Manufacturing method for producing balanced alkaline high-phosphorus compound fertilizer through ammonia-acid method roller granulation

Abstract

The invention relates to the technical field of chemical fertilizer production, and particularly discloses a method for producing a balanced alkaline high-phosphorus compound fertilizer through ammonia-acid method roller granulation. The raw materials comprise ammonium chloride, potassium chloride, ammonium sulfate, potassium sulfate, urea, monoammonium phosphate, phosphoric acid, gaseous ammonia, auxiliary materials and a composite coating agent composed of hydrophobic mineral oil and an alkaline stabilizer. The preparation method comprises the steps of raw material pretreatment and batching, ammonium phosphate slurry preparation, roller granulation and granulation, drying and screening, cooling and screening, coating treatment, tail gas treatment, resource recovery, process control and the like. The product can effectively adjust the acidity and alkalinity of the acid soil. In addition, according to the preparation method disclosed by the invention, through collaborative technologies such as returned material grading and partitioned adding, multi-section temperature control reaction and waste heat gradient utilization, alkaline compatible coating and tail gas Venturi pretreatment and resource recovery, the advantages of high particle size uniformity and strength of the product, energy conservation in the production process, good environment-friendly benefit and good product storage stability are obtained.

Description

Technical Field

[0001] This application relates to the field of fertilizer production technology, and more specifically, it relates to a method for producing balanced alkaline high-phosphorus compound fertilizer by roller granulation using the amino acid method. Background Technology

[0002] Compound fertilizer is a key agricultural input for ensuring crop growth and development in agricultural production. High-phosphorus compound fertilizers, in particular, contain phosphorus, a core nutrient element for root germination, flowering, and fruiting, playing a crucial role in enhancing crop resistance and yield. For a long time, acidic compound fertilizers have been widely used to meet the nutrient demands of large-scale planting due to their mature production processes and lower costs. However, long-term continuous application has exacerbated soil acidification and compaction problems. This not only fixes available phosphorus and potassium in the soil, reducing fertilizer utilization, but also damages the root growth environment, causing root burn, weakened growth, and other issues, severely impacting crop quality and yield. Therefore, developing alkaline high-phosphorus compound fertilizers that can regulate the pH of acidic soils has become an urgent need in agricultural production. The amino acid-based drum granulation process, with its uniform nutrient distribution, high production efficiency, and ease of large-scale implementation, has become the mainstream process choice for producing high-phosphorus compound fertilizers.

[0003] However, in existing amine-based drum granulation processes, the recycled material from the screening process is often directly mixed and reused without being graded according to particle size differences. This results in inaccurate matching between the nucleating core and the coating material within the granulator, leading to poor particle uniformity. Simultaneously, tubular reactors often employ single-stage temperature control, making it difficult for the neutralization reaction between ammonia and phosphoric acid to proceed fully, resulting in significant fluctuations in the slurry's pH. These factors collectively cause the final compound fertilizer product to have an unstable pH within the alkaline range of 7 to 9, leading to poor product performance consistency and an inability to reliably regulate the pH of acidic soils. This introduces uncertainty into agricultural applications and limits its widespread use in acidic soil planting scenarios. Summary of the Invention

[0004] To address the problem that existing high-phosphorus compound fertilizers produced by the amino acid method of drum granulation have difficulty maintaining a stable pH value within the alkaline range of 7-9 and cannot reliably adjust the pH of acidic soils, this application provides a method for producing balanced alkaline high-phosphorus compound fertilizers using the amino acid method of drum granulation.

[0005] A method for producing balanced alkaline high-phosphorus compound fertilizer using an amino acid-based drum granulation process includes the following steps: S1. Raw material pretreatment and batching: After measuring various raw materials, they are transported to the granulation process; a return material system is set up to collect the return material generated in the subsequent screening process and send it back to the granulation process; S2. Preparation of ammonium phosphate slurry: Phosphoric acid and gaseous ammonia are metered and fed into a tubular reactor for neutralization reaction to generate ammonium phosphate slurry. The slurry is controlled to be alkaline. The waste heat from the reaction is used for preheating. S3, Drum Granulation and Granulation: The raw materials conveyed by S1, the alkaline slurry obtained by S2, and the return material are added to the drum granulator to agglomerate the materials into granules. S4. Drying and primary screening: Dry the wet granules after granulation, screen the dried material, return the residue to S1 as return material, and enter the cooling process for qualified granules. S5. Cooling and secondary screening: The qualified particles are initially cooled by a cooler and then further cooled by a plate cooler. After cooling, the particles are screened twice to obtain the final finished particles. The residue is returned to S1 as recycled material. S6. Coating treatment: The final product granules are coated with a composite coating agent to prevent clumping. S7. Exhaust gas treatment and resource recovery: Purify the exhaust gas generated during granulation, drying and cooling processes to achieve resource recovery; S8. Finished Product Packaging and Storage: The coated finished granules are automatically weighed, sewn, stacked, and then metered and packaged before being stored in the warehouse. S9. Process Control: Monitor and adjust key parameters in the production process in real time to ensure the quality of the final product.

[0006] By adopting the above technical solution, the recycled material is collected in stages during the raw material pretreatment stage. Coarse and fine recycled material are distinguished based on particle size differences. The coarse recycled material serves as the nucleation core in the granulation process, while the fine recycled material forms a coating layer. This precisely matched material supply method, combined with the metered formula raw materials, enters the granulation process, ensuring accurate material proportions and laying the foundation for uniform particle agglomeration. The ammonium phosphate slurry preparation stage employs a multi-stage temperature-controlled tubular reactor. Ammonia and phosphoric acid gradually complete the neutralization reaction within different temperature ranges, ensuring sufficient reaction and stable alkalinity of the slurry. Multi-stage heat exchange coils on the reactor's outer wall recover waste heat from the reaction, which is used to preheat the phosphoric acid raw material, recycled material, and combustion air in the hot air furnace, improving material reactivity while reducing external energy input. During granulation, graded return materials, alkaline slurry, and formulated raw materials come into full contact with each other in a rotary drum granulator, where the rotation of the equipment helps the materials agglomerate into granules. Subsequently, excess moisture is removed by co-current drying with hot air generated by a hot air furnace. Materials of different particle sizes are then separated through two-stage screening; unqualified particles are returned to the granulation process for recycling. Qualified particles are initially cooled by a cooler and then further stabilized at the temperature by a plate cooler, creating suitable conditions for subsequent coating treatment. During coating treatment, a composite coating agent composed of hydrophobic mineral oil and an alkaline stabilizer is steadily taken from the coating oil buffer tank and sprayed onto the surface of the finished granules to form a protective layer. In the exhaust gas treatment stage, the drying and cooling exhaust gases are pretreated by a venturi tube and then purified by a dust collector. The dust collected from the drying exhaust gases is mixed with ammonia-containing washing liquid to form a nutrient recovery liquid, which is then fed into a tubular reactor. The washing liquid is reused in the raw material batching system in a specific ratio, achieving resource recycling. Meanwhile, key parameters such as the feed ratio of the tubular reactor, the temperature inside the granulator, and the temperature of the drying hot air are monitored in real time, and operating conditions are adjusted in a timely manner to ensure the stability of the process at each stage and achieve continuous production of the target product.

