In the Ruhr district of Germany, DSK Deutsche Steinkohle AG wins coal from depths of more than 1 000 m. During mining, besides the pure coal itself, a lower energy by-product is won, which is referred to as “dead rock”. The “dead rock” is separated from the more valuable coal in several crushing, screening and washing processes. After screening, the coarser material is stockpiled as deads. The finest fraction is processed by means of flotation and then dewatered in filter presses (»1). The filter cake produced is termed press or flotation tailings and is essentially composed of clay and coal. These filter cakes that are interesting for ceramics are loaded just-in-time after every pressing cycle (»2).
The companies Hubert Gerharz GmbH, owned by Jürgen Simon, and Arno Witgert, owned by Dipl.-Ing. (FH) Michael Liebig e.K., have concluded an agreement with the DSK sales subsidiary, RAG Ruhrkohle AG Verkauf, for the general distribution of these coal filter cakes in the ceramics industry. Together they perform the quality control of this raw material. Order processing and customer-specific body optimization have been divided up internally between the two companies depending on the different applications. At Gerharz, the coal filter cake is processed under the name “KFK” and at Witgert the material is known as “4024”.
Hubert Gerharz GmbH has been supplying special additive clays to the backing bricks industry for many years. In cooperation with various brickworks, the ceramic and energy properties of the “KFK” were tested in field tests and the potential applications coordinated with the bodies and production plants. “KFK” has enormous potential, not only with regard to energy savings, and is currently in regular use in more than 10 brickworks for backing bricks. Transport distances of more than 800 km still prove profitable on account of the energy saving in the plants.
The main features of this outstanding raw material are:
› ample and long-term availability
› low raw material costs
› good plastic behaviour, as it contains 60% clay minerals (kaolinitic-illitic)
› good drying behaviour as it is almost free of swelling clay minerals and a low content of ultrafines, approx. 43% < 2 µm
› supplied in an easy-to-process form as the filter cakes contain only limited coarse grain; processing without wear of the processing plants, extremely homogeneous
› approx. 30% finely dispersed coal, increase in micropores and reduction of the thermal conductivity of the body, low apparent density (1.1 g/cm3 )
› around 30% carbon content in the form of coal, which burns at much higher temperatures than the lignite contained in conventional coal clays. The energy released in the tunnel kiln can be used positively, which proved difficult with early combustion of the lignite
Dipl. Ing. (FH) Michael Liebig (Witgert) and Jürgen Simon (Hubert Gerharz GmbH)
