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PUMPS, VALVES & ACTUATORS
NAVIGATING THE ENERGY CRISIS
Clayton Mead, UK Water Industry Manager, ABB, explains how some of the pump-specific functionality built into variable speed drives (VSDs) can potentially help you to turn the challenge of increasing energy prices to your advantage
ahead for both domestic and industrial energy users. However, there’s nothing like a crisis to focus the mind, and against the backdrop of the water industry’s target of reaching Net Zero by 2030, it could be that the energy crisis acts as a catalyst to force meaningful change to improve efficiency, and in a much shorter timeframe than otherwise would have occurred. There are lots of ways to save energy, but
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the easiest way to reduce your bills, certainly in sectors like the water industry, is simply to use less of it. Energy accounts for some 45 per cent of the cost of water production, with electric motors thought to account for around two thirds of this. However, many motors do not have to be run at full speed all the time. The traditional approach to achieving this is to use a valve or some form of mechanical throttling to restrict flow, which is inefficient, as the motor is still running at full power regardless of output required. A variable speed drive (VSD) controls the motor electronically, ensuring
ith energy prices rapidly increasing, and further rises to come, it’s clear that there could be difficult times
that it only uses the energy it needs for a given output. For pumps in particular, the savings can be
quite profound. Variable torque applications such as centrifugal pumps can offer significant energy savings, as a small reduction in speed can correspond to a proportionally larger reduction in the amount of energy required to run. In practice this means that reducing pump speed by 10 per cent consumes 73 per cent of the energy, while slowing it down by 20 per cent consumes just 50 per cent of the energy compared to running at full speed and using mechanical throttling. When extrapolated across an installed base comprising dozens or even hundreds of pumps, this can equate to vast savings. Against the backdrop of rising energy
prices, this actually creates a situation where the higher the prices rise, the quicker the payback on energy saving equipment. Indeed, payback times that used to be measured in years have now been reduced to a matter of months, with ongoing energy savings thereafter.
Three ways VSDs can help Modern VSDs also increasingly include additional functionality designed to optimise and enhance the efficiency, performance and reliability of pumping processes. Level control – Pumping slower for longer
is generally more energy efficient than pumping intensively in short bursts. Level control is a VSD feature that allows a water tank or reservoir to be filled, or a wet well to be emptied at a matched rate from incoming or outgoing flow. Traditionally this would be achieved using a PLC with instrumentation to detect when levels rise or fall to predetermined points, along with float switches or other mechanical components. Level control ensures that the pumps within a configuration are operating at the best speed to balance energy efficiency against the required filling and/or emptying rate. For wet wells, this can also help to avoid caking and sedimentation.
2 JULY/AUGUST 2022 | PROCESS & CONTROL 6 Pump cleaning – Blockages in wastewater
treatment are a well-known problem. The typical way of dealing with this is to pull up the pump from the wet well, clean the pump and then reinstall it. This requires regular inspections, which creates downtime and can cause risks to health and safety. The pump cleaning (anti-jam or anti-ragging) function on a VSD instead uses a programmable sequence of forward and reverse rotations of the pump to shake off and remove any build-up of rags or other debris on the impeller, before continuing with normal operation. As well as preventing potential blockages before they can happen, this improves pumping efficiency, and decreases the need for manual inspections and cleaning. Intelligent Pump Control (IPC) – Since
centrifugal pumps are variable torque applications, running two pumps at 60 per cent speed can end up costing less to move the same volume of water compared to running one pump at 100 per cent speed. IPC permits the easy integration and operation of multi-pump systems, which typically consist of several pumps, each connected to a separate drive. This arrangement enables flexibility in load sharing, balancing the run time between the pumps and keeping each pump in the configuration running optimally. Multi-pump systems achieve a high level of redundancy, whereby if one pump fails or requires maintenance, then others can utilise spare capacity to pick up the slack. Replacing an installed base requires some
upfront investment, but a VSD can pay for itself within a comparatively short space of time through its superior efficiency. Moreover, there is more to VSDs than just energy saving. ABB’s ACQ range of drives features level control, pump cleaning and IPC as standard, helping to improve resilience and operational efficiency, while also making a contribution towards meeting the water industry’s Net Zero targets by 2030.
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