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In recent years, abnormal CO gas overruns have often occurred in coal mining workings. CO overruns were thought to be caused by the underground blasting work or spontaneous combustion of coal seams; however, minimal attention has been given to the causes of the desorption and release of adsorbed CO in the coal seams. Additionally, insufficient research has been conducted on the generation, distribution and adsorption and desorption characteristics of protogenetic CO in coal seams. Therefore, a self-built comprehensive testing system for coal seam adsorption and desorption was used to study the characteristics of the depressurization desorption and thermal desorption of coal with different degrees of metamorphism during coal seam mining. The results showed that under isothermal conditions, the amount of CO adsorption and desorption of coal samples increased with increasing pressure; under temperature rise conditions, the gas adsorption-desorption was in a dynamic equilibrium process under certain conditions. When the temperature increased, the equilibrium was beneficial to the desorption direction. The initial temperature range of CO production at different equilibrium pressures was 45–55°C. With increasing pressure, the initial temperature point of CO gas production moves forward and was significantly lower than the initial temperature of coal spontaneous combustion. Our research results further supplement the source of underground protogenetic CO gas and provide theoretical support for the accurate prediction of CO coal spontaneous combustion. [ABSTRACT FROM AUTHOR]

Conveyor belt fires are the most serious fires that occur exogenous mine fires. To study the thermal characteristics of the PVC conveyor belt during the fire process, the softening characteristics of the conveyor belt underground in the mine were simulated by using the temperature rise oxidation system. Based on the C600 microcalorimeter, the oxidation heat release law of the PVC conveyor belt and pulverized coal with different softening temperatures was studied at an environmental range of 40–500°C, and the combustion law, heat release and heat absorption, HRR,combustion stages and activation energy were analyzed. The results show that with increasing softening temperature, the law of heat absorption and heat release of the PVC conveyor belt in the initial stage of the independent reaction is opposite, while the heat absorption and heat release in the coupling with pulverized coal increase gradually, and 106% and 107% more heat is released in the rapid development state than in the independent reaction state. The change rule of the heat release acceleration of the PVC conveyor belt remains basically the same whether it is alone or coupled with pulverized coal. The maximum difference in heat release acceleration increases with increasing softening temperature. According to the division of the combustion stages of the conveyor belt according to the heat flow value, when the PVC conveyor belt reacts alone, the temperature range of the heated softening zone is approximately 140°C smaller than when it is coupled with pulverized coal, and the temperature range of the melting pyrolysis zone is expanded by 100°C.It shows that when the conveyor belt is coupled with pulverized coal, fire is more likely to occur and the fire risk is greater. The average HRR at the softening temperature of 100°C is the largest, the ignition time is the shortest, and the danger is the greatest. The activation energy decreases with increasing softening temperature when it is coupled with pulverized coal, indicating that the higher the softening temperature is, the more likely an oxidation reaction will occur. The heat release characteristics and combustion stages division of the conveyor belt proposed in this paper have certain guiding significance for the replacement and maintenance of mine conveyor belts and the prevention and control of mine fires. [ABSTRACT FROM AUTHOR]

An efficient, environmentally friendly, and economical polyphosphate/nitrogen-containing composite inhibitor (APNI) has been developed to prevent coal spontaneous combustion (CSC) disasters. Using temperature rise experiments during coal spontaneous combustion, mercury pressure experiments, and Fourier transform infrared spectroscopy (FTIR), the samples treated with the APNI were compared with those treated with MgCl2 and NH4H2PO4 inhibitors, and the inhibitory effects of the three inhibitors on CSC were studied. The results showed that the APNI effectively limited the reactions between the coal and oxygen, reduced the amount of CO gas generated, sealed most of the cracks, large pores and mesopores in the coal, and reduced the number of active functional groups in the coal. The APNI was more effective in preventing CSC than MgCl2 and NH4H2PO4. [ABSTRACT FROM AUTHOR]

Free radicals and metal ions are key factors causing coal spontaneous combustion. In order to effectively suppress coal spontaneous combustion, experiments were conducted using luteolin as an inhibitor, luteolin is abbreviated as LUT. The influence of different concentrations of LUT on the spontaneous combustion heat characteristics of coal was tested using a C600 high-precision microcalorimeter, and the inhibition mechanism was inferred by FTIR. The experimental results show that LUT is an effective coal oxygen inhibitor, under the same action conditions, different concentrations of LUT can absorb heat to different degrees, delay the initial exothermic temperature of coal, prolong the heat absorption phase of coal. Compared with raw coal, 6 wt% LUT absorbs the most heat, the starting exothermic temperature is delayed by 46°C, and the activation energy is increased by 47.89 kJ/mol, the functional group -OH content decreased by 43.4%, -CH3 decreased by 32.1%, -CH2-decreased by 37.76%. Based on this, the mechanism of inhibition is inferred, LUT not only removes free radicals (ROO•) during the chain initiation stage and captures free radicals (•OH) in the reaction chain but also chelates metal ions to inhibit the catalytic effect of metal ions during the free radical reaction, which can play a dual role in preventing free radical generation and interrupting the free radical chain reaction. The results of the study can provide a novel, environmentally friendly and effective way to prevent the spontaneous combustion of coal. [ABSTRACT FROM AUTHOR]

