CN115193089B - Multistage continuous crystallization method - Google Patents
Multistage continuous crystallization method Download PDFInfo
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- CN115193089B CN115193089B CN202210538576.8A CN202210538576A CN115193089B CN 115193089 B CN115193089 B CN 115193089B CN 202210538576 A CN202210538576 A CN 202210538576A CN 115193089 B CN115193089 B CN 115193089B
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- 238000002425 crystallisation Methods 0.000 title claims abstract description 311
- 230000008025 crystallization Effects 0.000 claims abstract description 283
- 239000013078 crystal Substances 0.000 claims abstract description 72
- 238000001816 cooling Methods 0.000 claims abstract description 13
- 238000002156 mixing Methods 0.000 claims description 98
- 239000007788 liquid Substances 0.000 claims description 54
- UIIMBOGNXHQVGW-UHFFFAOYSA-M Sodium bicarbonate Chemical compound [Na+].OC([O-])=O UIIMBOGNXHQVGW-UHFFFAOYSA-M 0.000 claims description 48
- 238000003756 stirring Methods 0.000 claims description 43
- 239000000725 suspension Substances 0.000 claims description 31
- 235000017557 sodium bicarbonate Nutrition 0.000 claims description 24
- 229910000030 sodium bicarbonate Inorganic materials 0.000 claims description 24
- 238000005507 spraying Methods 0.000 claims description 23
- 239000007787 solid Substances 0.000 claims description 22
- 230000009471 action Effects 0.000 claims description 13
- 125000004122 cyclic group Chemical group 0.000 claims description 7
- 239000012452 mother liquor Substances 0.000 claims description 6
- 239000012295 chemical reaction liquid Substances 0.000 claims description 3
- 210000001503 joint Anatomy 0.000 claims description 3
- 238000002360 preparation method Methods 0.000 claims description 2
- 238000000034 method Methods 0.000 abstract description 49
- 230000008569 process Effects 0.000 abstract description 45
- 239000002002 slurry Substances 0.000 abstract description 29
- 238000006243 chemical reaction Methods 0.000 abstract description 21
- 238000001704 evaporation Methods 0.000 abstract description 9
- 230000008020 evaporation Effects 0.000 abstract description 9
- 235000013339 cereals Nutrition 0.000 description 74
- 239000002245 particle Substances 0.000 description 46
- 239000000463 material Substances 0.000 description 23
- 239000000047 product Substances 0.000 description 16
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 8
- 239000012267 brine Substances 0.000 description 8
- HPALAKNZSZLMCH-UHFFFAOYSA-M sodium;chloride;hydrate Chemical compound O.[Na+].[Cl-] HPALAKNZSZLMCH-UHFFFAOYSA-M 0.000 description 8
- 238000004519 manufacturing process Methods 0.000 description 7
- 238000000926 separation method Methods 0.000 description 7
- 238000012546 transfer Methods 0.000 description 7
- 238000009835 boiling Methods 0.000 description 6
- 238000007599 discharging Methods 0.000 description 6
- 230000005484 gravity Effects 0.000 description 6
- 238000004062 sedimentation Methods 0.000 description 6
- 239000000126 substance Substances 0.000 description 6
- 238000010899 nucleation Methods 0.000 description 5
- ATRRKUHOCOJYRX-UHFFFAOYSA-N Ammonium bicarbonate Chemical compound [NH4+].OC([O-])=O ATRRKUHOCOJYRX-UHFFFAOYSA-N 0.000 description 4
- 229910000013 Ammonium bicarbonate Inorganic materials 0.000 description 4
- 235000012538 ammonium bicarbonate Nutrition 0.000 description 4
- 239000001099 ammonium carbonate Substances 0.000 description 4
- 230000015572 biosynthetic process Effects 0.000 description 4
- 238000010924 continuous production Methods 0.000 description 4
- 238000013461 design Methods 0.000 description 4
- 238000010586 diagram Methods 0.000 description 4
- 238000005516 engineering process Methods 0.000 description 4
- 239000012467 final product Substances 0.000 description 4
- 239000012530 fluid Substances 0.000 description 4
- 238000010438 heat treatment Methods 0.000 description 4
- 230000006911 nucleation Effects 0.000 description 4
- 239000002994 raw material Substances 0.000 description 4
- 238000010992 reflux Methods 0.000 description 4
- 239000011780 sodium chloride Substances 0.000 description 4
- 230000008901 benefit Effects 0.000 description 3
- 230000008021 deposition Effects 0.000 description 3
- 235000011868 grain product Nutrition 0.000 description 3
- 239000008187 granular material Substances 0.000 description 3
- 230000001105 regulatory effect Effects 0.000 description 3
- 238000003860 storage Methods 0.000 description 3
- UIIMBOGNXHQVGW-DEQYMQKBSA-M Sodium bicarbonate-14C Chemical compound [Na+].O[14C]([O-])=O UIIMBOGNXHQVGW-DEQYMQKBSA-M 0.000 description 2
- 239000003795 chemical substances by application Substances 0.000 description 2
- 230000001276 controlling effect Effects 0.000 description 2
- 238000000502 dialysis Methods 0.000 description 2
- 238000004090 dissolution Methods 0.000 description 2
- 238000009826 distribution Methods 0.000 description 2
- 230000002349 favourable effect Effects 0.000 description 2
- 239000003337 fertilizer Substances 0.000 description 2
- 238000005243 fluidization Methods 0.000 description 2
- 238000002347 injection Methods 0.000 description 2
- 239000007924 injection Substances 0.000 description 2
- 238000011031 large-scale manufacturing process Methods 0.000 description 2
- 239000011344 liquid material Substances 0.000 description 2
- 238000010907 mechanical stirring Methods 0.000 description 2
- 238000001000 micrograph Methods 0.000 description 2
- 238000011112 process operation Methods 0.000 description 2
- 230000002035 prolonged effect Effects 0.000 description 2
- 238000007493 shaping process Methods 0.000 description 2
- 239000011343 solid material Substances 0.000 description 2
- 239000000243 solution Substances 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000004581 coalescence Methods 0.000 description 1
- 238000004891 communication Methods 0.000 description 1
- 230000008878 coupling Effects 0.000 description 1
- 238000010168 coupling process Methods 0.000 description 1
- 238000005859 coupling reaction Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005265 energy consumption Methods 0.000 description 1
- 238000004880 explosion Methods 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 238000005086 pumping Methods 0.000 description 1
- 238000004064 recycling Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D9/00—Crystallisation
- B01D9/02—Crystallisation from solutions
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D9/00—Crystallisation
- B01D9/0059—General arrangements of crystallisation plant, e.g. flow sheets
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D9/00—Crystallisation
- B01D9/0063—Control or regulation
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- Chemical & Material Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
Abstract
The invention provides a multistage continuous crystallization method which is realized by a multistage circulation crystallization system device; the multistage circulating crystallization system device comprises at least two circulating crystallization devices which are sequentially connected in series; the multistage circulation crystallization method is suitable for any one of evaporation crystallization, solvent-out crystallization, cooling crystallization or reaction crystallization, and the multistage continuous crystallization has the stage number of 2-6 stages, preferably 3-4 stages. The multistage continuous crystallization method provided by the invention realizes the circulation and the size classification of crystal slurry through the specific configuration of the crystallizer, and solves the problems of small product size, serious equipment scaling, pipeline blockage, short operation period and the like in the continuous crystallization process.
