A cleaning method for a filter screen for lyocell pilot plant lines

Abstract

The present application relates to lyocell fiber production technical field, specifically disclose a kind of lyocell small test line filter screen cleaning method, comprising the following steps: cleaning filter screen residual glue;First-stage solvent dissolves cleaning;The filter screen after pretreatment is placed into first cleaning tank, using NMMO concentrated solvent, under constant temperature condition, the filter screen surface layer and shallow mesh hole cellulose residual glue are dissolved quickly, 70%~80% attached dirt is removed, and first-stage cleaning of filter screen is completed;Second-stage solvent gradient fine cleaning;Third-stage solvent deep cleaning;Ultrasonic washing;The cleaning method of the application can protect the filter screen body, prolong service life;No high-temperature calcination is needed throughout, avoid the damage of high temperature to the structure of metal filter screen, the filtration precision and mechanical strength of filter screen are effectively protected, which is the fundamental guarantee for realizing the repeated use of filter screen;Good cleaning effect;Filter screen recycling, cost reduction and efficiency improvement;Energy saving, environmental protection, green and low carbon;Simple operation, strong adaptability.

Description

Technical Field

[0001] This invention belongs to the field of lyocell fiber production technology, specifically relating to a cleaning method for a filter screen used in a small-scale lyocell pilot production line. Background Technology

[0002] Lyocell fiber is a new generation of regenerated cellulose fiber made from natural cellulose (such as bamboo and wood pulp) as raw material and N-methylmorpholine-N-oxide (NMMO) as solvent using a dry-jet wet spinning process. Its production process involves no chemical reaction and is hailed as the green fiber of the 21st century.

[0003] In the spinning process of lyocell fibers, the spinning solution must first be filtered through a filter to remove insoluble substances, gel particles, and other particulate matter that may clog the spinneret or affect spinning stability. The filter, as the core filtration element of the spinning assembly, is typically composed of 3-5 layers of stainless steel mesh with different mesh sizes, assembled by spot welding. As spinning time increases, a large amount of impurities and gel particles gradually accumulate on the surface and inside of the filter, gradually clogging the pores and causing a continuous decline in filtration efficiency. When the post-filtration pressure rises beyond the allowable range of the process, the filter can no longer meet the quality requirements of spinning production and must be replaced. Because a large amount of adhesive adheres to the surface and inside of the filter, conventional cleaning methods cannot completely remove the residual adhesive. Therefore, the filter is often discarded as a consumable after a single use. While this method is simple, treating the filter as solid waste results in resource waste and high production costs. Therefore, there is an urgent need to find a method or technology to solve the problem of the inability to reuse lyocell fiber filter screens.

[0004] Currently, there are related patent technologies disclosed for cleaning spinnerets and filters in lyocell fiber production. Invention patent CN115161780A discloses a cleaning process method for lyocell fiber spinning spinnerets. This invention utilizes a combination of high-pressure blowing, high-pressure cleaning, and ultrasonic cleaning to thoroughly clean the residue in the spinneret's filament holes. However, the spinneret has straight filament holes, while the filter assembly has a multi-layered stacked structure, so this patent is not applicable to the cleaning of the filter.

[0005] Invention patent CN121519178A discloses "a cleaning method for filter screens on spinnerets in lyocell fiber production processes". The technical solution includes the following steps: component disassembly → soaking and steaming → calcination and carbonization → high-pressure spraying → alkaline washing, acid washing, and ultrasonic cleaning → water washing and drying. The core of this solution is to carbonize the residual adhesive on the surface of the filter screen through high-temperature calcination, and then remove the carbon deposits through physical methods (high-pressure spraying and ultrasonic cleaning). The purpose of acid washing, alkaline washing, and ultrasonic cleaning is to remove the black carbon deposits on the surface of the metal filter screen component, so as to restore its original color and performance, thereby realizing the reuse of the filter screen.

