Stripping PSA Cycles for CO₂ Recovery from Flue Gas at High Temperature Using a Hydrotalcite-Like Adsorbent

A cyclic adsorption process simulator was used to study novel high-temperature pressure swing adsorption (PSA) cycles. Based on the use of a K-promoted hydrotalcite-like (HTlc) adsorbent and six different (vacuum swing) stripping PSA cycles, these cycles were designed to process a typical stack gas effluent at 575 K containing 15 vol % CO 2, 75 vol % N 2, and 10 vol % H 2 O into CO 2 -depleted and CO 2 -enriched streams. More than a thousand (1260) simulations were conducted to the periodic state to study and interpret the effects of the light-product purge-to-feed ratio, the cycle step time, the high-to-low pressure ratio, the heavy-product recycle ratio, and the feed throughput (θ) on the process performance. The cycle configuration was changed from 4-bed 4-step, 4-bed 5-step, and 5-bed 5-step designs that utilized combinations of light-reflux (LR) and/or heavy-reflux (HR) steps, and cocurrent depressurization (CoD) and/or countercurrent depressurization (CnD) steps. The process performance was judged in terms of the CO 2 purity in the heavy product ( y CO 2,HP ), with the CO 2 recovery ( R CO 2 ) and θ both being secondary process performance indicators. Any PSA process with a HR step outperformed any PSA process with only a LR step, regardless of whether a CoD step was added or not. The best performance was obtained from the 4-bed 4-step stripping PSA cycle with HR obtained from the CnD step, with y CO 2,HP = 82.7 vol %, R CO 2 = 17.4%, and θ = 14.4 L STP h -1 kg -1 . The next best performance was obtained from the 5-bed 5-step stripping PSA cycle with LR and HR obtained from LR purge, with y CO 2,HP = 75.5 vol %, R CO 2 = 48.8%, and θ = 23.1 L STP h -1 kg -1 . Overall, this study further substantiated the feasibility of a high-temperature stripping PSA cycle for CO 2 concentration from flue gas using an HTlc adsorbent. It also disclosed the importance of the PSA cycle configuration to the process performance, by gaining an understanding of and appreciation for the use of HR, and it exposed the rigor involved in determining the best PSA cycle sequence for a given application.