Process Of Spontaneous Combustion Research Articles

Monitoring and Occurrence of Heavy PAHs in Pomace Oil Supply Chain Using a Double-Step Solid-Phase Purification and HPLC-FLD Determination.

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental and processing contaminants generated by both spontaneous and anthropogenic incomplete combustion processes of organic matter. Contamination of PAHs in vegetable oils can result from several factors and processes, including environmental contamination, oil processing, and migration from food contact materials. The determination of PAHs in edible oil presents a challenge because of the complexity of the matrix. Since PAHs are present at lower levels than triglycerides, it is necessary to isolate the compounds of interest from the rest of the matrix. To this purpose, a new purification approach based on a double solid-phase extraction (SPE) step followed by high performance liquid chromatography–fluorometric detector (HPLC-FLD) analysis was developed. The method involves a first purification step by using a 5 g silica SPE cartridge, previously washed with dichloromethane (20 mL), dried completely, and then conditioned with n-hexane (20 mL). The triglycerides are retained by the silica, while the PAH-containing fraction is eluted with a mixture of n-hexane/dichloromethane (70/30, v/v). After evaporation, the residue is loaded on a 5 g amino SPE cartridge and eluted with n-hexane/toluene (70/30, v/v) before HPLC-FLD analysis. The focus was the evaluation of the contribution of the various phases of the pomace oil supply chain in terms of the heavy PAHs (PAH8) concentration. Data collected showed that pomace contamination increased (by 15 times) as storage time increased. In addition, the process of pomace drying, which is necessary to reduce its moisture content before solvent extraction of the residual oil, appeared to significantly contribute to the total heavy PAHs content, with increases in value by up to 75 times.

Feasibility investigation of utilizing spontaneous combustion energy of abandoned coal gangue by constructing a novel artificial heat reservoir

In this paper, we present a novel artificial heat reservoir system for extracting spontaneous combustion energy of abandoned coal gangue. The construction process and operation method of the proposed artificial heat reservoir are introduced in detail. A multi-physical fields coupling model of seepage, heat transfer and oxidation of coal gangue is established. The spatio-temporal variation of temperature field, seepage field, oxygen concentration field and residual fuel amount in the oxidation process of coal gangue were numerically investigated. Sensitivity analysis of key parameters was carried out to provide reference for the optimization of artificial heat reservoir. Finally, the heat extraction performance of artificial heat reservoir was studied by using steel U-shaped tube, and its heating potential was evaluated. The results indicates that the process of spontaneous combustion of coal gangue can be divided into two stages: slow heating stage and rapid heating stage. The proposed artificial heat reservoir system presents a “low temperature zone-high temperature zone-low temperature zone” distribution from bottom to top. This alternating and layered temperature zones in vertical direction will form a thermal siphon effect and drive the air to flow upwards. In the rapid heating stage, the temperature increases faster with the increase of ventilation rate. When the porosity is greater than 0.35, it has a great influence on the spatial design of the heat extraction system. The specific heat capacity only affects the changing rate of temperature field and oxygen seepage velocity, but does not affect their final states. The thermal conductivity of coal gangue has little influence on each physical field of reservoir. The heat transfer rate of the middle part of the U-shaped tube is relatively large, the average value of which is about 150 W/m. The heat transfer of U-shaped tube only affects the area within the radius of 2 m. The research can provide a new idea for coal gangue disposal and heat utilization.

