Plastic processors are looking for energy-efficient dryers and chillers that are easy to service and maintain as well as easy to operate, with simple operator interfaces and control systems. Suppliers have introduced new features to meet these needs.

Dryers

Hygroscopic resins (e.g., PET, polyamides, PLA) must be dried immediately before use to prevent moisture-related defects in the final part. Drying, however, is energy-intensive and is usually the second largest cost after the resin itself, says Jamie Jamison, product manager at Conair Group.

Technology to monitor and then more tightly control the drying process continues to advance. Conair, for example, recently introduced the third generation of its DM3-I patented Drying Monitor, which operates independently, and the DM3-e, which is embedded in the dryer control. “Unlike other products that measure moisture in the pellets only after they have exited the drying hopper, the Drying Monitor measures the temperature at up to six different points in the bed of plastic material,” explains Jamison.

“When the temperature profile is correct, you know that the resin is being properly conditioned at all times. If anything happens to cause temperatures to vary—a dirty filter or obstructed hoses that reduce airflow, for instance, or a change in throughput—the Drying Monitor acts as an early-warning system, alerting operators so problems can be resolved before bad parts are made.”

The monitor’s data can be used in Conair’s new TouchView dryer control with an Optimizer Mode that optimizes the temperature of the drying air. And, using a variable-frequency blower motor, it regulates air flow to maintain a stable temperature profile in the drying hopper regardless of throughput changes or variations in material temperature or ambient conditions, adds Jamison.

Conair has also web-enabled many of its auxiliaries to allow remote monitoring and control of conditions and settings. Any internet-connected device can display the control interface that appears on the machine’s control panel. “In today’s efficient plastics plant, machines run unattended. This technology lets customers access a Conair dryer from almost anywhere—the other side of the plant or the other side of the world. I would expect these types of controls to continue to grow in popularity as the cost for them comes down and customers recognize the benefit that they provide,” says Jamison.

Obtaining system data for troubleshooting and process optimization is increasingly important, adds John Fleischer, vice-president of sales and marketing at Una-Dyn. Dryer data sent to a company’s enterprise system can be used, for example, to track material if problems arise downstream, or to track energy use. The system can graph data and can be customized for the needs of different job functions, such as engineering, maintenance, and finance. Data can also be linked to Una-Dyn’s central control system, FACS (Factory Auxiliary Control System), which can be accessed remotely for faster troubleshooting.

Tight temperature control is important not only for energy savings, but also for bio-based resins that require lower drying temperatures than conventional resins, says Fleischer. Temperature stability is built into Una-Dyn’s PCT twin-bed desiccant dryer. PCT technology eliminates the common heat spike that can occur in a twin-bed system by equalizing the bed temperature before switching and ensuring that the temperature stays constant through the drying cycle. The technology also creates a drier air stream, which results in faster, more efficient drying. The current generation of PCT technology offers energy-saving functions, such as a heat-recovery system and variable-speed blowers.

Energy-efficient drying

A variety of technologies improve energy efficiency in dryers, notes Joe Dziedzic, application engineer manager at AEC. Variable-frequency drives for process blowers, variable air-flow, and a central control system, such as used in the company’s WH and MDB dual-bed desiccant dryer systems, reduce electrical load and thus improve efficiency. The company’s WH drying hoppers have improved insulation to minimize heat loss. Closed-loop regeneration, used in the MDB dryers, recovers waste heat and reintroduces it to the process and regeneration circuit(s) for additional energy savings.

Monitoring and control of the drying process is crucial for fine-tuning the process to reduce overall drying cost, notes Dziedzic. The new DryPro dryer control platform makes control easier with a touchscreen interface and Ethernet-based control capability, which allows users to access data from a smart device for remote servicing. The platform also provides data and service logging to troubleshoot and optimize the process.

“We’ve begun to tackle further energy savings by making equipment adaptable to process needs,” notes Michael Stark, division manager for material handling and auxiliaries at Wittmann Battenfeld. For example, the company’s new Aton2 portable dryer has an “eco mode” that adapts energy consumption to the dryer load. On larger dryers, a new variable-frequency drive adapts energy consumption to the load and also reduces or eliminates the need for chilled water. 

Reliability and ease of use, such as easy-to-visualize alarms and indicators, are other areas of improvement, adds Stark. Simplified designs are easier to maintain and thus have more uptime. The Aton2 dryer, for example, has a single-blower design with no valves and only one moving part.

Meanwhile, Moretto is building more energy efficiency into its dryers. Its Eureka system consists of a Flowmatik airflow management and distribution system, OTX hopper drier, and the X Max drier, which incorporates a multi-bed single molecular-sieve desiccant system with a heat-recovery system. The latest enhancement, introduced in 2014, is a multi-stage centrifugal blower that increases efficiency, says the company.

Low-throughput dryers are needed to efficiently dry resin for smaller molding machines, such as for the growing niche of medical applications, notes Charlie Sears, president of Dri-Air Industries. The company has developed small, portable dryers with two hoppers to hold a minimum amount (about one-quarter of a cup of resin) above the feed throat. “For medical molding, dryers must be stainless steel and easy to clean with no crevices that could trap material so that contamination is eliminated,” adds Sears.

