A method for controlled crystallization of ammonium sulfate fertilizer

Abstract

This invention relates to a method for controlled crystallization of ammonium sulfate fertilizer, belonging to the field of ammonium sulfate production technology. Based on the calculation formulas for the amount of ammonium sulfate crystals and the average particle size of ammonium sulfate crystals, this invention selects the ultrasonic power, the conventional heating time before crystal precipitation, and the total ultrasonic treatment time after crystal precipitation. The ammonium sulfate solution from ammonia desulfurization is heated to 92-98°C and evaporated and crystallized under normal pressure. Specifically, the ammonium sulfate solution is heated and held at this temperature for 20-40 minutes, then ultrasonic waves are activated to treat the solution until ammonium sulfate crystals precipitate. The ultrasonic treatment is then stopped for 2-3 minutes, and then activated again for 2-3 minutes. During the evaporation and crystallization process after crystal precipitation, the ultrasonic waves are repeatedly activated and deactivated. The reaction cutoff time is selected according to the calculation formula. The solid-liquid mixture is filtered to obtain ammonium sulfate crystals with a controllable amount of crystallization. This invention introduces ultrasonic waves into the atmospheric pressure evaporation and crystallization process of ammonium sulfate solution to controllably prepare ammonium sulfate crystals, thereby increasing the yield of ammonium sulfate.

Description

Technical Field

[0001] This invention relates to a method for controlled crystallization of ammonium sulfate fertilizer, belonging to the field of ammonium sulfate production technology. Background Technology

[0002] Utilizing sulfur dioxide from smelting flue gas to produce ammonium sulfate fertilizer, an industrial byproduct, is a crucial step in the non-ferrous metals industry to achieve comprehensive sulfur resource recovery and environmentally compliant emissions. The ammonium sulfate solution is sent to an evaporator crystallizer for heating, causing a large amount of water to evaporate. Generally, when the solid content reaches approximately 30%-50%, it is sent to a centrifuge for separation to obtain the ammonium sulfate product.

[0003] Ammonium sulfate evaporation crystallization technologies mainly include vacuum single-effect evaporation crystallization, multi-effect evaporation crystallization, and atmospheric single-effect evaporation crystallization. Vacuum single-effect evaporation crystallization is carried out under vacuum conditions, offering the advantage of good crystallization results, but the process is relatively complex and requires significant equipment investment. Multi-effect evaporation crystallization uses multiple evaporators connected in series, utilizing secondary steam generated by the preceding evaporators to heat the solution in the subsequent evaporators, saving steam consumption but increasing equipment costs. Atmospheric single-effect evaporation crystallization uses only one evaporator, operating under atmospheric pressure. It is simple to operate and has low equipment costs, but suffers from low ammonium sulfate yield, poor crystallization effect, uneven particle size, and long crystallization time.

[0004] To improve ammonium sulfate crystallization, CN218924284U discloses a method that reduces ammonia escape during production and controls over-acidity by adding dilute acid to the concentration, recovery, and washing sections of the desulfurization tower, thereby addressing the quality fluctuation problem of ammonium sulfate in ammonia-based desulfurization and improving the crystallization effect. However, since multiple processes are carried out in a highly acidic environment, equipment corrosion and waste acid generation are inevitable. Furthermore, national standards have strict requirements on the free acid content (i.e., residual acid) in ammonium sulfate products. Therefore, this process requires adjusting the pH value of the solution with a large amount of ammonia water before evaporation and crystallization. CN114832424A discloses a crystallization device and its application, as well as a method for preparing large-particle ammonium sulfate crystals. Specifically, it uses two evaporation crystallizers and sets up a reflux pipe on the evaporation crystallization device to form a rapid heating loop in the circulation pipe, allowing the crystal slurry to heat up quickly. The reflux flow rate is used to control the supersaturation, solid content, and suspension state in the crystallization chamber, making the crystallization process and particle size controllable, ultimately obtaining ammonium sulfate products with good crystallization effect. However, this method requires multiple evaporation crystallization devices and has high operating costs. CN202110704207.7 discloses a method and apparatus for the continuous preparation of granular ammonium sulfate using heterogeneous seed crystals. Specifically, the ammonium sulfate solution to be crystallized is crystallized in the presence of heterogeneous seed crystals. The resulting mixture is then separated. The mixture containing small particles undergoes crystallization elimination, arbitrary sequential separation, and selective concentration. The mixture containing large primary crystal particles is separated under conditions where the temperature difference before and after separation is no greater than 5°C. The resulting ammonium sulfate solution is then returned to the crystallization elimination stage. Finally, a large-particle, high-yield ammonium sulfate product is obtained. However, the process control is cumbersome and difficult. In summary, the existing preparation process of ammonium sulfate solution evaporation crystallization from ammonia desulfurization suffers from problems such as low yield, poor crystallization effect, and uneven particle size due to atmospheric pressure crystallization, and cannot controllably prepare ammonium sulfate crystals. Summary of the Invention

