Classification of raw materials:
Natural gypsum and industrial gypsum CaSo4.2H2O and CaSO4
According to the usage method, it can be divided into two categories:
1. It is used directly without calcination and is mainly used in the cement industry to adjust the setting time of cement.
2. Calcined plaster (CaSO4.0.5H2O), mainly used in building materials and ceramic molds and medical applications
Industrial by-product gypsum, commonly known as chemical gypsum, is mainly divided into phosphogypsum, desulfurization gypsum, fluorogypsum, and lemon gypsum.
Currently the most widely used is desulfurized gypsum.
Desulfurization gypsum formation process: The flue gas treated by the precipitator is introduced into the absorber, and the fine lime or limestone powder is sprayed to form the slurry, and the flue gas is washed in the absorber by spraying. It reacts with sulfur dioxide in the flue gas to form calcium sulfite, and then forcibly oxidizes calcium sulfite to calcium sulfate dihydrate by a large amount of air.
Temperature Required For Gypsum Calcination Dehydration
Calcination is divided into two modes:
1. a powder formed in saturated steam or water medium, commonly known as high-strength gypsum powder.
2. Produced under the condition of dry air, called ß powder, commonly known as ordinary cooked gypsum powder.
Calcination temperature: ordinary gypsum powder calcination temperature 125~180 °C. Anhydrite is produced above 180 °C.
The construction gypsum made of natural gypsum must pass through the process of crushing→homogenization→milling→calcining.
The production process has changed due to the different calcination processes.
Grinding and then calcination method is the most common
Calcination and then grinding is not commonly used after calcination
Calcination equipment: wok, rotary kiln, boiling furnace.
The wok is divided into batch type, continuous type and embedded type; the rotary kiln is divided into internal combustion type, external combustion type, external combustion plus internal fire tube type and sleeve type; the boiling furnace is generally vertical.
Features; early use of wok, high energy consumption, poor product quality stability; rotary kiln equipment is simple, investment is small, energy consumption is high, product quality is basically stable.
Boiling furnace features: It is a kind of high-efficiency, special equipment for calcining gypsum powder by using fluidization technology. Its heating medium is steam or heat transfer oil, which is the original technology of our country. It has obtained national patents and is currently the most widely used in China.
The boiling calcining furnace adopts the solid fluidization technology to make the material layer form a state like boiling water boiling, and the image is called a boiling furnace.
Composition: consists of furnace body, air chamber, air distribution plate, heating pipe, continuous feeder (screw conveyor), overflow port, electrostatic precipitator, blower, induced draft fan, main chamber and auxiliary room.
30,000 tons per annual
As for 80-325 mesh and D90 passing rate powder, you could choose MTW Series Euro-type trapezium mill of Shanghai Zenith Mineral Company. The MTW grinding mill is mainly applied to the material processing of metallurgy, building materials, chemical industry, mining and other industries. It can grind limestone, calcite,marble, dolomite，quartz with Moh’s hardness below 9 and humidity lower than 6%.
1. The vibrating feeder continuously and quantitatively feed materials into the main grinding chamber for grinding with the ground powder taken away by blower,after being separated by the classifier, the powder reaches the fineness requirement will be collected in the cyclone powder collector together with the airflow and then discharged from the powder discharge value as finished powder products, Subsequently the air flow again enters the blower from the return duct on the top of the cyclone powder collector,thus, a closed air circulation system is formed, with the air circulating under the condition of negative pressure.
2. The main mill works as follows: The bevel gear drives the central shaft to rotate, the shaft top is connected with a grinding roller hanger, on which a grinding roller devices is mounted to form a swinging pivot. The grinding roller device rotates around not only the central shaft but also along the grinding ring, with the grinding roller rotating itself under the action of the friction. The grinding roller hanger has a shovel blade installed at the bottom of roller, the shovel blade and the grinding roller throw up and feed the materials between the grinding rollers and ring during mutual rotation to form a bedding layer, which will produce an outward centrifugal force by the rotation of the grinding roller to crush the materials and thus achieve the goal of powder manufacturing
3. The classifier can classify the powder by adjusting the classifier impeller rotation speed, which can be adjusted according to the requirements for the particle size of finished powder.
Compared with the traditional mill, the MTW series European version of the trapezium mill has a larger feeder, higher output capacity, lighter total weight, finer finishing size and the best choice for processing coarse powder.