Coal Spontaneous Combustion Characteristics Research Articles

Optimization of coal spontaneous combustion characteristics and reaction kinetic model under lean-oxygen conditions

Optimization of coal spontaneous combustion characteristics and reaction kinetic model under lean-oxygen conditions

Effects of pre-oxidation temperature and air volume on oxidation thermogravimetric and functional group change of lignite.

To investigate the impact of the oxidation temperature and variations in airflow conditions on coal spontaneous combustion characteristics, pre-oxidized coal samples were prepared using a programmed temperature rise method. Synchronous thermal analysis experiments and Fourier transform infrared spectroscopy were conducted to explore changes in the thermal effects and functional group content of the coal samples, respectively. The results indicate that variations in pre-oxidation conditions primarily in fluence the activation temperature and maximum weight loss temperature of the coal samples, while exerting a lesser impact on the critical temperature and ignition point. Variations in air volume conditions predominantly affect the content of Ar-C-O- and -CH2 & -CH3 in the oxygen-containing functional group region. The trend of the average activation energy within a conversion rate range of 0.2 to 0.6 of pre-oxidized coal samples changing with the increased of pre-oxidation temperature under the air flow conditions of 25mL/min and 50mL/min is consistent, but opposite to that under the air flow conditions of 100mL/min and 200mL/min. Compared to raw coal, under an airflow rate of 50 mL/min and when oxidized to 110°C, the coal sample exhibits an increase in the content of OH…OH, accompanied by reductions in the critical temperature, activation temperature, ignition point, and maximum weight loss temperature to varying degrees, thereby rendering it more susceptible to oxidative spontaneous combustion.

Experimental study on the influence of CO2 injection on coal spontaneous combustion characteristics and molecular functional groups

The study aims to investigate changes in the spontaneous combustion characteristics of coal and its microscopic reaction mechanisms in a CO2 atmosphere. Programmed heating experiments and thermogravimetric analysis were conducted to examine index gas and combustion parameters in both air and CO2 atmospheres. Molecular functional group changes were analyzed via in situ infrared experiments, and their correlation with index gases was assessed using the grey correlation method. The results revealed that CO2 injection during the initial heating stage increased the production of CO, CH4, and C2H4. However, beyond 160 °C, CO2 effectively reduced the oxidation activity of functional groups and significantly inhibited the production of indicator gas. The characteristic temperature range of coal samples exhibited a 'lag' phenomenon under the influence of CO2, resulting in a prolonged combustion stage with reduced mass loss and heat discharge. Following CO2 injection, the -OH concentration significantly decreased, while C=O gradually increased. Additionally, the concentrations of -COOH, aliphatic hydrocarbons, and aromatic hydrocarbons initially increased with rising temperature and then declined. The contribution of these groups to gas generation followed the sequence of oxygen-containing functional groups > aliphatic hydrocarbons > -OH > aromatic hydrocarbons.

Comprehensive analysis-based experimental investigation on the oxidation characteristics of coal spontaneous combustion

Comprehensive analysis-based experimental investigation on the oxidation characteristics of coal spontaneous combustion

Characteristics of Coal Spontaneous Combustion Induced by Air Leakage in the Goaf of Shallow Buried Close-Distance Coalbed

ABSTRACT This study investigates the air leakage patterns and coal spontaneous combustion prevention in shallow-buried close-distance coalbed goafs during opposite mining, using the 2201 and 2206 working faces of Shaozhai coal mine as a case study. Through theoretical analysis, in-situ testing, and numerical simulation, we examine air leakage relationships in opposite working face goafs of shallow-buried close-distance coalbeds. We identify coal spontaneous combustion risk areas in single and composite goafs with a 100 m reverse spacing. Our results indicate that the mining method significantly affects air leakage patterns in the 2201 and 2206 working faces under opposite close-distance arrangement, with increased air leakage in composite goafs elevating coal oxidation risk. As working faces advance, air leakage channels in coal pillars increase, leading to mutual influence between the composite goafs of the 2201 and 2206 working faces. We delineate specific spontaneous combustion risk areas for both working faces and observe intensified air leakage in coal pillars between composite goafs within 100 m of opposite mining spacing. Based on these findings, we propose comprehensive prevention and control measures, including bundle tube monitoring, air leakage plugging, and inerting techniques. This study provides valuable insights for preventing and controlling coal spontaneous combustion in composite goafs of shallow-buried close-distance coalbeds.

