The Numerical Simulation And Characteristics Study Of Reverse Flow Reactor For Catalytic Combustion

The methane emissions in the oil and gas sector and coal mines have brought a series of problems in the global warming and production safety. The treatment and how to utilize the larger quantity low concentration methane is currently the focus of much international attention. The technology of catalytic combustion in reverse flow reactor integrates the reaction and heat recovery together effectively. The temperature in the catalytic combustion is much lower than the combustion in traditional way. The catalytic combustion has high conversion and lead to no secondary pollution almostly. Because catalytic combustion in a reverse reactor has high thermal efficiency and high stability, it is suitable for the treatment of lean methane. A systematic research in a reverse flow reactor for catalytic combustion was investigated by the methods of experiment and numerical simulation for the combustion of methane effectively and cleanly.The pressure drop profiles in a flow reversal reactor for the catalytic combustion were experimentally studied on a cold setup. Effects of packed bed height, superficial velocity and reciprocating time on the dynamic of the pressure drop profiles and the stability time of the reactor were tested. Pressure drop profiles vary periodically with rectangle-like waves as the flow reverse periodically. The stability time was slightly extended as the rise of packed bed height and superficial velocity. Pressure drop profiles were mainly depends on the property of the particles, bed height and superficial velocity. Empirical correlation coefficients for the reactor were obtained based on Ergun equation and test data.Catalytic combustion of lean methane in a reverse flow reactor was carried out in a large range of experimental conditions. The results show that the transient temperature profile was overall result in reaction and the heat lost to the surrounding. Operation conditions such as concentration, switch-time and superficial velocity have evident influence on the temperature profile which lead the reactor to the following three situation ultimately: pseudo-steady-state, temperature run-away, extinction. High concentration and low velocity will lead to saddle shape transient temperature profiles even temperature run-away. Decreasing the concentration or increasing the axial heat-transfer will reduce the possibility of temperature run-away. The low concentration and long switch-time will lead too much heat lost and extinction ultimately. When the concentration is too low to maintain auto-thermal situation, the use of electrical heater can solve the problem successfully. The conversion of methane depends to the temperature profile in a great degree. It is satisfying to find that when the concentration is higher than 0.4%, the conversion of methane almost was over 95%.Furthermore, based on some acceptable assumption, a heterogeneous one-dimensional model of the reactor was proposed that was valid after compared with the experiment. Based on the result of simulation, the influence of operation conditions, the properties of the fillers, the structure parameters of the reactor was discussed. Results obtained indicate that the concentration increase will lead higher temperature profile and wider high-temperature platform. When the velocity increased, the trend of the temperature profile is that enhancive first then descending. Short switch-time will obtain a higher temperature profile in the catalytic bed and a wider high-temperature platform, but long switch-time will obtain a steeper temperature profile. Fillers with different particle size have little influence on the temperature profile, material with higher thermal capacity will enhance the capacity of thermal storage and increase the temperature profile. Using larger inner diameter has the benefit to increase the temperature in the reactor. When the thickness of the insulation layer is less than a certain value, increase the thickness has profit to increase the temperature in the reactor, but when the thickness of the insulation layer is more than a certain value, increasing the thickness has no help to increase the temperature almost. Increasing the length of catalytic bed will bring a lower and more flat temperature profile, but if the length is enough short, it is more inclined to obtain a local narrow high-temperature platform. Increase the length of inert bed will bring a higher temperature profile and wider high-temperature platform, but the maximum temperature became lower.