Device and process for preparing large-particle ammonium sulfate crystals through reduced-speed crystallization

Abstract

The invention relates to the field of chemical application, and discloses a device for preparing large-particle ammonium sulfate crystals through reduced-speed crystallization. Comprising a neutralization reactor, a settling separation tank, a pre-crystallization solution tank, a first-stage intermittent jacket crystallizer, a second-stage intermittent jacket crystallizer, a filter powder sieving device, an ammoximation tert-butyl alcohol tower reboiler, a heat exchanger group, a stirrer group and a centrifugal pump group, wherein the centrifugal pump group consists of a centrifugal pump I, a centrifugal pump II, a centrifugal pump III, a centrifugal pump IV and a centrifugal pump V; the invention further discloses a process for preparing the large-particle ammonium sulfate crystals through speed-reducing crystallization. The process comprises the following steps: adding rearrangement liquid from a caprolactam rearrangement system and gas ammonia into the neutralization reactor through an external circulation pipeline. By fully utilizing heat in a neutralization reaction and crystallization process and combining with a compound additive, a seed crystal and a speed reduction crystallization technology, an efficient two-stage series crystallization mode is realized, the generation of large-particle ammonium sulfate crystals is promoted, the crystal quality is optimized, the energy consumption is reduced and the production efficiency is improved.

Description

Technical Field

[0001] The invention relates to the field of chemical application, and in particular to a device and a process for preparing large-particle ammonium sulfate crystals by speed reduction crystallization. Background Art

[0002] Caprolactam is a widely used organic compound, mainly used to manufacture chemical industrial products such as polymer compounds, coatings, paints, and plastics. In the traditional method for preparing caprolactam, the hydrolysis oximation method is usually used, but this method has problems such as low yield, generation of hazardous waste, and high cost, which makes it difficult to meet the needs of modern industry. In recent years, the ammoximation process has been widely used as a new type of cyclohexanone oxime production process. This process uses hydrogen peroxide, liquid ammonia and cyclohexanone as raw materials, directly generates cyclohexanone oxime through a one-step reaction, and then generates caprolactam through the action of fuming sulfuric acid. Compared with the traditional process, the ammoximation process has the advantages of short production process, simple control, general equipment requirements, and low three waste emissions. At present, there are many sets of devices used in industrial production in China.

[0003] In the production process of caprolactam, cyclohexanone oxime undergoes Beckmann rearrangement reaction in fuming sulfuric acid to produce crude caprolactam. In the rearrangement reaction process, the by-product ammonium sulfate is inevitable. Ammonium sulfate is usually obtained by neutralizing sulfuric acid with ammonia. Most ammonium sulfate production processes are to pass the rearrangement reaction liquid into a crystallizer to complete the neutralization and evaporation crystallization process. The common ammonium sulfate crystallization equipment is a DTB type crystallizer, the main disadvantage of which is that small-particle crystals are easily entrained in large-particle crystals when discharging, resulting in the mass fraction of ammonium sulfate crystals above 2 mm usually not exceeding 5%. However, large-particle ammonium sulfate is more valuable in the market, and the selling price per ton of large-particle ammonium sulfate is about US$30-45 higher than that of small particles. In addition, the caprolactam encapsulation loss in the traditional process is usually around 0.1%, which not only affects the yield of caprolactam, but also increases the production cost.

[0004] At the same time, the utilization rate of the low-temperature and low-pressure steam generated by the DTB and the top of the crystallizer in the existing process is low, and circulating water cooling is usually used, which fails to fully utilize the reaction heat in the crystallization process. This further increases energy consumption and reduces the economic efficiency of the process.

[0005] In summary, the process of ammonium sulfate crystallization in the prior art has the problems of small proportion of large crystal particles, insufficient energy utilization, large caprolactam encapsulation loss, etc. In view of these problems, the present invention provides a device and process for preparing large-particle ammonium sulfate crystals by reduced-speed crystallization. Summary of the invention

[0006] In view of the shortcomings of the prior art, the present invention provides a device and a process for preparing large-particle ammonium sulfate crystals by reduced-speed crystallization, which solves the problems of low yield of large-particle crystals, insufficient energy utilization and large caprolactam encapsulation loss in the existing ammonium sulfate crystallization process.

[0007] To achieve the above purpose, the present invention is implemented through the following technical scheme: a device for preparing large-particle ammonium sulfate crystals by speed reduction crystallization, comprising a neutralization reactor, a sedimentation separation tank, a pre-crystallization solution tank, a first-stage intermittent jacketed crystallizer, a second-stage intermittent jacketed crystallizer, a filter screener, an ammoximation tert-butyl alcohol tower reboiler, a heat exchanger group, an agitator group, a centrifugal pump group consisting of centrifugal pump one, centrifugal pump two, centrifugal pump three, centrifugal pump four and centrifugal pump five, a feeding port, a pipeline group and a low-pressure steam outlet group, characterized in that the bottom discharge end of the neutralization reactor is connected to the feed end of the heat exchanger group tube side through centrifugal pump one, and the discharge end of the heat exchanger group tube side is connected to the bottom of the sedimentation separation tank The bottom discharge end of the sedimentation separation tank is connected to the lower feed end of the pre-crystallization solution tank through centrifugal pump two, the bottom discharge end of the pre-crystallization solution tank is connected to the shell-side feed end of the heat exchanger group through centrifugal pump three, the shell-side discharge end of the heat exchanger group is connected to the middle and lower feed ends of the first-stage intermittent jacketed crystallizer, the first-stage jacketed crystallizer discharge port at the bottom of the first-stage intermittent jacketed crystallizer is connected to the middle and lower feed ends of the second-stage intermittent jacketed crystallizer through a filter screener, the pipeline group consists of pipeline one and pipeline two, the heat exchanger group consists of heat exchanger one, heat exchanger two and heat exchanger three, and the feeding port consists of upper feeding port one and upper feeding port two.

[0008] Preferably, the bottom discharge end of the neutralization reactor can also be directly connected to the lower feed end of the sedimentation separation tank, and the bottom discharge end of the pre-crystallization solution tank can also be directly connected to the middle and lower feed ends of the first-stage intermittent jacketed crystallizer.

[0009] Preferably, the ammonium sulfate solution in the neutralization reactor is circulated and mixed by a reactor circulation pump, the rearrangement liquid and gaseous ammonia both enter the neutralization reactor through an external circulation pipeline for reaction, the steam generated in the neutralization reactor enters the reboiler of the ammoximation tert-butanol tower through the high-pressure steam outlet, flows out from the shell outlet after exothermic condensation, and is passed into the circulating water inlet at the bottom end of the jacket of the first-level intermittent jacket crystallizer to continue to utilize the remaining heat, and at the same time, a part of the circulating water containing the remaining heat is supplemented at the circulating water replenishment port, the circulating water outlet at the top end of the jacket of the first-level intermittent jacket crystallizer is connected to the circulating water inlet at the bottom end of the jacket of the second-level intermittent jacket crystallizer, and a circulating water outlet is provided at the top end of the jacket of the second-level intermittent jacket crystallizer.

