Modeling the fragmentation of non-uniform porous char particles during pulverized coal combustion

Char fragmentation during pulverized coal combustion was studied using an A ustralian bituminous coal. The coal was combusted with air in a drop tube f urnace at a gas temperature of 1300 degrees C. The char samples were collec ted at different levels of char burnout, and their structure was examined u sing scanning electron microscopy. Approximately 40% of the char particles formed after pyrolysis were cenospheres with a highly non-uniform porous st ructure and a large central void. A large number of fine particles were als o observed in the char samples with burnout levels between 30 and 50 vol%, which suggests that significant fragmentation occurs during the early combu stion stage. A mathematical model was developed relating the fragmentation of cenospherical char particles with the macropores in the particle shell. The formation of these macropores partially results because of the carbon r emoval from the surface of the thin shell due to surface oxidation. A perco lation model was used to simulate the char structural changes during combus tion in regime III, and the predicted particle size distributions qualitati vely agreed with the experimental measurements. (C) 2000 Elsevier Science L td. All rights reserved.