COMBUSTION CHARACTERISTICS OF SIMULATED DRY AND WET COAL VOLATILES (FLAMES, FUEL SCIENCE, SLURRY)

The results of a comprehensive study of the combustion characteristics of coal volatiles are reported. The objective was to better understand the physical and chemical characteristics of wet and dry coal volatiles combustion. The approach was to simulate the gases that are evolved when a coal particle is rapidly heated by mixing together the appropriate components. These mixtures were then burnt under low pressure using a non-adiabatic flat-flame burner. The volatiles produced from three different ranks of coal were simulated: bituminous, subbituminous, and lignite. Water vapor was added in order to simulate the early phase of coal-water slurry combustion. Water vapor was also added to methane-air mixtures in order to determine its effect on a single-fuel flame.;The effect of added water vapor on all of the flames was to reduce the flame temperatures and to delay the combustion. The delay was not severe at the higher temperatures and varied with stoichiometry. The effect of added water vapor on the maximum OH concentration in methane flames was found to vary with temperature. Soot precursor concentration was found to be reduced when water was added to a flame.;Regarding coal volatiles combustion, it was determined that the global activation energy for combustion, which is related to the ease of ignition of a fuel, decreased with decreasing rank of the parent coal. In addition, the production of soot precursors was highest in the higher rank volatiles.;Superequilibrium concentrations of hydrogen were detected in the post-flame zone of the higher rank volatiles. Also, the water gas shift reaction was not equilibrated in any of the flames studied.;The physical and chemical microstructure of each flame was diagnosed by using fine-wire thermocouples, a water-cooled quartz microprobe in connection with a gas chromatograph, and an optical probe. Data collected included profiles of temperatures, stable gases, and OH radicals.