On the Combination of fuel-rich/lean burner with MILD combustion for further NOx emission reduction

Abstract

Moderate or Intensive Low-Oxygen Dilution (MILD) combustion as a newly developed technology has drawn much attention all over the world since it features the homogeneous combustion and extremely low NOx emission. Even though reduced NOx emission is reported in pulverized coal MILD combustion, its performance is not as comparable as that of gaseous and liquid fuels. In order to investigate the possibility of further reducing NOx emission in a MILD coal combustion furnace, horizontal fuel-rich/lean burner as another promising technology aiming to regulate NOx emission is employed in this study. Results have shown that fuel-rich/lean burner is able to further reduce NOx emission by about 4% when applied to a MILD coal combustion furnace. This is due to the combined effect of the reduction of thermal- and fuel-NO formation. Particles entrained in the fuel-rich stream is heated in a reducing atmosphere, so that the oxidation of hydrogen cyanide (HCN) and ammonia (NH3) released by volatile is hindered. Moreover, the NO released by char is reduced to molecular nitrogen. Thermal-NO is reduced because of the low local peak temperature in both streams.