Geothermal energy from mining waste
Mining dumps are a well known appearance in the landscape of coal-mining areas. The fact, that smouldering fires are a common phenomenon in mining dumps, is nearly unknown in public. The smouldering originates through the oxidation of residual coal. High temperatures within the mining dumps, that exist as a consequence of the smouldering fires, have a high potential for energetic usage, which has not received much attention yet. In co-operation with the Chair of Geotechnical Engineering at the RWTH Aachen University, the Fraunhofer Research Institute UMSICHT and the companies DMT and aix-o-therm, the possibilities of an energetic usage of smouldering fires are explored in a joint project funded by BMBF at a mining dump site in the western Ruhr-Area.
In one of the hot areas at the edge of the mining dump plateau three coaxial geothermal probes with a length of 25 m have been installed. In order to acquire some data of the temperature profile in the close surrounding of the probes, five measuring gauges were arranged in a semi-circle around the geothermal probes. For extracting material samples five test pits with a maximum depth of 9 m were applied as well. By investigating the thermal as well as the soil-mechanical properties of the samples, the material has been characterized in the laboratory. The results provide a basis for numerical analysis of the stability of the mining dump and for analysis of fire spreading within the mining dump.