Granulation process of large granular urea for coating

Abstract

The invention relates to a granulation process of large granular urea for coating. The preparation method comprises the following steps: taking screened granular urea as a granulation master batch, putting the master batch into a disc granulator, rotating a disc, spraying a urea formaldehyde solution as a granulation binder, and uniformly dispersing; the preparation method comprises the following steps: spraying a binder on a disc, simultaneously crushing small-particle urea to 10-80 meshes, uniformly scattering the crushed small-particle urea on the granulation master batch sprayed with the binder, rotating the disc for 1-3 minutes, completely wrapping the urea powder on the master batch, continuously spraying the binder and the urea powder, circulating for 4-15 times until the particle size is 3-4.75 mm, and introducing hot air for preliminary drying and preheating for 5-10 minutes. According to the invention, the granulation production cost is obviously reduced, the balling efficiency is improved, and the method is suitable for industrial production; the agglomeration powder coating granulation mode can reduce energy and time required by cooling, the large-particle urea prepared by the process is uniform and round in particle size, smooth in surface and high in particle strength, a coating material is easy to coat on the surface, the coating quality is improved, and the large-particle urea has great industrialization value.

Description

Technical Field

[0001] The invention belongs to the technical field of fertilizers, and in particular relates to a granulation process for large-particle urea for coating. Background Art

[0002] Large granular urea usually refers to urea granules with a diameter of more than 2.8mm. Large granular urea has a wide range of uses and is suitable for various crops, especially field crops such as wheat, corn, rice, etc., as well as orchards, landscaping and other fields. Large granular urea has the advantages of easy transportation and storage, not easy to agglomerate, good fluidity, easy processing, convenient application, and reduced environmental pollution. At present, the production process of large granular urea generally adopts melt granulation technology, which evaporates and concentrates the urea solution at high temperature, and then cools and solidifies it into granules.

[0003] After application, traditional granular urea fertilizers, especially in a humid environment, tend to decompose quickly and release ammonia, resulting in nitrogen loss, which not only reduces the effective utilization rate of fertilizers, but also may cause air and water pollution. In order to overcome these problems, scientists and engineers use coating technology to control the release rate of nitrogen by coating the surface of urea particles with slow-release film materials, so that it can be retained in the soil for longer for plant absorption. In the current production of coated urea, coating is mostly completed by spraying, dipping or fluidized bed coating process to ensure that each urea particle is evenly covered. However, when large-particle urea is used for coating, there are defects such as poor particle size uniformity, incomplete coating due to rough surface, and uneven coating thickness; and the traditional melt granulation method is used to prepare large-particle urea, which requires heating urea above the melting point, which consumes more energy, especially in winter; or a large amount of solvent needs to be added, so the subsequent drying step also requires more energy and time, increasing production costs. For example, the prior art CN117756573A discloses a large-particle urea production process through a fluidized bed, which not only requires the additional introduction of molecular sieves, gelatin, and sulfonate components, but also requires granulation at 100-120°C, which consumes a lot of energy and generates higher production costs in winter. The prior art CN112358327A does not require the use of other additives and auxiliary materials, but it uses urea solution for granulation, which requires evaporation and concentration, and the subsequent drying step also consumes a lot of time and energy, and its energy consumption needs to be further reduced.

[0004] Therefore, a new granulation process for large-particle urea for coating is urgently needed to solve the above problems. Summary of the invention

[0005] The purpose of the present invention is to provide a process for granulating large-particle urea for coating, which has low energy consumption, low cost, uniform product particles, smooth surface and is conducive to coating.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A process for granulating large-particle urea for coating comprises the following steps:

[0008] The screened granular urea is used as the granulation masterbatch, and a binder is sprayed on the surface of the masterbatch in a disc granulator. The disc is rotated to sprinkle urea powder onto the masterbatch with the binder, so that the urea powder is evenly coated on the surface of the masterbatch; the binder and urea powder are sprayed repeatedly, and the cycle operation is repeated until the particle size grows. No additional heating is added in the above steps; finally, hot air is introduced for slight drying to obtain the product.

[0009] Specifically, the steps include:

[0010] S1. The granular urea is screened, and the granular urea with a particle size of 1.5 to 3.5 mm is used as a granulation masterbatch, and the particle size of less than 1.5 mm is used as a small granular urea, which is crushed to obtain a urea powder for standby use;

[0011] S2. Put the masterbatch into the disc granulator and rotate the disc;

[0012] S3. Spray urea-formaldehyde binder solution onto the surface of the masterbatch, and after uniform dispersion, put the urea powder into the disc granulator, rotate the disc, so that the urea powder is evenly coated on the surface of the masterbatch;

[0013] S4. Repeat step S3 until the product particle size increases to 3 to 4.75 mm;

[0014] S5. Slightly dry and sieve the product to obtain large urea particles for coating.