[0007] Preferably, in step S1, the raw materials in the formula include ammonium chloride, potassium chloride, ammonium sulfate, potassium sulfate, urea, monoammonium phosphate, and auxiliary materials. Each raw material is metered and transported after being added to its respective silo. The return material system is equipped with a particle size classification device to classify and collect the return material generated in the subsequent screening processes S4 and S5 and send it back to the granulation process. The classification is into coarse return material and fine return material. The particle size range of the coarse return material is 2.5-4.25 mm, and the particle size of the fine return material is less than 1.0 mm. In step S3, the coarse return material is added from the feed end of the rotary drum granulator as a nucleation core, and the fine return material is added from the middle of the rotary drum granulator as a coating layer. The mass ratio of coarse return material to fine return material is 1:3 to 1:5.

[0008] By adopting the above technical solution, the auxiliary materials refer to micronutrient additives, which are used to supplement the essential nutrients required for crop growth other than nitrogen, phosphorus, and potassium. For example, they are compounds of at least one element selected from calcium, magnesium, sulfur, boron, zinc, iron, manganese, copper, and molybdenum. Their total addition amount typically accounts for 3-5% of the total mass of the raw materials in the formula. The return material system is equipped with a particle size classification device to accurately classify the return material generated during the screening process. Coarse return material, with its suitable particle size characteristics, is added from the feed end of the rotary drum granulator and quickly forms stable nucleation cores. Fine return material is added from the middle of the rotary drum granulator, utilizing its small particle size and large specific surface area to evenly coat the coarse return material cores, filling the gaps between the cores and enhancing particle adhesion. By controlling the specific mass ratio of coarse to fine return material, a dynamic match is formed between the number of nucleation cores and the supply of coating material. Combined with the rotation of the rotary drum granulator, the material is orderly agglomerated within the machine, reducing particle adhesion, clumping, or incomplete forming, ensuring the stable progress of subsequent drying and cooling processes.

[0009] Preferably, in step S2, phosphoric acid and gaseous ammonia are metered and continuously introduced into a tubular reactor for neutralization reaction; the concentration of phosphoric acid is 70-85 wt%; the molar ratio of ammonia to phosphoric acid is 1.05:1 to 1.25:1; the neutralization reaction is carried out at a reaction temperature of 60-120°C; and the pH value of the generated ammonium phosphate slurry is controlled to be 7 to 9.

[0010] By adopting the above technical solution, phosphoric acid within a specific concentration range is selected as the reaction raw material. This concentration range ensures the reactivity of phosphoric acid with gaseous ammonia while maintaining suitable fluidity of the reaction system. This avoids excessively high concentrations leading to violent local reactions and slurry clumping, or excessively low concentrations affecting the reaction rate and slurry solid content. Regulating the specific molar ratio of ammonia to phosphoric acid ensures the neutralization reaction proceeds fully towards the formation of alkaline ammonium phosphate. Combined with a reaction temperature control of 60-120℃, this guarantees the completeness and stability of the reaction and inhibits the residue of unreacted raw materials. The synergistic regulation of these parameters ensures the generated ammonium phosphate slurry remains stably within the target alkaline range. This alkaline slurry provides suitable viscosity for the subsequent granulation process and imparts the fundamental properties for adjusting soil pH to the final product, providing core raw material support for the stable operation of the entire production process and the achievement of the target product performance.

[0011] Preferably, in step S2, the outer wall of the tubular reactor is provided with multi-stage heat exchange coils and adopts a multi-segment temperature control structure, including a first reaction section, a second reaction section, and a third reaction section connected in sequence; the controlled temperature of the first reaction section is 60-80℃, the controlled temperature of the second reaction section is 80-100℃, and the controlled temperature of the third reaction section is 100-120℃; the multi-stage heat exchange coils are correspondingly arranged on the outer wall of each reaction section and are utilized in stages: the waste heat of the first reaction section is used to preheat the phosphoric acid raw material to 40-50℃, the waste heat of the second reaction section is used to preheat the return material in step S1 to 50-60℃, and the waste heat of the third reaction section is used to preheat the combustion air entering the hot air furnace.

[0012] By adopting the above technical solution, the tubular reactor uses a multi-stage temperature-controlled structure connected in sequence. By gradually increasing the temperature of each reaction stage, the neutralization reaction of ammonia and phosphoric acid is promoted in stages and in an orderly manner. The lower temperature of the first reaction stage provides a mild environment for the initial contact reaction of ammonia and phosphoric acid, avoiding excessively violent local reactions that could lead to local overheating or uneven composition of the material. After the material enters the subsequent reaction stages with gradually increasing temperatures, the neutralization reaction continues to proceed fully, ensuring the complete conversion of unreacted raw materials in the slurry and guaranteeing the uniform and stable alkalinity of the slurry. Multi-stage heat exchange coils are installed on the outer wall of each reaction stage of the reactor to achieve precise utilization of the waste heat in a stepped manner: the waste heat of the first reaction stage is used to preheat the phosphoric acid raw material, increasing the initial temperature of the phosphoric acid when it enters the reactor to match the needs of the subsequent initial reaction; the waste heat of the second reaction stage is used to preheat the return material, so that the return material is heated to a suitable temperature before entering the granulation process, improving the integration and coordination with the alkaline slurry; the high-temperature waste heat of the third reaction stage is used to preheat the combustion air of the hot air furnace, improving fuel combustion efficiency. This synergistic design of multi-stage temperature control and waste heat utilization ensures that the neutralization reaction is controllable and thorough, while achieving efficient energy recovery and reuse, reducing external energy input, and providing optimized material and energy conditions for the stable operation of subsequent processes such as granulation.

[0013] Preferably, in step S3, the material temperature inside the rotary drum granulator is controlled to be 55-75℃; the rotation speed of the rotary drum granulator is 10-18 rpm, the tilt angle is 1-3°, and the residence time of the material inside the machine is 5-10 min, so that the material can be fully agglomerated into granules.

[0014] By employing the above technical solutions, the temperature of the material inside the rotary drum granulator is controlled within a specific range, matching the viscosity characteristics of the alkaline slurry. This ensures a suitable bonding force between the coarse return material nucleation cores and the fine return material and formulation raw materials, preventing excessive slurry flow and loss due to overheating, or insufficient material viscosity and difficulty in agglomeration due to underheating. The rotational speed and tilt angle of the rotary drum granulator work together. The rotational speed determines the tumbling frequency and collision intensity of the material inside the machine, while the tilt angle controls the axial movement speed of the material within the machine. Together, these two factors create a uniform fluidization state within the machine, ensuring full contact and tight encapsulation between the nucleation cores and the coating material. A specific material residence time is set to provide sufficient time for the material to complete nucleation, encapsulation, and particle densification within the machine, allowing the coarse return material cores to be gradually encapsulated by the fine return material and formulation raw materials to form structurally complete particles. The coordinated control of temperature, rotation speed, tilt angle and residence time adapts to the characteristics of graded return material and the reaction requirements of alkaline slurry, enabling the material to complete nucleation, encapsulation and particle densification in an orderly manner in the machine, reducing the situation of excessively fine, excessively large or loosely structured particles, and providing intermediate products with regular shapes for subsequent drying and cooling processes.

