Granulation method for producing compound fertilizer by chelating urea sulfate

Abstract

The application provides a granulation method for urea sulfate chelate composite fertilizer, and belongs to the technical field of composite fertilizer.The granulation method for urea sulfate chelate composite fertilizer comprises the following steps: S01, mixing and grinding phosphorite powder and sulfuric acid, adding urea to obtain composite material one; S02, adding potassium chloride to the composite material one, mixing and crushing to obtain composite material two; and S03, mixing liquid urea sulfate with the composite material two to granulate and dry to obtain a product.The granulation method for urea sulfate chelate composite fertilizer can improve the quality and granulation rate of the composite fertilizer.

Description

Technical Field

[0001] The invention belongs to the technical field of compound fertilizers, and particularly relates to a granulation method for manufacturing compound fertilizers by chelating urea sulfate. Background Art

[0002] Compound fertilizers are a crucial material foundation for sustainable food production and play a vital role in food security. Agricultural fertilization and irrigation practices worldwide demonstrate that for stable and high crop yields, crops require adequate nutrients, particularly nitrogen, throughout their growth period. While my country's fertilizer application per unit area is three times the global average, its nitrogen utilization efficiency is only approximately 50% of the average in developed countries. Therefore, improving the nitrogen utilization efficiency of compound fertilizers is of great practical significance.

[0003] Studies have shown that urea sulfate compound fertilizer has a positive effect on improving nitrogen utilization. Furthermore, its acidic nature makes it beneficial for improving saline-alkali soils. Urea sulfate compound fertilizer, one of the many types of compound fertilizers, is attracting increasing attention due to its advantages in resource utilization, product performance, and environmental protection during its production process. Urea sulfate is a fundamental raw material in the production of urea sulfate compound fertilizers. Urea sulfate itself can be applied as an acidic fertilizer containing nitrogen and sulfur, which can reduce the volatilization of ammonium nitrogen from the soil topsoil and minimize nitrogen losses. Numerous studies have demonstrated that applying urea sulfate is more effective than applying urea alone and safer than applying ammonium sulfate alone. The emergence of urea sulfate compound fertilizers is crucial for improving nutrient utilization, improving soil quality, restoring soil fertility, and furthering the implementation of scientific and rational fertilization. Its market prospects are promising.

[0004] Furthermore, the cost of raw materials for phosphorus-supplying elements like monoammonium phosphate is increasing year by year, and alternative raw materials are under continuous research and development. While my country boasts abundant phosphate rock reserves, most are of medium- to low-grade (phosphorus pentoxide content below 28%) and primarily comprised of collophanite, making beneficiation difficult and costly. Furthermore, the overly concentrated distribution of phosphate rock significantly increases transportation costs for businesses. With the continuous depletion of phosphorus resources, the development and utilization of medium- and low-grade phosphate rock is of great significance for fully utilizing my country's resources, reducing production costs for businesses, and promoting the sustainable development of the phosphorus chemical industry.

[0005] In the prior art, patent document CN101508607A discloses a method for preparing a urea-sulfuric acid long-acting, slow-release compound fertilizer. This method involves first decomposing and activating phosphate rock with sulfuric acid to produce an active slurry, which is then reacted with urea to produce a composite slurry. The composite slurry is then neutralized with an alkaline weathered coal slurry and fed to a rotary drum granulator for granulation with potassium chloride, filler, an appropriate amount of urea, and return material. After drying, granular urea-sulfuric acid long-acting, slow-release compound fertilizer is produced. For another example, patent document CN108558556A discloses a method for preparing granular urea-based compound fertilizer using urea-sulfuric acid to decompose phosphate rock. This method includes the steps of preparing a urea-sulfuric acid aqueous solution, decomposing the phosphate rock, adding a physical property modifier, and granulation. The inventive method achieves a phosphate rock conversion rate exceeding 80%. The gaseous fluorine emission rate is reduced from 40% in the original acid-ore reaction to below 7%, effectively reducing fugitive fluorine emissions and environmental remediation costs. By adding a physical property modifier, the nitrogen-phosphorus binary fertilizer slurry can be used directly as a standalone nitrogen-phosphorus binary fertilizer or as an additive in compound fertilizer production. The fluorine in the inventive granular urea-based compound fertilizer is present in the form of urea fluosilicate, which has both pesticide and insecticide properties, reducing the use of chemical pesticides and increasing costs. Analysis and experimental research revealed that the quality stability of the compound fertilizer was low, and the granulation rate was low, requiring improvement. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a granulation method for manufacturing compound fertilizer by chelating urea sulfate in view of the shortcomings of the existing technology, so as to improve the quality and granulation rate of the compound fertilizer.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is: a granulation method for manufacturing compound fertilizer by chelating urea sulfate, comprising the following steps:

