Apparatus for crystallizing ammonium sulfate and method for crystallizing ammonium sulfate

Abstract

The application provides a crystallization device and a crystallization manufacturing method of ammonium sulfate. The crystallization device of ammonium sulfate comprises a crystal slurry circulating crystallizer, a clarification zone for eliminating a fine crystal outflow branch flow is formed in the crystal slurry circulating crystallizer, an external circulation feed inlet is arranged at the bottom of the crystal slurry circulating crystallizer, and the external circulation feed inlet is arranged below a stirrer of the crystal slurry circulating crystallizer. A fine crystal dissolution strengthening device comprises one fine crystal dissolution kettle or multiple fine crystal dissolution kettles connected in series, a liquid inlet of the fine crystal dissolution strengthening device is connected with the clarification zone so that the fine crystal outflow branch flow flows into the fine crystal dissolution strengthening device, a liquid outlet of the fine crystal dissolution strengthening device is connected with the external circulation feed inlet, and a raw material kettle is connected with the liquid inlet of the fine crystal dissolution strengthening device. The crystallization device has simple structure and low production equipment cost, can provide the production efficiency of ammonium sulfate crystal products, and can prepare large-particle ammonium sulfate crystals.

Description

Technical Field

[0001] This application relates to the field of ammonium sulfate manufacturing technology, and in particular to an ammonium sulfate crystallization apparatus and a method for manufacturing ammonium sulfate crystals. Background Technology

[0002] Ammonium sulfate (AmmoniµmSulpha, (NH4)2SO4, CAS Registry No. 7783-20-2), is a white orthorhombic crystal, commonly known as ammonium sulfate, with a density of 1.769 g / cm³. 3 Ammonium sulfate decomposes at 280℃. It is readily soluble in water but insoluble in alcohol, acetone, and chlorine. Ammonium sulfate is primarily used as a fertilizer, serving as an important nitrogen and sulfur fertilizer. Compared to other common nitrogen and sulfur fertilizers, ammonium sulfate possesses superior physical properties and chemical stability. Its solubility is 70% at 20℃, and it exhibits a neutral reaction in water. However, due to the presence of free acid in the product, it also presents a slightly acidic environment, making it suitable for alkaline and carbonaceous soils.

[0003] Currently, commercially available ammonium sulfate products generally have a high content of fine crystals, resulting in drawbacks such as easy agglomeration and poor flowability, requiring secondary processing before they can be used as fertilizer. Compared to ordinary ammonium sulfate or large-particle ammonium sulfate produced by extrusion granulation, large-particle ammonium sulfate produced through an enhanced crystallization process has an additional slow-release effect when used as fertilizer. Simultaneously, large-particle ammonium sulfate exhibits high flowability, high stability, and good anti-caking properties.

[0004] Yang Chunhe et al. disclosed a method and apparatus for crystallizing large-particle ammonium sulfate. This apparatus uses two-stage series crystallization reactors. The fine-particle slurry produced in the first-stage crystallization reactor is pumped into the second-stage reactor to obtain ammonium sulfate solids with a high proportion of large particles. Li Qiong et al., based on actual factory output, disclosed an improved process for large-particle ammonium sulfate, changing the original single-effect evaporation to multi-effect evaporation to increase the residence time of solid particles, thereby producing large-particle ammonium sulfate. Xu Huanhuan et al. added zinc sulfate, magnesium sulfate, and manganese sulfate as crystallization aids during the ammonium sulfate crystallization process, obtaining ammonium sulfate solids with relatively regular morphology and uniform particle size. Wang Rongrong et al., during the ammonium sulfate crystallization process, obtained ammonium sulfate solids with the largest average particle size by adding 2% (by mass) of calcium carbonate.

[0005] However, most current research on ammonium sulfate products focuses on reducing the production efficiency of ammonium sulfate or using additives to manufacture large-particle ammonium sulfate products. There is no research on improving the particle size distribution of ammonium sulfate simply through process intensification. Summary of the Invention

[0006] The first aspect of this application provides an ammonium sulfate crystallization apparatus, comprising:

[0007] The crystal slurry circulation crystallizer has an internal agitator and forms a clarification zone to eliminate runoff of fine crystals. The bottom of the crystal slurry circulation crystallizer is provided with an external circulation inlet, which is located below the agitator of the crystal slurry circulation crystallizer.

[0008] The fine crystal dissolution strengthening equipment includes one fine crystal dissolution vessel or multiple fine crystal dissolution vessels connected in series. The inlet of the fine crystal dissolution strengthening equipment is connected to the clarification zone to allow fine crystal elimination streams to flow into the fine crystal dissolution strengthening equipment. The outlet of the fine crystal dissolution strengthening equipment is connected to the external circulation feed inlet.

[0009] The raw material tank has its outlet connected to the inlet of the fine crystal dissolution and strengthening equipment.

