An apparatus for producing large granular ammonium sulfate

Abstract

The embodiment of the application provides a production device of large-particle ammonium sulfate, comprising: a grading unit which grades ammonium sulfate raw materials into first ammonium sulfate crystals with a particle size greater than or equal to a first threshold value d and second ammonium sulfate crystals with a particle size less than the first threshold value d; a crystallization unit connected with the grading unit, so that the first ammonium sulfate crystals enter the crystallization unit as crystal seeds with a conveying medium; a crystal dissolving unit connected with the grading unit, so that the second ammonium sulfate crystals enter the crystal dissolving unit with a conveying medium to be dissolved, and the saturated mother liquor after being dissolved is sent to the crystallization unit; and a separation unit connected with the crystallization unit, so that the crystal slurry of the crystallization unit enters the separation unit to be separated and dried to obtain large-particle ammonium sulfate products. The embodiment of the application saves the energy consumption required for the complete dissolution of the crystals, and uses the crystals with a certain particle size as crystal seeds to prepare large-particle ammonium sulfate, thereby greatly improving the efficiency of crystallization, and the yield of large-particle ammonium sulfate with a diameter greater than or equal to 2.0 mm reaches more than 90%.

Description

Technical Field

[0001] This application belongs to the field of chemical technology, specifically relating to a production device for large-particle ammonium sulfate that is matched with a caprolactam ammonium sulfate neutralization reaction crystallization device. Background Technology

[0002] Large-particle ammonium sulfate (particle size ≥ 2mm) has many advantages in physical properties compared to traditional powdered or small-particle ammonium sulfate. For example, it has better strength, is less prone to pulverization during loading and unloading, and does not generate dust; it has better flowability, preventing clumping during transportation and storage; it allows for mechanized and uniform spraying during fertilization, and is less likely to be blown away by the wind, reducing losses; it has no adhesion to crop leaves and stems, preventing "leaf burn," and also provides a slow-release effect, improving fertilizer utilization. These advantages make it highly favored in agricultural and industrial applications, and its price is much higher than that of powdered or small-particle ammonium sulfate.

[0003] The ammonium sulfate produced in caprolactam plants refers to the Beckmann rearrangement reaction of cyclohexanone oxime under the catalysis of fuming sulfuric acid during the production of caprolactam via the cyclohexanone-hydroxylamine route. This rearrangement yields a rearrangement solution containing sulfuric acid and caprolactam. To neutralize the fuming sulfuric acid in the rearrangement solution, ammonia neutralization is typically used. The rearrangement solution and ammonia are introduced into a neutralization crystallizer via a nozzle, and the heat of neutralization evaporates the water, yielding solid ammonium sulfate. This neutralization-crystallization process combines neutralization and evaporation in a single reactor (crystallizer), offering numerous advantages: efficient use of the heat of neutralization to evaporate water, resulting in rational energy utilization; elimination of extraction and stripping of the ammonium sulfate mother liquor, reducing benzene consumption; shorter processing flow, lower equipment investment, smaller footprint, and lower operating costs. Due to its economic advantages, this process is widely adopted in newly built caprolactam plants.

[0004] However, since the neutralization reaction and crystallization are carried out in the same crystallizer, the presence of amide oil and impurities affects the growth of crystals, resulting in an average particle size of about 0.8 mm for the ammonium sulfate solid particles obtained by this process, with large particles of ammonium sulfate larger than 2 mm accounting for less than 5%.

[0005] To produce large-particle ammonium sulfate and improve the product's economic efficiency, various companies have equipped their caprolactam units with crystallization-based large-particle ammonium sulfate production facilities. For example, one process involves neutralizing the rearranged liquid with ammonia, refining the upper amide oil, extracting the ammonium sulfate mother liquor with benzene, and then evaporating and crystallizing to obtain solid ammonium sulfate. This process, separating the neutralization reaction and evaporation crystallization, eliminates the influence of amide oil and impurities on crystal growth at the source, and the crystallization process conditions are controllable, enabling the production of large-particle ammonium sulfate. However, this process suffers from problems such as a long process flow, high investment, and inefficient energy utilization, and the proportion of large-particle ammonium sulfate produced is generally less than 50%. Utility Model Content

[0006] In view of the existing caprolactam ammonium sulfate equipment, the purpose of this application is to provide a production equipment for large-particle ammonium sulfate that is matched with the caprolactam ammonium sulfate neutralization reaction crystallization equipment (hereinafter referred to as caprolactam ammonium sulfate equipment) to improve the yield of large-particle ammonium sulfate.

