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• Inhibition of spontaneous coal combustion is best when the wall-to-core ratio of microencapsulated inhibitors is 4:1. • Reduction of free hydroxyl groups in coal samples after addition of microencapsulated inhibitor. • The addition of inhibitors increases the interaction energy of the system. • The hydroxyl group in the inhibitor interacts with the oxygen atoms in the water molecule more strongly. In order to solve the shortcomings of traditional inhibitors, which are easy to be interfered by the outside world during the inhibition process and the active ingredients are easy to be oxidized and invalidated, microencapsulated inhibitors were developed. In this study, we prepared microencapsulated inhibitors of varying wall-to-core ratios using a composite phase of polyethylene glycol 20,000 (PEG-20000) and octenyl amyl succinate (OSAS) as the wall material and a lauryl glucoside (APG-12) and butyl hydroxyanisole (BHA) phase as the core material. After thoroughly mixing the microcapsule inhibitor with coal samples, simultaneous thermal analyzer (TG/DSC) and a temperature-programmed system were used to evaluate the resisting qualities of the produced microencapsulated inhibitors. The results of the temperature programmed experiment showed that the overall CO release from the blocked coal samples was less than that of the original coal. According to thermogravimetric results, the most effective inhibition occurred when the wall/core ratio of the microcapsule inhibitor was 4:1. This also resulted in a reduction of the maximum coal weight loss rate from 1.34 to 0.96 %/min and an increase in the maximum coal weight loss temperature from 477.4 to 507.6 °C. The microencapsulated inhibitor melts in the wall at 57.4 °C, enabling temperature-sensitive intelligent control of core release. Following heating the raw and inhibited coal samples to 100 and 200 °C, respectively, Fourier infrared spectroscopy was conducted. At these temperatures, the amounts of ether bonds increased by 20.4 and 22.6 %, and the number of free hydroxyl groups decreased by 12.8 and 2.7 %, respectively, in the inhibited coal samples. Finally, molecular dynamics theory was applied to investigate the inhibitory mechanism. The prepared microcapsule retardant effectively inhibited the spontaneous combustion reaction of coal, suggesting this microcapsule inhibitor could be manufactured as a novel inhibitor for coal spontaneous combustion. [ABSTRACT FROM AUTHOR]

Gel-stabilized foam serves a critical role in preventing spontaneous combustion of coal by impeding heat transfer from the coal-fire area to adjacent safe areas. To elucidate the thermal characteristics of gel-stabilized foam, the microstructure and heat-transfer characteristics were investigated. The results revealed that gel-stabilized foam was an accumulation system of many stable and closed bubbles, and there was a layer of gel structure on the bubble surface. This gel layer endows the bubbles with exceptional heat-insulation capability by effectively encapsulating air. To further analyze the relationship of heat-transfer characteristics and foam structure parameters, a theoretical thermal-conductivity model was established to revel the thermal characteristics of gel-stabilized foam. Moreover, the experimental tests were conducted to verify the accuracy of theoretical model, and found that the fitting errors were around 8 %, affirming the model's suitability for gel-stabilized foam. Notably, the theoretical model demonstrated that foam's thermal-conductivity was only monotonically related to foam expansion ratios in theory. In addition, the heat-insulation experiments indicated that the heat-transfer rate of foam depended not only on the thermal-conductivity but also on the foam's stability, both of which were affected by the expansion ratio. Hence, the effective heat-insulation time (EHT) was proposed to assess gel-stabilized foam's heat-insulation characteristics. The heat-insulation ability tests results showed that EHT values initially increased and then decreased with rising foam expansion ratios, primarily influenced by the volume of air encapsulated within the foam. Particularly noteworthy were the test results indicating that gel-stabilized foam with an expansion ratio of 10 times and a stacking thickness of at least 15 cm exhibited excellent heat-insulation capability against heat transfer from the spontaneous combustion zones. The research may provide a theoretical foundation and offer guidance for the prospective utilization of gel-stabilized foam in coal mines. • A model was established to analyze thermal characteristics of gel-stabilized foam. • The forecasting method of thermal-conductivity of gel-stabilized foam were proposed. • Effective heat-insulation time was employed to reveal foam's heat-insulation ability. • The prevention mechanism of foam to spontaneous combustion of coal was summarized. [ABSTRACT FROM AUTHOR]

Safety and environmental problems caused by coal mining and utilization are becoming increasingly serious. Studies in the coal spontaneous combustion characteristics based on constant temperature difference guidance method, which is of great significance for mine safety prevention and environmental protection. In this paper, a new method, Constant Temperature Difference Guidance Method, was developed in this paper for studying coal spontaneous combustion characteristics. By creating a constant temperature difference between coal temperature and ambient temperature, self-heating of coal is guided in this new method, which largely improves the efficiency and success rate of coal spontaneous combustion testing. Through analysis, this method was proved capable of providing a comprehensive description of coal's low-temperature oxidation characteristics. Besides, through changing different values of the temperature difference, various factors of low-temperature coal oxidation under adiabatic environment can be calculated. Additionally, spontaneous combustion point and ignition point can be obtained by analyzing time-temperature curve of coal oxidation. These two points along with the duration to achieve these two points were used in this paper to develop a risk index for evaluating coal spontaneous combustion propensity. [ABSTRACT FROM AUTHOR]

To investigate the impact of stratified mining on the spontaneous combustion characteristics of lower coal in thick coal seams, an analysis was conducted on the macro pore structure, temperature rise, oxygen consumption characteristics, chemical structure, surface chemical properties, and functional group distribution of the upper and lower stratified coal samples (LSC, LSR) from the LinSheng Mine 1202 re-mining face. Post re-mining, the specific surface area, average pore diameter for adsorption, micropore volume, and mesopore volume of LSR showed a significant increase compared to LSC. The maximum mass loss rate for LSR was approximately three times that of LSC, and the characteristic temperature of LSR was lower. When the volumetric fraction of oxygen exceeded 12%, the oxygen consumption rate and CO generation rate of LSR surpassed those of LSC. The alkyl carbon content in LSR was 2% lower compared to LSC, while the oxygenated carbon content was higher by 4.37%. The oxygen content in LSR and the O/C ratio were higher than those in LSC. The structural order of LSR was lower by 11.3%, and the oxygen-containing functional groups were higher by 1.15%. These findings suggest that stratified mining increases the spontaneous combustion risk of lower coal layers. This study underscores the need for careful consideration of mining strategies to mitigate potential risks. [ABSTRACT FROM AUTHOR]

