A chemical fertilizer production system with a circulating crushing function and a circulating crushing method

Abstract

The application relates to the field of chemical fertilizer production, in particular to a chemical fertilizer production system with a circulating crushing function and a circulating crushing method. The system comprises, in sequence along a material conveying direction, an extrusion granulator, a pre-crusher, a primary crusher, a screening device and a secondary crusher, the screening device comprises coarse screening equipment and fine screening equipment, a sieve upper material outlet of the coarse screening equipment is communicated with a secondary crusher feeding port, a secondary crusher discharging port is communicated with a primary crusher feeding port to form a cross-stage closed loop circulation loop, and the system further comprises a corresponding circulating crushing method. The application can improve the material crushing efficiency and quality in chemical fertilizer production, make the product particle size more meet the requirements, reduce the generation of unqualified materials, realize the recycling of the materials, and reduce the production cost.

Description

Technical Field

[0001] This application relates to the field of fertilizer production equipment, and in particular to a fertilizer production system and method with a circulating crushing function. Background Technology

[0002] Extrusion granulation technology, due to its simple process, low energy consumption, and lack of the need for large amounts of binders, has become one of the mainstream processes for fertilizer (especially compound fertilizers and controlled-release fertilizers) granulation production. In a typical extrusion granulation fertilizer production line, the flaky or strip-shaped material produced by the extrusion granulator usually needs to undergo multi-stage crushing and screening to obtain semi-finished granules (2.0mm~4.75mm) that meet the particle size requirements before being sent to the subsequent coating process. Currently, the most common crushing and screening process in the industry is as follows: after the extrusion granulator discharges, the large flaky material is coarsely crushed into smaller particles by a pre-crusher, and then the material is sent to a primary crusher for further crushing via a conveying device. The crushed material is then sent to a screening device for grading and screening. After screening, the material that meets the target particle size range is used as a semi-finished product and enters the next process, while the large particles that do not meet the requirements are returned to the primary crusher for reprocessing by manual labor or a simple conveying device.

[0003] However, the above-mentioned existing technical routes still have the following technical problems in actual production: First, the unqualified large particles screened out by the coarse screen are usually returned directly to the inlet of the primary crusher for re-crushing by manual transfer or simple conveying device; Because primary crushers (such as impact crushers) are typically designed for high-impact crushing parameters of raw flaky materials, their crushing force is relatively too strong for oversize material that has reached a certain particle size but is not yet qualified. This results in the oversize material being over-crushed after returning to the primary crusher, producing a large amount of unusable fine powder (particle size less than 1.0 mm). This not only reduces the yield of particles in the target particle size range and increases the burden and energy consumption of fine powder recycling, but also exacerbates equipment wear. Secondly, existing technologies lack dedicated crushing methods for the targeted processing of oversize material from coarse screens. The oversize return path lacks a systematic design, and material is prone to conveying blockages and uneven return during the recycling process. This leads to large fluctuations in crusher load, affecting the stability of crushing efficiency and the continuous operation capability of the entire production line. In addition, existing systems often design crushing and screening in isolation, and coarse and fine screening are not effectively coordinated, resulting in a large amount of fine powder entrained in the semi-finished product, affecting the uniformity of subsequent coating processes and the quality of the finished product.

[0004] To address the shortcomings of existing technologies, there is an urgent need for a new fertilizer production system capable of selectively crushing the material on the coarse screen and reintegrating the crushed products into the crushing process in a closed-loop manner. This would effectively prevent over-crushing caused by mismatched crushing forces when the material is returned to the primary crusher, thereby improving the yield of particles in the target particle size range, reducing the fine powder generation rate, and ensuring the stable operation of subsequent processes. Simultaneously, it is desirable that the system's material circulation path enable automated recycling and re-crushing of unqualified materials from the screen, eliminating the need for manual transfer and thus reducing labor intensity and ensuring the continuous and stable operation of the production line. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, this application provides a fertilizer production system and a circulating crushing method with a circulating crushing function, which can realize selective secondary crushing and cross-stage closed-loop circulation of the material on the coarse screen, effectively avoid over-crushing, and improve the yield of particles in the target particle size range.

[0006] This application is achieved through the following technical solution: A fertilizer production system with a circulating crushing function includes an extrusion granulator, a pre-crusher, a primary crusher and a screening device arranged sequentially along the material conveying direction, and also includes a secondary crusher. The screening device includes a coarse screening device and a fine screening device. The coarse screening device is located downstream of the primary crusher, and the fine screening device is located downstream of the coarse screening device. The screen aperture of the coarse screening device is a first preset particle size, and the screen aperture of the fine screening device is a second preset particle size, wherein the first preset particle size is larger than the second preset particle size. The primary crusher uses impact crushing to crush the material, and the secondary crusher uses compression crushing to crush the material. The outlet of the coarse screening equipment is connected to the feed inlet of the secondary crusher, and the discharge outlet of the secondary crusher is connected to the feed inlet of the primary crusher, so as to form a one-way cross-stage closed loop that starts from the primary crusher, passes through the coarse screening equipment and the secondary crusher, and returns to the primary crusher. The outlet of the coarse screening equipment is connected to the inlet of the fine screening equipment.

