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The theory of spontaneous separations of coal and gas is based on the simultaneous effects of four natural factors: i) saturation of the coal stratum with gas; 2) pressure of the country rocks; 3) specific structure of the coal and the other components of the stratum; 4) initial impulse (mining operations, gravity, etc.).The idea that all the methane in the stratum is present in the free (compressed) state can be refuted. The comparatively small jointing (apart from geological fractu#es) of coal strata cannot account for their actual methane bearing capacity (up to 45 mS-ton-l).It has been noticed in [i] that metamorphism is associated with changes: i) in the chemical composition of the coal substance, and 2) in the physical properties of the strata (disperse structure, porosity, agglomeration of the components). These processes are of two types which develop at different rates independently of each other.In [2,3] it was shown that during general metamorphism, it is essential to distinguish the chemical changes which occur in the coal substance with increase in temperature, from the physical-structural changes related to geostatic pressure.During the metamorphism of 1 kg of coal, almost 200 liters of methane are produced, part of which is absorbed by the coal, the remainder is released from the stratum.In what state is the methane found in coal strata in the depths of the earth?The suggestion has been made recently that the gases in coal strata are in a condensed state. Chernitsyn [4], one of the first workers in Russia to study mine gases, wrote, "... the suggestion of a simple mechanical penetration of the gases through the pores of the coal mass does not answer the real question, since there is a great deal of data indicating the existence of other types of bonds between the coal substance and the methane..." "Wemaydistinguish... absorption, absorption and occlusion -direct absorption, as though dissolved by a compact solid body.., these subdivisions are not clear cut.., so for my basis I will use the term 'occluded.'" Occlusion is the absorption of gases by solid bodies (from the Latin word Oclussus -blocked). This is particularly appropriate for methane in coal layers. It appears 'blocked' at the place of its formation. The term occlusion is rarely used now, although it should be revived for the methane--coal system in coal strata.The requisite favorable combination of the above factors for discharge is determined by the indigenous conditions and by mining methods, but a prerequisite for discharge is the creation of conditions for changing the equilibrium of the condensed methane-free methane system.The formation of coal begins with the biochemical decomposition of vegetable remains and the formation of a hydrosol. The hydrosol is converted into a hydrogel with a coagulated structure. Particles of the dispersed phase are stabilized during coagulation, by the formation of an adsorbed layer of surface active substances on their surface.Further metamorphism leads to the fixation of the polar groups and the for...

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In recent years, physlcochemlcal studies of methane saturated coals, under both laboratory and natural conditions, have been directed mainly towards the determination of the rate of methane transfer through the coal, which is the main factor determining the ultimate concentration of methane in the mine a=mosphere.In many of the countries coal basins, the gas saturation of the strata is the main factor which determines has loading at the working face and the rate of cunting.In the future increase in r_he gas saturation is anticipated, which will add to the difficulties of ventilation and control of the gas release.For this reason, improved methods for predicting the rate of gas release in the mine workings have become even more esential to enable the ventilation system to be optimized.There are various well known methods for the experimental determination of the methane release from exposed surfaces of the coal strata and rocks, and also from broken-off coal. But it is difficult to use the data so obtained to derive the rate of gas release from workable strata.In fact, the data on the rate of gas release from exposed surfaces can only be used to form an opinion on the gas dynamics in the pre-face area, and does not provide any information on possible rapid gas releases from the more distant parts of the stratum, which may vary significantly according to the extent of tectonic transformation of the components of the coal. Most of the methods for calculating the rate of gas release from broken-off coal take no account of the nature of the porous structure of the coal, or the empirical data obtained from individual workings in other mines.Consequently, they are unsuitable for estimating the rate of gas release from working areas of different fracture.To improve the accuracy, the current standards for calculating the quantity of air required for ventilating, do allow for the particular local rock-geologlcal conditions of each coal basin. But, as shown in [I], the 'Manual for Calculating the Quantity of Air for Ventilating Coal Mines' [2], does not adequately reflect the nature of gas dynamic phenomena in worked coal strata, since even in a single basin, differences in the inherent properties of the strata may exist. The authors [i] emphasize that the current methods of calculating the rate of gas release take no account of differences in the microstructure or petrographic conditions of the coal, or other components of the strata, although even with similar rockgeological conditions, identical natural gas transfer, equal rates of advance of the face and other similar conditions, the rates of gas release can differ.It is therefore necessary to improve the methods used to predict the rate of gas release in mine workings, by the more accurate calculation of the particular porous structure of the stratum. This however, requires a scientific study of the relation beEween the properties of coals of different porous structures and the rate of methane transfer through the pores.The main theoretical concepts of methane diffusi...

