Dryers move beyond desiccant
Dryer manufacturers seem to agree that plastics processors consider dryers to be, at best, a necessary evil. "If customers could not dry at all they would be very happy not to," Mark Haynie, dryer pro...
Dryer manufacturers seem to agree that plastics processors consider dryers to be, at best, a necessary evil. “If customers could not dry at all they would be very happy not to,” Mark Haynie, dryer product sales manager at Baltimore, Md.-based Novatec Inc., said.
Like it or not, however, the industry can’t do without dryers, but the good news is that dryer manufactures are eager to make the process as easy as possible by giving their customers the most up-to-date features — and what the majority of processors want right now is energy savings. “With the cost of energy today, it has become more critical than ever to dry efficiently,” B. Patrick Smith, vice president of marketing and sales at Aston Pa.-based Maguire Products Inc., said.
And two areas in which progress has been made are vacuum dryers and desiccant wheel dryers.
DRYING IN A VACUUM
Traditional desiccant dryers use electric heaters and blowers to obtain the temperature and humidity-free air that is required to dry plastics. The technology, which has been in use for decades, has certainly been tested and found to work. “The problem is that desiccant drying is not energy efficient,” said Maguire’s Smith.
One alternative drying method that has met with some success recently is vacuum drying, during which resin is heated and then vacuum applied to draw out the moisture.
“Because a vacuum dryer doesn’t have desiccant that has to be regenerated, it uses up to 80 per cent less electricity than a traditional desiccant dryer,” Smith said. “It’s a huge energy savings, and we have customers that are experiencing paybacks in as little as 12 months.”
Santa Ana, Calif.-based thermoplastic processor Southern California Plastics Inc. (SCP), for example, recently began a large-scale changeover from conventional desiccant dryers to Maguire’s LPD vacuum resin dryers, and the company has already reported energy savings that, on an annualized basis, amounted to US$28,000, including an energy rebate from the state. “It’s just incredible. We have 10 more LPD dryers on order, and with subsequent rebates for energy savings, I expect to be able to recover 40 per cent of the investment cost,” D.E. Rodriguez, SCP’s president, said.
A new entry to the market is Novatec’s Nova Vac II vacuum dryer, which requires only 20 per cent of the energy of comparable desiccant dryers, the company said.
DESICCANT WHEELS KEEP TURNING
There are drawbacks to the vacuum dryers, however. Until recently, vacuum dryers were limited to a maximum throughput of between only 100 to 200 lbs. per hour, and throughput levels remain a problem today. Dryer manufacturers are attempting, however, to make vacuum throughput levels competitive with those of desiccant; in 2005, for example, Maguire commercialized its LPD-1000, for rates up to 1000 lbs. per hour, and the company plans a dryer targeting 2000 lbs. per hour.
But perhaps the biggest drawback of the vacuum system that dryer manufacturers have identified is its very newness. “It’s a departure from the normal way of drying,” Novatec’s Haynie said. “In vacuum drying you don’t circulate air, so you have to change the mindset in the industry towards drying air and using that dry air to dry resin.”
Fortunately, plastics processors who are reluctant to part entirely with the idea of desiccant have a way to save energy costs nonetheless by using a newer version of the process called desiccant wheel drying.
By using a lighter, honeycombed desiccant, the wheel system allows the dryers’ weight to be reduced, according to Pete Stoughton, commercial product manager, dehumidifying dryers, at Pittsburgh, Pa.-based Conair. “Previously, a 200 lbs. per hour Conair Carousel dryer had a desiccant weight of over 300 lbs.,” he said. “With the desiccant honeycombed wheel, that entire assembly for the same sized dryer has a desiccant weight of only 40 lbs., allowing you to reduce the thermal load that you have to heat up for regeneration, thereby saving a tremendous amount of energy.”
According to Joe Corturillo, product manager, material handling/drying at Markham, Ont.-based Nucon Wittmann, other advantages of the desiccant wheeled dryers include the proven performance of desiccant technology; a stable, adjustable temperature; and the ability to regenerate the desiccant wheel continuously, preventing temperature spikes. Nucon Wittmann’s CDD (continuous desiccant dryer) line has a desiccant wheel that creates regeneration airflow temperature of less than 350 Fahrenheit (F), allowing for reduced energy usage and longer regeneration heater life.
“The dryer uses less energy because it only needs to heat up the air to achieve the desired dewpoint level, based on ambient and material conditions,” Corturillo said.
Novatec’s Haynie suggested that the desiccant wheel is a good solution for those processors who want to break away from traditional twin tower desiccant systems but are wary of vacuum drying. “The desiccant wheel allows customers to think about desiccant in a different way. There are better mousetraps out there.”