[0007] By adopting the above technical solution, the outlet of the coarse screening equipment is connected to the feed inlet of the secondary crusher, and the outlet of the secondary crusher is connected to the feed inlet of the primary crusher, forming a cross-stage closed-loop circulation circuit that starts from the primary crusher, passes through the coarse screening equipment and the secondary crusher, and returns to the primary crusher. Furthermore, all the crushing products from the secondary crusher return to the feed inlet of the primary crusher and do not return to the secondary crusher itself. The core of this circuit structure lies in first feeding the coarse screening oversize material into the secondary crusher for targeted crushing, precisely controlling its particle size within the target range of a first preset particle size to a second preset particle size, making it qualified particles before returning it to the feed inlet of the primary crusher. During this process, the returned material is already qualified particles. When it enters the primary crusher along with fresh material, it only passes through the crushing chamber without undergoing forced crushing, thus effectively avoiding the problems of excessive impact force and over-crushing of material into a large amount of fine powder caused by directly returning the coarse screening oversize material to the primary crusher in existing technologies. Meanwhile, since the products of secondary crushing do not return to the secondary crusher itself, but instead all flow into the material flow of the primary crusher, energy waste and over-grinding caused by repeated crushing of materials in the same equipment are avoided. This results in a more concentrated particle size distribution throughout the crushing and screening section, significantly improving the yield of particles in the target particle size range, greatly reducing the fine powder generation rate, and making the system operation more stable and efficient. Furthermore, the primary crusher uses impact crushing, while the secondary crusher uses compression crushing; the two have fundamental differences in crushing mechanisms and complementary functions. Primary impact crushing targets large, flaky materials after pre-crushing, utilizing high-energy impact to achieve large-scale crushing. The first-stage crushing fully utilizes the advantage of a large crushing ratio; the second-stage extrusion crushing targets the coarse screen material with a certain particle size, using slow extrusion for gentle crushing. This allows for precise control of the upper limit of the product particle size without applying excessive impact energy to the material, thus avoiding over-crushing from the perspective of the crushing mechanism. The differentiated division of labor between impact crushing and extrusion crushing allows the two crushers to perform different functions of "open-circuit coarse crushing" and "closed-circuit fine crushing," respectively. This ensures both the production line's efficient processing capacity for large materials and the fine processing of the screen material. The synergistic effect of the two significantly improves the overall output rate of particles in the target particle size range.

[0008] Optionally, the first preset particle size ranges from 4.0 mm to 5.0 mm, and the second preset particle size ranges from 1.5 mm to 2.5 mm.

[0009] By adopting the above technical solution, the range of the first preset particle size is limited to 4.0 mm to 5.0 mm, and the range of the second preset particle size is limited to 1.5 mm to 2.5 mm. This range matches the requirements for finished particle size in the national standards for compound fertilizers and controlled-release fertilizers, ensuring that the screening thresholds of the coarse and fine screening equipment are highly consistent with the industry standard particle size classification. This enables the system to stably produce semi-finished particles that meet national standards, balancing screening efficiency and finished product yield, and demonstrating excellent industrial adaptability.

[0010] Optionally, the primary crusher is an impact crusher, and the secondary crusher is a double roll crusher; the roller spacing of the secondary crusher is 4.0mm~5.0mm, used to crush the oversize material with a particle size greater than the first preset particle size to a particle size range not greater than the first preset particle size.

[0011] By adopting the above technical solution, the primary crusher is an impact crusher, which utilizes the high-speed impact crushing principle to perform open-path coarse crushing of the pre-crushed flaky material, giving full play to its advantages of strong capacity for handling large materials and large crushing ratio; the secondary crusher is a double-roll crusher, which relies on the slow squeezing action of the rollers on the material for crushing. The roller spacing is set to 4.0mm to 5.0mm, which can accurately control the particle size of the crushed product to be no larger than the first preset particle size and no smaller than the second preset particle size. The combination design of the equipment selection and parameter settings fully considers the differentiated requirements of different crushing stages for material state and crushing mechanism: the primary crusher deals with the original flaky material with a large particle size, requiring strong impact force to achieve a significant reduction in particle size; the secondary crusher deals with the coarse screen oversize material that has already undergone pre-crushing and primary crushing treatment, whose particle size is relatively small. The slow squeezing method of the double-roll crusher can accurately crush unqualified large particles to the target particle size range with a lower crushing intensity, without producing over-crushing. The fundamental difference in crushing mechanism between impact crushers and double roll crushers allows the two-stage crushers to form a division of labor and cooperation in terms of open-circuit coarse crushing and closed-circuit fine crushing. This not only gives full play to their respective technical advantages, but also avoids the problem of over-crushing caused by the mismatch between crushing force and material state when a single device processes materials of different particle sizes, thus significantly improving the output ratio of particles in the target particle size range.

[0012] Optionally, the extrusion granulator includes a first extrusion granulator and a second extrusion granulator connected in parallel, and the pre-crusher includes a first pre-crusher and a second pre-crusher connected in parallel; the discharge port of the first extrusion granulator is connected to the feed port of the first pre-crusher, and the discharge port of the second extrusion granulator is connected to the feed port of the second pre-crusher; the discharge ports of the first pre-crusher and the second pre-crusher are both connected to the feed port of the primary crusher.

[0013] By adopting the above technical solution, both the extrusion granulator and the pre-crusher are configured in parallel, with the first extrusion granulator and the first pre-crusher connected in a one-to-one correspondence, and the second extrusion granulator and the second pre-crusher connected in a one-to-one correspondence. The discharge ports of the two pre-crushers are combined and connected to the feed port of the same primary crusher. When one of the extrusion granulators or pre-crushers needs maintenance or malfunctions, the other parallel equipment can still operate independently and maintain continuous production of the entire production line without requiring a complete shutdown, thereby significantly improving the operational reliability and overall operating rate of the production line. Simultaneously, the one-to-one connection ensures smooth material transport between the extrusion granulator and the pre-crusher, avoiding the pipeline complexity and blockage risks caused by cross-convenience material transport.

[0014] Optionally, the crushed products from the pre-crusher outlet are conveyed to the feed inlet of the crushing elevator via a granulation discharge conveyor, and then the crushing elevator transfers the crushed products to the feed inlet of the primary crusher; the oversize outlet of the coarse screening equipment is connected to the feed inlet of the secondary crusher via a coarse screening return conveyor; the crushed products from the secondary crusher are fed into the granulation discharge conveyor via the secondary crusher discharge conveyor and conveyed to the crushing elevator, and then fed into the feed inlet of the primary crusher by the crushing elevator.

