Effect of outer secondary air vane angles on combustion characteristics and NOx emissions for centrally fuel rich swirl burner in a 600-MWe wall-fired pulverized-coal utility boiler

To solve the high NOx emissions associated with a 600 MWe utility boiler with enhanced-ignition axial control low NOx (EI-XCL) burners, continuous improvement of the previously proposed centrally fuel-rich (CFR) burner technology lies on three aspects: (1) the 36 EI-XCL burners in the original furnace were retrofitted with CFR burners; (2) the 26 over fire air (OFA) ports in two layers have been added above the burners along the top row of the furnace; (3) the designed OFA ratio was 25%. Industrial-size measurements (i.e., adjusting outer secondary air vane angle of 20-30°) uncovered that, compared with the prior EI-XCL burners, the CFR burner exhibited the same good ignition performance and the O2 concentrations near the side walls were found to be above 6% when the secondary air mass flow rate of the burner decreases about 37% for all three outer secondary air vane angles. The NOx emissions decrease from 316 to 237 mg/m3 (O2 = 6%) when outer secondary air vane angle varies from 20° to 30°. Under the optimal outer secondary air vane angle, NOx emissions were found to decrease by 60.50% at a load of 600 MWe subsequent to retrofitting of the boiler.