A recycling system for NMMO waste adhesive in lyocell fiber production

Abstract

This application relates to a recycling system for NMMO waste adhesive in lyocell fiber production, comprising a pretreatment unit, an NMMO purification unit, a concentration unit, piping and heating systems, and auxiliary equipment. The pretreatment unit internally includes a primary ultrafiltration device, a two-stage flocculation and sedimentation device, and a primary nanofiltration device. This application has the advantage of achieving efficient recovery of NMMO solvent through multi-stage purification and concentration processes, enabling the resource utilization of waste adhesive that would otherwise be discharged. The ion exchange and adsorption processes in the purification unit work synergistically to effectively remove organic impurities and metal ions, improving the purity of the recovered NMMO, meeting the solvent reuse standards for lyocell fiber production, and reducing the amount of fresh solvent required. Removing suspended solids and macromolecular impurities from the waste adhesive reduces the load on subsequent treatment units and extends the service life of key equipment such as ultrafiltration and nanofiltration membranes.

Description

Technical Field

[0001] This application relates to the technical field of NMMO recycling, and in particular to a recycling system for NMMO waste adhesive in lyocell fiber production. Background Technology

[0002] Lyocell fiber, as a novel regenerated cellulose fiber, combines many advantages of both natural and synthetic fibers. It boasts a comfortable feel, excellent moisture absorption and breathability, as well as superior strength and flexibility. In the textile industry, lyocell fiber is widely used in the production of high-end clothing and home textiles. Fabrics made from it are soft to the touch, have a gentle luster, and excellent drape, making them highly popular with consumers. Simultaneously, in the industrial sector, lyocell fiber can also be used to manufacture filter materials and hygiene products, showing broad market application prospects. Throughout the production process, NMMO solvent plays a crucial role in dissolving cellulose. However, the spinning and subsequent processing stages generate a large amount of NMMO waste liquid, which contains unreacted NMMO solvent, cellulose degradation products, impurities, and moisture.

[0003] NMMO is an organic compound. Directly discharging NMMO-containing waste adhesives into the environment will pollute soil and water bodies. NMMO is difficult to degrade naturally in the environment. By recycling and processing NMMO waste adhesives, extracting and purifying the NMMO, and reusing the solvent, the amount of fresh NMMO solvent used can be significantly reduced, lowering raw material costs. Simultaneously, the recycled waste adhesives can reduce the volume and complexity of wastewater treatment, lowering wastewater treatment costs.

[0004] However, existing technologies for treating NMMO waste adhesive generally suffer from low solvent recovery rates and high energy consumption. Traditional evaporation processes lack energy optimization control, resulting in high steam consumption and incomplete impurity removal affecting solvent purity. At the same time, equipment is prone to shortening its service life due to crystallization blockage, and insufficient automation leads to poor operational stability. It is difficult to balance environmental emissions with resource recycling efficiency. Summary of the Invention

[0005] To address the issues of high steam consumption and incomplete impurity removal affecting solvent purity caused by the lack of energy optimization control in traditional evaporation processes, this application provides a method for recycling and treating NMMO waste adhesive in lyocell fiber production.

[0006] This application provides a recycling system for NMMO waste adhesive in lyocell fiber production, which adopts the following technical solution: A recycling system for NMMO waste adhesive in lyocell fiber production includes a pretreatment unit, an NMMO purification unit, a concentration unit, a pipeline and heating system, and auxiliary equipment;

[0007] The pretreatment unit is equipped with a primary ultrafiltration device, a two-stage flocculation sedimentation device, and a primary nanofiltration device.

[0008] In a preferred embodiment, the primary ultrafiltration device uses an external pressure hollow fiber membrane module. The membrane material is polyethersulfone, which has acid and alkali resistance and temperature resistance. The membrane fibers have a hollow structure and are fixed and sealed at both ends by the outer shell.