[0015] At present, the particle size distribution of granular urea on the market is relatively wide. The present invention screens the granular urea raw material, directly screens out urea particles larger than 3.5 mm and uses them as large granular urea, while urea particles smaller than 1.5 mm are used as small granular urea, and urea powder is obtained by crushing for subsequent granulation steps. On the one hand, the screening operation ensures that the granular urea used as the masterbatch has a relatively uniform particle size, which is conducive to improving the quality of the subsequent coating; on the other hand, the urea with smaller particles is crushed to prepare the powder, which not only reduces the energy consumption required for crushing, but also makes full use of the small particles and transportation losses in the granular urea, which has great value in industry. The screening means also improves the adaptability of the method of the present invention. Various granular ureas on the market can be used as raw materials for the method of the present invention. Since the granular urea used as the granulation masterbatch and the granular urea obtained by crushing to obtain the urea powder are from the same source, the method of the present invention will not cause compatibility problems, and both the process and the product are stable.

[0016] Preferably, the mass concentration of the urea-formaldehyde binder solution is 10-60%; more preferably, it is 20-50%.

[0017] Preferably, in step S3, the single feeding amount of the urea-formaldehyde binder solution accounts for 0.5-2% of the mass of the masterbatch.

[0018] In the granulation process of the present invention, by spraying a small amount of urea-formaldehyde binder solution multiple times, on the one hand, small and medium-sized urea particles can be prevented from agglomerating, and on the other hand, adhesion to the inner wall of the granulator can be reduced, thereby reducing loss; and, under the specific usage ratio of the urea-formaldehyde binder and the urea powder of the present invention, each layer of powder can be tightly and evenly bonded to the granular urea, thereby ensuring the uniformity of the internal structure and the mechanical strength of the large urea particles, and also being conducive to improving the uniformity of the particle size, which is more suitable for subsequent coating.

[0019] Preferably, the disc inclination angle of the disc granulator is 25 to 35°.

[0020] Preferably, the rotation speed of the disc granulator is 25-40 r / min.

[0021] Preferably, steps S1 to S4 are performed at room temperature without additional heating.

[0022] Compared with the traditional process of using molten urea or urea solution as raw material, the present invention uses urea powder as raw material to prepare large-particle urea. Not only does it not require an external heat source to melt the urea, but the present invention also uses agglomeration and powder coating to granulate, which is not affected by the ambient temperature and has high temperature adaptability. It can be produced at room temperature all year round and has high practical value in the industry.

[0023] After granulation, the water content of large granular urea is also very low, and only simple surface drying is required before entering the coating process, which further saves the energy required for drying and reduces production costs.

[0024] Preferably, the single feeding amount of urea powder in step S3 accounts for 2-8% of the mass of the masterbatch; more preferably, it is 4-7%.

[0025] Preferably, the pulverization in step S1 is performed by a pulverizer to 10-80 mesh.

[0026] Preferably, the pulverizer is a blade pulverizer or a chain pulverizer.

[0027] Preferably, the number of repetitions of step S3 in step S4 is 4 to 15 times; more preferably, it is 4 to 10 times.

[0028] Preferably, the slight drying in step S5 is drying by passing hot air, the hot air temperature is 50-150° C., and the drying time is 5-10 min.

[0029] After granulation is completed, hot air is introduced into the granulator to slightly dry the large-particle urea, which can not only increase the surface hardness of the large-particle urea, but also produce a certain polishing effect on the surface of the large-particle urea, making the surface smoother, which is conducive to providing the uniformity of subsequent coating, thereby improving the quality and performance of the coated large-particle urea. The large-particle urea prepared by the method of the present invention is subsequently used for coating, and the high temperature of the coating preheating process is sufficient to completely dry the inside of the large-particle urea, so it only needs to be slightly dried in the granulation stage, and the process of the present invention has a high energy utilization efficiency.

[0030] Furthermore, the product with particles smaller than 3 mm screened out in step S5 is returned to step S1 and continued to be used as granulation masterbatch.

