Classification and introduction of crystallizers

Industrial Crystallizer
1. Cooling crystallizer
Indirect heat exchange kettle cooling crystallizer is currently the most widely used type of cooling crystallizer. Cooling crystallizers are further divided into internal circulation cooling type and external and internal circulation cooling type crystallizers according to their cooling forms. The air-cooled crystallizer is the simplest open type crystallizer. It relies on the large open liquid level at the top and the heat exchange between the wall and the air to reduce its own temperature and achieve the purpose of cooling and precipitation. Crystallization is not added. seeding, without stirring, without any method to control the cooling rate and the formation of nuclei and crystal growth. The cooling capacity required for the cooling crystallization process is provided by a jacket or an external heat exchanger.

（1）. Internal circulation cooling crystallizer

In the internal circulation cooling crystallizer, the coolant and the solvent exchange heat through the jacket of the crystallizer. Because the heat exchange area of the heat exchanger is limited by the crystallizer, the heat exchanger capacity of this equipment is not large.
（2）. External circulation cooling crystallizer
The external circulation cooling crystallizer, the coolant and the solution exchange heat through the cooler outside the crystallizer. The heat exchange area of this equipment is not limited by the crystallizer, the heat transfer coefficient is large, and it is easy to realize continuous operation.
2. Evaporative crystallizer
The evaporative crystallizer is exactly the same as the ordinary evaporator used for solution concentration in equipment structure and operation. In this type of equipment (such as crystallization evaporators, forced circulation evaporators for crystal precipitation, etc.), the solution is heated to the boiling point, evaporated and concentrated to supersaturate and crystallized. However, it should be pointed out that when the evaporator is used to concentrate the solution to make it crystallize, since it is operated under reduced pressure, it can maintain a lower temperature and produce a larger degree of supersaturation in the solution. But it is difficult to control the particle size of crystals. Therefore, when it is necessary to strictly control the crystal size, the solution can be concentrated in the evaporator to a concentration slightly lower than the saturation concentration, and then transferred to another crystallizer to complete the crystallization process.

3. Diversion barrel crystallizer (DTB type evaporative crystallizer)

The crystallizer is a kind of high-efficiency crystallization equipment. The temperature of the material is controllable. Its unique structure and working principle determine that it has the characteristics of high heat transfer efficiency, simple configuration, convenient operation and control, and good operating environment.
The main body of the equipment is the outer cylinder and the diversion cylinder designed according to the fluid calculation. The special propeller realizes the efficient internal circulation, and there is almost no secondary crystal nucleus. According to the growth rate and crystal size of the cooling crystal, the cooling rate, The indicators such as stirring paddle speed are dynamically adjustable to facilitate the self-control of the system to meet the crystallization requirements.
The inner and outer walls of the guide tube are polished to reduce the scarring of the material on the inner wall; the guide tube itself has a high heat exchange surface, and a cooler can also be installed;
The supersaturation degree of the crystal slurry is uniform, the particle size distribution is good, and high efficiency is achieved;
Relatively low energy consumption; the lower part of the discharge valve can realize continuous production
Low speed, frequency conversion control, strong applicability, reliable operation and few failures.
Operation points: crystal removal rate, seed crystal addition rate, PH system adjustment, stirring rate
The lower part is connected with an elutriation column, and the device is equipped with a guide tube and a cylindrical baffle. During operation, the hot saturated feed liquid is continuously added to the lower part of the circulation pipe, mixed with the mother liquor with small crystals in the circulation 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 surface along the draft tube by the slowly rotating propeller. The solution evaporates and cools at the liquid surface to reach a supersaturated state, in which part of the solute is deposited on the surface of the suspended particles, causing the crystal to grow. There is also a settling zone on the periphery of the annular baffle. In the settling zone, the large particles settle, while the small particles enter the circulation pipe with the mother liquor and are dissolved by heating. The crystals enter the elutriation column at the bottom of the crystallizer. In order to make the particle size of the crystallized product as uniform as possible, part of the mother liquor from the sedimentation zone is added to the bottom of the elutriation column, and the small particles are returned to the crystallizer with the liquid flow by the action of hydraulic classification, and the crystallized product is discharged from the lower part of the elutriation column.