[0010] Preferably, the amide oil containing dilute ammonium sulfate in the upper layer of the neutralization reactor enters the sedimentation separator through the upper discharge port of the neutralization reactor, the caprolactam in the upper part of the sedimentation separator is recovered through pipeline 1, and the dilute ammonium sulfate solution in the lower part of the sedimentation separator is returned to the lower feed end of the neutralization reactor.

[0011] Preferably, the agitator group includes agitator 1, agitator 2, agitator 3 and agitator 4, and the agitator 1, agitator 2, agitator 3 and agitator 4 are respectively arranged at the top middle of the sedimentation separation tank, the pre-crystallization solution tank, the first intermittent jacketed crystallizer and the second intermittent jacketed crystallizer.

[0012] Preferably, the caprolactam in the upper part of the sedimentation separation tank is recovered again through pipeline 2, and the compound additive is added to the pre-crystallization solution tank through the upper feed port.

[0013] Preferably, the low-pressure steam outlet group includes a low-pressure steam outlet one and a low-pressure steam outlet two, and the low-pressure steam outlet one and the low-pressure steam outlet two are respectively arranged at the top of the first-level intermittent jacket crystallizer and the second-level intermittent jacket crystallizer, and are respectively connected to the condenser shell side inlet through the automatic regulating valve one and the automatic regulating valve two in the automatic regulating valve group, and the condenser shell side outlet is respectively connected to the condensate tank and the vacuum condensing unit, and the vacuum condensing unit discharges non-condensable gas through the exhaust pipe, and a part of the condensate in the condensate tank is used for replenishing the dissolved water in the second-level intermittent jacket crystallizer through the centrifugal pump four.

[0014] Preferably, a first-stage intermittent jacketed crystallizer discharge port is provided at the bottom of the first-stage intermittent jacketed crystallizer, and the ammonium sulfate crystals and mother liquor produced therein are filtered through a filter screener, and the crystals larger than 1.43 mm produced flow out through a connecting pipe, and the small-particle crystals and ammonium sulfate mother liquor continue to enter the second-stage intermittent jacketed crystallizer, and the feeding port includes a seed upper feeding port 1 and a seed upper feeding port 2, and the seed upper feeding port 1 and the seed upper feeding port 2 are respectively arranged on the upper parts of the first-stage intermittent jacketed crystallizer and the second-stage intermittent jacketed crystallizer.

[0015] Preferably, the discharge port of the secondary jacketed crystallizer is connected to a centrifuge, and the ammonium sulfate crystal particles at one end of the centrifuge discharge and the connecting pipeline are dried in a dryer to produce ammonium sulfate crystals that are discharged through a discharge pipe, and the other end of the centrifuge discharge is connected to a mother liquor tank, and the discharge end of the mother liquor tank is connected to a centrifugal pump five, and the centrifugal pump five is connected to the lower feed end of the pre-crystallization solution tank.

[0016] A process for preparing large-particle ammonium sulfate crystals by slowing down crystallization is prepared by using the above-mentioned device for preparing large-particle ammonium sulfate crystals by slowing down crystallization, comprising the following steps:

[0017] S1. The rearrangement liquid and gaseous ammonia from the caprolactam rearrangement system are added to the neutralization reactor through an external circulation pipeline. The solution in the reactor absorbs the heat released by the neutralization reaction and the dissolution of ammonia, and part of the water is vaporized. The pressure in the neutralization reactor is 110-120 kPa, the liquid phase temperature is 110-115°C, and the gas phase temperature is 100-110°C. The generated steam is used by the ammoximation device;

[0018] S2, the upper layer of the neutralization reactor is a caprolactam solution, the middle layer is dilute ammonium sulfate, and the lower layer is concentrated ammonium sulfate. A sedimentation separator is provided outside the neutralization reactor. The amide oil containing dilute ammonium sulfate in the upper layer enters the sedimentation separator through the upper discharge port of the neutralization reactor. The caprolactam in the upper part of the sedimentation separator is recovered through a pipeline, and the dilute ammonium sulfate solution at the bottom of the sedimentation separator is returned to the lower feed end of the neutralization reactor;

[0019] S3, the ammonium sulfate solution after the primary separation of amide oil is added with desalted water in a sedimentation separation tank to completely dissolve, releasing the caprolactam wrapped by the ammonium sulfate crystals, and the caprolactam in the upper part of the sedimentation separation tank is recovered again through a pipeline;

[0020] S4. After the secondary separation of amide oil, the ammonium sulfate solution is added with a compound additive in a pre-crystallization solution tank, wherein the mass fraction of manganese sulfate in the solution is 1.0% to 1.1%, and the mass fraction of ammonium sulfate in the solution is 0.70% to 0.75%;

[0021] S5. The operating conditions of the first and second intermittent jacket crystallizers are the same. After being preheated by the heat exchanger, the ammonium sulfate solution containing the compound additive enters the first intermittent jacket crystallizer. When the ammonium sulfate solution is close to saturation, seed crystals are added. The seed crystal particle size is 0.2-0.5mm, and the amount used accounts for 0.65% to 0.85% of the mass fraction of ammonium sulfate in the crystallizer;

[0022] S6, the solution pH is controlled at 5.0-5.2, the temperature is maintained at 60-62°C, the absolute pressure is maintained at 15-18kPa, and the mass fraction of water evaporation per hour in the crystallizer to the total ammonium sulfate in the crystallizer is 4.0% to 4.1%;

[0023] S7, the entire speed reduction crystallization program is from 700-750r / min to adding seed crystals, then the speed is reduced to 650-700r / min after 40min, then the speed is reduced to 600-650r / min after 40min, then the speed is reduced to 550-600r / min after 40min, then the speed is reduced to 500-550r / min after 40min, then the speed is reduced to 450-500r / min after 80min, then the crystallization is stopped and the material is discharged after 60min, and the crystallization time is 5h;

[0024] S8. The ammonium sulfate crystals and mother liquor produced at the discharge port of the first-stage intermittent jacket crystallizer are filtered through a filter screener, and crystals larger than 1.43 mm are sent to a dryer for drying from the solid phase discharge port, and small particle crystals and ammonium sulfate mother liquor continue to enter the second-stage intermittent jacket crystallizer from the liquid phase discharge port, and desalted water is added to make the ammonium sulfate mother liquor close to saturation. The operating conditions of the second-stage intermittent jacket crystallizer are the same as those of the first-stage intermittent jacket crystallizer;

[0025] S9. The material at the outlet of the secondary intermittent jacketed crystallizer is separated from the mother liquid by a centrifuge and the crystal particles enter the dryer for drying.

[0026] The present invention provides a device and process for preparing large-particle ammonium sulfate crystals by slowing down crystallization. It has the following beneficial effects:

[0027] 1. The present invention fully utilizes the heat of dissolution of gaseous ammonia and the heat of neutralization of the neutralization reaction of sulfuric acid and ammonia through the neutralization reactor, and uses the generated high-pressure steam externally. The energy of the device is reasonably and effectively utilized, and through the secondary separation effect of the sedimentation separator and the sedimentation separation tank, the ammonium sulfate solution and the amide oil are efficiently separated while reducing the packaging loss of caprolactam.

