Improving river abstraction efficiency
ABB's Martin Richardson outlines how a pump strategy using the latest variable speed drive technology can help lower energy costs, reduce abstraction demand and improve the environment.
Pumping systems are one of the most fundamental technologies that utilities use every day, and yet, in many river abstraction uses, they are not always implemented efficiently. Water is a heavy and expensive commodity to lift and is often removed using submersible pumps, which need vast amounts of energy, resulting in a large operational carbon footprint.
Many of these pumps have been installed for decades and simply turned “off” or “on”, with the latter resulting in the pump running at full power with flow rates controlled by partially throttled valves. This is an inefficient flow control technique as the physical restriction causes increased head loss across the partially closed delivery valve. To overcome this, the pump needs to work harder, thereby consuming far more energy than necessary, leading to excessive generation of carbon dioxide emissions.
Fitting a variable speed drive (VSD) to control the pump motor’s speed, energy use is reduced by fully opening the throttled delivery valve, thereby eliminating the physical energy sapping restriction. Flow rates can be regulated, leading to a reduction in pump energy usage by up to 60 percent, in some cases. Even greater energy savings can be achieved by using the very latest motor-VSD technology, known as a synchronous reluctance motor (SynRM).
But what if the amount of water abstracted could be reduced further up the supply chain? Preserving water by cutting leakage in UK water networks massively increases security of supply and reduces the cost and carbon footprint associated with taking water from the environment. Pressure is the main culprit in causing leaks. Control this and you can prevent many leaks from occurring in the first place. With a VSD, leakage can be cut significantly as a result. Even a small reduction in pressure can have a significant knock-on effect. A 20 percent pressure reduction can cut leakage rates by up to 50 percent.
VSDs can be set to produce a flow of water from the pump that offers the best combination of flow and pressure and ramp up the speed slowly to the desired level. Pressures are reduced, avoiding forcing water through existing gaps, while a steady speed cuts the need for frequent starts – when starts and stops are needed, they are gentler and less damaging. Using VSDs to tackle leakage has the double effect of not only cutting pressure, but also significantly lowering energy usage and costs.
VSDs help to ensure that abstraction is carried out sustainably when flows are healthy, while also helping to improve resilience, and provide mitigation against risks such as extreme weather events.
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