Goaf cavity filling - a special application of paste backfilling in coal mining

Deutsche Montan Technologie (DMT) has developed a new technique which makes possible to utilise residual material from processing and combustion of coal, from incineration of domestic refuse and sewage sludge as stowing material in underground coal mines. In a mixing and pumping station on the surface up to 200 m(3)/h high concentrated suspensions are produced from the above mentioned materials according to specific criteria to match both a desired high solids content and a low pressure loss. The pastelike slurry is pumped through pipes to the coal faces using powerful double piston pumps. The additional hydrostatic pressure makes possible to bridge piping distances up to 12 km. To supply the suspension to the excavated space so-called trailing pipes are used, Due to the extreme variations of the solids properties the mixing and pumping process is viscosity controlled to prevent piping interruptions based on blockages. This technique is successfully applicated since several years on Walsum Colliery (Deutsche Steinkohle GmbH).