A device and process for producing nitrogen compound fertilizer by using built-in fluidized bed rotating drum

Abstract

The application relates to the technical field of compound fertilizer production and manufacturing, and discloses an equipment and a process for manufacturing nitrogen compound fertilizer by using an internal fluidized bed rotary drum, which comprises a system control unit and a slurry preparation system, a seed feeding system, a granulation system, a wind net dust removal system, a screening and returning system and a cooling and outputting system which are in communication with each other; the liquid phase slurry of the slurry preparation system and the solid seed of the feeding system enter the internal fluidized bed rotary drum granulator, are atomized, coated and fluidized and formed under the action of hot air; the system control unit performs flow interlocking regulation based on the liquid level of the buffer tank, carries out delay compensation and zero protection on the seed belt scale; the hardware fault and process abnormality are distinguished by synchronously comparing the pipe network pressure difference and the induced fan current, the total returning rate and the screening machine power; and the air and water flow of the cooling system is linked and adjusted under a high-humidity environment. The application can suppress material fluctuation, eliminate single sensing data misjudgment and effectively prevent the secondary moisture return of finished fertilizer.

Description

Technical Field

[0001] This invention relates to the field of compound fertilizer production and manufacturing technology, specifically to a device and process for producing nitrogen compound fertilizer using a built-in fluidized bed rotary drum. Background Technology

[0002] In the continuous production of nitrogen fertilizer and compound fertilizer, in recent years, built-in fluidized bed rotary drum granulation equipment, which combines a rotary drum with a fluidized bed, has been widely adopted. Its basic process is to spray high-temperature liquid slurry onto the surface of rolling solid seed crystals, and achieve the growth and solidification of the material under the penetration of hot air at the bottom. The wet material after granulation then enters the screening and cooling process to form the final product.

[0003] In actual operation, the melting rate of the front-end solid raw materials and the amount of seed crystals fed often fluctuate, leading to an imbalance in the ratio of liquid slurry to solid seed crystals entering the granulator, directly affecting the quality of pellets. Existing equipment typically relies on basic single-loop feedback to adjust the feed rate. Due to the physical spatial layout, there is a distance between the weighing and speed measuring components, resulting in an inherent time difference in the measurement process. Conventional control logic struggles to accurately smooth out instantaneous flow fluctuations, easily leading to uncontrolled feeding.

[0004] Meanwhile, the compound fertilizer production environment is characterized by high dust and high humidity. In the ventilation and material screening stages, existing monitoring and control systems typically rely on a single sensor parameter for operational condition assessment. For example, they might rely on a differential pressure transmitter to determine pipeline negative pressure or solely on weight parameters to determine granulation efficiency. Under complex continuous production conditions, pressure gauges are easily clogged by wet dust, leading to data drift, and vibrating screens frequently become clogged due to the adhesion of highly moist materials. When such hardware blockages occur, data transmitted from a single sensor can mislead the control system, causing it to incorrectly interpret the granulation process as deterioration, thus triggering erroneous parameter adjustment commands and resulting in system instability.

[0005] Furthermore, the finished compound fertilizer product has extremely strict requirements regarding surface moisture content. Most existing cooling processes focus solely on controlling the discharge temperature, using a combination of continuously blowing in ambient-temperature cold air and circulating water for cooling. However, when the external climate is rainy and humid, directly drawing in large amounts of high-humidity air not only fails to effectively remove free water from the fertilizer surface, but the high-humidity cold air can also easily reach the dew point inside the cooler, causing the fertilizer granules to become damp again. This single-temperature control deficiency makes the finished product highly susceptible to clumping during subsequent storage and stacking, affecting the final product quality. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a device and process for producing nitrogen-based compound fertilizer using a built-in fluidized bed drum. This solves the problems of existing built-in fluidized bed drum compound fertilizer production equipment, which, in actual operation, lack an effective data synchronization compensation mechanism and multi-parameter joint diagnostic logic, making it difficult to cope with material flow fluctuations and interference from high-dust environments on sensors. Furthermore, the cooling system does not consider the impact of ambient humidity, which can easily lead to system regulation failure, equipment misjudgment, and secondary moisture re-dampening and clumping of the finished product.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a device for producing nitrogen-based compound fertilizer using a built-in fluidized bed rotary drum, comprising a system control unit, and further comprising:

[0008] The melting tank is connected to the buffer tank, the buffer tank is connected to the high-pressure spraying pump, and the high-pressure spraying pump is connected to the built-in fluidized bed rotary drum granulator.

[0009] The seed buffer bin is connected to the seed belt scale, the seed belt scale is connected to the seed bucket elevator, and the seed bucket elevator is connected to the built-in fluidized bed rotary drum granulator.

[0010] The heat exchanger is connected to a blower, which is connected to a built-in fluidized bed rotary drum granulator and a booster fan. The built-in fluidized bed rotary drum granulator is connected to a bag filter, which is connected to an induced draft fan.

[0011] The built-in fluidized bed rotary drum granulator is connected to a compound vibrating screen, and the small and medium particle discharge port of the compound vibrating screen is connected to the seed crystal buffer bin.

[0012] The ultra-large particle discharge port of the compound rotary vibrating screen is connected to the front-end feeding section;

[0013] The qualified particle outlet of the double-vibrating screen is connected to the tubular cooler, the booster fan is connected to the tubular cooler, and the tubular cooler is connected to the external cooling water circulation network.

[0014] During the operation and control of the equipment, the system control unit performs logical judgments and closed-loop adjustments by collecting sensor data. Furthermore, the level gauge inside the buffer tank monitors the slurry level in real time, and the system control unit executes interlocking control based on the slurry level and set upper and lower thresholds. When the slurry level reaches or falls below the set lower threshold, the system control unit triggers protection logic to limit or suspend the operation of downstream equipment to prevent pump cavitation; when the slurry level reaches or exceeds the upper threshold, the system control unit interlocks and adjusts the front-end feed rate to prevent material overflow and maintain stable fluid pressure at the outlet.

[0015] Furthermore, during the quantitative conveying of solid materials, the weighing sensor and speed sensor at the seed crystal belt scale synchronously collect the linear load per unit length of material and the instantaneous linear velocity of the belt. The system control unit performs delay compensation calculations by extracting the current running speed of the supporting belt of the seed crystal belt scale to compensate for the measurement time difference caused by the physical spatial distribution. The instantaneous input mass flow rate is obtained by calculating the product of the material linear load and the instantaneous linear velocity. The system control unit is equipped with a zero-reach protection mechanism. When the instantaneous linear velocity of the belt is zero or less than the set minimum safety threshold, the adjustment logic involving speed variables as denominators or factors in the system control unit will be automatically cut off, switching to a fixed-frequency operation state or directly triggering a shutdown alarm to avoid controller command errors caused by division by zero.

[0016] Furthermore, a micro differential pressure transmitter located on the upper part of the fluidized bed rotary drum granulator monitors the internal static pressure sequence data. The system control unit synchronously compares the static pressure sequence data with the instantaneous current data of the induced draft fan motor according to the sampling period. When the differential pressure data is within the normal range, but the instantaneous operating current of the induced draft fan drops sharply by more than 20% of the rated current, the system control unit, based on the positive correlation between the flow rate and power of the centrifugal fan, determines that there is an abnormal blockage in the pipeline network and outputs a corresponding anti-false alarm intervention command to eliminate data drift interference caused by blockage of a single pressure measuring hole.

[0017] Furthermore, the system control unit calculates the total return rate parameter in real time and compares it synchronously with the active power parameter of the compound vibrating screen motor. When the total return rate is momentarily high and the synchronously acquired motor active power drops by more than 15% of the rated value, the system control unit determines that the screen of the compound vibrating screen is clogged based on the motor load characteristics and triggers a screen cleaning alarm signal to distinguish between hardware blockage and return abnormalities caused by the granulation process itself.

[0018] Furthermore, temperature and humidity sensors in the tubular cooler's inlet duct collect the relative humidity of the pressurized cooling air. When the relative humidity exceeds 80%, the system control unit triggers a linkage adjustment logic, appropriately reducing the inlet damper of the booster fan to decrease the mass flow rate of the pressurized cooling air. Simultaneously, based on the heat exchange balance mechanism, the mass flow rate of the circulating cooling water is increased for heat compensation. This adjustment mechanism maintains the target discharge temperature while preventing moisture in the cooling air from reaching the dew point inside the equipment, thus avoiding secondary moisture reabsorption in the fertilizer.

