Active directional granulation method of high-dispersity instant compound fertilizer

Abstract

The invention relates to the technical field of fertilizer production processes, and particularly discloses an active directional granulation method of a high-dispersity instant compound fertilizer. Comprising the following steps: step 1, accurately weighing raw materials, and crushing the raw materials to 50-100 meshes; step 2, uniformly mixing the crushed raw materials, and adding ammonium bicarbonate and a pre-coating material; step 3, the mixed material is granulated through a double-roller extruder, the extrusion granulation temperature is about 60-150 DEG C, the extrusion pressure is 10-200 MPa, ammonium bicarbonate is decomposed under the action of temperature and pressure to generate carbon dioxide gas, the carbon dioxide gas escapes from fertilizer granules, and compound fertilizer granules with internal microporous structures are formed; and step 4, screening and cooling treatment: grading the fertilizer granules, refluxing fine powder for re-granulation, and cooling qualified granules to obtain the water-applied compound fertilizer. The technical problems that in the prior art, compound fertilizer particles produced through a double-roller extrusion technology are too high in compactness, low in porosity and poor in solubility, and one-time investment of a fertilizer high-tower granulation technology is large are solved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of fertilizer production processes, and particularly discloses an active directional granulation method for high-dispersibility instant compound fertilizer. BACKGROUND

[0002] Compound fertilizer water application refers to dissolving compound fertilizer in water and then applying the dissolved fertilizer solution to the vicinity of crop roots through an irrigation system (such as drip irrigation, sprinkler irrigation, etc.). This method can make the fertilizer more evenly distributed in the soil, improve the absorption and utilization rate of the fertilizer, and at the same time, reduce the direct damage to crops.

[0003] Compound fertilizer water application requires dissolving compound fertilizer particles in water, and only after the fertilizer is completely dissolved in water can modernized fertilizer water application such as drip irrigation and sprinkler irrigation be carried out. The traditional extrusion fertilizer production process is a roll extrusion process, which uses high-pressure molding, and the appearance of the finished product is rough and the particles are irregular. For example, the patent document with the publication number CN119183396A discloses a granulation process, production process and system for chemical fertilizer biological compound fertilizer, which uses a roll extruder for dry granulation and uses high pressure to form particles without the need for water or a binder. This extrusion fertilizer production process highly depends on high compression force molding, resulting in high particle density, low porosity (<3%), difficulty for water molecules to penetrate into the core, long particle dissipation time and poor solubility. To enhance the dissolution efficiency during compound fertilizer water application and improve the solubility of particles in water, in addition to selecting high solubility raw materials, increasing the porosity of particles is one of the key ways. In compound fertilizer production, the high-tower granulation process is a commonly used method to achieve high porosity. Before cooling and granulating the molten material, a small amount of ammonium bicarbonate (usually 0.3-0.5% by weight) is added, and ammonia and carbon dioxide gases are generated by the decomposition of ammonium bicarbonate at high temperatures. The process of gas escaping from the inside to the outside forms pores on the particles. For example, the patent document with the publication number CN102659461B discloses a high-porosity compound fertilizer high-tower granulation method and high-porosity compound fertilizer, which adds 0.3-0.5% by weight of ammonium bicarbonate to the molten material, mixes it uniformly and then granulates it by high-tower granulation. The compound fertilizer produced has high porosity. Although this high-tower granulation process can increase the porosity of compound fertilizer particles and thus enhance the dissolution efficiency, it relies on the advantage of the melting point of urea and can only produce high-nitrogen compound fertilizer, but cannot produce low-nitrogen high-phosphorus compound fertilizer. Moreover, the fertilizer high-tower granulation process requires the construction of a high tower, which involves a large one-time investment and is not suitable for small and medium-sized enterprises.

[0004] In summary, based on the fact that the compound fertilizer particles produced by the roll extrusion process in the prior art have high particle density, low porosity, difficulty for water molecules to penetrate into the core, long particle dissipation time and poor solubility, and the fact that the fertilizer high-tower granulation process involves a large one-time investment and is not suitable for small and medium-sized enterprises, there is an urgent need in the industry for an active directional granulation method for high-dispersibility instant compound fertilizer in the roll extrusion process. Summary of the Invention

[0005] The purpose of this invention is to provide a highly dispersible, fast-dissolving compound fertilizer active directional granulation method to solve the problems mentioned above in the prior art, such as excessively high density, low porosity, difficulty for water molecules to penetrate to the core, long particle dispersal time, and poor solubility of compound fertilizer particles produced by roller extrusion process. Furthermore, the high-tower granulation process for fertilizers requires a large initial investment, making it unsuitable for the current situation of small and medium-sized enterprises.

