Drying resin for energy and material savings

As costs for materials and energy rise, companies look to become more energy efficient. Not sure where to start? Finding the right drying system can drive down operating costs.

We all talk about saving money yet it seems we don''t really do enough about it. The biggest reason could be that we don''t know where to begin. One of the easiest places to look is at your drying system. Dryers can consume as much energy as a hydraulic molding machine unless they are properly engineered. When selecting dryers for your operations you should look for several features that not only save you money on energy but also on material. The typical twin-bed desiccant dryer offers at least two major ways to save money through more efficient airflow-element control for heating and valve control.

When air leaves the blower it typically travels through a desiccant bed past a heating element that heats the air to the required temperature. For most dryers, this temperature setting remains constant, ±5 deg F, to continually dry material. Even when the molding machine does not demand material, these dryers supply hot air to already dried material. This not only wastes energy, but the material suffers as well. Overdrying can lead to brittle parts, cracking, shrinkage, and more.

However, dryers equipped with material-protection features are designed to limit heating when a second setpoint is reached. This user-defined setting allows the operator to tell the dryer at which temperature it should automatically limit drying. The material in the hopper remains dry, but reduced heating element cycles prevent overdrying and reduce energy costs. Material protection can also be integrated on multiple hopper systems with microprocessor control of heating elements and motorized valves to reduce airflow to each hopper. Each valve operates independently according to the hopper''s individual needs.

For example.

Consider a facility operating on a standard three-shift schedule-24 hr/day or 168 hr/week with approximately 15 machines-all requiring dry material. The central drying system has a 600 ft3/min dryer and eight large hoppers of varying size, each with its own heating element to allow for individual drying needs; all operating at 480V, 3 ohms.

If this central dryer system were to run constantly without interruption, you would use about 50 amps or 24 kW. Realistically we can expect the amperage draw to be reduced by standard fluctuations in element usage and so forth by about 15% or to approximately 40 amps or 19.2 kW. Again, using a 168-hour week, we can determine our kilowatt-hour usage or kWh (to determine average usage, see box on p. 76 ). Using a U.S. average of about $.08/kWh, you can expect a cost of $12,902/yr for this drying cell''s electricity.

Now compare this to a dryer with a second setpoint. You can reduce your amperage load by an additional 25% for a total reduction in energy usage of 40%. This would equate to about 30 amps or 14.4 kW. This reduces energy costs to $9677/yr for a savings of $3225.20. This may not seem like much, but when you include the energy saved during mold-change times, periodic maintenance of molding machines, and other press downtimes, much larger savings result.

As an example, consider this scenario: If your operations had two to three mold changes/week, and each mold change took between 2 and 6 hours, depending on your machine size and other variables, operating your dryer during these expected downtimes would add an additional 18 unnecessary hours per week. That equates to about $110.59 a month, or an additional $1327 a year. Throw in material savings from the elimination of defects due to over-drying and a significant amount of money can be saved.

Proper control of airflow during the entire drying cycle can readily lead to significant savings in energy consumption. Correct dryer sizing, accurate drying temperatures, and several other factors contribute to added savings. Even controlling your airflow during regeneration cycles can facilitate a more efficient drying process by reducing temperature and dewpoint spikes. There are many more features incorporated into many of today''s dryers, and the key to finding out what works best is understanding how those features work.

Matt Chaponis, dryer product manager, Wittmann Inc. www.wittmann-ct.com