Carbon dioxide capture from flue gas by pressure swing adsorption at high temperature using a K‐promoted HTlc: Effects of mass transfer on the process performance

Using hundreds (640) of simulations obtained from a cyclic adsorption process simulator, two heavy reflux (HR) pressure swing adsorption (PSA) cycles were analyzed at the periodic state for the capture and concentration of CO 2 from flue gas at high temperature (575 K), using a K-promoted hydrotalcite like compound (HTlc). Since the values of the adsorption (k a ) and desorption (k d ) mass transfer coefficients of CO 2 in the K-promoted HTlc were uncertain, this study focused only on the effects of k a and k d on the process performance. Both, a 5-bed 5-step stripping PSA cycle with light reflux (LR) and HR from LR purge and a 4-bed 4-step stripping PSA cycle with HR from countercurrent depressurization were studied using a vacuum swing cycle with the high pressure fixed at 137.9 kPa and the feed set at 15 vol % CO 2 , 75 vol %, N 2 , and 10 vol % H 2 O. For the 5-bed process, increasing both k a (= 0.0058 s -1 ) and k d (= 0.0006 s -1 ) by a factor of five increased both the CO 2 purity and CO 2 recovery, achieving a CO 2 purity of nearly 90% at a CO 2 recovery of 72% and feed throughput (6) of 57.6 L STP/h/kg. Increasing k a and k d by a factor of ten further increased both the CO 2 purity and CO 2 recovery, achieving for the first time a CO 2 purity greater than 90% at a CO 2 recovery of 85% and 0 of 57.6 L STP/h/kg. Making k d = k a (= 0.0058 s -1 ) resulted in a CO 2 Purity of 89% with a CO 2 recovery of 72% at a 6 of 57.6 L STP/h/kg; and increasing that value by a factor of five led to a CO 2 purity of 91% at a high CO 2 recovery of 88% and 0 of 57.6 L STP/h/kg. These results suggested that the performance was desorption limited. For the 4-bed process, when k a and k d were both increased by a factor of five, the CO 2 Purity increased to 98% at a θ of 201.7 L STP/h/kg, but the CO 2 recovery decreased to 5%. Overall, it was proven that mass transfer effects were important to the performance of this high temperature CO 2 recovery process, with higher but acceptable values of k a and k d leading to CO 2 purities of greater than 90%, a needed limit for process viability.