Energy, Énergie, Environment, Environnement, Pollution, Sciences exactes et technologie, Exact sciences and technology, Sciences appliquees, Applied sciences, Genie chimique, Chemical engineering, Transferts de chaleur et de matière. Garnissages, plateaux de contact, Heat and mass transfer. Packings, plates, Adsorption, Pollution, Pollution atmosphérique, Atmospheric pollution, Généralités, General, Méthodes de prévention et d'épuration, Prevention and purification methods, Procédés généraux d'épuration et de dépoussiérage, General processes of purification and dust removal, Adsorption modulée pression, Pressure swing adsorption, Adsorción modulada presión, Coefficient transfert masse, Mass transfer coefficient, Coeficiente transmisión masa, Dioxyde de carbone, Carbon dioxide, Carbono dióxido, Dépressurisation, Depressurization, Depresionación, Désorption, Desorption, Desorción, Ecoulement contre courant, Countercurrent flow, Flujo contra corriente, Effluent gazeux, Gaseous effluent, Efluente gaseoso, Pollution air, Air pollution, Contaminación aire, Pureté, Purity, Pureza, Stripage, Stripping, Transfert masse, Mass transfer, Transferencia masa, PSA, carbondioxide sequestration, heavy reflux, hydrotalcite, and stack gas treatment
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 (ka) and desorption (kd) mass transfer coefficients of CO2 in the K-promoted HTlc were uncertain, this study focused only on the effects of ka and kd 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 %, N2, and 10 vol % H2O. For the 5-bed process, increasing both ka (= 0.0058 s-1) and kd (= 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 (6) of 57.6 L STP/h/kg. Increasing ka 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 0 of 57.6 L STP/h/kg. Making kd = ka (= 0.0058 s-1) resulted in a CO2 Purity of 89% with a CO2 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 CO2 purity of 91% at a high CO2 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 ka and kd were both increased by a factor of five, the CO2 Purity increased to 98% at a θ 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 ka and kd leading to CO2 purities of greater than 90%, a needed limit for process viability.