Characteristic Temperature Points Research Articles

A study of the inhibition properties of gallic acid/lignin-modified hydrogel inhibitor prepared via graft copolymerization

In view of the shortcomings of pure hydrogels, such as a single inhibition effect and poor stability at high temperatures, this study aims to develop a new composite hydrogel inhibitor and to study its inhibition mechanism. To this end, gallic acid and lignin were added to modify the hydrogel, and a gallic acid/lignin-modified hydrogel (GA/LG-PAA) inhibitor was prepared. By scanning electron microscope, it was discovered that inhibited coal samples treated with gallic acid hydrogel (GA-PAA) and GA/LG-PAA had bigger particles. By using thermogravimetric analysis, it was found that after the inhibition treatment with GA/LG-PAA, the coal samples’ characteristic temperature points have increased to different degrees. Among these, the dry cracking temperature was increased by 53.87 °C, the ignition temperature was increased by 20.23 °C, and the burnout temperature was increased by 19.79 °C. Thermogravimetric experiments therefore showed that GA/LG-PAA had the best inhibition effect. Through infrared diffuse reflection experiments, it was found that the peak areas of methylene, carbonyl, carbon-carbon double bond, ether bond and other functional groups were all increased in coal samples after inhibition. The GA/LG-PAA inhibited spontaneous combustion by forming ether bonds. The results show that GA/LG-PAA can effectively inhibit coal spontaneous combustion.

Effect on the oxidation characteristic at lignite of two types of endogenous microorganisms from coal

In recent years, coal biotechnology has gained considerable popularity due to its economic, eco-friendly, and sustainable advantages, which offer a novel perspective and pathway for the development of green technologies aimed at preventing and controlling coal spontaneous combustion (CSC). Two endogenous microorganisms from lignite were succeeded in extracting in this work, namely Aspergillus and Bacillus velezensis. Subsequently, the effect of these microorganisms on the microscopic structure and macroscopic oxidation characteristics of coal was investigated by X-ray diffraction, Fourier-transform infrared spectroscopy, and thermogravimetric analysis. The results revealed that both Aspergillus and Bacillus velezensis treatments altered the microcrystalline structure of the coal, disrupting the aliphatic hydrocarbon structure and oxygen-containing functional groups of the coal molecules. Particularly, the OH − O hydrogen bond of two kinds of microbial treatment coal samples content respectively decreased significantly by 17.29 % and 11.06 % compared to the raw coal sample. However, the effects of different microorganisms on coal varied. Thermodynamic behavior demonstrated that the critical temperature of the two treated coal samples was delayed by 29.44 °C and 26.62 °C, and the ignition temperature was delayed by 11.31 °C and 5.18 °C. Overall, all characteristic temperature points of the Aspergillus group were delayed, but the maximum weight loss rate temperature and the burn-out temperature of the Bacillus velezensis group exhibited slight advancement. The thermal mass loss characteristics also changed during the oxidation combustion stage. In addition, the average activation energies of oxidized combustion stage calculated by the Kissinger-Akahira-Sunose method were 74.26 kJ/mol and 78.61 kJ/mol, respectively, and 82.41 kJ/mol and 86.15 kJ/mol for the Friedman method, which were both increased compared to the raw coal. The results indicate that both Aspergillus and Bacillus velezensis have effects with varying degrees on the coal oxidation characteristics. It can be observed that the effect of treatment with Aspergillus is better than Bacillus velezensis from the overall changes in characteristic temperature points. This work lays the foundation for investigating the effect of microbial action on the oxidative properties of CSC.

