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Semi-Continuous Polymerisation Plant, PTMEG and MDI Storage, Pre-Polymer Reactor

Description

  1. Raw Material Storage
    1. Ptmeg (polyol) is the main raw material of the plant (about 76% on dry product).
    2. Two heated and stirred tanks are provided for the storage of ptmeg.
    3. The polyol is maintained in a liquid state by heating the tank jackets and is delivered in closed circuits directly to the pre-polymer reactor by pumps and dosing systems in a jacketed pipeline.
    4. Mdi is the second raw material of the process (about 16% on dry product).
    5. Two heated and stirred tanks are available for the storage of mdi and direct unloading of the raw material in case of heated truck deliveries.
    6. If mdi delivery is in drums, they are stored in a cold room and shall be heated in a hot room before usage.
    7. Mdi equipment and distribution are designed and mounted properly and carefully in order to avoid dead-spots in piping and fittings which would lead to under / overheating problems.
    8. All other raw materials and additives necessary in the dope synthesis, like amines in drums, antioxidants in bags or carton containers and spin finish oils in drums are stored in a warehouse and then are prepared for process in heated and stirred tanks.
  2. Semi-Continuous Polymerisation Plant
    1. Pre-polymer: in a stirred and thermocontrolled batch reactor ptmeg, directly fed from the storage tanks, and mdi in excess, fed from the storage / melting tank, react exothermically in order to form a nco-terminated pre-polymer, suitable for the following chain extension.
    2. Amines solutions: required amines are mixed with solvent, to obtain a proper mixture for both the chain extension and the chain termination, and stored in stirred and heated tanks.
    3. Additive solution: a solution of additives (antioxidants, uv absorbers and others), delivered as powder or liquid, is prepared and then stored in a couple of stirred and heated tanks.
    4. The previously mentioned product streams are metered into special mixers (3 steps) in order to adjust the polymer chain length to required value by proper addition of diamines, and then to inject additives into the polymer to obtain the desired final polymer properties.
    5. The finished polymer is endly fed to heated and stirred storage tanks with the necessary final viscosity for the downstream dry spinning process.
    6. Two complete polymerisation lines, in parallel, are available for obtaining the final capacity.
  3. Dry Spinning Process
    1. The polyurethane polymer solution containing 65% of solvent (dmac) is pumped from the storage tanks to the spinning lines by high quality gear pumps.
    2. Before spinning, the dope is properly filtered to remove impurities which can cause interruptions in the spinning process.
    3. The plant is divided in several production lines, of different geometry for specific purposes.
    4. Each line consists of 8-10 columns, which are vertical long heated channels, where the diluted polymer metered inside is transformed into yarn by the evaporation of the solvent under controlled process conditions.
    5. Each column (called "cell" as well) can spin a variable number of ends, depending on the cell geometry and the yarn fineness (dtex), e.g. for 17, 22 and 44 dtex the number of ends will be max. 32.
    6. Inert gas (nitrogen) is blown from the top and extracted from the bottom of each cell.
    7. It carries off the solvent by evaporation under safety conditions.
    8. The solvent-enriched gas passes then a condensation unit, where dmac is separated as a liquid.
    9. Then the nitrogen gas is blown at low pressure via a heat recovery and following heat exchanger to heat it up to a final temperature of 250-300°c, then entering again the top of the columns, in a highly efficient closed circuit.
    10. Thermal oil is used as heat transfer medium at high temperatures.
    11. At the bottom of the columns a certain vacuum is applied by a gas extractor, for safety conditions.
    12. The sucked-off gas stream, containing a certain amount of dmac vapours, is sent to a water scrubber for solvent removal and recovery.
    13. The condensed solvent is fed to the distillation plant together with the water solution obtained from the scrubber.
    14. The yarn ends emerging from each column are drawn-off by a cold godet roll.
    15. By a following oiling roll, spin finish is applied.
    16. Then the yarn bundle is separated by another two cold godets system and endly wound up on high quality winders (comoli, murata, iwka).
    17. Under each spinning position, 2 winders are installed.
    18. Each winder can take-up max 16 ends on standard plastic or carton tubes of 57 mm length.
    19. For a waste-less continuous production, automatic revolving winders are utilized.
    20. After reaching the predetermined diameter, the machine automatically changes the spindle and the operator can take off the full bobbins which are carried to the end product storage.
  4. Solvent Recovery Plant
    1. A high efficient distillation plant and a wet scrubber system are provided to recover the dmac condensed from the spinning gas and dmac from the solvent/water solution leaving the scrubber system.
  5. Auxiliary and Utility Plants
    1. To supply polymerization, spinning and solvent recovery with necessary utilities, the plant comprises a complete range of utility systems to produce soft water, cooling water, chilled water, compressed air, nitrogen, vacuum system and high temperature heat transfer medium, power supply with ups and emergency specific sections.