it may be assumed that microorganisms after
adaptation might survive at concentrations up to 50 g/L acrylic acid.
The current literature reports only very low yields of acrylate on
sugars (Straathof et al., 2005). Still, several attractive candidate metabolic pathways for converting sugars to acrylate have been identified (see
Figure 4). The efficient expression of any of the candidate pathways in a
host organism will require extensive genetic engineering and might even
require some as yet unknown enzyme activities and export proteins.
Some pathways might result invery high yields of acrylate on sugar,
without aeration. However, these pathways, including export of acrylic
acid out of the cell, still need to be evaluated in more detail to show that
a microorganism could generate ATP from them. If not, pathways that
will lead to economically less attractive routes might be required instead.
104
Figure 4. Potential metabolic pathways to acrylic acid. 3-HP = 3-hydroxypropanoate.
Assuming that a host organism can be constructed for the effective
production of acrylate, a fermentation process including removal of pure
acrylic acid was conceptually designed and economically evaluated. This
process (Figure 5) uses known technology.
Figure 5. Flow sheet of the hypothetical process designed for the production
of acrylic acid from sucrose. Only major equipment and steams are shown.
105
An economic evaluation shows that the designed process will be
feasible. The cumulative net present value and internal rate of return
were found to be 220 million euros and 34%, respectively. This indicates
that there is a clear incentive for development of the required microbial
host and the process, in particular considering the environmental sustainability of the designed process (Straathof et al., 2005).
Conclusions
The case studies presented here clearly indicate positive opportunities for biobased processes using industrial biotechnology for chemical
alternatives. In both scenarios, relatively conventional technology was
employed to strengthen the view that these opportunities are within
reach. The case studies also underline the need to develop second generation processes on the basis of lignocellulosic and other residual flows.
In part the need originates from indications of limited availability of
conventional sugar-based fermentation feedstocks (see other contributions in this work). But moreover, a straightforward and not fundamentally reconsidered approach will not fully utilize the innovation
potential of the biobased opportunities that the near future forces humanity to embrace.
Acknowledgements
These investigations were supported (in part) by the Netherlands
Ministry of Economic Affairs through the Netherlands Organisation for
Scientific Research (NWO) in the NWO-ACTS research programme BBasic and in part by Fundação de Amparo à Pesquisa do Estado de São
Paulo, Brazil FAPESP).
106
Adrie J. J. Straathof a, Çagri Efe a,
Peter M.M. Nossin b
Telma T. Francoc and Luuk A. M. van der Wielen
a
a*
Department of Biotechnology, Delft University of Technology,
Julianalaan 67, 2628 BC Delft, The Netherlands
b
DSM, Corporate Technology,
P.O. Box 18, 6160 MD Geleen,
The Netherlands
c
Chemical Engineering School, State University of Campinas
(Unicamp),
P.O. box 6066, Campinas, São Paulo, 13081-970 Brazil
* Corresponding author.
Tel.: +31-15-2782361. Fax +31-15-2782355.
E-mail: [email protected]
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biobased products industry. Appl Biochem Biotechnol 113-16: 871-885.
Danner H, Braun R (1999) Biotechnology for the production of commodity
chemicals from biomass. Chemical Society Reviews 28: 395-405.
Straathof AJJ, Sie S, Franco TT, van der Wielen LAM (2005) Feasibility of
acrylic acid production by fermentation. Appl. Microbiol. Biotechnol.
67: 727-734.
Willke T, Vorlop KD (2004) Industrial bioconversion of renewable resources as an alternative to conventional chemistry. Appl Microbiol
Biotechnol 66: 131-142.
Rabou, L.P.L.M., Deurwaarder E.P., Elbersen, H.W., and Scott, E.L. (2006),
Biomass in the Netherlands Energy Household in 2030. Platform Groene
Grondstoffen , jan 2006.
Advances of the Brazilian production
of chemicals and other products from biomass
Introduction
Brazil is fortunate for the abundant and diverse agricultural and
forest resources. Occupying a total area of 8,511,996 km2 between 5°16’N
and 33°44’S, Brazil has a broad climatic and geomorphologic variety,
which is responsible for the presence of several important biomes and
ecosystems, which lodge about 10% to 20% of the world’s known living
species [1].
In the last 50 years, Brazilian agribusiness is developing into a
more modern, more efficient and much more competitive sector. The
Brazilian climate, the reasonable rain distribution, the solar energy, the
abundance of water resources and the size of the available land are
factors which make 390 million hectares suitable for agriculture. However, not all this land is used so far for this purpose. In the year 2005,
thirty and three percent of the GNP (gross national product) resulted
from agribusiness, which provided 37% of the jobs in Brazil and was
responsible for 42% of the national exports. The main products of Brazilian agribusiness are coffee, sugar cane, ethanol, fruits and processed
fruit juices, soybean, cattle and beef, chicken products, tobacco, leather,
cotton [[2].
Besides of nature, there were target directed efforts to improve Brazilian agriculture as the creation of Embrapa, Brazilian Agricultural Research Corporation’s, in 1973 by the Ministry of Agriculture in order to
speed the development of agriculture technologies & innovation. It helped
108
Brazil to increase the offer of food while, at the same time, conserving
natural resources and the environment and diminishing external dependence on technologies, basic products and genetic materials. Networking
of research centers, service centers and central divisions of Embrapa
make that almost all the states of the Union have an Embrapa local
agency. For each Brazilian main agribusiness there is usually at least
one Embrapa local agency close to the producers [3].
Another important and direct effort was targeted towards the study
of the biodiversity. The first program was designed in 1999 in Sao Paulo
state supported by Fapesp, which is the Biota program (Fapesp is the
The State of São Paulo Research Foundation). Biota, in less than 5
years, managed to aggregate more than 500 researchers from different
50 projects in a virtual network and described more than 4 thousand
species of plants, animals and microorganisms of Sao Paulo State. The
success of the program is registered by the online journal Biota neotropica [4]. A similar program was created later by the Science and
Technology Ministry (CNPq) aiming to identify the national biodiversity.
A very important action was taken in order to improve the in depth
knowledge of the main Brazilian crops. Several projects on plant genomics have been developed in the last five years, also with the support of
Fapesp and CNPq (orange, sugar cane, coffee, eucalyptus, banana, etc.).
Therefore, the discussed maturity of the Brazilian sugar cane agribusiness is not a result of random causes, but of several organized initiatives developed by national and local administrations and by the associations of the producers (i.e: Copersucar earlier, CTC more recently) with
research centers.
1. Recent advances of genetic engineering of the Brazilian
sugar cane
In 2003, it was announced that a team of Brazilian scientists had
sequenced the genome of sugarcane. Their findings, published in a forthcoming issue of Genome Research, suggest that 2,000 of the more than
33,000 genes in the sugarcane genome are associated with sugar production in the plant. The sequencing of the genome was co-ordinated by Paulo
ADVANCES OF THE BRAZILIAN PRODUCTION OF CHEMICALS...
109
Arruda of the State University of Campinas (Unicamp). More than 200
scientists from 22 Brazilian research groups were involved in the study,
which started in 1999 [5]. Earlier, these Brazilian laboratories participated
in the Sugarcane Expressed Sequence Tag Project (SUCEST), which was
launched in September 1998. The project was supported by CTC (a private
company) and the Fapesp. Different aspects were mainly targeted, as pathogen response, photoreceptors, cell cycle, and aluminum tolerance [6].
Genetic engineering has given to Canavialis, a Brazilian company
targeted to sugar cane development, a new tool for development of novel
varieties. With this tool, one is able to identify the DNA sequences that
confer a desired trait and transfer that trait from one plant to another
without having to perform crosses, and without altering the other traits
of that variety. The gene marked for insertion can come from a plant of
the same species, or from other plants of different species, or even from
other organisms and animals. Thus, the possibilities for advancement
through the use of this technology are broad. In this scenario, classic or
conventional genetic improvement breeding is fundamental since the
traits introduced through genetic engineering should be added to elite
varieties adapted to the soil and climate conditions of the sugarcanegrowing regions. Therefore, transgenic sugar cane plants have also been
studied by Brazilian laboratories in cooperation with local industries [7].
2. Top value added chemicals from biomass
A study developed by the Pacific Northwest National Laboratory
(PNNL) and the National Renewable Energy Laboratory (NREL) of USA
in 2004 described a series of top value products from all biomass components, identified a group of promising sugar-derived chemicals and
materials that could serve as an economic driver for a biorefinery. Top
value added chemicals from biomass, 2004). [8] Initially a group of 300
possible building blocks was identified from a variety of resources, however after the development of a more critical screening criteria, this number
was reduced to 30 and later to 12. These building block chemicals which
can be produced from sugars via biological or chemical conversions were
identified and selected and the subsequent conversions into a number
110
of high-value bio-based chemicals or materials were studied. The final
list of the American study is the following: 1,4-diacids (succinic, fumaric
and malic), 2,5-furan dicarboxylic acid, 3-hydroxy propionic acid,
aspartic acid, glucaric acid, glutamic acid, itaconic acid, levulinic acid,
3-hydroxybutyrolactone, glycerol, sorbitol, and xylitol/arabinitol.
Building blocks are molecules with multiple functional groups, which
can be later transformed into other group of molecules, by chemical or
biological conversion.
As, potentially, a group of desirable chemical building blocks can
be obtained from biomass, the current literature already describes the
efforts to establish technologies to develop flow-chart models for products
derived from biomass feedstock, similarly to the flow-charts previously
developed for the petrochemical industry. The idea of flow charts is based
on chemical data, known market data, properties, performance of the
potential candidates and the prior industry experience.
The current literature already describes the achievements and the
planning of some large industries on the development of products based
on biorenewables, like the 1,3 propanediol (DuPont, USA), polylactic acid
(Cargil, USA), PHB (joint 50 ton plant: Metabolix + ADM, USA and another plant by PHB, Brazil), fermentative route for caprolactam (DSM,
Netherlands), the development of L-methionine, L-lysine and L-threonine
routes (plans of Degussa) [9].
Brazilian situation towards top value added chemicals from
biomass
This present work aims to review the main Brazilian results on the
use of sugar cane as a biomass to produce chemicals or chemical products, besides of the bioethanol.
Four hundred million tons of sugar cane is currently employed in
Brazil for the production of 20 million tons of raw sugar-cane and 15
billion liters of bioethanol yearly. The potential of the sugar cane is not
new, since it played a central role in Brazil’s culture and economy since
the beginning of the colonial period, when a significant amount of sugar
was exported to Europe.
111
Research on the fermentation of sugar cane has extensively been
investigated in Brazil, mainly towards the bioethanol and yeast production. Therefore, initially this present work focused on a survey to identify
the work done in Brazil on the production of these twelve building blocks,
described by the American screening. However, very little information
was found on those building blocks production, most of the information
found was related to organic acids, aminoacids and biopolymers.
The most often produced chemicals in Brazil by fermentation of
sugar cane as feedstock, as also other products obtained from biomass
were identified (Figure 1 and Table 1) and will be described.
Figure 1: Chemicals and products produced from sugar cane as biomass, in Brazil.
112
Table 1: Chemicals and products produced from sugar cane as biomass, in Brazil.
113
3. Organic acids produced by fermentation of biomasses
Besides the two industries which produce and commercialize citric
acid and lactic acid in Brazil, several processes were developed in universities and research centers on this topic, where submerged and solid state
fermentation were mainly employed. Soccol and collaborators have extensively studied the possibility of producing reasonable concentrations of
lactic and fumaric acid in culture media using agricultural wastes as a
solid substrate. They also studied the optimization of processes to achieve
twenty grams per liter of fumaric acid by fermentation of Rhizopus strains
in culture media containing cassava hydrolysates and for bioconversions
to produce organic acids, flavours, aromas and mushrooms [10-12].
Submerse aerobic fermentation also leads to fumaric acid production
by Rhizoups, then it was purified by precipitation with CaOH in H2SO4,
when the achieved yield is 0.6 kg/ reducing sugars. The chemical route
for fumaric acid can be cheaper, but the fermented route is nowadays
preferred due to the clients preference for natural products. Acetic acid
is mainly produced in Brazil by chemical route; however there is some
production by fermentation with Acetobacter at 30 to 35 C and initial
pH 4.5. The acid is further recovered by liquid extraction or by distillation.
Fermentation yields of acetic acid can reach 115 g/l [13].
Lactic acid and lactates are produced by PURAC Sínteses in Campos,
Rio de Janeiro state, in plants located next to sugar mills. [14] Sucrose is
used as main substrate in a relatively simple fermentation route and the
produced lactic acid is then recovered by ion exchangers. Despite of the
lactic acid production in Brazil, there is currently no production of polylactates there.
Citric acid is also produced by submerse fermentation of Aspergillus
niger in the Mercocítrico Fermentações S.A., in Ribeirão Preto, São Paulo
state, and is further recovered. [15] Currently there is no chemical process
for citric acid production.
4. Production of biodegradable plastic in Brazil
PHB Industrial S.A. is a Brazilian company created by Biagi and
114
Balbo groups, two large producers of the sugar & bioethanol sector,
located in Serrana, São Paulo state (Figure 2). Their joint area of land
for sugar cane crop is approximately 100,000 hectares, from where 20
million pack of sugar (50 kg/pack) and 500 million litres of bioethanol
are obtained. This year, this company announced an investment of U$
50 million to scale up the production of 2,000 tons/ year of polyhidroxybutyrate, which would allow the preparation of 4,000 tons of
composites/ year [16].