[0010] The second aspect of this application provides a method for crystallizing ammonium sulfate:

[0011] A saturated ammonium sulfate solution at temperature T1, used as the raw material, is continuously added to the fine crystal dissolution and strengthening device. Simultaneously, a fine crystal elimination stream from the clarification zone of the crystal slurry circulating crystallizer is continuously conveyed to the fine crystal dissolution and strengthening device. The saturated ammonium sulfate solution and the fine crystal elimination stream are mixed and dissolved in the fine crystal dissolution and strengthening device to form an unsaturated ammonium sulfate feed solution at temperature T2. The raw material solution is obtained by adjusting the pH of the ammonium sulfate aqueous solution, a byproduct generated in the methionine hydroxy analog preparation process, to 3.0-3.5 with an alkaline agent. The ammonium sulfate aqueous solution contains 20%-45% ammonium sulfate by mass, 0.8%-8.0% sulfur-containing organic matter by mass, and the remainder is water.

[0012] Unsaturated ammonium sulfate feed liquid is transported into the crystal slurry circulating crystallizer with an internal temperature of T3 through an external circulation inlet located at the bottom of the crystal slurry circulating crystallizer. During the operation of the crystal slurry circulating crystallizer, the liquid is continuously discharged and the internal liquid level remains stable.

[0013] Where T1 < T3 < T2, T2 - T3 = ΔT1, and the range of ΔT1 is 9℃ to 19℃.

[0014] In some optional embodiments of the second aspect of this application, T3-T1=ΔT2, where ΔT2 ranges from 35°C to 60°C.

[0015] In some optional embodiments of the second aspect of this application, the vacuum degree of the slurry circulating crystallizer is 0.1~0.3 bar, and the stirring speed is 300rpm~600rpm.

[0016] In some optional embodiments of the second aspect of this application, the flow rate ratio of the fine crystal elimination stream to the feed liquid is 5~30:1.

[0017] In some optional embodiments of the second aspect of this application, the value of T2 ranges from 94°C to 125°C, the value of T3 ranges from 85°C to 115°C, and the value of T1 ranges from 45°C to 85°C.

[0018] In some optional embodiments of the second aspect of this application, the slurry circulation crystallizer is a DTB crystallizer, and the average residence time of the slurry circulation crystallizer is 3 to 8 hours.

[0019] In some optional embodiments of the second aspect of this application, the fine grain dissolution strengthening device includes at least two fine grain dissolution vessels connected in series, and the temperature difference between two adjacent fine grain dissolution vessels in the fine grain dissolution strengthening device with continuous liquid flow is 2°C to 5°C.

[0020] In some optional embodiments of the second aspect of this application, the solution volume inside each fine crystal dissolving vessel is equal, and the ratio of the solution volume of the crystal slurry circulating crystallizer to the total solution volume inside all fine crystal dissolving vessels is 10:1.5~9.

[0021] In some optional embodiments of the second aspect of this application, the fine crystal dissolution strengthening device includes a single fine crystal dissolution vessel, and the ratio of the solution volume of the crystal slurry circulating crystallizer to the solution volume inside the single fine crystal dissolution vessel is 10:1~3.

[0022] Beneficial effects:

[0023] The ammonium sulfate crystallization apparatus provided in the first aspect of this application eliminates fine crystals in the stream by setting a fine crystal dissolution enhancement device outside the crystal slurry circulation crystallizer. The crystallization apparatus has a simple structure and avoids the problem of long production dwell time caused by multi-stage crystal slurry circulation crystallizers in the prior art for producing ammonium sulfate crystallized products. The production equipment cost is low, and while improving the production efficiency of ammonium sulfate crystallized products, it can also prepare large-particle ammonium sulfate crystals.

[0024] The ammonium sulfate crystallization manufacturing method provided in the second aspect of this application dissolves and eliminates fine crystals in the crystallizer by using a fine crystal dissolution strengthening device. This increases the particle size of the ammonium sulfate crystals solely through process intensification, without the need for additives, and improves production efficiency by avoiding excessively long residence times. In this method, the unsaturated ammonium sulfate feed solution flowing from the fine crystal dissolution strengthening device into the crystal slurry circulation crystallizer undergoes cooling and evaporation crystallization, effectively controlling the ΔT1 range to 9℃~19℃, thus achieving the goal of producing large-particle ammonium sulfate crystals. The fine crystal dissolution strengthening device enhances process robustness, and fine crystals generated by unexpected fluctuations can be eliminated as the crystallization process progresses. The ammonium sulfate crystallization manufacturing method provided in the second aspect of this application exhibits strong process stability, maintaining a median particle size of approximately D50 = 2000µm during the continuous crystallization process, with low fluctuations over time. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a flow chart of the ammonium sulfate crystallization manufacturing process in the embodiments of this application;

[0027] Figure 2 This is a diagram of the ammonium sulfate crystal product prepared in the embodiments of this application.

[0028] Figure label:

[0029] C1 - Fine crystal elimination flow outlet; C2 - External circulation feed inlet. Detailed Implementation

[0030] The technical solutions of this application will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0031] In the description of this application, it should be noted that the terms "first", "second", and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0032] Furthermore, the technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0033] The first aspect of this application provides an ammonium sulfate crystallization apparatus, comprising:

[0034] The crystal slurry circulation crystallizer has an internal agitator and forms a clarification zone to eliminate runoff of fine crystals. The bottom of the crystal slurry circulation crystallizer is provided with an external circulation inlet, which is located below the agitator of the crystal slurry circulation crystallizer.

