Diffusion MILD Combustion of Firing Pulverized-coal at a Pilot Furnace

This paper presents the computational investigation of the diffusion MILD (Moderate or Intense Low-oxygen Dilution) combustion of firing pulverized-coal at a pilot furnace. Dependences of the combustion performance are examined on the injection parameters, e.g., the fuel injection angle and the separation between the primary and secondary nozzles. Calculations are performed to examine the combustion characteristics, e.g., velocity and temperature distributions, CO and NO emissions, and char burnout. The validation of the modeling is carried out using the experimental measurements of Weber et al. (Proc. Combust. Inst. 30, 30 (2), 2623–2629 2005). Results reveal that an increase in the fuel injection angle or the separation reduces the peak temperature in the confluence region of the primary and secondary streams and thus the exhaust NO emission. During the coal MILD combustion, the (destroying) NO reburning mechanism is strongly involved so that the NO emission is below the NO production from the fuel-NO route, given that other routes of NO formation are unimportant. It is also found that the gasification reactions of char with CO2 and H 2O in coal MILD combustion appear to compensate for depression of the low O2 concentration on the coal burnout. In addition, several suggestions are made that could be useful for design of coal MILD burners.