Spontaneous Combustion In Goaf Research Articles

Measurement and Numerical Simulation of Coal Spontaneous Combustion in Goaf under Y-type Ventilation Mode.

In the process of advancing the working face, the temperature rise and oxidation characteristics of residual coal in goaf and the prediction of index gas are of great significance to mine fire prevention and safety production. Based on the coal spontaneous combustion test, the oxygen consumption and heat release characteristics of coal spontaneous combustion were analyzed by taking coal samples at the working face and carrying out temperature-programmed experiments in the laboratory. The characteristic temperature and index gas of coal spontaneous combustion were determined as the judgment bases of “three zones” of spontaneous combustion in goaf, and the influencing factors of coal spontaneous combustion in goaf under Y-type ventilation were analyzed. Based on the test results, the changes of gas composition in goaf during the advancing of the W1310 working face were monitored. According to the actual situation of the W1310 working face in the Gaohe energy mine of Lu’an group, the multifield three-dimensional numerical simulation calculation and analysis of gas composition in goaf were carried out, and the distribution of oxygen concentration field in goaf under different air volume ratios of machine roadway and air roadway was studied. Through the analysis of the parameters of porous media in the goaf, combined with the actual situation, the user-defined function was compiled for the key parameters such as porosity, viscous resistance coefficient, and inertial resistance coefficient of porous media in the goaf. The three-dimensional seepage field, gas concentration field, oxygen concentration field, and pressure field of the gas components in goaf during the advancement of the goaf working face were simulated. The comparison of the numerical simulation results with the field-measured results shows good agreement. In order to consider safety, the numerical simulation results with a wide oxidation temperature rise zone are used for linear regression, and the regression equation is used to dynamically determine the O2 concentration at a point away from the goaf and to determine the “three-zone” state of the point, which is of great significance to guide the progress of the working face and safe production.

Effective thermal conductivity of loose residual coal in goaf: Comparative analysis of experiment and model

The effective thermal conductivity (ETC) model of loose residual coal in goaf is a method to study the heat transfer law of spontaneous combustion in goaf. In order to study the effect of coal particle size and ambient temperature on heat transfer, coal samples of different sizes were taken from the FuSheng (FS) mine, and the void fraction, the thermal conductivity (TC) of the residual coal under different ambient temperature were tested. Additionally, four types of ETC models of loose residual coal in goaf were obtained and the average relative errors of the TC were analyzed. The results showed that the void fraction, the coal particle size and ambient temperature have different effects on the spontaneous combustion of the residual coal. The effect of coal sample size on the heat transfer is 100 times that of the ambient temperature. The changes in the ETC and average relative error of the different models were consistent. The heat transfer in the spontaneous combustion of residual coal has a direct relationship with the spatial distribution and heat transfer modes of the loose residual coal in the goaf.

Experimental Study on Gas Migration Laws at Return Air Side of Goaf under High-Temperature Conditions

ABSTRACT In recent years, accidents of gas explosions caused by spontaneous combustion of coal have occurred from time to time. A goaf simulation experiment table was self-built to explore the influence of coal spontaneous combustion in goaf on the gas migration laws. Specifically, the gas migration laws at the return air side of goaf with or without high-temperature points at the wind velocity of 0.2, 0.6, and 1.0 m/s on the working face were analyzed. Results showed that, given the high-temperature points at the return air side, the gas concentration close to the high-temperature zone was obviously increased, the contour line of gas concentration was bent at high-temperature points, the quantity of dangerous gas explosion zone was also increased compared with that at normal temperature, and the variation amplitude of gas concentration was reduced with the increase in the distance of vertical direction from high-temperature point. The study results provide an essential experimental basis for the gas control of highly gassy coal seams susceptible to spontaneous combustion, and they have certain reference values in practical production.

Distribution Law of Coal Spontaneous Combustion Hazard Area in Composite Goaf of Shallow Buried Close Distance Coal Seam Group

ABSTRACT The spontaneous combustion of residual coal in compound goaf formed by shallow and close coal seam mining is one of the difficulties in mine fire prevention and control. In order to explore the mechanism of spontaneous combustion of residual coal in 22304 working face of Huojitu minefield in Daliuta coal mine, the causes of spontaneous combustion of residual coal in 22304 working face are studied by comprehensively applying the methods of experiment, numerical calculation, and field measurement, the limit parameters of spontaneous combustion of 22304 working face are obtained, and the risk of spontaneous combustion in 22304 working faces is divided. The results show that the critical oxygen concentration of coal in 22304 face is 8%, and the width of inlet airside and return airside of oxidation temperature rise zone in composite goaf is 245 m and 170 m. When the advancing speed of 22304 working face is greater than 7.42 m/d, it can effectively avoid spontaneous combustion in goaf. Finally, the fire prevention and extinguishing measures of composite goaf after temporary shutdown when the working face passes through faults and other geological structures are discussed. The findings have certain reference significance for the division of goaf spontaneous combustion risk areas and the formulation of fire prevention and extinguishing schemes under similar conditions.

