Formation of NO_x 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.