At the Rottleberode plant, for example, Knauf returns the edge breaks which occur during the production of gypsum fibreboard to the material flow in the same way as the dust during surface grinding. “Every crumb of gypsum is important for us. This is why raw materials should no longer be disposed of during production,” emphasises plant manager André Materlik. His company is the only one within the Knauf Group which exclusively processes natural gypsum from the quarries in the southern Harz region. In view of the move away from lignite mining, industry experts argue that only those companies which develop and secure mining areas in the long term will continue to exist – and demand for gypsum in Germany alone is already high at around ten million tonnes per year. According to Materlik, around 450,000 tons of finished product leaves the Rottleberode plant every year, with around 100 truckloads a day.

Stucco plaster, fine cellulose from waste paper and water: this is the mixture from which gypsum fibreboards are made. ISS Schüttguttechnik GmbH from Wilnsdorf in the Siegerland region plans and builds blow moulding machines to supply the mixers. ISS had already done a good job at Knauf before the new fibreboard plant was built, and had successfully got to grips with the problems involved in conveying and metering pulverised lignite. The fuel develops the necessary heat for calcining the rough stones. In the process, the natural gypsum loses a large part of its crystallised water content. “For uniform thermal processes, the constant transport of lignite without pressure or volume fluctuations is essential,” explains the plant manager. Any deviation from the ideal line is noticeable and can affect the product quality of the stucco, the deposits in the calcining mill, the CO values in the exhaust gas flow or the energy consumption of the screw compressors. “Uniform processes require less air,” says ISS Sales Managing Director Robert Partzsch, who speaks from experience.