Combustion characteristics and NOx release of sludge combustion with coal in a 660 MW boiler

Abstract

This article analyses the effects of sludge moisture content and blending ratio on combustion characteristics, furnace temperature distribution and NOx release during co-firing with coal in a 660 MW tangentially fired boiler using CFD. When the sludge water content increases from 10 % to 30 %, the water in the fuel is rapidly released during the initial combustion process and absorbs the reaction heat, resulting in a 2.8 % decrease in the temperature of the main combustion zone and a gradual decrease in the heat flux density, while the presence of water leads to the intensification of the incomplete combustion, resulting in the increase of the NOx conversion rate. With the increase of sludge blending ratio from 5 % to 25 % and the increase of water, the combustion temperature in the main combustion zone decreased by 4.0 %, and the heat flow density decreased significantly in the whole furnace and MBR area, by 6.43 % and 12.78 %, respectively. However, the nitrogen content present in the sludge is much higher than that of coal, and the fuel-based NOx produced by the combustion process increased dramatically, which led to the boiler exit NOx increasing by 35.4 %. Reasonable selection of sludge blending ratio and water content is a key issue to be considered for boiler co-combustion.