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The drying air, after passing through the drying hopper where it removes moisture from the PET pellets, is filtered and has the excess moisture removed by means of an adsorption material such as a molecular sieve. The air is then heated once again and recycled through the drying hopper. In order to achieve preforms of good quality, it is of great importance to dry the PET pellets properly and thoroughly. The quality of the drying process depends very much on the dewpoint of the drying air, as well as the drying temperature, the dwell time of the pellets in the drying bin and, last but not least, the air flow rate.

• Drying air temperature should be no more than 180 °C (Figure 1)
• Drying air dewpoint should be a maximum of –30°C (Figure 2)
• Drying air flow should be at least 2m3 per kg/hr of resin throughput
• Residence time in the dryer hopper should be 4-5 hours depending upon the cycle time and the weight of the produced perform (Figure 1)