Differences in reactivity of pulverised coal in air (O2/N2) and oxy-fuel (O2/CO2) conditions

The reactivity of four pulverised Australian coals were measured under simulated air (O2/N2) and oxy-fuel (O2/CO2) environments using a drop tube furnace (DTF) maintained at 1673 K and a thermogravimetric analyser (TGA) run under non-isothermal (heating) conditions at temperatures up to 1473 K. The oxygen concentration, covering a wide and practical range, was varied in mixtures of O2/N2 and O2/CO2 in the range of 3 to 21 vol.% and 5 to 30 vol.%, respectively. The apparent volatile yield measured in CO2 in the DTF was greater than in N2 for all the coals studied. Pyrolysis experiments in the TGA also revealed an additional mass loss in a CO2 atmosphere, not observed in a N2 atmosphere, at relatively high temperatures. The coal burnout measured in the DTF at several O2 concentrations revealed significantly higher burnouts for two coals and similar burnouts for the other two coals in oxy-fuel conditions. TGA experiments with char also revealed higher reactivity at high temperatures and low O2 concentration. The results are consistent with a char–CO2 reaction during the volatile yield experiments, but additional experiments are necessary to resolve the mechanisms determining the differences in coal burnout.