Distribution Law Of Carbon Dioxide Injection In Goaf And Optimization Of Process Parameters

Coal seam mining with fully mechanized coal caving technology has the advantages of high single production,high efficiency,low cost and small roadway driving,but it is also accompanied by many defects in the goaf,which can easily cause spontaneous combustion and so on.Spontaneous combustion of coal in goaf will not only affect production,but also lead to gas explosion and other serious consequences,endangering the safety of personnel.As a means to prevent and control the spontaneous combustion of the goaf,it can effectively reduce the oxygen concentration in the goaf and shorten the range of natural oxidation zone.Therefore,setting up reasonable carbon dioxide injection parameters,that is,different pressure injection position and pressure injection flow,is an important basis for determining the effect of pressure injection.The 7271 working face of Yao Qiao mine is used as the first mining face of 7#coal seam,using top coal mining method,the thickness of coal is 5m,the length of the working face is 260m.It is lack of experience and specific parameters for the prevention and control of spontaneous combustion of coal in goaf with large length tendency.Therefore,the reasonable parameter of carbon dioxide injection is obtained by quantitative and qualitative analysis by means of field measurement and numerical simulation,which is the future of this paper.The coal mine goaf provides an important parameter basis for carbon dioxide fire prevention work.The research contents are as follows:?1?Using FLUENT computer simulation software to establish 7271 full mechanized working face physical model,simulating oxygen concentration distribution before and after CO₂ injection in goaf.The simulation results show that the inlet side 28.6?85.7m is a spontaneous combustion zone,and the air inlet is 57.1m,the maximum oxidation zone in the middle of the goaf is 15.7?95.7m,and the oxidation bandwidth is 80m.?2?On the basis of determining the reasonable goaf model,we simulate carbon dioxide injection under different injection parameters.By comparing the three zones of spontaneous combustion in 5 groups of different carbon dioxide injection positions,the distribution of the three zone of spontaneous combustion in the goaf indicates that the maximum width of the oxidation zone is reduced by X=20m?the distance of the pressure injection to the working face?,and the maximum of the oxidation zone is reduced to 41%.X=20m is selected as the position of carbon dioxide injection,and the three zone distribution of spontaneous combustion in the goaf is compared with the 5 groups of different carbon dioxide pressure injection flow.When the width of the maximum oxidation zone of 2000m³/h is reduced by 52.8m,the difference between the inerting effect of the mined area and the working face is little difference,and it is more beneficial to the safe production of the working face.Therefore,the reasonable pressure injection position adopted in the 7271 working face is X=20m and reasonable pressure is determined.The flow rate is 2000m³/h.?3?The change of oxygen concentration measured by a beam tube monitoring system at the inlet side of 7271 fully mechanized caving face before and after carbon dioxide injection is compared:25.2?84.0m is a spontaneous combustion zone after the working face of the forward wind side without carbon dioxide,and the width of the oxidation zone is 58.8m.After injection of carbon dioxide,the 18.9?65.1m is the spontaneous combustion zone and the width of the oxidation zone is 46.2m.It is found that the natural band width is reduced by 12.6m,and the natural band range is about 20m.This indicates that carbon dioxide injection can effectively reduce the natural band width.By comparing the beam tube monitoring data with the numerical simulation results,the results are basically the same,and the error is within the required range,which ensures the applicability of the model.?4?The distribution of carbon dioxide concentration in the"three zone"simulation of spontaneous combustion in goaf under the parameters of carbon dioxide is analyzed.The concentration distribution of carbon dioxide is mainly divided into three concentration regions.The concentration of carbon dioxide at the center of carbon dioxide will form more than 90%carbon dioxide clouds,and the concentration of the two ends of the carbon dioxide is decreasing,and the two ends are small in the middle.The concentration near the working face and inlet is about 50%,and the closer to the working surface,the lower the concentration;the depth of carbon dioxide in the goaf is reduced as the porosity increases with the depth of the buried depth.