[0008] S01, mixing and grinding phosphate rock powder and sulfuric acid, and adding urea to obtain composite material 1;

[0009] S02, adding potassium chloride to the composite material 1, mixing, and crushing to obtain a composite material 2;

[0010] S03, mixing the liquid urea sulfate and the second composite material into granules, and drying to obtain a product.

[0011] Preferably, in the S01, the mass fraction of sulfuric acid is 72-80%, the grinding time is 18-25 min, the grinding pressure is 10-15 MPa, and the grinding speed is 80-120 r / min.

[0012] Optionally, the mass fraction of sulfuric acid is 72%, 73%, 75%, 78%, or 80%; the grinding time is 18 minutes, 19 minutes, 20 minutes, 21 minutes, 22 minutes, 23 minutes, 24 minutes, or 25 minutes; the grinding pressure is 10 MPa, 11 MPa, 12 MPa, 13 MPa, 14 MPa, or 15 MPa; and the grinding speed is 80 r / min, 85 r / min, 90 r / min, 95 r / min, 100 r / min, 105 r / min, 110 r / min, 115 r / min, or 120 r / min. Under the above grinding conditions, the grinding force and speed are appropriate, the phosphate rock and sulfuric acid are fully contacted, the reaction is more complete, and at the same time, no wasted work is generated, which causes increased vibration of the material and reduces the reaction efficiency.

[0013] Preferably, in S01, the weight ratio of the phosphate rock powder, the sulfuric acid and the urea is 100:(86-92):(7-30).

[0014] Optionally, the weight ratio of the phosphate rock powder, the sulfuric acid and the urea is 100:86:7, 100:87:10, 100:88:15, 100:89:18, 100:90:20, 100:90:23, 100:91:25, 100:92:28 or 100:92:30.

[0015] In S01, the amount of sulfuric acid is 100-110% of the theoretical amount (for example, 100%, 101%, 103%, 105%, 107%, 108% or 110%), the grinding time is 18-25 min (for example, 18 min, 19 min, 20 min, 21 min, 23 min or 25 min), and the mass fraction of sulfuric acid is 72-80% (for example, 60%, 61%, 62%, 63%, 65%, 67%, 69% or 70%). The effective phosphorus content (calculated as phosphorus pentoxide) in the obtained composite material 1 is significantly improved, and the phosphorus conversion rate can reach more than 85%.

[0016] Preferably, the viscosity of the urea sulfate at 20° C. is 1000-2000 mPa·s (e.g., 1000 mPa·s, 1100 mPa·s, 1200 mPa·s, 1500 mPa·s, 1600 mPa·s, 1800 mPa·s, or 2000 mPa·s), and the pH is 6.0-6.3 (e.g., 6.0, 6.1, 6.2, or 6.3).

[0017] Preferably, the urea sulfate is made from urea, sulfuric acid and water, and the molar ratio of the urea, the sulfuric acid and the water is (1.5-3.5):1:1.