[0019] A second aspect of the present invention provides a process for producing nitrogen-based compound fertilizer using a built-in fluidized bed rotary drum, applied to the aforementioned equipment, comprising the following steps:

[0020] Solid raw materials enter the melting tank and are heated to form a liquid slurry. The slurry flows into the buffer tank for pressure stabilization and temporary liquid level storage. The high-pressure spray pump pressurizes the slurry in the buffer tank and pumps it into the built-in fluidized bed rotary drum granulator.

[0021] The small and medium-sized particles returned from the latter section enter the seed buffer bin as the bottom seed crystals. The seed belt scale feeds the small and medium-sized particles quantitatively. The quantitatively fed material is then lifted by the seed bucket elevator into the built-in fluidized bed rotary drum granulator.

[0022] External cold air absorbs heat from the steam in the heat exchanger and is heated up. The blower then forces the hot air into the bottom of the built-in fluidized bed rotary drum granulator.

[0023] High-pressure slurry is atomized and sprayed onto the surface of the seed crystals through nozzles inside the built-in fluidized bed rotary drum granulator. Hot airflow penetrates the material layer upwards, causing the material to form a fluidized state. The surface slurry loses moisture and solidifies, resulting in an increase in particle size.

[0024] The waste gas generated during granulation is drawn out by an induced draft fan and enters a bag filter for gas-solid separation. The clean gas after dust separation is discharged by the induced draft fan and released into the external environment. The wet material discharged from granulation is transported to a double vibrating screen for particle size classification. The small and medium-sized particles produced by screening are transported back to the seed crystal buffer as return material, while the oversized particles are returned to the front-end process.

[0025] Qualified particles that meet the particle size range standard are fed into the tubular cooler. The booster fan pressurizes the cold air diverted from the blower and sends it into the tubular cooler. Inside the tubular cooler, the qualified particles exchange heat with the flowing cold air and circulating cooling water to cool down. The solidified finished fertilizer is discharged from the tubular cooler and output.

[0026] In the process flow, the slurry preparation stage disperses solid powder in a liquid carrier through heating and eutectic melting. A buffer storage stage stabilizes the upstream material flow rate, providing continuous and stable fluid pressure downstream. In the granulation stage, pressurized slurry is broken into fine droplets that adhere to the surface of tumbling solid seed crystals. Hot air from the bottom penetrates the material layer, providing heat to evaporate moisture and promote the crystallization of soluble salts on the seed crystal surface. The screening stage classifies materials based on their geometric differences, with oversized particles being crushed and recirculated, and small and medium-sized particles being directly recirculated, establishing an internal mass transfer cycle. In the cooling stage, pressurized cold air removes sensible heat and residual water vapor from the material through convection heat exchange, while circulating cooling water absorbs heat through pipe wall heat conduction, completing the dehumidification, cooling, and solidification of the final product.

[0027] This invention provides a device and process for producing nitrogen-based compound fertilizer using a built-in fluidized bed rotary drum. It offers the following advantages:

[0028] 1. This invention effectively absorbs the flow fluctuations during the phase change of the slurry and solid feeding process by setting interlocking control logic based on the upper and lower limits of the liquid level in the buffer tank and introducing a delay compensation and zero-reaching protection mechanism in the seed belt scale metering. This control method ensures that the downstream high-pressure pump and granulator can obtain continuous and stable fluid back pressure and solid bottom material, avoiding equipment cavitation failures and granulation material ratio imbalances caused by instantaneous material interruption or accumulation.

[0029] 2. This invention employs a multi-parameter synchronous comparison fault diagnosis logic in the ventilation and material screening sections. By comparing the micro-pressure difference data of the granulator cylinder with the operating current of the induced draft fan, and comparing the total return rate with the active power of the compound vibrating screen motor, the system can accurately distinguish whether the abnormality is caused by hardware physical faults such as pipe blockage or screen clogging, or by the deterioration of the granulation process itself. This approach eliminates control misjudgments caused by blockage of a single sensor orifice or data drift, thus improving the reliability of continuous system operation.

[0030] 3. This invention sets up a linkage adjustment mechanism based on the humidity of the incoming air for the cooling output system. When the relative humidity of the introduced pressurized cold air is detected to be greater than the set humidity threshold, the control unit reduces the input of high-humidity air by closing the air inlet damper of the booster fan and simultaneously increases the circulating cooling water flow of the tubular cooler to compensate for heat exchange. This linkage control ensures the cooling requirements of the discharged material while cutting off the introduction of excess moisture in a high-humidity environment, avoiding secondary moisture re-dampening of the finished fertilizer in the cooler and ensuring the anti-caking quality of the finished product. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the system architecture of the present invention;

[0032] Figure 2 This is a flowchart of the method steps of the present invention;

[0033] Figure 3 This is a logic block diagram of the buffer tank level interlock and high-pressure pump start / stop protection of the present invention;

[0034] Figure 4 This is a flowchart of the seed belt scale delay compensation and division-to-zero protection algorithm of the present invention;

[0035] Figure 5 This is the logic diagram for closed-loop control of the screening return ratio and anti-clogging diagnosis of the present invention;

[0036] Figure 6 This is a flowchart of the multi-variable joint diagnosis process for air network micro-negative pressure and induced draft fan of the present invention;

[0037] Figure 7 This is a block diagram of the temperature and humidity weighted linkage adjustment and control of the cooling system of the present invention;

[0038] Figure 8 This is a line graph comparing the stability of the ball formation pass rate of the present invention.

[0039] The components include: 1. Seed buffer bin; 2. Seed belt scale; 3. Seed bucket elevator; 4. Built-in fluidized bed rotary drum granulator; 5. Melting tank; 6. Buffer tank; 7. High-pressure spray pump; 8. Bag filter; 9. Exhaust fan; 10. Gas venting tank; 11. Heat exchanger; 12. Blower; 13. Screening feed belt conveyor; 14. Compound rotary vibrating plug; 15. Bucket elevator; 16. Tube cooler; 17. Pressure booster fan; 18. Finished product belt conveyor. Detailed Implementation

[0040] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] Please see the appendix Figure 1 This invention provides a device for producing nitrogen-based compound fertilizer using a built-in fluidized bed rotary drum, which may include: a pulping system, a seed crystal feeding system, a granulation system, a dust removal system, a screening and return system, and a cooling and output system.

[0042] The pulping system is connected to the granulation system. The outlet of the melting tank 5 is connected to the inlet of the buffer tank 6. The outlet of the buffer tank 6 is connected to the inlet of the high-pressure spray pump 7 via a pipeline. The outlet pipeline of the high-pressure spray pump 7 extends into the interior of the built-in fluidized bed rotary drum granulator 4.

[0043] The seed crystal feeding system is located at the feed front end of the built-in fluidized bed rotary drum granulator 4. A seed crystal belt scale 2 is installed below the bottom discharge port of the seed crystal buffer bin 1. The output end of the seed crystal belt scale 2 is connected to the bottom feed port of the seed crystal bucket elevator 3. The top discharge end of the seed crystal bucket elevator 3 is connected to the solid feed port of the built-in fluidized bed rotary drum granulator 4.

[0044] The dust collection system is connected to the inlet and outlet of the built-in fluidized bed rotary drum granulator 4. A steam pipeline connects to heat exchanger 11. The hot air outlet of heat exchanger 11 connects to the inlet of blower 12. The outlet of blower 12 connects to the bottom air inlet area of ​​the built-in fluidized bed rotary drum granulator 4 via a main duct. The top exhaust port of the built-in fluidized bed rotary drum granulator 4 connects to the dust-laden gas inlet of bag filter 8. The clean air exhaust port of bag filter 8 connects to the inlet of induced draft fan 9. The output of induced draft fan 9 connects to gas venting tank 10.

[0045] The discharge port of the granulation system is connected to the screening and return system. The discharge port of the built-in fluidized bed rotary drum granulator 4 is connected to the feed end of the compound vibrating screen 14 via the screening feed conveyor 13. The discharge port of the compound vibrating screen 14 for small and medium particles is connected to the top feed port of the seed buffer bin 1 via the first return pipeline. The discharge port of the compound vibrating screen 14 for large particles is connected to the front-end feeding section via the second return pipeline.

[0046] The screening and return system is connected to the cooling output system. The qualified particle outlet of the double vibrating screen 14 is connected to the feed end of the bucket elevator 15. The discharge end of the bucket elevator 15 is connected to the feed end of the tubular cooler 16. A bypass branch is led out from the main air outlet of the blower 12, and this bypass branch is connected to the air inlet of the booster blower 17. The air outlet of the booster blower 17 is connected to the cooling air inlet of the tubular cooler 16. The cold water inlet and outlet of the tubular cooler 16 are respectively connected to the external cooling water circulation network. The discharge port of the tubular cooler 16 is connected to the finished product conveyor belt 18.