• The mechanism by which diphenylamine inhibits the spontaneous combustion of coal has not yet been studied by anyone. • The spontaneous combustion of coal and the inhibition process of diphenylamine has been studied more systematically. • Two complementary analytical tools are applied to predict the active site of the reaction and the results are more reliable. • It is demonstrated that the capture of hydroxyl radicals by diphenylamine has no transition state at the current level of calculation. Diphenylamine has been applied to suppress coal spontaneous combustion with good results, but its microscopic reaction mechanism is not clear. In this paper, the free radical reaction process of coal spontaneous combustion is calculated more systematically, and the quantum chemical method is applied to analyze in detail the process of diphenylamine depletion of reactive free radicals in coal from three perspectives: hydrogen atom transfer, direct radical capture, and regeneration cycle chain. By destroying the molecular structure of coal to generate free radicals as the initial condition of coal spontaneous combustion, the oxidation process of the free radical chain reaction was analyzed, the thermodynamic data of all reactions were calculated, the microscopic mechanism of free radical capture by diphenylamine was revealed, and the transition state structure model of the reaction process was given. The active sites of each reactant were determined by quantitative molecular surface analysis, the spontaneity of the reaction was measured by the free energy change, and the interaction relationship between different conformations was graphically represented by applying the IRI (interaction region indicator) method. The results show that most of the free radical reactions during the spontaneous combustion of coal are exothermic, and they provide heat for the spontaneous combustion of coal, which can react directly with oxygen when accumulated to a certain temperature. Diphenylamine can break the N-H bond, allowing hydroxyl radicals and carbon radicals to obtain hydrogen atoms to form stable compounds, and the generated diphenylamine radicals can reduce the content of free radicals in coal by direct capture. In addition, the process of diphenylamine inhibition of coal spontaneous combustion has a circular regeneration chain, which can indeed effectively reduce the content of reactive radicals and inhibit the spontaneous combustion of coal, which is reflected in the macroscopic level of reducing the generation of coal spontaneous combustion indicator gas, which is consistent with the experimental results. [ABSTRACT FROM AUTHOR]

The inhibitory effects of two ionic liquids (ILs), ethyltributylphosphonium bromide ([P4,4,4,2]Br) and the hydroxyl functional 1-hydroxyethyl-3-methyl imidazolium tosylate ([Hemim]Tos), on spontaneous combustion of coal were investigated and compared. The changes in various active functional groups of coal under IL inhibition were measured by in situ FTIR and analysed semi-quantitatively. Additionally, the impact of the ILs on the heat release rate of coal oxidation was examined by a micro-calorimetric technique. Subsequently, kinetic calculations were employed to elucidate the changes in the intrinsic mechanism of coal oxidation in the presence of ILs. The results revealed that [P4,4,4,2]Br and [Hemim]Tos exhibited distinctive inhibition characteristics on spontaneous combustion of coal. [P4,4,4,2]Br significantly reduced the associative hydroxyl group of coal by destroying the hydrogen bonds and forming stable ether structures. This kind of IL manifested significant inhibition of heat release at the slow oxidation stage of spontaneous combustion of coal. On the other hand, the reductive [Hemim]Tos afforded hydrogen ions from the functionalised O-H bonds to eliminate the reactivity of the peroxide radicals. This led to a reduction in the formation of C=O double bond intermediates in the transition and rapid oxidation stages at higher temperatures. [ABSTRACT FROM AUTHOR]

ABSTRACT In order to study the variation of electrical parameters in the process of spontaneous combustion of coal, first, 9 characteristic temperature points of 5 kinds of coal samples at low temperature oxidation stage and high temperature spontaneous combustion stage were obtained based on temperature programmed experiment and thermogravimetric experiment. According to these experiments samples at characteristic temperature points were prepared. Then, the complex impedance parameters of each coal sample are measured at the alternating current of 20 Hz to n × 106 Hz, and the volume resistivity and the complex permittivity of the coal sample are obtained by calculation. Finally, the volume resistivity temperature model and the complex dielectric constant temperature model of coal samples are obtained by fitting the electrical parameters at 100 kHz test frequency. The results showed that the volume resistivity of coal samples decreased rapidly in the mid-low frequency and slowly in the mid-high frequency. Under the fixed test frequency, the volume resistivity of coal samples rises first and then decreases with the increase of temperature. Both the real and imaginary parts of the complex relative permittivity of coal samples decrease with the increase of temperature, and the slope of the curve decreases gradually. Highlights • Resistivity of coal decreases rapidly in mid-low frequency and slowly in mid-high. • At fixed frequency coal's resistivity rises first and then decreases with temperature. • The real and imaginary parts of coal relative permittivity show a same change rule. • Permittivity decreases with increasing temperature; the slope gradually decreases. [ABSTRACT FROM AUTHOR]

Spontaneous fire hazard in underground collieries threatens the safe production of coal. Thus, globally, there is a growing interest in identifying and adapting novel methods for inhibiting the spontaneous combustion of coal. Although Cl-containing minerals exhibit retardant properties in the low-temperature range, they fail to control the combustion of coal at high temperatures. Therefore, to control the fire hazard caused by spontaneous combustion of coal at high temperatures effectively, phosphates and MgCl 2 were innovatively used as synergistic inhibitors for suppressing self-ignition of coal. Laboratory tests such as thermal analysis, infrared spectrum analysis and oxidation analysis were performed to evaluate the behavior of coal samples before and after treatment. Experimental results indicated that the combined utilization of MgCl 2 , Zn 3 (PO 4 ) 2 , and (NH 4 PO 3 ) n could significantly reduce the heat emission during coal combustion, as well as the yield rate of CO. The optimal effect can be obtained with a Cl-to-P ratio of 2:1. In addition, functional groups such as OH and CH 2 in treated samples decreased markedly. Hence, underground coal fire can be prevented more effectively using a combination of Cl and P, instead of using Cl-based retardants alone. [ABSTRACT FROM AUTHOR]

