Effect of H2O on the NO emission characteristics of pulverized coal during oxy-fuel combustion

The NO emission characteristics of Datong bituminous coal and Yangquan anthracite in O-2/H2O/CO2 atmospheres were investigated by using a fixed-bed reactor system, and the emission characteristics were compared with the experimental results from O-2/N-2 and O-2/CO2 atmospheres, especially at low O-2 concentrations and high temperatures. The results showed that NO emissions of pulverized coal in O-2/CO2 environments were less than those in the O-2/N-2 environments, regardless of the O-2 concentration and the furnace temperature. Adding H2O decreased the possibility of reactions between the reductive groups (NH) and the oxygen radical during devolatilization, which led to a decrease in NO emissions at 1000 degrees C. However, as the furnace temperature increased, "additional" nitrogen precursors (HCN and NH3) generated by enhanced char-H2O gasification were quickly oxidized to generate a large amount of NO during char oxidation that exceeded the amount of NO reduced by NH during devolatilization. Thus, the NO emissions in O-2/CO2/H2O atmosphere were higher than those in O-2/CO2 atmosphere at a low O-2 concentration. However, as the O-2 concentration increased, the NO emissions in O-2/CO2/H2O atmosphere became lower than those in O-2/CO2 atmosphere because the effect of H2O gasification became weaker. The NO emissions of Yangquan anthracite (YQ) were higher than those of DT, but the changing trend of YQ was similar to that of DT.