Taum Sauk Upper Reservoir Restoration Project

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  • Topic: Grid energy storage, Energy storage, Pumped-storage hydroelectricity
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Taum Sauk Upper Reservoir Restoration Project
4/21/2011
By:

A. Identify a current engineering issue or project related to fluid mechanics: The Taum Sauk Hydroelectric Reservoir is a pumped storage plant located in the Ozark Mountains in Missouri, about 90 miles south of St. Louis. The purpose of the plant is not to provide water for the citizens of the region but instead it is used as a way to store and produce electrical power. The power generation/storage complex is made up of two separate water reservoirs, an upper reservoir and a low reservoir. The upper reservoir is located on the top of Proffit Mountain and is formed by a kidney-shaped earth and rock-fill dyke up to 90 feet high, with a 10 foot parapet wall (Rogers, 1). This reservoir holds 1.5 billion gallons of water when it is filled up (FERC, 10). The lower reservoir is on the East Fork of the Black River and is a natural basin where water can be drawn from. These two reservoirs are connected by a tunnel containing reversible pumps and generators so that electricity can be generated by gravity flow in one direction and the water can be pumped in the other direction in the same tunnel at a later time. The largest section of the tunnel is a 451 foot long, 27.2 foot diameter vertical shaft that originates at the Upper Reservoir. The next section of this tunnel going towards the lower reservoir is a 4,765 foot long, 25 foot diameter tunnel that slopes 5.7 percent, and then the final section is a 1,807 foot long, horizontal steel-lined tunnel that is 18.5 feet in diameter (FERC, 11-12). As anyone with an understanding of fluid mechanics can see, the lowest section of the tunnel needs to be the strongest because of the hydrostatic pressures on it from all the water above it. That is why the lowest section is lined with steel. By a rough calculation, using the slopes and lengths of the tunnels plus the height of water in the upper reservoir (result: ≈800 ft difference in water elevation) and a water density of 62.4 pounds per cubic foot, the pressure in the lowest section of the tunnel could reach over 350 psi, or 24 MPa. This water elevation difference means that the Taum Sauk Hydroelectric Reservoir has more available head than the Hoover Dam. The upper reservoir and pumping systems were built in the 1960s as a way to meet the electricity demand of the nearby areas. The power company was having trouble making enough energy during the day, since people use a lot more electricity in the day time than the night. The water reservoirs and pumping systems basically work like a large battery, and they let the power company handle the peak demand during the day. The pumping cycle works like this: in the evening when extra power is available from the grid (around 10 pm), the plant begins pumping water from the Black River to the upper reservoir. This continues until around 6 in the morning. From 6am until noon, the local power plant is able to handle the electricity demand without help from the Taum Sauk reservoir, so the water level stays the same during this time. At noon, when the peak electricity demand starts, the upper reservoir begins releasing water into the tunnels. Near the base of the tunnels is a power station where two 225MW-rated reversible pump-turbine generators convert the flow to electrical energy. Therefore, by neglecting hydraulic losses, this pump system could output 450MW of electricity. The electricity generation period lasts until around 9 PM, and around that time the turbines pause for a half hour then reverse into pumping mode. (FERC, 12-13) Another advantage of the Taum Sauk Reservoir is that for example in the event of a blackout, the potential energy of the upper reservoir would be able to restart the power grid. Coal or nuclear power plants require external power to restart (Rogers, 4). After the construction of Taum Sauk in the 1960s, the system ran successfully for over 40 years until December 14, 2005 when a...
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