Semi-continuous granular fertilizer polyurethane coating production device and production method thereof

Abstract

This invention provides a semi-continuous polyurethane coating production device and method for granular fertilizers, belonging to the field of granular fertilizer coating technology. Through the core configuration of "two polishing machines and one coating machine," that is, two polishing machines connected in parallel corresponding to one coating machine, the coating machine can work continuously in outdoor conditions with a low temperature of -28℃ in Northeast China without the need for any additional insulation equipment. Compared with the traditional "one polishing machine and one coating machine" process, the insulation energy consumption is reduced by 100%, and the heat utilization efficiency is increased by more than 50%. It is suitable for the transformation of intermittent granular fertilizer coating production processes that are suitable for low-temperature conditions, low energy consumption, and easy installation. It is applicable to the coating processing of various granular fertilizers, especially suitable for industrial production in low-temperature areas of northern China.

Description

Technical Field

[0001] This invention relates to the field of granular fertilizer coating technology, specifically to a semi-continuous granular fertilizer polyurethane coating production apparatus and its production method. Background Technology

[0002] Coated controlled-release fertilizer, as a new type of fertilizer, meets the agricultural need for simplified cultivation and is more suitable for the current state of green agricultural development in my country. Coated controlled-release fertilizer overcomes the natural mismatch between the timing of nutrient supply from fast-acting fertilizers and nutrient absorption by crops, achieving synchronization between nutrient release and crop absorption throughout the entire growth cycle. Furthermore, it avoids fertilizer ineffectiveness in the soil and the damage to seedlings or roots caused by high salt concentrations, and allows for one-time basal application for each crop season, saving labor costs. Advanced membrane technology is leading a new round of controlled-release fertilizer development in my country. Due to the requirements of green agricultural development, biodegradable membrane materials are undoubtedly the future trend of the industry, driving the development of controlled-release fertilizer membrane materials towards biodegradability and environmental friendliness. Currently, biodegradable membrane materials are generally polyurethane materials.

[0003] Currently, continuous coating production lines exist in China. For example, CN215141998U discloses a high-efficiency continuous anti-clogging coating production line for organic fertilizer production, which includes a polishing machine and a coating machine connected in sequence and operating continuously. A resin injector is fixedly connected to the top of the inner cavity of the coating machine, and a curing agent injector is installed at the bottom of the resin injector. However, this type of continuous coating production line is not suitable for the coating production process of granular fertilizers using polyurethane as the coating material, because the coating reaction of polyurethane involves multiple reaction stages with different viscosities, which cannot be prepared by a continuous coating production line.

[0004] For the production process of polyurethane coating of granular fertilizer, an intermittent production process is still required. However, the existing technology has many drawbacks: 1. Material conveying requires multiple uses of lifting equipment. Multiple stages from screening to coating require power conveying, resulting in a large number of equipment, a complex process, and high energy consumption in procurement and operation; 2. The traditional process is configured with "one polishing preheater corresponding to one coating machine." In low-temperature environments such as Northeast China where temperatures drop to -28°C, the coating machine is prone to failure to operate continuously due to the low temperature, requiring the addition of a large amount of insulation equipment, resulting in high energy consumption and low heat utilization efficiency; 3. Polishing machines and coating machines mostly use gear transmission with reducers, which places strict requirements on the civil engineering foundation. Special reinforced foundations are required, resulting in long construction cycles and high installation costs; 4. The polishing liquid in the polishing machine is sprayed at a single point and in a single application, resulting in uneven polishing of the particle surface, affecting the adhesion of subsequent coatings, and leading to a low finished product qualification rate.

[0005] In summary, for the production process of polyurethane coating of granular fertilizers, developing a semi-continuous polyurethane coating production device and its production method that is simple in equipment, low in energy consumption, easy to install, and adaptable to low-temperature conditions has become an urgent problem to be solved in the industry. Summary of the Invention

[0006] In view of the problems existing in the prior art, the present invention provides a semi-continuous polyurethane coating production device and method for granular fertilizers. Through the core configuration of "two polishing machines and one coating machine", that is, two polishing machines connected in parallel to one coating machine, the coating machine can work continuously in the low temperature outdoor conditions of -28°C in Northeast China without the need for any additional heat preservation equipment. Compared with the traditional "one polishing machine and one coating machine" process, the heat preservation energy consumption is reduced by 100% and the heat utilization efficiency is increased by more than 50%. It is suitable for the transformation of intermittent granular fertilizer coating production process with low temperature conditions, low energy consumption and easy installation. It is applicable to the coating processing of various granular fertilizers, especially suitable for industrial production in the low temperature areas of northern China.

