Experimental study of an air-staged and low NO_x emission-based combustion modification to a 200 MW boiler

To reconstruct the combustion system of a 200 MW bitumite-fired boiler in a power plant in Beijing region for reducing NO_x emissions, a cubic-staged low-NO_x emission combustion system combining overfired air (OFA) with low-NO_x emission burners of horizontal bias-combustion was used. After the modification, the NO_x emissions concentration has been improved conspicuously. The above-mentioned concentration can be reduced by 45% to 60% when an equalization air distribution mode was adopted. The use of a proper horizontal swinging angle for the OFA nozzle will effectively lessen the flue gas temperature deviation at the furnace outlet, which can be controlled within a range of 50°C. In addition to a marked lowering of NO_x emissions, the boiler efficiency can be enhanced by about 1%. After the modification, the NO_x emissions concentration at any operating condition is all below 400 mg/m³ and in the meantime, this can provide more favorable inlet conditions for tail portion flue-gas SCR (Selective Catalyst Reduction) device.