[0006] The existing technology still has the following shortcomings: 1. High-temperature calcination causes thermal damage to metal filter screens; existing technology uses calcination and carbonization to remove residual adhesive on the surface of the filter screen. High-temperature treatment will cause damage to the metal filter screen, affecting the filtration accuracy and mechanical strength of the filter screen, and shortening the service life of the filter screen. Second, there are safety hazards and environmental problems; the residual rubber decomposes rapidly when heated during the calcination process, which may cause an explosion hazard. In addition, the toxic and harmful gases and irritating odors produced by combustion seriously pollute the environment and harm human health, which is inconsistent with the green production process of lyocell fiber. Third, it has high energy consumption and complex operation. The calcination process needs to be run at a high temperature of 350℃-600℃ for 4-8 hours. The equipment has high power and high energy consumption. At the same time, the entire cleaning process requires at least 6 steps to complete, and the operation is cumbersome and complicated. Fourth, it takes a long time; after high-temperature calcination for 4-8 hours, it needs to be cooled down for a long time. The whole process takes a long time, usually several hours or even more than ten hours. Summary of the Invention

[0007] The purpose of this invention is to provide a cleaning method for a filter screen used in a Lyocell pilot production line, so as to solve the problems mentioned in the background art.

[0008] To achieve the above objectives, the present invention provides the following technical solution: A method for cleaning a filter screen for a Lyocell small test line includes the following steps: S1: Clean the filter screen of residual adhesive; After removing the spinning assembly, immerse the filter screen to be cleaned completely in hot water to solidify the adhesive on the surface of the filter screen. Then (use a scraper or other tools) to scrape off large pieces of residual adhesive on the surface of the filter screen. After completing the pretreatment, the initial impurities are removed, which greatly reduces the load of subsequent solvent cleaning. S2: First-stage solvent dissolution and cleaning; The pretreated filter screen is placed in the first cleaning tank and immersed in N-methylmorpholine-N-oxide (NMMO) concentrated solvent under constant temperature conditions to quickly dissolve the cellulose residue on the surface and shallow mesh of the filter screen, remove 70% to 80% of the attached dirt, and complete the first-stage cleaning of the filter screen. S3: Secondary solvent gradient cleaning; after the primary cleaning, the filter screen is transferred to the second cleaning tank and continuously immersed in the same concentration of N-methylmorpholine-N-oxide (NMMO) solvent at the same temperature to dissolve the shallow residual adhesive layer and fine impurities, remove 15% to 20% of the attached dirt, and complete the secondary cleaning of the filter screen. S4: Three-stage solvent deep cleaning; the filter screen after the second-stage cleaning is transferred to the third cleaning tank and soaked in the same concentration of N-methylmorpholine-N-oxide (NMMO) concentrated solvent at a constant temperature. This process is used to deeply peel off the trace amounts of residual adhesive embedded in the deep pores and gaps of the multi-layer filter screen, achieving fine impurity removal and completing the three-stage cleaning of the filter screen. S5: Ultrasonic water washing; The filter screen after the three-stage solvent cleaning is placed in a room temperature water washing tank and cleaned under ultrasonic conditions. The ultrasonic cavitation effect generates micro-jets and impact forces to thoroughly remove fine glue residue and ultrafine powder impurities from the mesh, eliminate cleaning dead corners, and complete the ultrasonic water washing of the filter screen. S6: Drying and microscopic inspection; After ultrasonic cleaning, the filter screen is dried and the mesh transparency and impurity residue are observed through an industrial microscope. The filter screen with transparent mesh, no impurity blockage, and intact appearance can be reused for spinning.

[0009] Preferably, the soaking time in S1 is 20-40 minutes.

[0010] Preferably, the concentrated solvent in S2 is N-methylmorpholine-N-oxide (NMMO) with a concentration of 83% to 85%.

[0011] Preferably, the constant temperature condition in S2 is 90–105°C.

[0012] Preferably, the soaking time in S2 is 1 to 3 hours.

[0013] Preferably, the soaking time in S3 is 1 to 2 hours.

[0014] Preferably, the soaking time in S4 is 1 to 2 hours.

[0015] Preferably, the ultrasonic conditions in S5 are 20-30 Hz, and the cleaning time is 30-40 min.

[0016] Preferably, the drying temperature in step S6 is 80–90°C.

