Experimental study on NOx reduction performance by ammonia solution injection into the fuel-rich zone in a 75 t/h coal-fired industrial boiler

Industrial-scale trials of NOx reduction by ammonia solution injection into the fuel-rich zone were conducted in a 75 t/h corner-tangentially coal-fired boiler, and impacts of SOFA ratio, secondary air distribution modes, and ammonia solution injector configurations on the NOx reduction performance were discussed in detail. Results indicated that the waist air distribution mode and the increase in SOFA ratio could reduce the oxygen concentration in the reduction zone, which was conducive to the NOx reduction performance of injected ammonia solution. Ammonia solution injector configurations also had a remarkable influence on NOx reduction performance. Ammonia solution injected from injectors in the top layer and at four corners yielded lower NOx emissions than that in the bottom layer and on four walls, respectively. Meanwhile, more ammonia solution injectors in service were favorable for the reducing agent mixing with flue gas, thereby enhancing the NOx reduction performance. The lowest NOx emissions of 48 mg/m3 and a corresponding maximum NOx reduction efficiency of 86.09 % were achieved under the optimized conditions, i.e., 30 % SOFA ratio, the waist air distribution mode, and all 16 ammonia solution injectors in service. However, the boiler efficiency test indicated that the retrofit led to a reduction of 0.28 % in the boiler thermal efficiency simultaneously, necessitating further studies to mitigate the adverse effects.