[0007] The technical solution adopted in this application embodiment is a production device for large-particle ammonium sulfate, comprising:

[0008] The classification unit includes a feed pipeline, a first conveying pipeline, and a second conveying pipeline. The feed pipeline is used to feed ammonium sulfate raw material into the classification unit. The classification unit classifies the ammonium sulfate raw material into first ammonium sulfate crystals with a particle size greater than or equal to a first threshold d and second ammonium sulfate crystals with a particle size less than the first threshold d. The first ammonium sulfate crystals are output through the first conveying pipeline under the action of the conveying medium in the classification unit, and the second ammonium sulfate crystals are output through the second conveying pipeline under the action of the conveying medium in the classification unit.

[0009] A crystallization unit is connected to the grading unit via the first feed pipeline, so that the first ammonium sulfate crystal enters the crystallization unit with the conveying medium as a seed crystal for further crystallization.

[0010] The crystal elimination unit is connected to the grading unit through the second conveying pipeline, so that the second ammonium sulfate crystals enter the crystal elimination unit with the conveying medium for crystal elimination. The crystal elimination unit is connected to the crystallization unit through the return pipeline, so that the saturated mother liquor formed after crystal elimination is sent into the crystallization unit for crystal growth.

[0011] A separation unit is connected to the crystallization unit via a crystal slurry delivery pipeline, so that the crystal slurry of the crystallization unit enters the separation unit for separation and drying to obtain large-particle ammonium sulfate with a particle size ≥2mm;

[0012] Wherein, the first threshold d is 0.5mm to 1.2mm.

[0013] In an optional embodiment, the grading unit includes a first particle size classifier; the first particle size classifier is selected from a vibrating screen or a hydrocyclone; and / or

[0014] The crystallization unit includes a graded crystallizer; the graded crystallizer is selected from a crystallizer with particle size classification that includes a flow guide tube, baffles and a stirrer.

[0015] In an optional embodiment, the crystal elimination unit includes a crystal elimination vessel, a crystal elimination heat exchanger, and a circulating pump. The crystal elimination vessel, the crystal elimination heat exchanger, and the circulating pump are connected in sequence through a circulating pipeline to form a closed circulation loop. The second feed pipeline is connected to the circulating pipeline between the crystal elimination vessel and the crystal elimination heat exchanger, and is used to allow the second ammonium sulfate crystals to enter the crystal elimination heat exchanger for heating and crystal elimination. The circulating pump is used to transport the clear liquid after crystal elimination to the crystal elimination vessel. The crystal elimination vessel is connected to the classifying crystallizer through the return pipeline, so as to provide the clear liquid in the crystal elimination vessel to the classifying crystallizer for cooling or depressurization evaporation to provide supersaturation for crystal growth.

[0016] In an optional embodiment, the heat source for the crystallization heat exchanger is provided by the negative pressure steam at the top of the caprolactam neutralization reaction crystallization device after compression by a steam recompression system.

[0017] In an optional embodiment, the production apparatus further includes a mother liquor tank, which has a mother liquor inlet and a mother liquor outlet. The top of the classifying crystallizer is connected to the mother liquor inlet via a fine crystal overflow pipeline so that the slurry containing a small amount of fine crystals with secondary nucleation overflows into the mother liquor tank. The mother liquor outlet is connected to the classifying unit to provide the classifying unit with mother liquor as a dispersion medium and a transport medium.

[0018] In an optional embodiment, the mother liquor tank further includes a mother liquor discharge port and a mother liquor inlet. The mother liquor discharge port is connected to a mother liquor discharge pipeline for discharging the mother liquor containing impurities from the mother liquor tank to the caprolactam ammonium sulfate device. The mother liquor inlet is connected to the caprolactam ammonium sulfate device for replenishing the mother liquor tank with fresh, low-temperature saturated mother liquor.

[0019] In an optional embodiment, the crystallization unit further includes a particle size monitoring component, which includes a particle size monitoring sensor and a particle size monitoring analyzer. The particle size monitoring sensor is located inside the classifying crystallizer and is used to detect the proportion of fine crystals with a particle size <0.5mm and feed the results back to the particle size monitoring analyzer for analysis.