[0017] Compared with the prior art, the beneficial effects of the present invention are: 1. Protects the filter body and extends its service life; the entire process does not require high-temperature calcination, avoiding damage to the metal filter structure caused by high temperatures. The filtration accuracy and mechanical strength of the filter are effectively protected, which is the fundamental guarantee for the multiple reuse of the filter. 2. Excellent cleaning effect: Through a combination of multiple N-methylmorpholine-N-oxide (NMMO) solvent gradient dissolution and ultrasonic water washing processes, residual adhesive on the surface and inside the mesh of the filter screen can be thoroughly removed. Microscopic examination of the qualified filter screen shows no significant difference in post-filtration pressure compared to a new screen during the spinning process, proving that its filtration performance has been restored to its original level. 3. Reusable filters reduce costs and increase efficiency; This solution allows filters to be reused 1-2 times. Compared to treating them as disposable consumables, the consumption of filters can be reduced to 1 / 3 to 1 / 2 of the original amount, resulting in significant cost reduction and efficiency improvement. 4. Energy-saving and environmentally friendly, green and low-carbon: This solution does not require high-temperature calcination, which greatly reduces energy consumption; the cleaned N-methylmorpholine-N-oxide (NMMO) waste liquid can be directly fed into the factory's existing N-methylmorpholine-N-oxide (NMMO) recovery system, which is seamlessly connected with the existing production process to achieve solvent recycling; the reuse of filter screens reduces the generation of solid waste, which is in line with the development direction of green manufacturing and circular economy. 5. Simple operation and strong adaptability: This solution only requires a conventional cleaning tank and ultrasonic equipment. It is easy to operate and can be promoted and applied on existing lyocell fiber production lines without the need for large-scale modification of production equipment. Attached Figure Description

[0018] Figure 1 This is a flowchart of the preparation method of the present invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Example:

[0021] Please see Figure 1 As shown, remove the clogged filter from the spinning assembly and soak it in hot water at 70-80℃ for 20-30 minutes to allow the adhesive on the surface of the filter to solidify. Remove it and let it air dry to room temperature. Use a special scraper to gently scrape off any obvious residual adhesive from the surface of the filter.

[0022] Example 1 Process parameter settings: N-methylmorpholine-N-oxide (NMMO) concentration 83%, cleaning temperature 85℃, three-level gradient soaking time 2h, 2h, 1h respectively, magnetic stirring 200r / min, 20HZ ultrasonic water washing 30min.

[0023] Test results: There were no obvious adhesive lumps on the surface of the filter screen, but there were a lot of pore blockages in the deep mesh, which could not meet the requirements for spinning and reuse.

[0024] Example 2: Process parameter settings: N-methylmorpholine-N-oxide (NMMO) concentration 84%, cleaning temperature 95℃, three-level gradient soaking time 2h, 2h, 1h respectively, magnetic stirring 300r / min, 30HZ ultrasonic water washing for 30min.

[0025] Test results: The filter screen surface was clean, with very few impurities and slight pore blockage. The overall cleanliness was high, but there were still risks in the fine functional fiber spinning process, and reuse was not recommended.

[0026] Example 3: Process parameter settings: N-methylmorpholine-N-oxide (NMMO) concentration 85%, cleaning temperature 105℃, three-level gradient soaking time 2h, 1h, 1h respectively, magnetic stirring 300r / min, 30HZ ultrasonic cleaning 30min.

[0027] Test results: The filter screen surface is clean, the mesh is transparent and uniform, there are no impurities or clogging, the filter screen retains its original silver metallic appearance, and it can be reused to replace a new filter screen.

[0028] Comparative Example 1: This comparative example uses the same process parameters as Example 3, but omits the secondary and tertiary gradient cleaning processes and only uses single-tank solvent immersion cleaning for 5 hours.

[0029] Test results: There was a small amount of residual adhesive on the filter screen surface, the filter screen pores were not transparent, there was a lot of clogging, and the cleaning was not thorough.

[0030] Comparative Example 2: This comparative example follows the three-stage gradient cleaning process, solvent concentration, cleaning temperature, and ultrasonic parameters of Example 3, except that the soaking time of the first and second stage solvents is shortened to 1 hour.

[0031] Test results: The filter screen surface was clean, but the filter screen pores were not transparent, with a lot of blockage, indicating that the cleaning was not thorough.

[0032] Comparative Example 3: This comparative example uses a complete three-stage gradient cleaning process, cleaning temperature, and ultrasonic parameters, only adjusting the N-methylmorpholine-N-oxide (NMMO) solvent concentration to 75%.

