Study on the reaction of $CaCO_3$ sorbent particle in an $O_2/CO_2$ atmospheric condition

Abstract

Due to increasingly strict greenhouse gas emission regulations, $O_2/CO_2$ combustion systems were introduced as a promising $CO_2$ recovery technique for use in power plants. Moreover, in furnace desulfurization techniques can be adapted to the system, because of to their high sulfation efficiency. In this study, reactions of $CaCO_3$ particles, which can be used as sorbents for in-furnace desulfurization, were investigated in an $O_2/CO_2$ atmosphere. To determine the size effect of the $CaCO_3$ sorbent particles, three different particle sizes (9, 23, and 40 μm by mean diameter) were used. In an air atmosphere, calcination occurred actively within shorter residence times as the particle size increased. In contrast, the calcination trend was reversed in an $O_2/CO_2$ atmosphere compared with that in an air atmosphere. Based on experimental results, calcination reactions were suggested for each atmospheric condition. To examine the sulfation mechanism of $CaCO_3$ sorbent particles, thermogravimetric analysis (TGA) was conducted using gas streams containing air- and $O_2/CO_2$-balanced $SO_2$ (3000 ppm). A sulfation rate was calculated by measuring the mass change of the sorbent particles. After TGA reactions were complete, surface morphology changes and cross sections of the particles were observed using focused ion beam-scanning electron microscopy (FIB-SEM). Chemical composition of the interior of the particles was analyzed using energy dispersive X-ray spectroscopy (EDS) to observe the distribution of S-containing compounds. As particle size increased, the degree of sulfation decreased, and the total decrease was greater in an air atmosphere than with an $O_2/CO_2$ atmosphere. Furthermore, $SO_2$ molecules were adsorbed over the entire region of the particles through crack-like pores in an air atmosphere. In an $O_2/CO_2$ atmosphere, however, $SO_2$ permeated from the outside to the inside of the particles.