Energy-Conservative CO₂-Recovery Performance of K₂CO₃-on-Activated Carbon in Bench Scale

Abstract

Potassium carbonate (K₂CO₃) has been employed for a chemical absorption method (Benfield process) to recover CO₂ from flue gases. Potassium carbonate reacts with both CO₂ and H₂O to form potassium hydrogencarbonate (KHCO₃) by the reaction K₂CO₃ + CO₂ + H₂O = 2KHCO₃, followed by the decomposition of hydrogencarbonate to release CO₂ on flushing with steam to shift the reaction in reverse. Porous supports, such as activated carbon (AC), impregnated with K₂CO₃ work as a chemical absorbent and make it possible to recover CO₂ from moist flue gases by fixed-bed operations. In this study attempts are made to recover CO₂ recovery by employing a bench-scale apparatus in order to elucidate characteristic of the K₂CO₃-on-AC process and to obtain performance data for practical applications. Moist CO₂ gas (13%CO₂+10%H₂O) was supplied to a column (45mmø×800mmL) which was packed with K₂CO₃-on-AC at 333 K to sorb CO₂ selectively. After breakthrough of CO₂, steam at 423 K was flushed to the column to release CO₂ sorbed. By cooling the released gas through a heat exchanger, the steam was condensed to separate from the released gas, giving high purity (>99%) of CO₂ gas. Parameters in the process with K₂CO₃-on-AC relevant to each step such as CO₂ sorption, CO₂ release and cooling of the column were optimized. Cyclic operations of the each step demonstrated a steady, and energy- conservative performance of pure CO₂ recovery, showing as a potential technology to practical applications.