Thermodynamic exploration of two-stage vacuum-pressure swing adsorption for carbon dioxide capture

Adsorption technology is recognised as a promising CO2 capture method due to its characteristics of low regeneration temperature. Analysis model based on carbon pump concept could be used to reveal thermal performance of various carbon capture technologies. However, the concept still has a large gap to become a comprehensive theory. This paper aims to evaluate thermodynamic performance of two-stage vacuum-pressure swing adsorption (VPSA) from a new definition of single-stage VPSA cycle. Energy consumption and exergy efficiency of VPSA cycles are evaluated and compared. Results indicate that introduction of the second stage can significantly elevate the concentration of product gas with less energy input increase. Also, energy consumption decreases from 114.53 kJ mol−1 to 28.23 kJ mol−1 when initial concentration of CO2 rises from 15% to 75%. However, there is a maximum value of exergy efficiency, 7.01% when initial concentration is 45%. Non-discharged CO2 molecules remained in the void of bed after evacuation process will significantly influence the concentration of product gas. The final concentration of product gas achieves the minimum of 91.90% when concentration differences are both 10% at two stages. One remarkable fact is that a new definition of VPSA cycle may be more feasible for thermal analysis in real applications. •Performance of a two-stage VPSA cycle is explored based on carbon pump concept.•Introducing the second stage to original cycle is beneficial to improve product gas purity.•Unused percentage have great effects on thermal cycle performance.•Residual CO2 molecules have the influence on the purity of product gas significantly.