Modeling, Simulation, and Optimization of Postcombustion CO₂Capture for Variable Feed Concentration and Flow Rate. 2. Pressure Swing Adsorption and Vacuum Swing Adsorption Processes

This paper reports studies on CO 2 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 CO 2 from the feed, and compression to almost pure CO 2 for sequestration at 150 bar. Each process alternative is optimized over a range of feed CO 2 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 CO 2 composition are also developed for the PSA- and VSA-based CO 2 capture and compression for the first time. Furthermore, a cost-based comparison of four leading CO 2 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 CO 2 capture and storage (CCS) technology for diverse emission scenarios. Results indicate that CO 2 can be captured with the least cost using a MEA-based chemical absorption when the feed CO 2 composition is less than 15–20%. For higher CO 2 compositions, VSA is the preferred process.