Water & Wastewater Treatment

Project focus: Pumps and pumping systems 22 | MAY 2015 | WWT | www.wwtonline.co.uk During off-peak hours and seasons, pumps are automatically adjusted to meet reduced flow demand and are constantly monitored to detect any problems or unauthorized operation by untrained personnel. Accessed by a manhole immediately in front to the walls leading into the abbey, the pump station has been constructed in a specially designed subterranean chamber. Given the space and access constraints, KSB and SOGEA North West have delivered a robust and energy efficient pump solution that meets both the existing usage demand, and can accommodate future growth in demand. "Pump stations are o†en oversized to handle the possibility of increased demand, or are dimensioned to accommodate exceptional flows that may occur only every 10 to 20 years," says Stéphane Quertain. "Thus, in normal operation they are too large and too powerful resulting in high energy costs. Because fixed speed pumps only operate at peak flow, the load losses are constant. Variable speed pumps operate on instant flow so the load losses are proportional to the instant flow, leading to a reduction in consumption of between VF and VV: 10-50%." At Mont St Michel, the Amarex KRT pumps only operate on demand and by varying the speed, each pump adapts to the actual flow rate, which can o†en be less than the peak flow. Therefore, load losses are proportional to the flow so if the flow drops below peak demand then the load losses are reduced. As a result of load losses between instant flows and peak flows, variations in pump speeds contribute to energy gains. The economic impact in the case of Mont St Michel over 84% of the time that the pumps are running delivers an instant flow rate of less than 50m³/h, or 62% of the peak flow. By undertaking a comparative study to estimate the potential savings between a traditional fixed speed Amarex KRT and the variable speed instant flow version recommended for Mont St Michel, KSB was able to show that the energy saving could reach 30%. The result of the combined efforts of KSB and SOGEA North West is an energy efficient, compact and robust wastewater pump station designed for long term continuous operation and capable of transferring waste matter to a treatment plant some 2.5km distant. Access to the pump station is through a manhole in the vehicle parking area in front of the abbey The compact arrangement of the pumps reduces the footprint area

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