A method for preparing environment-friendly compound fertilizer by using a roller granulation technique

Abstract

This application discloses a method for preparing environmentally friendly compound fertilizer using drum granulation technology, relating to the field of fertilizer and soil improvement technology. Specifically, this application involves mixing urea, ammonium chloride, monoammonium phosphate, potassium chloride, and a modified calcium carbonate slow-release composite material in a primary mixer, then adding copper sulfate, zinc sulfate, and borax to obtain a second mixture. This second mixture is then fed into a secondary mixer, where 98% concentrated sulfuric acid is added in a sealed environment and the pH is adjusted for reaction. The mixture then enters a drum granulator, where the moisture content during granulation is controlled through a closed-loop system of inlet water addition and online moisture detection at the outlet. After drying, cooling, and sieving, the environmentally friendly compound fertilizer is obtained. The product obtained by this application has uniform granules, combines long-lasting slow release with soil improvement effects, has high nutrient utilization, and is produced in an environmentally friendly and clean manner.

Description

Technical Field

[0001] This application relates to the field of fertilizer and soil improvement technology, specifically to a method for preparing environmentally friendly compound fertilizer using drum granulation technology. Background Technology

[0002] Rotary drum granulation is one of the mainstream processes in compound fertilizer production, boasting advantages such as high capacity, low cost, and strong adaptability, and is widely used in bulk compound fertilizer production. With the advancement of green and high-quality agricultural development, reducing nutrient loss, improving fertilizer utilization, and minimizing pollution during production have become important development directions for the compound fertilizer industry.

[0003] Existing rotary drum granulation compound fertilizers generally suffer from rapid nutrient release and low utilization rate in the current season. Nitrogen is easily volatilized and leached, while phosphorus is easily fixed by the soil, resulting not only in waste of fertilizer resources but also in corresponding pollution risks. To improve the slow-release performance of rotary drum granulation compound fertilizers, some production technologies directly mix slow-release fillers or nitrification inhibitors into the material. However, the slow-release components have poor dispersion uniformity and weak binding force with the fertilizer matrix, making them prone to phase separation under the action of granulation machinery, resulting in large fluctuations in the slow-release effect. In addition, coated slow-release fertilizers often use non-degradable polymer resins, which can easily cause microplastic residues in the soil. Moreover, the production process is complex and costly, making it difficult to popularize them in field fertilizer application.

[0004] At the production process level, traditional drum granulation often employs an open-type acid injection method, resulting in severe acid mist volatilization, a poor working environment, and high environmental remediation costs. Moisture control during granulation relies heavily on manual experience, leading to poor batch stability, low pellet formation rate, uneven particle size, and persistently high energy consumption during subsequent drying. Furthermore, the process of mixing macro- and micro-elements in a single step is prone to segregation due to differences in particle size and density, resulting in uneven distribution of micro-elements and affecting fertilizer efficacy stability. Simultaneously, most existing compound fertilizer products have a single function, failing to achieve a synergistic effect of nutrient supply and soil improvement.

[0005] Therefore, there is an urgent need to develop a more advantageous method for preparing environmentally friendly compound fertilizer using drum granulation technology. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this application involves mixing urea, ammonium chloride, monoammonium phosphate, potassium chloride, and a modified calcium carbonate slow-release composite material in a primary mixer. Copper sulfate, zinc sulfate, and borax are then added to obtain a second mixture. This second mixture is then fed into a secondary mixer, where 98% concentrated sulfuric acid is added in a sealed environment and the pH is adjusted for reaction. The mixture then enters a drum granulator, where the moisture content during granulation is controlled through a closed-loop system of inlet water addition and online moisture detection at the outlet. After drying, cooling, and sieving, an environmentally friendly compound fertilizer is produced. The product obtained in this application has uniform granules, combines long-lasting slow release with soil improvement effects, boasts high nutrient utilization, and is produced in an environmentally friendly and clean manner.

[0007] To achieve the above objectives, this application adopts the following technical solution:

[0008] This application provides a method for preparing environmentally friendly compound fertilizer using drum granulation technology, comprising the following steps:

[0009] S1. According to the formula, urea, ammonium chloride, monoammonium phosphate, potassium chloride and modified calcium carbonate slow-release composite material are added to the primary mixer by the PLC automatic control system to obtain the first mixture;

[0010] S2. Add copper sulfate, zinc sulfate and borax to the primary mixer and mix them further with the first mixture to obtain the second mixture;

[0011] S3. The second mixture is fed into the secondary mixer. 98% concentrated sulfuric acid is added to the secondary mixer through a closed pipeline by an acid pump and an automatic control valve. The pH value of the material is then monitored and adjusted in real time while stirring. After the reaction, a mixed product is obtained.

[0012] S4. The mixed product is conveyed to the drum granulator, the process parameters of the drum granulation are controlled, and water is added at the inlet of the drum granulator.

[0013] S5. The discharge moisture content is detected by an online moisture detector at the outlet of the drum granulator, and the opening of the water inlet valve is adjusted according to the discharge moisture content.

[0014] S6. The qualified output material is successively dried, cooled, screened and coated, and then weighed and sealed by an automatic packaging machine to obtain environmentally friendly compound fertilizer.

