Formation of NOx precursors during the pyrolysis of coal and biomass. Part IX. Effects of coal ash and externally loaded-Na on fuel-N conversion during the reforming of coal and biomass in steam

Ash interacts strongly with char and volatiles in a gasifier, especially in a fluidised-bed gasifier. This study aims to investigate the effects of ash or ash-forming species on the conversion of fuel-N during gasification. A Victorian (Loy Yang) brown coal and a sugar cane trash were gasified in two novel fluidised-bed/fixed-bed reactors where the interactions of ash with char and/or volatiles could be selectively investigated. Our results show that the interaction of ash with char and/or volatiles could lead to increases in the yield of NH3 and decreases in the yield of HCN although the increases were not always matched exactly by the decreases. Loading NaCl or Na2CO3 into the brown coal was also found to affect the formation of HCN and NH3 during gasification. In addition to the possible catalytic hydrolysis of HCN into NH3 particularly at high temperatures, two other causes were identified for the changes in the HCN and NH3 yields. It is believed that some ash species could migrate into the char matrix to affect the local availability of H radicals or to catalyse the formation of NH3 selectively. The interactions of ash (or Na loaded into the coal) with volatiles could enhance the formation of soot-N, which would be gasified favourably to form NH3.