[0006] To solve the above problems, the technical solution adopted by the present invention is as follows: a method for active directional granulation of highly dispersible, fast-dissolving compound fertilizer, comprising the following steps: Step 1: Raw material preparation: Weigh the required raw materials for water-applied compound fertilizer according to the formula design ratio, and then crush the weighed raw materials to 50-100 mesh; the raw materials for water-applied compound fertilizer include urea, ammonium phosphate, potassium fertilizer, and filler; Step 2, Ingredient Mixing: The crushed compound fertilizer raw materials are mixed evenly using a horizontal mixer, and 1-10% ammonium bicarbonate and 1%-3% of water-soluble pre-coating material by weight of ammonium bicarbonate are added during the mixing process to obtain the mixture. Step 3, Extrusion Granulation: The mixture with added ammonium bicarbonate is granulated through a roller extruder. The extrusion granulation temperature is about 60-150 degrees Celsius and the extrusion pressure is 10-200 MPa. This allows the pre-coated material to react with the carbon dioxide from the decomposition of ammonium bicarbonate and encapsulate other raw materials. Under the action of temperature and pressure, ammonium bicarbonate decomposes to produce carbon dioxide gas that escapes from the fertilizer granules, forming compound fertilizer granules with an internal microporous structure. Step 4, Screening and Cooling: Use a drum screen or vibrating screen to classify the fertilizer granules, return the fine powder to re-granulate, and cool the qualified granules to obtain water-applied compound fertilizer.

[0007] The beneficial effects of this implementation plan are as follows: 1. Existing technologies using roller extrusion processes produce compound fertilizer granules with excessively high density and low porosity, making it difficult for water molecules to penetrate the core, resulting in long dissolution times and poor solubility. Furthermore, high-tower granulation processes require significant initial investment, making them unsuitable for small and medium-sized enterprises. This application utilizes the property of ammonium bicarbonate decomposing at 60°C. By adding a certain amount of ammonium bicarbonate during the extrusion granulation process, the mixture undergoes rapid decomposition of the ammonium bicarbonate under pressure and temperature at approximately 100°C during granulation. Carbon dioxide gas rapidly escapes from the fertilizer granules, filling them with micropores from the inside out. Additionally, the presence of urea, with its low melting point, results in a semi-melted state at 150°C. This semi-melted urea solidifies after granulation, strengthening the fertilizer structure. Therefore, this application significantly increases the fertilizer dissolution time without affecting granule strength, enabling rapid dissolution during application—a rate far exceeding that of fertilizers produced by traditional spraying and drum processes. This achieves the desired effect of compound fertilizer application via water.

[0008] 2. When applying the method of adding ammonium bicarbonate to create pores in the high-tower granulation process of fertilizer to the roller extrusion process, the raw material particles are mainly bound together by van der Waals forces and adsorption forces due to the high compression force used in roller extrusion. Compared with fertilizer particles formed by melting and convective cooling of materials in a high-tower process, the internal bonding force is weaker. When ammonium bicarbonate decomposes into gases such as ammonia and carbon dioxide, the released gases can easily damage the structure of the compound fertilizer particles. After the fertilizer is formed, its strength is too low (below 8N), and it is prone to pulverization during transportation. The pulverized and dispersed compound fertilizer particles have reduced dispersibility and fertilizer potency. This application discovered this problem during the research and development process and finally adopted a pre-coating technology, using the carbon dioxide generated during the decomposition of ammonium bicarbonate as an indispensable part of the film-forming reaction of the pre-coating material. This ensures that the fertilizer particles are coated and strengthened while creating micropores in the fertilizer particles. Ultimately, this overcomes the technical bottleneck of the roller extrusion granulation process, which makes it impossible to simultaneously achieve "high dispersibility," "instantaneous dissolution," and "strength" in compound fertilizer.

[0009] Furthermore, the pre-coating material is an aqueous solution of α-cyclodextrin-propylene oxide ether and lysine, and the molar ratio of epoxy group to amino group in the pre-coating material is 1:1.2-1.5.

