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Spontaneous combustion of coal gangue (CG) hills has caused varieties of secondary disasters that seriously endanger the ecological environment of the world. The emission law of index gases and their oxidation kinetics during the secondary oxidation process of CG with different ranks of oxidation were studied by using the temperature programmed device and online mass spectrometer (MS). Fourier transform infrared spectroscopy (FTIR) was used to reveal the changes of the CG internal active functional groups. The results showed that the energy required for the combustion of CG with low rank of pre-oxidation was significantly lower than that of the raw sample. However, as the oxidation rank increased, due to amounts of volatile components were released in the process of oxidation reaction, the CG in the combustion process of the emission of index gases and its oxygen consumption rate gradually reduced; the rapid oxidation stage shifted to the direction of the high temperature. In this study, the risk of spontaneous combustion of CG after oxidation at 80 ℃ under 3% oxygen concentration was the strongest. The results of this paper are of great guiding significance for exploring the spontaneous combustion characteristics of CG hills and their prevention by traditional covering method., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Coal fire is a global catastrophe. Xinjiang suffers the most severe coal fire in China and even in the world. Coal firefighting work has been being conducted for decades in Xinjiang. In this paper, coal fire detection, extinguishing, and monitoring approaches that were derived from coal firefighting experience are introduced in detail by taking the Fifth Fire Area (FFA) of the Heshituoluogai coal fire for instance. We first introduce the geology and fire situation in the FFA. Before developing efficient strategies to extinguish it, magnetic and self-potential methods are adopted to delineate the extent of the fire. A composite index is proposed to better indicate the fire. The comprehensive coal firefighting method is illustrated in detail, which consists of surface cooling, excavation and leveling, borehole drilling, borehole water injection and grouting, and loess backfill. The subsequent temperature and CO monitoring records show that the fire is extinguished successfully without burnback. The methodology presented here provides guidance and reference for putting out other coal fires around the world.

Coal fires are a serious threat to the workers' security and safe production in open pit mines. The coal fire source is hidden and innumerable, and the large-area cavity is prevalent in the coal seam after the coal burned, causing the conventional extinguishment technology difficult to work. Foams are considered as an efficient means of fire extinguishment in these large-scale workplaces. A noble foam preparation method is introduced, and an original design of cavitation jet device is proposed to add foaming agent stably. The jet cavitation occurs when the water flow rate and pressure ratio reach specified values. Through self-building foaming system, the high performance foams are produced and then infused into the blast drilling holes at a large flow. Without complicated operation, this system is found to be very suitable for extinguishing large-scale coal fires. Field application shows that foam generation adopting the proposed key technology makes a good fire extinguishment effect. The temperature reduction using foams is 6-7 times higher than water, and CO concentration is reduced from 9.43 to 0.092‰ in the drilling hole. The coal fires are controlled successfully in open pit mines, ensuring the normal production as well as the security of personnel and equipment.

The cutting dust created by the shearer drum is the main source of dust on a fully mechanized coal face. However, overexposure to respirable dust may cause pneumoconiosis in coal workers, while coal dust may lead to serious explosions. The fully mechanized face known as II1051 Face, found at the Zhuxianzhuang Coal Mine located in east China, generates dust by way of the drum on a high-power shear. The coal seam involves hard rock parting so there is a high concentration of cutting dust when the shearer is working. Thus, we developed a new foam dust suppression method with an air self-suction system based on an analysis of the dust generation characteristics that suppressed the shearer cutting dust level. The new foam system was evaluated in a field test where the dust concentration was measured at two points. The results showed that the foam reduced the cutting dust concentration significantly. The respirable dust exposure levels were reduced from 378.4 mg/m(3)to 53.5 mg/m(3)and the visibility was enhanced dramatically. Thus, we conclude that our new foam system is highly efficient at capturing cutting dust, and it has a much lower water consumption. [Supplementary materials are available for this article. Go to the publisher's online edition of Journal of Occupational and Environmental Hygiene for the following free supplemental resource: Contact angle of cutting dust sample, migration trajectory of cutting dust, technological process for suppressing shearer cutting dust using foam, the layout of the foam dust suppression system on coal face, real object of the air self-suction type foam generator, the special foam nozzle used for shearers, relevant experimental results of the air self-suction foam system.].