Experimental Study on the Influence of Staged Oxygen Consumption on the Oxidation Characteristics of Coal Spontaneous Combustion

The oxidation characteristic parameters of residual coal in working face change with the advance of coal seam. To explore the influence of dynamic oxygen-consuming environments, we examined the influence of reducing the oxygen concentration on the formation characteristics and characteristic parameters of coal oxidation products, conducted with temperature-programmed experiments under staged oxygen consumption. The correlation between the characteristic oxidation parameters was determined, and the critical oxygen concentration that determined the gas yield was obtained. The results show that after staged oxygen-consumption, the oxidation of coal is stronger than that under constant low oxygen, the oxidation products are greatly affected, and the influence of pyrolysis gas is small. The oxidation characteristic parameters such as gas product volume fraction, production rate, and heat release intensity are positively correlated with the oxygen-consumed temperature. We found that the oxidation reaction heat of coal is 180~330 kJ·mol−1, and the maximum and minimum exothermic intensities are significantly linearly correlated with the oxygen consumption rate. Finally, the critical oxygen concentrations for gas production rate under oxygen-consumed conditions were 17, 9, and 5%. These results have practical significance for strengthening the prevention and control of spontaneous combustion disasters in goafs.

Study on the Optimization of Culture Parameters of Oxygen-Consuming Bacterium for Preventing CSC and Its Effect on the Coal Oxidation Characteristic

ABSTRACT Microorganisms can work together to prevent coal spontaneous combustion (CSC) by consuming oxygen and changing coal oxidation characteristics. In order to explore the influence of oxygen-consuming microorganisms on coal spontaneous combustion characteristics, a highly oxygen-consuming bacterium was isolated and identified from the soil near mine drainage, named ZQ-1. The oxygen consumption characteristics of microorganisms were investigated and optimized by single-factor and response surface experiments. Further, the effect of microorganisms on CSC was analyzed from both macroscopic and microscopic perspectives by using programmed warming, simultaneous thermal analysis, and Fourier-transform infrared spectroscopy (FTIR). The results revealed that the isolated bacterium was Pseudomonas aeruginosa. Its optimal culture conditions were pH = 6.98, temperature 28.15°C, and carbon nitrogen ratio (C/N) = 12.94 when the oxygen consumption rate was maximum. After bacterial action, coal showed a decrease in the release of the indicator gas CO during the combustion process, a delay in the cross point temperature (CPT) by 18.63°C, and an increase in the residual mass at the end of combustion. In addition, the average activation energy of the coal samples in the oxidative combustion stage was increased by 2.05721 kJ/mol. Finally, the FTIR results showed that microorganisms were able to destroy the reactive groups in the coal samples, especially hydroxyl, aliphatic hydrocarbon, and oxygen-containing functional groups, which resulted in the inhibition of CSC. This paper has important theoretical research value and practical significance for CSC prevention and control.

Exploration and Frontier of Coal Spontaneous Combustion Fire Prevention Materials

Mine fires have always been one of the disasters that restrict coal mining in China and endanger the life safety of underground workers. The research and development of new fire prevention materials are undoubtedly important to ensure the safe and efficient production of modern mines. At present, the main inhibiting materials used are grout material, inert gas, retarding agent, foam, gel, and so on. In order to explore the current situation of coal spontaneous combustion (CSC) fire prevention, the existing fire prevention materials were reviewed and prospected from three aspects: physical, chemical, and physicochemical inhibition. The results show that, at present, most of the methods of physicochemical inhibition are used to inhibit CSC. Antioxidants have become popular chemical inhibitors in recent years. In terms of physical inhibition, emerging biomass-based green materials, including foams, gels, and gel foams, are used to inhibit CSC. In addition, CSC fire-fighting materials also have shortcomings, including incomplete research on the mechanism of material action, poor stability of inhibitory properties, low efficiency, and economic and environmental protection to be improved. The future research direction of fire-fighting materials will be based on theoretical experiments and numerical simulation to study the mechanism and characteristics of CSC and develop new directional suppression materials with physicochemical synergies. These findings have extremely important implications for improving materials designed to prevent CSC.