[0015] The method for preparing environmentally friendly compound fertilizer provided in this application employs PLC-automated feeding, followed by automatic valve control of 98% concentrated sulfuric acid addition. Combined with online pH and moisture monitoring, this enables precise production throughout the entire process, improving batch stability and reducing human error and labor intensity. Furthermore, the introduction of modified calcium carbonate slow-release composite material enhances the slow-release performance of the prepared environmentally friendly compound fertilizer, reducing nutrient leaching and volatilization. Simultaneously, calcium carbonate neutralizes soil acidity, providing soil improvement value. Moreover, in S1 and S2, components with higher proportions are first mixed in a primary mixer to form a uniform matrix; the addition of components with lower proportions shortens the mixing path, avoiding component segregation due to differences in particle size and density, and ensuring uniform distribution of trace nutrients in the overall material. In S3, concentrated sulfuric acid is added through a closed pipeline and acid pump, reducing acid mist volatilization and improving production safety and environmental friendliness. In S4 and S5, the control method of adding water at the inlet and online detection and adjustment of moisture at the outlet during the granulation process can stabilize the amount of liquid phase added during the granulation process and improve the pelleting rate and particle size uniformity of the environmentally friendly compound fertilizer.

[0016] In one possible implementation, in S1, the mass ratio of urea, ammonium chloride, monoammonium phosphate, potassium chloride and modified calcium carbonate slow-release composite material is (44.5-46.5): (3.5-5.5): (22.5-25.0): (18.5-21.0): (5.0-7.5).

[0017] The combination of urea and ammonium chloride forms a combination of readily available and long-lasting nitrogen sources. Monoammonium phosphate provides both phosphorus and some ammonium nitrogen, while potassium chloride provides potassium. The nitrogen forms cater to both early-stage fertilization and long-term sustained effectiveness. The controlled proportion of modified calcium carbonate slow-release composite material allows it to fully exert its effects of enhancing slow release and improving soil, without excessively diluting nutrient concentration. It can also be used as a granulation filler to improve the mechanical strength of the granulated particles.

[0018] In one possible implementation, in S1, the method for preparing the modified calcium carbonate slow-release composite material is as follows:

[0019] Take calcium carbonate raw material, crush it and pass it through a 200-300 mesh sieve to obtain calcium carbonate powder;

[0020] Calcium carbonate powder is put into a high-speed mixer and a surface modifier is added in the form of spray while stirring at a speed of 15-20 Hz at room temperature. Then, stirring is continued for 5-10 minutes to obtain modified calcium carbonate.

[0021] After stirring the modified calcium carbonate and the slow-release coating solution at a stirring rate of 200-300 rpm for 30-60 minutes, the coating layer is dried at 50-70°C to solidify, thus obtaining the modified calcium carbonate slow-release composite material.

[0022] In the preparation method of modified calcium carbonate slow-release composite material, the calcium carbonate powder after sieving through a 200-300 mesh sieve has a relatively large specific surface area and many surface active sites, providing sufficient reaction interfaces for subsequent surface modification and coating, thus improving the modification and coating effects. Furthermore, adding the surface modifier in a spray form under high-speed stirring (15-20 Hz) allows the surface modifier to be rapidly dispersed and adsorbed onto the surface of the calcium carbonate powder in a mist form, improving its compatibility with the subsequent organic coating liquid, reducing interfacial tension, and allowing the coating liquid to spread more evenly on its surface. The slow-release coating liquid encapsulates the modified calcium carbonate particles under stirring, and during the drying process at 50-70℃, the water evaporates, and the film-forming substances in the coating liquid cross-link and solidify, forming a continuous and dense barrier film layer, reducing the exchange rate of substances between the nitration inhibitor and the external environment.

[0023] In one possible implementation, the surface modifier comprises any one or more of mono(polyethylene glycol) succinate, 2-(2-methoxyethoxy)acetic acid, and 2-carboxyethyl acrylate; the amount of the surface modifier added is 0.5% to 2.0% of the mass of the calcium carbonate powder.

[0024] Mono(polyethylene glycol) succinate, 2-(2-methoxyethoxy)acetic acid, and 2-carboxyethyl acrylate all contain carboxyl groups (-COOH), which can chemically bond (to the surface of calcium carbonate, Ca) 2+ These molecules (forming calcium carboxylate) or adsorb firmly onto the calcium carbonate surface through hydrogen bonding; the polyethylene glycol ether chains, ester groups, and other segments at the other end of these molecules extend to the outside of the particles, making it easier for them to combine with humic acid, water-soluble polymers, etc. in the slow-release coating liquid through intermolecular forces such as hydrogen bonding, thereby improving interfacial adhesion and preventing the coating layer from falling off; it can also further promote the stable retention of nitration inhibitors in the coating liquid in the barrier film layer when the film-forming material crosslinks and solidifies.

[0025] In one possible implementation, the mass ratio of the modified calcium carbonate to the sustained-release coating solution is (70-80):(20-30); the sustained-release coating solution comprises humic acid, a water-soluble polymeric film-forming agent, a nitration inhibitor, and deionized water; the mass ratio of the humic acid, the water-soluble polymeric film-forming agent, the nitration inhibitor, and deionized water is (5-15):(2-8):(5-10):(70-80).

[0026] In the slow-release coating solution, humic acid is a natural organic colloid that can adsorb nutrients, improve soil aggregate structure, and participate in the formation of the coating, increasing the density and biodegradability of the coating layer. The water-soluble polymeric film-forming agent is the skeleton component of the coating, providing mechanical strength and continuity of the membrane and preventing damage to the coating during granulation and transportation. The nitrification inhibitor is embedded in the coating and is slowly released as the coating degrades, effectively inhibiting soil nitrification and reducing nitrogen loss from environmentally friendly compound fertilizers. Deionized water serves as a solvent to evenly disperse the various functional components and will evaporate after drying to form a solid functional coating.

[0027] In one possible implementation, the water-soluble polymeric film-forming agent comprises any one of polyvinyl alcohol, carboxymethyl cellulose, and sodium alginate; the nitration inhibitor comprises any one of dicyandiamide, 3,4-dimethylpyrazole phosphate, and nitropyridine.

