Prediction Model for Spontaneous Combustion of Coal around Boreholes Using Bedding Gas Drainage

Abstract

To accurately and reliably predict the time of spontaneous combustion of fractured coal around a borehole induced by gas drainage along the seam, this study performed an orthogonal test taking the No. 10 Coal Mine of Pingdingshan as the research object, in terms of the suction negative pressure and coal seam buried depth. COMSOL Multiphysics was used to model the orthogonal test results, and a multielement statistical analysis of four factors and their relationships with the spontaneous combustion of coal around the borehole and a single-factor analysis in line with the site conditions were performed on the modeling results through multiple regression. The results showed a nonlinear regression relationship between the sealing hole length, sealing hole depth, negative pressure, and coal seam depth and the spontaneous combustion of the coal around the gas drainage borehole; the prediction regression model is significant. Taking the field gas drainage in the No. 10 Coal Mine of Pingdingshan as an example, the relationship between the time of spontaneous combustion of gas drainage and the drainage pressure follows a power of two. When the drainage negative pressure is less than 45 kPa, the coal around the borehole is more likely to undergo spontaneous combustion with increasing pressure, and the sealing hole length has a positive linear correlation with the time of spontaneous combustion of the coal around the borehole. When the sealing hole length is 23 m, the time of spontaneous combustion of the coal around the gas drainage hole is >500 days, and the coal around the borehole does not easily undergo spontaneous combustion. When the sealing depth is 15 m, the time of spontaneous combustion of the coal around the gas drainage hole is 76 days, which is most likely to cause spontaneous combustion.

Development and Application of Water Sealing Technology for Gas Drainage Boreholes

“…The destruction of the structure of the coal around the gas extraction borehole by drilling is the main reason for the failure of borehole seal, as it reduces the strength and compression capacity. Furthermore, the coal is prone to plastic deformation after compression, leading to a large number of microcracks in the coal and rock mass around the borehole. − In addition, new fissures evolve through the influence of mining and other factors from the microfissures in the borehole and its surrounding channels, thus further increasing the problem of sealing gas drainage boreholes. , Using conventional yellow earth, cement mortar, polyurethane grouting hole sealing process such as fixed after forming, although before the fixed shape around the drilling and the drilling of microcracks have certain effects to block, but the new fracture cannot be affected by mining derived after sealing effect, at the same time the traditional solid hole sealing material cannot with the forced deformation of the drill, it is easy to cause the failure of borehole seal. − Therefore, sealing the drilling hole and the surrounding coal body to trap the gas in the coal body effectively , and extract the gas efficiently through the drilling hole has become one of the key technologies to process the co-mining of coal gas − and the green mining of coalbed methane. − …”

Prevention Technology of Coal Spontaneous Combustion Induced by Gas Drainage in Deep Coal Seam Mining

“…Coal spontaneous combustion occurs under three conditions: oxygen concentration, wind speed, and time [32][33][34][35]. Only when the ventilation and oxygen supply conditions are continuous and stable for a period of time, enough to combine the coal with sufficient oxygen, the oxidation process is fully carried out and the coal body can spontaneously ignite when a certain amount of heat is accumulated [36,37]. Therefore, choosing the appropriate critical oxygen concentration and airflow velocity is the key to classifying the spontaneous combustion of coal around the gas drainage hole.…”