High-temperature coal oxidation generates a substantial amount of CO and CO2, especially CO, rapidly, which is a primary factor leading to casualties. The oxygen concentration is the predominant factor affecting the high-temperature oxidation of coal, particularly in the generation of CO and CO2. Understanding the generation patterns and relationship characteristics of CO and CO2 under various oxygen concentrations is important for predicting high-temperature coal oxidation and ensuring personnel safety. The paper used TG–MS and FTIR to study the formation characteristics of isothermal oxidation of CO and CO2 in long-flame coal under different oxygen concentrations. The results indicate that there exists an optimal threshold for CO production when the oxygen concentration is about 9% during the isothermal temperature oxidation process at 200.00–350.00 °C. When the oxygen concentration is less than 13%, the influence of oxygen on CO2 production is weakened. As the temperature increases, the pattern of CO + CO2 production and CO/CO2 is reversed, with CO + CO2 increasing and CO/CO2 decreasing. The relationship between the total production of CO and CO2 and the loss of coal mass follows the function y = a + bx at the isothermal temperatures of 300.00 °C and 350.00 °C. An increase in oxygen concentration does not alter the linear relationship. In the isothermal oxidation process of coal, carbonyl and carboxyl groups are the key groups for CO and CO2 production. At 200.00 °C and 250.00 °C, carbonyl and carboxyl groups increase, and other groups are being converted to carbonyl and carboxyl groups while decomposing into CO and CO2. At 300.00 °C and 350.00 °C, the relative content of carboxyl groups decreases. The research findings play a fundamental role in coal mine disaster prevention and control. [ABSTRACT FROM AUTHOR]

Coal refuse pile fires are a serious health, safety, and environment hazard. The fires in Guoshan Coal Refuse Pile affect daily life of the local residents. Although conventional fire control methods (water injection, grouting and surface sealing) were used to control the fires, they rekindled soon after the fire-fighting engineering was quitted. Thus, effective methods need to be applied to extinguish the fires completely without reignition. In this paper, the environmental impact of the fire on the local land, water and air is illustrated by sample analysis and photos. The self-potential method, which achieves remote detection from the ground surface, is adopted to delineate the scope of the fires to give support for the efficient and economical extinguishment of them. The three-phase foam containing water, gas and loess is proposed to control and extinguish the fires. The corresponding fire-fighting system is also invented to fit the field work and put out the fires more efficiently and conveniently. The temperature monitoring result shows that the fires are extinguished successfully with no sign of reignition. [ABSTRACT FROM AUTHOR]

Coal dust explosions (CDE) are one of the main threats to the occupational safety of coal miners. Aiming to identify and assess the risk of CDE, this paper proposes a novel method of fuzzy fault tree analysis combined with the Visual Basic (VB) program. In this methodology, various potential causes of the CDE are identified and a CDE fault tree is constructed. To overcome drawbacks from the lack of exact probability data for the basic events, fuzzy set theory is employed and the probability data of each basic event is treated as intuitionistic trapezoidal fuzzy numbers. In addition, a new approach for calculating the weighting of each expert is also introduced in this paper to reduce the error during the expert elicitation process. Specifically, an in-depth quantitative analysis of the fuzzy fault tree, such as the importance measure of the basic events and the cut sets, and the CDE occurrence probability is given to assess the explosion risk and acquire more details of the CDE. The VB program is applied to simplify the analysis process. A case study and analysis is provided to illustrate the effectiveness of this proposed method, and some suggestions are given to take preventive measures in advance and avoid CDE accidents. [ABSTRACT FROM AUTHOR]

