A high-efficiency stirring device and method for cellulose diacetate acetone solution

Abstract

This invention relates to a high-efficiency stirring device and method for cellulose diacetate (CDA) acetone solutions. The core of the device includes a sealed explosion-proof vessel, a coaxial reverse drive system, a central eight-bladed airfoil shear assembly, a lower anchor-type composite stirring assembly, and a positive-pressure isolation double-end-face sealing system. The device synchronously drives the hollow short shaft and the solid long shaft to rotate in opposite directions via a bevel gear set. The central impeller forms an axial main circulation flow field and a high-intensity shear zone, while the lower anchor-type impeller sweeps the vessel wall and bottom to eliminate low-speed dead zones. Together, they construct a three-dimensional composite flow field of "upward push and downward disturbance," effectively improving the dissolution efficiency of high-solids-content, high-viscosity CDA acetone solutions. The positive-pressure double-end-face sealing system uses back-to-back dynamic and static rings and an inert isolation liquid to achieve zero acetone vapor leakage, meeting chemical explosion-proof safety standards. The accompanying method, through staged speed control and flow field optimization, adapts to the viscosity changes at different dissolution stages and is suitable for continuous industrial production scenarios.

Description

Technical Field

[0001] This invention relates to the field of high-viscosity organic solution preparation and stirring equipment, and in particular to a stirring device and method for the efficient dissolution of cellulose diacetate in acetone. Background Technology

[0002] Cellulose diacetate (CDA) is an important polymer material prepared from natural cellulose. Due to its excellent film-forming properties, high transparency, and superior biocompatibility, it is widely used in cigarette filters, separation membranes, optical base films, functional coatings, and medical materials. In industrial production, CDA needs to be dissolved in acetone to prepare a high-concentration solution before being processed into the final product through spinning, casting, or coating processes. To increase production capacity and reduce solvent recovery costs, the industry generally pursues high-concentration CDA acetone solutions with a solid content of over 25% and a viscosity of 110-200 Pa·s. However, existing stirring devices are difficult to adapt to such extreme conditions: CDA acetone solutions exhibit typical shear-thinning characteristics, easily forming agglomerates and viscoelastic networks in the initial dissolution stage. Conventional single-axis stirring easily creates dead zones and stratification areas, leading to impaired mass transfer, long dissolution times, high energy consumption, and localized undissolved particles that can cause blockages in subsequent filtration processes.

[0003] Acetone, as a low-boiling-point flammable solvent, creates a solvent-rich vapor environment inside the vessel during dissolution, posing an inherent flaw to traditional sealing technologies. Packing seals or single-end-face seals cannot operate stably for extended periods and are prone to minor leaks due to shaft vibration and dry friction, resulting in solvent loss and safety hazards. Ordinary double-end-face seals are mostly designed for aqueous or low-concentration systems and are not optimized to meet the comprehensive requirements of high-viscosity CDA acetone solutions in terms of sealing fluid pressure, cooling capacity, and axial stiffness. They struggle to balance high sealing performance and low wear during long-term operation and lack explosion-proof safety design, failing to meet chemical production standards.

[0004] Existing high-viscosity solution stirring devices suffer from functional fragmentation and poor adaptability to operating conditions. Single-layer impellers can only achieve a single stirring function and cannot simultaneously handle bottom flow propulsion, vessel wall scraping, and mid-section shear dispersion. Some double-layer impellers or coaxial reversing structures are mostly designed for ordinary viscous slurries and have not been designed with impeller and shaft system matching to the high viscosity, high solids content, and strong volatility characteristics of CDA acetone solutions. Fixed-pitch structures cannot adapt to viscosity changes at different loading levels or dissolution stages, and the circulation efficiency drops significantly under full-load conditions, making it difficult to meet the needs of continuous industrial production.

[0005] Current research and patent disclosures on related technologies suffer from shortcomings such as isolated structural designs, weak application to specific operating conditions, and low system integration. The optimization of the impeller type and the design of the sealing system are independent, failing to consider the impact of shaft vibration on sealing performance under high viscosity conditions. Most solutions passively address high viscosity by increasing power or thickening the shaft diameter, without proactively designing from the perspectives of flow field coupling and mass transfer enhancement. There is a lack of integrated solutions that combine efficient dissolution, reliable sealing, and adaptability to multiple operating conditions, making it difficult to meet the comprehensive requirements of stability, safety, and efficiency in the CDA acetone solution preparation process.

