Water & Wastewater Treatment

30 | july 2014 | WWT | www.wwtonline.co.uk Digging deeper Blowing energy usage out of the water M anaging energy consumption is typically the biggest challenge facing any industrial facility, and a water treatment plant is no exception, so adapting water quality to suit your specific needs can generate considerable savings within your water cycle. Likewise, the recycle and reuse of water where appropriate not only helps improve efficiency but also reduces environmental impact. Today, modern innovations in recirculation technolo- gies bring enhanced sustainability and safety to the reclamation and reuse of wastewater. But, these are big decisions, so where do engineers and technicians begin? One option is to look at a significant new innovation in aeration blowers, which are used throughout the wastewater sector as part of the biological treatment process. Traditional aeration blowers The activated sludge process, invented in Man- chester in 1914, remains to this day, at the heart of the wastewater treatment process worldwide. The process relies on the injection of air into tanks con- taining wastewater, to encourage the large scale growth of natural bacteria that break down the impurities it contains. Depending on the type of wastewater being treated, the resulting liquid from this aeration process can usually be returned to the environment, although in some cases further treatment processes may be required. The traditional compressors, or "blowers", used to inject air into wastewater use large quan- tities of electricity. For example, Severn Trent spends around £9m a year on electricity to run 300 blowers at its treatment works, more than half of the entire cost of wastewater treatment in the region. And industry estimates suggest that 1% of all of the UK's electricity is consumed by compres- sors used for the aeration of wastewater at the nation's utility companies. Traditionally, these aeration blowers have been powered by induction motors with me- chanical gearing and oil-film bearings. Although reliable, this configuration suffers from high energy consumption and power losses, account- With traditional aeration blowers accounting for up to 80% of a wastewater treatment plant's total energy consumption, a system that offers a 40% energy-use reduction and payback within a year could be an industry game-changer. Industry estimates suggest that 1% of all of the uK's electricity is consumed by compressors used for the aeration of wastewater at the nation's treatment plants. • Drivers It is projected that by 2030, nearly half the world's population could be facing a scarcity of water, with demand exceeding supply by 40%. With this in mind, there is a growing need to develop a more advanced and efficient wastewater treatment process. The traditional centrifugal blower concept relies on an induction motor with mechanical gearing and oil film bearings and typically suffers from high power losses and wear issues. The maintenance costs of such conventional technology are high. Moreover, the blowers consume energy, representing typically 50% or more of the water- treatment plant's total energy use. In fact, up to 80% of the life-cycle costs of a blower relate to electricity consumption. www.wwtonline.co.uk | WWT | JULY 2014 | 31 ing for up to 80 percent of the lifecycle costs of an aeration blower. Although the introduction of variable speed drives has helped to reduce energy consump- tion, this e ect has been limited. Given the cost of electricity consumption – and the associated CO2 emissions – water companies have been investigating alternative solutions with lower energy costs, improved operational e• ciency and reduced environmental impact. The new aeration blower system With the introduction of a new system combin- ing direct drive, high speed permanent magnet motors, active magnetic bearings and a magnetic bearing controller, it is possible for energy con- sumption to be signi• cantly reduced. The new aeration blower system comprises a high-speed permanent magnet motor (PMM) available in sizes 75 kW-350 kW, active magnetic bearings (AMB) and integrated AMB control system. There are a number of features that enhance performance. For example, unlike tra- ditional induction motors, the PMM maintains e• ciency at half-load and half-speed operation. An energy-e• cient high speed motor/mag- netic bearings system for aeration blowers also uses fewer mechanical parts than a traditional drive system, which means reduced mainte- nance, while powerful built-in monitoring and diagnostic capabilities maintain high perfor- mance and reliability. Additionally, the new system provides higher e• ciency under nominal or partial loads, is more reliable and quieter, and is almost maintenance free. Energy e• cient aeration blowers with high ' Innovations ● Higher effi ciency with nominal and partial loads (10% gain over conven- tional motors) ● Increased equipment reliability ● Virtually no need for maintenance ● Decreased construc- tion costs due to a more compact design ● Powerful diagnostics tools ● Optimised process control ● Prolonged overall oper- ating lifetime ● Reduced noise ● Meets regulation requirements speed motors and magnetic bearing systems now have the capability to reduce energy consump- tion by up to 40 percent. In wastewater facilities, the aeration blower system can demand as much as 80 percent of the plant's total energy consumption, so the new solution o ers the potential to make huge energy savings. When used in one of the largest 350 kW blowers it may result in annual savings of 500,000 kWh, which equals a 375-ton reduction in CO2 emissions. This innovation represents a new and sustain- able approach to the problem that targets the market challenges faced by the water and waste- water industry, namely a high speed motor/mag- netic bearing system for aeration blowers that meets the demand for energy e• ciency, and the need for a reduction of maintenance and service costs, as well as the requirement to comply with air quality and safety standards. Compared with a traditional blower, one of the new wave of motors in a 350 kW centrifugal air blower o ers payback on investments in one year from energy savings alone. Given the cost of electricity consumption – and the associated CO2 emissions – the new aeration blower solution o ers the opportunity to lower energy costs, improve operational ef- • ciency and lifecycle costs and reduce environ- mental impact. Kevin Walker is product manager bearing and units at SKF Used in one of the largest 350kW blowers the new system may result in annual savings of 500,000 kWh, which equals a 375-ton reduction in CO2 emissions. ' In action A wastewater treatment facility in France serving a city of 100,000 inhabitants and local industry had been operating with four 80 kW lobe-type blowers, and these presented the operator with several issues, including frequent breakdowns, high energy consumption, high noise levels and treatment process problems. A er replacing the lobe blowers with two new 120 kW centrifugal blowers that featured the SKF high-speed permanent magnet motor solution, the treatment process improved signifi cantly. Noise levels fell from 110 dBA to 70 dBA, the facility achieved a regulation of the fl ow rate, and maintenance demands dropped considerably. The bottom-line reductions in energy use were even more impressive. A er only a year in operation, the blowers equipped with the SKF solution cut plant CO 2 emissions by 375 tonnes and operating costs by 54,000 euros. The upgrade to more effi cient magnetic bearing blowers off ered a short payback (less than two years) from the energy savings alone.

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