Oxidation of coal in industrial conditions. 4. Coal temperature in heap storage

Abstract

The temperature variation of coal on open storage in heaps is investigated. Analysis shows that the temperature rise on storage observed for all coal in both summer and winter, regardless of its metamorphic development, may be divided into two stages: rapid increase, followed by slower increase. The higher temperature at the end of the first stage in summer (45°C) than in winter (30°C) may be explained in that the rate of peroxide formation increases with increase in the temperature, while the content of peroxides declines. A correlation is found between the duration of the first stage and the metamorphic development of the coal (its yield of volatiles Vdaf). A similar correlation is found for the rate of temperature rise in the first stage and the coal’s metamorphic development. Analysis of the results shows that, in both summer and winter, there is an extremum at moderate metamorphic development (Vdaf = 27.3–30.5%). This confirms that the oxidation mechanism is different for coal at different metamorphic stages. Since the coal does not reach the critical temperature for self-ignition (∼60°C) on storage in both summer and winter, the coal temperature in the heap is of no interest in selecting the limiting storage time.