[0020] In an optional embodiment, the separation unit includes a second particle size classifier, a solid-liquid separator, and a dryer connected in sequence. The second particle size classifier is connected to the bottom slurry outlet of the classifying crystallizer via the slurry conveying pipeline, and is used to concentrate and classify the slurry from the bottom of the classifying crystallizer. The dryer and the solid-liquid separator are used to separate and dry the slurry concentrated by the second particle size classifier to obtain large-particle ammonium sulfate products. The solid-liquid separator is connected to the mother liquor tank, and is used to send the separated mother liquor into the mother liquor tank to form a circulating mother liquor with the slurry overflowing from the top of the classifying crystallizer.

[0021] In an optional embodiment, the top of the second particle size classifier is connected to the classifying crystallizer via a medium crystal overflow pipeline, which is used to introduce the supersaturated slurry with medium crystals of 1.0 mm to 2.0 mm overflowing from the upper part of the second particle size classifier into the classifying crystallizer.

[0022] In an optional embodiment, the feed line of the grading unit is connected to the thickener outlet of the caprolactam ammonium sulfate unit, or the outlet of the centrifuge, or the outlet of the drying bed.

[0023] Compared with the prior art, the beneficial effects of the embodiments of this application are as follows:

[0024] 1. This application addresses the current situation where the ammonium sulfate produced by existing caprolactam ammonium sulfate devices already has a certain size. It adopts a particle size classification unit to force classification of ammonium sulfate raw materials from the source. Crystals with a certain particle size enter the crystallization unit as seed crystals for crystallization, while the remaining fine crystals enter the crystal elimination unit for complete dissolution into a clear liquid, which is then transported to the crystallization unit for cooling (or vacuum evaporation) to provide supersaturation for crystal growth. Compared with the conventional dissolution-recrystallization process, this crystal elimination-cooling (or evaporation) coupled crystallization process saves energy consumption that would otherwise require complete dissolution of crystals. Furthermore, the use of crystals with a certain particle size as seed crystals to prepare large-particle ammonium sulfate greatly improves the crystallization efficiency, with the yield of large-particle ammonium sulfate with a diameter ≥2.0 mm reaching over 90%.

[0025] 2. This application reduces the dissolution energy consumption of recrystallization from the source, and uses the low-pressure steam of the neutralization reaction crystallization device to provide heat energy for the crystallization elimination unit, further reducing steam consumption;

[0026] 3. The crystallization-cooling (evaporation) coupled crystallization process adopted in this application makes it easier to control the supersaturation and regulate the crystallization process. It can control the proportion of fine crystals with a particle size <0.5mm at a low level (<0.5%), keep the secondary nucleation of crystallization units at a low level, eliminate the influence of secondary nucleation in the crystallization process, and greatly improve the preparation efficiency and yield of large-particle ammonium sulfate. The prepared large-particle ammonium sulfate can meet market demand without screening.

[0027] It should be understood that the foregoing general description and the following detailed description are exemplary and illustrative only, and are not intended to limit this application.

[0028] The overview of various implementations or examples of the technology described in this application is not a full disclosure of the entire scope or all features of the disclosed technology. Attached Figure Description

[0029] In drawings that are not necessarily drawn to scale, the same reference numerals may describe similar parts in different views. The drawings generally illustrate various embodiments by way of example rather than limitation and are used, together with the description and claims, to illustrate the claimed embodiments. Where appropriate, the same reference numerals are used in all drawings to refer to the same or similar parts.

[0030] Figure 1 This is a schematic diagram of a production apparatus for large-particle ammonium sulfate according to an embodiment of this application.

[0031] Figure label:

[0032] 1-First particle size classifier; 2-Classifying crystallizer; 3-Crystallization kettle; 4-Second particle size classifier; 5-Solid-liquid separator; 6-Dryer; 7-Mother liquor tank; 8-Vapor recompression system; 9-Crystallization heat exchanger; 10-Condensate storage tank; 11-Mother liquor heat exchanger; 12-Crystal slurry transfer pump; 13-Feed pump; 14-Circulation pump; 15-Mother liquor transfer pump; 16-Condensate transfer pump; 17-Condensate discharge pipeline; 18-Mother liquor discharge pipeline; 19-Feed pipeline; 20-First feed pipeline; 21-Second feed pipeline; 22-Fine crystal overflow pipeline; 23-Crystal slurry transfer pipeline; 24-Medium crystal overflow pipeline; 25-Particle size monitoring sensor; 26-Particle size monitoring analyzer; 27-Replenishment pipeline; 28-Circulation pipeline; 29-Return pipeline. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the described embodiments of this application without creative effort are within the scope of protection of this application.