[0015] Preferably, in step S4, the drying process specifically employs hot air produced by a hot air furnace at 100-140°C to dry the wet particles in a parallel flow; the inlet temperature of the hot air is controlled at 110-130°C, and the moisture content of the dried material is 1.0-2.5wt%; during the sieving process, the fine powder with a particle size less than 1.0mm and the large particles with a particle size greater than 4.25mm are returned to step S1 as return material, wherein the large particles need to be crushed first, and the particles with a particle size between 1.0-4.25mm are qualified particles that enter the cooling process.

[0016] By adopting the above technical solution, hot air generated by a hot air furnace is used to dry wet particles in a parallel flow. The hot air and material flow in the same direction, forming a reasonable temperature and humidity gradient, which allows the surface moisture of the wet particles to evaporate rapidly while avoiding local overheating that could damage the particle structure. Combined with controlling the hot air inlet temperature within a specific range, the drying rate is precisely controlled, ensuring a stable and controllable drying process. After drying, the moisture content of the material is controlled within a specific range, removing excess moisture from the particles to ensure particle strength, while avoiding excessively low moisture content that could cause brittleness and breakage, providing a suitable material state for subsequent screening processes. Screening achieves precise separation of materials with different particle sizes: fine powder with a particle size less than 1.0 mm is directly returned to the granulation process to re-agglomerate, while large particles with a particle size greater than 4.25 mm are crushed and returned to granulation, retaining only particles with a particle size between 1.0 and 4.25 mm as qualified particles for subsequent processes. This screening and recycling design allows unqualified materials of different particle sizes to re-participate in granulation, improving raw material utilization while ensuring uniform particle size of the material entering the cooling process, providing conditions for the stable progress of subsequent processes.

[0017] Preferably, in step S5, the cooler uses ambient temperature air for countercurrent cooling to reduce the material temperature to 35-45℃; the flow rate of the cooling air is 1.2-2.0m / s, and the cooling time is 8-15min; after secondary screening, particles with a diameter of 2.0-4.0mm are the final finished particles, and the sieve residue is returned to step S1 as recycled material.

[0018] By adopting the above technical solution, countercurrent cooling is performed between ambient temperature air and the material. The countercurrent design ensures that the cooling air and high-temperature particles come into contact in opposite directions, creating a reasonable temperature gradient. This improves cooling efficiency while using ambient temperature air to avoid additional energy consumption and prevents over-cooling that could damage the particle structure. Controlling the cooling airflow rate and cooling time ensures that the material is fully in contact with the air within the cooler, guaranteeing a stable temperature drop to a specific range. This temperature range prevents excessively high particle temperatures from affecting subsequent coating adhesion and also prevents excessively low temperatures from causing moisture condensation on the particle surface. The cooled material undergoes a second screening for precise grading. The residue is returned to the granulation process for recycling, while only particles within a specific size range are retained as the final product. This improves the overall utilization rate of raw materials while ensuring uniform particle size in the finished product, providing a suitable material state for subsequent coating processing.

[0019] Preferably, in step S6, the coating treatment is carried out at 40-55°C; a composite coating agent is taken from the coating oil buffer tank and sprayed onto the final finished particles; the composite coating agent is composed of hydrophobic mineral oil and alkaline stabilizer, and its addition amount is 0.5-1.5 wt% of the mass of the finished particles; the mass ratio of hydrophobic mineral oil to alkaline stabilizer in the composite coating agent is 8:1 to 10:1, and the alkaline stabilizer is at least one of hydrogenated castor oil derivative or magnesium stearate.

[0020] By adopting the above technical solution, the coating process is controlled within a specific temperature range, which is compatible with the temperature of the cooled finished particles. This ensures that the composite coating agent has suitable fluidity, facilitating uniform coverage of the particle surface by spraying. Simultaneously, it avoids excessively high temperatures that could cause the coating agent components to volatilize or deteriorate, and excessively low temperatures that could result in insufficient fluidity and uneven coating. The composite coating agent is composed of hydrophobic mineral oil and an alkaline stabilizer: the hydrophobic mineral oil forms a dense hydrophobic protective layer on the particle surface, inhibiting contact between external moisture and the particles; the alkaline stabilizer enhances the bonding strength between the coating layer and the particle surface, improving the structural stability of the coating layer. The two are compounded at a specific mass ratio to achieve synergistic optimization of protective and adhesion performance. Hydrogenated castor oil derivatives or magnesium stearate are both suitable for the composite coating agent system. The amount of composite coating agent added is controlled within a specific proportion of the finished particle mass to ensure the formation of a complete coating layer while avoiding excessive addition that would result in an overly thick coating layer affecting nutrient release, or insufficient addition that would lead to poor protective effect. The coordinated control of temperature, coating agent composition and dosage ensures that a uniform and stable protective layer is formed on the surface of the finished granules, preventing the granules from agglomerating and sticking together during subsequent storage.

[0021] Preferably, in step S7, the exhaust gas purification treatment specifically includes: the drying exhaust gas and cooling exhaust gas are first pretreated by a venturi tube, and then purified by a dust collector; the granulation exhaust gas is washed and absorbed, and part of the washing liquid is reused; the dust collected from the purified drying exhaust gas is introduced into a washing system and mixed with an ammonia-containing washing liquid; the washing system includes a phosphoric acid buffer tank and a washing circulation tank, the pH value of the washing liquid in the washing circulation tank is maintained at 6.0 to 7.0, and the amount of washing liquid reused in the raw material batching system accounts for 20-40% of the total washing liquid volume; the nutrient recovery liquid formed by the mixture of dust and ammonia-containing washing liquid is added to the tubular reactor in step S2 at 2-5% of the phosphoric acid feed flow rate.

[0022] By adopting the above technical solution, the washing system consists of a phosphate buffer tank and a washing circulation tank working together. The phosphate buffer tank regulates the pH value of the washing liquid in the washing circulation tank, keeping it stable within a suitable range to ensure the absorption efficiency of ammonia in the granulation tail gas, while avoiding pH fluctuations that could affect the compatibility of the washing liquid with subsequent processes. The washing liquid in the washing circulation tank is recycled to the raw material batching system in a specific ratio, realizing the recycling of water resources and residual nutrients in the washing liquid and reducing material and water waste. The dust collected from the drying tail gas purification contains nutrients such as phosphorus and nitrogen. It is introduced into the washing system and mixed with ammonia-containing washing liquid to fully dissolve the nutrients in the dust and form a nutrient recovery liquid. This recovery liquid is added to the tubular reactor in a specific ratio according to the phosphate feed flow rate, allowing the recovered nutrients to participate again in the neutralization reaction between ammonia and phosphate. The specific addition ratio can avoid excessive recovery liquid leading to abnormal slurry concentration or reaction imbalance, and can also avoid insufficient addition causing waste of recovered nutrients. Combined with the recycling of washing liquid, a complete resource recovery closed loop is constructed.