Chinese lignite coal from the Beizao mine which located in Shandong Province of China was studied using a combination of ultrasonic extraction under mild conditions (which generate minimal chemical changes) in conjunction with modern analytical instrumental techniques. This procedure allowed the development of a structural model. Calculations with the Gaussian 09W package generated an optimized structural geometry and also determined the activities of various functional groups. The initial stages of oxidation were found to consist of the oxidation of hydroxyl groups, the rupture of C–O and C–C bonds, and the dehydrogenation of carboxyl groups. In contrast, both the decarboxylation and decarbonylation reactions were determined to require significant energy inputs and thus occur only at high temperatures. In situ Fourier transform infrared analyses were used to confirm the results of the theoretical calculations. [ABSTRACT FROM AUTHOR]

Carboxyl groups play an important role during the development of coal self-heating. The real-time changing characteristics of carboxyl groups were obtained using anin situFourier Transform Infrared Spectroscopy method. They are significantly influenced by reaction atmospheres. Under dry-air atmosphere, their quantity obviously decreases before reaching 120°C and then increases with temperature rise. Under oxygen-free atmosphere, it decreases before reaching 80°C and then increases with temperature rise. In contrast with direct oxidation process, the quantity of carboxyl groups is smaller and the decrease phenomenon at the beginning almost disappears during the oxidation process following oxygen-free reaction. The results indicate that the carboxyl groups have different reaction pathways during coal self-heating. These pathways can be divided into two kinds, that is, oxidation pathways and self-reaction pathways. The study proposed the reaction sequences of carboxyl groups during coal self-heating, which are helpful for revealing the mechanism of coal spontaneous combustion. [ABSTRACT FROM AUTHOR]

This study details an in situ Fourier transform infrared spectroscopy analytical system that was employed to follow chemical variations in the functional groups on coal surface during the oxidation process at low temperatures. In the reported in situ Fourier transform infrared spectroscopy system, a special chamber was used to contain the coal powders, and a gas inlet tube and a programmable heater were used to simulate different reaction atmospheres and temperatures. The comparisons between in situ and ex situ Fourier transform infrared spectroscopy spectra indicate that the in situ Fourier transform infrared spectroscopy data offer a more accurate reflection of changes in the functional groups. The real-time changes of aliphatic hydrocarbon groups and oxygen-containing groups in a lignite coal sample were analyzed from 30°C to 220°C using in situ Fourier transform infrared spectroscopy. The experimental results indicate that the chemical variations in the functional groups are affected by their relative chemical activities. The results show that the presence of aliphatic groups on the coal surface varies with temperature. Over the range of 30–70°C the presence of these groups decreases, but then their abundance increases over the range of 70–180°C and finally decreases again when the temperature is increased to between 180°C and 220°C. With respect to oxygen-containing functional groups, three various trends were observed as the test temperature was varied. Our conclusion was that these variations are a function of the reaction activities of the various oxygen-containing functional groups. [ABSTRACT FROM AUTHOR]

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To further understand the problems of coal combustion and coalfield fire reignition, this paper researched the reaction characteristics of coal pyrolysis and low oxygen combustion and the reburning oxidation characteristics of residual structure by thermal analysis methods. The results show that temperature promotes both pyrolysis and low oxygen combustion reactions, but low oxygen combustion reaction is more sensitive to temperature changes. As the constant temperature rises, the mass reduction rate of low oxygen combustion of coal samples reaches 80% on average, which is 4 times that of pyrolysis, and the variations of thermogravimetric parameters are also significantly higher than those of pyrolysis. However, the higher the pyrolysis degree of the residues, the stronger their oxidizability, which greatly enhances the intensity and concentration of the secondary combustion, and the mass of residues is reduced by 90% on average. Conversely, because the combustible components are continuously consumed during low oxygen combustion, the reburning characteristics of residues become less obvious. For instance, the weight loss rate slows down, the burning becomes dispersed, and the burning intensity is weakened. In addition, the heat release is reduced from 8662 to 444.5 J/g, and the change trend is just opposite to that of pyrolysis. The above results show that as the constant temperature rises, the pyrolysis reaction greatly shortens the reburning process, while the low oxygen combustion reaction largely inhibits the reburning. [ABSTRACT FROM AUTHOR]

