Process and apparatus for the production of round granular, large-particle ammonium sulfate

Abstract

The present application relates to a kind of round granular large particle ammonium sulfate production method and device.The device includes adsorption unit, crystallization unit and separation unit, wherein the crystallization unit includes crystallizer, vapor re-compression system, circulating mother liquor heater and acid-base adjustment unit;The separation unit includes thickener and centrifugal drying component, the overflow surface of the thickener upper end is also connected with the boiling surface of crystallizer by pipeline.This application also provides the method for producing large particle ammonium sulfate by the above device.The device and method of the present application save the amount of steam while improving the proportion of ammonium sulfate particles with a diameter of ≥2.0mm and the yield of large particle ammonium sulfate.

Description

Technical Field

[0001] This invention belongs to the field of chemical engineering, specifically relating to a method and apparatus for producing large-particle ammonium sulfate. More specifically, this invention relates to a method and apparatus for the continuous production of clean, spherical large-particle ammonium sulfate using a DTB crystallizer. Background Technology

[0002] Currently, most coking plants in China use the saturator method to produce ammonium sulfate, which is used to remove and recover ammonia from coal gas. This method has advantages such as simple process flow and low equipment investment. However, the ammonium sulfate produced by the traditional saturator method has small particles, mostly powdered ammonium sulfate less than 1mm. Powdered ammonium sulfate is prone to caking and has poor flowability, making it difficult to achieve mechanized fertilization when used as fertilizer, and it is easy to generate dust and be lost during application. Compared with powdered ammonium sulfate, large-particle ammonium sulfate has many advantages in physical properties, such as: better strength, no dust during loading and unloading; less prone to caking during storage and transportation; better flowability, allowing for mechanized and uniform spraying during fertilization; less likely to be blown away by the wind, reducing losses; no adhesion to crop leaves and stems, avoiding "leaf burning"; and it also has a slow-release effect, improving fertilizer utilization. Due to these advantages, large-particle ammonium sulfate (particle size ≥ 2mm) is priced 25-90 USD / ton higher than small-particle or powdered ammonium sulfate.

[0003] However, due to differences in raw material sources, production processes, and even different operating conditions within the same production process, the resulting large-particle ammonium sulfate exhibits numerous variations in shape. Common shapes of large-particle ammonium sulfate include rod-shaped (or long rice-grain-shaped, aspect ratio L / D = 2~3:1; smaller crystals appear needle-like), spherical (aspect ratio L / D = 1:1; smaller crystals appear as regular square crystals; larger crystals become spherical due to edge wear), and thick plate-shaped (aspect ratio L / D = 0.3~0.4 / 1; smaller crystals appear as flakes or plates). Among these different shapes, neither the rod-shaped nor the plate-shaped types can withstand mechanical processing well; their irregular shapes make rod-shaped crystals prone to breaking in the middle, and plate-shaped crystals more easily have their edges knocked off. This leads to the formation of more fine crystals during crystal growth, reducing the overall crystal size; and the product is also more prone to pulverization during storage, loading, unloading, transportation, and spraying. More importantly, when mixed with phosphate or potash fertilizers, granular ammonium sulfate, due to its similar shape to phosphate or potash fertilizers, can be quickly mixed in any proportion, thus having an advantage in the uniformity of mixed spraying compared to other shapes of ammonium sulfate.

[0004] The production of ammonium sulfate using a pickling tower-crystallizer method, also known as the non-saturator method, involves ammonia absorption and ammonium sulfate crystallization in separate units with independently controllable operating conditions. Ammonia absorption occurs in the pickling tower, resulting in an unsaturated ammonium sulfate solution that enters the crystallizer for evaporation and crystallization. Effective control of the supersaturation of the ammonium sulfate mother liquor in the crystallizer, as well as the residence time of the crystals, allows for the production of large-particle ammonium sulfate.