Description
Technical Field
The invention belongs to the technical field of crystallization, and relates to a multistage continuous crystallization method.
Background
The crystallization process can be classified into two modes of continuous crystallization and batch crystallization according to the operation modes. The common crystallizer is a kettle type stirring crystallizer, and the production is intermittent, so that the method is suitable for products with smaller annual output. Because of the characteristics of the operation mode, the intermittent crystallization has the advantages of time-varying process operation control parameters, multiple influencing factors, strong control variable coupling, unstable product quality and process yield due to the fact that experience and regulation precision of operators are very depended, poor product consistency, uneven grain size and the like caused by large batch-to-batch differences, and can not meet the demands of customers. Because the intermittent crystallization operation is discontinuous, the production and preparation efficiency is not high, and the equipment number or the occupied area is large. And most of domestic crystallizers are cooled by a jacket, so that the crystalline substances are firstly bonded on the kettle wall, thick crystalline substances can be formed on the kettle wall, and the heat transfer efficiency is greatly affected.
The continuous crystallizer is a device capable of realizing continuous crystallization production compared with the traditional single-tank intermittent crystallization, is suitable for large-scale industrial crystallization processes, can be realized by one or more crystallization devices connected in series, each crystallization device is called a stage, the technological parameters of each stage of crystallization device are constant and do not change with time, and the crystallization process is more stable and easy to control, so that the stability and consistency of the quality of a crystal grain product are ensured, and the influence of human factors on the crystallization process is greatly reduced. Different from a single-tank intermittent crystallization mode, the continuous crystallizer realizes the continuous operation process of continuously adding materials to be crystallized and continuously taking out crystallizer products from the crystallizer, and the feeding and the discharging are simultaneously carried out. The large-particle crystallization grains at the bottom of the existing continuous crystallizer cannot be concentrated rapidly, part of the large-particle crystallization grains are easy to mix and flow into the upper liquid for dissolution in the continuous production process, and the production efficiency is reduced. However, at the same time, one difficulty in continuous crystallization equipment and process operation is product granularity control, if the amount of fine crystals in the system is large, after the system is balanced and steady-state operation, the regulation and control means are not many, and the process parameter conditions such as evaporation rate, cooling rate, feeding rate, seeding and the like of materials cannot be changed like intermittent operation, namely the supersaturation degree cannot be regulated in real time, a large amount of fine crystal particles cannot be effectively reduced or eliminated, and the whole granularity of the continuous crystallization product is smaller. In addition, large-particle crystallization grains at the bottom of the existing continuous crystallizer cannot be concentrated rapidly, part of large-particle crystallization grains are easy to mix and flow into upper-layer liquid for dissolution in the continuous production process, and the production efficiency is reduced.
CN111054294B discloses a method for returning small crystal grain particles in the slurry discharged from the reaction crystallizer, which is to make the slurry discharged from the reaction crystallizer enter a slurry storage tank, then be sucked out by a venturi tube, and be mixed and diluted with the clear liquid from a clear liquid circulating pump, then make the diluted slurry enter a hydrocyclone to make continuous separation of small crystal grain particles, and make the small crystal grain flow back into a sedimentation reflux tank to settle and flow back into the reaction crystallizer to continue growing. This method has the following disadvantages: (1) All the slurry is discharged and is filled into a storage tank, so that equipment and energy consumption are increased; (2) The recycling step requires multiple tanks and pumps and takes up a lot of space. (3) The natural sedimentation time is long, the efficiency cannot be ensured, and the method is not suitable for large-scale application and production.
CN112774243a discloses a mother liquor circulating type continuous crystallizer, including crystallization device, drive arrangement, heat transfer device and reflux unit, circulating reflux barrel one end is connected with wide-mouth skirt body, the wide-mouth skirt body of twice diameter reduces circulating reflux barrel fluid feed's velocity of flow, avoid great velocity of flow fluid to drive the circulation flow with the shaping great granule, do benefit to the bottom deposition of great granule, the wide-mouth skirt body outer wall of horizontal plane contained angle forty-five degrees is convenient for the edge of the great shaping granule to pile up simultaneously, the swivel becket rotates simultaneously, a plurality of stirring pieces that drive the bottom carry out the bottom deposition stir towards the discharging pipe, the ejection of compact of being convenient for. The bottom deposition of large particles of the invention is easy to cause coalescence of certain crystalline particles, and the applicable crystallization range is limited.
Although the multistage continuous crystallization technology and the equipment have advantages, the technology and the equipment have problems in the aspects of small granularity, scale formation of the equipment, easy flow blockage, short operation period and the like, and further research and improvement are needed. Therefore, a multifunctional crystallizer and a continuous crystallization method are needed, which not only can ensure the separation of crystallization particles with different sizes, but also have wide application range and are suitable for large-scale popularization.
Disclosure of Invention
Aiming at the defects existing in the prior art, the invention provides a multistage continuous crystallization method which is realized by a multistage circulating crystallization system device, the multistage circulating crystallization system device comprises at least two circulating crystallization devices with the same structure, the circulating crystallization devices effectively regulate and control crystal nucleation and growth by controlling and adjusting the circulating speed, and the crystallizer realizes the combination of functions of an OSLO crystallizer and a DTB crystallizer and the realization of the particle size classification of crystal particles by innovative design, thereby improving the problems of small product particle size, serious equipment scaling, short operation period and the like in the continuous crystallization process, improving the stable operation period of the continuous crystallization process and ensuring the product quality.