4. OSLO fluidized bed cooling crystallizer
Main features: The supersaturation area and the crystal growth area are two separate parts of the crystallizer. The crystals are fluidized and suspended in the circulating mother liquor, which provides better conditions for crystal growth and can produce larger and uniform crystals.
Technological process: it adds a tube cooler on the circulating pipeline, the mother liquor circulates upward through the tube in one pass, and the concentrated feed liquid is added before the circulating pump, mixed with the circulating mother liquor, and then cooled by the cooler together to produce supersaturation, Then it enters the crystallizer for fluidized suspension to produce crystals with larger and uniform particle size. The product (crystal) suspension is drawn from the bottom of the crystallizer cone.
The control system adopts PLC controller with system information upload interface. It is required to be able to automatically monitor and control the crystallization temperature and crystal size. The axial flow pump adopts frequency conversion control, and the feeding and discharging operations can be automatically controlled; OSLO crystallizers are divided into two categories: evaporative OSLO crystallizers and cooling OSLO crystallizers. The evaporative OSLO crystallizer is to heat the circulating liquid by an external heater and enter the vacuum flash chamber to evaporate to supersaturation, and then enter the suspended bed through a vertical pipe to make the crystal grow. Due to the special structure of the OSLO crystallizer, the larger particles The first contact with the supersaturated solution grows first, followed by the smaller volume solution; the cooling type OSLO crystallizer cooler uses an external cooler to cool the saturated feed liquid to supersaturate, and then enters the suspended bed through a vertical pipe to grow the crystals. Due to the special structure of the OSLO crystallizer, the particles with larger volume first contact the supersaturated solution to grow preferentially. Therefore, the crystals produced by the OSLO crystallizer have large volume, uniform particles and large production capacity. And it has the advantages of continuous operation and low labor intensity.
Features:
1) Due to the special structure of OSLO, the products produced have the advantages of larger particles and narrower particle size distribution;
2) The circulation volume of the solution is large, the supersaturation of the solution is small, and it is not easy to generate secondary crystal nuclei c;
3), continuous production, the output can be large or small;
4) There is no crystal broken problem in the clear liquid circulation;
5) The uniform supersaturation in the suspension bed provides good conditions for crystal growth, d>20μ.
The supersaturation generating equipment of the OSLO cooling crystallizer is a cooling heat exchanger, and the solution passes through the tube side of the heat exchanger, and the tube side is two-pass. The cooling medium passes through the shell side. It should be pointed out that the circulation mode of the cooling medium on the shell side. The design limit of the supersaturation degree of the solution passing through the tube side is controlled by the flow rate of the main circulating pump, and the fresh cooling medium of the cooling medium needs to have a suitable flow rate.
Graded clear liquid circulation type: mainly control the circulating pump to suck the clear solution that basically does not contain crystals, and then transport it to the cooler for cooling, and increase the supersaturation in the circulating mother liquor through cooling. The lower crystal grower mainly makes the supersaturated solution extend straight into the bottom of the grower through the central downcomer, and then slowly passes through the fluidized crystal bed layer, so that the supersaturation phenomenon disappears and the crystal grows gradually. According to the size of the particle size, it is automatically classified and arranged from bottom to top, and the concentration of the crystal slurry is also gradually decreased from bottom to top, and it has become clear liquid when it rises to the vicinity of the inlet of the circulating pump. The grading operation method separates the grains at the bottom and the grains on the top that have not grown to the size of the product. The take-out tube is inserted at the bottom, so the products taken out are all uniform spherical large-grain crystals, which is its biggest advantage. However, the delivery volume of the circulating pump is constant in the entire crystallizer, which results in the limitation of the terminal velocity of the fluidization of the crystal grains in the crystallizer and the concentration of the crystal slurry (that is, the size of the porosity), which will inevitably bring about two Disadvantages: The first is that the degree of supersaturation is large, but the safe supersaturated metastable region is generally very narrow, and production is often not allowed to cross the upper limit of the metastable region, generally in the middle or partial of the metastable region. previous point. So the elasticity of production capacity is very small. The second disadvantage is that the production capacity of the equipment of the same diameter is several times lower than that of the slurry circulation operation due to the existence of the above phenomenon.
5. External circulation type crystallizer
Referred to as FC crystallizer, it consists of crystallizing chamber, circulating pipe, circulating pump, heat exchanger, etc. The crystallizing chamber has a cone-shaped bottom. After the crystal slurry is discharged from the bottom of the cone, it is pumped through the heat exchanger by axial flow circulation through the circulation pipe, and then enters the crystallizing chamber again after being heated or cooled. The crystal slurry discharge port is located near the bottom of the cone of the crystallization chamber, and the feed port is located at a lower position below the discharge port. It can be operated continuously or intermittently.
The crystallizer can be generally used for crystallization by evaporation method, partition cooling method or vacuum cooling method. In the latter case, the heat exchanger is not necessary, and the crystallization chamber is connected to a vacuum system to maintain a relatively high vacuum in the chamber. This form of crystallizer is suitable for the production of sodium chloride, barium chloride, potassium chloride, urea, sodium hypophosphite, sodium sulfate, ammonium sulfate, citric acid and some other inorganic and organic crystals. Product particle size is about 0.05 ~ 1mm range

