High‐burnout and low‐NOx combustion characteristics in a 600‐MWe W‐shaped flame furnace: Air‐regulating solution selection as varying overfire air and impact of the overfire air ratio

Abstract

AbstractIn order to establish an efficient air‐regulating solution as varying overfire air (OFA) and recommend an appropriate OFA ratio for a 600‐MWe W‐shaped flame furnace equipped with the proposed cascade‐arch‐firing low‐NOx and high‐burnout configuration (CLHC), four air‐regulating solutions were established by respectively adjusting the air into secondary air, tertiary air, and hopper air or proportionally varying the air into the three jets in a uniform distribution form, which were labeled in turn as SA, TA, HA, and UD, respectively. After the efficient air‐regulating solution fixed, four OFA ratios of 15%, 17.5%, 20%, and 22.5% were evaluated. Among the four air‐regulating solutions, only UD develops symmetrical combustion. An order of TA < HA < SA < UD in the final performance indexes enables UD as the efficient air‐regulating solution as varying OFA. A symmetrical flow field and combustion pattern develop at the former three OFA ratios. The excessive OFA ratio of 22.5% achieves a severely deflected flow field and asymmetric combustion. Increasing the OFA ratio generates a decrease‐to‐increase trend in burnout and a continuous decrease trend in NOx emissions. Consequently, the 20% setting is preferred as an appropriate OFA ratio, showing the best low‐NOx and high‐burnout accomplishment. The improvement in both burnout and NOx emissions as opening OFA to deepen air staging is attributed to the improved symmetrical combustion and the strengthened OFA penetration in the upper furnace.