Evolution and oxidation properties of the functional groups of coals after water immersion and air drying

The evolution of functional groups, the gas generation laws in oxidation and temperature increase, and the oxidation kinetics parameters of the coal samples immersed in water for 30 days, 90 days, and 150 days (hereinafter referred to as 30 d coal, 90 d coal, and 150 d coal, respectively) were analyzed through Fourier transform infrared spectrometer, programmed temperature increase test system, and thermal gravimetric analyzer to disclose spontaneous combustion and the influencing mechanism of long-flame coals immersed in water for a long period. Results show that the aliphatic hydrocarbon and the hydroxyl contents of the coal samples increase after water immersion and air drying. In particular, the aliphatic hydrocarbon contents in 30 d coal, 90 d coal, and 150 d coal increase from 12.61 % for raw coal to 15.84 %, 14.08 %, and 13.90 %, respectively, whereas the hydroxyl content increases from 48.75 % for raw coal to 50.77 %, 50.13 %, and 49.23 %, respectively. In the low-temperature oxidation process, the CO output increases, and the apparent activation energy declines. When the temperature is 200 °C, the CO outputs of 30 d coal, 90 d coal, and 150 d coal are 28088, 25421, and 22112 ppm, which are 37.4 %, 24.4 %, and 8.2 % higher than the CO output of raw coal (20437 ppm), respectively. The apparent activation energy decreases from 65.7 kJ mol−1 for raw coal to 61.12 kJ mol−1, 63.08 kJ mol−1, and 64.5 kJ mol−1. According to the comparison of characteristic temperature points, the temperature of the mass extreme (T3) and the temperature of ignition point (T4) of the immersed coal samples both decrease. The T3 values of 30 d coal, 90 d coal, and 150 d coal decrease from 282.71 °C for raw coal to 274.87, 278.33, and 280.50 °C, whereas their T4 values decrease from 424.24 °C for raw coal to 419.23, 420.14, and 423.42 °C, respectively. This study proves that water immersion increases the oxidative activity of coals, thereby simplifying spontaneous combustion.

Coal Secondary Oxidation Thermodynamic Behaviors Affected by Pre-Heating at Different Oxygen Concentrations

ABSTRACT To investigate the impact of pre-oxidation oxygen concentration on the propensity of coal spontaneous combustion, thermogravimetric analysis was used to obtain thermal characteristic curves for raw coal and pre-oxidized coal with five different oxygen concentrations. The coal spontaneous combustion process was categorized into three phases: water-loss and weightlessness, oxygenation and weight gain, and combustion phase. It reveals that characteristic temperature points of oxidized coal were lower than that of raw coal, and pre-oxidation plays a role in enhancing the coal oxidation to varying degrees. During the phase of oxygenation and weight gain, the activation energy of oxidized coal decreases from 44% to 84% of that of raw coal. The positive effect on coal secondary oxidation is initially reduced, then increased with the increasing of pre-oxidation oxygen concentration. The sample pre-oxidized with 15% oxygen concentration is the most easily spontaneous combustion, and the total activation energy of its oxidation reaction is 57% of that of the raw coal, the characteristic temperature of which lowered by an average of 7.4°C. It will be conducive to revealing reignition mechanism of coal and preventing coal secondary spontaneous combustion.

Application of Sunflower Husk Pellet as a Reducer in Metallurgical Processes.

In relation to the climate policy being introduced, the search for a replacement for solid fossil fuels with renewable raw materials is ongoing. In this study, a potential biomass (sunflower husk pellet) application in the process of copper slag reduction was assessed. For the purpose of raw material characterisation, thermogravimetric tests were carried out and characteristic temperature points were determined with the use of a high-temperature microscope. The slag reduction tests led to the recovery of 97% of copper and a decrease in this metal content in the slag to less than 0.5% Cu, which enables safe storage or use in other industrial branches.

