A method of conditioning stucco comprises the steps of supplying a quantity of stucco particles to a reaction vessel, the stucco particles comprising calcium sulphate hemihydrate and/or calcium sulphate anhydrite, as well as calcium sulphate dihydrate; and conditioning the stucco particles at a temperature of at least 100°C and a humidity of at least 70%. During the step of conditioning the stucco particles, the bulk density of the stucco particles within the reaction vessel is at least 1 g/cm³.

The instant invention is concerned with the post-treatment of β-hemihydrate plasters for the purpose of stabilization. The invention relies in the addition of a retardant to the calcined β-hemihydrate. It is also the purpose of the invention to provide stabilized β-hemihydrate plasters which exhibit advantageous properties.

Disclosed is a process for the continuous modification of dihydrate gypsum. The process includes a hemihydration step of calcining the dihydrate gypsum as a raw material into hemihydrate gypsum and a recrystallization step of hydrating and recrystallizing the hemihydrate gypsum in an aqueous slurry to convert the hemihydrate gypsum into modified dihydrate gypsum of a crystalline form different from the dihydrate gypsum as the raw material. In the recrystallization step, the aqueous slurry in a recrystallization reaction tank is maintained at a constant temperature under stirring such that the aqueous slurry becomes uniform, and a feed rate of the hemihydrate gypsum to the recrystallization reaction tank and a discharge rate of the recrystallized and modified dihydrate gypsum from the recrystallization reaction tank are controlled such that the feed rate and the discharge rate become substantially equal to each other, whereby the feeding of the hemihydrate gypsum and the discharging of the recrystallized and modified dihydrate gypsum are conducted continuously or intermittently. According to the process, dihydrate gypsum as a starting raw materialcan beconvertedintohigh-purity,modified dihydrate gypsum of large crystals by recrystallizing the starting dihydrate gypsum after it is once calcined into hemihydrate gypsum although such modified dihydrate gypsum is not available in general.

Die Erfindung betrifft ein Verfahren zum Kalzinieren von pulverförmigem oder feinkörnigem Gut umfassend zwei Schritte, ein Kalzinieren des Guts in einer Kalziniermühle (3) und ein Nachkalzinieren des heißen Guts in einem Reaktionsbehälter (6). Erfindungsgemäß ist vorgesehen, dass dem Reaktionsbehälter (6) als ausschließliche Wärmequelle neben dem heißen Gut Systemabgas (4) der Kalzinieranlage, insbesondere der Kalziniermühle (3), als Reaktionsgas zugeführt wird. Die Erfindung erreicht ohne zusätzlichen Energieaufwand eine Vervollständigung der Kalzinierung, wobei zusätzlich unerwünschte Anhydritanteile verringert werden. Die Produktqualität steigt dadurch. Die Temperatur in der vorgelagerten Kalziniermühle (3) kann so gesenkt werden, was eine zusätzliche Energieeinsparung ermöglicht. Die Erfindung kann auch angewendet werden zur Beschleunigung der Alterung des kalzinierten Guts.

The invention provides a process for stabilizing plaster and an apparatus for implementing the moistening part of the process. The process comprises the following steps: a) providing a heated HH-plaster preferably at temperatures over 100°C; b) feeding the hot plaster in a moistening device having walls heated to at least 100°C; c) injecting water and/or steam into the moistening device in conditions that such not yet moistened surfaces of the plaster are exposed to the injected water and/or steam; d) maintaining an atmosphere in the moistening device at a level of the dew point in the range of 75 to 99°C; e) feeding the moistened blend into a curing device; f) maintaining an atmosphere in the curing device above 75°C for at least 3 minutes; g) feeding the moistened and cured blend into a drying device; and h) drying said moistened and cured blend.

The invention also provides an apparatus for moistening β-hemihydrate plaster comprising a rotating drum with lifting blades inside where all walls in contact with the product are externally heated at a temperature above 100°C.

The invention finally provides specific uses for plasters obtainable by the process of the invention.