[0015] By adopting the above technical solution, the crushed products from the pre-crusher outlet are conveyed to the crushing elevator via the granulation discharge conveyor, and then transferred to the primary crusher inlet by the crushing elevator. The oversize outlet of the coarse screening equipment is connected to the secondary crusher inlet via the coarse screening return conveyor. The secondary crusher outlet is connected to the granulation discharge conveyor via the secondary crusher discharge conveyor, and the crushed products from the secondary crusher are collected into the granulation discharge conveyor, and together with the pre-crushed products, are sent to the primary crusher inlet via the crushing elevator. This conveying path design achieves a closed-loop connection at the material conveying level: the secondary crushed products return to the primary crusher via the existing pre-crushed product conveying channel after being collected into the granulation discharge conveyor, eliminating the need for additional independent return lifting equipment, simplifying the system structure and reducing equipment investment and maintenance costs. Meanwhile, the secondary crushing products and pre-crushed products are fully mixed in the granulation discharge conveyor and crushing elevator, so that the returned qualified particles are evenly distributed in the fresh material flow, avoiding concentrated impact on the feeding load of the primary crusher, ensuring the continuity and uniformity of feeding, and helping to maintain the stability of the crusher's operating conditions.

[0016] Optionally, the material is conveyed to the feed inlet of the granulation elevator via a material collection and conveying mechanism, and then transferred by the granulation elevator to the feed inlet of the material collection and mixing machine. The material at the discharge outlet of the material collection and mixing machine is conveyed to the feed inlet of the extrusion granulator via a material distribution conveyor. The oversize outlet of the fine screening equipment is connected to the feed inlet of the polishing machine. The material at the undersize outlet of the fine screening equipment and the waste outlet of the polishing machine is conveyed to the return buffer bin via a main return conveyor. The material at the discharge outlet of the return buffer bin is conveyed to the material collection and conveying mechanism via a metering conveyor, so as to drive the material in the return buffer bin to be distributed to the material collection and conveying mechanism according to a preset metering.

[0017] By adopting the above technical solution, the material is fed into the extrusion granulator by a distribution conveyor after passing through the material collection and conveying mechanism, the granulation elevator, and the material collection and mixing machine. The oversize material from the fine screening equipment is sent to the polishing machine for surface treatment as a semi-finished product. The undersize material from the fine screening equipment and the unqualified fine powder material discharged from the waste outlet of the polishing machine are transported to the return buffer bin for temporary storage by the main return material conveyor. Then, they are distributed to the material collection and conveying mechanism according to a preset ratio by the metering conveyor, mixed with fresh raw materials, and re-enter the granulation process. The design of this return path realizes the centralized recovery and quantitative return of fine powder materials in the system. The setting of the return buffer bin can buffer the flow fluctuation of fine powder materials, and the metering conveyor can accurately control the return ratio to ensure the stability of the ratio of returned materials to fresh raw materials, thereby maintaining the consistency of the composition of the feed material to the extrusion granulator, which is conducive to ensuring the stability of granulation quality and the material balance of the entire production line.

[0018] Optionally, a material falling channel is provided between the feed inlet of the primary crusher and the discharge outlet of the upstream crushing elevator, and a guide filter is provided in the material falling channel; the guide filter is used to divert qualified particles with a particle size between the second preset particle size and the first preset particle size to the crushing blind zone of the primary crusher, so that the qualified particles are discharged from the crushing chamber of the crusher without being crushed, and to divert unqualified particles with a particle size larger than the first preset particle size to the impact zone of the primary crusher for crushing.

[0019] By adopting the above technical solution, a guide filter is installed in the material falling channel between the feed inlet of the primary crusher and the discharge outlet of the upstream elevator. The gravity of the material during its fall is used to achieve particle size classification and guidance. Qualified particles with a diameter between the second and first preset diameters are identified by the guide filter and diverted to the crushing blind zone before entering the primary crusher. This blind zone is a low-energy area within the crushing chamber that is not covered by the rotor and hammer's movement trajectory. Qualified particles in this zone do not contact the hammers during their fall and are discharged through the crushing chamber without further crushing. Unqualified particles larger than the first preset diameter are diverted by the guide filter to the impact zone for crushing. The functional design of this guide filter forms a close synergy with the multi-stage closed-loop circulation loop: the secondary crusher is responsible for converting the material oversize from the coarse screen into qualified particles, while the guide filter protects these qualified particles at the primary crusher inlet from further over-crushing. Together, they constitute a complete technical chain from generating qualified products to protecting them. By pre-diverting particle size at the feed inlet of the primary crusher, the guide filter ensures that the crushing energy of the primary crusher is applied only to the large, unqualified particles that truly need to be crushed, thus avoiding the waste of crushing energy. At the same time, it effectively maintains the particle size integrity of the secondary crushing products as they pass through the primary crusher, further reducing the amount of fine powder generated in the system and significantly improving the overall yield of particles in the target particle size range.

[0020] Optionally, the guide filter includes multiple guide strips, which are obliquely arranged in the material falling channel and parallel to each other in the transverse direction of the material falling channel. The distance between adjacent guide strips is equal to the first preset particle size. Particles with a particle size not greater than the distance between adjacent guide strips fall through the gap between adjacent guide strips into the crushing blind zone in the crushing chamber of the primary crusher and are not crushed during the process of passing through the crushing chamber. Particles with a particle size greater than the distance between adjacent guide strips abut against the upper surface of the guide strips and slide down along the oblique extension direction of the guide strips under the action of gravity into the impact area in the crushing chamber for crushing.

[0021] By adopting the above technical solution, the guide filter screen is composed of multiple obliquely arranged and parallelly spaced guide strips, with the spacing between adjacent guide strips equal to a first preset particle size. Particles with a diameter no larger than this spacing fall directly through the gaps between adjacent guide strips into the crushing blind zone under the action of gravity, and are not crushed during their passage through the crushing chamber; particles with a diameter larger than this spacing are intercepted by the upper surface of the guide strips and slide down along their oblique extension direction to the impact area for crushing. This guide strip structure cleverly utilizes the gravity of the material as the grading power, requiring no external energy input or vibration mechanism. It is a completely static grading and guiding device, characterized by its simple structure, no moving parts, zero energy consumption, and extremely low maintenance cost. Because the spacing between adjacent guide bars is precisely equal to the first preset particle size, the grading threshold of this structure is consistent with the screening threshold of the coarse screening equipment. This ensures that all qualified particles after being processed by the secondary crusher can smoothly pass through the gap between the guide bars and enter the crushing blind zone, while all unqualified particles larger than the first preset particle size are intercepted and diverted to the impact area for crushing. The grading boundary is clear and the diversion path is well-defined, ensuring the reliability and accuracy of the grading function of the guide filter from the perspective of physical structure.

