Research On Coal Combustion Characteristics Under Different Gas Atmospheres And Space Inerting Technology In Fully Mechanized Caving Goaf

As a main manifestation of coal combustion,self-ignition of coal in goaf is an extremely complex and chemical reaction process.From the perspective of mine fire prevention,over-consideration of the micro-reaction details is weakly related to the realities of the site.Meanwhile,large-scale physical experiments are not only time-consuming and labor-intensive but also poorly repeatable.In this paper,a series of studies were launched around the burning and inerting of coal from a macroscopic perspective.Based on the Gpyro pyrolysis model,the paper starting with the basic theory of combustion,processed the water drying process and the volatilization analysis process simultaneously under coal pyrolysis conditions,and constructed a comprehensive pyrolysis model of coal.The fixed carbon oxidation model,the soot formation and oxidation model and the DOM radiation model were introduced to form a coal general combustion model founded on the improved EDC turbulent combustion model.Based on the OpenFOAM platform and the built-in fireFOAM solver,the integrated coal pyrolysis model and coal general combustion model were coupled to establish a new type of solve,the coalfireFOAM,which is suitable for coal combustion,and a numerical simulation was made to simulate the coal combustion process.During the simulation process,the required thermophysical parameters were obtained by experimental methods and the chemical reaction kinetic parameters were solved by the GA algorithm to construct the objective function that obtained the minimum error of mass loss rate between the thermogravimetric prediction results and the thermogravimetric experimental data.The numerical simulation results of coal combustion were compared with the results of cone calorimeter experiments to verify the validity,integrity and accuracy of the pyrolysis aiid combustion models.Further,the combustion characteristics of coal under double inerting conditions of nitrogen and carbon dioxide were investigated by changing the gas phase atmosphere of coal combustion and it turns out that with the increase of the volume fraction of inert gas,the heat release rate and mass loss rate are both getting smaller and smaller.and the peak time becomes longer.When the integral number of inert gas mixes into the air reaches 60%or more,the effect of suppressing coal combustion is obvious;while when the inert gas concentration is lower than 40%,the inhibitory effect of inert gas on coal combustion is very little once the coal reaches the intense combustion stage,which shows low concentrations of inert gas has little effect on coal fires that have already occurred.The above research not only provides a new idea for the research of coal combustion and inerting,but also contributes some basic theoretical supports for the establishment of the technical scheme for mine fire prevention.The key to coal combustion in goaf is the continuous supply of oxygen to loose coal.So the pore distribution of the goaf was studied with the help of PFC software.The goaf was divided into three regions to compile porosity and permeability of the UDF partition based on the pore distribution characteristics.The porosity of the high porosity region near the roadsides was based on the calculation results of the PFC incline model,while the porosity of the intermediate region was based on the PFC strike model.Then,the established porous media seepage model in the goaf was introduced into the software Fluent,and the gas flow field in the goaf was simulated.The oxygen concentration was used as the main criterion to judge the dangerous zone of spontaneous combustion in goaf.So according to the determination of the“three-band”measurement of spontaneous combustion on site,it verifies the accuracy of the method based on the flow field distribution of the porous medium to determine dangerous zone of spontaneous combustion in goaf.Finally,considering the advantages and characteristics of nitrogen and carbon dioxide in fire prevention,a space inerting scheme that included hybrid injection scheme and split injection scheme was proposed to control the spontaneous combustion danger zones in fully mechanized caving areas.By using numerical simulation to analyze the inerting effect of each scheme,it is found that the split injection scheme is superior to the single injection scheme.A more effective fire prevention was obtained on site after using the parametrically optimized split injection scheme,which guaranteed the safe recovery of working face.