The Town of Trumbull in Connecticut was looking for a way to increase the operating performance of one of its 10 sewage pumping stations. Built in 1971, the station consisted of twin sewage handling pumps (40-hp direct drive, wound rotor motor) vertically mounted below ground, handling 340,000 gallons of raw sewage per day. The system used one pump to handle the entire peak flow under normal operation, and used the second pump in only extreme conditions. Each pump rarely operated more than five minutes at a time. The system experienced frequent breakdowns, occasional flooding, and sewage spills.
Decision
With the help of Xylem’s Flygt brand, engineers investigated total system performance and decided to add a smaller, 10-hp pump with direct online motor starters and a level control system with float switches. The new pump handles the same volume as the original pumps during non-peak periods, but runs for longer periods of time. The old pumps handle infrequent peak flows. The two compressors for the bubbler level control system and the two circulating pumps for the old motor control system were also eliminated, and lighting efficiencies were implemented.
Rationale
This decision produced the following results:
Reduced energy consumption by almost 44% due to:
• lower outflow rate reduced losses in the piping system
• lighting system upgrades
• elimination of the bubbler level control and cooling water pumps
Reduced cleaning and maintenance requirements (supplies and labor) and associated downtime
• eliminated the need to replace two mechanical seals per year
• new, submersible pump is much easier to swap out if repair/replacement is needed
Extended equipment’s expected life due to longer operating times and reduced power input
Increased system capacity 25%, potentially deferring need for additional pump stations
Decreased noise from new pump, improving relations with local residents
These modifications can be easily replicated at other sites (new sites or retrofit). A new pump site under construction in Trumbull is using the submersible pump technology and saving an additional $10,000-$12,000 by eliminating the need to dig a second hole.
Value Added: Equipment cost, fully installed: $12,000
Annual Savings: Energy savings $2,600 31,900 kWh/yr
Maintenance Savings: Supplies $1,800 2 seals/yr ($900 each)
Labor $1,800
Total $6,200
Motor Challenge, administered by the Office of Industrial Technologies, is a voluntary partnership program with U.S. industry to promote the use of energy-efficient electric motor systems. Thousands of industrial partners have joined Motor Challenge and are improving their, and in turn, the nation’s competitiveness and efficiency.
Motor Challenge assists the OIT Industries of the Future by identifying near-term gains in energy efficiency these industries can achieve by adopting existing technologies.