[0005] Although the crystallizer with pickling tower can produce large-particle ammonium sulfate, there are still many defects: (1) Ammonia absorption and crystallization are divided into different operating units. The neutralization heat in the ammonia absorption stage is not fully utilized, the steam consumption in the crystallization section is large, and the system energy consumption is high; (2) The pH value of the ammonium sulfate solution in the crystallizer fluctuates greatly with the pH value of the pickling section, resulting in a large fluctuation in the particle size of the ammonium sulfate product, which affects the yield of large-particle ammonium sulfate; (3) The impurities in the ammonium sulfate solution are relatively complex, which affects both the crystallization rate of ammonium sulfate and the crystal shape and color of the product, ultimately affecting the quality of the product; (4) Due to the influence of the pickling unit, the pH value of the ammonium sulfate mother liquor in the crystallization unit is low. Under acidic conditions and the influence of impurities in the ammonium sulfate solution, the coking ammonium sulfate product often appears as rod-shaped or plate-shaped crystals, which do not have shape advantages; (5) The yield of large-particle ammonium sulfate is low, the production cost is high, and the investment payback period of the project is long.

[0006] Therefore, the key challenge of this project is how to reduce energy consumption, improve the yield and quality of large-particle ammonium sulfate, and obtain granular ammonium sulfate with the preferred crystal shape through process improvement. Currently, most domestic research and production facilities focus on producing coking large-particle ammonium sulfate, with limited research on improving the yield, product quality, and obtaining crystals with the preferred crystal shape.

[0007] Wei Hongyuan (CN101531382B) uses low-pressure steam evaporated from part of the crystallizer to heat the circulating mother liquor in the external circulation channel in order to save energy consumption of the crystallizer mother liquor circulation. However, the calorific value of low-pressure steam is limited, and the energy consumption is reduced by only 20% to 40%.

[0008] The coal gas purification process at Shanghai Baosteel Chemical Meishan Branch uses an acid washing tower + DP crystallizer method to produce ammonium sulfate. The product has large particles and a free acid content that meets superior standards. However, due to impurities such as tar and coal dust in the ammonium sulfate solution, the product contains a significant amount of black impurities after a period of operation, requiring frequent shutdowns for crystallizer cleaning. After process improvement (CN108658096B), a full-flow trough was added to facilitate tar removal. This reduced the number of black particles entrained in the ammonium sulfate mother liquor, significantly improving the product's appearance. However, this method has limited impurity removal capabilities, failing to remove some soluble organic and inorganic substances. The ammonium sulfate crystallization process remains significantly affected by impurities; particles larger than 1mm account for over 80% of the product, while particles larger than 2mm account for only about 20%. The large particles are rice-grain shaped and are sold directly without screening, priced only 10% higher than powdered ammonium sulfate, limiting economic viability.

[0009] Some studies have found that the average particle size of the product exhibits a cyclical variation during crystallization, leading to cyclical fluctuations in the yield of large-particle products and thus affecting the final product yield. JFE patent JP6060820(B2) suggests that the pH value of the ammonium sulfate mother liquor in the crystallizer varies depending on the amount of coke oven gas generated and the concentration of ammonia. Since the pH value of the ammonium sulfate mother liquor fluctuates greatly between 1 and 6.5, the particle size of the resulting ammonium sulfate may also fluctuate significantly. To reduce pH fluctuations, ammonia from the ammonia stripping tower is used as the alkali source, and an alkali adjustment unit is added to the ammonium sulfate mother liquor to adjust the pH value between 1.8 and 2.4, thereby reducing the fluctuation in the ammonium sulfate particle size distribution. Mitsubishi Chemical patent JP2000226211A uses aminosulfonate and metal ions as crystallizing agents in a concentrated ammonium sulfate solution to obtain coarse-grained ammonium sulfate crystals with stable average particle size, uniform particle size distribution, and no cyclical phenomenon during crystallization. However, these methods still do not consider issues such as controlling product morphology.

[0010] International research has found that the irregular rod-shaped or plate-shaped structure of coking granular ammonium sulfate, compared to the spherical caprolactam-grade granular ammonium sulfate, has an inherent disadvantage in morphology, leading to drawbacks in production, transportation, storage, and use. Therefore, companies are adding crystallizing agents to produce spherical coking granular ammonium sulfate, based on the existing coking granular ammonium sulfate production process, in order to gain greater market acceptance.

[0011] JFE's patent JP3534430 (B2) modifies the aspect ratio of ammonium sulfate particles by adding low concentrations of ammonium aminosulfonate and guanidine aminosulfonate as crystallizers, thereby preparing large and almost spherical particles with the same strength as crystals prepared without adding crystallizers.

[0012] Nippon Steel's early patents JPS56109816A and JPS63103820A produced large-particle-size spherical crystalline ammonium sulfate by adding 1%-10% ammonium nitrate and ammonium aminosulfonate as crystallizing agents.