Thermodynamics of Imidazolium-Based Ionic Liquids for Inhibiting the Spontaneous Combustion of Sulfide Ore

Spontaneous combustion of sulfide ore is one of the most common disasters in the process of ore mining, storage, and transportation, which can lead to a series of safety and environmental problems, thus affecting sustainable development in society. In this paper, four imidazolium-based ionic liquids: [BMIM][I], [BMIM][BF4], [EMIM][BF4], and [BMIM][NO3], were selected for inhibition experiments with sulfide ores to reveal the inhibition performance of ionic liquids against spontaneous combustion. The results show that the main products from the reaction were Fe2O3 and SO2, produced during the process of oxidation and spontaneous combustion and that the reaction moves towards a higher temperature under the action of ionic liquid, indicating that ionic liquids have a significant inhibition effect on the spontaneous combustion of sulfide ore. At the same temperature, the apparent activation energies of the samples treated with ionic liquids were all greater than those of the control samples, indicating that imidazolium-based ionic liquids can effectively reduce the spontaneous combustion tendency of sulfide ores. In addition, compared with other ionic liquids, [BMIM][NO3] had a more pronounced inhibition effect, with the activation energies of both ore samples maximally increased by 8.4% and 10.2% after [BMIM][NO3] treatment. This is due to the ability of [BMIM][NO3] to better isolate the samples from oxygen in the air and reduce the effective collisions between active molecules, thus inhibiting and retarding the spontaneous combustion of sulfide ores.

Experimental Study on Crushing Characteristics of Lignite under Different Load Conditions

Coal particle size and the degree of compaction significantly affect the goaf heritage ventilated environment and the process of spontaneous combustion of coal, the distribution of particle size and compaction degree are also affected by the load size and the application process, and the distribution of stress in goaf is not uniform, resulting in the distribution of particle size and compaction degree of mined-out coal. It is necessary to carry out experimental studies on coal crushing granularity and compaction degree under different loads and loading processes to clarify its distribution law. Therefore, experiments on the coal crushing were conducted, to analyze the compression behaviors and the distributions of the particle size with different loading speeds and loads. The results show that, in the process of slow pressure application, the lump coal was constantly compressed, compacted, and broken. With the increase in the axial load, the coal compressibility increased, and the coefficient of fragmentation and porosity decreased. When the stress was greater than the compressive strength, the variation trend slowed. When the stress was greater than two times the strength, as the load continued to increase, compression basically did not occur. The thickness and porosity of coal will be reduced to 0.5 times that of loose coal when a significant change of the compression ratio occurs. After the coal body was under pressure, the degree of crushing intensified. The fractal dimension of the particle sizes of broken coal particles followed a logarithmic relationship with the increase in the stress. With the increase of stress, the degree of crushing increased, and in the process of pressure crushing, the particle size of 2.5 mm was an important boundary. When the stress was more than two times the strength value, the degree of crushing under the increased load did not increase significantly. When the residual coal in a goaf is affected by pressure, if there is no impact, the influence of the initial pressure and periodic pressure variations on the residual coal in the goaf will not be significant, and the accumulation and crushing degree of residual coal will only be affected by the peak stress.

Influence of particle diameter on the scattering characteristics of pre-oxidized coal in THz band

In this study, the effect of scattering caused by particle diameter on the quantitative analysis of pre-oxidized coal applying terahertz (THz) was investigated by Synchronous Thermal Analysis, THz time-domain spectral (THz-TDS), and Scanning Electron Microscopy. Through analysis of the characteristic temperatures of coal, the combustion process of coal was divided into water evaporation, oxygen absorption, and spontaneous combustion process. The THz-TDS experiments in the range 0.5–1.25 THz showed regular variation in the refractive index and the extinction coefficient of coal. Some characteristic temperatures locate at the inflection points of the imaginary component of the dielectric constant and the extinction coefficient of coal. Moreover, similar trend was observed in the imaginary component and the extinction coefficient of coal with increasing pre-oxidation temperature. The intrinsic absorption of coal and the scattering caused by coal, air void, and high-density polyethylene (HDPE) attenuate the THz wave. The extinction coefficient of coal is remarkably correlated linearly with coal particle size of diameter more than 180 mesh before 225 °C. When coal particle size is less than 180 mesh, the extinction coefficient of coal showed a relatively small change with decreasing coal size. The relationship between the extinction coefficient of coal and coal size is low after 225 °C. This study demonstrated the capability of THz to identify the pre-oxidized coal and showed decreased scattering impact on the THz results.

