抄録
A novel combustion system with introducting overfire air and injecting vent air into the furnace below the arches was applied to a 600 MW down-fired pulverized-coal utility boiler specifically for severe unstable combustion and particularly high NOx emissions. The aim of the present work is to evaluate the performance (including combustion and NOx emission characteristics) of the furnace with the new technology with respect to different vent air (VA) angles (i.e., 10°,20°,30°,40°, respectively) and then to obtain an optimal setup to recommend as a retrofit for the furnace. A computational fluid dynamics (CFD) program, known as Fluent 6.3.26, was used to conduct the numerical simulations here. The numerical results were greatly agreed with the tested results. These results demonstrate that as increasing the vent air declined angle, O_2 concentration and gas average temperature at the furnace outlet, as well as the carbon content in fly ash and NOx emission, gradually decreases, while gas average temperature in the ash hopper region increases. In considering the relatively low carbon content in fly ash, low NOx emission and the safety of ash hopper walls, a set of vent air angle at 30° was recommended. Retrofitting was conducted to incline the VA angle with an inclined angle of 30°. The experimental test results showed that the carbon content in fly ash is 4.56% and 4.54%, NOx emission is 751mg/m^3 and 648 mg/m^3, at 600MW and 450MW loads, respectively.