Suppression of thermal coupling noise in the SERF atomic co-magnetometer

Heating the alkali metal vapor cell to obtain high atomic density is a prerequisite for realizing the high-precision measurement for spin-exchange relaxation-free (SERF) co-magnetometer. However, the thermo-magnetic and thermo-optical coupling noise caused by the temperature diffusion from the alkali vapor cell is one of the main factors restricting the co-magnetometer performance at present. Here the influence of heating on the SERF co-magnetometer was comprehensively studied, and the thermal error model of the system was established. A novel heat insulation structure for the co-magnetometer was designed, and the effectiveness was verified through monitoring of characteristic temperature points. Compared to the conventional oven support, the average maximum temperature difference within 12 h of the optical path and magnetic shielding systems (OPMSS) decreased by 52%, the bias instability of the co-magnetometer decreased by 24%, and the noise of the co-magnetometer at 1 Hz decreased by 33%. The experimental results demonstrate that this method reduces the temperature fluctuation of the OPMSS, effectively suppresses the thermal coupling noise, and thus improves the performance of the SERF co-magnetometer. Moreover, this method is also applicable to other quantum sensors based on alkali metal vapor cell.

Self-Healing Gels Based on Bimetallic ion Cross-Linking for Mining Fire Prevention and Extinguishing

ABSTRACT To address the environmentally friendly issue of fire prevention and extinguishing materials in coal mines, a new biomass gel material was prepared using sodium carboxymethyl cellulose (CMC) as the matrix, ferro aluminum citrate (Fe-AlCit) as the cross-linking agent, and gluconic acid-δ-lactone (GDL) as the pH modifier. Through performance tests of gel micromorphology, thermal stability, viscoelasticity and yield stress, it was found that the CMC-3 gel material with a ratio of 2.5% CMC + 4% Fe-AlCit +2% GDL had a dense surface structure, good thermal stability and moderate viscosity, which was the most suitable for pipeline transport. A metal coordination bond favorable to the stability of CMC-3 gel is formed by the carboxylate ion in CMC and the double high-valent metal ions Fe3+ and Al3+ dissociated by Fe-AlCit. CMC-3 gel exhibits excellent fire prevention and extinguishing properties. The results of the programmed warming experiments showed that the inhibition rate of the coal sample treated with CMC-3 gel against CO and C2H4 gases reached 44.84% and 46.57% at 220°C, respectively, and the growth rate of the activation energy in the first and second stage reached 17.63% and 22.68%, respectively, which plays a significant inhibitory role. The infrared spectroscopy test showed that after adding CMC-3 gel, the content of -OH and Ar-C-O in the coal samples was reduced by 49.58% and 40.82%, respectively, and the content of stable C=C in the aromatics was increased by 6.14%, which effectively blocked the coal-oxygen chain reaction and reduced the tendency of coal spontaneous combustion. The thermogravimetric test showed that the characteristic temperature points of the coal sample treated with CMC-3 gel were all increased to different degrees. The fire extinguishing test showed that CMC-3 gel could significantly reduce the temperature of coal sample and extinguish the coal fire quickly. Moreover, the CMC-3 gel material also has excellent self-healing properties, which can self-repair the damaged network through the abundant reversible hydrogen and ionic bonds inside the gel in only 90 s. The study has certain guiding significance for the development of efficient and environmentally friendly self-healing mining fire prevention and extinguishing materials.

Study on the Influence of Coal Structure and Oxidation Performance by Endogenous Bacterium

