Microstructure analysis of fluidized preheating pulverized coal under O2/CO2 atmospheres

The high efficient and clean coal combustion with fundamental deep low pollution emission was extensively explored worldwide. In this work, the Shenmu bituminous coal was preheated in a circulating fluidized bed (CFB) and this modified fuel including the preheated fuel and the coal gas was burned in a down-fired combustor (DFC) under the O-2/CO2 atmospheres. The microstructure change of fuel was analyzed to reveal the reaction process and particle change behavior during high temperature coke combustion. Analysis at the micro scale was important for understanding macro phenomena and achieving deep low pollution emission. The results showed that the main forms of N, C, and O elements in coal were pyrrole, hydrocarbon (aromatics or aromatic substituted alkanes), and carbon-oxygen single bond (including ether and hydroxyl) respectively. During the preheating process, pyrrole converted to pyridine, the coal char reached a state of deep oxidation on the surface, and the stable structure between carbon and oxygen was destroyed. Besides, the number of reacting sites increased after preheating process, which was beneficial to the further combustion.