Numerical Simulation Study on Low-NOx Combustion of Pulverized Coal Swirl Burner with Flue Gas Recirculation

Coal is the ballast stone for ensuring national energy security, with coal-fired power generation playing a dominant role in NO_x emissions. Therefore, research into low-NO_x combustion of coal is of significant importance. This paper focuses on the issue of high NO_x emissions at a 600 MW pulverized coal opposed-fired boiler. A study was conducted on the low-NO_x combustion of a pulverized coal swirl burner used in this boiler, operating under air-staged combustion. The effects of different primary air duct structures, flue gas interlayer (FGI) widths, and flue gas recirculation ratios on combustion characteristics and NO_x emission were investigated using CFD numerical simulation, and the reasons why this structure can reduce NO_x were analyzed. The results indicate that, without introducing recycled flue gas, adding a coal powder concentrator structure to the primary air duct can reduce the nitrogen oxide content from 73.98 mg/m³ to 54.24 mg/m³; Under the same flue gas recirculation rate conditions, compared with directly mixing recirculating flue gas and secondary air, installing FGI structure between the primary and secondary air and introducing recirculating flue gas can reduce the concentration of nitrogen oxides from 60.71 mg/m³ to 41.66 mg/m³. It shows that the FGI structure helps to reduce the oxygen concentration in the main combustion zone, promotes the formation of a reducing atmosphere, and effectively inhibits the emission of NO_x. The results of this study have important engineering practical value and can provide useful guidance for the optimization design of similar whirlpool burners.