Equipment Recycling and VFDs Bring Redundancy, Reliability and Flexibility to Pump Station

By Tony Boahn, PE, Vice President, McKim & Creed
Don Betz, Executive Director, Lower Cape Fear Water and Sewer Authority

By recycling pumps and revamping a pump configuration, the Lower Cape Fear Water and Sewer Authority has streamlined operations and boosted efficiency, and will ultimately double capacity at its raw water pump station. The Kings Bluff Pump Station provides water from the Cape Fear River to municipal and commercial customers in Brunswick and New Hanover counties in North Carolina.

The Authority is also under contract to provide 6 mgd to Pender County upon completion of the county’s water treatment plant. In March, the Authority completed a $9-million expansion of the Kings Bluff facility that:

 - replaced three vertical turbine pumps with state-of-the-art 1600 HP vertical turbine pumps featuring variable frequency drive (VFD) electric motors,

- integrated two existing pumps in the new station configuration,

- added an additional wet well and one surge tank,

- improved the supervisory control and data acquisition (SCADA) system, and

- added a new electrical building and control room.

With the addition of a parallel intake pipeline from the Cape Fear River to the station, which is scheduled for completion in 2010, and a future parallel raw water transmission main, the facility will have the capacity to pump more than 96 mgd. This will more than double the Authority’s current 45 mgd raw water capacity and will provide for a more efficient operation both in labor and energy.

VFDs Reduce Stress and Costs

The three pumps used at the facility prior to the expansion allowed some flexibility of flow, but 60 percent of the configurations required the station to operate with at least one pump in high speed. This created instances in which excessively high pumping rates were needed to meet customer demands, resulting in inefficient operation and elevated electrical costs.

The new pumps featuring VFDs allow each pump to operate at any point within its safe operating range and can closely match the pump yields with customer demands. The VFDs also enable the pumps and motors to gradually ramp up to the desired operating speed, which reduces mechanical stress, extends the life of the equipment, and decreases maintenance, repair and electrical costs.

Salvaging Pumps Adds Redundancy

The  team realized that an opportunity existed to salvage two of the three existing pumps at Kings Bluff. A condition assessment helped determine that two of the three were in relatively good condition, considering their age. With minimal additional construction costs, these two pumps were integrated with the new pump station configuration. Two of the three new pumps provide the station’s ultimate capacity, with one serving as a backup. By integrating the two existing pumps, a second level of pumping redundancy was provided.

Future Plans

Within the near future the Authority intends to complete two more projects that will provide raw water capacity for conveyance to current and future customers. The Authority has already begun preliminary planning to install a 60-inch intake pipe and screen assembly that will operate in parallel with the existing 48-inch raw water intake pipe and screens. This new parallel intake will offer a level of redundancy for the intake system that provides added benefit for routine maintenance as well as emergency management of the system.

Also scheduled is the installation of a parallel raw water transmission main. These projects, combined with the upgrade and expansion of the Kings Bluff Pump Station, will enable the Authority to meet its projected raw water demands of 52 mgd by 2010 and 96 mgd by 2030.

BEFORE: Shown here is the Kings Bluff Pump Station prior to the upgrade and expansion.

AFTER: The expanded facility features five pumps, three surge tanks, an improved SCADA system and a new electrical building and control room. The design team included McKim & Creed as the consulting engineer, Heyward, Inc. as the manufacturer, Richard Mills as the electrical engineer, and Land Management Group as the environmental consultant. T.A. Loving Company served as the general contractor.

Excavation for the wet well is under way.

The wet well base slab is installed.

Work begins on the electrical building foundation.

The raw water main piping is installed.

One of the 1600-HP variable frequency drive electric motors is installed.

The electrical building is under construction.

Shown here are two of the three new state-of-the-art 1600-HP vertical turbine pumps featuring variable frequency drive electric motors.