Future of Hydraulic Turbines
The history and innovation in hydropower turbine technology have been associated with a high demand for maximum power generation. Over the last two decades, however, a focus on decreasing fish mortality has become increasingly important. Turbines are available and in continued development to offer solutions to some of hydropower’s biggest issues — particularly the safe downstream passage of fish through turbines and increases in generation through reductions in the spill.
In the early 2010s, turbine entrainment was as high as 2,500 fish per hour, according to the Federal Energy Regulatory Commission. This alarming number of fish injuries and mortalities was in part due to the pressure placed on the hydropower industry to operate at peak efficiency — plus or minus 1 percent — even during fish passage season.
One of the main solutions to downstream fish passage protection issues has been to implement direct spillage, which in turn has resulted in significant generation loss. Another technique to lower fish mortality numbers has been explored through turbine manufacturing. While turbines have historically become smaller and faster over the year, Alden Research Laboratory, one of the leaders in turbine innovation, has moved in the opposite direction — making its turbines bigger and slower.
This runner geometry was incorporated into a sector model and a simulation was completed at the selected design condition for School Street Station (Hnet = 92 ft, Q = 1500 cfs). The initial calculation was performed to first evaluate (1) the velocity profile at the runner exit and (2) the calculated pressure levels along the blade surface.
Fig 1 Unit arrangement drawing by Alden research laboratory
Alden turbine -
Efforts to develop a more fish-friendly turbine started in the ‘90s with efforts by the U.S. Army Corps of Engineers’ Turbine Survival Program and the U.S. Department of Energy’s Advanced Hydropower Turbine Systems Program. The joint effort kicked off with a financial contribution of $500,000 from the Electric Power Research Institute and a coalition of industry supporters. The DOE matched this contribution and solicited proposals from the industry to develop environmentally-enhanced hydropower turbine technologies that were also efficient for generating hydropower.
From this solicitation, awards were made for the design of fish-friendly hydro-turbines to two teams: one led by Voith Hydro, and the other by Alden Research Laboratory. The Voith concept focused on modifying an existing Kaplan runner design, while the Alden concept focused on a radical new runner design created specifically for safely passing fish.
The Alden turbine, which features a helical-shaped runner with only three blades, is intended for new units in smaller rivers and fish bypasses. Original DOE laboratory tests with the Alden turbine demonstrated that fish survival, when scaled to a full-size field installation, would be over 98 percent for many fish species. Following initial proof-of-concept testing, an optimized conceptual design of the Alden turbine with boosted power density to be competitive with existing designs was conducted.
Once the conceptual design was finished, EPRI and DOE-funded Alden and Voith Hydro to enhance the turbine’s performance through modification of the hydraulic passageways, including the spiral case, distributor, runner, and draft tube. The final stage of the Alden turbine design effort included a model test at Voith Hydro’s hydraulic laboratory in York, Penn., in addition to the updated mechanical and balance of plant equipment sizing necessary for actual field installation. Model testing indicated a maximum prototype efficiency of almost 94 percent at conditions corresponding to a prototype net head and flow of 92.0 ft and 1,504 cubic feet per second.
The Alden turbine is currently undergoing a field demonstration project. Toward that goal, EPRI in 2010 launched an industry solicitation for potential demonstration sites. After applications were received, sites were ranked numerically until one site, Brookfield Renewable Power’s 38 MW School Street Project in Cohoes, N.Y., was chosen as the preferred location for the development of the demonstration program. An alternate site, Electricity de France’s 8 MW Perinat project, was identified in the event that the preferred site could not be developed.
Speed | Runner diameter | Froude Number | Computational model sped | Computational model Dia. |
112.5 rpm | 11.8 ft | 0.72 rpm | 365.9 rpm | 1.1 ft |
Doug Dixon, senior program manager for EPRI’s Fish Protection Program, said a power purchase agreement is expected to occur in the summer of 2016, and installation is expected to start in about two years. EPRI also received a $1.5 million grant from DOE in September that must be matched by EPRI and the hydropower industry.
In 2017, 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. Utilities also are 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 Electricity 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. The 2019 funding supported the preliminary engineering design, which included Computational Fluid Dynamics (CFD) modeling, efficiency improvements, and hydraulic model testing.
Fig.2 Alden turbine Configuration
Hydraulic development -
The Alden runner reduces blade strike mortality through several modifications:
- Reducing the number of blades relative to conventional applications
- Employing special blade leading-edge geometries
Rotating slower than conventional turbines. The current Alden turbine design incorporates a runner that features three blades that rotate at a speed of 120 revolutions per minute (rpm). Application of conventional turbine technologies for the target site results in a 13-bladed Francis turbine that rotates at 189.5 rpm, or a five-bladed Kaplan turbine that rotates at 267.9 rpm.
The blades feature relatively thick semi-circular entrance edges to minimize strike damage to fish, extremely long blades with nearly 180 degrees of blade wrap, and a runner height that is larger than a conventional turbine of similar diameter. Each blade is fixed to a central hub (crown) and an external shroud (band), eliminating all gaps and resulting leakage vortices within the runner passage.
Runner geometry was evaluated according to three distinct design criteria, with fish friendliness being the most important, followed by increased power production, and finally reduced supply costs. Although the runner is being developed to provide a new family of fish-friendly hydro turbines for smaller machines across a range of head and flow applications, Alden and Voith Hydro focused the design effort for potential pilot application at a project with operating conditions corresponding to 92 feet of neThead with a discharge rate of 1,500 cubic feet per second (cfs).
