College of Mining, National University of Science and Technology – MISIS, Moscow, Russia:

V. L. Shkuratnik, Professor, Doctor of Engineering Sciences, ftkp@mail.ru
E. A. Novikov, Associate Professor, Candidate of Engineering Sciences
R. O. Oshkin, Post-Graduate Student
M. G. Zaitsev, Student

The article considers the experimental test data on thermally induced acoustic emission (TAE) in the intact and pre-frozen-and-thawed samples of different rank lignite and bituminous coal. The authors propose and validate methodical approaches to thermal stimulation of acoustic emission effects in coal in order to assess coal susceptibility to formation of crack–porous structure under cyclic treatment by freezing and thawing. The physical preconditions and mechanisms of the acoustic emission effects are explained. The interconnections between the TAE parameters chosen for the tests and the velocity of cryogenic formation of the crack–porous structure in coal are shown. Based on the analysis of the specific features of these interconnections, the numerical acoustic emission criterion Rt is offered and substantiated for the estimation of climatic influences on the rate of structural transformations in coal. It is proved that this criterion is unexposed to interfering effect of random factors inherent to a control object such as inclusions with anomalous material constitution, size and shape of a sample, nonuniform crack network etc. It is demonstrated that the proposed criterion is highly sensitive to variation in calorific capacity of coal as a consequence of cryogenic disintegration and intensification of oxidation. It is shown that the process of cryogenic disintegration is stagewise. The scope of the discussion encompasses applicability of the obtained results. It is proved that evaluation of change in Rt in periodically sampled coal products, either under storage or haulage, allows estimation of cryogenic disintegration intensity in coal and prediction of degradation of its useful quality under specific conditions. Based on that, it is possible to obtain information for the calculation of expediency and schedule of oxidation source confinement and secondary protection of coal from climatic impacts. As compared wit the conventional methods, the key advantages of TAE approach are high measurement rate and serviceability under field conditions in the mode of express-control. It is also of no little significance that TAE method provides information about the whole volume of a tested coal sample rather about its surface as in the microexamination techniques, for example.
This study has been supported by the Russian Foundation for Basic Research, Grant No. 16-05-00033 А.

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