Comparative Study on Sulfur Capture Mechanisms of Shell and Limestone

摘要

Three types of shells and two types of limestones are used as sorbent material in this research. The experiments were conducted in a muffle furnace and a fluidized-bed reactor at 800～950°C, at atmosphere and analog flue-gas respectively. The pore shape and the crystal structure of samples were observed by SEM and sulfation property was analyzed by mercury injection apparatus and thermo-gravimetric analyzer. SEM photos show that CaO of calcined shells is composed of a size distribution of cylindrical and connective pores, the hole-wall of which is relative smooth; the large pores can be observed in the sulfated shells. The experimental data show that porosity of original shells varies from 2.45% to 7.23%, but that of the limestone is about 0.10%. According previous research that the calcined shells have a better pore size distribution and connectivity of the pore structure than the calcined limestone, the sulfur capture capability of shells greatly exceeds that of the limestone, which can not be explained well based only on pore structure. Based on gas diffusion theory and solid-state ions diffusion theory, a conclusion has been drawn that the pore structure of shells allows for greater product layer expansion, which aids the penetration of the reaction gases and improves the utility of the intraparticle surface area; the calcined shells have a higher lattice defects concentration than the calcined limestone, which makes the shells have a higher ions diffusion through the product layer at the later stage of sulfation reaction.