Dynamic prediction model of spontaneous combustion risk in goaf based on improved CRITIC-G2-TOPSIS method and its application.

Due to the problems related to the numerous factors affecting the spontaneous combustion of goaf coal, such as sudden, uncertain, and dynamic changes, and the fact that the weight of the indexes in the prediction model of the spontaneous combustion risk is difficult to determine, an improved Criteria Importance Through Inter-criteria Correlation (CRITIC) modified Technique for Order of Preference by Similarity to Ideal Solution G2-(TOPSIS) dynamic prediction model of goaf spontaneous combustion was developed. An optimal decision-making model was established by introducing the Euclidean distance function, and the function-driven type G2 weighting method was modified using the differential-driven type weighting method of the CRITIC. In addition, the comprehensive weights of each index were obtained. An update factor was introduced to obtain the dynamic weight, and the primary-secondary relationship of the risk factors affecting the spontaneous combustion of goaf was evaluated. Based on the G2 weighting method, which approximates the driving function principle of the ideal solution ranking method (TOPSIS), a G2-TOPSIS goaf spontaneous combustion risk assessment model was established. The degree of closeness was analyzed and the risk grade of the goaf spontaneous combustion was finally predicted. The sub-model was applied to the goaf of working face 1303 in the Jinniu Coal Mine. It was concluded that the air leakage duration was the dominant factor inducing the risk of the spontaneous combustion of the goaf. The risk grade of spontaneous combustion of the goaf is Class III, and the predicted results are consistent with the actual situation. The improved CRITIC-G2-TOPSIS dynamic model was demonstrated to be scientific in predicting the goaf spontaneous combustion risk, and these research results have important popularization and application value.

Experimental investigation on microstructure evolution and spontaneous combustion properties of aerobic heated coal

Since coal oxidation and heat accumulation are prerequisites for coal spontaneous combustion, it is of great significance to study the characteristics of coal oxidation and heat accumulation to grasp characteristics of spontaneous combustion of residual coal and to locate the area with coal spontaneous combustion in goaf. In this study, three types of lignite and bituminous coal with a strong spontaneous combustion tendency were selected to prepare raw coal samples and aerobic heated coal samples. Then ultimate and proximate test, core pore and surface area test, SEM test, TG test, FTIR test and temperature-programmed test were undertaken, respectively. After coal undergoes aerobic heated progress, its surface micro-cracks, internal pore volume and specific surface area surge, and the active functional groups vary significantly; the contents of C and H fall, and that of O rises. These changes are conducive to coal oxidation. The temperatures corresponding to the first peak points in the DTG curves for the aerobic heated coal samples are lower than those for the raw coal samples, which indicates that the aerobic heated coal samples enter the self-oxidation acceleration stage earlier. Besides, according to the results of the temperature-programmed experiment, the cross-point temperatures of CO generation for the aerobic heated coal samples and the raw coal samples are 91 °C, 82 °C and 76 °C, respectively. A comprehensive analysis discloses that the aerobic heated coal samples are more likely to combust spontaneously in the initial stage of oxidation and to generate more CO. The heat dissipation zone, oxidation zone and suffocation zone were divided by monitoring the oxygen concentration changes in goaf at different stages on 5–20101 working face. It is determined that the oxidation zone of the goaf is 71–152 m on the inlet side and 59–128 m on the return side.

Evolution of methane ad-/desorption and diffusion in coal under in the presence of oxygen and nitrogen after heat treatment

