Modeling, Simulation, and Optimization of Postcombustion CO2 Capture for Variable Feed Concentration and Flow Rate. 2. Pressure Swing Adsorption and Vacuum Swing Adsorption Processes

This paper reports studies on CO2 capture technologies and presents the mathematical modeling, simulation, and optimization of adsorption-based process alternatives, namely, pressure swing adsorption (PSA) and vacuum swing adsorption (VSA). Each technology includes feed dehydration, capture of at least 90% of CO2 from the feed, and compression to almost pure CO2 for sequestration at 150 bar. Each process alternative is optimized over a range of feed CO2 compositions and flow rates. A superstructure of alternatives is developed to select the optimum dehydration strategy for feed to each process. A four-step process with pressurization, adsorption in multiple columns packed with 13X zeolite, N-2 purging, and product recovery at moderate to low vacuum is configured. A nonlinear algebraic and partial differential equation (NAPDE) based nonisothermal adsorption model is used, which is fully discretized and solved via a kriging model. Explicit expressions for costs as functions of feed flow rate and CO2 composition are also developed for the PSA- and VSA-based CO2 capture and compression for the first time. Furthermore, a cost-based comparison of four leading CO2 capture technologies, namely, absorption-, membrane-, PSA-, and VSA-based processes, is presented over a range of flue gas compositions and flow rates. This enables selection of the most cost-effective CO2 capture and storage (CCS) technology for diverse emission scenarios. Results indicate that CO2 can be captured with the least cost using a MEA-based chemical absorption when the feed CO2 composition is less than 15-20%. For higher CO2 compositions, VSA is the preferred process.