To Lift or Boost? Modifying the Operation of an Existing Pump Station to Maximize Energy Efficiency

摘要

At the Greater Cincinnati Water Works (GCWW), energy management is an important component of operating all pumping facilities. During a recent energy management analyses of a 35 mgd pump station, it was determined that significant energy savings could be achieved if the pumping operation was radically changed. The normal operation of the facility was a “dump and pump” operation, where the water from the upstream distribution system fills the reservoir, and then the water is pumped from the reservoir to the next pressure zone. Because the inlet pressures to the reservoir were significantly higher than anticipated (70 psi versus 20 psi), an innovative solution was developed to convert the pump station from a “dump and pump” operation to a booster pump operation. Extensive hydraulic and economic analyses were performed to determine if the existing pumps could be modified to efficiently operate as booster pumps, thereby lowering the required horsepower usage and capturing significant energy savings. However, the pump’s ability to also operate as a lift pump had to be maintained to continue using part of the 2.5 MG storage reservoir for water quality purposes. The hydraulic analyses showed that by carefully trimming the pump impellers, the pumps could be converted to pump efficiently in both the booster mode and the lift mode. The economic analysis showed that the cost of modifying the existing pumps could be recovered with the projected energy savings in less than three years. The long-term electrical savings were estimated at about 20 percent of the current electrical costs. Also, the 70-psi inlet pressure had to be reduced to about 10 psi before entering the reservoir. Throttling the water into the reservoir was causing premature failure of a critical inlet valve and resulted in undesirable pressure fluctuations on the upstream distribution system. In conjunction with the pump modifications, the control valve to the reservoir inlet was replaced with a unique valve called a sleeve valve.