When fire occurs in an underground goaf, with the high temperature and a gas environment of injected nitrogen, the coal structure is affected and the methane adsorption characteristics are changed. In this study, coal samples were heated in different gas atmospheres; isothermal adsorption, scanning electron microscopy, and proximate analysis were conducted to study the evolution of coal adsorption characteristics during heat treatment. It was found that an increase in the heat-treated temperature leads to the development of pores and cracks, providing more adsorption sites for methane. It was also found that in a high-temperature environment, oxygen reacts with coal to form oxygen-containing functional groups, leading to an increase in the methane adsorption capacity. The hysteresis of methane desorption first decreases and then increases with the increase of temperature. We think that the decrease of hysteresis may be due to the decrease of moisture and volatile content, which makes the pores more unblocked. And the increase of hysteresis may be caused by the increase of pores and the narrowing of pore throat. The diffusivity of methane first decreases and then increases with an increase in temperature. The thermal expansion of the coal caused by heat treatment leads to a change in pore structure and diffusivity. The SEM experiment shows that the pore and crack structure changes with an increase of heat-treated temperature. With oxidation, the coal surface melts and produces a “bark-like” structure. Through proximate analysis, it was found that heat treatment leads to a significant decrease in volatile and a significant increase in fixed carbon content, which is closely related to the methane adsorption capacity. The research results provides valuable information to the engineering of prevention of spontaneous combustion in goaf and the control of methane disasters.

Experimental study to assess the explosion hazard of CH4/coal dust mixtures induced by high-temperature source surface

The explosion accident caused by the spontaneous combustion surface of coal after the coal dust is rolled up by the gas gushing from the goal seriously threatens the safety of coal coal mining. Based on this hazard, self-developed gas explosion equipment is used to detonate the CH4/coal dust mixture by high-temperature source. The process and mechanism of gas/coal dust explosion induced by coal spontaneous combustion in goaf were simulated, and its risk was evaluated. It is of great significance to understand the initiation mechanism of gas-solid mixture through coal spontaneous combustion in goaf. The results show that the explosion pressure (Pgd), explosion temperature (Tgd), rate of pressure rise ((dP/dt)gd), and explosion index (K) of CH4/coal dust mixtures are closely related to the temperature of high-temperature source and volatile content. The role of coal dust volatiles in homogeneous and nonhomogeneous reactions was revealed. Combined with three explosion parameters (Pgd, Tgd, K), the most dangerous explosion combination concentration of the selected CH4/coal dust mixture is (9.5 %, 500 g/m3), (9.5 %, 400 g/m3), and (8.5 %, 500 g/m3) at 1073 K ignition temperature. The involvement of coal dust leads to a lower explosion limit for CH4/air. The Jiang model has better applicability to the prediction of lower explosion limits for CH4/coal dust mixtures induced by the high-temperature source surface.

Study on Multi-field Evolution and Influencing Factors of Coal Spontaneous Combustion in Goaf

ABSTRACT The coupled disaster of coal spontaneous combustion and gas explosion in the goaf threatens coal mine safety production. In order to further study the mechanism of coupled disasters and provide theoretical basis for disaster prevention and control, the multi-field evolutions and the key influencing factors of coal spontaneous combustion within methane gas condition of coal mine goaf had been investigated based on the special designed hot experimental platform and numerical simulations. Results show that the leakages of ventilation air into the goaf is positively related to the intensity of coal spontaneous combustion, but that is negatively related to the ranges of methane accumulations in the goaf. During the early stage of coal spontaneous combustion, the distributions of oxygen and methane in the goaf is less affected by the temperatures. When the temperature of coal spontaneous combustion exceeds 200°C, the oxygen-poor area, methane accumulation areas and a banded high-temperature distributions area in the non-spontaneous combustion areas would be clearly formed in the goaf. The changes of gas density in the goaf indicates that coal spontaneous combustion temperature in the goaf is another important factor influencing the change of gas density and gas accumulations, in addition to the ventilation air leakages.

Research on determining reasonable negative pressure based on the control of the goaf

In order to study the law of spontaneous combustion in goaf under the condition of gas extraction, the method of beam tube monitoring and numerical analysis is adopted to obtain three dimensional distribution of oxygen concentration and contour map under the condition of different negative pressure. Based on the way of regression analysis, reasonable negative pressure are determined. The results show that with the increase of negative pressure, the spontaneous combustion “three-zone” in goaf: the heat dissipation zone and the spontaneous combustion zone become wider and the suffocation zone narrows. At the same time, the trend of spontaneous combustion zone presents to the deep part of the goaf; the amount of gas extraction increases first and then decreases with the increase of negative pressure. Combined with the trend of spontaneous combustion zone and the amount of gas extraction in goaf, and the reasonable negative pressure value is 32kpa and verified.