[0028] Polyvinyl alcohol, carboxymethyl cellulose, and sodium alginate are all hydrophilic polymers with numerous polar groups such as hydroxyl and carboxyl groups in their molecular chains, which can cross-link with each other through hydrogen bonds. When water evaporates, these polymers form a continuous and flexible polymer film, and these materials can be gradually degraded into small molecules by soil microorganisms, without causing residual soil pollution. In addition, the nitrification inhibitor used in this application inhibits the AMO enzyme activity of nitrite-oxidizing bacteria in the soil, blocking the oxidation process of ammonium nitrogen to nitrite nitrogen, thereby reducing nitrate nitrogen formation. Nitrate nitrogen is easily lost through water leaching and denitrification, so reducing nitrate nitrogen formation can prolong the retention time of nitrogen in the soil, achieving a long-term slow-release effect, improving nitrogen fertilizer utilization, and reducing nitrate pollution.

[0029] In one possible implementation, in S2, the mass ratio of copper sulfate, zinc sulfate and borax is 1:1:1, and the total mass of copper sulfate, zinc sulfate and borax is 1.5% of the total mass of the second mixture.

[0030] Copper sulfate, zinc sulfate, and borax provide copper, zinc, and boron, respectively, for environmentally friendly compound fertilizers. Copper participates in crop photosynthesis and respiration, zinc participates in auxin synthesis and enzyme metabolism, and boron promotes reproductive organ development and carbohydrate transport. All three are essential micronutrients for crops. Furthermore, the ratio of these three components can be adapted to the micronutrient absorption ratios of most crops, avoiding antagonistic interactions between elements.

[0031] In one possible implementation, in S3, the amount of 98% concentrated sulfuric acid added is 4%–6% of the total mass of the second mixture, and the pH value of the material is adjusted to 5.5–6.5.

[0032] When 98% concentrated sulfuric acid is added to the material, it reacts with urea, monoammonium phosphate, and other substances in the system to produce viscous double salts or acid salts such as urea sulfate and ammonium dihydrogen phosphate. These salts can act as binders during granulation, promoting the agglomeration and growth of fine powder, significantly improving the pellet formation rate and mechanical strength. The purpose of adjusting the pH value of the material is that: in a weakly acidic environment of pH 5.5 to 6.5, ammonium nitrogen has high chemical stability and is not easily decomposed into ammonia gas and lost through volatilization; at the same time, phosphorus mainly exists in the form of water-soluble dihydrogen phosphate, which has high availability; if the pH is too low, it will accelerate equipment corrosion, and if the pH is too high, ammonium nitrogen will easily decompose and volatilize, and phosphorus will easily combine with calcium ions to form insoluble substances, reducing fertilizer efficiency.

[0033] In one possible implementation, in S4, the process parameters of the drum granulation include: the drum rotation speed of the drum granulator is 10 r / min, the material temperature inside the drum granulator is maintained at 20-25°C, and water is added at the inlet of the drum granulator at a ratio of 100L per ton of material.

[0034] Rotary granulation relies on centrifugal force and friction to lift the material along the cylinder wall, then it falls under gravity to form a rolling material curtain. This rolling agglomeration promotes particle growth. A rotation speed of 10 r / min creates a stable material curtain, ensuring sufficient rolling time. Too high a speed causes excessive centrifugal force, causing the material to adhere to the cylinder wall and preventing agglomeration. Too low a speed results in insufficient material lifting height, weak rolling force, difficulty in nucleation, and a high pulverization rate. Furthermore, within the ambient temperature range of 20–25℃, the moisture evaporation rate is relatively stable, the viscosity and surface tension of the liquid phase fluctuate little, and the particle growth rate is uniform. If the material temperature is too high, moisture evaporates rapidly, resulting in insufficient liquid phase and easy pulverization. If the material temperature is too low, the material becomes too viscous and easily adheres to the cylinder wall, causing agglomeration. Finally, adding 100L of water per ton provides suitable conditions for powder agglomeration, allowing fine powder to agglomerate and gradually grow into uniform particles; adding too much water will cause the material to be too wet, resulting in particle deformation, agglomeration, or even sticking to the wall; adding too little water will result in insufficient liquid phase binding force, difficulty in nucleation, more fine powder, and low pelleting rate.

[0035] In one possible implementation, in S5, the discharge moisture content is 10%, and the method for adjusting the opening of the water inlet valve is as follows: when the discharge moisture content is greater than 10%, the water inlet valve is closed to reduce the amount of water added; when the moisture content is less than 10%, the water inlet valve is opened to increase the amount of water added.

[0036] Controlling the discharge moisture content is to ensure that the resulting granules have good plasticity, are not easily broken, and have a regular shape. Excessive discharge moisture content will increase the heat energy consumption of subsequent drying, and the granules are prone to deformation and sticking during transportation. Excessive discharge moisture content will result in brittle granules that are easily broken and pulverized, leading to a decrease in the yield.

[0037] Beneficial technical effects:

[0038] The method for preparing environmentally friendly compound fertilizer provided in this application enhances the sustained-release performance of the prepared environmentally friendly compound fertilizer by introducing a modified calcium carbonate slow-release composite material, reducing leaching and volatilization of nutrients. Simultaneously, calcium carbonate neutralizes soil acidity, thus also possessing soil improvement value. In the specific process flow, high-proportion components are first mixed in a primary mixer to form a uniform matrix; low-proportion components are added subsequently to shorten the mixing path, avoiding component segregation due to differences in particle size and density, and ensuring uniform distribution of low-proportion trace nutrients in the overall material. Subsequent addition of concentrated sulfuric acid through a closed pipeline and acid pump reduces acid mist volatilization, improving production safety and environmental friendliness. Furthermore, concentrated sulfuric acid can react with urea, monoammonium phosphate, etc., in the system to generate viscous double salts or acid salts such as urea sulfate and ammonium dihydrogen phosphate. These salts act as binders during granulation, promoting the agglomeration and growth of fine powder, significantly improving particle formation rate and mechanical strength. Finally, the control method of adding water at the inlet and online monitoring and adjustment of moisture at the outlet during the granulation process can stabilize the amount of liquid phase added during granulation, thereby improving the pelleting rate and particle size uniformity of the environmentally friendly compound fertilizer. Attached Figure Description