[0034] Unless otherwise defined, the technical or scientific terms used in this application shall have the ordinary meaning understood by one of ordinary skill in the art to which this application pertains. The terms "first," "second," and similar terms used in this application do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0035] To keep the following description of the embodiments of this application clear and concise, detailed descriptions of known functions and known components are omitted.

[0036] This application provides a production apparatus for large-particle ammonium sulfate. The production apparatus uses ammonium sulfate powder of a certain size prepared by a caprolactam neutralization reaction crystallization apparatus (hereinafter referred to as caprolactam ammonium sulfate apparatus) as raw material to produce ammonium sulfate products with a large-particle ammonium sulfate content of more than 90%.

[0037] It should be noted that the large-particle ammonium sulfate involved in this application refers to granular ammonium sulfate with a particle size ≥ 2 mm; all percentages involved in this application are mass percentages.

[0038] The production apparatus for large-particle ammonium sulfate of this application includes a classification unit, a crystallization unit, a crystallization elimination unit, and a separation unit.

[0039] The grading unit is equipped with a feed line 19, a first conveying line 20, and a second conveying line 21. The feed line 19 is used to feed ammonium sulfate raw material into the grading unit. The grading unit classifies the ammonium sulfate raw material into first ammonium sulfate crystals with a particle size greater than or equal to a first threshold d and second ammonium sulfate crystals with a particle size less than the first threshold d. The first ammonium sulfate crystals are output to the crystallization unit through the first conveying line 20 under the action of the conveying medium (mother liquor) in the grading unit, and the second ammonium sulfate crystals are output to the crystallization unit through the second conveying line 21 under the action of the conveying medium (mother liquor) in the grading unit.

[0040] The crystallization unit is used to allow the first ammonium sulfate crystal that enters it with the conveying medium to continue crystallizing as a seed crystal.

[0041] The crystal elimination unit is used to eliminate the second ammonium sulfate crystals that enter it with the conveying medium. The crystal elimination unit is connected to the crystallization unit through the return pipeline 29. The saturated mother liquor (clear liquid) formed after crystal elimination is sent into the crystallization unit, and the crystallization unit is cooled (or evaporated under reduced pressure) to provide supersaturation for crystal growth.

[0042] The separation unit is connected to the crystallization unit through the crystal slurry delivery pipeline 23, so that the crystal slurry of the crystallization unit enters the separation unit for separation and drying to obtain large-particle ammonium sulfate with a particle size ≥2mm.

[0043] Wherein, the first threshold d should be less than 2 mm. Specifically, the first threshold d can be 0.5 mm to 1.2 mm. The particle size of the first ammonium sulfate crystal is greater than 0.5 mm to 1.2 mm, and the particle size of the second ammonium sulfate crystal is less than 0.5 mm to 1.2 mm.

[0044] The production apparatus of this application uses ammonium sulfate from the caprolactam ammonium sulfate plant as raw material. First, the ammonium sulfate raw material is forcibly classified at the source in a classification unit. Crystals of a certain particle size (particle size ≥ first threshold d, d = 0.5–1.2 mm) are transported with the mother liquor to the crystallization unit as seed crystals for growth. The remaining fine crystals (particle size < first threshold d) are transported with the mother liquor to a crystallization elimination unit to eliminate crystals into a clear liquid, which is then sent to the crystallization unit for cooling (or evaporation crystallization) to provide supersaturation. The crystal slurry at the bottom of the crystallization unit enters the separation unit for separation and drying to obtain large-particle ammonium sulfate. This application uses a crystallization-cooling (evaporation) coupled crystallization process, which makes it easier to control supersaturation and regulate the crystallization process, greatly improving the preparation efficiency and yield of large-particle ammonium sulfate. This application can prepare powdered ammonium sulfate from the caprolactam ammonium sulfate plant into large-particle ammonium sulfate with a particle size ≥ 2 mm and a particle size ratio > 90%.

