Impact of the Overfire Air Location on Combustion Improvement and NOx Abatement of a Down-Fired 350 MWe Utility Boiler with Multiple Injection and Multiple Staging

Abstract

A new technology based on multiple injection and multiple staging has been developed specifically for severe asymmetric combustion and particularly high NOx emissions within a down-fired 350 MWe utility boiler. The aim of the present work is to evaluate the performance of the furnace with the new technology with respect to different overfire air (OFA) locations and then to obtain an optimal setup to recommend as a retrofit for the furnace in the future. Numerical simulations of combustion characteristics and NOx emissions were conducted within the furnace at three different OFA location settings, i.e., OFA on arches but close to the furnace center, OFA on the furnace throat, and OFA on the upper furnace. Good agreement was found between simulations and in situ measurements with the original technology. Asymmetric combustion removals and significant NOx reductions were validated for all three OFA location settings. NOx emissions, carbon in fly ash, and gas temperatures at the furnace exit varied largely over different OFA settings. Both carbon in fly ash and gas temperatures in the furnace outlet for OFA on the furnace throat and OFA on the upper furnace are higher than for OFA on arches. The setting with OFA on the upper furnace achieved the highest NOx emissions, whereas that with OFA on arches enabled the lowest. To establish efficient furnace-operating conditions with the new technology, OFA on arches but close to the furnace center was recommended as the optimal OFA location according to simulation results.