Numerical Simulation And Optimization Of Combustion And NO_x Emission Characteristics Of Top Fired Burner

Hydrogen manufacturing reformer is the core equipment of steam conversion reaction to produce raw gas for ammonia and hydrogen in petrochemical field.Under the current requirements for energy conservation and emission reduction,new requirements have been put forward for the combustion efficiency and NO_x emission of the hydrogen manufacturing reformer.As the core component of reformer,the burner performance and NO_x emission have important influence on the combustion and pollutant generation of the whole reformer.At present,most large-scale reformer use top fired burner.Therefore,the top fired burner was studied in this paper,and the combustion and NO_x generation of the burner was investigated and optimized through numerical simulations.Three-dimensional structured grid modeling of top fired combustion unit was performed,and the grid independence was verified by using different mesh densities.Numerical simulation on the burner was carried by selecting appropriate calculation models.Through detailed analysis of its velocity field,temperature field,composition distribution,flame shape,radiative heat transfer and NO_x production,it is believed that the generation of NO_x is mainly affected by high temperature zone and the degree of mixing of fuel and air,Optimization study on reducing NO_x generation of burner should focus on controlling the size of the high temperature zone and optimizing the mixing of fuel and air.Based on the above research ideas,influence of the changes of excess air ratio,air preheating temperature,diameter of air inlet and fuel injection angle on the combustion and NO_x generation were explored.The research shows that the changes of the above four parameters have a great influence on the velocity field,temperature field,flame shape,radiative heat transfer and NO_x generation in the furnace,and show a certain regularity.The increase of excess air coefficient increases the average velocity of furnace,the inhomogeneity of temperature distribution,the concentration of high temperature area and the thick flame,which leads to the decrease of radiation capacity and the production of NO_x increases first and then decreases.Comprehensive analysis shows that the excess air coefficient of 1.01 is the best.With the increase of preheating air coefficient,the combustion rate and temperature level are increased,and the formation of NO_x increases monotonously in the flame shape and radiation capacity.From the point of view of economy and NO_x formation,it is considered that 400K is the best preheating temperature.With the increase of air inlet diameter,the inlet gas velocity of air decreases and the mixture of fuel and air become worse.Although the combustion temperature is higher and the amount of radiation is also increased,the production of NO_x increases more quickly,so 230mm is the best choice.With the angle of inclination increasing,the shear action increases gradually.so that the combustion is advanced,the flame front surface is closed to the center,the temperature is also higher,the flame length becomes shorter,and the amount of NO_x production increases,so that the inclination angle of 7 is the optimum value.On the basis of the above research,it is found that adding diluent to the combustion system is one of the effective ways to reduce NO_x,and there is no need for any modification of the burner.In this paper,EI_NOx?Emission index of NO_x?at the exit of the furnace is studied by adding diluents Ar,CO₂,N₂,and H₂O to the fuel side.The results show that the above four diluents can reduce NO_x production,and the order of NO_x inhibition ability is:N₂>H₂O>CO₂>Ar at the same dilution rate.,The thermal efficiency decreases with the increase of the addition of Ar,but when addition of CO₂,H₂O and N₂,the thermal efficiency increases with the dilution rate first and then decreases.The dilution ratio of CO₂ and H₂O as diluent was found to be the best in the range of 0⁰.1 by comprehensive analysis of NO_x production and thermal efficiency.