Fleet Pump and Service Group Case Studies
Wet Well Retrofit Increases Efficiency and
Cuts Costs for Rockefeller Center
Wet Well Retrofit Increases Efficiency and Cuts Costs for Rockefeller Center
The chief engineer at one of the buildings at Rockefeller Center in New York City had a problem: they were spending upwards of $21,000 annually for pit cleaning, odor control and enzyme treatment to soften solids of a sewage pit in addition to the cost of maintenance calls and overtime.
Rockefeller Center had a sewage pit at One Rockefeller Plaza with extremely heavy solids built up and laying on top of the water and grease built up on the walls. They were using vertical shaft sewage pumps as a duplex system with actuator style ball floats for level control and no real logic for controls. The pumps constantly failed from clogging and required a lot of attention. The check valves had been replaced several times due to rags caught on the flapper and the gate valves had failed due to wear.
GA Fleet provided a Duplex Flygt Submersible Sewage Pump system using model NP 3127 10 HP submersible pumps, each with a Flygt mix flush valve for suspending solids in the wet well. We provided state-of-the art, while simple to operate, controls with a unique Fleet control methodology for removing surface solids and preventing grease ring build up. All the functionality of a sewage pump station are built into the controller i.e. on, off, lead, lag, high alarm, low alarm and alternation. The levels are completely field-adjustable and there is no longer a need to enter the wet well.
To facilitate installation Fleet provided a unique FPS SubRig pipe and valve assembly. The SubRig is a pre-engineered, modular submersible pump piping system. Fully integrated with the frames and covers, and the electrical connection system, the SubRig facilitates easy, correct installation and uses components of better quality than the industry normally installs for this application. Engineers throughout NYC are now specifying SubRigs on new installations and many experienced plumbing contractors request them as well.
With the retrofit of the wet well the building has achieved a more efficient and far less tasking system than before, as well as saving on the life-cost of the equipment with minimal maintenance.
The Pumps that Went to College
This upgrade earns an A+ for eliminating clogs and saving energy.
By Jane Alexander
Set among 1,100 lush, wooded acres on the affluent north shore of Long Island, NY the campus of Stony Brook University bustles daily with approximately 20,000 students. Located 65 miles east of New York City, this SUNY College in the village of Stony Brook has grown tremendously during the 44 years since its founding. Students arrive each year from 50 states and 80 foreign countries.
The once quaint, idyllic college is now recognized as one of the nation's leading centers of learning and scholarship-fulfilling the mandate given by the New York State Board of Regents in 1960 to become a university that would "stand with the finest in the country." Identified as a Type I Research University by the Carnegie Foundation-the highest classification and a distinction granted to fewer than 2% of all colleges and universities nationwide-Stony Brook joins the ranks of such institutions as Harvard, Yale, Johns Hopkins, Princeton, and Stanford as the newest addition to the 63 members of the Association of American Universities (AAU). Stony Brook offers 119 undergraduate majors and minors, and 102 Masters, 40 Doctoral, and 31 Graduate Certificate programs.
Out of Sight, Out of Mind (But Not for Long)
Not surprisingly, as the university's academic reputation had grown, its enrollment had been swelling and its facilities multiplying at such a vigorous rate, that parts of the campus infrastructure had not kept pace. As often happens with both public and private institutions during periods of rapid growth, systems that are not visible can easily be overlooked or moved to a "deferred maintenance" list. In this case, one of the more notable systems to fall off the radar screen was the lift station that pumps the school's wastewater to its treatment plant. The results of this oversight were neither pretty, nor cheap!
As a matter of fact, the pumps in the Stony Brook Lift Station used to clog so frequently that crews for Suffolk County Department of Public Works (SCDPW) came to anticipate such an event as part of their weekly routine, recalls Ron Warren, Maintenance Director of the Division of Sanitation, Operations & Maintenance.
"The clogging became quite predictable," he says. "Every week to 10 days we'd have to go out there and free an impeller that had become jammed with rags or some other debris."
The problem-prone 3-MGD facility is just one of 87 pump stations and 24 wastewater treatment plants maintained by the Department. Built years ago, when the campus was smaller and generated less flow, the station and its original equipment simply couldn't keep up with the demands placed on it by the much larger university center and three outlying areas that comprise the Stony Brook of today. Although it would appear that the station's three, 60-HP pumps had ample capacity; the size of these units and their variable speed drives defininitely contributed to the clogging problem during low flow periods (which is most of the day).
Unfortunately, the problems that the SCDPW faced at the Stony Brook lift station are shared by many organizations that are responsible for similar stations equipped with large, variable speed pumps.
Searching for A Workable Solution
The Stony Brook station was designed with a 20,000-gallon wetwell and three 60-HP end-suction pumps mounted horizontally in the dry pit. Approximately two years ago, when the pumps were clogging as often as twice a week, SCDPW asked G.A. Fleet Associates, Inc., an engineering consulting group and manufacturer's rep, based in Harrison, NY, to recommend a workable solution that SCDPW's own engineering staff and crews could implement.
"Clogging is a problem we typically encounter when dealing with large, older pumps with variable speed drives," explains Mark Cavanagh, Service Sales Engineer with G.A. Fleet. "It was common practice in the past to oversize pumps, but that resulted in a unit running at minimum speed most of the day. Low-velocity flow contributes to rags and other material getting entangled on conventional impellers and eventually clogging the pumps. An oversized pump also demands a wasteful amount of energy."
After reviewing the original specifications and spending several months monitoring the station's flow, Fleet recommended replacing all three existing units with N-Pumps from ITT Flygt. This new type of pump has an innovative self-cleaning impeller incorporating a volute with a special relief groove that prevents rags, high-fibrous material, grease or solids from clogging the pump. The Fleet team based its recommendations on the results of tests at other installations where fouled impellers had been a recurring problem. During those tests, the N-pumps not only operated for extended periods without becoming clogged, they also achieved dramatic energy savings.
Figure 1. One of Stony Brook's three newly installed ITT Flygt N-Pumps.
G. A. Fleet further recommended changing the sizes of the three pumps to a combination of two, 60-HP Flygt Model NZ3300 pumps to handle peak flows (Figure 1), and a Base-Load pump to handle the low-flow conditions (See Sidebar). Instead of a third 60-HP unit, however, the Base-Load pump Fleet specified was a 20-HP Model NZ3152 model that would help reduce the station's energy consumption. Additional upgrades included a Flygt MultiTrode® Liquid Level Control System, a conductivity probe-based system that is fully compatible with SCDPW's new SCADA system, which operates on Citex software. According to Ron Warren, as a first step towards a full-blown, continuously monitored operation, SCDPW plans to add more MultiTrode systems and gradually network eight stations with SCADA.
Lessons Learned
One doesn't have to be a math major to calculate the return on investment for this successful project.
Today, over a year later, Stony Brook's Base-Load pumping system continues to run as designed-smoothly and efficiently. While G.A. Fleet Associates and the engineers and maintenance crews from SCDPW may not have been sitting in on any classes, they clearly earned an A+ for their teamwork on this particular college project!
For more information on the application and products referenced in this article, please contact: G.A. Fleet Associates 914-835-4000
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