[0022] Optionally, the guide filter further includes an installation frame and an adjustment mechanism. Multiple guide strips are fixed to the installation frame, and the installation frame is rotatably mounted on the side wall of the material falling channel via the adjustment mechanism. The adjustment mechanism is used to adjust the tilt angle between the guide strips and the horizontal plane.

[0023] By adopting the above technical solution, the guide filter is also equipped with an installation frame and an adjustment mechanism. Multiple guide strips are fixed to the installation frame, which is rotatably mounted on the side wall of the material falling channel via the adjustment mechanism. Operators can change the inclination angle between the guide strips and the horizontal plane through the adjustment mechanism. When the moisture content, viscosity, or other properties of the material change, adjusting the inclination angle can change the sliding speed of the material on the surface of the guide strips, preventing material from accumulating and clogging due to excessively slow sliding or from insufficient diversion due to excessively fast sliding. This enhances the adaptability of the guide filter to different material conditions and ensures the grading effect and operational reliability of the guide filter under various production conditions.

[0024] A circulating crushing method for a fertilizer production system, employing the aforementioned fertilizer production system with circulating crushing function, includes the following steps: S1: After the material is extruded and granulated by an extrusion granulator, it is fed into a pre-crusher for pre-crushing, and then fed into a primary crusher for primary crushing; S2: The material after primary crushing is fed into a coarse screening device for screening, separating the oversize material with a particle size greater than a first preset particle size and the undersize material with a particle size not greater than the first preset particle size; S3: The oversize material is fed into a secondary crusher for secondary crushing, and all the material after secondary crushing is returned to the feed inlet of the primary crusher, mixed with the new material after pre-crushing, and then subjected to primary crushing and subsequent steps again to form a closed loop; the material after secondary crushing is not returned to the secondary crusher itself; S4: The undersize material is fed into a fine screening device for screening, separating the fine powder material with a particle size not greater than a second preset particle size and the target particle material with a particle size between the second preset particle size and the first preset particle size.

[0025] By adopting the above technical solution, the secondary crushing step is placed after the coarse screening step, and only the material on the screen is processed. After the secondary crushing, it is forced to return all of it to the primary crushing step instead of returning it to the secondary crushing step itself. From the perspective of process sequence and material flow, it is ensured that each qualified particle only undergoes secondary crushing treatment once. This avoids the process defect of the same material being repeatedly processed in the secondary crushing step. Thus, at the method level, the same technical effect of avoiding over-crushing and improving the yield of particles in the target particle size range is achieved as in the system solution.

[0026] In summary, this application includes at least one of the following beneficial technical effects: The outlet of the coarse screening equipment is connected to the feed inlet of the secondary crusher, and the outlet of the secondary crusher is connected to the feed inlet of the primary crusher, forming a cross-stage closed-loop circulation loop. This avoids the problem of over-crushing caused by the coarse screening material being directly returned to the primary crusher, improves the particle yield of the target particle size range, reduces the fine powder generation rate, and makes the system operation more stable and efficient. In this application, both the extrusion granulator and the pre-crusher are set up in parallel and connected to each other. When one of the machines is under maintenance or malfunctions, the other can operate independently, which improves the reliability and overall operating rate of the production line and avoids the pipeline complexity and blockage risk caused by cross-transportation of materials. This application installs a guide filter screen in the material falling channel between the feed inlet of the primary crusher and the discharge outlet of the upstream elevator to divert qualified particles to the crushing blind zone and unqualified particles to the impact zone. In coordination with the cross-stage closed-loop circulation loop, it reduces the amount of fine powder generated in the system and improves the overall yield of particles in the target particle size range. Attached Figure Description

[0027] Figure 1This is an overall schematic diagram of the fertilizer production system with cyclic crushing function described in Embodiment 1 of this application; Figure 2 This is a schematic diagram of the arrangement structure of the primary crusher and the secondary crusher described in Embodiment 1 of this application; Figure 3 This is an overall schematic diagram of the fertilizer production system with cyclic crushing function described in Embodiment 2 of this application; Figure 4 This is an overall schematic diagram of the fertilizer production system with cyclic crushing function described in Embodiment 2 of this application; Figure 5 This is a schematic diagram of the arrangement structure of the material falling channel described in Embodiment 3 of this application; Figure 6 This is a schematic diagram of the arrangement structure of the guide filter described in Embodiment 3 of this application; Figure 7 This is a schematic diagram of the guide bar described in Embodiment 3 of this application; Figure 8 This is a schematic diagram of the arrangement structure of the guide filter described in Embodiment 4 of this application; Figure 9 This is a schematic diagram of the structure of the rotating shaft described in Embodiment 4 of this application; Figure 10 This is a schematic diagram of the structure of the fixing seat described in Embodiment 4 of this application; Figure 11 This is a flowchart of the cyclic crushing method of the fertilizer production system described in Embodiment 5 of this application.

[0028] In the diagram: 1. Extrusion granulator; 11. First extrusion granulator; 12. Second extrusion granulator; 13. Material conveying mechanism; 14. Granulation elevator; 15. Material mixer; 16. Distribution conveyor; 17. Main return conveyor; 18. Return buffer silo; 19. Metering conveyor; 2. Pre-crusher; 21. First pre-crusher; 22. Second pre-crusher; 3. Primary crusher; 31. Crushing chamber; 32. Crushing blind zone; 33. Impact crusher. 4. Secondary crusher; 41. Secondary crusher discharge conveyor; 5. Coarse screening equipment; 6. Fine screening equipment; 7. Granulation discharge conveyor; 8. Crushing elevator; 81. Material drop channel; 82. Guide filter screen; 821. Guide bar; 822. Mounting frame; 8221. Rotating shaft; 8222. Adjusting screw; 823. Fixed seat; 8231. Arc-shaped adjusting groove; 824. Locking nut; 9. Coarse screening return conveyor; 10. Polishing machine. Detailed Implementation

