Influence of demineralization using acid wash on N migration and transformation during pyrolysis of Shengli brown coal

This paper is to examine effects of inherent minerals in coal on N migration and transformation during the fast pyrolysis of Shengli brown coal at the temperatures of 773~1173 K in a bench-scale fluidized-bed quartz reactor. Based on the comparison between raw coal and acid-washed coal, we can find that the alkali Na and alkaline Ca were the key reasons for the difference in N evolutions from raw coal and demineralized coal during the pyrolysis. The Na and Ca could efficiently facilitate the formation of NH₃ and inhibit the production of HCN. The metallic species had obvious catalytic effects for the conversion from tar-N to NH₃. Meantime, the existence of alkali and alkaline metals has enhanced the cracking reactions of coal char, thus reducing the yields of char and char-N. In addition, the relative amount of pyridinic (N-6) in demineralized coal char was higher than that in raw coal, while less quternary type nitrogen (N-Q) and pyrrolic nitrogen (N-5) were found in the demineralized coal char.