PET Processors Save up to 67% of Drying Energy With First-Ever EnergySmart™ Drying System from Conair

Recycling hot dry air to raise the temperature of new resin entering the drying hopper, the new EnergySmart™ polymer drying system from Conair can reduce energy consumption in high-volume PET molding operations by up to two-thirds, compared to conventional desiccant dryers. After using the pilot EnergySmart™ system in a lengthy beta test, a major PET bottle producer estimated it could save over half a million dollars per year in energy costs if their entire operation was converted to the new Conair drying system.

“When it comes to drying, PET can be a real challenge,” explains Pete Stoughton, PET Sales Manager. “If drying procedures are not meticulously followed and residual moisture remains above 0.005%, the material will undergo a chemical change during melt processing, losing intrinsic viscosity (IV) and physical properties.”

“In a high-volume PET processing operation,” he concludes, “polymer drying is an area where huge energy savings are possible.” Conventional dryers, he says, can consume up to 12% of the total energy consumed in a bottle plant, and up to 25% of the energy consumed in the preform-molding process.

Energy challenges are especially acute in PET drying because the material needs to be dried at very high temperatures. Resin producers recommend that their material be dried in the range of 300 to 350°F (48 to 177°C) for extended periods of time — four to six hours. Raising the temperature of thousands of pounds of resin and holding it at 350°F for up to six hours can be very costly. And yet the need for product quality allows for no alternative… until now.

Recycling Energy

The EnergySmart™ drying system is different because it actually recycles the wasted heat that would otherwise be drained through the drying system’s return air heat exchanger. In a conventional PET dryer, the air exiting the drying hopper is still quite hot, about 200°F. Because desiccant is much less effective at removing moisture at elevated temperatures, the return air must pass through a heat exchanger where the temperature is reduced to about 120°F. In other words, 80°F of heat energy is essentially wasted in a conventional dryer.

That’s why the EnergySmart™ dryer is a “two-stage” system, incorporating a hot-air circuit and a dehumidified-air circuit. In the hot-air circuit, that otherwise-wasted energy is captured. Some of the return air exiting the top of the drying hopper is channeled through a filter and then reheated to 350°F before it is re-introduced to the drying hopper through a unique inlet cone located in the middle of the hopper. The Conair system saves energy by not removing heat in the return air heat exchanger and by not having to add as much heat to the air for its next trip through the hopper.

“This recycled air is not quite as dry as normal drying-process air,” explains Pete Stoughton. “Its dew point is between -20 and 0°F instead of the -40°F resin manufacturers recommend. However, the primary function of the re-circulated hot air in this new system is to pre-heat the polymer in the top half of the hopper to the selected drying temperature. The low moisture level required for PET is achieved in the EnergySmart™ system’s dehumidified circuit.”

Dehumidified Drying

The dehumidified circuit of the EnergySmart™ system is comprised of a standard, although smaller, Conair Carousel Plus™ dryer. Air is dried to a -40°F dewpoint and heated to 350°F, as recommended by PET resin suppliers. Then it is introduced into the drying hopper through an inlet cone at the bottom of the hopper. The hot, dry air rises through the material bed, which has already been preheated in the hot air circuit, maintaining the optimum drying temperature and reducing the moisture content of the material to manufacturer-recommended levels.

“Because we have preheated the PET pellets to the ideal drying temperature in the hot air section of the hopper,” Conair’s Stoughton continues, “we need a considerably smaller volume of desiccated air in the dehumidifying zone. 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-efficient dryer.

Precise Control for Proper Drying

Energy efficient drying demands that temperature and airflow be controlled exactly to ensure that the resin manufacturer’s specifications are met. In the EnergySmart™ system, the Conair Drying Monitor™ helps provide that precise control. A long probe in the drying hopper extends through the material bed and six integral temperature sensors register the temperature at each position. Data is sent to the EnergySmart™ controller, where the temperature profile within the hopper is continuously updated and displayed on the operator screen.

The temperature readings from the Drying Monitor™ are also used to adjust and fine tune the volume of air in both air circuits, so that just enough heat energy is added to the bed of material to maintain the optimum temperature profile throughout the hopper. Too much air-flow will result in wasted energy, too little air-flow will result in poor drying performance. The EnergySmart™ drying system controls have the ability to fine-tune the airflow and dewpoint to achieve optimum drying performance.

If all the temperatures are in the normal range, users know they are operating efficiently and the material is being properly conditioned. If the temperatures are too high, the system is wasting energy. In that case, airflow to the drying hopper can be reduced for increased efficiency. Likewise, in a low-temperature situation, air flow or temperature can be increased to restore optimum drying conditions.

The EnergySmart™ system has other features that enhance efficiency:

• Gas Heat… In high-volume drying applications, gas-fired air heaters are often more cost-efficient than electrical heaters. The new Conair drying system can use either gas or electric fuel.
  
• Unique Hopper Air Distribution Design… The EnergySmart™ drying hopper utilizes an ingenious air distribution design. Dual air inlets and a tube-in-tube system are used to introduce hot closed-loop air into the hopper mid-section and hot closed-loop dehumidified air into the lower section of the drying hopper. The dual air inlets are located in the top section of the drying hopper to minimize the impact on mass flow.
  
• Insulation… To prevent unnecessary heat loss, the hopper and all hot-air ductwork are heavily insulated.
  
• Carousel Plus™ Technology… The dryers used in the dehumidified-air circuit of the EnergySmart™ system are among the most efficient available. The desiccant-wheel assembly has less structural mass and less desiccant to heat and cool than other dryers.

Recognizing that your success in today’s competitive global plastics marketplace is the only true measure of our own performance, Conair is committed to finding and delivering process solutions that make a real difference to our customers. To that end, we listen carefully to learn what matters most to you. We seek to understand the driving issues that affect how you do business today. Then we work to help you transform your business with game-changing products and services that reduce your costs, increase your productive up-time and boost your efficiency.

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