[0035] The fine crystal dissolution strengthening equipment includes one fine crystal dissolution vessel or multiple fine crystal dissolution vessels connected in series. The inlet of the fine crystal dissolution strengthening equipment is connected to the clarification zone to allow fine crystal elimination streams to flow into the fine crystal dissolution strengthening equipment. The outlet of the fine crystal dissolution strengthening equipment is connected to the external circulation feed inlet.

[0036] The raw material tank has its outlet connected to the inlet of the fine crystal dissolution and strengthening equipment.

[0037] The ammonium sulfate crystallization apparatus provided in the first aspect of this application eliminates fine crystals in the stream by setting a fine crystal dissolution enhancement device outside the crystal slurry circulation crystallizer. The crystallization apparatus has a simple structure and avoids the problem of long production dwell time caused by multi-stage crystal slurry circulation crystallizers in the prior art for producing ammonium sulfate crystallized products. The production equipment cost is low, and while improving the production efficiency of ammonium sulfate crystallized products, it can also prepare large-particle ammonium sulfate crystals.

[0038] The second aspect of this application provides a method for crystallizing ammonium sulfate:

[0039] A saturated ammonium sulfate solution at temperature T1, used as the raw material, is continuously added to the fine crystal dissolution and strengthening device. Simultaneously, a fine crystal elimination stream from the clarification zone of the crystal slurry circulating crystallizer is continuously conveyed to the fine crystal dissolution and strengthening device. The saturated ammonium sulfate solution and the fine crystal elimination stream are mixed and dissolved in the fine crystal dissolution and strengthening device to form an unsaturated ammonium sulfate feed solution at temperature T2. The pH of the ammonium sulfate aqueous solution, a byproduct generated in the methionine hydroxy analog preparation process, is adjusted to 3.0-3.5 using an alkaline agent. The ammonium sulfate aqueous solution contains 20%-45% ammonium sulfate by mass, 0.8%-8.0% sulfur-containing organic matter by mass, and the remainder is water.

[0040] Unsaturated ammonium sulfate feed liquid is transported into the crystal slurry circulating crystallizer with an internal temperature of T3 through an external circulation inlet located at the bottom of the crystal slurry circulating crystallizer. During the operation of the crystal slurry circulating crystallizer, the liquid is continuously discharged and the internal liquid level remains stable.

[0041] Where T1 < T3 < T2, T2 - T3 = ΔT1, and the range of ΔT1 is 9℃ to 19℃.

[0042] The ammonium sulfate raw material used in the crystallization manufacturing method of ammonium sulfate comes from the recovery of ammonium sulfate, a byproduct generated in the preparation process of methionine hydroxy analogues.

[0043] This application relates to the resource recovery of ammonium sulfate, a byproduct generated during the preparation process of methionine hydroxy analogs. The ammonium sulfate byproduct is obtained by reacting 2-hydroxy-4-methylthiobutyronitrile with sulfuric acid through hydration and hydrolysis to obtain a mixture of methionine hydroxy analog, ammonium bisulfate, and ammonium sulfate. Ammonia is then added to neutralize the ammonium bisulfate in this mixture, resulting in a heterogeneous aqueous solution containing methionine hydroxy analog, sulfur-containing organic matter, and ammonium sulfate. The solution is subjected to static phase separation at 70℃~90℃. The upper layer is an organic phase containing a small amount of ammonium sulfate and water, and the lower layer is an aqueous solution of ammonium sulfate. The ammonium sulfate aqueous solution contains 20%~45% ammonium sulfate by mass, 0.8%~8.0% sulfur-containing organic matter by mass, and the remainder is water. The sulfur-containing organic matter includes thioethers, methylthioaldehydes, and hydroxymethionine.

[0044] The above-mentioned ammonium sulfate aqueous solution was used for evaporation crystallization. The pH value was adjusted to 3.0~3.5 with an alkaline agent. When the evaporation volume was 1 / 50, crystals began to precipitate. Subsequently, nucleation occurred, producing a large number of fine crystals. Therefore, it is necessary to carefully set the range of ΔT1 to avoid the following: When ΔT1 exceeds the maximum temperature difference range, due to the excessive supersaturation difference, nucleation will occur at the external circulation inlet C2 of the crystal slurry circulating crystallizer, producing a large number of fine crystals; when it is below the minimum temperature difference, since the liquid flow entering the crystal slurry circulating crystallizer (DTB crystallizer) from the external circulation inlet C2 and the internal liquid flow of the crystal slurry circulating crystallizer in the crystallization zone near the external circulation inlet C2 have similar temperatures, there is no particle growth effect, and it is difficult to produce large-particle ammonium sulfate crystals.

[0045] Add 25% ammonia solution to the above ammonium sulfate aqueous solution (ammonium sulfate content is 20%~45%, sulfur-containing organic matter content is 0.8%~8.0%, and the remainder is water) to adjust the pH value of the solution to 3.0-3.5, and store it in the raw material tank as the raw material solution.