[0006] In summary, the existing technology still lacks a stirring device and process method specifically designed for the preparation of CDA acetone solution that can achieve efficient dissolution under high concentration and high viscosity conditions, while also possessing high shaft rigidity and reliable explosion-proof sealing performance. There is an urgent need to propose a systematic and innovative solution to solve the above-mentioned technical problems. Summary of the Invention

[0007] The purpose of this invention is to solve the above-mentioned problems existing in the prior art and to provide a stirring device for the efficient dissolution of cellulose diacetate in acetone.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A high-efficiency stirring device for cellulose diacetate acetone solution includes: a sealed explosion-proof vessel body for constructing a sealed space for dissolving cellulose diacetate in acetone solvent, suitable for flammable and volatile environments containing acetone vapor; a coaxial reverse drive system disposed on the top of the sealed explosion-proof vessel body, including a drive motor, a rigid retainer, a bevel gear set, a hollow short shaft, a solid long shaft, and a support frame; the drive motor is fixedly mounted on the top of the sealed explosion-proof vessel body via the rigid retainer; the support frame is fixedly mounted on the bevel gear set; the output shaft of the drive motor extends downward and is sequentially connected to the bevel gear set, the hollow short shaft, and the solid long shaft; wherein, the hollow short shaft is a hollow cylindrical structure, the upper end of which is connected to the bevel gear set, and the lower end passes through the vessel cover of the sealed explosion-proof vessel body and extends into the upper part of the sealed explosion-proof vessel body; the solid... A long shaft coaxially passes through the internal cavity of a hollow short shaft, with its upper end coaxially connected to a bevel gear set, and its lower end passing through the bottom opening of the hollow short shaft, extending to the bottom of the sealed explosion-proof vessel. The drive motor synchronously drives the hollow short shaft and the solid long shaft to rotate in opposite directions along the same central axis via the bevel gear set. The middle shearing and dissolving assembly, fixed to the lower end of the hollow short shaft, is an eight-bladed airfoil impeller. The lower composite stirring assembly, fixed to the lower end of the solid long shaft, includes an anchor impeller coaxially connected to the eight-bladed airfoil impeller in the middle region. The anchor impeller is used to sweep and renew the material on the vessel wall and bottom of the sealed explosion-proof vessel. A positive pressure isolation double-end face sealing system is set at the vessel cover position where the hollow short shaft passes through the sealed explosion-proof vessel. Through the back-to-back arrangement of dynamic and static rings and the positive pressure isolation liquid, a zero-leakage seal for acetone vapor is achieved.

[0009] Preferably, the bevel gear set includes: a driving bevel gear connected to the output shaft of the drive motor, an intermediate bevel gear meshing with the driving bevel gear, and a driven bevel gear fixedly connected to the hollow short shaft and the solid long shaft respectively. The intermediate bevel gear meshes with both the driving bevel gear and the driven bevel gear, so that the hollow short shaft and the solid long shaft obtain power output in opposite directions of rotation.

[0010] Preferably, the blades of the eight-bladed impeller are installed at a downward tilt angle, which generates an axial downward thrust when rotating, thereby enhancing the overall circulation efficiency of the material inside the vessel.

[0011] Preferably, the anchor-type stirring paddle has an anchor-type mountain-shaped structure, with its impeller hub rigidly connected to a solid long shaft. Multiple paddle arms extend outward to near the vessel wall and fold at the outer edge to form a mountain-shaped frame. A scraping gap of 5mm to 15mm is maintained between the outer side of the paddle arms and the vessel wall for sweeping and renewing the high-viscosity slurry near the vessel wall.

[0012] Preferably, the diameter of the eight-bladed impeller is 55% to 65% of the inner diameter of the sealed explosion-proof vessel, and is used to form an axial main circulation flow field and a high-intensity shear dissolution zone in the middle of the vessel.

[0013] Preferably, the axial distance between the middle shear-dissolving component and the lower composite stirring component is 1.0 to 1.5 times the diameter of the middle stirring paddle, and is adjustable in stages through the following structure: At least two sets of circumferentially distributed flat keyways are provided along the axial direction on the solid long shaft. The lower composite stirring assembly has a matching keyway in the impeller hub, which transmits torque through a common flat key, and achieves axial positioning and locking through a combination of shaft shoulder, positioning spacer, elastic retaining ring and locking nut.

[0014] Preferably, the positive pressure isolation double-end face sealing system includes: two sets of back-to-back dynamic and static ring pairs, a sealing cavity, and an external isolation liquid circulation pipeline. The isolation liquid pressure in the sealing cavity is 0.05 to 0.1 MPa higher than the internal pressure of the vessel body. The friction pair of the double-end face mechanical seal structure is made of silicon carbide paired resin impregnated graphite or tungsten carbide paired tungsten carbide. The auxiliary sealing ring is made of acetone-resistant perfluoroether rubber. The sealing cavity integrates a cooling jacket for heat dissipation.

[0015] Another objective of this invention is to provide a method for efficient stirring of cellulose diacetate acetone solution.

[0016] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for efficient stirring of cellulose diacetate acetone solution includes the following steps: (1) Sealing preparation stage: Add metered acetone solvent to the sealed explosion-proof vessel, start the positive pressure isolation double end face sealing system, adjust the isolation liquid pressure to be 0.05-0.1MPa higher than the pressure inside the vessel, and establish a positive pressure explosion-proof sealing environment; (2) Flow field initialization stage: Start the coaxial reverse drive system at a low speed to make the middle shear dissolution component and the lower composite stirring component rotate in opposite directions to build the initial circulating flow field; (3) Raw material dissolution stage: under the condition of controlling the temperature inside the kettle, add cellulose diacetate raw material in batches, and gradually increase the stirring speed according to the dissolution process. The material dispersion and dissolution are promoted by the synergistic effect of middle shear and lower sweeping. (4) Homogenization and monitoring stage: After the material is added, continue stirring until the solution is uniform. Monitor the pressure and temperature of the isolation liquid throughout the process. When the pressure of the isolation liquid is lower than the set value, automatically replenish or adjust the operation of the circulation pump to ensure that there is no acetone vapor leakage throughout the dissolution process.

