Formation of NO x and SO x precursors during the pyrolysis of coal and biomass. Part IV. Pyrolysis of a set of Australian and Chinese coals

Abstract

The formation of HCN and NH 3 from the pyrolysis of a small set of Chinese and Australian coals were studied using a novel fluidised-bed/fixed-bed reactor and a fluidised-bed/tubular reactor. The fluidised-bed/fixed-bed reactor 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 NH 3 to be carried out on a similar basis for a wide range of coals. The thermal cracking of volatiles was investigated in a tubular reactor in tandem with the fluidised-bed/fixed-bed reactor where the nascent volatiles were generated in situ from the pyrolysis of coal. Our experimental results 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 NH 3 during pyrolysis. Among the few Chinese and Australian 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 favours the formation of H radicals in the pyrolysing solid over a ‘correct’ temperature range to overlap with the activation and subsequent hydrogenation of the N-containing ring systems for the formation of NH 3 in the solid. If the coal properties favour the release of coal-N as volatiles, the formation of HCN in the gas phase is more likely. Under the current experimental conditions, where volatiles may be deposited on the reactor wall, the formation and destruction of the sooty materials on the reactor wall play an important role in the formation of HCN from the cracking of volatiles.