https://doi.org/10.1016/j.ccst.2021.100011
“Sorbent regeneration had been proceeded under different sweep gases including N2, CO2, pure steam and CO2 with steam dilution. As expected, the adsorbent regenerated in a pure N2 flow achieved higher CO2 removal efficiency (76.3%) than that regenerated using pure CO2 as sweep gas (50.7%). This was due to the regeneration conversion of K2CO3/Al2O3 relied on the concentration driving force effect. When CO2 was introduced as sweep gas for regeneration, the concentration gradient of CO2 at the solid-gas interface was low, and this had altered the chemical equilibrium state between the adsorbent and CO2. A higher temperature and more energy consumption were required for full regeneration of the adsorbent in CO2 stream. Partial regeneration in a steam diluted CO2 flow could be a promising alternative strategy, and this strategy retained the active species as K2CO3•1.5H2O for reduced energy demand for regeneration and facilitated carbonation reactivity (Sengupta et al., 2018; Sengupta et al., 2014b). The scale-up commercial application of K2CO3/Al2O3 would require the regeneration being proceeded in a pure CO2 and steam-diluted CO2 flow instead of using N2 as a sweep gas, to obtain high-purity CO2 for sequestration and utilization. Laboratory tests indicated that the regeneration conversion of K2CO3/Al2O3 showed no much difference when proceeded in pure CO2 and CO2/H2O atmospheres (Zhao et al., 2012c). Olk et al. and Zhao et al. also highlighted that partial regeneration of the spent potassium-based adsorbents in a pure steam or steam-diluted CO2 flow via temperature and water vapor pressure swing could be a novel approach, with respect to the significant role of the hydrated species of K2CO3•1.5H2O in minimizing total energy consumption and promoting carbonation efficiency (Olk, 2015; Zhao, W. et al., 2013). Recently, Won et al. employed the partial regeneration mode and they found that the adsorbents regenerated in a 4%H2O+96%CO2 stream at 195°C exhibited good carbonation performance in a circulated fluidized bed reactor, with about 88% CO2 removal efficiency, 5.6 wt.% dynamic sorption capacity, and 4.85 GJ/t CO2 for regeneration energy (Fig. 7) (Won et al., 2020).”
“Fig. 7. Dynamic CO2 capture and sorbent regeneration processes of 200 kg potassium-based sorbent in a circulated fluidized bed reactor. Reproduced with permission from (Won et al., 2020). Copyright 2020 Elsevier B. V.”