Effect of the presence of HCl on cyclic CO2 capture of calcium-based sorbent in calcium looping process

Abstract

The effect of the presence of HCl on cyclic CO2 capture behavior of calcium-based sorbent in the calcium looping process was investigated. When HCl was present in the carbonation atmosphere, the effects of carbonation temperature, calcination temperature, HCl concentration and particle size on CO2 capture of the limestone in the multiple calcination/carbonation cycles were studied in a dual fixed-bed reactor. The presence of HCl in the carbonation atmosphere improves CO2 capture capacity of the limestone in the previous a dozen cycles, but sharply decreases its reactivity with further increasing the cycle number above a dozen. The presence of HCl intensifies the effects of carbonation temperature and calcination temperature on CO2 capture capacity of the limestone. The optimum carbonation temperature and the feasible calcination temperature for cyclic CO2 capture of the limestone in the presence of HCl should be 700°C and below 900°C, respectively. The cyclic CO2 capture capacity of the limestone in the previous a dozen cycles achieves the maximum in the presence of 300ppm HCl with increasing the HCl concentration from 100 to 1000ppm. The higher CO2 capture capacity of the limestone is achieved with smaller particle size in the presence of HCl. The presence of HCl may destroy the compact CaCO3 product layer and it is beneficial to CO2 diffusion through the layer in the initial cycles. The chlorination conversion and the molten CaCl2–CaCO3 product layer thickness of the limestone in the presence of HCl increase with the number of calcination/carbonation cycles. It severely aggravates the sintering of the limestone once the cycle number is above about a dozen, which can be proved by microstructure analysis of the limestone experienced the multiple cycles in the presence of HCl.