[0007] To achieve this objective, the present invention adopts the following technical solution: One of the objectives of this invention is to provide a semi-continuous polyurethane coating production device for granular fertilizer, which includes, along the flow direction of the granular fertilizer, a feeding module, a screening module, a metering module, a polishing module, a coating module, a cooling module, and a packaging module connected in sequence. The metering module includes two parallel polishing metering hoppers, and the polishing module includes two parallel polishing machines. The polishing metering hoppers and polishing machines are one-to-one and interconnected, forming two sets of parallel metering-polishing combinations. The coating module includes a coating machine. The discharge port of each polishing machine is independently connected to the inlet of the coating machine, so that the two polishing machines alternately feed the polished material into the coating machine, and the coating machine operates semi-continuously.

[0008] This invention utilizes a core configuration of "two polishing machines and one coating machine," where two polishing machines operate in parallel to one coating machine. This allows the coating machine to operate continuously in outdoor conditions as low as -28°C in Northeast China, without requiring any additional insulation equipment. Compared to the traditional "one polishing machine and one coating machine" process, insulation energy consumption is reduced by 100%, and heat utilization efficiency is increased by over 50%. It is suitable for the modification of intermittent granular fertilizer coating production processes under low-temperature conditions, with low energy consumption and easy installation. It is applicable to the coating processing of various granular fertilizers, and is particularly suitable for industrial production in cold northern regions. The production device described in this invention features simplified equipment, low energy consumption, and convenient installation. It produces uniformly polished granules with strong coating adhesion, enabling continuous automated production of intermittent coatings, significantly improving production efficiency, reducing production costs, and achieving a high finished product qualification rate.

[0009] It should be noted that after the coating machine completes a full coating process, it continuously enters the next operating cycle to perform a coating operation on the granular fertilizer in another polishing machine that has reached the preheating and polishing requirements. The reaction heat generated by the exothermic reaction of polyurethane is used to keep the coating machine warm, which reduces energy consumption in the production process and enables the coating machine to work continuously at an ambient temperature of -28°C without the need for additional insulation equipment.

[0010] As a preferred technical solution of the present invention, the feeding module includes a feeding hopper and a raw material elevator connected in sequence, which are used to transport granular fertilizer to the screening module.

[0011] As a preferred embodiment of the present invention, the screening module includes a vibrating screen.

[0012] Preferably, the vibrating screen is a rotary grading screen.

[0013] As a preferred technical solution of the present invention, a Y-type flap pneumatic valve is provided at the discharge port of the vibrating screen, and the two discharge ports of the Y-type flap pneumatic valve are respectively connected to the inlet ports of the two polishing metering hoppers.

[0014] It should be noted that the preferred vibrating screen of this invention is a rotary grading screen, and a Y-type flap pneumatic valve is installed at the discharge port. Through the height difference and the Y-type flap pneumatic valve, the granular fertilizer that meets the requirements after screening flows into the polishing metering hopper by its own gravity. The polishing metering hopper is a double hopper, which corresponds to the preheating polishing cylinder of two parallel polishing machines. When the weight of one polishing metering hopper reaches the set value, the Y-type flap pneumatic valve is controlled to automatically adjust to the other polishing metering hopper for weighing. If both hoppers reach the set weight and neither has entered the polishing machine, the raw material elevator and vibrating screen are controlled to automatically stop feeding. After either hopper has finished discharging, the raw material elevator and vibrating screen are automatically restarted to feed.

[0015] As a preferred technical solution of the present invention, each of the polishing machines includes a preheating polishing cylinder; the preheating polishing cylinder is placed horizontally, and an exhaust port is provided at the tail of the preheating polishing cylinder. The exhaust port is connected to a duct with a bag filter and a hot air blower, and the gas is blown into the preheating polishing cylinder through a steam heat exchanger for preheating the material entering the polishing machine.