Figure 2: PHB Industrial S.A. plant located in Serrana, São Paulo state.
According to Rossell [17] PHB is an environmentally degradable
material belonging to the polyhydroxyalkanoates (PHA) family, polyesters which were first described in 1926. It has some unique characteristic among thermoplastics because it presents a complete cycle starting
from sugar cane and bacterial fermentative synthesis. In the absence of
microorganisms biodegradability the hydrolysis of PHB in aqueous environments is slow, because of its hydrophobicity. Thus, in principle, the
115
lifetime of a stored PHB product is unlimited; after its disposal, however,
PHB becomes clearly biodegradable in domestic effluent-treatment systems. PHB is a biocompatible, biodegradable, thermoplastic, hydrophobic,
and stereospecific material. It has a high molecular mass, high crystallinity (55 to 75%), good chemical resistance, and its barrier properties
enable practical packaging applications. Polyhydroxybutyrate can be
processed as a conventional thermoplastic in most industrial transformation processes, including extrusion, injection, and thermopressing
and can be transformed into rigid shapes (for example pipes) and films
for packaging. PHB can also be modified by extrusion by incorporation
of additives (stabilizers, plasticizers, and pigments), immiscible additives
(e.g. wood and starch powder), or by mixing with other plastics.
The investigation on the feasibility of the production of PHB in Brazil
was developed during the 90’s, with a partnership between Centro de Tecnologia Canavieira (ex-Copersucar, nowadays CTC), the Institute of Technological Research (IPT) of the State of São Paulo and the Institute of
Biomedical Sciences of the University of Sao Paulo. In the year 2000, the
rights for the production of PHB were sold from Copersucar to the PHB
Industrial S.A. The production capacity was at that time about 1.5–2.0
t/ year and currently, it operates a capacity of 60 t/yr, by fermentation of
the sucrose from sugarcane by Ralstonia eutropha (Alcaligenes eutrophus) [16].
According to this industry, there is a technical limitation to scale
up the PHB production, which is the size of the anaerobic fermenters.
The largest feasible anaerobic tanks have capacities of 500 m3, but the
most often used ones have 200 m3. The cells of the microorganisms in
the PHB Industrial SA can produce up to 100g PHB/ /L, with cell concentrations up to 180 g /L (60 to 70% of cell mass is PHB); being the biopolymer extracted from the cell with alcohol at high temperatures. The achieved quality, properties and resistance of their purified polymer are similar
to non-biodegrable polymers.
Besides the Brazilian PHB Industrial S.A., there is only one company
which also produces PHB, Metabolics (created in 1996 in the USA). This
company has announced the scaling up of their PHB production to 50,000
tonn/year.
116
6. Xylitol
Different techniques have been used by Faenquil’s group to produce
xylitol by fermentation, always employing hemicellulose hydrolysates.
The most used substrates described by the group were the hydrolysates
of rice straw, sugar cane bagasse and the most described microorganism
was Candida guilliermondii.. Xylitol concentrations as high as 36 g/L
were achieved, corresponding to a xylose-to-xylitol yield factor (YP/S)
up to 0.79 g/g. Different processes to produce xylitol were compared
and Table 2 shows that the conversion factors of xylose into xylitol and
the volumetric productivities were strongly affected by the source of the
hydrolyzed biomass [18].
Table 2: Effect of the raw source hydrolysates on the conversion
factors (Yp/s ) of xylose into xylitol and the volumetric productivities Qp.
Raw material
hydrolysates
Yp/s (g/g)
Qp (l/h)
Rye bran
0.61
0.33
Corn cob
0.71
0.60
Corn cob
0.52
0.26
Sugar cane bagasse
0.79
0.52
Corn leaves
0.64
0.36
Eucalyptus wood
0.63
0.41
Eucalyptus wood
0.04
0.02
Rice straw
0.72
0.57
Source: [18]
7. Aminoacids production by fermentation
Lysine is currently produced by Ajinomoto in Sao Paulo State, by
fermentation process, due to the large demand of feed industries. Glutamate is also produced there to attend the demand for flavor enhancers
and large part of the production is exported to several countries. Another
117
plant for lysine in Sao Paulo state was recently announced by a Korean
industry, which should be ready this year.
8. Other products
Different products were developed by the former Coopersucar (CTC)
and by several research Brazilian groups in order to aggregate value to
sucrose and to sugar cane. Technologies were developed for microbial
production of xanthan gum, dextrans and other biopolymer, some other
organic acids, polyols, aminoacids and enzymes. Also, sugar cane bagasse applications were developed for paper and packing industries as
also for composites (already commercialized).
Processes for the production of solvents have extensively been
studied and more recently, many companies are developing methods on
alcohol chemistry to produce solvents, polymers and other products
derived from bioethanol.
Chemical Engineering School,
P.O. box 6066, Unicamp, Campinas, 13081-970, Brazil
e-mail: [email protected]
118
References
1. Motta, R.S The economics of biodiversity in Brazil. Texto para
discussao: Ipea, ISSN1415-4765, 1998.
2. Ministério da Agricultura Brasil (http://www.agricultura.gov.br)
3. Embrapa (www.embrapa.br)
4. www.biotaneotropica.org.br
5. Vettore, A. L., Silva, F. R., Kemper, E. L., et al. (2003), Genome
Res. 13, 2725–2735.
6. Pessoa Jr. A; Roberto, I.C; Menossi, M; dos Santos, R.R; Ortega
Filho, S.; Penna, T.C.V.Perspectives on Bioenergy and Biotechnology in
Brazil. Applied Biochemistry and Biotechnology 121–124, 2005.
7. www.canavialis.br
8. Pacific Northwest National Laboratory (PNNL) and the National
Renewable Energy Laboratory (NREL) of USA in 2004.
(http://www.osti.gov/bridge/)
9. Kirchner, M, Chemical industry, white biotechnology and renewables. Renewable resources and biorefineries, Ghent, 2005.
10. Soccol, CR, Marin, B, Raimbault, M, Lebeaut, JM . Breeding and
growth of Rhizopus in raw cassava by solid state fermentation. Appl.
microbiol.biotech. 41 (3): 330-336, 994.
11. Carta, F.C; Soccol, CR; Ramos LP and Fontana. J. D. Production
of fumaric acid by fermentation of enzymatic hydrolysates derived from
cassava bagasse. Bioresource Technology 81-97. 2000.
12. Pandey, A, Soccol, CR, Nigam, P, Soccol, V.T. Vandenberghe, LPS,
and Mohan.R Biotechnological potential of agro-industrial residues. II:
cassava bagasse. Bioprocessing and Characterization of Lignocellulosics
Bioresource technology 68 (1): 23-28, 1999.
13. Coopersucar – personal communication.
14. PURAC Sínteses, personal communication
15. Mercocítrico Fermentações S.A.
16. PHB produzirá plástico a partir do açúcar. Jornal Valor Econômico, 21 feb.2006:B15.valor econômico, 2006.
17. Rossell, C.V; Mantelatto, P.E.; Agnelli,J.A.M. Sugar-based Biorefinery – Technology for Integrated Production of Poly(3-hydroxybutyrate),
119
Sugar, and Ethanol. Biorefineries Industrial Processes and Products.
Staus quo and future directions. Ed. Birgit Kamm, Patrick Gruber and
Michel Kamm, 2005.Wiley-VCH, Germany.
Roberto, I.C. Biotecnologia ciência e desenvolvimento 2002.
http://www.biotecnologia.com.br/revista/bio28/28_produ.asp
Section 3
Role of Bioethanol
in the Energy Landscape
Conversion of lignocellulose biomass
(bagasse and straw) from the sugar-alcohol
industry into bioethanol
Introduction
The purpose of this study is to evaluate lignocellulose-based raw
materials that remain after cutting, harvesting and processing sugarcane,
to obtain sugar and ethanol (and in the future other products), by hydrolyzing those materials into a mixture of reducing sugars, followed by fermentation and recovery of the products.
Most studies on hydrolysis of lignocellulose derivatives performed
in the last 100 years were directed towards the use of wood or wood wastes
as raw materials.
The advent of sugarcane to produce bioethanol from sugarcane extractable sugars has generated a large surplus bagasse that can be potentially converted into ethanol and increase significantly the offer of
this fuel without requiring a proportional increase in cultivation areas.
Under this new condition, sugarcane will be fully used.
An analysis of the characteristics of the sources of lignocellulosic
matter included in the sugar processing remains is fundamental to develop a hydrolysis technology specific for the sugar and alcohol sector. The
lignocellulosic matter left over after the sugarcane is processed consists
of bagasse and harvest wastes [1].
At the current stage, sugar mills and distilleries do not recover harvest residues, but partially burn them during the sugarcane destalking
to serve as soil coverage, the surplus being incinerated in the field.
124
This situation will gradually be modified due to changes occurred during
the cutting and harvesting practices, where the destalking with fire will
be eliminated according to schedules designed to reduce the environmental impact of land burning [2].
The increasing interest in using lignocellulosic matter as primary
fuel will also significantly contribute to further valuation of lignocellulosic wastes that are left over after cutting down and harvesting the cane.
Thus, bagasse is the lignocellulosic residue currently available to
be converted into ethanol.
Sugarcane bagasse
Sugarcane bagasse is the resulting biomass fraction obtained after
the procedures of cleaning, preparation (reduction, using sets of leveling
rotating blades and defibering using sets of oscillating hammers) and
extraction of sugarcane juice (using sets of three roller crushers or diffusers).
Bagasse is not a homogeneous biomass, and shows changes in
composition and morphological structure, due to the cut procedure and
industrial processing.
The following factors influence significantly bagasse composition:
··
·
·
Straw removal (or not) by fire, previous to cutting.
The harvesting and loading procedures, with more or less soil,
sand and vegetal waste dragout, such as manual cut, mechanical cut,
sugarcane crushing, cut including the top, and so on.
The type of soil where sugarcane is cultivated (latosoils, sandy
soils, others).
There are different procedures for cane cleaning, such as dry
cleaning using revolving tables, dragout cleaning and pneumatic cleaning. The geometry and other constructive details of the revolving tables,
as well as the water volume per ton of sugarcane (cane stems after the
cut) can influence the bagasse composition.
The efficiency of the extraction equipment influences directly the
residual sugar content in the bagasse, and the ether extract content is
·
125
CONVERSION OF LIGNOCELLULOSE BIOMASS (BAGASSE AND STRAW)...
in inverse proportion to the percentage of sugarcane burnt before being
cut.
The most important morphological characteristics of bagasse are
dimension and form, which are fundamentally associated with the procedures to prepare and extract cane juice.
Several authors describe typical compositions for bagasse [1, 3].
Table 1 shows the typical results according to studies conducted at ICICDA,
the Cuban Institute for Research on Sugarcane Derivatives.
Composition %
Bagass
Fiber
Kernel
Straw
Cellulose
46.6
47.7
41.2
45.1
Pentose polymer
25.2
25.0
26.0
25.6
Lignin
20.7
19.5
21.7
14.1
Organo-soluble
2-3
Water-soluble
2-3
Ashes
2-3
8
Product humidity
48-52
9.7
(Dry basis)
3.5
Table 1. Sugar cane bagass and straw composition (according to ICIDCA)
An inspection of these results shows that the content of moisture
in the bagasse is within the 48-52% range (average: 50%), which is typical
and some water loss is caused by the roller crushers (or the final water
loss associated with diffusers).
A water-soluble fraction consisting basically of sugars is the result
of the juice extraction procedure; the lower the content of this fraction,
the higher the efficiency of the extraction procedure. In South Central
126
Brazil, pol sugar values after extraction range from 1.5 to 2.8 %, average:
1.85% [4].
Most of the mineral matter results from mineral impurities from
the soil and sand that are dragged out together with the sugarcane; the
rest consists of ashes that form the plant, plus ferrous metals and heavy
metals produced by the wear and tear of the preparation and extraction
equipment. The content of mineral matter varies considerably and is associated with the cutting, harvesting and the extraction and preparation
processes. Unpublished data provided by Linero [5] who conducted samplings in several mills located in Sao Paulo state show this variability.
The mineral matter content in bagasse ranges from 1.6 to 5.0%.
The organo soluble (ethanol + benzene) extract corresponding,
among others, to the wax associated with the external surface of the
cane stem, has a waterproofing protective function and also varies
expressively. This fluctuation is associated with the cutting and harvesting process, and the stems that were not burnt will present higher contents of wax. According to Sousa [6], the ethanol + benzene extract
represents 2.7% (w/w) of untreated bagasse. Fatty acids (45%), longchain fatty alcohols (44%) and sterols (5%) are the main fractions of this
extract [3].
Sousa [6] and Silva [7] conducted detailed studies about procedures
of delignification and fractioning of the bagasse to be employed as source
of inputs for the chemical industry. These authors presented data concerning the composition of the three fractions of bagasse, namely, hemicellulose, cellulose and lignin. The studies of this group serve as references
to develop a process of saccharification of the sugarcane biomass: whole
bagasse or its fractions fiber and medulla, plus harvest wastes, leaves,
tops and so on.
Sousa [6] analyzed a bagasse sample from Sao Paulo state sugar
mills and found that 22% (w/w) content of lignin (dry base and bagasse
exempt from mineral impurities) and a 78% content of holocellulose
(hemicellulose + cellulose). These data (Table 2) confirmed the previous
results described in [1] and [3] and also the fact that, both for hemicellulose and cellulose, the changes of their contents in the bagasse are relatively small from variety to variety of sugarcane, or from region to region.