An investigation of the effects of igneous intrusions on the physicochemical structure and spontaneous combustion characteristics of coal is important for safe production in coal mines. In this study, unaltered coal and thermally-altered coal affected by igneous intrusions were collected from Daxing Mine. The mineral and ash composition, surface functional groups, surface morphology and pore structure were characterized by XRD, XPS, SEM, N 2 adsorption and mercury intrusion porosimetry. The spontaneous combustion propensity of coal samples was investigated using oxidation kinetics experiment. Mineral and ash composition analysis revealed that igneous intrusions increased the relative contents of calcite and CaO in the thermally-altered coal. The results of XPS tests indicated that the content of C C/C H slightly increased and an obvious π − π ∗ shake-up satellite peak appeared in the thermally-altered coal, but that the contents of C O , C O, and COO showed a decreasing trend. Compared with the pore structure of the unaltered coal, higher porosity, larger pore volume, and larger average pore diameter were found in the thermally-altered coal. Moreover, more pores with diameter >20 nm were formed due to igneous intrusions, which would improve the transport capacity of O 2 in pores to react with active sites on pore surfaces in the thermally-altered coal. Moreover, igneous intrusions increased the O 2 consumption rate of the thermally-altered coal, and decreased its crossing point temperature and spontaneous combustion propensity evaluating index I . This study concluded that igneous intrusions improved the spontaneous combustion risk of Daxing bituminous coal. [ABSTRACT FROM AUTHOR]

Colloidal gas foam concrete (CFC) was successfully prepared by high water retention of colloidal gas aphrons (CGA) and cement slurry. The preparation conditions of colloidal gas foam concrete with optimal performance and the addition ratio between its components were determined based on single-factor experiments and orthogonal tests. Then, the compressive strength, water retention, water content, and ability to inhibit coal spontaneous combustion of colloidal gas foam concrete were systematically studied. CFC's performance test to prevent spontaneous combustion of coal showed that CFC could form a hard protective shell of oxygen barrier on the surface of coal, thus inhibiting spontaneous combustion of coal. In addition, compared with traditional aqueous foam concrete (AFC), the water content of CFC increased from 0.65 to 1.40, and the protective shell formed by CFC could still retain some water after seven days without cracking. The programmed temperature rise experiment showed that CFC inhibited coal spontaneous combustion better than traditional AFC, and the cross-point temperature of coal treated by CFC was higher. This paper provides a high-performance mine fireproof material, which is important for the safe and efficient production of mines. • Analysis of the formation mechanism and characteristics of colloidal gas aphrons. • Successful preparation of colloidal gas foam concrete (CFC). • Study of the properties of CFC to prevent spontaneous combustion of coal. [ABSTRACT FROM AUTHOR]

• New dry water material is prepared for fire prevention and extinction in coal mines. • Nano-aluminum hydroxide is added as modifiers to improve the physical and chemical properties. • A preparation parameter suitable for nano-aluminum hydroxide-modified dry water was determined. • Nano-aluminum hydroxide-modified dry water shows the best flame-retardant and smoke-suppression properties. This work aimed to effectively prevent the spontaneous combustion of coal in goafs by preparing a type of dry water material with a solid-in-liquid structure through the mechanical stirring method, with nano-aluminum hydroxide aqueous solution as the core material and hydrophobic nano-silicon dioxide as the wall material. The effects of solid-to-liquid ratio, stirring time, and mass concentration of nano-aluminum hydroxide on the particle size and microstructure of dry water were studied. Results showed that the prepared dry water powder was the most uniform and fine when nano-silica, nano-aluminum hydroxide, and water were mixed at a mass ratio of 5:0.75:49.25 and stirred at a speed of 23,000 r/min for 25 s. The samples were characterized by using a temperature-programmed oxidation device, a thermogravimetric analyzer, and a Fourier-transform infrared spectrometer, and the inhibition performance of dry water was evaluated. Results revealed that dry water effectively slowed the oxidation rate of coal and inhibited the release of CO in the low-temperature environment, and the cross-point temperature increased from 125.1 °C to 155.4 °C for raw coal. In a high-temperature environment, dry water delayed the process of spontaneous combustion of coal, the temperature leading to the maximum mass increased from 308.6 °C to 369.4 °C, and the ignition temperature rose from 458.2 °C to 484.7 °C. In addition, the dry water material can inhibit the oxidative decomposition of aliphatic hydrocarbons and the transformation of oxygen-containing functional groups in coal samples, thus indicating, from a microscopic level, that it has good inhibition performance. [ABSTRACT FROM AUTHOR]

The heat release of coal oxidation lead to the thermal decomposition of carboxylic groups, which include carboxylic acid and carboxylate. However, few researchers have studied the effect of the decomposition of intrinsic carboxylate structure on coal self-ignition process. In this work, different coal samples were selected and treated with alkali solutions to form organic carboxylate structures, and the thermal decomposition of the raw and alkali-treated coals followed by the room temperature oxidation process were analyzed. The effect of the carboxylate structures on the thermal behavior, elemental distribution, and functional groups of coal was also studied by means of TGA, FTIR, XPS and EPR. The results showed that the carboxylic groups in coal were transformed into carboxylate structures by ion exchange. In addition, highly reactive free radical active sites were produced and accumulated along with the decomposition of carboxylates, thus accelerating the self-heating of coal. In the room-temperature oxidation experiment, the temperature of alkali-treated Wulan coal was spontaneously raised by 13.9℃, while that of raw coal was 4.3 ℃. The results showed that the thermal decomposition of organic carboxylate played an important role in promoting the spontaneous combustion of coal, and acid pretreatment could be a potential method to effectively inhibit the coal self-ignition process. • Alkali-treated sample was found with higher reactivity in low temperature oxidaiton. • Opposite effect of carboxylate was found at different temperatures in oxidation. • Carboxylate in coal remarkable promoted the generation of free radical active sites. • Carboxylate has a greater effect than carboxylic acid in low temperature oxidation. [ABSTRACT FROM AUTHOR]

The fire of coal pillars caused by spontaneous combustion in contiguous coal seams at the Dongrong2# colliery in China was examined. The reasons of spontaneous combustion of coal pillars in 16# coal seam were investigated. Based on testing results, the scope of high temperature was judged. To deal with the problem of significant air leakage together with a large fire area and the hidden fire source easily re-ignite, a series of key techniques for extinguishing the fire of coal pillars was put into practice. These mainly included plugging air leakage channel, high-flow injection of liquid nitrogen, and infusion of a large quantity of foam inhibitor into flame locations by drillings. The results showed that these integrated measures rapidly extinguish the fire of coal pillars, reduce carbon monoxide (CO) concentration from 1.6% to about 0.001% and temperature in the closed area of 16# coal seam from 81℃ to less than 20℃. In a word, the fire of coal pillars is successfully controlled in contiguous coal seams, which protect the safety of personnel and equipment. [ABSTRACT FROM AUTHOR]