In order to solve the defects of traditional coal spontaneous combustion prevention technology in a closed goaf, a strain of aerobic endogenous bacteria was isolated from coal and used as a blocking raw material. Based on the metabolic and reproductive characteristics of microorganisms, the experimental study on the inhibition of coal spontaneous combustion by microorganisms was carried out. The colonies were isolated and purified by the dilution concentration plate method and the scribing plate method. The growth morphology of microorganisms was analyzed, and the growth curve was determined. The strains were identified by seamless cloning technology for high-throughput sequencing. The surface morphology of coal was analyzed by SEM, the differences of oxidation characteristic temperature points were analyzed by TG–DTG–DSC images, a programmed heating experiment was used to analyze the concentration of the indicator gas CO, and the changes in microscopic groups before and after microbial action were analyzed by FTIR and XPS spectra. Therefore, the inhibition of coal oxidation by endogenous bacteria was verified from macroscopic and microscopic perspectives. The results show that the coal bacteria isolated from the coal is Lysinibacilus sp. After the culture of Lysinibacilus sp., the surface of the coal demonstrated less detritus, and was relatively smooth. In the early stage of low temperature oxidation of coal spontaneous combustion, the characteristic temperature point of coal oxidation and the reaction between coal and O2 could be delayed by Lysinibacilus sp., and the total heat release was reduced in the combustion process. Not only that, Lysinibacilus sp. could also reduce the CO concentration during coal heating. After the coal was decomposed by Lysinibacilus sp., the C=C thick ring skeleton structure had little effect; however, the aromatic substitution pattern changed. This bacterium had an effect on the C-O bond, reducing the percentage of -CH2- and increasing the percentage of -CH3. It might also use the crystalline water in coal for life activities. The carboxyl carbon in coal changed the most, with a decrease of 12.03%, so it might become the carbon source required for microbial growth. The reproductive metabolism of microorganisms also affected the form of nitrogen, and the percentage of pyridine nitrogen in coal was reduced. The ratio of single-bond carbon to double-bond carbon in raw coal was about 3:2, but after this bacterial action, the ratio of the two was about 1:1. The analytical conclusions of XPS and FTIR spectra were consistent, and the results supported each other.

Inhibition Characteristics of Gel-Based TiO2/OPC/CPAAM Composite Inhibitor to Control Coal Spontaneous Combustion

ABSTRACT Spontaneous combustion of coal is a major problem in coal industry. In order to improve the environmental performance and effectiveness of existing inhibitors used to inhibit coal spontaneous combustion, this study utilized physical inhibitors such as chitosan (CS), acrylic acid (AA), and acrylamide (AM) and copolymerized them with the chemical inhibitor procyanidin (OPC). The resulting composite inhibitor was then in situ polymerized with modified nano-TiO2 to create an environmentally friendly gel-based composite inhibitor, referred to as TiO2/OPC/CPAAM. Scanning electron microscopy analysis revealed a significant increase in the number of laminar folds and pores within the inhibited coal samples. Additionally, thermogravimetric analysis showed that all characteristic temperature points of the inhibited coal samples were raised, with an average increase of 21.34%. Differential scanning calorimetry also indicated a reduction in the total heat release and heat release intervals of the inhibited coal samples. Gas infrared spectroscopy provided evidence that the inhibitory treatment significantly slowed the growth of CO and CO2 during the heating process of the coal samples, leading to an improvement in environmental performance. Furthermore, diffuse reflection infrared spectroscopy testing demonstrated that the inhibitory treatment resulted in the passivation of active groups’ free hydroxyls and an increase in the content of stable group ether bonds. Overall, the results of this study indicate that the composite inhibitor TiO2/OPC/CPAAM offers superior inhibition effects on coal spontaneous combustion.

Reaction heat effect and change characteristics of key groups in coal-oxygen intrinsic reaction path.