[0046] The ammonium sulfate crystallization manufacturing method provided in the second aspect of this application dissolves and eliminates fine crystals in the crystallizer by using a fine crystal dissolution enhancement device. This method increases the particle size of ammonium sulfate crystals solely through process enhancement, eliminating the need for additives and improving production efficiency while avoiding excessively long residence times. In this method, the unsaturated ammonium sulfate feed solution flowing from the fine crystal dissolution enhancement device into the crystal slurry circulation crystallizer undergoes cooling and evaporation crystallization, effectively controlling the ΔT1 range to 9℃~19℃, thus achieving the goal of producing large-particle ammonium sulfate crystals. The fine crystal dissolution enhancement device enhances process robustness, eliminating fine crystals caused by unexpected fluctuations as the crystallization process progresses. The ammonium sulfate crystallization manufacturing method provided in the second aspect of this application exhibits strong process stability, maintaining a median particle size of approximately D50=2000µm during continuous crystallization with low fluctuations over time. The manufacturing method uses only water as a solvent, resulting in a simple process and large, uniformly sized product particles. This reduces the economic and equipment costs of subsequent industrial processing, enhancing the economic value of the ammonium sulfate product.

[0047] In some optional embodiments of the second aspect of this application, T3-T1=ΔT2, where ΔT2 ranges from 35°C to 60°C.

[0048] In some optional embodiments of the second aspect of this application, the vacuum degree of the slurry circulating crystallizer is 0.1~0.3 bar, and the stirring speed is 300rpm~600rpm.

[0049] In some optional embodiments of the second aspect of this application, the flow rate ratio of the fine crystal elimination stream to the feed liquid is 5~30:1.

[0050] In some optional embodiments of the second aspect of this application, the value of T2 ranges from 94°C to 125°C, and the value of T3 ranges from 85°C to 115°C.

[0051] In some optional embodiments of the second aspect of this application, the value of T1 ranges from 45°C to 85°C.

[0052] In these embodiments, products with different average particle sizes of ammonium sulfate can be obtained by adjusting the temperature distribution of T1, T2, and T3.

[0053] In some optional embodiments of the second aspect of this application, the slurry circulation crystallizer is a DTB crystallizer (Draft Tube Baffle Crystallizer), and the average residence time of the slurry circulation crystallizer is 3 to 8 hours. In this embodiment, there is no need to use multiple DTB crystallizers in series; continuous discharge can be achieved solely within the DTB crystallizer, resulting in a short residence time and high production efficiency.

[0054] In some optional embodiments of the second aspect of this application, the fine grain dissolution strengthening device includes at least two fine grain dissolution vessels connected in series, and the temperature difference between two adjacent fine grain dissolution vessels in the fine grain dissolution strengthening device with continuous liquid flow is 2°C to 5°C.

[0055] In these embodiments, as the solution flows from the raw material vessel to the slurry circulating crystallizer, the temperature of the series-connected fine crystal dissolving vessels is gradually increased to enhance the fine crystal dissolving capacity.

[0056] In some optional embodiments of the second aspect of this application, the solution volumes inside each fine crystal dissolving vessel are equal.

[0057] In some optional embodiments of the second aspect of this application, the ratio of the solution volume of the slurry circulating crystallizer to the total solution volume in all fine crystal dissolving vessels is 10:1.5~9.

[0058] In some optional embodiments of the second aspect of this application, the fine crystal dissolution strengthening device includes a single fine crystal dissolution vessel, and the ratio of the solution volume of the crystal slurry circulating crystallizer to the solution volume inside the single fine crystal dissolution vessel is 10:1~3.

[0059] like Figure 1As shown, the fine crystal dissolution enhancement equipment used in Examples 1 to 4 consists of three fine crystal dissolution vessels connected in series. Each vessel is equipped with a stirring paddle and a heater, enabling stirring, mixing, and heating of the solution within. An external circulation inlet C2 is located at the bottom of the DTB crystallization vessel, below the stirring paddle. A clarification zone is formed near the sidewall at the top of the DTB crystallization vessel. During operation, a fine crystal elimination stream containing fine crystals flows from the clarification zone through the fine crystal elimination stream outlet C1 and enters the subsequent fine crystal dissolution enhancement equipment for further fine crystal dissolution enhancement.

[0060]

Example 1

[0061] S10: Under the condition that the rotation speed of the raw material tank is 100 rpm to 300 rpm, the saturated ammonium sulfate solution at 45°C in the raw material tank is continuously added to the first fine crystal dissolving tank at 90°C to form an unsaturated ammonium sulfate solution. The unsaturated ammonium sulfate solution in the first fine crystal dissolving tank is mixed with the fine crystal elimination stream flowing out from the clarification zone of the DTB crystallizer to obtain a first mixed solution, so as to dissolve the fine crystals in the fine crystal elimination stream.

[0062] S20: The first mixed solution is continuously pumped into the second-stage fine crystal dissolving vessel at a temperature of 92℃ to obtain the second mixed solution;

[0063] S30: The second mixed solution in the second-stage fine crystal dissolving vessel is continuously pumped into the third-stage fine crystal dissolving vessel at a temperature of 94℃ to obtain the third mixed solution;

[0064] S40: The third mixed solution from the third-stage fine crystal dissolving vessel is continuously pumped into the DTB crystallizer at a temperature of 85°C, a vacuum of 0.3 bar, and a stirring speed of 500 rpm through the external circulation inlet of the DTB crystallizer for evaporation and crystallization.

