LAYING OF DN3000 GRP FLOWTITE PIPES

Autor: Roland Gruber , 05.02.2013

At the highly traditional Neumühle in the community of Argenbühel in Germany's western Allgäu region, the power of water has been harnessed on the Untere Argen river for centuries.

At the end of the 19th century, the site was electrified by the founders of the Argen works and in 1918 it was equipped with a Francis machine unit. During the course of the 1970s, the operators at the time sold the hydroelectric power plant to the Winter miller family, whose son Hubert Winter then decided to fundamentally modernise the Neumühle power plant, which was showing its age. The new plant concept envisages the installation of pipes for the lower part of the works water channel; the biggest GRP spiral pipes from the Flowtite system with the dimension DN3000 produced by the company AMITECH in Germany were used here.

The most striking aspect about the comprehensive renovation of the Neumühle plant is the relocation of the power production unit from the old mill site to a new powerhouse 50 metres further down the channel, right by the mouth feeding into the Untere Argen river. The old drainage channel, which is approx. 350 metres long, is still used as far as the old mill, but from there the works water will in future be guided via a siphon line with a subsequent suction pipe into the newly laid GRP pipe string with a diameter of 3.0 metres, which is then guided directly into the new turbine house.

RAPID LAYING OF THE GRP PIPES THANKS TOINNOVATIVE CONNECTOR SYSTEM
When in mid-March 2013 the AMITECH FLOWTITE pipes DN3000 for the new works water pipeline and DN2000 for the necessary undersluice channel are delivered, the construction company Ebert has already perfectly prepared the channel excavation below the old power plant site together with the rough and fine levelling. Under the watchful eyes of AMITECH project manager Jochen Auer and construction site engineer Uwe Pletz, the 6-metre-long sections of pipe made from glass-fibre-reinforced polyester resin are lifted by crane into the construction pit and moved into position there. The construction company has specially produced a steel cross which matches the diameters of the pipes and is attached to the coupling of the GRP pipe which is to be laid. A digger then uses its scoop to press against the attached steel cross and pushes the new section of pipe into the coupling of the existing pipe string which has been well greased beforehand. The AMITECH connector system of the patented FLOWTITE series with an interlocking seal produces a specific noise when the sections of pipe are locked together: "When it clicks, it fits," says Jochen Auer in describing the audible sign of success when joining the pipes together with a wink, "with this system we are able to lay up to over 100 metres a day when the conditions on the construction site are in our favour."

HYDRAULIC PIPE PROPERTIES PERSUADE THE OPERATOR
In addition to its sealing function, another advantage of the connector system is also a certain flexibility when laying the FLOWTITE GRP pipes. The pipe is moved straight into the coupling and it can then be adjusted slightly so that it is possible to work flexibly in a certain range, but not beyond the sealing element. In total, 48 metres of DN3000 pipes of the pressure class PN6 for the works water and 61 metres of DN2000 pipes for the undersluice channel of the new power plant are being laid at the Neumühle site. The developer Hubert Winter is also very satisfied with the GRP pipe strings from the company Amitech: "With the relocation of the powerhouse further down the channel and the hydraulically perfect properties of the AMITECH FLOWTITE pipes, we have now gained a total of approx. 70 cm of net drop for generating power at the new site." With a current total gradient of around 7  metres, the boost in power gained from the new plant concept is therefore around 40 kW.

EFFICIENTLY DESIGNED KAPLAN TURBINEDELIVERS NOTABLE BOOST IN PERFORMANCE
And in order now to also make efficient use of the optimised drop in gradient in the new powerhouse in energy terms, Hubert Winter decided to install a double-regulated Kaplan turbine from the company  HSI Hydro Engineering there. This 5-vane turbine with a vertical axis and an impeller diameter of 1.50 metres will by the end of 2013 replace the almost 100-year-old Francis machine unit from the old mill site and, together with an equally new residual water turbine at the restored discharge weir, now supply twice the annual working capacity to the grid. Incidentally, at the weir a water volume of up to 10.5 m3/s can be drawn into the discharge of the works water channel, but with the design of the Kaplan  turbine the main attention was paid to the throughflows of between 4 and 8 m3/s as in this range, with an opening of approx. 45 – 80%, the turbine can be operated in the best efficiency range of around 90%. Coupled directly to the turbine shaft, a permanent magnet generator will turn the mechanical work into electrical energy. The PM generator, which is smaller and lighter compared with conventional units, also offers a persuasive choice with high efficiency in the partial load range.

NEW TYPE OF FISHWAY UNDER DISCUSSION
As part of the restoration work, a series of measures to support the ecology of the waterways will also be implemented, for example a specially laid lock flow bypass which, competing with the turbine outflow from the new powerhouse, is intended to point the fish fauna in the Untere Argen river in the right direction towards the discharge channel in the direction of the weir. And if the power plant operator Hubert Winter gets his way, a new and innovative type of migration aid should soon enable the fish at the weir to climb up into the headwater. This is because, in addition to the conventional solutions, consideration is also being given to a newly developed fish lift which in a vertical DN3000 GRP pipe is intended to transport the aquatic water fauna into the headwater by means of a floating acrylic glass basket. Developer Hubert Winter is still coy about revealing too many details of this pioneering idea, but the advantages of rapid and straightforward transportation of the fish to the headwater with drops of up to 30 metres and more, coupled with a design which saves space and costs and has comparatively low operational throughflows, seem to be hard to deny. The operator would like to be connected to the grid with his fully renovated plant by the end of this year. Together with his Thalerschachen hydroelectric power plant, which is also situated in Argenbühel, Hubert Winter will thus be generating a considerable proportion of the power required by this Allgäu community. The steel cross made especially for the laying process is used by a digger to press against the pipe sections.

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Crane at work

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A crane is used to lift the 6-metre-long GRP pipe sections into the construction pit and move them into position on the prepared substrate at the construction site. (photo: zek)

Special low weight pipes

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The low weight of the spiral pipes made from glass-fibre-reinforced polyester resin makes them quick and straightforward to handle at
the construction site. (photo: zek)

Preparing the couplings

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The couplings of the pipe sections are prepared for being joined together. (photo: zek)

Special steel cross

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The steel cross made especially for the laying process is used by a digger to press against the pipe sections. (photo: zek)