[0018] Optionally, the molar ratio of the urea, the sulfuric acid and the water is 1.5:1:1, 1.6:1:1, 1.8:1:1, 2.0:1:1, 2.1:1:1, 2.3:1:1, 2.5:1:1, 2.8:1:1, 3.0:1:1, 3.2:1:1 or 3.5:1:1. The viscosity and pH of the obtained urea sulfate are more conducive to granulation when urea, sulfuric acid and water are reacted in a specific ratio, and the granulation effect of the product outside the ratio range is obviously inferior to that of the present application.

[0019] Preferably, the method for preparing the urea sulfate comprises: mixing and dissolving urea with water, slowly adding sulfuric acid into the urea aqueous solution to react, and obtaining liquid urea sulfate.

[0020] In the preparation of the urea sulfate, the amount of sulfuric acid is 105-125% of the theoretical amount, the molar ratio of urea, sulfuric acid and water is (1.5-3.5):1:1, the reaction temperature is 60-70℃, the reaction time is 20-25min, the stirring speed is 700-750r / min, and the mass fraction of sulfuric acid is 90-98℃. Under the process conditions, the conversion rate of the urea sulfuric acid decomposition of phosphate rock can reach 96.25%.

[0021] In S02, the crushing is performed using a crushing device commonly used in the technical field and currently sold on the market to crush the mixture of the composite material 1 and potassium chloride to a particle size of less than 5mm.

[0022] Preferably, in S03, the temperature for granulation is 65-75℃ (for example, 65℃, 68℃, 70℃, 71℃, 72℃, 73℃ or 75℃). The specific granulation temperature and material particle size in the present application are conducive to improving the efficiency, granulation quality and particle strength of the urea sulfate granulation.

[0023] In S03, the drying is performed using a drying device commonly used in the technical field and currently sold on the market to reduce the water content of the granulation product to less than 2.0%.

[0024] Preferably, the particle size of the phosphate rock powder is not greater than 80 mesh.

[0025] The phosphate rock powder can be crushed and sieved before use to make the particle size uniform, facilitate full contact with sulfuric acid after grinding, and improve the reaction efficiency.

[0026] Preferably, the granulation method for manufacturing the compound fertilizer by the urea sulfate chelation further comprises:

[0027] In the composite material 2, trace elements are added.

[0028] Among them, trace elements can be added in appropriate amounts according to crop needs. Other commonly used trace elements include: calcium, magnesium, manganese, iron, zinc, molybdenum, cobalt and boron, one or more. For example, calcium, magnesium, manganese, iron, zinc, molybdenum, cobalt or boron, or a combination of two or more of these elements.

[0029] The present invention also provides a urea sulfate chelate compound fertilizer obtained by the above granulation method, wherein the mass fraction of total nutrients (N+P2O5+K2O) is ≥30%, the mass fraction of sulfur (S) is ≥13%, and the percentage of amide nitrogen in total nitrogen is ≥70%.

[0030] As described in the background, my country's phosphate rock is primarily low- to medium-grade. Treatment methods for these ore types primarily focus on flotation, acid leaching, thermal calcination, and direct application. Current research indicates that whether using acid, thermal, or flotation methods to treat low- and medium-grade phosphate rock for subsequent use, or directly applying it as fertilizer, inevitably results in resource waste, environmental pollution, and increased production costs.

[0031] Research on the sulfuric acid method for treating low- and medium-grade phosphate rock has been ongoing for a long time, but its application in industry has been difficult. This method involves mixing low- and medium-grade phosphate rock with a certain concentration of sulfuric acid and soaking it to remove the magnesium and other impurities it contains, thereby purifying the phosphate rock. However, during the demagnesiation process, phosphorus loss is significant, and experimental results are inconsistent. Sulfuric acid has a strong decomposition ability, making it difficult to effectively select magnesium carbonate. When decomposing magnesium carbonate, it also reacts with phosphate rock, resulting in significant phosphorus loss. Furthermore, large local concentration differences often occur within the reaction vessel, which can lead to poor reaction selectivity and difficulty achieving stable production operating indicators. These issues significantly limit the practical application of the sulfuric acid method. Therefore, if phosphate rock powder is to be directly used in compound fertilizer production, it is necessary to process the phosphate rock powder from the perspective of compound fertilizer utilization, changing the approach to overcome the above-mentioned problems.

