Water & Wastewater Treatment

The PumPing STaTion - PumP and ValVe SuPPlemenT 2016 9 In Depth: Pumping and Energy Driving energy efficiency in water and wastewater pumps W ater utilities operating in the Totex-led regulatory environment of AMP6 should have more incentive than ever to save energy in their operations – and with pumps making up some of their most energy-intensive assets, they should be a natural focus for these efforts. There are many ways of saving energy on pumps - spanning product design, selection, control, motor optimisation, maintenance, monitoring and optimal time of replacement - and the potential rewards can be significant. Anglian Water, for example, has 28,000 pumps and its annual energy bill for pumping alone is £24M, or around 35% of its total energy use across its business. It is easy to see how achieving a relatively small energy saving of 1-5% could yield a six-or seven-figure annual benefit in monetary terms, together with a reduced carbon footprint. Pump design and motor efficiency So where can these gains be made? On the clean water side at least, the answer is usually not in the design of the pump itself. The hydraulic efficiency of pump impellers for water has for some decades been at as high a level as it is likely to get, so much more work in recent years has concentrated on the drives and motors powering pump sets, explains Christoph Pauly, a spokesman for German pump manufacturer KSB. "The most efficient pump we ever had in KSB had something like 93 per cent efficiency; it was a huge water pump that was built in South America 40 years ago, and it's still going," says Whether it is impeller design, motor specification or the timing of maintenance and replacement, much can be done to make pumps operate more efficiently. James Brockett runs a rule over the latest trends in the quest to save energy Large pumps on the clean water side usually already run at a high efficiency, but any marginal energy gains can be extremely valuable Pauly. "When transporting clean water, very o˜en the efficiency of the pump is more than 90 per cent so there isn't much progress to make. The progress in recent years has been around the engine part. It used to be the case that you'd have pumps running at the same speed no matter if it was needed; what you find now in the water industry is that many of those pumps are equipped with a frequency inverter to reduce the speed and just deliver the water that is needed by the customer." It's now the norm for pumps to be supplied with a motor and inverter in a matched group, so there is no reason for utilities to miss out on these benefits. Pump design has a greater role to play in wastewater, where concerns over energy use have traditionally taken second place to ensuring the pump does not block. There will always be a trade-off between efficiency and avoiding clogging, which is why the hydraulic efficiency of pumps in operation can be anything between 20% and 80% depending on the size and exact application. Yet recent improvements such as non-clog impellers, solids separation systems and impellers that can better cope with methane gas can all make a real difference as to where a pump is positioned on this spectrum.

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