Circulating Fluid-Bed Studies for CO₂ Capture from Flue Gas using K₂CO₃/Al₂O₃ Adsorbent

Abstract

Recent research has concentrated on the adsorption-based CO2 capture process with dry regenerable adsorbents that follows carbonate–bicarbonate chemistry in a thermal-swing mode. The potential advantages of solid adsorbents for CO2 capture were assessed on a pilot scale. The performance of 35 wt % K2CO3 supported on alumina was investigated in both batch (non-circulating) and continuous operation with adsorbent circulation mode. The effect of various parameters, such as adsorption and desorption temperatures, water vapor content in the flue gas stream, gas-hourly space velocity, mode of adsorbent regeneration, etc., were investigated in the system comprised of bubbling fluidized-bed adsorber and desorber. It has been found that the formation of hydrated species of K2CO3 during the desorption process in turn facilitates the CO2 adsorption reaction in the adsorber. The overall energy demand seems to be reduced during partial regeneration of the adsorbent, as against the requirement of 141 kJ/mol for full regeneration, and is thoroughly validated by DSC. It implies a reduced energy demand for adsorbent regeneration as compared to the conventional amine absorption process. The results showed more than 80% CO2 removal using a simulated flue gas stream comprised of 8.3 vol % CO2, 15.8 vol % H2O, and the rest N2. The adsorbent displayed excellent structural stability even after 144 h of continuous operation with adsorbent circulation. The stability and lower energy demand for adsorbent regeneration in the continuous fluidized-bed reactor system at the pilot scale were very promising and encouraging for the economic viability of the capture process.