United States Gypsum Company

Usg Corporation

Michael L Cloud

Weixin David Song

Kirk S Moore

Daniel J Milligan

George E Rowland

Qiang Yu

John W Wilson

Qingxia Liu

Dennis Mark Lettkeman

Raymond A Kaligian

Michael R Lynn

W David Song

Qiangxia Liu

Raymond A Ii Kaligian

A method for preparing a modified beta-stucco from calcined natural rock gypsum that includes preparing a solution of liquid diethylene-triamine-pentaacetic acid in water, applying the solution onto beta-stucco while hot from the calciner, forming a wetted beta-stucco, and allowing the wetted stucco to dry and heal, forming the modified beta-stucco.

Method of modifying beta stucco using diethylene-triamine-pentaacetic acid

A process is disclosed for making a blend of alpha- and beta-stucco including a slurry calcination step to produce alpha calcium sulfate hemihydrate followed by a fluidized bed calcination step to produce beta calcium sulfate hemihydrate. The process starts with 50-75% gypsum-containing solids slurry, and then steam calcines the slurry in a first reactor to form partially calcined gypsum slurry which contains calcium sulfate dihydrate and alpha calcium sulfate hemihydrate. The partially calcined slurry is then dewatered. Then the filter cake is fed into a kettle to complete the calcination process by converting the calcium sulfate dihydrate of the filter cake material into beta calcium sulfate hemihydrate.

Process for manufacturing ultra low consistency alpha- and beta- blend stucco

A method and system for calcining gypsum to recover gypsum in a form consisting essentially of calcium sulfate anhydrite is disclosed. The method includes the steps of feeding the ground gypsum material into a first kettle and heating the ground gypsum in the first kettle to the first predetermined temperature. The first predetermined temperature is preferably below 400.degree. F. so that the gypsum will still contain a sufficient amount of chemically-combined water so that it will self-fluidize by release of water vapor so that it will flow through the apparatus. The ground gypsum is then overflowed through at least one subsequent stage and heated to a final predetermined temperature to produce an anhydrite product. To produce insoluble calcium anhydrite or dead burn material, the final predetermined temperature is greater than 900.degree. F. and preferably within the range of about 900.degree. F.-1300.degree. F. In the subsequent stages, the gypsum powder is heated and simultaneously fluidized with a fluidizing media, preferably air, so that the ground gypsum will flow through the apparatus. In the preferred embodiment, the ground gypsum is fluidized by a plurality of mixing blades having air injection pipes along their breaking edges for injecting air into the gypsum and a plurality of air injection nozzles disposed radially about a periphery of the kettles. The fluidization of the ground gypsum in the subsequent stages ensures that it will flow through the apparatus for production of an anhydrite product.

Method for multi-stage calcining of gypsum to produce an anhydrite

A method and apparatus is disclosed for the continuous calcining of gypsum material in a high-efficiency, refractoryless kettle preferably heated by a multiple series of separate immersion tube burner coils, each coil operating within a specific calcining zone inside the kettle. The lowest, i.e., initial, burner tube coil is formed with a low profile to permit use of a small initial gypsum charge, and hence, a quick kettle start-up cycle. That low profile initial burner design also helps keep the agitator motor's load at a minimum during cycle start-up. Due to the immersion tube burner coil construction, no refractory structure for the kettle is required. Also, no separate hot pit structure is required, as the kettle is used to merely hold the material being calcined and no residual heat is present. A relatively thin kettle can be constructed, as it need only withstand relatively low operating temperatures. The kettle's staged, interiorly-disposed burner tube coils act to directly transfer burner tube heat to the kettle's contents, and the coils exhaust exteriorly of the kettle. The present calcining method and apparatus permits substantially improved tonnage output of calcined material, for a kettle of a given size. A modification to the present apparatus includes structure for recovering and recycling a portion of the spent burner gases, and also separate structure for forced aeration air, both preferably for introduction through the kettle bottom. One alternate embodiment concerns a differently-shaped kettle design. Another alternate embodiment concerns a modified kettle which uses a single immersion burner tube coil to provide the total heating of the kettle's contents, for use in certain calcining applications.

Apparatus for continuous refractoryless calcining of gypsum

Method and system for multi-stage calcining of gypsum to produce an

Method for continuous refractoryless calcining of gypsum

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Canton, OK, United States of America

Michael L Cloud