[0017] Preferably, during the dissolution process, the stirring intensity of the middle shear dissolution component and the lower composite stirring component is optimized by adjusting the output speed ratio of the coaxial reverse drive system according to the change in system viscosity, so as to adapt to the flow field requirements of different dissolution stages.

[0018] Due to the adoption of the above technical solution, the beneficial effects obtained by the present invention include: 1. This invention utilizes a coaxial dual-reverse rotation stirring system (with a hollow short shaft and a solid long shaft rotating synchronously in opposite directions), combined with the axial thrust of the central eight-bladed impeller and the radial disturbance of the lower composite stirring assembly, to form a three-dimensional composite flow field of "upward thrust and downward disturbance, internal and external circulation" within the vessel. Even in a high-solids-content, high-viscosity cellulose diacetate acetone solution system, it can still maintain efficient material circulation, solving the technical bottleneck of low circulation efficiency and uneven mixing in traditional single-shaft stirring under high-viscosity conditions. 2. In this invention, the central eight-bladed impeller constructs a high-intensity shear-dissolution zone in the middle of the vessel, which can precisely break down cellulose agglomerates and accelerate solvent penetration and molecular chain deentanglement. The lower composite stirring assembly, through the synergistic effect of the anchor-type impeller sweeping and the enhanced eight-bladed impeller, eliminates the low-speed dead zones on the vessel wall and bottom, promoting continuous material renewal into the shear zone. The combination of these two components effectively shortens the dissolution time compared to traditional stirring systems, meeting the efficiency and quality stability requirements of large-scale continuous production. 3. In view of the flammable and volatile nature of acetone, this invention adopts a back-to-back double-end mechanical seal and a positive pressure isolation fluid system. An inert isolation fluid with a pressure 0.05~0.1MPa higher than that inside the vessel is constructed to form a dynamic barrier, completely blocking axial leakage of vapor. The sealing friction pair is made of wear-resistant and corrosion-resistant materials such as silicon carbide / tungsten carbide, which, together with the cooling circulation system, enables long-term leak-free operation and fully meets the chemical explosion-proof safety specifications. At the same time, it can also reduce the wear of the sealing surface, significantly extending the service life and operational stability of the equipment. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of an embodiment of a high-efficiency dissolving and stirring device for cellulose diacetate acetone solution according to the present invention; Figure 2 This is a partial structural schematic diagram of the stirring vessel of an embodiment of a high-efficiency dissolving and stirring device for cellulose diacetate acetone solution according to the present invention; Figure 3 This is a schematic diagram of one embodiment of the bevel gear set in this invention; Figure 4 This is a schematic diagram of one embodiment of the double-end mechanical seal structure in this invention.

[0020] The attached figures are labeled as follows: 11. Sealed explosion-proof vessel body; 12. Vessel lid; 2. Drive motor; 221. Coupling; 3. Rigid cage; Bevel gear set; 41. Driving bevel gear; 42. Intermediate bevel gear; 43. Driven bevel gear; Hollow short shaft; 6. Solid long shaft; 66. Support frame; 7. Eight-bladed airfoil impeller; 8. Anchor-type impeller; 9. Flat keyway; 10. Double-end sealing system; 13. Bushing; 14. First stationary ring seat; 15. First spring seat; 16. First stationary ring; 17. First moving ring; 18. First moving ring seat; 19. Second spring seat; 20. Second moving ring seat; 21. Second moving ring; 22. Second stationary ring; 23. Second stationary ring seat. Detailed Implementation

[0021] Please see Figure 1-4As shown, this invention mainly provides a stirring vessel for a high-efficiency dissolution and stirring device for cellulose diacetate acetone solution, which solves the problems of low dissolution efficiency of high viscosity systems, obvious dead corners and material buildup in the vessel, and insufficient sealing reliability in the acetone environment in the prior art, thereby improving dissolution and stirring efficiency and enhancing operational safety; it specifically includes: a sealed explosion-proof vessel body 1, a coaxial reverse drive system, a middle shear dissolution component, a lower composite stirring component, and a positive pressure isolation double-end face sealing system; wherein, the middle shear dissolution component and the lower composite stirring component are both located inside the sealed explosion-proof vessel body 1, and the positive pressure isolation double-end face sealing system is integrated into the vessel cover penetration at the top of the sealed explosion-proof vessel body; Specifically, the sealed explosion-proof vessel 1 is used to construct a sealed space for dissolving cellulose diacetate in acetone solvent, which is suitable for flammable and volatile environments containing acetone vapor.

