Numerical Study On Catalytic Combustion Of Low Concentration Methane In Microchannels

A large amount of coal mine methane was released during coal mining processes.Methane with a concentration of less than 8%is emitted directly into the air in large quantities without effective use which result in energy waste and environmental pollution.Catalytic combustion is an effective way to process low concentration methane.In this thesis,a microchannel reactor based on monolithic honeycomb ceramic catalysts for catalytic combustion of low concentration methane is studied,and numerical simulations of the methane catalytic combustion in the microchannel were carried out using ANSYS Fluent.The present works were listed as follows:（1）The effect of the grid parameters on the calculation results was investigated.The numerical results of the catalytic combustion in a microchannel was verified.The effects of grid refinement at the entrance and wall and the grid quality on the numerical results were studied.（2）The mechanism of methane catalytic combustion reaction in the microchannel was analyzed.The process was divided into gas preheating phase,heterogeneous reaction phase,homogeneous reaction phase and post-combustion phase according to the characteristic of species concentrations and temperature.The axial positions between the four phases in a reactor were different for different reaction conditions.Incomplete combustions of methane in the reactor at some conditions were found.The desorption of O（s）and the adsorption of H₂O（s）promoted the heterogeneous and homogeneous reactions.（3）The effect of reaction conditions on the catalytic combustion characteristics of low concentration methane in the microchannel was studied.Gas inlet conditions,wall thermal conductivity and emissivity,and reactor gap size affect the temperature distribution,methane concentration distribution and location of homogeneous ignition in the reactor.（4）The interactions effect between gas inlet conditions and wall thermal conductivity on the catalytic combustion characteristics of methane were studied.The interaction effects between two factors of these operating conditions were significant and the effects on the combustion characteristics were different in different phases.