Next-generation dyers: raising the standard.
Investing in the latest generation of material dryers is a sure-fire way to make big savings in energy bills, as technology suppliers exhibiting at the Fakuma show in Germany late last year were quick to point out. There are also moves afoot to introduce a standard to help processors make sense of all the energy-saving claims being made by dryer suppliers.
Energy efficiency is critical with dryers. Running costs can quickly outweigh the initial investment cost, so a more expensive but more energy-efficient dryer, treating, for example, 15 kg/hr of granules, should pay for itself in under six months.
Virtually all suppliers promote their units as being highly efficient, but often, little data is readily available to support their claims. There is general agreement among suppliers to the European market that the industry needs a standard test protocol for measuring dryer energy consumption.
Last year Wittmann introduced energy rating "standard" (it is the only one to use it so far; details at www.wittmann-robot.com), developed for dry-air dryers, which established the ambient conditions under which measurements should be taken, as well as the specific parameters for energy measurement.
Company president Michael Wittmann says that a commonly agreed Euromap standard is what is really needed. The company has already submitted its in-house standard as a basis for discussion. This is likely to be the beginning of a long process, with numerous other competing companies submitting counterproposals. But at least the ball is rolling.
A standard would allow processors to make their own comparison between different dryer manufacturers and dryer designs, capacities, and energy-saving features. "For example, the difference in dew-point behaviour can be determined under precisely defined and controlled ambient conditions during testing," says Wittmann. (Dew point is the temperature at which water condenses out of any given sample of air, and is thus a measure of its humidity.)
Not surprisingly, Wittmann's Drymax ER60, which uses its new segment-wheel technology, comes out well. Higher energy efficiency results from the use of chambers full of loose desiccants rather than honeycombs with desiccants glued to their walls that are found inside some other segmented-wheel dryers.
Segmented-wheel systems work on the same principle as dual-bed dryers, with desiccants that first adsorb water from the air, and which are then heated to drive off the moisture before being cooled down prior to reuse. But here all three phases occur simultaneously, with each segment being in a different phase. In a sense, they are a form of triple-bed dryer.
Michael Wittmann says the problem with honeycomb wheels is that if they are damaged--for example by contaminated air passing through them, something that is not a rarity--then the whole honeycomb has to be thrown away, at not inconsiderable cost. With Drymax ER types, the zeolites can be easily removed and replaced. Plus, the surface area of the zeolites exposed to the air is much greater than that of the desiccant used in honeycomb wheels.
Wittmann dryers now have green stickers on them, rather like those found on various pieces of electrical consumer goods, with a number indicating their energy efficiency according to its standard.
The stickers at Fakuma showed Wittmann's dual-bed dryers still have a better energy rating than its segmented-wheel types. With the wheel dryers, regeneration is permanently on, and so consuming energy. With the dual-bed dryers, this is not the case (for example, when one bed is drying and the other is cooling). Wittmann says segmented-wheel types are better suited to use in humid climates.
Another advocate of creating a standard for dryers is Paul Edmonson, general manager for Maguire Europe. "I think it's a very sensible and logical move," he says. "As an industry, we need to think more about energy. Very often, we are talking to production people, whose focus on energy is not as high priority as maybe it should be. And they've got a budget that they want to squeeze as much capital equipment into as they possibly can. But in the end, they may be adding to the total cost."
Maguire's flagship LPD vacuum dryers were introduced in 2001. They use no desiccant and are said to be six times faster than a conventional desiccant model. They put the granules under a low vacuum (675 mm Hg), making water boil at 56[degrees]C. The warm, wet air is expelled to the atmosphere, dispensing with the need for desiccants.
Edmonson says 'the system is much faster than a regular desiccant dryer, and more energy-efficient. He says it uses 50%-80% less energy than a standard dehumidifying dryer. There are now four models for nominal outputs of 15, 50, 90, and 250 kg/hr.
But he also says large parts of the market are not oriented towards the use of vacuum dryers. "It requires a different operator interface, and different procedures to follow." One reason why company owner Stephen Maguire took a major share in Novatec Systems in 2006, providing him with more drying options and at the same time a more complete systems offering that also includes materials handling, conveying and blending. Novatec machines are badged Maguire in Europe.
At Fakuma, the company showed models originating from Novatec. NovaWheel dryers are segmented-wheel dryers with the desiccant glued to a honeycomb. Two new models in the range have nominal throughput capacities of 14 and 27 kg/hr. In contrast to Wittmann, Maguire says these wheel dryers provide up to 35% energy savings in comparison with dual-bed systems (which it does not make). The new models are aimed at moulders of micro and precision parts for medical, electronic, and other applications.
Drying With a Membrane
The NovaDrier is rather like the LPD, in that it uses no desiccants; but rather than a vacuum, it uses flowing compressed air that passes through an adsorption membrane. Maguire says it consumes up to 75% less air than other systems using compressed air. Latest version is the NovaDrier 75, which accommodates throughputs up to 35 kg/hr.