[0032] Furthermore, agricultural fertilizers account for approximately 70% of phosphate rock consumption in my country, with the remaining 30% generally used to extract yellow phosphorus, phosphoric acid, and other phosphate products. Most of these products are low-tech, resource-intensive, and low in added value. Consequently, the comprehensive utilization rate of phosphate rock is significantly low, reflecting the difficulty of utilizing it. Among these, the technology of using urea sulfate to decompose phosphate rock to produce compound fertilizers has attracted significant attention within the industry, offering significant advantages such as increased phosphorus conversion, available phosphorus content, and nitrogen content. CN101508607A, mentioned in the background art, mixes phosphate rock with water, reacts it with concentrated sulfuric acid, then adds urea and neutralizes it with an alkaline weathered coal slurry. Finally, the mixture is sprayed into a granulator and mixed with solid materials for granulation, followed by drying and screening to obtain a finished product. This technology yields a high water-soluble phosphorus content, indicating that the phosphate rock treatment process is relatively effective. However, the addition of an alkaline weathered coal slurry made of weathered coal, alkali solution, urea, and water to adjust the pH before granulation results in poor granulation results, a high amount of rework, and an intangible increase in production costs and process control difficulties. CN108558556A directly adds phosphate rock to an aqueous solution of urea sulfate for reaction, followed by blending and granulation. This method can achieve a phosphorus conversion rate of 80% in the phosphate rock, but other nutrient indicators in the compound fertilizer and its granulation effect still need to be improved.

[0033] Therefore, the granulation effect of urea sulfate compound fertilizer also plays an important role in improving the quality of compound fertilizer. The granulation rate determines the production efficiency of the granulation equipment, which is crucial to production costs and its promotion and application. At the same time, the properties of the granules obtained by granulation also have a significant impact on their transportation and application effects, such as the content of active ingredients and sustained release. Therefore, for different materials, their granulation processes and parameters need to be targeted and studied. In the granulation process of compound fertilizer, the properties of the binder, including viscosity, are key parameters, which affect the appearance, performance, transportation, warehousing and other aspects of the product and are therefore of great concern. Nowadays, with the development of urea sulfate compound fertilizer, the treatment of urea sulfate and phosphate rock powder and the preparation of related compound fertilizers are also closely related and are constantly evolving. Liquid urea sulfate is often used as a binder or treating agent. Its viscosity varies greatly under different reaction conditions, which has unpredictable effects on the bonding granulation of the material and its treatment effect.

[0034] Therefore, when studying the process of preparing urea sulfate compound fertilizer, while paying attention to product quality, we must also pay special attention to factors such as the controllability, stability and feasibility of the process. Comprehensive considerations should be made from a holistic perspective to develop compound fertilizers with high quality and good granulation effect to better meet the effectiveness and convenience of use, transportation and warehousing.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The present application provides a granulation method for manufacturing compound fertilizer by urea sulfate chelation based on the above technical scheme, and the compound fertilizer obtained by using the method has high quality, high granulation rate, and is convenient for storage and transportation; after the urea sulfate compound fertilizer product is dissolved in water, a uniform suspension is formed inside the liquid, and the urea sulfate compound fertilizer product has unique heat preservation, nitrogen preservation and slow release effects, and can slow down the loss of nitrogen to a certain extent.

[0037] Firstly, the reaction of the phosphorite powder and sulfuric acid is a solid-liquid two-phase reaction, and grinding is used to promote the contact between the two to make the reaction more complete, wherein the mass fraction of sulfuric acid is preferably 60-70%, the amount of sulfuric acid is 100-110% of the theoretical amount, and the grinding time is preferably 18-25 min, so that the reaction is more complete and the effective content of the product is significantly increased; the amount of sulfuric acid is controlled reasonably in the present application, so that too much free acid is not caused in the product, and the product is convenient for subsequent processing, wherein the content of free acid is below 9%.