[0023] Preferably, in step S9, the key parameters that are monitored and adjusted in real time include the feed ratio of ammonia to phosphoric acid in the tubular reactor, the material temperature in the rotary drum granulator, and the drying hot air temperature. The corresponding operating parameters are adjusted according to the monitoring results to ensure stable operation of the production process.

[0024] By adopting the above technical solution, a dynamic feedback control mechanism for the production process is constructed by real-time monitoring of three core process parameters: the feed ratio of ammonia to phosphoric acid in the tubular reactor, the material temperature in the rotary drum granulator, and the drying hot air temperature. Monitoring and adjusting the feed ratio of ammonia to phosphoric acid promptly corrects material ratio deviations in the neutralization reaction, ensuring the alkalinity stability of the ammonium phosphate slurry. Monitoring and adjusting the material temperature in the rotary drum granulator adapts to the agglomeration requirements of graded return material and alkaline slurry, maintaining suitable material viscosity during granulation. Monitoring and adjusting the drying hot air temperature precisely controls the drying rate, avoiding over- or under-drying of wet granules. Based on the monitoring results of each parameter, corresponding operating parameters are adjusted in a timely manner to ensure coordinated adaptation of process conditions in key steps such as neutralization reaction, granulation, and drying, achieving continuous and stable operation of the entire production process and ensuring consistent final product performance.

[0025] In summary, this application has the following beneficial effects: 1. This application adopts an amino acid drum granulation process that includes graded return material addition and a multi-stage temperature-controlled tubular reactor process. Since the return material is graded into coarse and fine types and added from different positions in the granulator, and the reaction is carried out under segmented temperature control, the effect of stably producing alkaline high-phosphorus compound fertilizer products with a pH value of 7 to 9 is achieved. This product has the function of adjusting the pH of acidic soil.

[0026] 2. In this application, multi-stage heat exchange coils are preferred to utilize the waste heat of the tubular reactor in stages. Since the heat exchange coils are installed on the outer wall of the reactor and the waste heat at different temperatures is used to preheat the phosphoric acid raw material, return material and combustion air of the hot air furnace, the overall energy consumption of the production system is reduced and the reaction heat is effectively recovered.

[0027] 3. The method of this application coats the finished product granules with a composite coating agent made of hydrophobic mineral oil and a specific alkaline stabilizer. Since the alkaline stabilizer in the coating agent is compatible with the alkaline fertilizer system, it achieves the effect of improving the anti-caking performance of alkaline high-phosphorus compound fertilizer products during storage and extending the product shelf life.

[0028] 4. This application pre-treats the drying and cooling exhaust gas through a venturi tube and coordinates it with the granulation exhaust gas scrubbing system. Since the venturi tube can pre-treat the dust in the exhaust gas and the collected dust is introduced into an ammonia-containing scrubbing liquid for nutrient recovery, the exhaust gas purification efficiency is improved and the nutrient resource recovery from the dust is achieved. Attached Figure Description

[0029] Figure 1 This is a flowchart of the method for producing balanced alkaline high-phosphorus compound fertilizer using the amino acid method drum granulation provided in this application. Detailed Implementation

[0030] The present application will be further described in detail below with reference to embodiments and comparative examples. Unless otherwise specified, the experimental methods used below are conventional methods. Unless otherwise specified, the materials, reagents, methods and instruments used are all conventional materials, reagents, methods and instruments in the art, which can be obtained by those skilled in the art through commercial channels or prepared according to literature methods.

[0031] Technical concept: Existing amino acid-based drum granulation processes for producing alkaline high-phosphorus compound fertilizers generally suffer from technical problems, including difficulty in consistently controlling the product's pH value within the alkaline range of 7-9 and the inability to reliably adjust the pH of acidic soils. The core reasons lie in two aspects: First, the waste material handling method is crude; waste material generated during the screening process is directly mixed and reused without being graded and adapted according to particle size differences. This leads to an imbalance between the nucleation core and the coating material during granulation, resulting in poor particle uniformity. Second, tubular reactors often employ a single-stage temperature control design, making it difficult to fully and smoothly advance the neutralization reaction between ammonia and phosphoric acid. This results in significant fluctuations in the alkalinity of the slurry, and the lack of a coordinated control mechanism for key parameters in each process further exacerbates the instability of product performance.

[0032] This technical solution addresses the aforementioned problems by constructing a complete solution through multi-stage collaborative technical means: First, it employs a return material grading and location-based addition process, using a particle size classification device to separate the return material into coarse and fine categories, which are then added from different locations in the granulator as nucleation cores and coating layers, respectively, ensuring the uniformity of granule formation; Second, it utilizes a multi-stage temperature-controlled tubular reactor combined with waste heat utilization to ensure the neutralization reaction proceeds in stages and in an orderly manner, precisely controlling the alkalinity of the ammonium phosphate slurry; Simultaneously, by collaboratively regulating key parameters in granulation, drying, and cooling processes, coupled with composite coating treatment and tail gas resource recovery design, and combined with real-time parameter monitoring and dynamic adjustment mechanisms, it ensures stable and adaptable process conditions for each process, ultimately achieving stable control of the pH value of alkaline high-phosphorus compound fertilizer products, solving the core problems of existing technologies.