[0047] Please see the appendix Figure 2 This invention provides a process for producing nitrogen-based compound fertilizer using a built-in fluidized bed rotary drum, comprising the following steps:

[0048] S10, solid raw materials enter the melting tank 5 and are heated to melt to form liquid slurry. The slurry flows into the buffer tank 6 for pressure stabilization and temporary liquid level storage. The high-pressure spray pump 7 pressurizes the slurry in the buffer tank 6 and pumps it into the built-in fluidized bed rotary drum granulator 4.

[0049] S20, the small and medium-sized particles returned from the back end of the system enter the seed buffer 1 as the bottom seed crystals, the seed belt scale 2 feeds the small and medium-sized particles quantitatively, and the quantitatively fed material is lifted by the seed bucket elevator 3 into the built-in fluidized bed rotary drum granulator 4.

[0050] S30, external cold air absorbs steam heat in heat exchanger 11 and heats up, and blower 12 presses hot air into the bottom of built-in fluidized bed rotary drum granulator 4.

[0051] S40, the high-pressure slurry is atomized and sprayed onto the surface of the seed crystal through nozzles inside the built-in fluidized bed rotary drum granulator 4. The hot airflow penetrates the material layer upward to make the material fluidized. The surface slurry loses moisture and solidifies, thus increasing the particle size.

[0052] S50, the waste gas generated by granulation is drawn out by the induced draft fan 9 and enters the bag dust collector 8 for gas-solid separation treatment. The clean gas after separating and intercepting dust is discharged into the gas exhaust bucket 10 and discharged to the external environment.

[0053] S60, the wet material discharged from granulation is conveyed to the double vibrating screen 14 by the screening feed belt 13 for particle size classification. The small and medium particles produced by screening are returned to the seed buffer 1 as return material, and the oversized particles are returned to the front-end process of the system.

[0054] S70, qualified particles that meet the particle size range standard are sent to the tubular cooler 16 by the bucket elevator 15. The booster fan 17 pressurizes the cold air diverted from the blower 12 and sends it to the tubular cooler 16. The qualified particles exchange heat with the flowing cold air and circulating cooling water inside the tubular cooler 16 to cool down. The solidified finished fertilizer is discharged from the tubular cooler 16 and falls into the finished product belt conveyor 18 for conveying and output.

[0055] The pulping system establishes a physical transformation and pressurized fluid transport path from solid raw materials to liquid slurry. In this embodiment, the pulping system mainly includes a melting tank 5, a buffer tank 6, and a high-pressure spray pump 7. The implementation method of the pulping process and equipment setup includes the following steps:

[0056] S101, a multi-component solid raw material is fed into the melting tank 5 for heating and co-melting. The solid raw material includes monoammonium phosphate, ammonium chloride, urea, and potash fertilizer. Since urea has a low melting point, it melts upon heating and acts as a liquid phase carrier, promoting the dissolution or uniform dispersion of other high-melting-point powder components through heat transfer and compatibility, thereby forming a fluid, homogeneous, high-concentration liquid slurry. The melting tank 5 is equipped with a heating component, which is either a steam jacket heating structure or a built-in steam coil heating structure. High-temperature steam from outside is introduced into the heating component, transferring heat to the solid raw material in the melting tank 5 through heat conduction through the pipe walls. For the motor-driven stirring device and temperature transmitter installed in the melting tank 5, those skilled in the art can conventionally select and install them according to the fluid mixing and temperature measurement requirements. The specific mechanical connections and electrical wiring methods are well-known in the art and will not be elaborated here.

[0057] In a continuous engineering operation environment, the mass input and output of the system during eutectic slurry preparation must meet a dynamic balance. Its general calculation principle follows the law of mass conservation within a steady-state flow control volume; the output mass flow rate of the mixed liquid slurry is equivalent to the sum of the input mass flow rates of monoammonium phosphate, ammonium chloride, urea, and potash fertilizer. Based on this mass balance, sufficient heat energy is required for the melting process to ensure complete phase change. The total heat flow rate required to be input into the system includes the sum of the sensible heat of each independently input solid raw material component and the latent heat of fusion of the phase change material. Regarding the range of the target eutectic temperature and its determination basis, its lower threshold must be higher than the lowest eutectic point temperature of the multi-component mixture to ensure complete fluid liquefaction, while its upper threshold must be strictly lower than the critical temperature at which heat-sensitive substances such as urea undergo biuretization or decomposition, thereby avoiding nutrient loss while ensuring fluidity.

[0058] Please see the appendix Figure 3S102. Considering the unavoidable fluctuations in the feeding action and melting phase change rate of the multi-component solid materials in actual production, directly pumping the fluctuating slurry downstream could easily cause pressure imbalance in the granulation section. To mitigate these fluctuations, a homogeneous, high-concentration liquid slurry flows out from the outlet of the melting tank 5 and enters the buffer tank 6 for pressure stabilization and temporary level storage. The buffer tank 6 has an internal cavity volume, serving as an intermediate buffer node in the fluid transport pipeline to provide residence time for the slurry, thereby absorbing instantaneous peaks or troughs in the upstream flow. A level gauge is installed inside the buffer tank 6 to monitor the slurry level in real time, maintaining a dynamic balance between the inlet and outlet liquid levels. When the level gauge detects that the liquid level is approaching the set lower threshold, the system triggers protection logic to limit or suspend the operation of downstream equipment to prevent cavitation caused by pump cavitation; conversely, when the liquid level is approaching the upper threshold, the feed rate at the front end is adjusted to prevent overflow of the high-temperature slurry. This interlocking control logic based on the upper and lower limits of the liquid level ensures that a stable initial static pressure head is formed at the liquid outlet of buffer tank 6.

[0059] S103, the liquid slurry, after pressure stabilization and temporary storage, continuously flows from the outlet of the buffer tank 6 into the inlet of the high-pressure spray pump 7. The high-pressure spray pump 7 performs mechanical work on the liquid slurry, increasing its hydrostatic and dynamic pressure, allowing the pressurized slurry to overcome the frictional resistance along the pipeline and be delivered into the downstream built-in fluidized bed rotary drum granulator 4. In this embodiment, the specific type of the high-pressure spray pump 7 includes a high-pressure gear pump, a positive displacement screw pump, or a high-pressure diaphragm pump. The setting parameter of the working pressure at the output end of the high-pressure spray pump 7 has a clear boundary judgment basis. This working pressure value must be greater than the superposition value of the total frictional resistance loss along the pipeline and the design critical back pressure required by the tail-end atomizing nozzle, ensuring that the liquid slurry has the atomization kinetic energy to be converted into fine droplets and sufficient dispersion and penetration force within the built-in fluidized bed rotary drum granulator 4.

[0060] The seed crystal feeding system receives solid materials returned from the downstream of the system, and temporarily stores, quantitatively weighs, and vertically conveys them as physical feedstock for subsequent granulation processes. In this embodiment, the seed crystal feeding system mainly includes a seed crystal buffer bin 1, a seed crystal belt scale 2, and a seed crystal bucket elevator 3. The implementation method of the seed crystal feeding system and process settings includes the following steps:

[0061] S201, the small and medium-sized particles produced by the 14-stage compound vibrating screen in the latter part of the system are transported through the first return pipeline and fall into the seed buffer bin 1. The seed buffer bin 1 adopts an inverted conical structure with a tapered bottom to facilitate the downward flow of solid particles under their own gravity. Since residual free water usually adheres to the surface of compound fertilizer materials, they are easily affected by ambient humidity in a static temporary storage state, resulting in liquid bridging and solidification, which leads to material agglomeration. This change often causes physical bridging and arching at the tapered bottom of the bin. To break this unintended adhesion, a bin wall vibrator is installed on the outer wall of the conical part of the seed buffer bin 1, or a mechanical arch-breaking device is installed inside. The triggering mechanism of this device is not based on simple timing control, but on the flow monitoring feedback below the discharge port. When the discharge flow rate is lower than the preset warning threshold of the process, the system control logic triggers the bin wall vibrator to vibrate at high frequency, breaking the static friction and internal adhesion between materials, ensuring that small and medium-sized particles are continuously discharged from the bottom discharge port of the seed buffer bin 1 to the downstream equipment.

