Optimisation of a Hybrid CO2 Purification Process

Multi-stage compression is the normal method to achieve pipeline pressures of 100 bara for the transport of carbon dioxide (CO2) after capture in a carbon capture and storage (CCS) scheme. An alternative method is to partially compress the gas, liquefy it and then pump the liquid CO2 to the required pressure. The advantage of this process is that the CO2 stream can be further purified through liquefaction and this allows separation processes that do not produce a pure CO2 product such as vacuum swing adsorption (VSA) and membranes to be considered. In this study, the following two cases were analysed: 1) VSA as the primary separation process followed by a liquefaction process 2) VSA as the primary separation process followed by liquefaction and a membrane process Cryogenic conditions are required to liquefy the CO2 and this was achieved by using a mixed refrigerant process comprising ethane and propane. Multi-objective optimisation was performed on the hybrid systems to determine the minimum power for the maximum CO2 yield for each case.