Assessment of water-based compositions efficiency for cooling place of lignite spontaneous combustion in strip mines

Places of spontaneous coal combustion cause significant economic losses to the mining operations due to coal losses and accident elimination costs, while toxic gases and high temperatures threaten the health and life of employees. Coal cooling is a necessary condition to eradicate spontaneous fire seats. The most effective way to eliminate spontaneous fires is excavation of heated coal. Coal cooling can take place due to heat exchange with the atmosphere or the supplied refrigerants. The performed studies have shown that air-cooled lignite shows increased oxygen sorption capacity. As the initial temperature of the coal goes up, the activity of cooled coal increases. Thus, if natural coal was characterized with the oxygen sorption rate constant of 0.1348 ml/(g∙h), the coal cooled down upon heating up to 50°C already showed 0.2191 ml/(g∙h), while with coal being heated up to 100°C this parameter went up to 0.3153 ml/(g∙h). The latent time of spontaneous combustion of air-cooled lignite significantly decreases with the increasing heating temperature (2-3 times) due to lignite activation and reduction in its moisture content, which increases the danger of recurrent spontaneous firing. The use of water and water-based compositions for lignite cooling significantly reduces the coal's oxygen sorption rate constant and increases the latent time of spontaneous combustion. Calcium chloride proved to be the most effective means for cooling lignite among the investigated water-based compositions, while liquid glass (sodium silicate) had the least effect. Air cooling of coal leads to intensified emission of carbon monoxide, while cooling with water and water-based compositions reduces the release of this hazardous gas by several times.