The heat generated from the reactions of oxygen-containing functional groups in coal has been studied using organic chemistry and quantum chemistry analysis methods. Structural models of the oxygen-containing functional groups in coal were established and used to analyze the reactions of these groups during spontaneous combustion. The Gibbs free energy and enthalpy changes associated with these reactions were determined using quantum mechanical analysis, and the results indicated that the dehydration and dehydrogenation reactions of the hydroxyl groups in coal were only mildly exothermic, whereas reactions involving the oxidation of the carbonyl groups were much more exothermic. In contrast, reactions resulting in the generation of carbon monoxide were endothermic. By comparing the heat release characteristics of the reactions of the oxygen-containing functional groups with the levels of oxygen consumption and gas production, as well as temperature profiles of the reactions, it was concluded that the decomposition of oxygen-containing functional groups is critical to the production of heat during the initial stages of the spontaneous combustion of coal and that oxidation does not occur during this period. These results also explain why the temperature of coal rises slowly during the initial stages of its spontaneous combustion. [ABSTRACT FROM AUTHOR]

Coal fires originate from coal spontaneous combustion caused by oxidation starting even at low temperatures. In order to evaluate the heating and oxidation of coal placed inside a container, a Temperature-Programmed System (TPS) is used under various flow and oxidation conditions for temperatures ranging from 40 to 250 °C. As the coal samples are heated in the container within the TPS, the concentration histories of the gaseous products are measured as well as the temperature history at the center of the container. The Crossing-point Temperature (CPT) is the temperature (temperature and corresponding time) at which the increasing coal temperature is equal to the increasing oven temperature within the TPS. We have developed energy and oxygen mass conservation equations for the coal pile in a container inside the TPS oven assuming uniform conditions for temperature and oxygen concentrations, both assumptions partially justified because the heating rate in the oven is very low (1 °C/min). By subtracting the convective heat from the thermal inertia of the coal pile in the energy equation, we have obtained from the experimental data the heat owing to oxygen reaction or moisture evaporation. From the oxygen conservation and measurements, we have determined apparent activation energy and pre-exponential factor for oxidation assuming that oxidation is proportional to oxygen concentration. This information is useful for the mathematical modeling of oxidation and heating in the present experiments. Subsequently, the energy and mass conservation equations were solved after being transformed to non-dimensional form, which shows that four dimensionless parameters control the heating of coal in the present experiments. Only three of these parameters are examined in detail, namely a dimensionless flow time, a heat release parameter B , and a Damkohler number Da whereas a moisture parameter is discussed qualitatively. Based on the present analysis and data, four stages are identified: (I) initial heating with essentially no reaction or evaporation, (II) evaporation period with essentially no reaction, (III) an unsteady accelerated oxidation period during which crossover may occur and (IV) a heating late period where all the oxygen reacts inside the container. [ABSTRACT FROM AUTHOR]

To solve the problem of poor effect of plugging air leakage in the prevention and control of coal spontaneous combustion by traditional inorganic solidified foam, Janus-type composite solidified foam (JCSF) was proposed in this study. An ultra-stable aqueous foam (UAF) was synthesized via the modification of the gas-liquid interface by forming a "Janus bilayer" of hydrophobic nano-silica and hydrophilic polyvinyl alcohol. Different techniques were used to study the stability of UAF. In addition, by using non-combustible inorganic materials such as cement and fly ash as the matrix and organic materials as the reinforcement, JCSF was synthesized by the prefabricated foam method, and its formulation was optimized by the response surface methodology. The stability test of UAF indicated that the "Janus bilayer" could effectively inhibit the Ostwald ripening, continuous coalescence, and drainage of the foam. The air leakage plugging efficiency, flame retardancy, fire extinguishing, and stacking characteristics showed that JCSF combined the advantages of traditional inorganic solidified foams and reactive polymer foams. It also showed a higher air leakage plugging efficiency, lower heat production, excellent fire prevention and extinguishing, and strong accumulation capacity. • A Janus-type composite solidified foam was synthesized. • Stabilization mechanism of JCSF was elucidated. • AcCumulation and diffusion characteristics of JCSF were studied. • Optimization of JCSF formulation by response surface methodology. [ABSTRACT FROM AUTHOR]

To alleviate the environmental pressure caused by enteromorpha (EP) and improve the efficiency of inhibiting spontaneous combustion of coal, attapulgite (ATP) was combined with EP to prepare an enteromorpha-based composite inhibitor (EPH-ATP). The effect of adding different substances on the surface morphology of the synthesized inhibitor was investigated using scanning electron microscopy (SEM). The effects of three inhibitors (enteromorpha hydrogel (EPH), ATP, and EPH-ATP) were analyzed using thermal analysis kinetics and in situ fourier transform infrared spectroscopy (FTIR). The results showed that the addition of ATP had little effect on the apparent morphology and was uniformly distributed in EPH. At heating rates of 5.0, 10.0, 15.0, and 20.0 K/min, it was found that the degree of the completion of spontaneous combustion of coal was directly related to the heating rate, and coal was more likely to react at low heating rates. In addition, during the combustion and decomposition stage, the average activation energy of coal samples treated with EPH-ATP increased by 306%, which greatly improved the reaction difficulty of the spontaneous combustion of coal. According to the changes in the functional groups with temperature, the in situ infrared process was divided into three stages of slow reaction, violent reaction and stable reaction for the first time. Moreover, the mechanism of EPH-ATP reducing the intensity of reaction by scavenging free radicals was clarified. The results show that the enteromorpha-based composite inhibitor has a good inhibitory effect, realizes the sustainable use of EP, and provides a new scientific basis for the prevention and control of the spontaneous combustion of coal. • An EP-based antioxidant type compound inhibitor was prepared. • Resource utilization of EP was realized. • Thermodynamic characteristics of composite inhibitor were studied. • Reaction mechanism of compound inhibitor in scavenging free radicals was studied. [ABSTRACT FROM AUTHOR]

