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Arti, Wet Spinning Plant for Spandex Scrap Recycling

Description

  1. Overview
    1. This listing is for a complete spandex (elastane) yarn production plant.
    2. The plant is designed to process spandex scrap as the primary raw material.
    3. The process includes raw material storage, polymer preparation, wet spinning, solvent recovery, and all auxiliary systems.
    4. The plant is focused on producing yarn titres between 420 and 1880 dtex.
  2. Raw material storage
    1. Basic raw material is spandex scrap, collected in bags, big-bags, octabyns, or similar devices in the raw material warehouse.
    2. Main chemical mediums (water and DMF) are stored in big vessels outdoors.
    3. Other chemicals and additives can be stored in drums, bags, or similar in the raw material warehouse.
  3. Polymer preparation plant
    1. Preparation starts with thin and accurate special grinding of solid spandex scraps (from dry or wet technology).
    2. Obtained microfilaments are dissolved in a highly polar organic solvent (DMF) in a heated and stirred batch tank, with chemical additives (antioxidants, lubricating additives, UV absorbers, etc.).
    3. The final solution is filtered to remove solid impurities.
    4. Solution is prepared by dosing each component under metering control systems to ensure required concentration.
    5. Final product is a high viscosity elastomer solution ("dope"), consisting of a 21-25% dry polymer solution in DMF.
    6. Dope is stored in heated and stirred tanks under nitrogen atmosphere ("blanketing").
    7. When transferred to spinning, the polymer is degassed under vacuum to remove gas bubbles and filtered through a filter-press to remove secondary solid impurities and gels.
  4. Wet spinning process
    1. Polymer solution ("dope") is pumped through degassing and filtering section, then extruded by metering gear pumps through spinneret capillary holes horizontally into a first ("spinning") vat containing a solution of DMF in water at controlled temperature.
    2. Filaments progressively lose solvent due to higher chemical affinity to the water solution.
    3. Filament solidification is completed by passing through a second ("washing") vat containing a more diluted solution of DMF in water.
    4. Filaments are then dried on a dry roll section ("drying") in contact with steam-heated steel roll surfaces.
    5. Dried yarn is lubricated with a finishing oil to guarantee good unwinding properties.
    6. If a round shaped filament cross section is required, twisters are applied to the spinning machine.
    7. Yarns are wound up on a winder section at a speed range of about 30-60 meters/minute.
    8. When the desired bobbin dimension is reached on each machine position, the machine automatically generates a signal for collection and restarting without interruption.
    9. Water-DMF liquid solution from spinning vats is stored for successive distillation and recovery (closed loop).
    10. Water and solvent vapours from spinning vats are blown and collected to a scrubber, where the gas stream is washed in counter-current with a water stream; final gas emission is clean from solvent, and column bottom collects a liquid water-DMF solution for the solvent recovery plant.
    11. Spinning department includes a section for preparation of spin and wash solutions under specified thermal conditions, and a section for preparation of finishing oil.
    12. Spinning section contains 4 spinning machines and correspondingly 2 double winding machines.
    13. Each spinning machine is completely independent and formed by 4 sections of 12 positions each (total: 48 positions).
    14. Each spinning machine can produce each of the foreseen products.
    15. Final products are bobbins of elastane (spandex) yarn, collected on plastic cylindrical tubes of 114 mm length.
  5. Solvent recovery plant
    1. A double-effect distillation plant is installed for high-efficient recovery of solvent (DMF).
    2. The closed loop of the solvent guarantees high economical yield and very limited environmental impact.
    3. Distillation plant is fed by water-DMF solution streams from the spinning process (vats) and from the scrubber bottom.
    4. It is formed by an atmospheric distillation tray-column and a second distillation tray-column under vacuum.
    5. Feeding of the atmospheric column is a vapour stream; feeding of the vacuum column is liquid.
    6. Vapour stream of the atmospheric column is used to obtain evaporation of the liquid bottom of the vacuum column (multiple effect).
    7. Needed purges (liquid streams) are collected for a final squeezing section (evaporation and final recovery of solvent in a batch heated tank under vacuum).
    8. Extraction points of main products are optimized to minimize impurities content.
    9. Main products are "pure" DMF and "pure" water; obtained purity rate allows these products to be used back in the plant (preparation of spinning baths and washing top stream for scrubber), so only limited reintegration is necessary.
  6. Auxiliary and utility plants
    1. Plant comprises a complete range of utility systems: soft water, cooling water, chilled water, hot water, process air, compressed air, vacuum system, nitrogen, high temperature heat transfer mediums (steam, HTMS), electrical power system, UPS and emergency supply generators, HVAC packages, and safety systems and devices (fire fighting systems, etc.).
  7. Automation and control system
    1. A modern and efficient control system maintains under control and logs continuously all main process parameters (temperatures, pressures, flows, dosing of single components, levels) as well as binary information (alarms, switch parameters, on-off status, etc.) in a user-friendly way for production operators.
    2. System is scalable to apply complex and step procedures, can be easily integrated with plant sections outside battery limits, and can be interoperable with higher level management control systems.
  8. Other facilities
    1. Spinneret workshop: one section of spinning plant is devoted to spinneret preparation, including cleaning (with warm solvent) after production life and spin pack assembling, ready for reinstallation on the spinning machine.
    2. Chemical and textile laboratory: quality control laboratory is divided into two sections – chemical analysis on raw materials from suppliers and process analysis (polymer, solution composition, dope viscosity, etc.), and textile analysis on yarn to verify properties and specifications (mechanical properties like elongation, load, tenacity, recovery, denier uniformity, etc.).
    3. Maintenance workshop: an important part of workshop is devoted to machines maintenance and repair; main maintenance equipment and spare parts are available.