Design and experiment of high-productivity two-stage vacuum pressure swing adsorption process for carbon capturing from dry flue gas

A two-stage vacuum pressure swing adsorption (VPSA) process that coupled kinetically controlled and equilibrium controlled separation process with reflux has been investigated for capturing carbon dioxide from dry flue gas (85% N₂/15% CO₂). In the first enriching stage, carbon molecular sieve (CMS), which shows kinetic selectivity for CO₂/N₂, is adopted as the adsorbent to remove most N₂ in feed gas, thereby upgrading CO₂ and significantly reducing the amount for further refinement. The second stage loads zeolite 13X as adsorbent to purify the CO₂-rich flow from the first stage for meeting the requirements of National Energy Technology Laboratory. Series of experiments have been conducted for adsorption isotherms measuring and lab-scale experimental validation as well as analysis. The effect of feed composition on the separation performance of the PSA system was studied experimentally and theoretically here. The optimal results achieved 95.1% purity and 92.9% recovery with a high CO₂ productivity (1.89 mol CO₂·h^-1·kg^-1) and an appropriate energy consumption of 1.07 MJ·(kg CO₂)^-1. Further analysis has been carried out by simulation for explicating the temperature, pressure, and concentration distribution at cyclic steady state.