Investigation of NOx emission under different burner structures with the optimized combustion model

Abstract

As restrictions on NOx (nitrogen oxides) emission become increasingly stringent, many efforts have been put into the development of NOx control strategies. The burner structures of the heating furnace can affect NOx formation by the means of changing the flame temperature. To simulate the turbulent combustion process, the Steady Diffusion Flamelet (SDF) model is used and coupled with detailed mechanisms. It is found that some key flamelet parameters of the SDF model will greatly affect the accuracy of the simulation results. In this study, an efficient optimization procedure is proposed to optimize the combustion model parameters with the surrogate assisted evolutionary algorithm K-RVEA. The surrogate model is used to reduce the computational time of the optimization procedure. Using the optimized model parameters, the temperature field and the concentration fields obtained by the simulations are in good agreement with the measurements. Based on this, the investigation of the impact of the length of pilot wall and jet wall on NOx emission is carried out. The results show that the outlet NOx concentration reaches a local minimal value when the length of pilot wall and jet wall are equal. The length of monotonic increasing interval, where the outlet NOx concentration increases when increasing the length of the pilot wall, is 30 mm. If the length of pilot wall is relatively 30 mm longer than that of the jet wall, the outlet NOx concentration will be further reduced. The proposed optimization procedure and obtained results will benefit the improvement of the burner structure of the heating furnace.