The intrinsic reaction of coal with oxygen in the process of low-temperature oxidation is the main reaction path leading to self-heating and spontaneous combustion of coal. Most of the existing studies regard the coal oxidation as an overall reaction, ignoring the multi-path characteristics of coal low-temperature oxidation, and it is difficult to accurately explore the intrinsic reaction characteristics between coal with oxygen. Therefore, the low-temperature oxidation process of coal was studied by using a C80 microcalorimeter and in situ FTIR technology from the macro and micro levels. The "profile subtraction method" was used to study the coal-oxygen intrinsic reaction process, and the reaction heat effect and the change characteristics of key functional groups in the process were analyzed. Furthermore, the gray correlation analysis method was used to study the relevant characteristic parameters in the reaction process and grasp the essential structure-activity relationship. The experimental results show that, compared with the overall reaction process in air atmosphere, the change in the heat release of the coal-oxygen intrinsic reaction path has changed to different degrees, and the change in the slow oxidation stage is the most significant (the heat absorption decreases by 70.1-90.9%). In addition, the characteristic temperature points show different degrees of advance, of which the initial exothermic temperature point is the largest (about 21-46 °C), which directly leads to a significant shortening of the slow oxidation stage (30.1-47.4%). The changes of functional groups in the intrinsic reaction path are more regular. With the increase of temperature, the oxygen-containing functional groups -C=O and the aliphatic hydrocarbon functional groups -CH2- and -CH3 showed a fluctuating trend of increasing and decreasing, respectively. The oxidation heat-contributing functional groups of coal are mainly related to the degree of metamorphism and the functional group reaction characteristics during the reaction. With the deepening of coalification degree, the main heat-contributing functional groups as a whole showed the change rule of oxygen-containing functional groups → aliphatic hydrocarbon functional groups → aromatic hydrocarbon functional groups. In addition, the change of -OH content in the three coal samples has a high correlation with the change of the total heat release of coal.

Characteristics and mechanism of Glutathione in inhibiting coal spontaneous combustion

Inhibitors play an important role in preventing and controlling coal spontaneous combustion (CSC). In this study, the inhibitory effects of antioxidant-reduced glutathione (G-SH) on CSC were examined. Thermogravimetric-differential scanning calorimetry (TG-DSC), cross-point temperature (CPT), and oxidation product tests were used to examine the effect of G-SH on the tendency of CSC and compare the discrepancy in the inhibition effect of G-SH and the halogen inhibitor. The changes in the free radical type, concentration, and surface functional groups in coal before and after the addition of G-SH were analyzed using electron spin resonance spectroscopy (ESR) and Fourier transform infrared spectroscopy (FT-IR). Six common active radical models were constructed, and the thermodynamic parameters of the reaction were calculated using density functional theory (DFT). The results revealed that G-SH inhibits the spontaneous combustion of coal. The inhibitory effect of G-SH was significantly stronger than that of the halogen salt inhibitors CaCl2 and MgCl2, and the higher the concentration of G-SH, the stronger is the inhibitory effect. The characteristic temperature points in the thermogravimetric experiment of coal samples with G-SH shifted to a higher temperature zone, and the CO concentration and oxygen consumption were lower than those of raw coal. After G-SH treatment, the type and relative concentration of free radicals in coal were lower than those in raw coal, the content of aliphatic hydrocarbon functional groups and oxygen-containing functional groups decreased, and the content of sulfur-containing functional groups increased. According to the calculation of Gibbs free energy and reaction enthalpy, G-SH can effectively neutralize the active free radicals in the process of coal oxidation, and the reaction activity with the free radicals in the process of coal oxidation is ·OOH > ·OH > ·CH3 > RO· > R· > ROO·. According to the experimental results, it is inferred that G-SH continuously supplies a large number of hydrogen donors (·H) for the reaction during the oxidation process and simultaneously neutralizes carbon free radicals and carbon oxygen free radicals, thereby reducing the concentration and reactivity of free radicals in the whole chain reaction process and blocking the occurrence of coal-oxygen composite reaction.

Experimental investigation on coal desorption characteristics and spontaneous combustion properties evolution under the coupled effect of temperature and pressure

