Shooting sound waves into water can remove dissolved gases from hydropower production that harm wildlife in rivers. For many years, scientists have been investigating various methods in the laboratory, and they are ready to test the best on a large scale in real hydropower plants.
The phenomenon of gas supersaturation occurs when air enters water-filled hydropower inlets and is then exposed to high pressure. When this water is subsequently released into the river, it is almost like opening a bottle of champagne, filling the river with bubbles.
Too much air in the water can harm fish and other species. In the worst case, fish can die from gas bubble disease – a disease similar to decompression sickness in humans.
There are currently no requirements in place to monitor and limit gas supersaturation in rivers downstream of hydropower plants in Norway, but studies have shown that this may be a problem in more power plants than previously thought. before.
If requirements are introduced to prevent the problem of gas supersaturation, this solution could help power companies avoid costly shutdowns of their plants when the problem occurs – as well as improve the environment.
An ultrasound ‘speaker’
The scientists conducted ultrasound tests in a specially developed water channel at the Norwegian University of Science and Technology’s (NTNU’s) Waterpower Laboratory.
The technical solution is a type of speaker that creates ultrasound. This creates pressure waves in the water that cause dissolved gas molecules to accumulate and form bubbles (acoustic cavitation).
The bubbles merge, become larger and rise to the surface. The method was tested in small and medium-sized laboratories, and W. Ludwig Kuhn showed in his doctoral thesis that the method immediately reduces gas saturation.
Collaboration leads to beneficial results
Cooperation with the energy industry and biologists has been important in the implementation of the project. “Natural scientists have contributed important knowledge about the consequences and extent of gas supersaturation, and the ability to discuss different solutions with experts from industry is invaluable.
At first, we thought we could put the ultrasound technology inside the suction pipe in the hydropower plant,” Kuhn said.
This was not well received by the industry, as installing equipment close to the turbine was too risky. They fear that it might affect the flow of water and thereby affect other parts of the hydropower plant.
“Therefore, the conclusion is that the equipment should be placed in the river at the outlet of the hydropower plant,” said Kuhn.
Big tests on hydropower rivers
Scientists are now planning to conduct field tests to investigate the extent to which this technology can be used in the hydropower industry. The hydropower inlets are enormous, carrying up to a million liters of water per second.
Laboratory tests show that it is not a good idea to build a giant version of the ‘ultrasound speaker’ (actually called a transducer), but it is more useful to use several smaller installations that can do the job together. When it is tested downstream of the hydropower plant, it will be a major technical installation.
Great potential
“So far, the results in the DeGas project have exceeded all expectations. The benefits to the hydropower industry have greater potential than we thought at the beginning,” said supervisor and project manager Ole Gunnar Dahlhaug . He is a professor in NTNU’s Department of Energy and Process Engineering.
“The method is efficient and likely to have relatively low costs in terms of installation, operation and maintenance.”
Collaborators flocked to view tests conducted by doctoral research fellow W. Ludwig Kuhn on the DeGas project, which is linked to the HydroCen research center.
“It was great to present the tests to our research partners and industry. Even the Minister of Energy Terje Aasland stopped by. It was very useful to get input from many different sides,” said by Kuhn.