[0009] The primary ultrafiltration unit operates in a cross-flow filtration mode, maintaining a stable filtration effect by controlling the membrane surface flow rate and operating pressure. The system automatically monitors flux changes, triggering a cleaning procedure when the flux drops to a certain level. The cleaning system is equipped with an online chemical cleaning module, using alternating alkaline and acidic cleaning agents for rinsing. Regular maintenance is performed to restore membrane flux and ensure long-term stable operation.

[0010] In a preferred embodiment, the two-stage flocculation and sedimentation device is internally configured with: a primary flocculation reaction unit, a primary sedimentation and separation unit, a secondary mixing and flocculation unit, and a secondary solid-liquid separation unit;

[0011] Primary flocculation reaction unit: A baffled reaction tank is adopted, and the reaction intensity is controlled by multi-stage stirring. An appropriate amount of flocculant is added to promote the coagulation of impurities. The pH value is monitored during the reaction to optimize the flocculation effect. After a certain period of time, it enters the sedimentation stage.

[0012] Primary sedimentation separation unit: adopts an inclined tube sedimentation structure, utilizes the principle of shallow sedimentation to improve separation efficiency, and is equipped with a sludge scraper at the bottom to periodically discharge sludge, while the supernatant enters subsequent treatment.

[0013] Secondary mixing and flocculation unit: The primary settled sludge and nanofiltration concentrate are mixed in proportion and uniformly mixed by a static mixer. Flocculants are then added to further enhance the removal of impurities.

[0014] Secondary solid-liquid separation unit: A chamber filter press is used for deep dewatering. The separated mud cake is transported off-site for processing, and the filtrate is returned to the system for recycling after adsorption purification.

[0015] In a preferred embodiment, the membrane element of the primary nanofiltration device is a spiral-wound aromatic polyamide composite membrane element, which has high retention performance and selectivity, good retention effect on small molecule impurities, and at the same time ensures the permeability of NMMO.

[0016] The membrane stack arrangement design of the first-stage nanofiltration device adopts a multi-stage series arrangement, and improves the separation efficiency by reasonably configuring the number and arrangement order of membrane elements. The pressure vessel is made of corrosion-resistant material to adapt to the operating environment.

[0017] The circulation and control unit of the primary nanofiltration unit includes a concentrate circulation system. The separation effect is controlled by adjusting the circulation flow rate and recovery rate. The concentrate conductivity is monitored online to prevent over-concentration and ensure stable system operation. The permeate treatment unit receives the permeate through a collection manifold into a buffer tank. Level control ensures stable delivery to subsequent purification units, and periodic sampling and analysis ensure water quality meets standards.

[0018] In a preferred embodiment, the NMMO purification unit internally comprises anion and cation exchange membrane stacks: a homogeneous ion exchange membrane stack design is adopted, with each stack containing 100–150 alternating cation and anion membranes. The membrane materials are perfluorosulfonic acid resin (cation membrane) and perfluorocarboxylic acid resin (anion membrane), with a thickness controlled at 0.15–0.2 mm to reduce resistivity. The membrane stacks are pressed together by titanium alloy end plates, and the seal is achieved using EPDM rubber gaskets. The operating pressure is maintained at 0.3–0.5 MPa, and the allowable continuous operating temperature range is 60–90 °C. The inter-membrane flow channel width is 8–10 mm, and an internal diamond-shaped flow guide mesh promotes feed turbulence and improves mass transfer efficiency.

[0019] In a preferred embodiment, the NMMO purification unit is internally equipped with an organic adsorbent filling system: porous styrene-divinylbenzene copolymer microspheres with a particle size distribution of 50–100 μm are filled between the anion and cation membranes, and the surface is grafted with quaternary ammonium and sulfonic acid active groups, achieving a static adsorption capacity of 120 mg / g for NMMO molecules. The adsorbent is fixed by a detachable screen and regenerated in situ every 800 hours of operation, with the regeneration solution being alternately rinsed with 0.5 mol / L hydrochloric acid and 0.3 mol / L sodium hydroxide.

