Hydropower screw

Two hydropower screws working in parallel, each with an output of 75 kW

The principle of a hydropower screw: The water (here the red ball) causes the screw to rotate as it flows downwards (here rolling).

Play media file

Video of a hydropower screw on the Schwarzen Lacke , Munich

A hydropower screw is a hydropower machine , i. H. a technical system ( hydroelectric power station ) for converting potential energy into mechanical energy (rotating movement of a shaft), which is usually used to drive an electrical generator . Hydropower plants with hydropower screws are classified as small hydropower .

functionality

Construction of a hydropower screw, section of the information board at the Stadtbachstufe in Munich

One parameter is the number of helixes (number of flights); 3 or 4 are typical

In principle, a hydropower screw can be described as the energetic reversal of the Archimedean screw . The central component is the rotor, which consists of an elongated, cylindrical central part, on whose shell the single or multiple, helical screw winding is arranged. This runner is located in a trough which is precisely matched to the outer diameter of the screw and which encloses the screw at least on the lower half, but mostly two-thirds or more. The entire device is installed at an angle of approx. 20 to 30 ° between the upper and lower water of the power plant, usually on a weir . The lower edges of the front sides of the trough are each below the lowest upper and lower water level and form the inlet and outlet of the headwater. When the screw rotates, chambers separated by the pitch of the screw helix form between the fixed trough and the rotor, in which the driving water flows from the upper to the lower water. The water only flows in the lower sector of the cross-section of the screw - even in systems in which the trough completely surrounds the screw in a tubular shape.

While it moves down in the chambers between the threads, it sets the rotor in a rotary motion through the weight force exerted on the worm turns. In order to keep the friction and momentum losses low during energy conversion, the screw rotates relatively slowly (20 to 60 revolutions per minute). In contrast to most turbine types , there is no overpressure in the open arrangement; Runner, trough and the chamber volumes formed by the rotation are connected to the surrounding atmosphere.

The runner is mounted on a traverse at the lower and upper end . After being translated by a gearbox , an electric generator, which is usually mounted in a flood-proof manner at the upper end of the device, is driven at a higher speed. With a hydropower screw, watercourses (amount of water per screw up to 10 cubic meters per second) that have to overcome a small difference in height (up to about ten meters) can be used to generate energy. The largest systems built move at 8 m³ / s and a drop height of 6 meters.

Efficiency

In measurements by Lashofer et al. (2011) on 14 existing systems in Germany, Austria and South Tyrol, system efficiencies of over 75% were measured. The average of all systems with different admission was 69%. The system efficiency includes the product of the efficiency of the screw, bearing, gear, generator and own consumption. So it describes how much of the water's energy is converted into available electricity.
In laboratory measurements at the University of Natural Resources and Life Sciences, Vienna (BOKU), Lashofer et al. (2013) determined the screw efficiency (including storage). In the partial load range, efficiencies well over 90% were achieved (at around 40% of the nominal admission). Usual efficiencies ranged between 75 and 85%.

advantages

The advantages of hydropower snails are their low sensitivity to fluctuations in the amount of water (from 0.1 cubic meters per second), flotilla tolerance and the relatively low risk to fish and aquatic life that pass the snail downstream. In contrast to run-of-river power plants equipped with turbines, systems can be operated economically at locations with a smaller usable gradient . The civil engineering work is also less expensive and therefore more cost-effective. No fine screening systems are required, so there is also less screening material to be disposed of. Depending on the design, hydropower screws equipped with watertight nacelles can continue to operate even when they are flooded. In comparison to the water wheel , a better degree of efficiency can be achieved.

disadvantage

Enclosed hydropower screw in Kiefersfelden

In comparison to the screw pump, the reversal of the flow direction of the water leads to some surprising effects. Most noticeable is the beating noise development. It occurs when a blade in the upper inflow releases an inflow channel. The water accelerates and shoots out on the opposite side. This always takes place at the same point and was referred to by Kantert in the "Praxishandbuch worm pump" as the "shot point". The load is so high that older hydropower screws suffered mechanical damage and corrosion after about two years. For newer systems, an average service life of around 30–40 years is assumed. Similar to a dynamic pressure screw, the water in the outflow area falls behind every blade. The accelerated run-off from the last screw thread causes rhythmic noises.

