Effect of co-flow oxygen concentration on the MILD combustion of pulverised coal

This paper reports the impact of surrounding oxygen (O2) concentrations on the burning characteristics of pulverised brown coal under MILD (Moderate or Intense Low-oxygen Dilution) combustion conditions. A combined experimental and computational study is conducted to probe the volatiles’ release and reactions from the micro sized coal particles and its effect on the production of CO, CO2 and NOx in a vertical furnace. Pulverised high volatile Victorian brown coal was introduced into the furnace utilising CO2 as a carrier gas through a central jet with a constant bulk jet Reynolds number Rejet = 20,000, and two co-flow oxygen concentration of 5.9% and 8.9%. For all the cases investigated, stable MILD combustion was achieved, featuring a uniform temperature distribution within the furnace. It was found that the co-flow O2 concentration significantly influences the CO emission. The measured CO emission for the 5.9% co-flow O2 concentration case is approximately eight times higher than that of the 8.9% co-flow O2 concentration case. In addition, the CFD analysis showed that an increase in the local O2 concentration leads to an increase in the volatiles release and reaction rates. Also, up to 63% more NO is produced for the 5.9% co-flow O2 concentration case in comparison with the 8.9% O2 case through the fuel-NO route.