[0005] To address the technical problems of low yield, poor crystallization effect, and uneven particle size in existing ammonium sulfate solution evaporation and crystallization processes during ammonia desulfurization, as well as the inability to controllably prepare ammonium sulfate crystals, this invention proposes a method for controllable crystallization of ammonium sulfate fertilizer. This invention introduces ultrasound during the ammonium sulfate solution evaporation and crystallization process, utilizing the cavitation and mechanical effects of ultrasound to improve diffusion and mass transfer, promoting crystal nucleus formation and crystal growth. By precisely controlling the introduction stage and duration of ultrasound, specifically, continuous ultrasound is activated before crystal precipitation to promote ammonium sulfate crystal nucleus formation. After crystal precipitation, ultrasound can prevent crystal agglomeration and promote crystal growth, while also breaking down primary crystal nuclei into more secondary crystal nuclei, thus reducing particle size. Therefore, indirect ultrasound is used at this stage. This achieves the goals of increasing ammonium sulfate yield, shortening crystallization time, and ensuring more uniform ammonium sulfate particle size while maintaining the desired product particle size.

[0006] A method for controlled crystallization of ammonium sulfate fertilizer, the specific steps of which are as follows:

[0007] (1) Select the ultrasonic power, conventional heating time before crystal precipitation, and total ultrasonic treatment time after crystal precipitation based on the calculation formula of ammonium sulfate crystal amount and the calculation formula of average particle size of ammonium sulfate crystals.

[0008] (2) The ammonium sulfate solution of ammonia desulfurization is heated to 92-98℃ and evaporated and crystallized under normal pressure. Specifically, the ammonium sulfate solution is heated and kept at the temperature for 20-40 minutes. Ultrasonic waves are turned on to act on the solution until ammonium sulfate crystals precipitate. Then the ultrasonic action is stopped for 2-3 minutes, and then the ultrasonic action is turned on again for 2-3 minutes. During the evaporation and crystallization process after crystal precipitation, the ultrasonic waves are turned on and off repeatedly. The reaction cutoff time is selected according to the calculation formula. The solid-liquid mixture is filtered to obtain ammonium sulfate crystals with a controllable amount of crystallization.

[0009] The formula for calculating the amount of ammonium sulfate crystals in step (1) is as follows:

[0010] y = (29x1 + 0.6x2 + 40x3) 1.4 +5(x3-7)-550) / 100

[0011] The formula for calculating the average particle size of ammonium sulfate in step (1) is as follows:

[0012] z = 257 - (1.1x2) 0.7 +1.1x3 1.7 -2x1 0.9 )

[0013] In the formula: y is the amount of ammonium sulfate crystals, in g; z is the average particle size of the ammonium sulfate product, in μm; x1 is the conventional heating time before crystal precipitation, in min; x2 is the ultrasonic power, in W; x3 is the total ultrasonic treatment time after crystal precipitation, in min.

