Effect of the heat transfer surface on prevention of spontaneous combustion of coal

The increased use of coal for power generation has increased the demand for low-rank coal, such as lignite and sub-bituminous coal, and during its supply, it may need to be stored for long periods. Because low-quality coal is more susceptible to spontaneous combustion than highquality coal, its storage could potentially cause work-related accidents. One method being developed to control the temperature of stored coal to prevent spontaneous combustion is the immersion of heat exchangers in coal piles. This method can be used to control the temperature during both the storage and transportation processes. The purpose of this study was to test this method and, in particular, study the effect of changes in the heat-exchange surface area on the effectiveness of temperature control. An experiment was set up to control the temperature of a laboratory-scale coal pile using a heat exchanger made from copper tubes. Coal samples were placed in a cylindrical container with a spiral-shaped heat exchanger, placed in the center of the cylindrical container, and cooled with ~27o seawater. Tests were carried out using several configurations of heat exchanger dimensions to determine the effect of changing the ratio of heatexchange surface area to volume of combustible material. The test results showed that greater heat-exchange surface area produced a greater amount of cooling load and temperature difference.