To study the variation laws of the mechanical properties of coal with different oxidation degrees, coal samples were subjected to constant temperature oxidation at 80°C, 120°C, 160°C and 200°C by using a coal oxidation spontaneous combustion test system. Through a uniaxial compression experiment, the variation laws of mechanical parameters, failure characteristics and energy dissipation law of coals with different oxidation degrees were analyzed and obtained. The study shows that the stress – strain curves of coal with different oxidation degrees vary in different stages. The peak stress, elastic modulus, secant modulus and Poisson's ratio appear to decrease to different degrees with the deepening of oxidation, and the peak strain increases. The cracks on the surface of the coal samples increase and become more with the deepening of oxidation, the exothermic characteristics of the coal samples decrease, and the failure characteristics of the coal samples change from single shear-type failure characteristic to conjugate shear-type characteristic and then to shatter-type failure characteristic. With an increasing degree of oxidation, the total energy required for coal destruction gradually decreases, the conversion rate of total energy into elastic energy decreases, the dissipation energy gradually increases, and the release rate of elastic energy and the increase rate of dissipation energy gradually slow down after the peak strain. [ABSTRACT FROM AUTHOR]

Transition metal ions in coal can catalyze the oxidation of coal, reduce the activation energy of the coal-oxygen reaction, and promote spontaneous combustion. Adding a metal chelating agent to coal can form chelates with metal ions so that the metal ions lose their catalysis. A green metal chelating agent, L-malic acid (L-MA), was proposed in this study. A C600 microcalorimeter was used to study the inhibitory effect of L-MA on spontaneous coal combustion. The results show that under the same temperature-programmed conditions, the heat absorption capacity of coal treated with L-MA solution is higher than that of raw coal, but the heat release capacity of treated coal is lower. With increase in the concentration of the L-MA solution, the inhibitory effect first increased and then decreased. The maximum heat flow of raw coal is 292 mW, and the maximum heat flow of coal samples treated with malic acid is 246 mW, 237 mW, 232 mW, 240 mW and 255 mW, respectively. The maximum heat flow of 15 wt% coal sample is 20.55% lower than that of raw coal. Based on the thermal analysis, kinetic theory, and experimental data, the activation energy of each coal sample can be calculated. The activation energy of raw coal is the lowest, and the activation energy of each group first increases and then decreases with increasing L-MA concentration, which is in agreement with the law of heat flow data. Combined with the microscopic process of coal oxidation at different temperature stages, the mechanism of L-MA inhibiting spontaneous coal combustion was explored. In summary, L-MA can effectively reduce the concentration of related free radicals in the chain reaction of spontaneous coal combustion and inhibit spontaneous coal combustion. [ABSTRACT FROM AUTHOR]

Gob is one of the most serious areas of coal spontaneous combustion. With the continuous increase of mining depth, the residual coal in gob bears increased axial stress, the rise of ground temperature, and the degree of fragmentation of mining coal and rock continues to increase, the external water in the mining process changes the water content of broken residual coal, under the influence of multiple factors, the prevention and control situation of coal spontaneous combustion in gob is becoming more serious. Based on the actual accumulation environment of residual coal in gob, this paper carried out the oxidation and temperature rise experiment of broken coal under the condition of water bearing and pressure. The variation laws of oxidation characteristic parameters such as outlet oxygen concentration, oxidation derived gas, oxygen consumption rate and heat release intensity were obtained. It is found that with the increase of water content of coal sample, the water content first promotes and then inhibits the oxidation process of coal. It is found that after water molecules form a relatively stable hydrogen bond with oxygen-containing functional groups, the total energy of the two-phase materials decreases, and the reason for the decrease of wetting heat release is analyzed. The influence mechanism of axial stress loading on coal spontaneous combustion oxidation process is studied. It is found that the increase of axial stress first promotes and then inhibits the process of coal spontaneous combustion. [ABSTRACT FROM AUTHOR]