Methane gas explosions and spontaneous combustion of coal severely threaten mining production safety and efficiency. Methane drainage can reduce the risk of a methane explosion while it may intensify the self-ignition of coal. To understand the relationship between these two issues, a working face of the Xinji No.2 Coal Mine in China was studied. A model of high drill holes extraction (HDHE) is established and the methane concentration distribution and air leakage under four different drainage pressures (below atmospheric) were determined. The simulation results show that drainage pressures can control the methane concentration in the air, so as not to exceed a threshold value. However, these drainage pressures enlarged the size of the zone where spontaneous combustion could occur due to the increase in air leakage. The possibility of the coexistence of a methane explosion and spontaneous coal combustion was proposed. This is an important index for the selection of a reasonable methane drainage pressure. The monitoring data from the mine were used to validate the model. [ABSTRACT FROM AUTHOR]

• Employing carbonated fly ash slurry to prevent the spontaneous combustion of coal. • The carbonated fly ash slurry inhibits the oxidation reactivity of coal. • The carbonated slurry lowers the specific surface area and pore volume of coal. • The amount and rate of CO 2 sequestration are gained by novel calculation methods. An innovative approach of utilizing fly ash waste to sequester CO 2 and employ the carbonated slurry to prevent spontaneous combustion of coal (SCC) in mining areas is proposed. This paper examines the CO 2 sequestration capacity of fly ash based on novel calculation methods, and the functions of carbonated fly ash (CFA) slurry on the microstructure of coal and the inhibitory properties of SCC is investigated. Kinetic experiments demonstrate that the quantity of CO 2 sequestration and the initial rate of CO 2 sequestration increment generally with the initial CO 2 pressure and the water-to-solid ratio. CO 2 sequestration of the fly ash (Class F) amounts to 54.9 g/kg and the initial rate of CO 2 sequestration gained 0.035 mol/kg/s at an initial CO 2 pressure of 20 bar and a water-to-solid ratio of 6. The specific surface area and pore volume of the coal treated by the filtrate of CFA slurry were diminished. When the water-to-solid ratio of the slurry is 6 and the slurry-to-coal ratio reaches 3: 1, the crossing point temperature increments by 13.8 ℃ compared with the origin coal. The risk of SCC greatly diminishes based on the evaluating index I of the propensity of SCC, and CFA slurry demonstrates a great suppression function on SCC. The approach proposed in this paper effectively actualizes the combination of CO 2 sequestration, utilization of solid waste, and prevention of SCC. [ABSTRACT FROM AUTHOR]

• The capture model of free radical in coal by TEMPO, including capture radicals directly, regenerative cycle chain and hydrogen transfer. • TEMPO can reduce the concentration of free radicals in coal by directly capturing them, and it is effective for ∙ OH and alkyl radicals. • TEMPO can capture peroxide radicals and alkyl radicals in coal through regenerative cycle chains, and then reduce the concentration of these two types of free radicals. • TEMPO can continuously reborn to maintain the efficiency of its capture by regenerative cycle chains and its activity gradually increases with increasing temperature. • For coals under acidic conditions, TEMPO can bind to H+ first and then transfers hydrogen with oxygen-containing radicals in the coal. Due to the presence of hydrogen bonds, TEMPO is more likely to bind to free radicals. The inhibitory effect of free radical scavenger 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) on the spontaneous combustion process of coal has been experimentally confirmed. However, the mechanism of free radical trapping in coal by TEMPO is not clear. This paper revealed the mechanism of free radical capture in coal by TEMPO from three perspectives by quantum chemistry method, including capture radicals directly, regenerative cycle chain and hydrogen transfer. It was regarded as a beginning that the formation of free radicals (R-CH 2 ∙, CH 3 ∙) by breaking alkane groups in the side chain of the coal molecule. The oxidation process of these free radicals was analyzed and the capturing models of radicals were described. The thermodynamic data for reactions (R2 ∼ R5) are calculated to reveal the initial reaction process of coal. The adsorption energy and thermodynamic data for reactions (Process1 ∼ 4, R6 ∼ R10, R12 ∼ R13) are computed to illustrate spontaneity and difficulty of traps free radicals by TEMPO. The results indicate that the initial reaction (R2, R4) of free radicals with oxygen in coal is exothermic and some other reactions (R3, R5) need to overcome large reaction energy barriers. TEMPO can capture free radicals in coal directly, reducing the concentration of free radicals, and is most effective in capturing ∙OH and alkyl radicals. At the same time, TEMPO can capture peroxide radicals and alkyl radicals in coal through regenerative cycle chains and keep reborn to maintain the efficiency of its capture. For coals under acidic conditions, TEMPO can bind to H+ first, then transfers hydrogen with oxygen-containing radicals in the coal. This process is prone to occur due to the presence of hydrogen bonds. In future applications, the pH value of TEMPO can be appropriately reduced to enhance the effect of capturing free radicals in coal. [ABSTRACT FROM AUTHOR]

In this study, we developed a modified antioxidant-type inhibitor (MAT-inhibitor) to address the disadvantages of the inhibitors that are currently used in coal mines, namely single effect, poor thermal stability, and low versatility. Sodium acrylate, tert -butyl hydroquinone (TBHQ), and montmorillonite were used as raw materials. X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA) were adopted to analyze the inhibition performance and mechanism of the MAT-inhibitor. Research indicates that the MAT-inhibitor is able to fully cover the coal surface, and has strong water absorption qualities. TBHQ in the inhibitor significantly reduces the content of methyl (-CH 3), methylene (–CH 2 –), hydroxyl (-OH), and carboxyl groups (-COOH) in the coal radical chain reaction. In the meantime, it increases the stable ether bond content (C–O–C). After treatment with the MAT-inhibitor, the dry cracking temperature of the coal sample increased by 52.8 °C, and the maximum thermal mass loss rate decreased by 0.84%/min. This proved that the inhibitor has superior thermal stability and high inhibition performance. Therefore, regardless of the physical, chemical, and thermal stability aspects, the MAT-inhibitor can be used to control the spontaneous combustion of coal. • The application of TBHQ in the field of coal oxidation inhibition was studied. • The TBHQ was grafted onto sodium polyacrylate by graft polymerization. • The O-MMT was used for nano-modification to prepare the inhibitor. • The physical inhibition mechanism was studied through microscopic characterization. • The anti-oxidation mechanism was explained through free radical reaction. [ABSTRACT FROM AUTHOR]

