By Lisa Poole, Manager of Engineering Services, Quadna

Springerville Generating Station Unit 4 in Springerville, Ariz., uses lined ponds to hold water collected from its cooling towers. With the construction of Unit 4, Salt River Project (SRP)—one of Arizona’s largest utilities—wanted to increase the capacity of pumps used to move effluent from one pond to another to avoid the possibility of overflow.

The lined pond collects effluent water and the plant’s pumping system is used to deliver collected effluent water to one of two evaporation ponds. SRP wanted to investigate the concept of using a vertical turbine on a floating barge on the pond.

Pump house enclosure unit processing the plant’s effluent water. Photo, Quadna.Click here to enlarge image

Originally, a specification request was placed with Quadna to use submersible pumps hanging from a floating barge on the pond with an associated piping manifold extending to the barge’s edge. Quadna, which engineers, fabricates and services mechanical systems that move fluids and gases for industrial applications, devised a plan for the ancillary barge equipment that included a discharge manifold with flanged connections, check valves, isolation valves and an overhead trolley for servicing the two pumping units. The barge would also house a 40-foot-long floating walkway to access the shoreline and a duplex pump control panel.

However, the price for the barge pumping system was more than SRP wanted to spend. This option also posed an additional problem: SRP did not want any liner impingement so the pumps and pipe could not be secured.

There were other challenges, too. The generating station is at 7,000 feet of elevation in a remote area known as the Gateway to the White Mountains. As a result, the solution had to accommodate occasional sub-zero temperatures and fluctuating pond levels, the result of rainwater and snow run-off. In the White Mountains of Arizona, temperatures can range from 12 F to 94 F with wind speeds up to 90 miles per hour.

The Quadna team discussed other options with SRP including the use of submersible turbines supported by a pipe at the edge of the pond on a 45-degree angle or self-priming pumps situated on the pond’s dry bank.

The second option was the most viable way to protect the pumps from the elements. Quadna decided to use two Gorman Rupp T2 series model T2A60 v-belt driven pumps with 10 horsepower US Electric Motors. These pumps were chosen for their reliability and because of the limited net positive suction head available (NPSHa).

Next, the pump protection issue was tackled. With little human supervision, the automated pumps and piping had to be protected. Insulating the pumps in a durable structure equipped with space heaters and temperature controls was the most cost-effective and dependable solution.

The final step was to enclose the pumps in an 8-foot-by-10-foot house supplied by Kysor Panel Systems. The fiberglass enclosure featured ventilation for summer and heat for winter to protect the pumps, piping, valves, lighting and control panel housed within the building.

Effluent pond leak detection pumps were also provided. The pumps lie on top of the secondary liner and are used only when, and if, the primary pond liner leaks. If a leak occurs, the level floats and pumps are activated. For this, Quanda used submersible pumps centralized in a pipe with three Teflon wheels for each installation and servicing.