Investigation on Fuel-N Transformation Properties of Coal/Biomass Heating Process in CO2 Atmosphere

To understand the effect of a CO 2 atmosphere on the properties of the transformation from fuel-N to NO x precursors (mainly NH 3 and HCN), pyrolysis experiment on Pingliang coal (PL coal), wheat straw and their corresponding blends was carried out in a fluidized bed reactor within a temperature range of 750°C to 850°C. The results indicated that the PL coal and wheat straw show different NO x precursor formation properties owing to the discrepancy between the N-containing structures in the raw materials. Compared with an argon atmosphere, CO 2 can effectively suppress the formation of NH 3 . For HCN, the HCN yield of PL coal is suppressed and the HCN yield of wheat straw is promoted. Furthermore, CO 2 can suppress the overall nitrogen conversion rate of NH 3 +HCN for both coal and biomass, which causes more fuel-N to convert into tar-N and N 2 -N. For the blends of PL coal and wheat straw, the copyrolysis synergistic effect of coal/biomass influences the selectivity of HCN and NH 3 . The copyrolysis synergistic effect favors the formation of copyrolyzed HCN but has an opposite impact on the transformation from fuel-N to NH 3 . The synergistic effect of coal/biomass promotes the overall nitrogen conversion rate of NH 3 +HCN under a CO 2 atmosphere, and the overall nitrogen conversion rate of NH 3 +HCN is suppressed under an argon atmosphere, conversely. In addition, the synergistic effect of coal/biomass suppresses the yield of environmentally harmless N 2 , and more fuel-N was retained in the char.