Effect of H2O on the NO emission characteristics of pulverized coal during oxy-fuel combustion
2018
Lei, Ming | Sun, Cen | Zou, Chan | Mi, Hang | Wang, Chunbo
The NO emission characteristics of Datong bituminous coal and Yangquan anthracite in O₂/H₂O/CO₂ atmospheres were investigated by using a fixed-bed reactor system, and the emission characteristics were compared with the experimental results from O₂/N₂ and O₂/CO₂ atmospheres, especially at low O₂ concentrations and high temperatures. The results showed that NO emissions of pulverized coal in O₂/CO₂ environments were less than those in the O₂/N₂ environments, regardless of the O₂ 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 °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 O₂/CO₂/H₂O atmosphere were higher than those in O₂/CO₂ atmosphere at a low O₂ concentration. However, as the O₂ concentration increased, the NO emissions in O₂/CO₂/H₂O atmosphere became lower than those in O₂/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.
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