Simplified Study On The Combustion Characteristics And Mechanism Of Methane Under CO₂/H₂O

In recent years,the strategic adjustment of China's energy structure has gradually realized a clean and low-carbon primary energy structure.Under this background,the proportion of clean energy such as natural gas will gradually increase.With the successful test of exploiting combustible ice at sea in 2017,this has further promoted the use of natural gas.The main component of natural gas is methane.Compared with coal and other energy sources,it has the characteristics of cleanness and high combustion efficiency,but there is still the problem that pollutants such as CO and NOx exceed the standard.Based on flue gas recirculation technology,it is an effective way to reduce pollutant emissions by adding diluent.The addition of diluent has changed the combustion characteristics and the generation path of pollutants,and the Combustion characteristics has changed.Many related problems have not been solved in this process.Firstly,PREMIX model is used to simulate the influence of various factors in flue gas circulation technology on flame speed under the framework of GRImech3.0 mechanism.In order to judge the chemical effects brought by CO₂ and H₂O,the virtual substances such as FH₂O and FCO₂ that do not participate in chemical reactions are additionally defined in the mechanism.The main work contents are as follows:when the equivalent ratio is 1 and the CO₂dilution is 10%,the flame speed will decreased about 3/5.Among them,the influence level of each effect of CO₂ on flame speed is:thermal effect>dilution effect>chemical effect,accounting for 38.1%,37.4%and 24.5%.Under the same conditions,when the dilution of H₂O is 10%,the flame speed has decreased about 1/4.Among them,the influence degree of H₂O effects on flame speed is:dilution effect>thermal effect>chemical effect,accounting for70.8%,22.7%and 0.7%.The inhibition effect of the same amount of CO₂ on flame speed is higher than that of H₂O,both of which mainly play a role through thermal effect and dilution effect,and the chemical effect of CO₂ is higher than H₂O,which cannot be ignored.Secondly,the concentration distribution of pollutants in CO₂ diluted environment is environment simulated,and the generation path is analyzed and compared with the conventional air.The results show that when the equivalent ratio is 1 and the CO₂ dilution was10%,the NO concentration decreases from 236ppm to 51ppm after reaction equilibrium,but the CO concentration increases from 3.92%to 4.59%.And in the environment of CO₂ dilution,the generation of CO mainly through the path:CH₄?CH₃?CH₂O?HCO?CO.It consistent with the main reaction path in air environment.However,the intermediate products and contribution rate has changed,the obvious reaction is CH₂?S?+CO₂=>CO+CH₂O,it promote the formation of CH₂?S?and make CH₄?CH₃?CH₂?S??CH₂O?HCO?CO?CO₂become another main path.Fuel concentration will change the NO generation path.Under rich combustion conditions,the main path of NO generation is N₂?HCN?NH₂?NH?HNO?NO.However,under lean combustion conditions,the generation of NO is mainly formed by direct oxidation of N+NO<=>N₂+O.Finally,GRImech3.0 is simplified by DRG,SA and PCA,and verified in PREMIX model.The complex mechanism of 53 substances,325 reactions is simplified to 17 substances and 43reactions within the acceptable error range,which provides basic data for the actual combustion reaction flow simulation in the future.