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RSSCase Study: Supplemental Pump System Eases Low Water Threat To Iowa Power Plant
January 5, 2006
•Case Study: Supplemental Pump System Eases Low Water Threat To Iowa Power Plant
The Missouri River evolves steadily from a swift trout stream in Montana into a turbid highway for barge traffic by the time it passes MidAmerican Energy's George Neal Energy Center south of Sioux City, Iowa. The Neal North complex and a sister station two miles away designated Neal South, are among the seven power plants that MidAmerican Energy operates along Iowa's stretch of the Missouri River to serve 690,000 customers.
Even with six dams upstream from the plant, the Missouri River can still unleash floods or shrink from drought and manipulation of its flow. The river serves many roles – recreation, agricultural, community drinking water and barge commerce – and is the very lifeblood of power plant facilities like the Neal Energy Center.
The often-low river level at the 515-megawatt Neal #3 intake during winter months has concerned plant operators for many years. Extended drought and more conservative releases from upstream reservoirs controlled by the U.S.Army Corps of Engineers have limited the river's flow during winter months. Ice jams in the shallows near Ponca, Nebraska can further aggravate the problem.
MidAmerican Energy needed an effective engineering solution to ensure a reliable flow of cooling water to Neal #3, the largest – and most vulnerable – of three units located at Neal North.
"Neal #3 requires the most cooling water but also is the most susceptible to low river stages," said Kevin Calloway, plant mechanical engineer with the Generation Engineering Department. "We've experienced flows low enough to have forced it off line in the past.
"When that happens we lose over 12,000 megawatt-hours each day – over half of Neal North's capacity," he said. "That's a big financial hit to the utility, especially when we're forced to buy replacement power on the open market."
The 135-megawatt Neal #1 consists of a cyclone-fired boiler while the 300-megawatt Neal #2 and 515-megawatt Neal #3 have pulverized coal boilers. All three rely on a once-through cooling water system. Neal #1 and #2 share a common intake structure, while Neal #3 has a standalone intake located 200 feet upstream.
Under normal conditions, cooling water is drawn from the river for Neal #1 by two 37,500-gpm vertical pumps while Neal #2 relies on twin 65,000-gpm vertical pumps. Two 145,000 gpm vertical pumps supply Neal #3. These permanent circulating water pumps for Neal #3 require 8-1/2-ft. of submergence, compared to 6 ft. for Neal #1, and 5 ft. for adequate submergence to serve Neal #2. The floor of the intake structures are at elevation 1045.25, with the base of the pump bells at elevations of 1046.7 for Neal #1, 1048.25 for Neal #2 and 1047.5 for Neal #3.
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