Numerical Simulation Study On Low Nitrogen Combustion Of Natural Gas Dispersion Vortex Burner

Fossil fuels are still an indispensable natural resource for human beings.Compared with coal and fuel oil,natural gas combustion can greatly reduce the emissions of sulfur dioxide,dust and carbon dioxide,and help reduce the formation of acid rain and slow down the global greenhouse effect.To fundamentally improve environmental quality.Therefore,natural gas has been widely used in industry as a clean alternative fuel in recent years.The main problem in the process of natural gas combustion is the emission of nitrogen oxides,and the emission standards of air pollutants in my country are becoming increasingly stringent.So designing and developing a new type of natural gas low nitrogen burner is of great significance to the project.Based on the above research needs,combined with low-oxygen dispersion combustion technology and flue gas recirculation technology,a new type of natural gas low-nitrogen vortex burner is designed.In the study,the composition of natural gas was first selected,and the low calorific value and flue gas composition were calculated.Then the theoretical calculation of the burner was carried out,and the adiabatic combustion temperature was calculated to be 2073°C.In the design work,to ensure that the burner is maintained at 1300°C,the flue gas recirculation method is adopted.In order to accurately calculate the circulating flue gas volume,the basic parameters of the burner,namely the oxygen partial pressure in the mixed gas and the flue gas preheat temperature,were determined by numerical simulation.The simulation results show that the combustion temperature and the amount of nitrogen oxides decrease as the oxygen partial pressure in the combustion chamber decreases,but after the oxygen partial pressure drops to 13%,the change is not obvious,and the carbon monoxide mass fraction increases.When the flue gas preheating temperature gradually increases,the temperature distribution tends to be uniform,and the amount of nitrogen oxides generated gradually decreases,but when the flue gas preheats to above 300°C,the combustion temperature will be higher than 1400°C,and nitrogen oxides will be generated.The amount increases.Therefore,the oxygen partial pressure of the mixed gas is designed to be 13%,and the preheating temperature of the mixed gas is designed to be 300°C.Based on the calculation results of basic parameters,the diameters and length-diameter ratios of the combustion chambers at various levels were selected,and the inlet sizes of various gases were calculated according to the air volume and wind speed.The structure of the burner is optimized through numerical simulation.The optimized structural parameters include the angle of change between the combustion chambers at all levels and the inlet position of the tangential low oxygen partial pressure mixed gas.The numerical simulation calculation results show that with the reduction of the interstage variable-diameter angle of each stage of the combustion chamber,the local loss in the combustion chamber decreases,the swirl mixing becomes stronger,and the combustion temperature decreases.When the change angle between the combustion chamber stages is 30°,the central recirculation zone of the combustion chamber is obvious,and the recirculation speed is the largest.At the same time,the local high temperature area in the combustion chamber is the smallest,and the production of nitrogen oxides and carbon monoxide is the smallest.When the inlet position of the tangential mixed gas gradually moves backward,the return flow rate of the burner center decreases,the combustion temperature increases,the local high temperature area increases,the production of nitrogen oxides and carbon monoxide increases,the combustion reaction area moves backward,and the combustion stability decreases.Therefore,the angle of the variable diameter between the combustion chambers of all levels is designed to be 30°,and the design of the tangential mixed gas inlet is the most reasonable at the head of each combustion chamber.Then the numerical simulation of the burner's operating parameters was carried out.Including the determination of the excess air coefficient during the operation of the burner,the determination of the ratio of premixed fuel to non-premixed fuel,and the effect of recirculated flue gas components on the combustion characteristics.The numerical simulation calculation results show that the increase in excess air coefficient has little effect on the overall temperature of the burner,but the local high temperature area increases.When the excess air coefficient is 1.1,the amount of nitrogen oxides generated is the smallest.When the ratio of premixed fuel to non-premixed fuel is changed,the combustion characteristics in the burner are greatly changed.When the proportion of nonpremixed fuel increases,the combustion reaction area moves forward,the combustion temperature decreases,and the local high temperature area decreases first and then increases.When the ratio of non-premixed fuel to premixed fuel is 8 to 1,the mass of nitrogen oxides and carbon monoxide.The production volume is the lowest.When the CO₂ content in the circulating flue gas increases,the peak pressure in the burner decreases,the combustion reaction rate decreases,the combustion temperature decreases,the flame thickness increases,and the flame core temperature decreases.The addition of CO₂ in the recycled flue gas has a more obvious inhibitory effect on the formation of nitrogen oxides,but it will move the combustion reaction area backward and the combustion is incomplete,resulting in an increase in the content of carbon monoxide.