A system for fertilizer production and method of use thereof

Abstract

This invention belongs to the technical field of fertilizer production equipment, specifically disclosing a system for fertilizer production and its usage method. The system includes a fluidization and spraying subsystem, a feeding subsystem, an external temperature control subsystem, and an intelligent control and online monitoring subsystem. Its core is a fluidized bed with an enlarged section, a cylindrical section, and a conical bottom cylinder. Through multi-zone gas distribution components, layered spraying modules, and zoned temperature control design, the fluidized bed integrates fertilizer granulation and coating processes. Combined with the integrated design of other systems, it achieves integrated continuous production of self-disintegrating functional fertilizers, solving the problems of process fragmentation, low efficiency, and poor product consistency in multi-layered fertilizer production. It ensures the integrity of the gas-producing core of the self-disintegrating fertilizer granules, the uniformity and consistency of the thickness of each functional layer, and the stability of batch-to-batch disintegration performance, achieving a leap from laboratory formulation to large-scale stable production.

Description

Technical Field

[0001] This invention belongs to the field of fertilizer production equipment technology, specifically relating to a fluidized bed coating system for preparing multi-layer structured fertilizers, which is particularly suitable for producing self-disintegrating functional fertilizer granules consisting of a gas-generating core, a fertilizer carrier layer, and a controlled-release coating layer. Background Technology

[0002] Currently, fertilizer production, especially the preparation of functional fertilizers with complex structures, largely relies on fluidized bed coating granulation technology. This technology, by placing powder or granular materials in a fluidized state and spraying atomized binders or coating liquids, can achieve particle agglomeration and surface modification. Existing fluidized bed equipment, when dealing with complex processes, largely depends on the combination of discrete units and human experience intervention, lacking deep integration at the system level. Its core shortcomings are: the equipment has a single function, making it difficult to flexibly adapt to vastly different granulation and coating process parameters within the same chamber; and the separation between processes leads to discontinuous production flow and low efficiency. This discrete, passive, and experience-based production mode, reliant on manual labor, has become a major bottleneck restricting the large-scale and stable manufacturing of high-performance multilayer composite granule products. Summary of the Invention

[0003] To address the aforementioned issues, the present invention aims to provide an integrated fluidized bed coating system capable of precision manufacturing of complex multilayer fertilizer granules, which is of vital importance for promoting the next generation of smart fertilizers from the laboratory to field applications.

[0004] This invention focuses on the industrial production of multilayer granular fertilizers. Its core challenge lies in the efficient and precise sequential construction of a chemical dynamics unit, nutrient carrier unit, and intelligent control unit through an integrated system. Existing technologies often employ segmented production in separate equipment followed by assembly, or involve coarse process layering within a single fluidized bed. This not only results in lengthy and energy-intensive production processes but, more importantly, fails to guarantee the integrity, uniformity, and functional coupling of the interfaces between layers. For example, the brittleness of the core requires mild fluidization and spraying conditions, while the construction of the fertilizer carrier layer requires strong binder penetration and particle growth kinetics. Subsequent controlled-release coating demands extremely low humidity and a specific solvent evaporation environment. Traditional single-mode fluidized beds cannot dynamically adapt to such a wide and contradictory process windows within a single production cycle. The lack of a dedicated production system for multilayer heterogeneous granular structures leads to large dispersion in product disintegration time, uneven nutrient distribution, and unstable slow-release performance, thus failing to reliably achieve the agronomically expected "delayed-burst-slow-release" effect. This invention, through fluidized bed structure optimization, system integration design, and optimization of supporting process parameters, ensures the integrity of the gas-producing core of self-disintegrating fertilizer granules, the uniformity and consistency of the thickness of each functional layer, and the stability of batch-to-batch disintegration performance, thus achieving a leap from laboratory formulation to large-scale stable production.

[0005] To achieve the above objectives, the specific technical solution adopted by the present invention is as follows:

[0006] In a first aspect, the present invention provides a fluidized bed for preparing multi-layered fertilizers. Wherein:

[0007] The fertilizer is a self-disintegrating multi-layered fertilizer, comprising, from the inside out, a gas-generating core, a fertilizer carrier layer, and a controlled-release coating layer. The gas-generating core generates gas upon contact with water, providing the disintegration impetus. Specifically, it can be formed by mixing and pressing citric acid and sodium bicarbonate (the citric acid-sodium bicarbonate combination generates carbon dioxide upon contact with water). The fertilizer carrier layer provides fertilizer nutrients and can be formed by granulating a fertilizer slurry containing organic fertilizer powder, chemical fertilizer powder (such as urea and potassium dihydrogen phosphate), and biochar powder using a binder. The organic fertilizer can be selected from one or more of the following: well-rotted livestock and poultry manure, well-rotted straw, kitchen waste fertilizer products, humic acid, distiller's grains, mushroom residue, etc., and appropriate products can be purchased according to nutrient requirements. The controlled-release coating layer controls the water penetration rate and delays the disintegration initiation time. Specifically, it can be a hydrophobic polymer (such as polylactic acid PLA, ethyl cellulose), chitosan (whose acetylation needs to be adjusted to control solubility), sodium alginate (stability can be regulated by cross-linking with calcium ions), or zein membrane, etc.

