Sulfur Capture during Combustion of High Sulfur Coals Impregnated with Calcium Acetate as a Desulfurization Sorbent

摘要

Combustion of Datong coal, with impregnation of calcium acetate onto it, was carried out in a drop tube furnace. Its pyrolysis was first conducted to study the morphology of the resultant chars, and the mode of occurrence of calcium, sulfur and their association within char were studied as well. Secondly, combustion of chars was carried out to reveal the emission of sulfur, transformation of char structure and that of calcium- and sulfur-based compounds in this process. For the raw coal, the sulfur emission during its combustion was continued until all the carbon burnt out. The thick wall was formed for the pyrolyzing char. The SO_2 emission during combustion of impregnated coals was decreased considerably compared to that in the cases of raw coals. More than half the emitted sulfur was captured by added calcium in coal pyrolysis. The sulfur removal in the following char compounds varied with both reaction temperature and coal type. During coal pyrolysis, the added calcium, which penetrated into coal due to the impregnation, moved to the surface of porous char, where it met the emitted sulfur, capturing it quickly. Little calcium reacted with the inherent aluminosilicate in this step. In the beginning of char combustion, the reaction of oxygen with volatile and char led to the increase of char temperature, as a result, the sulfation of calcium was inhibited to certain extent; whilst the formation of calcium aluminosilicate was facilitated. With char combustion progressed, the porous calcium network consisting of unreacted calcium and the molten calcium aluminosilicate was formed as the consequence, which reacted with SO_2 readily, hence, the sulfur removal efficiency was increased eventually.