Shake some energy savings out of your auxiliary equipment.
Auxiliary equipment of all kinds present opportunities to shave power costs. One of the most striking examples is gas-fired dryers, which can potentially save 60-70% or more of energy costs compared with electric dryers, depending on the relative prices of gas and electricity in your area. This factor has caused a recent surge of interest in gas dryers - but mainly for large-sized units, where power savings offset the higher purchase price (see PT, March '95, p. 84; June '95, p. 92).
As shown by the examples cited below, at least a few processors have found that other types of auxiliaries, such as granulators and chillers, may include energy-efficient features or low-cost options that help to trim their energy bills.
PUT A CHILL ON POWER USE
Production Plastics Corp., a custom injection molder in Saukville, Wis., has enlisted Mother Nature to help its plant save energy. The firm installed a roof-mounted winter cooler - also known as a dry coil - that draws on cold ambient air during winter months. Although the idea of switching from conventional chiller operation to ambient-air cooling is not new, Production Plastics' solution improves on previous "all-or-nothing" approaches, says John Kunes, v.p. of engineering and manufacturing. The secret is allowing the winter cooler to act as a secondary cooling unit when the outdoor temperature falls within a certain range.
The system, supplied by Thermal Care, Niles, Ill., consists of three main components. The 51-ton winter cooler is a galvanized steel frame with a series of copper coils inside. Fans are mounted on top of the unit and water/ethylene glycol coolant flows through the copper coils. As coolant returns from the process carrying heat, the fans pull cold ambient air across the coils. The second component is a conventional central chilling system with 200-ton evaporative tower modules. The third element is a three-way valve controlled by a PLC that monitors both outdoor air temperature and chiller tank temperature.
Depending on outside air temperature, the system uses 100% ambient air for chilling through the winter cooler, uses the winter cooler to achieve partial air cooling, or uses only the central chiller. Whenever the outside ambient temperature is 40 F or below, the unit supplies water/ethylene glycol coolant at 50 F to the injection molds without having to run the chiller. If the temperature falls between 40 F and 46 F, the dry coil removes a portion of the BTUs carried by the coolant as it returns from the process, and the chiller runs as necessary to remove the balance. When the outdoor temperature rises above 46 F, the dry coil is bypassed and the system operates only with the chiller.
Production Plastics specified four 10-hp scroll-type chiller compressors for its central chilling unit. Chiller manufacturers say scroll compressors are more efficient than traditional semi-hermetic-type compressors. They allowed this system to achieve 46 tons of cooling capacity, whereas semi-hermetic compressors reportedly would provide 38 tons of capacity under the same conditions.
Projected savings for the system are $3500/yr, according to Daniel W. Lyons, Production Plastics' president, who expects the system to pay for itself in four years. Kunes researched local temperature readings from a nearby airport. He calculated 3595 hr/yr in which the temperature was below 40 F, and an additional 510 hr/yr when the temperature was 40-44 F, allowing partial winter cooling. That would leave only 1895 hr, or 32% of the year (running three shifts), when his chillers would carry the full cooling load.
Kunes says the water-chilling system operates well under a power-curtailment program that Production Plastics participates in with its local utility, Wisconsin Electric Power in Waukesha. The program asks the molder to voluntarily cut back on its power usage for specified periods of time, in return for a discount on its electric rate. When power consumption is curtailed, the system senses the lower load and automatically stages down to just one compressor. The system has a large-capacity chiller tank, which is also an advantage here, because it takes 40 min for the water temperature to rise just 6-7 [degrees] F, adds Kunes.
Another approach to winter cooling has been taken by Sage Plastics, an injection molder in Crystal Lake, Ill. Five years ago, Sage installed a plate-and-frame heat exchanger on its central chiller system, supplied by AEC/Application Engineering, Wood Dale, Ill. The heat exchanger is located at the pump tank, where it transfers heat from the chiller loop to a separate water loop circulating through the cooling tower. During the winter, central chillers are manually switched off, sending warm process water directly to the pump tank. Thus, the cooling tower does all the work of heat removal. Dick DuPlain, director of manufacturing, estimates that Sage, which pays 7[cents]/kwh, saves over $2100 per 30-day period by switching off its 70-ton chiller in the winter. The company now is considering ways to switch automatically from the chiller system to ambient-air cooling when outdoor conditions permit.
