The scale of these units requires large heaters to maintain a constant temperature. These units function well and typically last a very long time. Desiccant dryers, however, tend to consume a lot of energy. When this technology was invented more than 50 years ago, energy was affordable and consumption wasn’t a major concern for processors.

Unfortunately, today’s ultramodern facilities demand a better use of energy to maintain quality and lower the bottom line. This is why drying systems that use honeycomb rotary bed, compressed air, vacuum, and natural gas technologies have been introduced to the market. These units offer alternative drying methods, and each is designed to use energy more efficiently.

So Many Different Dryers

Natural gas dryers are similar in function to the twin tower desiccant units. However, they offer a heating source that is an alternative to electric heaters.

Hot air dryers can be a solution in areas that remain at relatively low humidity levels throughout the year. A hot air dryer with a 65-lb hopper costs around $775 with insulation. Given the correct conditions, this is an economical solution for processors.

Honeycomb rotary bed drying units are now available at an affordable price, thanks to recent advances in silica, molecular sieve, and other drying mediums. A honeycomb dryer with 50 cfm of unrestricted air now costs around $5400, with the suggested return-air cooler. Even at decreased prices, the technology is sometimes not chosen because molders are not familiar with it. Honeycomb rotary-bed drying units are similar to other forms of drying technology, except for the dehumidifying media used to remove moisture from the air. These dryers use crystallized molecular sieves and silica gels that are baked onto the drying wheel to yield dehumidified air and material. The silica gel does not create dust like a desiccant unit, which can contaminate parts. It also absorbs and releases moisture much more efficiently than any other type of dryer. The honeycomb wheel allows air to pass easily over the drying media, and because it releases moisture better than desiccant beads, only a small blower and electric heater are required, saving considerable energy.

Honeycomb dryers operate in constant process drying so that the dewpoint of the drying air is constant. Thanks to these modern silica and sieves, a lower dewpoint also can be achieved than with desiccant. The advanced honeycomb media can be washed with soapy water if it becomes dirty and can last up to 10 years vs. the two-year life of desiccant. This means that maintenance and service costs are greatly reduced. The energy savings pay off on the bottom line, and the modern silica allows for better yields in a modern facility.

Energy savings and total cost savings are very important in the purchase of any new equipment. Some recent technology in drying has come not as a result of new dryer designs, but in the systems built around these designs. One design gaining popularity with nylon and polyethylene terephthalate (PET) molders is that of weigh drying, a technology that weighs all material being dried and calculates drying settings.

These patented systems also perform complex functions such as recording and controlling the drying temperature, dewpoint, residence time of the resin, and resin usage per machine for every shot of material in the facility. What this means is that a processor can guarantee to its customers that the product it is purchasing has been dried appropriately.

The weigh dryer is a good match for captive molders using high volumes of hygroscopic materials, such as nylon and PET, or heat sensitive materials. However, the system does require high-quality controls.

In the case of nylon and some other polymers, mishandling or overdrying is known to result in everything from discoloration to product failure. Weigh-drying systems give molders the ability to prove their handling conditions for every part and eliminate costly part returns and reruns of parts. A weigh system can generally be retrofitted onto an existing drying system or purchased complete. By retrofitting these systems, modern processors save money, use the equipment they already have, and are able to achieve consistent, high-quality production yields.