South Tyrolean trash rack cleaning technology operates on the innovation track

Autor: Roland Gruber , 31.12.2018

A high technical standard, customised solutions and striking design are the ingredients for the recipe which characterises the hydraulic steel and mechanical engineering designs of the industry specialist Wild Metal.

Its hydraulic steel engineering solutions are now very much in demand not just in the DACH countries and Italy, but also internationally. It is little surprise that the company from the town of Ratschings is therefore also one of the providers that power plant operators turn to when they are planning new horizontal trash racks and the trash rack cleaning machines to go with them. Numerous reference installations bear testament to this.

The inflow trash rack is often the decisive factor in determining how effectively a hydroelectric power plant will perform and how much power it will generate annually. It is all about providing the best possible flow conditions on the one hand and ensuring general availability on the other. In addition, another aspect comes into play and this is the ecological compatibility or, to put it another way, how friendly the system is to fish. EU-wide targets and national legislation is increasingly making it necessary to come up with designs in which there is no damage to fish wherever possible.
In recent times, one very good solution to this question that has become established is the use of horizontal trash racks aligned at an angle to the direction of flow which act on the one hand as a protective barrier and on the other hand as a ladder to guide the migration of fish. Horizontal trash racks thus combine the necessary friendliness to fish with the essential hydraulic criteria for efficient power plant operation. The latter depends not only on the hydraulic design chosen for the trash rack bars that are used, but also on the efficiency and reliability of the trash rack cleaning machine that is deployed. Operators are therefore also well advised, when it comes to designing horizontal trash racks, to talk to the industry specialists, such as the company Wild Metal, which is located just a few kilometres south of the Brenner Pass. In recent years, the company has highlighted how high quality and innovation can combine to deliver optimum technical solutions.

Precision over a length of 16 metres
For example, the requirements that the construction of the Gohlhaus power plant in Lützelflüh in the Swiss canton of Bern were to place on the experienced engineers from Wild Metal were very particular. Above all the trash rack length of 16 m at the Emme power plant, which opened in the summer of 2016, was a step into a new dimension. The fine trash rack has a clear bar width of 15 mm and thus meets the strict requirements for fish protection. The trash rack cleaning machine was designed in such a way that the arm with the trapping rake skims off the floating debris at the side, as a result of which it is then guided further over the sluice gate into the lower water. The cleaning operation itself proceeds very swiftly. The cleaning arm, driven by a high-quality servo motor, moves at a speed of 80 cm/s fully automatically over the inlet. Thanks to precise positioning, the plant always has information about the position of the cleaning arm to the nearest millimetre. In addition, the trash rack cleaning machine was also given a very robust design because ultimately it must also be able to withstand the floods on the River Emme which are a very frequent occurrence.

Cleaning process in whisper mode
The South Tyrolean industry specialist only recently completed a brand-new reference project for a horizontal trash rack with a trash rack cleaning machine in Windischgarsten in Upper Austria. For the Kaufmannsmühle diversion power plant on the Dambach right in the heart of the community, Wild Metal also supplied, as part of the package for all the hydraulic steel engineering equipment, a modern horizontal trash rack with an inlet width of 6 m and an immersion depth of 1.2 m which is cleaned by a fully automatic trash rack cleaning machine. The low opening width of 18 mm in combination with a low flow speed at the trash rack effectively prevents fish from being “sucked into” the trash rack and perishing there. From the operator’s point of view, great importance was attached to the trash rack cleaning machine which, in addition to its solid functionality, also had to satisfy another criterion: low noise. As residents live in the immediate vicinity of the water catchment, the movement of the cleaning arm was to make as little noise as possible. Thanks to the sophisticated operating technology, with the speed being controlled via frequency converters, and a high-quality design, it ultimately proved possible to guarantee operation that is as quiet as a whisper. For safety reasons – a path leads directly to the rear of the catchment area – the trash rack cleaning machine was fully encapsulated with a polycarbonate cover. The plant operator was extremely pleased with the technical solutions provided by Wild Metal.

The solution to prevent “crushed ice”
The two power plants that have been mentioned - Gohlhaus and Kaufmannsmühle - are reference examples of low-pressure plants. But nowadays horizontal trash racks are also increasingly being installed in high-pressure plants. One example of a project showcasing this is the water catchment at the Susasca power plant not far from the famous Flüela Pass. In 2016, the plant not only received an upgrade to the electromechanical equipment, but also saw the water catchment being converted. A new horizontal trash rack with a gap width of 18 mm was to be installed in place of the five-year-old, vertical trash rack. There were two reasons for this: the intention was firstly to improve the fish ecology, and secondly to rectify a recurring problem that had been happening in the winter months as a result of small pieces of “crushed” ice. This ice became stuck inside the trash rack and blocked it. After the machine was shut down, the trash rack was cleared out manually and the machine was restarted, there were repeated surges in the residual water section. Wild Metal provided the solution to this with a special horizontal trash rack which can be heated on three sides. This prevents the formation of ice at the trash rack itself. The winters that followed demonstrated impressively that the solution works.
It is with good reason that the team from Wild Metal led by Markus Wild has a reputation for being able to respond very quickly to customer demands and specific requirements. Individual technical solutions which meet the highest standards when it comes to functionality and reliability are now regarded as the hallmark of the South Tyrolean hydraulic steel construction company. In addition, Wild Metal also provides hydroelectric power customers with the “icing on the cake” – namely the typical, distinctive design of a hydraulic steel construction company with real stature.


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The benefits of the horizontal trash rack were opted for at the Hard power plant near Winterthur. The fine trash rack and the trash rack cleaning machine to go with it were installed by the South Tyrolean industry specialist Wild Metal.

photo credits: zek

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An acrylic glass housing provides excellent protection for the trash rack cleaning machine on the alpine water catchment of the Susasca power plant.

photo credits: zek

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A vertical fine trash rack was converted into a horizontal trash rack at the Susasca power plant.

photo credits: zek

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The horizontal trash rack for the 6 MW Susasca power plant was installed in 2016 instead of a vertical fine trash rack. The engineers from Wild Metal came up with a special solution to a very unpleasant problem that had previously existed with small pieces of ice that froze together inside the trash rack: ensuring that the trash rack component can now be heated on three sides prevents ice from forming on the trash rack bars.

graphics: Wild Metal

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The horizontal trash rack cleaning machine can cover a cleaning width of 16 m at the inlet of the Gohlhaus power plant in the canton of Bern.

photo credits: zek

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The new trash rack cleaning machine on the horizontal trash rack of the Kaufmannsmühle power plant operates as quietly as a whisper.

photo credits: Wild Metal

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As a path leads directly behind the water catchment of the
Kaufmannsmühle power plant, the trash rack installation was encapsulated with a polycarbonate cover to provide protection.

photo credits: Wild Metal