Oxidation Behavior and Kinetics Parameters of a Lean Coal at Low Temperature Based on Different Oxygen Concentrations

The method of dividing the “three zones” of spontaneous combustion in goaf by oxygen volume fraction is the most widely used and effective method at present. However, the oxygen volume fraction method does not consider the influence of methane concentration in goaf, which is only applicable to low-gas goaf, not high-gassy goaf. In this work, the oxidation behavior and kinetics parameters of a lean coal at low temperatures under five different oxygen concentrations, including methane and its kinetics during low-temperature oxidation, were studied using temperature programming tests and thermogravimetric tests. The results showed that the decrease of oxygen content improves the adsorption capacity of coal to absorb different atmospheres at the initial stage. In the whole reaction process, there is a negative correlation between the strong-to-weak order of exothermicity and adsorption capacity, with a significant increase in apparent activation energy E. A marked hysteresis of the precipitation time of CO and CO2 and a decrease in their precipitation amount and a rise in the initial temperature for the generation of CO and CO2 were found.

Experimental study on the mechanism of radon exhalation during coal spontaneous combustion in goaf

There is a good positive correlation between the high-temperature environment formed by coal spontaneous combustion in goaf and the radon exhalation in coal. The higher the temperature is, the greater the radon exhalation will be. Increasing concentrations of released radon gas will accumulate in an enclosed goaf and ultimately migrate upwards to form a radon anomaly on the ground surface. Based on this principle, the surface-based radon detection method can determine the location of underground hidden heat sources by detecting high-concentration radon areas on the ground. At present, the surface-based radon detection method has been applied in multiple fire zones as an effective technique. However, the research on the mechanism of radon exhalation during coal spontaneous combustion is insufficient, which severely restricts the detection accuracy of heat source locations of coal spontaneous combustion. In this study, radon exhalation from coal samples with different degrees of metamorphism (lignite, long-flame coal, coking coal and lean coal) at different temperatures was measured, and six main factors affecting radon exhalation (moisture, specific surface area, crack development, minerals, temperature, and gas production) were further explored. The experimental results show that with the increase of temperature, the radon exhalation from coal samples increases first and then decreases. The dissolution of radon in water and the adsorption and closure of radon in capillary pores are the main existing ways of radon in coal. When the temperature rises, the radon dispersion caused by pore water evaporation and the radon migration in cracks and pores caused by coal pyrolysis are the main reasons for the significant increase of radon exhalation.

Numerical simulation study on the influence of surface air leakage in shallow thick coal seam on coal spontaneous combustion in goaf

Numerical simulation study on the influence of surface air leakage in shallow thick coal seam on coal spontaneous combustion in goaf

Prediction method of coal mine goaf temperature and its practical application

Spontaneous combustion of coal seams in goaf seriously threatens the development of the coal mining industry. The prediction of goaf temperature is of great significance for mine disaster prevention. Based on the energy conservation equation of floating coal in goaf, the analytical solution of the steady-state temperature field in goaf is derived in this paper, and the temperature of goaf can be calculated simply through a series of physical and chemical parameters. This method is applied to Kaida Coal Mine to calculate the temperature of goaf at the return air side of 46205 working face. The results show that although there is some error between the calculated value and the measured value of the temperature in goaf, the predicted results can reflect the change rule of the temperature in goaf, and provide some guidance for the prevention and control of coal spontaneous combustion in goaf. With the increase of buried depth, the floating coal temperature rises first and then decreases. It is estimated that the maximum temperature of goaf is 27.11 °C, which is located 25m deep in goaf.

Influence of methane on the prediction index gases of coal spontaneous combustion: A case study in Xishan coalfield, China

Lean-oxygen environment caused by methane in high gassy coal mine goaf has a significant influence on the prediction index gases of residual coal spontaneous combustion. The coal sample from Xishan coalfield in China was used to conduct the low-temperature oxidation experiments under different lean-oxygen environments. The experimental results show that different lean-oxygen environments had a significant delay effect on the formation of CO, CO2, H2 and C2H6, and the lower the O2 concentration, the more obvious the delay effect, and the delay effect of methane was greater than that of N2. A lean-oxygen environment caused by methane also had a significant influence on the values of CO/ΔO2 ratio and CO2/ΔO2 ratio. However, when the temperature was < 170 °C, the change of O2 concentration had no significant influence on the value of CO/CO2 ratio, and the relationship between the value of CO/CO2 ratio and temperature T can be accurately expressed by exponential function. The absolute amount of CO, CO2 and C2H6 generated by 1kg residual coal (CCO, CCO2 and CC2H6), which can reduce the influence of air leakage and residual coal mass on prediction index gases, were introduced to predict the spontaneous combustion in high gassy coal mine goaf. Then, the distribution diagrams of CCO, CCO2 and CC2H6 with temperature and O2 concentration were obtained, so as to accurately predict the degree of spontaneous combustion in high gassy coal mine goaf. The research results are of great significance to the prevention of spontaneous combustion in goaf of high gassy mine.