Evolution and mechanisms of low-temperature oxidation and coal–oxygen coupling processes of a specific low-rank bituminous coal with various microscale particle sizes

ABSTRACT Coal fires are very typical hazards caused most significantly by uncontrolled spontaneous combustion processes in coal mines, seams, and the like. By thermogravimetry (TG) experiments, evolution behaviors and properties of thermal oxidation processes at low temperature of a bituminous coal with five microscale particle sizes (L1 215.20 μm; L2 151.90 μm; L3 80.22 μm; L4 43.71 μm; and L5 19.21 μm) were investigated. A two-step reaction model was developed by using Coats–Redfern method and pyrolysis kinetics parameters were calculated. Results show that in stage 1 (65.0–160.0°C) segments of water evaporation and gas desorption dominate, while in stage 2 (160.0–320.0°C) segments of generation of coal–oxygen complex and structure oxidation contribute most. Five macro-characteristic temperatures (critical temperature T1, xerochasy temperature T2, activity temperature T3, mass peak temperature T4, and ignition temperature T5) move to the low temperature direction with decreasing particle sizes except T4. Reaction processes during coal–oxygen interactions are proposed. Activation energies decrease as particle sizes reduce during both stage 1 (15.01–32.47 kJ·mol−1) and stage 2 (64.29–96.34 kJ·mol−1) since specific surface areas are augmented and more active groups are exposed. This work is expected to better monitoring of temperature thresholds for coal spontaneous combustion processes.

Study on the Change Law of Red-Green-Blue Values of Infrared Thermal Image in the Process of Anthracite Oxidation and Spontaneous Combustion

As the coal with the highest degree of coalification, anthracite is usually regarded as a mixture composed of organic and inorganic substances, with the characteristics of polymers and composites. It is very important to study the oxidation and spontaneous combustion characteristics of anthracite for the thermal properties of coal-based polymers and composites. Anthracite exhibits varying oxidation and spontaneous combustion characteristics at various stages of the oxidation and spontaneous combustion process, which cannot be fully demonstrated by the coal temperature alone. As a result, this paper develops an online method for characterizing the RGB values of infrared thermal images. The variation of the RGB value of an infrared thermal image during the oxidation and spontaneous combustion of anthracite was investigated. The findings show that there is a clear relationship between R (red), G (green), B (blue), RGB (red/green/blue) values, and coal temperature during the oxidation and spontaneous combustion of anthracite. The R and the G value curves each have one characteristic peak and two characteristic valleys in the experiment. However, the overall change range of the G value curve is relatively small; the B value curve has two characteristic peaks and one characteristic valley. There are no characteristic peaks and valleys in the RGB value curve, despite the influence of experimental instruments and the experimental environment.

Study on Spontaneous Combustion Characteristics and Risk of Oil Shale

ABSTRACT This paper studies the spontaneous combustion process of two kinds of oil shale to grasp the characteristics and mechanism of spontaneous combustion, which provides a theoretical basis for preventing spontaneous combustion of oil shale. Based on thermal analysis and low-temperature adsorption, the risk of spontaneous combustion of Wangqing oil shale (WQOS) and Beipiao oil shale (BPOS) (China) are studied. Based on the thermal analysis data, advanced kinetics and technology solution (AKTS) software is used to predict and evaluate the risk of spontaneous combustion. The kinetic model, which is obtained by combining the Gaussian fitting method with the peak analysis method, can effectively describe the combustion of the volatilization. The results show that, the combustion process of the volatilization can be divided into three stages. The predicted results show that, for the same initial temperature, the tendency of spontaneous combustion of BPOS is greater than that of WQOS, which is consistent with the results of thermal analysis and static oxygen absorption.

Experimental study on the effect of high-temperature oxidation coal mechanical characteristics.