[0065] S50: Continuous discharge from the DTB crystallizer maintains a stable liquid level within the crystallizer. The average residence time within the crystallizer is 8 hours. The ratio of the actual solution volume in the DTB crystallizer to the solution volumes in the first, second, and third stage fine crystal dissolving kettles is 10:0.5:0.5:0.5, respectively. That is, the ratio of the solution volume in the crystal slurry circulation crystallizer to the total solution volume in all fine crystal dissolving kettles is 10:1.5. The ratio of the flow rate of the fine crystal elimination stream to the feed stream entering the fine crystal dissolving enhancement equipment (i.e., initially entering the first stage fine crystal dissolving kettle) is 5:1. The average particle size of the ammonium sulfate crystallized product is 2200μm, and the angle of repose is 15.3°.

[0066]

Example 2

[0067] S10: Under the condition that the rotation speed of the raw material tank is 100 rpm to 300 rpm, the saturated ammonium sulfate solution at 45°C in the raw material tank is continuously added to the first fine crystal dissolving tank at 100°C to form an unsaturated ammonium sulfate solution. The unsaturated ammonium sulfate solution in the first fine crystal dissolving tank is mixed with the fine crystal elimination stream flowing out from the clarification zone of the DTB crystallizer to obtain a first mixed solution, so as to dissolve the fine crystals in the fine crystal elimination stream.

[0068] S20: The first mixed solution is continuously pumped into a second-stage fine crystal dissolving vessel at a temperature of 102℃ to obtain a second mixed solution;

[0069] S30: The second mixed solution in the second-stage fine crystal dissolving vessel is continuously pumped into the third-stage fine crystal dissolving vessel at a temperature of 104℃ to obtain the third mixed solution;

[0070] S40: The third mixed solution from the third-stage fine crystal dissolving vessel is continuously pumped into the DTB crystallizer at a temperature of 95°C, a vacuum of 0.2 bar, and a stirring speed of 400 rpm through the external circulation inlet of the DTB crystallizer for evaporation and crystallization.

[0071] S50: Continuous discharge from the DTB crystallizer maintains a stable liquid level within the crystallizer. The average residence time within the crystallizer is 5 hours. The ratio of the actual solution volume in the DTB crystallizer to the solution volumes in the first, second, and third fine crystal dissolving kettles is 10:0.5:0.5:0.5, respectively. That is, the ratio of the solution volume in the crystal slurry circulation crystallizer to the total solution volume in all fine crystal dissolving kettles is 10:1.5. The ratio of the fine crystal elimination stream flow to the feed stream flow from the raw material kettle into the fine crystal dissolving enhancement equipment (i.e., initially entering the first-stage fine crystal dissolving kettle) is 10:1. The average particle size of the ammonium sulfate crystallized product is 1800 μm, and the angle of repose is 19.7°.

[0072]

Example 3

[0073] S10: Under the condition that the rotation speed of the raw material tank is 100 rpm to 300 rpm, the saturated ammonium sulfate solution at 85°C in the raw material tank is continuously added to the first fine crystal dissolving tank at 120°C to form an unsaturated ammonium sulfate solution. The unsaturated ammonium sulfate solution in the first fine crystal dissolving tank is mixed with the fine crystal elimination stream flowing out from the clarification zone of the DTB crystallizer to obtain a first mixed solution, so as to dissolve the fine crystals in the fine crystal elimination stream.

[0074] S20: The first mixed solution is continuously pumped into a second-stage fine crystal dissolving vessel at a temperature of 122℃ to obtain a second mixed solution;

[0075] S30: The second mixed solution in the second-stage fine crystal dissolving vessel is continuously pumped into the third-stage fine crystal dissolving vessel at a temperature of 124℃ to obtain the third mixed solution;

[0076] S40: The third mixed solution from the third-stage fine crystal dissolving vessel is continuously pumped into the DTB crystallizer at a temperature of 105°C, a vacuum of 0.1 bar, and a stirring speed of 300 rpm through the external circulation inlet of the DTB crystallizer for evaporation and crystallization.

[0077] S50: Continuous discharge from the DTB crystallizer maintains a stable liquid level within the crystallizer. The average residence time within the crystallizer is 4 hours. The ratio of the actual solution volume in the DTB crystallizer to the solution volumes in the first, second, and third fine crystal dissolving kettles is 10:3:3:3, respectively. That is, the ratio of the solution volume in the crystal slurry circulation crystallizer to the total solution volume in all fine crystal dissolving kettles is 10:9. The ratio of the flow rate of the fine crystal elimination stream to the feed stream entering the fine crystal dissolution enhancement equipment (i.e., initially entering the first-stage fine crystal dissolving kettle) is 15:1. The average particle size of the ammonium sulfate crystallized product is 1600μm, and the angle of repose is 21°.

[0078]

Example 4

[0079] S10: Under the condition that the rotation speed of the raw material tank is 100 rpm to 300 rpm, the saturated ammonium sulfate solution at 75°C in the raw material tank is continuously added to the first fine crystal dissolving tank at 108°C to form an unsaturated ammonium sulfate solution. The unsaturated ammonium sulfate solution in the first fine crystal dissolving tank is mixed with the fine crystal elimination stream flowing out from the clarification zone of the DTB crystallizer to obtain a first mixed solution, so as to dissolve the fine crystals in the fine crystal elimination stream.