[0008] The fluidized bed includes:

[0009] The shell, from top to bottom, includes an enlarged section, a cylindrical section, and a conical bottom cylinder;

[0010] The inlet and outlet include a gas phase outlet located at the top of the enlarged section, a feed inlet located on the outer wall of the cylindrical section for inputting the gas-generating core micro-core, and a discharge outlet and a gas phase inlet located at the bottom of the conical bottom cylinder.

[0011] A spraying module is installed inside the cylinder section and below the feed inlet. The module includes at least two sets of nozzles, one upper and one lower. Each set of nozzles has multiple nozzles arranged circumferentially. The lower set of nozzles is used to spray fertilizer slurry and adhesive, and the upper set of nozzles is used to spray coating liquid.

[0012] A multi-zone gas distribution component is disposed inside the conical bottom cylinder and above the gas phase inlet. It is used to obtain a uniform and stable fluidization state for the particulate material above (including the gas-generating core and composite particles) through differentiated air supply, thereby enabling gentle suspension.

[0013] The temperature control component includes a jacket wrapped around the outer wall of the cylindrical section and an infrared heating component located in the enlarged section; heating gas is introduced through the gas phase inlet and heat transfer oil is introduced into the jacket. The infrared heating component is turned on to form a bottom air inlet preheating zone, a cylindrical fluidized reaction zone and a top coating drying zone in the fluidized bed.

[0014] Preferably, the spray module includes three sets of nozzles from bottom to top for spraying fertilizer slurry and adhesive, switching between spraying different functional slurries, and spraying coating liquid. The upper nozzle uses two precision fan-shaped nozzles, the middle nozzle uses two air atomizing nozzles, and the bottom nozzle uses four wide-angle solid cone nozzles.

[0015] Preferably, the multi-zone gas distribution component includes, from bottom to top, an air supply chamber, a second orifice plate, a guide cavity, and a first orifice plate. The air supply chamber has an annular partition to divide it into a central zone and an annular gap zone. The central zone and the annular gap zone are respectively connected to air inlet pipes. Differential air supply is achieved by controlling the air inlet flow of the two air inlet pipes (the air inlet flow of the annular gap zone is greater than that of the central zone, so as to form an internal circulation flow pattern that is conducive to material circulation). The aperture of the first orifice plate is smaller than that of the second orifice plate. The first orifice plate, as a pore uniform distribution layer, has densely arranged pores with a small aperture (e.g., 50-100μm). The second orifice plate, as an air supply orifice plate, has a larger aperture (e.g., 2-15mm). After passing through the air supply chamber, the airflow passes through the second orifice plate, the guide cavity, and the first orifice plate in sequence. The outlet air velocity and pressure are uniformly distributed on the bed cross-section, which enables the material to be stably and gently suspended. The difference in the total air volume between the two zones is converted into the macroscopic material circulation power inside the bed.

[0016] Preferably, a one-way gas valve is provided at the gas inlet; a temperature probe is installed on the top inner wall of the conical bottom cylinder; the infrared heating component can be an infrared heating plate, a combination of an infrared heating plate and a hot air ring, or other equipment with infrared heating function.

[0017] Preferably, a manhole is provided on the outer wall of the conical bottom cylinder for personnel to enter for construction, inspection or maintenance.

[0018] In a second aspect, the present invention provides a system for fertilizer production, comprising:

[0019] The fluidization and spraying subsystem includes the aforementioned fluidized bed and an exhaust gas treatment unit for treating the gas phase outlet exhaust gas of the fluidized bed;

[0020] The feeding subsystem includes a core feeding unit, a slurry feeding unit, and a coating liquid feeding unit that provide raw materials for each layer of fertilizer to the fluidized bed;

[0021] An external temperature control subsystem is used to adjust the inlet temperature of the fluidized bed gas phase inlet.

[0022] Preferably, the exhaust gas treatment unit includes a cyclone separator and a bag filter connected in sequence, and the inlet of the cyclone separator is connected to the gas phase outlet of the fluidized bed.

[0023] Preferably, the core feeding unit includes a vacuum feeder, a loss-in-weight feeder, and a screw feeder connected in sequence, with the outlet of the screw feeder connected to the inlet of the fluidized bed; the slurry feeding unit includes multiple independent mixing tanks for preparing fertilizer slurry, adhesive solution, or spare cleaning solvent, and a diaphragm pump connecting the mixing tanks to the fluidized bed nozzles; the coating liquid feeding unit includes a storage tank and a peristaltic pump connecting the storage tank to the fluidized bed nozzles.

[0024] Preferably, the external temperature control subsystem includes a blower, an air heater, and an air compressor connected in sequence, with the outlet of the air compressor connected to the gas phase inlet of the fluidized bed.

