Hydro technology extracts energy from sewage water

Hydropower plants developed by the Austrian company VA Tech Hydro use sewage water to generate power in treatment plants in France, Jordan, and Switzerland.

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Hydropower plants developed by the Austrian company VA Tech Hydro use sewage water to generate power in treatment plants in France, Jordan, and Switzerland.

VA Tech Hydro’s Valloire Project in the Alps, near Col du Galibier, is the first hydropower plant in France designed to extract energy from untreated sewage water. This innovative project uses raw water from the village that is transported into the valley where a single jet horizontal Pelton unit economically dissipates the 650-m water column before entering the treatment plant.

The Valloire is well known for skiing in the winter and the Tour de France in the summer.

Along with the success of VA Tech’s projects in Jordan and Switzerland, this project should open new horizons to many more ski resorts in the Alps with similar conditions.

Hydro energy can be found in a number of diverse locations, such as treatment plants in the Jordan desert, or in the valleys below a ski resort, as at Valloire in France. The only requirement, as with any other hydro plant, is an economical combination of head and flow.

VA Tech’s pioneering project at Le Châble, Switzerland, first introduced this type of hydro turbine in 1992 when engineers installed a horizontal 700-kW Pelton unit at Le Châble, using energy from the untreated sewage water at the famous ski resort of Verbier.

The first use of this technique was a challenge, using a 447-m head. The project overcame some tough problems that arose during its initial installation. Concerns were raised over the wear and tear of the mechanical resistance of the runner and nozzle since untreated water contains solid elements. Another concern was the corrosion resistance, as untreated water also contains H2S acid, which destroys carbon steel within weeks. Design engineers overcame both problems by using highly valuable Duplex stainless steel and adequate ceramic coating. Consequently, the unit has been in operation for 12 years.

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Bifurcation used at As Samra
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This project is noteworthy for various economic reasons. The entire infrastructure for water supply and energy release is available via the power plant, built at the intake of the treatment plant. Significantly, the turbine does not replace the energy dissipation system. Instead it is mounted parallel, so that if any maintenance must be carried out, the water can still flow through the bypass.

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Stainless steel Pelton units
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The VA Tech As Samra Project in Jordan includes two power plants that incorporate the new technology. The first plant pumps untreated water from the capital Amman 40km through the desert and over hills to the treatment plant built by Infilco Degremont (USA-France). On arrival, sewage water powers two vertical 5-jet Pelton turbines before entering the treatment plant. The treated water then flows in a 3-km penstock to the second plant where two horizontal Francis units recover the energy.

The Pelton units have been adapted to cope with the high H2S acid concentration created during the long transit time of the raw water in the sun-heated penstock. Special measures have been taken to prevent acid gas leaking. Duplex steel (26% chromium), a special corrosion resistant material, is used for the runners, nozzles, housing, shaft ends and deflection cones. Additionally, the nozzles have an inventive design, with no internal guiding across the needle to avoid blockages as a result of the solid content. Whilst the Francis units remain standard, special corrosion protection measures have been put in place to combat anticipated high levels of chlorine, compared to the amount in usual river water.

In the final stage of the Jordan project, treated water will be available in the desert for irrigation purposes, after having produced nearly 4MW of electrical energy.

Author’s Note

Pierre Duflon is the sales manager for compact hydro at Va Tech Bouvier Hydro SA, located in Fontaine, France.

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