Aeration of hydraulic turbines to increase downstream dissolved oxygen concentration

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In warm climates warm temperatures cause thermal stratification in hydropower reservoirs inhibiting mixing and leading to deoxygenation of waters in the hypolimnion of the reservoir. Turbines withdrawing water at depth from the hypolimnion results in little to no dissolved oxygen in the downstream flow which can have a large negative impact on the downstream riverine ecosystem. Legislation in the USA and elsewhere now requires hydropower operators to guarantee meeting minimum limits for dissolved oxygen concentrations in downstream flows. Two broad categories of methods for re-aerating turbine flows exist. The first are regulatory approaches that are successful but lead to a loss of revenue and energy production. The second are technological approaches that are viewed as more cost-effective in the industry. Andritz Hydro Canada has initiated this project to optimize the elbow deflectors used in draft tube aeration, which is a retrofit approach not excessively impacting operation schedules. They have implemented one of the first prototypes of draft tube aeration using elbow deflectors at the John H. Kerr power plant, demonstrating the viability of the system. The main deliverables will be the optimization of the elbow deflectors, through a parametric study of the design parameters involved in maximizing bubble surface area and bubble concentration to result in an increase in dissolved oxygen concentration, and a set of data for validation of Andritz's CFD model, which will enable them to produce prototype designs meeting DO specifications. A physical scale model of the elbow deflector will be built and tested in the McGill laboratory. A parametric study will allow for both an understanding of the physical processes and for a set of quantitative data to be obtained for validation of CFD models. The project will benefit from the 15 years of experience in R&D of hydropower hydraulics of Prof. Gaskin. Andritz Hydro Canada will position itself as a leader for hydropower projects in which environmental impacts of low dissolved oxygen are important (countries with warm climates, e.g. USA, Spain) able to guarantee meeting (or exceeding) the regulatory requirements for dissolved oxygen while optimizing turbine performance.