[0020] In a preferred embodiment, the concentration unit is internally equipped with an MVR evaporator core component and a novel evaporation concentrator;

[0021] The core components of the MVR evaporator include: a single-stage centrifugal steam compressor with an impeller made of duplex stainless steel 2205, a compression ratio of 3.5–4.2, and a rated power of 55–75 kW, which raises the secondary steam temperature by 15–20°C before returning it to the heating chamber. The heating chamber uses a vertical shell-and-tube heat exchanger structure with φ25×2mm 316L stainless steel tubes, 3m in length, 2 tube passes, and a shell-side design pressure of 1.0MPa. The separator has a diameter of 1.2–1.5m and a built-in baffle-type demister with a separation efficiency of ≥99.9%, preventing NMMO loss due to mist entrainment.

[0022] The novel evaporator concentrator features a horizontal scraped-film evaporator design with a cylindrical diameter of 0.6–1.0 m and an effective heating length of 2.5 m. The inner wall is coated with a PTFE non-stick coating. The scraping system consists of three sets of adjustable scrapers with a scraper-to-cylinder wall gap of 0.5–1.0 mm and a linear velocity of 1.5–2.0 m / s, ensuring a uniform liquid film formation. The distributor employs a spiral groove structure, achieving a feed distribution uniformity error of ≤5%. The equipment vacuum is maintained at -0.092–-0.095 MPa, and the operating temperature is controlled at 85–95℃ to reduce the risk of NMMO thermal decomposition.

[0023] In a preferred embodiment, the MVR evaporator in the concentration unit is equipped with an adaptive energy optimization control module. An adaptive control algorithm based on dynamic energy balance and fuzzy PID is designed. Its core function is to minimize energy consumption per unit throughput and prevent the solution temperature from exceeding 120°C while ensuring the NMMO solution is concentrated to the target concentration of 85% through real-time adjustment of compressor frequency, feed flow rate, and heating power. The system collects 12 real-time parameters, including temperature, pressure, solution concentration, and compressor current within the evaporator, and achieves optimized control through the following steps:

[0024] Dynamic modeling layer: Based on the material conservation and heat transfer equations, a nonlinear relationship model is established between the NMMO solution concentration change rate and the evaporation rate and feed rate.

[0025] Fuzzy decision layer: Mamdani fuzzy logic reasoning is used to map the concentration deviation (ΔC=C_target-C_real) and the deviation change rate (ΔC / Δt) into compressor frequency correction Δf and heating power correction ΔQ;

[0026] Adaptive execution layer: The membership function parameters in the fuzzy rules are dynamically adjusted through the particle swarm optimization algorithm, so that the system can maintain stable operation when the feed concentration fluctuates by ±15% and the ambient temperature changes by ±5℃.

[0027] The coupling optimization formula is:

[0028] ;

[0029] In the formula:

[0030] Δf represents the compressor frequency correction amount (Hz), with a positive value indicating an increase in frequency and a negative value indicating a decrease in frequency;

[0031] k eff The energy efficiency weighting coefficient (Hz·min / kg) is obtained by optimization using the PSO algorithm, with a typical value of 0.85~1.2.

[0032] ΔC / Δt represents the concentration change rate (% / min), reflecting the current evaporation efficiency;

[0033] T real This indicates the actual temperature inside the evaporator (°C).

[0034] T safe This indicates the safe temperature threshold for NMMO (120℃).

[0035] ΔT max This indicates the maximum permissible temperature difference (10℃) to prevent system oscillation when the temperature rapidly approaches the threshold.

[0036] k safe The safety weighting factor (Hz) is linearly related to the pressure deviation, with a typical value of 5 to 8.

[0037] P real This indicates the actual pressure inside the evaporator (kPa).

[0038] P set This represents the target operating pressure (kPa, determined by the saturated vapor pressure at 85% concentration).

