Assessment of the Likelihood of Underground Coal Oxidation and Self-Ignition: A Review
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Assessment of the Likelihood of Underground Coal Oxidation and Self-Ignition: A Review S. A. Semenovaa, *, Yu. F. Patrakova, **, and A. E. Majorova, *** a
Federal Research Center of Coal and Coal Chemistry, Siberian Branch, Russian Academy of Sciences, Institute of Coal, Kemerovo, Russia *e-mail: [email protected] **e-mail: [email protected] ***e-mail: [email protected]
Received February 26, 2020; revised February 26, 2020; accepted March 11, 2020
Abstract—Standard and alternative methods of assessing the likelihood of coal oxidation and self-ignition in the bed are analyzed. These methods are based on the change in the petrographic, physicomechanical, chemical, and thermal properties of the coal on oxidation. Most of the methods are unsuitable for identification of the initial stage of coal oxidation. The onset of self-heating may be better determined on the basis of the surface properties of the coal: in particular, the hydrophobic–hydrophilic balance and the sorptional properties of internal surfaces. The extraction, transportation, and analysis of the coal sample from the bed must prevent contact with the air. Keywords: coal, coal beds, low-temperature oxidation, self-heating, endogenous processes, localization, cracked coal, coal oxidation, self-ignition, risk assessment DOI: 10.3103/S1068364X20050063
Coal mining today is characterized by increase in working speed, cutting depth, and gas content. Highproductivity equipment is employed, with collapse of the mined chambers. In these conditions, low-temperature oxidation and self-ignition of the coal’s organic mass is a problem. If the coal is oxidized in the bed before extraction to the surface, transportation, and storage, its quality will be impaired, with loss of calorific value and also of clinkering and coking properties. Underground fires affect the mine atmosphere and worker safety; depress coal quality; and cause resource losses, with corresponding economic impact [1, 2]. Although fires occur predominantly in exhausted sections of the mine, self-heating within the coal bed that is still being worked is of greater concern. Factors that complicate control of the coal bed’s properties and maintenance of thermal equilibrium in the coal–oxidant system include limited access; and the complexity of diagnostic methods and means of localizing and suppressing self-ignition. The development of self-ignition in coal mines depends on factors such as the type of oxidant, the high chemical activity of the freshly cut coal surface, the moisture content of the coal, and the content of mineral impurities. The following factors are assumed to affect the development of endogenous fires [1, 3– 5]: the chemical maturity of the coal (its rank composition), its ash content, the presence of iron sulfides
and carbonates, the properties of the surrounding rock, and the presence of coal intercalations in the rock. The contact time of the coal’s organic mass and the oxidant is extended on account of complex geological conditions (seam thickness, coal falls, geological faults,
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