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

To understand the effect of a CO2 atmosphere on the properties of the transformation from fuel-N to NOx precursors (mainly NH3 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 NOx precursor formation properties owing to the discrepancy between the N-containing structures in the raw materials. Compared with an argon atmosphere, CO2 can effectively suppress the formation of NH3. For HCN, the HCN yield of PL coal is suppressed and the HCN yield of wheat straw is promoted. Furthermore, CO2 can suppress the overall nitrogen conversion rate of NH3+HCN for both coal and biomass, which causes more fuel-N to convert into tar-N and N2-N. For the blends of PL coal and wheat straw, the copyrolysis synergistic effect of coal/biomass influences the selectivity of HCN and NH3. The copyrolysis synergistic effect favors the formation of copyrolyzed HCN but has an opposite impact on the transformation from fuel-N to NH3. The synergistic effect of coal/biomass promotes the overall nitrogen conversion rate of NH3+HCN under a CO2 atmosphere, and the overall nitrogen conversion rate of NH3+HCN is suppressed under an argon atmosphere, conversely. In addition, the synergistic effect of coal/biomass suppresses the yield of environmentally harmless N2, and more fuel-N was retained in the char.