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    Common gypum calcination methods and equipment

    From : clirik ?? Date : 2019-02-21 10:23

    1. Indirect heating method

    a. Continuous wok

    It is a straight circular pot with a cross-fire tube. The heat is transferred from the outer wall of the pot, the bottom of the pot and the fire tube to the dihydrate gypsum in the pot, and the water vapor and circulating hot gas generated by mechanical stirring and gypsum dehydration Stirring, and presenting a fluidized state, in which case the dihydrate gypsum is dehydrated to form a hemihydrate gypsum, which is continuously discharged by means of the overflow principle.
    The temperature of the material in the pot is about 150 °C, and the calcination time of the material is 1 to 1.5 hours. It belongs to the low temperature slow calcination method. Continuous wok calcined gypsum is a mature technology at home and abroad, stable production, easy operation, and balanced product quality. It is suitable for calcining powdered gypsum. If it is used for industrial production of gypsum, a set of airflow drying device is needed to remove more than 10% of free water. The wok can be used in solid, liquid or gaseous fuels. The heat consumption of coal-fired continuous frying pan is about 270,000-300,000 baht/ton of hemi-hydrated gypsum. If it is calcined with about 10% of industrially-produced gypsum, its energy consumption is between 36 and 370,000 baht/ton of hemihydrate gypsum.

    b. Internal heating tube rotary kiln

    There are many inner tubes in the rotary kiln. The tubes are heated by steam or heat transfer oil. The materials receive heat in the kiln. The materials stay in the kiln for a long time. They are low-temperature calcined and the product quality is balanced and stable. Some companies in Japan use this method to calcine natural and industrial by-product gypsum. China's Shandong Xinwen Mining Bureau has introduced a set of steam calcining equipment from Germany, which is suitable for places with stable steam source. According to Japanese data, calcining 1 ton of dihydrate gypsum consumes 0.94 tons of steam. After conversion, the heat consumption per ton of building gypsum is about 560,000 kcal, and the energy consumption is high.

    c. Boiling furnace

    The vertical straight-shaped container is provided with a gas distribution plate at the bottom, and the airflow is uniformly entered into the bed from the bottom during operation. The bed is provided with a large number of heating pipes, and the medium in the pipe is saturated steam or heat-conducting oil, and the gypsum particles enter the furnace. The heat is in a fluid state, and heat is transferred to the fluidized gypsum powder through the pipe wall to cause boiling and dehydration. This calcination process was developed and manufactured in the 1980s for the production of gypsum board. The equipment adopts low-temperature calcination, and the gypsum is not easy to be over-fired. As long as the flow is stable, the discharge temperature is controlled appropriately, and most of the finished products are hemihydrate gypsum. In recent years, there have been many applications in Shandong, and the products are mostly supplied with gypsum board production lines and other products. The boiling furnace equipment is small, the production capacity is large, the structure is simple, the equipment is compact, the land occupation is small, and the energy consumption is low. For example, the output of 12t / hr boiling furnace, heat consumption is about 220,000 kcal / ton of finished products, its own thermal efficiency is above 95%, thermal efficiency of 57 ~ 67% when using steam, heat transfer oil 67 ~ 76%, the furnace is easy to operate, infrastructure investment Province, operating costs are low, such as 10t / hr a set of boiling furnace investment of about 180 to 2 million yuan, 20t / hr a set of boiling furnace investment of about 3 million yuan. At present, the domestic boiling furnace is mainly used for calcining natural gypsum. Because there is no mandatory stirring device in the furnace, the limited airflow cannot blow the agglomerated wet material, and the free water in the material should not be too high, generally controlled within 5%. For industrially-produced gypsum with about 10% calcined free water, a set of airflow drying device is needed, which increases equipment investment and increases heat consumption, but the total heat consumption is estimated to be 28-290,000 kcal/ton finished product. Within, it is still low.

