Dehydration and Compression of Contaminated CO2-rich Gas
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The use and demand of energy by exploiting fossil fuels is increasing. Carbon Capture and Storage (CCS) may be the solution to achieve decreased emissions, from various emitters of climate gases such as carbon dioxide. By permanent storage, the emissions of carbon dioxide will not reach the atmosphere, avoiding the greenhouse effect. The CO2-rich streams resulting from carbon capture need to be processed before transport and storage. Typical CO2 processing systems consist of compression, free-water removal and dehydration. The focus of this thesis is on the processing of captured CO2 from natural gas. Most often, the captured CO2-rich streams from natural gas are not 100% pure, and may contain several impurities in addition to water. The presence of impurities like methane and nitrogen may have a noticeable effect on the choice of design and process operability of the CO2 processing system. The effect of impurities on the phase behaviour of CO2-rich mixtures has been analysed. Predictions from different thermodynamic models have been evaluated and compared with experimental data from literature. Regression of binary interaction parameters has been done based on the assembled empirical data. Aspen Properties has been used to perform the regressions. The following cases were found relevant for design and process operability; four-stage system with reservoir pump, three-stage system with reservoir pump, effect of high level of impurities, effect of type of impurity, effect of impurity concentration, compression-only system (no pump), maximum free-water removal and handling of impurities. Technical solutions for dehydration of CO2 have been discussed. Basic concepts of absorption and adsorption are given together with relevant block diagrams and other key information.