Simulation Study On Combustion Characteristics Of Natural Gas Mixed With Hydrogen In Ceramic Shuttle Kiln

With the upgrading of the economic industry chain,the country’s attention to carbon compliance and carbon neutrality has gradually increased.Energy conservation and emission reduction has been the top priority in China’s industrial field.The CO₂ emission of ceramic industry is nearly 47 million tons per year.Therefore,it is urgent for ceramic kiln enterprises to reduce carbon emissions and increase energy efficiency.Kiln firing is the link with the most pollutant emissions and the largest energy consumption in the entire ceramic production system.Therefore,exploring cleaner and more efficient combustion methods is crucial to reducing carbon emissions.At present,there are few studies on mixed combustion in ceramic kiln industry.Shuttle kiln is the main production kiln type of daily and artistic ceramics,which is characterized by flexible production and adaptation to firing in reducing atmosphere.Therefore,this paper chooses shuttle kiln as the research kiln.Methane,the most important component of natural gas,was used to replace natural gas^[1].The method of air/fuel non-premixed combustion and methane/hydrogen mixed combustion was used.The furnace burner,the existing natural gas shuttle kiln and the optimized structure shuttle kiln were selected as the research objects.The effects of hydrogen on flame temperature,temperature field uniformity,combustion elementary reaction rate and combustion reaction generation elements in furnace combustion were investigated by comparing the mixed combustion of hydrogen and methane in different proportions.Five hydrogen concentrations of 0%,10%,20%,30%and 40%and air excess coefficients of 1.1 and 0.8 were selected.The effect of hydrogen-doped combustion on the whole ceramic kiln industry was studied.The main conclusions of this paper are as follows:（1）The addition of hydrogen does not change the overall flame model in the combustion chamber.Through the analysis of the reaction mechanism of a single burner in the non-premixed diffusion hydrogen-doped combustion state,it is found that a large amount of methane will produce hydrogen during the combustion process,which is related to the large amount of hydrogen free radicals produced by the combustion of methane itself.（2）The mixed combustion of hydrogen can increase the flame temperature and accelerate the flame generation rate.Increasing the temperature in the combustion chamber promotes the formation of thermal NOx.Promote NO production rate and inhibit NO₂production rate.The addition of hydrogen in the combustion chamber can promote the generation efficiency of combustion free radicals O,OH and H,and advance the free radical generation area.Hydrogen can accelerate the reaction units related to methane consumption and accelerate fuel decomposition.Hydrogen can increase the combustion reaction rate and accelerate the progress of fuel oxidation.（3）The optimal hydrogen concentration of the existing natural gas shuttle kiln is 10%,and the temperature promotion effect is the weakest when the hydrogen concentration is30%.By analyzing the products of the actual kiln reduction stage,the simulated kiln is consistent with the actual kiln.Hydrogen can increase the temperature in the combustion chamber and improve the uniformity of the temperature field in the combustion chamber.Reduce the content of carbon compounds in the combustion chamber and increase the content of water and NO.However,the impact on the temperature of the existing natural gas shuttle kiln for hydrogen is limited,mainly because the complete flame model cannot be displayed in the existing natural gas shuttle kiln.（4）Structural optimization The optimal hydrogen blending ratio of shuttle kiln is 40%.Based on the previous two simulation studies,the structure of the shuttle kiln was optimized to fully display the flame model,so as to maximize the role of hydrogen in promoting combustion.The combustion chamber temperature in the optimized shuttle kiln increases with the increase of hydrogen concentration,and the flame temperature increases with the increase of hydrogen concentration.The moisture content in the whole furnace is positively correlated with the hydrogen concentration.Hydrogen can promote the generation of thermal NOx,and hydrogen can reduce the CO concentration in the combustion chamber.Mixed combustion can improve the combustion efficiency of fuel and increase the flame temperature.（5）The influence of hydrogen on flame temperature uniformity is limited when the furnace is in the case of reduction combustion.When the hydrogen concentration is higher than 20%,hydrogen will reduce the flame temperature uniformity.In the case of reducing combustion,hydrogen will still increase the flame temperature,inhibit the production of CO and CO₂,and increase the production of water and NO in the combustion chamber.Changing the existing natural gas ceramic shuttle kiln fuel to hydrogen and natural gas mixed fuel is beneficial to reduce the carbon emission of the kiln and increase the uniformity of the temperature field in the oxidation stage of the ceramic kiln.Hydrogen can improve the firing temperature of the existing natural gas shuttle kiln to a certain extent.By optimizing the structure of the kiln,the effect of hydrogen on temperature promotion can be maximized.The combustion of hydrogen in the ceramic kiln is in line with the current background of energy saving and emission reduction.Mixed combustion can be used to optimize the fuel of the ceramic kiln and promote the greener and more environmentally friendly ceramic kiln industry.