After long-term oxidation and energy storage, broken coal body borehole walls and drainage shaft walls may cause spontaneous combustion during gas extraction. The high-temperature thermal shock caused by the spontaneous combustion of coal incurs thermal damage on adjacent coal, which, in turn, causes changes in the mechanical properties of the coal. However, only a few studies have been conducted in this context, which has limited our understanding of the thermal damage characteristics of coal bodies in such situations. This study aimed to experimentally investigate the correlation between the crack evolution law and the mechanical properties of coal bodies at different temperatures (50-300°C) using heat-force loading considering Ping Mei No. 10 coal mine as the research object. The results suggest that the coal body experiences a large amount of visible damage, and becomes increasingly complex. At 50-300°C, some indexes (such as longitudinal wave velocity, Poisson's ratio, compressive strength, elastic modulus, impact energy index, and pre-peak strain) are positively correlated with temperature. In addition, the dynamic failure time and temperature show a negative correlation, and the overall change slope is small. The relationship between each index and temperature at 200-300°C is opposite to that at 50-200°C, and the overall change slope is larger. Moreover, when the oxidation temperature exceeds 200°C, the destruction of the coal body changes from elastic brittleness to ductility-plasticity. High-temperature oxidation incurs irreversible thermal damage of coal. Hence, it is necessary to focus on the changes in mechanical properties of coal after a spontaneous combustion process is extinguished.

A comparative kinetic study between TGA & DSC techniques using model-free and model-based analyses to assess spontaneous combustion propensity of Indian coals

Kinetic study of coal was carried out using simultaneous thermal analysis (STA) technique to assess the spontaneous combustion propensity of coal samples collected from various Indian coalfields having both fiery and non-fiery seams. The kinetic parameters were estimated by using both model-free and model-based analysis for both TGA & DSC data. The model-based method comprises four different consecutive reaction steps, viz. A→B→C→D→E for the spontaneous combustion process and the second reaction step (B→C) were used for this investigation. Chemometric analysis was applied to know the relation between the proximate analysis and activation energy of the samples using model-free and model-based techniques. The activation energy for the second reaction step of the model-based method for both TGA and DSC data showed a good relationship with the standard methods i.e., crossing point temperature (XPT) and Tgign of the samples. It indicates that the activation energy values at the oxidation stage (2nd stage) play a significant role in the spontaneous combustion propensity of coal. The study also reveals that the model-based analysis provided better results in comparison to model-free analysis to assess the spontaneous combustion propensity of coal.

Study of the Effect of Drive Gas Type on the Inhibition of Coal Spontaneous Combustion by Ternary System Foam

ABSTRACT Evaluation of the fire extinguishing capacity of homemade foams under different driving gases by thermogravimetric experiments. When the concentration of LS-99/SDS/isobutyl alcohol is 0.1%, the expansion ratio can be 52.54 times, 25% drainage time is 210s. Coal spontaneous combustion processes shift toward the high temperature region under the action of foam. The maximum mass loss velocity is reduced. Activation energy analysis shows that the composite inhibition rate of air foam is 64.56%, and nitrogen foam has a 28.18% increase compared to air foam. The heat release decreases under the action of air foam. The coal sample exhibits a heat absorption process in the presence of nitrogen foam. In addition, the mechanism of foam inhibition of coal spontaneous combustion was analyzed from physical and chemical perspectives. In summary, nitrogen foam is more effective than air foam in extinguishing spontaneous coal combustion processes.

САМОВОЗГОРАНИЕ УГЛЕЙ В УСЛОВИЯХ КРИ0ЛИТ030НЫ

Taking into account the prospects for the growth of coal production in the conditions of the North-East, the countries require further development of research to more reliably justify measures to prevent endogenous fires in the permafrost zone, which cause serious economic damage and worsen the environmental situation due to the release of large amounts of toxic gases. The authors have studied the chemical activity and tendency to spontaneous combustion of coals in the permafrost zone. The effect of ambient temperature on the dynamics of oxidative processes in coal accumulations is shown. These studies have identified the main factor in preventing the endogenous fire hazard of coal deposits in the North-East of the country, which consists in maintaining negative or low air temperatures to prevent the intensification of oxidative processes in the coals of the permafrost zone. In laboratory conditions, the influence of physical and chemical factors on the process of spontaneous combustion of frozen coals was studied. Field experiments were carried out on many coal mines in the permafrost area. A system analysis and generalization of domestic and foreign methods of prevention of spontaneous combustion of coals has been carried out. Antipyrogenic compositions have been proposed to reduce the oxidizing ability of coals