[0039] Figure 1 This is a physical image of the environmentally friendly compound fertilizer prepared in Example 3 of this application;

[0040] Figure 2 This is a schematic flowchart of the method for preparing environmentally friendly compound fertilizer using drum granulation technology provided in this application. Detailed Implementation

[0041] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the application will be further described in detail below with reference to embodiments. However, this should not be construed as limiting the scope of this application to the following examples. All other embodiments obtained by those skilled in the art without creative effort without departing from the above-described methodological spirit of this application are within the scope of protection of this application.

[0042] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application.

[0043] The singular forms “for,” “or,” “a,” “any,” and “the” used in this application are intended to include the plural forms unless the context clearly indicates otherwise.

[0044] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0045] The following describes in detail, with reference to different embodiments, a method for preparing environmentally friendly compound fertilizer using drum granulation technology provided in this application.

[0046] Example 1

[0047] First, a modified calcium carbonate slow-release composite material is prepared, including the following steps:

[0048] T1. Take calcium carbonate raw material, crush it and pass it through a 200-mesh sieve to obtain calcium carbonate powder;

[0049] T2. Add calcium carbonate powder into a high-speed mixer. At room temperature, add 0.5% (by weight) mono(polyethylene glycol) succinate of calcium carbonate powder in the form of a spray while stirring at a speed of 15 Hz. Then continue stirring for 5 minutes to obtain modified calcium carbonate.

[0050] T3. After stirring the modified calcium carbonate and the slow-release coating liquid at a stirring rate of 200 rpm for 30 min, dry at 50°C to solidify the coating layer, thus obtaining the modified calcium carbonate slow-release composite material.

[0051] The modified calcium carbonate to the sustained-release coating solution has a mass ratio of 70:30; the sustained-release coating solution comprises humic acid, polyvinyl alcohol, dicyandiamide and deionized water; and the mass ratio of humic acid, polyvinyl alcohol, dicyandiamide and deionized water is 5:5:10:80.

[0052] Then, environmentally friendly compound fertilizer is prepared using drum granulation technology. The preparation method is as follows: Figure 2 As shown, it includes the following steps:

[0053] S1. According to the formula, urea, ammonium chloride, monoammonium phosphate, potassium chloride and modified calcium carbonate slow-release composite material are added to the primary mixer by the PLC automatic control system to obtain the first mixture;

[0054] The mass ratio of urea, ammonium chloride, monoammonium phosphate, potassium chloride, and modified calcium carbonate slow-release composite material is 44.5:3.5:24.0:21.0:7.0.

[0055] S2. Add copper sulfate, zinc sulfate, and borax in a mass ratio of 1:1:1 to the primary mixer and further mix with the first mixture to obtain a second mixture. The total mass of copper sulfate, zinc sulfate, and borax is 1.5% of the total mass of the second mixture.

[0056] S3. The second mixture is fed into a secondary mixer. 98% concentrated sulfuric acid is added to the secondary mixer through a closed pipeline by an acid pump and an automatic control valve. The amount added is 4% of the total mass of the second mixture. Then, while stirring, the pH value of the material is monitored and adjusted to 5.5 in real time. After the reaction, a mixed product is obtained.

[0057] S4. The mixed product is conveyed to the rotary drum granulator. The rotary drum granulator rotates at 10 r / min. The material temperature inside the rotary drum granulator is maintained at 20℃. Water is added at the inlet of the rotary drum granulator at a ratio of 100L per ton of material.

[0058] S5. Detect the discharge moisture using an online moisture detector at the outlet of the drum granulator. If the discharge moisture is greater than 10%, close the inlet valve and reduce the amount of water added; if the moisture is less than 10%, open the inlet valve and increase the amount of water added.

[0059] S6. The qualified output material is successively dried, cooled, screened and coated, and then weighed and sealed by an automatic packaging machine to obtain environmentally friendly compound fertilizer.

[0060] Example 2

[0061] First, a modified calcium carbonate slow-release composite material is prepared, including the following steps:

[0062] T1. Take calcium carbonate raw material, crush it and pass it through a 300-mesh sieve to obtain calcium carbonate powder;

[0063] T2. Add calcium carbonate powder to a high-speed mixer. At room temperature, add 2.0% (by weight) of 2-(2-methoxyethoxy)acetic acid of calcium carbonate powder in the form of a spray while stirring at a speed of 20 Hz. Continue stirring for 10 min to obtain modified calcium carbonate.

[0064] T3. After stirring the modified calcium carbonate and the slow-release coating liquid at a stirring rate of 300 rpm for 60 min, dry at 70°C to solidify the coating layer, thus obtaining the modified calcium carbonate slow-release composite material.

[0065] The modified calcium carbonate to the sustained-release coating solution has a mass ratio of 80:20; the sustained-release coating solution comprises humic acid, carboxymethyl cellulose, 3,4-dimethylpyrazole phosphate and deionized water; the mass ratio of humic acid, carboxymethyl cellulose, 3,4-dimethylpyrazole phosphate and deionized water is 15:8:7:70.

[0066] Then, environmentally friendly compound fertilizer is prepared using drum granulation technology. The preparation method is as follows: Figure 2 As shown, it includes the following steps:

[0067] S1. According to the formula, urea, ammonium chloride, monoammonium phosphate, potassium chloride and modified calcium carbonate slow-release composite material are added to the primary mixer by the PLC automatic control system to obtain the first mixture;

[0068] The mass ratio of urea, ammonium chloride, monoammonium phosphate, potassium chloride, and modified calcium carbonate slow-release composite material is 46.5:5.5:22.5:18.5:7.0.

