Numerical Simulation And Structural Optimization Design Of Nature Gas And Hydrogen Un-premixed Combustor

This thesis is based on the low nitrogen retrofit project of 18 MW heating furnace for conduction oil in a chemical enterprise in Jiangsu Province.Designing suitable burners for heating furnace to meet the emission standards of pollutants issued by the local Environmental Protection Bureau.Because the mixed gas containing 75% hydrogen during chemical production,a combustor with mixed combustion of natural gas and hydrogen is designed to meet the power requirement and low nitrogen emission combustor,based on structure of low NOx combustor both on china and abroad.Based on this prototype burner,in order to reduce the emission of nitrogen oxides and ensure its combustion efficiency,the structure optimization design of the burner is carried out by ANSYS Fluent.The gas distribution mode and the relevant load conditions are carried out to guide the design and operation of the burner based on numerical simulation analysis.Firstly,the prototype burner is modeled abstractly and unstructured meshes are generated.In order to obtain more accurate calculation results,consult the previous work to select the appropriate mathematical model.Based on this,the irrelevance of the grid is checked.In order to reduce the emission of nitrogen oxides,three structures of prototype burner,matching of internal and external swirl angle,size and lengthening of hydrogen side nozzle,and flow distribution on both sides of the same inlet,were optimized.Previous work has studied the distribution of air through different air intake channels.In this paper,the only air inlet is used to distribute air by using different effective flow areas,which is more realistic.The results show that the internal and external swirls deviate from 45 degrees,and the concentration of nitrogen oxides at the outlet of the prototype burner decreases by 17.46% when the internal and external swirls are 30 degrees and 50 degrees respectively.Based on the above modification,the hydrogen side lengthening tube has no obvious effect on the nitrogen oxides.When the number of hydrogen jet holes is 12,the nitrogen oxides concentration is 26.6% lower than that of the prototype burner.When the effective area is used to distribute the internal and external swirl flow,it is found that the combustion emission effect is the best when the area of internal and external swirl equals the air ratio of internal and external fuel.Based on the optimized structure,the numerical simulation of different excess air coefficients,central air ratio and load emissions was carried out.The results show that when the air excess coefficient is 1.2 and the proportion of central air is 10%,the emission of Nitrogen oxide is low.For each load node,the nitrogen oxide emission from the boiler can meet the local environmental protection requirements.