Ignition of Coal Microparticles in an Air Atmosphere and Their Influence on the Inflammation of Methane
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Journal of Engineering Physics and Thermophysics, Vol. 93, No. 4, July, 2020
IGNITION OF COAL MICROPARTICLES IN AN AIR ATMOSPHERE AND THEIR INFLUENCE ON THE INFLAMMATION OF METHANE V. V. Leshchevich, O. G. Penyazkov, and S. Yu. Shimchenko
UDC 662.612.12+662.612.16
The spontaneous combustion of the coal microparticles of fractions 1–20 μm and 20–32 μm in an air atmosphere and the inflammation of the coal microparticles of fraction 20–32 μm in a methane–air mixture at temperatures of 700–1100 K were investigated with the use of a rapid compression machine. A contactless measurement of the temperature of the coal particles ignited spontaneously in a gas has shown that this temperature can reach 2500 ± 200 K and substantially exceeds the temperature of the gas at the end of its compression stroke. It was established that the coal microparticles burning in a stoichiometric methane–air mixture are local hotbeds of fire in this mixture at a temperature as high as 1400 K and that the gas is ignited in the neighborhood of these hotbeds. The limiting temperatures of ignition of the coal microparticles in an air atmosphere free of methane and in a methane– air mixture were determined. The measured times of delay in the ignition of the methane by the coal microparticles in a hybrid methane–air mixture agree with the delay times of ignition of a pure methane–air mixture under the same conditions to within the experimental error. Keywords: ignition, hybrid mixture, methane, coal microparticles, rapid compression machine. Introduction. Disperse materials are used in many technological processes in the chemical, coal, electric-power, and other industries, which leads to the appearance of solid particles suspended in the air of production floor-areas and technological apparatus. It is significant that such a gas suspension can ignite spontaneously and, as a result, can cause an anthropogenic catastrophe or a damage of equipment. The consequences of accidents caused by the explosions of the particles in reactive mixtures have given rise to a large number of experimental and theoretical works on this subject. The first investigations of the ignition and combustion of gas fuel mixtures containing an oxidizer and a suspension of reactive particles were carried out by Engler in 1885 [1]. It was established that the mixing of a coal dust with the methane in an air atmosphere in which the concentration of the methane is lower than that necessary for its ignition (5 wt.%) can cause an explosion of the hybrid gas mixture. For elucidation of the reasons for such behavior of heterogeneous (hybrid) gas mixtures [2–5], a large number of different investigations have been performed [6–10]. Many works were devoted to the forecasting of the conditions of ignition of disperse mixtures and the propagation of a flame in them. In these works, prominence was given to the formation of a cloud of solid particles in the methane in a mixture and to its ignition by local heat sources because such combustion of the methane can give rise to detonation wave
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