[0022] The coaxial reverse drive system, located at the top of the sealed explosion-proof vessel 1, includes a drive motor 2, a rigid retainer 3, a bevel gear set 4, a hollow short shaft 5, a solid long shaft 6, and a support frame 66. The drive motor 2 is bolted to the top platform of the rigid retainer 3, which is fixedly mounted on the vessel cover of the sealed explosion-proof vessel. The support frame 66 is a rigid support structure, fixedly installed inside the top transmission cavity of the sealed explosion-proof vessel 1, providing precise installation positioning and operation guidance for the bevel gear set 4, ensuring stable meshing clearance and transmission accuracy of the bevel gear set. The output shaft of the drive motor 2 extends downward into the support frame 66 and is sequentially connected to the bevel gear set 4, the hollow short shaft 5, and the solid long shaft 6 via a coupling. The support frame is made of rigid cast steel, providing rigid support for the transmission system. It can be fixedly connected to the bearing seat of the bevel gear set with bolts to ensure the meshing accuracy of the bevel gears and the coaxiality of the stirring shaft.

[0023] The hollow short shaft 5 is a hollow cylindrical structure. Its upper end is connected to the bevel gear set 4, and its lower end passes through the lid 11 of the sealed explosion-proof vessel body 1 and extends into the upper part of the sealed explosion-proof vessel body 1. The solid long shaft 6 is coaxially inserted into the internal cavity of the hollow short shaft 5 and extends downward to the lower part of the sealed explosion-proof vessel body 1. Its upper end is coaxially connected to the bevel gear set 4, and its lower end is fixedly connected to the composite lower stirring assembly. The solid long shaft 6 is made of high-strength corrosion-resistant metal material, and its deflection and vibration are limited by the reasonable selection of shaft diameter and support span, so as to improve the operational stability of the high viscosity system during stirring and reduce the adverse effects on the mechanical seal end face.

[0024] In this embodiment, the bevel gear set 4 includes: a driving bevel gear 41 connected to the output shaft of the drive motor 2, an intermediate bevel gear 42 meshing with the driving bevel gear 41, and a driven bevel gear 43 fixedly connected to the hollow short shaft 5 and the solid long shaft 6 respectively. The intermediate bevel gear 42 meshes with both the driving bevel gear and the driven bevel gear 43, so that the hollow short shaft 5 and the solid long shaft 6 obtain power output in opposite directions of rotation.

[0025] Specifically: The output shaft of drive motor 2 is rigidly connected to the drive bevel gear 41 via coupling 221, directly transmitting the motor torque to the drive bevel gear 41 as the power input of the entire transmission system (after startup, it drives the drive bevel gear to rotate at a set speed, providing initial power to the entire transmission system); the drive bevel gear is vertically arranged on the upper part of the support frame and directly connected to the output shaft of the drive motor via coupling, with its teeth meshing vertically with the horizontally arranged intermediate bevel gear, converting the horizontal output torque of the motor into vertical transmission; the intermediate bevel gear is horizontally mounted on the bearing seat in the middle of the support frame 66, meshing with both the upper drive bevel gear and the lower driven bevel gear, realizing 90° steering and bidirectional power splitting, and is the core hub for converting single power input to dual-shaft output; the drive bevel gear and the driven bevel gear are coaxially arranged vertically. The driven bevel gears are rigidly connected to the hollow short shaft and the solid long shaft respectively, transmitting torque synchronously to the two coaxial stirring shafts. The driven bevel gears are fixedly connected to the upper end of the hollow short shaft via a flat key / spline, receiving the torque transmitted by the intermediate bevel gear 42 and driving the hollow short shaft 5 to rotate. The driven bevel gears are fixedly connected to the upper end of the solid long shaft 6 in the same way, receiving the torque transmitted by the intermediate bevel gear 42 and driving the solid long shaft 6 to rotate. The driven bevel gears 43 and the intermediate bevel gears 42 mesh in opposite directions, causing the hollow short shaft 5 and the solid long shaft 6 to rotate synchronously in opposite directions along the same central axis, realizing the reverse operation of the upper and lower stirring blades. This structure, through the precise meshing of the bevel gear set 4, achieves the reverse rotation of the coaxial dual shafts while ensuring transmission efficiency, providing a power basis for the formation of a composite flow field inside the vessel.

[0026] In addition, the working principle of bevel gear set 4 is as follows: it uses a three-stage meshing structure to complete the steering and distribution of power. The driving bevel gear 41 meshes vertically with the intermediate bevel gear 42, converting the horizontal output torque of the motor into vertical power transmission, which is suitable for the axial stirring requirements at the top of the vessel. At the same time, the intermediate bevel gear 42 meshes with the driven bevel gear 43, transmitting power synchronously to the two coaxially arranged stirring shafts. Through the difference in the meshing rotation direction, the driven bevel gear obtains the opposite rotation direction. Driven bevel gear 43 is rigidly connected to the hollow short shaft 5 and the solid long shaft 6 respectively: the driven bevel gear connected to the hollow short shaft 5 drives it to rotate in the forward direction, driving the central eight-bladed airfoil impeller to push the flow downward; the driven bevel gear connected to the solid long shaft 6 drives it to rotate in the reverse direction, driving the lower composite stirring assembly to disturb upward; the two shafts rotate synchronously in opposite directions along the same central axis, with a speed ratio of 1:1, ensuring that the upper and lower flow fields form a complementary composite cycle.