In order to achieve the aim of the invention, the invention adopts the following technical scheme:
the invention aims to provide a multistage continuous crystallization method which is realized by a multistage circulation crystallization system device; the multistage circulating crystallization system device comprises at least two circulating crystallization devices with the same structure which are sequentially connected in series;
the circulating crystallization device comprises a shell, wherein a guide structure of a funnel structure is arranged in the shell, the guide structure comprises a guide cone section and a guide tube section which are sequentially butted from top to bottom, and the edge of the large end face of the guide cone section is butted with the inner wall of the shell in the circumferential direction;
the shell cavity above the diversion cone section forms a mixing bin, the shell cavity at the periphery of the diversion cone section forms a crystallization bin, the bottom of the inner cavity of the shell is provided with a stirring device, the outer wall of the mixing bin is provided with a feed inlet and at least one circulation inlet, the upper part of the outer wall of the crystallization bin is provided with at least one circulation outlet, the circulation inlet and the circulation outlet are communicated through an external circulation pipeline, the bottom of the outer wall of the crystallization bin is provided with a discharge outlet, and the discharge outlet is connected with the circulation pipeline of the next-stage circulation crystallization device or the feed inlet of the next-stage circulation crystallization device;
the material liquid is introduced into the mixing bin, mixed and enters the crystallization bin for crystallization along the flow guiding structure, under the action of the stirring device, small-grain-size grains form rotational flow in the crystallization bin, the rotational flow returns to the mixing bin through the circulating pipeline for circulating crystallization, and large-grain-size grains are deposited and enter the next-stage circulating crystallization device through the discharge hole for multistage continuous crystallization.
The multistage circulation crystallization method provided by the invention not only can ensure that the separation of crystallization particles with different sizes is realized, but also has a wide application range, and is suitable for large-scale popularization.
Preferably, the multi-stage circulation crystallization method is suitable for any one of evaporative crystallization, solvent-out crystallization, cooling crystallization or reaction crystallization, and each stage of crystallizer can be externally provided with a heating/cooling heat exchanger according to the crystallization mode to provide heat/cold energy input required by the crystallization process.
Preferably, the multistage continuous crystallization has a number of stages of 2 to 6, preferably 3 to 4, and more preferably 4;
preferably, the technology of multistage continuous crystallization is four stages, the feeding of the first-stage circulating crystallization device is unsaturated crystallization feed liquid or reaction liquid, the solid suspension amount in the first-stage circulating crystallization device is controlled to be 2% -10%, the solid suspension amount in the second-stage circulating crystallization device is controlled to be 10% -20%, the solid suspension amount in the third-stage circulating crystallization device is controlled to be 20% -30%, and the solid suspension amount in the fourth-stage circulating crystallization device is controlled to be 30% -45%.
In addition, in order to ensure that crystal grains fully grow in each stage of crystallization process, the invention also improves the internal structure of each stage of circulating crystallization device, realizes the internal circulation and the particle size classification of crystal slurry in a single stage of crystallization process, and in the single stage of crystallization process, the crystal slurry enters a crystallization bin along a funnel-shaped flow guide structure after entering a mixing bin, and the crystal slurry moves upwards under the action of a stirring device and the gravity of the crystal grains by utilizing the mobility of the crystal slurry, so that the crystal grains with small particle size can move upwards under the action of the stirring device and form a certain circulating flow field in the crystallization bin, and the crystal grains with small particle size are suspended at the upper part of the crystallization bin to form a rotational flow circulating state and do not agglomerate at the bottom; and the grains with large grain size can be settled to the bottom of the crystallization bin and discharged from the discharge port to enter the feed inlet of the next-stage crystallizer or discharged as a final product, so that the grains are classified, and the grain size of the final product is improved. In addition, in the operation process, the feed liquid containing small particles can be led out from a circulating outlet at the upper part of the crystallization bin, and the feed liquid has the characteristics of low crystal slurry density, small solid particle size, so that the problem that crystal grains with large particle size or fallen massive scale substances enter a pipeline to be easily blocked is avoided.
The traditional OSLO crystallizer and the traditional DTB crystallizer are suitable for evaporation crystallization and are not suitable for solid-liquid reaction crystallization, in order to meet the requirements of solid-liquid continuous reaction crystallization technology, solid-liquid feeding and solid-liquid reaction, and also in order to meet continuous and large-granularity products, the structure of the crystallizer is designed, the crystallizer is designed according to the technological matching, the rapid dispersion of solids and the promotion of solid-liquid reaction are realized through upper stirring, the generated crystal nucleus is fully grown in a growth area, the small particles are returned to a supersaturation degree generation area for re-growth through a circulating pipeline, and the granularity regulation, growth and granularity grading are realized. The height of the central circulation pipe can be controlled without special control by matching with the bottom stirring effect, otherwise, the height of the central circulation pipe of the OSLO crystallizer is strictly controlled.
As a preferable technical scheme of the invention, the circulating pump is arranged on the circulating pipeline.
The suspension in the crystallization bin is settled due to sedimentation, so that the grains with large grain size are mainly concentrated in the lower layer of the crystallization bin, the upper layer of the crystallization bin is suspension or clear liquid containing small grain size, and the circulating pump pumps out part of the feed liquid from the circulating outlet and returns the feed liquid to the mixing bin for further crystal growth and circulation and reciprocation until the grains with ideal grain size are obtained.
And a delivery pump is arranged on a connecting pipeline between a discharge port of the circulating crystallization device and a circulating pipeline of the next-stage circulating crystallization device.
As a preferable technical scheme of the invention, the discharge port of the circulating crystallization device at the last stage is externally connected with a post-treatment system.
As a preferable technical scheme of the invention, a mixing device is arranged in the mixing bin, and the mixing device comprises at least two layers of stirring paddles.
In the invention, the mixing device preferably comprises two layers of stirring paddles, which is favorable for the residence time of materials in the mixing bin, ensures the uniform mixing of the materials, and under the action of mechanical stirring, a plurality of strands of feed liquids with different temperatures and concentrations are quickly, fully and efficiently mixed in the guide cylinder, so that the heat transfer and mass transfer are uniform, the supersaturation degree of the feed liquids is uniform, and the burst nucleation caused by too high local supersaturation degree is avoided. The stirring paddles in the circulating crystallization device have the function of uniformly mixing fluid, the type and the size of the stirring paddles are not particularly required and are particularly limited, and a person skilled in the art needs to select the stirring paddles with proper sizes according to the size difference of the crystallization device.
The mixing bin is internally provided with a spraying device, the spraying direction of the spraying device is opposite to the inner wall of the mixing bin, and the spraying device is used for spraying diluted mother liquor to the inner wall of the mixing bin.
According to the invention, the spraying device is arranged at the upper part of the inner cavity of the shell, the spraying device can be an annular spraying pipe, diluted mother liquor is sprayed to the inner wall of the shell at regular time through the spraying device, so that scale layers attached to the inner wall can be effectively washed, the scale formation condition of the inner wall near the steam-liquid boiling interface of the crystallizer is greatly reduced, the condition that large scale layers fall off to smash the inner parts of the crystallizer or enter an external circulation heating/cooling heat exchanger to block a pipeline is avoided, and the continuous production period is prolonged.