[0080] S20: The first mixed solution is continuously pumped into a second-stage fine crystal dissolving vessel at a temperature of 110℃ to obtain a second mixed solution;

[0081] S30: The second mixed solution in the second-stage fine crystal dissolving vessel is continuously pumped into the third-stage fine crystal dissolving vessel at a temperature of 112℃ to obtain the third mixed solution;

[0082] S40: The third mixed solution from the third-stage fine crystal dissolving vessel is continuously pumped into the DTB crystallizer at a temperature of 95°C, a vacuum of 0.12 bar, and a stirring speed of 350 rpm through the external circulation inlet of the DTB crystallizer for evaporation and crystallization.

[0083] S50: Continuous discharge from the DTB crystallizer maintains a stable liquid level within the crystallizer. The average residence time within the crystallizer is 4 hours. The ratio of the actual solution volume in the DTB crystallizer to the solution volumes in the first, second, and third stage fine crystal dissolving kettles is 10:1:1:1, respectively. That is, the ratio of the solution volume in the crystal slurry circulation crystallizer to the total solution volume in all fine crystal dissolving kettles is 10:3. The ratio of the flow rate of the fine crystal elimination stream to the feed stream entering the fine crystal dissolving enhancement equipment (i.e., initially entering the first stage fine crystal dissolving kettle) is 20:1. The average particle size of the ammonium sulfate crystallized product is 1650μm, and the angle of repose is 22.4°.

[0084] A comparison of Examples 2 and 4 shows that the continuous pumping temperature at the external circulation inlet of the DTB crystallizer in step S40 is the same in both Examples 2 and 4, both being 95°C. However, the temperatures of the solutions flowing out of the third-stage fine crystal dissolving vessel differ between Examples 2 and 4.

[0085] Generally, in a DTB crystallizer, with a constant vacuum level, the lower the rotation speed, the more fine crystals are produced; at the same rotation speed, an increase in vacuum level will also lead to the production of more fine crystals.

[0086] The vacuum level in Example 4 is greater than that in Example 2, and the stirring speed in Example 4 is lower than that in Example 2. By adjusting the vacuum level and speed in the DTB crystallizer, the average particle size of the products obtained in Examples 2 and 4 is made closer. Moreover, the sodium sulfate crystal products in Examples 2 and 4 have larger particle sizes. This indicates that the embodiments of this application can obtain large-particle ammonium sulfate crystals through the fine crystal dissolution enhancement method outside the DTB crystallizer. The process has good robustness and can effectively cope with fluctuations in vacuum level, speed, etc., to ensure the stability of crystal particle size distribution.

[0087] The fine crystal dissolution enhancement device used in Example 5 below is specifically a single fine crystal dissolution vessel, which is equipped with a stirring paddle and a heater to achieve stirring, mixing and heating of the solution in the fine crystal dissolution vessel.

[0088]

Example 5

[0089] S10: Under the condition that the rotation speed of the raw material tank is 100 rpm to 300 rpm, the 85°C saturated ammonium sulfate solution in the raw material tank is continuously added to the first fine crystal dissolving tank at a temperature of 124°C to form an unsaturated ammonium sulfate solution. The unsaturated ammonium sulfate solution in the first fine crystal dissolving tank is mixed with the fine crystal elimination stream flowing out from the clarification zone of the DTB crystallizer to obtain a first mixed solution, so as to dissolve the fine crystals in the fine crystal elimination stream.

[0090] S20: The first mixed solution in the first fine crystal dissolving vessel is continuously pumped into the DTB crystallizer, which has a temperature of 105°C, a vacuum of 0.1 bar, and a stirring speed of 300 rpm, through the external circulation feed port of the DTB crystallizer for evaporation and crystallization;

[0091] S30: Continuous discharge from the DTB crystallizer maintains a stable liquid level within the crystallizer. The average residence time within the crystallizer is 4 hours. The ratio of the actual solution volume in the DTB crystallizer to the solution volume in the first-stage fine crystal dissolving vessel is 10:1. That is, the ratio of the solution volume in the crystal slurry circulation crystallizer to the total solution volume in a single fine crystal dissolving vessel is 10:1. The ratio of the flow rate of the fine crystal elimination stream to the feed stream entering the fine crystal dissolving enhancement equipment (i.e., initially entering the first-stage fine crystal dissolving vessel) is 15:1. The average particle size of the ammonium sulfate crystallized product is 1800μm, and the angle of repose is 23°.

[0092] The fine crystal dissolution enhancement device used in Example 6 below is specifically two fine crystal dissolution vessels connected in series. Each fine crystal dissolution vessel is equipped with a stirring paddle and a heater, which can realize the stirring, mixing and heating of the solution in the fine crystal dissolution vessel.

[0093]

Example 6

[0094] S10: Under the condition that the rotation speed of the raw material tank is 100 rpm to 300 rpm, the saturated ammonium sulfate solution at 75°C in the raw material tank is continuously added to the first fine crystal dissolving tank at 118°C to form an unsaturated ammonium sulfate solution. The unsaturated ammonium sulfate solution in the first fine crystal dissolving tank is mixed with the fine crystal elimination stream flowing out from the clarification zone of the DTB crystallizer to obtain a first mixed solution, so as to dissolve the fine crystals in the fine crystal elimination stream.

