Numerical study on flame structure and NOx generation under different Coal/NH3 co-firing strategies in a 1000 MW utility boiler

Coal/ammonia (NH3) co-firing in power plants is acknowledged as a promising technology for mitigating carbon emissions at source. However, due to the high nitrogen content in NH3, there is a risk of NOx emissions. This study conducts a numerical simulation on coal/NH3 co-combustion in a 1000 MW ultra-supercritical boiler, exploring the impacts of injection strategies on combustion and NO generation characteristics. The strategies investigated include: (1) uniformly injecting NH3 through all burners, (2) non-uniform NH3 injection through selected burners, and (3) NH3 injection via NH3 nozzles. Results reveal that, when NH3 is uniformly injected through all burners, a high co-firing ratio (40 % by calorific value) is needed to establish an elongated flame structure at the burner outlet. Under this condition, NO concentrations at the furnace outlet are reduced to 142.3 ppm, respectively, which are lower than that in pure coal combustion. Non-uniform NH3 injection through selected burners leads to the formation of elongated flame at lower NH3 co-firing ratios, thus diminishing NO production. When introduced through nozzles at the lower section of the primary combustion zone, NH3 tends to move downward to the ash hopper, where intense pyrolysis occurs, limiting the conversion of NH3 to NO and reducing NO emissions.