Experimental Study On Ignition Temperature And Flame Propagation Characteristics Of Low Concentration Gas

Coal mine gas escapes in the process of mining, whose main combustible component is methane. In the air the explosion limit of coal mine gas ranges from 5% to 15%. According to the Coal Mine Safety Regulation Rules, if gas is applied to industries, the methane concentration must be higher than 30%. If the methane concentration is less than 30%, gas has to empty into the air. Methane is a kind of greenhouse gas and comparing to CO2, the greenhouse effect of methane is 21 times of CO2. The discharge of the low concentration methane can not only lead to waste energy but also the environment pollution. If the low concentration gas can be used to generate electricity, it will improve the economic benefits, social benefits and environmental benefits significantly. In order to use the low concentration gas directly in the pulverized coal fired boiler, it is necessary to study the ignition temperatures and the flame propagation characteristics of the low concentration gas and pulverized coal coupling system.Experimental systems were designed and built based on the theories of the gas combustion in this thesis to investigate ignition temperature and flame propagation characteristics. It was analyzed about the influence of the methane concentration, oxygen concentration, initial temperature and other factors on ignition temperature and flame propagation characteristics. Moreover on the basis of previous studies, this thesis studied the influence of coal concentrations, coal diameters and volatiles on ignition temperature and flame propagation characteristics of the low concentration gas and pulverized coal coupling system.The results indicate that with the increase of methane concentration, the ignition temperature of low concentration gas decreases firstly and then increases. When the methane concentration is 6%, the ignition temperature is 764?, which is the lowest ignition temperature. When the methane concentration is less than 6%, the ignition temperatures decrease with the increase of oxygen concentration. While the methane concentration is more than 6%, with the increase of oxygen concentration, oxygen almost does not have any effect on the ignition temperature. When the initial temperature of the low concentration gas ranges from 20? to 180?, the ignition temperature decreases by 10?. The flame limit of the low concentration gas is 5.5% to 15% in the air. The flame propagation velocity first increases and then decreases with the increase of the methane concentration. The maximum flame propagation velocity appears in methane concentration of 9.5%, and the farther the distance to the ignition position, the greater the flame propagation velocity.The ignition temperature of the coupling system decreases at the same methane concentration compared with the low concentration gas. With the increase of methane concentrations, the ignition temperature of the coupling system increases. When methane concentrations remain constant, with the increase of the coal concentrations, the ignition temperature of coupling system decreases firstly and increases, and there is an optimum coal concentration so that the ignition temperature of coupling system is the minimum. With the decrease of the coal diameters, the ignition temperature of coupling system decreases. The ignition temperature of coupling system decreases with the increase of the volatiles. With respect to the low concentration gas, the flame limit of coupling system decreases. When the volatiles is 8.99% and coal concentration is 100g/m3, the lower flame limit of the coupling system is 3.5% and the upper flame limit is 14.5%. With the increase of the coal concentrations, the flame propagation velocity of the coupling system firstly increases and then decreases. Therefore there is an optimum coal concentration so that the flame propagation velocity of coupling system is the maximum. With the increase of coal diameter, the flame propagation velocity of the coupling system increases. With the increase of volatile pulverized coal, the flame propagation velocity of the coupling system increases.