127
The composition of the sugarcane biomass shows that holocellulose
prevails, followed by lignin.
A more realistic profile of the content of recoverable sugars is shown
in Table 3, except for acetyl groups and other non-sugars associated
with hemicellulose and also quantifying the hexose fraction.
Components of sugar canebagass
%
Holocellulose
77.8
Acid-insoluble lignin
20.4
Acid-soluble lignin
1.4
Soluble in ethanol-benzene (II)
5.4
Soluble in hot water (III)
10.2
Ashes (I)
3.3
Uronic acid (as anhydride)
4.2
(I) Based on the dry unextracted bagass.
(II) Based on the dry unextracted bagass and not corrected for ashes.
(III) Based on the dry bagass extracted with ethanol-benzene.
Table 2.Chemical composition of sugar cane bagass.
According to Sousa (1985), organosolv
Polysaccharides:
% (I)
% (II)
Glocose (hexose)
42.9
60.8
Xylose (pentose)
23.1
32.8
Arabinose (hexose)
3.3
4.7
Galactose (hexose)
1.2
1.7
Total
70.5
100
(I) In the ground bagass, extracted, dryed and not corrected for ashes..
(II) Based on total carbohydrates.
Table 3. Carbohydrates in sugar cane bagass.
According to Sousa (1985).
128
These studies also present important data on lignin composition in
terms of evaluation of the impact of degradation and formation of
undesired lignin by-products during cane processing [1, 6].
Studies by Sousa [6] and Silva [7] allowed us to formulate a standard bagasse composition (Tables 2 and 3), which be used to quantify
the potential of using bagasse in the hydrolysis process.
Table 4. Standard bagass (calculated composition)
Impact of bagasse components on saccharification processes
Moisture
The moisture associated to the bagasse has no effects either on the
conversion of the bagasse into total recoverable sugars, nor in the conversion rate. Most pretreatment processes, such as steam cracking,
129
thermal hydrolysis or organosolv processes are performed in the presence
of water, usually mixed with an organic solvent. The only exception lies
in the pretreatment processes that use concentrated acids (sulfuric acid
or mixtures of sulfuric acid + phosphoric acid).
Water-soluble fraction
The water-soluble fraction, where reducing sugars prevail, is decomposed during the pretreatment processes and produces hydroxymethyl
furfural (HMF) due to high temperatures (above 150°C) and pH below
3.5. Thus, these reducing sugars have no effect on the hydrolysis process
and are not used. However, if the HMF remains until the hydrolysis fluids
are fermented, it will contribute to inhibit alcohol fermentation.
Mineral matter
Ferrous metals and heavy metals act as catalysts in the organosolv
delignification processes [6] and can favor hydrolysis, depending on their
content and composition in the bagasse.
It seems that the different morphologies of fibers and the medulla
can lead to different contents of inorganic impurities, justifying future
determinations of the content of these compounds.
The presence of dispersed mineral matter (sand and soil) has a deep
abrasive effect on the equipment employed in the process, requiring the
use of more expensive alloys reducing the useful life of components and
increasing the operating costs and investments in fixed capital.
Ether extract
The possible influence of the bagasse ether extract on the pretreatment and hydrolysis reactions should be evaluated taking into account
that its main natural function is to form a protective film on the stem
surface. This may interfere with the industrial processes if they are performed at intermediate temperatures, where some components remain
solid, preventing the penetration of the solvents used in hydrolysis.
130
Similarly, solidification on surfaces of equipment, tubing and parts may
cause clogging and loss of thermal exchange capacity, among others.
Characteristics of particles present in the bagasse and their
impact on saccharification processes
Ponce and Friedman [8] analyzed the form and size of bagasse particles. After classifying the samples, the authors found a spongy fraction
and a fiber fraction with a high thinness ratio. It was found that rectangular prisms formed both fractions. The size distribution and the characteristic dimensions and properties such as equivalent diameter, specific area, form factor, thinness factor and apparent density were presented.
Nebra and Macedo [9] performed measurements in bagasse samples
and, unlike previous studies, these authors assigned an ellipsoidal-base
prism model to fibers, while the spongy fraction was considered similar
to spheres. This study was performed on a bagasse sample from a sugar
mill located in the central southern region and prepared using two sets
of leveling rotating blades, a defibering device and a 37" × 78" milling set
which represent the typical conditions of bagasse production in Brazil.
The fiber fraction with equivalent diameter between 150 and 3,210
µm ?and thinness factors between 10 and 60 accounts for 71% of the
total mass, while the medulla, with equivalent diameter between 180
and 1,680 µm?and thinness factors between 1.7 and 3.2 accounts for
the rest of the initial mass of bagasse. Another interesting fact pointed
out by the authors is that the calculated apparent densities (dry base)
of the fiber fraction increase from 210 to 600 kg/m³ as the equivalent
diameter of the fiber fraction decreases. Their explanation for this increase in density is that the fibers with larger diameters are formed by
aggregates of fibers and medulla, which contributes to reduce the apparent density.
The characterization of the particles composing the bagasse shows
three fractions, namely, fibers, medulla and rind (fibrous particles from
the outer cortex of the stalk). The form and size of these three components
are considerably different [10].
131
·
·
·
The medulla is formed by spongy particles with relatively regular
form and a length/width ratio approximately equal to 1, which means
that they can be considered as nearly spherical.
The fraction corresponding to the rind is quite larger and looks
like near-rectangular blades.
The fibers can be represented as cylinders with a thinness factor
of approximately 50 and considered similar to cylinder of infinite length.
After measuring the apparent density of the medulla, fiber and rind,
as well as the real density of the bagasse (density of the skeleton), they
reported the methods and difficulty to obtain representative results. Both
the bagasse and its fractions have low apparent densities. An apparent
density of 220 kg/m³ was found for the medulla, while this value is 520
kg/m3 for fibers and for the rind it is 550 kg/m³. The real density of bagasse reaches the value of 1,470 kg/m³, which is consistent with the
1,380 kg/m³ and 1,510 kg/m³ previously reported (for dry bagasse) respectively by Crawford and Pidduck. These results confirm the statements
below:
·
The porosity of the three components of bagasse is very important
and should be taken into account in any study on bagasse pretreatment
and saccharification, regardless its nature, considering that the reactions
are heterogeneous and involve a solid-fluid interface.
The apparent density of the medulla fraction is approximately
half the value of the fiber density. This causes an increase in the ration
between the mass of the fluid medium and the mass of lignocellulosic
matter during the pretreatment and hydrolysis processes to maintain
the reaction medium vigorously stirred and the final fluid diluted. It
will also negatively influence the separation of finer particles that did
not react during hydrolysis and are harder to separate based on differences in density.
We assign great importance to the morphology of bagasse particles
concerning the optimization of hydrolysis reactions.
Preliminary studies to enlighten the possible impact of bagasse
morphology on the hydrolysis reaction are commented below [11]. A
·
·
132
sample of bagasse was dried to approximately 12-15% of moisture, demedullated and subjected to a pneumatic classification in order to separate
the characteristic fractions. Images of these fractions were scanned
(Figures 1 and 2) and visually assessed. Figures 1a and 1b represent fiber
samples. Their format support the model earlier [10, 11].
In our case, fibers are quite uniform and compact, in the form of
elliptic cylinders and with a thinness factor similar to the one determined
by those authors.
The form of these fibers should favor the retention of particles inside
the reactor, regardless the reduction in diameter. A larger specific area
per unit volume would probably favor the hydrolysis reaction.
Figure 1a. Bagass fiber
133
Figure 1b. Bagass fiber (zoom)
Figures 2a and 2b represent medulla samples. Lignocellulosic matter
is expanded and has low apparent density. Comparatively, the particle
size is quite smaller than the size of fibers. The medulla is darker, indicating its ability to adsorb foreign mineral matter, e.g. clay and metals formed by wear of the preparation and milling equipment.
From the morphological perspective, we can suggest that the medulla
is not convenient for hydrolysis. Its spongy structure and low apparent
134
density will require a higher liquid reaction medium / lignocellulosic
matter mass ratio that causes additional dilution in the final fluid, as
well as an increase in energy consumption.
The particle size will be reduced more rapidly than the fiber size
throughout the hydrolysis reaction, achieving the diameter above which
they can go through the solid retention system in the continuous reactor.
This will translate into a larger fraction of matter that did not fully
react and will escape from the reactor, reducing the yield or requiring
additional equipment and costs to recover and recycle this fraction.
Figure 2a. Bagass kernel
135
Figure 2b. Bagass kernel, zoom
Data from Table 1 indicated that fiber and medulla have different
chemical compositions, the first being richer in cellulose, the preferred
polymer for hydrolysis conversion. The medulla presents higher percentages of hemicellulose and lignin. These differences in composition indicate a comparative advantage of fibers in terms of hydrolysis yield.
Sugarcane straw
These harvest wastes consist of sugarcane green leaves, dry leaves
and tops, being also a source of lignocellulosic raw materials. Although
this source is not currently used, this situation will be reversed in the
136
medium range, given that the environmental legislation foresees gradual
extinction of the practice of destalking using fire. References [1] and [3]
describe the approximate composition of this residue for other sugarcane
regions such as Cuba (see Table 1), but no typical values are available
for Brazil.
The composition of sugarcane straw is somewhat similar to that of
bagasse in terms of cellulose and hemicellulose. However, the lignin
content in the straw is approximately 30% lower than that of bagasse or
its component fractions. Another feature to be considered for future use
of straw for hydrolysis is its high ash content, which is about twice the
content in the bagasse.
Although no data concerning the shape and size of straw are available, visual inspection shows that it is highly heterogeneous, since it
comes from different fractions of the sugarcane plant and was not prepared beforehand.
According to studies performed at CTC [4] concerning the potential
of straw available, depending on the harvesting procedures, it is possible
to recover an amount of dry biomass equivalent to 14% of the sugarcane
mass (harvested stems) delivered to the mill.
The potential of straw as a source to increase the offer of lignocellulosic biomass, either for hydrolysis processes or as a source of primary energy, justifies deeper studies to determine the composition and
physical and chemical properties of straw.
Availability of bagasse and straw for hydrolysis processes
Nowadays, mills and distilleries do not recover stalk, which is not
available for use. The availability of bagasse is linked to the energy
efficiency of the mill. Currently, the available surplus bagasse for hydrolysis or other purposes varies from 7 to 10% the total bagasse, which is
approximately 280 kg per ton of cane. The rest of the bagasse obtained
by processing the sugarcane is employed as primary fuel to generate
steam and electric power. This condition is present in sugar mills with
annexed distilleries, which operate cycles of steam and power generation
with pressure levels of 21 bar.
137
Bagasse surpluses up to 50% of the bagasse obtained after the
sugarcane is processed can be achieved by optimizing the system of
production of steam and power and generating steam at a pressure
between 65 and 80 bar and using highly efficient turbines and generators.
Potential to convert bagasse into reducing sugars and ethanol
The stoichiometric conversion of standard bagasse, as well as its
maximum potential to produce ethanol are presented in Table 4. Only
the reducing sugars that can be potentially recovered from hemicellulose
and cellulose were considered.
In order to quantify the potential of bagasse to produce ethanol as
a function of technological advances in hydrolysis, we have established
five scenarios that gradually incorporate the increases in efficiency of conversion of hexoses and pentoses to be subjected to hydrolysis catalyzed
by diluted acids and enzymes, and fermentation of pentoses to give ethanol.
These scenarios were drawn upon data on hydrolysis techniques
published by Ogier [12]. The results of proposed scenarios are presented
in Table 5 and the scenarios are the following.
1. Pretreatment and diluted acid hydrolysis of hexoses at the current
technological stage.
2. Pretreatment, diluted acid hydrolysis of hexoses and optimization
of the hydrolysis reaction to the best values achieved as reported in
literature.
3. Pretreatment, diluted acid hydrolysis of hexoses and pentoses
and optimization of the hydrolysis reaction to the best values achieved
as reported in literature.
4. Pretreatment and enzyme hydrolysis of hexoses at the current
technological stage.
5. Pretreatment and enzyme hydrolysis of hexoses and pentoses
with optimized technology.
If we refer to one ton of bagasse in natura, the impact of the introduction of hydrolysis processes becomes apparent. Starting with a reasonable optimized technique it is possible to achieve an ethanol production
of 69.1 liters per ton of bagasse.
138
With optimized saccharification processes, the yield rises to 94.2 97 liters. Once the barrier to alcohol fermentation of pentoses is overcome, the yield will amount to 132.2 – 149.3 liters per ton of bagasse.
Considering a 10% surplus of bagasse, the introduction of hydrolysis
will represent an 8.1% increase over the 85 liters of ethanol per ton of
cane currently obtained in an autonomous distillery.
Under the best condition and using fully optimized technology and
50% surplus of bagasse, it is possible to obtain an additional 87.8%.
Using the straw, optimizing the cycles of energy generation and
possibly introducing fiber-rich sugarcane varieties, can further increase
these values.