[0016] It should be noted that the temperature inside the preheating polishing cylinder is automatically controlled by a sensor. The heating air inlet automatically closes when the set upper limit temperature is reached, and automatically opens when the temperature falls below the set limit. In this invention, the material entering the polishing machine is preheated via a hot air duct. This duct is connected to the main hot air duct, and the main hot air duct is the air duct connected to the exhaust port at the tail of the preheating polishing cylinder, which includes a bag filter and a hot air blower. During actual operation, to promptly remove water vapor from the preheating and polishing process, a pneumatic regulating valve is installed at the outlet of the hot air blower, located between the hot air blower and the steam heat exchanger.

[0017] It should be noted that the polishing machine described in this invention is placed horizontally, with both the inlet and outlet located at the center height of the cylinder at both ends. It feeds clockwise and discharges counter-clockwise. During counter-clockwise rotation, a specially arranged spiral guide chute transports the material to the outlet, completing the discharge process. Specifically, when the polishing machine feeds clockwise, the material filling level is generally around 15% (calculated based on the internal volume of the cylinder excluding the end caps). After feeding, the normal material layer height is approximately 0.8 meters.

[0018] As a preferred embodiment of the present invention, the coating module includes a coating discharge hopper, which is disposed at the discharge port of the coating machine and is used to transport the coated material to the cooling module.

[0019] As a preferred embodiment of the present invention, the cooling module includes a cooling lift and a cooling machine connected in sequence.

[0020] It should be noted that the cooling machine described in this invention is preferably a drum cooler. On the one hand, it exchanges heat with the cold air introduced by the fan to reduce the temperature of the granular fertilizer. On the other hand, it sprays an anti-caking agent to prevent the polyurethane-coated granular fertilizer from clumping. The coating raw material is conveyed to the coating machine by the membrane material storage, heating, and metering system. After coating, the material is lifted by a bucket elevator and conveyed to the drum cooler for cooling. The cooled coated fertilizer is then conveyed to the packaging hopper by an elevator. Under the packaging hopper, an automatic weighing scale is used for weighing and packaging to obtain the coated fertilizer product. After packaging, the finished product is conveyed to the finished product warehouse for storage.

[0021] As a preferred embodiment of the present invention, the packaging module includes a packaging elevator and a packaging hopper connected in sequence.

[0022] As a preferred technical solution of the present invention, the polishing machine is provided with polishing liquid nozzles inside, which are used to spray a quantitative amount of polishing liquid at multiple points and multiple times.

[0023] It should be noted that the polishing machine is equipped with polishing fluid pipes and evenly distributed polishing fluid nozzles. The polishing fluid is stored in a polishing fluid storage tank and is sprayed into the polishing machine by a special centrifugal pump after being measured by a polishing fluid flow meter.

[0024] And / or, the coating machine is internally equipped with a polyurethane A material spray nozzle, a polyurethane B material spray nozzle, and a curing agent spray nozzle, which are used to spray polyurethane A material, polyurethane B material, and curing agent respectively, thereby forming a polyurethane coating.

[0025] It should be noted that the coating machine of this invention is horizontally placed, with both the inlet and outlet located at the center height of the cylinders at both ends. It feeds counter-clockwise and discharges clockwise. During clockwise rotation, a specially arranged spiral guide chute transports the material to the tail outlet, completing the discharge process. After feeding, it continues to rotate clockwise, causing the granular fertilizer inside the coating machine to continuously roll. The material's direction of movement is influenced by the built-in baffles, resulting in a reciprocating horizontal motion within the coating machine. The coating machine feeds counter-clockwise, and after feeding, it is evenly distributed. Once evenly distributed, the coating program is initiated, and evenly distributed nozzles within the coating machine perform a pre-set spraying process. The spraying material comes from the membrane material storage tank system. After coating is complete, the coating machine stops operating and waits for a set time before resuming clockwise discharge. During clockwise rotation, a specially arranged spiral guide chute transports the material to the tail outlet, completing the discharge process. After completing a full coating process, the coating machine will continuously enter the next operating cycle to perform coating operations on another granular fertilizer in the polishing machine that has reached the preheating and polishing requirements. The coating machine can work continuously in an ambient temperature of -28°C without the need for additional insulation equipment.

[0026] In terms of civil engineering installation, both the polishing machine and the coating machine in this invention adopt a polyurethane-coated tow wheel drive method. The polyurethane-coated tow wheel drive method includes several polyurethane-coated tow wheels, a drive motor and connecting components. The tow wheels are evenly supported on the outside of the cylinder of the polishing machine / coating machine. The drive motor drives the tow wheels to rotate and drives the cylinder to rotate. The equipment can be directly installed on ordinary cement ground without the need for a special civil engineering equipment foundation.