[0029] The technical solutions of various embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. Example 1

[0030] Reference Figures 1 to 2 This application discloses a fertilizer production system with a circulating crushing function, including an extrusion granulator 1, a pre-crusher 2, a primary crusher 3, and a screening device arranged sequentially along the material conveying direction, and also including a secondary crusher 4; the screening device includes a coarse screen 5 and a fine screen 6, the coarse screen 5 being located downstream of the primary crusher 3, and the fine screen 6 being located downstream of the coarse screen 5; the screen aperture of the coarse screen 5 is a first preset particle size, and the screen aperture of the fine screen 6 is a second preset particle size, the first preset particle size being larger than the second preset particle size; in this embodiment, the first preset particle size is preferably 4.75 mm, and the second preset particle size is preferably 2.0 mm. mm, this value corresponds exactly to the target particle size range (2.0mm~4.75mm) of the finished product granules in the national standards for compound fertilizers and controlled-release fertilizers; the outlet of the oversize material of the coarse screening equipment 5 is connected to the feed inlet of the secondary crusher 4, and the outlet of the secondary crusher 4 is connected to the feed inlet of the primary crusher 3, so as to form a cross-stage closed-loop circulation loop starting from the primary crusher 3, passing through the coarse screening equipment 5 and the secondary crusher 4, and returning to the primary crusher 3; wherein, all the crushed products of the secondary crusher 4 are returned to the feed inlet of the primary crusher 3, and do not return to the secondary crusher 4 itself; the outlet of the undersize material of the coarse screening equipment 5 is connected to the feed inlet of the fine screening equipment 6.

[0031] Specifically, refer to Figure 1 and Figure 2 After being extruded and granulated by the extrusion granulator 1, the material produces flaky or strip-shaped material. This material enters the pre-crusher 2 for pre-crushing, which coarsely crushes the large flaky material into smaller particles. The pre-crushed material is then conveyed to the feed inlet of the crushing elevator 8 by the granulation discharge conveyor 7. The crushing elevator 8 lifts the material and transfers it to the feed inlet of the primary crusher 3. The primary crusher 3 performs primary crushing on the material, and the crushed material is then conveyed to the coarse screening equipment 5 for the first grading and screening.

[0032] Reference Figure 1 and Figure 2In one embodiment, the extrusion granulator 1 includes a first extrusion granulator 11 and a second extrusion granulator 12 arranged in parallel, and the pre-crusher 2 includes a first pre-crusher 21 and a second pre-crusher 22 arranged in parallel; wherein, parallel arrangement means that the first extrusion granulator 11 and the second extrusion granulator 12 operate independently and do not interfere with each other, and their material flows are combined after being discharged from their respective pre-crushers; similarly, the first pre-crusher 21 and the second pre-crusher 22 operate independently, and their discharges are combined and enter the same primary crusher 3; the discharge port of the first extrusion granulator 11 is correspondingly connected to the feed port of the first pre-crusher 21, and the second extrusion granulator 2... The discharge port of the pellet mill 12 is connected to the feed port of the second pre-crusher 22; the discharge ports of the first pre-crusher 21 and the second pre-crusher 22 are both connected to the feed port of the primary crusher 3; so that when the first extrusion pellet mill 11 or the first pre-crusher 21 needs to be repaired or malfunctions, the second extrusion pellet mill 12 and the second pre-crusher 22 can still operate independently and maintain the continuous production of the entire production line without the need for a complete shutdown, thereby greatly improving the operational reliability and overall operating rate of the production line, ensuring smooth material conveying between the extrusion pellet mill 1 and the pre-crusher 2, and avoiding the pipeline complexity and blockage risk caused by cross-conveying of materials.

[0033] Reference Figure 1 and Figure 2 The screen aperture of the coarse screening device 5 is the first preset particle size (4.75mm). After screening by the coarse screening device 5, the oversize material B (unqualified large particles) with a particle size greater than 4.75mm is sent to the feed inlet of the secondary crusher 4 through the coarse screening return conveyor 9; the undersize material with a particle size not greater than 4.75mm is sent to the feed inlet of the fine screening device 6 through the undersize material outlet of the coarse screening device 5 for a second fine screening.

[0034] After receiving the material from the coarse screening equipment 5, the secondary crusher 4 performs secondary crushing on it to crush it to a particle size range of not more than 4.75 mm and not less than 2.0 mm. All the material after secondary crushing is fed into the granulation discharge conveyor 7 via the secondary crusher discharge conveyor 41. After mixing with the discharge from the pre-crusher 2, it is sent together to the feed inlet of the primary crusher 3 via the crushing elevator 8 to form a cross-stage closed-loop circulation. During this process, the crushed products of the secondary crusher 4 are not returned to the secondary crusher 4 itself. In one embodiment, the primary crusher 3 is an impact crusher, and the secondary crusher 4 is a double roll crusher. The roller spacing of the secondary crusher 4 is 4.0mm to 5.0mm, which is used to crush the oversize material with a particle size greater than the first preset particle size (4.75mm) to a particle size range of not greater than 4.75mm and not less than 2.0mm. Among them, the impact crusher uses the high-speed impact crushing principle to perform open-circuit coarse crushing on the pre-crushed flaky material, giving full play to its advantages of strong ability to handle large materials and large crushing ratio. The double roll crusher relies on the slow squeezing action of the rollers on the material to crush it. Its roller spacing is set to 4.0mm to 5.0mm, which can accurately control the particle size of the crushed product to be not greater than 4.75mm and not less than 2.0mm. The combination design of the equipment selection and parameter settings fully considers the different requirements of material state and crushing mechanism at different crushing stages, so that the two-stage crushers form a division of labor and cooperation relationship of open-circuit coarse crushing and closed-circuit fine crushing. This not only gives full play to their respective technical advantages, but also avoids the problem of over-crushing caused by the mismatch between crushing force and material state when a single device processes materials of different particle sizes.

