40 n WATER INDUSTRY October 2024 www.drivesncontrols.com PM-driven mixers slash wastewater plant’s bills A wastewater treatment plant near Naples, Italy, which is part of Europe’s largest treatment scheme, has been equipped with innovative technologies to improve water quality while reducing energy use. At the core of the crucial denitrification process are submersible mixers driven by permanent magnet motors, which could cut the site’s annual energy bills by up to €45,000. The project aims at improve the quality of the waters around Naples by revamping and upgrading water and wastewater treatment facilities in the region. The programme, the biggest European investment in water purification and decontamination for 20 years, is treating about 900,000m3 of wastewater every day – equivalent to that produced by more than 4.5 million people. One of the five facilities gathers wastewater from a large area in the northern part of Naples and can process 240,000m3 of water per day – the amount generated by around 1.2 million inhabitants. Major improvements were needed to optimise the sewage treatment processes to reduce energy consumption, while complying with the regulations. The wastewater treatment plant includes 14 denitrification tanks which remove nitrogen from effluents. The tanks have an unusual geometry, being 22m long, but only 7.85m wide and 4.8m high. It was therefore necessary to use mixers with limited-diameter propellers, even though they are usually regarded as being difficult to adjust to reduce energy usage. “To address the specific needs of this application, we suggested the use of our XRW 400 submersible mixers,”says Elisabetta Sardi, area manager for Sulzer, which supplied the mixers.“These are extremely compact, delivering an effective processing of wastewater, and are equipped with premium-efficiency IE3-equivalent, sensorless, permanent-magnet motors that are controlled by variable-frequency drives. “This means that they can adjust their speed to suit the real-time environmental conditions, rather than maintaining a set speed at all times,” she continues. “As a result, it is possible to reduce energy use whenever possible, delivering significant benefits when it comes to operational costs and environmental performance.” If conventional mixers powered by IE3 squirrel-cage motors had been used, they could have cut energy costs at the plant by €8,000. The PM-powered machines are delivering savings of up to €45,000. The drives incorporate self-cleaning functions, extending the lives of the mixers, while reducing downtime and the need for maintenance. Following the installation and commissioning the 28 mixers, the denitrification tanks have been running smoothly, efficiently processing large volumes of wastewater while meeting environmental standards for effluents. “The XRW 400 mixers are the first to run via permanent-magnet motors and represent the only solution of this kind that would meet the equipment specifications for the denitrification tanks,” says Sardi. “We are sure there will be many other treatment plants that will look to collaborate with us and achieve similar benefits.” n A wastewater treatment plant near Naples has installed 28 submersible mixers in 14 denitrification tanks which are used to remove nitrogen from effluents. The mixers, powered by IE3 permanent magnet motors, have cut the plant’s annual energy costs by up to €45,000. The Cuma water treatment plant is achieving considerable energy savings by installing submersible mixers powered by PM motors and drives Pump drives with extra-long pipes solve Angolan problem In an unusual upgrade contract, two pump drives with extra-long piping have been supplied for a water supply project in Angola that draws water from the Kwanza River and moves it over a distance of 17km, climbing 135m to a water treatment plant outside the capital, Luanda. The previous pumps had been installed inside the pipework and could not be removed. The operator therefore needed complete replacement pump systems including drives and connection pipework. The German motor-maker Menzel Elektromotoren produced two of the new pumps at its Pawils Elektromaschinenbau factory. The pumps were adapted to match the mechanical interfaces of the existing installation and were fitted with pipes and motors designed specifically for the application. Each system is about 12m long and is designed for a flow rate of 900m³/min. The pumps are powered by 6kV motors with nominal power ratings of 500kW, operating at 1,475 rpm. Initially, two out of the site’s three identical pump systems were replaced. The third original system was kept to ensure continued operation of the water supply. After successful commissioning of the first two, Menzel is now expecting an order for a third system to replace the remaining original pump. One of the 12m-long replacement pumps for the Angolan project
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