There are different approaches to reducing noise emissions. Modifications to the blade ends, a larger number of flights (also improves the efficiency), only one-sided fastening of the lower bearing, etc. Many modifications brought hardly any improvement. For example, the diameter of the discharge blades on a hydropower screw in the urban area of Munich was reduced. Most effective, however, is complete enclosure, which can hardly be avoided, especially in the vicinity of residential areas, and which significantly increases investment costs. This was also the case in the aforementioned facility in Munich.

Fish compatibility

In scientific investigations of the double-conical hydropower screw in the power station in the Jeßnitz no injured fish were found.

There are already some independent expert opinions and reports on fish tolerance (Schmalz, 2010 and 2011) that speak of a high tolerance. However, individual fish species or even age groups can be affected by poor maintenance or insufficient production. In Krechting (Rhede) in the Münsterland region , the local municipal utilities operate a hydropower screw, on which the effects of the hydropower snails on the fish fauna as well as possible optimizations to improve fish conservation through screw power plants are examined. In Austria, the impact on the fish tolerance of a hydropower screw with an integrated fish lift in Neubruck (Lower Austria) in the Jessnitz power station was examined by the Institute for Hydrobiology and Water Management (IHG) of the University of Natural Resources and Life Sciences (BOKU) Vienna. The study showed that most fish species could pass the hydropower screw in both directions. Injured fish were not found.

history

Originally described by Archimedes as a screw pump for lifting water, it has been used again in polder drainage in modern times. In combination with a windmill, the screw pump raised water over the dykes.

As early as 1819, the French engineer Claude Louis Marie Henri Navier expressed the idea of operating the screw as a kind of water wheel. Presumably he was watching what happens when you let go of a screw pump filled with water. The forces that occur can destroy a conventional screw pump, which is why they are usually also equipped with backstops (hydropower screws with brakes).

Perhaps the oldest description of a hydropower screw in the patent literature comes from William Moerscher.

In 1991 the water lifting screw engineer Karl-August Radlik registered the invention of the water power screw for a patent. This was granted in 1992 and sold to a German manufacturer of screw pumps in 2001. However, a patent dispute with a competitor could not be won.

The first hydropower screw was manufactured by a Czech manufacturer, from 1995 to 1997 at the TU Prague by Prof. Dr. Brada tested and then by the Förderverein Wind- und Wasserkraft Ostalb e. V. used. It has been running since 1997 in the Upper Schlägweidmühle on the Eger in Bopfingen- Aufhausen with 4 kW generator power. A special feature is the ability to change the installation angle.

In 2001 the first two commercial plants went into operation. The Rödermühle with 7.5 kW on the Franconian Saale in Diebach near Hammelburg and a system with 18.5 kW on the Nethe in Höxter - Godelheim .

Walter Albrecht registered another patent in 2012 for a hydropower screw that has an integrated fish lift.

distribution

As of mid-2013, it can be assumed that there will be more than 250 systems in operation worldwide and about the same number in preparation. Since the technology has proven itself, mainly larger systems are now being built and many are in the range from 140 to over 200 kW.

One of the largest hydropower screws is in Kindberg, Austria .

Further hydropower screws are available:

in the Bavarian town of Kiefersfelden : head 3.8 m, hydropower screw diameter 3.0 m, length 9.0 m, since 2005

in mills in Taufers

in Derendingen SO, Switzerland : head 1.2 m, hydropower screw diameter 1.6 m, length 3.3 m, since 2006

in the Swiss Hirschthal

in Niklasdorf in Upper Styria

in Lunz am See in Lower Austria

in Freiburg im Breisgau an der Dreisam (since 2008)

In Hann Münden (Lower Saxony) integrated into the weir area of a lock on the Werra. Manufacturer: Rehart GmbH

in Lobenhausen an der Jagst, since 2013.

in Bocholt on the Bocholter Aa in front of the Aa lake (since 2014) and 4.5 km further up the river in Rhede-Krechting (since 2006).

at the Url near Amstetten in Lower Austria, it is used in combination with a parallel fish ascent screw .

A hydropower screw with an integrated fish lift has been in operation in Neubruck (Lower Austria) since 2015. The operator is the manufacturer and developer company Hydroconnect.

In Retznei (Styria), the association has also been operating a hydropower screw with an integrated fish lift since 2015, which is based on the same patent as the system in Neubruck.

The Stadtbachstufe built in Munich in 2006 also works on the principle of the hydropower screw. A hydropower screw on the Diemel River has been meeting the electricity needs of a brewery in Warburg since 2012 .