6. Vacuum crystallizer

The difference between a vacuum crystallizer and an evaporative crystallizer is that the former has a higher degree of vacuum and requires that the saturated vapor pressure (absolute) at the operating temperature be equal to the total vapor partial pressure of the solution at this temperature. The operating temperature is generally lower than the atmospheric temperature or the highest is close to the air temperature. The raw material solution of the vacuum crystallizer is mostly preheated by a heater outside the device, and then injected into the crystallizer. After entering the vacuum evaporator, the flash evaporation effect occurs immediately, and the steam can be pumped away in an instant, and then the cooling process continues. When a stable state is reached, the temperature of the solution is balanced with the saturated steam pressure. Therefore, the vacuum crystallizer has both the evaporation effect and the refrigeration effect, that is, it simultaneously removes the solvent and cools the solution. The solution changes along the two directions of solution concentration and cooling, rapidly approaching the metastable region.
Vacuum crystallizers generally do not have heaters or coolers, which avoids precipitation of crystals on complex surface Heat Exchangers, prevents the phenomenon of reducing heat exchange capacity due to scaling, and prolongs the service life of heat exchangers. The evaporation and cooling of the solution are carried out on the boiling liquid level of the evaporation chamber, so there is no scaling problem. However, during flash evaporation in the evaporation chamber, the splashing of droplets on the boiling interface is very serious. It still has to adhere to the wall of the evaporation chamber to form crystal scale. It is necessary to attach a special washing nozzle or washing water overflow ring to the top of the evaporation chamber, which is sprayed toward the wall of the evaporator, and clean it with clean water regularly during the production process to avoid the decline in production capacity caused by the gradual reduction of the section of the evaporator, and The cleaning effect can be obtained without interrupting production.
7, Vacuum cooling crystallizer
The vacuum cooling crystallizer is to add the hot saturated solution into a crystallizer that is insulated from the outside world. Since a high vacuum is maintained in the device, the boiling point of the solution retained in it is lower than the temperature of the solution added. In this way, when the solution enters the crystallizer, it is cooled to an equilibrium temperature corresponding to the pressure in the vessel through adiabatic flash evaporation.
Vacuum cooled crystallizers can be operated batchwise or continuously. Figures 7-9 show a continuous vacuum cooling crystallizer. The hot raw material liquid is continuously added from the feeding port, the crystal slurry (suspension of crystal and mother liquid) is continuously discharged by the pump, and the circulating pump on the pipeline at the bottom of the crystallizer makes the solution circulate forcibly to promote the uniform mixing of the solution and maintain favorable conditions. crystallization conditions. The evaporated solvent (vapor) escapes from the top of the device and is condensed in the high-level mixing Condenser. A two-stage steam jet pump is used to create and maintain a vacuum within the crystallizer. Generally, the operating temperature in the vacuum crystallizer is very low, and the generated solvent vapor cannot be condensed by water in the condenser. At this time, a steam jet pump can be installed in the front of the condenser to compress the solvent vapor to improve the its condensation temperature.
8. Rotary drum crystallizer
Drum flakes are a cooling and crystallization process. The molten material in the tray contacts the cooled drum to form a film on the surface of the drum. Through the heat exchange between the film and the drum, the film is cooled, crystallized, and crystallized. The material is scraped off by a scraper and becomes a flake product. Drum drying is a continuous operation equipment that heats and dries the liquid phase material or strip material attached to the outer wall of the drum by means of heat conduction through the rotating drum.