Possible
scenario
Forcasted conversion
Ethanol Ethanol
Hexoses Pentoses
Ethanol
Total
[1]
hexoses: 60% fermentation: 89%
pentoses: 70 % fermentation: 0%
distillation: 99,5 %
69.1
0
69.1
[ 2]
pentoses: 78.5 % fermentation: 0%
distillation: 99.75 %
94.2
0
94.2
[ 3]
pentoses: 85% fermentation: 50%
94.2
37.9
132.2
[4]
97
0
97
[5]
111.4
37.9
149.3
Table 5. Transformation potencial of bagass to ethanol (liters/ton of bagass)
Conclusions
Although some of the results and statements above require
experimental determinations and technical and economic studies to be
139
validated, it is possible to make a preliminary diagnosis to better use
bagasse as source of carbon to produce ethanol on a large scale.
The bagasse cannot be considered a homogeneous material and it
is necessary to separate it into fractions for saccharification.
The inorganic matter (e.g. soil, sand, metals) that is washed out
with the bagasse should be removed before starting the treatments, since
it would accumulate in the reactor and other equipment of the process
and cause abrasive wear. The distribution of these components of mineral
origin in the fractions that form the bagasse should be characterized in
order to determine their impact on the reactions. Previous treatment is
required to remove these impurities both to have a better performance
at later stages and to extend the useful life of equipment.
The classification of bagasse into its typical fractions, namely fibrous and spongy, is recommended in order to achieve better efficiency
in the conversion of holocellulose. A study of the most appropriate processes of classification, as well as their economic evaluation should be
performed. The processes of demedullation of bagasse to separate it into
fiber and medulla must be evaluated as a first alternative to processing
the bagasse in order to improve the performance of hydrolysis.
Since the pretreatments and saccharification are catalyzed by mineral acids or by enzymes, the heterogeneous reactions occurring on
the solid-fluid interface, as well as the influence of particle size, geometry
and porosity should be taken into account in kinetic studies, as well as
the reactor design, by introducing concepts of heterogeneous kinetics in
porous media.
Physical and chemical properties of the fractions that form the bagasse, such as morphology, size, porosity, real and apparent densities,
typical pore dimensions, specific area of the particles, friction coefficients,
chemical composition of fractions, etc, should be determined.
The impact of other components such as waxes and other components that can be extracted with organic solvents should be evaluated
in order to check for possible interference with pretreatments, acid or
enzyme saccharification, and ethanol production.
Analytical methods capable of quickly and accurately establishing
the chemical composition of bagasse fractions and the profile of sugars
140
and by-products formed during the pretreatments and saccharification
must be introduced.
Wastes from cutting and harvesting should be typified using the
same method employed for bagasse.
Based on this information it will be possible to diagnose the potential of straw as a raw material for ethanol production, and establish the
pretreatments to be performed if the straw requires adaptation to yield
a more effective saccharification. In case the characteristics of straw
show that its application in hydrolysis is unfavorable, the straw may be
diverted to replace bagasse as primary fuel in the boilers and increasing
the amount of bagasse available for saccharification.
Due to the advances in the hydrolysis process followed by conversion
of reducing sugars into ethanol, the scenarios in this study show the
potential of bagasse (and in the future, of straw) as a raw material to
increase the offer of ethanol.
It is worth noticing that the increase in production of ethanol occurs
with no need of additional planted areas and leads to full utilization of
sugarcane.
Grupo Energia - Projeto Etanol (MCT/NIPE), Caixa Postal 6192,
Campinas, SP 13084-971, Phone +55 19 3512-1121, e-mail:
[email protected]
141
References
1. Paturau JM. By-products of the sugar cane industry. Elsevier
Science Publishers B.V., The Netherlands, 1989.
2. Macedo I.; editor. A energia da cana de açúcar. ÚNICA. São Paulo,
Brazil 2005.
3. Taupier OG, editor. Manual dos derivados da cana de açúcar.
ICIDCA/ABIPTI (Cuban Institute for Research on Sugarcane Derivatives /
Brazilian Association of Institutions for Technological Research). Brasilia, Brazil 1999.
4. CTC. Relatório do controle mútuo. Piracicaba, SP, Brazil 2001.
5. Linero F. Unpublished data. Piracicaba, SP, Brazil 2000.
6. Sousa MFB. Separação e identificação dos constituintes do bagaço
de cana e sua conversão em insumos químicos pelo processo Organosolv.
Master’s Thesis, Unicamp, Campinas, SP, Brazil 1985.
7. Silva FT. Obtenção de Insumos Químicos a partir do Aproveitamento Integral do Bagaço de Cana. Doctor’s Degree Thesis, Unicamp,
Campinas, SP, Brazil 1995.
8. Ponce N, Friedman P, Leal D. Geometric properties and density of
bagasse particles. Int Sugar Journal 1983;205: 291-295.
9. Nebra SA, Macedo IC. An Experimental Study about Typical Shapes and Sizes for Sugar Cane Bagasse Particles and about their Free
Settling Velocity. Int Sugar Journal 1988; 90:168-170.
10. Rasul MG, Rudolph V, Carsky M. Physical Properties of Bagasse.
Fuel 1999;78:905-910.
11. Olivares E, Roca G. Unpublished data on studies of bagasse
particle structure. Unicamp, March 2006.
12. Ogier JC, Ballerini D, Leigue JP, Rigal L, Pourquié J. Production
d’ethanol à partir de biomasse lignocellulosique. Oil and Gas Science and
Technology- Revue de l’IFP 1999;54:67-94.
142
Acknowledgments
To FAPESP (Foundation for Research Support in Sao Paulo State)
for financial support to the DHR (Dedini Rapid Hydrolysis) project. To
Dedini Indústria de Base S.A. for the support provided to this project. To
Grupo Energia - NIPE/UNICAMP for the support provided to this project.
Author’s note
This study, whose objective was to present processing methods and
discuss the potential of bagasse as a raw material to produce ethanol
(as well as other chemicals) was based on pioneering studies such as
those by Nebra SA and Macedo IC, Silva FT. Although these authors are
mentioned in the references, we wish to further emphasize that the use
of data, figures, definitions and concepts from their publications was
fundamental to meet the objectives of the present study.
Abbreviations:
TC: ton of sugarcane harvested and placed at the conveyor belt of
the mill
Glossary
Biomass: This term refers to fresh organic matter produced by live
animal and vegetal organisms. However, within the context of this study,
this term will be used to indicate only recent organic matter of vegetal
origin, which in our case is limited to bagasse and its fractions and to
post-harvest sugarcane wastes.
Bagasse: Residue after juice is extracted from milled sugar cane.
Demedullation: Process of separation into fiber and medulla.
Fiber: Vegetal tissue formed by bundles of lignocellulosic matter
that give support to the plant.
Medulla: The non-fibrous portion of parenchimal tissue.
Harvest wastes: Sugarcane green leaves, dry leaves, and tops.
Advanced techniques for generation
of energy from biomass and waste
H. J. Veringa
P. Alderliesten
1. INTRODUCTION
Biomass contributes as the world’s fourth largest energy source
today up to 14% of the world’s primary energy demand. In developing
countries it can be as high as 35% of the primary energy supply. Biomass
is a versatile source of energy in that it can be readily stored and transformed into electricity and heat. It has also the potential that it is used
as a raw material for production of fuel and chemical feedstock. Production units range from small scale up to multi-megawatt sizes.
Development of biomass use contributes to both energy and other
non-energy policies.
None energy related arguments are:
·
Environmental and climate change. CO2 is the main gas responsible for climate change, and it is observed that the gas emissions from
road transport are the main contributors to the increase of the total
level of emission in recent years, in spite of levelling off or even reduction
of CO2 emissions from other activities in the European Union.
Environmental Policy: The life cycle of biomass as a renewable
material has a neutral effect on CO2 emission. It also offers the possibilities of a closed mineral and nitrogen cycle. The environmentally hazardous sulphur dioxide (SO2), which is produced during combustion of
fossil fuels, leading to acid deposition, is not a major problem in biomass
·
144
systems due to the low sulphur content of biomass (< 1% compared to 1
to 5% for coal).
Agricultural Policy: CAP (Common Agricultural Policy) and the search
for alternative uses of set-aside land. It is estimated that 20 million hectares of agricultural land and 10-20 million hectares of marginal land could
already be made available for non-food production by the year 2000.
Social Policy: Estimates show that 11 jobs are created per MW of
installed biomass conversion capacity so that 5% of coverage of the EU
energy needs on the basis of biomass would lead to 160,000 additional
jobs (Wright report).
Regional Policy: Biomass can be used as a decentralised energy
source where conversion plants are located close to the source of biomass.
This would lead to stabilisation of employment in rural areas and
regional development.
Security of supply. 98% of the transport market is dependent on
oil. In the case of no policy on the level of the EU, the external energy
dependence will reach 70% before 2030. This dependence will be up to
90% when it concerns oil imports.
·
·
·
·
Energy related motivations for use of biomass are:
·
Biomass can readily be used in boilers to produce directly heat
and/or steam to generate electricity. This is being done at a small scale
at remote locations and in a centralized way in large production units
of more than 50 Megawatts. Co-firing with coal is an attractive option
with a relatively low need for additional investments.
Gasification is, although the technology exists already for decades, it is still being developed for advanced uses of biomass and waste.
The gas which can be produced this way, a syngas, is a well known
commodity in the energy generation and chemical process industry and
offers excellent options for high efficiency large scale electricity production and chemicals.
The EU has put forward the objective to substitute 20% of traditional fuels by alternatives in the road transport sector by the year 2020,
which has lead to a Directive on the promotion of biofuels. This draft
Directive contains a proposal for an obligation on member states to
·
·
ADVANCED TECHNIQUES FOR GENERATION OF ENERGY FROM BIOMASS...
145
ensure that, from 2005, a minimum share of transport fuel sold on their
territory will be bio-based, whereas the individual member states sell a
minimum proportion of biofuel of 2%. This level should grow by a yearly
amount of 0.75% in the following years up to a level of 5.75% in 2010.
In 2020 8% of the fossil fuel based transportation fuels has to be
substituted by biofuels. To meet this 2020 EU-goal large scale robust,
reliable and cost-effective biofuel production facilities have to be
developed and implemented, with final production costs of 10 Euro/GJ.
Biofuel currently represents 0.3% of the total diesel and gasoline
consumption in the market, which is basically the result of 6 member
countries amounting to a level of 700 ktons in 2000.
Major oil companies in the EU have formulated their strategies
in view of their responsibilities to contribute to a sustainable development, but also advocate a seamless introduction. This means that any
replacement of conventional fuels by biofuel should not induce major
changes in the current supply and distribution infrastructure. For the
next decades any biofuel should have such properties that they can be
blended into the current conventional fuels without major adaptation
of the technological infrastructure. This means that carbon based renewable fuels are for the next decades the only option for a substantial
replacement of the fuel pool.
Obviously, there is a good chance for natural gas to become a transportation fuel, which, however, does need extensive adaptations in the
supply infrastructure, but only minor modifications on the car engine.
Natural gas has lower CO2 emissions per unit of delivered mechanical
energy and consequently less emission. Also dependence on supply from
outside the EU is less than in the case of mineral oil. In the long run hydrogen will become important, giving other renewable energy sources a
chance to contribute. However, technology is still in its infancy and a distribution and supply infrastructure is non-existent. It is believed that
hydrogen will break through after the year 2020 or even later.
The major candidates for short term replacement of fuel out of
mineral oil like biodiesel (RME), pressed vegetable oils (PVO), and conventional bio-ethanol from starch and sugar crops show manufacturing
costs of between 12 and 21 dollar per Gigajoule, which compares with
·
·
·
·
146
the costs including excise duty and taxation of mineral diesel between
17 and 30 dollar per Gigajoule. This latter depends on the price per
barrel of crude oil, which for this analysis is taken between 15 and 25
dollar per barrel. This means that a policy based on exemption of excise
duty on biofuels, and an increase of the price of mineral oil, will create
the economic conditions for replacement. In the (near) future FischerTropsch diesel and bio-ethanol from lignocellulosic biomass can offer
lower prices than current biodiesel and conventional bioethanol fuels.
Already a surprising number of actions are undertaken with
promising results:
·
·
·
·
In Austria, the contribution of biomass for district heating has
increased 6-fold [1] in Sweden 8-fold [2] during the last decade thanks
to positive stimulation at federal and local level.
In the USA, already more than 8000 MWe installed capacity based
on biomass has been installed, primarily stimulated by the PURPA-Act [3].
In France, direct combustion of wood represents almost 5% of
the primary energy use [4].
In Finland, bio-energy already amounts by 18% of the total energy
production and if foreseen to grow to 28% by 2025 [5].
It is obvious that the above given arguments underline the dependence of the introduction of biofuels in the transportation sector on
external factors like commitment of EU member states to international
agreements and directives as well as local circumstances such as industrial infrastructure, crude oil price, availability and contractibility of biomass, taxation policy and choice of the best option for development of
renewable energy recourses.
On the other hand, the technological development can severely influence the production costs and large-scale availability of biofuels. It is
for the time being still in debate which is the best option for the conversion technology starting from biomass supply all the way to the enduse. Further, the actual choice will depend on local circumstances such
as potential set aside agricultural land in the EU, the availability of
waste vegetable oil and fats and/or other derived organic waste streams.
147
2. PRESENT SITUATION
This section summarises the current status of biomass technology
from biomass crops, conversion technologies to end products, technologies available and end products of the conversion process.
Figure 2.1 gives an overview of the different routes from biomass
to end products.
This system focuses on distributed production, which is the area
where nowadays the very challenging developments are underway. However, particularly in the Netherlands, the main contribution to renewable energy generation is co-conversion with coal-fired stations and in
the future with gas turbines.