As a preferable technical scheme of the invention, the outer wall of the crystallization bin comprises a first cone section, a cylinder section and a second cone section which are sequentially butted from top to bottom, the small end face of the first cone section is butted with the mixing bin, the large end face of the first cone section is butted with one end of the cylinder section, and the other end of the cylinder section is butted with the large end face of the second cone section.
The large end surface outer edge of the diversion cone section is positioned at the joint of the first cone section and the mixing bin.
As a preferable technical scheme of the invention, at least two circulating inlets are symmetrically arranged at the outer wall of the mixing bin, at least two circulating outlets are symmetrically arranged at the outer wall of the first cone section, and one circulating outlet is correspondingly connected with one circulating inlet through an independent circulating pipeline.
The invention is preferably provided with two circulation outlets and two circulation inlets, the circulation outlets are connected with the corresponding circulation inlets through independent circulation pipelines, and each circulation pipeline is provided with a circulation pump; the two circulation outlets are distributed in a symmetrical structure by the central shaft of the crystallization device, and the connecting line between the two circulation outlets is perpendicular to the direction of the stirring blade.
The top of mixing bin is provided with the feed inlet, the outer wall lower part of second cone section is provided with the discharge gate.
It should be noted that, for the crystallization process requiring injection of materials in different states, the circulation inlet defined in the present invention may serve as a liquid inlet at the same time. In the first-stage circulating crystallization device, solid materials can enter through a feed inlet at the top of the shell, liquid materials enter through a circulating inlet, and a liquid inlet pipe can be independently connected into the shell or connected into a circulating pipeline.
The material inflow mode of the circulating crystallization device of each stage is two types: firstly, a discharge hole of a previous-stage circulating crystallization device is connected with a circulating pipeline of a next-stage circulating crystallization device, suspension liquid (comprising grains with large grain diameter) discharged by the previous-stage circulating crystallization device is introduced into the circulating pipeline of the next-stage circulating crystallization device, and mixed with crystal slurry circulating by the next-stage circulating crystallization device and then introduced into a mixing bin; secondly, the suspension discharged from the discharge port of the upper-stage circulating crystallization device is connected to the feed port of the lower-stage circulating crystallization device, the suspension (comprising large-grain-size grains) discharged from the upper-stage circulating crystallization device is introduced into the mixing bin through the feed port of the lower-stage circulating crystallization device, and the suspension discharged from the upper-stage circulating crystallization device and the crystal slurry circulated by the lower-stage circulating crystallization device are mixed in the mixing bin.
As a preferred technical scheme of the invention, the diameter of the cylinder body of the mixing bin is smaller than that of the cylinder section.
The height of the cylinder body of the mixing bin is larger than or equal to the diameter of the cylinder body of the mixing bin.
The height of the first cone section is smaller than the height of the cylinder section.
In a preferred embodiment of the present invention, the diameter of the cylinder of the mixing chamber is 0.6 to 0.8 times the diameter of the cylinder section, and may be, for example, 0.6 times, 0.62 times, 0.64 times, 0.66 times, 0.68 times, 0.7 times, 0.72 times, 0.74 times, 0.76 times, 0.78 times, or 0.8 times, but the present invention is not limited to the above-mentioned values, and other values not mentioned in the above-mentioned numerical ranges are equally applicable.
The diameter of the cylinder of the mixing chamber is 1.2 to 3.5 times the height of the cylinder of the mixing chamber, and may be, for example, 1.2 times, 1.4 times, 1.6 times, 1.8 times, 2.0 times, 2.2 times, 2.4 times, 2.6 times, 2.8 times, 3.0 times, 3.2 times, 3.4 times, or 3.5 times, but is not limited to the recited values, and other non-recited values within the range of values are equally applicable.
The invention specially designs part of size parameters in the circulating crystallization device, has unique crystallizer configuration and flow operation, and can solve the problems of small product particle size, serious scaling on the inner wall of the crystallizer, pipeline blockage, short operation period and the like in the continuous crystallization process. The diameter of the cylinder body of the mixing bin is 1.2-3.5 times of the height of the cylinder body of the mixing bin, the diameter of the cylinder body is increased, the evaporation area can be increased, the boiling strength of the unit area is reduced, the splashing condition of materials is lightened, and the material entrainment caused by the boiling of the material liquid in the evaporation crystallization process is reduced to cause the material scaling on the inner wall of the crystallizer near the gas-liquid interface.
The height of the first taper section is 0.6 to 0.8 times the height of the cylindrical section, and may be, for example, 0.6 times, 0.62 times, 0.64 times, 0.66 times, 0.68 times, 0.7 times, 0.72 times, 0.74 times, 0.76 times, 0.78 times, or 0.8 times, but is not limited to the recited values, and other non-recited values within the range of values are equally applicable.
The diameter of the cylindrical section is 4 to 10 times, for example, 4 times, 5 times, 6 times, 7 times, 8 times, 9 times or 10 times, the diameter of the guide pipe section, but the present invention is not limited to the recited values, and other values not recited in the range of the recited values are equally applicable.
The length of the guide pipe section is 1/3 to 2/3 of the total height of the crystallization bin, for example, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6 or 0.65, but the guide pipe section is not limited to the listed values, and other non-listed values in the range of the values are equally applicable.
As a preferred embodiment of the present invention, the guide cone section is arranged coaxially with the guide tube section.
The diameter of the large end face of the guide cone section is 4 to 10 times the diameter of the guide cone section, and may be, for example, 4 times, 5 times, 6 times, 7 times, 8 times, 9 times or 10 times, but is not limited to the recited values, and other values not recited in the numerical range are equally applicable.
As a preferable technical scheme of the invention, the shell further comprises a bottom bin which is in butt joint with the small end face of the second cone section, and the stirring device is positioned in the bottom bin.
The periphery of the stirring device is sleeved with a guide cylinder.
According to the invention, the guide cylinder is sleeved on the periphery of the stirring device, so that the suspension liquid in the crystallization bin moves downwards in the guide cylinder, and the outside of the guide cylinder moves upwards, thereby realizing uniform mixing of crystal slurry.
The system refers to an equipment system, a device system or a production device.
