Energy in Drying

Dryers can be a key component when injection molders or extruders look to save energy in their production process.

"One way for injection molders who use resins that require pre-drying to cut production costs significantly, is to switch to new, advanced-technology dryers," says Frank Kavanagh, Vice President, Global Sales & Marketing, Maguire Products. "Currently tens of thousands of dryers in operation worldwide are more than ten years old. The energy savings achieved with new dryers would easily justify the equipment investment. The savings are huge when the switch from standard desiccant dryers to ULTRA vacuum dryers from Maguire Products. Desiccant dryers - even the newer models - are at a disadvantage for two reasons. Firstly, they use significantly more energy than vacuum dryers to dry resin; and secondly, they consume additional energy to regenerate desiccant."

He says a vacuum dryer works by heating the resin to a required temperature, then, in a separate vessel, evacuating air. As air pressure drops, water boils, at lower temperatures. Under normal conditions, with atmospheric pressure at 760 mm (29.92 in) of mercury, water boils at 212°F (100°C), but in an ULTRA dryer, pressure is reduced to only 635 mm (25.00 in). Here the boiling point of water is reduced to 133°F (56°C) and any residual moisture contained within a resin pellet literally boils, becoming water vapor. 

Kavanagh says: "This is a very rapid process - much faster than what happens inside a desiccant dryer. While the kW energy to heat raw material from ambient to required drying temperature is the same for all drying processes, the energy to dry raw material is where the difference occurs. While the ULTRA would run at 19W per pound in the drying cycle, an energy efficient desiccant dryer would typically run at 60W per pound of material, and a new desiccant dryer with only standard energy performance could run at 100W per pound. Comparably, a 10- or 15-year old desiccant dryer that a new dryer would replace, the energy might run as high as 150W per pound. On the basis of energy savings alone, a new ULTRA dryer could pay for itself in a matter of months. Over a ten year period, the energy cost savings with an ULTRA dryer range from US$85,000 - 125,000."

ULTRA vacuum dryers consume 60% less energy than a comparable desiccant dryer. Normally, an ULTRA dries material 6 times faster than conventional desiccant dryers and substantially reduces the heat history to which polymer is exposed. ULTRA fast drying time provides quicker start-ups, and achieves properly dried polymer in only 30-40 minutes after cold start, depending on the polymer.

Read the rest of the article, Energy Use by All Types of Machines, at Injection World in their Energy Management section.