[0010] Furthermore, the concentration of the lysine solution is 10-15%. Furthermore, in the extrusion granulation process of step 3, the extrusion roller is controlled to gradually increase in temperature, specifically: feeding zone ≤60℃ → hole forming zone 80-100℃ → structural reinforcement zone 150℃ → discharge port 40℃.

[0011] Further, the raw material quality ratio of the water-applied compound fertilizer is: urea 15-20%, ammonium phosphate 20-25%, potassium fertilizer 20-25%, ammonium sulfate 18-24%, and filler 8-10%, and 5-10% of ammonium bicarbonate is added in the batching mixing section.

[0012] Further, the raw material quality ratio of the water-applied compound fertilizer is: urea 15-20%, ammonium phosphate 20-25%, potassium fertilizer 20-25%, ammonium sulfate 18-24%, and filler 8-10%, and 5-10% of ammonium bicarbonate is added in the batching mixing section.

[0013] Further, the raw material in step 1 is crushed to 500-100 mesh.

[0014] Further, the pre-coating material is an ethylene oxide polyethylene glycol solution with ethylene oxide as the solvent and polyethylene glycol as the solvent; a catalyst DBU is added, and the proportion of ethylene oxide in the pre-coating material is controlled to be higher than 20%.

[0015] Further, the polyethylene glycol has a molecular weight of 4000-6000, and the ethylene oxide molecules are dispersed in the polyethylene glycol crystals.

[0016] Further, the molecular weight of the polyethylene glycol is less than 600, and the ethylene oxide is dissolved in the liquid polyethylene glycol. BRIEF DESCRIPTION OF DRAWINGS

[0017] Fig. 1 The process flowchart of the present application is, Fig. 2 The apparent diagram of the compound fertilizer method of the present application is. DETAILED DESCRIPTION

[0018] The following will be further described in detail through specific embodiments: As Figs. 1-2 shown: Example 1 The active directional granulation method of high-dispersibility instant compound fertilizer comprises the following steps: Step 1, raw material preparation: all the raw materials required for preparing the compound fertilizer, such as nitrogen, phosphorus, potassium water-soluble raw materials, and pre-coating materials, are taken out according to the formula, accurately weighed according to the formula design, and crushed to 50-100 mesh.

[0019] The water-soluble raw materials include urea, ammonium phosphate, potassium fertilizer, and filler, and the mass ratio of each raw material in this embodiment is: urea 20%, ammonium phosphate 20%, potassium fertilizer 20%, ammonium sulfate 20%, and filler 10%; combined with 10% of ammonium bicarbonate added in the batching mixing section, which just forms 100% of the raw material ratio.

[0020] Step 2, ingredient mixing: the pulverized compound fertilizer raw materials are mixed uniformly using a horizontal mixer. The specific mixing process is as follows: first, urea, ammonium phosphate, potassium fertilizer, and filler are mixed uniformly, then 10% ammonium bicarbonate is gradually added, and finally, 3% pre-coating material of ammonium bicarbonate is added during the mixing process to form a mixture. The pre-coating material is an alpha-cyclodextrin-epoxypropane ether and a lysine aqueous solution, with a lysine solution concentration of 10-15% and an epoxy group:amino molar ratio of approximately 1:1.2-1.5.

[0021] Step 3, extrusion granulation: the mixture is granulated by an extruder, where the screw of the extruder generates pressure to make the mixture pass through the perforated plate to form granules, while the pre-coating material is extruded from the mixture and gathered on the surface of the fertilizer granules to form a coating film. Then, the temperature gradually rises, and ammonium bicarbonate decomposes to produce carbon dioxide gas under the action of temperature and pressure. The gas escapes to form a fertilizer granule with an internal microporous structure on the surface of the granule, obtaining a fertilizer granule with a microporous structure.

[0022] The specific operation is as follows: Step 301, forced feeding: the mixture is uniformly and continuously fed into the feed inlet of the double-roll extrusion granulator through a screw conveyor or a vibrating feeder. Some equipment is equipped with a constant material level device to ensure stable feeding.

