Influence of external flue gas recirculation on gas combustion in a coke oven heating system

•External flue gas recirculation (EFGR) is applied to a coke oven heating system.•A 3-D pseudo steady-state numerical model for the coke oven heating system was used.•The influence of the EFGR on the temperature uniformity and NOx generation was analysed.

In this study, external flue gas recirculation was considered to reduce nitrogen oxides (NOx) emissions in the heating flues of a coke oven battery. The thermal and prompt NO formation was numerically investigated employing an accurate 3-D representation of the heating flue geometry that the most popular Polish coke oven battery. Originally the developed model was experimentally validated as a transient coupled model for the representative heating flue and the two coke ovens. Then the coupled model was simplified to the heating flue model only with realistic boundary conditions on the heating flue and coke oven interface. As a result of the heating flue model simulations, the range of the reversed flue gas ratio was found for typical thermal loadings of the heating wall to effectively reduce NOx formation. The obtained results showed the significant effect of the considered flue gas recirculation on NOx formation reduction. Namely, the recirculation ratio of 0.2 resulted in 50% of the NOx reduction efficiency.