Simulation of CO2 behavior in flow and depressurization:
Treatment of formation of solid CO2
Anders Granskogen Bjørnstad1, Geir Berge2
Petrell AS, Trondheim, Norway
Thermodynamic treatment of solid CO2
Background and motivation
Treatment of CO2 in the oil & gas and process
industry has become more focused over the last
years. This concerns processing, transportation
and storage. The combination of a rapid
pressure drop and low temperatures in a CO2
rich mixture can lead to formation of solid CO2
(dry ice). There are several aspects within CCS
where this subject arises, e.g.:
In collaboration with Tore Haug-Warberg (assoc. Prof at NTNU), a new thermodynamic module is being
developed. The module consists of different models for specific equations of state (EOS), and a powerful
and flexible equation solver part using Newton’s method. The equation solving classes utilize the interface
provided by the model system of Haug-Warberg. Different multiphase concepts can use different
specialized equation setups, ensuring consistency throughout the solution of a control volume.
L1
PT-diagram, simulated results v.s. correlations from Span & Wagner (4)
δQ1
δN1
10000
V1
1000
100
Pressure [Bar]
Blowdown of process equipment with
high content of CO2. During a blowdown
process there is a risk of forming solid CO2.
Solid particles might clog openings such as
restriction orifices, reactor or column
inventories and pipes. This may lead to a
series of threats to the safety of installations.
10
Calculated
S&W VLE
1
S&W SVE
S&W SLE
0.1
L2
δN2
δQ2
0.01
V2
Figure 1: Schematic drawing of the thermodynamic control volume.
Phases L1 and V2 are reference phases that handle condensation
and evaporation, respectively.
0.001
100
150
200
250
300
350
Temperature [Kelvin]
CH4-CO2 VSE Frost Point isotherms
50
45
Pressure [Bar]
Accidental depressurization during wellinjection of CO2. Knowledge and ability to
predict behavior of CO2 is crucial when
modeling depressurization (or blow-out) of
an injection well.
210K
40
203K
35
193K
183K
30
173K
25
153K
20
Pikaar 210K
15
Pikaar 203K
10
Pikaar 193K
Pikaar 183K
5
0.81
0.86
0.91
Pikaar 153K
0.96
Mol fraction CH4
Test case: Depressurization of a CO2 tank
As a first test case, a depressurization
simulation of a CO2 filled tank has been
performed. This has been done to demonstrate
the current capabilities of treating formation and
handling of dry-ice in a typical VessFire
scenario. In order to validate against
experimental data, the model was created
similar to the CO2 tank of Eggers & Green (3).
The following conditions were used in the test
case:
50L CO2 tank, Phase masses
30
7.00E+06
6.00E+06
25
5.00E+06
Mass [kg]
• Starting pressure: 60 bar
• Starting temperature: 295 K
• Initial level of liquid CO2: 86 vol%
• Volume of tank: 50L
• Time of depressurization: 400 s
• Steel wall thickness: 35 mm
4.00E+06
15
3.00E+06
Pressure [Pa]
20
Liquid mass
Vapor mass
Solid Mass
Pressure
10
2.00E+06
5
1.00E+06
0
0.00E+00
0
100
200
300
400
500
600
700
800
900
Time [s]
Time trace of phases in PT diagram
50L CO2 tank, simulated temperatures and pressure
100
10
Saturation lines
Vapor trace
310
1.20E+07
290
1.00E+07
270
8.00E+06
Vapor temperature
250
6.00E+06
Pressure [Pa]
VessFire (2) is a Brilliant-based simulation
system, tailor made for analysis of
depressurization of process equipment.
VessFire will utilize the knowledge and
technology developed during this project.
Addressing the thermo-mechanical response of
vessels and pipes subject to extreme
temperatures, e.g. in relation to cold blow-down
or blow-down when the process system is
exposed to fire, is important when designing
and dimensioning process equipment. With the
aid of this project, VessFire will be able to
accurately handle CO2 and CO2-rich mixtures,
including formation of dry ice.
0.76
Temperature [K]
Petrell is currently further developing the
simulation system Brilliant (1) , as part of the
JIP SolidCO2Sim. Brilliant is a general finite
volume based CFD-system (Computational
Fluid Dynamics) with integrated FEM abilities
(Finite Element Method) for stress analysis.
Brilliant is designed to fully support multiphysics applications. With the introduction of
thermodynamic models capable of treating solid
CO2 in Brilliant, complex scenarios involving
possible dry ice formation may be simulated in a
fully 3-dimensional and transient framework.
Figure 2: Solid is treated as particles dispersed into a bulk vapour or
liquid phase
Pressure [Bar]
Long distance transport of CO2-rich
mixtures in pipe lines. As the pressure
drops, there a risk for solid CO2 formation
that can influence flow conditions.
Pikaar 173K
0
E&G T6 (low)
E&G T3 (middle)
E&G T1 (high)
Liquid trace
230
1
Liquid temperature
4.00E+06
Pressure
E&G Pressure
210
2.00E+06
190
0.1
100
150
200
250
300
350
0.00E+00
0
100
200
300
400
500
600
700
800
900
Time [s]
Temperature [Kelvin]
Perspectives
In the continuing work of the SolidCO2Sim project, important issues include: Multiphase flow with solids
(i.e. particle flow), improved solution procedure for flow with large density variations, development and
finalization of the thermodynamic module and GUI development.
References
Acknowledgements
(1) www.brilliant-cfd.com
(2) www.vessfire.com
(3) Pressure discharge from a pressure vessel
filled with CO2. Eggers, E. og Green, V. 1990, J.
Loss Prev. Process Ind.
(4) A New Equation of State for Carbon Dioxide
Covering the Fluid Region from the Triple-Point
Temperature to 1100K at Pressures up to
800MPa. Span, R. and Wagner, W.. 1996, J.
Phys. Chem. Ref. Data, Vol 25
Petrell gratefully acknowledges the partners contributing to this JIP:
Total, Statoil, Gassco and NRC (Climit).
Contact information
1 Anders Granskogen Bjørnstad
[email protected]
(+47) 99445720
2
Geir Berge
[email protected]
(+47) 93200020
Petrell AS
Olav Tryggvasons gate 40
7011 Trondheim
NORWAY
www.petrell.no