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

Abstract

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 NO_x 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.