Figure 2.1 Potential paths for biofuel-based distributed energy production
(taken from “Energy Visions 2030 for Finland)[5]
148
In the year 2004, some 9 PJoule of bioelectricity generated by cofiring is expected besides 20 PJoule generated in small-scale units in
the Netherlands. The plans exist to achieve in 20010 34 PJoule by cofiring against 26 PJoule in small-scale operations.
Co firing in coal fired power stations is a very attractive option as
the biomass or biomass derived waste is taken with the coal into the
boiler. This bio-fuel can either be ground down to the size of the pulverized coal particles and mixed up with the coal, or it can be injected in
separate units into the same boiler. In both cases the grinding is a critical
step and can substantially influence the costs of the electricity generated
due to the co-firing. For the rest, the downstream equipment remains
the same and no major investments are necessary. R&D work at ECN
has resulted in a thermal pre-treatment for bio-fuel (Torrefaction). [21]
which gives the fuel similar properties as the coal concerning the ignitability, next to other benefits like hydofobicity and reduced weight. In
the end even homogeneous properties can be given to a broad band of
bio-fuels and wastes so that the specificity for fuels might become less
severe. The negative side obviously is an extra process step.
The co-firing potential of current units is the limitation due to the
fact that ashes with different properties than coal are mixed up which
can lead to unwanted, or at least, not well understood ash behaviour in
the applications which it is now being used for. A way out of this problem
is to separately gasify the biomass and inject the syngas into the boiler.
In this way, in principle, more freedom exists in choosing the balance
between coal and biomass input and the ashes are entirely separated.
The draw back is the extra gasifier that has to be invested.
Figure 2.2 gives an example of a gasification unit for co-conversion
with a 600 MW power plant.
149
Figure 2.2 Indirect cofiring by upstream gasification (Amer-9 power plant of Essent)
The waste incineration area has recognized that, next to elimination
of municipal waste material, the generation of electricity will become more
and more interesting from both societal and economic point of view.
This is also stimulated by the fact that, for instance in the Netherlands,
up to 50% can be considered as renewably generated electricity which
has all the benefits of selling price, tax exemption and subsidees.
In view of this up to now, some 12 Petajoules of fossil input is replaced by electricity generated from waste. The plans are to increase this
amount to 20 Petajoules by the year 2010 [19].
The initiative recently taken by the “Afval Energiebedrijf “in Amsterdam envisages to build a 530.000 tons per year waste incineration
unit based on grate combustion and employing flue gas recirculation,
improved steam conditions in combination with advanced materials in
the hot zones, adding up to an output efficiency of more than 30%.
Figure 2.3 shows a schematic of this new unit being build up along
with the steam flow and conditions and some other performance factors.
150
2.1 Biomass material
The main biomass resources include the following: short rotation
forestry (Willow, Poplar, Eucalyptus), wood wastes (forest residues, sawmill and construction/industrial residues, etc.), sugar crops (Sugar beet,
Sweet Sorghum, Jerusalem Artichoke), starch crops (Maize, Wheat), herbaceous lignocellulosic crops (Miscanthus), oil crops (Rapeseed, Sunflower), agricultural wastes (straw, slurry, etc.), municipal solid waste
and refuse, and industrial wastes (e.g. residues from the food industry).
Current and future biomass resources in the EU are given in Table 2.1.
It can be seen from the table that in the long term, energy crops can be
an important biomass feedstock. At present, however, wastes, either in
the form of wood wastes, agricultural wastes, municipal or industrial
wastes, are the major biomass sources and, consequently, the priority
fuels for energy production. There is also an additional environmental
benefit in the use of residues such as municipal solid waste and slurry
as feedstocks as these are withdrawn from polluting land filling.
Figure 2.3 Flow scheme and characteristics of the new AEB Amsterdam
new waste incineration unit
151
Raw Material
Current Resources (dry)
Mt./yr.
Future Resources
Mt./yr.
Short Rotation Forestry
Wood Wastes
Energy Crops
Agricultural/Wastes
MSW/Refuse
Industrial Wastes
5
50
100
60
90
75-150
70
250-750
100
75
100
Table 2.1 Current and future EU biomass resources [6], [7], [8]
Research on biomass energy crops is concentrating on generating
reliable data on potential yield, environmental impact, limitations and
economics. Developments are done through networks of research groups
such as the Miscanthus Network, the Sweet Sorghum Network etc. There
is also a number of other European and national projects which carry
out research on a range of biomass materials.
2.2 Conversion processes
Biomass combustion or gasification?
Biomass combustion results in either heat or electricity. Biomass
gasification results in a combustible gas, which can be used for the generation of different products: heat, electricity, synthetic natural gas (SNG),
transportation fuels and chemicals. So only if heat and/or electricity is
required, combustion and gasification are competing processes.
If heat is the only product required, combustion seems to be preferable. Small-scale heat producing plants however suffer from bad economics1, especially if high emission standards are to be met. Large-scale
generation of SNG by biomass gasification (and subsequent distribution
1
Small-scale generally is relatively expensive, and also small-scale heat consumers (often
space heating) only need heat during the cold season, which means that the “plant”
only operates limited time.
152
to small-scale users where the SNG is burned to produce heat) is considered to be an attractive alternative.
If electricity is the desired product from biomass, combustion and
gasification compete. Gasification however, can reach higher electric
efficiencies because of Carnot’s law2. The advantage becomes even larger
if a fuel cell is added to the gasification system, since the efficiency of a
fuel cell does not depend on Carnot’s law. In reality, thermodynamic
optimum systems cannot be made due to different losses and non-ideal
behaviour. The main conclusion however remains valid: conversion by
gasification leads to a higher electric efficiency than conversion by combustion. Furthermore, by gasification more products can be produced
(liquid fuels like diesel, methanol and gaseous products like “natural
gas” and chemicals like H2). Even if only heat is required, gasification
probably plays a crucial role by producing SNG, which can be stored,
distributed and burned where and when heat is desired.
Combustion
Combustion can be represented by:
———>
C6H10O5 + 6 O2
Biomass + Oxygen (air)
2
6 CO2 + 5 H2O + 17.5 MJ / Kg.
Carbon dioxide + water + heat.
Carnot’s law states that the maximum efficiency from heat to work that can be obtained is equal to 1- Tlow/Thigh. A gas turbine is powered by gas with much higher temperatures (up to 1200°C) than the steam powered steam turbines (up to 600°C). This is the
principal reason why gasification can reach higher electric efficiencies. Assume the
following systems: combustion with 95% efficiency to steam and with 600°C to 100°C
steam cycle and gasification with 80% gas yield with combined cycle (1200°C turbine
inlet temperature to 100°C steam exit temperature) and 20% heat with steam cycle
from 400 to 100°C. The theoretical maximum (thermodynamic) efficiencies are 69%
and 54% for gasification and combustion respectively. If the gas from gasifier at 900°C
can be used in the gas turbine directly (without intermediate cooling/steam generation),
the maximum efficiency even rises to 74%. These are absolute maximum values, but it
illustrates the difference between combustion and gasification.
153
The majority of biomass and agricultural waste derived energy
comes from wood combustion. There is a constant drive to improve the
combustion efficiency up to more than 30% and a reduction in pollutant
emissions. The major development in this area is in large combined
heat and power plants (CHP). Direct combustion processes for heat
production and driving a steam cycle are commercialised already. New
developments towards better overall thermodynamic efficiencies of the
steam cycle and firing of biomass powder in ceramic gas turbines are
envisaged.
The amount of heat produced depends on the humidity of the biomass source, the level of excess air required and whether or not complete
combustion is accomplished. Today, combustion technology is extremely
well advanced, permitting widespread industrial application. Two types
of boiler are commonly in use:
··
Boiler with fixed or travelling grates.
Boilers with fluidised-beds.
The former type is very common, ranging from the household boiler
to large scale 50 MW industrial furnaces, and can accommodate heterogeneous combustible material in terms of composition, humidity and
granularity. On the other hand, load following is difficult. Figure 2.4 shows
the principle of a household boiler of the Herz company in Slovakia, the
capacity ranges up to 150 kW.
In a fluidised-bed, shown in Figure 2.5, the combustible particles,
together with the granular bed material, are carried by a constant flow
of gas in upward direction. The fuel is constantly injected into this bed.
The bed itself constitutes the major heat capacity of the system and
therewith stabilizes the process. In this way, effective heat and mass
transfer are being taken care of. Such a system can combust a wide
range of materials including fuels of non-biological origin. From an
investment point of view, this fluidised-bed technology becomes attractive
at plant sizes larger than 10 MW(th).
154
2. Ventilator for off gases
3. Heat exchanger
4. Ash removal
5. Combustion space
6. Burner surface
Figure 2.4 The principle of a household boiler of the Herz company in Slovakia.
155
Their main advantage is the possibility to use mixtures of various
types of biomass (woody, non-woody) and/or to co-fire them with other
fuels. Nevertheless, compared to grate-fired boilers, their operation in
partial load is problematic.
As already mentioned, a promising development in combustion for
efficient biomass conversion is co-combustion. This can be applied in
existing coal plants of a large capacity, allowing for high efficiency of
electricity production. New boiler concepts, where biomass is combusted
together with coal, peat, RDF (refure-derived fuel, i.e., upgraded urban
waste fractions) or other fuels can achieve high efficiencies, due scale
factors and reduced risks as more than one type of fuel can be used, e.g.,
to compensate seasonal influences in bio-feedstock availability (see also
Figure 2.2).
Gasification
As the gasification reaction itself is endothermic, heat has to be
supplied to the system by external sources. This heat can be brought to
the reaction zone through the wall of the reactor, by the bed material
itself or through a hot process gas stream. Due to the fact that, usually,
no air (or oxygen) is taken up into the process gas, a product gas with
middle or high calorific value is produced (10-18 MJ/Nm3). Such a high
calorific value gas is attractive since volume streams are reduced making
downstream processing like gas cleaning, compression or any kind of
catalytic process relatively simple and therefore cheaper. In this respect
a wealth of highly advanced processes are being developed and demonstrated or are awaiting demonstration at a sizeable scale [11], [12], [13],
[16].
The other way to generate the heat necessary for the gasification
reaction is to partially combust the biomass fuel giving the most direct
supply of heat to the gasification process itself. The overall reaction reads:
C6H10 O5 + 0.5O2 = 6CO + 5H2 + 1.85 MJ/kg
but it also produces some CO2 and H2O in the fuel gas stream.R.P.
Overend, Battelle, 505 King Avenue, Columbus, OH 43201.
156
Figure 2.5 Circulating fluidised-bed.
In the simplest system, air is used for the supply of oxygen, so that
the syngas produced is diluted with nitrogen. Calorific values are in the
range of 3- 8 MJ/Nm3, depending on the system applied. Air gasification
itself is relatively cheap, but downstream processing to clean the gas is
expensive due to large volumes to be handled. Gasification with pure
oxygen requires an oxygen supply, which is expensive, particularly at
small scales.
Fixed bed downdraft gasification, Figure 2.6B, concerns small scale
by definition, the maximum capacity is several tens of MWth. Furthermore, the conversion generally is low. Downdraft gasifiers can also be
made “slagging”, which means that inert material leaves the gasifier as
a liquid slag and the conversion rises to almost 100%. This generally
requires oxygen in order to reach the desired high temperatures.
Fixed bed updraft gasifiers Figure 2.6A, are characterized by high
conversion and high efficiency. The exit gas temperature is generally
157
100-300°C due to the counter current flow of solid fuel and hot gas. The
product gas contains large amounts of hydrocarbons. Tar (large hydrocarbons) make up approximately 15% of the energy content of the gas.
The biomass fuel specifications are mild, but there is a risk of too highpressure drops over the bed if too much small particles are fed. Fuels
with slagging tendency can cause problems in the hot bottom zone, but
updraft gasifiers can also be made “slagging”. This means that inert
material leaves the gasifier as a liquid slag. This generally requires oxygen in order to reach the desired high temperatures.
Fluidised bed gasifiers, Figure 2.6C are characterized by the presence
of an inert heat carrier like silica sand. Fluidised bed gasifiers can be
separated in three types: BFB, CFB, and coupled fluidised beds (indirect).
BFB (bubbling fluidised bed) is the simplest concept. It also seems suitable for applications where oxygen (and steam) must be used instead of
air. CFB: circulating fluidised bed as shown in Figure 2.6C, reactors are
often seen as the most suitable for large-scale applications. BFB as well
as CFB gasifiers show a limited conversion of 90-95%. This can be increased to approximately 98% by using smaller fuel particles. Indirect gasifiers contain two reactors where gasification and combustion are separated. Two gases are produced: a N2-free product gas and a “conventional” flue gas. Because the conversion is complete, indirect gasifiers seem
to be the attractive alternative of oxygen/steam-blown fluidised beds
when N2-free gas is required.
Entrained flow reactors, Figure 2.6D, are practically empty vessels,
where small fuel particles (or liquids) are converted at high temperature.
It can either be slagging or non-slagging. Slagging gasifiers are preferable
if biomass is used. The conversion is almost complete, but oxygen is
needed to achieve the high temperatures needed. Biomass should be
pulverized to a size of 1 mm. Entrained flow gasifiers are used to produce
syngas to be used either as syngas or for electricity generation. This
means that these gasifiers in practice operate at elevated pressure. The
entrained flow technology (Figure 2.6D) is primarily developed in the
petrochemical industry as a means to gasify heavy residues. It is now
being used successfully for high-pressure gasification of pulverized coal
and will be applied for centralized gasification of pre-treated and pulve-
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rized biomass. The high temperature reactor in the Carbo V system is an
example of such an entrained flow reactor (Figure 4.2).
