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 CO2 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 CO2 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 % CO2, 75 vol % N-2, and 10 vol % H2O. 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 CO2 purity and CO2 recovery, achieving a CO2 Purity of nearly 90% at a CO2 recovery of 72% and feed throughput (0) of 57.6 L STP/h/kg. Increasing k(a) and kd by a factor of ten further increased both the CO2 purity and CO2 recovery, achieving for the first time a CO2 purity greater than 90% at a CO2 recovery of 85% and theta of 57.6 L STP/h/kg. Making k(d) = k(a) (= 0.0058 s-1) resulted in a CO2 Purity of 89% with a CO2 recovery of 7296 at a theta of 57.6 L STP/h/kg; and increasing that value by a factor of five led to a CO2 purity of 91916 at a high CO2 recovery of 88916 and 0 of 57.6 1 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 CO2 purity increased to 98% at a 0 of 201.7 L STP/h/kg, but the CO2 recovery decreased to 5%. Overall, it was proven that mass transfer effects were important to the performance of this high temperature CO2 recovery process, with higher but acceptable values of k(a) and k(d) leading to CO2 purities of greater than 90%, a needed limit for process viability. (c) 2006 American Institute of Chemical Engineers Environ Prog, 25: 334-342, 2006.