[0025] Preferably, the system further includes an intelligent control and online monitoring subsystem, which includes a machine vision unit, an online weighing feedback unit, and a central controller. The machine vision unit is a high-resolution industrial camera and a high-speed image processing system installed at the observation window. The online weighing feedback unit is a high-precision weighing sensor installed under the fluidized bed for real-time monitoring of bed weight changes. The observation window can be installed in different locations according to actual needs, generally at the bottom of the cylinder section, for observing whether the particle fluidization state is uniform.

[0026] Thirdly, the present invention provides a method for producing multi-layered fertilizer using the above-described system, comprising the following steps:

[0027] S1. Initialization: Start the system and raise the temperature of each zone in the fluidized bed to the set temperature through the internal temperature control components and the external temperature control subsystem;

[0028] S2. Core fluidization and fertilizer carrier layer granulation: Gas-producing core micro-cores are fed into the fluidized bed feed inlet through the core feeding unit. After the fluidization is stable, the bottom nozzle is started and the binder and fertilizer slurry delivered to the bottom nozzle by the slurry feeding unit are alternately sprayed according to the preset program for granulation.

[0029] S3. Controlled-release coating step: Switch to the upper nozzle and spray the coating liquid delivered to the top nozzle by the coating liquid supply unit onto the particle surface;

[0030] S4. Drying and Discharging Steps: After coating is completed, maintain fluidization and heat up to dry. Finally, send the finished granules to the cooling and screening section through the bottom discharge port.

[0031] Preferably, in step S1, the fluidizing air volume is set to a fluidizing air velocity of 0.3-0.5 m / s, and the temperatures of each temperature zone are set as follows: bottom air inlet preheating zone 45°C, cylinder fluidizing reaction zone 45±2°C, top coating drying zone 35±2°C; and / or, in step S2, the diameter of the gas-generating core micro-core is 1.0-1.5 mm, the feeding rate of the gas-generating core micro-core is 0.5-5.0 kg / h; the atomization pressure (the pressure of compressed air acting inside the nozzle to break the liquid slurry or coating liquid into tiny droplets, used for gas-liquid mixing at the nozzle) is 0.2-0.4 MPa, and the droplet size Dv50 is controlled at 80-120 mm. μm; the spraying rate of the adhesive and fertilizer slurry is 1.5L / h until the particle size grows to 3-5mm, during which the growth rate is monitored in real time by an online weighing feedback unit and a machine vision unit; and / or, in step S3, the upper nozzle sprays the coating liquid onto the particle surface at a constant rate of 0.8L / h.

[0032] Preferably, during fertilizer production, the exhaust gas from the fluidized bed gas phase outlet is treated by a tail gas treatment unit for dust removal and solvent vapor condensation.

[0033] The integrated fluidized bed coating system provided by this invention, through the synergistic design of multiple feeding units and switchable spraying, achieves continuous production of self-disintegrating multilayer fertilizer granules from core support and fertilizer carrier layer construction to controlled-release coating, significantly improving equipment utilization and production efficiency. Compared with the prior art, this invention has the following beneficial effects:

[0034] 1. It can achieve efficient and continuous processing of three materials with very different physical properties—low-density gas-producing core, fertilizer slurry, and polymer coating liquid—within the same fluidized bed, reducing the multi-stage process conversion time to less than 30 minutes.

[0035] 2. The system's optimized fluidization field and targeted spraying mode ensure that the integrity of the brittle gas-producing core is no less than 98% during the process, avoiding insufficient internal air pressure caused by breakage, thus laying the foundation for product functionality. Combined with online weighing and machine vision dual-feedback closed-loop control, it achieves precise control of the thickness of each functional layer (fertilizer carrier layer ±10%, controlled-release coating layer ±5%), which significantly improves the stability of batch product disintegration time (fluctuation ≤ ±15%), meeting the agronomic requirements for precise release.

[0036] 3. An integrated online quality monitoring and feedback control system enables 100% real-time monitoring of key intermediate product quality parameters, ensuring that the performance qualification rate of the final product is increased to over 95%.

[0037] 4. The system of this invention has excellent process flexibility and can quickly adapt to different raw material formulas (complete the switching of different formula products within 2 hours), providing core equipment support for the large-scale and stable production of high-performance intelligent fertilizers. Attached Figure Description

[0038] Figure 1 : Schematic diagram of the fluidized bed structure of the present invention. In the figure, 211-shell, 212-multi-zone gas distribution component, 213-spray module, 214-jacket, 215-temperature probe, 216-gas phase outlet, 217-feed inlet, 218-discharge outlet, 219-gas phase inlet, 220-gas one-way valve, 221-manhole, 222-spray matrix; 2111-expansion section, 2112-cylinder section, 2113-conical bottom cylinder.

[0039] Figure 2 : Schematic diagram of a multi-region gas distribution component. In the figure, 2121-first orifice plate, 2122-guide cavity, 2123-second orifice plate, 2124-gas supply chamber, 2125-inlet pipe; 2124a-central region, 2124b-annular region.