[0045] In the specific implementation method, the ammonium sulfate raw material for the classification unit comes from the thickener discharge of the caprolactam ammonium sulfate unit, or the centrifuge discharge, or the discharge after the drying bed; that is, the feed line 19 of the classification unit is connected to the thickener discharge port of the caprolactam ammonium sulfate unit, or the centrifuge discharge port, or the drying bed discharge port. The preferred source of ammonium sulfate raw material is the thickener discharge, which reduces the influence of amide oil and saves energy consumption of the caprolactam ammonium sulfate unit to the greatest extent.

[0046] In some embodiments, such as Figure 1As shown, the grading unit includes a first particle size classifier 1; the first particle size classifier 1 is selected from a vibrating screen or a hydrocyclone. When the ammonium sulfate raw material is discharged from a centrifuge or a drying bed, a vibrating screen is preferred; when the raw material is discharged from a thickener, a hydrocyclone is preferred. The crystallization unit includes a graded crystallizer 2; the graded crystallizer 2 can be selected from a graded crystallization device with particle size classification, having a guide tube, baffles, and a stirrer. That is, the graded crystallizer 2 is a DTB crystallizer (Draft Tube Baffled Crystallizer).

[0047] In some embodiments, continue to combine Figure 1 The crystal removal unit includes a crystal removal vessel 3, a crystal removal heat exchanger 9, and a circulation pump 14. The crystal removal vessel 3, the crystal removal heat exchanger 9, and the circulation pump 14 are connected sequentially through a circulation pipeline 28 to form a closed circulation loop. A second feed pipeline 21 is connected to the circulation pipeline 28 between the crystal removal vessel 3 and the crystal removal heat exchanger 9. This pipeline allows the second ammonium sulfate crystals (fine crystals with a particle size < d, d = 0.5~1.2 mm) separated by the first particle size classifier 1 to enter the crystal removal heat exchanger 9 with the mother liquor for heating and crystal removal, completely dissolving into clear liquid. The circulation pump 14 then transports the clear liquid (saturated mother liquor) after crystal removal to the crystal removal vessel 3. The crystal removal vessel 3 is connected to the classifier crystallizer 2 of the crystallization unit through a return pipeline 29. This allows the clear liquid in the crystal removal vessel 3 to be supplied to the classifier crystallizer 2. After cooling or depressurization evaporation in the classifier crystallizer 2, supersaturation is provided for crystal growth, allowing the crystals to cool and crystallize on the seed crystals in the classifier crystallizer 2, resulting in a crystalline suspension.

[0048] Furthermore, the heat source for the crystallization heat exchanger 9 of the crystallization unit can be provided by the negative pressure steam at the top of the neutralization reaction crystallizer of the caprolactam ammonium sulfate unit, compressed by the steam recompression system 8. Utilizing the compressed steam at the top of the neutralization reaction crystallizer to provide heat energy for the crystallization unit reduces steam consumption.

[0049] Specifically, such as Figure 1 As shown, the negative pressure steam B at the top of the neutralization reaction crystallizer of the caprolactam ammonium sulfate unit enters the vapor recompression system 8 (MVR system) and is compressed. Then, it enters the hot fluid side of the crystallization heat exchanger 9 and exchanges heat with the mother liquor carrying the second ammonium sulfate raw material (fine crystals) flowing through the cold fluid side of the crystallization heat exchanger 9. This causes the second ammonium sulfate raw material to completely dissolve and form a saturated mother liquor. The steam is cooled and condensed, and the condensate enters the condensate storage tank 10. Under the action of the condensate transfer pump 16, it is discharged through the condensate discharge pipeline 17, and a portion of the condensate is returned to the vapor recompression system 8 to participate in the circulation.

[0050] The vapor recompression system 8 is selected from either a mechanical vapor recompression system 8 (MVR) or a thermal vapor recompression system 8 (TVR).