[0069] S2. Add copper sulfate, zinc sulfate, and borax in a mass ratio of 1:1:1 to the primary mixer and further mix with the first mixture to obtain a second mixture. The total mass of copper sulfate, zinc sulfate, and borax is 1.5% of the total mass of the second mixture.

[0070] S3. The second mixture is fed into the secondary mixer. 98% concentrated sulfuric acid is added to the secondary mixer through a closed pipeline by an acid pump and an automatic control valve. The amount added is 6% of the total mass of the second mixture. Then, while stirring, the pH value of the material is monitored and adjusted to 6.5 in real time. After the reaction, a mixed product is obtained.

[0071] S4. The mixed product is conveyed to the rotary drum granulator. The rotary drum granulator rotates at 10 r / min. The material temperature inside the rotary drum granulator is maintained at 25℃. Water is added at the inlet of the rotary drum granulator at a ratio of 100L per ton of material.

[0072] S5. Detect the discharge moisture using an online moisture detector at the outlet of the drum granulator. If the discharge moisture is greater than 10%, close the inlet valve and reduce the amount of water added; if the moisture is less than 10%, open the inlet valve and increase the amount of water added.

[0073] S6. The qualified output material is successively dried, cooled, screened and coated, and then weighed and sealed by an automatic packaging machine to obtain environmentally friendly compound fertilizer.

[0074] Example 3

[0075] First, a modified calcium carbonate slow-release composite material is prepared, including the following steps:

[0076] T1. Take calcium carbonate raw material, crush it and pass it through a 250-mesh sieve to obtain calcium carbonate powder;

[0077] T2. Add calcium carbonate powder into a high-speed mixer. At room temperature, add 1.2% (by weight) of 2-carboxyethyl acrylate of calcium carbonate powder in the form of a spray while stirring at a speed of 18 Hz. Then continue stirring for 8 minutes to obtain modified calcium carbonate.

[0078] T3. After stirring the modified calcium carbonate and the slow-release coating liquid at a stirring rate of 250 rpm for 45 min, the coating layer is dried at 60°C to solidify, thus obtaining the modified calcium carbonate slow-release composite material.

[0079] The modified calcium carbonate to the sustained-release coating solution has a mass ratio of 75:25; the sustained-release coating solution comprises humic acid, sodium alginate, nitropyridine and deionized water; the mass ratio of humic acid, sodium alginate, nitropyridine and deionized water is 10:5:7.5:77.5.

[0080] Then, environmentally friendly compound fertilizer is prepared using drum granulation technology. The preparation method is as follows: Figure 2 As shown, it includes the following steps:

[0081] S1. According to the formula, urea, ammonium chloride, monoammonium phosphate, potassium chloride and modified calcium carbonate slow-release composite material are added to the primary mixer by the PLC automatic control system to obtain the first mixture;

[0082] The mass ratio of urea, ammonium chloride, monoammonium phosphate, potassium chloride, and modified calcium carbonate slow-release composite material is 45.5:4.5:23.5:20.5:6.0.

[0083] S2. Add copper sulfate, zinc sulfate, and borax in a mass ratio of 1:1:1 to the primary mixer and further mix with the first mixture to obtain a second mixture. The total mass of copper sulfate, zinc sulfate, and borax is 1.5% of the total mass of the second mixture.

[0084] S3. The second mixture is fed into the secondary mixer. 98% concentrated sulfuric acid is added to the secondary mixer through a closed pipeline by an acid pump and an automatic control valve. The amount added is 5% of the total mass of the second mixture. Then, while stirring, the pH value of the material is monitored and adjusted to 6.0 in real time. After the reaction, a mixed product is obtained.

[0085] S4. The mixed product is conveyed to the rotary drum granulator. The rotary drum granulator rotates at 10 r / min. The material temperature inside the rotary drum granulator is maintained at 22℃. Water is added at the inlet of the rotary drum granulator at a ratio of 100L per ton of material.

[0086] S5. Detect the discharge moisture using an online moisture detector at the outlet of the drum granulator. If the discharge moisture is greater than 10%, close the inlet valve and reduce the amount of water added; if the moisture is less than 10%, open the inlet valve and increase the amount of water added.

[0087] S6. The qualified output material is successively dried, cooled, screened and coated, and then weighed and sealed by an automatic packaging machine to obtain environmentally friendly compound fertilizer.

[0088] Example 4

[0089] First, a modified calcium carbonate slow-release composite material is prepared, including the following steps:

[0090] T1. Take calcium carbonate raw material, crush it and pass it through a 250-mesh sieve to obtain calcium carbonate powder;

[0091] T2. Add calcium carbonate powder to a high-speed mixer and add 1.0% (by weight of calcium carbonate powder) of 2-(2-methoxyethoxy)acetic acid in the form of a spray while stirring at 16 Hz at room temperature. Continue stirring for 7 minutes to obtain modified calcium carbonate.

[0092] T3. After stirring the modified calcium carbonate and the slow-release coating liquid at a stirring rate of 220 rpm for 40 min, the coating layer is dried at 55°C to solidify, thus obtaining the modified calcium carbonate slow-release composite material.

[0093] The modified calcium carbonate to the sustained-release coating solution has a mass ratio of 72:28; the sustained-release coating solution comprises humic acid, carboxymethyl cellulose, dicyandiamide and deionized water; and the mass ratio of humic acid, carboxymethyl cellulose, dicyandiamide and deionized water is 8:4:8:80.