[0027] A second objective of this invention is to provide a method for producing a semi-continuous granular fertilizer polyurethane coating production apparatus according to one objective, the method comprising the following steps: Step S1: The granular fertilizer to be coated is conveyed, screened, and metered; the granular fertilizer to be coated passes through the feeding module and the screening module in sequence, and the screened material is periodically fed into two parallel polishing and metering hoppers in sequence. Step S2: Polishing of the coated granular fertilizer; Each batch of polished and metered material is fed into a polishing machine corresponding to it for polishing. Two polishing machines connected in parallel are used alternately to obtain polished material. Step S3: Coating of polished granular fertilizer; the polished material from one polishing machine enters the coating machine, and the corresponding coated material enters the cooling module. Then, the polished material from another polishing machine enters the coating machine for polyurethane coating, making the coating machine operate semi-continuously. Step S4: Cooling and packaging of the coated granular fertilizer; After coating, the material enters the cooling module and the packaging module in sequence for cooling and packaging, respectively, to obtain the finished polyurethane coated granular fertilizer. Preferably, in step S1, the particle size range of the sieved material is 2-4.5 mm; Preferably, in step S4, the cooling module includes an anti-caking agent nozzle for spraying anti-caking agent onto the granular fertilizer during the cooling process.

[0028] As a preferred technical solution of the present invention, along the flow direction of the granular fertilizer, the production device of the present invention includes a feeding hopper, a raw material elevator, a vibrating screen, two parallel polishing metering hoppers, two parallel polishing machines, a coating machine, a coating discharge hopper, a cooling elevator, a cooling machine, a packaging elevator, and a packaging hopper connected in sequence; the polishing metering hoppers correspond one-to-one with the polishing machines and are connected to each other, forming two sets of parallel metering-polishing combinations; the discharge port of each polishing machine is independently connected to the inlet of the coating machine, so that the two polishing machines alternately feed the polished material into the coating machine, and the coating machine operates semi-continuously.Accordingly, the production method of the present invention includes the following steps: S1, conveying, screening, and metering of granular fertilizer to be coated: granular fertilizer is lifted from the feeding hopper to the vibrating screen by a raw material elevator. Qualified granular fertilizer (e.g., granular fertilizer with a particle size range of 2-4.5mm) flows by gravity into the polishing metering hopper (e.g., with an internal volume of 3 cubic meters). Unqualified particles are placed in ton bags below the chute. The bottom of the polishing metering hopper is equipped with a pneumatic gate valve. Two polishing metering hoppers are provided, and the Y-type flap pneumatic valve of the vibrating screen controls the polishing metering hopper to be metered. When the granular material reaches the polishing metering level... After the weight is preset in the measuring hopper, a signal is sent to adjust the Y-type flap pneumatic valve, switching the material feeding from the vibrating screen to another empty polishing measuring hopper. When both polishing measuring hoppers reach their preset weights and neither has entered the subsequent polishing machine, the raw material elevator automatically stops feeding. After either polishing measuring hopper finishes discharging, the raw material elevator and vibrating screen automatically start feeding. S2, Preheating and polishing of the granular fertilizer to be coated: The granular fertilizer measured by the polishing measuring hopper flows by gravity and enters the empty, forward-running polishing machine after the pneumatic discharge gate valve at the bottom of the polishing measuring hopper opens according to a preset program. Two polishing machines are set up and correspond to each other. A subsequent coating machine; the polishing machine operates in the forward direction and feeds the material. The hot air inside the polishing machine exchanges heat with the granular fertilizer, and a metered amount of polishing liquid is sprayed onto the granular fertilizer using a multi-point, multi-stage spraying method. The temperature inside the polishing machine is automatically controlled by a sensor; the heating air inlet automatically closes when the preheating upper limit temperature is reached, and automatically opens when the temperature drops below the set temperature. After the polishing machine operates in the forward direction for the set polishing time, it stops and reverses to discharge the preheated and polished granular fertilizer, which flows by gravity from the discharge port into the coating machine below. S3, Coating of the preheated and polished granular fertilizer: The preheated and polished granular fertilizer... After the fertilizer is fed into the coating machine, the machine rotates forward to even out the material. Once even out the material is evenly distributed, the coating operation begins. Different coating materials are fed into the coating machine in batches according to a pre-set time and metering. As the equipment operates, the materials are sprayed and coated onto the surface of the granular fertilizer. After coating, the machine reverses to discharge the fertilizer. S4: Cooling and packaging of the coated granular fertilizer: The coated granular fertilizer discharged from the coating machine flows into the cooling elevator by gravity. The elevator then transports the fertilizer to the cooling cylinder, where it exchanges heat with the cold air introduced by the fan to reduce the temperature of the granular fertilizer. After being sprayed with an anti-caking agent, the fertilizer is transported to the packaging hopper. After metering and packaging, the fertilizer is transferred to the finished product warehouse for storage.