[0051] In some embodiments, such as Figure 1As shown, the production unit also includes a mother liquor tank 7, which provides the dispersion and transport medium for the first particle size classifier 1 of the classification unit, serving as the raw material for ammonium sulfate. The mother liquor tank 7 is equipped with a mother liquor inlet and a mother liquor outlet. The top of the classifying crystallizer 2 is connected to the mother liquor inlet via a fine crystal overflow pipeline 22. The fine crystals containing secondary nucleation that have been classified by the classifying crystallizer 2 to its upper part overflow through the fine crystal overflow pipeline 22 into the mother liquor tank 7. From the mother liquor tank 7, the crystals are sent to the first particle size classifier 1 for classification and then enter the crystal elimination unit for crystal elimination, thereby minimizing the impact of secondary nucleation during the crystallization process in the classifying crystallizer 2.

[0052] The mother liquor outlet is connected to the first particle size classifier 1 of the classification unit, so that the mother liquor from the mother liquor tank 7 is fed into the first particle size classifier 1, providing the first particle size classifier 1 with a dispersion medium and a conveying medium for the ammonium sulfate raw material. That is, the first particle size classifier 1 uses the ammonium sulfate saturated mother liquor as a suspension.

[0053] Continue to combine Figure 1 A mother liquor heat exchanger 11 and a mother liquor transfer pump 15 are installed on the pipeline between the mother liquor tank 7 and the first particle size classifier 1. The mother liquor heat exchanger 11 is used to heat the mother liquor to a certain stable temperature, and then the mother liquor transfer pump 15 is used to transport it to the first particle size classifier 1 as a classification suspension.

[0054] Furthermore, continue to combine Figure 1 The mother liquor tank 7 also includes a mother liquor discharge port and a mother liquor replenishment port. The mother liquor discharge port is connected to a mother liquor discharge pipeline 18, which is used to discharge the mother liquor containing more impurities in the mother liquor tank 7 to the caprolactam ammonium sulfate unit, preventing the enrichment of amide oil and impurities carried in the ammonium sulfate raw material input source from affecting crystal growth. The mother liquor replenishment port is connected to the caprolactam ammonium sulfate unit through a replenishment pipeline 27, which is used to replenish the mother liquor tank 7 with fresh low-temperature saturated mother liquor to ensure the circulation volume of mother liquor in the entire production unit.

[0055] In some embodiments, the crystallization unit further includes a particle size monitoring component for monitoring secondary nucleation in the graded crystallizer 2. The particle size monitoring component includes a particle size sensor 25 and a particle size analyzer 26, see [link to documentation]. Figure 1 The particle size monitoring sensor 25 is installed inside the classifier crystallizer 2 to detect the proportion of fine crystals with a particle size <0.5mm and feed the data back to the particle size monitoring analyzer 26 for analysis.

[0056] like Figure 1As shown, a feed pump 13 is installed on the return pipeline 29. The supersaturation of the classifier 2 is controlled by adjusting the feed rate of the feed pump 13, keeping the proportion of fine crystals with a particle size <0.5mm in the classifier 2 at a low level (<0.5%). This prevents the formation of excessive crystals due to a surge in secondary nucleation caused by an increased proportion of fine crystals. For example, when the proportion of fine crystals with a particle size <0.5mm in the classifier 2 exceeds 0.5%, the speed of the feed pump 13 is reduced to decrease the delivery of saturated mother liquor into the classifier 2. Alternatively, the proportion of fine crystals with a particle size <0.5mm in the classifier 2 can also be controlled by adjusting the vacuum level of the evaporation and crystallization process in the classifier 2.

[0057] In some embodiments, continue to combine Figure 1 The separation unit includes a second particle size classifier 4, a solid-liquid separator 5, and a dryer 6 connected in sequence. The second particle size classifier 4 is connected to the bottom slurry outlet of the classifying crystallizer 2 via a slurry conveying pipeline 23, so that the slurry at the bottom of the classifying crystallizer 2 enters the second particle size classifier 4 for secondary classification. The solid-liquid separator 5 is connected to the bottom of the second particle size classifier 4, so that the concentrated slurry containing large-particle ammonium sulfate at the bottom of the second particle size classifier 4 enters the solid-liquid separator 5 (e.g., a centrifuge) for solid-liquid separation. The separated mother liquor enters the mother liquor tank 7 and forms a circulating mother liquor with the slurry overflowing from the top of the classifying crystallizer 2. The separated solids enter the dryer 6 for further drying to obtain the large-particle ammonium sulfate product. That is, the slurry at the bottom of the classifying crystallizer 2 undergoes classification, separation, and drying in sequence through the separation unit to obtain a large-particle ammonium sulfate product with a particle size ≥2mm.

