THERMOGRAVIMETRIC EXPERIMENTAL STUDIES OF THE EXPLOSION HAZARD OF COAL DUST AND ITS MIXTURES WITH STONE DUST

Abstract

Представлены результаты экспериментального исследования пыли 7 марок углей по получению базовых термогравиметрических характеристик, а также сопоставительных экспериментов для состояния пыли до взрыва и после взрыва. Проведено выделение 4 представительных брутто-стадий термической деструкции угля и смесей. Отработаны методы термогравиметрического анализа (ТГА) для определения влажности образцов, аналитической зольности и стадийного выхода летучих веществ с разделением органической и негорючей газовых составляющих. Методом сопоставления ТГА характеристик определены стадии устойчивого снижения и стадии роста выхода летучих веществ при воздействии взрыва, позволяющие однозначно трактовать участие угольной пыли во взрыве, исследовать динамику фронта пламени. The article presents the results of an experimental study of dust of various grades of coal in order of increasing degree of metamorphism (D, DG, G, GZh, Zh, K, A) to obtain basic thermogravimetric characteristics. The samples were examined in an inert atmosphere with a change to an air atmosphere after the completion of coking. The temperature of the heating zone increased linearly with a heating rate DТо = 20 °C/min (the second mode is DТо = 100 °C/min) in the range from 25 °C to 850 °C. The mass of the sample was measured 30 times per minute. When 850 °C was reached, isothermal heating was carried out for 15 minutes until the coking process was completed, then the inert atmosphere was replaced with an air one in order to afterburn the coke and to determine the ash Ad. Additional comparative experiments were carried out for the state of dust «before the explosion» – «after the explosion». There was carried out the isolation of 4 gross stages of thermal destruction of coal and mixtures under the thermal effects of fire or explosion: the stage of analytical moisture release Wа(MRS – Moisture Removal Stage) from 25 °C up to 130 °C; the stage of «primary» volatiles release (PVS – Primary Volatiles Stage) from 400 °C up to 600 °C; the stage of «secondary» volatiles release (SVS - Secondary Volatiles Stage) from 600 °C up to 750 °C; the stage of carbon dioxide release in coal and stone dust mixtures (CDS – Carbon Dioxide Stage) from 700 °C up to 840 °C. It was determined that the maximum release rate of volatiles at the PVS stage is reached at a temperature of 465 °C – 505 °C, the presence and output value of volatiles at this stage determines the explosive properties of dust. The SVS stage exists in coals of a high stage of metamorphism and anthracites, however, the hazard of such dust from explosions has not been experimentally confirmed. There was carried out the study of dust after explosions in an explosive 20-liter chamber and dust collected in mines after explosions. For dust obtained from full–scale mine explosions, there was determined a sharp (in 3.5–5 fold) decrease in the residual volatile yield in the PVS stage with a simultaneous increase in the volatile yield at the SVS stage. And also there was determined the appearance of low-temperature differential thermogravimetry (DTG) peaks (at a temperature of 200 °C – 300 °C). Dust from 59 coal seams was examined, the total number of thermogravimetric studies was more than 150. The methods of selecting logically related dust samples at emergency sites during the elimination of explosions at mines (2013–2021) were tested. There were elaborated both stable method for numerical recognition of dust involvement in an explosion and methods of thermogravimetric analysis of coal and stone dust mixtures, and also the methods of retrospective analysis of the dynamics of explosion development during the investigation of technical factors of accidents in coal mines.