[0094] Then, environmentally friendly compound fertilizer is prepared using drum granulation technology. The preparation method is as follows: Figure 2 As shown, it includes the following steps:

[0095] S1. According to the formula, urea, ammonium chloride, monoammonium phosphate, potassium chloride and modified calcium carbonate slow-release composite material are added to the primary mixer by the PLC automatic control system to obtain the first mixture;

[0096] The mass ratio of urea, ammonium chloride, monoammonium phosphate, potassium chloride, and modified calcium carbonate slow-release composite material is 46.0:5.0:25.0:19.0:5.0.

[0097] S2. Add copper sulfate, zinc sulfate, and borax in a mass ratio of 1:1:1 to the primary mixer and further mix with the first mixture to obtain a second mixture. The total mass of copper sulfate, zinc sulfate, and borax is 1.5% of the total mass of the second mixture.

[0098] S3. The second mixture is fed into a secondary mixer. 98% concentrated sulfuric acid is added to the secondary mixer through a closed pipeline via an acid pump and an automatic control valve. The amount added is 4.5% of the total mass of the second mixture. Then, the pH value of the material is monitored and adjusted to 5.8 in real time while stirring. After the reaction, a mixed product is obtained.

[0099] S4. The mixed product is conveyed to the rotary drum granulator. The rotary drum granulator rotates at 10 r / min. The material temperature inside the rotary drum granulator is maintained at 21℃. Water is added at the inlet of the rotary drum granulator at a ratio of 100L per ton of material.

[0100] S5. Detect the discharge moisture using an online moisture detector at the outlet of the drum granulator. If the discharge moisture is greater than 10%, close the inlet valve and reduce the amount of water added; if the moisture is less than 10%, open the inlet valve and increase the amount of water added.

[0101] S6. The qualified output material is successively dried, cooled, screened and coated, and then weighed and sealed by an automatic packaging machine to obtain environmentally friendly compound fertilizer.

[0102] Example 5

[0103] First, a modified calcium carbonate slow-release composite material is prepared, including the following steps:

[0104] T1. Take calcium carbonate raw material, crush it and pass it through a 280-mesh sieve to obtain calcium carbonate powder;

[0105] T2. Add calcium carbonate powder to a high-speed mixer. At room temperature, add 1.8% (by weight) of mono(polyethylene glycol) succinate of calcium carbonate powder in the form of a spray while stirring at a speed of 19 Hz. Then continue stirring for 9 minutes to obtain modified calcium carbonate.

[0106] T3. After stirring the modified calcium carbonate and the slow-release coating liquid at a stirring rate of 280 rpm for 55 min, the coating layer is dried at 65°C to solidify, thus obtaining the modified calcium carbonate slow-release composite material.

[0107] The modified calcium carbonate to the sustained-release coating solution has a mass ratio of 78:22; the sustained-release coating solution comprises humic acid, polyvinyl alcohol, 3,4-dimethylpyrazole phosphate and deionized water; the mass ratio of humic acid, polyvinyl alcohol, 3,4-dimethylpyrazole phosphate and deionized water is 12:6:6:76.

[0108] Then, environmentally friendly compound fertilizer is prepared using drum granulation technology. The preparation method is as follows: Figure 2 As shown, it includes the following steps:

[0109] S1. According to the formula, urea, ammonium chloride, monoammonium phosphate, potassium chloride and modified calcium carbonate slow-release composite material are added to the primary mixer by the PLC automatic control system to obtain the first mixture;

[0110] The mass ratio of urea, ammonium chloride, monoammonium phosphate, potassium chloride, and modified calcium carbonate slow-release composite material is 45.0:4.0:23.0:20.5:7.5.

[0111] S2. Add copper sulfate, zinc sulfate, and borax in a mass ratio of 1:1:1 to the primary mixer and further mix with the first mixture to obtain a second mixture. The total mass of copper sulfate, zinc sulfate, and borax is 1.5% of the total mass of the second mixture.

[0112] S3. The second mixture is fed into a secondary mixer. 98% concentrated sulfuric acid is added to the secondary mixer through a closed pipeline via an acid pump and an automatic control valve. The amount added is 5.5% of the total mass of the second mixture. Then, the pH value of the material is monitored and adjusted to 6.2 in real time while stirring. After the reaction, a mixed product is obtained.

[0113] S4. The mixed product is conveyed to the rotary drum granulator. The rotary drum granulator rotates at 10 r / min. The material temperature inside the rotary drum granulator is maintained at 24℃. Water is added at the inlet of the rotary drum granulator at a ratio of 100L per ton of material.

[0114] S5. Detect the discharge moisture using an online moisture detector at the outlet of the drum granulator. If the discharge moisture is greater than 10%, close the inlet valve and reduce the amount of water added; if the moisture is less than 10%, open the inlet valve and increase the amount of water added.

[0115] S6. The qualified output material is successively dried, cooled, screened and coated, and then weighed and sealed by an automatic packaging machine to obtain environmentally friendly compound fertilizer.

[0116] Example 6

[0117] First, a modified calcium carbonate slow-release composite material is prepared, including the following steps:

[0118] T1. Take calcium carbonate raw material, crush it and pass it through a 220-mesh sieve to obtain calcium carbonate powder;

[0119] T2. Add calcium carbonate powder into a high-speed mixer. At room temperature, add 1.5% (by weight) of 2-carboxyethyl acrylate of calcium carbonate powder in the form of a spray while stirring at a speed of 17 Hz. Then continue stirring for 6 minutes to obtain modified calcium carbonate.

[0120] T3. After stirring the modified calcium carbonate and the slow-release coating liquid at a stirring rate of 260 rpm for 50 min, the coating layer is dried at 62°C to solidify, thus obtaining the modified calcium carbonate slow-release composite material.

