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Evaporative mold product details

信息来源: | 发布日期: 2016-12-29 | 浏览量:

First, the product overview

Evaporation of the mold is also a kind of evaporator, construction and operation of the same with the evaporator, the solvent heated under reduced pressure evaporation, the solution reached the supersaturated and precipitated crystals. Sometimes the solution is concentrated to a certain concentration in an evaporator and then poured into another crystallizer to complete the crystallization process. The evaporator is composed of a suspension chamber, a heating chamber, a separation chamber and a circulating pump. Its main characteristic is that the area formed by the supersaturation and the crystal growth area are respectively placed in the separation chamber and the suspension chamber of the mold. The crystal is fluidized and suspended in the circulating mother liquor, which provides a smooth condition for the crystal growth and can produce a large particle size While the uniform crystal.


Second, the product category

1, intermittent evaporative crystallization of the crystallization of the crystallization tank: it is the principle of a one-time feed after the continuous evaporation and concentration, to supersatize the precipitation of crystals, which configuration mixing system. The intermittent evaporative crystallization tank is suitable for small crystal production or high concentration feed evaporation crystallization production.


2, continuous evaporative mold sub-forced circulation evaporative mold, DTB evaporative mold, OSLO evaporative mold and so on. These three are also the current mainstream of the evaporative mold. They can be in the design according to the nature of different materials to change the process, the process flow downstream, mixed flow and countercurrent.


Third, the application areas

It is widely used in the chemical industry, the smelting of metal mining, the pickling waste liquid of large steel mills, the wet desulfurization waste treatment of power plants, etc. (sodium chloride, phenylalanic acid, Sodium sulfate, ammonium chloride, ammonium chloride; barium chloride, zinc sulfate, calcium chloride, ammonium sulfate, sodium hydroxide).


Fourth, operational control

Crystallization is a process of generating a new phase in a supersaturated solution involving solid-liquid phase equilibria. For specific target products and products, through the experiment to determine the appropriate crystallization conditions, to meet the crystallization product quality requirements, improve the crystallization capacity, reduce process costs.

1. Supersaturation
Increasing the supersaturation of the solution can increase the nucleation rate and growth rate, which is beneficial to improve the crystallization production capacity. But the over-saturation of the General Assembly problems:
1) nucleation rate is too fast, resulting in a large number of tiny crystals, crystallization is difficult to grow;
2) crystal growth rate is too fast, affecting the crystallization quality;
3) Mold wall is prone to scale.
There is a maximum over-saturation, can guarantee the higher nucleation and growth rate at the same time, does not affect the quality of crystallization, it is not easy to produce the scale of the supersaturation.、

2. Temperature
The temperature of the different crystal form and crystal water will change, the temperature is generally controlled in a small temperature range. Cooling crystallization, if the cooling rate is too fast, the solution quickly reached a high degree of supersaturation, resulting in a large number of small crystals, affecting the quality of crystalline products. The temperature is preferably controlled between the saturation temperature and the supersaturation temperature.
Evaporation of crystallization, the evaporation rate is too fast, the solution of the large supersaturation, the formation of tiny crystals, attached to the crystal surface, affecting the quality of crystalline products. Evaporation rate should be compatible with the crystal growth rate, to maintain the solution of the supersaturation certain. Industrial crystallization operation often use vacuum adiabatic evaporation, no external circulation heating device, evaporative indoor temperature is low, to prevent the dramatic changes in supersaturation.

3. Stir and mix
Increasing the stirring speed can increase the nucleation and growth rate, stirring speed will cause the crystal shear broken, affecting the crystallization of product quality. In order to obtain a better mixing state, while avoiding the crystallization of broken, can be used gas-type mixing method, or the use of larger diameter or blade stirring blade, reducing the speed of the paddle.

4. Solvent and pH
The solvent and pH used in the crystallization operation should be such that the solubility of the target solute is low to increase the yield of the crystals. Solvents and pH have an effect on the crystal form. Such as procaine penicillin in aqueous solution for the crystallization of square crystals, in the crystallization of butyl acetate in a long rod-like. In the design of crystal operation before the experiment to determine the crystal crystal form better solvent and pH.

5. Seed crystal
Adding a uniform seed crystal to the supersaturated solution in the metastable zone. For the solution viscosity of the higher system, the nucleus is difficult to produce, and in the high over saturation, once the nucleus, it will also appear a large number of nuclei, prone to polycrystalline phenomenon, product quality is not easy to control. The high viscosity system must be used to add seed crystals to the metastable zone.

6. Crystal pulp concentration
The higher the concentration of crystal pulp, the greater the crystal surface area in the unit volume crystallizer, the faster the crystallization growth rate, which is beneficial to increase the crystallization production rate (yield). However, when the concentration of the slurry is too high, the fluidity of the suspension is poor and the mixing operation is difficult. The concentration of the pulp should be maximized within the permissible range of operating conditions. In intermittent operation, the amount of seed crystal should be based on the size of the final crystal products to meet the maximum concentration of high concentration of production requirements.

7. Circulation flow rate
When using an external circulation mold, the circulation flow rate is set to be reasonable.
Improve the circulating flow rate
1) is helpful to eliminate the supersaturation distribution in the equipment, so that the crystal nucleation rate and the growth rate of the equipment are evenly distributed.
2) can increase the mass transfer coefficient of solid-liquid surface and improve the crystal growth rate;
3) to improve the heat transfer efficiency, inhibition of heat exchanger surface scale scale generation;
Circulation flow rate is too high will cause the crystallization of wear and tear broken. Circulation flow rate should be in the range of non-crystalline wear broken range to take a larger value. If the crystallizer has a crystallization grading function, the circulating flow rate should not be too high, should ensure that the grading function of the normal play.

8. Crystal scale
Mold wall and the circulatory system to produce crystal scale, affecting the crystallization process efficiency. To prevent the scale or remove the scale method:
1) the inner surface of the wall using organic coatings, to keep the wall smooth, to prevent the two-dimensional nucleation on the wall of the occurrence of the phenomenon;
2) to improve the fluid flow rate in the crystallization system, so that the flow velocity distribution evenly, to eliminate low flow rate area;
3) if the outer circulating liquid is supersaturated solution, so that it does not contain seed;
4) the use of jacket insulation to prevent the wall near the saturation is too high;
5) add crystal scale eradication device, regularly add solvent dissolved crystal scale;
6) evaporation wall wall is easy to produce crystal scale, spray solvent can be used to dissolve crystal scale.

9. Impurities
The object of crystallization is a multi-component system, to selectively crystallize the target product.
If the concentration of coexisting impurities is low, there is no significant effect on the crystallization of the target product. However, if the impurity content is increasing in the crystallization operation (as in the case of evaporative crystallization), the accumulation of impurities will seriously affect the purity of the target product.
Crystallization operations need to control the content of impurities, often in the crystallization system to add impurities in the equipment. Ion exchange column or waste discharge.