[0028] 2. The present invention promotes the growth of large-particle ammonium sulfate crystals and effectively regulates the crystal structure of the crystals by adding compound additives such as manganese sulfate and ammonium sulfamate. The addition of seed crystals reduces the supersaturation of the solution, avoids explosive nucleation, and allows newly precipitated ammonium sulfate particles to grow in an orderly manner on the surface of the seed crystals, thereby controlling the number of crystals while making full use of fine crystals, thereby improving the efficiency and quality of crystal growth.

[0029] 3. The present invention uses the high-speed circulation of the stirring paddle to make the seed crystal circulate along the sleeve in the crystallizer. The early high-speed circulation is conducive to the rapid growth of small-particle seed crystals. However, as the crystals grow and the water evaporates, the movement space of the crystals gradually decreases, and the collision between the crystals and the wall and each other intensifies, which hinders the continued growth of the crystals. Therefore, the deceleration crystallization procedure can effectively alleviate this negative impact and ensure more stable crystal growth.

[0030] 4. The present invention adopts an intermittent crystallization operation mode, combined with compound additives, seed crystals and reduced-speed vacuum evaporation crystallization technology, so that the prepared ammonium sulfate large-particle crystals are full, uniform in shape, high in hardness, and have excellent crystal form. At the same time, the two-stage series crystallization mode further increases the proportion of large-particle crystals, shortens the operation time, saves energy consumption, and optimizes process efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a three-dimensional diagram of the device of the present invention;

[0032] Figure 2Flow chart of the method of the present invention.

[0033] Among them, 1. Neutralization reactor; 2. Sedimentation separation tank; 3. Pre-crystallization solution tank; 4. Primary intermittent jacketed crystallizer; 5. Secondary intermittent jacketed crystallizer; 6. Sedimentation separator; 7. Filter screen; 8. Centrifuge; 9. Dryer; 10. Mother liquor tank; 11. Condensate tank; 12. Ammoximation tert-butyl alcohol tower reboiler; 13. Heat exchanger group; 13-1. Heat exchanger 1; 13-2. Heat exchanger 2; 13-3. Heat exchanger 3; 14. Condenser; 15. Vacuum condensing unit; 16. Agitator group; 16-1. Agitator 1; 16-2. Agitator 2; 16-3. Agitator 3; 16-4. Agitator 4; 17. Reactor circulation pump; 18. Centrifugal pump group; 18-1. Centrifugal pump 1; 18-2. Centrifugal pump 2; 18-3. Centrifugal pump 4 Centrifugal pump three; 18-4, centrifugal pump four; 18-5, centrifugal pump five; 19, automatic regulating valve group; 19-1, automatic regulating valve one; 19-2, automatic regulating valve two; 20, heavy discharge liquid; 21, gas ammonia; 22, additive feed port; 23, feeding port; 23-1, upper feeding port one of seed crystal; 23-2, upper feeding port two of seed crystal; 24, circulating water replenishment port; 25, pipeline group; 25-1, pipeline one; 25-2, pipeline two; 26, high-pressure steam outlet; 27, low-pressure steam outlet group; 27-1, low-pressure steam outlet one; 27-2, low-pressure steam outlet two; 28, primary jacketed crystallizer discharge port; 29, secondary jacketed crystallizer discharge port; 30, connecting pipeline; 31, circulating water outlet; 32, exhaust pipe; 33, discharge pipe. DETAILED DESCRIPTION

[0034] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] Please see attached Figure 1The embodiment of the present invention provides a device for preparing large-particle ammonium sulfate crystals by speed reduction crystallization, comprising a neutralization reactor 1, a sedimentation separation tank 2, a pre-crystallization solution tank 3, a primary intermittent jacketed crystallizer 4, a secondary intermittent jacketed crystallizer 5, a filtering screen 7, an ammoximation tert-butyl alcohol tower reboiler 12, a heat exchanger group 13, an agitator group 16, a centrifugal pump group 18 composed of a centrifugal pump 18-1, a centrifugal pump 2 18-2, a centrifugal pump 3 18-3, a centrifugal pump 4 18-4 and a centrifugal pump 5 18-5, a feeding port 23, a pipeline group 25 and a low-pressure steam outlet group 27, characterized in that the bottom discharge end of the neutralization reactor 1 is connected to the feed end of the tube side of the heat exchanger group 13 through the centrifugal pump 18-1, and the discharge end of the tube side of the heat exchanger group 13 is connected to the lower feed end of the sedimentation separation tank 2. The bottom discharge end of the sedimentation separation tank 2 is connected to the lower feed end of the pre-crystallization solution tank 3 through the centrifugal pump 18-2, the bottom discharge end of the pre-crystallization solution tank 3 is connected to the shell feed end of the heat exchanger group 13 through the centrifugal pump 3 18-3, the shell discharge end of the heat exchanger group 13 is connected to the middle and lower feed ends of the first-stage intermittent jacketed crystallizer 4, the first-stage jacketed crystallizer discharge port 28 at the bottom of the first-stage intermittent jacketed crystallizer 4 is connected to the middle and lower feed ends of the second-stage intermittent jacketed crystallizer 5 through the filter screen 7, the pipeline group 25 consists of pipeline one 25-1 and pipeline two 25-2, the heat exchanger group 13 consists of heat exchanger one 13-1, heat exchanger two 13-2 and heat exchanger three 13-3, and the feeding port 23 consists of upper feeding port one 23-1 and upper feeding port two 23-2.

[0036] Specifically, in the present invention, the neutralization reactor 1 is responsible for neutralizing the sulfuric acid in the rearrangement liquid with the gaseous ammonia to generate an ammonium sulfate solution, and using the heat generated in the reaction to generate high-pressure steam for use by external devices, thereby reducing the demand for external energy. The bottom of the neutralization reactor 1 is used to transport the generated solution to the heat exchanger group 13 through a centrifugal pump 18-1, and the remaining heat of the solution is used to preheat the ammonium sulfate solution in the crystallizer feed, thereby improving the efficiency of the subsequent crystallization operation.

[0037] The ammonium sulfate solution after waste heat utilization enters the sedimentation separation tank 2 from the tube discharge end of the heat exchanger group 13, in which the ammonium sulfate is completely dissolved by adding desalted water, and the caprolactam therein is effectively separated, reducing the loss of caprolactam wrapping. The bottom discharge of the sedimentation separation tank 2 is transported to the pre-crystallization solution tank 3 through the centrifugal pump 2 18-2. During this process, compound additives such as manganese sulfate and ammonium aminosulfonate are added to the solution. The additives can promote the growth of ammonium sulfate crystals and optimize the crystal structure. The pre-crystallization solution tank 3 is preheated by the centrifugal pump 3 18-3 through the heat exchanger group 13, and then sent to the first-stage intermittent jacketed crystallizer 4.