    2. Direct heating method - or gas flow calcination

    The gas stream is calcined, that is, the hot gas is directly contacted with the powder, and the dihydrate gypsum is rapidly dehydrated to form the hemihydrate gypsum. This method has reasonable heat utilization, compact equipment, simple use and high efficiency, and is suitable for natural gypsum and industrial by-product gypsum. Both Salzgitter and BMH in the United States have this equipment. The former is called Shahki Polishing and the latter is called Delta Grinding. Commonly known as "airflow calcination mill", this "grinding" uses a high-speed rotating hammer to throw the material up and crush, crush, and meet the airflow to complete the drying and calcination process. The mounting method of the hammer body in the above two devices, the number of the hammer head, the direction in which the classifier is placed, and the like are different, but the working principle is the same.

    a. Salzgitter polished

    In Germany, the United States, Norway, the Netherlands, India, South Korea and other countries have established production lines of different scales, from 2t / hr ~ 30t / hr of different scales of the series of products, gas, liquid (oil) can be used as fuel, from the data Introduction, when calcining 95% natural gypsum, the heat consumption per ton of product is: 240,000 kcal / ton, power consumption: 30KWh / ton. For the in situ digestion of the desulfurization gypsum discharged from the flue gas desulfurization unit of the enterprise,Beijing Guohua Jiedi Company introduced a set of 6t/hr calcination desulfurization gypsum equipment from the German SARSK company.The equipment consists of a main unit such as a calciner with two high-speed rotating rotors, a cyclone separator and forced aging.
    It has been running for 2 to 3 years, and the fuel is heavy oil. It has not yet reached the design capability at the beginning of production, and the product can satisfy the same
    This is the demand for the introduction of German block production lines. The calcining device has a small outer shape, low noise and simple structure
    Compact and balanced product quality. After the mill is fully digested and absorbed, it should have a good development prospect in China.

    b. Delta mill

    The mill is an impact mill with two chambers in the horizontal direction, one hammer grinding rotor chamber and one grader chamber. The material enters the hammer grinding chamber first, and the high-speed rotating hammer breaks up the material and “smashes” the material. At the same time, it merges with the hot air flow to dry and calcine. The hot flue gas brings the ground material into the classifier in the system. The rotating blades return the larger particles to the hammer grinding chamber to continue grinding, and the qualified fine materials are collected into the silo through the high temperature dust collector. According to the data, the heat consumption of grinding 80% natural gypsum and 3% of free water is 22.0 kcal/ton of finished product. If it is used for desulfurization gypsum (more than 90%) of 10% free water, the heat consumption is about It is 28~300,000 kcal/ton finished product. According to BMH, this mill has a reasonable design, high efficiency, and low equipment operation rate. The fineness of the product can be adjusted, the equipment has less compact footprint, high thermal efficiency, low energy consumption, and uniform calcined building gypsum, especially suitable for calcination.
    Industrial by-product gypsum.

    c. Stead dynamic calciner

    It is a self-developed gas flow calcination device. The shape is a vertical cylinder, and the vertical shaft with the disperser at the bottom is connected with the motor to generate a rotary motion, the middle and lower parts of one side are fed, the lower part of the other side is filled with hot air, and the top is discharged to the trap for gas-solidification. After separation, the machine is transported to the storage bin. The basic principle is that the material and the hot gas are rapidly mixed, and a rotary motion is generated in the axial direction of the furnace body, so that the material and the heat carrier rapidly exchange heat to achieve the purpose of dehydration of the dihydrate gypsum, and this method can also be called a cyclonic calcination. It is characterized by continuous operation and fast heat exchange, which takes only a few seconds from feeding to discharging. This technology is a gypsum calcination method developed by Northeastern University on the basis of various drying and calcining equipment. A small industrialized experimental device has been established, and the desulfurization gypsum and phosphogypsum have been calcined and certain technical parameters have been obtained. Based on the experimental research, two kinds of technological routes have been designed: one is “one-step method” and will be dried and The calcination is combined in one step and completed in the same equipment; the other is a two-step method in which drying and calcination are carried out in two devices, and the effect requires a large amount of engineering to verify.

