Study Of Flammable Limits And Flame Quenching For Ventilation Air Methane

Ventilation air methane mitigation are gradually taken seriously in recent years. In order to ensure security and eliminate potential danger in ventilation air methane mitigation system, flammable limits of CH4/O2/N2/CO2mixtures should be tested and flame arresting after unexpected ignition need to be studied. Consequently, our work will mainly focused on these two aspects to give reference to industrial security and flame arrester designing.As to flammable limits, numerical method is used first to predict flammability of mixtures. Then based on the calculated results, experiments will be designed to measure the flammable limits.ChemKin module, which is based on chemical equilibrium method, is used to calculate adiabatic flame temperature of mixtures with different compositions. In the calculation,1450K is chosen as the critical temperature to judge whether a mixture is flammable. According to this criterion, effect of additives like nitrogen and carbon dioxide on flammable limits is studied, and flammable limits of mixtures that are composed with fixed mole ratio of methane to carbon dioxide are estimated.In7L test vessel, photoelectric sensors mounted at a distance of100mm from ignition source are used to record flame signal. Mixtures are regarded as nonflammable if no flame signal is recorded in3experiments, otherwise they are judged as flammable. With this method, flammable limits of mixtures that represent mixing of outburst gas and air in coal mine are tested, and the results are amended with proper method to obtain the flammable limits of CH4/CO2in air.To prevent flame propagating in pipeline after unexpected ignition in ventilation air methane mitigation system, flame arresters are required to be mounted at proper positions. Crimped ribbon flame arrester is a frequently used type, of which the cross section shape is triangle. And there is a conversion relationship between sectional dimensions of channels with different cross section shapes. Our work provide reference to flame arrester designing by experimental research on flame propagation and quenching in channels with rectangular cross section and numerical research on flame quenching in channels with different cross section shapes. Channel device with a series of different narrow channels is mounted in a shock tube with rectangular cross section. Flame propagates into channel device after acceleration and its speed at the entrance of channel device can be adjusted by changing the initial concentration of methane.In the experiments, high speed photography is implemented to record flame propagation and quenching process in narrow channels, which helps to find out the relationship between quenching length and channel width under conditions of different flame velocity and give out a corresponding empirical formula.Simulation of flame propagation and quenching in narrow channels is done with Fluent.In the simulation, temperature contour of1OOOK is chosen to represent the flame front, a boundary of burned and unburned gas. In this way, we qualitatively analyze the effect of flame velocity at the entrance of channel device, channel width, and cross section shape on quenching length.Flammable limits of CH4/CO2mixtures in air obtained in our work can provide a reference to industrial security. Besides, relationship between quenching length, flame velocity and channel width obtained from narrow channel experiments can be used to direct flame arrester designing, which is of great significance.