[0039] In a preferred embodiment, the main pipeline of the heating system is made of 304 stainless steel seamless pipe, designed according to ANSI B31.3 chemical piping standards, and suitable for conventional operating pressure and temperature ranges. A flanged shut-off valve is installed at the pump outlet; the valve body and core are made of corrosion-resistant materials, ensuring convenient operation and reliable sealing performance. The flow meter uses an electromagnetic measurement principle, possessing high accuracy and stability. The bypass pipeline is equipped with a manual ball valve for easy media switching during equipment maintenance.

[0040] The heating pipes of the heating system are made of 304 stainless steel and feature an integral welded jacket structure to ensure uniform heat transfer. A filter and a self-regulating temperature control valve are installed at the steam inlet to precisely control the heating temperature and maintain a stable fluctuation range. The condensate drainage system uses a float-type steam trap to efficiently remove condensate, and a drain valve is installed at the lowest point of each heating unit to regularly clean impurities and ensure heating efficiency.

[0041] In a preferred embodiment, the auxiliary equipment employs a plate heat exchanger to recover waste heat from the condensate. The plates are made of 316L stainless steel, and the corrugated structure design enhances the heat exchange effect. Condensate from the MVR evaporator is introduced on the hot side, while the feed liquid flows on the cold side. This heat exchange increases the temperature of the feed liquid, significantly saving steam consumption.

[0042] The auxiliary equipment's dilute solution storage tank adopts a vertical elliptical head structure, with a polished inner wall to reduce impurity residue. It is equipped with a side-entry stirrer to maintain solution homogeneity and a level gauge to monitor liquid level changes in real time. The control system uses PLC integrated control, enabling parameter setting and real-time monitoring through a configuration interface. Multiple alarm mechanisms are set for key control points to ensure safe and stable system operation.

[0043] In summary, this application includes at least one of the following beneficial technical effects:

[0044] 1. A multi-stage purification and concentration process achieves efficient recovery of NMMO solvent, enabling the resource utilization of previously discharged waste adhesive. The ion exchange and adsorption processes in the purification unit work synergistically to effectively remove organic impurities and metal ions, improving the purity of the recovered NMMO and meeting the solvent reuse standards for lyocell fiber production, thus reducing the amount of fresh solvent required. The concentration unit employs MVR evaporation technology, coupled with an adaptive energy optimization control module, which dynamically adjusts the vapor compression ratio and heat exchange efficiency based on real-time parameters such as feed concentration and temperature, minimizing energy consumption while avoiding the loss of NMMO due to high-temperature decomposition during traditional evaporation, thereby improving solvent recovery rate.

[0045] 2. By using pipeline heating and automated control, the risk of solvent crystallization and blockage during transportation is reduced. Waste heat recovery devices in auxiliary equipment further improve energy utilization and reduce steam consumption during production. The combined application of two-stage flocculation sedimentation and membrane separation processes effectively removes suspended solids and large molecular impurities from waste adhesives, reducing the load on subsequent processing units and extending the service life of key equipment such as ultrafiltration and nanofiltration membranes. The control system's multiple alarm mechanisms and PLC integrated management enable real-time monitoring and anomaly response of all process parameters, ensuring continuous and stable system operation, reducing production interruptions due to equipment failure, and improving overall production efficiency. Attached Figure Description

[0046] Figure 1 This is the overall system block diagram of this application;

[0047] Figure 2 This is a block diagram of the preprocessing unit system of this application.

[0048] Explanation of reference numerals in the attached diagram: 1. Pretreatment unit; 2. NMMO purification unit; 3. Concentration unit; 4. Piping and heating system; 5. Auxiliary equipment; 6. First-stage ultrafiltration unit; 7. Two-stage flocculation and sedimentation unit; 8. First-stage nanofiltration unit. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0050] The following is in conjunction with the appendix Figure 1 - Appendix Figure 2 This application will be described in further detail.