Влияние температуры окружающей среды на инкубационный период и склонность угля к самовозгоранию

Crushing coal during mining significantly increases the contact area of combustible components with atmospheric oxygen. The heat released during coal oxidation can lead to an increase in the temperature of the coal accumulation and the appearance of places of spontaneous combustion. For the timely prevention of endogenous fires, it is required to know the incubation period of spontaneous combustion, which is necessary for the coal accumulation to reach the critical temperature. Based on this parameter, the category of coal propensity to spontaneous combustion is established, and measures are developed to reduce the endogenous fire hazard. The known method for estimating the incubation period does not sufficiently consider the influence of the environmental parameters on coal heating. The discrepancy between the calculated and actual duration is observed for coal at a negative temperature, for example, in the mines, and the open-casts in the permafrost areas, as well as in the warehouses in winter on a significantly large territory of Russia. Studies showed that a decrease in temperature significantly reduces the rate constant of oxygen sorption by the coal, and the release of heat in the coal accumulation. The process of spontaneous combustion of coal also slows down due to additional heat losses for the phase transition of water from solid to liquid state. For improving the accuracy of calculating the incubation period of spontaneous combustion of coal at negative temperatures, it is proposed to consider the specific heat of melting ice, and to determine the oxygen sorption rate constant at a constant temperature from –10 to –20 ° C. The influence of negative temperatures of coal accumulation increases the incubation period of spontaneous combustion of coal by 2–3 times allowing to reduce the cost of measures to prevent endogenous fires.

Comparative Experimental Analysis on Coal Spontaneous Combustion

The goal of this study was to investigate coal quality features and their relationship to coal spontaneous combustion characteristics in multi-seam coal mines to better predict when coal spontaneous combustion is likely to occur. To that end, coal samples of various particle sizes were obtained from five coal seams (Nos. 6, 8, 9, 12 and 20) in the Shuangyashan City Xin’an Coal Mine. The samples were then respectively heated using a temperature programming system to observe and compare similarities and differences in the spontaneous combustion process of different particle sizes in response to rising temperature. The experimental results show, that in all five coal seams, the concentration of CO, C2H4, and C2H6 increased with a certain degree of regularity as a function of rising temperature. However, of these three gasses, only CO and C2H4 can be used as indicators to predict coal mine spontaneous combustion. The critical temperature for samples from all five coal seams ranged from 50–85°C, while the dry cracking temperature of coal seams 8 and 12 (80–100°C) were lower than those of 6, 9, and 20 (100–120°C). Furthermore, the production rate of CO, C2H4, and C2H6 is related to both coal particle size and temperature. The smaller the particle size, the faster the production rate; and the higher the temperature, the more gas that gets produced. All five coal seems are mainly composed of long flame coal. However, they differ in that the No. 12 coal seam contains weak cohesive coal; the No. 8 coal seam contains lean and gas coal; and the Nos. 6, 9, and 20 coal seams contain a certain amount of anthracite. During the programmed coal heating, the CO, C2H4, and C2H6 release trend for the coal seams was No. 12 > No. 8 > Nos. 6, 9, and 20. These results demonstrate that the presence of weak cohesive coal and anthracite highly influence the concentration of CO, C2H4, and C2H6 released during coal spontaneous combustion.