[0035] Reference Figure 1 and Figure 2 The screen aperture of the fine screening device 6 is the second preset particle size (2.0mm). After screening by the fine screening device 6, fine powder materials with a particle size not greater than 2.0mm are discharged as unqualified materials and returned to the front end of the system for regranulation; materials with a particle size between 2.0mm and 4.75mm are qualified semi-finished products and enter the subsequent process.

[0036] The implementation principle of this embodiment is as follows: the material (particle size greater than 4.75mm) from the coarse screening device 5 is first fed into the secondary crusher 4 for targeted crushing, so that the majority of the particle size is precisely controlled within the target range of 2.0mm to 4.75mm, and then returned to the feed inlet of the primary crusher 3. During this process, when the returned qualified particles enter the primary crusher 3 along with the fresh material, due to their small size and mass, most of the qualified particles simply pass through the crushing chamber 31 without being subjected to forced crushing. This effectively avoids the problem of excessive impact force and over-crushing of material into a large amount of fine powder (particle size less than 1.0mm) caused by directly returning the coarse screening material to the primary crusher 3 in the prior art. At the same time, since the secondary crushing product does not return to the secondary crusher 4 itself, but instead all flows into the material flow of the primary crusher 3, the energy waste caused by the repeated crushing of material in the same equipment is avoided. Example 2

[0037] Reference Figure 3 and Figure 4 The difference between this embodiment and the first embodiment is that it also includes a polishing machine 10 arranged downstream of the fine screening device 6.

[0038] Reference Figure 3 and Figure 4 Specifically, the outlet of the fine screening equipment 6 is connected to the inlet of the polishing machine 10. The semi-finished particles (particle size between 2.0mm and 4.75mm) screened out by the fine screening equipment 6 are sent to the polishing machine 10 for surface polishing treatment to improve the surface smoothness of the particles. The polishing machine 10 has a built-in screening function, and the qualified particles after polishing are sent to the subsequent process.

[0039] In addition, refer to Figures 3 to 4 The material is conveyed to the feed inlet of the granulation elevator 14 through the material collection conveyor 13, and then transferred by the granulation elevator 14 to the feed inlet of the material collection mixer 15. The material at the discharge outlet of the material collection mixer 15 is conveyed to the feed inlet of the extrusion granulator 1 through the material distribution conveyor 16. The material C (fine powder material with a particle size not greater than 2.0 mm) at the outlet of the fine screening equipment 6, the material D at the discharge outlet of the polishing machine 10, and the unprocessed material A on the material distribution conveyor 16 are conveyed to the return buffer bin 18 through the main return material conveyor 17. The material at the discharge outlet of the return buffer bin 18 is conveyed to the material collection conveyor 13 through the metering conveyor 19, so that the material in the return buffer bin 18 can be distributed to the material collection conveyor 13 according to the preset metering.

[0040] The implementation principle of this embodiment is as follows: by setting up the return material buffer bin 18 and the metering conveying mechanism 19, the centralized recovery and quantitative return of fine powder materials are realized. The return material buffer bin 18 can buffer the flow fluctuation of fine powder materials, and the metering conveying mechanism 19 can accurately control the return ratio to ensure the stable ratio of returned materials to fresh raw materials, thereby maintaining the consistency of the composition of the feed material of the extrusion granulator 1, which is conducive to ensuring the stability of granulation quality and the material balance of the entire production line. Example 3

[0041] Reference Figures 5 to 7 The difference between this embodiment and embodiment one is that a material falling channel 81 is provided between the feed inlet of the primary crusher 3 and the discharge outlet of the upstream crushing elevator 8, and a guide filter 82 is provided in the material falling channel 81.

[0042] The guide filter 82 includes multiple guide strips 821, which are arranged obliquely in the material falling channel 81 and are arranged in parallel and spaced along the transverse side of the material falling channel 81; the spacing between adjacent guide strips 821 is equal to the first preset particle size (4.75 mm).

[0043] In one embodiment, the primary crusher 3 is an impact crusher, which mainly includes a casing, a rotor, hammers, and an impact plate; the inside of the casing forms a crushing chamber 31, with a feed inlet at the top and a discharge outlet at the bottom; the rotor is rotatably disposed in the crushing chamber 31, and the hammers are fixedly installed on the rotor and rotate at high speed with the rotor; the impact plate is disposed on the inner wall of the crushing chamber 31, located above or to the side of the rotor, and maintains a certain gap with the hammers.

[0044] The crushing chamber 31 forms an impact zone 33 and a crushing blind zone 32. The impact zone 33 refers to the space swept by the hammer when the rotor rotates at high speed and the area covered by the movement path of the material being thrown towards the impact plate under the impact of the hammer. The material falling into the impact zone 33 will be forcibly crushed by the high-speed impact of the hammer and the impact of the impact plate. The crushing blind zone 32 refers to the low-energy area in the crushing chamber 31 located outside the movement trajectory of the rotor and hammer and not directly hit by the hammer. Specifically, it is located in the crushing chamber 31 near the discharge port and in a position not covered by the movement trajectory of the hammer. When the material falls in the crushing blind zone 32, it will not come into contact with the hammer and therefore will not be forcibly crushed.

[0045] In actual operation, the mixed material slides from the feed inlet along the material falling channel 81 into the crushing chamber 31. During the sliding process, particles with a diameter not greater than 4.75 mm (i.e., qualified particles with a diameter between 2.0 mm and 4.75 mm) fall through the gap between adjacent guide bars 821 and slide along the lower wall of the material falling channel 81 into the crushing blind zone 32 located below the hammer plate in the crushing chamber 31 of the primary crusher 3. These particles are not crushed during their passage through the crushing chamber 31. Particles with a diameter greater than 4.75 mm (i.e., unqualified large particles) abut against the upper surface of the guide bars 821 and, under the action of gravity, slide along the oblique extension direction of the guide bars 821 into the impact area 33 within the crushing chamber 31 for crushing. In this application, the guide filter 82 diverts the qualified particles to the crushing blind zone 32 area, preventing them from contacting the hammer plate and thus avoiding over-crushing.