Typical material:
Polyethylene oligomers, petroleum resins, oxidized polyethylene and other polymer products; Phthalic anhydride, maleic anhydride, naphthalene, peregal, higher aliphatic alcohols, chloroacetic acid, trihydroxypropane, guanidine nitrate, bisphenol a, isophthalic acid Organic chemical products such as fatty acid; inorganic chemical products such as sulfur, alkali sulfide, caustic soda, sodium hydrosulfide, calcium chloride.
The equipment is compact in structure and occupies a small area; the drum has high precision and good product uniformity; multiple sets of scrapers are used, which can be adjusted flexibly; half-pipe jacket type material tray, safe and reliable; .
9. Surface continuous crystallizer (casing crystallizer)
Scraping the surface of the continuous crystallizer is a cooling and crystallization process. The high-viscosity material liquid contacts the cooling inner tube wall to form a cooling and crystallization material film on the surface. The rotating scraper blade continuously scrapes off the crystalline material film layer on the tube wall that hinders heat transfer. , and continuously push the material forward to bring out the crystallization. The cooling area can be determined according to the specific production situation, and the equipment unit can be selected.
Equipment advantages:
1 Wide crystallization temperature range (-60 C to +100 C).
2 Suitable for the crystallization of high solid content or high viscosity oil and fat materials
3 The equipment is operated continuously, and various indicators can be easily controlled
4 The equipment occupies a small area and has a large processing capacity, which can replace large vacuum crystallizers, and there is no complicated auxiliary equipment such as condensers, vacuum systems, etc.
Application areas: dewaxing of lubricating oil, crystallization of high-viscosity organics, viscous liquid cooling, etc. ammonia cooling and heat exchange; heat exchange area can be designed and manufactured according to user needs
10. Horizontal crystallizer
Crystallization is a common chemical unit operation process in pharmaceutical and chemical production. It is a process closely related to temperature, time and stirring state. The crystallization process is generally a cooling process, and cooling at different rates within a certain period of time is the basic feature of the crystallization process. Different products have different crystallization process curves, and for the same product, different crystallization processes have a great influence on the internal quality and appearance quality of the product. Because the crystallization process has the characteristics of long time, small temperature difference, high control index, and volatile crystallization curve, artificial control of the crystallization process often fails to meet the ideal requirements. Therefore, this crystallizer adopts a special crystallization curve process control system. , in order to adapt to the crystallization process of various materials to improve the quality of products.
The horizontal crystallizer is a high-efficiency crystallization equipment. The temperature of the material is controlled by the computer, and the crystallization curve is smoothly carried out according to the preset crystallization curve. Its automatic control system has the following functions:
(1) Measurement range: 0 ~ 200 0C measurement accuracy 0.5;
(2) Control law: continuous PID cascade;
(3) Control accuracy: ±1°C overshoot <5%;,
(4) Hand/auto switch without disturbance;
(5) Online setting and modification of crystallization curve, online setting and modification of control parameters:
(6) The program segment is greater than 10 segments, and the time length is greater than 1 month;
(7) It can be equipped with a communication interface, which is convenient for distributed control;
(8) Control parameters: alarm, control;
(9) It can have explosion-proof function:
(10) With real-time and historical recording functions, it is convenient for data analysis.