Illustratively, the cyclic crystallization device provided by the invention is used for carrying out the crystallization reaction of sodium bicarbonate, and the crystallization process specifically comprises the following steps:
(1) Under normal temperature, chemical fertilizer solid containing ammonium bicarbonate enters from a feed inlet at the top of a shell, liquid brine containing sodium chloride enters into a mixing bin tangentially through a circulating inlet (a liquid inlet), the mixing device is used for mechanically stirring and mixing, the stirring rotating speed is preferably 20-100 rpm, sodium bicarbonate produced by the mixing reaction of sodium chloride and ammonium bicarbonate in the brine enters into a crystallization bin downwards along a funnel-shaped flow guide structure under the action of the mixing device and self gravity;
(2) After entering a crystallizer bin, under the upward acting force of a bottom stirring device, sodium bicarbonate crystal slurry is upwards along the inner wall of the crystallizer bin, a circulation loop is formed at the periphery of a straight pipe section of a flow guide structure to reach a fluidization state, sodium bicarbonate crystal grains with large grain size are settled under the action of gravity, and sodium bicarbonate crystal grains with small grain size are suspended at the upper layer of the crystallizer bin, so that the automatic circulation of crystal slurry in the crystallization bin body and the grain size grading of grains are realized, and finally, the sodium bicarbonate crystal grains with large grain size are gathered at the middle lower layer of the crystallizer bin;
(3) The sodium bicarbonate crystal grains with small grain size are returned to the mixing bin through the circulating pump in the suspension process by the circulating pipeline, at the moment, along with the continuous feeding of the brine raw material from the circulating inlet (liquid inlet), the circulating sodium bicarbonate crystal grains with small grain size and the new brine raw material are combined and then fed tangentially by the circulating inlet, the process is repeated, and the sodium bicarbonate crystal grains with small grain size are subjected to circulating crystal growth;
(4) And (3) collecting large-particle sodium bicarbonate crystal grains to the bottom of a crystallization bin, discharging the large-particle sodium bicarbonate crystal grains from a discharge hole at the bottom, discharging the large-particle sodium bicarbonate crystal grains along with suspension liquid at the discharge hole to enter a next-stage circulating crystallization device, performing the operation steps of steps (1) - (4) in the next-stage circulating crystallization device, performing multistage continuous crystallization, performing evaporation crystallization, solution crystallization, cooling crystallization or reaction crystallization, completing the multistage continuous crystallization process, and performing solid-liquid separation on discharge liquid of the final-stage circulating crystallization device to obtain a crystal grain product.
It should be noted that, the multistage circulation crystallization system device provided by the invention is suitable for multistage crystallization operations such as evaporative crystallization, dialysis crystallization, cooling crystallization or reaction crystallization, but specific operation process conditions need to be adjusted by a person skilled in the art based on different crystallization modes, and the invention is not particularly required and limited, for example: the operation pressure and temperature of each stage of crystallizer for reduced pressure evaporation crystallization are gradually reduced, and the reaction crystallization/solvency crystallization is gradually increased by adding reaction materials or solvency agent materials into each stage of circulating crystallization device. In addition, the number of stages of the circulating crystallization device is determined by the solid content in the crystal slurry, and the solid content and the particle size of the crystal grains in the final-stage circulating crystallization device are the largest.
Compared with the prior art, the invention has the beneficial effects that:
(1) The multistage circulation crystallization system device provided by the invention not only can ensure the separation of crystallization particles with different sizes, but also has a wide application range, and is suitable for large-scale popularization.
(2) The multistage continuous crystallization method provided by the invention adopts a multistage continuous crystallization device, does not need to add an excessive sedimentation tank and a power device, is energy-saving and environment-friendly, and realizes large-scale production and application.
Drawings
FIG. 1 is a schematic diagram of a two-stage circulation crystallization system according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a four-stage circulation crystallization system according to an embodiment of the present invention;
FIG. 3 is a schematic structural diagram of a cyclic crystallization device according to an embodiment of the present invention;
wherein, 1-a feed inlet; 2-a mixing device; 3-a first recycle inlet; 4-a first recycle outlet; 5-a discharge hole; 6-stirring device; 7-a second recycle inlet; 8-a mixing bin; 9-a second recycle outlet; 10-crystallizing bin; 11-a flow guiding structure; 12-a guide cylinder; 13-a bottom bin; 14-a cyclic crystallization device; 15-a circulation pump; 16-a transfer pump;
FIG. 4 is a schematic view showing the crystal distribution of the cyclic crystallization device according to an embodiment of the present invention;
FIG. 5 is a scanning electron microscope image of a product prepared by a multistage continuous crystallization method according to an embodiment of the present invention.
Detailed Description
It is to be understood that in the description of the present invention, the terms "center", "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. indicate orientations or positional relationships based on the drawings, are merely for convenience in describing the present invention and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and thus are not to be construed as limiting the present invention. Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first", "a second", etc. may explicitly or implicitly include one or more such feature. In the description of the present invention, unless otherwise indicated, the meaning of "a plurality" is two or more.
It should be noted that, in the description of the present invention, unless explicitly specified and limited otherwise, the terms "disposed," "connected," and "connected" are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. The specific meaning of the above terms in the present invention can be understood by those of ordinary skill in the art in a specific case.
It will be appreciated by those skilled in the art that the present invention necessarily includes the necessary piping, conventional valves and general pumping equipment for achieving process integrity, but the foregoing is not a major innovation of the present invention, and that the present invention is not particularly limited thereto as the layout may be added by themselves based on the process flow and the equipment configuration options.
The technical scheme of the invention is further described below by the specific embodiments with reference to the accompanying drawings.
In one embodiment, the present invention provides a multi-stage circulating crystallization system apparatus, as shown in fig. 1 and 2, comprising at least two circulating crystallization apparatuses 14 of identical structure connected in series in sequence;
as shown in fig. 3, the circulation crystallization device 14 includes a housing, a funnel-shaped flow guiding structure 11 is disposed in the housing, the flow guiding structure 11 includes a flow guiding cone section and a flow guiding pipe section that are sequentially butted from top to bottom, and a large end surface edge of the flow guiding cone section is butted with an inner wall of the housing in a circumferential direction;
the shell cavity above the diversion cone section forms a mixing bin 8, the shell cavity at the periphery of the diversion cone section forms a crystallization bin 10, the bottom of the inner cavity of the shell is provided with a stirring device 6, the outer wall of the mixing bin 8 is provided with a feed inlet 1 and at least one circulation inlet, the upper part of the outer wall of the crystallization bin 10 is provided with at least one circulation outlet, the circulation inlet and the circulation outlet are communicated through an external circulation pipeline, the bottom of the outer wall of the crystallization bin 10 is provided with a discharge hole 5, and the discharge hole 5 is connected into a circulation pipeline of a next-stage circulation crystallization device 14 or the feed inlet 1 of the next-stage circulation crystallization device 14;
fig. 4 is a schematic crystal distribution diagram of a circulation crystallization device according to an embodiment of the present invention, as shown in fig. 4, after the feed liquid is introduced into the mixing bin 8, mixed and enters the crystallization bin 10 along the guiding structure 11 for crystallization, under the action of the stirring device 6, small-grain-size grains form a rotational flow in the crystallization bin 10, and return to the mixing bin 8 through the circulation pipeline for circulation crystallization, and after the large-grain-size grains settle, the grains enter the next-stage circulation crystallization device 14 through the discharge port 5 for multistage continuous crystallization.
