Fire accidents caused by coal spontaneous combustion usually lead to a large loss of coal resources and casualties. Not only that, the greenhouse effect is polluted while the environment is polluted. At present, the commonly used fire-extinguishing materials such as water, inhibitors, and organic foams have the disadvantages of poor stability and short fire-extinguishing cycles. It is difficult to effectively suppress coal spontaneous combustion and quickly extinguish the fire for a long time. To suppress the spontaneous combustion of coal, the research team proposed an inorganic three-phase foam with a high foam expansion rate, good cohesiveness, and excellent stability. In the formulation, pulverized fly ash (PFA) is used as the matrix, sodium dodecyl benzene sulfonate (SDBS) and α-olefin sulfonate (AOS) are used as foaming agents, curdlan is used as the foam stabilizer, and sodium silicate is the binder. The compound foaming agent with the best performance is optimized, through the two-group compounding test. The composite foaming agent’s optimal compound ratio is SDBS/AOS (3:2). The optimal ratio of inorganic three-phase foam (ITPF) components was obtained through the control variable method experiment. The water–cement ratio is 5:1, the composite foaming agent is 0.2%, the curdlan is 0.5%, and the sodium silicate is 1.6%. In addition, it has been determined by experiments that ITPF has the strongest foaming ability when the pH value is 9 and the temperature is 60 °C. The fire-extinguishing performance of the new material ITPF was investigated by thermogravimetry and coal spontaneous combustion tendency test. It has been observed that the new material has the effect of cooling down and isolating coal from contact with oxygen. The results show that the new material ITPF has the potential to prevent coal spontaneous combustion.
The spontaneous combustion parameters of lignite at different oxygen concentrations and temperatures were studied by temperature-programmed oxidation experiments. The characteristic parameters, tendency, oxygen consumption rate, kinetic parameters of oxidation reaction, and heat release intensity of coal’s spontaneous combustion were studied. The results show that the variation of export oxygen volume fraction of coal samples under different oxygen concentrations is similar. It has a general s-shaped downward trend. The change trend of the CO concentration of the coal sample export is basically the same at different oxygen concentrations. The CO concentration at the outlet of the coal sample increases with the increase in coal temperature. The CO concentration at 0–200 °C increased exponentially with the coal temperature. The distribution pattern of CO/CO2 ranging from 0 to 320 °C was similar at different oxygen concentrations. With the increase of coal temperature, CO/CO2 first increases and then decreases after reaching the extreme point. The change curve of CH4 with coal temperature under different oxygen concentrations meets the exponential change rule. At different oxygen concentrations, the concentration of ethylene at 0–300 °C changes exponentially, but at 300–400 °C there is no rule. When the oxygen concentration is 20.9%, according to the comprehensive judgment index method and cross temperature method, the comprehensive determination of the spontaneous combustion trend of coal samples is grade II. Under different oxygen concentrations, the oxygen consumption rate of coal increases with the increase of temperature; the oxygen consumption rate increases with the increase of oxygen concentration at the same temperature. The activation energy of coal samples increases with the decrease of oxygen supply concentration or the increase of temperature. The thermal strength of the coal sample is consistent with the change trend of the oxygen consumption rate. The heat release intensity of coal samples conforms to an exponential function and polynomial function in the early and late stages, respectively.
This is because text mining can reduce the time invested in pre-contextual research on coal mine safety in China. Therefore, this paper uses a combined BiLSTM-CRF model to handle the recognition of data. The optimal number of topics for LDA is determined by combining the perplexity and the topic variance, and this is done by manually annotating the coal mine safety corpus with the BIO annotation method. The BiLSTM-CRF combined model was then used to initially split the data into words and manually correct them. The combined BiLSTM-CRF model was repeatedly trained until the combined model met the word separation requirements. Finally, the LDA model was used to mine the data for topics. The results show that the combined BiLSTM-CRF model is able to recognise long proper nouns and achieve recognition in both English and Chinese. The combination of confusion and topic variance to determine the optimal number of topics for LDA can provide a reference for manual determination of the optimal number of topics for LDA.
To study the importance of the adsorption mechanism of methane (CH4) and carbon dioxide (CO2) in coal for coalbed methane development, we aimed to reveal the influence mechanism of adsorption pressure, temperature, gas properties, water content, and other factors on gas molecular adsorption behavior from the molecular level. In this study, we selected the nonsticky coal in Chicheng Coal Mine as the research object. Based on the coal macromolecular model, we used the molecular dynamics (MD) and Monte Carlo (GCMC) methods to simulate and analyze the conditions of different pressure, temperature, and water content. The change rule and microscopic mechanism of the adsorption amount, equal adsorption heat, and interaction energy of CO2 and CH4 gas molecules in the coal macromolecular structure model establish a theoretical foundation for revealing the adsorption characteristics of coalbed methane in coal and provide technical support for further improving coalbed methane extraction.
Compared with that of equal-length working faces, the mechanical evolution mechanism of overburden rocks in “knife handle”-type mining sites is more complex. The form of roof fracture of knife handle-type mines is more variable, and the stress distribution near the interface is more concentrated, thereby severely threatening the safety of mining. To elucidate the mechanical evolution characteristics of rocks in knife handle-type fully mechanized top-coal caving mining sites, the geological conditions of the 22401 fully mechanized top-coal caving face in Hanjiawa coal mine are investigated. FLAC3D software is used to numerically simulate the abutment pressure, horizontal stress, and vertical displacement of the fully mechanized knife handle top-coal caving face. This provides an effective theoretical and technical framework for subsequent problems, such as mine pressure control, roof management, and support withdrawal under similar mining conditions. The simulation results indicate that when the working face is mined within the range 20–30 m before and after the knife handle caving, the stress distribution is considerably asymmetric, the abutment pressure and horizontal stress are overconcentrated, the maximum vertical stress is 18.41 MPa, and the maximum horizontal stress is 16.45 MPa. Influenced by mining stress and self-weight, the roof subsides and the floor bulges. The maximum sinkage of the roof is 268.9 mm and the maximum bottom drum displacement is 10.01 mm.
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