Thermal conductivity of coal mining wastes in the thermally active zone of a waste dump - In situ study

Coal mining wastes accumulated at dumps include a certain part of carbon. It is one of the components that reacts with the oxygen contained in air. Due to the natural oxidation process, self-heating of the waste material occurs which - in favourable conditions - leads to a fire. In view of fire prevention, possible heat recovery or studies and modelling of thermal phenomena occurring in a waste dump, thermal conductivity of mining wastes may be considered a significant parameter. The value of the thermal conductivity coefficient constitutes a part of the information that is necessary in the study of the heat transfer within the mass of the dump. The paper presents the results of tests conducted at one of the thermally-active dumps located in the Upper Silesian Coal Basin. The conducted tests consisted in the reception of heat from the heated material using vertical heat exchangers. Based on the measurement results of temperature changes of the wastes in the surroundings of the exchanger and the temperature of the flowing coolant, the thermal conductivity coefficient of the coal mining wastes accumulated at the waste dump was established. Due to the variable character of the thermal condition in the direct vicinity of the heat exchanger, the parameter for the steady state was determined by extrapolating the obtained calculation results. The obtained values of the coefficient fit within the range from 0.406 to 1.09 Wm^-1°C^-1.