By Nancy Spring, Senior Editor
Blocked passages for fish and turbine-induced mortality of downstream migrating fish are major environmental issues for hydropower projects. Direct spillage is one method to protect downstream fish passage but can result in generation loss. Various turbine fish bypass technologies have been developed but generally have been expensive and their effectiveness less than optimal.
A new turbine design that reduces fish passage injury and mortality could change everything. Developed under the U.S. Department of Energy’s (DOE) Advanced Hydro Turbine Systems (AHTS) program by Alden Research Laboratory, results from pilot-scale testing done in 2001 and 2002 were promising. In 2009, the Electric Power Research Institute (EPRI) received an award from the DOE to conduct a multi-year program to continue the turbine’s development and bring it to full-scale deployment.
“The Alden turbine is very promising, it offers an alternative to the mortality that occurs with existing turbines,” said Doug Dixon, senior program manager for EPRI’s Fish Protection Program. “It’s new, it’s cutting edge and we are sponsoring this research because we believe it has something to offer the industry and the public.”
Utilities are also supporting the project to help make sure the turbine’s potential is fulfilled. South Carolina Electric & Gas, Puget Sound Energy, Dairyland Power, Southern Co. and Electricité de France along with the New York Power Authority, the New York State Energy Research and Development Authority and Brookfield Renewable Power are funding the project to augment the DOE grant EPRI received.
Alden’s goal was to develop a turbine that permitted the safe passage of downstream migrating fish thereby mitigating either the need for expensive protection technologies or non-generation spill. The Alden turbine is a new hydro turbine design.
The design has some similarities to screw pumps that can be used to safely transfer fish, said Stephen Amaral, senior fisheries biologist, Alden Research Laboratory, but the Alden turbine was developed specifically for generation, the reverse of pumping.
Most conventional Kaplan hydropower turbines have five or six blades; other types have many more. A Francis turbine, for instance, will have 14 to 18 blades, increasing the occurrence of blade strike and injury to fish, said Dixon. In addition, typical hydropower turbines have gaps between the blades and the turbine hub where fish can get caught. These turbines are designed to be small and spin fast to extract the most energy at the lowest initial cost.
The Alden turbine, by contrast, looks like a corkscrew. It has three blades, no gaps, is big and rotates more slowly. But the design compensates so energy production doesn’t suffer.
“When you make it rotate slower you have to compensate by increasing the turbine’s size,” said Dixon. “The outside edge goes at the same speed so that it generates the same amount of electricity.”
|Computational fluid dynamic model of the Alden turbine. Full-scale operation of the turbine is expected to result in turbine passage survival rates higher than 98 percent for many fish.|
With this design, fish move down a smooth channel with a few blades that are turning more slowly than traditional hydro turbines, resulting in less chance for injury.
Pilot-scale biological evaluation of the turbine was conducted at Alden Laboratory in 2001 and 2002 under the DOE’s AHTS program, which has since been replaced by a new water power program that incorporates improvements to hydro for efficiency and environmental performance. (EPRI was not involved at that time.) It was the first pilot-scale biological evaluation of a turbine. Testing was done using a closed-loop system driven by a 2,000 hp pump, with the turbine output absorbed and speed controlled by a dynamometer. Test results and data were also collected on the power conversion efficiency of the turbine using this facility.
“We injected fish into the turbine test loop upstream of the turbine to determine passage-related injury and survival,” said Amaral. “It is probably the most intensive and rigorous evaluation of turbine passage survival that has ever been conducted, with more than 40,000 fish used in the evaluation.”
A technical committee of DOE staff, industry professionals and resource agency biologists and engineers decided on the operational parameters and which species to evaluate.
“We weren’t really sure at the time exactly where its application would fall, but to start we wanted to focus on a sort of prototype design,” said Amaral, who coordinated the biological testing.
Two operational heads and runner rotational speeds were selected: 40 feet at 240 rpm and 80 feet at 345 rpm. Testing was done with and without wicket gates. Biocriteria developed through research funded under other DOE programs was incorporated into the design to minimize blade strike, reductions in pressure, flow shear and turbulence.
“We used the ‘white lab rat’ of fish, rainbow trout, because they are representative of many species, particularly salmonids, and readily available in a variety of sizes,” said Amaral.
Other species representative of important fish that commonly occur at hydro projects in various areas of the U.S. were included in the test program, such as alewife, smallmouth bass, coho salmon, American eel and white sturgeon.
The range of pilot-scale survival rates for American eels and white sturgeon were considerably higher than would be achieved by other turbine designs at many sites, showing the importance of fish morphology and physiology in turbine passage survival.
One surprising finding was the survival rates of the American eel. Eel behavior is opposite that of salmons: eels migrate as adults from fresh water to the ocean to spawn. They have to migrate upstream as young fish past the dams and then down when older. Little is known about them once they get into the oceans.