[0033] Example 1: A method for producing balanced alkaline high-phosphorus compound fertilizer using an amino acid-based drum granulation process, comprising the following steps: S1. Raw material pretreatment and batching: Various raw materials containing ammonium chloride, potassium chloride, ammonium sulfate, potassium sulfate, urea, monoammonium phosphate and auxiliary materials are added to their respective silos, metered and then transported to the granulation process; at the same time, a return material system is set up to collect and return the return material generated in the screening process in subsequent steps S4 and S5 to the granulation process. The return material system is equipped with a particle size classification device to classify the return material into coarse return material and fine return material; the particle size range of coarse return material is 3.375mm, and the particle size of fine return material is less than 1.0mm. S2. Preparation of ammonium phosphate slurry: Phosphoric acid and gaseous ammonia are metered and continuously fed into a tubular reactor with multi-stage heat exchange coils on the outer wall to carry out a neutralization reaction to generate ammonium phosphate slurry, and the slurry is controlled to be alkaline; the waste heat from the reaction discharged by at least one stage of heat exchange coils is used to preheat the returned material or phosphoric acid raw material. The concentration of phosphoric acid was 77.5 wt%; the molar ratio of ammonia to phosphoric acid was 1.15:1; the neutralization reaction was carried out at a reaction temperature of 90℃; and the pH value of the generated ammonium phosphate slurry was controlled to be 8. The tubular reactor adopts a multi-stage temperature control structure, including a first reaction section, a second reaction section, and a third reaction section connected in sequence. The controlled temperature of the first reaction section is 70℃, the controlled temperature of the second reaction section is 90℃, and the controlled temperature of the third reaction section is 110℃. Multi-stage heat exchange coils are correspondingly installed on the outer wall of each reaction section and are utilized in stages: the waste heat of the first reaction section is used to preheat the phosphoric acid raw material to 45℃, the waste heat of the second reaction section is used to preheat the return material in step S1 to 55℃, and the waste heat of the third reaction section is used to preheat the combustion air entering the hot air furnace. S3. Drum granulation and pelletizing: The raw materials conveyed in step S1, the alkaline slurry obtained in step S2, and the graded return material are added together to the drum granulator to agglomerate the materials into pellets. The coarse return material is added from the feed end of the rotary drum granulator as the nucleation core, and the fine return material is added from the middle of the rotary drum granulator as the coating layer. The mass ratio of coarse return material to fine return material is 1:4. The material temperature inside the rotary drum granulator is controlled at 65℃; the rotation speed of the rotary drum granulator is 14 rpm, the tilt angle is 2°, and the material residence time inside the machine is 7.5 min. S4. Drying and primary screening: Dry the wet granules after granulation, and then screen the dried material. The fine powder and large particles separated are returned to step S1 as return material, and qualified particles enter the cooling process. Specifically, the drying process involves using 120°C hot air from a hot air furnace to dry the wet particles in a parallel flow. The inlet temperature of the hot air is controlled at 120°C, and the moisture content of the dried material is 1.75 wt%. After sieving, particles smaller than 1.0 mm are classified as fine powder, particles larger than 4.25 mm are classified as large particles and are crushed and returned to the furnace, and particles with a diameter between 1.0 and 4.25 mm are classified as qualified particles. S5. Cooling and secondary screening: After the qualified particles are initially cooled by the cooler, they are sent to the plate cooler for further cooling. After cooling, they are screened a second time to obtain the final finished particles. The residue is returned to step S1 as recycled material. The cooler uses ambient temperature air for counter-current cooling to reduce the material temperature to 40℃; the airflow rate is 1.6m / s and the cooling time is 11.5min; after secondary screening, particles with a diameter of 3.0mm are the final finished product particles. S6. Coating treatment: The final finished particles are sprayed with a composite coating agent taken from the coating oil buffer tank to achieve anti-caking coating treatment. The coating process is carried out at 47.5℃; the composite coating agent is composed of hydrophobic mineral oil and alkaline stabilizer, and its addition amount is 1.0 wt% of the finished particle mass; the mass ratio of hydrophobic mineral oil to alkaline stabilizer in the composite coating agent is 9:1, and the alkaline stabilizer is a hydrogenated castor oil derivative. S7. Exhaust gas treatment and resource recovery: The exhaust gas generated during granulation, drying and cooling processes is purified; the drying exhaust gas and cooling exhaust gas are first pretreated by a venturi tube and then purified by a dust collector; the granulation exhaust gas is washed and absorbed, and part of the washing liquid is reused; the dust collected from the purified drying exhaust gas is introduced into the washing system and mixed with ammonia-containing washing liquid. The washing system includes a phosphate buffer tank and a washing circulation tank. The pH value of the washing liquid in the washing circulation tank is maintained at 6.5. The amount of washing liquid recycled to the raw material batching system accounts for 30% of the total washing liquid volume. The nutrient recovery liquid formed by mixing dust and ammonia-containing washing liquid is added to the tubular reactor in step S2 at 3.5% of the phosphate feed flow rate. S8. Finished Product Packaging and Storage: The coated finished granules are automatically weighed, sewn, and stacked for metering and packaging before being stored in the warehouse. S9. Process Control: Monitor and adjust key parameters in the production process in real time to ensure the quality of the final product.

[0034] Specifically, this involves real-time monitoring and adjustment of the feed ratio of ammonia to phosphoric acid in the tubular reactor, the material temperature in the rotary drum granulator, and the drying hot air temperature. Based on the monitoring results, the corresponding operating parameters are adjusted to ensure stable operation of the production process.

[0035] Example 2: A method for producing balanced alkaline high-phosphorus compound fertilizer using an amino acid-based drum granulation process, comprising the following steps: S1. Raw material pretreatment and batching: Various raw materials containing ammonium chloride, potassium chloride, ammonium sulfate, potassium sulfate, urea, monoammonium phosphate and auxiliary materials are added to their respective silos, metered and then transported to the granulation process; at the same time, a return material system is set up to collect and return the return material generated in the screening process in subsequent steps S4 and S5 to the granulation process. The return material system is equipped with a particle size classification device to classify the return material into coarse return material and fine return material; the particle size range of coarse return material is 2.5mm, and the particle size of fine return material is less than 1.0mm. S2. Preparation of ammonium phosphate slurry: Phosphoric acid and gaseous ammonia are metered and continuously fed into a tubular reactor with multi-stage heat exchange coils on the outer wall to carry out a neutralization reaction to generate ammonium phosphate slurry, and the slurry is controlled to be alkaline; the waste heat from the reaction discharged by at least one stage of heat exchange coils is used to preheat the returned material or phosphoric acid raw material. The concentration of phosphoric acid was 70 wt%; the molar ratio of ammonia to phosphoric acid was 1.05:1; the neutralization reaction was carried out at a reaction temperature of 60℃; and the pH value of the generated ammonium phosphate slurry was controlled to be 7. The tubular reactor adopts a multi-stage temperature control structure, including a first reaction section, a second reaction section, and a third reaction section connected in sequence. The controlled temperature of the first reaction section is 60℃, the controlled temperature of the second reaction section is 80℃, and the controlled temperature of the third reaction section is 100℃. Multi-stage heat exchange coils are correspondingly installed on the outer wall of each reaction section and are utilized in stages: the waste heat of the first reaction section is used to preheat the phosphoric acid raw material to 40℃, the waste heat of the second reaction section is used to preheat the return material in step S1 to 50℃, and the waste heat of the third reaction section is used to preheat the combustion air entering the hot air furnace. S3. Drum granulation and pelletizing: The raw materials conveyed in step S1, the alkaline slurry obtained in step S2, and the graded return material are added together to the drum granulator to agglomerate the materials into pellets. The coarse return material is added from the feed end of the rotary drum granulator as the nucleation core, and the fine return material is added from the middle of the rotary drum granulator as the coating layer. The mass ratio of coarse return material to fine return material is 1:5. The material temperature inside the rotary drum granulator is controlled at 55℃; the rotation speed of the rotary drum granulator is 10 rpm, the tilt angle is 1°, and the material residence time inside the machine is 5 min. S4. Drying and primary screening: Dry the wet granules after granulation, and then screen the dried material. The fine powder and large particles separated are returned to step S1 as return material, and qualified particles enter the cooling process. Specifically, the drying process involves using 100°C hot air from a hot air furnace to dry the wet particles in a parallel flow. The inlet temperature of the hot air is controlled at 110°C, and the moisture content of the dried material is 1.0 wt%. After sieving, particles smaller than 1.0 mm are classified as fine powder, particles larger than 4.25 mm are classified as large particles and are returned after crushing, and particles with a diameter between 1.0 and 4.25 mm are classified as qualified particles. S5. Cooling and secondary screening: After the qualified particles are initially cooled by the cooler, they are sent to the plate cooler for further cooling. After cooling, they are screened a second time to obtain the final finished particles. The residue is returned to step S1 as recycled material. The cooler uses ambient temperature air for counter-current cooling to reduce the material temperature to 35℃; the airflow rate is 1.2m / s and the cooling time is 8min; after secondary screening, particles with a diameter of 2.0mm are the final finished product particles. S6. Coating treatment: The final finished particles are sprayed with a composite coating agent taken from the coating oil buffer tank to achieve anti-caking coating treatment. The coating process is carried out at 40°C; the composite coating agent is composed of hydrophobic mineral oil and alkaline stabilizer, and its addition amount is 0.5 wt% of the finished particle mass; the mass ratio of hydrophobic mineral oil to alkaline stabilizer in the composite coating agent is 8:1, and the alkaline stabilizer is magnesium stearate. S7. Exhaust gas treatment and resource recovery: The exhaust gas generated during granulation, drying and cooling processes is purified; the drying exhaust gas and cooling exhaust gas are first pretreated by a venturi tube and then purified by a dust collector; the granulation exhaust gas is washed and absorbed, and part of the washing liquid is reused; the dust collected from the purified drying exhaust gas is introduced into the washing system and mixed with ammonia-containing washing liquid. The washing system includes a phosphate buffer tank and a washing circulation tank. The pH value of the washing liquid in the washing circulation tank is maintained at 6.0. 20% of the washing liquid is reused in the raw material batching system. Nutrient recovery liquid formed by mixing dust and ammonia-containing washing liquid is added to the tubular reactor in step S2 at 2% of the phosphate feed flow rate. S8. Finished Product Packaging and Storage: The coated finished granules are automatically weighed, sewn, and stacked for metering and packaging before being stored in the warehouse. S9. Process Control: Monitor and adjust key parameters in the production process in real time to ensure the quality of the final product.

