Mapping coal fires using Normalized Difference Coal Fire Index (NDCFI): case study at Khanh Hoa coal mine, Vietnam

Khanh Hoa coal mine (Thai Nguyen province) is one of the largest coal mines in the north of Vietnam. For many years, this area suffered from underground fires at coal mine waste dumps, seriously affecting production activities and the environment. This paper presents the results of classification of underground fire areas at Khanh Hoa coal mine using Normalized Diference Coal Fire Index (NDCFI). 03 Landsat 8 OLI_TIRS images taken on December 2, 2013, December 10, 2016, and December 3, 2019 were used to calculate NDCFI index, and then classify the underground fire areas by thresholding method. In the study, the land surface temperature was also calculated from Landsat 8 thermal infrared bands data, and then compared with the results of underground coal fire classification at Khanh Hoa coal mine. The obtained results showed that the NDCFI index can be used effectively in detecting and monitoring underground fire areas at coal mines. The use of the NDCFI index also has many advantages due to its calculation simplicity and rapidness compared to other methods for classifying underground coal fire areas.

PERSPECTIVE DIRECTIONS OF GASIFICATION OF THE REPUBLIC OF TUVA

Based on the analysis of the current situatim with gas supply in the Republic of Tuva (low gas supply to the population, lask of gas based heat generation), the article duscusses possible ways to solve the problem of gas supply to cites, towns and rural settlements of the republic in line with current trends in the development of gasification processes in the regions of Russia. The gas requirements of all categories of consumers: the population, heat generation enterprises, social and household spheres in the region are estimated. The prospects for gas supply in the centext of solving envitonmentae problems are to reduce air pollution in cities and towns. The directions of solving the problem of gasification of Tuva in the long term are substantiated, also considered option for transferring the economy of republic to the main gas supply, construction of an oil product pipeline are considered. The following effective ways to increase the level of gasification in Tuva are identified: the realization of the potential for gas production from coal deposits, the use of thermal energy from an underground fire and the development of autonomous gasification, which can be carried out during stage I of gasification. At the second stage, it is possible to transfer the economy and social sphere to the main gas supply though the construction of Tuva gas pipeline or the oil product pipeline.

Critical velocity analysis for safety management in case of tunnel fire

Heat, smoke and other toxic products may spread along the tunnel, in both directions from the seat of fire, causing different kinds of damage to people. Anyway, underground fire causes complicated results, which is preventing factor for life rescue and evacuation, creating difficulties for firemen and life rescue crew. Analysis of the critical speed, which is necessary for the effective management of combustion products, has been made for tunnel fires with high heat release rate. The characteristic changes in the critical Froude number in the work are presented in accordance with the critical speed. Particularly, it was noted that the formula determining the critical speed requires knowledge of the average smoke temperature, while the formula for calculating the last value includes the value of the required critical speed. In order to overcome this, Froude’s critical number Frc=4.5 has been introduced, which is not the way of solution, as it directly means constant critical velocity for the fire of any power and accordingly, does not correspond to experimental data.

Detection and location of places of spontaneous combustion of coal in mines due to gas anomalies on the earth’s surface

The effectiveness of localization and extinguishing of places of underground fires that occur in mine worked out spaces depends on information about the location of a place of spontaneous combustion. Existing methods to detect the processes of coal spontaneous combustion in mines include monitoring the content of gases in mine atmosphere, released during the spontaneous combustion of coal. However, this control method does not allow determining the location of a place of combustion, since the paths of gas movement in the worked out space are unknown. The surface gas survey allows to determine the location of the underground fire. The calculations showed that gases, generated in the fire seat, spread to the earth’s surface due to molecular diffusion, the thermal depression developed by the fire seat and the drops of air pressure created by the ventilation fans. The dependences of the distribution of fire gases content in rocks on the rate of drops of air pressure between the worked out space in a mine with a fire seat and the atmosphere on the surface of the earth are obtained. Mine researches have confirmed the formation of anomalies of fire gases in rocks and soil over places of spontaneous combustion of coal occurred in worked out space. When conducting a gas survey, it is sufficient to measure the content of fire gases in the soil at a depth of 0.5-1.0 m.

Finding of native tellurium in sublimates of a natural underground fire in the tract Kukhi-Malik at the Fan-Yagnob coal deposit (Tajikistan)

Описывается находка самородного теллура в сублиматах высокотемпературных фумарол на природном подземном угольном пожаре в урочище Кухи-Малик около кишлака Рават на Фан-Ягнобском угольном месторождении в Согдийской области Таджикистана. Теллур представлен хорошо образованными призматическими кристаллами (0.1 мм), на которых наиболее развиты грани m 1010, 0112, r 1011, реже встречаются с 0001 и ряд неидентифицированных форм. В ассоциации с теллуром находятся сульфаты Fe и K, сульфат Tl и K и англезит. Кристаллы теллура зональные, центральная часть обогащена селеном (до 10 мас.). Приведены физические свойства и основные отражения рентгеновской порошкограммы.

Pauflerit β-VO (SO4) in the sublimates of a natural underground fire in the tract Kuhi-Malik (Rawat) at Fan- Yagnob coal deposit, Tajikistan

Приведено описание находки пауфлерита -VO(SO4) в возгонах высокотемпературных выходов газов природного угольного пожара в урочище Кухи-Малик близ кишлака Рават, Фан-Ягнобское угольное м-ние, Таджикистан, в брекчированных алевролитах. Кристаллы пауфлерита удлиненно-призматические, имеют размеры 40100 мкм простые формы: b010, m 101 (наиболее развита), е 110, p 111, 212. Наблюдаются двойники по (010) (). Минерал прозрачный, зеленого цвета, хрупкий. Блеск стеклянный. Пауфлерит оптически двуосный, 2V близок к 90. Дисперсия оптических осей очень слабая, v r. Плоскость оптических осей перпендикулярна удлинению кристаллов np 1.733(2), nm 1.778(3), ng расч. 1.823(4). Плеохроизм: по Ng зеленая окраска, по Nm и Np светло-зеленая. Схема абсорбции Ng Nm Np. Состав (ср. по 3 ан., электронно-зондовые данные, мас.): VO2 49.87, SO3 50.01, сумма 99.88. Эмпирическая формула V0.97O(S1.02O4). Параметры ромбической элементарной ячейки (): a 7.392(3), b 6.272(2), c 7.064(3). Впервые приведены порошковая рентгенограмма и чертежи кристаллов пауфлерита. По присутствию минеральных фаз V, Cd, Mo, Tl, Bi, Sn, In, Sb, Se, Te, As возгоны угольного пожара на Фан-Ягнобском месторождении близки к возгонам вулканических фумарол Камчатки, Курил, Италии, что связано с общностью механизмов извлечения газами этих элементов из вмещающих пород, их переноса и отложения в зонах разгрузки.