Safe mining is the premise and guarantee of sustainable development of coal energy. Due to the combination of excellent properties of polymers and traditional soft matters, polymer-containing soft matters are playing an increasingly important role in mine disaster and hazard control. To summarize the valuable work in recent years and provide reference and inspiration for researchers in this field, this paper reviewed the recent research progress in polymer-containing soft matters with respect to mine dust control, mine fire control, mine gas control and mine roadway support. From the perspective role of polymers in a material system, we classify mine polymer-containing soft matters into two categories. The first is polymer additive materials, in which polymers are used as additives to modify fluid-like soft matters, such as dust-reducing agents (surfactant solution) and dust-suppressing foams. The second is polymer-based materials, in which polymers are used as a main component to form high performance solid-like soft matters, such as fire prevention gels, foam gels, gas hole sealing material and resin anchorage agent. The preparation principle, properties and application of these soft matters are comprehensively reviewed. Furthermore, future research directions are also suggested. [ABSTRACT FROM AUTHOR]

• The emissions of gases during high temperature oxidative pyrolysis of coal was studied online. • The ratio of CO 2 /CO in high-temperature oxidative pyrolysis is temperature-dependent. • The gas release at high temperatures is proportional to the specific surface area of coal char. The study examined the oxidative pyrolysis of raw and residual coals extracted with tetrahydrofuran, as well as the CO/CO 2 /H 2 /CH 4 emissions at high temperatures (200∼900 °C). Tetrahydrofuran was found to extract aromatic and aliphatic hydrocarbons from lower metamorphic coal, as well as hydroxyl, increasing the specific surface area of char formed by oxidative pyrolysis of residual coal. The CO 2 /CO ratio was temperature dependent, and the increase period was fit by a polynomial and a linear function, with critical temperature of around 570 °C. The greater CO 2 /CO ratio of raw coal suggested that oxidative pyrolysis produced more CO 2. The kinetic analysis showed that the change in activation energy is inconsistent with the gas production, and the gases were found to be proportionate to the specific surface area of the coal chars, implying that the char structure has a significant influence on gaseous product emissions and the coal oxidative pyrolysis at high temperatures is a diffusion-controlled heterogeneous reaction. The findings of this study could be useful for determining the status of coal fire. [ABSTRACT FROM AUTHOR]

As dust is one of the main hazards generated by coal cutting, understanding the properties of dust generation is essential for preventing and controlling its propagation. This paper therefore aims to investigate the influence of coal brittleness on dust generation. A system was devised to produce dust and the density, uniaxial compressive strength, and Brazilian tensile strength of dust samples were then measured. The results showed that the cumulative proportions of fine particulate matter and respirable dust increased with brittleness, while a declining trend was observed from the mass ratio of total dust to coal sample. B14 (half of the product of compressive and tensile strength) had the strongest correlation with the properties of dust generation, and accounted for more than 95% of B15 (half of the sum of compressive and tensile strength). Unlabelled Image • Different correlations are found between brittleness formulas and dust generation. • B14 is discovered to have the most significant correlation with dust generation. • Positive relationships are observed between cumulative proportions and brittleness. • Mass ratio of total dust is observed to decline with ascending brittleness of coal. [ABSTRACT FROM AUTHOR]