[0051] Example:

[0052] See Figure 1-2 A recycling system for NMMO waste adhesive in lyocell fiber production includes a pretreatment unit 1, an NMMO purification unit 2, a concentration unit 3, a pipeline and heating system 4, and auxiliary equipment 5.

[0053] The pretreatment unit 1 is equipped with a primary ultrafiltration device 6, a two-stage flocculation sedimentation device 7, and a primary nanofiltration device 8.

[0054] The primary ultrafiltration unit 6 uses an external pressure hollow fiber membrane module. The membrane material is polyethersulfone, which has acid and alkali resistance and temperature resistance. The membrane fibers have a hollow structure and are fixed and sealed at both ends by the outer shell.

[0055] The primary ultrafiltration unit 6 operates in a cross-flow filtration mode, maintaining stable filtration performance by controlling membrane flow rate and operating pressure. The system automatically monitors flux changes, triggering a cleaning procedure when the flux drops to a certain level. The cleaning system is equipped with an online chemical cleaning module, using alternating alkaline and acidic cleaning agents for rinsing. Regular maintenance is performed to restore membrane flux and ensure long-term stable operation.

[0056] The two-stage flocculation sedimentation device 7 is internally equipped with: a primary flocculation reaction unit, a primary sedimentation separation unit, a secondary mixing flocculation unit, and a secondary solid-liquid separation unit;

[0057] Primary flocculation reaction unit: A baffled reaction tank is adopted, and the reaction intensity is controlled by multi-stage stirring. An appropriate amount of flocculant is added to promote the coagulation of impurities. The pH value is monitored during the reaction to optimize the flocculation effect. After a certain period of time, it enters the sedimentation stage.

[0058] Primary sedimentation separation unit: adopts an inclined tube sedimentation structure, utilizes the principle of shallow sedimentation to improve separation efficiency, and is equipped with a sludge scraper at the bottom to periodically discharge sludge, while the supernatant enters subsequent treatment.

[0059] Secondary mixing and flocculation unit: The primary settled sludge and nanofiltration concentrate are mixed in proportion and uniformly mixed by a static mixer. Flocculants are then added to further enhance the removal of impurities.

[0060] Secondary solid-liquid separation unit: A chamber filter press is used for deep dewatering. The separated mud cake is transported off-site for processing, and the filtrate is returned to the system for recycling after adsorption purification.

[0061] The membrane element of the first-stage nanofiltration unit 8 is a spiral-wound aromatic polyamide composite membrane element, which has high retention performance and selectivity, good retention effect on small molecule impurities, and at the same time ensures the permeability of NMMO.

[0062] The membrane stack arrangement design of the first-stage nanofiltration unit 8 is as follows: a multi-stage series arrangement is adopted, and the separation efficiency is improved by reasonably configuring the number and arrangement order of membrane elements. The pressure vessel is made of corrosion-resistant material to adapt to the operating environment.

[0063] The circulation and control unit of the first-stage nanofiltration unit 8: It is equipped with a concentrate circulation system, which controls the separation effect by adjusting the circulation flow rate and recovery rate. The concentrate conductivity is monitored online to prevent over-concentration and ensure stable system operation. Permeate treatment unit: The permeate enters a buffer tank through a collection main pipe and is stably delivered to subsequent purification units through level control. Regular sampling and analysis ensure water quality meets standards.

[0064] The NMMO purification unit 2 is internally equipped with anion and cation exchange membrane stacks: employing a homogeneous ion exchange membrane stack design, each stack contains 100–150 alternating cation and anion membranes. The membrane materials are perfluorosulfonic acid resin (cation membrane) and perfluorocarboxylic acid resin (anion membrane), with a thickness controlled at 0.15–0.2 mm to reduce resistivity. The membrane stacks are clamped together by titanium alloy end plates, and sealed with EPDM rubber gaskets. The operating pressure is maintained at 0.3–0.5 MPa, and the allowable continuous operating temperature range is 60–90 °C. The inter-membrane flow channel width is 8–10 mm, and an internal diamond-shaped flow guide mesh promotes feed turbulence and improves mass transfer efficiency.