American eels can be 3 to 4 feet in length in many river systems. Length is an important factor—the longer the fish, the greater the probability they’ll be hit by turbine blades. Where they have done field studies with eels, said Amaral, survival rates are typically lower than they would be with a smaller fish.
But in the Alden turbine, American eels had the highest survival rate. They were the largest fish tested, measuring up to 18 inches. Within an hour of testing all the eels that passed through survived. When latent mortality rates were factored in, such as 96-hour post-passage survival, the smaller eels had 100 percent survival rate; the 18-inch eels had about 99 percent total survival rates.
“That surprised us, that’s a key finding,” said Amaral. “Eels are one of those species that the agencies are focused on because there have been declines in populations.”
White sturgeon also had statistically higher survival rates compared to the other species, including bass, trout, salmon and alewife.
“What’s different about them is they are cartilaginous, less susceptible to injury from strike,” Amaral said. Like American eels, they don’t have scales, making them less subject to secondary infections.
Based on pilot-scale test results, predictions suggested at least a 96 percent fish survival rate for a full-scale unit. Turbine passage survival depended primarily on fish length and operational head, a finding consistent with blade strike as the primary cause of fish mortality.
“With our turbine, we think we have designed-out issues related to shear and turbulence and pressure,” said Amaral. “The primary mechanism for injury is blade strike and we think we have reduced that quite a bit because we only use three blades.”
Continued development of the Alden turbine that has been funded by EPRI includes a re-design of the scroll case to double its flow-handling capability and a re-design of the runner. EPRI is also investigating the relationship of turbine leading edge blade shape, thickness and speed to fish injury and mortality to add to the environmental performance of the turbine.
“We know at the pilot scale it is effective and when you take those results and scale them up to full scale, you should have extremely high survival, greater than 98 percent for most species,” said Dixon.
Next Step: Engineering
EPRI, Alden and Voith Hydro will work together to conduct the developmental engineering needed to prepare the Alden turbine for full-scale deployment.
EPRI signed a contract with Voith Hydro in late December 2009. Over the next six to eight months, Voith will take the turbine concept from computer drawings to engineered design. Dixon expects that by the first quarter of 2011 a final engineering design and report for the project will be ready.
“We are working on an expedited schedule,” said Dixon. “As the engineering design is developed, they are also going to build a model about 15 inches in diameter.” Later this year, the physical model will be tested in Voith’s hydraulic test stand facility in York, Pa.
The scope of engineering includes:
- Refining the runner geometry to increase turbine efficiency, enhance fish survival and to allow for practical construction methods based on calculated loads.
- Adjusting the spiral case, stay vane and wicket gate geometries based on calculated forces and FEA evaluation for structural integrity. Axial thrust and transient forces will be measured in the physical model.
- Preparing mechanical designs of turbine shafting, head cover, stay ring, gate operating system, bearings and seals.
Testing a “real-world” Alden turbine will take place in a few years. When that happens it will mark the first time that federal and state fisheries management agencies have agreed to consider passing fish through a turbine.
Brookfield Renewable Power’s 38 MW School Street hydroelectric project, on the Mohawk River north of Albany, N.Y., had been proposed as the first test site. Uncertainty exists, however, because of some unrelated licensing issues. A competing application for the project has been prepared and EPRI is announcing a new program to solicit alternate test sites.
Benefits and Economics
Although the Alden turbine could be used on 1,000 MW projects like those on the Columbia River, its potential use may be greater at smaller hydro projects where the greatest gains in fish survival and additional power production can be achieved.
Based on estimates of downstream passage or minimum flow release requirements at FERC-licensed and non-federal developments under FERC’s jurisdiction (plus potential projects), as many as 1,000 projects exist where the Alden turbine could be applicable.
The turbine’s potential market is even larger when based on estimates of generating capacity available for development in the U.S. According to the DOE, 21,000 MW of generating capacity can be added at existing dams. Some 19,000 MW could be generated at new small hydro developments of 1 MW to 30 MW. Assuming that half of this additional generation is suitable for units in the 5 to 20 MW range, a potential market exists for 2,000 Alden turbines with an average capacity of 10 MW per turbine.
“We haven’t quite nailed it down, but are using a broad guide from about 20 feet of head up to 120 feet of head,” said Amaral. The School Street project is still considered the design point. When Voith engineering is finished, however, they will have an 80 percent design that can be applied to other sites.
By using the Alden turbine instead of screening, spillage or other practices for downstream fish passage, generating capacity is expected to increase while O&M costs for downstream fish passage facilities are expected to decrease. Full-scale operation of the turbine could result in turbine passage survival rates higher than 98 percent for many fish.
“We think it’s important to the industry and most people recognize it as high priority,” said Amaral. “EPRI has been the one to pick up the ball after the original DOE program ended. We wouldn’t be where we are today without them.”