[0014] In step (2), the ammonium sulfate solution contains SO4 2- The concentration is 300-400 g / L, the ultrasonic power is 100-500 W, and the total ultrasonic treatment time after crystal precipitation is 5-12 min.

[0015] The beneficial effects of this invention are:

[0016] (1) This invention introduces ultrasound into the ammonium sulfate crystallization process. Ultrasound promotes diffusion and mass transfer, strengthens the nucleation and growth process of ammonium sulfate, thereby increasing crystallization yield, reducing the time required for crystallization, and making the ammonium sulfate particle size more uniform.

[0017] (2) This invention controls the particle size of ammonium sulfate products by precisely controlling the introduction stage and action time of ultrasound, so as to improve the yield and crystallization effect while ensuring the particle size of ammonium sulfate products, thus achieving controllable crystallization of ammonium sulfate fertilizer. Attached Figure Description

[0018] Figure 1 SEM image of ammonium sulfate crystals prepared in Example 1;

[0019] Figure 2 SEM image of ammonium sulfate crystals prepared for Comparative Example 1. Detailed Implementation

[0020] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the content described.

[0021] Example 1: A method for controlled crystallization of ammonium sulfate fertilizer, the specific steps of which are as follows:

[0022] (1) Based on the calculation formula for the amount of ammonium sulfate crystals (15.8g of ammonium sulfate crystals prepared from 100mL of ammonium sulfate solution for ammonia desulfurization) and the calculation formula for the average particle size of ammonium sulfate (171.6 μm average particle size), the ultrasonic power (400W), the conventional heating time before crystal precipitation (30min), and the total ultrasonic treatment time after crystal precipitation (10min) were selected.

[0023] The formula for calculating the amount of ammonium sulfate crystals is:

[0024] y = (29x1 + 0.6x2 + 40x3) 1.4 +5(x3-7)-550) / 100

[0025] The formula for calculating the average particle size of ammonium sulfate is as follows:

[0026] z = 257 - (1.1x2) 0.7 +1.1x3 1.7 -2x1 0.9 )

[0027] In the formula: y is the amount of ammonium sulfate crystals, in g; z is the average particle size of the ammonium sulfate product, in μm; x1 is the conventional heating time before crystal precipitation, in min; x2 is the ultrasonic power, in W; x3 is the total ultrasonic treatment time after crystal precipitation, in min;

[0028] (2) Add 100 mL of ammonium sulfate solution from ammonia desulfurization (the ammonium sulfate solution contains SO42-) 2-A solution with a concentration of 320 g / L was added to a 250 mL beaker and heated under normal pressure to evaporate and crystallize. Specifically, the ammonium sulfate solution was heated and kept at 92–98 °C for 30 min, and then ultrasonic waves (400 W) were turned on to sonicate the solution until ammonium sulfate crystals precipitated. The ultrasonic waves were stopped for 2 min, and then turned on again for 2 min. During the evaporation and crystallization process after crystal precipitation, the ultrasonic waves were repeatedly turned on and off. The reaction cutoff time was selected according to the calculation formula. The solid-liquid mixture was filtered, and the solid was dried at a constant temperature of 65 °C to a constant weight to obtain ammonium sulfate crystals with a controllable amount of crystallization.

[0029] In this embodiment, the total ultrasonic treatment time after crystal precipitation was 10 minutes, and the total evaporation and crystallization time of ammonium sulfate was 70 minutes. The amount of ammonium sulfate crystals was 15.8 g, which is consistent with the expected amount of ammonium sulfate crystals prepared. The product particle size range was 80–360 micrometers, with an average particle size of 170.15 micrometers. The expected average particle size of the prepared ammonium sulfate was 171.6 micrometers. SEM images of the ammonium sulfate crystals prepared in this embodiment at different magnifications are shown below. Figure 1 ,from Figure 1 It can be seen that ultrasonic crystallization produces particles with clearer outlines, more uniform particle size, and better crystallization results.