[0038] Secondly, potassium chloride is added to increase the fertilizer efficiency, and the potassium chloride and the compound material can coexist stably, the temperature in this step is controlled below 60 DEG C, preferably 50-60 DEG C, the humidity is preferably controlled below 30%, and the granulation time is 8-12 min, so as to avoid the volatilization of effective elements and reduce the moisture absorption, and improve the storage performance of the compound fertilizer.

[0039] Thirdly, the liquid urea sulfate shows more prominent binding and granulation effects on the compound material two, so that the granulation efficiency of the compound material two is higher, and the granulation rate is higher than 90%.

[0040] The above preparation steps cooperate and interact with each other, and form the granulation method for manufacturing compound fertilizer by urea sulfate chelation as a whole, which provides favorable support for the improvement of the quality of the compound fertilizer and the enhancement of the granulation effect. The mass fraction of total nutrients (N+P2O5+K2O) in the compound fertilizer obtained by the granulation method for manufacturing compound fertilizer by urea sulfate chelation is ≥30%, the percentage of water-soluble phosphorus in the effective phosphorus is ≥70%, the mass fraction of sulfur (S) is ≥13%, the percentage of ammonia volatile nitrogen in the total nitrogen is <15%, the percentage of amide nitrogen in the total nitrogen is ≥70%, and the quality is high.

[0041] Moreover, the particle strength of the compound fertilizer is an important indicator for measuring the properties of the compound fertilizer particles, and higher particle strength is conducive to the transportation, storage and other aspects of the particles, and the particles are not easy to be crushed, and the effective ingredients are not easy to be lost, and the particle strength of the present application is above 40 N; at the same time, the high and low of the granulation rate is an important standard for judging whether the granulation process is suitable and popularized, and the particle mass of the prepared compound fertilizer product with a particle diameter standard (1-4.75 mm) accounts for more than 90% of the total mass of the used granulation raw materials, so the present application is very suitable and convenient for popularization. Specific embodiments

[0042] For a better understanding of the present application, reference will be made to the following examples which further illustrate the application but are not meant to limit the scope thereof. In the following description, numerous specific details are set forth in order to provide a more thorough understanding of the present application. However, it will be apparent to one skilled in the art that the present application can be practiced without one or more of these specific details.

[0043] In all examples shown and discussed herein, any specific values should be interpreted as merely exemplary, and not as a limitation. Thus, other examples of the exemplary embodiments can have different values.

[0044] Unless otherwise indicated, all starting materials are commercially available and, unless otherwise indicated, contain no other impurities than the unavoidable impurities that occur naturally in the stated reaction materials.

[0045] In the following examples, the mass fraction of K2O in potassium chloride is 60%; the mesh number of phosphate rock powder is 80 mesh, and the content of diaphosphorus pentoxide is 18%.

[0046] Example 1: Preparation of composite material one

[0047] Provided are phosphate rock powder, sulfuric acid, and urea; take the phosphate rock powder, add sulfuric acid with a mass fraction of 75%, the grinding pressure is 12 MPa, the grinding speed is 100 r / min, and the grinding time is 20 min; then add urea to obtain the composite material one; wherein the mass ratio of the phosphate rock powder, the sulfuric acid, and the urea is 100:90:20.

[0048] The effective phosphorus content in the composite material one is measured to be 12.05%, and the conversion rate of phosphorus is 86.06%.

[0049] Example 2: Preparation of composite material one

[0050] Provided are phosphate rock powder, sulfuric acid, and urea; take the phosphate rock powder, add sulfuric acid with a mass fraction of 72%, the grinding pressure is 10 MPa, the grinding speed is 120 r / min, and the grinding time is 18 min; then add urea to obtain the composite material one; wherein the mass ratio of the phosphate rock powder, the sulfuric acid, and the urea is 100:92:13.

[0051] The effective phosphorus content in the composite material one is measured to be 11.38%, and the conversion rate of phosphorus is 84.57%.

