Method for the production of polyester granulates from highly viscous polyester melts and also device for the production of the polyester granulates
The invention relates to a method and device for the direct production of polyester granulate from a highly viscous polyester melt with a polymerization degree of 132 to 165, as well as the granulates formed thereform. In the method, the highly viscous polyester melt is subjected to a pre-drying and drying/degassing after a hot cutting method. Hot cutting is implemented at water temperatures of 70° C. to 95° C. and with a liquid to solid ratio of 8 to 12:1.
1. A device directly producing a polyester granulate from a highly viscous polyester melt (hiV) with a polymerisation degree (PG) of 132 to 165, said device comprising a hot cutter, a pre-dryer and a drying and degassing device, wherein the pre-dryer is configured as an agitating centrifuge, and the drying and degassing device is configured in the form of a vertically standing cylindrical container with a temperature-control zone and a cooling zone, said cooling zone having a heat exchanger with a tube bundle configured with machining which is free of dead surfaces on an upper side.
2. The device according to claim 1 , wherein the agitating centrifuge has a tangential inlet for liquor.
3. The device according to claim 2 , wherein the inlet is configured such that the agitating/conveying spiral is configured in the form of an open screw.
4. The device according to claim 3 , wherein additional conducting elements are present in the form of a plate or turbine agitator.
5. The device according to claim 1 , having a centrifuge groove widened conically from the base to the top.
6. The device according to claim 5 , wherein the resultant cone has a cone base/basic area diameter of 0.75 to 0.6.
7. The device according to claim 1 , wherein a classifying device is connected after the pre-dryer.
8. The device according to claim 7 , wherein a collecting container is disposed between classifying device and drying and degassing device.
9. The device according to claim 1 , wherein the heat exchanger can be purged by conditioned air in counterflow to the granulate.
10. The device according to claim 1 , said heat exchanger tubes having a free surface relative to the container surface is 1:4 to 1:6.
11. The device according to claim 1 , having a L/D ratio of the heat exchanger of at least 1.2:1.
12. The device according to claim 1 , wherein introduction of dry air below the tube bundle of the heat exchanger is effected through an annular gap which is produced by a double cone.
13. The device according to claim 1 , having a hot gas outlet disposed on an upper side of the cylindrical container of the drying and degassing device.
14. The device according to claim 1 , having at least three measuring points disposed over the entire cylinder height for monitoring the temperature profile.
15. The device according to claim 1 , wherein at least the cylindrical part of the container is equipped with active insulation.
16. The device according to claim 15 , wherein the active insulation is electrical heating or half pipe coil jackets.