[0040] Figure 3 This is an overview diagram of the fertilizer production system of the present invention. In the diagram, 1-feeding subsystem, 2-fluidization and spraying subsystem, 3-external temperature control subsystem, 4-intelligent control and online monitoring subsystem; 11-vacuum feeder, 12-loss-in-weight feeder, 13-screw feeder, 14-batching tank, 15-diaphragm pump, 16-storage tank, 17-peristaltic pump; 21-fluidized bed, 22-cyclone separator, 23-bag filter; 31-blower, 32-air heater, 33-air compressor; 41-central controller.

[0041] Figure 4 This invention Figure 3 The diagram shows the component connections of the fertilizer production system. In the diagram, a, b, c, d: solid material feeding direction; e, f / e', f': liquid material feeding direction; g, h: air outlet direction; i, j, k, l: air inlet direction; m: intelligent control direction.

[0042] Figure 5 This is a side cross-sectional three-dimensional structural diagram of the self-disintegrating slow-release organic compound fertilizer granules of the present invention. In the figure: A - controlled-release coating layer, B - fertilizer carrier layer, C - gas-producing core. Detailed Implementation

[0043] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0044] Example 1: Fluidized bed for preparing multi-layered fertilizer

[0045] This embodiment provides a fluidized bed 21 for preparing multi-layered fertilizers. The multi-layered fertilizer is as follows: Figure 5As shown, this is a self-disintegrating functional fertilizer granule composed of a gas-generating core C, a fertilizer carrier layer B, and a controlled-release coating layer A. The gas-generating core C generates gas upon contact with water, providing the disintegration impetus. The fertilizer carrier layer B provides fertilizer nutrients, and the controlled-release coating layer A controls the water permeation rate and delays the disintegration initiation time. The fluidized bed 21 structure is as follows... Figure 1 As shown, it includes a housing 211, an inlet and outlet, a multi-zone gas distribution component 212, a spray module 213, and a temperature control component.

[0046] The housing 211 includes, from top to bottom, an enlarged section 2111, a cylindrical section 2112, and a conical bottom cylinder 2113.

[0047] The inlet and outlet include a gas phase outlet 216 located at the top of the enlarged section 2111, a feed inlet 217 located on the outer wall of the cylindrical section 2112 for inputting the gas-generating core microchip, and a discharge outlet 218 and a gas phase inlet 219 located at the bottom of the conical bottom cylinder 2113; a one-way gas valve 220 is provided at the gas phase inlet 219. A manhole 221 is provided on the outer wall of the conical bottom cylinder 2113.

[0048] The multi-region gas distribution component 212 is disposed inside the conical bottom cylinder 2113 and above the gas phase inlet 219. From bottom to top, it includes a gas supply chamber 2124, a second orifice plate 2123, a flow guide chamber 2122, and a first orifice plate 2121. The gas supply chamber 2124 has an annular partition to divide it into a central region 2124a and an annular gap region 2124b. The central region 2124a and the annular gap region 2124b are respectively connected to an air inlet pipe 2125. By controlling the air inlet flow of the two air inlet pipes 2125 (for example, by configuring independent precision flow regulating valves on the two air inlet pipes or by using two independent variable frequency fans), differentiated air supply between the central region and the annular gap region can be achieved. The first orifice plate 2121 serves as a flow equalization layer with a pore diameter of 50-100μm, and the second orifice plate 2123 serves as a gas supply orifice plate with a pore diameter of 2-15mm. In actual operation, the air intake volume in the annular gap zone 2124b typically accounts for 60%-70% of the total air volume, while that in the central zone 2124a accounts for 30%-40%, forming an internal circulation flow pattern conducive to material circulation. After the airflow passes through the second perforated plate 2123, the middle guide cavity 2122 (mixing and buffering to eliminate turbulence), and the first perforated plate 2121 in sequence, the outlet air velocity and pressure achieve a uniform distribution across the bed cross-section. The difference in the total air volume between the two zones is then converted into the macroscopic material circulation power within the bed. In multi-layer structure fertilizer production, the fluidizing air volume is set to a fluidizing velocity of 0.3-0.5 m / s (referring to the apparent air velocity of the gas entering the fluidized bed after passing through the first perforated plate 2121, i.e., the total intake airflow divided by the bed cross-sectional area). The external central controller independently adjusts the valve opening or fan speed of the two intake pipes 2125 through a PID algorithm, thereby achieving precise and dynamic differential control of the air intake volume in the annular gap zone and the central zone. The design of the multi-zone gas distribution component 212 ensures that both the low-density core and the subsequently formed composite particles can obtain a uniform and stable fluidization state, with a fluidization non-uniformity index of less than 1.05.