[0030] Comparative Example 1: The method for evaporating and crystallizing ammonium sulfate fertilizer, the specific steps are as follows:

[0031] Ammonium sulfate solution for ammonia desulfurization (SO4 in ammonium sulfate solution) 2- The concentration of 320 g / L was added to a 250 mL beaker and heated to 92 °C. The mixture was evaporated and crystallized for 74 min under normal pressure and at 92–98 °C to obtain a solid-liquid mixture. The solid-liquid mixture was filtered, and the solid was dried at 65 °C to constant weight to obtain ammonium sulfate crystals.

[0032] In this comparative example, the ammonium sulfate precipitation time was 55 min, the ammonium sulfate crystal yield was 10.46 g, the particle size ranged from 15 to 570 μm, and the average particle size was 207.84 μm. SEM images of the ammonium sulfate crystals prepared in this comparative example at different magnifications are shown below. Figure 2 ,from Figure 2 It can be seen that the ammonium sulfate crystals have unclear particle outlines, uneven particle size, and poor crystallization effect.

[0033] Comparative Example 2: The method for evaporating and crystallizing ammonium sulfate fertilizer, the specific steps are as follows:

[0034] Ammonium sulfate solution for ammonia desulfurization (SO4 in ammonium sulfate solution) 2-A solution with a concentration of 320 g / L was added to a 250 mL beaker and heated to evaporate and crystallize under normal pressure. Specifically, the ammonium sulfate solution was heated and kept at 92–98 °C for 30 min, and then ultrasonically treated with 500 W for 70 min to obtain a solid-liquid mixture. The solid-liquid mixture was filtered, and the solid was dried at 65 °C to constant weight to obtain ammonium sulfate crystals.

[0035] The ammonium sulfate solid content in this comparative example was 17.73 g, with a particle size range of 10–310 μm and an average particle size of 105.82 μm. Continuous ultrasonic crystallization breaks down the primary ammonium sulfate crystals formed in the solution, generating more ammonium sulfate crystal nuclei and promoting rapid crystallization, ultimately resulting in a higher ammonium sulfate yield. However, it inhibits particle growth and severely affects particle size. Therefore, continuous ultrasonic crystallization can yield a higher ammonium sulfate yield, but the particles are small. Small ammonium sulfate particles have problems such as easy agglomeration, poor flowability, and powder loss during fertilization.

[0036] Therefore, compared with conventional evaporation crystallization, introducing ultrasound can effectively reduce crystallization time, shorten crystal precipitation time, improve ammonium sulfate quality and yield, and thus reduce processing costs; by precisely controlling the introduction stage and action time of ultrasound, the particle size of ammonium sulfate products can be controlled to ensure the particle size of ammonium sulfate products.

[0037] Example 2: A method for controlled crystallization of ammonium sulfate fertilizer, the specific steps of which are as follows:

[0038] (1) Based on the calculation formula for the amount of ammonium sulfate crystals (10.7g of ammonium sulfate crystals prepared from 100mL of ammonium sulfate solution for ammonia desulfurization) and the calculation formula for the average particle size of ammonium sulfate (197.4 μm average particle size), the ultrasonic power (450W), the conventional heating time before crystal precipitation (30min), and the total ultrasonic treatment time after crystal precipitation (6min) were selected.

[0039] The formula for calculating the amount of ammonium sulfate crystals is:

[0040] y = (29x1 + 0.6x2 + 40x3) 1.4 +5(x3-7)-550) / 100

[0041] The formula for calculating the average particle size of ammonium sulfate is as follows:

[0042] z = 257 - (1.1x2) 0.7 +1.1x3 1.7 -2x1 0.9 )

[0043] In the formula: y is the amount of ammonium sulfate crystals, in g; z is the average particle size of the ammonium sulfate product, in μm; x1 is the conventional heating time before crystal precipitation, in min; x2 is the ultrasonic power, in W; x3 is the total ultrasonic treatment time after crystal precipitation, in min;