[0036] Specifically, this involves real-time monitoring and adjustment of the feed ratio of ammonia to phosphoric acid in the tubular reactor, the material temperature in the rotary drum granulator, and the drying hot air temperature. Based on the monitoring results, the corresponding operating parameters are adjusted to ensure stable operation of the production process.

[0037] Example 3: A method for producing balanced alkaline high-phosphorus compound fertilizer using an amino acid-based drum granulation process, comprising the following steps: S1. Raw material pretreatment and batching: Various raw materials containing ammonium chloride, potassium chloride, ammonium sulfate, potassium sulfate, urea, monoammonium phosphate and auxiliary materials are added to their respective silos, metered and then transported to the granulation process; at the same time, a return material system is set up to collect and return the return material generated in the screening process in subsequent steps S4 and S5 to the granulation process. The return material system is equipped with a particle size classification device to classify the return material into coarse return material and fine return material; the particle size range of coarse return material is 4.25mm, and the particle size of fine return material is less than 1.0mm. S2. Preparation of ammonium phosphate slurry: Phosphoric acid and gaseous ammonia are metered and continuously fed into a tubular reactor with multi-stage heat exchange coils on the outer wall to carry out a neutralization reaction to generate ammonium phosphate slurry, and the slurry is controlled to be alkaline; the waste heat from the reaction discharged by at least one stage of heat exchange coils is used to preheat the returned material or phosphoric acid raw material. The concentration of phosphoric acid was 85 wt%; the molar ratio of ammonia to phosphoric acid was 1.25:1; the neutralization reaction was carried out at a reaction temperature of 120℃; and the pH value of the generated ammonium phosphate slurry was controlled to be 9. The tubular reactor adopts a multi-stage temperature control structure, including a first reaction section, a second reaction section, and a third reaction section connected in sequence. The controlled temperature of the first reaction section is 80℃, the controlled temperature of the second reaction section is 100℃, and the controlled temperature of the third reaction section is 120℃. Multi-stage heat exchange coils are correspondingly installed on the outer wall of each reaction section and are utilized in stages: the waste heat of the first reaction section is used to preheat the phosphoric acid raw material to 50℃, the waste heat of the second reaction section is used to preheat the return material in step S1 to 60℃, and the waste heat of the third reaction section is used to preheat the combustion air entering the hot air furnace. S3. Drum granulation and pelletizing: The raw materials conveyed in step S1, the alkaline slurry obtained in step S2, and the graded return material are added together to the drum granulator to agglomerate the materials into pellets. The coarse return material is added from the feed end of the rotary drum granulator as the nucleation core, and the fine return material is added from the middle of the rotary drum granulator as the coating layer. The mass ratio of coarse return material to fine return material is 1:3. The material temperature inside the rotary drum granulator is controlled at 75℃; the rotation speed of the rotary drum granulator is 18 rpm, the tilt angle is 3°, and the material residence time inside the machine is 10 min. S4. Drying and primary screening: Dry the wet granules after granulation, and then screen the dried material. The fine powder and large particles separated are returned to step S1 as return material, and qualified particles enter the cooling process. Specifically, the drying process involves using hot air at 140℃ produced by a hot air furnace to dry the wet particles in a parallel flow. The inlet temperature of the hot air is controlled at 130℃, and the moisture content of the dried material is 2.5wt%. After sieving, particles with a diameter less than 1.0mm are classified as fine powder, particles with a diameter greater than 4.25mm are classified as large particles and are returned after crushing, and particles with a diameter between 1.0-4.25mm are classified as qualified particles. S5. Cooling and secondary screening: After the qualified particles are initially cooled by the cooler, they are sent to the plate cooler for further cooling. After cooling, they are screened a second time to obtain the final finished particles. The residue is returned to step S1 as recycled material. The cooler uses ambient temperature air for counter-current cooling to reduce the material temperature to 45℃; the airflow rate is 2.0m / s and the cooling time is 15min; after secondary screening, particles with a diameter of 4.0mm are the final finished product particles. S6. Coating treatment: The final finished particles are sprayed with a composite coating agent taken from the coating oil buffer tank to achieve anti-caking coating treatment. The coating process is carried out at 55°C; the composite coating agent is composed of hydrophobic mineral oil and alkaline stabilizer, and its addition amount is 1.5 wt% of the finished particle mass; the mass ratio of hydrophobic mineral oil to alkaline stabilizer in the composite coating agent is 10:1, and the alkaline stabilizer is a hydrogenated castor oil derivative. S7. Exhaust gas treatment and resource recovery: The exhaust gas generated during granulation, drying and cooling processes is purified; the drying exhaust gas and cooling exhaust gas are first pretreated by a venturi tube and then purified by a dust collector; the granulation exhaust gas is washed and absorbed, and part of the washing liquid is reused; the dust collected from the purified drying exhaust gas is introduced into the washing system and mixed with ammonia-containing washing liquid. The washing system includes a phosphate buffer tank and a washing circulation tank. The pH value of the washing liquid in the washing circulation tank is maintained at 7.0. 40% of the washing liquid is reused in the raw material batching system. Nutrient recovery liquid formed by mixing dust and ammonia-containing washing liquid is added to the tubular reactor in step S2 at 5% of the phosphate feed flow rate. S8. Finished Product Packaging and Storage: The coated finished granules are automatically weighed, sewn, and stacked for metering and packaging before being stored in the warehouse. S9. Process Control: Monitor and adjust key parameters in the production process in real time to ensure the quality of the final product.