[Display omitted] • Response surface methodology was used to optimize formulation of solidified foam. • Mechanism of foaming and curing reaction of NICF was clarified. • Rice husk ash with high pozzolanic activity replaced fly ash. • Core parameters of the mixing device were determined by numerical simulations. The spontaneous combustion of coal seriously threatens the safe operation of coal mines. In order to solve the problems of the traditional inorganic solidified foam (TICF), i.e., a long gelation time, difficulty in uniform mixing, and low efficiency for blocking air leakage, a novel inorganic solidified foam (NICF) was proposed in this study to prevent the spontaneous combustion of coal; it was prepared by using rice husk ash (RHA), xanthan gum (GX), and sodium silicate (WG) as modifiers. Plackett-Burman experiments and response surface methodology were used to optimize the expansion ratio, stability coefficient, and gelation time of NICF and to determine the formulation of NICF in order to achieve rapid sealing of air leakage channels. A spiral hollow mixing device (SHMD) was developed based on the characteristics of NICF. The mixing effect of an aqueous foam (AF) and compound seriflux (CS) was numerically simulated by the ANSYS FLUENT software, and the SHMD parameters were determined with a high expansion ratio and uniform mixing of grout. The mechanism of the foaming and curing reaction of NICF and its mechanism for preventing the spontaneous combustion of coal were obtained by means of scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and X-ray diffraction (XRD). The experimental results indicated that WG hydrolyzed to produce an orthosilicic acid sol and sodium hydroxide in the process of particle hydration, and the sol could bind the particles to the hydration products. In addition, WG dissociated to generate a large amount of orthosilicate ions ([SiO 4 ]4-), which combined with the calcium ions present in a high concentration on the surface of the hydrated particles; this considerably reduced the gelation time of NICF. Ca2+ on the surface of the hydrated particles chelated with the active functional groups such as the hydroxyl and carboxyl groups in GX, improving the compressive strength of NICF in the initial hydration stage. Compared with fly ash, rice husk ash has higher pozzolanic activity, and it undergoes a secondary hydration reaction with numerous calcium hydroxide crystals, increasing the hydration degree. This study can provide a theoretical basis for reducing the gelation time of NICF and explaining its foaming and curing reaction mechanism. [ABSTRACT FROM AUTHOR]

[Display omitted] • The advantages of polymer gels and inorganic sodium silicate gels were combined, and the stability of the hydrogel was greatly improved. • Only 5 wt% additives (Total mass of SA, P, B, Ca/Total mass of the gel) were needed to obtain a gel within 50 s. • The problem of poor gel stability caused by rapid ionic crosslinking has been solved to a certain extent. To combine the advantages of polymer gels and inorganic sodium silicate gels for preventing and controlling the spontaneous combustion of coal, a new type of SA/P/B/Ca (sodium alginate/non-ionic polysaccharide/inorganic boron crosslinking agent/calcium carbonate) gel was designed in this paper. Based on the ionic crosslinking reaction of sodium alginate and Ca2+, the inorganic boron crosslinker was used to release the masked Ca2+ to achieve rapid in-situ gelation and a controllable gelation time. Simultaneously, the complex reaction between cis-diols and B(OH) 4 − formed a second network. The formulation of the SA/P/B/Ca gel was studied by orthogonal experiments. Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), temperature-programmed oxidation experiments, and thermogravimetric analysis were used to study the synthesis mechanism and inhibitory effects of the gel. The results showed that only 5 wt% additives (total mass of SA, P, B, Ca/Total mass of the gel) was needed to obtain a gelation time of 50 s. This can greatly reduce material transport burdens. The double-crosslinked network of SA/P/B/Ca also showed improved stability and water retention compared with traditional water glass gels and single-network gels. It delayed the characteristic temperature of coal by 11–12 ℃, reduced the heat release by 19%, and showed superior inhibition and fire extinguishing performance against coal spontaneous combustion. [ABSTRACT FROM AUTHOR]

Abstract: The susceptibility of coal to spontaneous combustion is a physical–chemical property of coal that can be determined by a laboratory test. A number of laboratory methods verifying the coal susceptibility to spontaneous combustion exist, e.g. the oxidation method under adiabatic conditions, method according to the author Olpinski, method of pulse calorimetry, and CPT (Crossing Point Temperature) method. Any versatile method has not been so far developed, which would become a generally respected and utilized laboratory procedure of objective assessment. The paper deals with the verification of the widely used adiabatic oxidation method. The modification of the method in question consists in the adjustment of the test process by increasing the initial temperature. This procedure enables shortening the test process. Shortening the laboratory test duration creates conditions for wider utilization of the method in practice. The paper presents results of 36 tests of Ostrava–Karvina Coalfield coal samples which confirmed an applicability of the modified adiabatic method in practice. [Copyright &y& Elsevier]

Abstract: On the basis of the four factors of spontaneous combustion of coal, the causes of such combustion in the tunnel fall of ground were comprehensively analyzed. The causes include the generation of float coal, influence of hot wind pressure on the laneway, and airflow dynamic pressure caused by sloping roadways. According to the characteristics of a fire that occurred in the intake airflow roadway of working face 12190 in the Geng Cun Coal Mine, a three-phase foam composed of mud, nitrogen, and water was used to extinguish the fire. The foam was injected into the fire zone through boreholes on the tunnel roof. Given the precise scheme and reliability of the technology, the fire was successfully extinguished. The specific technological process and parameters of the technology are discussed in detail. It is concluded that the three-phase foam is useful in preventing spontaneous combustion of coal in the tunnel fall of ground. It serves as a new method for preventing such phenomenon in extra-thick coal seam. [Copyright &y& Elsevier]

Abstract: The traditional identification of spontaneous combustion hazard of coal in China is unilateral and inaccurate, which is singly attributed to the properties of coal. Based on current research findings on coal fires, we''ve reconsidered the influential factors that lead to the spontaneous combustion of coal seams, and have ultimately built a comprehensive system for evaluating the hazard of spontaneous combustion. Applying holistic scoring method and Analytic Hierarchy Process, we integrated all of the factors into a quantitative model, and classified the ratings into five levels. Additionally, a Visual Basic 6.0 based application program has been developed to assist the evaluation, as well as three domestic colliery cases with varying fire hazards have been tested. Through practical application, the hazard evaluations have proved to be objective and valid, so the system is applicable to Chinese coal mines. [Copyright &y& Elsevier]

