Study On The Minimum Ignition Energy And Combustion Mechanism Of Methane In Low Temperature CO₂/O₂ Atmosphere

Low temperature deoxidation of oxygen bearing coal bed methane is the premise of its utilization.Many studies have shown that,at the top of the distillation column in the low temperature liquefaction process,the temperature is lower,and the pressure is in the range of 0.1⁰.3MPa,and the concentration of methane in the gas phase is within the limits of explosion.When there is an external energy greater than the minimum ignition energy（MIE）of methane,the whole process is explosive.The uncertainty of the MIE of methane is further increased when the CO₂ impurity gas is present at the top of the distillation column.However,there is a lack of experimental data on the MIE of methane in CO₂/O₂ atmosphere at low temperatures.As a kind of inert gas,CO₂ is involved in the process of methane explosion,and it is different from N₂ in the extent and mechanism of methane explosion.So the study of methane MIE and reaction mechanism in CO₂/O₂atmosphere under low temperature conditions can enhance the understanding of the explosion characteristics of methane under low temperature,can provide reference basis for improving safety measures of distillation tower,and it also has important significance to reveal the CO₂ inerting mechanism.In this paper,a set of experimental device and experimental scheme is designed to test the MIE of methane in the low temperature condition in distillation process.Based on the experimental results,the sensitivity conditions of methane explosion were obtained,and the MIE of methane in CO₂/O₂ atmosphere under the condition of 0.1⁰.7MPa、-90⁰℃was further determined under the sensitive conditions.Based on the test data,the relationship between the MIE and the initial temperature and initial pressure is studied.It is found that,the MIE of methane decreased with the increase of initial temperature,and it is linearly related to the reciprocal of initial temperature;the MIE of methane also decreased with the increase of the initial pressure,and it is linearly related to the reciprocal of the square of initial pressure;when the test conditions are the same,the MIE of methane in CO₂/O₂ atmosphere is greater than that in N₂/O₂ atmosphere.A numerical simulation method based on the mechanism of G3 is used to study the reaction mechanism of methane explosion in CO₂/O₂ atmosphere.The key element reactions to promote the positive reaction are R38,R155 and R156,and the key reactions of explosion suppression are R53 and R158.The path of explosion reaction contains the main path composed of CH₄,CH₃,CH₃O,CH₂O,HCO,CO and CO₂ and the branch and non critical paths composed of CH₂（S）,CH₂,CH,C₂H₆ and others.Compared with the explosive reaction mechanism of methane in N₂/O₂ atmosphere under the same condition,the moment of the explosion in the CO₂/O₂ atmosphere is behind the former,and the highest temperature,the maximum explosion pressure and the active free radical concentration were lower than the former.It is also different from the former in generating CH₂O and CO₂ on the main path and some other branch paths.