[0013] Nippon Steel's patents JP2002193614A, JP2004010406A, and JP2004010408A state that ammonium sulfate solution contains iron ions (Fe). 3+ This causes ammonium sulfate to easily form needle-like crystals, while organic acids such as citric acid, malic acid, and oxalic acid have a shielding effect on iron ions. Therefore, adding one or more of citric acid, malic acid, and oxalic acid to the ammonium sulfate mother liquor, or mixing ammonium aminosulfonate or ammonium nitrate with one or more organic acids, can produce large-particle granular ammonium sulfate.

[0014] However, this method of adding a crystallizer to produce granular ammonium sulfate also has disadvantages: (1) the crystallizer is expensive and the amount added is large, which increases the manufacturing cost of large granular ammonium sulfate; (2) during the crystallization process, the amount of loss and recyclable amount of the crystallizer is difficult to quantify in real time, and the replenishment of the crystallizer is complicated; (3) the addition of the crystallizer will affect the quality of the product. Summary of the Invention

[0015] The purpose of this invention is to address the aforementioned technical problems by providing a process and apparatus for producing large, spherical ammonium sulfate particles. This apparatus purifies the unsaturated ammonium sulfate solution from the coking pickling unit through adsorption, reducing the impact of impurities on the crystallization process at its source. During crystallization, a pH adjustment device stabilizes the pH in the crystallizer to reduce fluctuations in product particle size distribution, while controlling the pH value to 4.5-5.5 to maintain an aspect ratio (L / D) of approximately 1:1 for the ammonium sulfate crystals. Steam from the top of the crystallizer is compressed using a mechanical vapor recompression (MVR) system and used as a heat source for the circulating mother liquor. The supersaturated ammonium sulfate mother liquor with fine crystals overflowing from the thickener is introduced into the boiling surface of the crystallizer, rapidly consuming the supersaturation on the boiling surface. This invention reduces steam consumption, minimizes product particle size fluctuations, improves product quality and the yield of large-particle ammonium sulfate, and produces clean, large, spherical ammonium sulfate crystals.

[0016] On one hand, the present invention provides a production apparatus for spherical large-particle ammonium sulfate, the apparatus comprising the following components: 1. An adsorption unit comprising an adsorption tower and used for purifying an unsaturated ammonium sulfate solution from a coking pickling unit; 2. Crystallization unit The crystallization unit includes: (i) A crystallizer connected to the adsorption unit via a pipeline, wherein the unsaturated ammonium sulfate solution purified by the adsorption unit enters the crystallizer along with the circulating mother liquor and undergoes evaporation and crystallization therein. Preferably, the crystallizer is a guide tube and baffle evaporator crystallizer including a guide tube, baffles, and a stirrer. (ii) A vapor recompression system (MVR) connected via pipeline to the top of the crystallizer for compressing the vapor at the top of the crystallizer as a heat source for the circulating mother liquor heater; (iii) A circulating mother liquor heater, which is connected to the crystallizer and the vapor recompression system via a circulating pipeline outside the crystallizer, and is used for heating and crystallizing the ammonium sulfate mother liquor with fine crystals flowing out of the crystallizer; (iv) Acid-base adjustment unit, which is connected to the crystallizer via pipeline and is used to adjust the pH value within the crystallizer. 3. Separation Unit The separation unit includes: (i) a thickener, wherein the thickener is connected via a pipeline to the bottom of the crystallizer to concentrate the slurry from the bottom of the crystallizer, and the overflow surface at the top of the thickener is also connected via a pipeline to the boiling surface of the crystallizer to introduce the supersaturated ammonium sulfate mother liquor overflowing from the top of the thickener into the boiling surface of the crystallizer; and (ii) A centrifugal drying component, which is connected to the bottom of the thickener via a pipeline and is used for centrifugal drying of the material discharged from the bottom of the thickener.

[0017] In a specific embodiment, the adsorption unit consists of two parallel, switchable adsorption towers.

[0018] In a specific embodiment, the steam in the compression system is selected from one of a mechanical steam recompression system (MVR) or a thermal steam recompression system (TVR).

[0019] In a specific embodiment, the acid-base adjustment unit consists of a flow regulating valve, a mother liquor pH controller, and a mother liquor pH sensor.

[0020] In a specific embodiment, the device further includes a vacuum pump connected to the top of the crystallizer to provide negative pressure to the crystallizer to facilitate the evaporation of the ammonium sulfate mother liquor.

