ABB Drives Save Costs At Water Treatment Plant

Leixlip Water Treatment Plant is saving more than EUR500,000 (GBP437,000) a year on its pumping costs after the installation of ABB variable-speed drives. The Leixlip Water Treatment Works in Kildare is the second largest water treatment facility in Ireland. With a capacity of 175,000m3 a day, it supplies more than 30 per cent of the drinking water requirements of the Greater Dublin Region, serving Fingal, Kildare and the northern part of Dublin City.

The treatment works has six pumps in two sets of three, one used for duty and the other on standby. In each set of three motors, two were controlled by soft starts and one was controlled by a variable-speed drive (VSD). The control method used was to vary the speed of the one pump with the VSD and bring in the others as required. All three motors were running constantly to keep up with demand. The pumps have butterfly valves that were throttled to maintain the required head.

Contractor Aecom (formerly Earthtech) and ABB were asked to investigate the pumps' energy use and come up with a solution to reduce it. The 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 VSD-driven motor drawing 450kW. The proposal concluded that major savings could be achieved by opening the valves and employing four more VSDs. Four 710kW ABB cabinet-built drives were installed in place of the existing soft starts and now work in conjunction with the two drives previously installed.

Each new drive was installed without any disruption to the plant, maintaining full operation at all times. Before each drive was installed the associated motor was sent off site to be fitted with insulated bearings on the non-drive end to resist the bearing currents generated by the drives and prevent the damage these could cause. It was also necessary to transfer the previous control logic and safety relays from the soft starts to the new VSDs.

Among this additional work, Leixlip was required to remain 100 per cent operational at all times. Following installation of the drives, all three motors run at the same speed, providing a flow of 5,700m3/hr - the balance of the plant's capacity is routed via other methods, such as gravity feed. The new absorbed power is 1,326kW, a saving of 364kW. With 24-hour, 365-day operation, this offers a total saving of 3,179,904kWh.

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