Gray Correlation Analysis of CO Generation Pattern during Process of Low-temperature Spontaneous combustion of Jurassic Coal

ABSTRACT Spontaneous combustion of coal is a phenomenon that exists in all coal mining countries. The characteristics of CO production during the spontaneous combustion of coal are the focus of attention of researchers. A novel programmed oxidation heating simulation system with a small-sample size was developed to study the combustion characteristics. The device was used to study the characteristics of CO generation during low-temperature coal oxidation under different conditions (three coal ranks, six particle sizes, four air volumes, and four oxygen concentrations). The microscopic characteristics of the coal structure were tested through Fourier-transform infrared spectroscopy (FTIR), and three types of active functional groups were observed. Ten factors affecting gas production in the low-temperature oxidation stage were analyzed by gray correlation. This study found that moisture in coal had the greatest effect on CO generation, followed by O-containing functional groups. Aliphatic hydrocarbons had the least correlation with CO generation. Further, the CO concentration increased exponentially during the heating process in low-temperature oxidation. In the low-temperature stage, carboxyl, carbonyl, and side-chain C–O bonds of the benzene ring were the main sources of CO generation.

Physico-chemical characteristics of pulverized coals and their interrelations-a spontaneous combustion and explosion perspective.

Characteristics of pulverized coals have significant influence on the spontaneous combustion and explosion processes. This paper presents an experimental and theoretical framework on physico-chemical characteristics of coal and their interrelations from spontaneous combustion and explosion perspectives. The chemical properties, morphology, bulk density, particle size, and specific surface area of pulverized coals from nine different coal subsidiaries of India are vividly investigated in five distinct sizes. Moreover, the effects of particle size on bulk density, specific surface area, and N2 adsorption capacity of pulverized coals are critically analyzed. With decrease in particle size, the bulk density of pulverized coals decreased, and the specific surface area and N2 adsorption capacity increased. The relationships of bulk density and specific surface area of pulverized coals with particle size are established. Moreover, the specific surface areas determined by both the particle sizing and BET methods are compared, and correlation factors between them are determined. This study generated insightful coal characteristic data, which can be useful for furthering research on spontaneous combustion and explosion involving pulverized coals.

Study on the Microscopic Mechanism of Spontaneous Combustion and Oxidation Kinetics of Water-Leached Coal

In this article, a series of experiments have been carried out to study the spontaneous combustion and oxidation mechanism of coal after water immersion and investigate its tendency to spontaneous combustion, analyze the difficulty of spontaneous combustion of coal samples under different water immersion conditions, and establish a kinetic model of water immersion coal oxidation (taking the Bulianta 12# coal as a case study). They rely on physical oxidation adsorption, scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), thermogravimetry, and oil bath heating. SEM has been used to analyze the characteristics of coal pore structure under different water immersion conditions (water-saturated coal samples under different water loss conditions until the coal samples are completely dried); FTIR served to investigate the characteristics of the molecular chemical structure of the coal surface before and after the coal is immersed in water. Through programmed temperature oxidation experiments combined with FTIR analyses and gas chromatographic (GC) analysis of gaseous products, it has been possible to study the changes of molecular structure and gas products on the surface of coal samples at different temperatures and water immersion conditions. The oxidation reaction rate of the 12# coal samples of Shendong Mine’s Bulianta Mine under different water content conditions during the spontaneous combustion process has been quantitatively studied. The difficulty of spontaneous combustion of coal samples has been correspondingly addressed. A kinetic model from the perspective of oxygen consumption has been proposed. Thermogravimetry-differential scanning calorimetry (TG-DSC) has been used to analyze and study the exothermal oxidation process before and after coal immersion. From the perspective of the exothermic intensity of the coal-oxygen reaction, an oxidation kinetic model for immersed coal samples has been developed to qualitatively determine its spontaneous combustion tendency. Results have shown that the increase in the specific surface area increases the risk of spontaneous combustion, and coal samples after soaking and drying have a stronger tendency to spontaneous combustion than raw coal. The moisture content of the coal sample leading to the easiest ignition conditions is 16.05%. Regardless of the moisture content, the critical temperature is maintained at 65–75°C, and the temperature of the left coal in the goaf should be prevented from exceeding this critical value.