[0038] In the first-stage jacketed crystallizer 4, when the solution is close to saturation, a seed crystal (upper feed port 23-1) is added through the feed port 23 to start the deceleration crystallization operation. Under the high-speed circulation of the stirring paddle, the seed crystal moves upward in the crystallizer sleeve and downward outside the sleeve in a circular high-speed motion. The early high-speed stirring is conducive to the uniform distribution and rapid growth of the seed crystal. However, as the crystals gradually grow, the water in the solution continues to evaporate, the movement space of the crystals gradually decreases, and the collisions between the crystals and the crystals with the wall increase. In order to prevent the crystals from further breaking, the stirring speed is gradually reduced to achieve stable deceleration crystallization and ensure the smooth growth of large-particle crystals.

[0039] After the crystallization of the primary jacketed crystallizer 4 is completed, the material enters the filter screener 7 through the bottom discharge port 28, which is used to separate large and small crystals. Large ammonium sulfate crystals with a diameter of more than 1.43 mm are screened out and sent to the dryer 9, while the mother liquor and small crystals continue to pass through the filter screener 7 and enter the secondary intermittent jacketed crystallizer 5.

[0040] In the secondary jacketed crystallizer 5, the remaining ammonium sulfate mother liquor is brought close to saturation again by adding part of the condensed water, and the same speed reduction crystallization procedure as the primary crystallizer is repeated, and seed crystals are added from the upper feed port 23-2, and the seed crystals are grown by controlling the stirring speed to further obtain large-particle crystals. After the secondary crystallization is completed, the material is separated from the mother liquor and the crystals by the centrifuge 8, and the crystal particles enter the dryer 9 for drying, and the mother liquor is refluxed to the pre-crystallization solution tank 3 by the centrifugal pump 5 18-5 for recycling.

[0041] The heat exchanger group 13 uses the heat generated by the neutralization reaction to preheat the feed ammonium sulfate solution of the crystallizer, and the circulating water in the jacket of the jacketed crystallizer provides the operating temperature for the jacketed crystallizer, ensuring the temperature control during the entire crystallization process and further improving the energy utilization efficiency. At the same time, the low-pressure steam generated during the crystallization process is discharged through the low-pressure steam outlet group 27 and enters the condenser 14 for condensation recovery.

[0042] The bottom discharge end of the neutralization reactor 1 can also be directly connected to the lower feed end of the sedimentation separation tank 2, and the bottom discharge end of the pre-crystallization solution tank 3 can also be directly connected to the middle and lower feed ends of the first-stage intermittent jacketed crystallizer 4.

[0043] Specifically, the bottom discharge end of the neutralization reactor 1 can not only be connected to the tube feed end of the heat exchanger group 13 through a centrifugal pump 18-1, but can also be directly connected to the lower feed end of the sedimentation separation tank 2. Through this direct connection method, the ammonium sulfate solution can directly enter the sedimentation separation tank 2 without the waste heat of the heat exchanger to perform the caprolactam separation operation. This direct connection method makes the process more flexible, suitable for different process requirements and energy utilization conditions, and can simplify the operation process and improve efficiency under certain circumstances.

[0044] At the same time, the bottom discharge end of the pre-crystallization solution tank 3 can not only be connected to the shell feed end of the heat exchanger group 13 through the centrifugal pump 3 18-3, but also directly connected to the middle and lower feed ends of the first-stage intermittent jacket crystallizer 4. Through this direct connection, the ammonium sulfate solution can bypass the heat exchanger and directly enter the crystallizer, which can accelerate the crystallization process and shorten the production cycle when preheating is not required or the appropriate temperature has been reached. This not only improves efficiency, but also makes the process more adaptable.

[0045] The ammonium sulfate solution in the neutralization reactor 1 is circulated and mixed by the reactor circulation pump 17, and the rearranged liquid 20 and the gas ammonia 21 enter the neutralization reactor 1 through the external circulation pipeline for reaction. The steam generated by the neutralization reactor 1 enters the ammoximation tert-butyl alcohol tower reboiler 12 through the high-pressure steam outlet 26, flows out from the shell outlet after heat release and condensation, and is passed into the circulating water inlet at the bottom end of the jacket of the first-level intermittent jacket crystallizer 4 to continue to utilize the remaining heat. At the same time, a part of the circulating water containing the remaining heat is supplemented at the circulating water replenishment port 24. The circulating water outlet at the top end of the jacket of the first-level intermittent jacket crystallizer 4 is connected to the circulating water inlet at the bottom end of the jacket of the second-level intermittent jacket crystallizer 5. The top end of the jacket of the second-level intermittent jacket crystallizer 5 is provided with a circulating water outlet 31. Most of the circulating water at the outlets of the jackets of the first and second-level jacket crystallizers is discharged through the outlet 31, a part of which goes to the neutralization reactor 1 as the evaporated high-pressure steam replenishment water, and another small part goes to the sedimentation separation tank 2 as dissolved water.

[0046] Specifically, first, the ammonium sulfate solution in the neutralization reactor 1 is circulated and mixed by the reactor circulation pump 17 to ensure the uniformity of the materials in the reactor and the adequacy of the reaction. In this process, the rearrangement liquid 20 and the gaseous ammonia 21 are added to the neutralization reactor 1 through the external circulation pipeline to carry out the neutralization reaction. This circulation design can effectively promote the material transfer in the reactor, make the neutralization reaction more sufficient, and thus improve the output efficiency of ammonium sulfate.

[0047] During the reaction, the steam generated by the neutralization reactor 1 is transported to the ammoximation tert-butyl alcohol tower reboiler 12 through the high-pressure steam outlet 26. After the steam enters the tower, the heat of the steam is used for heat release condensation, and the condensed steam is discharged from the shell outlet. This design not only realizes the recovery and utilization of heat energy, but also reduces the consumption of external steam, making the overall process more energy-efficient.

[0048] The waste heat of the condensed steam is further utilized by passing it into the jacket of the first-stage intermittent jacket crystallizer 4 to heat the ammonium sulfate solution and help the speed reduction crystallization operation. In this process, a portion of the circulating water containing waste heat is supplemented through the circulating water replenishment port 24 to maintain the operating temperature in the jacket and ensure the continuous stability of the crystallization process.

[0049] At the same time, in the secondary intermittent jacket crystallizer 5, a circulating water outlet 31 is provided at the top of the jacket for discharging circulating water. This allows the operating temperature in the secondary crystallizer to be effectively controlled, ensuring the secondary crystallization and growth of the remaining ammonium sulfate solution, thereby increasing the output ratio of large-particle ammonium sulfate.

[0050] The amide oil containing dilute ammonium sulfate in the upper layer of the neutralization reactor 1 enters the sedimentation separator 6 through the upper discharge port of the neutralization reactor 1, the caprolactam in the upper part of the sedimentation separator 6 is recovered through a pipeline 25-1, and the dilute ammonium sulfate solution in the lower part of the sedimentation separator 6 is returned to the lower feed end of the neutralization reactor 1.