[0065] The NMMO purification unit 2 is equipped with an organic adsorbent packing system: porous styrene-divinylbenzene copolymer microspheres with a particle size distribution of 50–100 μm are filled between the anion and cation membranes, and their surfaces are grafted with quaternary ammonium and sulfonic acid active groups, achieving a static adsorption capacity of 120 mg / g for NMMO molecules. The adsorbent is fixed by a detachable screen and regenerated in situ every 800 hours of operation. The regeneration solution is used for alternating rinsing with 0.5 mol / L hydrochloric acid and 0.3 mol / L sodium hydroxide.

[0066] The internal components of the concentration unit 3 include the core components of an MVR evaporator and a new type of evaporation and concentration machine;

[0067] The core components of the MVR evaporator include: a single-stage centrifugal steam compressor with an impeller made of duplex stainless steel 2205, a compression ratio of 3.5–4.2, and a rated power of 55–75 kW, which raises the secondary steam temperature by 15–20°C before returning it to the heating chamber. The heating chamber uses a vertical shell-and-tube heat exchanger structure with φ25×2mm 316L stainless steel tubes, 3m in length, 2 tube passes, and a shell-side design pressure of 1.0MPa. The separator has a diameter of 1.2–1.5m and a built-in baffle-type demister with a separation efficiency of ≥99.9%, preventing NMMO loss due to mist entrainment.

[0068] The novel evaporator concentrator features a horizontal scraped-film evaporator design with a cylindrical diameter of 0.6–1.0 m and an effective heating length of 2.5 m. The inner wall is coated with a PTFE non-stick coating. The scraping system consists of three sets of adjustable scrapers with a scraper-to-cylinder wall gap of 0.5–1.0 mm and a linear velocity of 1.5–2.0 m / s, ensuring a uniform liquid film formation. The distributor employs a spiral groove structure, achieving a feed distribution uniformity error of ≤5%. The equipment vacuum is maintained at -0.092–-0.095 MPa, and the operating temperature is controlled at 85–95℃ to reduce the risk of NMMO thermal decomposition.

[0069] The MVR evaporator in concentration unit 3 is equipped with an adaptive energy optimization control module. An adaptive control algorithm based on dynamic energy balance and fuzzy PID is designed. Its core function is to minimize energy consumption per unit throughput and prevent the solution temperature from exceeding 120°C while ensuring the NMMO solution is concentrated to the target concentration of 85% through real-time adjustment of compressor frequency, feed flow rate, and heating power. The system collects 12 real-time parameters, including temperature, pressure, solution concentration, and compressor current within the evaporator, and achieves optimized control through the following steps:

[0070] Dynamic modeling layer: Based on the material conservation and heat transfer equations, a nonlinear relationship model is established between the NMMO solution concentration change rate and the evaporation rate and feed rate.

[0071] Fuzzy decision layer: Mamdani fuzzy logic reasoning is used to map the concentration deviation (ΔC=C_target-C_real) and the deviation change rate (ΔC / Δt) into compressor frequency correction Δf and heating power correction ΔQ;

[0072] Adaptive execution layer: The membership function parameters in the fuzzy rules are dynamically adjusted through the particle swarm optimization algorithm, so that the system can maintain stable operation when the feed concentration fluctuates by ±15% and the ambient temperature changes by ±5℃.

[0073] The coupling optimization formula is:

[0074] ;

[0075] In the formula:

[0076] Δf represents the compressor frequency correction amount (Hz), with a positive value indicating an increase in frequency and a negative value indicating a decrease in frequency;

[0077] k eff The energy efficiency weighting coefficient (Hz·min / kg) is obtained by optimization using the PSO algorithm, with a typical value of 0.85~1.2.