To investigate the characteristics of coal dust generation when cut by a roadheader, a system was designed for performing cutting experiments. The aerodynamic diameter distribution of dust was tested by a laser particle size analyzer. Correlations between the coal proximate compositions and the characteristics of dust generation were studied. Results showed that fixed carbon had significantly positive correlations with the cumulative proportion of respirable dust and the rate of dust generation. The bonded high-density pulverized core could be responsible for reducing the correlation with fine particulate matter. The presence of moisture had inhibitory effects on dust generation. Volatile matter had a slightly negative influence on dust generation, and ash was considered to have no effect. More attention should be focused on heading faces with high fixed carbon and low moisture. This study provides essential guidance for understanding the characteristics of dust generation and improving dust reduction technologies. Unlabelled Image • The effects of fixed carbon on dust generation are significantly positive. • The bonded high-density pulverized core can reduce the generation of fine particle. • The effects of volatile matter on dust generation are slight. [ABSTRACT FROM AUTHOR]

The lean-oxygen combustion of incompletely pyrolyzed char dominated at the combustion front of coalfield fires. Functional group distributions and carbon micro-crystal dimensions were characterized for developing the molecular model (C 184 H 124 N 2 O 16 S) of pyrolyzed coal char at 400 °C (TLG P400). The overall combustion process of TLG P400 under various oxygen/fuel ratios (Ω) were simulated in an intuitive approach with ReaxFF. The findings indicated that the primary carbon-containing intermediates transformed from large pieces of aromatic fragments C 40+ with self-similarity to heavy components of C 15 –C 40 in initial combustion stage, then to light components of C 5 –C 14 in late stage. With Ω increasing from 1.0 to 5.0, the final carbon conversion was found to rise from 78.50% to 96.32%, while the CO/CO 2 ratio in the products sharply decreased from 2.575 to 0.213. The apparent activation energy was calculated as 194.49 kJ/mol for TLG P400 combustion at Ω = 1.0. Higher oxygen concentration enhanced the adsorption proportion of edge carbon, resulting in the generation of unstable intermediates featuring meta - or para -semiquinone. These transformations promoted the detachment of edge carbon and weakened the bottle-neck effect of the single-benzene ring on rapid oxidation. This study provides valuable insights into combustion mechanism and monitoring approaches for controlling coalfield fires. • A molecular model of coal char is developed based on measured structural components. • Product and structural evolutions of coal char burning are elucidated by ReaxFF MD. • Effect of oxygen-supply on reburning reactivity of pyrolyzed coal char is clarified. • Single-ring residues contribute to the delayed lean-oxygen combustion of coal char. [ABSTRACT FROM AUTHOR]

• Pore evolution during lean-oxygen reburning of pyrolyzed semicoke was clarified. • Oxygen diffusion mechanism transforms from Knudsen to transition diffusion at 650 °C. • Warning temperature for accelerating spread of coal fire was determined as 650 °C. The lean-oxygen combustion of incompletely pyrolyzed char dominates at the combustion front of coalfield fires. Using non-local-density functional theory (NLDFT) and Barrette-Joynere-Halenda (BJH) analysis based on N 2 and CO 2 composited adsorption isotherms, the pore (0.4–300 nm) structure characteristics of pyrolyzed char during lean-oxygen combustion were obtained. The results indicate that the main pore morphology changes from irregular ink-bottle shape of raw coal to cylindrical shape of pyrolyzed char, then to slit-shaped and wedge-shaped pores under the effect of oxidative expansion, and finally coalesce into amorphous macropores during combustion. For the weak-caking coal, softened colloids diffuse and block the mesopores, leading to the reverse development of mesopores into smaller-sized pores. The pore development changes from the generation of secondary micropores in pyrolysis stage to the progressive expansion mode of mesopores in initial combustion stage, then to the free coalescence mode of macropores in late combustion stage. The dominant internal oxygen diffusion mechanism transforms from Knudsen diffusion to transition diffusion at 650 °C, and the carbon-oxygen reaction interfaces shift from the inner surface of deep micropores to the shallow mesopores and macropores. Finally, 650 °C is determined as the early-warning temperature for the accelerating spread of coalfield fires. [ABSTRACT FROM AUTHOR]

Highlights: [•] It is a linear relationship between and the adiabatic R 70 self-heating rate. [•] A rapid method was developed to determine R 70, which need a time shorter than 1.5h. [•] The was used as an index to classify the spontaneous combustion tendency of coal. [ABSTRACT FROM AUTHOR]