Abstract: The gas explosions often occur under mine gas and spontaneous combustion coupling in coal mines. The coupling of mine gas and spontaneous combustion is a complex disaster, and the character of the disaster is not clear now. The paper primarily discussed the character of gas explosion under mine gas and spontaneous combustion coupling. The explosion concentration range of mixed gases including CH4 and CO is studied. And the potential area and the course of explosion detonated by spontaneous combustion of coal is analyzed. When the spontaneous combustion of coal occurs, it can produce plenty of CO and fire-heating air pressure in the goaf. Experiments show that the upper limit of explosion concentration rises rapidly and the lower limit rises slowly with the increase of CO in the mixed gas of CH4 and CO. The fire-heating air pressure results in continuous mix of the gases and heat convection under vortex action between the combustion zone and non-firing zone. Thus, gas explosion occurs. In order to prevent high-concentration gas in the goaf and spontaneous combustion which detonates gas explosion in the coal mine, three-phase foam with nitrogen is adopted to restrain gas explosion and reduce coal temperature. [Copyright &y& Elsevier]

Abstract: The propensity of coal to spontaneous combustion demonstrates the inherent character of the oxidation capacity at normal temperature. Currently, based on simulating spontaneous combustion of coal using adiabatic oxidation and temperature-programmed experiment, many overseas countries test characteristic parameters of spontaneous combustion of coal, such as SHT, HR, R70, CPT, high-temperature activation energy, and so on. Oxygen adsorption method is used to test the absorbed oxygen at 30 °C in China. According to the deficiency of the present research using partial stage parameters to demonstrate the whole process, Oxidation Kinetics which reflects the entire dynamic process is put forward, through testing the concentration of oxygen in the outlet of sample vessel at 70 °C and CPT later. With results repeated well and simple manipulation, the method can reflect the self-heating character very well and thus has a vital significance for the prevention and control of the mine fire. [Copyright &y& Elsevier]

For understanding the extinguishing effectiveness of gel-stabilized foam fluids, the rheological law, flow characteristics, and extinguishment process were analyzed systematically in this study. The results revealed that gel-stabilized foam was non-Newton fluids, and the foam demonstrated shear-thinning behavior due to the orientation changes in molecular chains and structure destruction of three-dimensional gel at high shear rate. By fitting shear rate-shear stress curves, it was found that power-law equation of pseudoplastic fluid could descript the rheological behavior of foam well, and coefficients of determination for fitting results in all expansion ratios were lager than 0.9950. In addition, a simplified experiment platform of the goaf filled with coals was employed to investigate the flow characteristics of the foam fluids to extinguish coal fire. Analysis showed that gel-stabilized foam presented the hemispherical diffusion shape in porous media, and foam fluids would quickly cover to extinguish the open coal fire with excellent thermal stability. Moreover, the foam fluids also captured the hidden fire source efficiently in porous media by the quick seepage, finally cooling the high-temperature coal fire from 760 °C to 30 °C after injecting foam. The research would provide theoretical guidance for extinguishing coal fire using gel-stabilized foam. • The rheological law and fluid type of gel-stabilized foam was investigated. • The rheological constitutive equation of gel-stabilized foam was obtained. • The study exhibited the flow process of gel-stabilized foam in porous media. • The flow law of gel-stabilized foam to extinguish coal fire were revealed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Studied effects of intrinsic properties, particle size, SSA on coal spontaneous combustion. • Analyzed spontaneous combustion mechanism from particle size, SSA and gas adsorption perspectives. • Spontaneous combustion tendency increased with decrease in size and increase in SSA. • Critical particle size for spontaneous combustion determined 38–74 µm (D 50 = 50.56 µm). • Developed spontaneous combustion prediction models based on particle size and SSA. This study examines the effects of intrinsic properties, particle size, and specific surface area (SSA) of coal on spontaneous combustion. Moreover, it analyzes the underlying mechanism of spontaneous combustion from particle size, SSA and gas adsorption perspectives. The susceptibility of coal to spontaneous combustion is studied by wet-oxidation potential (WOP) method. Coal residues left after the WOP experiment are analyzed for change in structural and compositional behaviour. The study revealed an inverse relationship between the particle size and SSA of coal. Spontaneous combustion susceptibility increased with increase in volatile matter and decreased with increase in fixed carbon content of coal. The optimum moisture content of coal resulting maximum spontaneous combustion tendency is determined 6%. Decrease in particle size and increase in SSA augmented the spontaneous combustion propensity of coal. With decrease in coal particle size from 425 to 850 to < 38 µm, the mean D 50 value decreased by 27 times, the mean SSA increased by 42 times and coal spontaneous combustion susceptibility increased almost by 2 times. Critical coal particle size is determined 38–74 µm (D 50 = 50.56 µm), below which no appreciable change in oxidation rate is observed. Moreover, two models are developed to predict the spontaneous combustion susceptibility of coal based on particle size (D 50) and SSA. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ben improves water retention of acrylic/sodium acrylate resins. • MLT provides lone pair electrons to trap free radicals in coal. • The flame retardant mechanism of anti-oxidation composite inhibitor is revealed. To improve the efficiency of inhibitors in preventing the spontaneous combustion of coal, an antioxidant-type high-efficiency composite inhibitor (SAP + MLT + Ben) was synthesized by solution polymerization. Scanning electron microscopy, Fourier transform infrared spectra, Electron spin resonance, and programmed temperature experiment were employed to clarify the inhibition mechanism of SAP + MLT + Ben on coal oxidation. Results revealed that (1) The combined effect of Ben and acrylic acid/sodium acrylate leads to the improvement in the water absorption properties of the hydrogel; (2) Melatonin captures hydroxyl radicals, lipoxy radicals, and lipoperoxy radicals in coal by providing lone pairs of electrons, thereby reducing the concentration of easily oxidizable hydroxyl, methyl, and methylene groups and increasing the number of stable ether bonds; (3) The concentration of free radicals in the coal sample treated with SAP + MLT + Ben is 6.00% less than that of the original coal sample, the temperature to reach the maximum weight loss rate is delayed by 24.53 °C, and the retention rate of heated water gets increased by 13.93%. This study provides a scientific basis for the prevention of spontaneous combustion of coal and development of novel composite inhibitors. [ABSTRACT FROM AUTHOR]

