Numerical investigation on the effects of air-staged strategy and ammonia co-firing ratios on NO emission characteristics using the Conjugate heat transfer method

Abstract

Ammonia co-firing is recognized as a promising approach within the realm of achieving carbon neutrality. This method not only effectively mitigates carbon emissions but also augments the stability of ammonia combustion. However, achieving low NO emissions in ammonia combustors remains a formidable challenge. The present study employed numerical simulations to assess the impact of an air-staged strategy and varying ammonia co-firing ratios on NO emissions within a 10-kW industrial ammonia co-firing furnace. To accurately represent the thermal conditions at the furnace walls, a Conjugate Heat Transfer (CHT) model encompassing both solid materials and reacting flow regions was utilized. Initially, the numerical results were compared with experimentally measured NO emissions, validating the accuracy of the customized solver. Subsequently, the effectiveness of the air-staged strategy under the parallel injection system was verified. This approach created a fuel-rich region near the burner primary nozzle, significantly reducing NO production. Under different ammonia co-firing ratios, with ammonia injection levels increasing from 0% to 100%, NO emissions at the furnace outlet displayed an initial increase, followed by a decrease, peaking at a co-firing ratio of 50%. Further analysis of the Rate of Production (ROP) of NO within the furnace revealed that at higher ammonia co-firing ratios, ammonia serves both as a reducing agent and as a fuel for heat release. These findings provide valuable insights for the development and application of ammonia-based industrial furnaces.