[0021] In a specific embodiment, the centrifugal drying component includes a centrifuge, a mother liquor tank, and a drying unit.

[0022] In a specific embodiment, the device further includes a flow regulating valve disposed before the adsorption tower.

[0023] On the other hand, the present invention provides a method for producing spherical large-particle ammonium sulfate using the above-described apparatus, the method comprising the following steps: (1) Purification of ammonium sulfate solution in the adsorption unit Unsaturated ammonium sulfate solution enters the adsorption tower from the top through a flow regulating valve for purification. (2) Evaporation and crystallization of ammonium sulfate mother liquor in the crystallization unit In this step, the ammonium sulfate mother liquor purified in step (1) enters the crystallizer. Under the high temperature of the circulating mother liquor heater and the optional negative pressure of the vacuum pump, water vapor is evaporated, and the ammonium sulfate mother liquor in the crystallizer is concentrated to crystallize ammonium sulfate crystals. The density of the slurry in the crystallizer is maintained at 1.300~1.400 g / cm³. 3 To prevent the mother liquor from becoming more supersaturated than the level that can be maintained in a metastable state during the evaporation and concentration process; The crystallization process in the crystallizer is as follows: the baffle plate divides the crystallizer into a dynamic zone and a static zone. Under the action of stirring at the bottom of the crystallizer and the guide tube, the ammonium sulfate mother liquor forms an internal circulation in the dynamic zone. The fine ammonium sulfate crystals rise to the vicinity of the boiling surface in the guide tube and consume supersaturation, thus growing larger. In the static zone formed by the baffle plate and the crystallizer wall, large particles of ammonium sulfate settle. Furthermore, the pH of the ammonium sulfate mother liquor in the crystallizer is controlled at 4.5-5.5 through the adjustment of the acid-base adjustment unit. The ammonium sulfate mother liquor containing fine crystals is heated and crystallized by a circulating mother liquor heater outside the crystallizer via a circulation pipeline, and then returned to the crystallizer from the bottom; large-particle ammonium sulfate is discharged with the crystal slurry by a discharge pump to the separation unit; and Among them, a vapor recompression system is used to mechanically compress the vapor at the top of the crystallizer and use it as the heat source for the circulating mother liquor heater; (3) Separation of granular ammonium sulfate in the separation unit The slurry at the bottom of the crystallizer enters the thickener for concentration. The concentrated ammonium sulfate product is discharged from the bottom of the thickener and enters the centrifuge for centrifugation. The filtrate goes to the mother liquor tank, and the solid goes to the drying unit. After drying, the product is obtained. The ammonium sulfate mother liquor with fine crystals overflowing from the top of the thickener goes to the boiling surface of the crystallizer.

[0024] In a specific embodiment, the unsaturated ammonium sulfate solution in step (1) is derived from the coking pickling unit and has a concentration of 30wt%-45wt%, for example, a concentration of 40wt%.

[0025] In a specific embodiment, the adsorption tower in step (1) is a packed tower, and the packing material is selected from activated carbon, white carbon black, cation exchange resin or a combination thereof. The adsorption temperature is 40-50℃ and the residence time is 30 minutes.

[0026] In a specific embodiment, sulfuric acid and / or ammonia are used to adjust the pH value of the ammonium sulfate mother liquor in the crystallizer for the acid-base adjustment unit.

[0027] In another aspect, the present invention provides spherical large-particle ammonium sulfate prepared by the above method, wherein particles with a diameter ≥ 2.0 mm account for more than 48%.

[0028] In another aspect, the present invention provides the application of the above-mentioned round-shaped large-particle ammonium sulfate in the preparation of compound fertilizers.

[0029] In another aspect, the present invention provides a compound fertilizer comprising the above-mentioned spherical large-particle ammonium sulfate.

[0030] The beneficial effects of this invention are: (1) By adding an adsorption purification section, the carbon black, organic matter, and Fe in the ammonium sulfate solution are purified. 3+ Al 3+ Metal ions were absorbed. Trace amounts of carbon black in the ammonium sulfate solution cause black impurities in the ammonium sulfate product after a period of operation, requiring periodic shutdowns for cleaning; trace amounts of organic matter in the ammonium sulfate solution, Fe... 3+ Al 3+ Metal ions cause ammonium sulfate crystals to appear yellowish-brown or grayish-white and affect the crystal growth rate, resulting in small crystal size. After adsorption purification, the ammonium sulfate mother liquor is then evaporated and crystallized, which greatly improves the product quality of ammonium sulfate crystals and the yield of large-particle ammonium sulfate, significantly improving economic efficiency.

