RATES OF OXIDATION OF MILLIMETER-SIZED CHAR PARTICLES - SIMPLE EXPERIMENTS

Rates of oxidation of 5-10 mm particles of chars from six coals at various temperatures were measured in air at ambient pressure in simple devices: a muffle furnace, a Meker burner, and a heated ceramic tube. The chars were first prepared from the coals in the Meker burner at comparable temperatures. As well as coal type and oxidation temperature, initial char particle mass and number of particles were varied. The char particles were oxidized in incremental steps of several minutes for periods up to 1 h. The cube root of particle mass decreased linearly with increasing time in all tests. Ash layers formed and usually remained in place around the particle. Average mass reactivities increased with decreasing initial particle mass. With decreasing furnace temperature, char reactivity decreased at the lower temperatures. Two or four closely spaced char particles burned much more slowly than single particles of the same size. Correlative equations are consistent with the data, elucidating the roles of kinetic reaction and oxygen diffusion.