Gas desorption patterns and microscopic pore structure morphology in coal are influenced by the coupled effects of temperature and pressure, and their effects on the spontaneous combustion (SC) characteristics of coal cannot be ignored. In this paper, two types of coal samples, lean coal and fat coal from high gas-prone SC mines, are used as test objects. A self-designed experimental platform for coupling gas adsorption and desorption with coal spontaneous combustion (CSC) and heating and oxidation was used. Firstly, orthogonal tests on the desorption of methane from coal under the coupling effect of different temperatures and pressures were carried out to obtain a gradual decrease of methane desorption from coal with increasing temperature under the same pressure conditions. The results show that the pore volume and specific surface area of coal show a monotonic decreasing pattern with increasing temperature and pressure, while the percentage of micropores and mesopores, which promote the oxygen reaction of coal, show an increasing trend. In addition, a comparative analysis of the characteristic temperature points of the first stage showed that the characteristic temperature points of the desorbed coal were higher than those of the original coal, reflecting the higher SC activity of the desorbed coal; and the crossover temperature points of the lean coal and the fat coal were 79 °C and 88 °C, respectively, after desorption during the heating and oxidation process, which also confirmed the high SC activity of the desorbed coal. Based on the above findings, the methane concentration calculation model of the mining area was applied to redraw the oxidation zone using the mining area of the 41,201 working face of Hongyang No. 2 Mine as an example, and the area was reduced by 39.5%. The research results of the paper can provide guidance for the prevention and control of fire hazards in mines with high gas-prone SC.

Study on the influence of key active groups on gas products in spontaneous combustion of coal

In order to reveal the internal relationship between the active groups and gas products in spontaneous combustion of coal, the correlation between the content of active functional groups and the production of gas products was studied by temperature programmed experiment and in situ infrared spectroscopy analysis experiment. The results show that there are three characteristic temperature points in the gas release curve of Jurassic coal spontaneous combustion in northern Shaanxi, which can be divided into slow oxidation stage, critical temperature stage, rapid oxidation reaction stage and combustion stage. CH3, CH2, C–H and OH are actively consumed in the spontaneous combustion of coal. CO gradually increased, which is an important oxidation product during Jurassic coal oxidation in northern Shaanxi. The chain length CH2/CH3 is attacked and the fracture shortened, while the oxygen enrichment degree of CO/CC in coal increases gradually. The correlation values of key active groups of CH3, CH2, C–H, OH, CO, CH2/CH3, and CO/CC with oxygen, carbon and oxygen gases and alkane and olefin gases in the process of coal oxidation heating in different coal seams in northern Shaanxi during Jurassic period are obtained. The results show that CH3, CH2 and CH2/CH3, are the main parts of oxygen molecules attacking and binding in the Jurassic coal oxidation process in northern Shaanxi, and the oxygen-rich products of coal decompose into carbon oxygen gas and alkane alkene gas. Due to the different activation energies of various active groups, the spontaneous combustion of coal shows different reaction degrees in each stage. The research results can be used to understand the occurrence and development degree of spontaneous coal combustion, and have important guiding significance for the monitoring and warning of spontaneous coal combustion and the targeted prevention and control of spontaneous coal combustion disasters.

Effect of Na2O content on wettability, crystallization and performances of sealing glass

As an encapsulation material, glass has been used in electronic encapsulation, aerospace, and fuel cell applications due to its ease of fabrication, heat resistance, and stability. Thereinto, shear strength is one of the significant criteria for evaluating sealing glass. Nevertheless, shear strength is frequently influenced by the wettability of glass and interfacial interactions. Thus, the effect of Na2O content on the characteristic glass temperature, wettability, and crystallization was investigated to promote shear strength. Due to the fluxing effect of Na2O, the characteristic temperature points tend to drop as its concentration increases from 3 wt% to 12 wt%, and the wettability increases. Furthermore, Na2O promotes the precipitation of more types of lead-containing crystals in sealing glasses. With the sodium content of the glass reaching 12 wt% showed the best properties that shear strength of 326 MPa. The sodium-containing sealed glass was securely attached at the interface after being co-sintered with the Si substrate. This implies that the lead-containing crystalline phase will promote shear strength and improve the sealing ability of the glass. This gives sealing glass great potential for application in electronic packaging fields.

