May 2019

34 n MOTORS SUPPLEMENT May 2019 www.drivesncontrols.com Geared motors clean up at German sewage works T he Ensdorf sewage treatment plant, located on the River Saar, close Germany’s borders with France and Luxemburg, processes the waste water generated by the region’s 50,000-odd inhabitants, together with effluent produced by several local industries. Like most modern sewage treatment facilities, the plant relies on a combination of mechanical and biological processes to remove dissolved contaminants and solid materials from the incoming effluent. Its job is to ensure that water leaving the facility meets strict cleanliness rules, allowing it to be discharged safely into the Saar, and that the remaining solids are also transformed into a condition suitable for safe disposal, typically as agricultural soil enhancers. That’s a delicate balancing act. The inflow rate to the plant can vary significantly, from 26,000m 3 per day in dry weather, to 57,888m 3 during periods of heavy rain. The volumes of contaminants and solid wastes processed by the facility vary similarly over time. To keep the plant’s processes running properly, the plant’s staff must adjust the operating speeds of equipment across the facility as demand rises and falls. Originally, speed control in some of the plant’s vital equipment was achieved mechanically. As part of the dewatering process, the pumps that supply sludge to the two centrifuges were powered by 7.5kW asynchronous geared motors with belt drive adjustments. Additional pumps were used a similar system with 4kWmotors to transport the thickened sludge away from the centrifuges and on to the next process. While the belt drive approach did allow the necessary speed control, the system proved unreliable in operation. Adjusting the belts frequently was inconvenient, and breakages were common, leading to downtime and disruption. In search of a better approach, the site’s managers contacted the drive technology specialist, Klebs + Hartmann, which suggested a way of not only resolving the reliability issues, but also achieving useful energy savings. Matthias Klee, the company’s project engineer for drive technology, and Peter Siepel, its project engineer for inverter systems, worked together to develop a bespoke system based on high-efficiency permanent magnet gear-motors used with variable-speed drive (VSD) controls. Their new approach solved Ensdorf’s reliability challenges at a stroke. The introduction of VSDs eliminated the need for belts and allowed speed control in the transport systems for the centrifuges to be automated. The higher efficiency of the modern gear- motors – supplied by Bauer Gear Motor – enabled significant energy savings. In fact, the new IE3 motors are so much more efficient than the old, unrated machines they replaced that significant downsizing was possible. The pumps that supply the centrifuges are now powered by 6.3kWmotors rather than 7.5kW, and the downstream pumps are powered by 3kWmotors instead of 4kW. The new motors are also IP66-protected, providing increased protection against corrosion and the risk of water damage from cleaning activities. Following successful testing on one of the centrifuges, Ensdorf has now installed the new gear-motors at all four locations. While the change has made life easier for the plant’s operating and maintenance teams, and provided useful energy savings, it is unlikely that the people of the region, or the record numbers of fish now thriving in the Saar, have noticed any difference. n A German sewage treatment works has replaced unreliable belt drive systems with modern gear-motors and variable-speed drives. The result has been enhanced control, fewer breakdowns and improved efficiency. The Ensdorf sewage treatment plant serves a population of around 50,000 in southern Germany After successful testing in one of its centrifuges, Ensdorf has now installed the gear-motor and VSD combinations on four pumps.

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