[0062] Please see the appendix Figure 4 In step S202, based on the continuous discharge requirement of the bottom material, small and medium-sized particles discharged from the seed buffer bin 1 fall onto the carrying belt of the seed belt scale 2 for dynamic quantitative measurement. The seed belt scale 2 is equipped with a weighing sensor and a speed sensor. The material moves horizontally forward with the belt, and the weighing sensor collects the linear load of the material per unit length of the belt in real time, while the speed sensor simultaneously collects the instantaneous running linear velocity of the belt. For the synchronous processing of the above multi-sensor data, the control unit has preset time delay compensation logic. Due to the spatial longitudinal distance between the speed measuring roller and the weighing roller in the physical structure, the system performs delay compensation calculation by extracting the current running speed of the belt to ensure that the linear load and linear velocity of the material participating in the calculation at the same moment correspond to the material state of the same physical cross section. Based on the aligned synchronous working condition data, the control unit calculates the instantaneous input mass flow rate as the product of the linear load of the material per unit length of the belt detected by the weighing sensor and the instantaneous running linear velocity of the belt detected by the speed sensor. The purpose of this dynamic weighing calculation process is to provide accurate data support for the solid-liquid ratio in the front-end granulator.

[0063] In actual operation control, the system incorporates PID control logic to compare the calculated instantaneous input mass flow rate with the target flow rate set by the process. When a deviation exists, the system adjusts the variable frequency motor to change the instantaneous linear speed of the belt, thereby dynamically correcting the feed rate. Considering the extreme anomalies in speed parameters under shutdown or physical jamming conditions, a zero-approach protection mechanism is added to the algorithm's judgment logic for the instantaneous linear speed of the belt. When the instantaneous linear speed of the belt approaches zero or falls below the set minimum safety threshold, the adjustment logic involving speed variables as denominators or factors in the system will automatically cut off, switching to fixed-frequency operation or directly triggering a shutdown alarm. The determination of the aforementioned minimum safety threshold is based on the low-frequency heat dissipation limit of the variable frequency motor and the minimum resolution blind zone of the speed sensor. By setting this control lower limit threshold, feed loss control caused by controller calculation overflow or control command divergence is avoided.

[0064] S203, the material that has completed quantitative weighing and measurement leaves the end discharge area of ​​the seed belt scale 2 and slides along the chute into the bottom feed inlet of the seed bucket elevator 3. The seed bucket elevator 3 is equipped with an annular traction component and buckets evenly distributed on the traction component. After the buckets receive the material in the bottom feed area, the motor drives the traction component to overcome the material's own gravity and vertically lift it. The material is lifted to the top discharge end, and with the physical reversal of the traction component, the material leaves the bucket under the combined action of centrifugal force and gravity, and continuously slides down through the discharge chute into the solid feed inlet of the built-in fluidized bed rotary drum granulator 4.

[0065] For the backstop and tensioning device installed on the seed bucket elevator 3, those skilled in the art can conventionally select and match them based on the vertical conveying height and the total load of the equipment. The specific anti-reverse and belt anti-slip mechanical principles are well-known technologies in the field and will not be elaborated here. To ensure the matching of the overall system's material throughput capacity, the upper limit threshold of the rated vertical conveying capacity of the seed bucket elevator 3 is set to 1.2 to 1.5 times the maximum full-load flow rate of the seed belt scale 2. The determination of this redundancy range is based on absorbing the transient material peaks at the initial stage of system startup. Through the mechanical coordination of constant traction speed and standard bucket volume, the continuity and uniformity of the material flow rate after being metered by the seed belt scale 2 are maintained, preventing instantaneous accumulation of solid seeds when entering the built-in fluidized bed rotary drum granulator 4.

[0066] The granulation system, acting as a hub connecting the upstream slurry preparation and feeding processes, enables the three-phase physical interaction and thermal solidification of liquid slurry, solid seed crystals, and gaseous hot air. In this embodiment, the main equipment of the granulation system is a built-in fluidized bed rotary drum granulator 4. The implementation method of the granulation process and equipment setup includes the following steps:

[0067] The S301, a built-in fluidized bed drum granulator 4, consists of a rotatable cylindrical drum and a fixed fluidized bed air distribution plate arranged at its inner bottom. The inner wall of the drum is equipped with longitudinally extending lifting plate structures. When the drum is driven by an external motor for continuous rotation, the lifting plates lift the solid seed material fed by the seed bucket elevator 3 to a specific geometric height and then scatter it, forming a cross-sectional material curtain inside the drum. Simultaneously, multiple sets of atomizing nozzles are evenly distributed on the pipeline extending from the high-pressure spray pump 7 into the granulator. The spray cone angle and physical spacing of the atomizing nozzles need to be matched in an array according to the geometry of the material curtain. The purpose of this spatial arrangement design is to ensure that the atomized liquid droplets can uniformly cover the falling solid particle group, preventing localized areas from becoming oversaturated due to slurry overload, which could lead to bed collapse or dead-angle agglomeration. For the support roller structure and large gear ring transmission assembly of the drum body, those skilled in the art can perform conventional mechanical design based on the total load of the equipment. The support and transmission principles are well-known technologies in this field and will not be elaborated here.

[0068] In S302, the high-pressure liquid slurry is broken into fine droplets at the nozzle outlet due to the surface tension of the fluid. These droplets impact and adhere to the tumbling seed crystal surface, where the surface tension and liquid bridging force bind multiple fine particles together, creating an agglomeration effect, or they spread across the surface of a single larger particle, forming a coating layer. To accelerate the evaporation of free water in the liquid slurry and promote the crystallization and solidification of soluble salts, a thermal network is introduced to provide heat input. High-temperature, constant-pressure hot air, forced in by blower 12, passes through the fluidized bed air distribution plate at the bottom of the drum, uniformly penetrating the moving material layer from bottom to top.

[0069] In S303, based on the balance between the penetrating drag of the airflow and the weight of the material itself, the material layer forms a fluidized state above the air distribution plate. This fluidization feature expands the effective heat transfer area between the gas and solid phases, accelerates heat and mass exchange at the gas-solid interface, and avoids large-area adhesion of high-moisture materials on the inner wall of the cylinder. For this granulation process, the process control logic needs to establish a reliable data benchmark. The system mass transfer must satisfy the mass balance relationship, and its dynamic mass conservation equation for the granulation section is:

[0070] ;

[0071] In the formula, This indicates the total mass flow rate of the wet material; This indicates the mass flow rate of small and medium-sized particle seed crystals. Indicates the mass flow rate of the liquid slurry; This represents the mass flow rate of moisture removed by evaporation. The purpose of this calculation is to guide the parameter setting and dynamic adjustment of upstream and downstream material throughput.

[0072] To maintain a steady-state distribution of the particle size range in the granulation output and prevent agglomeration or a decrease in pelletizing rate within the equipment, feedback control parameters are introduced into the process control logic. The return ratio formula is:

[0073] ;

[0074] In the formula, This indicates the instantaneous return ratio.

[0075] Considering extreme unsteady-state conditions such as equipment start-up, shutdown, or severe material blockage, the denominator... It may approach 0 infinitely; therefore, the system's measurement and control logic has added division-to-zero protection logic for the division operation of this formula. Once measured... If the material feed rate falls below the sensor's minimum resolution threshold, the system will automatically lock the frequency converter feeding command to prevent internal division by zero errors from causing the arithmetic unit to malfunction. Under normal continuous production conditions, the instantaneous return ratio... The target threshold is typically set within the range of 2.0 to 4.0. This range is determined based on the critical liquid phase quantity required for compound fertilizer pelleting.

[0076] When the instantaneous return ratio is below 2.0, it indicates that the liquid phase ratio in the system is too high, posing a risk of wall adhesion; when it is above 4.0, it indicates an excess of solid carrier and low pelletizing efficiency. In actual control, the system is adjusted based on multivariable parameters. When the ambient humidity is too high or the slurry moisture content is too high, the system will increase the frequency converter speed. By increasing the instantaneous return ratio, excess moisture is absorbed and dispersed using the physical sensible heat of the solid seed crystals. This combined regulation mechanism based on material properties and environmental conditions maintains the stability of the pelleting environment.

[0077] S304, the wet material that has completed particle size growth and crystallization solidification overflows from the tail discharge port of the built-in fluidized bed rotary drum granulator 4 under the combined drive of the drum installation angle and material flowability, and falls onto the screening feed belt conveyor 13 to be transferred to the downstream screening system. The dust-laden high-temperature exhaust gas generated during the granulation heat exchange process is collected and drawn out under the micro negative pressure gradient established by the external induced draft fan 9. The specific control of this micro negative pressure state is achieved by installing a micro differential pressure transmitter on the inner wall of the granulator cylinder. When the absolute value of the internal negative pressure is detected to be too low, the system closed loop increases the frequency of the variable frequency operation of the induced draft fan 9 or opens the damper to establish a dynamic micro negative pressure range to prevent dust particles from escaping to the external environment of the workshop.

