Formation of NOx and SOx precursors during the pyrolysis of coal and biomass. Part I. Effects of reactor configuration on the determined yields of HCN and NH3 during pyrolysis

The formation of HCN and NH₃ during the pyrolysis of a biomass (bagasse) and a set of rank-ordered coal samples has been studied in a novel reactor. The reactor has some features of both a drop-tube reactor and a fixed-bed reactor: the reactor allows the coal/biomass particles to be heated up rapidly as well as to be held for a pre-specified period of time at peak temperature. The experimental results obtained suggest that a considerable amount of the nitrogen in the nascent char could be converted into HCN and NH₃ if the char is held at high temperatures for long time. The formation of NH₃ from the thermal cracking of char was seen to last for more than an hour even at temperatures as high as 700–900°C. The formation of HCN went to completion much more rapidly than that of NH₃. Compared with the results in the literature from the pyrolysis of coals in a fluidised-bed reactor, the reactor configuration used in this study allows the effects of fuel rank to be studied on an unbiased basis towards the type of fuel. The yields of HCN and NH₃ from the present study decrease with increasing rank. The experimental results suggest that the differences in reactor configurations used by various researchers would account at least partially for some of the discrepancies in the literature regarding the formation of HCN and NH₃ during the pyrolysis of coals.