[0121] The modified calcium carbonate to the sustained-release coating solution has a mass ratio of 76:24; the sustained-release coating solution comprises humic acid, sodium alginate, nitropyridine and deionized water; and the mass ratio of humic acid, sodium alginate, nitropyridine and deionized water is 13:2:5:80.

[0122] Then, environmentally friendly compound fertilizer is prepared using drum granulation technology. The preparation method is as follows: Figure 2 As shown, it includes the following steps:

[0123] S1. According to the formula, urea, ammonium chloride, monoammonium phosphate, potassium chloride and modified calcium carbonate slow-release composite material are added to the primary mixer by the PLC automatic control system to obtain the first mixture;

[0124] The mass ratio of urea, ammonium chloride, monoammonium phosphate, potassium chloride, and modified calcium carbonate slow-release composite material is 44.8:4.2:24.5:20.5:6.0.

[0125] S2. Add copper sulfate, zinc sulfate, and borax in a mass ratio of 1:1:1 to the primary mixer and further mix with the first mixture to obtain a second mixture. The total mass of copper sulfate, zinc sulfate, and borax is 1.5% of the total mass of the second mixture.

[0126] S3. The second mixture is fed into a secondary mixer. 98% concentrated sulfuric acid is added to the secondary mixer through a closed pipeline by an acid pump and an automatic control valve. The amount added is 5.0% of the total mass of the second mixture. Then, the pH value of the material is monitored and adjusted to 6.0 in real time while stirring. After the reaction, a mixed product is obtained.

[0127] S4. The mixed product is conveyed to the rotary drum granulator. The rotary drum granulator rotates at 10 r / min. The material temperature inside the rotary drum granulator is maintained at 23℃. Water is added at the inlet of the rotary drum granulator at a ratio of 100L per ton of material.

[0128] S5. Detect the discharge moisture using an online moisture detector at the outlet of the drum granulator. If the discharge moisture is greater than 10%, close the inlet valve and reduce the amount of water added; if the moisture is less than 10%, open the inlet valve and increase the amount of water added.

[0129] S6. The qualified output material is successively dried, cooled, screened and coated, and then weighed and sealed by an automatic packaging machine to obtain environmentally friendly compound fertilizer.

[0130] Comparative Example 1

[0131] This comparative example provides a method for preparing environmentally friendly compound fertilizer using drum granulation technology. The difference between this comparative example and Example 3 is that the calcium carbonate powder is not treated with a surface modifier. Instead, the calcium carbonate powder is directly mixed and stirred with the slow-release coating liquid. Other process parameters and operating steps are exactly the same as in Example 3.

[0132] Comparative Example 2

[0133] This comparative example provides a method for preparing environmentally friendly compound fertilizer using drum granulation technology. The difference from Example 3 is that this comparative example does not mix and stir the calcium carbonate powder with the slow-release coating liquid, but only treats the calcium carbonate powder with a surface modifier. Other process parameters and operating steps are exactly the same as in Example 3.

[0134] Comparative Example 3

[0135] This comparative example provides a method for preparing environmentally friendly compound fertilizer using drum granulation technology. The difference between this comparative example and Example 3 is that this comparative example does not treat the calcium carbonate powder with a surface modifier, nor does it mix the calcium carbonate powder with the slow-release coating liquid. Instead, it directly uses only the calcium carbonate powder. Other process parameters and operating steps are exactly the same as in Example 3.

[0136] The environmentally friendly compound fertilizers prepared in Examples 1-6 and Comparative Examples 1-3 were tested.

[0137] The mass percentage of particles with a diameter of 1.0 to 4.0 mm in each embodiment and comparative example was calculated by screening and weighing, thereby reflecting the granulation rate of the environmentally friendly compound fertilizer of this application.

[0138] Referring to GB / T41667-2022, the proportion of cumulative nitrogen leaching to total nitrogen over 28 days was determined by soil column leaching test, thereby demonstrating the long-term slow-release effect of the environmentally friendly compound fertilizer of this application.

[0139] By randomly selecting 20 environmentally friendly compound fertilizer granules from Examples 1-6 and Comparative Examples 1-3, and then measuring the radial compressive strength and taking the average value, the mechanical properties of the environmentally friendly compound fertilizer granules of this application are demonstrated.

[0140] The results of the above tests are shown in Table 1.

[0141] Table 1. Test results of Examples 1-6 and Comparative Examples 1-3

[0142]

[0143] As shown in Table 1, the environmentally friendly compound fertilizers prepared in Examples 1-6 have significantly better performance than the environmentally friendly compound fertilizers prepared in Comparative Examples 1-3.

[0144] This is because, in the methods provided in Examples 1-6, the surface of calcium carbonate is first modified by a surface modifier to improve the interfacial compatibility between the powder and the coating liquid, and then the slow-release coating liquid is used to solidify into a film, so that the nitrification inhibitor is stably embedded in the film layer. The two work together to achieve long-term slow release. At the same time, the modified calcium carbonate slow-release composite material can also be used as a granulation filler to improve the formability and mechanical strength of environmentally friendly compound fertilizer particles.

[0145] Compared with Example 3, Comparative Example 1 did not treat the calcium carbonate powder with a surface modifier. Instead, the calcium carbonate powder was directly mixed and stirred with the slow-release coating liquid. As a result, the slow-release effect decreased, the nitrogen leaching rate increased, and the particle strength and pelletizing rate also decreased slightly.

[0146] Compared with Example 3, Comparative Example 2 did not mix and stir the calcium carbonate powder with the slow-release coating liquid, but only treated the calcium carbonate powder with a surface modifier. Therefore, the nitrogen leaching rate increased further and the slow-release effect was further weakened. At the same time, the lack of the binding and filling effect of the coating layer also further reduced the particle sphericity and compressive strength.