[0078] The dust collection system provides heat and aerodynamic input for the fluidization and evaporation processes in continuous manufacturing, while also handling gas-solid separation and emission control of the exhaust gas. In this embodiment, the dust collection system mainly includes a heat exchanger 11, a blower 12, a bag filter 8, an induced draft fan 9, and a gas exhaust tank 10. The implementation method of the dust collection system and process setup includes the following steps:

[0079] S401, an external steam pipeline connects to heat exchanger 11, and ambient cold air simultaneously enters the cold side channel of heat exchanger 11. Inside heat exchanger 11, the cold air undergoes indirect physical heat exchange with the high-temperature steam and its temperature rises. Heat exchanger 11 adopts a steel-aluminum composite finned tube structure, utilizing externally extended fins to expand the effective heat transfer area on the gas phase side, overcoming the defect of high thermal resistance in the gas boundary layer. Blower 12 forces heated, constant-temperature hot air through the main air duct into the bottom air inlet area of ​​the built-in fluidized bed rotary drum granulator 4, providing latent heat of vaporization for the granulation process. Based on the law of conservation of energy, the heat flow absorbed by the main air during the heat exchange process is equivalent to the product of the main air mass flow rate, the air's specific heat capacity at constant pressure, and the temperature difference between the hot and cold air before and after heating. The purpose of this heat calculation process is to guide the opening control of the front-end steam regulating valve.

[0080] In actual production conditions, the target threshold for the heated air temperature is limited to the range of 90℃ to 120℃. This parameter range is determined based on the physicochemical properties of compound fertilizer: the lower threshold of 90℃ is used to ensure the provision of a heat transfer temperature difference driving force to accelerate the evaporation of moisture in the slurry; the upper threshold of 120℃ is to avoid the urea-like substances at the bottom of the granulator from undergoing secondary melting or thermal degradation into biuretization due to excessively high hot air temperature.

[0081] Please see the appendix Figure 6 In S402, the hot air blown in penetrates the material layer, carrying free moisture and dust, forming granulation exhaust gas. The top exhaust port of the built-in fluidized bed rotary drum granulator 4 is connected to the dust-laden gas inlet of the bag filter 8. To meet the exhaust and anti-escape requirements of the aforementioned granulation section, at the end of the system, an induced draft fan 9 draws in air through a pipeline, establishing a decreasing negative pressure gradient along the airflow direction in the entire pneumatic network. A micro differential pressure transmitter is installed on the upper part of the granulator cylinder to monitor the static pressure inside the cylinder in real time. The system sets the target range of micro negative pressure inside the granulator to -150Pa to -50Pa. When the monitored pressure is higher than -50Pa, it indicates that the system is tending to be in a positive pressure state, and there is a risk that dust-containing exhaust gas will escape from the inlet and outlet. The control unit interlocks to increase the frequency of the induced draft fan 9 to increase the exhaust volume. When the monitored pressure is lower than -150Pa, the excessive suction force not only increases the energy consumption of the motor, but also easily causes the fine crystals that have not been granulated to be extracted as dust from the system. At this time, the control unit reduces the frequency of the induced draft fan 9.

[0082] Because a single pressure measuring port is easily clogged in a dusty environment, leading to pressure data drift, the system incorporates the instantaneous operating current of the induced draft fan 9 motor as an auxiliary judgment condition in the exhaust regulation program to address this interference. The control unit synchronously compares the static pressure sequence data collected by the micro differential pressure transmitter with the instantaneous motor current data according to the sampling period. When the compared differential pressure data is within the normal range, but the instantaneous operating current of the induced draft fan 9 drops sharply by more than 20% of the rated current, the system determines that there is a false blockage in the pipeline network based on the positive correlation between the flow rate and power of the centrifugal fan. This multi-condition joint diagnostic logic avoids the induced draft fan surge or pipeline negative pressure loss caused by the measurement and control system relying solely on a single static pressure parameter for one-sided judgment.

[0083] S403, the collected dust-laden exhaust gas is sent into the bag filter 8 through the inlet. Within the structural cavity of the bag filter 8, the sudden expansion of the airflow cross-section causes a decrease in velocity, and large dust particles fall into the bottom ash hopper due to gravity. As the remaining fine dust particles penetrate the filter bag fibers with the airflow, the solid phase dust is trapped on the outer surface of the filter bag due to the combined effect of inertial collision and interception of the dust particles, while the gaseous exhaust gas enters the clean air chamber.

[0084] The bag filter 8 is equipped with a pulse jet cleaning device. Based on the pressure difference feedback data before and after the filter bag, the control system triggers the electromagnetic pulse valve to release high-pressure compressed air. The high-pressure airflow is instantaneously introduced into the filter bag, causing it to expand and vibrate. The dislodged dust falls into the bottom ash hopper and is periodically discharged by the ash discharge valve. In this embodiment, the system control unit sets the upper and lower limit pressure difference thresholds for pulse triggering to 1000 Pa and 1500 Pa, respectively. The determination of this parameter range is based on the balance of gas-solid separation resistance: when the pressure difference between the inside and outside of the filter bag is less than 1000 Pa, initiating pulse cleaning will damage the initial dust layer on the surface of the filter bag, reducing the interception efficiency of fine dust and wasting compressed air; while when the pressure difference is greater than 1500 Pa, the total aerodynamic resistance of the system is too high, easily inducing the operating point of the induced draft fan 9 to deviate from the stable range. Regarding the selection of filter material for the bag filter 8, the specific mechanical structure of the pulse solenoid valve, and its electrical wiring method, those skilled in the art can perform conventional engineering matching design based on the temperature and humidity parameters of the specific exhaust gas and the original dust concentration. The relevant technical content belongs to the well-known technology in this field and will not be elaborated here.

[0085] S404, the clean gas, after gas-solid separation treatment, is drawn out from the clean gas exhaust port of the bag filter 8 and enters the air inlet of the induced draft fan 9. After the impeller of the induced draft fan 9 rotates and pressurizes the clean gas, it is delivered to the gas venting tank 10. The venting tank 10 has a physical noise reduction and buffer expansion structure. It reduces the flow velocity at the air outlet by abruptly changing the cross-sectional area, and finally allows the cooled and noise-reduced clean gas to be discharged into the external atmosphere.

[0086] The screening and return system establishes a classification and multi-directional closed-loop return path for the granulated material, enabling a circulation of quality transfer within the system. In this embodiment, the screening and return system mainly includes a screening feed belt conveyor 13 and a double-layer vibrating screen 14. The implementation method of the screening and return system and process settings includes the following steps:

[0087] S501, the wet material discharged from the built-in fluidized bed rotary drum granulator 4 has a trace amount of free water on its surface, and this material falls onto the bearing surface of the screening feed belt conveyor 13. Considering that high-moisture materials are prone to surface adhesion during transportation, leading to wear on the non-working surface of the belt and spillage on the return trip, a polyurethane scraper cleaner is installed below the discharge roller at the head of the screening feed belt conveyor 13. This cleaner maintains a constant contact pressure with the belt surface through a mechanical spring, forcibly scraping off the residual adhered powder and guiding it to the feed end of the compound vibrating screen 14, thereby maintaining the continuity of material flow on the conveying route.

[0088] S502, the material is fed into the inlet of the compound vibrating screen 14 from the end of the conveyor belt. The compound vibrating screen 14 has a first layer of large-aperture screens and a second layer of small-aperture screens arranged vertically from top to bottom. A motor drives an eccentric weight to rotate, generating a high-frequency excitation force that causes the material to form a diffusion trajectory on the inclined screen surface. Due to the geometric differences in particle size, the material undergoes probabilistic screening and mechanical separation during its movement. The selection of damping springs and the adjustment mechanism of the eccentric weight angle for the compound vibrating screen 14 can be calculated using conventional engineering methods based on the expected excitation force amplitude. The related transmission design is well-known in the field and will not be elaborated upon here.

[0089] Please see the appendix Figure 5 In S503, after screening by the double-vibrating screen 14, the material group is cut into three independently flowing graded products. Based on continuous steady-state production conditions, the mass flow calculation of the screening node satisfies the law of conservation of mass. The total mass flow rate of the wet material entering the screen is equal to the sum of the mass flow rate of qualified particles that pass through the upper screen and are intercepted by the lower screen, the mass flow rate of small and medium-sized particles that pass through both screens and fall into the chassis, and the mass flow rate of oversized particles that cannot pass through the upper screen and are intercepted. The purpose of this flow calculation is to quantitatively evaluate the pelletizing efficiency of the front-end granulation process.

