The Allam Cycle is an oxy-fuel power generation process which uses hydrocarbon fuels, with nearly all atmospheric emissions including the generated carbon dioxide (CO2) being captured. In designing the compressors/pumps of the Allam Cycle, it is required that the vapour-liquid equilibrium (VLE) phase behaviour of the working fluid can be predicted.
The Objectives
The objective of this project was to investigate the performance of two widely used models for predicting phase equilibrium. This required the modification of an experimental apparatus to be capable of measuring these mixtures, which was employed to experimentally studying mixtures of sCO2 with different impurities. The measurements were conducted using custom-built microwave resonators to perform dew- and bubble-point measurements over a range of compositions and conditions.
Project Findings
The apparatus designed and assembled for this project was successful in generating the required phase behaviour measurements to discriminate the performance of the two models. Experiments were performed along isochoric, isobaric, and isothermal pathways to access different regions of the somewhat complex phase diagram. A unique methodology was developed for preparing mixtures with low water content as an impurity and handling of the mixtures, to access aqueous dew points and to avoid phase separation during sample loading. The results obtained in this work reveal that the two thermodynamic models investigated can both be reliably used to predict VLE phase envelops for the CO2 streams used in the Allam cycle. However, the selection of preferred model is dependent on the stream composition and stage of the Allam cycle, according to the inlet/outlet conditions of the compressors and pumps.
Future Work and Recommendations
Building on the current study, there is an opportunity to continue the experimental work and establish a comprehensive overview of the phase behaviour of Allam cycle mixtures (over a wider range of pressure and temperature) so that a single equation of state can be developed for these mixtures. It is also recommended that the experimental apparatus developed at UWA be used to continue broader studies of CO2 mixtures and impure CO2 streams with moisture. There is a need for accurate phase behaviour data to support CCUS operations, such as in pipeline transport, blending, and sequestration specifications, as well as for the prediction of impurity reactions and optimisation of synthetic fuel production.
Project Reseachers
- Prof. Eric F. May
- A/Prof. Paul L. Stanwix
- Dr Liam Tenardi
- Dr Ehsan Sadeghi Pouya
Project Status
Complete
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