[0029] Compared with existing technical solutions, the present invention has at least the following beneficial effects: (1) Simplified equipment and low operating energy consumption: The conveying method of one-time lifting + full gravity flow reduces lifting and power conveying equipment by more than 30%, which greatly reduces equipment procurement costs and operating energy consumption; the hot air circulation design makes the heat utilization efficiency reach more than 85%, further reducing heat loss. (2) Adaptable to low temperature working conditions, no insulation required: The core configuration of "two polishing and one wrapping" is that two polishing machines in parallel correspond to one wrapping machine, which can enable the wrapping machine to work continuously in the outdoor working conditions of -28℃ in Northeast China without adding any insulation equipment. Compared with the traditional "one polishing and one wrapping" process, the insulation energy consumption is reduced by 100%, and the heat utilization efficiency is increased by more than 50%. (3) Low installation requirements and short construction period: The polyurethane coated tow wheel drive replaces the gear transmission of the reducer. The equipment can be directly installed on ordinary cement ground without the need for special civil engineering reinforcement foundation. The construction period is shortened by more than 60% and the installation cost is reduced by more than 40%. (4) Uniform polishing and excellent coating effect: The multi-point and multi-time polishing liquid spraying method achieves uniform polishing of the surface of granular fertilizer, solves the problem of uneven polishing of single-point and single-time spraying, improves coating adhesion by more than 30%, and the finished product qualification rate reaches more than 99%. (5) Intermittent coating continuous production with high degree of automation: The parallel design of dual metering hoppers and dual polishing machines, combined with the automatic control of pneumatic valves and sensors, enables 24-hour continuous production of semi-continuous coating. The control is simple and reliable with a low failure rate, reducing the number of production operators by more than 50% and lowering labor costs. (6) Green and environmentally friendly, in line with industry trends: The process is compatible with the coating process of biodegradable film materials, which is in line with the green development direction of controlled-release fertilizer film materials in my country. Moreover, there are no additional heat preservation materials or equipment redundancy issues throughout the process, which meets the requirements of green agricultural production. (7) The present invention has the above six significant beneficial effects, and the effects are synergistic, comprehensively improving production efficiency, reducing costs and optimizing the quality of finished products. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the semi-continuous granular fertilizer polyurethane coating production device described in Embodiment 1 of the present invention. Detailed Implementation

[0031] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0032] To better illustrate the present invention and facilitate understanding of its technical solutions, typical but non-limiting embodiments of the present invention are as follows: Example 1 This embodiment provides a semi-continuous polyurethane coating production apparatus for granular fertilizers, such as... Figure 1As shown, along the flow direction of the granular fertilizer, the production device of the present invention includes a feeding hopper, a raw material elevator, a vibrating screen, two parallel polishing metering hoppers, two parallel polishing machines, a coating machine, a coating discharge hopper, a cooling elevator, a cooling machine, a packaging elevator, and a packaging hopper, connected in sequence. The polishing metering hoppers correspond one-to-one with the polishing machines and are connected to each other, forming two sets of parallel metering-polishing combinations. The discharge port of each polishing machine is independently connected to the inlet of the coating machine, so that the two polishing machines alternately feed the polished material into the coating machine, while the coating machine operates semi-continuously.