[0031] (2) The pH value of the ammonium sulfate mother liquor from the pickling unit will fluctuate depending on factors such as the amount of coke oven gas generated, the concentration of ammonia, and the amount of sulfuric acid added to the absorbent. Large fluctuations in pH value will lead to significant variations in the particle size distribution of ammonium sulfate produced in the crystallization section. Increasing the pH adjustment in the crystallization section and maintaining the pH value in the crystallizer within the range of 4.5-5.5 can not only reduce the fluctuations in the particle size distribution of the product, but also produce large, round ammonium sulfate crystals.

[0032] (3) The steam at the top of the crystallizer is compressed by the mechanical vapor recompression system (MVR) and then used to heat the circulating mother liquor, which greatly saves steam consumption.

[0033] (4) The ammonium sulfate mother liquor with fine crystals overflowing from the top of the thickener is introduced into the boiling surface of the crystallizer. The fine crystals act as seed crystals to quickly consume the supersaturation on the boiling surface, preventing explosive nucleation and the formation of too many fine crystals, thus effectively improving the yield of large-particle ammonium sulfate. In addition, this operation is also beneficial to increasing the proportion of particles with a diameter ≥2.0 mm, which is conducive to the formation of large-particle ammonium sulfate. Attached Figure Description

[0034] Figure 1 : Process flow diagram of the present invention; Figure 2Comparative Example 1: Ammonium sulfate mother liquor (a) without adsorption tower purification and Comparative Example 2: Ammonium sulfate mother liquor (b) purified by adsorption tower.

[0035] Figure 3 Photographs of the large-particle ammonium sulfate prepared in this application, wherein (a): prepared in Comparative Example 1; (b): prepared in Comparative Example 2; (c): prepared in Example 1.

[0036] Figure Labels 1: Adsorption tower; 2: Vacuum pump; 3: Condenser; 4: MVR compressor; 5: Circulating mother liquor heater; 6: Condensate storage tank; 7: Crystallizer; 8: Thickener; 9: Centrifuge; 10: Mother liquor tank; 11: Mother liquor pH controller; 12: Mother liquor pH sensor; P1~P4: Inlet / outlet pumps; BV-1~BV-5: Flow regulating valves Detailed Implementation The technical solutions of this application are described in detail below through specific embodiments, so that those skilled in the art can better understand the present invention.

[0037] the term: In this article, "fine crystals" in ammonium sulfate mother liquor refers to tiny solids that cannot settle and remain suspended in the mother liquor in the static zone and can be carried away by the external circulation of the mother liquor.

[0038] The technical solution of this application is as follows: Figure 1 As shown, a 40% unsaturated ammonium sulfate solution from the coking pickling unit is purified by adsorption tower 1 (two parallel, switchable adsorption towers are shown in the figure), and then directly enters crystallizer 7 via the BV-3 feed valve along with the circulating mother liquor for continuous evaporation and crystallization. The evaporation temperature is 80℃, the absolute pressure of the crystallizer is 40kPa, and the vacuum is provided by vacuum pump 2. A condenser 3 is added before the vacuum pump to condense non-condensable vapors and protect the vacuum pump. The pH in the crystallizer is adjusted by a pH adjustment unit consisting of a flow regulating valve BV-5, a mother liquor pH controller 11, and a mother liquor pH sensor 12, all located on the acid-base adjustment pipeline. Ammonia / sulfuric acid is used to adjust the pH to 5.5.

[0039] Steam from the top of the crystallizer is mechanically compressed by the MVR compressor 4 and then exchanges heat with the circulating mother liquor heater 5 for heating the circulating mother liquor and eliminating crystals. After heat exchange, the high-pressure steam condensates into the condensate storage tank 6. Part of the condensate in the condensate storage tank 6 is sent to the MVR compressor via the feed pump P4 to adjust the high-pressure steam to the required temperature and pressure, while the other part goes to the mother liquor tank. The condensate generated during the adjustment process goes to the condensate storage tank 6.

