Operational optimization of air staging and flue gas recirculation for NOx reduction in biomass circulating fluidized bed combustion

Cost effective nitrogen oxide (NOx) reduction technology is crucial for industries and power plants owing to the stringent environmental regulations to which industries and power plants must adhere. Herein, the aim was to optimize the operational conditions for NOx reduction in forest biomass using circulating fluidized bed combustion (CFBC) combined with air staging and flue gas recirculation (FGR). The profiles of temperature and solid suspension density in the combustor, NO and CO emissions, fuel-N conversion, slagging and fouling tendencies, and combustion efficiency were comprehensively observed during combustion. The main operating parameters are the FGR ratios, optimal ratios of air staging [Primary air (PA):Secondary air (SA):Tertiary air (TA)] and FGR, and supply height of TA in the combustor. Notably, under the optimal operational conditions (air staging ratio; PA:SA:TA = 70:10:30, FGR ratio; 8%, and TA supply height; 8.1 m), the NO and CO emissions were simultaneously reduced to 25.9% and 18.2%, respectively, compared with that for the base scenario which excluded air staging and FGR. Furthermore, a high combustion efficiency of 99.72% was maintained without any ash-related problems at well-controlled bed temperatures owing to the constant solid circulation afforded by FGR. A thorough analysis of the this literature has been performed to ensure that the commercialization of the combination of air staging and FGR in biomass CFBC plants is feasible, which could be an inexpensive option for NO reduction. [Display omitted] •Investigated the effects of air staging and flue gas recirculation (FGR) on NO reduction.•Air staging and FGR were optimized for circulating fluidized bed combustion.•Simultaneous reduction of 25.9% NO and 18.2% CO was achieved by air staging and FGR.•FGR can solve combustor temperature instability caused by air staging combustion.•A high combustion efficiency of 99.72% was reached without ashes-related issues.