[0051] Specifically, in the neutralization reactor 1, the mixture after the reaction will naturally separate into layers, with the upper layer being the caprolactam solution, the middle layer being the dilute ammonium sulfate, and the lower layer being the concentrated ammonium sulfate. The upper layer contains amide oil of dilute ammonium sulfate, which is discharged through the upper discharge port of the neutralization reactor 1 and enters the sedimentation separator 6. In the sedimentation separator, the mixture continues to separate, and the caprolactam and the ammonium sulfate solution are effectively separated.

[0052] In the upper part of the sedimentation separator 6, caprolactam is recovered through a pipeline 25-1. This part of caprolactam can be transported to a recovery device through a pipeline for further refining or treatment.

[0053] At the same time, the solution containing dilute ammonium sulfate in the lower part of the sedimentation separator 6 is returned to the lower feed end of the neutralization reactor 1. Through this circulation design, the solution enters the neutralization reactor 1 again to continue the reaction. This method not only improves the separation efficiency of caprolactam, but also ensures the circulation operation of the system.

[0054] The agitator group 16 includes an agitator 1 16-1, an agitator 2 16-2, an agitator 3 16-3 and an agitator 4 16-4. The agitator 1 16-1, the agitator 2 16-2, the agitator 3 16-3 and the agitator 4 16-4 are respectively arranged at the top middle part of the sedimentation separation tank 2, the pre-crystallization solution tank 3, the first intermittent jacketed crystallizer 4 and the second intermittent jacketed crystallizer 5.

[0055] Specifically, the agitator group 16 includes four independent agitators, which are used for different key equipment to ensure the full mixing and uniformity of materials at each stage. These agitators improve the process efficiency and product quality of the entire system through reasonable layout and effective operation.

[0056] Agitator 16-1 is installed in the middle of the top of the sedimentation separation tank 2. Its main function is to ensure that the ammonium sulfate solution and the amide oil can be fully mixed during the sedimentation separation process, promote the stratification of the liquid and the separation of caprolactam. The use of the agitator helps to accelerate the separation of the amide oil and the ammonium sulfate solution, ensuring that the separation effect of the sedimentation separation tank 2 is more efficient.

[0057] The agitator 2 16-2 is arranged at the middle of the top of the pre-crystallization solution tank 3, and is responsible for fully mixing the ammonium sulfate solution and the additives after the compound additives (such as manganese sulfate and ammonium sulfamate) are added to ensure the uniformity of the solution. This ensures that the additives play an effective role in the crystallization process, promotes the growth of large-particle crystals, and ensures that the shape of the crystals is more regular.

[0058] The stirrer 16-3 is located at the top middle of the first-stage intermittent jacket crystallizer 4. The stirrer is used to provide moderate stirring during the process of speed reduction crystallization of the ammonium sulfate solution. It can control the flow state of the solution by gradually reducing the speed, ensuring that the seed crystals are evenly distributed in the crystallizer and grow stably under suitable conditions. The operation of the stirrer maintains a high speed in the early stage of crystallization to promote crystal formation; as the crystals grow, the stirring speed is gradually reduced to avoid collision and breakage between crystals.

[0059] Agitator 4 16-4 is installed in the middle of the top of the secondary intermittent jacket crystallizer 5 and is responsible for stirring the solution during the secondary crystallization process. Similar to the primary crystallizer, agitator 4 is also responsible for controlling the solution flow and crystal growth during the crystallization process. In the secondary crystallization stage, the remaining ammonium sulfate mother liquor continues to be used to crystallize large-particle crystals. Agitator 4 accurately controls the rotation speed to ensure that the crystals have the ideal size and shape in the final stage.

[0060] The caprolactam in the upper part of the sedimentation separation tank 2 is recovered again through the pipeline 25-2, and when the compound additive is added to the pre-crystallization solution tank 3, it is added through the upper feed port 22.

[0061] Specifically, first, the upper part of the sedimentation separation tank 2 is responsible for separating caprolactam. After the ammonium sulfate solution and the caprolactam oil undergo a separation process in the sedimentation separation tank 2, the caprolactam is effectively separated. The caprolactam in the upper part is recovered again through the pipeline 25-2. This recovery system can effectively reduce the waste of caprolactam, so that it can enter the subsequent refining link to further improve the yield of caprolactam, while reducing its package loss and improving the purity of ammonium sulfate crystals.

[0062] Next, when the pre-crystallization solution tank 3 processes the ammonium sulfate solution, the addition of the compound additive can promote the growth of the ammonium sulfate crystals and optimize the morphology of the crystals.

[0063] The low-pressure steam outlet group 27 includes a low-pressure steam outlet 1 27-1 and a low-pressure steam outlet 27-2. The low-pressure steam outlet 1 27-1 and the low-pressure steam outlet 27-2 are respectively arranged at the top of the first-level intermittent jacket crystallizer 4 and the second-level intermittent jacket crystallizer 5, and are respectively connected to the shell side inlet of the condenser 14 through the automatic regulating valve 1 19-1 and the automatic regulating valve 2 19-2 in the automatic regulating valve group 19. The shell side outlet of the condenser 14 is respectively connected to the condensate tank 11 and the vacuum condensing unit 15. The vacuum condensing unit 15 discharges non-condensable gas through the exhaust pipe 32. A part of the condensate in the condensate tank 11 is used to replenish the dissolved water in the second-level intermittent jacket crystallizer 5 via the centrifugal pump four 18-4.

[0064] Specifically, as water evaporates during the crystallization process, a certain amount of low-pressure steam will be generated in the crystallizer, and the steam will be discharged through the two outlets respectively.

[0065] The discharged steam enters the next step of processing through the respective automatic regulating valves. The low-pressure steam outlet 1 27-1 and the low-pressure steam outlet 2 27-2 are connected to the shell side inlet of the condenser 14 through the automatic regulating valve 1 19-1 and the automatic regulating valve 2 19-2 in the automatic regulating valve group 19, respectively. Through these automatic regulating valves, the vacuum degree in the first and second intermittent jacket crystallizers 4 and 5 can be accurately controlled to ensure efficient operation of the crystallization quality.

[0066] In the condenser 14, the low-pressure steam is cooled and condensed into water, and the condensed water flows into the condensed water tank 11 through the shell outlet of the condenser. Part of the condensed water in the condensed water tank 11 is transported back to the secondary intermittent jacket crystallizer 5 through the centrifugal pump 18-4 as a replenishment of dissolved water. The function of the vacuum condensing unit 15 is to provide the required vacuum environment during the crystallization process, and at the same time, discharge the non-condensable gas generated during the condensation process through the exhaust pipe 32.

[0067] A first-stage intermittent jacketed crystallizer discharge port 28 is provided at the bottom of the first-stage intermittent jacketed crystallizer 4. The ammonium sulfate crystals and mother liquor produced therein are filtered through the filter screener 7, and the crystals with a size of 1.43 mm or larger are produced and flow out through the connecting pipe 30, and the small-particle crystals and ammonium sulfate mother liquor continue to enter the second-stage intermittent jacketed crystallizer 5. The seed upper feeding port 1 23-1 and the seed upper feeding port 2 23-2 are respectively arranged at the upper parts of the first-stage intermittent jacketed crystallizer 4 and the second-stage intermittent jacketed crystallizer 5.

