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 (O-2/N-2) and oxy-fuel (O-2/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 O-2/N-2 and O-2/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 N-2 for all the coals studied. Pyrolysis experiments in the TGA also revealed an additional mass loss in a CO2 atmosphere, not observed in a N-2 atmosphere, at relatively high temperatures. The coal burnout measured in the DTF at several O-2 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 O-2 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. (C) 2009 Elsevier B.V. All rights reserved.