Experimental study and thermodynamic analysis of coal spontaneous combustion characteristics

Spontaneous coal combustion is one of the most common disasters in coal mine production. In order to explore the mechanism of coal spontaneous combustion more deeply, coal samples from the Yangdong wellfield of Jizhong Energy were selected for oxidative heat energy analysis experiments. A temperature-programmed experiment was selected to study the changes in characteristic parameters during the low-temperature oxidation of coal under different air supply conditions. TG-DSC experiments were conducted to study the characteristic temperature changes and thermodynamic characteristics of coal combustion processes at different heating rates. The study results show that the coal is most easily oxidised in the low-temperature oxidation stage when the air supply is 120 ml/min. The oxygen consumption rate, CO generation rate, and maximum and minimum heat release intensity are all greater at this airflow than under other conditions. The process of spontaneous combustion of coal has six characteristic temperature points and is divided into five stages. The characteristic temperature of the coal sample increased with the increase of the heating rate, and the TG/DTG curve showed a hysteresis phenomenon. DSC temperature curve shifts toward the high temperature with the increase of the heating rate, and the exothermic region is expanded. Isokinetic analysis (F-W-O and V-W) and Coats-Redfern model for calculating thermodynamic parameters. The activation energy of the samples decreased with the increase of the heating rate in the range of 2∼20°C·min−1 and showed a decreasing trend with the increase of the conversion rate.

Thermal reaction characteristics and microstructure evolution of aluminium nano-powder in various mixtures of oxygen and nitrogen atmosphere

Aluminium nano-powder has a small particle size, large specific surface area, and high surface energy, therefore when using it, the risk of fires or explosions is high. In this study, synchronous thermal analyser was used to determine the thermal reaction characteristics of aluminium nano-powder for various oxygen and nitrogen mixtures. The results showed that the oxidation behaviour of aluminium nano-powder could be considered to occur in four stages, according to the characteristic temperature points and polymorphic phase changes. Under experimental heating rates of 5, 10, 15, and 20 K/min, the mass gain and thermal effects of the samples were tested, and also for different oxygen concentrations of 9, 15, and 21 vol%. Changes in the microstructure of the samples were analysed. Oxide layer thickness was found to increase as temperature increased, and this trend was the same for mass change. Surface morphology images of the aluminium particles exhibited agglomeration, melting deformation, rupture, and fragmentation at the different pretreated temperatures of 500, 650, 800, and 900 °C. The results of this study could be used as a basis for exploring oxidation kinetics, and had significance for explosion-proofing technology, particularly with respect to aluminium nano-powder.

Experimental study and molecular simulation of spontaneous combustion of coal gangue by oxidation under different water contents

ABSTRACT To determine the effect of water contents on the oxidation spontaneous combustion of coal gangue, the properties and combustion characteristics of coal gangue were studied using industrial and elemental analyses and Thermo Gravimetry-Differential Scanning Calorimetry (TG-DSC). The molecular dynamics simulation (MDS) and giant regular Monte Carlo simulation (GCMC)were used to investigate the adsorption isotherms of oxygen and coal gangue (kaolinite) under different water molecules (400, 500, 600, 700). The results of thermogravimetric showed that with increasing moisture content, the characteristic temperature points T3-T5 of CG4 were much lower than those of the other samples, the combustion conversion rate is the highest and the spontaneous combustion effect is the best at the same temperature. The molecular simulation results show that under 700 water-oxygen system, the adsorption of oxygen molecules and kaolinite (001) surface is the strongest. The interface has the fewest water molecules and the largest diffusion coefficient.

