Equations of State for modelling CO 2 outflow from pipelines

CO2 Transportation

• Scale of CCS operations envisioned suggests CO2transportation will mainly be by pipeline

• Safe operation of these pipelines is paramount

• Ability to predict fluid properties during blowdown can inform:

• Pipeline design, safety features and operational protocols

• Consequences of release

• Emergency response

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Modelling Outflow

• The fluid flow predictions made are based on the solution of the conservation equations for mass, momentum and energy:

• ρ, u, P and h are the density, velocity, pressure and specific enthalpy of the homogeneous fluid as function of time, t, and space, x. qh is the heat transferred through the pipe wall to the fluid

• Conservation equations solved using Method of Characteristics (MOC)3

Study Objectives

• This study investigates the accuracy of various cubic Equations of State (EoS) for predicting the properties of CO2 fluids during outflow when used in the UCL Outflow Model

• EoS used were Peng Robinson (PR), modified PR of Wu (MPR), Stryjeck-Vera modified PR (PRSV-1) and the Soave-Redlich-Kwong (SRK)

• Predicted outflow data is compared with “large scale” experimental measurements kindly provided by National Grid

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Experimental set-up

• The National Grid shock tube is 144 m long, 150 mm internal diameter, it is horizontal and insulated externally

• Instrumented with fluid pressure and temperature sensors

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Inventory Compositions and Initial Conditions

•High frequency data available for tests 3, 6 and 11

•Lower frequency data available for tests 19 and 26

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CO2 H2 N2 SO2 O2 CH4 Pressure (bara)

Temperature (°K)

3 100 - - - - - 39.11 278.25

6 95.97 - 4.03 - - - 38.91 278.45

11 89.23 3.24 3.84 1.24 1.32 1.13 39.01 278.15

19 100 - - - - - 153.4 278.35

26 95.92 - 4.08 - - - 141.4 293.15

Test 3 results (pure CO 2 – gas phase)Observed experimental plateau consistently lower than simulation plateau –ascribed to delayed nucleation of inventory.

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Test 6 results (96% CO 2 – gas phase)Delayed nucleation observed, MPR results diverging significantly.

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Test 11 results (89% CO 2 – gas phase)Delayed nucleation observed , MPR results diverging significantly.

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Test 19 results (100% CO 2 – dense phase)

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Temperature history at a fixed point near the closed end of the shock tube.

Test 19 results (100% CO 2 – dense phase)

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Pressure history at a fixed point near the closed end of the shock tube.

Test 26 results (96% CO 2 – dense phase)

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Temperature history at a fixed point near the closed end of the shock tube.

Test 26 results (96% CO 2 – dense phase)

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Pressure history at a fixed point near the closed end of the shock tube.

Conclusions

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Cosham, A., Jones, D., Armstrong, K., Allason, D., & Barnett, J. (2011). The decompression behaviour of CO2 in the gas phase. International Forum on the Transportation of CO2 by Pipeline. Newcastle.

Cosham, A., Jones, D. G., Armstrong, K., Allason, D., & Barnett, J. (2012). The Decompression Behaviour of Carbon Dioxide in the Dense Phase. Proceedings of the 2012 9th International Pipeline Conference. Calgary.

Stryjek, R., & Vera, J. H. (1986). PRSV: An improved Peng-Robinson equation of state for pure compounds and mixtures. The Canadian Journal of Chemical Engineering, 64(2), 323–333.

Versteeg, H. K., & Malalasekera, W. (1995). An Introduction to Computational Fluid Dynamics, The Finite Volume Method. Harlow: Longman Scientific and Technical.

Wu, D., & Chen, S. (1997). a Modified Peng-Robinson Equation of State. Chemical Engineering Communications, 156(1), 215–225.

Useful References