Observation of Coal Fly Ash Shapes Produced at High Combustion Temperature

Coal fly ash components, morphologies, and the crystal structure produced under high combustion temperatures were observed with an electron microscope. Coal was burnt using the high-temperature tandem-type staged drop-tube furnace. Reaction temperature, reaction time, and particle concentrations were adjusted to those used in actual boilers and sub-bituminous coal and bituminous coal were investigated. When coal was burnt under high temperature fuel-rich conditions in the first furnace, solid carbon compounds which differ from char were observed. Elemental analysis revealed that the solid carbon compounds were soot. To evaluate the effect of coal properties on soot formation, emission properties of unburned carbon in fly ash （UBC） were examined for sub-bituminous coal and bituminous coal. In the case of sub-bituminous coal, UBC decreased once then increased again with increasing combustion temperature. By contrast in the case of bituminous coal, UBC steadily decreased with increasing combustion temperature. Electron microscope images showed that high crystallized carbon compounds were present in the soot of sub-bituminous coal.