[0095] S20: The first mixed solution is continuously pumped into a second-stage fine crystal dissolving vessel at a temperature of 123°C to obtain a second mixed solution;

[0096] S30: The second mixed solution in the second-stage fine crystal dissolving vessel is continuously pumped into the DTB crystallizer at a temperature of 111°C, a vacuum of 0.2 bar, and a stirring speed of 600 rpm through the external circulation inlet of the DTB crystallizer for evaporation and crystallization;

[0097] S50: Continuous discharge from the DTB crystallizer maintains a stable liquid level within the crystallizer. The average residence time within the crystallizer is 4 hours. The ratio of the actual solution volume in the DTB crystallizer to the solution volume in the first-stage and second-stage fine crystal dissolving kettles is 10:3:3. That is, the ratio of the solution volume in the crystal slurry circulation crystallizer to the total solution volume in all fine crystal dissolving kettles is 10:6. The ratio of the flow rate of the fine crystal elimination stream to the feed stream entering the fine crystal dissolving enhancement equipment (i.e., initially entering the first-stage fine crystal dissolving kettle) is 10:1. The average particle size of the ammonium sulfate crystallized product is 2000μm, and the angle of repose is 20°.

[0098] It should be noted that the rotation speed of each fine crystal dissolution vessel in the fine crystal dissolution enhancement equipment of Examples 1 to 6 is 100 rpm to 300 rpm. The raw material solution is obtained by adjusting the pH of the ammonium sulfate aqueous solution, a byproduct generated in the methionine hydroxy analog preparation process, to 3.0-3.5 with an alkaline agent. The mass content of ammonium sulfate in the byproduct ammonium sulfate aqueous solution is 20% to 45%, the mass content of sulfur-containing organic matter is 0.8% to 8.0%, and the remainder is water.

[0099] like Figure 2 As shown, the ammonium sulfate crystals obtained in the embodiments of this application are relatively large and have a uniform particle size distribution.

[0100] Comparative Example 1

[0101] S10: Select commercially available ammonium sulfate byproduct of caprolactam, dissolve it in water at 45°C to prepare a saturated solution, and continuously add the 45°C saturated ammonium sulfate solution from the raw material vessel to the first fine crystal dissolving vessel at 100°C under the condition that the rotation speed of the raw material vessel is 100 rpm to 300 rpm to form an unsaturated ammonium sulfate solution. The unsaturated ammonium sulfate solution in the first fine crystal dissolving vessel is mixed with the fine crystal elimination stream flowing out from the clarification zone of the DTB crystallizer to obtain a first mixed solution to dissolve the fine crystals in the fine crystal elimination stream.

[0102] S20: The first mixed solution is continuously pumped into a second-stage fine crystal dissolving vessel at a temperature of 102℃ to obtain a second mixed solution;

[0103] S30: The second mixed solution in the second-stage fine crystal dissolving vessel is continuously pumped into the third-stage fine crystal dissolving vessel at a temperature of 104℃ to obtain the third mixed solution;

[0104] S40: The third mixed solution from the third-stage fine crystal dissolving vessel is continuously pumped into the DTB crystallizer at a temperature of 95°C, a vacuum of 0.2 bar, and a stirring speed of 400 rpm through the external circulation inlet of the DTB crystallizer for evaporation and crystallization.

[0105] S50: Continuous discharge from the DTB crystallizer maintains a stable liquid level within the crystallizer. The average residence time within the crystallizer is 5 hours. The ratio of the actual solution volume in the DTB crystallizer to the solution volumes in the first, second, and third stage fine crystal dissolving vessels is 10:0.5:0.5:0.5, respectively. That is, the ratio of the solution volume in the crystal slurry circulation crystallizer to the total solution volume in all fine crystal dissolving vessels is 10:1.5. The ratio of the fine crystal elimination stream flow to the feed stream flow entering the fine crystal dissolution enhancement equipment (i.e., initially entering the first stage fine crystal dissolution vessel) is 10:1. When the evaporation rate is 1 / 50, no crystals precipitate. Further evaporation to 1 / 10 causes solid precipitation. The final solid ammonium sulfate crystal product has an average particle size of 1000 μm and an angle of repose of 31.3°. The difference between Example 2 and Comparative Example 1 lies in the source of the ammonium sulfate product in the saturated ammonium sulfate solution in the feed vessel. It is understandable that ammonium sulfate products obtained from different processes contain different material impurities (such as the types and contents of sulfur-containing organic compounds) and different distributions of various components. Under the same process parameters, commercially available ammonium sulfate products produced as a byproduct of caprolactam are unlikely to form large-grained ammonium sulfate crystals.

[0106] The source and impurity analysis of the ammonium sulfate product, a byproduct of caprolactam, are detailed in Table 1 below.

[0107] Table 1

[0108]

[0109] During the synthesis of caprolactam, since the target product does not contain sulfur, no additional sulfur-containing organic compounds are introduced or generated. For example, in the oxime synthesis route of caprolactam, cyclohexanone first reacts with hydroxylamine (usually provided by hydroxylamine sulfate) to generate cyclohexanone oxime and sulfuric acid; the cyclohexanone oxime undergoes a Beckmann rearrangement under the catalysis of fuming sulfuric acid, generating crude caprolactam and sulfuric acid. The sulfuric acid produced in the above two steps is neutralized with ammonia water to generate ammonium sulfate as a byproduct.

[0110] In the methionine industry, because the target product methionine contains sulfur, sulfur-containing organic compounds are introduced / generated during the synthesis process; the impurity classifications of the two products are quite different.