Calculations show that the improved flow environment through the final turbine is expected to produce significant efficiency improvements (5% at the design conditions listed above) with the same or slightly improved fish-friendly characteristics as compared with the original Alden concept. While some small performance improvements are predicted for the final distributor, the majority of the efficiency improvement is realized in the final runner and draft tube as a result of the improved runner-draft tube interaction at the selected design condition.
After the modified turbine hydraulic passageways were defined and structural analysis was performed for the anticipated operating range, the hydraulic shapes were released for model manufacture, including the inlet pipe, transition piece, spiral case, stay ring, wicket gates, runner and draft tube. Physical model testing was conducted in 2010 at Voith Hydro’s S. Morgan Smith Memorial Hydraulic Laboratory in York, Pa. Data was collected on performance, thrust, runaway speed, pressure pulsations, minimum pressures, cavitation and wicket gate torques to characterize the hydraulic behavior of the turbine and identify the acceptable operating range for the target site design.
Results of the hydraulic testing also were incorporated into the final sizing of the mechanical equipment. Voith Hydro manufactured the physical model at a scale of 1:8.71 and conducted the tests at a speed of 900 rpm. During testing, a model peak efficiency of 91.85% was recorded. The prototype efficiency adjustment translates into a maximum calculated prototype efficiency of 93.64%.
Benefits -
Once demonstration tests have been completed, the Alden turbine will likely discover its greatest demand to be at small hydro projects, where the highest gains in fish survival and additional power production can be achieved.
Based on estimates of downstream passage or minimum flow release requirements at developments licensed by FERC 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.
According to the DOE, 21,000 MW of generating capacity can be added to existing dams in the U.S.
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.
The Alden turbine continues to improve fish passage numbers, with over 98 percent survival expected. “We’re looking at very high survival,” Hogan said. “I think the public would see that as environmental stewardship.”
Although the Alden turbine may have a higher upfront cost, the payback is in increased generation with the flow that is otherwise wasted. “Use of the turbine may also preclude the need for expensive screening systems and downstream bypasses,” Hogan said.
Fig 4. Original Alden turbine runner. Photo courtesy Alden Research Laboratory.
Norm Perkins, the senior civil engineer with Alden, said that the Alden turbine and technologies like it will help keep hydropower’s name of being a clean, renewable technology. While Renewable Portfolio Standards have been under scrutiny for hydro developments in recent years, Perkins said that advancements like the Alden turbine “could continue hydro’s ability to being considered for RPS in the U.S.”
A physical model of the turbine was manufactured and tested with data collected for power and efficiency, cavitation limits, runaway speed, axial and radial thrust, pressure pulsations, and wicket gate torque. All parameters were observed to fall within ranges expected for conventional radial flow machines. Based on these measurements, the expected efficiency peak for prototype application is 93.64%. These data were used in the final sizing of the supporting mechanical and balance of plant equipment. The preliminary equipment cost for the design specification is $1450/kW with a total supply schedule of 28 months. This equipment supply includes a turbine, generator, unit controls, the limited balance of plant equipment, field installation, and commissioning.
Based on the selected head and flow design conditions, fish passage survival through the final turbine is estimated to be approximately 98% for 7.9-inch (200-mm) fish, and the predicted survival reaches 100% for fish 3.9 inches (100 mm) and less in length. Note that fish up to 7.9- inches (200 mm) in length make up more than 90% of fish entrained at hydro projects in the United States. Completion of these efforts provides a mechanical and electrical design that can be readily adapted to site-specific conditions with additional engineering development comparable to costs associated with conventional turbine designs.
Comparison with conventional Turbines -
| Alden Turbine | Conventional Francis Turbine | Conventional Kaplan Turbine |
Sizing | |||
Diameter (mm) | 3900 | 2510 | 2650 |
Maximum Power [MW] | 13.6 | 13.6 | 13.6 |
Costing | |||
Turbine | 1.00 | 0.50 | 0.05 |
Generator | 0.80 | 0.65 | 0.65 |
Installation | 0.25 | 0.25 | 0.25 |
Automation | 0.25 | 0.25 | 0.25 |
Relative Cost | 2.30 | 1.65 39% | 1.70 35% |
Summary and next steps -
The work performed to date has improved the performance characteristics of the Alden turbine while maintaining its fish-friendly characteristics.
The preliminary engineering required to make the turbine commercially available has been completed. Design modifications to the turbine components have improved efficiency to almost 94% at the selected design point, while providing the same or slightly improved fish passage survival. These turbine modifications were also selected to decrease manufacturing and supply costs, resulting in a solution that is economically competitive with conventional turbines. The improved turbine is now available for commercial deployment.
In 2011, in response to another DOE funding opportunity announcement, EPRI was selected to receive $1.5 million of support with a cost-share match requirement to install and test the Alden turbine at a site to be determined.
References -
[1] “Fish Friendly” Hydropower Turbine Development and Deployment: Alden Turbine Preliminary Engineering and Model Testing, EPRI Report 1019890 prepared by Alden Research Laboratory, 2018.
[2] Evaluation of the Effects of Turbine Blade Leading Edge Design on Fish Survival, EPRI Report No. 1014937 prepared by Alden Research Laboratory, 2018.
[3] Demonstration Development Project: Solicitation and Selection of a Site to Test a Fish-Friendly Hydropower Turbine, EPRI Technical Update No. 1022538 prepared by Alden Research Laboratory, 2017.
[4]Amaral, S.V., et al, “Effects of Leading Edge Turbine Blade Thickness on Fish Strike Survival and Injury,” Proceedings of Hydro Vision 2008, HCI Publications, Kansas City, Mo., 2008.
Authors -
Harsha Mamdyal
Vaishnavi Mane
Pratham Matal
Muthu Krishnan
Shivani Padamwar
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