[0040] The slurry at the bottom of the crystallizer is discharged by the discharge pump P2 and enters the thickener 8. At the bottom of the thickener, the ammonium sulfate mother liquor from the mother liquor tank 10 is pumped by the feed pump P3 to wash the slurry in the crystallizer. Fine crystals rise with the mother liquor, overflow from the top of the thickener, and are introduced into the boiling surface of the crystallizer. Large ammonium sulfate crystals are concentrated. The concentrated ammonium sulfate product is discharged from the bottom of the thickener and enters the centrifuge 9 for centrifugation. The filtrate goes to the mother liquor tank 10, and the solid goes to the drying unit for drying to obtain the final product.

[0041] Example 1: A 40% (w / w) unsaturated ammonium sulfate solution from the coking pickling unit is purified by adsorption tower 1 and then enters crystallizer 7 via the BV-3 feed valve along with the circulating mother liquor for continuous evaporation and crystallization. The evaporation temperature is 80℃, the absolute pressure in the crystallizer is 40 kPa, and the pH in the crystallizer is adjusted to 5.5 (the pH is adjusted by a pH adjustment unit located on the acid-base adjustment pipeline, which consists of a flow control valve BV-5, a mother liquor pH controller 11, and a mother liquor pH sensor 12). The top steam is mechanically compressed by MVR compressor 4 and then exchanges heat with the circulating mother liquor heater 5 for heating the circulating mother liquor and eliminating crystals. The slurry at the bottom of the crystallizer is discharged by discharge pump P2 and enters thickener 8 for concentration. The concentrated ammonium sulfate product is discharged from the bottom of the thickener and enters centrifuge 9 for centrifugation. The filtrate goes to the mother liquor tank 10, and the solid goes to the drying unit for drying to obtain the product. The ammonium sulfate mother liquor with fine crystals overflowing from the top of the thickener goes to the mother liquor tank. A photograph of the large ammonium sulfate particles obtained is shown below. Figure 3 As shown in (c).

[0042] Example 2: The specific operation is the same as in Example 1, except that the pH in the crystallizer is adjusted to 4.5.

[0043] Example 3: The specific operation is the same as in Example 1, except that the ammonium sulfate mother liquor with fine crystals overflowing from the top of the thickener is introduced into the boiling surface of the crystallizer instead of going to the mother liquor tank.

[0044] Comparative Example 1: The specific operation is the same as in Example 1, except that the 40% unsaturated ammonium sulfate solution from the coking pickling unit is not purified by adsorption tower 1 and enters crystallizer 7 directly with the circulating mother liquor. Also, the flow control valve BV-5 on the acid-base adjustment pipeline is closed, and the pH of the ammonium sulfate mother liquor in the crystallizer is not adjusted. A photograph of the ammonium sulfate mother liquor in this example is shown below. Figure 2 As shown in (a), the final image of the large ammonium sulfate particles is as follows. Figure 3 As shown in (a).

[0045] Comparative Example 2: The specific operation is the same as in Example 1, except that the flow control valve BV-5 on the acid-base adjustment pipeline is closed, meaning that the pH of the ammonium sulfate mother liquor in the crystallizer is not adjusted. A photograph of the ammonium sulfate mother liquor in this example is shown below. Figure 2 As shown in (b), the final image of the large ammonium sulfate particles is as follows. Figure 3 As shown in (b).

[0046] Comparative Example 3: The specific operation is the same as in Example 1, except that the pH in the crystallizer is adjusted to 2.0.

[0047] Comparative Example 4: The specific operation is the same as in Example 1, except that the pH in the crystallizer is adjusted to 2.5.

[0048] Comparative Example 5: The specific operation is the same as in Example 1, except that the pH in the crystallizer is adjusted to 3.5.

[0049] Comparative Example 6: The specific operation is the same as in Example 1, except that the pH in the crystallizer is adjusted to 6.5.

[0050] Test example: The ammonium sulfate products obtained in the above embodiments and comparative examples were measured in the following aspects: 1. Proportion of particles with a diameter ≥ 2.0 mm: Ammonium sulfate products are screened using a 2 mm test sieve that meets the requirements of GB T 6003.1-2012. The proportion of particles with a diameter ≥ 2.0 mm = mass of ammonium sulfate retained by the sieve / total mass of ammonium sulfate × 100%, also known as the yield of large particle ammonium sulfate (≥ 2.0 mm).

[0051] 2. Crystal aspect ratio L / D: The ratio of the maximum grain size L of the crystal to the maximum grain size D in the direction perpendicular to the measurement direction of the maximum grain size.