[0023] Step 302, high-pressure extrusion molding: the material enters between two synchronously counter-rotating rollers with specific shaped perforated plates (such as hemispherical, flat spherical, etc.) on the surface. Under the high pressure (usually 10-200 MPa) provided by the hydraulic or spring system, the material is instantaneously compressed into dense granules. This process relies on mechanical force to enhance the molecular interaction between particles, eliminate air gaps, and form high-strength green bodies. At the same time, the temperature gradually rises during the extrusion process, specifically: feeding zone ≤60℃ (mainly to form high-strength green bodies by high pressure) → pore forming zone 80-100℃ (ammonium bicarbonate decomposition, carbon dioxide migration to form pores) → structure strengthening zone 150℃ (urea semi-melting and shaping) → discharge port 40℃ (cooling and molding).

[0024] Since the epoxy group (-O-CH2-CH-) of the α-cyclodextrin-epoxy propane ether can undergo ring-opening polymerization with the primary amino group (-NH2) of lysine under heating and pressurization conditions to form a network polymer; and the reaction is most efficient at 60-100℃ and 8-12 MPa. Therefore, in the extrusion granulation process, the α-cyclodextrin-epoxy propane ether and lysine materials are subjected to high pressure (usually 5-20 MPa) under the action of the screw or roller, forcing the cyclodextrin derivative to closely contact with lysine, strengthening the formation of cross-linked network. And ammonium bicarbonate decomposes during the extrusion process, producing a large amount of carbon dioxide (such as decomposition of fertilizers), accelerating the deprotonation of lysine and improving the reaction rate. The pre-coated material forms a coating film on the surface of the fertilizer particles, forming a structure reinforcement.

[0025] Since the pre-coated material has a film-forming reaction at 60℃, the surface of the fertilizer particles will first heat up to 60℃ at the initial stage of extrusion granulation, and the pressure reaches 8 MPa, which rapidly produces a coating film on the surface of the fertilizer particles, and as the temperature is transferred to the interior of the fertilizer particles, the temperature inside the particles rises, and the ammonium bicarbonate inside the material begins to decompose, with the chemical reaction formula being: NH4HCO3— 加热 NH3↑+H2O+CO2↑, the carbon dioxide generated by decomposition escapes from the interior of the particles, forming a pore structure on the fertilizer particles at the same time, and escaping to the surface of the fertilizer particles, so that the coating film forms a porous structure, and the ammonia gas generated by decomposition reacts with monoammonium phosphate to form diammonium phosphate, improving the pH value of the fertilizer, making the product more stable, and reducing the probability of pipe blockage during spraying and drip irrigation for crop fertilization.

[0026] Step 4, screening and cooling treatment: use a drum screen or a vibrating screen to classify the fertilizer particles, and the particles are classified by a vibrating screen: qualified particles (such as Φ2.5-10mm) enter the subsequent process; fine powder and oversized particles return to the mixing system for re-granulation, and the qualified particles are cooled during the screening process to obtain compound fertilizer.

[0027] Step 5, packaging into storage and detection: put the qualified fertilizer balls after screening into a packaging machine for packaging into storage, and then detect the nitrogen, phosphorus and potassium content.

[0028] Example 2 Embodiment 2 is different from Embodiment 1 in that the pre-coating material is an ethylene oxide (EO) polyethylene glycol solution with ethylene oxide (EO) as the solvent and polyethylene glycol with a molecular weight lower than 600; and a catalyst DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) is added. The pre-coating material is added in an amount of 1% of the mass of ammonium bicarbonate; during the formation of the coating film, carbon dioxide and ethylene oxide decomposed from the internal ammonium bicarbonate are used as raw materials to synthesize low-molecular-weight polycarbonate diol under the action of a catalyst, and then polyethylene glycol (PEG) side chains are grafted to form a coating film for the fertilizer particles. The content of ethylene oxide in the pre-coating material is higher than 20%, and the coating film is completely water-soluble. In this embodiment, the mass ratio of each raw material is as follows: urea 15%, ammonium phosphate 25%, potassium fertilizer 25%, ammonium sulfate 24%, and filler 8%; 3% of ammonium bicarbonate is added in the mixing section to form a 100% raw material ratio.

[0029] Embodiment 3 Embodiment 3 is different from Embodiment 2 in that high-molecular-weight PEG with a molecular weight of 4000-6000 is used; the EO molecules are dispersed in the PEG crystal, and are liquefied when the temperature is raised to above 65°C during the extrusion granulation process, and finally transferred to the surface of the fertilizer particles to form a coating film under the adjustment of 60°C and 20 megapascals.

