The gain to the pit on account of degassing and utilization of the methane is 120,000 rubles per annum, of which 53,000 are due to the gain in coal output and 67,000 to the utilization of the methane.
At present, treatment with gel-forming [i] or antipyrogenic [2, 3] compositions is used to prevent self-ignition of the coal in a worked-out mine area, thereby isolating part of the surface of the coal pieces from the oxygen present in the air filtering through the permeable mass.To estimate the efficiency of such methods, the heating of coal has been investigated using the simplest mathematical model.It is assumed that the heating conditions of the coal correspond to the third stage [4], in which the evaporation of the moisture present in pores of the coal is basically complete and any intense increase in the surface of oxidation of the coal is over. On the basis of the model of filtration through a porous medium, i.e., considering the air and the solid phase as interpenetrating materials with uniformly distributed sources, it may be supposed that the heat accumulation of the air is described by the term X(82T/Sx 2) and that of the coal by the term %C(82T/Sx2), where % and %C are the thermal conductivity of the air and the coal, respectively, kW/m'K.The heat-conduction equation for air filtered through the permeable mass in the direction of the filtration rate takes the form i)where T is the temperature of the reacting medium, K; T T is the temperature of the permeable mass that is not subject to oxidation, K; t is the time, sec; u is the air filtration rate through the mass, m3/m2"sec; Cp is the isobaric specific heat of the air, kJ/kg'K; p is the air density, kg/m3; qv is the specific power of the heat sources in the mass, kW/m 3.For the sake of simplicity, Cp, %, %C, ~, and u are assumed to be constant and equal to their mean values in the given temperature range in the analysis.The quantity v is expressed as a function of the oxygen consumed in oxidation [5] , Oe q,, = o% ~, where G is the volume flow rate of air through the given mass, m3/sec; q0 is the amount of heat released in the oxidation of coal in the consumption of unit volume of oxygen, kJ/ m3; c is the concentration of oxygen consumed in oxidation, m3/m3; v is the volume of broken rock with coal content through which the air filters at a rate G, m 3.With a constant cross section sf of the filtrational flowThe law describing oxygen consumption from the air along the given flow is specified in the form where Cin, c L are the oxygen concentrations in the air flow entering the mass and that Kuznetsk Polytechnic Institute.
A n urgent problem for safety conditions in working thick steep seams is that of spontaneous fires, most of which arise in the worked-out areas in working and isolated districts.Factors governing the formation of heat emission centers and heat propagation in the worked-out area include not only the physical properties of the coal and the percentage oxygen content but also the flow rates of the air filtration currents. Present methods of isolating worked-out areas (various types of stoppings and antifire pillars) only partly prevent access of air to isolated districts, because they do not prevent leaks through deformed rocks between seams. The activity of the aerodynamic, thermal, and diffusion processes in underworked or overworked strata is largely governed by their degree of disturbance, and determination of the boundaries of the air-permeable sections of the deformed rock reduces to calculating the boundaries of fissure formation in the disturbed strata.By observations in underworked strata and investigations on models [1, 2] it was found that the depth and size of the crack formation cones in systems with caving are primarily governed by the dimensions of the working, the thickness of the worked seam, and the structure and strength properties of the surrounding rocks.Calculations of the displacements around an extraction working are based [3] on the unit influence function of the worked-out area affecting the displacement of any point in the rune of influence; this takes the following form:, where H is the distance from the center of the working m the point along the line of maximum subsidence, in meters, B is the width of the worked-out area (m the dip), in meters, and n is an index representing the influence of the lithological composition and strength properties of the country rocks on the displacement process.The lithologieal composition index is determined from the graphs in Fig. 1 as the mean value of the percentage sandstone and argiIlite contents of the strata, with allowance for their strength characteristics.Investigations with models and analydcal calculations [2,3] show that the displacement process in underworked strata develops in the form of closed isolines of complex shape and variable deformation. In general form the character of the displacement isolines was determined as elliptical. The values of the contours and their deformations decrease with increasing distance from the working.We also found that from the qualitative view point the attenuation of the displacements foliows the same law in any direction away from the center of the working as given by Eq. (1).The maximum displacement in the underworked strata is determined quantitatively from the angle of m aximum subsidence, which is given by VostNII, Kemerovo.
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