[0033] The vibrating screen is a rotary grading screen. A Y-type flap pneumatic valve is installed at the discharge port of the vibrating screen, and the two discharge ports of the Y-type flap pneumatic valve are respectively connected to the inlets of the two polishing metering hoppers. The screen mesh size of the vibrating screen is 2mm for fine screening and 4.5mm for coarse screening, which can screen granular fertilizer with a particle size range of 2-4.5mm. The qualified granular fertilizer flows into the two parallel polishing metering hoppers by gravity, and the Y-type flap pneumatic valve controls the flow into different polishing metering hoppers. The bottom of the polishing metering hopper is pneumatically controlled. The system consists of a gate valve and two hoppers in the polishing metering hopper, each corresponding to a different polishing machine for feeding and metering. The coating machine and drum cooler work by feeding preheated and polished granular fertilizer through a reverse rotation of the polishing machine into the coating machine. After coating, the fertilizer is lifted by a rotating bucket and transported to the drum cooler for cooling. The coating material is also transported to the coating machine from a film material storage, heating, and metering system. Finally, the cooled coated fertilizer is conveyed to the packaging hopper by an elevator. An automatic weighing scale is used below the packaging hopper to weigh and package the fertilizer, resulting in the finished coated fertilizer. The packaged product is then transported to a finished product warehouse for storage. The vibrating screen, polishing metering hopper, polishing machine, and coating machine are arranged in a top-to-bottom three-dimensional structure, allowing materials to enter each system by gravity.

[0034] Each of the polishing machines includes a preheating polishing cylinder; the preheating polishing cylinder is placed horizontally, and an exhaust port is provided at the tail of the preheating polishing cylinder. The exhaust port is connected to a duct with a bag filter and a hot air blower, and the gas is blown into the preheating polishing cylinder through a steam heat exchanger to preheat the material entering the polishing machine.

[0035] The polishing machine is equipped with polishing fluid pipes and evenly distributed nozzles. The polishing fluid is stored in a polishing fluid storage tank and is metered by a special centrifugal pump and then added to the preheated polishing cylinder.

[0036] The polishing machine feeds material clockwise and discharges material counterclockwise. When it rotates counterclockwise, a specially arranged spiral guide trough transports the material to the discharge port to complete the discharge process.

[0037] The vibrating screen is a rotary grading screen that transports qualified granular fertilizer to the polishing metering hopper through a height difference and a Y-type flap pneumatic valve. The polishing metering hopper is a double hopper that corresponds to two preheated polishing cylinders. When the weight of the polishing metering hopper reaches the set value, the Y-type flap pneumatic valve automatically adjusts to the other hopper for weighing. When both hoppers reach the set weight and neither has entered the polishing machine, the elevator automatically stops feeding. After either hopper finishes discharging, the raw material elevator and vibrating screen are automatically restarted for feeding.

[0038] The polishing machine is placed horizontally, with the inlet and outlet located at the center height of the cylinders at both ends. It feeds in clockwise and discharges in counterclockwise. When it rotates counterclockwise, a specially arranged spiral guide chute transports the material to the discharge port at the tail end, completing the discharge process.

[0039] The two polishing machines are connected to the main heat supply air duct in a certain way. The exhaust air at the tail of the polishing cylinder is connected to the bag filter through a horizontal sealed air duct. The bag filter is connected to the heat supply fan, and the gas is then blown into the polishing machine through a steam heat exchanger to preheat and polish the granular fertilizer.

[0040] The coating machine is placed horizontally, with the inlet and outlet located at the center height of the cylinders at both ends. It feeds material counterclockwise and discharges material clockwise. When rotating clockwise, a specially arranged spiral guide chute transports the material to the tail outlet to complete the discharge process.

[0041] The coating machine feeds material counterclockwise, then evens it out. After evening, the coating program is started, and the spray nozzles inside the machine are evenly arranged to carry out the spraying process according to the preset program. The spraying material comes from the film material storage tank system. After coating is completed, the coating machine stops running and waits for a set time before starting to discharge material clockwise. During clockwise rotation, a specially arranged spiral guide chute transports the material to the tail discharge port to complete the discharge process. After discharge, the material enters the cooling and metering packaging system.

[0042] The polishing metering hopper uses a bottom-mounted weighing sensor for metering. Polishing fluid metering employs a metering pump and flow meter to control the total flow rate for each spray. Coating fluid metering uses a weighing method, pumping the fluid into the coating machine according to a set membrane material weight. The polishing fluid metering uses a rotor flow meter, while the coating fluid metering uses a gravity-fed fixed tank weighing loss-in-weight scale.