[0090] S504, to guide the dynamic closed-loop adjustment of the front-end operating conditions, establishes feedback calculation logic within the system control unit for non-conforming materials. The system calculates the total return rate parameter in real time:

[0091] ;

[0092] In the formula, Indicates the instantaneous total return rate; This represents the mass flow rate of small and medium-sized particles that penetrate two layers of screens and fall into the chassis. This indicates the mass flow rate of ultra-large particles that cannot penetrate the upper screen and are trapped. This indicates the total mass flow rate of the wet material.

[0093] During the start-up, no-load, or batch change cleaning phase of chemical equipment, the flow rate input to the screening system may experience extreme fluctuations. To address this unsteady-state condition, the control unit's internal calculation program incorporates division-by-zero protection logic. When the zero-divide-off logic is detected (as part of the denominator), the logic will prevent such fluctuations. When the value is below the zero-point dead zone threshold set by the system, the control program directly suspends the division operation instruction of the total return rate to avoid the microprocessor causing an error due to division by zero.

[0094] Under normal load operation, high humidity can easily cause localized clogging of the screen mesh, leading to a decrease in screening efficiency. Therefore, the system incorporates the active power parameters of the screening machine motor for synchronous comparison in the return rate determination logic. When the calculated total return rate... When the instantaneous high value is detected, and the synchronously acquired motor active power decreases by more than 15% of the rated value, the system determines, based on the motor load characteristics, that the anomaly is not due to a deterioration in the granulation process, but rather to screen pore blockage causing the material to lose effective excitation and throwing. This logic based on multi-variable joint judgment avoids one-sided misjudgments that rely solely on a single flow direction quality extreme value.

[0095] After ruling out hardware blockage faults, the actual deterioration of ball-forming efficiency and instantaneous total repatriation rate are considered. The upper limit of operation is constrained to within 30%. This threshold is determined based on the design limits of the overall system's heat load and increased transport capacity. When the flow rate exceeds 30% continuously, the system triggers the frequency reduction action of the front-end high-pressure spray pump 7 to reduce the liquid phase injection volume.

[0096] S505, the three streams of material that have completed physical classification enter their respective directional flow pipelines. The portion of the flow consisting of oversized particles is led out through the second return pipeline. Because the particle size of this portion of material is too large, directly using it as seed material would disrupt the fluidization state of the bed. Therefore, a double-roll crusher is connected in series downstream of this second return pipeline. Based on the principle of mechanical extrusion crushing, the double-roll crusher crushes and downgrades the oversized particles before sending them back to the front-end feeding section to participate in melting and pulping again. The portion of small and medium-sized particles serving as seed material flows directionally back to the seed buffer silo 1 through the first return pipeline, forming an internal closed loop of solid phase material circulation. The portion of qualified particles that meet the particle size specifications of the compound fertilizer finished product is discharged from the middle discharge port of the compound vibrating screen 14, awaiting entry into the cooling output system for shaping.

[0097] The cooling output system performs heat removal and shaping tasks for qualified high-temperature materials, establishing an anti-caking treatment path for the materials before they enter the final packaging. In this embodiment, the cooling output system mainly includes a bucket elevator 15, a tubular cooler 16, a booster fan 17, and a finished product conveyor belt 18. The implementation method of the cooling output system and process settings includes the following steps:

[0098] S601, the qualified granules produced by the double-layer vibrating screen 14 retain the latent heat released during the granulation phase change process and the sensible heat transferred by the external hot air. This high-temperature material is discharged from the middle discharge port and enters the bottom receiving area of ​​the bucket elevator 15. The bucket elevator 15, driven by a motor, uses a ring traction belt and buckets to overcome the gravity difference and vertically lift the high-temperature qualified granules to a high position in the process plant, and continuously guides them from the discharge port to the feed end of the tubular cooler 16. For the selection of the drive unit and the matching design of the bucket geometry of the bucket elevator 15, those skilled in the art can perform conventional calculations based on the preset rated capacity of the production line. Its mechanical transmission and vertical conveying principles are well-known technologies in the field and will not be elaborated here.

[0099] S602, to achieve material cooling and surface dehumidification, a gas-liquid two-phase cold source loop is set up inside the system. The cold water inlet and outlet of the tubular cooler 16 are respectively connected to the external cooling water circulation network, forming a liquid phase cooling medium channel. Before connecting to the heat exchanger 11, the main air outlet of the blower 12 leads out a bypass branch, which draws ambient temperature air and connects to the air inlet of the booster fan 17. Due to the fluid resistance of the material accumulation layer inside the tubular cooler 16, the booster fan 17 pressurizes the ambient temperature air and forces the pressurized cold air into the cooling air inlet of the tubular cooler 16, forming a gas phase cooling medium channel.

[0100] Please see the appendix Figure 7 In the tube cooler 16 (S603), high-temperature materials undergo gas-liquid-solid multiphase heat exchange with cold water and cold air. The tube cooler 16 adopts a rotary tube structure with a shell-side water-cooled jacket and an internal airflow distribution pipe. During the tumbling movement of the rotating drum, the high-temperature material transfers heat to the counter-current cooling water in the jacket through heat conduction through the tube wall. At the same time, pressurized cold air penetrates the material layer, removes the sensible heat of the material through gas-solid convection heat exchange, and carries away the residual water vapor on its surface through the exhaust port.

[0101] Based on the law of energy conservation in a three-phase countercurrent and cross-flow heat exchange system involving solid, liquid, and gas, the heat balance principle inside the tubular cooler 16 is: the total sensible heat released before and after qualified particles are discharged from the cooler is equal to the sum of the heat absorbed by the circulating cooling water entering and exiting the pipe network and the heat absorbed by the pressurized cold air entering and exiting the cooler. The purpose of this thermodynamic conversion mechanism is to establish a cold source flow feedback regulation mechanism based on the target discharge temperature. In actual production conditions, the upper limit threshold of the target temperature after qualified particles are discharged from the cooler is usually set at 40℃. This threshold is determined based on the phase transition critical point of the salt crystals inside the compound fertilizer. When the discharge temperature is higher than 40℃, the material is prone to caking due to crystal bridges caused by continued crystal precipitation during subsequent static stacking. The control unit collects the discharge temperature in real time through a temperature probe. When the temperature approaches the upper limit threshold, the system calculates the amount of cooling required to be compensated based on the above heat exchange balance mechanism and adjusts the variable frequency water pump to increase the mass flow rate of the circulating cooling water.

[0102] In the feedforward control logic that calculates the required increase in cooling water based on the aforementioned temperature difference heat transfer mechanism, there is a division operation instruction with the inlet and outlet temperature difference of the cooling water as the denominator. When the system is in the start-up water injection stage or under extremely low load, the cooling water has not yet undergone effective heat transfer, and the inlet and outlet temperature difference may approach 0 infinitely. To address this physical boundary condition, a temperature difference dead zone protection logic has been added to the control logic. When the sensor resolution dead zone of less than 1.0℃ is detected for the inlet and outlet water temperature difference, the system directly suspends the variable frequency control instruction generated based on the temperature difference, forcibly locking the operating frequency of the chilled water circulation pump to the current fixed frequency state, avoiding control instruction errors caused by division by zero. This fault-tolerant mechanism, derived from operating condition synchronization, ensures the continuity of the liquid phase cold source supply.

[0103] Since relying solely on the discharge temperature cannot comprehensively assess the physical dehumidification and shaping quality of compound fertilizer, an additional evaluation parameter for gas-phase dehumidification capacity is introduced into the system's measurement and control logic. Temperature and humidity sensors are installed in the air inlet duct of the tubular cooler 16. When the relative humidity of the pressurized cold air exceeds 80%, it indicates that the current climate is in a high-humidity state, and the latent heat of vaporization of the cold air carrying away moisture is approaching its physical limit. Under this combined operating condition, even if the discharge temperature meets the standard, the control unit will still trigger a linkage adjustment logic: appropriately reducing the air inlet damper of the booster fan 17 to decrease the mass flow rate of the pressurized cold air, while simultaneously increasing the mass flow rate of the circulating cooling water by an equal amount according to the heat exchange balance mechanism to compensate for heat loss. This linkage adjustment based on environmental correlation avoids the high-humidity cold air reaching the dew point inside the cooler, thus preventing secondary moisture return to the surface of the compound fertilizer.

[0104] S604, the finished compound fertilizer granules, after cooling, dehumidification, and solidification, are discharged from the discharge box at the end of the tubular cooler 16 and slide down onto the bearing belt surface of the finished product conveyor 18 by gravity. The finished product conveyor 18 transfers them to the downstream finished product packaging buffer silo. The solid raw materials undergo melting and pulping, feeding, granulation, screening, and cooling and solidification to finally complete the continuous conversion manufacturing process.

