A numerical study of the behaviour of carbon dioxide in control valves for optimising carbon sequestration

Master thesis (2022)

Authors

B.S. Fluttert Mechanical Engineering

Contributors

Rene Pecnik Energy Technology - Mechanical, Maritime and Materials Engineering (mentor)
W.P. Breugem Multi Phase Systems - Mechanical, Maritime and Materials Engineering (graduation committee member)
A. Twerda TNO (graduation committee member)
M.J.B.M. Pourquie Fluid Mechanics - Mechanical, Maritime and Materials Engineering (graduation committee member)
Faculty
Mechanical Engineering, Mechanical Engineering
Copyright: © 2022 Bob Fluttert
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Published Date

21-10-2022

Language

English

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Faculty

Mechanical Engineering

Abstract

The Intergovernmental Panel on Climate Change (IPCC) believes that multiple solutions must be deployed simultaneously to reduce the emission of greenhouse gases into the atmosphere. Carbon, Capture & Storage (CCS) is an unavoidable technique within this portfolio as an intermediate solution. CCS requires transport of CO2 through pipeline systems and into wells. There are still large uncertainties on the thermodynamics of the CO2 in flow through valves. The CO2 flow undergoes significant changes in pressure, temperature and phase distribution when it passes this control valve. Therefore, the behaviour of the CO2 flow flowing through a control valve is examined in this study.

The simulation of CO2 in a 3D valve including phase transitions is complex. Furthermore, few validation experiments are available. As a first step, more simple nozzles are simulated. In these devices, the same processes occur and validation data is available. These simulations are validated with experimental data by Nakagawa et al. to examine the accuracy. Three types of models (isenthalpic, Euler and Enhanced Mass Transfer (EMT)) are implemented in increasing levels of complexity to investigate the differences between these models and to consider when complexity is needed or simplifications are valid.

The validation cases show experimental pressure data of high-pressure CO2 flow through converging-diverging nozzles with phase transitions. The results showed that the EMT model matched the experimental data best. A substantial similarity was achieved regarding the pressure data. The mass transfer mechanism, however, needed adjustments in its coefficients to match the experimental data. Finally, after finding the right values, the EMT shows the best technique for modelling flashing or cavitation.

In short, the overall consequences of the transition in a valve are substantial and must be considered. The behaviour of the high-pressure CO2 flow is heavily influenced by flowing through a valve. Substantial amounts of vapour are formed, but only after the throat. This is the same for choking condition, which is achieved in the diverging section of the nozzle. The large expected drop in temperature due to pressure reduction has also been noted.

Although a high degree of similarity between the results of the model with experimental data is obtained, there is room for improvement regarding the model. A flaw was discovered in the handling of the thermodynamic properties of the fluid near critical points. Also, the surface tension has not been considered, but might have a substantial influence. Next steps in the research are 2D and 3D simulations of actual valves, but require experimental validation data.