The sewer utility for the City of Andalusia, Ala., is among scores of municipal and regional operations across the nation that benefited from the American Recovery and Reinvestment Act of 2009. Andalusia qualified for a $250,000 U.S. Department of Energy Block Grant. However, the proposed use—for replacing aging pumps at two lift stations along the municipal sewage collection system—had to be fully demonstrated to be eligible.
Project
A local engineering firm—Goodwyn, Mills and Cawood Inc.—called the grant to the city’s attention and collaborated in providing input to prepare the application and proposal before leading the eventual project. The prerequisite for eligibility required at least 30 days of documented monitoring to substantiate a guaranteed 25 percent reduction in electrical consumption by the replacement pumps versus the existing pumps. The final report on the project’s scope and monthlong monitoring results required the scrutiny—and seal—of a licensed professional engineer to verify the facts for grant eligibility.
As in many cases, the city’s sanitary sewer collection system remains generally out of sight, out of mind until the monthly electric bills arrive or a failed pump demands an immediate response to prevent an overflow.
Solution
Flygt N-pumps were specified as replacements. The semi-open, self-cleaning impeller on an N-pump represents a patented innovation that makes the companion wastewater-handling pumps that are fitted with them more energy-efficient and reliable. The pump’s design keeps the leading edges of the impeller vanes unobstructed where fouling often sets the stage for clogging. The leading edges of the impeller vanes pass across a stationary relief groove that clears any snared fibrous solids, grease or sludge, creating a self-cleaning flow path through the pump. The self-cleaning feature inherently reduces an impeller’s vulnerability to tangling material that results in a drag on pump speed; energy consumption remains constant throughout this process. Therefore, the patented volute and impeller are the features that contribute to the pump’s improved energy efficiency.
Result
The advanced engineering features of the high-performance pumps delivered energy-use reductions of 48.1 percent at one location and 56.1 percent at another. And although clogging reduction is not addressed in the grant requirements, these unique pumps have a superior record of reducing the clogging that is experienced at lift stations elsewhere.
Earl Johnson, the multi-term mayor of Andalusia who also serves as chairman of the (sewer, electric, water) utilities board, said, “We not only replaced aging pumps that were well beyond their expected life, but the new pumps will help us save thousands of dollars worth of electricity every year.” The savings Andalusia will accrue in electricity costs should have a favorable—and compounding—impact on the bottom line of the sewage department’s operations and maintenance budget.
With firsthand experience in how the advanced pumps conserve energy, engineer Bob Carter, P.E., foresees a future when energy conservation is a partial goal of pump station retrofits.
“I’ve become a believer in N-pump technology through this process requirement at Andalusia,” he said. “As engineers, we are always trying to get the most efficient equipment for our clients. If another client is in a similar situation, I would specify their project this same way, no question.”
