GEBR. PFEIFFER SE

Grinding and calcining of gypsum with Pfeiffer grinding plants

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1 Two different modifications of the hemihydrate CaSO₄ x ½ H₂O are produced

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2 Pfeiffer vertical roller mill of the type MPS-GC

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3 Schematic diagram of the process

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4 The kettle with its hot gas pipes

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5 Schematic diagram of the kettle – the introduced heat is very uniformly distributed

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Tab 1 The specific thermal energy requirement is about 20 % higher than when the gypsum is calcined directly in the gypsum calcining mill

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6 The crystal water content is reduced by a rising exhaust gas temperature

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Gypsum powder

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For the production of plaster products natural gypsum, synthetic gypsum or a mixture of both are calcined. Depending on the production process two different modifications of the hemihydrate CaSO₄ x ½ H₂O are obtained.

When gypsum is calcined in an atmosphere saturated with water vapour at an overpressure of several bars, a-hemihydrate is formed (Fig. 1). The outstanding feature of this plaster is a relatively regular crystal form. It is created due to the fact that the crystal water is able to escape from the intermediate lattice structure of the CaSO₄slowly and uniformly as escaping is greatly hampered by the counter-pressure built up by the water vapour.

Due to the relatively regular crystal structure and the large individual crystals of the a-hemihydrate, there are few contact surfaces for...