Optimisation of pump station level controls gives fast payback

Paul Boughton

Traditional methods for controlling the levels in wet wellsreservoir pump operations and similar applications in the water and waste water treatment industries are not without their problems. Howeverone water company has eliminated such problems and saved money by using ultrasonic level controllers.

Yorkshire Water Services Limited has installed 2000 HydroRanger and 400 HydroRangerPlus controllerswith payback periods as low as 12 months. Supplied by Siemens Automation and Drives Process Instrumentation and Analyticsthese ultrasonic level controllers are suitable for a variety of tasks. As well as level controlthey can also be used for open channel flow monitoring and volumetric measurementwith the added advantage that the HydroRanger Plus has energy-saving algorithms.

The system is effective even in applications where foam and turbulence would cause problems for alternative technologiesand the corrosion-resistant Echomax transducer can be fitted with optional submergence shields to ensure consistent operation in wet wells where flooding can occur.

The main benefit that Yorkshire Water has enjoyed is energy savings. By optimising the pump ‘on’ and ‘off’ levelsusually so that the span is as wide as possiblethe number of times the pump switches on over a given period is reduced.

Figures from Yorkshire Water show that increasing the pump operating span by 200percent leads to an 8.69percent fall in energy consumption. While a 200percent increase in span may sound largeYorkshire Water achieved a 325percent increase in span at its Cutthorpe pumping stationwith a direct saving of £57.66 per year on the 3.1kW pump. Yet most of the company’s pumping stations have much larger pumpswhich leads to greater potential energy savings. Brinsworthfor examplehas a 30kW pump on which a 250percent increase in span was achievedgiving a £628 annual saving in energy costs. Some pumps operated by Yorkshire Water are rated at 300kWso the annual savings with these are considerably greater.

In many cases Yorkshire Water found thatprior to the HydroRanger controllers being introducedpumps were only operating for a relatively short period andas suchnever actually reached their full pumping rate before the 'off' level was reachedso never operated at their maximum efficiency. Once the HyrdroRanger was installed and the span increasedthese pumps would usually achieve their peak efficiency and maintain their maximum flow rate for a considerable time before the pump cycle was complete.

Trials conducted by Yorkshire Water also demonstrated that further energy savings are achieved when raising the pump ‘on’ level because of the increased head. By raising the head one metre on a Flygt3127LT pumpthe flow went up by 12.0l/swhich is a substantial increase for a 4.7kW pump.

Aside from energy savingsHydroRanger controllers are also helping to cut maintenance costs. Peter WardYorkshire Water asset engineersaid: “I have held discussions with Flygt Pumps and The Pump Centreleading me to conclude that reduced maintenance costs are worth even more than the energy savings. Wear occurs in pumps mainly when they start and stop; the sudden torque puts strain on bearingssealsshaftsimpellerscontactsrising mains and elsewhere. Reducing the number of starts definitely cuts maintenance costs.”

Another way maintenance is being reduced is by programming the HydroRanger controllers to snort the wet wells clean once every 24 hours. By running the pump past its normal ‘off’ pointdebris and floating solids are removed from the wet wellwhich prevents the pump from blocking and reduces the need to clean the wet well. At one site Yorkshire Water was previously clearing three blockages per weekbut there have been none since the HydroRanger was installed and the snorting function programmed.

With the newer HydroRanger PlusYorkshire Water is also conducting tests to evaluate the algorithms for peak tariff avoidance. As a resultit is likely that further financial savings will be possible.

For more information visit www.siemens.com/processinstruments


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