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CN-121971878-A - Forced circulation continuous cooling crystallization system and process

CN121971878ACN 121971878 ACN121971878 ACN 121971878ACN-121971878-A

Abstract

The invention discloses a forced circulation continuous cooling crystallization system and a forced circulation continuous cooling crystallization process, and belongs to the technical field of crystallization. The system comprises a mixer, a hydrocyclone, a clear liquid settler, a circulating pump and an external cooler which are sequentially connected through pipelines. The core is that the supersaturation degree generation, crystal growth, particle size classification and pre-separation processes are integrated into a high-strength cyclone field by using a cyclone reaction-classifier which is a cyclone crystallizer to synchronously finish the process of 'instant crystallization and instant separation'. The stock solution and the cooled circulating solution are instantaneously mixed in a mixer to be cooled and then enter a hydrocyclone crystallizer tangentially. The separated clear liquid is circularly used after sedimentation and cooling. The invention also has the function of on-line heating medium scar removal, realizes the continuous and automatic operation of the whole process, and has the advantages of compact equipment, uniform product granularity, low energy consumption and long-period stable operation.

Inventors

  • GENG HAITAO
  • SUN LIMIN

Assignees

  • 北京道思克能源设备有限公司

Dates

Publication Date
20260505
Application Date
20260209

Claims (15)

  1. 1. The forced circulation continuous cooling crystallization system is characterized by comprising an external cooler (1), a circulating pump (2), a mixer (3), a hydrocyclone crystallizer (4) and a clear liquid settler (5) which are sequentially connected through pipelines and form a circulation loop; The mixer (3) is provided with a stock solution feed inlet (31), a circulating solution inlet (32) and a mixer outlet (33); the hydrocyclone crystallizer (4) is provided with a tangentially arranged circulating feed back opening (41) and an overflow outlet (42) arranged at the top; the clear liquid settler (5) is provided with a clear liquid feeding port (52), a circulating discharging port (51), a crystal slurry discharging port (55) and a clear liquid discharging port (56); the mixer outlet (33) is communicated with a circulation feed-back opening (41) of the hydrocyclone (4), an overflow outlet (42) of the hydrocyclone (4) is communicated with a clear liquid feed-in opening (52) of the clear liquid settler (5), a circulation discharge opening (51) of the clear liquid settler (5) is communicated with an inlet of the circulation pump (2), an outlet of the circulation pump (2) is communicated with a material inlet (15) of the external cooler (1), and a material outlet (16) of the external cooler (1) is communicated with a circulation liquid inlet (32) of the mixer (3).
  2. 2. The system according to claim 1, characterized in that the hydrocyclone (4) is configured to generate a centrifugal force field strength (i.e. centrifugal separation factor, RCF) in its cyclonic crystallization zone (44) of 200 to 1000 times the gravitational acceleration, such that the average residence time of the crystals in this zone is controlled between 30 and 60 seconds to inhibit secondary nucleation.
  3. 3. The system according to claim 1, characterized in that the hydrocyclone (4) comprises inside an overflow zone (43), a cyclonic crystallization zone (44) and a downcomer (45) in top-down communication, wherein the cyclonic crystallization zone (44) is configured for crystal nucleation and growth and the downcomer (45) is configured for guiding the grown crystals to a slurry zone (54) of the supernatant settler (5).
  4. 4. The system according to claim 1, characterized in that the external cooler (1) is further provided with a heat medium inlet (13) and a heat medium outlet (14).
  5. 5. The system according to any of claims 1 or 4, characterized in that the external cooler (1) is a double tube Cheng Lie tube heat exchanger, a plate heat exchanger or a spiral plate heat exchanger.
  6. 6. The system of claim 1, further comprising a thickener and centrifuge connected downstream of the magma discharge port (55), and a mother liquor treatment or recovery unit connected downstream of the clear liquor discharge port (56).
  7. 7. A forced circulation continuous cooling crystallization process employing the system of any one of claims 1-6, comprising the steps of: s1, mixing the stock solution with cooling circulation liquid from the external cooler (1) in the mixer (3) for cooling; s2, enabling the mixed solution to enter the hydrocyclone crystallizer (4) tangentially, crystallizing in a cyclone field and performing centrifugal separation, discharging crystals from a crystal slurry discharge port (55) after the crystals enter a crystal slurry area (54) of the clear liquid settler (5), and overflowing clear liquid containing fine crystals through an overflow outlet (42); s3, enabling overflowed clear liquid to enter a clear liquid settler (5) for further sedimentation and clarification, and dividing clarified mother liquid into two paths of circulating liquid and surplus clear liquid; S4, cooling the circulating liquid by the external cooler (1), and returning the cooled circulating liquid to the mixer (3) for recycling.
  8. 8. The process according to claim 7, characterized in that the centrifugal separation factor (RCF) of the internal flow field of the hydrocyclone (4) is 800 to 1500.
  9. 9. The process according to claim 7, wherein the volume flow ratio of the circulating liquid to the stock liquid, i.e. the circulation rate, is from 5:1 to 15:1.
  10. 10. The process according to claim 7, further comprising an on-line scar removal step of introducing a heating medium to the external cooler (1) to replace the cooling medium when scar removal is required, and maintaining the system to be operated circularly, and heating the circulating liquid to dissolve crystal scars in the system.
  11. 11. The process of claim 10, wherein the online scar removal step comprises: a) Suspending raw liquid feeding and product discharging; b) Based on the monitoring signal of the heat exchange efficiency reduction of the external cooler (1), switching the medium of the external cooler from a refrigerant to a heating medium; c) Maintaining the forced circulation of the system, and heating the circulating liquid to a temperature sufficient for dissolving the crystal scars and maintaining the circulating liquid; d) Switching the medium of the external cooler (1) from a heating medium to a cooling medium, and cooling the circulating liquid to the crystallization temperature in a gradient way at a controlled rate; e) Recovering the feed of the primary liquid and the discharge of the product.
  12. 12. Process according to claim 10 or 11, characterized in that the triggering condition of the on-line scar removal step is that the temperature difference between the material inlet (15) and the material outlet (16) of the external cooler (1) is monitored to decrease by an extent of 10% or more than the initial steady-state operating temperature difference.
  13. 13. The process according to claim 11, wherein in step d) the rate of gradient cooling is from 3 ℃ to 10 ℃ per hour.
  14. 14. A forced circulation continuous cooling crystallization process according to any one of claims 1-6, comprising a continuous crystallization mode and an on-line scar removal mode; In a continuous crystallization mode, performing the steps of any one of claims 7-13; When the triggering condition of the heat exchange efficiency reduction of the external cooler (1) is monitored, the external cooler is automatically switched to an on-line scar removing mode, the steps a) to e) of claim 11 or 12 are sequentially executed, and after the temperature of the circulating liquid is recovered to the crystallization temperature, the external cooler is automatically switched back to the continuous crystallization mode.
  15. 15. A method of preparing a crystalline product, characterized in that a crystalline product having a particle size coefficient of variation of less than 15% is prepared using the system of any one of claims 1 to 6 or using the process of any one of claims 7 to 14.