[0068] The discharge port 29 of the secondary jacketed crystallizer is connected to a centrifuge 8. The ammonium sulfate crystal particles at one end of the centrifuge 8 and the connecting pipe 30 are dried in the dryer 9 to produce ammonium sulfate crystals that are discharged through a discharge pipe 33. The other end of the centrifuge 8 is connected to a mother liquid tank 10. The discharge end of the mother liquid tank 10 is connected to a centrifugal pump 5 18-5. The centrifugal pump 5 18-5 is connected to the lower feed end of the pre-crystallization solution tank 3.

[0069] Specifically, the bottom of the first intermittent jacket crystallizer 4 is provided with a discharge port 28 leading to the second intermittent jacket crystallizer 5. The ammonium sulfate crystals and mother liquor generated in the first crystallizer are firstly screened by the filter screener 7. During the screening process, ammonium sulfate crystals larger than 1.43 mm flow out through the connecting pipe 30 and are directly sent to the drying process; while the crystals with smaller particles and the ammonium sulfate mother liquor continue to enter the second intermittent jacket crystallizer 5, and a proper amount of condensed water is added to the second crystallizer to dissolve the fine crystals so that the solution is close to saturation. Similarly, seed crystals are added and crystallized again, which increases the crystallization rate while also increasing the mass proportion of large particles.

[0070] In the secondary crystallizer, after the secondary crystallization operation, the material is discharged through the secondary jacket crystallizer discharge port 29 and connected to the centrifuge 8. The function of the centrifuge 8 is to perform solid-liquid separation on the material after the secondary crystallization. During the separation process, the ammonium sulfate crystals and the mother liquor are completely separated, and the crystal particles are discharged from one end and the mother liquor is discharged from the other end.

[0071] The ammonium sulfate crystals discharged from the discharge end of the centrifuge 8 enter the dryer 9 together with the large particle crystals of 1.43 mm or more flowing out through the connecting pipe 30, and are further dried in the dryer 9, and finally the dried ammonium sulfate crystals are discharged through the discharge pipe 33, completing the entire crystallization production process. These dried ammonium sulfate crystals are of high quality and uniform particles, and the mass proportion of large particles of ammonium sulfate is far higher than the industry level.

[0072] At the same time, the mother liquor at the other end of the centrifuge 8 is discharged into the mother liquor tank 10. In order to improve the utilization rate of resources, the mother liquor in the mother liquor tank 10 is returned to the pre-crystallization solution tank 3 through the centrifugal pump 5 18-5, so as to realize the recycling of the mother liquor. After the mother liquor is returned to the pre-crystallization tank, it can continue to be mixed with the new ammonium sulfate solution, and after the addition of compound additives and further treatment, it re-enters the crystallization process. This design not only reduces the waste of raw materials, but also improves the economy and environmental protection of production.

[0073] Please see attached Figure 2 A process for preparing large-particle ammonium sulfate crystals by slowing down crystallization is prepared by using the above-mentioned device for preparing large-particle ammonium sulfate crystals by slowing down crystallization, comprising the following steps:

[0074] S1, the rearrangement liquid 20 and the gaseous ammonia 21 from the caprolactam rearrangement system are added to the neutralization reactor 1 through the external circulation pipeline, the solution in the reactor absorbs the heat released by the neutralization reaction and the dissolution of ammonia, and part of the water is vaporized. The pressure in the neutralization reactor 1 is 110-120 kPa, the liquid phase temperature is 110-115°C, and the gas phase temperature is 100-110°C. The generated steam is used for the ammoximation device;

[0075] S2, the upper layer of the neutralization reactor 1 is a caprolactam solution, the middle layer is dilute ammonium sulfate, and the lower layer is concentrated ammonium sulfate. A sedimentation separator 6 is provided outside the neutralization reactor 1. The amide oil containing dilute ammonium sulfate in the upper layer enters the sedimentation separator 6 through the upper discharge port of the neutralization reactor 1. The caprolactam in the upper part of the sedimentation separator 6 is recovered through a pipeline, and the dilute ammonium sulfate solution at the bottom of the sedimentation separator 6 is returned to the lower feed end of the neutralization reactor 1;

[0076] S3, the ammonium sulfate solution after the primary separation of amide oil is added to the desalted water in the sedimentation separation tank 2 to completely dissolve, releasing the caprolactam wrapped by the ammonium sulfate crystals, and the caprolactam in the upper part of the sedimentation separation tank 2 is recovered again through the pipeline;

[0077] S4, adding a compound additive to the ammonium sulfate solution after the secondary separation of amide oil in the pre-crystallization solution tank 3, wherein the mass fraction of manganese sulfate in the solution is 1.0% to 1.1%, and the mass fraction of ammonium sulfate in the solution is 0.70% to 0.75%;

[0078] S5, the operating conditions of the primary and secondary intermittent jacket crystallizers 4 and 5 are the same. After being preheated by the heat exchanger, the ammonium sulfate solution containing the compound additive enters the primary intermittent jacket crystallizer 4. When the ammonium sulfate solution is close to saturation, seed crystals are added. The seed crystal particle size is 0.2-0.5mm, and the amount used accounts for 0.65% to 0.85% of the mass fraction of ammonium sulfate in the crystallizer;

[0079] S6, the solution pH is controlled at 5.0-5.2, the temperature is maintained at 60-62°C, the absolute pressure is maintained at 15-18kPa, and the mass fraction of water evaporation per hour in the crystallizer to the total ammonium sulfate in the crystallizer is 4.0% to 4.1%;

[0080] S7, the entire speed reduction crystallization program is from 700-750r / min to adding seed crystals, then the speed is reduced to 650-700r / min after 40min, then the speed is reduced to 600-650r / min after 40min, then the speed is reduced to 550-600r / min after 40min, then the speed is reduced to 500-550r / min after 40min, then the speed is reduced to 450-500r / min after 80min, then the crystallization is stopped and the material is discharged after 60min, and the crystallization time is 5h;

[0081] S8, the ammonium sulfate crystals and mother liquor produced at the discharge port of the first-level intermittent jacket crystallizer 4 are filtered through a filter screener, and crystals larger than 1.43 mm are sent to the dryer 9 from the solid phase discharge port for drying, and small particle crystals and ammonium sulfate mother liquor continue to enter the second-level intermittent jacket crystallizer 5 from the liquid phase discharge port, and desalted water is added to make the ammonium sulfate mother liquor close to saturation. The operating conditions of the second-level intermittent jacket crystallizer 5 are the same as those of the first-level intermittent jacket crystallizer 4;

[0082] S9, the material at the discharge port of the secondary intermittent jacketed crystallizer 5 is separated from the mother liquid by the centrifuge 8, and the crystal particles enter the dryer 9 for drying.