[0027] In this embodiment, through coaxial counter-rotation, the upper and lower stirring paddles construct a composite flow field with opposite directions and superposition within the vessel: the central eight-bladed airfoil stirring paddle 7 forms an axial main circulation from top to bottom, establishing a shear dissolution zone in the middle; the lower composite stirring assembly enhances material renewal in the bottom and near-wall areas of the vessel, eliminating low-speed dead zones; the two work together to maintain efficient circulation and shearing of the high-viscosity solution under full-load conditions, significantly improving the dissolution efficiency and uniformity of cellulose diacetate; and the transmission system, through a precise bevel gear meshing design, optimizes the stirring flow field while ensuring transmission efficiency, serving as the core power foundation for the efficient dissolution and safe operation of the entire device.

[0028] In this embodiment, the central shear-dissolution component, fixed to the lower end of the hollow short shaft 5, is arranged in the upper middle region of the sealed explosion-proof vessel 1. It is an eight-bladed airfoil impeller 7, used to establish a top-down axial main circulation flow in the vessel and form a stable shear-dissolution zone in the middle region of the vessel, thereby promoting the wetting, dispersion, and dissolution mass transfer of cellulose diacetate aggregates. The blades of the eight-bladed airfoil impeller 7 are installed at a downward tilt angle, generating an axial downward thrust when rotating, enhancing the overall circulation efficiency of the material in the vessel. The diameter of the eight-bladed airfoil impeller 7 is 60% of the inner diameter of the sealed explosion-proof vessel, preferably 55% to 65% of the inner diameter of the vessel, used to form an axial main circulation flow field and a high-intensity shear-dissolution zone in the middle of the vessel. In this embodiment, the lower composite stirring assembly is fixed to the lower end of the solid long shaft and includes an anchor stirring paddle 8 coaxially connected to the eight-bladed impeller 7 in the middle region. The anchor stirring paddle 8 is used to sweep and renew the material on the vessel wall and bottom. The anchor stirring paddle 8 has an anchor-shaped structure with its impeller hub rigidly connected to the solid long shaft. Multiple paddle arms extend outward to near the vessel wall and bend at the outer edge to form a mountain-shaped frame. A scraping gap of 5mm to 15mm is maintained between the outer side of the paddle arms and the vessel wall. When rotating, it is used to sweep and renew the high-viscosity slurry near the vessel wall.

[0029] Specifically, the anchor-type agitator 8 can drive the material deposited at the bottom of the vessel into the main circulating flow field and suppress material adhesion and local concentration accumulation on the vessel wall. It mainly acts on the boundary layer of the vessel wall and the bottom region, eliminating low-speed dead zones near the wall, promoting solvent renewal in the boundary layer, and preventing material adhesion and deposition. The eight-bladed airfoil agitator 7 enhances the axial and radial flow in the middle and lower regions of the vessel, accelerates the migration of material at the bottom of the vessel to the central region, strengthens the circulation connection between the upper and lower flow fields, mainly acts on the lower central region of the vessel, increases the speed at which material at the bottom of the vessel participates in the overall circulation, and forms a continuous axial circulating flow field in conjunction with the middle agitator. Moreover, the eight-bladed airfoil agitator 7 and the anchor-type agitator 8 are rigidly connected coaxially and rotate synchronously in opposite directions, forming a composite flow field of "upward push and downward disturbance" in the vessel. The synergistic effect of the two can improve the overall circulation and dissolution efficiency of high-viscosity solutions under full-load conditions, reduce the risk of stirring dead zones and material adhesion in the bottom and near-wall regions, and significantly improve the overall dissolution efficiency and uniformity of high-viscosity cellulose diacetate acetone solutions.

[0030] In this embodiment, the axial distance between the middle shear dissolution assembly (eight-bladed impeller 7) and the lower composite stirring assembly (anchor impeller 8) is 1.0 to 1.5 times the diameter of the middle impeller, to ensure effective connection between the upper and lower flow fields and avoid energy waste or excessive local shear caused by strong interference between impellers. Furthermore, the axial distance is a segmented adjustable structure. Multiple sets of flat keyways 9 at preset positions are set on the solid long shaft 6, and the lower anchor impeller 8 hub is set with a matching keyway. Ordinary flat keys are used to transmit torque (during assembly, ordinary flat keys are placed into the shaft keyway of the selected position, and then the impeller hub is fitted with the long shaft so that the torque is transmitted through the flat key). The shaft shoulder, positioning sleeve / spacer and retaining ring and / or locking nut are used for axial limiting and locking, thereby realizing the adjustment of the distance between the upper and lower impellers at different positions to adapt to the dissolution requirements of different loading liquid levels and viscosity stages (wherein, the flat keyways can be arranged radially evenly or in a single reference direction in the circumferential direction to ensure assembly positioning consistency and transmission reliability). Preferably, the loading coefficient of the vessel during dissolution operation is 80% to 90% (approximately 85%) to meet the requirements of industrial full-load preparation and to match the above-mentioned composite flow field structure; the stirring paddle material can be selected according to the working conditions as a material that is acetone resistant, wear resistant and meets the strength requirements, such as a stainless steel base material with a corrosion resistant coating, or high-performance engineering materials as local wear resistant / corrosion resistant components, etc. (no limitation).

