Microcharacteristic analysis of CH4 emissions under different conditions during coal spontaneous combustion with high-temperature oxidation and in situ FTIR

The recent concept of inherent safety uses the properties of a material or process to eliminate or reduce the risk thus removing or minimizing the hazard at the source as opposed to accept the hazard and looking to mitigate the effects. In this framework the control of particle size in dust explosion prevention and mitigation is recognized as a major inherent safety methodology. Indeed, the increase of particle size may allow significant reduction of particle reaction rate eventually reducing the risk. 
 
In this paper a novel model is developed to quantify the effect of particle size on dust reactivity in an explosion phenomenon. The model takes into account all of the steps involved in a dust explosion: internal and external heating, devolatilization reaction and volatiles combustion. Varying the dust size can establish different regimes depending on the values of the characteristic time of each step and of several dimensionless numbers (Damkohler number, Da; Biot number, Bi; thermal Thiele number, Th). Results from the model are reported in terms of the deflagration index (KSt) as a function of dust diameter in all regimes and at varying Da, Th and Bi. Comparison with experimental data from polyethylene explosion tests shows promising results. Finally, the results of the model are presented in the form of a dust explosion regime diagram, which is helpful to make a draft evaluation of the role of dust size on explosion behavior and severity.

Modelling the effect of particle size on dust explosion

H2SO4-treated Malaysian low rank coal for methylene blue dye decolourization and cod reduction: Optimization of adsorption and mechanism study

Energy storage systems towards 2050

Effect of water immersion on active functional groups and characteristic temperatures of bituminous coal

Correlation analysis of the functional groups and exothermic characteristics of bituminous coal molecules during high-temperature oxidation

Research on the micro- and macrocharacteristics of different metamorphic degrees of coal helps improve the control and protection techniques used during spontaneous combustion. Nine coals with different properties were thoroughly investigated in this study. Fourier transform infrared spectroscopy and a self-designed temperature-programmed oil bath experimental system were adopted to analyze the molecular structure and macrocharacteristic parameters of the spontaneous combustion of coal. Additionally, the influence of particle size on spontaneous combustion was considered. Various functional groups were employed as microcharacteristic parameters to capture the principal active groups in oxidation. The gas production rate, oxygen consumption rate, gas concentration, heat energy release rate, and characteristic temperatures were evaluated as macrocharacteristic parameters to investigate the changes in coal during oxidation. The results establish that the microcharacteristics of coal molecules determine the degree of spontaneous combustion based on intrinsic properties and that changes in the macrocharacteristics of the spontaneous combustion of coal reflect the microstructural changes. The contents of the hydroxyl groups, carbonyl groups, alkyl ether and aryl ether in the coal molecules gradually decrease with the metamorphic increase. Oxygen-containing functional groups have higher reactivities and easily react with oxygen, causing the macroparameters, such as the oxygen consumption rate, the gas generation rate and the heat energy release rate, to consistently decrease with the increase of the metamorphic degree. Small-particle-size coal molecules have more active aliphatic hydrocarbons, oxygen-containing functional groups and a larger specific surface area, increasing the chances of adsorbing the oxygen of active groups and promoting the reaction between coal and oxygen. The experimental results indicate that coal samples with higher metamorphic degrees or larger sizes exhibit lower tendencies toward spontaneous combustion. Evaluation of the spontaneous combustion of coal based on a temperature-programmed oil bath experimental system is of great practical importance for preventing the spontaneous combustion of coal during storage, processing and utilization and can serve as a convenient reference for production safety in mining applications.

Evaluation of the spontaneous combustion characteristics of coal of different metamorphic degrees based on a temperature-programmed oil bath experimental system

Granularity is one of the primary extrinsic factors that can influence the process of coal spontaneous combustion. Lignite was selected for studying the influence of granularity. A self-developed temperature-programmed oil bath experimental system was adopted to capture the changes in the spontaneous combustion characteristic parameters for different particle sizes. Moreover, the microcrystalline structure and functional group distribution of different granularities were obtained using an X-ray diffractometer and Fourier transform infrared spectrometer. The results show that the microcrystalline structure, the types of functional groups and the release order of gases of different granularities have equal influence during the process of coal spontaneous combustion. A smaller granularity has a lower aromatic group content and a higher content of high-activity hydroxyl groups, aliphatic hydrocarbons and oxygen-containing functional groups. Moreover, a smaller particle size results in a lower critical temperature. The distributions of coal granularity also affect the characteristic of coal spontaneous combustion. A wide particle size distribution produces a larger surface area for contact between coal and oxygen than a narrow distribution, which results in a coal with a stronger spontaneous combustion tendency.

Influence of granularity on thermal behaviour in the process of lignite spontaneous combustion

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Correlation analysis of the functional groups and exothermic characteristics of bituminous coal molecules during high-temperature oxidation

Evaluation of the spontaneous combustion characteristics of coal of different metamorphic degrees based on a temperature-programmed oil bath experimental system

Influence of granularity on thermal behaviour in the process of lignite spontaneous combustion