[0031] In order to ensure the quality of the coating, it is necessary to control the particle size distribution of the large-particle urea used for coating within a narrow range as much as possible. The present invention screens the granulated product and selects large-particle urea of ​​3 to 4.75 mm for coating. In actual production, it can also be adjusted according to actual needs.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. The present invention adopts the powder coating method for the first time to granulate large urea particles, which has a simple process, greatly reduces the use of heat energy, effectively reduces energy consumption, and significantly saves production costs. The production cost can be reduced by 30-50% compared with the fluidized bed secondary granulation technology;

[0034] 2. The granulation process of the present invention fully utilizes the loss of raw materials and reduces the loss in the granulation process, further reducing the production cost and having great industrial value;

[0035] 3. The large granular urea prepared by the present invention has uniform particle size, good surface hardness and smooth surface, and is suitable for subsequent coating to prepare coated large granular urea, which is beneficial to improving the uniformity and quality of the coating;

[0036] 4. The large granular urea prepared by the present invention can enter the coating preheating and polishing process without cooling down after preliminary drying, which not only shortens the process time, but also the preheating and polishing before coating can further dry and round the large granular urea, making full use of energy and saving costs;

[0037] 5. The granulation process of the present invention has little restriction on raw materials, high adaptability, and is applicable to various commercially available granular urea. DETAILED DESCRIPTION

[0038] The specific implementation modes of the present invention are further described below in conjunction with examples. The following examples are only used to more clearly illustrate the technical solutions of the present invention, and are not intended to limit the protection scope of the present invention.

[0039] The urea-formaldehyde binder selected in the embodiment of the present invention is urea-formaldehyde 563 purchased from Zhengzhou Hongxing Chemical Industry, which is diluted with water to form a solution of corresponding concentration. In the embodiment of the present invention, steps S1 to S4 are not additionally heated and are performed at room temperature, with an ambient temperature of about 25°C.

[0040] Example 1

[0041] This embodiment provides a process for granulating large-particle urea for coating, comprising the following steps:

[0042] S1. The commercially available granular urea is sieved, and the granular urea with a particle size of 1.5 to 3.5 mm is used as the granulation masterbatch, and the granular urea with a particle size of less than 1.5 mm is used as the small granular urea, which is crushed by a blade mill for 5 min to obtain a urea powder of 10 to 80 mesh, and set aside;

[0043] S2. The masterbatch is put into the disc granulator, the disc of the disc granulator is tilted at an angle of 30 °, the disc is rotated, and the disc speed is set to 30r / min;

[0044] S3. Spraying a 20% urea-formaldehyde binder solution on the surface of the masterbatch, the spraying amount is 1.5% of the masterbatch mass, and after the turntable is evenly dispersed, 5% of the masterbatch mass of urea powder is put into the disc granulator, and the urea powder is evenly coated on the surface of the masterbatch by rotating the disc;

[0045] S4. Repeat step S3 5 times until the product particle size increases to 3 to 4.75 mm;

[0046] S5. Pass hot air at 90°C to dry the product slightly for 8 minutes, and screen out products with a particle size of 3 to 4.75 mm. The large urea particles are ready for coating without cooling; the screened products with particles smaller than 3 mm are returned to step S1 and continued to be used as granulation masterbatch.

[0047] Example 2

[0048] This embodiment provides a process for granulating large-particle urea for coating, comprising the following steps:

[0049] S1. The commercially available granular urea is sieved, and the granular urea with a particle size of 1.5 to 3.5 mm is used as the granulation masterbatch, and the granular urea with a particle size of less than 1.5 mm is used as the small granular urea, which is crushed by a blade mill for 5 min to obtain a urea powder of 10 to 80 mesh, and set aside;

[0050] S2. The masterbatch is put into the disc granulator, the disc of the disc granulator is tilted at an angle of 30 °, the disc is rotated, and the disc speed is set to 25r / min;

[0051] S3. Spraying a 15% urea-formaldehyde binder solution on the surface of the masterbatch, the spraying amount is 2% of the mass of the masterbatch, and after the turntable is evenly dispersed, 4% of the mass of the masterbatch is put into the disc granulator, and the urea powder is evenly coated on the surface of the masterbatch by rotating the disc;

[0052] S4. Repeat step S3 7 times until the product particle size increases to 3 to 4.75 mm;

[0053] S5. Pass hot air at 90°C to dry the product slightly for 10 minutes, and screen out products with a particle size of 3 to 4.75 mm. The large urea particles are ready for coating without cooling; the screened products with particles smaller than 3 mm are returned to step S1 and continued to be used as granulation masterbatch.