[0052] Example 3: Preparation of composite material one

[0053] Provided are phosphate rock powder, sulfuric acid, and urea; take the phosphate rock powder, add sulfuric acid with a mass fraction of 80%, the grinding pressure is 15 MPa, the grinding speed is 80 r / min, and the grinding time is 25 min; then add urea to obtain the composite material one; wherein the mass ratio of the phosphate rock powder, the sulfuric acid, and the urea is 100:86:27.

[0054] The effective phosphorus content in the composite material 1 was measured to be 11.52%, and the phosphorus conversion rate was 85.21%.

[0055] Example 4: Preparation of liquid urea sulfate

[0056] Sulfuric acid, urea and water are provided, urea and water are mixed and dissolved, and sulfuric acid is slowly added to the urea aqueous solution for reaction to obtain liquid urea sulfate; wherein the mass fraction of sulfuric acid is 95°C, the molar ratio of urea, sulfuric acid and water is 3.2:1:1, the reaction temperature is 65°C, the reaction time is 23 minutes, and the stirring speed is 700 r / min.

[0057] The viscosity of urea sulfate at 20°C was measured to be 1752 mPa·s, and the pH was 6.2.

[0058] Example 5: Preparation of liquid urea sulfate

[0059] Sulfuric acid, urea and water are provided, urea and water are mixed and dissolved, and sulfuric acid is slowly added to the urea aqueous solution for reaction to obtain liquid urea sulfate; wherein the mass fraction of sulfuric acid is 90°C, the molar ratio of urea, sulfuric acid and water is 3.5:1:1, the reaction temperature is 70°C, the reaction time is 25 minutes, and the stirring speed is 750 r / min.

[0060] The viscosity of urea sulfate at 20°C was measured to be 1306 mPa·s, and the pH was 6.1.

[0061] Example 6: Preparation of liquid urea sulfate

[0062] Sulfuric acid, urea and water are provided, urea and water are mixed and dissolved, and sulfuric acid is slowly added to the urea aqueous solution for reaction to obtain liquid urea sulfate; wherein the mass fraction of sulfuric acid is 98°C, the molar ratio of urea, sulfuric acid and water is 1.5:1:1, the reaction temperature is 60°C, the reaction time is 20 minutes, and the stirring speed is 720 r / min.

[0063] The viscosity of urea sulfate at 20°C was measured to be 1824 mPa·s, and the pH was 6.2.

[0064] Example 7: Preparation of compound fertilizer

[0065] Potassium chloride, a composite material 1 prepared in Example 1, and liquid urea sulfate prepared in Example 4 are provided. Potassium chloride is added to the composite material 1, mixed at 58° C., and crushed to obtain a composite material 2. Liquid urea sulfate is sprayed onto the composite material 2, mixed and granulated in a granulator at a temperature of 72° C., a humidity of 30%, a granulation time of 10 minutes, and drying at 65° C. to obtain a composite fertilizer.

[0066] Example 8: Preparation of compound fertilizer

[0067] Potassium chloride, a composite material 1 prepared in Example 2, and liquid urea sulfate prepared in Example 5 are provided. Potassium chloride is added to the composite material 1, mixed at 53° C., and crushed to obtain a composite material 2. Liquid urea sulfate is sprayed onto the composite material 2, mixed and granulated in a granulator at a temperature of 70° C., a humidity of 28%, a granulation time of 8 minutes, and drying at 65° C. to obtain a composite fertilizer.

[0068] Example 9: Preparation of compound fertilizer

[0069] Potassium chloride, a composite material 1 prepared in Example 3, and liquid urea sulfate prepared in Example 6 are provided. Potassium chloride is added to the composite material 1, mixed at 60° C., and crushed to obtain a composite material 2. Liquid urea sulfate is sprayed onto the composite material 2, mixed and granulated in a granulator at a temperature of 75° C., a humidity of 30%, a time of 12 minutes, and drying at 65° C. to obtain a composite fertilizer.