[0046] The implementation principle of this embodiment is as follows: the guide filter 82 uses the gravity of the material during the falling process to achieve particle size classification and guidance; qualified particles with a particle size between 2.0mm and 4.75mm are identified by the guide filter 82 and diverted to the crushing blind zone 32 before entering the primary crusher 3. The crushing blind zone 32 is located in a low-energy area within the crushing chamber 31 where the rotor and hammer movement trajectory cannot be covered. When qualified particles fall in this area, they do not come into contact with the hammer and pass through the crushing chamber 31 without being crushed and are discharged; unqualified particles with a particle size greater than 4.75mm are diverted by the guide filter 82 to the impact zone 33 for crushing. The functional design of the guide filter 82 forms a close synergistic relationship with the cross-stage closed-loop circulation loop: the secondary crusher 4 is responsible for converting the material on the coarse screen (greater than 4.75mm) into qualified particles (2.0mm~4.75mm), while the guide filter 82 protects these qualified particles at the inlet of the primary crusher 3 from being over-crushed again. Example 4

[0047] Reference Figures 8 to 10 The difference between this embodiment and embodiment three is that the guide filter 82 also includes a mounting frame 822 and an adjustment mechanism.

[0048] The mounting frame 822 is rectangular and is set inside the material falling channel 81. Multiple guide strips 821 are arranged in parallel at intervals, and the two ends of each guide strip 821 are fixedly connected to the two side frames of the mounting frame 822. One side frame of the mounting frame 822 is rotatably connected to the side wall of the material falling channel 81 through a rotating shaft 8221, and an adjustment mechanism is provided on the other side frame of the mounting frame 822.

[0049] The adjustment mechanism includes a fixed base 823, an adjusting screw 8222, and a locking nut 824. The fixed base 823 is fixedly installed on the side wall of the material falling channel 81. An arc-shaped adjusting groove 8231 is provided on the fixed base 823, and the center of the arc of the arc-shaped adjusting groove 8231 coincides with the axis of the rotating shaft 8221. An adjusting screw 8222 is fixedly connected to the other side frame of the mounting frame 822. The adjusting screw 8222 passes through the arc-shaped adjusting groove 8231 and extends out of the fixed base 823. The locking nut 824 is threadedly connected to the end of the adjusting screw 8222 that extends out of the fixed base 823.

[0050] After loosening the locking nut 824, the operator can push the adjusting screw 8222 along the arc-shaped adjusting groove 8231, causing the mounting frame 822 to rotate around the rotating shaft 8221. This, in turn, causes the multiple guide bars 821 fixed on the mounting frame 822 to rotate synchronously, thereby adjusting the tilt angle between the guide bars 821 and the horizontal plane. After adjusting to the desired angle, tightening the locking nut 824 will fix the mounting frame 822 and the guide bars 821 at that angle.

[0051] The implementation principle of this embodiment is as follows: By adjusting the tilt angle between the guide bar 821 and the horizontal plane, the sliding speed of the material on the upper surface of the guide bar 821 can be adjusted, preventing the material from accumulating and clogging due to excessively slow sliding or from insufficient diversion due to excessively fast sliding. This enhances the adaptability of the guide filter 82 to different material conditions and ensures the grading effect and operational reliability of the guide filter 82 under various production conditions. The adjustment mechanism has a simple structure. The angle is adjusted by the cooperation of the rotating shaft 8221 and the arc-shaped adjustment groove 8231, and the locking after adjustment is achieved by the cooperation of the adjusting screw 8222 and the locking nut 824. The operation can be completed without special tools and is suitable for long-term reliable operation in the industrial environment of fertilizer production lines. Example 5

[0052] Reference Figure 11 This application also discloses a circulating crushing method for a fertilizer production system, which employs the circulating crushing function of the fertilizer production system described in any of the above embodiments, and specifically includes the following steps: S1: After the material is extruded and granulated by the extrusion granulator 1, it is sent to the pre-crusher 2 for pre-crushing, and then sent to the primary crusher 3 for primary crushing.

[0053] S2: The material after primary crushing is fed into the coarse screening equipment 5 for screening, separating the oversize material with a particle size greater than the first preset particle size (4.75mm) and the undersize material with a particle size not greater than 4.75mm.

[0054] S3: The material oversize is fed into the secondary crusher 4 for secondary crushing. All the material from the secondary crushing is returned to the feed inlet of the primary crusher 3, where it is mixed with the pre-crushed new material and then subjected to primary crushing and subsequent steps again, forming a closed-loop cycle. The material from the secondary crushing is not returned to the secondary crusher 4 itself. The secondary crusher 4 crushes the oversize material with a particle size greater than 4.75mm to a particle size range of no greater than 4.75mm and no less than 2.0mm.

[0055] S4: The undersize material is fed into the fine screening equipment 6 for screening to separate fine powder material with a particle size not greater than the second preset particle size (2.0mm) and target particulate material with a particle size between 2.0mm and 4.75mm.

[0056] The implementation principle of this application embodiment is as follows: by placing the secondary crushing step after the coarse screening step and only processing the material on the sieve (greater than 4.75mm), and forcibly returning all of it to the primary crushing step instead of returning it to the secondary crushing step itself after the secondary crushing, this method ensures that each qualified particle undergoes only one secondary crushing process from the perspectives of process sequence and material flow, thus avoiding the process defect of the same material being repeatedly processed in the secondary crushing step.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the technical solutions of the embodiments of this application.

Claims

1. A fertilizer production system with a circulating crushing function, comprising an extrusion granulator (1), a pre-crusher (2), a primary crusher (3), and a screening device arranged sequentially along the material conveying direction, characterized in that, It also includes a secondary crusher (4); The screening device includes a coarse screening device (5) and a fine screening device (6). The coarse screening device (5) is located downstream of the primary crusher (3), and the fine screening device (6) is located downstream of the coarse screening device (5). The screen aperture of the coarse screening device (5) is a first preset particle size, and the screen aperture of the fine screening device (6) is a second preset particle size, wherein the first preset particle size is larger than the second preset particle size. The primary crusher (3) crushes the material by impact crushing, and the secondary crusher (4) crushes the material by compression crushing. The oversize outlet of the coarse screening device (5) is connected to the feed inlet of the secondary crusher (4), and the discharge outlet of the secondary crusher (4) is connected to the feed inlet of the primary crusher (3), so as to form a one-way cross-stage closed loop starting from the primary crusher (3), passing through the coarse screening device (5) and the secondary crusher (4), and returning to the primary crusher (3). The undersize outlet of the coarse screening device (5) is connected to the feed inlet of the fine screening device (6).

