Resolution of Circulating Water Pump Problems Caused by Low River Levels at the Neal North Generating Station

Low winter water levels are causing reliability problems with once-through circulating water pump systems at several coal-fired power generating plants sited along the Missouri and Mississippi Rivers. River bottom degradation and potential COE river management changes make low river levels a likely on-going problem especially during drought years currently being experienced in the Midwest. This paper outlines circulating water pumping problems that have occurred at MidAmerican Energy’s Neal North Energy Center due to low water levels in the Missouri River, and the steps taken to resolve these problems. Remedial design solutions that were either considered or implemented, such as supplemental pumps, vacuum lift systems, suction scoops, a new river water intake, and converting to a closed-loop cooling tower system, will be discussed. An in-depth discussion will be made on the supplemental pump system installed in the fall of 2002 and currently in operation on the Unit 3 river intake. Applicable permitting requirements will also be discussed. The new supplemental pump system consists of six submersible axial flow pumps mounted on the front of the existing Unit 3 intake. The total flow capacity of the six supplemental pumps is around 220,000 gpm which is discharged into the existing intake to maintain an acceptable wet well water level for the existing circulating water pump to operate. Other system components include an overhead monorail system to facilitate annual supplemental pump installation/removal, a floating ice deflector system, and a warm-water discharge splash plate. The supplemental pumps are installed and operated during winter months when river levels are low, and removed during the river navigation season when the COE maintains higher river flows.