Edmonson says the moisture-removing efficiency of the textile membrane is so great that process air with a -40[degrees]C dew point is flowing through the system in less than four minutes after start-up. Energy efficiency is not as good as on a vacuum dryer, but is still said to be better than a wheel dryer, providing throughputs are low.
Mann+Hummel ProTec's Somos dryers incorporate ALAV, an automatic procedure that adjusts the energy input to the drying hopper to the required throughput; and Super Somos, a software module that automatically adjusts the regeneration frequency of the desiccant to the moisture quantity actually adsorbed. This yields a constant dew point of -35[degrees]C, regardless of the time of year or climatic fluctuations.
The new mobile Somos T/TF eco dryers consist of a dry-air generator and an insulated, stainless-steel drying hopper. The TF-version has an integrated conveyor for automatic processing-machine feeding. The dryers are tailored to small quantity requirements of approximately 3 kg/hr to material throughputs of 80-100 kg/hr. Drying temperatures of 60[degrees]C-140[degrees]C are covered.
Piovan has been offering the HR series since 2006. This uses a honey-comb desiccant wheel, coated with silica gel, so there is no powder generated by the movement of the wheel. Piovan says the units are therefore well suited to medical applications. Like most dryers from leading suppliers now on the market, the units recover the heat used during desiccant regeneration.
Piovan's latest HR series of segmented-wheel dryers currently have air-flows up to 300 [m.sup.3]/hr (a 600 [m.sup.3]/hr unit will be launched soon). The HR300 can be coupled with drying hoppers having capacities up to 800 litres. Standard energy saving features include the Intelligent Energy Supervisor and Intelligent Material Drying, which self-adjust parameters according to actual machine throughput.
More Twin-Bed Dryers
Moretto's X Dryers are twin-bed types, with regeneration based on temperature rather than time, and with process energy recovery. The company also claims very little fluctuation in the dew point.
The X Dryer has an "anti-stress" system that minimises thermal stress on the plastic granules by limiting their exposure to high temperatures. It does this by keeping the temperature constant, independent of the flow of material out of the hopper.
Stefano Cavallaro from the company's marketing department cites the dryer's great flexibility and process performance. "An operator only has to input two parameters--the required throughput per hour and the type of material," he says. "Related to the specific properties of any polymer used, the dryer will process and automatically control all process variables."
The X Dryer automatically controls residence time, process temperature, air-flow throughput, and the anti-stress function. "It yields energy savings of up to 72% over more conventional equipment," claims Cavallaro. "This means 48 watts per kilogram of material in the end."
Koch-Technik's Eko twin-bed dryers are said to offer particularly gentle drying, making them suitable for sensitive plastics such as nylons, polycarbonate, LCPs, and acetals. The company says that by recirculating the heat, up to 30% of energy costs can be saved. In combination with the Oko control system, which protects thermally sensitive materials from excessively long drying times, this figure can even rise to 40%. Once again, regeneration is based on moisture content of the granulate and on the required material quantity.
The company's new KKT series of compact mobile dryers have the drying container behind the dryer, making filling more convenient and allowing the unit to be easily moved through narrow gangways.
Motan, which offers a wide range of drying options, premiered the Metrolux A 80 desiccant-bed dryer at Fakuma, a small system with selectable drying-bin combinations. It features an integrated conveying system for feeding several machines. Optional purge valves can be integrated in the suction boxes of the drying bins. This ensures that dried material is not subject to ambient air during conveying breaks.
Material protection, as well as reproducible drying results, are provided by Motan's DryingOrganizer. If the residence time in the bin increases because throughputs fall, the drying temperature is lowered automatically to an appropriate value. And during production interruptions, the DryingOrganizer automatically adjusts the drying temperature to a non-critical standby value. It also detects if throughput is too high--thus causing drying time to fall below the specified amount--and displays a warning message. Integrated dew-point control is available as an option.
Motan also featured a compressed-air dryer, the Luxor CA 15, at Fakuma. It says this is a cost-effective solution for hygroscopic materials, and ideal for small throughputs when used with its Metro VL Venturi loader.
Numerous suppliers of desiccant-bed dryers say compressed-air dryers are more expensive, simply because of the cost of the air. This is true up to a point. Compressed air is not expensive when used in moderation, says Helios, which concentrates on this type of dryer. It says in units up to 150 litres, it can demonstrate how compressed-air dryers are always more energy-efficient than any other type.
"Drying 4 kg/hr of ABS, a compressed-air dryer will consume 800 watts," says area sales manager Thomas Gradl. "A desiccant dryer, on the other hand, will use 2 to 3 kW. Compressed-air units are therefore the best types for handling material throughputs from small amounts through to 25 to 30 kg/hr."
His comments underscore the need for processors to take into consideration a whole host of factors when choosing a new dryer whether it be likely throughput, the type of plastics they are using, or the ambient conditions--and not just the sticker price. If and when that Euromap standard gets published, it won't be a moment too soon.
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|Article Type:||Cover story|
|Date:||Feb 1, 2009|
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