[0078] ΔC / Δt represents the concentration change rate (% / min), reflecting the current evaporation efficiency;

[0079] T real This indicates the actual temperature inside the evaporator (°C).

[0080] T safe This indicates the safe temperature threshold for NMMO (120℃).

[0081] ΔT max This indicates the maximum permissible temperature difference (10℃) to prevent system oscillation when the temperature rapidly approaches the threshold.

[0082] k safe The safety weighting factor (Hz) is linearly related to the pressure deviation, with a typical value of 5 to 8.

[0083] P real This indicates the actual pressure inside the evaporator (kPa).

[0084] P set This represents the target operating pressure (kPa, determined by the saturated vapor pressure at 85% concentration).

[0085] The main pipeline of the piping and heat tracing system 4 is made of 304 stainless steel seamless pipe, designed according to ANSI B31.3 chemical piping standards, and is suitable for the normal operating pressure and temperature range. A flanged gate valve is installed at the pump outlet; the valve body and core are made of corrosion-resistant materials, ensuring convenient operation and reliable sealing performance. The flow meter uses an electromagnetic measurement principle, possessing high accuracy and stability. The bypass pipeline is equipped with a manual ball valve for easy media switching during equipment maintenance.

[0086] The heat tracing piping of the piping and heat tracing system 4 is made of 304 stainless steel and adopts an integral welded jacket structure to ensure uniform heat transfer. A filter and self-regulating temperature control valve are installed at the steam inlet to precisely control the heat tracing temperature and maintain a stable fluctuation range. The condensate drainage system uses float-type steam traps to efficiently remove condensate, and a drain valve is installed at the lowest point of each heat tracing unit to regularly clean impurities and ensure heat tracing efficiency.

[0087] Auxiliary equipment 5 uses a plate heat exchanger to recover waste heat from the condensate. The plates are made of 316L stainless steel, and the corrugated structure design enhances the heat exchange effect. The hot side is supplied with condensate from the MVR evaporator, while the cold side carries the feed liquid. Through heat exchange, the temperature of the feed liquid is increased, significantly saving steam consumption.

[0088] The dilute solution storage tank of auxiliary equipment 5 adopts a vertical elliptical head structure, with polished inner walls to reduce impurity residue. It is equipped with a side-entry agitator to maintain solution uniformity, and a level gauge is installed to monitor liquid level changes in real time. The control system adopts PLC integrated control, and parameter setting and real-time monitoring are realized through the configuration interface. Multiple alarm mechanisms are set for key control points to ensure safe and stable operation of the system.

[0089] From the above, we can conclude that:

[0090] In this invention, a multi-stage purification and concentration process achieves efficient recovery of NMMO solvent, enabling the resource utilization of waste adhesive that would otherwise be discharged. The ion exchange and adsorption processes in the purification unit work synergistically to effectively remove organic impurities and metal ions, improving the purity of the recovered NMMO and meeting the solvent reuse standards for lyocell fiber production, thus reducing the amount of fresh solvent required. The concentration unit employs MVR evaporation technology, coupled with an adaptive energy optimization control module, which dynamically adjusts the vapor compression ratio and heat exchange efficiency based on real-time parameters such as feed concentration and temperature, minimizing energy consumption while avoiding the loss of NMMO due to high-temperature decomposition during traditional evaporation, thereby improving solvent recovery rate.

[0091] In this invention, pipeline heating and automated control reduce the risk of solvent crystallization and blockage during transportation. The waste heat recovery device in auxiliary equipment further improves energy utilization and reduces steam consumption during production. The combined application of two-stage flocculation sedimentation and membrane separation processes effectively removes suspended solids and large molecular impurities from waste adhesives, reducing the load on subsequent processing units and extending the service life of key equipment such as ultrafiltration and nanofiltration membranes. The control system's multiple alarm mechanisms and PLC integrated management enable real-time monitoring and anomaly response of all process parameters, ensuring continuous and stable system operation, reducing production interruptions due to equipment failure, and improving overall production efficiency.

