New Drying Methods

New technologies are being developed in response to the need to reduce energy consumption in drying

Compressed air drying allows conventional compressed air to expand to reduce the dew point and dry the polymer. These dryers have no moving parts, no desiccant, and low maintenance. If additional drying capacity is required then it is possible to upgrade these dryers with a moisture-removal membrane to further dry the polymer. The process can be very effective for relatively low-volume throughput.

Low-pressure drying (LPD) uses a vacuum applied to a dryer cabinet to accelerate the drying process. Using vacuum as a driving force reduces the drying time by up to 80% and reduces the direct energy use (including the energy for the vacuum) by 50-80%. LPD is suitable for small-to-medium volume throughput.

Infrared drying (IRD) uses the energy from IR radiation to directly heat the bulk material of the polymer granule or flake. IRD is particularly suited to the drying of reprocessed PET, as it combines recrystallization and drying in one pass. IRD can also be used with a vacuum to further increase process efficiency and reduce energy use. IRD is suitable for high-volume throughput.

Actions:

Processors should examine the new technologies to see if these are suitable for their operations.
If considering compressed air dryers, then make sure that the cost of generating the compressed air is used in the costing of the process, and that the site has adequate compressed air capacity.

Note: Dr. Robin Kent is the author of Energy Management in Plastics Processing, published by Plastics Information Direct, and managing director of Tangram Technology Ltd., consulting engineers specializing in energy management in plastics processing. rkent@tangram.co.uk.