The risk of coal spontaneous combustion in goaf is one of the disasters in coal mining, ventilation and extraction often aggravate air leakage from the goaf. Due to the unclear rule of expansion law and air leakage, the risk space for coal spontaneous combustion continues to occur. To investigate the influence of ventilation and extraction on the evolution of the risk space of coal spontaneous combustion (CSC) in goaf, further reveal the characteristics of air leakage and extraction in goaf and obtain the expansion law of CSC risk space. A three-dimensional model of goaf under surface drilling and gas extraction was developed. Using FLUENT numerical simulation software, taking a coal mine in Anhui Province, this study analyzes the influence factors, evolution law, and influence characteristics of CSC through field observations and numerical simulation. The research indicates that ventilation keeps the risk space of CSC expanding. The extraction of single drilling showed a local space expansion, while the extraction of double drilling shows the overall space expansion of the goaf. The air leakage flow path in goaf, air flow velocity vector in working face, gas concentration loss, and gas extraction characteristic parameters are determined. The loss of air leakage along the working surface meets four-stage: "strong in – flow - mixed flow – steady inflow – sudden outflow." It can be determined that the extraction intensity of single drilling should be greater than 34.8 m3/min, and the double drilling should be greater than 18.7 m3/min. The relationship between the coupling influence of ventilation and extraction and the expansion law of CSC risk space is determined, and the maximum risk space width of CSC can be predicted. The research results are of guiding significance for CSC prevention and gas efficient extraction. [ABSTRACT FROM AUTHOR]

As coal mining continues to progress to deeper levels, the temperature of the coal and rock continues to rise, causing coal spontaneous combustion disasters to become increasingly prominent. This paper studies the spontaneous combustion characteristics of coal in a high temperature environment before and after coal seam mining. The results were as follows: 1) Before mining, under the action of a constant ground temperature, the deep coal seam continuously and slowly released heat, and the higher the ground temperature was, the more heat was released. 2) During mining, after air entered, the coal samples initially maintained the continuous slow heat release. With the continuous entry of air, the coal samples were in an endothermic state. Higher ground temperature provides favorable conditions for coal sample heat absorption and coal spontaneous combustion. 3) When the local temperature rises, the associated hydroxyl groups in the coal sample are gradually activated and become free hydroxyl groups that are more prone to chemical reactions; the methyl groups are destroyed to generate more methylene groups; the aromatic hydrocarbons change significantly after oxygen supply. The long-term high ground temperature environment could lead to an increase in the chemical activity of coal. [ABSTRACT FROM AUTHOR]

Kilometer-deep mines have become the new norm in coal mining. To study the influence of high stress-high ground temperature coupling conditions in deep mines on the oxidative exothermic characteristics of coal, this paper pre-treats coal samples under different stress and different temperature coupling conditions, and then conducts oxidation temperature tests on coal samples. By analyzing the parameters of initial exothermic temperature, exothermic heat and apparent activation energy of coal, the influence law of stress-temperature coupling on the oxidative exothermic properties of coal was obtained. The results show that when the initial temperature is 313 K, the initial exothermic temperature of coal decreases first and then increases with increasing initial stress. The exothermic heat and activation energy change trends in the initial exothermic stage are the same, both show atrend of first decreasing and then increasing, and both reach their minimum values at 10 MPa. When the initial stress is 5 MPa, the initial exothermic temperature of coal first increases and then decreases with increasing initial temperature. Both the exothermic and apparent activation energy of coal in the initial exothermic stage showed atrend of increasing and then decreasing, and reached the inflection point at the initial temperature of 323 K. The research results provide theoretical support for the prevention and control of spontaneous combustion in deep mines. [ABSTRACT FROM AUTHOR]

As the depth of coal mining continues to increase, the weight of the overlying strata and the ground stress on the residual coal in goaves also increase. At the same time, the temperature of the coal rocks continues to rise, and the high ground temperature environment of the mining and heading faces becomes more severe. As a result, coal oxidation and spontaneous combustion disasters become more prominent. In this work, an anaerobic heating experiment of coal under the thermal-mechanical coupling effect was performed. The effects of thermal-mechanical coupling on the thermal stability of coal were studied by analyzing parameters such as the heat flow peak temperature, endothermic peak value, heat absorption, and activation energy. The results showed that the heat flow peak temperature exhibited hysteresis as the initial temperature and the initial stress increased. At the same time, the endothermic heat flow peak value and the heat absorption decreased. Under the same initial stress, the activation energy gradually decreased as the initial temperature of the coal sample increased; the higher the initial stress, the lower the decrease in the activation energy. At the same initial temperature, the activation energy first increased and then decreased as the initial stress increased; the higher the initial temperature, the more sensitive this change in the activation energy was to stress. In this study, the influence of thermal-mechanical coupling on the thermal stability of coal was obtained. This work provides on-site guidance for the prevention and control of spontaneous coal combustion in deep mining. [ABSTRACT FROM AUTHOR]