[0111] In summary, both single and multiple fine-crystal dissolving vessels connected in series can enhance the crystallization process of ammonium sulfate, resulting in larger, more uniformly distributed particles with an average size between 1200 and 2200 μm. These particles exhibit high fluidity and an angle of repose between 15° and 30°, reducing the economic and equipment costs of subsequent industrial processing and enhancing the economic value of the ammonium sulfate product. The angle of repose refers to the angle between the inclined plane of a cone and the horizontal plane when crystal particles naturally accumulate to form a cone. This angle directly reflects the fluidity of the particles: a smaller angle of repose (usually less than 30°) indicates better fluidity. It is understood that in the embodiments of this application, large-particle ammonium sulfate crystals generally refer to ammonium sulfate crystals with a median particle size D50 greater than 1.5 mm and / or an average particle size greater than 1000 μm. The embodiments of this application can improve the particle size distribution of ammonium sulfate and increase the particle size of the ammonium sulfate crystal products simply by process intensification. This allows for the production of large-particle ammonium sulfate while ensuring production efficiency, thereby improving the bulk density, flowability, and anti-caking properties of the product, ultimately affecting the subsequent use of ammonium sulfate.

Claims

1. A method for crystallizing ammonium sulfate, characterized in that, The production of crystalline ammonium sulfate products using an ammonium sulfate crystallization apparatus, wherein the ammonium sulfate crystallization apparatus comprises: The crystal slurry circulation crystallizer has an internal agitator and forms a clarification zone to eliminate runoff of fine crystals. The bottom of the crystal slurry circulation crystallizer is provided with an external circulation inlet, which is located below the agitator of the crystal slurry circulation crystallizer. A fine crystal dissolution strengthening device includes one or more fine crystal dissolution vessels connected in series. The inlet of the fine crystal dissolution strengthening device is connected to the clarification zone so that the fine crystal elimination stream flows into the fine crystal dissolution strengthening device. The outlet of the fine crystal dissolution strengthening device is connected to the external circulation feed inlet. The raw material vessel has its outlet connected to the inlet of the fine crystal dissolution strengthening device; A saturated ammonium sulfate solution at temperature T1, used as the raw material, is continuously added to a fine crystal dissolution enhancement device. Simultaneously, a fine crystal elimination stream from the clarification zone is continuously fed into the fine crystal dissolution enhancement device. The saturated ammonium sulfate solution and the fine crystal elimination stream are mixed and dissolved in the fine crystal dissolution enhancement device to form an unsaturated ammonium sulfate feed solution at temperature T2. The pH of the ammonium sulfate aqueous solution, a byproduct generated in the methionine hydroxy analog preparation process, is adjusted to 3.0-3.5 using an alkaline agent. The ammonium sulfate aqueous solution contains 20%-45% ammonium sulfate by mass, 0.8%-8.0% sulfur-containing organic matter by mass, and the remainder is water. The unsaturated ammonium sulfate feed liquid is transported into the crystal slurry circulation crystallizer with an internal temperature of T3 through the external circulation inlet. During the operation of the crystal slurry circulation crystallizer, the liquid continuously discharges while the internal liquid level remains stable. Where T1 < T3 < T2, T2 - T3 = ΔT1, and the range of ΔT1 is 9℃ to 19℃.

2. The method for crystallizing ammonium sulfate according to claim 1, characterized in that, T3-T1=ΔT2, where ΔT2 ranges from 35℃ to 60℃.

3. The method for crystallizing ammonium sulfate according to claim 1, characterized in that, The vacuum degree of the slurry circulation crystallizer is 0.1~0.3 bar, and the stirring speed is 300rpm~600rpm.

4. The method for crystallizing ammonium sulfate according to claim 1, characterized in that, The flow rate ratio of the fine-crystal elimination stream to the raw material liquid is 5~30:

1.

5. The method for crystallizing ammonium sulfate according to claim 1, characterized in that, The value of T2 is in the range of 94℃ to 125℃, the value of T3 is in the range of 85℃ to 115℃, and the value of T1 is in the range of 45℃ to 85℃.

6. The method for crystallizing ammonium sulfate according to claim 1, characterized in that, The slurry circulation crystallizer is a DTB crystallizer, and the average residence time of the slurry circulation crystallizer is 3 to 8 hours.

7. The method for crystallizing ammonium sulfate according to any one of claims 1 to 6, characterized in that, The fine-grain dissolution strengthening device includes at least two fine-grain dissolution vessels connected in series, and the temperature difference between two adjacent fine-grain dissolution vessels with continuous liquid flow in the fine-grain dissolution strengthening device is 2℃~5℃.

8. The method for crystallizing ammonium sulfate according to claim 7, characterized in that, The volume of solution inside each of the fine crystal dissolving vessels is equal; the ratio of the solution volume of the crystal slurry circulating crystallizer to the total volume of solution inside all the fine crystal dissolving vessels is 10:1.5~9.

9. The method for crystallizing ammonium sulfate according to any one of claims 1 to 6, characterized in that, The fine crystal dissolution strengthening device includes a single fine crystal dissolution vessel, and the ratio of the solution volume of the crystal slurry circulating crystallizer to the solution volume inside the single fine crystal dissolution vessel is 10:1~3.

Images