The gas obtained by gasification can be combusted in a diesel, gas
or “dual fuel” engine, or in a gas turbine. Several biomass gasification
processes have been and are being developed for electricity generation.
In BIG-ISTIG (Biomass Integrated Gasifier-Steam Injected Gas turbine),
steam is recovered from exhaust heat and injected back into the gas
turbine. In this way, more power can be generated from the turbine at
higher electrical efficiency.
A
B
C
D
Figure 2.6 Schematics of different direct gasification reactors.
As the gasification temperature is high (up to 2000°C) tar production
is absent and a relatively pure syngas is produced which will be used
for catalytic biofuel production.
Pyrolysis/Carbonisation
Pyrolysis is a process of decomposition at elevated temperature
(300 to 700 OC) in the absence of oxygen. The products obtained by
pyrolysis of lignocellulosic matter are: solids (charcoal), liquids (pyrolysis
159
oils) and a mix of combustible gases. The properties of each of the products is dependent on the reaction parameters i.e. the temperature,
heating rate, residence time and the actual pressure at which the process
takes place. Pyrolysis has been practised for centuries for the production
of charcoal (carbonisation). This process is running at relatively low
reaction temperatures and high residence times to maximise solid char
yield at around 35%.
In recent years more attention has been paid to the production of
pyrolysis oils, which have the advantage of being easier to handle than
the starting biomass and have a much higher energy density. Yields of
up to 80% by weight of liquid may be obtained from biomass material
by using fast or flash pyrolysis at moderate reaction temperatures.
These liquids, currently referred to as bio-oils or biocrudes, are intended to be used in direct combustion in boilers, engines or turbines.
Nevertheless, some improvements on the product are necessary to overcome unwanted properties such as poor thermal stability and heating
value, high viscosity and corrosivity.
For use as a fuel for combustion engines, or even more advanced
applications, extensive upgrading will be necessary liker deoxygenation
by catalytic hydrotreating at high pressure or zeolite cracking at atmospheric pressure. Both processes are being developed at laboratory scale
[14]. The main advantage of fast pyrolysis for the production of liquids
is that fuel production can be done separated from power generation,
and can be considered as a densification step to facilitate transportation
and inevitable elaborate handling. Although it reduces transportation
costs, the extra step of in-site pyrolysu8is offsets the costs involving
direct transportation of the raw biomass [22].
Figure 2.7 shows the fast pyrolysis unit based upon the “Rotating
Cone Principle” in operation at Biomass Technology Group at Enschede.
This unit is now being upscaled to high capacity (> 1 MW output). Here
biomass falls in hot sand, which is transported over the inner surface of
a spinning cone. Sand takes care of heat transfer and residence time is
determined by the cone size and rotation speed. The char is the source
of heat in this reactor.
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Features:
! No carrier gas
! High heat transfer
! High solids throughput
Characteristics:
! Solids residence time: 0.1-5 seconds
! Gas residence time: 0.1-5 seconds
Figure 2.7 “Rotating Cone Principle”.
Pyrolysis, either to produce a solid carbon material or a liquid can
be of interest in combustion with existing systems for large-scale
electricity production. If biomass fuel is to be imported, to meet national
goals for introduction of renewables into the energy chain or to achieve
emission reduction, it may be argued that pyrolysis is a step to be taken
at the location of the biomass production, so that only highly concentrated energy carriers are transported.
Also the solid pyrolysis product (char) has properties similar to
coal, and therefore can be easily accommodated as a renewable or a CO2
emission free energy carrier, which can be mixed up with coal. Same
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applies to the liquid pyrolysis product, but in this case separate injection
technology is to be applied with coal fired boilers.
Further, pyrolysis is applied as a means to reduce the size of waste
streams, like electronic scrap, plastics etc. In some processes, even high
calorific value gas is generated, precious metals are recovered and
environmentally hazardous waste metals are immobilized [15].
A number of technologies combining pyrolysis and gasification are
developed to overcome the drawbacks of both technologies separately
by combining their respective advantages. Like in the case of advanced
gasification technologies, these processes are awaiting demonstration
at realistic scales [16], [17].
The largest plant built today is 2 tonnes/h but plans for 4 and 6
tonnes/h (equivalent to 6-10 MWe) are at an advanced stage of planning.
Over the past years, it has become less and less obvious whether pyrolysis
oil can be a viable feedstock for transportation fuel as it was believed
earlier.
Liquefaction
Hydrothermal upgrading
This is a low temperature (250-500°C), high-pressure (up to 150
bar) process in which a reducing gas, usually hydrogen, is added to the
slurried feed. The product is an oxygenated liquid with a heating value
of 35-40 MJ/kg, compared to 20-25 MJ/kg for pyrolysis oils. Interest in
liquefaction is reduced due to the high cost of pressure reactors, the
need for feed preparation and problems with feeding slurries. Some R&D
is being carried out on batch reactors and catalytic hydro cracking.
The so-called hydrothermal upgrading is a similar process. It takes
place in a high-pressure reactor close by the critical point of water [18].
During this process biomass decomposes into CO2 and a so-called
biocrude. This latter product is easily separated from water in which it
forms, but still has to be hydrogenated to become a fuel comparable
with conventional ones. The work has been started to generate an
alternative to the ever-increasing oil price some decades ago. Now the
future of this technology looks uncertain.
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Supercritical gasification
The process of supercritical gasification [24]is basically the same
as Hydrothermal upgrading, but occurs at more extreme conditions in
terms of temperature and pressure. Therefore the product yield will be
composed of gaseous products rather than liquid in the case of HTU.
Water becomes supercritical at temperatures over 374oC and a pressure
of 221 bar and the distinction between gas and liquid phases disappear.
Usually the reaction temperature is chosen much higher than this latter.
In the phase change from sub to supercritical, the properties of water
change dramatically. It becomes highly reactive and can break C-C, C-H
and C-O bonds in such a way that smaller fractions are obtained if higher
temperatures are applied. The selectivity and efficiency is, however, significantly enhanced by the presence of a catalyst. Under the most extreme
conditions temperatures over 600C the organic molecules are split into
the smallest possible entities like H2 and CO2, but at more moderate temperatures the selectivity towards CH4 becomes larger. Even lower temperature than say 400oC will yield complicated waxes and higher hydrocarbons. A typical reaction reads as follows:
2C6H12O6 + 7H2O ——> 9CO2 + 2CH4 + CO + 15H2
ÄH = 1.3 MJ/kg
It can be seen that the water participates in the reaction, not only
as an effective carrier for heat transfer to the biomass, but also as a
reagent. Possibly the water is consumed in a reforming process of the
large molecular fragments generated by cleavage of the biomass
molecules. This might also be the explanation why a reforming catalyst
is so important in the process.
A possible process is shown in Figure 2.8. Actually the process
schedule is rather simple, but the problems are due to the feeding of the
wet biomass and the heat exchanging. This latter heat exchanging process becomes more critical when process temperatures are increasing.
The advantages of supercritical gasification are:
··
·
Complete transformation of all organic material
Short residence times: .5-2 minutes
Product gas, including CO2 is liberated at high pressure. This CO2
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is primarily dissolved in the water phase and can be easily flashed out
to a high CO2 concentration, which will be of value when sequestration
is foreseen.
The yield is relatively clean as gaseous by-products remain dissolved in the water phase.
·
Process costs can be high as expensive materials and reactor systems
are to be used. It may well be that ultimately the process is best for producing Synthetic Natural Gas along with CO2 storage as the economically
most viable application in the long run.
Figure 2.8 Schematic of the supercritical gasification process.
Esterification
Esterification is the chemical modification of vegetable oils into
vegetable oil esters, which are suitable for use in engines. Vegetable oils
are produced from oil crops (e.g. rapeseed, sunflower) using pre-pressing
and extraction techniques. The by-product of the oil production is a
protein ‘cake’ which is a valuable feedstuff for animal feeding.
Esterification is needed to adapt the properties to the requirements
of diesel engines. This process eliminates glycerides in the presence of
an alcohol and a catalyst (usually aqueous sodium hydroxide or potassium hydroxide). Methyl esters are formed if methanol is used while
ethyl esters are formed if ethanol is used. The most common vegetable
oil ester for biofuel is RME (rape methyl ester).
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The schedule of the process is represented below. This example considers an initial biomass (raw material) quantity of 3000 kg of rapeseed.
During the extraction process this is converted to approx. 1000 kg of
rape oil and 1900 kg of protein feedstuff. In the esterification process
the rape oil is treated with methanol to produce 1000 kg RME and 110
kg of glycerine.
Extraction
Esterification
Vegetable oil esters can be used in mixtures with diesel fuel up to
100%.
The most promising product at present emerges as RME, a methyl
ester based on vegetable oil, which is obtained from rapeseed or sunflower and further processed by cross-esterification of fatty acids and
alcohol (methanol). Results from the Thermie programme on biofuel utilisation have shown that no special problem have been detected with
conventional diesel engines working on mixtures of up to 50% rapeseed
methyl ester.
Compared to conventional diesel, RME produces lower emissions
and therefore contribute to reducing of health problems e.g. respiratory
problems and cancer. Rapeseed oil doesn’t produce sulphur dioxide, which
impairs lung function and contributes to acid rain. There may, however,
be problems with odour (similar to cooking oil) when pure RME is used
as a fuel.
Biological/Biochemical Processes
Anaerobic digestion of wastes produces methane. It is a well-established technology for waste treatment. This is the natural breakdown of
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organic matter, such as biomass, by bacterial populations in the absence
of air into biogas, i.e., a mixture of methane (40-75% v/v) and carbon
dioxide. This bioconversion takes place in “digesters,” i.e., sealed, airless
containers, offering ideal conditions for the bacteria to ferment the
organic feedstock to biogas. A simplified stoichiometry for the digestion
of plant carbohydrates follows:
C6H10O5 + H2O —— > 3 CH4 + 3 CO2
During anaerobic digestion, typically 30-60% of the input solids
are converted to biogas; by-products consist of undigested fibre and
various water-soluble substances.
Biogas, either raw or usually after some enrichment in methane,
could be used to generate heat and electricity through gas, diesel of
“dual fuel” engines, at capacities up to 10 MW(e).
The average production rate is 0.2-0.3m3 biogas per kg dry solids.
Nowadays 80% of the industrialised world ‘biogas production’ is from
commercially exploited landfill. R&D is mainly concentrating on factors
affecting microbial population growth. High solids digesters are being
developed for the rapid treatment of large volumes of dilute effluents
(wastes) from agro-industrial processes. This process has the advantage
of a low cost feedstock and offers substantial environmental benefits as
a waste management method.
Figure 2.9 shows an example of an anaerobic digestion plant in the
Netherlands.
digestion: 55°C
2-3 weeks
10-15% dry matter
230 kt/y gives
92 kt/y ODW,
10 kt/y biogas,
23 kt/y digestate
waste water
Figure 2.9 Anaerobic digestion for CHP production Vagron Groningen plant.
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Another product from acid and enzyme hydrolysis, fermentation
and distillation is ethanol, which is used as a transport fuel, on the European level mainly in the form of ETBE (a mixture of ethanol and isobutane). The process scheme is shown in Figure 2.10. In the USA however,
ethanol is used as a mixture called gasohol (ethanol mixed with gasoline),
while in Brazil either pure ethanol or gasohol is used.
Presently the techniques of hydrolysis, fermentation and distribution are all commercialised for sugar and starch substrates. Acid hydrolysis for (ligno)cellulosic feedstocks is expected to be economical in about
5 to 10 years. Enzyme hydrolysis is at the pre-pilot stage. It is expected
to be commercial in 5-10 years and economical in 10-15 years. The economic competitiveness will be increased by improvement of industrial
productivity and efficiency. Recently, major enzyme manufacturers (Genencor, Novozymes) have claimed a 20-fold reduction of cellulosic production costs. Acid and enzymatic hydrolysis of cellulosic materials are
not commercial technologies, furthermore, they need a strong R&D development before commercial demonstration.
1. raw biomass
2. disclosure
3. hydrolysis
4. fermentation
5. distillation
6. dehydration
7. fuel adaptation and distribution
8. heat and power production
Figure 2.10 Bio-ethanol, power and heat from biomass (waste) streams.
167
The raw materials for bio ethanol can be sugars or starch feedstocks
such as wheat, sugar beet, potato, Jerusalem artichoke and sweet sorghum. Maize grain in the US and sugarcane in Brazil are the most utilised
biomass material for alcohol production.
Bioethanol can be used as a pure fuel as it is applied in the Proalcool
Programme in Brazil or mixed with motor gasoline*. If bioethanol is
used at 100%, engines should be adapted while for mixed utilisation,
non-adapted engines can be used.
Since the production of bioethanol in Brazil has shown large yearly
variations, the availability is experienced to be limited, or at least uncertain. This made people reluctant to invest in new cars with adapted
engines. Presently new cars, which run on pure ethanol, are not produced
anymore.
Ethanol can be used to substitute for MTBE (Methyl Tertiary Butyl
Ether) and added to unleaded fuel to increase octane ratings. In Europe,
the preferred percentage, as recommended by the Association of European
Automotive Manufacturers (AEAM), is a 5% ethanol or 15% ETBE mix
with gasoline.