Consider the possible forms in which methane can be present in coal strata: 1) methane may be present in the gaseous state in the pores of the coal strata; 2) methane may exist in the condensed state, either adsorbed or absorbed. Adsorption is applicable only to solids which have a large internal surface and is not applicable to the majority of coal types. This leaves only absorption, i.e., the presence of methane throughout the entire volume of the coal. Absorption of methane leads to the idea of the formation of a methane-coal solid solution.It is difficult to give a strict criterion to distinguish between the concepts of "solution" and "mixture." The definition, accepted by the International Chemical Society, runs --"The word solution is used to describe liquid and solid phases, containing more than one substance, when for convenience, one of the substances (which may be a mixture) called the solvent can be considered separately from the other substances, called the dissolved substances."A true solution is regarded as a macroscopic single phase thermodynamic equilibrium system, of variable composition, containing two or more components. In a true solution, there is no surface of separation between the dissolved substance and the solvent. The Gibbs energy (isobaric--isothermal potential) of a true solution is a minimum. This is the consequence of all the possible types of interaction between the parts of the system. The majority of researchers agree that 5-10% of the stratal methane exists in the free state.By carefully cooling a saturated solution from a high temperature, it is possible to obtain a supersaturated solution. This solution is not in equilibrium with the dissolved substance and the introduction of an insignificant quantity of it into the supersaturated solution leads to the separation of the dissolved substance. Sometimes the transition can be caused by simply shaking or stirring. If the methane--coal system is a supersaturated solid solution, then any mechanical action (mining operations) may release the excess methane into the system.The formation of a solution is accompanied by a change in the properties of the solvent and the dissolved substance. In a solution, forces operate to create both molecular interactions (electrostatic, Van der Waals forces), which are manifest over comparatively large distances, and specific interactions (donor-acceptor, hydrogen bonding) effective over comparatively small distances.The mechanism of dissolution of gases in a liquid has not been well developed. What happens in a liquid when a gas is dissolved in it? Obviously, in pure solvents, short range order (i.e., an ordered distribution of adjacent molecules) exists.With increasing concentration of the solution, the interaction between the particles is increased and the structure of the solution becomes complex (the entropy is reduced).The idea of solid solutions and the name were introduced by Vant Hoff. Is it possible that coal forms a solid solution with methane? Methane is known to form solid solutions, e.g....

Gas-saturated and gas-free coal seams are in a state of mechanical and chemical equilibrium produced by long-term geologic and physicochemical processes during their geologic history.The internal energy of an equilibrium system can be changed in two ways:(I) by performing some work on the system and (2) by introducing heat into the system or extracting it from the system, i.e., AU -AQ + AA, where AU is the change in the internal energy of the system; AQ is the quantity of heat introduced or extracted from the system; and AA is the mechanical work done on the system. The internal energy of an equilibrium system in an intact coal seam is changed by technogenic interference.When a seam is opened and coal is extracted, irreversible physicochemical processes disrupt the equilibrium, which is manifested, among other things, in changes of the temperature in either direction, during the development of coal seams.A lowering of coal temperature during the course of excavation was reported long ago by Chernitsy~ [1]. As coal is degassed, it becomes cooler. The study of this phenomenon showed that the cooling depends on the quantity of methane released and the rate of releaseA rise of coal seam temperature during excavation was first noted recently. Experimental studies in loading specimens of degassed coal [I0, ii] and investigations in situ in mines on blocks of coal [12] indicated that coal temperature rises as the stresses created by artificial loading are increased.This results in a rise of coal temperature depending on the rock pressure during the course of coal seam excavation [i0, 13-16].Temperature variation in the near-face zone yields data on physicochemical processes in the coal seam. These processes include a drop in heat quantity caused by the phase transition of sorbed methane into the free state and expansion of the gaseous methane and mechanical work applied to the coal seam through technogenic interference (additional load, development of support pressure zones, etc.). These components produce an algebraic sum reflecting the changes in the internal energy of the system. A number of investigators studied the work applied to the coal seam.In [17] it was noted that coal bed temperature variation provides data on the deformation processes in the bed. The authors interpreted these changes as resulting from disruption of natural equilibrium by seam working, with the transition to a new equilibrium after redistribution of stresses. The rheologic deformations are irreversible, and a portion of the energy accumulated in the form of stress is converted to heat, changing the temperature field in the coal seam.The same investigators [18], studying the effect of mining on coal seam and enclosing rock temperature in permafrost conditions, demonstrated that stress redistribution around the workings modifies the temperature of the enclosing rocks.In [19], the thesis that the temperature of the coal seam rises as its stressed state is intensified was confirmed, drawing the conclusion that coal seam temperature variation c...

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