Influence of composite chloride salt retardant on the characteristics of coal spontaneous combustion and comprehensive evaluation methodology

ABSTRACT In this study, we aimed to improve the efficacy and longevity of single inhibitors. NaCl, CaCl2, MgCl2, and layered double hydroxides (LDHs) were selected as the inhibitory components for experimental study. The impact of the composite inhibitors on the spontaneous combustion characteristics of the coal was studied through temperature programmed experiment, thermal analysis experiments, thermogravimetric mass spectrometry and entropy weight method, and the optimal inhibitor was determined. The findings indicate that the apparent activation energy (E a ) of the coal sample, with the addition of inhibitors during the oxidation stage, was improved. E a of MgCl2 +1.0 LDHs + Coal was the highest (127.28 kJ/mol), i.e. 35.99 kJ/mol higher than that of the original coal. The inclusion of the inhibitor increased the characteristic ignition temperatures of the coal samples compared with the original coal. The highest ignition temperature was observed for MgCl2 +0.5 LDHs + Coal, reaching (323.98°C), i.e. 11.42°C higher than that of the original coal. The addition of inhibitors significantly inhibited the production of CO. Among the three chloride salts, MgCl2 exhibited the strongest inhibitory effect on CO production. According to the entropy weight method, MgCl2 +0.5 LDHs showed the best inhibitory effect. The results show that the composite halogen inhibitor can effectively inhibit the spontaneous combustion of coal.

Effect of axial stress-induced coal particle breakage on the evolution laws of coal spontaneous combustion characteristics and limit parameters of loose broken coal

Coal particles are broken to varying degrees under the axial stress, thereby affecting the particle size distribution, which has an essential impact on coal spontaneous combustion (CSC). This work investigated the evolution behavior of the characteristic parameters and limit parameters of the coal oxidation process under different breakage degrees. Results showed that as the axial stress increased, the breakage degrees of coal gradually increased, while the permeability gradually declined. The increase in the breakage degree of particle induced by axial stress would promote the CSC process and increase the risk of CSC. The promotion effect reached the most prominent at 12 MPa and began to decrease at 15 MPa. Particle breakage and increasing specific surface area caused by stress were responsible for the change in CSC characteristic parameters. The reduction in permeability caused by stress dominated the changes in CSC limit parameters.

Effects on environmental conditions and limiting parameters for spontaneous combustion of residual coal in underground goaf

This study collected coal from the Meihuajing Coal Mine, Ningxia, China, and employed a temperature-programmed experimental setup to investigate the characteristics of coal spontaneous combustion (CSC) and determine the primary parameters influencing coal temperature in the goaf of this underground mine. The obtained results indicated that positive correlations existed between CO concentration, CO2 concentration, oxygen consumption rate, exothermic intensity, and coal temperature. Principal component analysis (PCA) was employed to examine the correlations of three limiting parameters—namely maximum air leakage intensity (Qmax), minimum oxygen volume fraction (Cmin), and minimum thickness of residual coal (Hmin)—with coal temperature (30–170 °C) during coal oxidation. The results of a PCA indicated that among these parameters, Qmax was most strongly correlated with coal temperature. In addition, gray correlation analysis (GCA) was adopted to examine the primary parameters influencing the occurrence of CSC during different stages. The results of GCA indicated that the primary parameter influencing the occurrence of CSC varied with the coal oxidation stage. At coal temperatures between 80 and 90 °C, Cmin and Hmin were the primary parameters influencing coal temperature. The correlation curves of Cmin and Hmin with respect to coal temperature fit well with the GaussMod model. The findings of this research provide a theoretical foundation for mitigating CSC in underground goafs.

Study on the Effect of Pore Evolution on the Coal Spontaneous Combustion Characteristics in Goaf

Understanding the characteristics of coal spontaneous combustion (CSC) in goaf under different porosities is crucial for comprehending the mechanism of CSC and its prevention and control. In this paper, a multi-field coupled model of CSC in the goaf, considering porosity variation, is developed to investigate the effect of porosity on the CSC characteristics in the goaf. The results indicate that, as the goaf depth increases, both porosity and permeability decrease. When the highest goaf porosity is 25%, the average airflow velocity is between 0.00134 and 0.00139 m/s. In contrast, the average airflow velocity in the goaf with a porosity of 40% is approximately six times greater than that of the goaf with a porosity of 25%. As the goaf porosity increases, the overall oxygen concentration, temperature, and oxidized zone area also rise. Moreover, the oxidation zone area can be quantified and visualized, thereby enabling more effective prediction of the CSC risk in the goaf. The findings of the study have a positive significance in guiding the prevention and control of coal fires.