[0054] Example 3

[0055] This embodiment provides a process for granulating large-particle urea for coating, comprising the following steps:

[0056] S1. The commercially available granular urea is sieved, and the granular urea with a particle size of 1.5 to 3.5 mm is used as the granulation masterbatch, and the granular urea with a particle size of less than 1.5 mm is used as the small granular urea, which is crushed by a blade mill for 5 min to obtain a urea powder of 10 to 80 mesh, and set aside;

[0057] S2. The masterbatch is put into the disc granulator, the disc of the disc granulator is tilted at an angle of 30 °, the disc is rotated, and the disc speed is set to 35r / min;

[0058] S3. Spray a 30% urea-formaldehyde binder solution on the surface of the masterbatch, the spraying amount is 1% of the mass of the masterbatch, and after the turntable is evenly dispersed, 5% of the mass of the masterbatch urea powder is put into the disc granulator, and the urea powder is evenly coated on the surface of the masterbatch by rotating the disc;

[0059] S4. Repeat step S3 5 times until the product particle size increases to 3 to 4.75 mm;

[0060] S5. Pass hot air at 90°C to dry the product slightly for 8 minutes, and screen out products with a particle size of 3 to 4.75 mm. The large urea particles are ready for coating without cooling; the screened products with particles smaller than 3 mm are returned to step S1 and continued to be used as granulation masterbatch.

[0061] Example 4

[0062] This embodiment provides a process for granulating large-particle urea for coating, comprising the following steps:

[0063] S1. The commercially available granular urea is sieved, and the granular urea with a particle size of 1.5 to 3.5 mm is used as the granulation masterbatch, and the granular urea with a particle size of less than 1.5 mm is used as the small granular urea, which is crushed by a blade mill for 5 min to obtain a urea powder of 10 to 80 mesh, and set aside;

[0064] S2. The masterbatch is put into the disc granulator, the disc of the disc granulator is tilted at an angle of 30 °, the disc is rotated, and the disc speed is set to 35r / min;

[0065] S3. Spraying a 50% urea-formaldehyde binder solution on the surface of the masterbatch, the spraying amount is 1% of the mass of the masterbatch, and after the turntable is evenly dispersed, 7% of the mass of the masterbatch is put into the disc granulator, and the urea powder is evenly coated on the surface of the masterbatch by rotating the disc;

[0066] S4. Repeat step S3 4 times until the product particle size increases to 3-4.75 mm;

[0067] S5. Pass hot air at 90°C to dry the product slightly for 8 minutes, and screen out products with a particle size of 3 to 4.75 mm. The large urea particles are ready for coating without cooling; the screened products with particles smaller than 3 mm are returned to step S1 and continued to be used as granulation masterbatch.

[0068] Example 5

[0069] This embodiment provides a process for granulating large-particle urea for coating, comprising the following steps:

[0070] S1. The commercially available granular urea is sieved, and the granular urea with a particle size of 1.5 to 3.5 mm is used as the granulation masterbatch, and the granular urea with a particle size of less than 1.5 mm is used as the small granular urea, which is crushed by a blade mill for 5 min to obtain a urea powder of 10 to 80 mesh, and set aside;

[0071] S2. The masterbatch is put into the disc granulator, the disc of the disc granulator is tilted at an angle of 30 °, the disc is rotated, and the disc speed is set to 25r / min;

[0072] S3. Spraying a 10% urea-formaldehyde binder solution on the surface of the masterbatch, the spraying amount is 0.5% of the mass of the masterbatch, and after the turntable is evenly dispersed, 2% of the mass of the masterbatch is put into the disc granulator, and the urea powder is evenly coated on the surface of the masterbatch by rotating the disc;

[0073] S4. Repeat step S3 15 times until the product particle size increases to 3 to 4.75 mm;

[0074] S5. Pass hot air at 90°C to dry the product slightly for 8 minutes, and screen out products with a particle size of 3 to 4.75 mm. The large urea particles are ready for coating without cooling; the screened products with particles smaller than 3 mm are returned to step S1 and continued to be used as granulation masterbatch.

[0075] Performance Testing

[0076] 1. Roundness

[0077] The large urea particles prepared in Examples 1 to 5 were observed to see whether the large urea particles had rounded shapes. The results are recorded in Table 1.

[0078] 2. Granularity

[0079] The particle sizes of the products of Examples 1 to 5 were determined according to the method of GB / T 2441.7-2010, and a set of test sieves of 3 mm and 4.75 mm were selected. The calculated particle sizes were recorded in Table 1.