[0043] The preheating polishing cylinder of the polishing machine has a specification of Ф2200×5000×12mm; the polishing measuring hopper has a size of 2200×2200×(600+850)×5mm, where 5mm is the thickness of the plate of the polishing measuring hopper and (600+850)mm is the size of the bottom of the cone corresponding to the 2200×2200mm hopper body; the coating machine has a specification of Ф2200×5000×12mm.

[0044] The PLC control system controls the start and stop of equipment such as raw material elevators, vibrating screens, preheating fans, and drum coolers, as well as the manual and automatic switching of polishing and coating machines.

[0045] Application Example 1 This application example provides a production method using the semi-continuous granular fertilizer polyurethane coating production apparatus described in Example 1, the production method comprising the following steps: Step S1: Conveying, screening, and metering the granular fertilizer to be coated; 40-50 kg of granular fertilizer to be coated in bags or packages is fed into the raw material feeding hopper. The hopper is made of 304 stainless steel and has dimensions of 2500×2500×(1600+850) mm. The raw material is then conveyed to the vibrating screen by the raw material elevator. The vibrating screen uses a rotary vibrating screen with a screening capacity of 8 tons / hour or more. The screen mesh size is 2 mm for fine screening and 4.5 mm for coarse screening. The qualified granules enter the polishing and metering hopper. After reaching the preset weight, the granular fertilizer enters the polishing machine by its own gravity through the automatically opened discharge gate valve.

[0046] Step S2: Polishing the coated granular fertilizer; When the feeding program of the polishing machine is started, the polishing machine continues to rotate forward. After all the granular fertilizer has entered the polishing machine, the Y-type pneumatic valve automatically closes, and the hot air inlet of the polishing machine head automatically opens to preheat and polish the granular fertilizer in the rotating cylinder. After the polishing machine completes the polishing and preheating of the granular fertilizer according to the set program and time, it enters a continuous forward rotation waiting for discharge. When the coating machine is in the forward rotation of the set program's idle state, the polishing machine starts the discharge program. When discharging, the polishing machine stops rotating forward and starts to reverse to discharge. After the discharge is completed, the polishing machine stops reversing and enters a forward rotation waiting for feeding.

[0047] Step S3: Coating of polished granular fertilizer; the polished material from one polishing machine enters the coating machine. After feeding, the coating machine rotates forward continuously, starting the fully automatic process of uniform material distribution and multiple coating operations pre-set in the coating program; after the coating machine completes the predetermined coating program, it enters the discharge program, stops rotating forward and quickly switches to reverse discharge mode, discharging the material into the coating machine discharge hopper; subsequently, the polished material from another polishing machine enters the coating machine for polyurethane coating, making the coating machine operate semi-continuously.

[0048] Step S4: Cooling and packaging of coated granular fertilizer; The coated granular fertilizer is transported to the cooling cylinder by the cooling elevator connected to the coating discharge hopper, cooled and discharged, and then enters the packaging elevator to be transported to the packaging hopper for metering and packaging to obtain the finished coated fertilizer product.

[0049] In this application example, each polishing machine has a polishing time of approximately 2400 seconds. The two polishing machines operate in parallel, alternating between them. The coating machine's operating procedure includes feeding, uniform mixing, multiple coating processes, and discharging, with a total time of approximately 1200 seconds. The two alternating polishing machines correspond to one coating machine, achieving fully continuous operation of the coating machine. In this application example, the coating machine completes one full coating process before continuously entering the next operating cycle to coat the granular fertilizer in another polishing machine that has already met the preheating and polishing requirements. This allows the coating machine to operate continuously at an ambient temperature of -28°C without requiring additional insulation equipment.

[0050] In summary, this invention provides a semi-continuous polyurethane coating production device and method for granular fertilizers. Through a core configuration of "two polishing machines and one coating machine"—two polishing machines connected in parallel to one coating machine—the coating machine can operate continuously in outdoor conditions as low as -28°C in Northeast China without requiring any additional insulation equipment. Compared to the traditional "one polishing machine and one coating machine" process, insulation energy consumption is reduced by 100%, and heat utilization efficiency is increased by more than 50%. This invention is suitable for the modification of intermittent granular fertilizer coating production processes that are adaptable to low-temperature conditions, low-energy consumption, and easy to install. It is applicable to the coating processing of various granular fertilizers, and is especially suitable for industrial production in low-temperature regions of northern China.

