Strengthening low‐NOx combustion with flue gas recirculation in a 600‐MWe down‐fired furnace

Abstract

AbstractFor a down‐fired furnace using a cascade‐arch‐firing low‐NOx and high‐burnout configuration (CLHC, which includes flue gas recirculation and is taken as a strengthened low‐NOx combustion solution), the gas/particle flow, coal combustion, and NOx emissions were investigated at various flue gas recirculation (FGR) ratios of 5%, 10%, 15%, and 20% (labeled as settings of FGR = 5%, 10%, 15%, and 20%, respectively). The aim was to disclose the FGR role on the strengthened low‐NOx combustion characteristics and meanwhile obtain an available FGR ratio. With increasing FGR, although the downward flame penetration increased continuously, the large local high‐temperature zone favoring combustion in the furnace shrunk. Increasing FGR lowered gas temperatures and strengthened the reductive atmosphere in the downstream of the reburning zone to restrain combustion and meanwhile weaken the NO‐reduction effect of reburning. Trends of the final performance indexes with the FGR ratio showed that NOx production increased continuously, while burnout loss generally undergone an increase‐to‐decrease trend. In view of the above findings and the gained optimal furnace performance (i.e., NOx emissions of 530 mg/m3 at 6% O2 accompanied by carbon content in fly ash at 5.28%), low FGR levels such as FGR = 5% with a hot‐air dilution in FGR should be preferred for the CLHC furnace where FGR is used to deliver the fine pulverized‐coal particles for reburning. In comparison to an advanced in‐service low‐NOx art, the CLHC reduced further NOx production by 41.4% while remained a high burnout achievement except a limited increase in CO emission.