Influence of mudstone on coal spontaneous combustion characteristics and oxidation kinetics analysis

To explore the spontaneous combustion characteristics and hazards of the low-temperature oxidation (LTO) stage in the process of spontaneous combustion of coal and mudstone, the pore structure, spontaneous combustion characteristic parameters, and exothermic characteristics of coal and mudstone were tested and studied, and the oxidation kinetic parameters were calculated. The results show that mudstone has a larger specific surface area and pore volume than coal. From the fractal characteristics, the pore structure of mudstone is more complex than that of coal. According to the comparison of theoretical and actual gas generation and oxygen consumption rate curves, it is found that there is an interaction between coal and mudstone in the LTO process. With the increase of mudstone mass ratio, gas production, and its oxygen consumption rate increase. Among them, CM-4 (Coal:Mudstone = 1:1) has the highest exothermic intensity and the exothermic factor (A) and fire coefficient (K) increase with the increase of mudstone content. The apparent activation energy of the mudstone sample is lower than that of the raw coal, indicating that the sample after adding mudstone is more likely to have spontaneous combustion in the LTO stage.

Response of Macroscopic Coal Oxidation and Pyrolysis Parameters to Different Extractants

ABSTRACT The active structure of coal molecules is one of the key factors affecting the characteristics of coal spontaneous combustion (CSC). By actively stripping or reducing the key active structure of coal molecules, and then studying the influence of different structures on the oxidation characteristics of coal, it is helpful to accurately and efficiently inhibit CSC. Herein, using coal samples from Caojiatan Mine in Shaanxi Province, China, the CSC characteristics of 10 coal groups treated with different solvents and the response of the macroscopic coal oxidation and pyrolysis parameters to each extractant were investigated. The extractant type considerably affected CSC, and the oxidization of coal was most responsive to biomass extraction agents, which had the best weakening effect on CSC. The order of CSC characteristics of extracted coal from strong to weak is AE> YM> CYC> AOT> CYH> EG> MT> TP> THF> CYC + AOT + AE> EG + TP. In general, all extraction reagents in each group have a certain weakening effect on the CSC activity of coal samples. The extraction of aromatic hydrocarbon structures can effectively delay the oxidation of coal. The study provides new insights for the development of CSC mitigation technology and have important practical significance for active prevention and control of CSC risks.

Study on the Inhibition Characteristics of Coal Spontaneous Combustion by Silica Gel Foam.

The spontaneous combustion of residual coal in abandoned mining areas severely affects the safe and efficient extraction of coal, employee occupational health, and regional environmental ecology. A technical measure for preventing and controlling the spontaneous combustion of residual coal involves injecting antispontaneous combustion materials into abandoned areas. In this study, the composition, preparation, and mechanism of action of silica gel foam, a material used to suppress spontaneous combustion during coal mining, were investigated to improve the performance of materials designed to prevent spontaneous combustion in abandoned areas. The inhibitory efficiency improved, and the mechanical strength and stability of the foam liquid film increased upon adding modified antioxidants and nanosilica particles to the gel foam. Macro performance tests, microstructural characterization, and chemical inhibition mechanism analyses verified the efficacy of silica gel foam for suppressing spontaneous combustion. The air leakage resistance of the silica gel foam effectively increased the air leakage resistance of the coal samples at different pressures. New radicals formed during the spontaneous combustion of coal comprising different inhibitors, as indicated by the g-factor results of electron paramagnetic resonance (EPR) spectroscopy analysis; the formation of radicals initially decreased and then increased when the inhibitor material changed. The concentration of free radicals decreased markedly during the spontaneous combustion process of both raw and inhibited coal samples at low oxidation temperatures (∼60-100 °C), indicating a marked inhibitory effect.

Thermal behaviors and kinetic characteristics of coal spontaneous combustion at multiple airflow rates by TG − DSC

Thermal behaviors and kinetic characteristics of coal spontaneous combustion at multiple airflow rates by TG − DSC

Spontaneous combustion characteristics of coal based on the oxygen consumption rate integral

According to the different characteristics of coal spontaneous combustion (CSC), different countermeasures can effectively prevent CSC. In this paper, a new characteristic parameter, the oxygen consumption rate integral (OCRI), was proposed. The characteristics of CSC during the latent period and the effect of low oxygen concentration (0–20.96 %) on the CSC were comprehensively examined. Using a lab-built closed oxidation system, isothermal oxidation experiments were performed on different grades of coals at different temperatures. The OCRI was obtained by integrating the oxygen consumption rate as a function of oxygen concentration. The OCRI expresses the sum of the rates of oxygen consumption at different concentrations of oxygen and can be used as an identification index for the propensity of CSC. The kinetic basis for this approach is the variability of initial oxygen consumption rates and oxygen reaction orders for different coals. Finally, the physicochemical structure of the coal was measured by N2 adsorption and IR analysis. The results were correlated with the OCRI. On this basis, the main microscopic reaction pathways affecting the CSC were revealed. The results can aid in the future direction for research and development of high-efficiency inhibitors.

