Regenerative Thermal Oxidation Of Ventilation Air Methane

Methane is an important source of greenhouse gas, as it is the second leading greenhouse gas, next to CO2, in contribution to global warming. The global warming potential(GWP) of methane is20times of CO2on the condition of the same mass. The methane emission of coal mining industry accounts for22%of the whole energy industry. About30billion m3methane are discharged from the worldwide coal mining process, while the amount of20billion m3are generated by China. Among this emission, more than70%comes from ventilation air methane(VAM). An effective treatment and utilization of ventilation air methane have an important meaning for greenhouse gas reduction and energy saving. The oxidation process of methane can realize the reduction of greenhouse gas. As the concentration of methane in ventilation air methane are far lower than the combustion limit, the oxidation process is hard to achiever in conventional condition. The most prospective technology applied to the treatment of ventilation air methane is thermal flow-reversal reactor(TFRR). This paper established a TFRR experimental device and a dynamic TFRR simulation model to show the parameter influence, and then a TFRR design model was put forward and had been verified by experiments:1. Parameter analysis of thermal flow-reversal reactorExperimental system of the regenerative thermal oxidation for ventilation air methane and the fixed bed reactor of lean methane-air mixture oxidation were established. The fundamental condition of the lean methane-air mixture oxidation process is proposed. The effect factors on the regenerative thermal oxidation process of ventilation air methane were analyzed with the help of dimensionless analysis.2. One dimensional model of regenerative thermal oxidation of VAMAn one-dimensional model was proposed for the regenerative thermal oxidation of VAM, and it was employed to simulate the working conditions, and compared with the experiment. The governing equations were solved by the method of lines using an open source software(MatMOL) based MATLAB language. Results show that the regenerative heat exchange conditions involving feed gas velocity, periodic switch time, structure of honeycomb ceramics are critical for stable operation of the reactor. The feed gas velocity has multiple influence on the steady of the reactor because of the relatively fixed heat loss of the reactor.3. Three dimensional model of regenerative thermal oxidation of VAMA heterogeneous three dimensional continuum model of the reactor was established using the user defined scalar in the commercial software Fluent. Flow distribution, temperature profile and concentration profile of the reactor were studied. The calculation results show that the rectifying effect of the honeycomb ceramic zone is very obvious. Heat loss of the reactor will affact the methane conversion, and improvement of central cavity on the methane conversion was very limited. The switch time should be properly prolonged due to the gas-trap effect.4. Design method of thermal flow-reversal reactor for VAMA method of calculating the stable operating parameters of thermal flow-reversal reactor was proposed. The regenerative heat exchange model and the criterion of the stability were established in thermal flow-reversal reactor. Based on the solution of the established model, the lowest self-sustaining methane concentration of the reactor was calculated. The calculated results are basically consistent with the experimental results, which shows the validity of the proposed model. The ventilation rate ranges of the reactor’s stable operation, the flow rates of the withdrawal gas, the self-sustaining honeycomb ceramic demands are also calculated using this model.