PET flake crystallizing and drying: one step instead of two
How PET bottle flake is conventionally crystallized and dried, why that takes 5–6 hours, and how infrared does both in 15–25 minutes.
The conventional route
The standard industry method uses two separate machines and two separate steps. A crystallizer, a hopper with an agitator, heats amorphous PET through its glass transition to achieve crystallization, which takes approximately 1 hour. The crystallized material is then moved to a dryer, hot air, desiccant wheel, compressed air, membrane or vacuum, and dried at 150–180 °C for a further 4–5 hours.
Total processing time before the extruder can run: 5–6 hours.
Where the conventional route falls short
- Energy intensive. The dryer heats air first. The air then heats the material from the outside in, with losses at every step.
- Space intensive. Two machines, two hoppers and transfer equipment make a large footprint.
- Non-uniform heating. Hot air does not penetrate the material evenly, so surface and core temperatures differ.
- Desiccant contamination. Post-consumer PET flakes release volatiles during drying that contaminate and degrade desiccant beds, requiring additional treatment and replacement.
- Seasonal variability. Hot air dryer performance is affected by ambient humidity, so results vary between summer and winter, even on the same line.
- Difficult to clean. Multiple vessels, transfer points and air circuits make changeover and maintenance time-consuming.
How infrared changes it
Cryst-O-Dry® combines crystallization and drying in a single step, using shortwave infrared radiation in a continuously moving, patented rotary drum. Infrared needs no transfer medium. Shortwave infrared penetrates directly into the granule and heats it from the inside out. The bulk of the granule and its internal moisture are heated together, while the surrounding air stays at ambient temperature.
Material moves continuously through the drum, which is fitted with an internal helix. Tumbler fins expose every particle to uniform infrared heating throughout its residence time. Three heating zones set the temperature profile along the drum to the material’s moisture content and crystallization requirement.
The two routes side by side
| Parameter | Conventional system | Cryst-O-Dry® |
|---|---|---|
| Steps required | 2 (crystallizer + dryer) | 1 |
| Total processing time | 5–6 hours | 15–25 minutes |
| Moisture reduction | 5,000–6,000 ppm → ~300 ppm | 5,000–6,000 ppm → 300–400 ppm |
| Heating principle | Outside-in (air medium) | Inside-out (no medium) |
| Desiccant required | Yes | No |
| Footprint | Large (2 machines) | Compact (1 machine) |
Conventional processing times are established industry practice. Figures for PET; your result depends on the material and its starting moisture.
Energy
Cryst-O-Dry uses 0.22 kWh/kg on PET bottle flake, which is 20–30% less energy than the two-step route.
Where to go next
See the Cryst-O-Dry® machine page for the specification and cleaning details, or Solutions to start from the job you need to do. Also written crystalliser, the UK spelling.
Request a quote
Tell us the material, the throughput and the machine it has to feed. The person who reads your enquiry is the person who designs the machine.
A.B. Plastech · Modern Industrial Estate, Bahadurgarh, Haryana
pawar@abplastech.co.in
abautomech@hotmail.com