[0044] (2) Add 100 mL of ammonium sulfate solution from ammonia desulfurization (the ammonium sulfate solution contains SO42-) 2- A solution with a concentration of 320 g / L was added to a 250 mL beaker and heated under normal pressure to evaporate and crystallize. Specifically, the ammonium sulfate solution was heated and kept at 92–98 °C for 30 min, and then ultrasonic waves (450 W) were turned on to sonicate the solution until ammonium sulfate crystals precipitated. The ultrasonic waves were stopped for 2 min, and then turned on again for 2 min. During the evaporation and crystallization process after crystal precipitation, the ultrasonic waves were repeatedly turned on and off. The reaction cutoff time was selected according to the calculation formula. The solid-liquid mixture was filtered, and the solid was dried at a constant temperature of 65 °C to a constant weight to obtain ammonium sulfate crystals with a controllable amount of crystallization.

[0045] In this embodiment, the total ultrasonic treatment time after crystal precipitation was 6 minutes, the total ammonium sulfate evaporation and crystallization time was 62 minutes, the amount of ammonium sulfate crystallized was 10.9 g, the expected amount of ammonium sulfate crystallized was 10.7 g, the product particle size range was 90-360 micrometers, the average particle size was 198.3 micrometers, and the expected average particle size of the prepared ammonium sulfate was 197.4 micrometers. In this embodiment, the ammonium sulfate particles crystallized by ultrasonication had clearer outlines, more uniform particle size, and better crystallization effect. In this embodiment, the ammonium sulfate crystal yield of Comparative Example 1, which took 70 minutes of total ammonium sulfate evaporation and crystallization, could be obtained in 62 minutes of total ammonium sulfate evaporation and crystallization.

[0046] Example 3: A method for controlled crystallization of ammonium sulfate fertilizer, the specific steps of which are as follows:

[0047] (1) Based on the calculation formula for the amount of ammonium sulfate crystals (15.3g of ammonium sulfate crystals prepared from 100mL of ammonium sulfate solution for ammonia desulfurization) and the calculation formula for the average particle size of ammonium sulfate (184.3 μm average particle size), the ultrasonic power (500W), the conventional heating time before crystal precipitation (36min), and the total ultrasonic treatment time after crystal precipitation (8min) were selected.

[0048] The formula for calculating the amount of ammonium sulfate crystals is:

[0049] y = (29x1 + 0.6x2 + 40x3) 1.4 +5(x3-7)-550) / 100

[0050] The formula for calculating the average particle size of ammonium sulfate is as follows:

[0051] z = 257 - (1.1x2) 0.7+1.1x3 1.7 -2x1 0.9 )

[0052] In the formula: y is the amount of ammonium sulfate crystals, in g; z is the average particle size of the ammonium sulfate product, in μm; x1 is the conventional heating time before crystal precipitation, in min; x2 is the ultrasonic power, in W; x3 is the total ultrasonic treatment time after crystal precipitation, in min;

[0053] (2) Add 100 mL of ammonium sulfate solution from ammonia desulfurization (the ammonium sulfate solution contains SO42-) 2- A solution with a concentration of 320 g / L was added to a 250 mL beaker and heated under normal pressure to evaporate and crystallize. Specifically, the ammonium sulfate solution was heated and kept at 92–98 °C for 36 min, and then ultrasonic waves (500 W) were turned on to sonicate the solution until ammonium sulfate crystals precipitated. The ultrasonic waves were stopped for 3 min, and then turned on again for 2 min. During the evaporation and crystallization process after crystal precipitation, the ultrasonic waves were repeatedly turned on and off. The reaction cutoff time was selected according to the calculation formula. The solid-liquid mixture was filtered, and the solid was dried at a constant temperature of 65 °C to a constant weight to obtain ammonium sulfate crystals with a controllable amount of crystallization.