[0038] Specifically, this involves real-time monitoring and adjustment of the feed ratio of ammonia to phosphoric acid in the tubular reactor, the material temperature in the rotary drum granulator, and the drying hot air temperature. Based on the monitoring results, the corresponding operating parameters are adjusted to ensure stable operation of the production process.

[0039] Comparative Example 1: The only difference between this comparative example and Example 1 is that: in step S1, the return material system does not have a particle size classification device, and the return material generated in the screening process is mixed without distinguishing between coarse and fine return material; in step S3, all the mixed return material is added from the feed end of the rotary drum granulator, and the strategy of adding coarse return material as the nucleation core and fine return material as the coating layer is not implemented, and there is no control over the mass ratio of coarse and fine return material.

[0040] Comparative Example 2: The only difference between this comparative example and Example 1 is that in step S2, a single-section tubular reactor without a multi-stage temperature control structure and without multi-stage heat exchange coils on the outer wall is used for the neutralization reaction. The waste heat of the reaction is not recovered and utilized, and the phosphoric acid raw material and return material are not preheated.

[0041] Comparative Example 3: The only difference between this comparative example and Example 1 is that in step S6, conventional hydrophobic mineral oil without added hydrogenated castor oil derivatives or basic stabilizers such as magnesium stearate is used for coating treatment.

[0042] Comparative Example 4: The only difference between this comparative example and Example 1 is that in step S7, the drying exhaust gas and the cooling exhaust gas directly enter the dust collector for treatment without pretreatment by the venturi tube; at the same time, the dust collected by the drying exhaust gas purification is directly discarded and is not introduced into the washing system to mix with the ammonia-containing washing liquid to form a nutrient recovery liquid.

[0043] I. Comprehensive performance test of particles Take 10 kg of each of the compound fertilizer materials produced in Examples 1-3 and Comparative Examples 1-4. According to the GB / T15063-2020 "Compound Fertilizer" standard, first screen qualified particles with a particle size of 2.0-4.0 mm through a standard inspection sieve. The percentage of qualified particles to the total mass of the material is the granulation rate. Then, randomly select 50 particles from each sample of qualified particles and use a particle strength tester to measure the compressive strength of each particle. Take the average value as the particle compressive strength of the sample. During the test, record the appearance integrity of each sample particle to ensure that there are no obvious cracks or powder shedding.

[0044] II. Product Storage Stability Test Five kg each of the qualified finished product granules from Examples 1-3 and Comparative Examples 1-4 were placed in well-sealed polyethylene bags and stored in a constant temperature and humidity chamber at 25°C and 60% relative humidity for 30 days. The anti-caking performance was tested according to the HG / T4214-2011 standard "Fertilizer Anti-caking Agent". After storage, the material in the bags was poured out naturally and sieved using a standard test sieve. The percentage of material passing through the sieve holes relative to the total stored material mass was the anti-caking rate. At the same time, the hardness of the caking material that did not pass through the sieve was observed, and the degree of looseness of the caking was recorded by gently rubbing it by hand. The anti-caking rate data combined with the data reflected the stability of the product during storage.

[0045] III. Production Energy Consumption and Exhaust Gas Purification Efficiency Test In the production processes of Examples 1-3 and Comparative Examples 1-4, the total electrical and thermal energy consumed in producing 1 ton of compound fertilizer was recorded, and the comprehensive energy consumption per ton of fertilizer was calculated. Simultaneously, sampling points were set up at the exhaust gas outlets of each production process. Following the relevant provisions of GB13223-2011 "Emission Standard of Air Pollutants for Thermal Power Plants" and GB4915-2013 "Emission Standard of Air Pollutants for Cement Industry," exhaust gas samples were continuously collected for 3 hours using a flue gas analyzer and a dust sampler, and the average values ​​of dust concentration and ammonia concentration in the exhaust gas were measured. By comparing the comprehensive energy consumption per ton of fertilizer and the pollutant concentration data in the exhaust gas, the advantages of innovative features such as the cascade utilization of waste heat from the tubular reactor, the synergistic recovery of exhaust gas heat and mass, and the Venturi tube pretreatment in energy saving, consumption reduction, and environmental purification were demonstrated.

[0046] The experimental data for producing balanced alkaline high-phosphorus compound fertilizer by amino acid drum granulation are shown in Table 1.

[0047] Table 1:

[0048] As can be seen from Examples 1-3 and Comparative Example 1, and Table 1, when the return material generated in the screening process is not graded by particle size and is added entirely from a single feed end of the rotary drum granulator, the granulation rate and average compressive strength of qualified particles both show a downward trend. This is because the mixed return material cannot effectively utilize the different functions of coarse particles as nucleation cores and fine powder as coating layers during the granulation process, affecting the agglomeration kinetics of the material in the drum, resulting in uneven particle growth and insufficient structural density.

[0049] Combining Examples 1-3 and Comparative Example 2 with Table 1, it can be seen that when using a single-stage tubular reactor without a multi-stage temperature control structure and external wall heat exchange coils, and without utilizing reaction waste heat to preheat the raw materials, the overall energy consumption per unit mass of product increases, and the ammonia concentration in the tail gas also rises. This reflects the role of the multi-stage temperature control structure in maintaining the stability of the neutralization reaction process, and the impact of cascaded recovery of reaction waste heat for preheating the raw materials on reducing the system's external heat energy demand.

[0050] As can be seen from Examples 1-3 and Comparative Example 3, and in conjunction with Table 1, when conventional hydrophobic mineral oil without the addition of a specific alkaline stabilizer is used in the coating process, the anti-caking rate of the finished product after storage decreases significantly. This indicates that, for alkaline fertilizer systems, the presence of an alkaline stabilizer in the composite coating agent plays a crucial role in maintaining the integrity of the coating layer under alkaline conditions and preventing the formation of salt bridges between particles, and is a key factor affecting the long-term storage stability of the product.

[0051] Based on Examples 1-3 and Comparative Example 4, and referring to Table 1, it can be seen that when the drying and cooling exhaust gas is directly treated without venturi tube pretreatment and the collected dust is directly discarded without being recycled in conjunction with the scrubbing system, both the dust concentration and ammonia concentration in the exhaust gas emissions increase. This indicates that the synergistic effect of venturi tube pretreatment on the coagulation of fine dust, and the further absorption and fixation of ammonia in the gas phase by introducing dust into the scrubbing system, both factors jointly affect the final exhaust gas purification efficiency.