[0049] The spray module 213 includes three sets of nozzles: an upper, middle, and lower set. The lower set uses four wide-angle solid cone nozzles for spraying fertilizer slurry and adhesive (the fertilizer carrier layer is granulated by alternating spraying of fertilizer slurry and adhesive). The middle set uses two air atomizing nozzles for switching between spraying different functional slurries (whether to activate depends on actual needs). The upper set uses two precision fan-shaped nozzles for spraying coating liquid. The three sets of nozzles form a spray matrix 222.

[0050] The temperature control component includes a jacket 214 wound around the outer wall of the cylindrical section 2112, and an infrared heating component located in the enlarged section 2111. The infrared heating component includes an infrared heating plate and a hot air ring (a conventional component, not shown in the figure); a temperature sensor 215 is installed on the top inner wall of the conical bottom cylinder 2113. The fluidized bed is divided into three independent temperature control zones according to the different temperature requirements of each process stage:

[0051] Bottom air intake preheating zone (conical bottom cylinder 2113): formed by inputting heated gas through gas phase inlet 219, providing precisely temperature-controlled fluidizing air for the fluidized bed;

[0052] Fluidized reaction zone of the cylinder (including cylinder section 2112): heat transfer oil is circulated and kept warm by the jacket 214, with a temperature control accuracy of ±2°C.

[0053] Top coating drying zone (expanded section 2111): Through the action of infrared heating plates and auxiliary hot air rings, the coating solvent is ensured to evaporate quickly and evenly, avoiding particle adhesion.

[0054] This embodiment integrates fluidized bed granulation and coating functions, enabling the integrated production of multi-layered fertilizers. The specific process and mechanism are as follows:

[0055] The gas-generating core micro-core is fed into the feed inlet 217 and gently suspended by differentiated air supply through the multi-zone gas distribution component 212 (wind speed 0.3-0.5 m / s, core integrity rate ≥98%). Then, the bottom nozzle is opened to alternately spray the adhesive and fertilizer slurry in a top spray manner, and "onion-style" granulation is carried out at 45±2℃ to the target particle size. After granulation is completed, the upper nozzle is activated to spray the coating liquid (containing pore-forming agent) onto the particle surface in a bottom spray manner until the coating layer thickness reaches the standard (deviation ≤±5%). Finally, the infrared heating plate and hot air ring are turned on to perform radiation-convection composite drying, and the particle moisture content is reduced to ≤2.0% before being discharged through the bottom outlet 218.

[0056] Example 2: System for fertilizer production

[0057] This embodiment provides a fertilizer production system based on the fluidized bed of Embodiment 1. The system structure is as follows: Figure 3-4 As shown, it includes a feeding subsystem 1, a fluidization and spraying subsystem 2, an external temperature control subsystem 3, and an intelligent control and online monitoring subsystem 4. The specific structure of each system is as follows:

[0058] I. Material Feeding Subsystem

[0059] The feeding subsystem 1 includes a core feeding unit, a slurry feeding unit, and a coating liquid feeding unit that provide raw materials for each layer of fertilizer to the fluidized bed.

[0060] The core feeding unit includes a low-shear vacuum feeder 11, a loss-in-weight feeder 12, and a screw feeder 13 connected in sequence. The outlet of the screw feeder 13 is connected to the feed inlet 217 of the fluidized bed. The core feeding unit continuously and stably feeds the gas-generating core micro-core (diameter 1.0-1.5 mm) to the top of the multi-zone gas distribution component 212 of the fluidized bed 21 at a rate of 0.5-5.0 kg / h.

[0061] The slurry feeding unit includes multiple independent mixing tanks 14 for preparing fertilizer slurry, adhesive solution, and spare cleaning solvent, and diaphragm pumps 15 connecting the mixing tanks 14 to the fluidized bed nozzles (each mixing tank is independently equipped with a diaphragm pump, and the two form a conveying line, with multiple conveying lines connected in parallel); the mixing tanks 14 are made of stainless steel and are used to prepare fertilizer carrier layer adhesive solution (such as PVA), fertilizer carrier layer slurry (containing organic fertilizer, chemical fertilizer, biochar powder), and spare cleaning solvent, etc.; each tank is equipped with a high-speed dispersion and constant temperature stirring (30±2°C) device, and is connected to a dual-fluid atomizing nozzle through the diaphragm pump 15, with a slurry delivery accuracy of ±1.5%.

[0062] The coating solution supply unit adopts a constant pressure supply system with solvent recovery function to transport polymer coating solution (such as PLA-dichloromethane solution). Specifically, it includes a storage tank 16 (a low temperature storage tank with temperature controlled at 5-10°C) and a peristaltic pump 17 connecting the storage tank 16 and the fluidized bed nozzle to ensure the stability of the coating solution viscosity and solid content.

[0063] II. Fluidization and Spray Subsystem

[0064] The fluidization and spraying subsystem 2 includes the fluidized bed 21 of Example 1 and an exhaust gas treatment unit for treating the exhaust gas from the gas phase outlet 216 of the fluidized bed 21.