[0054] In this embodiment, the total ultrasonic treatment time after crystal precipitation was 8 minutes, the total evaporation and crystallization time of ammonium sulfate was 70 minutes, the amount of ammonium sulfate crystallized was 15.0 g, the expected amount of ammonium sulfate crystallized was 15.3 g, the product particle size range was 100-310 micrometers, the average particle size was 183.15 micrometers, and the expected average particle size of the prepared ammonium sulfate was 184.3 micrometers. In this embodiment, the ammonium sulfate particles crystallized by ultrasonication had clearer outlines, more uniform particle size, and better crystallization effect.

[0055] Example 4: A method for controlled crystallization of ammonium sulfate fertilizer, the specific steps of which are as follows:

[0056] (1) Based on the calculation formula for the amount of ammonium sulfate crystals (18.4g of ammonium sulfate crystals prepared from 100mL of ammonium sulfate solution by ammonia desulfurization) and the calculation formula for the average particle size of ammonium sulfate (183.5 μm average particle size), the ultrasonic power (200W), the conventional heating time before crystal precipitation (33min), and the total ultrasonic treatment time after crystal precipitation (12min) were selected.

[0057] The formula for calculating the amount of ammonium sulfate crystals is:

[0058] y = (29x1 + 0.6x2 + 40x3) 1.4 +5(x3-7)-550) / 100

[0059] The formula for calculating the average particle size of ammonium sulfate is as follows:

[0060] z = 257 - (1.1x2) 0.7 +1.1x3 1.7 -2x1 0.9 )

[0061] In the formula: y is the amount of ammonium sulfate crystals, in g; z is the average particle size of the ammonium sulfate product, in μm; x1 is the conventional heating time before crystal precipitation, in min; x2 is the ultrasonic power, in W; x3 is the total ultrasonic treatment time after crystal precipitation, in min;

[0062] (2) Add 100 mL of ammonium sulfate solution from ammonia desulfurization (the ammonium sulfate solution contains SO42-) 2- A solution with a concentration of 320 g / L was added to a 250 mL beaker and heated under normal pressure to evaporate and crystallize. Specifically, the ammonium sulfate solution was heated and kept at 92–98 °C for 33 min, and then ultrasonic waves (200 W) were turned on to sonicate the solution until ammonium sulfate crystals precipitated. The ultrasonic waves were stopped for 3 min, and then turned on again for 3 min. During the evaporation and crystallization process after crystal precipitation, the ultrasonic waves were repeatedly turned on and off. The reaction cutoff time was selected according to the calculation formula. The solid-liquid mixture was filtered, and the solid was dried at a constant temperature of 65 °C to a constant weight to obtain ammonium sulfate crystals with a controllable amount of crystallization.

[0063] In this embodiment, the total ultrasonic treatment time after crystal precipitation was 12 minutes, the total evaporation and crystallization time of ammonium sulfate was 76 minutes, the amount of ammonium sulfate crystallized was 18.1 g, the expected amount of ammonium sulfate crystallized was 18.4 g, the product particle size range was 60-350 micrometers, the average particle size was 186.45 micrometers, and the expected average particle size of the prepared ammonium sulfate was 183.5 micrometers. In this embodiment, the ammonium sulfate particles crystallized by ultrasonication had clearer outlines, more uniform particle size, and better crystallization effect.

[0064] Example 5: A method for controlled crystallization of ammonium sulfate fertilizer, the specific steps of which are as follows:

[0065] (1) Based on the calculation formula for the amount of ammonium sulfate crystals (15.3g of ammonium sulfate crystals prepared from 100mL of ammonium sulfate solution for ammonia desulfurization) and the calculation formula for the average particle size of ammonium sulfate (151.8 μm average particle size), the ultrasonic power (300W), the conventional heating time before crystal precipitation (20min), and the total ultrasonic treatment time after crystal precipitation (12min) were selected.