[0070] In Examples 7-9, the compound fertilizer is made from compound material 1, potassium chloride and liquid urea sulfate. Based on 1000 kg, the mass of compound material 1 is 600-700 kg, the mass of potassium chloride is 270-350 kg, and the mass of liquid urea sulfate is 30-50 kg.

[0071] The raw material compositions of Examples 7-9 are shown in the following table:

[0072]

[0073] Comparative Example 1: Preparation of Composite Material 1

[0074] Providing phosphate rock powder, sulfuric acid and urea; taking the phosphate rock powder, adding 95% sulfuric acid by mass, grinding at a pressure of 18 MPa, a grinding speed of 150 r / min, and grinding for 20 minutes; then adding urea to obtain a composite material 1; wherein the mass ratio of the phosphate rock powder, sulfuric acid and urea is 100:90:25.

[0075] The effective phosphorus content in the composite material 1 was measured to be 9.82%, and the phosphorus conversion rate was 79.25%.

[0076] Comparative Example 2: Preparation of liquid urea sulfate

[0077] In the presence of zeolite powder, solid urea and 95% by mass sulfuric acid are mixed in a urea to sulfuric acid molar ratio of 2:1 to obtain liquid urea sulfate. The amount of zeolite powder is 1% based on the total weight of the liquid urea sulfate. The reaction temperature is 65°C, the reaction time is 23 minutes, and the stirring speed is 150 r / min.

[0078] The viscosity of urea sulfate at 20°C was measured to be 5427 mPa·s, and the pH was 6.0.

[0079] Comparative Example 3: The difference between this comparative example and Example 7 is that the liquid urea sulfate is prepared by the method of Comparative Example 2, and the other steps are the same as Example 7.

[0080] Comparative Example 4: The difference between this comparative example and Example 8 is that the compound material is prepared by Comparative Example 1, and the liquid urea sulfate is prepared by the method of Comparative Example 2, and the other steps are the same as Example 8.

[0081] Preparation of compound fertilizer

[0082] Phosphate rock, potassium chloride and liquid urea sulfate prepared in Example 4 are provided, the phosphate rock is added to the liquid urea sulfate, reacted at 80°C for 15 min, then weathered coal is added as a physical property regulator, enters the formation chamber to solidify for 30 min, and finally potassium chloride is added for mixing, granulation, drying, and the product is obtained.

[0083] In this comparative example, the addition amount of phosphate rock, liquid urea sulfate and potassium chloride is the same as Example 7, the addition amount of weathered coal is 5% of the total weight of the compound fertilizer, and the other process parameters are the same as Example 7.

[0084] The following evaluates the related indexes of the compound fertilizers prepared in Examples 7-9 and Comparative Examples 3-5.

[0085] 1. According to the industry standard HG / T5516-2019, the related indexes of the compound fertilizers prepared in Examples 7-9 and Comparative Examples 3-5 are determined, and the results are shown in the following table:

[0086]

[0087] The above results show that the mass fraction of total nutrients (N+P2O5+K2O) in the compound fertilizers prepared in Examples 7-9 is ≥30%, the percentage of water-soluble phosphorus in available phosphorus is ≥70%, the mass fraction of sulfur (S) is ≥13%, the percentage of ammonia volatile nitrogen in total nitrogen is <15%, and the percentage of amide nitrogen in total nitrogen is ≥70%, and the comprehensive quality is excellent.

[0088] The sulfur content, ammonia volatile nitrogen and amide nitrogen of the compound fertilizer prepared in Comparative Example 3 are lower than those of Example 7; the various indexes of the compound fertilizer prepared in Comparative Example 4 are significantly deteriorated compared with Example 8, indicating that the treatment of phosphate rock and / or the preparation of liquid urea sulfate in the compound fertilizer will affect the related indexes of the product. The water-soluble phosphorus, sulfur content and amide nitrogen content of the compound fertilizer prepared in Comparative Example 5 change significantly, indicating that under the condition of basically the same raw materials, the change of the process will cause unpredictable changes in the comprehensive indexes of the product.

