Controlling LOI from coal reburning in a coal-fired boiler

Combustion simulations were conducted to investigate the parameters controlling the formation of unburned carbon in fly ash from coal reburning in a coal-fired boiler. Unburned carbon (UBC or Loss on ignition, LOI) was generally caused by particles flowing through fuel-rich regions and/or spending insufficient residence time in the furnace. LOI contributions by each individual coal source were identified and quantified. The LOI from the main burners was found to depend mainly on the availability of combustion air in the burner zone. However, the LOI from the reburning jets depended on both the amount of air in the reburning jets and the available over-fire air (OFA) downstream. Moving some air from the lower burners to the upper burners to compensate for the shorter residence time was found to significantly reduce the overall LOI without adverse impacts on the NOx emissions in this study.