ESTIMATED SAVINGS OF "WATT/WATTCHER" ANNUAL SAVINGS(a), $ Granulator 5-Day 6-Day 7-Day Motor size Week Week Week 5 hp 303 364 424 7.5hp 410 492 574 10 hp 508 610 711 15 hp 629 754 881 20 hp 763 917 1069 25 hp 932 1119 1304 a Assumes rate of 10[cents]kwh; three-shift operation. Source: Telar Corp.
GRINDERS CHEW UP LESS ENERGY
Another plant that recently investigated ways to reduce energy consumption of its auxiliary equipment is Discas Inc., a recycler, compounder, and molder in Waterbury, Conn. Energy costs are an important issue for Discas. Its electricity rate of 9[cents]/kwh is typical for the Northeast but higher than regional rates in the Southeast and Canada, where Discas' main competitors are located. That difference is significant, given the relatively low profit margins in recycling, Discas sources say.
Discas looked for energy savings from both its granulators and its primary equipment because size reduction is an integral part of the recycling process. The company decided on five strategies to reduce its energy costs by reducing its peak power demand:
* First, material is precut with a guillotine device before granulation.
* Second, plastic is metered gradually into the granulator to reduce energy spikes.
* Third, Discas invested in a granulator rotor designed to take small nibbles of the plastic rather than large bites, also to reduce peak amperage draw. The SMS granulator, supplied by New Herbold Inc., Sutton, Mass., has a "deflection wedge" in the cutting chamber, which allows use of three bed knives. This combination reportedly prevents the rotor from accepting large parts too quickly and eliminates blocking and stalling.
* Fourth, Discas specified energy-efficient motors on the granulator and also on densifiers for PS foam and film. (More efficient motors will be mandated by law next year - see sidebar.)
* Discas also installed capacitors on its injection machines to improve their power factors. All of these steps combined have resulted in about 20% energy-cost savings.
Tenax Corp., a custom molder in Danbury, Conn., also specified energy-efficient motors on a granulator it purchased from Polymer Systems Inc., Kensington, Conn. Jack Bowne, Polymer's v.p. of sales and marketing, estimates that only 15% of his customers specify energy-efficient motors at present, although they are offered as an option across the product line. Mike Santos, director of technology support at Tenax, also chose carbon steel blades, a harder steel that he expects will stay sharper longer. "That means the motor is not going to have to work as hard when cutting the plastic, and with the energy-efficient motor, we are using fewer kilowatts to do the same job," Santos says.
Bowne notes that several other mechanical features can add to a granulator's energy efficiency. Blades mounted for a scissors cutting action result in less energy consumption than parallel cuts. A steep angle between the rotor and bed knives requires less force to cut the plastic than when knives are mounted in a semi-radial position, he says. Also, heavy flywheels on the rotor provide more mechanical force to drive the blades, so the motor works less hard.
Another energy-saving option is two-stage cutting with a high-torque, low-speed shredder mounted atop a conventional high-speed granulator. Bowne notes that adding a 15-hp shredder to a 30-hp, 16 x 24 in. granulator increases the overall output capacity from 700 lb/hr to 2000 lb/hr. Thus the two-stage system with a total of 45 hp has a throughput capacity equivalent to a 150-hp granulator without a shredder.
Another energy-saving option offered by most major granulator suppliers is the Watt/Wattcher, supplied by Telar Corp., Cleveland. This device runs the granulator only when material is fed into the machine and automatically turns the motor off when the cutting chamber is empty. An electric eye at the feed throat detects when material is tossed into the throat and starts up the machine. The unit senses when chopping is complete by means of a vibration sensor. The sensor is calibrated to detect a vibration level corresponding to idle conditions and then shuts the machine off automatically. The Watt/Wattcher can also operate blowers for conveying regrind from the granulator bin.
