Working Process Simulation Of Low Concentration Gas Preheating Catalytic Oxidation Device

The ventilation air methane(VAM) that exists in coal mine is a kind of clean energy. But it is also a kind of greenhouse gas. China is rich in coal, so it is also rich in the ventilation air methane. At present, the ventilation air methane reserves are about 36 trillion cubic meters, ranking third in the world. If most of ventilation air methane is emitted to atmosphere directly, it may cause serious environmental pollution and great energy loss. So the use of the ventilation air methane has attracted human attention.Based on the preheating catalytic oxidation reactor designed by Shandong university of Technology, the preheating catalytic oxidation characteristics of low concentration gas in a channel coated by catalyst Pd of the preheating catalytic oxidation reactor was investigated with the mathematical software of FlexPDE in this paper. In addition, the equilibrium state of ventilation air methane without heat extraction and the equilibrium state of ventilation air methane with heat extraction were carried out. The main contents include:(1) The mathematical model of low concentration gas preheating catalytic oxidation reactor was set up. A heterogeneous one dimensional continuum model was chosen for preheating catalytic oxidation reactor, and it includes four conservation equations as follow, the fluid concentration conservation equation, solid concentration conservation equation, fluid temperature conservation equation and solid temperature conservation equation. The model of preheater was built with lumped parameter method. The temperature distribution of preheating catalytic oxidation reactor was simulated by FlexPDE, and the results were compared with experimental results. The result shows that the simulation results show a good agreement with the experimental results. The both trends of temperature field are the same basically. The temperature distribution in preheating catalytic oxidation reactor drops slowly after a significant rise. So the mathematical model can roughly describe the preheating catalytic oxidation characteristics of low concentration gas, and it can be used for the later simulation work to explore the influencing factors of the equilibrium state of ventilation air methane.(2) The preheating catalytic oxidation characteristics of ventilation air methane were simulated. The effects of methane concentration, air volume and the heat transfer area of preheater for the axial temperature of reactor, methane conversion rate, preheating temperature and exhaust gas temperature were explored. The results show that the axial temperature of reactor, methane conversion rate, preheating temperature and exhaust gas temperature increase with methane volume concentration increasing. With air volume increasing, the axial temperature of reactor, preheating temperature and exhaust gas temperature increase, and methane conversion rate decreases. With the heat transfer area of preheater increasing, the axial temperature of reactor, methane conversion rate and preheating temperature increase, and exhaust gas temperature decreases.(3) The equilibrium state of ventilation air methane without heat extraction was simulated. Firstly, when the preheating catalytic oxidation reactor is in the equilibrium state and the exhaust gas temperature is 373 K, the relationship between methane volume concentration and the heat transfer area of preheater under the same air volume was explored, and the relationship between methane volume concentration and preheating temperature under the same methane flow was explored. The results show that the heat transfer area of preheater increases and the preheating temperature increases with methane volume concentration increasing. Finally, the polynomial functions were used to fit them. Secondly, when the preheating catalytic oxidation reactor is in the critical equilibrium state, the relationship between methane concentration and the critical heat transfer area of preheater under the same air volume was explored. The results show that the critical heat transfer area of preheater decreases with methane volume concentration increasing. Finally, the exponential function was used to fit it.(4) The equilibrium state of ventilation air methane with heat extraction was simulated. When the preheating catalytic oxidation reactor is in the critical equilibrium state, the relationship between methane concentration and the best percentage of heat extraction under the same air volume was explored. The results show that the best percentage of heat extraction increases with methane volume concentration increasing. Finally, the polynomial function was used to fit it.