Optimisation of post-combustion carbon dioxide capture by use of a fixed site carrier membrane

This study presents a superstructure based mathematical model for the optimisation of the CO2 capture process from flue gas by use of a fixed site carrier membrane. The goal is to determine the optimum process flow sheet that gives the minimum total cost whilst achieving 90 % recovery and 95 % purity of CO2. The model is applied to a case study of a coal-fired power plant to assess the merits of the optimisation and the feasibility of implementing the membrane at a large scale. The membrane properties used in the simulation are obtained from the literature. This work involves the use of an accurate expression for CO2 permeance of CO2 in a poly-amine fixed site carrier membrane in relation to CO2 partial pressure. This allows pressure to be a variable in the optimisation problem. The use of water vapour as sweep is also explored and compared to the vacuum-driven only process. The application of the model results in a decrease in membrane area requirement of 46 % and a decrease of 13.6 % in the cost of CO2 avoided compared to a pre-determined two stage cascade process operating at uniform pressure. The results show that the use of water vapour as sweep in conjunction with vacuum pumps on the other membrane stages is more economical compared to the use of vacuum pumps only.