Mass transfer enhanced CaO pellets for CO2 sorption: Utilization of CO2 emitted from CaCO3 pellets during calcination

Abstract

In the preparation of CaO-based CO2 sorbents, particle densification during pelletization significantly limits the mass transfer of CO2, thereby decreasing the CO2 sorption performance. In this study, mass transfer enhanced CaO pellets (CaO-PC) were prepared through the formation of channels using CO2 evacuation from the inside of the pellets. Calcination of CaCO3 pellets induced CO2 evacuation and the remaining evacuation pathways provided excellent mass transfer channels for CaO-PC. Conventional CaO pellets (CaO-CP) were also prepared for comparison. Unlike the severely agglomerated (or blocked) morphology of CaO-CP, well-developed channels were observed in CaO-PC. It was experimentally confirmed that these channels directly contributed to the initial stage of CO2 sorption in CaO-PC, which significantly accelerated the CO2 sorption kinetics. CaO-PC had increased CO2 sorption uptakes of 58.9, 65.1, and 67.0 wt% at 500, 600, and 700 degrees C, respectively, whereas those for CaO-CP were 47.6, 55.4, and 56.8 wt%. In addition to CO2 sorption, enhanced mass transfer had a positive effect on CO2 release after capture. Under CO2 flow, the regeneration of CaO-PC was faster than that of CaO-CP, even at lower temperatures. Both the fast CO2 sorption and regeneration kinetics of CaO-PC significantly enhance the energy efficiency of continuous CO2 capture processes. These improvements were accomplished easily without the need of any additional energy-consuming treatments other than the conventional preparation methods.