Influence of atmosphere for K2CO3 regeneration

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., 2018Sengupta 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, 2015Zhao, 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.”

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