A novel composite inorganic retarding gel for preventing coal spontaneous combustion

In order to better control the fire problem due to coal oxidations, a novel composite inorganic retarding gel material processed from sodium-based bentonite junction and kaolin, silica, hydrogen peroxide and silicon oxide is developed. For studying the gel's properties the scanning electron microscopy (SEM) and the thermogravimetry (TG-DTG) are used to characterize microscopical structures and mass losses with the temperature change process, respectively. For quantifying the inhibitory effect of the novel gel on the spontaneous combustion process of coal oxidation, laboratory tests such as temperature-programmed oxidation and infrared spectroscopy are carried out. Changes of the gases generated from the treated coal sample by the novel gel under the temperature increasing are analyzed. The inhibitory effects of mud and MgCl2 solutions on coal spontaneous combustion are compared. The results show that the surface of the gel is flat and smooth in microscopic scale. Under the a high-temperature, the gel is stable and is not easy to decompose. In detail, the quality loss is within 10%. The novel gel with a concentration of 20% has a good inhibitory effect on CO release and spontaneous combustion in coal combustion. In addition, the novel gel can significantly reduce the consumption of –OH, –CH and other functional groups in the low-temperature oxidation reaction. Hence, the novel gel is a kind of Inhibitor material with a better comprehension performance. This study provides a novel gel for better preventing and controlling the coal spontaneous combustion hazard.

Determination and dynamic variations on correlation mechanism between key groups and thermal effect of coal spontaneous combustion

This study is aimed at exploring the relationship between the variations of micro-groups and the thermal effect during the heating process of coal spontaneous combustion (CSC). To this end, the thermal effect and microstructure variation characteristics of CSC were analyzed by means of differential scanning calorimetry and in-situ infrared spectroscopy. The results reveal that the exothermic reaction of CSC falls into five stages: water evaporation, desorption-induced heat absorption, slow heat release, benzene ring pyrolysis and combustion. Aliphatic hydrocarbons in coal oxidize into carbonyl which further oxidizes into carboxyl. The dynamic variations of key groups during the different stages of CSC were determined through grey correlation analysis. In addition, structural contribution, a new parameter to characterize the contribution of microstructure to thermal effect of CSC, was defined. The results disclose that the correlations between the thermal effect and the microstructure variation in different stages differ, but the key groups follow the change process of hydroxyl → aliphatic hydrocarbons → oxygen-containing functional groups → aromatic hydrocarbons on the whole. The change of key groups is related to the thermal effect and microstructure reaction characteristics of CSC. The contribution of a microstructure to the thermal effect of CSC is determined by the comprehensive product of its initial content, variations in different stages and correlation. Different microstructures correspond to varying contributions in different stages of CSC. The key to preventing CSC is to hinder the oxidative consumption of –OH(f) and the oxidation of aliphatic hydrocarbons with the highest contents into -C = O and –COOH.

Determination of ignition temperature and kinetics and thermodynamics analysis of high-volatile coal based on differential derivative thermogravimetry

In order to accurately determine the ignition temperature (Ti) of coal, Coal spontaneous combustion (CSC) process was tested by a simultaneous thermal analyzer. Next, the abrupt change point of the differential derivative thermogravimetric curve (DDTG) of coal after the high adsorption temperature was taken as the Ti of CSC. Besides, variations of kinetics and thermodynamics during the CSC before and after the Ti were calculated. It was found that the mass loss, heat releases and gaseous products of coal changed slowly before the Ti and surged sharply after the Ti. The coal at ignition temperature was in thermodynamic equilibrium with low activity. However, when the temperature was greater than Ti, the aromatic hydrocarbons in coal begin to decompose, resulting in the increased of active sites and the release of volatiles, and the coal enters an irreversible combustion stage. At this time, upward trends were obtained for the apparent activation energy, pre-exponential factor, enthalpy change, and entropy change, while a gradual decrease was observed for the Gibbs free energy change. Moreover, reaction intensity between oxygen and coal would be increased due to increased of active sites in the coal and enhanced of volatiles release under a slower heating rate.