Experimental investigation on using antioxidants to control spontaneous combustion of lignite coal

To investigate the effects of antioxidants on the microstructure and characteristic parameters of coal during the oxidation process of coal, three antioxidants (tea polyphenols, resveratrol, and β-carotene) at different mass ratios (1 wt%, 3 wt%, 5 wt%, and 7 wt%) were selected to treat raw coal samples. Fourier transform infrared spectroscopy was conducted to explore the changes in functional group content before and after antioxidant treatment of coal samples. The results show that the content of functional groups in coal had a trend of decreasing and then increasing with a rising mass fraction of antioxidants, and the optimum mass ratio of antioxidants was predicted. On this basis, the effects of antioxidants on characteristic temperature points and gas products of coal samples were determined by the thermogravimetric-infrared experiment. The test results show that the critical temperature and dry cracking temperature of the antioxidant-treated coal samples increased to different degrees compared to the raw coal during the low-temperature oxidation stage. Meanwhile, the concentration and yield of CO, CO2, and CH4 of the antioxidant-treated coal samples showed a decreasing trend compared to raw coal. The chemical kinetics method was used to determine the apparent activation energy in the process of coal oxidation. The apparent activation energies of TP, Res, and β-Car inhibited coal samples in the stage of water evaporation and gas desorption increased by 39 %, 30 %, and 26 %, respectively, compared with the raw coal, while the apparent activation energies in the oxygen absorption and weight gain stage were respectively increased 19.4 %, 12.9 %, and 14.3 % higher than raw coal. The ability of antioxidants to inhibit the spontaneous combustion of coal is TP > Res > β-Car. The results enrich the research on antioxidant inhibition of coal spontaneous combustion and provide a theoretical basis for preventing coal spontaneous combustion.

Experimental investigation on spontaneous combustion oxidation characteristics and stages of coal with different metamorphic degrees.

Coal spontaneous combustion (CSC) is a major disaster threatening coal mine safety; therefore, the investigation of coal spontaneous combustion and oxidation characteristics has been a hot topic in the long term. In this paper, the experimental temperature programmed system is used to carry out the simulation experiment of coal spontaneous combustion and oxidation of three kinds of coal with different metamorphic degrees under three oxygen concentrations (9%, 15%, 21%). The effects of metamorphic degree and oxygen concentration on coal oxidation characteristics were analyzed, and the variation laws of crossing point temperature, three characteristic point temperature, and apparent activation energy were qualitatively discussed. Finally, coal oxidation reaction stages were evaluated and divided. The results show that the concentrations of CO and C2H4 are negatively correlated with the degree of deterioration but increase with the increase of oxygen concentration. High metamorphic coal corresponds to high crossing point temperature (CPT). The average error between the CPT value calculated from the BM empirical correlation and the experimental data is very small, which is 6.42%. The higher the metamorphic degree of coal, the higher the three characteristic temperature points (critical temperature, xerochasy temperature, and activity temperature). The oxidation process of the three coal samples is divided into four stages: surface oxidation, oxidation self-heating, accelerated oxidation, and deep oxidation. The apparent activation energy of each stage exhibits significant variability, with varying patterns displayed with the degree of metamorphism.

Advanced critical temperature method for steel beams exposed to different fire scenarios

The early-warning of fire-induced failure of structural members is becoming more and more attractive to the fire department since it can provide warning signal to the firefighters at the scene of a building fire. Temperature is a type of easily-measured parameter in fire condition, and can reflect the ultimate state of structural members to some extent, therefore it has the application potential to indicate the failure of structural members in fire. The traditional critical temperature method (CTM) in Eurocode 3 or Chinese standard GB 51249–2017 has been widely used in the fire safety design of steel members, but it cannot be extended to the early-warning of fire-induced failure directly. Based on the traditional CTM, this paper presents an advanced critical temperature method for simply-supported H-shaped steel beams under different fire scenarios. Finite element analysis (FEA) models were established and validated to investigate the critical temperatures of H-shaped steel beams. Based on the numerical analysis, guidelines for confirming the positions of characteristic temperature points (CTPs) and values of refined critical temperatures (RCTs) on H-shaped steel beams were proposed, and parametric analysis results indicated that the longitudinal fire scenario, perimeter of beam section and beam load ratio were the key influencing parameters. Finally, a design table was proposed to determine the positions of CTPs and values of RCTs of simply-supported H-shaped steel beams with 2-hour fire rating time, which can be used in the early-warning of fire-induced failure directly.