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Minimize Energy. Maximize Savings.

Minimize Energy. Maximize Savings.

Article written by Peter Mapleston for Injection World Magazine, March 2021. 

Plastics granules are not always everything they appear to be. Hygroscopic materials, especially polyesters like PET, PBT and polycarbonate, and also most polyamides, absorb significant amounts of water from their surroundings. That makes drying just before processing a necessity if a processor wants to avoid material degradation and substandard moldings. And sometimes, especially in regions where the air tends to be humid much of the time, even non-hygroscopic materials may benefit from drying. 

Dryers can work with various technologies, such as simple hot air, desiccant-dried air, compressed air, vacuum-assist, and more. But across the board, suppliers continue to up their game to make the drying task as painless as possible. There are new models that use less energy, that are easier to use, which fit into ‘smart’ operations, and which are better suited for use with recycled plastics and newer types of plastics such as those derived from renewables (many of which are polyesters). 

The range of ULTRA low energy dryers were extended in 2019, with the launch of the ULTRA-600 at K-show 2019. This has a throughput of up to 600 lb/h (272 kg/h). Models range from the ULTRA-150 to the ULTRA-1000. All are said to use much less energy than many desiccant dryers: the company claims that drying with ULTRA can save up to 92w/kg, which equates to a saving of $6,500/yr, with a throughput of 100kg/hr (based on US costs), while doing the same job.

Both types of dryer can use the same amount of energy to bring the material up to drying temperature from ambient temperature. The difference is in the energy used to dry: according to Maguire, a desiccant dryer can use ten times the amount of energy of an ULTRA dryer. ULTRA units heat the material in a vacuum, so the water comes off at a much lower temperature (around 56ºC). 

ULTRA dryers use no desiccant to remove moisture from the air. Desiccant has to be regenerated regularly to remove the water it has absorbed - which is energy intensive - and the amount of moisture in the air is calculated periodically by measuring dew point, which Maguire says is not reliable. On ULTRA units, what counts is the level of the vacuum, which can be measured constantly and accurately. 

The process is also much faster. Citing a system drying polycarbonate, Maguire says some desiccant dryers take three to four hours to dry, versus 30-40 minutes with an ULTRA dryer. 

Chris Crittenden, who oversees global marketing strategy from the Maguire IMEA offices in Dubai, says ULTRA dryers can be used in the same applications as desiccant dryers. He says the company is seeing “snowball effects” in adoption as the technology catches on in certain sectors. 

Further Reading