Bulat A.F., Dyrda V.I. Nonlinear evolution-structural model of gas-dynamic phenomena in a coal massif

Details
Parent Category: Geo-Technical Mechanics, 2020
Category: Geo-Technical Mechanics, 2020, № 151

Geoteh. meh. 2020, 151, 3-26

DOI: https://doi.org/10.15407/geotm2020.151.003

Nonlinear evolution-structural model of gas-dynamic phenomena in a coal massif

1Bulat A.F., 1Dyrda V.I.

1Institute of Geotechnical Mechanics named by N. Poljakov of NAS of Ukraine

UDC 622.831.323

Language: Russian

Abstract.

Based on extensive experimental information, a cluster-synergetic evolutionary-structural model of gas-dynamic phenomena (GDP) in a coal mass was constructed. It was based on the following key points. In the coal massif, hotbeds of danger of GDP are formed mainly in geological time under the influence of tectonic and geochemical processes: their formation in historical time is also possible. The evolution of the coal – gas – moisture system is local and discrete. At the apex of a moving crack, local heating can achieve partial thermal destruction of the substance, which will contribute to intense methane generation and crushing of coal, up to the formation of nanoparticles.

Microcracks in the coal can dissipate, i.e. dissipate energy, which reduces stresses in the mouth of cracks and stops their growth. The zones formed with the changed structure of the substance can be combined to form a gigantic fluctuation (main crack), the stopping of which involves the formation of a source of danger.

Compared to the untouched massif, danger zones will always have a higher temperature, free gas pressure, increased entropy production, and all chemical reactions will proceed more rapidly.

Accepting these provisions, the model of gas-dynamic phenomena can be presented as follows.

In the coal – gas – moisture system, during the evolution of the source of danger under the influence of rock pressure and gas pressure, the concentration of microcracks increases up to the state when they begin to merge and locally form zones with a substantially changed structure of the substance. Such zones are in a quasi-equilibrium state for some time, and the oscillations of their main parameters (stress, gas pressure, methane generation rate, etc.) do not go beyond the permissible limits.

When the basic parameters reach some critical values under the influence of small perturbations of anthropogenic or natural nature, the quasiequilibrium state of a nonlinear nonequilibrium system can be violated. This is expressed in the growth of a tree-like ensemble of cracks and anomalous methane generation from moving cracks; energy dissipation increases sharply, which increases the temperature and energy dissipation. Such an interaction between temperature and dissipation leads to a sharp nonlinear increase in temperature; the process from metastable turns into labile, which leads the system to thermal explosion. At the same time, the principle of temperature-time superposition is preserved.

The criteria for a thermal explosion will be similarity criteria, known as the Semenov or Frank-Kamenetsky criteria.

Based on modern concepts of nonlinear nonequilibrium thermodynamics, important remarks are formulated for the model of gas-dynamic phenomena in a coal mass. It is shown that in the ejection zone during the collapse period, certain parts of the zone (core) have different rates of structure evolution and gas ejection. According to the authors, in the evolution of the ejection zone, an asymmetry of the main information parameters (pressure, methane generation rate, etc.) arises, which can lead to the formation of small disturbances that can inhibit the process, which usually leads to a thermal explosion. Thus, along with external disturbances of a natural and technogenic nature, the small asymmetry of the internal parameters of the nuclei can also cause the start of the thermal explosion process.

Keywords:

simulation model, gas-dynamic phenomena, coal mass, collapse, thermal explosion, coal and gas emissions, dynamic phenomena

References:

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2.   Bulat, A.F. and Dyrda, V.I. (2013), “Some problems of gas-dynamic phenomena in coal massif in the context of nonlinear nonequilibrium thermodynamics”, Geo-technical Mechanics, no. 108, pp. 3-31.

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About the authors:

Bulat Anatolii Fedorovych, Academician of the National Academy of Science of Ukraine, Doctor of Technical Sciences (D.Sc.), Professor, Director of the Institute, Institute of Geotechnical Mechanics named by N. Poljakov of National Academy of Science of Ukraine, Dnipro, Ukraine, This email address is being protected from spambots. You need JavaScript enabled to view it.

Dyrda Vitalii Illarionovych, Doctor of Technical Sciences (D.Sc.), Professor, Head of Department of Elastomeric Component Mechanics in Mining Machines, Institute of Geotechnical Mechanics named by N. Poljakov of National Academy of Science of Ukraine, Dnipro, Ukraine, This email address is being protected from spambots. You need JavaScript enabled to view it.