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Coal spontaneous combustion (CSC) is a global, long-standing thermal hazard in coal mining that causes serious environmental damage, particularly in developing countries. Ionic liquids (ILs) are environmentally friendly, green, economical, and a new type of fire-preventing material that inhibits coal oxidation and alleviates thermal production. In this study, 1-butyl-3-methyl imidazole tetrafluoroborate ([BMIM][BF4]) and 1-butyl-3-methyl imidazole ([BMIM][I]) at various mass ratios (0.0, 0.5, 2.0, 5.0, and 10.0 mass%) were used to treat three types of coal (lignite, 1/3 coking coal, and anthracite) for CSC. The combustion-mass loss and thermal release rate of ILs treated relative to untreated coal samples were investigated using a synchronous thermal analyzer, and the optimal addition mass ratio of ILs was predicted. Not only do ILs have the most efficient inhibiting effect, but they also consider the economic benefit. Per thermogravimetric-differential scanning calorimetry, for the content of 5.0 mass% [BMIM][BF4], the inhibiting effect is favorable for universal applications. In addition, coal samples treated with 5.0 mass% [BMIM][BF4] were subjected to programmed-temperature heating experiment testing. The oxygen consumption rate, inhibiting effect, as well as apparent activation energy, were determined. The inhibiting effect at 120.0–150.0 °C was the most obvious, which provided the basis of the application for CSC prevention. [ABSTRACT FROM AUTHOR]

Ionic liquids (ILs) are a type of environmentally friendly solvents. Several studies have proven that ILs can inhibit the spontaneous combustion of coal (SCC). In this study, a synchronous thermal analyzer was used to analyze the effects of the imidazolium-based IL [BMIM][BF4] on coal of three metamorphic grades. A coal sample exhibiting the optimal inhibiting result was selected to investigate the effect of the oxygen concentration on IL inhibition. The results revealed that the influence of IL on the mass loss process of the three metamorphic grades of coal varied considerably. High inhibition was observed in lignite. However, the IL promoted the mass loss process in 1/3 coking coal and anthracite. The IL delayed the ignition temperature of lignite by 42 °C, whereas those of 1/3 coking coal and anthracite were advanced by 10 and 8 °C, respectively. Furthermore, the initial exothermic temperature of the three treated coal samples was higher than those of the raw coal samples. Compared with the raw coal samples, the heat released per gram of lignite, 1/3 coking coal, and anthracite was reduced by 1142, 353, and 226 J, respectively. The results indicated that the IL had a prominent inhibiting effect on the exothermic properties of the three coal samples, and the inhibiting effect decreased with an increase in the metamorphic grade of coal. Moreover, the oxygen concentration did not alter the inhibition properties of the IL on the SCC. However, the inhibiting effect weakened as the oxygen concentration decreased. [ABSTRACT FROM AUTHOR]

Thermal analysis was used to investigate the oxidation and heat-release characteristics of four coal samples from the Huainan mining area in China. Temperature and the evolution of heat and gaseous products were studied to identify each sample's ignition temperature and inform fire-prevention advice to avoid the spontaneous combustion of the coals studied. Thermogravimetry–differential scanning calorimetry (TG–DSC) tests demonstrated lower heating rates resulted in lower characteristic temperatures, corresponding to a greater propensity for spontaneous combustion. Using the Flynn–Wall–Ozawa method, spontaneous combustion was predicted from approximately 300°C, which agreed well with the TG–DSC analysis. The apparent activation energies for combustion were also obtained and gas products that were released throughout the entire oxidation process were monitored. Simultaneous thermal analysis–Fourier transform infrared spectroscopy was used to explain the changes in the evolution of CO and CO2, the results of which agreed well with those of TG. [ABSTRACT FROM AUTHOR]

Coal fire disasters occur frequently in exposed or underground coal zones or gobs, which usually triggered by pre-oxidised coal spontaneous combustion (PCSC). The thermal mass loss characteristics and thermal effects of pre-oxidised coal with the oxidation temperature and oxygen concentration were investigated. The thermogravimetry (TG) results revealed that the oxidation reaction occurred earlier for the pre-oxidised coal than for raw coal. The pre-oxidised coal had a poor ignition performance and burnout capacity than that of raw coal. In addition, the comprehensive combustion performance of pre-oxidised coal is weaker than that of raw coal, but its combustion rate and short-term combustion intensity are higher than raw coal. The differential scanning calorimetry (DSC) results indicated that the temperature at which the thermal release of pre-oxidised coal increases rapidly lags behind that of raw coal. Moreover, the maximum thermal release power and thermal release for the pre-oxidised coal were less than those for raw coal. The risk of PCSC changes with the increase of oxidation temperature, and there is a critical value of oxidation temperature. When the oxidation temperature was less than the critical value the risk of PCSC is higher than that of raw coal. Furthermore, the critical value decreases with the increase of oxygen concentration. [ABSTRACT FROM AUTHOR]