    d. Peter Mill

    It is also a kind of rapid calcination equipment for airflow. It is a calcining equipment integrating grinding-drying-calcining. It is developed by CLAUDISPETERS of Germany and is called Peters Mill. It is a kind of annular ball mill. The bottom of the mill is the main transmission device, which drives the lower grinding disc to rotate. The grinding disc has a plurality of hollow garden balls with a diameter of φ 600-800mm. Above the ball is a non-rotating upper grinding disc. Gypsum is fed from the upper side feed pipe to the center of the grinding body (feed size up to 60 mm.) Under the action of centrifugal force, the material is pushed outwards and pushed to the ground between the lower part of the ball and the grinding ring. Grinding. At the same time, the hot gas of 500-600 °C is introduced into the mill from the lower side of the grinding body, so that the gypsum is directly contacted with the hot air flow to rapidly dehydrate the building gypsum. This mill can calcine natural gypsum or gypsum mixed with natural gypsum and industrially-produced gypsum. Its characteristics are: small equipment, high production efficiency, low energy consumption, stable product quality, suitable for large-scale continuous production of gypsum products production line. It is one of the mature gypsum calcining equipments. There are 16-52t/hr series products in foreign countries. According to the data, nearly 90 units in the world are currently in operation. Domestic BNBM companies have introduced two 30t/hr and one 40t/hr. The mill is used in a gypsum board production line. When calcining natural gypsum, the energy consumption is between 24 and 270,000 calories per ton of product.

    3. Direct heating rotary kiln

    The heat medium is directly contacted with the gypsum material to dehydrate it into hemihydrate gypsum or anhydrite. The gypsum rotates in a small angle 2% inclination cylinder, the heat medium moves in the same direction or in the opposite direction, and the gypsum dehydration is completed during the movement. The continuous feeding and discharging are continuous operations, because the direct fire is more than the external combustion. The kiln has high heat efficiency, and the fuel can be used for gas, oil and coal. In recent years, there are rotary kiln production of different scales in Hebei, Shandong and other places. There are several production lines with 4~5 tons/hour and 14 tons/hour, and nearly 30 tons of large internal combustion rotary kiln. Coming soon. The direct-heating rotary kiln that has been produced is calcined natural gypsum. The fuel is coal. The calcining energy consumption is about 22~230,000 / / ton of finished product, and the product quality is better in downstream. It is feasible to calcine natural gypsum in a direct heating rotary kiln. If the calcining industry pays gypsum, it does not need to be dried before calcination, but the kiln should have a certain length of drying belt, and the dehumidification and dust collection should be designed. A production line using phosphogypsum as a raw material recently built in Henan has been commissioned, and industrial tests for calcination of desulfurized gypsum are also underway. It is estimated that the calorific value of calcined desulfurized gypsum should be less than 300,000 calories per ton of finished product. The rotary kiln equipment structure is relatively simple, and there are many mature equipments and manufacturing plants in China, and the equipment cost is lower than that of the wok. Has a price advantage.

    4. Fluidized bed calciner

    The furnace is a product of the Australian RBS Rapid Building Systems Co., Ltd. in the 1990s, called the "RFC Fluidized Bed Roaster". The fluidized bed type calciner has a vertical cylindrical shape, and the lower part of the middle side feeds the hot air on the other side, the lower part of the furnace body is called a bed, and the bottom of the bed is provided with a gas flow distributor, so that the hot gas flow can reach different speed gradients as required. The gypsum powder is blown up to be in suspension, and heat exchange is performed at the same time (the maximum feed size of the calciner is ≤10 mm) to dehydrate the dihydrate gypsum into hemihydrate gypsum. The bed temperature and gas pressure are strictly controlled, and the temperature gradient of the material layer is small, so that the dihydrate gypsum in the bed is maximally changed into hemihydrate gypsum, which ensures the quality of the product.
    According to the Australian side, this furnace can be used to calcine natural gypsum and industrially-produced gypsum. It can be processed with a wide range of raw materials and particle sizes with any fuel and heat energy. It has self-cleaning function, strict calcination temperature control and stable product performance. The furnace is low-temperature slow calcination, the material temperature is 130-150 ° C, and it stays in the furnace for 40-50 minutes or even 1 hour. The phase composition of the calcined product is mostly hemihydrate gypsum, only a very small amount of anhydrite III and dihydrate. Gypsum, no anhydrite II. The calcination energy consumption for desulfurized gypsum is: for purity greater than 90%, the energy consumption is 1467GJ/ton of finished product (~350,000 Leica/ton) when the free water is 10%, the electricity consumption is 30 KWh/ton.
    gypsum calcination equipment

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