Jackson Energy Authority serves nearly 40,000 residences, businesses and industrial customers in and around Jackson, Tenn.
Two aging 7.5-hp three-phase pumps in the utility’s Rolling Acres Lift Station were experiencing frequent outages that required increasing man-hours for maintenance and repair. The electric meter at the duplex station showed high power consumption resulting from recurring drag on the impellers. As these combined factors drained more and more of the utility’s budget, the increasing frequency of pump failures raised the risk of sanitary sewer overflows.
Scope
The Rolling Acres Lift Station serves a mature residential area whose wastewater flows to a 6 mgd SBR wastewater treatment plant. Given the rising operating and maintenance costs of the facility’s aging pumps, plant operators needed to find a more efficient and reliable replacement.
“The Rolling Acres station presented ongoing problems for us due to age and clogging typically associated with older pumps,” said Andy Myracle, plant maintenance superintendent for Jackson Energy Authority. “We were spending 16 hours a month having two field technicians routinely clean and inspect the station. But the bigger costs occurred when the pumps quickly collected rags and other solids that required us to dispatch a crew to pull and reclean the pump impellers an average of twice or more a week, with additional incidents after hours presenting overtime charges. Keeping the station running had become an expensive proposition.”
Annual man-hour maintenance costs at the Rolling Acres station eventually reached $6,700. Power costs climbed to more than $900. After adding in a vehicle expense of $960, the total annual outlay associated with the old pumps reached more than $8,500.
Solution
Gulf States Engineering Co. Inc., a Xylem representative serving the Jackson area, recommended Xylem’s Flygt N-pump for the Rolling Acres station. The pumps have a reputation for reliability and energy efficiency, thanks to advanced hydraulic engineering features that prevent the clogging and energy-robbing drag imposed when waste materials accumulate on impellers.
The N-pump’s semiopen, screw-shaped impeller facilitates the passage of fibrous material associated with solids and the increasingly troublesome “disposable” cleaning and personal hygiene wipes being flushed into residential collection lines. Unlike traditional grinder pumps, the N-pump maintains continuous flow by passing the leading edge of the rotating impeller across a stationary relief groove at the suction port of the pump. The dynamic action removes rags, stringy materials and many solids without compromising hydraulic efficiency. Eliminating the drag imposed by such buildups reduces the N-pump’s energy requirement, resulting in an expected savings of tens of thousands of dollars for Jackson Energy over the expected service life of the replacement pumps.
Result
“The electrical cost reductions were immediate,” Myracle said. “Our monthly cost dropped from $78 per month to $39.95, and we’ve experienced a virtual elimination of high level alarms, which required emergency dispatches and extra man-hour expenses.
“Our total annual reduction in operating costs following the upgrade was $5,737.92. At that rate, the total cost to replace the two pumps could be recovered in just 1.19 years.”
With the new Flygt pumps in place, the Rolling Acres Lift Station now requires only one monthly inspection by one field technician. The station is monitored 24/7 on the utility’s SCADA at a central dispatch center, which has experienced significantly fewer alarms since installing the new pumps.