Effect of water soaking and air drying on the thermal effect and heat transfer characteristics of coal oxidation at the low-temperature oxidation stage

The microstructure, thermal behaviour (30 °C-300 °C) and thermophysical properties (30 °C-300 °C) of raw and water-soaked air-dried coal samples were analysed through scanning electron microscopy, differential scanning calorimetry and laser thermal conductivity meter to study the effect of water soaking and air drying on the thermal effect and heat transfer characteristics of coal at the low-temperature oxidation stage. Experimental results show that the action of water soaking and air drying changes the apparent morphology of coal, increasing the density of surface pore distribution and number of all pore types to different degrees. Under the same temperature conditions, water-soaked air-dried coal has lower heat absorption and heat release than raw coal. Moreover, the time required by water-soaked air-dried coal to reach thermal equilibrium is 32.4 s faster than that needed by raw coal. The activation energy of water-soaked air-dried coal calculated by using the KAS and FWO methods is reduced to about 83% of that of raw coal. This result indicates that water soaking and air drying increase the tendency of coal to self-ignite. The thermal diffusivity of water-soaked air-dried coal is higher than that of raw coal and shows a maximum difference of 0.005 mm2/g at 60 °C. The specific heat capacity and thermal conductivity of water-soaked air-dried coal are lower than those of raw coal and show the maximum differences of 0.19 J g/K and 0.18 W/m·K at 210 °C and 300 °C, respectively. Although the spontaneous combustion of water-soaked air-dried coal spreads at a faster rate than that of raw coal, the hazards following the spontaneous combustion is less than that of raw coal. This research contributes to understanding the effect of water soaking and air drying behaviour on coal spontaneous combustion characteristics.

Study on the variation in key functional groups of coal and the mechanism of CO and CO2 generation under the thermal effect of lean-oxygen conditions

Most closed fire areas in coal mines encounter rapid reignition after unsealing. To prevent the reignition of residual coal, it is necessary to study the impact of the lean oxygen conditions (LOCs) in closed fire areas on the characteristics of coal spontaneous combustion (CSC), evolution of the pore and fissure structures, and generation mechanisms of gases such as CO and CO2. A systematic study was conducted using in situ infrared, synchronous thermal analyzer (STA-DSC), scanning electron microscope (SEM), N2 adsorption, and programmed heating experiments. The results show that during the low-temperature oxidation process (LTOP), the temperature and oxygen concentration had a significant impact on the content variations of functional groups such as –OH, CO, COOH, CH2/CH3, and CC. Moreover, the higher the oxygen concentration, the higher was the effect. The concentration and heat release rate of CO and CO2 generation were positively correlated with the oxygen concentration. As the temperature increased, cracks developed gradually on the coal surface, and micropores transformed into mesopores and macropores. The specific surface area decreased gradually. When the temperature was below 110 ℃, the microstructure of the coal sample did not vary significantly. When the temperature was above 110 ℃, the effect was significant. The higher the oxygen concentration, the more significant was the impact on the pore characteristics of the coal. Two main pathways exist for CO and CO2 generation. CO2 generation requires a higher temperature than that required for CO. The research results provide a theoretical basis for the unsealing of closed fire areas and prevention of reignition.

Experimental research on the features of spontaneous combustion during secondary oxidation of coal with various particle sizes

The secondary oxidation of remaining coal in the process of secondary mining of coal seams poses a major threat to the safety of personnel and property, as well as the effortless re-mining of relict coal. The grain size composition of the relict coal in the mining area is complex, and it is an essential component determining the coal's spontaneous combustion characteristics, particularly the more complex secondary oxidation reaction. The secondary oxidation characteristics of coal treated with various pre-oxidation temperatures at different grain sizes were investigated using TG-DSC coupled experiments and electron paramagnetic resonance (EPR) experiments. The results showed that as the particle size of the coal samples decreased, the ignition point temperature T6 and the maximum burning rate temperature T7 decreased gradually; the burnout index and the comprehensive combustibility index increased gradually; the endothermic ‘ladder’ on the DSC curves are more pronounced, with the peaks shifting to lower temperatures; the activation energy of coal samples gradually declines from the ignition point temperature T6 to the maximum burning rate temperature T7 during the combustion process, as determined by Coats-Redfern and Achar-Brindley-Sharp-Wendworth respectively; the g-factor of coal samples tends to decrease, while the concentration of free radicals declines first and subsequently increases. With the same particle size, the g-factor of the coal samples remained virtually constant as the pre-oxidation temperature increased, whereas the free radical concentration gradually increased.