[0092] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A recycling system for NMMO waste adhesive in lyocell fiber production, characterized in that: It includes a pretreatment unit (1), an NMMO purification unit (2), a concentration unit (3), a pipeline and heat tracing system (4), and auxiliary equipment (5); The pretreatment unit (1) is equipped with a first-stage ultrafiltration device (6), a two-stage flocculation sedimentation device (7), and a first-stage nanofiltration device (8). The NMMO purification unit (2) is internally equipped with anion and cation membrane structures; The NMMO purification unit (2) is equipped with an organic adsorbent filling system, which fills the space between the anion and cation membranes with porous styrene-divinylbenzene copolymer microspheres with a particle size distribution of 50–100 μm and quaternary ammonium groups and sulfonic acid groups grafted onto the surface. The concentration unit (3) is equipped with an MVR evaporator core component and an evaporation concentrator. The MVR evaporator in the concentration unit (3) is equipped with an adaptive energy optimization control module, wherein the coupling optimization formula is: In the formula: Δf represents the compressor frequency correction amount; a positive value indicates an increase in frequency, and a negative value indicates a decrease in frequency. k eff This represents the energy efficiency weighting coefficient, which is obtained by optimization using the PSO algorithm, with a typical value of 0.85 to 1.

2. ΔC / Δt represents the rate of concentration change, reflecting the current evaporation efficiency; T real This indicates the actual temperature inside the evaporator. T safe Indicates the safe temperature threshold of NMMO; ΔT max This indicates the maximum permissible temperature difference, preventing system oscillation when the temperature rapidly approaches the threshold. k safe This represents the safety weighting coefficient, which has a linear relationship with pressure deviation, with a typical value of 5 to 8. P real This indicates the actual pressure inside the evaporator; P set This indicates the target operational pressure.

2. The NMMO waste adhesive recovery and recycling system for lyocell fiber production according to claim 1, characterized in that: The primary ultrafiltration device (6) adopts an external pressure hollow fiber membrane module; The primary ultrafiltration device (6) is equipped with a cleaning system.

3. The NMMO waste adhesive recovery and recycling system for lyocell fiber production according to claim 1, characterized in that: The two-stage flocculation sedimentation device (7) is internally equipped with: a primary flocculation reaction unit, a primary sedimentation separation unit, a secondary mixing flocculation unit, and a secondary solid-liquid separation unit.

4. The NMMO waste adhesive recycling system for lyocell fiber production according to claim 1, characterized in that: The membrane element of the primary nanofiltration device (8) is a spiral wound aromatic polyamide composite membrane element; The primary nanofiltration unit (8) is equipped with a concentrate circulation system.

5. The NMMO waste adhesive recycling system for lyocell fiber production according to claim 1, characterized in that: The core component of the MVR evaporator is equipped with a single-stage centrifugal steam compressor, and the impeller is made of duplex stainless steel. The evaporator is a horizontal scraped film evaporator with a polytetrafluoroethylene non-stick coating on the inner wall; the scraped film system consists of 3 sets of adjustable scrapers.

6. The NMMO waste adhesive recovery and recycling system for lyocell fiber production according to claim 1, characterized in that: The main pipeline of the pipeline and the heat tracing system (4) is a seamless 304 stainless steel pipe; a flanged shut-off valve is installed at the pump outlet. The pipeline and the heat tracing system (4) are made of 304 stainless steel pipes, and the steam inlet is equipped with a filter and a self-regulating temperature control valve.

7. The NMMO waste adhesive recovery and recycling system for lyocell fiber production according to claim 1, characterized in that: The auxiliary equipment (5) is equipped with a plate heat exchanger, and the plate material is 316L stainless steel. The auxiliary equipment (5) is equipped with a dilute solution storage tank with a vertical elliptical head structure.

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