[0083] 1. Example 1: Experiment on preparing large-particle ammonium sulfate crystals by slowing down crystallization

[0084] According to the production scale of comparative example 1, the rearrangement liquid is discharged at a flow rate of 24.65m 3 / h, gas ammonia with a flow rate of 7537.0Nm 3 / h enters the neutralization reactor 1, the pressure in the neutralization reactor 1 is 118.10kPa, the liquid phase temperature is 112.8℃, and the high-pressure steam generated on the top of the reactor is used externally; in the primary and secondary intermittent jacketed crystallizers 4 and 5, the mass fraction of manganese sulfate in the initial solution is 0.49%, the mass fraction of ammonium sulfamate in the initial solution is 0.33%, the amount of seed crystal added is 0.31% of the mass fraction of the initial solution, the crystallization temperature is 60℃, the solution pH is 5.1, the absolute pressure is 15.97kPa, the mass fraction of water evaporation per hour in the primary and secondary jacketed crystallizers is 4.10% of the total ammonium sulfate in the primary and secondary jacketed crystallizers, and the crystallization time is 5h.

[0085] 2. Comparative Example 1: Neutralization and crystallization process in Juhua caprolactam production workshop

[0086] The crystallization process adopts a DTB neutralization crystallizer. Ammonia gas at a flow rate of 1.41 kg / s and the rearrangement reaction liquid at a flow rate of 7.61 kg / s enter the guide tube through the annular distributor in the crystallizer respectively. Ammonia and sulfuric acid are neutralized in the guide tube to generate ammonium sulfate solution. The operating conditions are temperature 61.6°C, absolute pressure 14.36 kPa, and solution pH 4.21. The ammonium sulfate solution is stirred in the crystallizer, and the stirring paddle lifts the ammonium sulfate solution to the upper part of the guide tube. As the solution rises, the water gradually evaporates. During the crystallization process, the average residence time of the solution is 3.5 hours. The generated low-pressure steam is condensed through the condenser and returned to the circulation pipeline at the bottom of the crystallizer, which can balance the effect of reaction heat on water evaporation and dissolve fine crystals. The amide oil in the upper part of the clarification zone of the DTB crystallizer is separated from the ammonium sulfate solution and sent to the amide oil decanter for further separation. The ammonium sulfate solution separated in the decanter is returned to the DTB neutralization crystallizer for recycling.

[0087] 3. Test results and data:

[0088]

[0089]

[0090] Summary: This experiment verified the effectiveness of the speed reduction crystallization method in the production of ammonium sulfate crystals. Through the steps of neutralization reaction, two-stage speed reduction crystallization, solid-liquid separation and drying, this process successfully achieved the efficient production of large-particle ammonium sulfate crystals, especially the proportion of crystal particles larger than 2 mm increased significantly. At the same time, thanks to the use of additives and the optimization of the speed reduction program, the morphology of ammonium sulfate crystals is more uniform, with high hardness and excellent crystal form. The yield of large-particle crystals is significantly increased compared with the traditional process, and energy consumption is also reduced, further optimizing the economy and environmental friendliness of the overall process.

[0091] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A device for preparing large-particle ammonium sulfate crystals by speed reduction crystallization, comprising a neutralization reactor (1), a sedimentation separation tank (2), a pre-crystallization solution tank (3), a primary intermittent jacketed crystallizer (4), a secondary intermittent jacketed crystallizer (5), a filter screener (7), an ammoximation tert-butyl alcohol tower reboiler (12), a heat exchanger group (13), an agitator group (16), a centrifugal pump group (18) consisting of a centrifugal pump 1 (18-1), a centrifugal pump 2 (18-2), a centrifugal pump 3 (18-3), a centrifugal pump 4 (18-4) and a centrifugal pump 5 (18-5), a feed port (23), a pipeline group (25) and a low-pressure steam outlet group (27), characterized in that: The bottom discharge end of the neutralization reactor (1) is connected to the tube-side feed end of the heat exchanger group (13) through a centrifugal pump 1 (18-1), the tube-side discharge end of the heat exchanger group (13) is connected to the lower feed end of the sedimentation separation tank (2), the bottom discharge end of the sedimentation separation tank (2) is connected to the lower feed end of the pre-crystallization solution tank (3) through a centrifugal pump 2 (18-2), the bottom discharge end of the pre-crystallization solution tank (3) is connected to the shell-side feed end of the heat exchanger group (13) through a centrifugal pump 3 (18-3), the shell-side discharge end of the heat exchanger group (13) is connected to the first-stage intermittent jacketed crystallizer ( 4) are connected to the middle and lower feed ends of the first intermittent jacketed crystallizer (4); the first jacketed crystallizer discharge port (28) at the bottom of the first intermittent jacketed crystallizer (4) is connected to the middle and lower feed ends of the second intermittent jacketed crystallizer (5) through a filter screen (7); the pipeline group (25) is composed of a pipeline one (25-1) and a pipeline two (25-2); the heat exchanger group (13) is composed of a heat exchanger one (13-1), a heat exchanger two (13-2) and a heat exchanger three (13-3); and the feed port (23) is composed of an upper feed port one (23-1) and an upper feed port two (23-2).

2. The device for preparing large-particle ammonium sulfate crystals by slowing down crystallization according to claim 1, characterized in that: The bottom discharge end of the neutralization reactor (1) can also be directly connected to the lower feed end of the sedimentation separation tank (2), and the bottom discharge end of the pre-crystallization solution tank (3) can also be directly connected to the middle and lower feed ends of the first-stage intermittent jacketed crystallizer (4).

3. The device for preparing large-particle ammonium sulfate crystals by slowing down crystallization according to claim 1, characterized in that: The ammonium sulfate solution in the neutralization reactor (1) is circulated and mixed by a reactor circulation pump (17), and the rearrangement liquid (20) and the gaseous ammonia (21) both enter the neutralization reactor (1) through an external circulation pipeline. The steam generated by the neutralization reactor (1) enters the ammoximation tert-butyl alcohol tower reboiler (12) through a high-pressure steam outlet (26), and flows out from the shell outlet after heat release and condensation. In order to continue to utilize the remaining heat, the steam is passed into the circulating water inlet at the bottom end of the jacket of the first intermittent jacket crystallizer (4). The circulating water outlet at the top end of the jacket is connected to the circulating water inlet at the bottom end of the jacket of the second intermittent jacket crystallizer (5). A circulating water outlet (31) is provided at the top end of the jacket, and a portion of circulating water containing residual heat is supplemented at the circulating water replenishment port (24).

4. The device for preparing large-particle ammonium sulfate crystals by slowing down crystallization according to claim 1, characterized in that: The amide oil containing dilute ammonium sulfate in the upper layer of the neutralization reactor (1) enters the sedimentation separator (6) through the upper discharge port of the neutralization reactor (1), the caprolactam in the upper part of the sedimentation separator (6) is recovered through pipeline 1 (25-1), and the dilute ammonium sulfate solution in the lower part of the sedimentation separator (6) is returned to the lower feed end of the neutralization reactor (1).