The invention can realize multistage continuous crystallization by sequentially connecting a plurality of circulating crystallization devices 14 in series, is suitable for evaporative crystallization, solvent-out crystallization, cooling crystallization and reactive crystallization, and can be provided with a heating/cooling heat exchanger outside each stage of crystallizer according to the crystallization mode to provide heat/cold energy input required in the crystallization process. In the multistage continuous crystallization process, the solid suspension amount of each stage of crystallization process needs to be controlled, taking a four-stage crystallization process as an example, the feed of the first-stage circulating crystallization device 14 is unsaturated crystallization feed liquid or reaction liquid, the solid suspension amount in the first-stage circulating crystallization device 14 is controlled to be 2% -10%, the solid suspension amount in the second-stage circulating crystallization device 14 is controlled to be 10% -20%, the solid suspension amount in the third-stage circulating crystallization device 14 is controlled to be 20% -30%, and the solid suspension amount in the fourth-stage circulating crystallization device 14 is controlled to be 30% -45%. The multistage circulation crystallization system device provided by the invention not only can ensure the separation of crystallization particles with different sizes, but also has a wide application range, and is suitable for large-scale popularization.
In addition, in order to ensure that the crystal grains fully grow in each stage of crystallization process, the invention also improves the internal structure of each stage of circulating crystallization device 14, realizes the internal circulation and the particle size classification of crystal slurry in a single stage of crystallization process, and in the single stage of crystallization process, the crystal slurry enters the crystallization bin 10 along the funnel-shaped flow guide structure 11 after entering the mixing bin 8, and the crystal slurry moves upwards under the action of the wind force of the stirring device 6 and the gravity of the crystal grains by utilizing the fluidity of the crystal slurry, so that the crystal grains with small particle size form a certain circulating flow field in the crystallization bin 10 under the action of the wind force of the stirring device 6, so that the crystal grains with small particle size are suspended at the upper part of the crystallization bin 10 to form a rotational flow circulating state and do not agglomerate at the bottom; and the grains with large grain size can be settled to the bottom of the crystallization bin 10 and discharged from the discharge hole 5 to enter the feed inlet 1 of the next-stage crystallizer or discharged as a final product, thereby realizing the grading treatment of the grains and improving the grain size of the final product. In addition, in the operation process, the feed liquid containing small particles can be led out from the circulation outlet at the upper part of the crystallization bin 10, and because the feed liquid has the characteristics of low crystal slurry density, small solid particle size, the problem that crystal grains with large particle size or fallen massive scale layer substances enter a pipeline to be easily blocked is avoided, in addition, the crystallization residence time can be regulated by controlling the discharge speed of the feed liquid through the arranged circulation pipeline, the crystal grain nucleation and growth can be effectively regulated, and the crystallizer realizes the combination and innovative design of the functions of an OSLO crystallizer and a DTB crystallizer to realize crystal slurry circulation and particle size classification, thereby improving the problems of small product particle size, serious equipment scaling, short operation period and the like in the continuous crystallization process, avoiding the addition of redundant sedimentation storage tanks and power setting, saving energy, protecting the environment, realizing large-scale production in a serial connection mode, improving the stable operation period in the continuous crystallization process and ensuring the product quality.
Further, a circulation pump 15 is provided on the circulation line.
Since the suspension in the crystallization bin 10 is precipitated by sedimentation, the large-sized grains are mainly concentrated in the lower layer of the crystallization bin 10, the upper layer of the crystallization bin 10 is suspension or clear liquid containing small particle size, and the circulating pump 15 pumps out the part of the feed liquid from the circulating outlet and returns the feed liquid to the mixing bin 8, so that further crystals grow and circulate until the grains with the desired particle size are obtained.
A delivery pump 16 is arranged on a connecting pipeline between the discharge port 5 of the circulating crystallization device 14 and a circulating pipeline of the next-stage circulating crystallization device 14.
Further, the discharge port 5 of the last-stage circulating crystallization device 14 is externally connected with a post-treatment system.
Further, a mixing device 2 is arranged in the mixing bin 8, and the mixing device 2 comprises at least two layers of stirring paddles.
In the invention, the mixing device 2 preferably comprises two layers of stirring paddles, which is favorable for the residence time of materials in the mixing bin 8, ensures uniform mixing of the materials, and ensures that a plurality of strands of feed liquids with different temperatures and concentrations are quickly, sufficiently and efficiently mixed in the guide cylinder 12 under the action of mechanical stirring, so that the heat transfer and mass transfer are uniform, the supersaturation degree of the feed liquids is uniform, and the explosion nucleation caused by too high local supersaturation degree is avoided. The purpose of the stirring paddles in the circulation crystallizer 14 is to achieve uniform mixing of the fluid, and the invention is not limited to specific requirements and sizes of the stirring paddles, and one skilled in the art needs to select a stirring paddle of a suitable size according to the size difference of the crystallizer.
The mixing bin 8 is internally provided with a spraying device, the spraying direction of the spraying device is opposite to the inner wall of the mixing bin 8, and the spraying device is used for spraying diluted mother liquor to the inner wall of the mixing bin 8.
According to the invention, the spraying device is arranged at the upper part of the inner cavity of the shell, the spraying device can be an annular spraying pipe, diluted mother liquor is sprayed to the inner wall of the shell at regular time through the spraying device, so that scale layers attached to the inner wall can be effectively washed, the scale formation condition of the inner wall near the steam-liquid boiling interface of the crystallizer is greatly reduced, the condition that large scale layers fall off to smash the inner parts of the crystallizer or enter an external circulation heating/cooling heat exchanger to block a pipeline is avoided, and the continuous production period is prolonged.
Further, the outer wall of the crystallization bin 10 comprises a first cone section, a cylinder section and a second cone section which are sequentially butted from top to bottom, the small end face of the first cone section is butted with the mixing bin 8, the large end face of the first cone section is butted with one end of the cylinder section, and the other end of the cylinder section is butted with the large end face of the second cone section.
The large end surface outer edge of the diversion cone section is positioned at the joint of the first cone section and the mixing bin 8.
Further, at least two circulation inlets are symmetrically arranged at the outer wall of the mixing bin 8, at least two circulation outlets are symmetrically arranged at the outer wall of the first cone section, and one circulation outlet is correspondingly connected with one circulation inlet through an independent circulation pipeline.