[0058] The second particle size classifier 4 can be selected from either a thickener or a crystal slurry reactor with particle size classification. A crystal slurry delivery pump 12 is provided on the crystal slurry delivery pipeline 23, which provides power to continuously feed the crystal slurry into the second particle size classifier 4.

[0059] Furthermore, the top of the second particle size classifier 4 is connected to the classifier crystallizer 2 via a medium crystal overflow pipeline 24, which is used to introduce the supersaturated slurry with medium crystals of 1.0 mm to 2.0 mm overflowing from the upper part of the second particle size classifier 4 into the classifier crystallizer 2 to continue growing and crystallizing on the seed crystals.

[0060] The production process of the large-particle ammonium sulfate production device of this application is as follows: Given that the ammonium sulfate produced by existing caprolactam ammonium sulfate devices already has a certain size, a particle size classification unit is used to forcibly classify the ammonium sulfate raw material from the source. Crystals with a certain particle size (particle size ≥ d, d = 0.5~1.2 mm) are fed into the crystallization unit as seed crystals for crystallization. The remaining fine crystals (particle size < d, d = 0.5~1.2 mm) are fed into the crystal elimination unit and heated to completely dissolve into a clear liquid, which is then transported to the crystallization unit for cooling (or vacuum evaporation) to provide supersaturation for crystal growth. The feed rate of the feed pump 13 in the crystal elimination unit (or the evaporation crystallization rate in the crystallization unit) is adjusted. The supersaturation of the classifier 2 is controlled by vacuum degree, and the proportion of fine crystals <0.5mm is monitored by particle size monitoring unit to keep the secondary nucleation of the classifier 2 at a low level. The classifier 2 is equipped with an overflow port at its upper end to overflow the fine crystals from the secondary nucleation to the mother liquor tank 7, so as to minimize the impact of secondary nucleation in the crystallization process. The crystal slurry from the classifier 2 is further classified by the second particle size classifier 4 of the separation unit. The medium crystals separated from the top of the second particle size classifier 4 overflow to the classifier 2 for continued crystal growth. After the concentrated crystal slurry is centrifuged and dried, large particle ammonium sulfate product is obtained.

[0061] This application enables the preparation of powdered ammonium sulfate from existing caprolactam neutralization reaction crystallization apparatus into large-particle ammonium sulfate with a particle size ≥2mm and a particle size ratio >90%.

[0062] The above description is intended to be illustrative and not restrictive. Those skilled in the art can make variations, modifications, substitutions, and alterations to the above embodiments within the scope of this disclosure. Moreover, the above examples (or one or more of them) can be used in combination with each other, and these embodiments can be combined with each other in various combinations or arrangements.

Claims

1. A production apparatus for large-particle ammonium sulfate, characterized in that, include: The classification unit includes a feed pipeline, a first conveying pipeline, and a second conveying pipeline. The feed pipeline is used to feed ammonium sulfate raw material into the classification unit. The classification unit classifies the ammonium sulfate raw material into first ammonium sulfate crystals with a particle size greater than or equal to a first threshold d and second ammonium sulfate crystals with a particle size less than the first threshold d. The first ammonium sulfate crystals are output through the first conveying pipeline under the action of the conveying medium in the classification unit, and the second ammonium sulfate crystals are output through the second conveying pipeline under the action of the conveying medium in the classification unit. A crystallization unit is connected to the grading unit via the first conveying pipeline, so that the first ammonium sulfate crystal enters the crystallization unit with the conveying medium as a seed crystal for crystallization. The crystal elimination unit is connected to the grading unit through the second conveying pipeline, so that the second ammonium sulfate crystals enter the crystal elimination unit with the conveying medium for crystal elimination. The crystal elimination unit is connected to the crystallization unit through the return pipeline, so that the saturated mother liquor formed after crystal elimination is sent into the crystallization unit for crystal growth. A separation unit is connected to the crystallization unit via a crystal slurry delivery pipeline, so that the crystal slurry of the crystallization unit enters the separation unit for separation and drying to obtain large-particle ammonium sulfate with a particle size ≥2mm; Wherein, the first threshold d is 0.5mm to 1.2mm.

