Why Your CFO Loves VFDs

Variable-Frequency Drives, the Right Software and Motor-Control Centers Push Energy Savings to the Bottom Line

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By Nancy Bartels, Managing Editor

These days, it's both financially necessary and socially responsible to keep an eye out for all available energy savings. At home, that can be as simple as switching off unused electronics and lights in empty rooms. In process applications and plants, it's a little more complicated, but the right collection of hardware and software can bring big numbers to the bottom line and a smile to the CFO's face.

For example, when management at Vattenfall Europe Mining AG, Welzow Sud, Germany, decided to modernize the overburdened conveyor systems in its open-pit coal mine, it chose Rockwell Automation's (www.rockwellautomation.com) Intelligent Motor Control solution—a combination of variable-frequency drives (VFD), intelligent software and networked motor control centers. Rockwell Automation and its system integrator, BEA, installed Allen-Bradley PowerFlex 7000 medium-voltage AC drives. These drives allows users to employ standard motors, or to retrofit existing wound-rotor motors at 6.6 kV.

Before modernization, the conveyor used conventional fixed-speed drives and required 9 MW of power. After the upgrade, this conveyor with a 120% overload/overspeed capability moves at least the same amount of material with only 6 MW. Additionally, Vattenfall reduced its capital investment by reusing some existing equipment, such as its 10 MVA transformer.

Control How Energy Is Delivered

The beauty of VFDs and soft starters is that they improve the efficiency of how energy to start and run motors is delivered. You can gain significant energy savings by lowering speed or flow by just 20% using VFDs. If this reduction doesn't impact the process, it can reduce energy use by up to 50%. In many operations, this can equate to substantial energy savings and reduced production costs.

Modernize for Sustainability

Two years ago, Amtex, a Latin American manufacturer of  chemical products, modernized the production system at its plant in Colombia. Carboxymethylcellulose (CMC), an anionic polymer created from cellulose, is Amtex's most important product and is produced at three plants. The vegetable-based stabilizer is used in mining, paper, food, toothpaste, ceramic, detergent, paint and textiles. It dissolves easily in hot and cold water, acts as a thickener, a suspension agent and as a dispersion stabilizer. It also functions as a binder, and it can regulate flow properties.

Amtex produces 24000 tons of CMC annually. The Medellin, Colombia, plant has an 8200-ton CMC production capacity. But, the production system suffered inefficiencies because of increased energy consumption, leaks, oil spills in the hydraulic couplers and production downtime.

The comprehensive solution was to purchase two Allen-Bradley PowerFlex 700 drives for the mill, as well as for the number one reactor.

"We used to load both reactors (25000 liters capacity) with 2300 Kg of raw material (cellulose), and now we are loading them with 2550 Kg, showing an increment of production up to 6% (500 ton/year)," explains Alvaro Arango, Amtex's plant manager.

"This reflects interesting earnings, using the same resources in terms of energy consumption and labor. We reduced speed of reactors from 60 Hz to 43 Hz in most stages of the process—around a 15% energy savings."

Installing frequency inverters allowed Amtex to stop using hydraulic couplings for power transmission. This saves about U.S. $1000 per month related to oil and thermal fuses, Arango says. Safety also was improved because the hot oil is no longer expulsed from the hydraulic coupling.

Other gains from the installation include a reduction in electricity usage and in mechanical wear, thanks to the drive's self-starting capabilities. The use of a VFD also cut the maintenance caused by the hydraulic coupler and the periodic shutdown of the motor, which significantly increases production. Finally, speed variation helps to minimize process time.

Gain Complete System Control

"Energy" isn't just about electricity or fuel. There's also the energy that goes into design, production and delivery of products and/or systems. Saving energy in any one of those areas also shows up on the bottom line at some point. Brampton Engineering (BE), an OEM in Brampton, Ontario, Canada, is a good example.

When you go to the deli counter and buy a package of lunch meat in a see-through film package, chances are good that the film may have been developed and manufactured by BE. The films extend the shelf life of products and make them more appealing to consumers.

Flexible equipment designs are essential for BE to meet customer demands for specialized, one-of-a-kind lines that produce high-quality blown film as quickly as possible. The company needed simplified programming and integration, faster design time and improved troubleshooting capabilities to meet these demands
"The plastic resins processed by our equipment are mostly made from nonrenewable resources. They require energy to manufacture, transport and then process in our equipment to make the barrier films that will protect and increase the shelf life of food and medical products," explains Adolfo Edgar, BE's marketing manager. "As our lines operate more efficiently, our customers are able to manufacture packaging that wastes less raw material, saves on transportation, and requires less energy to manufacture."

As a result, BE chose Rockwell Automation's Integrated Architecture package, including an Allen-Bradley ControlLogix programmable automation controller (PAC) that provides integrated, scalable solutions for the full range of automation disciplines using one control platform, development environment and an open communication protocol.

The PAC governs the entire system, from the extruders that melt plastic pellets into a multilayer molten sheet, to the winders that collect the cooled film. Programmed with the latest version of Rockwell Software's RSLogix5000 software, the PAC provides fully integrated access to each individual machine component, including the controllers, HMIs, vector control drives and I/O modules.

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