Crystallizer

1. Definition: a crystallizer is a trough shaped container with a jacket on the wall or a snake tube in the mold to heat or cool the solution in the tank. The crystallization tank can be used as evaporation crystallizer or cooling crystallizer. In order to improve the intensity of crystal production, a stirrer can be added in the tank. The crystallization tank can be used for continuous operation or intermittent operation. The crystal obtained by intermittent operation is large, but the crystal is easy to be connected into crystal clusters and entrain mother liquor, which affects the purity of the product. The crystallizer has simple structure and low production intensity, and is suitable for the production of small batch products (such as chemical reagents and biochemical reagents).
2. Forced circulation
The utility model relates to a continuous crystallizer with crystal slurry circulation. During operation, the feed liquid is added from the lower part of the circulating pipe, mixed with the crystal slurry leaving the bottom of the crystallization chamber, and then pumped to the heating chamber. The crystal slurry is heated in the heating chamber (usually 2 ~ 6 ℃), but does not evaporate. After the hot crystal slurry enters the crystallization chamber, it boils to make the solution reach the supersaturated state, so part of the solute is deposited on the surface of the suspended grain to make the crystal grow up. The crystal slurry as a product is discharged from the upper part of the circulating pipe. Forced circulation evaporation crystallizer has large production capacity, but the particle size distribution of the product is wide.
3. DTB type
That is, the draft tube baffle evaporation crystallizer is also a crystal slurry circulating crystallizer (see the color picture). An elutriation column is connected to the lower part of the device, and a guide cylinder and a cylindrical baffle are set in the device. During operation, the hot saturated material liquid is continuously added to the lower part of the circulating pipe, mixed with the mother liquid with small crystals in the circulating pipe, and then pumped to the heater. The heated solution flows into the crystallizer near the bottom of the draft tube and is sent to the liquid level along the draft tube by a slowly rotating propeller. The solution is evaporated and cooled on the liquid surface to reach a supersaturated state, in which some solutes are deposited on the surface of suspended particles to make the crystal grow. There is also a settlement area around the annular baffle. In the settling area, large particles settle, while small particles enter the circulating pipe with the mother liquid and dissolve under heat. The crystal enters the elutriation column at the bottom of the crystallizer. In order to make the particle size of crystalline products as uniform as possible, part of the mother liquor from the settlement area is added to the bottom of the elutriation column, and the small particles return to the crystallizer with the liquid flow by using the function of hydraulic classification, and the crystalline products are discharged from the lower part of the elutriation column.
4. Oslo type
Also known as Kristal crystallizer, it is a mother liquor circulating continuous crystallizer (Fig. 3). The operating feed liquid is added to the circulating pipe, mixed with the circulating mother liquid in the pipe, and pumped to the heating chamber. The heated solution evaporates in the evaporation chamber and reaches supersaturation, and enters the crystal fluidized bed below the evaporation chamber through the central tube (see fluidization). In the crystal fluidized bed, the supersaturated solute in the solution is deposited on the surface of suspended particles to make the crystal grow up. The crystal fluidized bed hydraulically classifies the particles. The large particles are at the bottom and the small particles are at the top. The crystalline products with uniform particle size are discharged from the bottom of the fluidized bed. The fine particles in the fluidized bed flow into the circulating pipe with the mother liquid and dissolve the small crystals when reheating. If the heating chamber of Oslo evaporative crystallizer is replaced by the cooling chamber and the evaporation chamber is removed, the Oslo cooling crystallizer is formed. The main disadvantage of this equipment is that the solute is easy to deposit on the heat transfer surface and the operation is troublesome, so it is not widely used.
5. Breakout prediction
(1) Monitor the friction to predict breakout. The commonly used methods are to install a dynamometer on the vibration hydraulic cylinder, a tester on the vibration device, and an accelerometer and Dynamometer on the mold to detect the friction. Because the operation condition of the vibration device has a great impact on the measurement of friction, the measurement accuracy of friction is difficult to ensure. Although this method is simple, its accuracy is not very high, and it can only predict bonding breakout, which often leads to false alarm in production.
(2) Breakout prediction is carried out according to the change of heat transfer in the mold. The simplest and direct method is to measure the temperature difference between the inlet water temperature and outlet water temperature of the mold cooling water, but this method is often misleading. It is used to measure heat transfer to predict breakout. If the heat transfer per unit area of the mold is used for breakout prediction, the operator can take correct actions according to the heat transfer per unit area, such as reducing the drawing speed, increasing the drawing speed, stopping pouring, etc.
(3) Copper plate thermocouple measurement and breakout prediction. The accuracy of breakout prediction of copper plate thermocouple measurement is relatively high. The breakout prediction system of high-tech is mainly based on thermocouple breakout prediction. Its working principle is to install multiple thermocouples on the mold. The temperature value of the thermocouples is transmitted to the computer system. If it exceeds the specified value, it will give an alarm, and automatically take corresponding measures or operators take corresponding operations to avoid breakout. This method has the functions of predicting bond breakout, crack breakout, slag inclusion breakout, slab depression and visually displaying the solidification of slab shell in the mold. Its information is incorporated into the slab quality prediction system.


Post time: Apr-07-2022