Exothermicity is a key parameter for evaluating coal spontaneous combustion (CSC). A suitable oxygen concentration is essential for CSC. Ionic liquids (ILs), which are a popular type of fire prevention material, inhibit coal oxidation. 1-Butyl-3-methyl imidazole tetrafluoroborate ([BMIM][BF 4 ]) was used at various mass ratios (0, 2, 5, and 10 mass%) to treat coal to inhibit CSC. Through simultaneous thermal analysis tests, coal samples were investigated in atmospheres with oxygen concentrations of 5, 10, 15, and 21 vol%. The results indicated that the mass loss decreased with increasing IL content. However, the mass loss did not decrease indefinitely with increasing IL content. The lowest mass loss was observed at an IL concentration of approximately 7.5 mass%. The inhibition increased with decreasing oxygen concentrations. Moreover, the inhibiting effect first increased slowly until the IL concentration exceeded 10 mass%, after which the inhibiting effect increased rapidly. The relationship between the exothermic rate and the mass loss rate of the coal at Stage 2 of the reaction was comparatively analysed. The reaction rate between oxygen and coal was the key factor influencing the exothermic rate. In the oxidation of coal, both the oxygen concentration and inhibitor content affected the comprehensive combustion index of coal. • The relationship between the amount of IL added and the mass loss/CAIT was defined. • Fitted curves of the mass loss (y 3) and oxygen concentration (x 2) were obtained. • A high mass loss or heat accumulation led to an easy occurrence of CSC. • Comprehensive index parameters under different conditions were explored and elucidated. [ABSTRACT FROM AUTHOR]

• Effects of [Bmim][BF 4 on the exothermic and heat transfer characteristics of coal during low-temperature oxidation were investigated. • Effects of the IL on the exothermic and heat transfer characteristics of coal with different degrees of metamorphism were compared. • Effects of the IL on the coal exothermic process were analysed according to characteristic temperature and reaction time. • Inhibiting effect of the IL to CSC was not applicable to all coal types. The effects of the ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate [Bmim][BF 4 on the exothermic and heat transfer characteristics of three metamorphic grades of coal during low-temperature oxidation were investigated. The C80 microcalorimeter results showed that the IL inhibited the exothermic process and characteristics of long-flame and non-caking coals, whereas the IL had a growth-promoting influence on gas-fat coal. The kinetics calculation results showed that the apparent activation energy of long-flame and non-caking coals increased after treatment but gas-fat coal was subjected to the opposite effects. According to the consequences of the LFA457 laser flash system, the IL decreased the thermal diffusivity and increased the specific heat of long-flame and non-caking coals. It had a notable inhibiting effect on the heat transfer properties of the two coals. However, the influence of IL on the heat transfer characteristics of gas-fat coal shows a salient promoting effect. Therefore, we conclude that the IL inhibited the generation and transfer of heat during the low-temperature oxidation of long-flame and non-caking coals. This prevented the occurrence and development of coal spontaneous combustion, but it had the opposite effect on gas-fat coal. The effect of the IL on the thermal behaviour of coal oxidation at low temperature varied with the degree of metamorphism of coal, and such an influence played a dual role in this because of its inhibition and promotion in relation to this reaction. This demonstrated that the IL did not inhibit the spontaneous combustion of all types of coal. [ABSTRACT FROM AUTHOR]

Coal spontaneous combustion (CSC) is a major concern in the exploitation and utilisation processes of coal. Various technologies for inhibiting CSC have been developed, promoting industrial safety. With consideration of the complexity of the processes involved, efficient fire prevention and control techniques should be developed. Commonly used retardants for CSC prevention were reviewed. Based upon the necessary conditions required for CSC and coal − oxygen reaction mechanism, various materials used in CSC inhibition are analysed in detail and classified into physical-based, chemical-based, as well as composite retardants. The novel composite retardants combine both physical and chemical-based mechanisms in controlling CSC. The advantages and disadvantages of each CSC retardant are discussed and inter-compared. This review can promote research in the most needed areas to develop more efficient and affordable materials for CSC prevention. [ABSTRACT FROM AUTHOR]