[0033] Test results: There were a lot of glue clumps on the surface of the filter screen, and the filter screen holes were severely clogged.

[0034] Comparative Example 4: The filter screen is cleaned by calcining at 500℃ for 3 hours, followed by high-pressure rinsing and ultrasonic water washing. After cleaning, the filter screen is free of impurities and can be reused. However, the filter screen is oxidized and turns brass-colored, and the metal mesh is deformed, posing a risk of leakage.

[0035] The cleaned filter assemblies from Examples 1-3 and Comparative Examples 1-4 were examined under a microscope to observe whether there were impurities or debris inside the mesh and whether the mesh was clogged. The test results are shown in Table 1. Table 1. Microscopic examination results of the filter assembly: New filter components silver none none / Example 1 silver large amount large amount no Example 2 silver Very few Very few no Example 3 silver Almost none Almost none able Comparative Example 1 silver large amount large amount no Comparative Example 2 silver small amount small amount no Comparative Example 3 silver large amount large amount no Comparative Example 4 brass color Almost none Almost none able

[0036] This invention utilizes the excellent solubility of N-methylmorpholine-N-oxide (NMMO) solvent in cellulose to dissolve residual adhesive on the surface of a filter screen. Studies have shown that cellulose substances can be rapidly dissolved when the concentration of the N-methylmorpholine-N-oxide (NMMO) solution reaches 85%±2%. This method precisely controls the concentration of the N-methylmorpholine-N-oxide (NMMO) solvent within the preferred range of 85%±2% to ensure optimal dissolution of residual adhesive on the filter screen surface.

[0037] Compared with existing technologies, this technical solution mainly solves the following problems: 1. Avoids high-temperature calcination damage to the filter screen; This solution completely eliminates the calcination and carbonization step, and instead uses N-methylmorpholine-N-oxide (NMMO) solvent to physically dissolve the residual adhesive, fundamentally avoiding high-temperature damage to the filter screen material and effectively protecting the filter screen's filtration accuracy and mechanical properties; In addition, the concentrated N-methylmorpholine-N-oxide (NMMO) solvent used for cleaning comes from the production system and can be recycled in the solvent recovery section after use, realizing a closed-loop connection between the cleaning medium and the production system; 2. Eliminates safety hazards and environmental issues; This solution eliminates the risk of explosion due to high-temperature operation and thermal decomposition of residual adhesive throughout the entire process. At the same time, the entire cleaning process is free of smoke emissions and irritating odors, and the operating environment is safe and friendly, which is highly consistent with the green and environmentally friendly production process positioning of Lyocell fiber. In addition, the filter screen can be reused multiple times, reducing solid waste generation, which is in line with the development direction of green manufacturing and circular economy. 3. It solves the problems of high energy consumption and complicated operation; this solution does not require a high-temperature calcination furnace and a tail gas treatment system. The equipment power is low and the energy consumption is greatly reduced. In terms of operation process, this solution only requires "hot water soaking pretreatment → three N-methylmorpholine-N-oxide (NMMO) solvent cleaning → ultrasonic oscillation water washing → drying". The operation is simple, the equipment investment is low, and the threshold for industrial promotion is significantly reduced. 4. Reduced cleaning time: This solution eliminates the need for high-temperature calcination and cooling processes, allowing the overall cleaning cycle to be completed in a short time. Compared to existing technologies that require cleaning processes lasting several hours or even more than ten hours, this solution significantly shortens the cleaning cycle and improves cleaning efficiency.

[0038] This technical solution can be widely used in the cleaning of filter components in the production process of lyocell fibers, and has broad application prospects: 1. Urgent industry demand; As the production capacity of lyocell fiber as a green fiber continues to expand, the consumption of filter screens continues to grow. Currently, the industry generally uses filter screens as disposable consumables, resulting in serious waste. This technical solution can effectively solve this industry pain point, and the market demand is strong. 2. Significant economic benefits: After adopting this technical solution, the filter screen can be reused 1-2 times, and the procurement cost can be reduced by more than 50%. This cleaning process can be extended to the cleaning of filter screens in large-scale production. Taking a production line with an annual output of 100,000 tons of lyocell fiber as an example, the cost of filter screen consumption alone can be reduced by several million yuan per year, which is very economical. 3. Outstanding environmental benefits: This solution reduces the amount of filter screens discarded as solid waste, avoids energy consumption and exhaust emissions during the calcination process, and is highly consistent with Lyocell fiber's positioning as a "green fiber," which helps to enhance the company's environmental image. 4. Good technical compatibility: The N-methylmorpholine-N-oxide (NMMO) solvent used in this solution is the same as the main solvent in the production of lyocell fiber. The N-methylmorpholine-N-oxide (NMMO) waste liquid generated during cleaning can be directly incorporated into the factory's existing N-methylmorpholine-N-oxide (NMMO) recovery system to achieve solvent recycling. No additional waste liquid treatment facilities are required, and it is seamlessly integrated with the existing production process.

