Electric Steelmaking

INCREASING THE SUSTAINABILITY OF THE STEEL
PRODUCTION IN THE ELECTRIC ARC FURNACE
BY SUBSTITUTING FOSSIL COAL WITH BIOCHAR
T. Reichel, M.Sc.
T. Demus, M.Sc.; Dr.-Ing. T. Echterhof; Prof. Dr.-Ing. H. Pfeifer
4th Central European Biomass Conference
16th January 2014, Graz, Austria
1
Steel production processes
 Two major processes for producing steel:
Basic Oxygen Steelmaking (Blast Furnace Steelmaking)
Electric Steelmaking
www.worldsteel.org
2
Electric Steelmaking – General information
 Electric steel is produced in Electric Arc Furnaces by
converting steel scrap and other input materials into new
steel.
 Using steel scrap: Electric Steelmaking is less energy
intensive than the Basic Oxygen Steelmaking.
 Electric energy is used to melt the scrap by electric arcs.
 After finishing the melting process, the steel is tapped in a
ladle and later on treated metallurgically.
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Electric Steelmaking – Some statistics
 Electric Steelmaking is the second most important steel
production process!
Steel production in 2012
www.worldsteel.org
29.2%
452 million tSteel
41.7%
70 million tSteel
Electric Steel
EU 27
Other
World
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Electric Arc Furnace – Construction
www.siemens.com
Graphite electrodes
Furnace shell
Molten steel
Rocker tilt
Eccentric bottom tapping
(EBT)
Tilt cylinder
www.steeluniversity.org
Ladle
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Electric Arc Furnace – Process
Charging
Melting
Tapping
-Steel scrap
-HBI / DRI
-Coal, CaO/MgO
-Addition of
Oxygen / fuels
-Sampling
-Temperature
measurement
6
Electric Arc Furnace – General mass balance
Scrap,
HBI/DRI
CaO,
MgO
Electrode Consumption
Offgas
Coal,
Coke
Dust
Natural
Gas
Air
Oxygen
Slag
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Steel
Electric Arc Furnace – Why do we need coal and coke?
 Additional chemical energy input
 The combustion of coal and coke generates chemical energy. Thus expensive
electrical ernergy can be saved.
 The chemical energy input depends on the calorific values of the coal and
coke.
 Carburizing the steel
 By adding coal and coke, the carbon content of the steel is enriched.
 Thus the desired material properties can be adjusted.
 Foaming the process slag
 A foamy process slag has an advantageous effect on the process.
 Combined injection of carbon and oxygen leads to a voluminous slag.
 Increasing the energy efficiency by shielding the electric arcs…
8
Potential of biochar – Direct CO2 emissions
40%-70% of direct emissions!
Coal and coke
12 kg/tsteel
≙ 44 kgCO2/tsteel
Natural gas
150 MJ/tsteel
≙ 10 kgCO2/tsteel
Electrode consumption
1-2 kg/tsteel
≙ 4-7 kgCO2/tsteel
Direct CO2 emissions
60-100 kgCO2/tsteel
Other carbon sources
e.g. Scrap, DRI,
pig iron, CaCO3
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Potential of biochar – Possible savings
 Biochar is classified as CO2-neutral by the EU commission!
 Direct CO2 emissions: 12 kgCoal / tSteel
 44 kgCO2 / tSteel
 Potential CO2 savings (2012):
Germany
EU 27
World
Steel production
Potential CO2 savings
[million tSteel]
[million tCO2]
13
42
452
0,6
2
20
10
Investigated carbon carriers
Hydrothermal Carbonization (HTC)
Water
Ash
Volatile components
CFix
Carbon
Phosphorus
Sulfur
Chlorine
Unit
M.-%
M.-%
M.-%
M.-%
M.-%
M.-%
M.-%
M.-%
Anthracite coal
3.30
5.36
1.80
89.55
88.70
0.00013
1.12
0.03
vs.
Water
Ash
Volatile components
CFix
Carbon
Phosphorus
Sulfur
Chlorine
Fossil anthracite coal
Unit
M.-%
M.-%
M.-%
M.-%
M.-%
M.-%
M.-%
M.-%
HTC biochar
2.50
6.60
64.90
26.00
66.10
0.00827
0.32
0.02
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IOB Pilot Electric Arc Furnace
Some general characteristics:
 Water-cooled, two-pieced system.
 Movable furnace vessel.
 Operating in Direct Current (DC) mode
or in Alternating Current (AC) mode.
 Process Data Monitoring.
 Offgas system.
These experimental tests:
 Operating in Direct Current (DC) mode
 One single graphite electrode at the
top and a bottom electrode are used.
 50 kg of steel scrap and 1 kg of carbon.
 Maximum power of 300 kW.
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Biochar charged into the vessel
 Steel scrap, biochar and slag formers are charged into the
vessel.
 The biogenic carbon carriers are covered by steel scrap and
slag formers to avoid a fast and an unwanted combustion.
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Melting process
‘View‘ into the furnace
Introducing the tapping
14
Tapping the molten steel
15
General results
 The usage of biochar has no negative influence on the
process in the electric arc furnace and the final steel product.
 The duration of the experiments, in which biochar was used,
was shorter than the duration of the trials using anthracite
coal (30-40 minutes vs. 60 minutes).
Chemical Reactivity of the biochar is much higher.
Finer surface conditions and the high proportion of volatile matter in
biogenic carbon carriers.
 The fast combustion behaviour of the biogenic carbon leads
to a lower carburization rate in the molten steel.
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Composition of the produced steel
AnthraciteFossil
coal anthracite
Biocharcoal
HTC Biochar HTC
0.45
0.4
Concentration (w.-%)
Concentration (w.-%)
0.35
0.3
0.25
0.2
0.15
0.1
0.05
17
0
C
Si
Mn
P
S
Cr
Pb
Zn
Ni
Cu
Offgas chart – Anthracite coal
O2 [vol.-%]
CO [vol.-%]
CO2 [vol.-%]
25
O2, CO, CO2 [vol.-%]
20
15
10
5
0
0
500
1000
1500
2000
Time [s]
2500
3000
3500
18
Offgas chart – Biochar
O2 [vol.-%]
CO [vol.-%]
CO2 [vol.-%]
25
O2, CO, CO2 [vol.-%]
20
15
10
5
0
0
500
1000
1500
Time [s]
2000
2500
19
Conclusion
 Electric Steelmaking in Electric Arc Furnaces is one of the
most important steel production processes.
 From a technical point of view the usage of biochar in electric
steelmaking is possible and has no negative effects on the
final product steel.
 Biochar is classified as CO2-neutral by the EU and can
increase the sustainability of the Electric Steelmaking.
 The investigations of biochar usage should be continued.
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Coming soon…
 Other and different biogenic carbon carries will be tested:
Pyrolysis
Pyrolysis
Pyrolysis
Torrefaction
HTC
HTC
 Experimental tests in industrial scale will be performed.
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The authors gratefully acknowledge the financial support
from the European Community – Research Fund for
Coal and Steel (RFSR-CT-2009-00004 GREENEAF).
Thank you for your attention!
Contact:
Tim Reichel, M.Sc.
RWTH Aachen
Institut für Industrieofenbau und Wärmetechnik
Kopernikusstraße 10
52074 Aachen
[email protected]
www.iob.rwth-aachen.de
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