Conair Group Inc. has come up with a new form of recycling. The firm's two-stage EnergySmart resin dryer takes some heated air, which normally would be wasted in a heat exchanger, and recirculates it back into the drying hopper.
Conair said the EnergySmart desiccant dryer can slash energy consumption by up to two-thirds in a high-volume PET preform molding plant, compared with a traditional dryer.
Proper drying is critical for injection molding PET bottle preforms or extruding the material into sheet for packaging. Preform plants running high-cavitation molds can use a huge amount of resin. For example, an injection press equipped with a 96- or 144-cavity mold can consume 2,000 pounds of resin an hour.
``In a high-volume PET processing operation, polymer drying is an area where huge energy savings are possible,'' said Pete Stoughton, PET equipment sales manager at Conair. Conventional dryers account for 25 percent of the energy consumed in the preform molding process - second only to the injection molding machine itself.
Based on data from the first EnergySmart customer, the new Conair dryer could save $364,000 a year in energy costs for a preform factory using 120 million pounds of PET. He would not identify the customer, which he called ``one of the top preform molding plants in the country.''
So far, Conair has installed eight EnergySmart units at the customer's site, Stoughton said. The first one has been in operation for about a year and a half, giving Conair some real-world numbers to prove the energy savings.
Stoughton, a 28-year dryer veteran, discussed what Conair is billing as a dryer for the 21st century during an interview at Conair headquarters in Pittsburgh.
Traditionally, he said, auxiliary equipment makers have followed guidelines from resin suppliers that specified drying temperature, dew point, drying time and airflow to get the desired throughput.
``You look at dryers, and other than putting a microprocessor control on it, a dryer was a dryer was a dryer,'' Stoughton said.
But in today's world where giant injection presses can turn out 60,000-plus preforms an hour, the driving force is cutting energy use to run profitably. Old dryers had minimal or even no control over drying parameters, no monitoring of the drying hopper and major heat losses, he said.
``We're having processors come to us and demanding better dryers. They're asking us to get more involved in what the dryer must do,'' Stoughton said.
In traditional desiccant drying systems, all the heated air is fed back through the desiccant dryer, first passing through a heat exchanger to cool the air down again before it enters the dryer. Then it must be again heated up, to 300-350° F, before the resin enters the drying hopper.
``This is the most insidious waste of energy on a conventional drying system,'' Stoughton said.
Instead, EnergySmart divides the air coming out of the drying hopper into two separate return circuits, called the dry-air loop and the hot-air loop.
The dry-air loop uses a heat exchanger before the dryer.
But the hot-air loop has a different design, with no heat exchanger. Instead, the heated air is circulated directly back into the drying hopper. The otherwise-wasted hot air is filtered, then bumped up to the 300-350° F level and reintroduced to the hopper through an inlet cone in the middle of the hopper.
By splitting the air, Conair designers were able to use a smaller Carousel Plus dehumidifying dryer, a smaller heat exchanger and a downsized heater box for the dry-air loop. The dried air is introduced at the bottom of the hopper. The Carousel Plus uses a wheel to rotate filters containing the desiccant, to cut drying time.
``Because we have preheated the PET pellets to the ideal drying temperature in the hot-air stage, we need a considerably smaller volume of desiccated air in the dehumidifying stage. With less air going through the dehumidifying air circuit, we need less energy to heat a smaller volume of air, and we can use a smaller, more energy-efficient dryer,'' Stoughton said.
To control the process, EnergySmart uses the Conair Drying Monitor, a long probe that extends down through the hopper. The data is sent to the controller, where the temperature profile within the hopper is updated continuously and displayed on the operator screen.
Temperature readings from the Drying Monitor also are used to adjust and fine-tune the volume of air in both air circuits - again, trimming energy costs. For example, if the temperatures are too high, and out of the desired range, airflow to the drying hopper can be reduced to boost efficiency. If temperatures are too low, air flow or temperature can be increased, to restore optimum drying conditions.