[0031] In this embodiment, the positive pressure isolation double-end face sealing system 10 is set at the position where the hollow short shaft 5 penetrates the vessel cover 11. Through the back-to-back arrangement of dynamic and static rings and the positive pressure isolation liquid, the acetone vapor zero-leakage seal is achieved.

[0032] Specifically, such as Figure 4As shown, the positive pressure isolation double-end face sealing system 10 includes: a bushing 13, two sets of back-to-back arranged end face sealing pairs, a spring loading mechanism, an auxiliary sealing ring, and a sealing cavity shell forming an independent sealing cavity; wherein, the two sets of end face sealing pairs are respectively composed of a first stationary ring 16 and a first rotating ring 17, and a second stationary ring 22 and a second rotating ring 21; the first stationary ring 16 and the second stationary ring 22 are respectively embedded in the first stationary ring seat 14 and the second stationary ring seat 23, and the first stationary ring seat 14 and the second stationary ring seat 23 are fixedly installed at the inner cavity step of the sealing cavity shell to keep the stationary ring stationary; the first rotating ring 17 and the second rotating ring 21 are respectively installed on the first rotating ring seat 18 and the second rotating ring seat 20 and rotate with the bushing 13; the first rotating ring seat 18 and the second rotating ring seat 20 are used to axially position the rotating ring and bear the spring preload. The bushing 13 is fitted onto the outer circle of the hollow short shaft 5 and fixed with an interference fit. The bushing 13 rotates synchronously with the hollow short shaft 5, serving as the rotating mounting base for the rotating ring assembly. The spring loading mechanism includes a first spring seat 15, a second spring seat 19, and several compression springs disposed therein. One end of each spring abuts against the first spring seat 15 and the second spring seat 19, respectively, while the other end abuts against the first rotating ring seat 18, the second rotating ring seat 20, or the back of the rotating ring, thereby applying axial preload to the first rotating ring 17 and the second rotating ring 21. When the end face is worn or there is slight axial movement in the shaft system, the spring loading mechanism provides automatic compensation, keeping the end faces of the rotating and stationary rings in stable contact and forming a continuous sealing liquid film. To prevent the isolation fluid from leaking around the end face sealing pair and to ensure that the isolation chamber is independently controllable, a first auxiliary sealing ring is provided at the mating point of the first moving ring 17, the second moving ring 21 and the bushing 13; a second auxiliary sealing ring is provided at the mating point of the first stationary ring 16, the second stationary ring 22 and the first stationary ring seat 14, the second stationary ring seat 23 respectively; and a third auxiliary sealing ring is provided at the joint between the first stationary ring seat 14, the second stationary ring seat 23 and the sealing chamber housing and the end cover / cap.

[0033] Furthermore, the sealing friction pair preferably uses silicon carbide / resin-impregnated graphite or tungsten carbide / tungsten carbide pairing to balance wear resistance and chemical corrosion resistance; the auxiliary sealing ring is made of fluororubber or perfluoroether rubber to adapt to the acetone environment for a long time; the sealing cavity is equipped with a cooling jacket or circulation channel to introduce cooling water to remove frictional heat and prevent damage to the sealing surface caused by dry friction; the entire sealing assembly is modularly disassembled and assembled through a snap ring and threaded end cap structure, which is convenient for replacement and maintenance; its isolation fluid can be nitrogen (gas phase) or ethylene glycol aqueous solution (liquid phase), and the external isolation fluid circulation pipeline can be equipped with a pressure sensor and an automatic regulating valve to automatically replenish pressure when the isolation fluid pressure is lower than the pressure inside the vessel by 0.03MPa; the cooling jacket is circulated with cooling water at 20℃~30℃ to control the temperature of the sealing cavity to not exceed 50℃.

[0034] The present invention also provides a method for efficiently dissolving cellulose diacetate in acetone solution in conjunction with the above-mentioned apparatus, comprising the following steps: (1) Sealing preparation stage: Add metered acetone solvent to the sealed explosion-proof vessel, start the positive pressure isolation double end face sealing system, and adjust the isolation liquid pressure to be 0.05-0.1MPa higher than the pressure inside the vessel, so that a stable positive pressure isolation environment is formed at the double end face mechanical seal; (2) Initialization stage of flow field: Under the condition that the loading coefficient is 80% to 90% (preferably about 85%), the coaxial reverse drive system is started at a low speed of 10 to 30 r / min. The hollow short shaft and the solid long shaft are driven to rotate in opposite directions on the same axis through the bevel gear set, so that the dissolving stirring paddle in the upper part of the vessel and the composite lower stirring component in the lower part of the vessel work together to establish the initial circulating flow field; (3) Raw material dissolution stage: Add cellulose diacetate raw material in batches at a temperature of 25℃~40℃, and gradually increase the stirring speed to 50~80r / min according to the dissolution state, so that the dissolution stirring paddle forms the main circulation and shear dissolution zone in the middle. At the same time, the lower composite stirring component continuously sweeps and renews the bottom and near-wall materials and enhances axial / radial circulation to accelerate the disintegration of agglomerates and the renewal of boundary layer solvent. (4) Homogenization and monitoring stage: After the material is added, maintain stirring for 2 to 4 hours until the solution is homogeneous. Monitor the pressure and temperature of the isolation liquid throughout the process to ensure the stable operation of the sealing system.