• High-water-retaining foam was proposed to control spontaneous combustion of coal. • Crosslinking mechanism and characteristic of high-water-retaining foam were analyzed. • Stability and water retention performance of high-water-retaining were investigated. • High-water-retaining foam exhibited better extinguishment characteristic. For enhancing the wetting effect of foam on residual coal in goaf to control spontaneous combustion of coal efficiently, this study proposed the novel high-water-retaining foam with excellent water retention and extinguishment performance. Polymer composite (PC) as thickening agent and organic boron complex (OBC) as crosslinking agent were introduced into foam system to form gel structure by borate/ cis -hydroxy bonds in foam film to hold water. Preparation experiments indicated that high-water-retaining foam with the component range of 3.4 ~ 4.8 g/L PC and 2.0 ~ 3.4 g/L OBC showed the crosslinking time more than 30 min, which was conducive for foam to spread fully to cover and wet the residual coal in goaf. Considering the foam foamability and stability, this study revealed that the optimal component proportion of high-water-retaining foam was 4.0 g/L PC and 3.0 g/L OBC, exhibiting the largest foam comprehensive value of 529.82 and best foam performance. Water retention capacity of foam tests indicated that high-water-retaining foam could hold the water in foam system above 60% after placing 120 h, while traditional aqueous foam had lost 98% water. And coal-fire extinguishing tests indicated better extinguishment characteristic of high-water-retaining foam than that of traditional aqueous foam as evidenced by faster cooling and extinguishment rate to burning coal for the novel foam. Moreover, high-water-retaining foam would cover the coal fully for a long term to prevent oxygen from feeding the fire, finally controlling spontaneous combustion of coal efficiently. [ABSTRACT FROM AUTHOR]

• As the temperature increases, the heat of wetting continues to decrease. • The heat of wetting increases as the coal sample size decreases. • The heat of wetting accelerates the occurrence of coal spontaneous combustion. • Coal wetting is exothermic due to the formation of hydrogen bonds. In this study, the effect of the heat of wetting (H w) of coal on its spontaneous combustion was investigated. Specifically, the effects of the amount of water used in the wetting (W), temperature (T), and particle size (PS) on the wettability and exothermic behavior of a coal sample were examined using a C600 high-precision calorimeter. The trends of the Q curves under various conditions (W, T, and PS) were analyzed. The results show that the amount of H w decreased as T increased. The smaller the PS of a coal specimen was, the higher the amount of H w was. Additionally, a decrease in PS led to an increase in the H w release rate (HRR). Due to the generation and accumulation of H w , the oxidative heat storage system of coal is promoted, which accelerates the oxidative spontaneous combustion of coal at low temperature. [ABSTRACT FROM AUTHOR]

Novel aerosol particles were developed and utilised to prevent SCC in underground goafs. The ultrafine aerosol particles (UAPs) were synthesised by grinding ammonium dihydrogen phosphate, magnesium chloride, zinc borate, talcum powder, calcium stearate, sericite, bentonite, and silica to a an equivalent spherical diameter of less than 100 μm in the ratio of 144:36:8:5:5:6:4:2. Loading of 1–5% aerosol powders inhibited the activity of O-containing functional groups such as C–O in the lignite as well as retarding its exothermic behaviour. Scanning electron microscopic analysis indicated that the aerosol particles form a uniform insulating layer on the coal surface at temperatures beyond 160 °C. Fire-extinguishing experiments showed that the P–Cl aerosol particles reduced the temperature of the burning coal to less than 100 °C within 45 min and prevented its reignition. Particles of less than 10 μm in diameter around the fire source accounted for 38.7% of the total particles transported, indicating that aerosol particles had been uniformly diffused into the confined space. [ABSTRACT FROM AUTHOR]

• High-toughness P(AA-co-AM)/WG gel was prepared by free radical polymerization. • P(AA-co-AM)/WG gel is fit for coal-seam condition with high ground temperature. • P(AA-co-AM)/WG gel has advantages of plugging, resisting, and cooling. • P (AA-co-AM)/WG gel's formation, inhibition, and fire prevention mechanism is discussed. In order to address the issue of spontaneous combustion of coal, this paper proposes a high-toughness hydrogel (P(AA-co-AM)/WG gel) for fire prevention and extinction, which is suitable for the conditions of coal-seam with high ground temperatures. In the initial stage, the silicic acid molecules in the material system react under the action of the coagulant to form the first network structure. Simultaneously, the superabsorbent monomers in the material system use the geothermal energy in the mines to polymerize and form the second network structure. The first and second network cross each other, forming P(AA-co-AM)/WG gel with interpenetrating network structure and high toughness. The differences in WG gel, P(AA-co-AM), and P(AA-co-AM)/WG gels were analyzed via testing of their in-situ infrared, and viscoelasticity. The results indicate that P(AA-co-AM)/WG gel had the best water retention, elasticity, inhibitory performance, compression resistance and lowest cost among the studied gels. In addition, the fire extinction experiments of comparison with other fire extinction materials indicated that P(AA-co-AM)/WG gel could uniformly cover the surface of the burning coal body forming a dense enwrapping on the coal and densely filling the cracks. Moreover, the fire extinction effect of the proposed gel is stable as there was no re-ignition phenomenon. [ABSTRACT FROM AUTHOR]

• Gel-stabilized foam was successfully prepared to prevent and control spontaneous combustion of coal. • Gel-stabilized foam exhibited long-term stability and water-retaining property with half-life over 120 h. • The formation process and stability mechanism of gel-stabilized foam were investigated. • Gel-stabilized foam could form a film on coal surface to isolate coal from the oxygen. The gel-stabilized foam was prepared successfully by forming gel structure in the bubble film using thickening agent (TA) and crosslinking agent (CLA). The viscosity characteristic, foamability, stability, and microstructure of gel-stabilized foam were investigated systematically. The formation of gel structure reduced the foamability of foaming solution due to the increased viscosity, whereas it increased the foam stability significantly. By comprehensively considering foam expansion ratio >5 and half-life >120 h, the effective component range of gel-stabilized foam was determined as 3.4–5.5 g/L for TA and 2.1–4.0 g/L for CLA. Microstructure and liquid drainage kinetics analysis indicated that gel-stabilized foam demonstrated the smaller average bubble size, lower growth rate of bubble size and drainage rate compared to the traditional aqueous foam, mainly ascribing to the thickened bubble film and the formation of a viscoelastic shell on the bubble surface. The simulation experiment of spontaneous combustion of coal indicated the better inhibition efficiency of gel-stabilized foam to spontaneous combustion of coal than that of traditional foam, as evidenced by higher crossing point temperature, lower emission of carbon monoxide and ethylene for treated coal by gel-stabilized foam, which revealed its better water-retaining property to retard the oxidation of coal. Moreover, gel-stabilized foam will form a complete film on the surface of coal particles to isolate coal from the oxygen to inhibit spontaneous combustion. [ABSTRACT FROM AUTHOR]