Description

Forced circulation continuous cooling crystallization system and process Technical Field The invention relates to a forced circulation cooling crystallization system and a forced circulation cooling crystallization process, and belongs to the technical field of solution crystallization devices and processes. Background In the technical field of industrial crystallization, continuous crystallization process gradually replaces batch crystallization to become mainstream due to the advantages of high yield, stable operation and the like. However, continuous crystallization equipment often faces the problems of scarring, uneven product granularity, short operation period and the like in operation, and affects the production efficiency and the product quality. For this reason, various continuous crystallizers have been developed, but there is still room for improvement. Chinese patent CN 109806613A (publication No. 2021-5-11) discloses a continuous freezing crystallizer and a method for removing scab. The crystallizer comprises a crystal growing device, an external cooler and a circulating system, and prevents and removes scars through material circulation and temperature control. Its advantages are quick scar removing, no need of temp. rising and low energy consumption. However, the method relies on an external heat source (such as steam) or hot feed liquid to remove scars, may not be efficient under complex working conditions, and prevention of scars is mainly controlled by flow rate, so that the method has a large limitation. Chinese patent CN 110870984A (publication No. 2020-3-10) describes a continuous crystallizer and process thereof, which is operated continuously by a combination of a cooling crystallization system and a circulating constant temperature condensing system. The device has simple structure, can reduce wall hanging, but focuses on temperature control, does not specially solve the problem of scab, and has weaker granularity grading capability. Chinese patent CN 108939599A (publication No. 2020-12-8) proposes a self-circulation crystallizer and a multistage continuous crystallization method, which adopts unique configurations (such as W-shaped bottom and guide cylinder) to achieve particle size classification and anti-scaling. The technology is suitable for evaporation, cooling and reaction crystallization, the granularity of the product is uniform, but the equipment structure is complex, the cost is high, and the energy consumption can be increased due to multistage serial connection. Chinese patent CN 222765696U (publication No. 2025-4-8) relates to a nickel sulfate continuous crystallization system, which realizes continuous production by pretreatment, concentration and crystallization units, and integrates control unit optimization process. The system is convenient to operate, but is focused on specific application of nickel sulfate, has insufficient universality, and can increase maintenance burden due to dependence of scar treatment on external equipment (such as a thermal crystal eliminator). In summary, although the prior art has progressed in continuous crystallization, the following technical bottlenecks to be solved still remain: (1) The crystallization process is decoupled from the primary separation process in that conventional continuous crystallizers (e.g., DTB, OSLO type) typically perform crystal growth in a relatively gentle fluidization or agitation environment followed by size classification and separation by external cyclones or settling tanks. The step-by-step mode of 'first growth and then separation' ensures that the generated crystals stay in supersaturated mother liquor for too long, and are extremely easy to generate secondary nucleation, crushing and disordered growth, which is the root cause of wide particle size distribution (the variation coefficient is often more than 25 percent) of the product. Although CN108939599a mentions self-circulation and classification, its equipment structure is complex and instantaneous synchronization of crystallization and separation is not achieved. (2) The supersaturation degree is controlled inaccurately, namely, local supercooling points are very easy to generate in the mixing process of the high-temperature stock solution and the low-temperature circulating solution at the feeding point or the mixing point, so that explosive nucleation is caused, and a large amount of fine crystals are generated. The prior art (such as CN110870984 a) is mainly alleviated by temperature control, but fails to fundamentally solve the problem of uniform generation of supersaturation in space from the hydrodynamic design. (3) The anti-scarring capability contradicts the continuous run time in that although CN109806613a and CN222765696U propose a scar removal scheme, the former relies on external heat source introduction, possibly introducing impurities or causing system disturbances, and the latter relies on additional equipment. Both of the two cann