Turbine technology gives rivers an oxygen boost

New turbines at hydro plants add dissolved oxygen to the Catawba-Wateree River in South Carolina, improving the river’s health

Turning to innovative technology, engineers are installing a new type of turbine at two Duke Energy hydro stations in South Carolina to draw more oxygen into the water.

The payoff will come downstream: healthier rivers and possibly even better fishing.

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Air is delivered to the Voith turbine in the Unit 4 wheelpit at Wylie Hydro Station through four vertical pipes. The control system regulates the airflow with valves to ensure the required dissolved oxygen levels are met in the downstream river channel.
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The reassembled Wylie Unit 4 is in the project commissioning phase and is on schedule to provide continuous minimum flow and dissolved oxygen enhancement in 2020. 

The projects at Wylie Hydro Station and Wateree Hydro Station are part of licensing requirements from the Federal Energy Regulatory Commission (FERC) aimed at keeping the amount of dissolved oxygen at healthy levels. Though the reason behind the new technology might sound confusing at first, it is actually pretty simple. 

Fish and plants in water require oxygen to thrive, the way animals and plants do on land. Oxygen naturally mixes with water with the help of wind and waves. It also enters water through photosynthesis of aquatic plants. 

But during the summer, when temperatures rise, the ability of oxygen to dissolve in water decreases, especially at lower depths. 

“Typically, sometime between July and October is when this is really a problem,” said project engineer Patrick Bennett. “If you looked at a cross-section elevation of water upstream of a dam, you have dissolved oxygen at desirable levels near the top, and as you move down through the water column, dissolved oxygen drops until a point where everything below is deprived of dissolved oxygen.”

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The Voith turbine at Wylie Hydro uses the same technology shown in this photo. Air is drawn into the turbine blades through the head cover and exits through the slots in the trailing edge of each blade.

Aerating turbines allow Duke Energy to pass needed water downstream when the water quality upstream of the dams becomes unhealthy.

“Retrofitting existing turbines with minimum flow dissolved oxygen turbines is totally new to Duke Energy,” Bennett said. “We are sacrificing power output to improve environmental quality downstream in the river channel.”

The new continuous minimum flow turbines will take the technology a step further. The turbines will allow less water through the turbines but will run nonstop, continuously pulling in air and mixing it with water.

“On any day of the week moving forward, we will have a minimum flow that will always be coming out instead of zero flow at any point,” Bennett said. “It keeps the downstream river at a constant level that’s been deemed desirable by the U.S. Fish and Wildlife Service and other agencies.”

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This is the type of runner, the rotating part of the GE turbine that converts the energy of falling water into mechanical energy, that will be used at the Wateree hydro plant.

Bennett expects to finish work by July at Wylie, where engineers are installing Voith minimum flow turbines with a rated flow of 1,100 cfs, and begin work in May at Wateree, which will have General Electric Renewable Energy turbines with a rated flow of 1,040 cfs.

“Wylie was one of a kind and Wateree is second,” Bennett said. “They’re definitely cutting-edge in the hydro industry. This is the latest iteration for Duke Energy dating back to the 1990s and early 2000s when we had initial dissolved oxygen technology installed at a couple of locations.”

The new turbines are an important step toward maintaining the health of the water, said Lynne Dunn, hydro compliance manager at Duke Energy. 

“It’s just like when you go to the doctor and they do blood work,” Dunn said. “You’re doing everything you can, like eating healthy, but sometimes you might need medication to help you improve the quality of your health.”

In this case, the medication is dissolved oxygen.

“We’re helping to keep the levels up to provide better water quality for the aquatic habitat in the river. It’s one of the things we’re doing to continually improve.”

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Wylie Hydro Station began operating in 1925.
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Wateree Hydro Station began generating power in 1919.

Ways Duke Energy improves river oxygen levels

Duke Energy uses a number of technologies to improve downstream habitat and the dissolved oxygen levels before spilling it downstream: 

  • At multiple stations on the Catawba River, Duke Energy is using dissolved oxygen turbines, but without the minimum flow requirements.
  • At the Wateree and Wylie stations in South Carolina, the company implemented a rapid-pulse system – running a unit for one hour on, two hours off – during periods when at least one unit is not running continuously. 
  • At Lookout Shoals Hydro Station near Statesville, N.C., it installed metal plates that prevent the units from drawing water from lower levels.
  • At Lake Tillery in North Carolina, oxygen is piped into the forebay through a liquid oxygen diffuser system.