Study Of Deposited Coal Dust Explosion Due To GAS Explosion

The explosion occurred when coal dust cloud because of deposited coal dust rising reach a certain concentration, which is one of three prerequisite elements to ignite coal dust explosion; thus, it is essential for mining safety to prevent deposited coal dust from becoming coal dust cloud to promote explosion. Especially, when explosion is ignited by gas explosion, it is significant to restrain coal dust from adhering in the explosion. In order to seek the appropriate approaches to suppress explosion, it is necessary to reveal the mechanism of deposited coal dust forming the coal dust cloud due to external influences and the regularity of gas explosion igniting deposited coal dust explosion. Therefore, researching the characteristic and mechanism of gas and coal dust explosion is able to resolve safety production issue in miming and other industries, and it is meaningful to establish the technical measures of preventing,controlling,easing the explosive accident, which can generate significant social benefit and economic benefit.This dissertation, containing theoretical analysis, numerical simulation and explosive experiment, examined the mechanism of coal dust explosion and process of deposited coal dust rising due to gas explosion and involved in the explosion. The conclusions are:1)Based on theory of thermal explosion and theory of chain reaction, it is evident that coal dust explosion is a heterogeneous reaction ignited by thermal reaction and chain reaction jointly. In the real headway, the explosion process is a explosive spreading process with high temperature,high pressure and high speed, and the significant transport process of quality,momentum and energy between two phases is a turbulence multiphase combustion process. Based on force analysis, it is evident that the forces influencing the movement of particle in fluid motioflow mainly are aerodynamic drag,Saffman force,drifting force that is generated by turbulence effect and gravity.2)It established the physical and mathematical model of deposited coal dust rising due to gas explosion and illustrated the state of motion of deposited coal dust under the inductive effect of gas explosion based on theoretical analysis and numerical simulation respectively. It is provided that the deposited coal dust rising is mainly caused by shock wave and the turbulence effect after the wave. During the process of coal dust rising, the surface shear force maintains a threshold as to keep the rising speed in a certain range. Trough the analysis on velocity field of coal dust particle, it is believed that the rising process could be divided into three steps: Startup,Acceleration and Deceleration.3)The experiments was did in headway of ChongQing Branch of China Coal Research Institute to research the process of deposited coal dust explosion due to gas explosion. Comparing to the single gas explosion, the explosion involving coal dust is provided with characteristics of slower attenuation of explosive pressure wave,higher pressure peak,longer propagation distance,faster rate of flame spread,broader bound of flame influencing. Either Gas mixture explosion of methane and air mixture or coal dust explosion would generate shock wave which has effects of overlay,reflect and attenuation during spreading process. During process of deposited coal dust explosion ignited by gas explosion, in the beginning that coal dust was involved in the explosion, there was a long duration of explosive overpressure; moreover, the pressure had a rising phenomena in a long time. This point illustrates that the initial period of coal dust involving explosion must produce more serious destruction to headway and facilities. The exposure time of pressure peak is not postponed with corresponding to lengthening of propagation distance and increasing of pressure peak. If explosion process was divided into stage of initiating explosion,stage of contacting coal dust and causing coal dust rising and igniting coal dust,stage of gas and coal dust explosion spreading and stage of attenuation. Based on empirical analysis, it is evident that the exposure time of pressure peak appeared more early in stage of initiating explosion; exposure time of pressure peak in stage of contacting coal dust and causing coal dust rising and igniting coal dust appeared much more lately than that in the stage of gas and coal dust explosion spreading; and exposure time of pressure peak in stage of attenuation appeared most lately in all stage.