Just-in-time blending is another way to efficiently provide dry resin to the process. In Dri-Air’s PDII dryers, two materials can be dried to two different temperatures, volumetrically blended at the exit of the drying hoppers, and fed directly to the machine throat with dry-air conveying. “This method is as accurate as gravimetric feeding, and eliminates the problem of material gaining moisture in an extended time outside of the dryer,” says Sears.

Vacuum drying

The majority of dryers use desiccant bed (e.g., tower, carousel) technology, in which desiccant is used to dry air that flows over and draws moisture from the pellets. Vacuum dryers, in contrast, pull moisture out of resin pellets using a vacuum. “In this system, the boiling point of water is reduced to 50°C, so when vacuum is applied to wet pellets, all water trapped inside the pellet instantly becomes steam (water vapor),” explains B. Patrick (Pat) Smith, Maguire vice president of marketing and sales. “The very high vapor pressure inside the pellets seeks to reach equilibrium with the very low pressure environment (vacuum) outside the pellet. It takes only 40 minutes for vacuum to dry polymer—six times faster than a typical desiccant system.”

Faster drying allows shorter cold startups and reduces the risk of material degradation, since resin is exposed to elevated temperature for 80% less time, Smith notes. The vacuum method is more efficient and reduces energy consumption by up to 60% in comparison with desiccant dryers, he adds. Vacuum dryers eliminate the maintenance issues that can occur with desiccant and have a simple setup (setting only temperature and vacuum time), which reduces the likelihood of human error and can be automated if desired.

Maguire’s VBD™ vacuum dryer, first introduced in 2013, uses a new design that’s simpler, and therefore more reliable and less expensive, than first-generation vacuum dryers. The VBD uses gravity feeding, controlled by slide-gate valves, to move material from one stage to the next, which eliminates the indexing carousel used in Maguire’s LPD vacuum dryer, introduced in 2000.

In the VBD system, the resin is brought to temperature in a heating hopper, drops into a vacuum vessel, and then into a pressurized retention/take-away hopper that is continuously purged by a membrane air dryer to maintain target dryness until the material is discharged. The system also eliminates sealing gaskets and perforated screens, which reduces maintenance, the company adds.

Early in 2014, Maguire introduced an enhanced version of its VBD dryer with an “EasySlide” mechanism to give access for cleanout, plus an optional hopper extension to increase the dryer capacity by 25%. The Maguire VBD 150 vacuum dryer, originally rated for a throughput of up to 150 lb. (68 kg) per hour, has been found to exceed 200 lb. (90 kg) per hour with hygroscopic materials such as ABS, acrylic, nylon, polycarbonate, polyetherimide, and PBT, says Smith. The Maguire VBD-1000 vacuum dryer has a capacity of 1000 lb. (455 kg) per hour, and a series of smaller dryers will be introduced in coming months.

Chillers

Energy-saving technology is also crucial for process-cooling equipment. One such technology is energy-efficient scroll compressors, notes Tim Miller, product manager for heat transfer at Conair. These are are used on the company’s EarthSmart™ portable chillers, introduced last year. On larger central chilling systems, variable-frequency drives can replace fixed-speed motor controls to save energy.

An innovation in cooling-tower design that can save energy and minimize water use is the adiabatic tower. Process fluid flows in a closed loop through tubing in the tower, so it’s isolated from contamination and evaporation. Adiabatic wetted panels are mounted so that they’re in front of the cooling tower coil through which process water flows, explains Miller. When outdoor temperatures are high, ambient air passes through the wetted panels and the water evaporates, reducing the temperature of the air flowing into the unit so that it cools the process fluid. When air temperatures are low, cooling relies on ambient air. This saves water and energy. Conair’s EarthSmart Adiabatic Cooling Towers reduce water and energy consumption, the company says, while maintaining stable exit-fluid temperatures, even in hot weather.

Piovan’s new Ecosmart chilled-water systems self-adjust to match the variability of the production process. The heat load from a plastics production process is variable, but traditional chilled-water systems are not equipped with sufficient controls to cope with partial loads, explains Giorgio Santella, chief marketing officer at Piovan. Ecosmart, however, self-adjusts cooling power, water flow, and pressure in accordance with the current heat load, in real time, ensuring process stability and lowering energy use. Ecosmart can be air or water condensed, with cooling water supplied from a cooling tower or a dry cooler.

Reliability and serviceability are also important features in chillers used in plastics processes. “Maintenance staff at many of our customers has been reduced, making it even more critical now that equipment is up all the time, is easy to use, and is easy to service if needed,” says Michael Stark at Wittmann Battenfeld. The company’s new chillers, for example, feature an easy graphical display and QR symbols that pop up to assist troubleshooting. And a new temperature controller from Wittmann, the Tempro Plus D, has a color touchscreen interface that tracks the process and allows better process control.

The industry is moving towards additional data acquisition tools, such as additional sensors for diagnostics and remote access for logged data and alarm history, along with email or text notification of alarms, notes Rick Holzhauer, R&D engineering manager at AEC.

Energy efficiency remains a top priority, and chillers need to adapt to the operating environment. AEC has launched both screw and scroll central chiller designs with touchscreen displays, additional data acquisition and Modbus communication tools, and the ability to parallel up to five individual units for maximum efficiency and application flexibility.