Ethanol could in the future also be produced from lignocellulosic
feedstocks.
ETBE (Ethyl Tertiary Butyl Ether) production
A new product derived from the reaction of equal parts of ethanol
and the hydro carburant isobutane, which have fuel properties like octane
rating, volatility, heat efficiency and corrosivity superior to bioethanol.
Instead of MTBE**, ETBE can be added can be added to unleaded
motor gasoline to obtain a mixture of up to 15% without technical
problems. The resultant mixture exhibits the same performance
* Gasohol is the term used in the United States to describe a maize-based mixture of
gasoline (90%) and ethyl alcohol (10%). It should not be confused with gas oil, an oil
product used to fuel diesel engines.
** MTBE (Methyl Tertiary Butyl Ether). Obtained from fossil methanol (natural gas) and
added to unleaded fuel to rating. MTBE output is currently growing at the rate of 10%
annually in France. MTBE is the principal competitor of bioethanol and ETBE as an
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characteristics and engines do not have to be modified. ETBE can be
manufactured in plants currently producing MTBE. The first industrial
ETBE plant came on stream in 1990 at ELF France, using bioethanol
supplied by the French producers Beghin-Say and Ethanol Union.
3. ECONOMICS OF BIOMASS SYSTEMS
3.1 Cost of bio-feedstocks
The costs of biomass depend on the dynamics of local markets, as
well as on agreements, such as contracts between biomass users and producers. This cost includes all necessary transportation and handling, as
well as pre-treatment (drying, size changes). Exact estimates are very difficult to make, as the markets are “immature” and changes occur rapidly.
On the one end of the spectrum, we find some industrial residues,
e.g., from construction sites, that have nil of even negative costs (i.e.,
the industry is prepared to pay to get rid of them. On the other end, we
have biomass from energy plantations.
In the middle of the spectrum, forest and farm residues require the
application of costly harvesting and handling operations.
According to some recent calculations the following results are
derived:
·
In France (1996), the cost of wood transported over a distance of
40 km to be converted to bioelectricity by advanced gasification processes
- e.g., BIG-ISTIG, 20-50 MW(e) - is estimated at 1.54 • cents/kWh(e),
representing between 35 and 43% of the average cost of electricity.
A study (1998) by VTT (Finland) arrives to raw material (wood)
cost figures of 2-3 • cents/kWh(e) for transportation between 20 and 40
km; this is to be increased by 30% for transportation up to 100 km.
·
octane booster, with more than 10 million tonnes produced annually worldwide. The
price of MTBE is linked to that of methanol, which exhibited major price fluctuations
of between 95 - 190 ECU/tonne between 1987 and 1992. As a result, manufacturers
may favour ETBE whose market price is generally more stable. European regulations
currently specify maximum MTBE (and ETBE) content in engines as 10% by volume.
169
·
A Dutch study (1996) estimates the production costs of biomass
in the form of organic residues as 0-45 • /dry t. Energy crops 50-80 • /dry
t; to these figures we should add 10-20 • /t for transportation, and another
10-20 • /t for handling and pre-treatment.
3.2 Costs of bioelectricity
Many economic evaluations of electricity generation systems utilising biomass as a feedstock have been carried out. In the following
Table, a comparison of such calculations for the main technologies available is presented.
Technology
Applied
Efficiency
(%)
Generation Capacity (MWe)
Present
Future
Investment
Cost
(k• /kWe) cE/kWh(e)
Combustion
15 - 35
1 - 50
100
1.1 - 2.8
2.8 - 10
Co-combustion
Of existing
power station
Of existing
power station
Of existing
power station
0.5
3.6 - 10
Gasification
20 - 35
0.1 - 25
?
1.5 - 2.0
?
Gasification
* Combined cycle
30 - 47
< 12
25-120
1.3 - 2.4
4.4 - 8.4
Flash Pyrolysis
* Diesel
30 - 35
15-25
50
0.8 - 1.8
3.9 - 7.8
Biogas
* Urban Wastes
20 - 30
1?
< 10
9 - 15
23 - 80
Biogas
* Landfills
20 - 30
<1
?
0.5 - 1.2
2.9 - 5.6
Table 3.1 Main technological routes for producing electricity from biomass.
In these calculations, the cost of feedstock is assumed to be zero
only in the case of landfills; in the other cases the fuel price is assumed
to be:
··
·
combustion: 2.0 - 2.5 • cents/kWh(e);
gasification: 1.9-2.4 • cents/kWh(e);
pyrolysis: 37 • /t of biomass.
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Combined heat and power (CHP) generation is considered to be
another key potential market (see above). Table 3.2 outlines the
economics involved in a CHP plant, which uses willow as a feedstock,
and a fluidised-bed combustion system.
Specific Investment
1600 •/kW(e)
Lifetime
25 years
Capacity
10 MW(e) + 17 MW(th)
Biomass Costs (Short rotation, willow)
55 E/dry t
Bioelectricity Production Cost
7.6 •cents/kW(e) (bio-heat at zero cost)
Table 3.2 Costs of CHP plant (fluidised-bed
Considering biofuels the Figure 3.1 gives a comparison of different
commodity fuels prepared out of biomass. New products like bio-diesel
will add another 20-25 $/GJ to the price of petroleum based fuel [19].
Fischer Tropsch diesel produced out of biomass will become competitive
when produced centralised at large scale and with significant tax exemptions.
Figure 3.1 Estimated production costs of wood-based methanol, ethanol and pyrolysis
oil using various technologies (taken from “Energy Visions 2030 for Finland)[5]
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4. CHALLENGES FOR BIOMASS R&D
4.1 Long-term goals
The long-term goal of biomass R&D is to be competitive with fossil
fuels without subsidies on a level playing field of full costs, to increase
its contribution to energy demand of the EU to more than 20% of the
projected primary energy demand in 2025 and more than 30% in 2050.
In parallel, it is necessary that the gradual increases of biomass
energy contributions have to be realised in an environmentally sustainable way and accepted by the public.
Figure 4.1 shows the time path for the subsequent development
steps. These will be outlined in the following section.
• Maximising direct/indirect cofiring in conventional
coal-fired power plants
• Indirect cofiring (gasification) in natural
gas-fired boilers and CCs
• Decentral CHP production (gasification, pyrolysis -> GEs,
GTs, FCs)
• Gasification/methanation -> “green” natural gas
(SNG, LNG)
• Hydro-Thermal-Upgrading -> “biocrude”
• Supercritical gasification -> H2, CH4
Implementation time
Figure 4.1 Short and medium-term developments.
The easiest way to implement biomass as an energy resource presently is by producing process heat as it occurs to a large extent in the
wood, sugar and paper industry. In Scandinavia, biomass or organic
waste is combusted in large scale fluidised-bed boilers to raise steam or
hot water for heat supply and to a minor extent for electricity production,
basically in back pressure steam turbines. The full potential is not yet
completely explored. Further, combustion units of about 50 MW(th) driving condensing steam cycles to produces mainly electricity are in a state
of planning or are being started up. These systems will have to become
172
economically viable by the fact that subsidies on the “green” electricity
or heat are made available, or that customers are willing to pay extra.
As a next step, co-firing of biomass or waste (paper or sewage sludge
for instance) with existing and highly optimised coal boilers is in a state
of development. Presently an input of up to 10% of the calorific value of
the fuel is targeted, but values of up to 35% are envisaged. This cofiring
is achieved by injecting the fuel into the boiler next to the coal. In this
case the biomass will have to be chipped to small particles to make
injection possible. In some cases, like for sewage sludge, the waste can
be co-injected with the coal. An interesting option is to pyrolyse the
biomass or waste to bring it in a form, which resembles the coal so that
it is easily injected. The pyrolysis gas can be injected into the system
further down steam. Synergistic effect can be attained as it presents a
possibility to reduce NOx emissions from the boiler.
Another application of co-firing is to gasify the biomass and to
inject the syngas into the boiler (Figure 2.2). In this case the residues
from the coal-burning unit can be kept separated from the residues of
the biomass. This latter technology is also foreseen to be implemented
into existing gas fired combined cycle plants. This will open up an enormous potential for introducing biomass and waste into the energy-generating infrastructure.
For a county like the Netherlands, for instance, all the options of
co-firing mentioned are of importance to meet the goals for CO2 emission
reduction as well as generation of energy out of renewables. So far fuel
availability, but even more so, contractibility have been experienced as
the main obstacle for exploitation of the large-scale potential.
Next to this co-firing, at locations where also heat has a significant
economic value, stand-alone units may become attractive. Due to high
potential the efficiency and attractivity of temperature levels of the process, gasification is the main candidate technology. The size and type of
such plants depends on local conditions like fuel availability, its composition and morphology and the heat/power ratio required. In any case,
however, gas cleaning will be the critical step. This gas cleaning is not
only necessary to meet the demands of local legislation, but also, and
may be even more important, to be able to combust the gas in a prime
173
mover. At this moment it is not clear whether or not the costs for the
necessary gas cleaning technology to be involved will turn out to be
prohibitive for implementation. In this respect it may well be that more
advanced gasification technologies giving inherently low tar levels in
the product gas will ultimately be the final option for implementation.
Figure 4.2 gives an example of an advanced two-step gasification
process known as the “Carbo V” process developed at the EUT in Freiberg,
Germany. Here biomass is pyrolysed to char and gas. The gas is used to
create a high temperature zone in which later the char is injected. This
process suppresses tar formation and gives a medium calorific fuel gas.
A number of demonstration project in the EU and also elsewhere in
the world are planned, started up or running to get more insight into
the feasibility of the technology.
Figure 4.2 An example of an advanced to step gasification process.
Ultimately, biomass as a feedstock will be needed to replace existing
fossil recourses. Any kind of technology described here as for producing
bio-oil, biogas, or routes involving catalytic chemical synthesis will be
necessary to meet this future demand on chemical feedstock and transportation fuel.
174
It will be the main task of the biomass R&D community to make
this challenge become reality in the coming decades.
Figure 4.3 shows the concept of biorefinery, the ultimate integration
of biomass and waste in the energy and materials production. This will
be the main way to overcome shortage in raw material to combat unwanted emissions and to guarantee a sustainable society for generations to
come.
Figure 4.3 Biorefinery concept.
4.2 Obstacles
Fuels
The major obstacle to the large-scale implementation of biomass
systems will be the guaranteed supply of biomass feedstock.
In this respect distinction has to be made between availability and
contractibility. As a rule, 50% of the availability is presently taken for
the contractibility, but this number will have to grow to explore its potential. The commercial viability will be based on the financial margin
to producer or collector (gate price or production cost). For the energy
crops, this must compete with the lowest margin in conventional farming.
Acceptance of new crops into the agricultural system can only be achieved
175
if the farmer is confident with the new crop or has experience with the
crop for other uses (e.g. rapeseed oil). All demonstrations and field trials
should involve agricultural organisations.
Making biomass waste streams available is basically a matter of
organisation or logistics. Not only the quality like the amount of inorganic material in the stream but also long term guaranteed supply is of
importance in relation to the size of the plant where the biomass or
waste is processed. For small plants, pre-processing or conditioning can
be done on the premises, but for larger ones it can be decided as a consequence of economic optimisation, to partially pre-process the feed at
the production site or on the way to the conversion plant. The extreme
case is where biomass is imported as a regular fuel. Ultimately biomass
is converted on the production place into char, pyrolysis oil or pellets.
Local benefits may be achieved in such a case when also at the production
site by products can be integrated with the local energy demand (local
use of the gas as a by-product of the char production for instance).
It will be of high importance to find ways to optimise such energy
chains in an environmentally and economic way to achieve a situation
where biomass and organic waste is to a large extent implemented.
Energy crops
An obstacle to the growing of biomass for energy on set-aside land
is the possible emergence of new crops, which will be grown for nonfood and non-energy purposes (e.g. paper pulp and chemicals). These
crops will be suitable for growing on set-aside land and the products
may have higher value than biomass fuel, therefore, allowing the processor to pay more for the biomass. The price offered for the energy crop
must compete with prices offered for other crops, which may also be
grown on set aside land.
Clearly, growing of organic material for energy production needs
particular insight into possible ways to maximize soil depletion. Also
fertiliser and chemical constituents will have to be minimized. Of particular interest is integration of energy crop production regionally and
its economics.
176
Wastes
Agricultural waste is a by-product and obviously not optimised towards energy production purposes. At present these ‘residues’ are readily
available often at very low, zero, or in some situations, negative costs.
Some debate exists over the use of these residues and the decision to
use them is generally site-specific. Forest fires are a real threat in southern Europe thus necessitating the routine collection of forest residues,
which therefore are a potential biomass fuel. However, in other more
northern areas where forest fires are not a threat, residues are not harvested because they are considered to be a valuable part of the nutrient
cycle of the forest and also contribute to soil structure. In these cases
forest residues are usually not considered as a biomass fuel.
As a consequence, many of the steams have unfavourable properties
like abrasivity, corrosivity, ash and inorganic material content. Further,
local legislation leads to assignment of a certain percentage of the fuel
as green fuel. This makes the total pool of organic fuel substantial but
very inhomogeneous. Development of suitable fuel blends in relation
with particular conversion technologies and optimised morphology is
therefore of prime importance. It may be foreseen that a new branch of
economic activity will emerge: pre processed optimised fuel production
with added value like pellets, briquette, chips etc. R&D into conversion
technology with these new fuels is then of prime importance.