Most molders need a granulator to actually run only 10% of the time, according to Telar. The Watt/Wattcher costs $895 and the accompanying table shows how quickly it can pay for itself. The unit is available from granulator suppliers on new equipment or as a retrofit option from Telar and from IMS Corp., Chagrin Falls, Ohio.
TWEAKING FOR EXTRA SAVINGS
Security Plastics, a custom injection molder in Miami Lakes, Fla., has taken several steps to reduce energy consumption of its auxiliary equipment, according to manufacturing engineer Gene Wessel. All new auxiliaries are now specified with energy-efficient motors, he says. All new dryers, both press-mounted and portable, are now fully insulated, which was not the case in the past.
In addition, Security Plastics is making the transition to 480-volt service on all equipment, which Wessel says gives the benefit of lower electrical consumption. The lower current demand is expected to result in at least 25% lower energy costs for the plant overall, he says.
WORKING WITH UTILITIES
Utilities can help processors to find and exploit opportunities for energy savings. Programs offered by utilities vary widely and are subject to change as the utilities themselves struggle to adapt to deregulation, which started in California and is expected to spread nationwide in the next two to five years.
Anticipation of deregulation is blamed by some sources for the recent cancellation of all but a handful of utility programs that offer rebates to industrial customers based on the energy efficiency of their plant equipment. One utility that still has such a program is Massachusetts Electric Co., Westborough, Mass., which offers rebates averaging 20-30% on appropriate equipment, according to account manager Michael Horton.
Although most utilities have phased out rebate programs, many still offer help in saving energy. One example is Wisconsin Electric Power Co. (WEPCO), which conducts plant audits for its customers and recommends more efficient types of equipment, says account manager Rick Swiontek. WEPCO also structures financing packages for customers that want to invest in less power-hungry machines. WEPCO calculates the energy savings to be realized and uses the savings to lower the financing rate on a loan or lease package that WEPCO arranges on behalf of the customer.
WEPCO also goes a step further than leasing - it will help design and manage some auxiliary systems such as cooling or compressed air, essentially taking over responsibility for that system and allowing the customer to focus on his core manufacturing operations. This approach has been tried as a pilot program for five years and is now offered to the company's top 1800 customers. Savings can be significant Swiontek estimates that the average total electric bill for a medium-sized plastics-processing plant in his region is $200,000/yr, and that auxiliaries together can account for as much as 20% of the total bill, or $40,000/yr. He says it's reasonable for processors to achieve 30% savings on the auxiliaries' share of the total bill - in this case, $12,000/yr. WEPCO's electric rates of 44.5[cents]/kwh are the third lowest in the country, so a 30% savings in auxiliary-equipment power usage could be worth a lot more to some processors.
U.S. Law Mandates Energy-Efficient Motors
Energy-efficient motors will be required on certain equipment purchased after October 1997 under the Energy Policy Act (EPACT) of 1992. EPACT covers three-phase a-c motors from 1 hp to 200 hp in standard voltages, which are intended for general-purpose use. Provisions of the law - to be enforced by the U.S. Dept. of Energy - are complex: The specified efficiencies vary according to horsepower, rpm, and enclosure size. But in essence, the rules will raise the efficiency levels of these motors to a point halfway between today's "standard-efficiency" motors and existing "premium-efficiency" motors, explains Darryl Van Son, manager of market research at Baldor Electric Co., an electric motor manufacturer in Ft. Smith, Ark. The difference in nameplate efficiency between today's standard-efficiency motors and those mandated by EPACT are greatest in the low horsepower ranges. On a 1-hp motor, the difference on an electric bill is about 6%. However, improvements in larger motors will obviously have more of an impact on electric charges. The Energy Dept. has yet to decide exactly where the more efficient motors will be required.
Van Son says higher-efficiency motors generally are beefier and more expensive. Premium-efficiency types can cost 30% more than standard versions, but their sales have grown 40%/yr since they were introduced in late '70s, he notes. Van Son says the higher-efficiency motors mandated by EPACT may cost 10-15% more than today's standard motors.
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|Title Annotation:||includes related article on motor energy efficiency law; plastics industry equipment|
|Author:||Gaspari, John de|
|Date:||Oct 1, 1996|
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