[0089] 2. The particle strength and granulation rate of the compound fertilizers prepared in Examples 7-9 and Comparative Examples 3-5 are tested, wherein:

[0090] 2.1 Determination of particle strength: Spread the product particles on the sieve and divide them into four quadrants according to the center point. Randomly select 25 particles from each quadrant, for a total of 100 particles. The average particle strength of the 100 particles is used to measure the particle strength of the entire product. The average particle strength of the product is measured using a particle strength tester. The average particle strength is calculated using the following formula:

[0091]

[0092] Where: M is the average particle strength of 100 products, N; X is the particle strength of the i-th product, j = 1, 2...100.

[0093] 2.2 Determination of granulation rate: Screening is performed using standard sieves with apertures of 1 mm and 4.75 mm. The specific steps are as follows: stack sieves with apertures of 1 mm and 4.75 mm in sequence, place the granulated product on a 4.75 mm sieve, and manually shake to allow the particles to pass through the sieve apertures. Finally, remove all particles stuck in the sieve apertures, and weigh the total weight of the particles on the 1 mm sieve. The granulation rate can be calculated using the following formula:

[0094]

[0095] Where m1 is the total mass of particles in the 1 mm sieve, and m2 is the total mass of the material used for granulation.

[0096] 2.3 Test results:

[0097]

[0098] From the above results, it can be seen that the particle strength of the compound fertilizer obtained by the granulation method of the present invention is basically above 40N, and the granulation rate is as high as above 90%; the particle strength and granulation rate of the compound fertilizer prepared by Comparative Example 3, Comparative Example 4 and Comparative Example 5 show different degrees of reduction, indicating that the raw materials used and their preparation steps have an important influence on the granulation effect of the product.

[0099] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention and are not limiting. Other modifications or equivalent substitutions made to the technical solution of the present invention by ordinary technicians in this field should be included in the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solution of the present invention.

Claims

1. A granulation method for manufacturing compound fertilizer by chelating urea sulfate, characterized in that: The following steps are involved: S01, mixing phosphate rock powder and sulfuric acid and grinding them, wherein the content of phosphorus pentoxide in the phosphate rock powder is 18%, the mass fraction of sulfuric acid is 72-80%, the grinding time is 18-25 min, the grinding pressure is 10-15 MPa, and the grinding speed is 80-120 r / min, and urea is added, wherein the weight ratio of the phosphate rock powder, the sulfuric acid and the urea is 100:(86-92):(7-30), to obtain composite material 1; S02, adding potassium chloride to the composite material 1, controlling the temperature at 50-60° C. and the humidity below 30%, mixing, and crushing to obtain a composite material 2; S03, mixing liquid urea sulfate and composite material 2 into granules at a temperature of 65-75° C., and drying to obtain a product; The urea sulfate is prepared from urea, sulfuric acid and water, and the molar ratio of the urea, sulfuric acid and water is (1.5-3.5):1:

1. The preparation method comprises: mixing and dissolving urea with water, slowly adding sulfuric acid to the urea aqueous solution for reaction, the reaction temperature is 60-70°C, the reaction time is 20-25 minutes, the stirring speed is 700-750 r / min, and the mass fraction of sulfuric acid is 90-98%, thereby obtaining liquid urea sulfate, wherein the viscosity of the urea sulfate at 20°C is 1000-2000 mPa·s and the pH is 6.0-6.3; The mass fraction of N+P2O5+K2O in the compound fertilizer is ≥30%, the percentage of water-soluble phosphorus in available phosphorus is ≥70%, the mass fraction of sulfur is ≥13%, the percentage of ammonia volatile nitrogen in total nitrogen is <15%, and the percentage of amide nitrogen in total nitrogen is ≥70%.

2. The granulation method for preparing composite fertilizer by chelating urea sulfate as claimed in claim 1, wherein: Also includes: Adding medium and trace elements to the second composite material.

3. The composite fertilizer prepared by the granulation method according to claim 1 or 2.

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