Import/Export
For highly urbanized areas, but which still have renewable energy
targets, green fuel import can be important. For producing areas this
can lead to new economic activity and added employment. The issue of
import can mean that collection occurs over large areas. But conversion
takes place highly concentrated in co-conversion or dedicated plants but
with high capacity. In each particular case it has to be determined how
the logistics will look like: to what extent will pre-processing be done
and where. Minimization of transport costs is the main issue in this case.
But also local benefits may be of importance.
177
4.3 Conversion Processes
Combustion
The main development has been with fluidised-bed combustors. These
combustors have a high efficiency, can burn a mixture of fuels and fuels
that can contain up to 60% moisture. The largest boilers are grate systems
(up to 100 MW thermal), which can produce about 200 t steam/hr.
Direct combustion is commercialised at present and the firing of
biomass powder in ceramic gas turbines will be commercialised in the
years to come. These turbines will have a capacity of 100 kW - 500 kW.
Products are heat and/or high-pressure steam, which can be used to
produce power or combined heat and power.
The most promising developments in combustion for efficient biomass conversion is co-combustion. This can be done in existing coal plants
of a large capacity (which allows high efficiencies for production of electricity). New boiler concepts where biomass is combined with coal, peat,
RDF or other fuels offer high efficiencies because of their larger scale and
low risks in the power supply since more than one fuel can be used (e.g.
to compensate seasonal influences).
Most R&D is on technical aspects e.g. stoking, combustion air and
fuel conveyance. There have been large improvements in combustion
efficiency (>30%), in reduction of pollutant emissions (e.g. fly ash) and
in the development of CHP plants. R&D will also be required for Stirling
engines and pressurized combustion systems.
Main R&D tasks lay in the field of co-combustion: assessment of
possibilities of co-combustion in different situations, development and
demonstration of advanced boiler concepts. Specific research topics on
combustion are corrosion by alkalines and chlorides and options to prevent. Further, slagging prevention and applying difficult biomass fuels such
as straw, RDF, and grasses in different combustion systems is important.
The main barriers to overcome are the high cost, making use of the
economy of scale. The developments will be helped if up-front investment
is available. The involvement of industries in the development will be an
important issue and part of the R&D should concentrate on demonstra-
178
ting the environmental and energy benefits of the technologies to industries. One issue, which must be assessed in the studies, will be how well
the utilities meet the CO2 and other emission standards.
Gasification
Gasification is sensitive to changes in feedstock type, moisture content, ash content and particle size. The gas can be used for internal
combustion engines provided it is cleaned of tars, carryover dusts, some
of its water content, and cold enough. If cleaning does not take place,
tars may precipitate on inlet valves and clog up gas/air mixers. Dust
can clog carburettors, cause engine damage and act as a grinding powder
between the piston and cylinder wall.
The most effective and economical use of the gaseous product is
the production of electricity via gas turbines if combined with steam
cycles. Gasification produces a higher yield than combustion with respect
to electricity production for low power plants (50 kW to 1-10 MW) with
internal combustion engines. For higher power (1-10 MW to 50-100 MW)
combustion systems with steam turbines are more efficient than gasification systems. For very large-scale power plants (50-100 MW) gasification can reach exceptionally high levels of efficiency through a combined
gas turbine-steam turbine system R&D in gasification is aiming at large
scale (1000t/day) oxygen and/or air blown systems. Of prime importance
is the development of efficient systems for electricity production. IGCC
and STIG may ultimately achieve efficiencies of 42-47%.
To reach this goal, emphasis in R&D will have to be given to:
Development of simple and cheap gas cleaning technologies for
dust, NOx or ammonia, hydrochloric acid and alkaline components. This
development is needed for both large scale (>10 MW) units as well as
small ones. Ultimately stringent standards for fuel quality are needed.
Further, emphasis will have to be given to improving the tolerance of
gasifiers to different types of biomass and operation of gas engines or
gas turbines fired by low calorific gases.
Once efficient and cost effective gasification has been achieved,
the synthesis gas can be used for deriving of secondary fuels like metha-
179
nol or, more generally, chemical feedstock. The relative demand and
cost advantages are unlikely to become evident until after 2010 when
liquid fuel may increase in price or environmental requirements may
restrict the use of gasoline or petroleum additives.
Pyrolysis
Flash pyrolysis will produce the largest percentage of bio-oil (6080% by weight). Slow or conventional pyrolysis will produce more charcoal (35%-40%) than bio-oil. Flash pyrolysis is at a demonstration scale.
Upgrading processes are at a far lower degree of development than pyrolysis processes.
Bio-oil is expensive as a transport fuel (especially if no environmental credits are taken into account), but as a liquid, bio-oil presents the
advantage of easy handling, transport and storage. This bio-oil can be
combusted for heat and electricity and therefore it may become economically attractive.
Char can be used in small gasifiers (kW range) or may become important as import fuel as a transport fuel (diesel substitute), bio-oil needs
a stabilising step and maybe upgrading.
On the R&D side emphasis is to be given to:
·
··
·
improving the production of bio-oil (for MW power stations) and
upgrading using catalytic hydro-treatment,
solving the corrosive and toxic problems,
modification of diesel engines, which will be run with pyrolysis oil,
development of recovery of fine chemicals.
Esterification
The process for the production of RME is well developed and the
product is commercially available in France, Germany and Italy. EU nonfood oilseed production is confined to 700,000 ha-1.2 million ha and
this allocation is being quickly taken up by member states. In 1994
180
total EU area of oilseeds for non-food purposes was 0.62 million ha as
compared to 0.2 million ha in 1993. Most of this is accounted for by
rapeseed which increased to an estimated 0.4 million ha. The major
producers are France and Germany with respective areas of 173,000 ha
and 152,000 ha (1994).
Bio-diesel is expensive as a transport fuel (costing approx. 0.20-0.25
ECU/litre more than its mineral equivalent). In the countries where RME
is commercially available, it is competitive with fossil diesel due to tax
exemptions. At the EU political life an intensive debate is going on to
make biofuels economically competitive through a reduction in excise.
The main obstacles to the development of esterification processes
are the high production cost of RME, the limited amount of raw material
which is allowed to be grown in the EU and the opposition of some Member States and the lack of competitiveness of biofuels in comparison to
fossil fuels mitigate against the injection of capital into the development
of improved esterification methods.
R&D should concentrate on:
··
··
Testing RME in different types of engines.
Testing of engines for emissions (particulates) and reduction of
odour problems.
Improved Energy Ratios and greenhouse gas benefits.
Reduction of production costs, especially by using more efficiently
the by products (glycerine, cake).
Biological/Biochemical Conversions
Acid hydrolysis, fermentation and distillation of sugar/starch-based
substrates are all commercialised at present. Enzyme hydrolysis may
be commercially available in 5-10 years. Acid and enzymatic hydrolysis
of cellulose-based substrates are not commercial technologies. There is
still an economic gap between the price of fossil fuels (0.15 • /L) and the
price of liquid biofuels (0.4-0.6 • /L for ethanol in Europe). The gap is
expected to be reduced by improvement of industrial productivity and
efficiency, and use of new species. Methane (used for power) and compost
are other products commercially available from biochemical processes.
181
The main product is ethanol, which can be mixed with gasoline up
to 10% in normal engines. 100% ethanol can be used in adapted engines.
ETBE (a mixture of ethanol and isobutane) can be used as a lead substitute (up to 15%) in diesel/gasoline engines.
The main obstacle to the development of bioconversion technologies
is the lack of investment in RD&D. In the absence of this investment coordination activities should be initiated, also with the USA. R&D on this
topic is still in its infant phase and therefore an extensive list of topics
will have to be addressed:
Development of advanced methods for the chemical hydrolysis of
cellulose and lignocellulosic materials.
R&D in fermentation/distillation includes the use of novel yeasts,
bacteria and fungi.
Pre-treatment is being investigated to increase the ease of hydrolysis. The most cost-effective hydrolysis process developed so far is steam
explosion.
R&D in acetone-butanol fermentation is being carried out but
there has been no breakthrough as yet.
One step hydrolysis/fermentation stage where the hemicellulose
and cellulose are treated at the same time.
Niche markets should be identified and demonstrations should
be established to highlight the benefits of the technologies. Example of
niche markets are environmentally sensitive areas such as waterways
and leisure areas.
Development of new types of bioreactors.
Development of new strains of microorganisms for fermentations.
Development of cheap enzymes for enzymatic hydrolysis of lignin.
·
·
·
·
·
·
··
·
H.J. Veringa
P. Alderliesten
Energy research Centre of the Netherlands (ECN)
P.O. Box 1, 1755 ZG Petten, The Netherlands
Phone: +31 224 56 4628, Fax:+31 224 56 8487,
E-mail: [email protected]
182
5. REFERENCES
[1] Biomass technologies in Austria, Market Study Thermie Programme,
Action BM62, European Commission DGXVII, July 1995.
[2] Energy in Sweden 1994, NUTEK (The Swedish National Board for
Industrial and Technical Development).
[3] Donald Klass, Excerpt of Biomass in North American, Biomass for
Energy, Agriculture and Industry, vol 1 8th EC Conference, eds. P.
Chartiers, A.A.C.M. Beenackers, G. Grassi, 1995 pp 63-73, Pergamon
Press Oxford.
[4] P. Ballaire, Publication Interne ADEME 1996.
[5] Energy Visions 2030 for Finland, VTT Energy, ISBN-951-37-35966, 2001.
[6] G.T. Wrixon, A. Rooney, W. Palz, Renewable Energy 2000, Springer
Verslag, 1993.
[7] C.P. Mitchell, Resource Base, Biomass for Energy, Agriculture and
Industry, vol 1 8th EC Conference, eds. P. Chartiers, A.A.C.M. Beenackers, G. Grassi, 1995 pp. 116, Pergamon Press Oxford.
[8] Biofuels in Europe: Developments, applications and perspectives
1994-2004, Proceedings 1st European Forum on motor biofuels May
9-11 1994, Tours, Eds. Ph. Mauguin, Bonfils, Nacfaire.
[9] The Biomass Gasification Process by Battelle/Ferco: Design, Engineering, Construction and Startup, M. Farris, M.A. Paisley, J. Irving,
R.P. Overend, Battelle, 505 King Avenue, Columbus, OH 43201.
[10] CASST: A new and advanced process for biomass gasification, H.
den Uil, Netherlands Energy Research Foundation (ECN), ECN-RX—
00-026.
[11] The FICFB - Gasification Process, H. Hofbauer, G. Veronik, T. Fleck,
R. Rauch (Vienna University of Technology, Austria), H. Mackinger,
E. Fercher (Austrian Energy & Environment, Graz, Austria).
[12] Production of a bio-gasoline by upgrading biomass flash pyrolysis
liquids via hydrogen processing and catalytic cracking, M.C. Samolada, W. Baldauf, I. A. Vasalos, 1998.
[13] Staged thermal treatment combined with pyrometallurgical smelting
producing energy and products from waste, A.B.J. Oudhuis, H.
183
Boerrigter, J.P.A. Neeft, H. Zanting, Proceedings R’2000, 5th World
Congress on Integrated Resource Management, June 5-9, 2000,
Toronto, Canada.
[14] Upscaled two-stage gasification process; high efficient and low tar
gasification process for biomass and waste in small, medium and
large scale CHP-plants, COWI.
[15] Carbo-V-gasification; fuel gas, heat and electricity from biomass,
Umwelt- und Energietechnik Freiberg GmbH.
[16] Contributions ECN Biomass to “Developments in thermochemical
biomass conversion” Conference, 17-22 September 2000, Tyrol,
Austria, ECN-RX-00-026.
[17] Liquid fuels from biomass via a hydrothermal process, F. Goudriaan,
D.G.R. Peferoen, 1990.
[18] Shell zoekt nieuwe manieren om biobrandstoffen goedkoper te
produceren: benzine oogsten, H.P. Calis, Shell venster, November 2002.
[19] Daey Ouwens, J. Novem Statusdocument Bioenergy 2003, April
2004.
[20] Afval Energie Bedrijf Gemeente Amsterdam: High-efficiency Waste
Fired Power plant Technical innovations. (jonkhoff@afval energybedrijf.nl).
[21] Bergman, P.C.A., Boersma, A.R. Kiel, J.H.A. Torrefaction for Entrained
Flow Gasification of Biomass. Presented at the 2nd World Conference
and Technology Exhibition on biomass for Energy and Industry,
Rome 2004, see also ECN-RX-04-001.
[22] Calis, H. P. A.; Haan, H.; Boerrigter, H.; Broek, R. van den; Drift, A.
van der; Faaij, A. P. C.; Peppink, G.; Venderbosch, R. J. Pyrolysis and
Gasification of Biomass and Waste, Bridgewater, A.V. (ed.), CPL press,
Newbury, United Kingdom, 2003, pp. 403-417. - Preliminary technoeconomic analysis of large-scale synthesis gas manufacturing from
imported biomass feedstock.
[23] A. van der Drift, H. Boerrigter, B. Coda, M. K. Cieplik and K, Hemmes,
Entrained flow gasification, ash behaviour, feeding issues and system analysis, ECN report, Petten, Netherlands: ECN-C-04-039 (2004).
[24] Antal, M.J., Allen, S. G., Schuhman, D., Xu, X., Biomass gasification
in supercritical water. Ind Eng. Chem. Res, 39: p4040-4053.

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