Simulation of Flow Orifice in a depressurization line working

Simulation of Flow Orifice in a depressurization line working

Simulation of Flow Orifice in a
depressurization line working in critical flow.
Autores:
Victor Kanehiro Arume de Souza – ESSS
Leonardo Aquino Costa – Petrobras / CENPES
Cristhian Alberto Celestino Cortez – Petrobras / CENPES
Kaku Saito – Petrobras / CENPES
PRESENTATION TOPICS
• Company Overview;
• Problem Description;
• Methodology;
• Goals;
• Conclusion and next steps.
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Problem Description
• Flow Orifice study in the fast and slow
depressurization lines of a reactor;
• Last defense systems in case of a
uncontrolled temperature rise in reactors;
• Maintain the right depressurization rate it’s
a security issue:
– Depressurization to slow > Bad temperature
control;
– Depressurization to fast > Reactor damage /
Compromised Flare System;
Problem Description
• Divergence between designs of the detailed
project and the concept project;
• Lack of standards for critical flows;
• Different bibliographies gives different sizes
of FO;
Problem Description
• Two methodologies used:
– Concept Project: Based on the methodologies of flow
measurements under critical flow, described by Nelson
Martins [1];
– Detailed Project: Based on the methodologies of valve
controls under critical flow;
Concept
Fast Line
Line Diameter
Detailed
Fast Line
Concept
Slow line
215,9
Detailed
Slow line
124,4
Orifice Diameter
99,94
85
56,5
48,25
β
0,46
0,39
0,45
0,39
Plate Thickness
99,94
44,45
56,5
25,4
Geometry
• 2D axisymmetric simplification;
Real 3D geom
2D simplified geom
Flow Orifice
Upstream
Downstream
Thickness
Mesh
• Hexahedral Mesh:
FO Region
Detailed
Boundary Conditions
• Pressure–Pressure bc’s:
Fast Depressurization
Slow Depressurization
Pinlet = 1,54e+07 Pa
Poutlet = 1,27e+05 Pa
Pinlet = 1,52e+07 Pa
Poutlet = 4,81e+06 Pa
Wall
Axis
Inlet
Outlet
Boundary Conditions
• Fluid Properties:
– Temperature = 51 ºC
– Molecular Weight = 4,8 kg/mol
– Specific mass = ideal gas
– Viscosity and cp = process simulator
cp
Viscosidade
7300.00
1.80E-05
1.70E-05
Viscosidade [Kg/m.s]
cp [J/kg.K]
7200.00
7100.00
7000.00
6900.00
6800.00
y = 1.9494x + 6111.6
6700.00
300.00
400.00
500.00
Temperatura [K]
600.00
1.60E-05
1.50E-05
1.40E-05
1.30E-05
1.20E-05
y = 2E-08x + 5E-06
1.10E-05
300.00
400.00
500.00
Temperatura [K]
600.00
Results
• Mach:
Fast Depressurization
Detailed
Concept
Results
• Pressure:
Fast Depressurization
Detailed
Concept
Results
• Mach:
Slow Depressurization
Detailed
Concept
Results
• Pressure:
Slow Depressurization
Detailed
Concept
Results
• Achieved Mass Flow:
Fast Depressurization Line
Project
Detailed
Theoretical Mass
Flow (kg/s)
Concept
Slow Depressurization Line
Detailed
87,97
Concept
28,05
Mass Flow (kg/s) CFD
65,41
89,86
20,85
28,78
Error %
-25,65
2,15
-25,64
2,63
Each project step in the same range of error.
Conclusion and Comments
• Error between methodologies:
– CFD vs Concept = 2,5%
– CFD vs Detailed = 25%
• This work showed the validation of Nelson Martins [1]
for the project of Flow Orifices under critical flow;
• There’s still a supersonic flow at the outlet boundary at
the Fast Depressurization case:
– Another shock wave will happen at upstream;
– Raised the concern on the equipment after the FO
(vibration, erosion due high speeds, etc.)
Bibliography
[1] Martins, Nelson. Manual de medição de vazão: através de
placas de orifício, bocais e venturis. Rio de Janeiro;
Interciência; Petrobras, 1998.
[2] ANSYS Fluent (2010) Theory Guide. Versão 13, abril de
2009. Cannonsburg, USA.
[3] Ewan B.C.R. and Moodie K. 1986 “Structure and velocity
measurements in under-expanded jets” Combustion Science
and Technology 45 pp275-288.
[4] Miller, R.W. Flow Measurement Engineering Handbook;
McGraw-Hill Book Company
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