The invention preferably provides two circulation outlets (shown in figure 1 as a first circulation outlet 4 and a second circulation outlet 9 respectively) and two circulation inlets (shown in figure 1 as a first circulation inlet 3 and a second circulation inlet 7 respectively), the circulation outlets are connected into the corresponding circulation inlets through independent circulation pipelines, and each circulation pipeline is provided with a circulation pump 15; the two circulation outlets are distributed in a symmetrical structure by the central shaft of the crystallization device, and the connecting line between the two circulation outlets is perpendicular to the direction of the stirring blade.
The top of the mixing bin 8 is provided with the feed inlet 1, and the lower part of the outer wall of the second cone section is provided with the discharge outlet 5.
It should be noted that, for the crystallization process requiring injection of materials in different states, the circulation inlet defined in the present invention may serve as a liquid inlet at the same time. In the first-stage circulation crystallization device 14, solid materials can enter through a feed inlet 1 at the top of the shell, liquid materials enter through a circulation inlet, and a liquid inlet pipe can be independently connected into the shell or connected into a circulation pipeline.
The material flowing-in modes of the circulating crystallization device 14 of each stage are two types: firstly, a discharge hole 5 of a previous-stage circulating crystallization device 14 is connected into a circulating pipeline of a next-stage circulating crystallization device 14, suspension liquid (comprising large-grain-size grains) discharged by the previous-stage circulating crystallization device 14 is introduced into the circulating pipeline of the next-stage circulating crystallization device 14, and is mixed with crystal slurry circulating by the next-stage circulating crystallization device 14 and then introduced into a mixing bin 8; secondly, the suspension discharged from the discharge port 5 of the upper-stage circulating crystallization device 14 is connected to the feed port 1 of the lower-stage circulating crystallization device 14, the suspension (comprising large-grain-size grains) discharged from the upper-stage circulating crystallization device 14 is introduced into the mixing bin 8 from the feed port 1 of the lower-stage circulating crystallization device 14, and the suspension discharged from the upper-stage circulating crystallization device 14 and the crystal slurry circulated by the lower-stage circulating crystallization device 14 are mixed in the mixing bin 8.
Further, the diameter of the cylinder body of the mixing bin 8 is smaller than that of the cylinder section.
The height of the cylinder body of the mixing bin 8 is larger than or equal to the diameter of the cylinder body of the mixing bin 8.
The height of the first cone section is smaller than the height of the cylinder section.
Further, the diameter of the cylinder body of the mixing bin 8 is 0.6-0.8 times of the diameter of the cylinder body of the cylinder section. The diameter of the cylinder body of the mixing bin 8 is 1.2-3.5 times of the height of the cylinder body of the mixing bin 8.
The invention specially designs part of size parameters in the circulating crystallization device 14, has unique crystallizer configuration and flow operation, and can solve the problems of small product particle size, serious scale formation on the inner wall of the crystallizer, pipeline blockage, short operation period and the like in the continuous crystallization process. The diameter of the cylinder body of the mixing bin 8 is 1.2-3.5 times of the height of the cylinder body of the mixing bin 8, the diameter of the cylinder body is increased, the evaporation area can be increased, the boiling strength of unit area is reduced, the splashing condition of materials is lightened, and the material entrainment caused by the boiling of feed liquid in the evaporation crystallization process is reduced to cause the material scaling on the inner wall of the crystallizer near the gas-liquid interface.
The height of the first cone section is 0.6-0.8 times of the height of the cylinder section. The diameter of the cylinder section is 4-10 times of the diameter of the guide pipe section. The length of the guide pipe section is 1/3-2/3 of the total height of the crystallization bin 10.
Further, the guide cone section and the guide pipe section are coaxially arranged. The diameter of the large end face of the guide cone section is 4-10 times of the diameter of the guide cone section.
Further, the shell further comprises a bottom bin 13 which is in butt joint with the small end face of the second cone section, and the stirring device 6 is positioned in the bottom bin 13.
The periphery of the stirring device 6 is sleeved with a guide cylinder 12.
According to the invention, the guide cylinder 12 is sleeved on the periphery of the stirring device 6, so that the suspension in the crystallization bin 10 moves downwards in the guide cylinder 12, and the guide cylinder 12 moves upwards outwards, thereby realizing uniform mixing of crystal slurry.
In another embodiment, the circulating crystallization device 14 provided by the invention is used for carrying out the crystallization reaction of sodium bicarbonate, and the crystallization process specifically comprises the following steps:
(1) Under normal temperature, chemical fertilizer solid containing ammonium bicarbonate enters from a feed inlet 1 at the top of a shell, brine containing sodium chloride enters a mixing bin 8 tangentially through a circulating inlet (liquid inlet), the mixing device 2 is used for mechanically stirring and mixing, the stirring rotation speed is preferably 20-100 rpm, sodium bicarbonate produced by the mixing reaction of sodium chloride and ammonium bicarbonate in the brine enters a crystallization bin 10 downwards along a funnel-shaped flow guide structure 11 under the action of the mixing device 2 and self gravity;
(2) After entering a crystallizer bin, under the upward acting force of a bottom stirring device 6, sodium bicarbonate crystal slurry is upward along the inner wall of the crystallization bin 10, a circulation loop is formed at the periphery of a straight pipe section of a flow guide structure 11 to reach a fluidization state, sodium bicarbonate crystal grains with large grain size are settled under the action of gravity, and sodium bicarbonate crystal grains with small grain size are suspended at the upper layer of the crystallization bin 10, so that the automatic circulation of crystal slurry in the crystallization bin 10 and the grain size grading of grains are realized, and finally, the sodium bicarbonate crystal grains with large grain size are gathered at the middle lower layer of the crystallization bin 10;
(3) The sodium bicarbonate crystal grains with small particle size are returned to the mixing bin 8 through the circulating pump 15 in the suspension process by the circulating pipeline, at the moment, along with the continuous feeding of the brine raw material from the circulating inlet (liquid inlet), the circulating sodium bicarbonate crystal grains with small particle size are mixed with the new brine raw material and then fed tangentially by the circulating inlet, the process is repeated, and the sodium bicarbonate crystal grains with small particle size are subjected to circulating crystal growth;
(4) And (3) collecting large-particle sodium bicarbonate crystal grains to the bottom of the crystallization bin 10, discharging the large-particle sodium bicarbonate crystal grains from a discharge hole 5 at the bottom, discharging the large-particle sodium bicarbonate crystal grains from the discharge hole 5 along with suspension liquid to enter a next-stage circulating crystallization device 14, performing the operation steps of steps (1) - (4) on the next-stage circulating crystallization device 14, performing multistage continuous crystallization, performing evaporative crystallization, solution crystallization, cooling crystallization or reaction crystallization, completing the multistage continuous crystallization process, and performing solid-liquid separation on the discharged material liquid of the final-stage circulating crystallization device 14 to obtain a crystal grain product.
