Экспериментальные исследования и расчет условий теплового самовозгорания отработанного активного угля марки СКД

Abstract

По предшествующей (1989 г.) и новой (2018 г.) методикам определены условия теплового самовозгорания отработанного активного угля марки СКД. Новая методика, в отличие от предшествующей, учитывает кинетику процесса, позволяет рассчитывать условия самовозгорания для различных реальных геометрических форм и размеров горючих материалов при их хранении и транспортировании. Результаты расчетов могут быть использованы при прогнозировании и для предотвращения пожаров при хранении и транспортировании твердых дисперсных горючих веществ и материалов. Например, выполненные расчеты условий теплового самовозгорания отработанного активного угля марки СКД при транспортировании в вагонах-хопперах размерами 2,64  2,112  13,37 м, смонтированных на железнодорожных платформах, по территории России (с учетом максимальной летней температуры 40 °С), показали, что самовозгорания произойти не может. Исследование условий теплового самовозгорания отработанного активного угля марки СКД проводилось в соответствии с методикой, представленной в ГОСТ 12.1.044-2018.Analysis of fire properties of active coal of various grades shows that only for two of 11 grades of active coal (AP-14 and B) there was experimentally obtained the ignition temperature and there were defined the conditions for thermal self ignition. For other 9 grades no information is available. These data are not available for active waste coal of SKD grade. The self-heating arising in coal stacks initially can be General, i.e. over the whole stack volume including the surface layer of 0,3-0,5 m thick, but in process of temperature increase the centre moves insight the embankment where heat accumulates. The temperature growth in the centre is very slow and can be preserved or even reduced, for example, when pulling coal from the stack or when it is ventilated. At the temperature values above 50-60 °C the rate of coal self-heating in the stack can increase. This temperature is called a critical temperature. The main cause of spontaneous combustion of coals in piles or stacks is their ability to oxidize and adsorb vapours and gases even at low temperatures. In this case, oxidation process is slow and little heat is released. The formation of source of coal self-ignition in piles and stacks is associated primarily with the possible contact of the combustion source with air flows as well as with favourable conditions of heat accumulation inside coal deposits. For example, as for coal there are given observations on the combustion source origin on the stack slopes mainly at the height of 0,5-1 m from the base and at the depth of 0,5 m from the surface. If the stack is heterogeneous in density and size of the pieces, the self-ignition sources can arise in other places where smaller coal fractions with the lowest density are concentrated. Heat removal from the sources of spontaneous combustion is mainly due to the size of the stack (embankment) and heat removal by air flows. In large accumulations of coal, where heat transfer to the environment is difficult, spontaneous combustion occurs. Air flows can form as a result of temperature and material density gradients, as well as of air mass movement. The tendency of coals to spontaneous combustion in stacks and embankments is different. The greater the yield of combustible gases and vapours formed during the thermal-oxidative destruction of coal, the higher the dispersion (specific surface area), the lower the density inside the material mass and the greater the moisture content and pyrite in it, the higher is this tendency. The study of the conditions of thermal spontaneous combustion of waste active coal of SKD grade was carried out in accordance with the methodology, presented in GOST 12.1.044-2018, which takes into account the kinetics of the oxidation process of the investigated substance (material). It allows to calculate the conditions of spontaneous combustion for various real geometric shapes and sizes of combustible materials during their storage and transportation. The results of experimental studies as well as calculations of kinetic parameters such as the critical temperature of self-ignition, the critical size and time of induction for waste active SKD brand carbon showed that in real conditions of storage and transportation of this substance, taking into account the upper range limit of climatic air temperature drop of 40 °C, spontaneous combustion will not occur. For example, transportation in hopper cars of railway platforms, provided that the product fills the specified in the calculations shape and size of the hopper car, is fireproof and cannot lead to spontaneous combustion in transit.