[0105] Specific application examples:

[0106] To further illustrate the implementation effect of the present invention, this embodiment takes a urea-based nitrogen, phosphorus and potassium (N-P2O5-K2O ratio of 15-15-15) compound fertilizer production line with a nominal annual production capacity of 100,000 tons as an example to explain in detail the actual operating parameters of the system, the control process and the application of the measurement and control model.

[0107] Slurry preparation stage (S101-S103): Monoammonium phosphate, ammonium chloride, urea, and potassium chloride are fed into melting tank 5 according to the formula ratio. The control unit sets the target eutectic temperature to 115℃ (higher than the multi-component eutectic point, but lower than the pure phase melting point of urea at 132℃ and the temperature at which biuretization occurs violently). The slurry flows into buffer tank 6, and the level gauge is set with a safety control lower limit threshold of 20% and an upper limit threshold of 85%. The working pressure of high-pressure spray pump 7 is set to 1.5MPa to overcome pipe resistance and ensure a critical back pressure of not less than 0.8MPa at the atomizing nozzle.

[0108] Seed crystal feeding and granulation stage (S201-S304): During the initial system startup, the seed crystal belt scale 2 feeds the crystals using a variable frequency drive according to the set initial target flow rate. Inside the granulator 4, the temperature of the hot air blown in by the blower 12 is strictly controlled at 105℃. During continuous granulation, macroscopic mass transfer follows the dynamic mass conservation equation of the granulation section:

[0109] ;

[0110] This guides the parameter settings for upstream and downstream material throughput. The system's measurement and control unit collects the total output of wet materials in real time. With seed crystal feed rate And according to the return ratio formula:

[0111] ;

[0112] Calculate the instantaneous return ratio During the stable operation phase, the system maintains the target return ratio at 2.8. After 4 hours of operation, the micro differential pressure transmitter detected that the static pressure inside the granulator fluctuated to -30Pa (approaching the risk of positive pressure leakage). The control unit synchronously compared the motor current of the induced draft fan 9. After confirming that there was no pipeline blockage, the frequency of the induced draft fan 9 was immediately increased from 35Hz to 42Hz, and the static pressure was brought back to the set range of -90Pa within 30 seconds.

[0113] Screening and anomaly handling phase (S501-S505): During the 6th hour of operation, a temporary deterioration in the pelletizing rate occurred due to instantaneous pressure fluctuations in the front-end high-pressure pump. The control unit continuously monitors the mass flow rate of small and medium-sized particles that penetrate the two layers of screens and fall into the chassis. The intercepted mass flow rate of ultra-large particles and total mass flow rate of wet materials And substitute it into the system's total return rate parameter formula:

[0114] ;

[0115] The instantaneous total return rate was calculated. It surged to 32% (exceeding the 30% upper limit threshold). At this point, the denominator (total mass flow rate of wet material) The value was much larger than the zero-point dead zone, and the division-to-zero protection was not triggered. At the same time, the active power of the screening machine motor remained stable, ruling out the possibility of screen clogging. The system then determined that the actual granulation had deteriorated and triggered the high-pressure spray pump 7 to reduce the frequency by 2Hz to reduce the liquid phase injection volume. After 5 minutes, the total return rate returned to the normal range of 22%.

[0116] Cooling and Anti-Moisture Phase (S601-S604): During the 8th hour of operation, a sudden downpour occurred in the workshop. The temperature and humidity sensor at the air inlet duct of tubular cooler 16 recorded an ambient relative humidity of 88% (exceeding the 80% high humidity threshold). Although the discharge temperature was 38℃ (below the 40℃ upper limit), the control unit, based on the linkage adjustment logic, proactively reduced the opening of the air inlet damper of booster fan 17 from 100% to 60%, cutting off the input of excessive high-humidity air. Simultaneously, it activated the cold water circulation variable frequency pump, increasing the cooling water flow rate from 45m³ / h. 3 / h increased to 65m 3 Cooling compensation is performed at / h. The final moisture content of the finished product at the discharge port is 1.1%, effectively preventing secondary moisture re-dampening on the particle surface caused by high-humidity cold air.

[0117] Experimental verification and effect comparison:

[0118] To verify the superiority of the multi-source synchronous comparison and linkage adjustment process proposed in this invention, a 30-day continuous comparative verification test was conducted in the same factory area.

[0119] Experimental group (example): The built-in fluidized bed rotary drum granulation equipment and the complete set of dynamic linkage adjustment process of the present invention were used.

[0120] Control group (comparative example): The traditional built-in fluidized bed granulation equipment was used. Its feeding, air network dust removal and cooling systems all adopted traditional single-loop fixed frequency control (no dynamic closed loop for return ratio, no differential pressure, no current synchronization to prevent misjudgment logic, and no humidity-weighted cooling compensation logic).

[0121] The experiment included various typical climatic conditions such as sunny days, cloudy and rainy days with high humidity. The key comparative data and accompanying figures are explained below:

[0122] Comparison of ball formation pass rate and system stability:

[0123] Please see the appendix Figure 8 In the appendix Figure 8 In the diagram, the horizontal axis at the bottom serves as the x-axis, with a scale of 1 to 12. It represents the continuous operating time of the equipment system, measured in hours (h), and characterizes the time progression of the system during long-term, continuous production operations. The vertical axis on the left serves as the y-axis, with a scale of 70 to 95. It represents the first-pass pelleting yield of the granulation process, measured as a percentage (%). This value directly reflects the efficiency of the granulation system in converting liquid slurry and solid seed crystals into finished particles within a set particle size range at the corresponding time point. Meanwhile, the light gray dashed lines running through the plot area are background grid lines, serving as auxiliary reading lines for data alignment, facilitating intuitive comparison of the specific numerical differences between two sets of data at the same time point.

[0124] Example (Invention): Benefiting from the aforementioned return ratio in the granulation stage Closed-loop regulation and total return rate The cross-limit cascading frequency reduction mechanism ensures that the spherical environment remains in a critical liquid phase equilibrium state. (See attached...) Figure 8 The solid black line marked with a solid square represents the actual trajectory of the pelletizing pass rate over time in this embodiment of the invention (i.e., the use of dynamic return material closed-loop, multi-source data to prevent misjudgment, and air-water linkage adjustment and other measurement and control processes). Visually, this line is located at the top of the chart and fluctuates very little, maintaining a high level of around 92% with a stable trend. Statistically, there were 0 unplanned downtimes within 30 days, and the average first-pass pelletizing pass rate remained stable at 92.6%. This fully demonstrates that the invention possesses extremely strong resistance to operating condition interference and system stability.

[0125] Comparative example (traditional process): Due to the lack of dynamic return ratio adjustment and screening error prevention logic, the system is prone to localized over-wetting and adhesion of the bed when encountering material fluctuations. (See attached...) Figure 8The black dashed line marked with a hollow circle represents the pelleting success rate trajectory of a traditional comparative system. Visually, this dashed line is located in the lower area of ​​the chart, and a significant precipitous drop (i.e., a deep downward trough) appears at the 5th and 10th hours (the location can be accurately read using the background grid lines). This indicates that the traditional system, encountering fluctuations in the upstream slurry or high external humidity, suffers from a lack of automatic compensation mechanisms, leading to a deterioration in pelleting conditions and a sudden drop in pelleting rate. Statistically, within 30 days, there were 5 unplanned shutdowns for cleaning due to severe clumping on the inner wall of the pelletizer or blockage of the fluidized bed air distribution plate, with an average first-time pelleting success rate of only 81.4%, and the data fluctuated significantly with the temperature difference between day and night shifts.

[0126] Comparison of finished product moisture content and anti-caking effect (samples were stored for 30 days under a pressure of 0.1 MPa and a relative humidity of 85%):

[0127] Comparative example (traditional process): Because the cooling system relies solely on the discharge temperature for control, under continuous rainy conditions, the high-humidity air drawn in reaches the dew point inside the cooler, causing the fertilizer surface to become damp. The average moisture content of the finished product reaches 2.5%, and after 30 days, the caking rate of the stacked bags is as high as 8.7% (with a large number of hard lumps with severe crystal bridge connections appearing).

[0128] Example (Invention): The air / water cooling capacity linkage distribution logic under high humidity environment was successfully triggered, completely cutting off the secondary introduction of vapor phase moisture. The average moisture content of the finished product was strictly controlled at 1.2%, and the caking rate of the stacked bags after 30 days was only 0.4% (with only a trace amount of loose false lumps that crumbled easily when touched), and the physical shaping quality of the product was significantly improved.

