Efficient Recovery of Carbon Dioxide from Flue Gases of Coal-Fired Power Plants by Cyclic Fixed-Bed Operations over K₂CO₃-on-Carbon

Abstract

An efficient chemical absorption method capable of cyclic fixed-bed operations under moist conditions for the recovery of carbon dioxide from flue gases has been proposed employing K2CO3-on-carbon. Carbon dioxide was chemically absorbed by the reaction K2CO3 + CO2 + H2O ⇄ 2KHCO3 to form potassium hydrogencarbonate. Moisture, usually contained as high as 8−17% in flue gases, badly affects the capacity of conventional adsorbents such as zeolites, but the present technology has no concern with moisture; water is rather necessary in principle as shown in the equation above. Deliquescent potassium carbonate should be supported on an appropriate porous material to adapt for fixed-bed operations. After breakthrough of carbon dioxide, the entrapped carbon dioxide was released by the decomposition of hydrogencarbonate to shift the reaction in Eq.1 in reverse on flushing with steam, which could be condensed by cooling to afford carbon dioxide in high purity. Among various preparations of alkaline-earth carbonates (X2CO3, X = Li, Na, K) on porous materials, K2CO3-on-activated carbon revealed excellent properties for the present purpose. Preparation and characterization of K2CO3-on-carbon and illustrative fixed-bed operations under flue gas conditions in laboratory columns and a bench-scale plant are described.