22 water & wastewater
Improving river abstraction efficiency Although there are undeniable environmental concerns over river abstraction, it remains a critical method to ensure an adequate and reliable water supply. ABB’s Martin Richardson outlines how using the latest variable speed drive technology when operating pumps can lower energy costs, reduce abstraction demand and improve the environment.
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iver abstraction is a necessity for supplying water for drinking, farm irrigation, industry and power generation. Yet, abstraction comes with an environmental cost. By changing the natural flow pattern of lakes and rivers, abstraction can alter the amount of water in the environment, which in turn affects wildlife. Improving the efficiency of abstraction can allow water companies to maintain their green credentials, while still ensuring a healthy water supply. With concerns over the sustainability of current abstraction levels and the licences required, utilities are under increasing pressure to minimise the amount of water they remove. Over-abstraction can have a devasting impact on the environment, as witnessed in the Sonoran Desert in Arizona. Here water is taken for irrigation and urbanisation, which has resulted in land subsidence, water scarcity and loss of wildlife and habitat. In the UK, bodies such as the Environment Agency (EA) and Ofwat issue licenses and schemes to help control the abstraction rate. An example is Ofwat’s Abstraction Incentive Mechanism (AIM), which encourages water companies to help protect environmentally sensitive sites by restricting abstraction when surface water flows are low. Applying to all water companies from April 2020, AIM has sought to improve the sustainability and resilience of water supply networks. MAKING PUMPING MORE EFFICIENT Although pumping systems are used every day by water utilities, they are not always used efficiently. Water is often removed using submersible pumps, which need vast amounts of energy, resulting in a large production of carbon. The main problem is that many pumps are in situ for years and are used either ‘off’ or ‘on’, with their flow rates controlled by partially throttled valves. This is an inefficient way of controlling flow, as the physical restriction causes increased head loss across the partially closed delivery valve, making the pump work harder and using far more energy than necessary. INSTALLING VARIABLE SPEED DRIVES A better method is to fully open the delivery valve and use a variable speed drive (VSD) to control the pump motor’s speed and hence flow. Pump energy
Quarter 1 2021
use can be cut by up to 50%, while even more energy can be saved using the latest high-efficiency motor technology: such as the synchronous reluctance motor (SynRM). For example, Southern Water used a SynRM on a low lift pump that extracts around 25 million litres of water per day from the local river. The highly energyefficient SynRM cut maintenance demands of the pump while improving reliability. The existing 75kW DC motor required maintenance to its brushes every three months, and a recent failure had made it critical to find a more reliable solution. A major consideration for Southern Water was cutting operational and downtime costs as part of the total expenditure (TOTEX) approach adopted by Ofwat’s Asset Management Period. Besides improved reliability, the ABB drive is also expected to produce a 4% increase in motor efficiency. Ten years ago, the EA’s Shropshire Groundwater Scheme replaced fixed speed pump control with VSDs across seven pump sets, cutting daily energy use by
Although pumping systems are used every day by water utilities, they are not always used efficiently.
www.bpma.org.uk
