The calcination process of raw gypsum is divided into dry process and wet process. Dry calcination is the heating and dehydration of raw gypsum under normal pressure (or low partial pressure of water vapor), and β-type hemihydrate gypsum, type II anhydrite or burnt gypsum are formed depending on the temperature. This product is a plaster, cast gypsum or pre-product gypsum commonly used in construction. The wet calcination is to heat the raw gypsum under the pressure of water vapor in the autoclave or in a salt solution having a boiling point higher than 100 ° C at a low pressure, and the product is α-type hemihydrate gypsum, which can be used as a special gypsum base material for pouring. .
(II) Process Flow The production process of β-type plaster is generally: ore storage → crushing → homogenization → calcination dehydration → aging → grinding and mixing → packaging, first calcined with a wok and then calcined.
The raw gypsum dry calcination process is as follows: raw gypsum is transported and selected from the quarry to ensure continuous feeding and stable quality. The feedstock is subjected to a section of crushing ( chopper crusher ) to below 8 cm, and then to a second stage of crushing ( hammer crusher ) to less than 2 cm, and then calcined into a calcining kiln through a bucket elevator. By controlling the temperature of the kiln, β-type hemihydrate gypsum, anhydrite gypsum and burnt gypsum can be separately produced.
The α-type wet calcination process and process are generally: gypsum raw material warehouse → sieving machine → autoclave autoclaving and drying → broken pulverization → homogenization storage → α and β gypsum mixing → packaging and handling. The process for producing α-type hemihydrate gypsum by hydrothermal method is:
Gypsum ore → crushing → milling → reaction kettle (adding water and chemicals) → cleaning → dehydration drying → packaging.
(III) Commonly used technical equipment Commonly used equipment for gypsum crushing include jaw crusher , cone crusher , impact crusher, roller crusher and hammer crusher.
Dry calcination is commonly used in both direct calcination and indirect calcination. Direct calcination equipment such as rotary kiln, grinding and calcining integrated device (Peter mill, high temperature wind sweep, etc.). Indirect calcination equipment such as rotary calciner, wok (direct calcination of earth wok), horizontal calciner, vertical calciner, and the like.
The wet calcination equipment includes a horizontal type, a vertical autoclave, a vulcanization tank, and the like.
(IV) Dressing and processing practice The process of dry gypsum dry gypsum in the Gineng Gypsum Mine Gypsum Products Factory in Jingmen City, Hubei Province is shown in the figure below. Raw gypsum is transported and selected from the mining site to ensure continuous feeding and stable quality. The feedstock is subjected to a section of crushing (chopper crusher) to below 8 cm, and then to a second stage of crushing (hammer crusher) to less than 2 cm, and then calcined into a calcining kiln through a bucket elevator. The rotary kiln adopts a downstream type, and by controlling the temperature of the kiln, β-type hemihydrate gypsum (180-240 ° C), anhydrite gypsum (350 ° C) and burnt gypsum (450-700 ° C) can be separately produced. After the calcined calcined gypsum is homogenized, it is ground to 200-325 mesh by a pendulum mill, and the pendulum mill is a 4R-3216 produced by Guilin Mining Machinery Factory.
(5) Main types and applications of deep-processed products 1. Raw gypsum powder
Used in cement production as cement retarder, special cement raw material; used in chemical industry for sulfuric acid, ammonium sulfate, etc.; used in agriculture to improve soil or soil fertilizer; paint, pigment, paper, textile and other industries Used as a coating and filler and as a filler for industrial products such as toothpaste, cream and chalk, and as a carrier for pesticides; used in the food industry to purify water in breweries, to control the clarity of wine, or to coagulate edible tofu Agents and animal feed additives. Finely ground gypsum powder can be used to clarify turbid sewage, oil refining, polishing glass and some precious metals, and other decorations. Naturally pure anhydrite powder can also be used as a flux in the glass industry in place of sodium sulfate. Raw gypsum is also known as condensate stone, (Taiyin) mysterious stone, salt root, etc. in ancient Chinese books. It has been used as a traditional Chinese medicine stone since ancient times. It has the effects of slowing the spleen and replenishing qi, quenching thirst and removing fire, and relieving hunger and sweat.
2. Plaster powder used in the construction industry as a stucco material for building walls, plastering materials and prefabricated parts for making gypsum. It can be made into gypsum board, building partition wall, ceiling and other various plasters of various specifications. Preforms, etc.; used in the ceramic industry to make various ceramic molds; used in the foundry industry for the manufacture of molds; medically used in the manufacture of dental molds or surgical fixations. In the arts and crafts can be used as an art statue.
3. Gypsum products gypsum board has been an important wall material at home and abroad, including gypsum board, decorative gypsum board, fiber gypsum board, gypsum composite board, gypsum slag board, gypsum particle board, etc. Gypsum block is also used as wall material. In the rise, gypsum products have been widely used as building materials worldwide. Because of its non-toxicity and many other advantages, it is known as green building materials and has broad prospects.
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