Study On Chemical Kinetics And Combustion Stability Of Low Concentration Methane Utilization

There is very huge low concentration methane in the industrial. Because itsconcentration is very low, often0.1-5%, it is difficult to convert this methane gasmixture to usable energy with conventional combustion technologies, and it isgenerally emitted into air. The large amounts of methane are discharged into theatmosphere led not only the enormous wasted energy resource but also addsundesirable atmosphere pollutants. The development of low concentration methanegas direct combustion technology is of saving energy and environment friendly.Chemical kinetics mechanism and combustion stability are the core problems of theutilization of low concentration methane. Researchment has attention to the twoaspects, and main work and conclusions are as follows:Firstly, based on the theory of shock and methane combustion mechanism GRI3.0, low concentration methane combustion induced by shock wave was numericallystudied, and on this basis, especially, the ignition delay time of ventilation air methanein coal was numerically investigated by using Chemkin software. According thesensitivity analyzing of elementary reactions, the ignition delay time of ventilation airmethane was defined by the peak value of the mole fraction of CH₃. Then, mainattentions were focused on the effects of the ventilation air methane concentration,initial temperature and initial pressure, and the shock velocity on the ignition delaytime. It is found that, with the increment of the incident shock velocity, the initialtemperature and initial pressure of ventilation air methane, the ignition delay timewould shortened, however, the concentration of ventilation air methane, during0.1-1.0%, has no significant effect on the ignition delay time.Secondly, using the perfectly stirred reactor （PSR） and the plug-flow reactor（PFR） model, the combustion stability of low concentration methane was numericallystudied. Main attentions were focused on effect of residence time, methaneconcentration, preheating temperature, heat loss, mass flow rate and other parameterson the combustion stability. The results showed that:（1） To maintain the stablecombustion of low concentration methane, The residence time should be greater thanthe critical residence time or the mass flow rate be less than the critical mass flow;（2） When the concentration of methane is lower than4%, to maintain the combustionstability, the low concentration methane must be preheated, with the concentration ofmethane dropped1%, preheating temperature needs to raise about200K.（3）The heatloss would significantly reduce the initial temperature, and thus lead to critical massflow rate decreased.（4） Because of the influence of the ignition delay time, tomaintain the stability of low concentration methane combustion, enough length of thecombustion chamber must be ensured, and the length will be affected by methaneflow rate, methane concentration and heat loss.Finally, based on excess enthalpy theory, by the use of porous media built-inSwiss-roll experiment platform, combustion stability of low concentration methanewas studied. Analyzing the ignition scheme, the electric spark ignition in the center ofburner was choosed, and the ignition was successed. The low concentration methanecombustion stability experiments show that:（1） Both increasing methane flow rate atthe same concentration and decreasing concentration at the same flow rate, will makethe flame center to drift downstream;（2） To contrast the experimental results and thesimulation results, at the laws of blowout characteristic, both of them are wellcoincident, but due to the differences of experimental conditions and simulatedconditions, the experimental results show a lower combustion stability.