Tranquilizing Racks in Desanding Facilities: State of the Art and Field Study on Flow Field Improvement by Rack Modification
Publication: Journal of Hydraulic Engineering
Volume 150, Issue 6
Abstract
Desanding facilities (DFs) limit particle sizes and reduce the suspended sediment load in hydropower plants. Multiple successive tranquilizing racks (TRs) at settling chamber inlets are a cost-efficient structural measure to homogenize the flow and reduce local velocities and turbulence in the chambers. We summarized the state of the art of TRs and conducted detailed flow velocity measurements in the settling chambers of a DF with TRs. In the first campaign, a pronounced flow concentration beneath the vertical bars of the TRs was found, resulting in flow velocities along the invert of up to 3.5 times the average cross-sectional velocity. Because this impairs the trapping efficiency, the TR bars were extended downward to achieve a more even distribution of the flow resistance over the entire flow section. A subsequent measurement campaign confirmed a more homogeneous flow field and a considerable reduction of the turbulence intensities and turbulent kinetic energy, which were the lowest compared to six other DFs. The results highlight the potential to modify existing TRs at other DFs with inhomogeneous flow fields and the practical importance of TR design for new DFs.
Practical Applications
In hydropower plants (HPPs) with water intakes located at sediment-laden rivers, DFs are crucial for reducing the sediment load in the turbine water, consequently minimizing wear on the turbines. A DF usually consists of one or several chambers through which the water flows slowly, allowing sand particles to settle. However, for geometrical, hydraulic, and economic reasons, the flow at the chamber inlet is often not favorable for settling. In such situations, TRs can be installed to slow down and distribute the inflow more evenly. Because no general design guidelines for TRs are available, we reviewed the state of the art based on literature and present the field investigation of flow fields in a DF with TRs. We found an unfavorable flow concentration and modified the TRs to cover the whole flow section. This resulted in more favorable conditions for settling, also in comparison with other DFs. In DFs with inhomogeneous inflow conditions, suitably designed TRs enhance the trapping efficiency and contribute hence to the cost- and energy-efficient use of the hydropower potential at sediment-laden rivers.
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Data Availability Statement
Some or all data, models, or code generated or used during the study are available in a repository online in accordance with funder data retention policies (Kastinger et al. 2024, https://doi.org/10.5281/zenodo.10036895).
Acknowledgments
This work was financially supported by (1) the Swiss Federal Office of Energy (SFOE) within its hydropower research program (Project Nos. SI/501760-01 and 2018-2021), (2) Ouvra Electrica Susasca Susch (OESS) AG, the operator of the case study HPP, and (3) ETH Zurich. VAW’s hydropower research activities 2017–2020 were embedded in the Swiss Competence Center for Energy Research–Supply of Electricity (SCCER-SoE), Phase 2. The work of further team members of VAW, ETH Zurich, namely Daniel Gubser, Sebastian Davidis, Dorde Masovic, and Robert Pöschl, is gratefully acknowledged. We thank Markus Hintermann, Hydro-Solar Water Engineering, for his initiative, which led to the research project, and for having provided the relevant drawings. Further thanks go to OESS for the logistic support onsite and the good collaboration. We are also grateful to the two anonymous reviewers whose comments significantly contributed to improve this manuscript.
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Journal of Hydraulic Engineering
Volume 150 • Issue 6 • November 2024
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© 2024 American Society of Civil Engineers.
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Received: Nov 3, 2023
Accepted: Jul 11, 2024
Published online: Sep 14, 2024
Published in print: Nov 1, 2024
Discussion open until: Feb 14, 2025
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