Houston addresses flooding problem in bayou with new lift station using submersible pumps
The City of Houston required a new wastewater lift station in Sims Bayou, as the existing station had exceeded its useful life. Due to large variations in total daily head—a static head of 46 ft but reaching as high as 138 ft—pump selection was an issue. The concern centered on net positive suction head required when one pump was running by itself, especially since the consulting engineer, Klotz Associates, had ruled out the use of variable frequency drives (VFD). Also, the City of Houston preferred to build a “station in the round” because construction would cost less. The consultant proposed a 42-ft-diameter and 46-ft-deep wet well to accommodate six pumps.
Based on the pumps recommended by Hahn Equipment, a Xylem distributor—six Flygt CP3356, 280-hp submersible pumps—Xylem conducted a computational fluid dynamics (CFD) study to analyze potential fluid flow problems at the station. It revealed problems with flow distribution at the approach to the proposed pumps, as several of the pumps would suffer from excessive swirl and uneven velocity distribution at the impeller eye.
What followed was a conference call among the project manager, the consulting engineer and Hahn Equipment to discuss the problems. Suggested modifications to the pumps included enlarged inlet ports, as well as guide vanes inside the ports and the inlet chamber. These changes would significantly improve the hydraulic conditions and provide an example of how stakeholders working closely together are able to avoid costly future modifications.
The six CP3356 Flygt pumps were selected over competitive equipment, which actually offered higher-horsepower units.
Hahn Equipment convinced the City of Houston that the total horsepower of the six Flygt pumps would be less than five competitive pumps, resulting in a lower-cost solution to this pumping challenge.
Able to operate directly in the liquid being pumped, Flygt submersibles do not require special housings or superstructures to support them, considerably reducing construction costs. They are smaller than non-submersible counterparts because the motor and hydraulics are integrated into one compact unit, resulting in smaller pumping stations that are less complex to build. Finally, operating submerged they take up less space, and noise and cooling problems are virtually eliminated.
The City of Houston, Klotz Associates and Hahn Equipment worked arm-in-arm to deliver a successful pump station to the Sims Bayou Federal Flood Reduction Project in Texas. The Sims Bayou project was designed and constructed in an environmentally responsible manner, and an increasing number of birds and wildlife can already be seen along completed segments of the bayou and at the storm water detention basins.