[0065] The exhaust gas treatment unit includes a cyclone separator 22 and a bag filter 23 connected in sequence. The inlet of the cyclone separator 22 is connected to the gas phase outlet 216 of the fluidized bed. The cyclone separator 22 and the bag filter 23 are used to recover fine powder and realize the condensation and recovery of solvent vapor, with a recovery efficiency of ≥90%.

[0066] III. External Temperature Control Subsystem

[0067] The external temperature control subsystem 3 is used to adjust the inlet temperature of the fluidized bed gas phase inlet 219, and includes a blower 31, an air heater 32, and an air compressor 33 connected in sequence. The outlet of the air compressor 33 is connected to the fluidized bed gas phase inlet 219.

[0068] IV. Intelligent Control and Online Monitoring Subsystem

[0069] The intelligent control and online monitoring subsystem 4 includes a machine vision unit, an online weighing feedback unit, and a central controller 41.

[0070] The machine vision unit consists of a high-resolution industrial camera and a high-speed image processing system installed in the observation window to monitor the fluidization state, particle aggregation, and surface morphology in real time.

[0071] The online weighing feedback unit is a high-precision weighing sensor installed under the fluidized bed, used to monitor the changes in bed weight in real time and back-calculate the material deposition and coating weight gain rate with an accuracy of ±10 grams.

[0072] The central controller 41 integrates a PLC and an industrial computer, receiving signals from multiple sensors such as vision, weighing, temperature, and pressure sensors. Through a built-in expert system and PID algorithm, it dynamically adjusts the air intake, spray rate and atomization parameters of each nozzle, and temperature of each zone to achieve fully automated, closed-loop control production from "core feeding → fertilizer carrier layer granulation → controlled-release coating → drying and cooling".

[0073] The method for producing multi-layered fertilizer using the system of this embodiment is as follows:

[0074] S1. Initialization: Start the system and raise the temperature of each zone in the fluidized bed 21 (air inlet preheating zone, cylinder fluidization reaction zone and top coating drying zone) to the set temperature through the internal temperature control components and the external temperature control subsystem 3, and control the fluidization air velocity;

[0075] S2. Core Fluidization and Fertilizer Carrier Layer Granulation: Gas-producing core micro-cores are fed into the fluidized bed feed inlet 217 via the core feeding unit. After the fluidization stabilizes, the bottom nozzles are activated, and the binder and fertilizer slurry delivered to the bottom nozzles by the slurry feeding unit are alternately sprayed according to a preset program for granulation. The feeding rate of the gas-producing core micro-cores and the spraying rate of the binder and fertilizer slurry are controlled. The online weighing and machine vision dual feedback system monitors the particle growth to the target particle size in real time.

[0076] S3. Controlled-release coating step: After granulation, the system automatically switches process parameters, starts the upper nozzle, and sprays the coating liquid, which is supplied by the coating liquid supply unit to the top nozzle, onto the particle surface; controls the spraying rate of the coating liquid; and ensures that the coating layer thickness deviation is ≤±5% through precise weight gain control.

[0077] S4. Drying and Discharging Steps: After coating is completed, turn on the infrared heating element to maintain fluidization and heat up the drying process, reducing the moisture content of the particles to ≤2.0%. Finally, send the finished particles to the cooling and screening section through the bottom discharge port 218.

[0078] The entire process is automatically controlled in a closed loop by the central controller 41 based on the preset formula and real-time sensor data, realizing continuous and intelligent production from core material feeding to finished product output.

[0079] Example 3: System Integration Performance and Core Indicator Testing

[0080] This embodiment utilizes the system of Example 2 to produce self-disintegrating functional fertilizer granules consisting of a gas-generating core, a fertilizer carrier layer, and a controlled-release coating layer. The gas-generating core is made by pressing a mixture of citric acid and sodium bicarbonate in a 1:1.1 molar ratio into micro-cores (1.2 mm in diameter). The fertilizer carrier layer has a formulation of organic fertilizer: urea: biochar = 50:35:15 (w / w) and is formed by alternating atomization spraying of a fertilizer slurry containing organic fertilizer, urea, and biochar with an adhesive (8% polyvinyl alcohol solution). The coating solution is an 8% polylactic acid-dichloromethane solution, which contains polylactic acid (PLA), dichloromethane solvent, and polyethylene glycol 400 pore-forming agent. The mass fraction of polylactic acid in dichloromethane is 8%, and the polyethylene glycol 400 accounts for 10% of the mass of polylactic acid.

[0081] The gas-generating core micro-core, fertilizer slurry, binder, and coating solution were fed into the system equipment to produce fertilizer according to the method in Example 2. The system parameters were set as follows: the inlet air temperature was preheated to 45°C, the temperature of the fluidized reaction zone in the cylinder was maintained at 45±2°C, and the temperature of the top coating and drying zone was maintained at 35±2°C. The core feeding rate was 2.0 kg / h, the fertilizer slurry and binder spraying rate was 1.5 L / h, and the coating solution spraying rate was 0.8 L / h. The fluidization air velocity was 0.4 m / s, and a bottom-spray-top-spray combination mode was adopted.