[Display omitted] • Lowering the tip angle and rotating speed will diminish dust generation. • An innovative method for reducing dust in the origin was proposed. • The conical pick with a larger tip angle causes more cracks. • A larger attack angle reduces the peak cutting force and the work. Dust pollution is a serious environmental hazard during the tunneling in coal mines. Despite the presented dust control technologies, the method of reducing dust production has not been adequately investigated. This paper conducted cutting tests with various tip angles and attack angles using numerical models. A novel method for reducing the production of dust, based on the simulation results, was proposed and verified in the field experiments. The cutting force, work and crack extensions were analyzed. The concentrations of dust in laboratory tests were linked to the simulation results. The simulated results showed that the conical pick with a large tip angle could increase the cutting force and work and cause more cracks. The attack angle had a negative relation with the cutting force and work. The field experiments suggested that the amount of dust could be significantly reduced by using conical picks with a small tip angle. A slower rotation speed of the cutting head could alleviate dust hazards. The results are of momentous relevance for mine managers and researchers to reduce the production of dust during tunneling and control the dust more efficient. [ABSTRACT FROM AUTHOR]

• The Mono/Multi molecular models of LHG jet coal were constructed and verified. • The pyrolysis process of LHG jet coal was simulated by the ReaxFF MD method. • The pyrolysis process was divided into 3 stages including 3 key pyrolysis paths. • The formation mechanisms and reaction pathways of CO, H 2 S were revealed. • The detail chemical reactions of LHG jet coal pyrolysis were shown. Zhundong coalfield is the largest coalfield in China and the unclear stage evolution mechanism of Zhundong coal pyrolysis is the key factor restricting its coal fire control. Here, the monomolecular model (299 atoms) and large-scale multimolecular model (5083 atoms) were constructed for Liu huanggou (LHG) coal from Zhundong coalfield. The pyrolysis processes of the two models were calculated by ReaxFF MD method. Based on the reaction consistency analysis, the reaction paths tracing on pyrolysis stage evolution and toxic gases formation mechanisms were obtained. The LHG coal pyrolysis process is mainly because of the breakages of the ether oxygen bridge bonds, thioether bridge bonds and aliphatic hydrocarbon bridge bonds. It begins with the shedding of small molecules and then undergoes the thermal decomposition of the main structure and pyrolytic fragments. During the pyrolysis process, the LHG coal has constantly broken out tars, gases and other key products, accompanied by a large number of free radicals and intermediates produced. The main sources of CO are the active reaction sites where the carbonyl group and the carboxyl group located; H 2 S is directly produced from the sulfhydryl group. The research results will guide the staged control and directional transformation of coal fire. [ABSTRACT FROM AUTHOR]

We have developed a new class of aqueous Pickering foams, which were stabilized by sodium dodecyl sulfate (SDS)-modified micro fly ash (FA) particles and exhibited excellent stability and inhibition characteristics for coal spontaneous combustion. Specifically, this study aimed to characterize the microstructure, foaming behavior, evolution process and inhibition characteristic for coal spontaneous combustion of these Pickering foams. The evolution of these Pickering foams is quantified by measuring the rate of bubble growth as well as the kinetics of liquid drainage and the two processes are correlated. These data allow us to identify a transition time, separating two distinct stages of foam evolution. An increasing FA concentration in the Pickering foams lead to an increase in foam stability, which arises from the formation of a robust FA-armoured bubble structure. In addition, the coal acceleration oxidation experimental results show that these Pickering foams can improve the coal thermal stability and effectively inhibit the coal oxidation process by increasing crossing point temperature (CPT) and reducing CO emission. The results indicate that the prepared aqueous, low-cost and nontoxic FA-stabilized Pickering foams effectively slow the oxidation of coal, thereby demonstrating its application potentials in coal spontaneous combustion prevention and control. [ABSTRACT FROM AUTHOR]