Drives save Leixlip water treatment works €500,000 a year 15 October 2010

Leixlip water treatment plant, in Co. Kildare, reports saving more than €500,000 a year on its pumping costs, thanks to the installation of ABB variable speed drives.

Pat Nolan, plant supervisor for Leixlip, explains that the treatment works, which is the second largest in Ireland, has six pumps in two sets of three – one duty and the other standby. In each set of three motors, two were controlled by soft starts and one by a variable speed drive.

The control method used was to vary the speed of the one pump, with the drive, and bring in the others as required. All three motors ran constantly to keep up with demand, with pump throttling via butterfly valves to maintain the head.

Nolan asked contractor AECOM (formerly Earthtech) and ABB to investigate and cut the pumps' energy use. Their investigation found that the three motors had an absorbed power of 1,690kW – a total made up of two soft start motors drawing 620kW and the variable speed drive-driven motor drawing 450kW.

Major savings could be achieved, they said, by opening the valves and employing four more variable speed drives. As a result, four 710kW ABB cabinet-built drives were installed in place of the soft starts and now work in conjunction with the two drives previously installed.

Following installation, all three motors run at the same speed, providing a flow of 5,700 m3/hr – and the new absorbed power is 1,326kW, a saving of 364kW.

"The savings were very significant and even more than we expected," says Nolan. "Another benefit was the reduced wear and tear on the discharge valve through using the variable speed system."

Brian Tinham

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