Formation of NOx and SOx precursors during the pyrolysis of coal and biomass. Part IV. Pyrolysis of a set of Australian and Chinese coals

The formation of HCN and NH3 from the pyrolysis of a small set of Chinese a nd Australian coals were studied using a novel fluidised-bed/ fixed-bed rea ctor and a fluidised-bed/tubular reactor. The fluidised-bed/fixed-bed react or has some features of a fluidised-bed reactor and of a fixed-bed reactor, allowing the evaluation of the effects of coal properties on the formation of HCN and NH3 to be carried out on a similar basis for a wide range of co als. The thermal cracking of volatiles was investigated in a tubular reacto r in tandem with the fluidised-bed/fixedbed reactor where the nascent volat iles were generated in situ from the pyrolysis of coal. Our experimental re sults indicate that, in addition to coal rank, the petrographic composition and/or geographic origin of the coal are important factors influencing the formation of HCN and NH3 during pyrolysis. Among the few Chinese and Austr alian coals studied, the inertinite-rich Chinese coals tend to give more NH 3 during pyrolysis than the Australian coals of similar carbon contents. It is believed that the structure of inertinites of less caking properties fa vours the formation of H radicals in the pyrolysing solid over a 'correct' temperature range to overlap with the activation and subsequent hydrogenati on of the N-containing ring systems for the formation of NH3 in the solid. If the coal properties favour the release of coal-N as volatiles, the forma tion of HCN in the gas phase is more likely. Under the current experimental conditions, where volatiles may be deposited on the reactor wall, the form ation and destruction of the sooty materials on the reactor wall play an im portant role in the formation of HCN from the cracking of volatiles. (C) 20 01 Elsevier Science Ltd. All rights reserved.