Experimental Study of Volatile-N Conversion at O₂/CO₂ Atmosphere in a Drop Tube Furnace

In coal combustion, NOx is largely formed from the oxidation of volatile nitrogen compounds such as HCN and NH₃. The experiments on the volatile-N conversion to NO at O₂/CO₂ atmosphere were carried out in a drop tube furnace. The effects of the excess oxygen ratio λ (0.6–1.4), temperature (1,000–1,300 °C), O₂/CO₂ ratio, and as well as CH₄/NH₃ mole ratio were investigated. To further understand the importance of NO reburn during volatile combustion, experiments were also performed with different concentrations of background NO (0–950 ppm). The results show that volatile-N conversion to NO is sensitive to excess oxygen ratio λ at strongly oxidizing atmosphere. For volatile combustion, there is an optimal temperature and inlet O₂ concentration to minimize the volatile-N conversion to NO. The CH₄/NH₃ mole ratio plays an important role on the NO formation under oxidizing atmosphere. High levels of background NO prohibit the volatile-N conversion to NO significantly as the volatile-N conversion ratio decreases by 19–36%. The reburn fractions of recycle NO in fuel-rich and fuel-lean condition are 14.8 and 9.8% at 1,200 °C, respectively.