[0066] The formula for calculating the amount of ammonium sulfate crystals is:

[0067] y = (29x1 + 0.6x2 + 40x3) 1.4 +5(x3-7)-550) / 100

[0068] The formula for calculating the average particle size of ammonium sulfate in step (1) is as follows:

[0069] z = 257 - (1.1x2) 0.7 +1.1x3 1.7 -2x1 0.9 )

[0070] In the formula: y is the amount of ammonium sulfate crystals, in g; z is the average particle size of the ammonium sulfate product, in μm; x1 is the conventional heating time before crystal precipitation, in min; x2 is the ultrasonic power, in W; x3 is the total ultrasonic treatment time after crystal precipitation, in min;

[0071] (2) Add 100 mL of ammonium sulfate solution from ammonia desulfurization (the ammonium sulfate solution contains SO42-) 2- A solution with a concentration of 380 g / L was added to a 250 mL beaker and heated under normal pressure to evaporate and crystallize. Specifically, the ammonium sulfate solution was heated and kept at 92–98 °C for 20 min, and then ultrasonic waves (300 W) were turned on to sonicate the solution until ammonium sulfate crystals precipitated. The ultrasonic waves were stopped for 2 min, and then turned on again for 2 min. During the evaporation and crystallization process after crystal precipitation, the ultrasonic waves were repeatedly turned on and off. The reaction cutoff time was selected according to the calculation formula. The solid-liquid mixture was filtered, and the solid was dried at a constant temperature of 65 °C to a constant weight to obtain ammonium sulfate crystals with a controllable amount of crystallization.

[0072] In this embodiment, the total ultrasonic treatment time after crystal precipitation was 12 minutes, the total evaporation and crystallization time of ammonium sulfate was 67 minutes, the amount of ammonium sulfate crystallized was 15.6 g, the expected amount of ammonium sulfate crystallized was 15.3 g, the product particle size range was 50-380 micrometers, the average particle size was 153.25 micrometers, and the expected average particle size of the prepared ammonium sulfate was 151.8 micrometers. In this embodiment, the ammonium sulfate particles crystallized by ultrasonication had clearer outlines, more uniform particle size, and better crystallization effect.

[0073] The specific embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for controlled crystallization of ammonium sulfate fertilizer, characterized in that, The specific steps are as follows: (1) Select the ultrasonic power, conventional heating time before crystal precipitation, and total ultrasonic treatment time after crystal precipitation based on the calculation formulas for the amount of ammonium sulfate crystals and the average particle size of ammonium sulfate crystals; the calculation formula for the amount of ammonium sulfate crystals is: y = (29x1+0.6x2+40x3 1.4 +5(x3-7)-550) / 100; The formula for calculating the average particle size of ammonium sulfate crystals in step (1) is as follows: z = 257-(1.1x2 0.7 +1.1x3 1.7 -2x1 0.9 ); In the formula: y is the amount of ammonium sulfate crystals, in g; z is the average particle size of the ammonium sulfate product, in μm; x1 is the conventional heating time before crystal precipitation, in min; x2 is the ultrasonic power, in W; x3 is the total ultrasonic treatment time after crystal precipitation, in min; (2) The ammonium sulfate solution of ammonia desulfurization is heated to 92~98℃ and evaporated and crystallized under normal pressure. Specifically, the ammonium sulfate solution is heated and kept at the temperature for 20~40min, and the ultrasonic waves are turned on to act on the solution until the ammonium sulfate crystals precipitate. Then the ultrasonic action is stopped for 2~3min, and the ultrasonic waves are turned on again to act on the solution for 2~3min. During the evaporation and crystallization process after the crystals precipitate, the ultrasonic waves are turned on and off repeatedly. The reaction cutoff time is selected according to the calculation formula. The solid-liquid mixture is filtered to obtain ammonium sulfate crystals with a controllable amount of crystallization.

2. The method for controlled crystallization of ammonium sulfate fertilizer according to claim 1, characterized in that: In step (2), SO4 in the ammonium sulfate solution 2- The concentration is 300-400 g / L, the ultrasonic power is 100-500 W, and the total ultrasonic treatment time after crystal precipitation is 5-12 min.

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