[0052] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for producing balanced alkaline high-phosphorus compound fertilizer using an amino acid-based drum granulation process, characterized in that: Includes the following steps: S1. Raw material pretreatment and batching: After measuring various raw materials, they are transported to the granulation process; a return material system is set up to collect the return material generated in the subsequent screening process and send it back to the granulation process; S2. Preparation of ammonium phosphate slurry: Phosphoric acid and gaseous ammonia are metered and fed into a tubular reactor for neutralization reaction to generate ammonium phosphate slurry. The slurry is controlled to be alkaline. The waste heat from the reaction is used for preheating. S3, Drum Granulation and Granulation: The raw materials conveyed by S1, the alkaline slurry obtained by S2, and the return material are added to the drum granulator to agglomerate the materials into granules. S4. Drying and primary screening: Dry the wet granules after granulation, screen the dried material, return the residue to S1 as return material, and enter the cooling process for qualified granules. S5. Cooling and secondary screening: The qualified particles are initially cooled by a cooler and then further cooled by a plate cooler. After cooling, the particles are screened twice to obtain the final finished particles. The residue is returned to S1 as recycled material. S6. Coating treatment: The final product granules are coated with a composite coating agent to prevent clumping. S7. Exhaust gas treatment and resource recovery: Purify the exhaust gas generated during granulation, drying and cooling processes to achieve resource recovery; S8. Finished Product Packaging and Storage: The coated finished granules are automatically weighed, sewn, stacked, and then metered and packaged before being stored in the warehouse. S9. Process Control: Monitor and adjust key parameters in the production process in real time to ensure the quality of the final product.

2. The method for producing balanced alkaline high-phosphorus compound fertilizer by roller granulation using the amino acid method according to claim 1, characterized in that: In step S1, the raw materials in the formula include ammonium chloride, potassium chloride, ammonium sulfate, potassium sulfate, urea, monoammonium phosphate, and auxiliary materials. Each raw material is metered and transported after being added to its respective silo. The return material system is equipped with a particle size classification device to classify and collect the return material generated in the subsequent screening processes S4 and S5 and send it back to the granulation process. The return material is classified into coarse return material and fine return material. The particle size range of the coarse return material is 2.5-4.25 mm, and the particle size of the fine return material is less than 1.0 mm. In step S3, the coarse return material is added from the feed end of the rotary drum granulator as a nucleation core, and the fine return material is added from the middle of the rotary drum granulator as a coating layer. The mass ratio of coarse return material to fine return material is 1:3 to 1:

5.

3. The method for producing balanced alkaline high-phosphorus compound fertilizer by roller granulation using the amino acid method according to claim 1, characterized in that: In step S2, phosphoric acid and gaseous ammonia are metered and continuously introduced into a tubular reactor for neutralization reaction; the concentration of phosphoric acid is 70-85 wt%; the molar ratio of ammonia to phosphoric acid is 1.05:1 to 1.25:1; the neutralization reaction is carried out at a reaction temperature of 60-120℃; and the pH value of the generated ammonium phosphate slurry is controlled to be 7 to 9.

4. The method for producing balanced alkaline high-phosphorus compound fertilizer by roller granulation using the amino acid method according to claim 1, characterized in that: In step S2, the outer wall of the tubular reactor is equipped with multi-stage heat exchange coils and adopts a multi-segment temperature control structure, including a first reaction section, a second reaction section, and a third reaction section connected in sequence; the controlled temperature of the first reaction section is 60-80℃, the controlled temperature of the second reaction section is 80-100℃, and the controlled temperature of the third reaction section is 100-120℃; the multi-stage heat exchange coils are correspondingly arranged on the outer wall of each reaction section and are utilized in a tiered manner: the waste heat of the first reaction section is used to preheat the phosphoric acid raw material to 40-50℃, the waste heat of the second reaction section is used to preheat the return material in step S1 to 50-60℃, and the waste heat of the third reaction section is used to preheat the combustion air entering the hot air furnace.

5. The method for producing balanced alkaline high-phosphorus compound fertilizer by roller granulation using the amino acid method according to claim 1, characterized in that: In step S3, the material temperature inside the rotary drum granulator is controlled to be 55-75℃; the rotation speed of the rotary drum granulator is 10-18 rpm, the tilt angle is 1-3°, and the residence time of the material inside the machine is 5-10 min, so that the material can be fully agglomerated into granules.

6. The method for producing balanced alkaline high-phosphorus compound fertilizer by roller granulation using the amino acid method according to claim 1, characterized in that: In step S4, the drying process specifically uses hot air produced by a hot air furnace at 100-140℃ to dry the wet particles in a parallel flow. The inlet temperature of the hot air is controlled at 110-130℃, and the moisture content of the dried material is 1.0-2.5wt%. During the sieving process, fine powder with a particle size of less than 1.0mm and large particles with a particle size of more than 4.25mm are returned to step S1 as return material. The large particles need to be crushed first, and the particles with a particle size between 1.0-4.25mm are qualified particles that enter the cooling process.

7. The method for producing balanced alkaline high-phosphorus compound fertilizer by roller granulation using the amino acid method according to claim 1, characterized in that: In step S5, the cooler uses ambient temperature air for countercurrent cooling to reduce the material temperature to 35-45℃; the flow rate of the cooling air is 1.2-2.0m / s, and the cooling time is 8-15min; after secondary screening, particles with a diameter of 2.0-4.0mm are the final finished particles, and the sieve residue is returned to step S1 as recycled material.

8. The method for producing balanced alkaline high-phosphorus compound fertilizer by roller granulation using the amino acid method according to claim 1, characterized in that: In step S6, the coating treatment is carried out at 40-55°C; a composite coating agent is taken from the coating oil buffer tank and sprayed onto the final finished particles; the composite coating agent is composed of hydrophobic mineral oil and alkaline stabilizer, and its addition amount is 0.5-1.5 wt% of the mass of the finished particles; the mass ratio of hydrophobic mineral oil to alkaline stabilizer in the composite coating agent is 8:1 to 10:1, and the alkaline stabilizer is at least one of hydrogenated castor oil derivative or magnesium stearate.

9. The method for producing balanced alkaline high-phosphorus compound fertilizer by roller granulation using the amino acid method according to claim 1, characterized in that: In step S7, the exhaust gas purification treatment is as follows: the dry exhaust gas and the cooling exhaust gas are first pretreated by a venturi tube, and then purified by a dust collector; the granulation exhaust gas is washed and absorbed, and part of the washing liquid is reused; the dust collected by the purification of the dry exhaust gas is introduced into the washing system and mixed with the ammonia-containing washing liquid. The washing system includes a phosphate buffer tank and a washing circulation tank. The pH value of the washing liquid in the washing circulation tank is maintained at 6.0 to 7.

0. The amount of washing liquid recycled to the raw material batching system accounts for 20-40% of the total washing liquid volume. The nutrient recovery liquid formed by mixing dust and ammonia-containing washing liquid is added to the tubular reactor in step S2 at 2-5% of the phosphate feed flow rate.

10. The method for producing balanced alkaline high-phosphorus compound fertilizer by roller granulation using the amino acid method according to claim 1, characterized in that: In step S9, the key parameters that are monitored and adjusted in real time include the feed ratio of ammonia to phosphoric acid in the tubular reactor, the material temperature in the rotary drum granulator, and the drying hot air temperature. The corresponding operating parameters are adjusted according to the monitoring results to ensure stable operation of the production process.

Images