[0052] 3. Particle Size Distribution: Large-particle ammonium sulfate products were screened using a set of sieves conforming to GB / T 6003.1-2012, with diameters of 2.8 mm (7 mesh), 2.5 mm (8 mesh), 2.0 mm (10 mesh), 1.6 mm (12 mesh), and 1.0 mm (18 mesh). The particles retained on each sieve had diameters >2.8 mm, 2.5~2.8 mm, 2.0~2.5 mm, 1.6~2.0 mm, and 1.0~1.6 mm, respectively. The crystals on the bottom plate had a particle size <1 mm. The mass of each particle size was weighed, and the ratio of the mass of each particle size to the total mass of the large-particle ammonium sulfate products was calculated.

[0053] The results are shown in Tables 1 and 2 below.

[0054] Table 1

[0055] Table 2

[0056] The data in Table 1 above show that the pH value of the ammonium sulfate mother liquor in the crystallizer not only affects the yield of large-particle ammonium sulfate (≥2 mm) products, but also the aspect ratio (L / D) of the large-particle ammonium sulfate. Under conditions of pH = 2.0~3.5, the ammonium sulfate product is a rice-grain-like or rod-shaped crystal; under conditions of pH = 4.5~5.5, the ammonium sulfate product is a round-grained crystal or a regular square crystal; under conditions of pH = 6.5 (nearly neutral), the ammonium sulfate product is a plate-like or flaky crystal. Therefore, to obtain round-grained large-particle ammonium sulfate crystals, the pH value of the ammonium sulfate mother liquor needs to be weakly acidic (pH = 4.5~5.5).

[0057] As can be seen from the data in Table 2, introducing the ammonium sulfate mother liquor containing fine crystals overflowing from the top of the thickener into the boiling surface of the crystallizer instead of sending it to the main mother liquor tank is beneficial to the crystallization process. The fine crystals act as seed crystals, rapidly consuming the supersaturation of the boiling surface, thereby preventing explosive nucleation and generation of more fine crystals on the boiling surface. This is conducive to shifting the peak of the product's particle size distribution to the right, increasing the yield of large-particle ammonium sulfate (≥2 mm).

[0058] from Figure 2 and Figure 3 As can be seen from Comparative Example 1, the ammonium sulfate mother liquor was not purified, nor was the pH value in the crystallizer adjusted. The ammonium sulfate mother liquor in the crystallization system was darker in color. Figure 2 As shown in (a), due to the high acidity of the ammonium sulfate mother liquor from the pickling tower, the resulting ammonium sulfate particles are dark-colored rice-grain shaped, such as... Figure 3 (a) The yield of large-particle ammonium sulfate was also low (data not provided); in Comparative Example 2, the purified ammonium sulfate mother liquor was nearly transparent, such as Figure 2 (b) The color of its products has also been improved, such as Figure 3 As shown in (b). After adding a purification system and a pH adjustment system in Example 1, a white, spherical, large-particle ammonium sulfate product was obtained, as shown in [example image]. Figure 3 As shown in (c).

Claims

1. A production apparatus for spherical, large-particle ammonium sulfate, the apparatus comprising the following components: (1) An adsorption unit, which includes an adsorption tower and is used to purify an unsaturated ammonium sulfate solution from a coking pickling unit; (2) Crystallization unit The crystallization unit includes: (i) A crystallizer connected to the adsorption unit via a pipeline, wherein the unsaturated ammonium sulfate solution purified by the adsorption unit enters the crystallizer along with the circulating mother liquor and is evaporated and crystallized therein, and the crystallizer is a flow guide tube with baffles evaporation crystallizer including a flow guide tube, baffles and a stirrer; (ii) A vapor recompression system, which is connected to the top of the crystallizer via a pipeline, for compressing the vapor at the top of the crystallizer as a heat source for the circulating mother liquor heater; (iii) A circulating mother liquor heater, which is connected to the crystallizer and the vapor recompression system via a circulating pipeline outside the crystallizer, and is used for heating and crystallizing the ammonium sulfate mother liquor with fine crystals flowing out of the crystallizer; (iv) Acid-base adjustment unit, which is connected to the crystallizer via pipeline and is used to adjust the pH value within the crystallizer. (3) Separation unit The separation unit includes: (i) a thickener, wherein the thickener is connected via a pipeline to the bottom of the crystallizer to concentrate the slurry from the bottom of the crystallizer, and the overflow surface at the top of the thickener is also connected via a pipeline to the boiling surface of the crystallizer to introduce the supersaturated ammonium sulfate mother liquor overflowing from the top of the thickener into the boiling surface of the crystallizer; and (ii) A centrifugal drying component, which is connected to the bottom of the thickener via a pipeline and is used for centrifugal drying of the material discharged from the bottom of the thickener.