[0035] To verify the performance improvement effect of the high-efficiency dissolution and stirring device for cellulose diacetate acetone solution of the present invention, numerical simulation and experimental comparison were conducted. The simulation conditions were set as a typical shear-thinning non-Newtonian system. Numerical simulation software such as Fluent was used, and a flow model (e.g., laminar flow model) matching the system viscosity level and Reynolds number was selected. Under the same volume, same loading coefficient, same impeller structure and rotation speed, the stirring coverage effect and energy input level of different steering modes were evaluated. The stirring power per unit volume is used to characterize the energy input intensity obtained by a unit volume of fluid in the vessel, and can be defined as the ratio of stirring power to the total volume of liquid in the vessel, expressed as: PV = 2πMNV. To characterize the effective degree of fluid participation in the bulk mixing, the region where the flow velocity in the vessel is below a predetermined threshold is defined as the stirring dead zone; in this embodiment, it is preferable to define the region with a flow velocity U < 0.01U_tip as the stirring dead zone, and the remaining regions as the effective stirring zone. The effective stirring volume fraction ηV is defined as the percentage of the effective stirring zone volume to the total liquid volume in the vessel, and its calculation formula is: ηV = 1 - VU < 0.01UtipV × 100% The simulation results are shown in the table below:

[0036] The results show that the reverse rotation significantly increases the volume fraction of the active shear region, indicating that the structure can effectively break the laminar flow and improve the material dispersion rate and mixing uniformity. Although the energy consumption per unit volume increases, the improvement in stirring efficiency and mass transfer rate is even greater, indicating higher energy utilization efficiency. CFD simulation shows that the reverse shear zone forms a strong spiral downward mainstream and an upward convection overlap, which helps to suppress slurry deposition and achieve uniform heat distribution.

[0037] It should be noted that this invention uses a coaxial dual-reverse rotation stirring system (with the hollow short shaft and the solid long shaft rotating synchronously in opposite directions), combined with the axial thrust of the central eight-bladed impeller and the radial disturbance of the lower composite stirring assembly, to form a three-dimensional composite flow field of "upward thrust and downward disturbance, internal and external circulation" in the reactor. Even in a high-solids-content, high-viscosity cellulose diacetate acetone solution system, it can still maintain efficient material circulation, solving the technical bottleneck of low circulation efficiency and uneven mixing in traditional single-shaft stirring under high viscosity conditions. The central eight-bladed impeller creates a high-intensity shear dissolution zone in the middle of the vessel, precisely breaking down cellulose agglomerates and accelerating solvent penetration and molecular chain deentanglement. The lower composite stirring assembly, through the synergistic effect of the anchor impeller sweeping and the enhanced eight-bladed impeller, eliminates low-speed dead zones on the vessel wall and bottom, promoting continuous material renewal into the shear zone. The combination of these two components effectively shortens the dissolution time compared to traditional stirring systems, meeting the efficiency and quality stability requirements of large-scale continuous production. Meanwhile, the distance between the upper and lower stirring paddles can be adjusted in stages within the range of 1.0 to 1.5D (achieved by using a common flat key and multiple sets of preset keyways arranged along the axial direction, and by using an axial limiting and locking structure), and is matched with the loading coefficient (80% to 90%, about 85%), so that effective main circulation and reasonable shear distribution can still be maintained under full load conditions, which is suitable for industrial continuous batch preparation. In addition, the double-end mechanical seal can form a highly reliable sealing barrier, which can effectively prevent solvent vapor from leaking along the axis under the conditions of acetone volatility and flammability, improve the safety and sealing reliability of the device operation, and is suitable for cellulose ester related preparation processes.

[0038] The foregoing descriptions and embodiments are provided to enable those skilled in the art to understand and apply the present invention. It will be apparent to those skilled in the art that various modifications can be easily made to these contents, and the general principles described herein can be applied to other embodiments without creative effort. Therefore, the present invention is not limited to the foregoing descriptions and embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from its scope should be within the protection scope of the present invention.