[0030] The above only describes the embodiments of the present application, and the specific structures and properties of the known schemes are not described in detail. It should be noted that, for those skilled in the art, without departing from the structure of the present application, a number of modifications and improvements can be made, which should also be considered as the protection scope of the present application, and these will not affect the effect and practicality of the present application. The protection scope claimed in this application should be subject to the content of its claims, and the specific implementation modes and the like described in the specification can be used to explain the content of the claims.

Claims

1. A method for active directional granulation of highly dispersible, fast-dissolving compound fertilizer, characterized in that: Includes the following steps: Step 1, Raw material preparation: Weigh the required raw materials for water-applied compound fertilizer according to the formula design ratio, and then crush the weighed raw materials; the raw materials for water-applied compound fertilizer include urea, ammonium phosphate, potassium fertilizer, and filler; Step 2, Ingredient Mixing: The crushed compound fertilizer raw materials are mixed evenly using a horizontal mixer, and 1-10% ammonium bicarbonate and 1%-3% of water-soluble pre-coating material by weight of ammonium bicarbonate are added during the mixing process to obtain the mixture. Step 3, Extrusion Granulation: The mixture is granulated through a roller extruder at an extrusion temperature of about 60-150 degrees and an extrusion pressure of 10-200 MPa. This allows the pre-coated material to react with the carbon dioxide from the decomposition of ammonium bicarbonate and encapsulate other raw materials. Under the action of temperature and pressure, ammonium bicarbonate decomposes to produce carbon dioxide gas that escapes from the fertilizer granules, forming compound fertilizer granules with an internal microporous structure. Step 4, Screening and Cooling: Use a drum screen or vibrating screen to classify the fertilizer granules, return the fine powder to re-granulate, and cool the qualified granules to obtain water-applied compound fertilizer.

2. The method for active directional granulation of highly dispersible, fast-dissolving compound fertilizer according to claim 1, characterized in that: The pre-coating material is an aqueous solution of α-cyclodextrin-propylene oxide ether and lysine, wherein the molar ratio of epoxy group to amino group in the pre-coating material is 1:1.2-1.

5.

3. The method for active directional granulation of highly dispersible, fast-dissolving compound fertilizer according to claim 2, characterized in that: The concentration of the lysine solution is 10-15%.

4. The method for active directional granulation of highly dispersible, fast-dissolving compound fertilizer according to claim 1, characterized in that: In the extrusion granulation process of step 3, the extrusion roller is controlled to gradually increase in temperature, specifically: feeding zone ≤60℃ → hole forming zone 80-100℃ → structural reinforcement zone 150℃ → discharge port 40℃.

5. The method for active directional granulation of highly dispersible, fast-dissolving compound fertilizer according to claim 1, characterized in that: The raw material mass ratio of the water-applied compound fertilizer is: urea 5-50%, ammonium phosphate 5-50%, potassium fertilizer 5-50%, ammonium sulfate 18-24%, filler 8-10%, and 5-10% ammonium bicarbonate added in the batching and mixing stage.

6. The method for active directional granulation of highly dispersible, fast-dissolving compound fertilizer according to claim 5, characterized in that: The raw material mass ratio of the water-applied compound fertilizer is 20% urea, 20% ammonium phosphate, 20% potassium fertilizer, 20% ammonium sulfate, 10% filler, and 10% ammonium bicarbonate.

7. The method for active directional granulation of highly dispersible, fast-dissolving compound fertilizer according to claim 1, characterized in that: In step 1, the raw materials are crushed to 500-100 mesh.

8. The method for active directional granulation of highly dispersible, fast-dissolving compound fertilizer according to claim 1, characterized in that: The pre-coating material is an ethylene oxide-polyethylene glycol solution with polyethylene glycol as the solvent; and a catalyst DBU is added, and the proportion of ethylene oxide in the pre-coating material is controlled to be higher than 20%.

9. The method for active directional granulation of highly dispersible, fast-dissolving compound fertilizer according to claim 8, characterized in that: The polyethylene glycol has a molecular weight of 4000-6000, and ethylene oxide molecules are dispersed in the polyethylene glycol crystals.

10. The method for active directional granulation of highly dispersible, fast-dissolving compound fertilizer according to claim 9, characterized in that: The polyethylene glycol has a molecular weight of less than 600, and ethylene oxide is dissolved in the liquid polyethylene glycol.

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