2. The production apparatus for large-particle ammonium sulfate according to claim 1, characterized in that, The grading unit includes a first particle size classifier; the first particle size classifier is selected from a vibrating screen or a hydrocyclone; and / or The crystallization unit includes a graded crystallizer; the graded crystallizer is selected from a crystallizer with particle size classification that includes a flow guide tube, baffles and a stirrer.

3. The production apparatus for large-particle ammonium sulfate according to claim 2, characterized in that, The crystal elimination unit includes a crystal elimination vessel, a crystal elimination heat exchanger, and a circulating pump. The crystal elimination vessel, the crystal elimination heat exchanger, and the circulating pump are connected in sequence through a circulating pipeline to form a closed circulation loop. The second feed pipeline is connected to the circulating pipeline between the crystal elimination vessel and the crystal elimination heat exchanger, and is used to allow the second ammonium sulfate crystals to enter the crystal elimination heat exchanger for heating and crystal elimination. The circulating pump is used to transport the clear liquid after crystal elimination to the crystal elimination vessel. The crystal elimination vessel is connected to the classifying crystallizer through the return pipeline, so as to provide the clear liquid in the crystal elimination vessel to the classifying crystallizer for cooling or depressurization evaporation to provide supersaturation for crystal growth.

4. The production apparatus for large-particle ammonium sulfate according to claim 3, characterized in that, The heat source for the crystallization heat exchanger is provided by the negative pressure steam at the top of the caprolactam neutralization reaction crystallization device, which is then compressed by the steam recompression system.

5. The production apparatus for large-particle ammonium sulfate according to claim 2, characterized in that, The production apparatus also includes a mother liquor tank, which has a mother liquor inlet and a mother liquor outlet. The top of the classifying crystallizer is connected to the mother liquor inlet through a fine crystal overflow pipeline so that the slurry containing a small amount of fine crystals with secondary nucleation overflows into the mother liquor tank. The mother liquor outlet is connected to the classifying unit to provide the classifying unit with mother liquor as a dispersion medium and a transport medium.

6. The production apparatus for large-particle ammonium sulfate according to claim 5, characterized in that, The mother liquor tank also includes a mother liquor discharge port and a mother liquor inlet. The mother liquor discharge port is connected to a mother liquor outflow pipeline for discharging the mother liquor containing impurities from the mother liquor tank to the caprolactam ammonium sulfate device. The mother liquor inlet is connected to the caprolactam ammonium sulfate device for replenishing the mother liquor tank with fresh, low-temperature saturated mother liquor.

7. The production apparatus for large-particle ammonium sulfate according to claim 3, characterized in that, The crystallization unit also includes a particle size monitoring component, which includes a particle size monitoring sensor and a particle size monitoring analyzer. The particle size monitoring sensor is located inside the classifying crystallizer and is used to detect the proportion of fine crystals with a particle size <0.5mm and feed the results back to the particle size monitoring analyzer for analysis.

8. The production apparatus for large-particle ammonium sulfate according to claim 2, characterized in that, The separation unit includes a second particle size classifier, a solid-liquid separator, and a dryer connected in sequence. The second particle size classifier is connected to the bottom slurry outlet of the classifying crystallizer via the slurry conveying pipeline, and is used to concentrate and classify the slurry from the bottom of the classifying crystallizer. The dryer and the solid-liquid separator are used to separate and dry the slurry concentrated by the second particle size classifier to obtain large-particle ammonium sulfate products. The solid-liquid separator is connected to the mother liquor tank, and is used to send the separated mother liquor into the mother liquor tank to form a circulating mother liquor with the slurry overflowing from the top of the classifying crystallizer.

9. The production apparatus for large-particle ammonium sulfate according to claim 8, characterized in that, The top of the second particle size classifier is connected to the classifying crystallizer via a medium crystal overflow pipeline, which is used to introduce the supersaturated slurry containing medium crystals with a particle size of 1.0 mm to 2.0 mm overflowing from the upper part of the second particle size classifier into the classifying crystallizer.

10. The production apparatus for large-particle ammonium sulfate according to claim 1, characterized in that, The feed line of the grading unit is connected to the thickener outlet of the caprolactam ammonium sulfate unit, or the outlet of the centrifuge, or the outlet of the drying bed.

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