Claims

1. A high-efficiency stirring device for cellulose diacetate acetone solution, characterized in that, include: The sealed explosion-proof vessel is used to create a closed space for dissolving cellulose diacetate in acetone solvent, and is suitable for flammable and volatile environments containing acetone vapor. A coaxial reverse drive system, located at the top of the sealed explosion-proof vessel, includes a drive motor, a rigid retainer, a bevel gear set, a hollow short shaft, a solid long shaft, and a support frame. The drive motor is fixedly mounted above the top of the sealed explosion-proof vessel via the rigid retainer; the support frame is fixedly mounted on the bevel gear set; the output shaft of the drive motor extends downward and is sequentially connected to the bevel gear set, the hollow short shaft, and the solid long shaft; wherein, the hollow short shaft is a hollow cylindrical structure, with its upper end connected to the bevel gear set, and its lower end passing through the vessel cover of the sealed explosion-proof vessel and extending into the upper middle part of the sealed explosion-proof vessel; the solid long shaft is coaxially inserted through the internal cavity of the hollow short shaft, with its upper end coaxially connected to the bevel gear set, and its lower end passing through the bottom opening of the hollow short shaft and extending to the bottom of the sealed explosion-proof vessel; the drive motor synchronously drives the hollow short shaft and the solid long shaft to rotate in opposite directions along the same central axis via the bevel gear set; The central shearing and dissolving component, fixed to the lower end of the hollow short shaft, is an eight-bladed airfoil-shaped impeller. The lower composite stirring assembly is fixed to the lower end of the solid long shaft, including an anchor stirring paddle coaxially connected to the eight-bladed stirring paddle in the middle region. The anchor stirring paddle is used to sweep and renew the material on the vessel wall and bottom of the sealed explosion-proof vessel. The positive pressure isolation double-end face sealing system is set at the lid position of the hollow short shaft penetrating the sealed explosion-proof vessel body. Through the back-to-back arrangement of dynamic and static rings and the positive pressure isolation liquid, it achieves zero leakage sealing of acetone vapor.

2. The stirring device according to claim 1, characterized in that, The bevel gear set includes: a driving bevel gear connected to the output shaft of the drive motor, an intermediate bevel gear meshing with the driving bevel gear, and a driven bevel gear fixedly connected to the hollow short shaft and the solid long shaft respectively. The intermediate bevel gear meshes with both the driving bevel gear and the driven bevel gear, so that the hollow short shaft and the solid long shaft obtain power output in opposite directions of rotation.

3. The stirring device according to claim 1, characterized in that, The blades of the eight-bladed airfoil impeller are installed at a downward tilt angle, which generates an axial downward thrust when rotating, enhancing the overall circulation efficiency of the material inside the vessel.

4. The stirring device according to claim 1, characterized in that, The anchor-type stirring paddle has an anchor-type mountain-shaped structure. Its paddle hub is rigidly connected to a solid long shaft. Multiple paddle arms extend outward to near the vessel wall and fold at the outer edge to form a mountain-shaped frame. A scraping gap of 5mm to 15mm is maintained between the outer side of the paddle arms and the vessel wall for sweeping and renewing the high-viscosity slurry near the vessel wall.

5. The stirring device according to claim 1, characterized in that, The diameter of the eight-bladed impeller is 55% to 65% of the inner diameter of the sealed explosion-proof vessel, and it is used to form an axial main circulation flow field and a high-intensity shear dissolution zone in the middle of the vessel.

6. The stirring device according to claim 1, characterized in that, The axial distance between the middle shearing and dissolving component and the lower composite stirring component is 1.0 to 1.5 times the diameter of the middle stirring paddle, and is adjustable in stages through the following structure: At least two sets of circumferentially distributed flat keyways are provided along the axial direction on the solid long shaft. The lower composite stirring assembly has a matching keyway in the impeller hub, which transmits torque through a common flat key, and achieves axial positioning and locking through a combination of shaft shoulder, positioning spacer, elastic retaining ring and locking nut.

7. The stirring device according to claim 1, characterized in that, The positive pressure isolation double-end face sealing system includes: two sets of back-to-back dynamic and static ring pairs, a sealing cavity, and an external isolation liquid circulation pipeline. The isolation liquid pressure in the sealing cavity is 0.05-0.1 MPa higher than the internal pressure of the vessel body. The friction pair of the double-end face mechanical seal structure is made of silicon carbide paired resin impregnated graphite or tungsten carbide paired tungsten carbide. The auxiliary sealing ring is made of acetone-resistant perfluoroether rubber. The sealing cavity integrates a cooling jacket for heat dissipation.

8. A method for preparing a cellulose diacetate acetone solution based on the stirring apparatus according to any one of claims 1-7, characterized in that, Includes the following steps: (1) Sealing preparation stage: Add metered acetone solvent to the sealed explosion-proof vessel, start the positive pressure isolation double end face sealing system, adjust the isolation liquid pressure to be 0.05-0.1MPa higher than the pressure inside the vessel, and establish a positive pressure explosion-proof sealing environment; (2) Flow field initialization stage: Start the coaxial reverse drive system at a low speed to make the middle shear dissolution component and the lower composite stirring component rotate in opposite directions to build the initial circulating flow field; (3) Raw material dissolution stage: under the condition of controlling the temperature inside the kettle, add cellulose diacetate raw material in batches, and gradually increase the stirring speed according to the dissolution process. The material dispersion and dissolution are promoted by the synergistic effect of middle shear and lower sweeping. (4) Homogenization and monitoring stage: After the material is added, continue stirring until the solution is uniform. Monitor the pressure and temperature of the isolation liquid throughout the process. When the pressure of the isolation liquid is lower than the set value, automatically replenish or adjust the operation of the circulation pump to ensure that there is no acetone vapor leakage throughout the dissolution process.

9. The method according to claim 8, characterized in that, During the dissolution process, the stirring intensity of the middle shear dissolution component and the lower composite stirring component is optimized by adjusting the output speed ratio of the coaxial reverse drive system according to the changes in system viscosity, thus adapting to the flow field requirements of different dissolution stages.

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