Research On Performance Optimization Of Flue Gas Recirculation Natural Gas Premixed Burner

With the increasingly stringent NO_x emission standards for domestic gas boilers and the development and application of a variety of low-nitrogen combustion technologies in combination,more and more gas-fired boilers used natural gas premixed burners coupled with flue gas recirculation.However,there are some key issues in the application of the flue gas recirculation natural gas premixed burners such as the mixing non-uniformity of the fuel and air,the mixing non-uniformity of the flue gas and the premixed gas,and the instability of the flame.Based on the prototype natural gas premixed burner,this paper studied its mixing uniformity of the fuel and air and optimizes its mixing non-uniformity of the fuel and air from the point of view of structural optimization.Drawing on the structural design characteristics of low-nitrogen burners both at home and abroad,this paper designed the internal circulation structure of the flue gas on the basis of the prototype burner.And the structural design optimization of the mixing non-uniformity of the flue gas and the premixed gas,flame instability was carried out.Finally,a comparative analysis of prototype burner and optimized burner was conducted.According to the three key issues to be solved in this paper,the geometric model of the prototype burner was simplified and the fluid domain was structured.In order to obtain accurate numerical simulation results,the required mathematical models were analyzed and selected.The numerical simulation method chosen in this paper was compared with the numerical simulation method of similar research done by previous researchers to ensure that the numerical simulation method in this paper is feasible.Grid-independence verification was performed using the established complete structural grid and the selected numerical simulation method.In order to solve the problem of fuel-air mixing non-uniformity,this paper studied the mixing characteristics of prototype burners under different loads.From the three aspects of the length of the premixed section,the diameter of the fuel injection hole and the angular distance,the mixing characteristics of the fuel and air were optimized.The results showed that the spatial mixing deficiency(SMD)gradually decreases as the length of the premixed section increases,and the decreasing rate becomes slower and slower.The SMD declines firstly and then rises with the enlargement of the diameter of the fuel injection hole,and there is an optimum value.In the same way,the SMD declines firstly and then rises with the enlargement of the angular distance of the fuel injection hole,and there is an optimum value.In order to solve the problem of flue gas and premixed gas mixing non-uniformity and flame instability,the shape and the self circulation rate of the internal circulation structure of the flue gas,the installation angle and the eccentricity of the swirler,as well as the diameter of the center hole of the flame holder were optimized respectively.The results of the study indicated that the SMD of circular inner circulation holes is relatively lowest.The SMD increases with the increase of the self-circulation rate.With the increase of the installation angle of the swirler,the SMD increases firstly and then decreases,and the center backflow has a small increase.With the increase of the eccentricity of the swirler,the SMD decreases little and the center backflow slightly increases.With the enlargement of the diameter of the center hole,the SMD declines firstly,then rises and then declines,and the center backflow has less attenuation.In this paper,the optimized burner was analyzed from three aspects: mixing characteristics,combustion characteristics and emission characteristics.The analysis results showed that the SMD is lower,the flame structure is more reasonable,the combustion efficiency is closer to 100%,and the NO_x emissions are significantly lower in the optimized burner compared to the prototype burner.