Dynamic evolution of negative pressure impact of cross-cut on oxygen concentration field in coal mine Goaf

For further understanding the coal spontaneous combustion in goaf, the dynamic evolution of the oxygen concentration field influenced by the condition of negative pressure of cross-cut were analyzed. Based on the on-site testing results, the range of the oxidation zone on the headentry and tailentry side is determined as 30 ~ 75 m and 15 ~ 65 m respectively. This paper adopts a new method called “fixed grid, dynamic attribute” to dynamically describe the spatial change of goaf caused by working face advancing. The validated model which developed by field measured data is used to study the dynamic evolution of negative pressure impact of cross-cut on oxygen concentration field in goaf. The results demonstrate that when the cross-cut is located at different positions of three zones of coal spontaneous combustion, the negative pressure of the cross-cut has different impact rules on the distribution of oxygen concentration field. The results are hopeful for providing effective guidance for coal mine fire prevention in goaf.

Prediction and prevention of spontaneous combustion of coal from goafs in workface: A case study

Aiming at forecasting and preventing remnant coal spontaneous combustion in goaf, this thesis conducts determination on the spontaneous combustion tendency of coal seam, simultaneous thermogravimetry and differential scanning calorimetry(TG-DSC) analysis on coal samples, optimization on index gas of spontaneous combustion, and division of spontaneous combustion “three zones” with O2 concentration as the indicator. The conclusions are as follows: the spontaneous combustion period of remnant coal is 1–3 months, so the coal seam is easy to spontaneous combustion. CO and C2H4 are selected as the index gas for forecasting spontaneous combustion in No.12 coal seam and No.12-up coal seam because of their regular evolution tendency in concentration changing with coal temperature and easiness in detecting. As to the spontaneous combustion “three zones” divided by O2 concentration, the depth and width of both heat dissipation zone and left side oxidation zone in the goaf is slightly increased when the “Y” type ventilation is adopted, comparing with the “U” type ventilation, and the asphyxiation zone is extended to about 200 m behind the workface. Pressure balance method and ground fissure sealing are proposed for spontaneous combustion prevention and extinction, which offers some practical experiences for adjacent mine or similar coal seam.

Design of 3D Simulation System for Natural Ignition Law in Gob Area of Multi-source and Multi-sink

In order to comprehend the law of spontaneous combustion in “multi-source and multi-sink” goaf of coal mine, and to provide the basis for the prediction of early fire in goaf, the division of three zones of spontaneous combustion in goaf and the formulation of technical measures for fire prevention and extinguishing, a three-dimensional simulation system of spontaneous combustion law in goaf of “multi-source and multi-sink” coal mine is designed in this paper. The system uses energy conservation equation, Fick‘s law and mass conservation law to establish multi-source and multi-sink goaf flow field, oxygen concentration field, gas temperature field and caving coal and rock temperature field coupled mathematical model. The model is solved and programmed by using VB language mathematical model, which realizes the visual display of simulation results. The system is used to simulate the II929 mined-out area of Luling Mine, and good application results are obtained. The system has good operability and improves the calculation efficiency. It provides theoretical support for the prevention and control of spontaneous combustion in goaf of “multi-source and multi-sink” working face.

Micro-particles stabilized aqueous foam for coal spontaneous combustion control and its flow characteristics

The goaf is the location where coal mines are most prone to coal spontaneous combustion, 60 % of the spontaneous combustion fire occur in the goaf. The coal has a greater crushing degree at the top of the goaf, where the heat accumulation is not easy to dissipate and mine fires are more likely to occur. In order to prevent coal spontaneous combustion in goaf efficiently and comprehensively, the uniform and dense micro-particles stabilized aqueous foams with the bubble diameter of 350–400 micrometers are prepared in batch mode using a home-made foam generating column with an internal hollow tube. The micro-particles can disperse well in surfactant diluents with the concentration of 0.25 wt.% and have strong wettability with the contact angle of 82.2°. Similar simulation experiments for flow characteristics indicated that the foam fluid does not appear to flow as low as ordinary cement paste, the diffusions in the Y direction and Z direction occur simultaneously, and the whole high fracture of loose gangue heap can be fully accumulated and seeped by foam fluid. Based on the micro-element force analysis of foam fluid in highly inclined fractures, the relationship equations between pressure difference, time, shear force and dynamic viscosity under different fracture dip angles and azimuth angles are derived and amended. The error was compared with the residual measurement points, and the error value is 0.05 %–9.72 %, indicating the amended fitting formula has universal applicability.

Research on coupling law of gas and coal spontaneous combustion in goaf of high gas mine

Research on coupling law of gas and coal spontaneous combustion in goaf of high gas mine