5. The device for preparing large-particle ammonium sulfate crystals by slowing down crystallization according to claim 1, characterized in that: The agitator group (16) comprises an agitator one (16-1), an agitator two (16-2), an agitator three (16-3) and an agitator four (16-4), wherein the agitator one (16-1), the agitator two (16-2), the agitator three (16-3) and the agitator four (16-4) are respectively arranged at the top middle part of the sedimentation separation tank (2), the pre-crystallization solution tank (3), the first intermittent jacketed crystallizer (4) and the second intermittent jacketed crystallizer (5).

6. The device for preparing large-particle ammonium sulfate crystals by slowing down crystallization according to claim 1, characterized in that: The caprolactam in the upper part of the sedimentation separation tank (2) is recovered again through the second pipeline (25-2), and the compound additive is added to the pre-crystallization solution tank (3) through the upper feed port (22).

7. The device for preparing large-particle ammonium sulfate crystals by slowing down crystallization according to claim 1, characterized in that: The low-pressure steam outlet group (27) comprises a low-pressure steam outlet 1 (27-1) and a low-pressure steam outlet 2 (27-2). The low-pressure steam outlet 1 (27-1) and the low-pressure steam outlet 2 (27-2) are respectively arranged at the top of the first-stage intermittent jacketed crystallizer (4) and the second-stage intermittent jacketed crystallizer (5), and are respectively connected to the shell side inlet of the condenser (14) through the automatic regulating valve 1 (19-1) and the automatic regulating valve 2 (19-2) in the automatic regulating valve group (19). The shell side outlet of the condenser (14) is respectively connected to the condensate tank (11) and the vacuum condensing unit (15). The vacuum condensing unit (15) discharges non-condensable gas through the exhaust pipe (32). A part of the condensate in the condensate tank (11) is used to replenish the dissolved water in the second-stage intermittent jacketed crystallizer (5) through the centrifugal pump 4 (18-4).

8. The device for preparing large-particle ammonium sulfate crystals by slowing down crystallization according to claim 1, characterized in that: The bottom of the first-stage intermittent jacketed crystallizer (4) is provided with a first-stage jacketed crystallizer discharge port (28), and the ammonium sulfate crystals and mother liquor produced therein are filtered through a filter screener (7), and the produced crystals with a size of 1.43 mm or larger flow out through a connecting pipe (30), and the small particle crystals and the ammonium sulfate mother liquor continue to flow into the second-stage intermittent jacketed crystallizer (5). The seed upper feed port 1 (23-1) and the seed upper feed port 2 (23-2) are respectively arranged at the upper parts of the first-stage intermittent jacketed crystallizer (4) and the second-stage intermittent jacketed crystallizer (5).

9. The device for preparing large-particle ammonium sulfate crystals by slowing down crystallization according to claim 8, characterized in that: The discharge port (29) of the secondary jacketed crystallizer is connected to a centrifuge (8); the ammonium sulfate crystal particles at one discharge end of the centrifuge (8) and the connecting pipe (30) are all dried in a dryer (9) to produce ammonium sulfate crystals which are discharged through a discharge pipe (33); the other discharge end of the centrifuge (8) is connected to a mother liquid tank (10); the discharge end of the mother liquid tank (10) is connected to a centrifugal pump five (18-5); and the centrifugal pump five (18-5) is connected to a lower feed end of a pre-crystallization solution tank (3).

10. A process for preparing large-particle ammonium sulfate crystals by slowing down crystallization, characterized in that: The method of preparing large-particle ammonium sulfate crystals by using a device for preparing large-particle ammonium sulfate crystals by slowing down crystallization according to any one of claims 1 to 9 comprises the following steps: S1, the rearrangement liquid (20) and the gaseous ammonia (21) from the caprolactam rearrangement system are added to the neutralization reactor (1) through an external circulation pipeline. The solution in the reactor absorbs the heat released by the neutralization reaction and the dissolution of ammonia, and part of the water is vaporized. The pressure in the neutralization reactor (1) is 110-120 kPa, the liquid phase temperature is 110-115° C., and the gas phase temperature is 100-110° C. The generated steam is used for the ammoximation device; S2, the upper layer of the neutralization reactor (1) is a caprolactam solution, the middle layer is dilute ammonium sulfate, and the lower layer is concentrated ammonium sulfate. A sedimentation separator (6) is provided outside the neutralization reactor (1). The amide oil containing dilute ammonium sulfate in the upper layer enters the sedimentation separator (6) through the upper discharge port of the neutralization reactor (1). The caprolactam in the upper part of the sedimentation separator (6) is recovered through a pipeline, and the dilute ammonium sulfate solution at the bottom of the sedimentation separator (6) is returned to the lower feed end of the neutralization reactor (1); S3, adding desalted water to completely dissolve the ammonium sulfate solution after the primary separation of amide oil in a sedimentation separation tank (2), releasing caprolactam wrapped by ammonium sulfate crystals, and the caprolactam in the upper part of the sedimentation separation tank (2) is recovered again through a pipeline; S4, adding a compound additive to the ammonium sulfate solution after the secondary separation of the amide oil in the pre-crystallization solution tank (3), wherein the mass fraction of manganese sulfate in the ammonium sulfate solution is 1.0% to 1.1%, and the mass fraction of ammonium sulfamate in the ammonium sulfate solution is 0.70% to 0.75%; S5, the operating conditions of the first and second intermittent jacket crystallizers (4) and (5) are the same. After being preheated by a heat exchanger, the ammonium sulfate solution containing the compound additive enters the first intermittent jacket crystallizer (4). When the ammonium sulfate solution is close to saturation, seed crystals are added. The seed crystal particle size is 0.2-0.5 mm, and the amount used accounts for 0.65% to 0.85% of the mass fraction of ammonium sulfate in the crystallizer; S6, the solution pH is controlled at 5.0-5.2, the temperature is maintained at 60-62°C, the absolute pressure is maintained at 15-18kPa, and the mass fraction of water evaporation per hour in the crystallizer to the total ammonium sulfate in the crystallizer is 4.0% to 4.1%; S7, the entire speed reduction crystallization program is from 700-750r / min to adding seed crystals, then the speed is reduced to 650-700r / min after 40min, then the speed is reduced to 600-650r / min after 40min, then the speed is reduced to 550-600r / min after 40min, then the speed is reduced to 500-550r / min after 40min, then the speed is reduced to 450-500r / min after 80min, then the crystallization is stopped and the material is discharged after 60min, and the crystallization time is 5h; S8, the ammonium sulfate crystals and mother liquor produced at the discharge port of the first intermittent jacket crystallizer (4) are filtered through the filter screener (7), and the crystals larger than 1.43 mm are sent to the dryer (9) for drying from the solid phase discharge port, and the small particle crystals and ammonium sulfate mother liquor continue to enter the second intermittent jacket crystallizer (5) from the liquid phase discharge port, and desalted water is added to make the ammonium sulfate mother liquor close to saturation. The operating conditions of the second intermittent jacket crystallizer (5) are the same as those of the first intermittent jacket crystallizer (4); S9, the material at the discharge port of the secondary intermittent jacketed crystallizer (5) is separated from the mother liquid by a centrifuge (8), and the crystal particles enter a dryer (9) for drying.

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