Compared to other hydropower machines

Applications of hydropower machines in the field of small and micro hydropower

A large number of water power machines have been developed for generating electrical energy . Hydropower screws show their strengths in the small to medium flow range as well as small heads and show good partial load behavior. The structural and technical size limitations of hydropower screws (maximum head ~ 10 m, flow max. ~ 15 m³ / s) specify their use in the field of small and very small hydropower, as shown in the diagram on the right.

Comparative table:

	Cross-flow turbine	water wheel	Hydropower screw	Centrifugal pump	Francis	Chaplain	Pelton
Flow rate	small to medium	small to medium	small to medium	small to medium	medium	big	small to medium
Height of fall	small to medium	small	small to medium	large to medium	medium	small to medium	big
Partial load behavior	Well	Well	good to medium	bad	bad to medium	good to medium	Well

The following primary framework conditions are relevant when choosing a hydropower machine:

Flow rate
Height of fall
Degree of efficiency versus water volume (partial load behavior / parallel connection)
Possibly a necessary deepening due to cavitation
Achievable annual electrical output
Achievable monetary income and costs (operation / maintenance) per year
Investment costs

literature

PJ Kantert: Praxishandbuch screw pump . Hirthammer Verlag, 2008, ISBN 978-3-88721-202-5 .

PJ Kantert: Praxishandbuch worm pump - 2nd edition, 2020, DWA, ISBN 978-3-88721-888-1 .

A. Lashofer, F. Kaltenberger, B. Pelikan: How well does the hydropower screw perform in practice? In: water management. 101 (7-8), 2011, pp. 76-81.

D. Nuernbergk, C. Rorres: An Analytical Model for the Water Inflow of an Archimedes Screw Used in Hydropower Generation. In: Journal of Hydraulic Engineering. July 23, 2012.

Dirk M. Nuernbergk: Hydropower screws - calculation and optimal design of Archimedean screws as a hydropower machine. 1st edition. Moritz Schäfer Verlag, Detmold 2012, ISBN 978-3-87696-136-1 .

A. Lashofer, W. Hawle, B. Pelikan: Operating ranges and efficiencies of the hydropower screw. In: water management. 103 (7-8), 2013, pp. 29-34.

D. Nuernbergk, A. Lashofer, W. Hawle, B. Pelikan: Operating modes of hydropower screws. In: water management. 103 (7-8), 2013, pp. 35-40.

W. Schmalz: Investigations into fish migration and control of possible fish damage by the hydropower screw at the hydropower plant Walkmühle on the Werra in Meiningen - final report. Breitenbach 2010.

W. Schmalz: Fish descent through a hydropower screw at a diversion power plant. In: water management. 101 (7-8), 2011, pp. 82-87.

K. Brada: The hydropower screw enables electricity to be generated by small power plants. In: machine market. 14. 1999, pp. 52-56.

G. Nagel, K. Radlik: Water screw conveyors - planning, construction and operation of water lifting systems. Udo Pfriemer book publisher in the Bauverlag GmbH, Wiesbaden / Berlin 1988, ISBN 3-7625-2613-3 .

M. Reuter, Chr. Kohout: Practical handbook for the environmentally conscious use of turbine technologies in the field of small hydropower. Institute for Water Management, Sanitary Engineering and Ecology, September 2014.

Individual evidence

↑ LFV-Westphalia: Investigations into the migration and damage of fish to the Rhede-Krechting hydropower screw. ( Memento of the original from April 23, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2
↑ B. Zeiringer: Fish Passage through a Hydro Dynamic Double-Screw: An Alternative Solution for Restoring River Connectivity . American Fisheries Society, 145th Annual Meeting in Portland, OR, August 16-20, 2015: Abstract on the American Fisheries Society website
↑ Patent US1434138 : Water-power system. Applied on November 24, 1916 , published on October 31, 1922 , applicant: William Moerscher, inventor: William Moerscher. ‌
↑ Patent DE4139134 : Hydrodynamic screw for energy conversion - uses changes in water supply to regulate energy output. Registered on November 28, 1991 , published on December 4, 1997 , applicant: Karl-August Radlik, inventor: Karl-August Radlik. ‌
↑ Förderverein Wind- und Wasserkraft Ostalb e. V. Description of this hydropower screw.
↑ ^a ^b Patent AT512766 : Hydropower screw . Registered on January 13, 2012 , published on February 15, 2013 , applicant: Walter Albrecht, inventor: Walter Albrecht. ‌