[0082] After 8 hours of continuous operation, samples were taken for analysis. The integrity rate of the gas-producing core was 98.7%, the average thickness of the fertilizer carrier layer was 1.05 mm (standard deviation ±0.09 mm, deviation ±8.6%), and the average thickness of the controlled-release coating layer was 78 μm (standard deviation ±3.5 μm, deviation ±4.5%). 100 randomly selected finished granules were subjected to a disintegration test. The average disintegration time was 11.2 hours, with a standard deviation of ±1.3 hours (dispersion ±11.6%). The overall system performance qualification rate (based on disintegration time conforming to the design range of 10-12 hours) was 96.2%.

[0083] Example 4: Comparative Experiment with Traditional Intermittent Production Methods

[0084] Experimental group: Production was carried out using the continuous fluidized bed system described in this invention (configuration of Example 2).

[0085] Control group: The traditional batch production method with separate equipment was adopted. The process was as follows: granulation of fertilizer carrier layer using ordinary fluidized bed → discharge and transfer to oven for drying → cooling and then feeding into another coating pan for polymer coating → drying again.

[0086] Two groups of 500 kg each of self-disintegrating fertilizer granules with a target disintegration time of 12 hours were produced using the same raw material formula. The effects were compared, and the results are as follows:

[0087] Production efficiency: The experimental group ran continuously from feeding to producing finished products, with a total time consumption of 6.5 hours; due to multiple transfers, drying, and cooling in the control group, the total time consumption was 15 hours, and the efficiency of the experimental group increased by approximately 130%.

[0088] Product performance consistency: The disintegration time of the final products of both groups was tested. The standard deviation of the disintegration time of the experimental group was ±1.4 hours, and that of the control group was ±3.8 hours. The product performance consistency of the experimental group was significantly better than that of the control group.

[0089] Overall qualification rate and energy consumption: Taking the disintegration time within the range of 10 - 14 hours as qualified, the qualification rate of the experimental group was 95.5%, and that of the control group was 82.1%. Calculated per unit output, the overall energy consumption (electricity and heat) of the experimental group was reduced by approximately 35% compared with the control group.

[0090] Core protection and raw material utilization rate: The integrity rate of the gas-producing core of the experimental group was 98.7%, and the crushing loss was extremely small; during the transfer and secondary fluidization processes of the control group, the core crushing rate was relatively high, and the integrity rate was only 89.3%, resulting in the inability of some products to disintegrate normally due to insufficient gas-producing power.

[0091] In summary, the present invention provides an advanced fluidized bed coating system integrating integrated continuous production, modular functions, and intelligent perception control, realizing precise automatic control of the entire process from raw materials to finished products, breaking through the existing technical barriers, and promoting industrial upgrading.

[0092] This specific implementation manner is only an interpretation of the present invention and not a limitation thereof. Any changes made by those skilled in the art after reading the specification of the present invention will be protected by the patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A fluidized bed for preparing a multi-layer structured fertilizer, characterized in that, The fertilizer comprises, from the inside out, a gas-producing core, a fertilizer carrier layer, and a controlled-release coating layer; the fluidized bed (21) comprises: The shell (211) includes, from top to bottom, an enlarged section (2111), a cylindrical section (2112), and a conical bottom cylinder (2113). The inlet and outlet include a gas phase outlet (216) located at the top of the enlarged section (2111), a feed inlet (217) located on the outer wall of the cylindrical section (2112) for inputting the gas-generating core micro-core, and a discharge outlet (218) and a gas phase inlet (219) located at the bottom of the conical bottom cylinder (2113). The spray module (213) is located inside the cylinder section (2112) and below the feed inlet (217). The module includes at least two sets of nozzles, one upper and one lower. Each set of nozzles has multiple nozzles arranged circumferentially. The lower set of nozzles is used to spray fertilizer slurry and adhesive, and the upper set of nozzles is used to spray coating liquid. A multi-zone gas distribution component (212) is disposed inside the conical bottom cylinder (2113) and above the gas phase inlet (219) to obtain a uniform and stable fluidization state for the upper particulate material through differentiated air supply. The multi-zone gas distribution component (212) includes, from bottom to top, an air supply chamber (2124), a second orifice plate (2123), a guide cavity (2122), and a first orifice plate (2121). The air supply chamber (2124) has an annular partition to divide it into a central area (2124a) and an annular gap area (2124b). The central area (2124a) and the annular gap area (2124b) are respectively connected to an air inlet pipe (2125). Differentiated air supply is achieved by controlling the air inlet flow rate of the two air inlet pipes (2125). The aperture of the first orifice plate (2121) is smaller than that of the second orifice plate (2123). The temperature control component includes a jacket (214) wrapped around the outer wall of the cylindrical section (2112) and an infrared heating component located in the enlarged section (2111). Heating gas is introduced through the gas phase inlet (219), heat transfer oil is introduced into the jacket (214), and the infrared heating component is turned on to form a bottom air inlet preheating zone, a cylindrical fluidized reaction zone, and a top coating drying zone in the fluidized bed.

