Fuel, Vol.79, No.2, 109-121, 2000
Factors governing reactivity in low temperature coal gasification. Part 1. An attempt to correlate results from a suite of coals with experiments on maceral concentrates
This paper reports on the first stage of a study attempting to develop laboratory scale tests for the reliable determination and eventual prediction, of the effect of coal properties on the performance of coals in air blown gasifiers. The pyrolysis and gasification behaviour of a suite of coals have been matched, using a high-pressure wire-mesh reactor (WMR), with those of maceral enriched samples. Reaction conditions were selected to simulate those of the pilot-scale gasifier stage of the Air Blown Gasification Cycle operated by British Coal. Subsequent stages of the study have examined the role of mineral matter and char morphology. The suite of coals previously tested in the pilot scale reactor were originally selected to represent coals of a wide geographical spread, a limited range of properties and were commercially available in the EU. The maceral enriched samples were obtained from different coals, but were of similar rank to those examined in this study. Short hold time experiments (10 s) have been carried out in the laboratory scale reactor. Three distinct types of behaviour have been identified-arising from competing influences of the reactivity of the base char, the impact of secondary char deposition and the effect of melting on the reactivity of the ageing particles. The relative combustion reactivity of the residual chars was measured in an atmospheric pressure TGA test. The reactivities were all low, but differences were apparent between the different samples and were consistent with the observed gasification behaviour. The use of maceral analysis to predict the behaviour of the whole coals has been examined. Extrapolation from maceral behaviour was found to give reasonable estimates of the behaviour under pyrolysis conditions, but predictions of gasification behaviour were not reliable.