[0080] 3. Coating quality

[0081] Take Examples 1 to 5 and commercially available large-particle urea (purchased from Hualu Hengsheng) and coat them with polyurethane respectively. The coating process refers to the method described in Example 1 of Patent CN103772646A: Examples 1 to 5 and commercially available large-particle urea are respectively put into an efficient coating machine and heated to 65°C (in this process, the large-particle urea prepared by the embodiment of the present invention is further dried while preheating), and the prepared soybean oil polyol biodegradable slow-release fertilizer coating material is pumped into the continuously moving fertilizer surface in batches, and the coating material is quickly and evenly distributed to the surface of the urea particles. The input amount of the coating material each time is 1wt% of the total weight of the large-particle urea, and the coating material is repeatedly coated until the coating material accounts for 3wt% of the total amount of the large-particle urea. After curing for 4 minutes, the coating material is cured as a dense and tough film on the fertilizer surface. Finally, 0.2% paraffin wax of the total mass of the fertilizer is added to prevent adhesion between the fertilizer particles, and cooled to 20°C to obtain the corresponding coated large-particle urea.

[0082] At 25°C, the nitrogen release rate of coated large-particle urea was tested by static water extraction method. Samples were taken after 24 hours and the results are recorded in Table 1.

[0083] Table 1

[0084]

[0085]

[0086] The results show that the large-particle urea prepared by the coating large-particle urea granulation process of the present invention has good morphology, round particles, uniform particle size distribution, and is suitable for coating in the later stage; after the large-particle urea prepared by the present invention is coated, it shows a lower initial release rate than conventional commercial products, indicating that the large-particle urea prepared by the method of the present invention has better particle strength and coating quality. It can be inferred that it has good process stability and is conducive to extending the release period of coated urea. On the basis of excellent product quality, the process method of the present invention can also greatly save energy and cost, and from the perspective of industrial production, it also has universality of climate environment and production raw materials, and has practical industrial value.

[0087] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention is described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A process for granulating large-particle urea for coating, characterized in that: The steps include: The screened granular urea is used as the granulation masterbatch, and a binder is sprayed on the surface of the masterbatch in a disc granulator. The disc is rotated to sprinkle urea powder onto the masterbatch with the binder, so that the urea powder is evenly coated on the surface of the masterbatch; the binder and urea powder are sprayed repeatedly, and the cycle operation is repeated until the particle size grows. No additional heating is added in the above steps; finally, hot air is introduced for slight drying to obtain the product.

2. The process for granulating large-particle urea for coating according to claim 1, characterized in that: The specific steps include: S1. The granular urea is sieved, and the granular urea with a particle size of 1.5~3.5mm is used as a granulation masterbatch, and the particle size of less than 1.5mm is used as a small granular urea, and the urea powder is crushed to obtain a urea powder for standby use; S2. Put the masterbatch into the disc granulator and rotate the disc; S3. Spray urea-formaldehyde binder solution onto the surface of the masterbatch, and after uniform dispersion, put the urea powder into the disc granulator, rotate the disc, so that the urea powder is evenly coated on the surface of the masterbatch; S4. Repeat step S3 until the product particle size increases to 3-4.75 mm; S5. Slightly dry and sieve the product to obtain large granular urea for coating.

3. The process for granulating large-particle urea for coating according to claim 2, characterized in that: The mass concentration of the urea-formaldehyde binder solution is 10-60%.

4. The process for granulating large-particle urea for coating according to claim 2, characterized in that: The disc speed is 25-40 r / min.

5. The process for granulating large-particle urea for coating according to claim 2, characterized in that: In the step S3, the single spraying amount of the urea-formaldehyde binder solution accounts for 0.5-2% of the mass of the masterbatch.

6. The process for granulating large-particle urea for coating according to claim 2, characterized in that: In the step S3, the single feeding amount of urea powder accounts for 2-8% of the mass of the masterbatch.

7. The process for granulating large-particle urea for coating according to claim 2, characterized in that: In the step S1, the pulverization is performed by a pulverizer to pulverize into 10-80 meshes.

8. The process for granulating large-particle urea for coating according to claim 2, characterized in that: The number of repetitions of step S3 in step S4 is 4 to 15 times.

9. The process for granulating large-particle urea for coating according to claim 2, characterized in that: The slight drying in step S5 is drying by passing hot air, the hot air temperature is 50-150° C., and the drying time is 5-10 minutes.

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