2. The fertilizer production system with cyclic crushing function according to claim 1, characterized in that, The first preset particle size ranges from 4.0 mm to 5.0 mm, and the second preset particle size ranges from 1.5 mm to 2.5 mm.

3. The fertilizer production system with cyclic crushing function according to claim 1, characterized in that, The primary crusher (3) is an impact crusher, and the secondary crusher (4) is a double roll crusher; the roller spacing of the secondary crusher (4) is 4.0mm~5.0mm, which is used to crush the oversize material with a particle size greater than the first preset particle size to a particle size range not greater than the first preset particle size.

4. The fertilizer production system with cyclic crushing function according to claim 1, characterized in that, The extrusion granulator (1) includes a first extrusion granulator (11) and a second extrusion granulator (12) connected in parallel. The pre-crusher (2) includes a first pre-crusher (21) and a second pre-crusher (22) connected in parallel. The discharge port of the first extrusion granulator (11) is connected to the feed port of the first pre-crusher (21), and the discharge port of the second extrusion granulator (12) is connected to the feed port of the second pre-crusher (22). The discharge ports of the first pre-crusher (21) and the second pre-crusher (22) are both connected to the feed port of the primary crusher (3).

5. The fertilizer production system with cyclic crushing function according to claim 1, characterized in that, The crushed products from the discharge port of the pre-crusher (2) are conveyed to the feed port of the crushing elevator (8) via the granulation discharge conveyor (7), and then the crushing elevator (8) transfers the crushed products to the feed port of the primary crusher (3); the oversize outlet of the coarse screening equipment (5) is connected to the feed port of the secondary crusher (4) via the coarse screening return conveyor (9); the crushed products from the secondary crusher (4) are fed into the granulation discharge conveyor (7) via the secondary crushing discharge conveyor (41) and conveyed to the crushing elevator (8), and then sent to the feed port of the primary crusher (3) by the crushing elevator (8).

6. The fertilizer production system with cyclic crushing function according to claim 1, characterized in that, The material is conveyed to the feed inlet of the granulation elevator (14) through the material collection and conveying mechanism (13), and then transferred to the feed inlet of the material collection mixer (15) by the granulation elevator (14). The material at the discharge port of the material collection mixer (15) is conveyed to the feed inlet of the extrusion granulator (1) through the material distribution conveyor (16). The oversize outlet of the fine screening device (6) is connected to the feed inlet of the polishing machine (10). The undersize outlet of the fine screening device (6) and the waste outlet of the polishing machine (10) are conveyed to the return buffer bin (18) through the main return material conveyor (17). The material at the discharge port of the return buffer bin (18) is conveyed to the material collection and conveying mechanism (13) through the metering conveying mechanism (19) so that the material in the return buffer bin (18) can be distributed to the material collection and conveying mechanism (13) according to the preset metering.

7. The fertilizer production system with cyclic crushing function according to claim 1, characterized in that, A material falling channel (81) is provided between the feed inlet of the primary crusher (3) and the discharge outlet of the upstream crushing elevator (8). A guide filter (82) is provided in the material falling channel (81). The guide filter (82) is used to divert qualified particles with a particle size between the second preset particle size and the first preset particle size to the crushing blind zone (32) of the primary crusher (3), so that the qualified particles are discharged from the crushing chamber (31) of the crusher without being crushed, and unqualified particles with a particle size greater than the first preset particle size are diverted to the impact zone of the primary crusher (3) for crushing.

8. The fertilizer production system with a circulating crushing function according to claim 7, characterized in that, The guide filter (82) includes multiple guide strips (821), which are obliquely arranged in the material falling channel (81) and arranged in parallel intervals along the transverse direction of the material falling channel (81). The distance between adjacent guide strips (821) is equal to the first preset particle size. Qualified particles with a particle size not greater than the distance between adjacent guide strips (821) fall through the gap between adjacent guide strips (821) into the crushing blind zone (32) of the crushing chamber (31) of the primary crusher (3) and are not crushed during the process of passing through the crushing chamber (31). Unqualified particles with a particle size greater than the distance between adjacent guide strips (821) abut against the upper surface of the guide strips (821) and slide down along the oblique extension direction of the guide strips (821) under the action of gravity to the impact area (33) in the crushing chamber (31) for crushing.

9. The fertilizer production system with circulating crushing function according to claim 8, characterized in that, The guide filter (82) also includes an installation frame (822) and an adjustment mechanism. Multiple guide strips (821) are fixed on the installation frame (822). The installation frame (822) is rotatably mounted on the side wall of the material falling channel (81) via the adjustment mechanism. The adjustment mechanism is used to adjust the tilt angle between the guide strips (821) and the horizontal plane.

10. A circulating crushing method for a fertilizer production system, characterized in that, The fertilizer production system with a circulating crushing function as described in any one of claims 1 to 9 specifically includes: S1: After the material is extruded and granulated by the extrusion granulator (1), it is sent to the pre-crusher (2) for pre-crushing, and then sent to the primary crusher (3) for primary crushing. S2: The material after primary crushing is fed into the coarse screening equipment (5) for screening, separating the oversize material with a particle size greater than the first preset particle size and the undersize material with a particle size not greater than the first preset particle size. S3: The material on the screen is fed into the secondary crusher (4) for secondary crushing, and all the material after secondary crushing is returned to the feed port of the primary crusher (3) and mixed with the new material after pre-crushing before being crushed again and subsequent steps are carried out to form a closed loop; the material after secondary crushing is not returned to the secondary crusher (4) itself; S4: The undersize material is fed into a fine sieving device (6) for sieving to separate fine powder material with a particle size not greater than the second preset particle size and target particle material with a particle size between the second preset particle size and the first preset particle size.

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