CO₂ Capture from a Simulated Dry Exhaust Gas by Internally Heated and Cooled Temperature Swing Adsorption

Abstract

Herein, the CO₂ capture performance of a thermal swing adsorption (TSA) process, equipped with adsorbent-packed heat exchangers, was investigated taking the effective use of waste heat into account. Two typical CO₂ adsorbents—CaA and NaX zeolites—were examined with regard to their CO₂ adsorption properties from a simulated dry exhaust gas containing 9.5 vol% CO₂ and 90.5 vol% N₂. The effects of the hot water temperature supplied to the adsorber and the regeneration air flow rate on the separation performance were investigated, as a function of the adsorption/desorption switching time. Increasing the regeneration temperature was observed to improve the separation performance, and a regeneration temperature of 80°C, yielded a five-fold increase in the CO₂ concentration when compared with the feed gas at the optimal adsorption/desorption switching interval. A TSA process incorporating an adsorbent-packed heat exchanger is evidently an effective means of enriching CO₂, based on decreasing the regeneration of air by internal heating and removal of heat by internal cooling. The separation behaviors of both zeolites are similar, except that the CO₂ concentration in the desorbed gas and the recovery ratio of CaA, at a shorter adsorption/desorption interval, was somewhat larger than that of NaX. These findings suggest that the adsorption rate of CaA is largely dependent on the adsorbed uptake volume. Reducing the regeneration air flow rate to one fortieth of the original value further increased the CO₂ concentration at the desorption outlet, while lowering the CO₂ recovery ratio. Additionally, the time profiles of desorption outlet gas volume and CO₂ concentration indicated that the desorption outlet CO₂ concentration momentarily reached >70%. Furthermore, the findings also clarified the rapid desorption rate of the adsorbed N₂, which was almost completed within the initial desorption period, and which decreased the averaged CO₂ concentration over the regeneration period.