[0129] Summarize:

[0130] Combined with specific application examples and appendices Figure 8 The comparison between the solid and dashed lines intuitively demonstrates that the embodiments of this invention, by introducing multi-variable joint judgment based on engineering thermodynamics and fluid mechanics principles (such as differential pressure and current synchronous comparison), closed-loop mathematical measurement and control models (such as dynamic return ratio closed loop), and bypass fault tolerance mechanisms in each subsystem, successfully eliminated the problem of sudden drop in pelletizing rate caused by operating condition fluctuations in traditional processes, realized steady-state quality control of complex multiphase manufacturing processes, and effectively solved the technical bottlenecks of traditional equipment being prone to agglomeration, blockage, and poor environmental adaptability.

Claims

1. A device for producing nitrogen-based compound fertilizer using a built-in fluidized bed rotary drum, characterized in that, Including the system control unit, it also includes: The melting tank (5) is connected to the buffer tank (6), the buffer tank (6) is connected to the high-pressure spraying pump (7), and the high-pressure spraying pump (7) is connected to the built-in fluidized bed rotary drum granulator (4). The seed buffer (1) is connected to the seed belt scale (2), the seed belt scale (2) is connected to the seed bucket elevator (3), and the seed bucket elevator (3) is connected to the built-in fluidized bed rotary drum granulator (4). The heat exchanger (11) is connected to the blower (12), which is connected to the built-in fluidized bed rotary drum granulator (4) and the booster fan (17) respectively. The built-in fluidized bed rotary drum granulator (4) is connected to the bag filter (8), which is connected to the induced draft fan (9). The built-in fluidized bed rotary drum granulator (4) is connected to the compound rotary vibrating screen (14), and the small and medium particle discharge port of the compound rotary vibrating screen (14) is connected to the seed buffer bin (1). The ultra-large particle discharge port of the compound rotary vibrating screen (14) is connected to the front-end feeding section; The qualified particle outlet of the compound vibrating screen (14) is connected to the tubular cooler (16), the blower (12) is connected to the booster fan (17), the booster fan (17) is connected to the tubular cooler (16), and the tubular cooler (16) is connected to the external cooling water circulation network.

2. The equipment for producing nitrogen-based compound fertilizer with a built-in fluidized bed rotary drum according to claim 1, characterized in that, The output end of the induced draft fan (9) is connected to the gas venting tank (10). The discharge port of the built-in fluidized bed rotary drum granulator (4) is connected to the feed end of the compound vibrating screen (14) via a screening feed belt conveyor (13); The qualified particle discharge port of the compound rotary vibrating screen (14) is connected to the feed end of the bucket elevator (15), and the discharge end of the bucket elevator (15) is connected to the feed end of the tubular cooler (16). The outlet of the tubular cooler (16) is connected to the finished product conveyor belt (18).

3. The device for producing nitrogen-based compound fertilizer with a built-in fluidized bed rotary drum according to claim 1, characterized in that, The buffer tank (6) is equipped with a level gauge, which monitors the slurry level in real time. When the level gauge detects that the slurry level reaches or falls below the set lower limit threshold, the system control unit triggers protection logic to limit or suspend the operation of downstream equipment. When the liquid level reaches or exceeds the upper limit threshold, the system control unit adjusts the front-end feeding rate in an interlocking manner.

4. The equipment for producing nitrogen-based compound fertilizer with a built-in fluidized bed rotary drum according to claim 1, characterized in that, The seed belt scale (2) is equipped with a weighing sensor and a speed sensor. The system control unit performs delay compensation calculation by extracting the current running speed of the carrying belt of the seed belt scale (2). The system control unit calculates that the instantaneous input mass flow rate is the product of the linear load of the material per unit length of the belt detected by the weighing sensor and the instantaneous running linear speed of the belt detected by the speed sensor. When the instantaneous linear speed of the belt approaches zero or falls below the set minimum safety threshold, the adjustment logic in the system control unit involving speed variables as denominators or factors will be automatically cut off, switching to fixed-frequency operation or directly triggering a shutdown alarm.

5. The device for producing nitrogen-based compound fertilizer with a built-in fluidized bed rotary drum according to claim 1, characterized in that, The built-in fluidized bed drum granulator (4) is composed of a rotatable cylindrical drum and a fixed fluidized bed air distribution plate arranged at the bottom of the inside of the cylindrical drum. The inner wall of the cylindrical drum is provided with a longitudinally extending lifting plate structure. The high-pressure spray pump (7) extends into the pipeline inside the built-in fluidized bed drum granulator (4) and is evenly distributed with multiple sets of atomizing nozzles.

6. The device for producing nitrogen compound fertilizer with a built-in fluidized bed rotary drum according to claim 1, characterized in that, The built-in fluidized bed rotary drum granulator (4) is equipped with a micro differential pressure transmitter on the upper part of the cylinder. The system control unit synchronously compares the static pressure sequence data collected by the micro differential pressure transmitter with the instantaneous motor current data of the induced draft fan (9) according to the sampling period. When the differential pressure data after comparison is in the normal range, but the instantaneous operating current of the induced draft fan (9) drops sharply by more than 20% of the rated current, the system control unit determines that there is an abnormal blockage in the pipeline network and outputs the corresponding anti-false alarm intervention command.

7. The device for producing nitrogen-based compound fertilizer with a built-in fluidized bed rotary drum according to claim 1, characterized in that, The bag filter (8) is equipped with a pulse jet cleaning device. The system control unit triggers the electromagnetic pulse valve of the pulse jet cleaning device to release high-pressure compressed air based on the pressure difference feedback data before and after the filter bag of the bag filter (8).

8. The device for producing nitrogen-based compound fertilizer with a built-in fluidized bed rotary drum according to claim 1, characterized in that, The system control unit calculates the total return rate parameter in real time. The system control unit introduces the active power parameter of the screen motor of the compound rotary vibrating screen (14) into the return rate determination logic for synchronous comparison. When the calculated total return rate is instantaneously too high and the synchronously obtained motor active power drops by more than 15% of the rated value, the system control unit determines that the screen of the compound rotary vibrating screen (14) is clogged and triggers the screen cleaning alarm signal.

9. The equipment for producing nitrogen-based compound fertilizer with a built-in fluidized bed rotary drum according to claim 1, characterized in that, The air inlet duct of the tubular cooler (16) is equipped with a temperature and humidity sensor. When the relative humidity of the pressurized cold air is greater than 80%, the system control unit triggers the linkage adjustment logic: The air inlet damper of the booster fan (17) is appropriately reduced to decrease the mass flow rate of the boosted cold air, while the mass flow rate of the circulating cooling water is increased to compensate for heat according to the heat exchange balance mechanism.

10. A process for producing nitrogen-based compound fertilizer using a built-in fluidized bed rotary drum, characterized in that, An apparatus for producing nitrogen-based compound fertilizer using a built-in fluidized bed rotary drum, as described in any one of claims 1-9, comprises the following steps: Solid raw materials enter the melting tank (5) and are heated to melt and form a liquid slurry. The slurry flows into the buffer tank (6) for pressure stabilization and temporary storage of liquid level. The high-pressure spray pump (7) pressurizes the slurry in the buffer tank (6) and pumps it into the built-in fluidized bed rotary drum granulator (4). The small and medium-sized particles returned from the latter section enter the seed buffer bin (1) as the bottom seed crystals. The seed belt scale (2) feeds the small and medium-sized particles quantitatively. The quantitative material is then lifted by the seed bucket elevator (3) into the built-in fluidized bed rotary drum granulator (4). The external cold air absorbs steam heat in the heat exchanger (11) and heats up. The blower (12) forces the hot air into the bottom of the built-in fluidized bed rotary drum granulator (4). High pressure slurry is atomized and sprayed onto the surface of the seed crystals through nozzles inside the built-in fluidized bed rotary drum granulator (4). Hot airflow penetrates the material layer upwards, causing the material to form a fluidized state. The surface slurry loses moisture and solidifies, thus increasing the particle size. The waste gas generated during granulation is drawn out by the induced draft fan (9) and enters the bag filter (8) for gas-solid separation treatment. The clean gas after the dust is separated and intercepted is discharged by the induced draft fan (9) and discharged to the external environment. The wet material discharged from granulation is transported to a double-vibrating screen (14) for particle size classification. The small and medium-sized particles produced by screening are transported back to the seed buffer (1) as return material, while the large particles are returned to the front-end process. Qualified particles that meet the particle size range standard are sent into the tubular cooler (16). The booster fan (17) pressurizes the cold air diverted from the blower (12) and sends it into the tubular cooler (16). The qualified particles exchange heat with the flowing cold air and circulating cooling water inside the tubular cooler (16) to cool down. The solidified finished fertilizer is discharged from the tubular cooler (16) and output.

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