2. The fluidized bed according to claim 1, characterized in that, The spray module (213) includes three sets of nozzles from bottom to top for spraying fertilizer slurry and adhesive, switching between spraying different functional slurries, and spraying coating liquid. The upper nozzle uses two precision fan-shaped nozzles, the middle nozzle uses two air atomizing nozzles, and the bottom nozzle uses four wide-angle solid cone nozzles.

3. The fluidized bed according to claim 1, characterized in that, A one-way gas valve (220) is provided at the gas inlet (219); a temperature sensor (215) is installed on the top inner wall of the conical bottom cylinder (2113).

4. A system for fertilizer production, characterized in that, include: The fluidization and spraying subsystem (2) includes the fluidized bed as described in any one of claims 1-3 and an exhaust gas treatment unit for treating the exhaust gas from the gas phase outlet (216) of the fluidized bed; The feeding subsystem (1) includes a core feeding unit, a slurry feeding unit, and a coating liquid feeding unit that provide raw materials for each layer of fertilizer to the fluidized bed; An external temperature control subsystem (3) is used to adjust the inlet temperature of the fluidized bed gas inlet (219).

5. The system for fertilizer production according to claim 4, characterized in that, The exhaust gas treatment unit includes a cyclone separator (22) and a bag filter (23) connected in sequence. The inlet of the cyclone separator (22) is connected to the gas phase outlet (216) of the fluidized bed.

6. The system for fertilizer production according to claim 4, characterized in that, The core feeding unit includes a vacuum feeder (11), a loss-in-weight feeder (12), and a screw feeder (13) connected in sequence. The outlet of the screw feeder (13) is connected to the feed inlet (217) of the fluidized bed. The slurry feeding unit includes multiple independent mixing tanks (14) for preparing fertilizer slurry, adhesive solution or spare cleaning solvent, and a diaphragm pump (15) connecting the mixing tanks (14) to the fluidized bed nozzle. The coating liquid feeding unit includes a storage tank (16) and a peristaltic pump (17) connecting the storage tank (16) and the fluidized bed nozzle.

7. The system for fertilizer production according to claim 4, characterized in that, The external temperature control subsystem (3) includes a blower (31), an air heater (32), and an air compressor (33) connected in sequence. The outlet of the air compressor (33) is connected to the gas phase inlet (219) of the fluidized bed.

8. The system for fertilizer production according to claim 4, characterized in that, The system also includes an intelligent control and online monitoring subsystem (4), which includes a machine vision unit, an online weighing feedback unit and a central controller (41); the machine vision unit is a high-resolution industrial camera and a high-speed image processing system installed at the observation window, and the online weighing feedback unit is a high-precision weighing sensor installed under the fluidized bed for real-time monitoring of bed weight changes.

9. A method for producing fertilizer using the system according to any one of claims 4-8, characterized in that, Includes the following steps: S1. Initialization: Start the system and raise the temperature of each zone in the fluidized bed to the set temperature through the internal temperature control components and the external temperature control subsystem (3); S2. Core fluidization and fertilizer carrier layer granulation: Gas-producing core micro-cores are fed into the fluidized bed feed inlet (217) through the core feeding unit. After the fluidization is stable, the bottom nozzle is started and the adhesive and fertilizer slurry delivered to the bottom nozzle by the slurry feeding unit are alternately sprayed according to the preset program for granulation. S3. Controlled-release coating step: Switch to the upper nozzle and spray the coating liquid delivered to the top nozzle by the coating liquid supply unit onto the particle surface; S4. Drying and Discharging Steps: After coating is completed, fluidization is maintained and the temperature is increased for drying. Finally, the finished particles are sent to the cooling and screening section through the bottom discharge port (218).

10. The method according to claim 9, characterized in that, In step S1, the fluidizing air volume is set so that the fluidizing air velocity is 0.3-0.5 m / s, and the temperatures of each temperature zone are set as follows: bottom air inlet preheating zone 45°C, cylinder fluidizing reaction zone 45±2°C, top coating drying zone 35±2°C; And / or, in step S2, the diameter of the gas-generating core micro-core is 1.0-1.5 mm, the feeding rate of the gas-generating core micro-core is 0.5-5.0 kg / h; the atomization pressure is 0.2-0.4 MPa, and the droplet size Dv50 is controlled at 80-120 μm; the spraying rate of the adhesive and fertilizer slurry is 1.5 L / h, until the particle size grows to 3-5 mm; And / or, in step S3, the upper nozzle sprays the coating liquid onto the particle surface at a constant rate of 0.8 L / h.

11. The method according to claim 9, characterized in that, During the fertilizer production process, the exhaust gas from the fluidized bed gas phase outlet (216) is treated by dust removal and solvent vapor condensation in the tail gas treatment unit.

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