[0051] The present invention has been illustrated with the above embodiments to illustrate its detailed structural features. However, the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the components used in the present invention, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0052] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0053] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0054] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A semi-continuous granular fertilizer polyurethane coating production apparatus, characterized by, Along the flow direction of the granular fertilizer, it includes a feeding module, a screening module, a metering module, a polishing module, a coating module, a cooling module, and a packaging module connected in sequence; The metering module includes two parallel polishing metering hoppers, and the polishing module includes two parallel polishing machines. The polishing metering hoppers and polishing machines are one-to-one and interconnected, forming two sets of parallel metering-polishing combinations. The coating module includes a coating machine. The discharge port of each polishing machine is independently connected to the inlet of the coating machine, so that the two polishing machines alternately feed the polished material into the coating machine, and the coating machine operates semi-continuously.

2. The apparatus for semi-continuous granular fertilizer polyurethane coating production according to claim 1, characterized in that, The feeding module includes a feeding hopper and a raw material elevator connected in sequence.

3. The apparatus for semi-continuous granular fertilizer polyurethane coating production according to claim 1, characterized in that, The screening module includes a vibrating screener; Preferably, the vibrating screen is a rotary grading screen.

4. The apparatus for semi-continuous granular fertilizer polyurethane coating production according to claim 3, characterized in that, The vibrating screen is equipped with a Y-type flap pneumatic valve at the discharge port, and the two discharge ports of the Y-type flap pneumatic valve are respectively connected to the inlets of the two polishing metering hoppers.

5. The apparatus for semi-continuous granular fertilizer polyurethane coating production according to claim 1, characterized in that, Each of the polishing machines includes a preheating polishing cylinder; the preheating polishing cylinder is placed horizontally, and an exhaust port is provided at the tail end of the preheating polishing cylinder. The exhaust port is connected to a duct with a bag filter and a hot air blower, and the gas is blown into the preheating polishing cylinder through a steam heat exchanger to preheat the material entering the polishing machine.

6. The apparatus for semi-continuous granular fertilizer polyurethane coating production according to claim 1, characterized in that, The coating module includes a coating discharge hopper, which is located at the discharge port of the coating machine and is used to transport the coated material to the cooling module.

7. The apparatus for semi-continuous granular fertilizer polyurethane coating production according to claim 1, characterized in that, The cooling module includes a cooling lift and a cooling machine connected in sequence.

8. The semi-continuous granular fertilizer polyurethane coating production apparatus according to claim 1, characterized in that, The packaging module includes a packaging elevator and a packaging hopper connected in sequence.

9. The semi-continuous granular fertilizer polyurethane coating production apparatus according to claim 1, characterized in that, The polishing machine is equipped with polishing liquid nozzles inside, which are used to spray a quantitative amount of polishing liquid into multiple points and multiple times; And / or, the coating machine is internally equipped with a polyurethane A material spray nozzle, a polyurethane B material spray nozzle, and a curing agent spray nozzle, which are used to spray polyurethane A material, polyurethane B material, and curing agent respectively, thereby forming a polyurethane coating.

10. A production method of a semi-continuous granular fertilizer polyurethane coating production apparatus according to any one of claims 1-9, characterized in that, The production method includes the following steps: Step S1: The granular fertilizer to be coated is conveyed, screened, and metered; the granular fertilizer to be coated passes through the feeding module and the screening module in sequence, and the screened material is periodically fed into two parallel polishing and metering hoppers in sequence. Step S2: Polishing of the coated granular fertilizer; Each batch of polished and metered material is fed into a polishing machine corresponding to it for polishing. Two polishing machines connected in parallel are used alternately to obtain polished material. Step S3: Coating of polished granular fertilizer; the polished material from one polishing machine enters the coating machine, and the corresponding coated material enters the cooling module. Then, the polished material from another polishing machine enters the coating machine for polyurethane coating, making the coating machine operate semi-continuously. Step S4: Cooling and packaging of the coated granular fertilizer; After coating, the material enters the cooling module and the packaging module in sequence for cooling and packaging, respectively, to obtain the finished polyurethane coated granular fertilizer. Preferably, in step S1, the particle size range of the sieved material is 2-4.5 mm; Preferably, in step S4, the cooling module includes an anti-caking agent nozzle for spraying anti-caking agent onto the granular fertilizer during the cooling process.

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