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Case Study Ash Grove Cement Company Durkee, Oregon Field Testing the MagnaDrive Coupling Speed Control Technology on Northwest Industrial Applications Report on Mining Test Site Ash Grove Cement Company operates cement and lime plants in nine states across the US. The eight cement plants operating in the Ash Grove system are some of the most efficient and best maintained in the country. With an annual production capacity of more than 6.1 million tons of cement, Ash Grove is the fourth-largest cement manufacturer in the United States. The quality portland and masonry cements produced by Ash Grove are used for the construction of highways, bridges, commercial and industrial complexes, residential houses, and a myriad of other structures. The Ash Grove plant in Durkee, Oregon was selected as the first field test site for a MagnaDrive Coupling fan application in cooperation with the Northwest Energy Efficiency Alliance. Application Overview The application selected for the test was a 125 HP 1800 RPM motor running a centrifugal fan. The fan was belt-driven through sheaves, and moves air across a bag house where airborne dust is collected from the fan’s exhaust. During normal operations, the fan ran at full speed and inlet dampers were closed to maintain a constant pressure differential on the bag house. The fan is integral to the process, and any failure means lost production. The fan, located on the top (fifth) floor of the bag house, has caused problems since it was first installed. Turbulence and vibration created when throttling the dampers to maintain a pressure set point caused excessive shaking in the surrounding ductwork and corresponding support structure. Maintenance personnel were constantly repairing broken welds and stress cracks in the system, costing approximately $10,000 a year. In addition, high starting inertia and heat generated in the bearings and sheaves caused frequent belt failure, resulting in down time and lost production. Noise from the belts and excessive shaking could be heard throughout the plant. During start-ups the motor was energized with the input dampers closed. Locked rotor currents peaked at 875 Amps for duration of 10 seconds, causing voltage sags, brownouts, heat build-up and potentially reducing motor performance and shortening motor life. The motor starter, overload protection and wire had to be sized to handle this hard start. Impressive Results with the MagnaDrive Coupling The 125 HP motor was moved from its offset position, eliminating the sheaves and belts, and mounted in line with the fan shaft. A MagnaDrive Coupling was installed between the motor and fan shafts, with the existing damper control circuit being reused to adjust the MagnaDrive Coupling and fan speed. In comparison to the damper alone, the MagnaDrive Coupling reduced the motor’s energy consumption by 25%, saving approximately 155,000 kWh/year worth approximately $4,000 in Durkee, Oregon. Additional benefits of the MagnaDrive Coupling included elimination of turbulence caused by the dampers, dropping vibration from .5 inches/second to .05 inches/second. Workers in the vicinity of the installation note that noise levels have been reduced to the point where it is difficult to tell if the fan is actually running. Repair work on the fan estimated at nearly $10,000 per year will be eliminated. “I can see [MagnaDrive] eliminating a lot of our day to day and year to year maintenance on these machines, and extending the life of other equipment.” Mike Hennigan, Maintenance Planner Test Site Ash Grove Cement Company Durkee, Oregon Field test site for MagnaDrive Coupling fan application Problem Lost production due to frequent belt failure High operation and maintenance costs Ductwork and support structure damage caused by vibration from damper throttling turbulence Brownouts and voltage sags caused problems with electronic equipment Excessive noise and associated employee discomfort Solution The 125 HP motor was moved from the offset position, eliminating the sheaves and belts, and mounted in line with the fan shaft. A 14.5 MagnaDrive Coupling was installed between the two shafts, and the existing damper control circuit was reused to adjust the speed of the fan. Benefits Increased production due to reduced down time Elimination of structural damage caused by turbulence and vibration Improved employee satisfaction due to dramatic drop in noise levels Less disturbance of electronic equipment by eliminating voltage sags and brownouts Longer motor life due to reduced heat build-up in motor windings $10,000 annual maintenance savings 155,000 kWh savings on annual energy consumption Ash Grove Cement (Figure 1) MagnaDrive vs Dampers Figure 1 shows a comparison of estimated 1999 monthly energy usage for the MagnaDrive Coupling and the old damper control. Estimated run-time data for the year was supplied by the customer. Kilowatt load was measured from pre- and post audits. Calculated energy use corresponds to the motor maintaining a set point pressure of 110mm of water and an average production rate of 80 tons of dry portland cement per hour. The MagnaDrive Coupling also significantly reduced locked rotor current. During start-up of the fan in the original system, the customer experienced a 10-second brownout in the bag house facility. These brownouts created problems for electronic process control equipment such as Variable Frequency Drives. Also, when the motor was connected to the fan through belts, it had to overcome the inertia of the fan and the process air on start-up. Heat buildup in the motor windings during these hard starts contributed to reduced motor performance and shorter motor life. Installing the MagnaDrive Coupling allowed Ash Grove Cement to start the motor while uncoupled from the fan. This eliminated the problem with electronic process equipment due to brownout and voltage sag. By controlling the MagnaDrive Coupling to slowly add load to the motor, elevated motor temperature and brownouts are no longer an issue. “We see a tremendous drop in energy consumption, especially on start-up, compared to before when the motor was running, at times, actually in an overload condition. We’re pretty impressed with this thing.” Mike Hennigan, Maintenance Planner Ash Grove Motor Start-up Current (Figure 2) MagnaDrive vs Belt Drive Figure 2 shows motor start-up locked rotor current in Amps over relative time. The dashed blue line illustrates a typical hard start suffered by the 125 HP motor when coupled to the fan through belts. The curve shows peak start-up current in excess of 875 Amps (equivalent to 975 HP at 480 volts and 3-phase) for duration of 10 seconds. The solid red line shows the advantage of starting the motor disconnected from the fan with the MagnaDrive Coupling. The coupling reduced the duration of locked rotor current from 10 seconds to 1.5 seconds. No load running current was reduced from 142 Amps to 49 Amps which will save energy when the fan is not needed How the MagnaDrive Coupling Operates The MagnaDrive Coupling operates on the principle of magnetic induction. It consists of two independent components that have no physical contact. A precision rotor assembly containing high-energy permanent magnets is mounted on the load shaft. A conductor assembly with copper rings is connected to the motor shaft. Relative motion between the magnets and copper rings creates a magnetic field that transmits torque through the air gap between the coupling’s components. Varying the width of the gap changes the coupling force, producing a controlled and infinitely variable output speed. [BACK] FAQ | Contact Us | Home Copyright © 2008 MagnaDrive Corporation, All Rights Reserved.