[0147] Compared with Example 3, Comparative Example 3 did not treat the calcium carbonate powder with a surface modifier, nor did it mix the calcium carbonate powder with the slow-release coating liquid. Instead, it used only calcium carbonate powder directly. Therefore, the nitrification inhibitor was simply mixed with ordinary calcium carbonate powder without a controlled-release structure. As a result, the nitrogen slow-release effect was the worst and the nutrient utilization rate was the lowest. At the same time, the compatibility between ordinary calcium carbonate and fertilizer matrix was relatively poor, resulting in decreased granulation and the worst granulation rate and compressive strength.

[0148] The above results demonstrate and describe the basic principles and main features of this application, as well as its advantages.

[0149] The above description is merely a preferred embodiment of this application. The scope of protection of this application is not limited to the above embodiments. All technical solutions falling within the scope of this application's concept are within the scope of protection of this application. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of this application should also be considered within the scope of protection of this application.

Claims

1. A method for preparing environmentally friendly compound fertilizer using drum granulation technology, characterized in that, Includes the following steps: S1. According to the formula, urea, ammonium chloride, monoammonium phosphate, potassium chloride and modified calcium carbonate slow-release composite material are added to the primary mixer by the PLC automatic control system to obtain the first mixture; S2. Add copper sulfate, zinc sulfate and borax to the primary mixer and mix them further with the first mixture to obtain the second mixture; S3. The second mixture is fed into the secondary mixer. 98% concentrated sulfuric acid is added to the secondary mixer through a closed pipeline by an acid pump and an automatic control valve. The pH value of the material is then monitored and adjusted in real time while stirring. After the reaction, a mixed product is obtained. S4. The mixed product is conveyed to the drum granulator, the process parameters of the drum granulation are controlled, and water is added at the inlet of the drum granulator. S5. The discharge moisture content is detected by an online moisture detector at the outlet of the drum granulator, and the opening of the water inlet valve is adjusted according to the discharge moisture content. S6. The qualified output material is successively dried, cooled, screened and coated, and then weighed and sealed by an automatic packaging machine to obtain environmentally friendly compound fertilizer.

2. The method for preparing environmentally friendly compound fertilizer using drum granulation technology according to claim 1, characterized in that, In S1, the mass ratio of urea, ammonium chloride, monoammonium phosphate, potassium chloride and modified calcium carbonate slow-release composite material is (44.5~46.5): (3.5~5.5): (22.5~25.0): (18.5~21.0): (5.0~7.5).

3. The method for preparing environmentally friendly compound fertilizer using drum granulation technology according to claim 1, characterized in that, In S1, the preparation method of the modified calcium carbonate slow-release composite material is as follows: Take calcium carbonate raw material, crush it and pass it through a 200-300 mesh sieve to obtain calcium carbonate powder; Calcium carbonate powder is put into a high-speed mixer and a surface modifier is added in the form of spray while stirring at a speed of 15-20 Hz at room temperature. Then, stirring is continued for 5-10 minutes to obtain modified calcium carbonate. The modified calcium carbonate and the slow-release coating solution are stirred at a stirring rate of 200-300 rpm for 30-60 minutes, and then dried at 50-70°C to solidify the coating layer, thus obtaining the modified calcium carbonate slow-release composite material.

4. The method for preparing environmentally friendly compound fertilizer using drum granulation technology according to claim 3, characterized in that, The surface modifier includes any one or more of mono(polyethylene glycol) succinate, 2-(2-methoxyethoxy)acetic acid and 2-carboxyethyl acrylate; the amount of the surface modifier added is 0.5% to 2.0% of the mass of calcium carbonate powder.

5. The method for preparing environmentally friendly compound fertilizer using drum granulation technology according to claim 3, characterized in that, The mass ratio of the modified calcium carbonate to the sustained-release coating solution is (70-80):(20-30); the components of the sustained-release coating solution include humic acid, water-soluble polymeric film-forming agent, nitration inhibitor and deionized water; the mass ratio of the humic acid, water-soluble polymeric film-forming agent, nitration inhibitor and deionized water is (5-15):(2-8):(5-10):(70-80).

6. A method for preparing environmentally friendly compound fertilizer using drum granulation technology according to claim 5, characterized in that, The water-soluble polymeric film-forming agent includes any one of polyvinyl alcohol, carboxymethyl cellulose, and sodium alginate; the nitration inhibitor includes any one of dicyandiamide, 3,4-dimethylpyrazole phosphate, and nitropyridine.

7. The method for preparing environmentally friendly compound fertilizer using drum granulation technology according to claim 1, characterized in that, In S2, the mass ratio of copper sulfate, zinc sulfate and borax is 1:1:1, and the total mass of copper sulfate, zinc sulfate and borax is 1.5% of the total mass of the second mixture.

8. The method for preparing environmentally friendly compound fertilizer using drum granulation technology according to claim 1, characterized in that, In S3, the amount of 98% concentrated sulfuric acid added is 4%-6% of the total mass of the second mixture, and the pH value of the material is controlled between 5.5 and 6.

5.

9. A method for preparing environmentally friendly compound fertilizer using drum granulation technology according to claim 1, characterized in that, In S4, the process parameters of the drum granulation include: the drum rotation speed of the drum granulator is 10 r / min, the material temperature inside the drum granulator is maintained at 20-25℃, and water is added at the inlet of the drum granulator at a ratio of 100L per ton of material.

10. A method for preparing environmentally friendly compound fertilizer using drum granulation technology according to claim 1, characterized in that, In S5, the discharge moisture content is 10%. The method for adjusting the opening of the water inlet valve is as follows: when the discharge moisture content is greater than 10%, the water inlet valve is closed to reduce the amount of water added; when the moisture content is less than 10%, the water inlet valve is opened to increase the amount of water added.

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