Rolling in Energy Savings

After analyzing manufacturing processes at its plant in Clarksville, Ark., Greenville Tube Company, a manufacturer of stainless steel tubing, saw an opportunity to improve productivity and save some energy. The analysis, which was led by a team of experts including the U.S. Dept. of Energy, resulted in an upgrade for a machine used to “draw” or size stainless steel tubing.

The device, called an eddy-current drive, along with the motor servicing the machine, used 250 amps on average, but had much higher peak demands. Following the analysis, this existing equipment was replaced by an adjustable-speed drive (ASD) including an upgraded 200-hp premium-efficiency motor.

Motors and drives

Premium-efficiency motors can reap large energy and cost benefits when looking at lifetime estimates. This is due to the fact that the purchase price of a motor is miniscule when compared to the overall cost of its use. On a typical motor operated at full load for 24 hours a day, the purchase price is about 2% of the total lifetime cost. Factoring in the cost of one motor rewinding—0.7%—this means 97.3% of the lifetime operational costs can be attributed to electric consumption. Considering that operating even a typical 50-hp motor can cost $25,000 a year—at $0.07/kWh—the opportunity for cost savings is significant.

Additionally, the utilization of an ASD can further enhance energy savings. Instead of operating the motor at a fixed speed and adjusting the process system around it when varying levels of production are required, the ASD can adjust the motor speed according to process needs. This is why ASDs are increasingly being considered for application not only industrial processes, but HVAC and plumbing systems as well.

In the case of the Greenville Tube Company plant, the shift to a high-efficiency motor with an ASD drive produced immediate benefits. Following the replacement, process energy demands were 34% lower.

In addition, productivity benefitted because the force on the draw bench was increased from 35,000 to 50,000 lbs., eliminating multiple-sizing operations on the same piece. Production time, to meet the previous year’s volume, was also reduced by 600 hours, meaning more tubing can be manufactured with the same equipment. And because speed can be controlled more precisely, the tubing quality should be better.

Based on energy savings of $77,000 annually, it was determined that the payback for the upgrade was achieved in about five months.

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