[0039] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for cleaning a filter screen used in a Lyocell pilot production line, characterized in that, Includes the following steps: S1: Clean the filter screen of residual adhesive; After removing the spinning assembly, immerse the filter screen to be cleaned completely in hot water to solidify the adhesive on the surface of the filter screen. Then scrape off the large pieces of residual adhesive on the surface of the filter screen to complete the pretreatment and remove impurities, which greatly reduces the load of subsequent solvent cleaning. S2: First-stage solvent dissolution and cleaning; The pretreated filter screen is placed in the first cleaning tank and immersed in N-methylmorpholine-N-oxide concentrated solvent under constant temperature conditions to quickly dissolve the cellulose residue on the surface and shallow mesh of the filter screen, remove 70% to 80% of the attached dirt, and complete the first-stage cleaning of the filter screen. S3: Secondary solvent gradient cleaning; the filter screen after primary cleaning is transferred to the second cleaning tank and continuously soaked in the same concentration of N-methylmorpholine-N-oxide concentrated solvent at the same temperature to dissolve the shallow residual adhesive layer and fine impurities, remove 15% to 20% of the attached dirt, and complete the secondary cleaning of the filter screen. S4: Three-stage solvent deep cleaning; the filter screen after the second-stage cleaning is transferred to the third cleaning tank and soaked in the same concentration of N-methylmorpholine-N-oxide concentrated solvent at a constant temperature. This process is used to deeply peel off the trace amounts of residual adhesive embedded in the deep pores and gaps of the multi-layer filter screen, achieving fine impurity removal and completing the three-stage cleaning of the filter screen. S5: Ultrasonic water washing; The filter screen after the three-stage solvent cleaning is placed in a room temperature water washing tank and cleaned under ultrasonic conditions. The ultrasonic cavitation effect generates micro-jets and impact forces to thoroughly remove fine glue residue and ultrafine powder impurities from the mesh, eliminate cleaning dead corners, and complete the ultrasonic water washing of the filter screen. S6: Drying and microscopic inspection; After ultrasonic cleaning, the filter screen is dried and the mesh transparency and impurity residue are observed through an industrial microscope. The filter screen with transparent mesh, no impurity blockage, and intact appearance can be reused for spinning.

2. The method for cleaning a filter screen for a Lyocell pilot production line according to claim 1, characterized in that: The soaking time in S1 is 20-40 minutes.

3. The method for cleaning a filter screen for a Lyocell pilot production line according to claim 1, characterized in that: The concentrated solvent in S2 is N-methylmorpholine-N-oxide with a concentration of 83% to 85%.

4. The method for cleaning a filter screen for a Lyocell pilot production line according to claim 1, characterized in that: The constant temperature condition in S2 is 90–105°C.

5. The method for cleaning a filter screen for a Lyocell pilot production line according to claim 1, characterized in that: The soaking time in S2 is 1 to 3 hours.

6. The method for cleaning a filter screen for a Lyocell pilot production line according to claim 1, characterized in that: The soaking time in S3 is 1 to 2 hours.

7. The method for cleaning a filter screen for a Lyocell pilot production line according to claim 1, characterized in that: The soaking time in S4 is 1 to 2 hours.

8. The method for cleaning a filter screen for a Lyocell pilot production line according to claim 1, characterized in that: The ultrasonic frequency in S5 is 20-30 Hz, and the cleaning time is 30-40 min.

9. A method for cleaning a filter screen for a Lyocell pilot production line according to claim 1, characterized in that: The drying temperature in S6 is 80-90℃.

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