Fig. 5 is a scanning electron microscope image of the baking soda product prepared by the multistage continuous crystallization method, and as can be seen from fig. 5, the obtained product has larger particle size.
It should be noted that, the multistage circulation crystallization system device provided by the invention is suitable for multistage crystallization operations such as evaporative crystallization, dialysis crystallization, cooling crystallization or reaction crystallization, but specific operation process conditions need to be adjusted by a person skilled in the art based on different crystallization modes, and the invention is not particularly required and limited, for example: the operating pressure and temperature of the crystallizer at each stage of reduced pressure evaporative crystallization are gradually reduced, and the reaction crystallization/solvency crystallization is gradually increased by adding the reaction material or the solvency agent material into the circulating crystallization device 14 at each stage. In addition, the number of stages of the circulation crystallization device 14 is determined by the solid content in the crystal slurry, and the solid content and the grain size of the grains in the final circulation crystallization device 14 are maximized.
The applicant declares that the above is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be apparent to those skilled in the art that any changes or substitutions that are easily conceivable within the technical scope of the present invention disclosed by the present invention fall within the scope of the present invention and the disclosure.
Claims (11)
1. A multistage continuous crystallization method, which is characterized in that the multistage continuous crystallization method is realized by a multistage circulation crystallization system device; the multistage circulating crystallization system device comprises at least two circulating crystallization devices which are sequentially connected in series;
the circulating crystallization device comprises a shell, wherein a guide structure of a funnel structure is arranged in the shell, the guide structure comprises a guide cone section and a guide tube section which are sequentially butted from top to bottom, and the edge of the large end face of the guide cone section is butted with the inner wall of the shell in the circumferential direction;
the shell cavity above the diversion cone section forms a mixing bin, the shell cavity at the periphery of the diversion cone section forms a crystallization bin, the bottom of the inner cavity of the shell is provided with a stirring device, the outer wall of the mixing bin is provided with a feed inlet and at least one circulation inlet, the upper part of the outer wall of the crystallization bin is provided with at least one circulation outlet, the circulation inlet and the circulation outlet are communicated through an external circulation pipeline, the bottom of the outer wall of the crystallization bin is provided with a discharge outlet, and the discharge outlet is connected with the circulation pipeline of the next-stage circulation crystallization device or the feed inlet of the next-stage circulation crystallization device;
the feed liquid is introduced into the mixing bin, mixed and enters the crystallization bin for crystallization along the flow guiding structure, small-grain-size grains form rotational flow in the crystallization bin under the action of the stirring device, the rotational flow returns to the mixing bin for cyclic crystallization through the circulating pipeline, and large-grain-size grains are deposited and enter the next-stage cyclic crystallization device through the discharge hole for multistage continuous crystallization;
a mixing device is arranged in the mixing bin, and the mixing device comprises at least two layers of stirring paddles;
the outer wall of the crystallization bin comprises a first cone section, a cylinder section and a second cone section which are sequentially butted from top to bottom, the small end face of the first cone section is butted with the mixing bin, the large end face of the first cone section is butted with one end of the cylinder section, and the other end of the cylinder section is butted with the large end face of the second cone section;
the outer edge of the large end surface of the diversion cone section is positioned at the joint of the first cone section and the mixing bin;
the diameter of the cylinder body of the mixing bin is smaller than that of the cylinder section; the height of the cylinder body of the mixing bin is larger than or equal to the diameter of the cylinder body of the mixing bin; the height of the first cone section is smaller than that of the cylinder section;
the shell also comprises a bottom bin which is in butt joint with the small end face of the second cone section, and the stirring device is positioned in the bottom bin; the periphery of the stirring device is sleeved with a guide cylinder.
2. The multistage continuous crystallization method according to claim 1, wherein a circulation pump is provided on the circulation line;
and a delivery pump is arranged on a connecting pipeline between a discharge port of the circulating crystallization device and a circulating pipeline of the next-stage circulating crystallization device.
3. The multistage continuous crystallization method according to claim 1, wherein the discharge port of the circulating crystallization apparatus of the last stage is externally connected with a post-treatment system.
4. The multistage continuous crystallization method according to claim 1, wherein a spraying device is further arranged in the mixing bin, the spraying direction of the spraying device is opposite to the inner wall of the mixing bin, and the spraying device is used for spraying diluted mother liquor to the inner wall of the mixing bin.
5. The multistage continuous crystallization method according to claim 1, wherein at least two circulation inlets are symmetrically arranged at the outer wall of the mixing bin, at least two circulation outlets are symmetrically arranged at the outer wall of the first cone section, and one circulation outlet is correspondingly connected with one circulation inlet through an independent circulation pipeline;
the top of mixing bin is provided with the feed inlet, the outer wall lower part of second cone section is provided with the discharge gate.
6. The multistage continuous crystallization method according to claim 1, wherein the cylinder diameter of the mixing bin is 0.6 to 0.8 times the cylinder diameter of the cylinder section; the diameter of the cylinder body of the mixing bin is 1.2-3.5 times of the height of the cylinder body of the mixing bin; the height of the first cone section is 0.6-0.8 times of the height of the cylinder section; the diameter of the cylinder section is 4-10 times of the diameter of the guide pipe section; the length of the guide pipe section is 1/3-2/3 of the total height of the crystallization bin.
7. The multistage continuous crystallization method according to claim 1, wherein the guide cone section is disposed coaxially with the guide tube section; the diameter of the large end face of the guide cone section is 4-10 times of the diameter of the guide cone section.
8. The multistage continuous crystallization method according to claim 1, wherein the multistage cyclic crystallization method is applicable to any one of evaporative crystallization, solvent-out crystallization, cooling crystallization or reactive crystallization.
9. The multistage continuous crystallization method according to claim 1, wherein the number of stages of the multistage continuous crystallization is 2 to 6 stages.
10. The multistage continuous crystallization method according to claim 1, wherein the number of stages of the multistage continuous crystallization is four, the feed of the first-stage circulating crystallization device is unsaturated crystallization feed liquid or reaction liquid, the solid suspension amount in the first-stage circulating crystallization device is controlled to be 2% -10%, the solid suspension amount in the second-stage circulating crystallization device is controlled to be 10% -20%, the solid suspension amount in the third-stage circulating crystallization device is controlled to be 20% -30%, and the solid suspension amount in the fourth-stage circulating crystallization device is controlled to be 30% -45%.
11. The multistage continuous crystallization method according to claim 1, wherein the multistage continuous crystallization method is suitable for the preparation of baking soda crystals.
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