Process Equipment for Polyester Production

Next generation bottle resin polyester pellets will place new demands on solid state polymerisation systems. As a leading supplier of polyester crystallizing equipment to the textile, film and bottle industries, Hosokawa was asked to offer an alternative to the existing technologies.

The use of copolymers can create several benefits in the final product. One of the more desirable aspects copolymers have over homopolymers is the lower obtainable acetaldehyde level, which ensures flavour integrity of the bottle content. Another aspect is a further reduced oxygen transmission rate which will keep the content fresh longer. Finally copolymers perform better in the pre-forming and blow-moulding production stages.

Copolymers presented following challenge during crystallyzing. Extended residence times and the tendency of the chips to stick, necessitated reviewing of standard designs. Subsequent testing of pilot and production scale equipment showed that the Hosokawa continuous disc dryer / crystallizer with a few modifications will meet the demands of the next generation of materials.

Continuous disc dryer / crystallizer

The Hosokawa continuous disc dryer / crystallizer is an indirect heat exchanger capable of heating, cooling or drying. It consists of a tubular shaft with hollow discs mounted perpendicular to the shaft's axis. This rotor is then placed into a "U" shaped trough. Approximately 85 % of the total heat exchange area is in the rotor, and the remaining 15% for the jacket. Material conveyance is in an axial direction and occurs due to the displacement by feed material and the use of conveying plows placed on the periphery of the discs. Product is discharged through an overflow weir. The typical advantages of the Hosokawa continuous disc dryer / crystallizer design swayed the decision into using the Hosokawa continuous disc dryer / crystallizer for the crystallization of polyester chips.

Key features of the Hosokawa continuous disc dryer:

• Residence time in the 30 to 60 minute range, adjustable through weir height;
• High heat transfer coefficients allow for relatively small space requirements;
• Minimal amounts of gas required, thus reduced gas treatment facilities;
• Excellent track record for low maintenance requirements and high energy efficiency.

To meet the requirements for crystallizing copolymer polyester chips, the standard design had to be enhanced with some additional features:

• All heat is provided through the rotor, thus preventing particles sticking to stationary surfaces;
• A modified body shape to ensure even agitation throughout the unit, thus preventing fines generation and twinning of chips;
• Gas purge nozzles in the bottom of the vessel, to improve gas contact to remove water, organics and dust during the process;
• An evenly distributed feed introduction of amorphous chips.

An added benefit is that in case of an emergency shutdown, the bed remains flowable and the unit can be restarted without compromising chip quality.

Hosokawa Micron has met the challenge with the continuous disc dryer / crystallizer. This unit will provide you the residence time, agitation and gas contact to make your copolymer polyester of a quality that meets tomorrow's requirements. It is an economical unit that requires minimal maintenance and can operate for many months without a shutdown. We have already units operating in lines at 90 metric tons per day capacity.

Hosokawa Micron invites you to benefit from our experience and test your polymers in our pilot scale plant in the Netherlands.