2. The apparatus according to claim 1, wherein, The adsorption unit consists of two parallel, switchable adsorption towers.

3. The apparatus according to claim 1, wherein, The vapor recompression system is selected from one of mechanical vapor recompression (MVR) and thermal vapor recompression (TVR); and / or The acid-base adjustment unit consists of a flow regulating valve, a mother liquor pH controller, and a mother liquor pH sensor; and / or The centrifugal drying components include a centrifuge, a mother liquor tank, and a drying unit.

4. The apparatus according to claim 1, wherein, The apparatus also includes a vacuum pump connected to the top of the crystallizer to provide negative pressure to the crystallizer to facilitate the evaporation of the ammonium sulfate mother liquor; and / or The device also includes a flow regulating valve installed in front of the adsorption tower.

5. A method for producing spherical, large-particle ammonium sulfate using the apparatus as described in any one of claims 1 to 4, the method comprising the following steps: (1) Purification of ammonium sulfate solution in the adsorption unit Unsaturated ammonium sulfate solution enters the adsorption tower from the top through a flow regulating valve for purification. (2) Evaporation and crystallization of ammonium sulfate mother liquor in the crystallization unit In this step, the ammonium sulfate mother liquor purified in step (1) enters the crystallizer. Under the high temperature of the circulating mother liquor heater and the negative pressure of the vacuum pump, water vapor is evaporated, and the ammonium sulfate mother liquor in the crystallizer is concentrated to crystallize ammonium sulfate crystals. The density of the slurry in the crystallizer is maintained at 1.300~1.400 g / cm³. 3 To prevent the mother liquor from becoming more supersaturated than the level that can be maintained in a metastable state during the evaporation and concentration process; The crystallization process in the crystallizer is as follows: the baffle plate divides the crystallizer into a dynamic zone and a static zone. Under the action of stirring at the bottom of the crystallizer and the guide tube, the ammonium sulfate mother liquor forms an internal circulation in the dynamic zone. The fine ammonium sulfate crystals rise to the vicinity of the boiling surface in the guide tube and consume supersaturation, thus growing larger. In the static zone formed by the baffle plate and the crystallizer wall, large particles of ammonium sulfate settle. Furthermore, the pH of the ammonium sulfate mother liquor in the crystallizer is controlled at 4.5-5.5 through the adjustment of the acid-base adjustment unit. The ammonium sulfate mother liquor containing fine crystals is heated and crystallized by a circulating mother liquor heater through a circulation pipeline outside the crystallizer, and then returned to the crystallizer from the bottom; large-particle ammonium sulfate is discharged with the crystal slurry by a discharge pump to the separation unit; and Among them, a vapor recompression system is used to mechanically compress the vapor at the top of the crystallizer and use it as the heat source for the circulating mother liquor heater; (3) Separation of granular ammonium sulfate in the separation unit The slurry at the bottom of the crystallizer enters the thickener for concentration. The concentrated ammonium sulfate product is discharged from the bottom of the thickener and enters the centrifuge for centrifugation. The filtrate goes to the mother liquor tank, and the solid goes to the drying unit. After drying, the product is obtained. The ammonium sulfate mother liquor with fine crystals overflowing from the top of the thickener goes to the boiling surface of the crystallizer.

6. The method according to claim 5, wherein, In step (1), the unsaturated ammonium sulfate solution comes from the coking pickling unit and has a concentration of 30wt%-45wt%.

7. The method according to claim 5, wherein, In step (1), the unsaturated ammonium sulfate solution comes from the coking pickling unit and has a concentration of 40 wt%.

8. The method according to claim 5, wherein, The adsorption tower in step (1) is a packed tower. The packing material is selected from one or a combination of activated carbon, silica, and cation exchange resin. The adsorption temperature is 40-50℃ and the residence time is 30 minutes.

9. The method according to claim 5, wherein, For the acid-base adjustment unit, sulfuric acid and / or ammonia are used to adjust the pH value of the ammonium sulfate mother liquor in the crystallizer.

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