In 2009 the permit for the almost century-old hydropower plant in the market town of Mühlbach was up for re-application. But not the region’s big players of the energy supply industry won the project.

So finally two ambitious businessmen from Bozen at the head of the Pustertal won the project. Their well-conceived, sustainable concept won the day – and the permit. Dr Karl Pichler and Hellmuth Frasnelli – who each hold a 37.25% stake in plant operator Eisackwerk Mühlbach GmbH –  showed great determination and patience during the ensuing legal negotiations. In the end, their perseverance was rewarded with the successful startup of their innovative hydropower station in the autumn of 2012.

Built in the 1940s and 1950s, the double hydropower plant in the South Tyrolean Pustertal region was a local landmark of sorts, with its two penstocks running straight across the town of Mühlbach, much to the displeasure of the local population. For one thing, the humming of the turbines and generators in the nearby power house at the Mühlbach reservoir were clearly audible far and wide during the night. Also, the steely twin pipe, through which the waters were constantly gushing with an inside pressure of more than 60 bar, represented a considerable danger.

PRIVATE PROJECT APPLICANTS WIN OUT WITH INNOVATIVE CONCEPT
It was precisely these two rather unpleasant characteristics of the existing facilities that the two private project applicants decided to address with their new implementation concept. Deviating from the project designs of the competing energy suppliers, which called for an overground penstock to the old power station, the Eisackwerk Mühlbach GmbH proposed to install the motive water pipework under ground through a 430 m tunnel leading to a new cavern power plant inside the mountain. “One mustn’t forget that the existing penstock pipes had been subjected to pressures of up to 62 bar for 60 and 70 years, respectively. Who knows what might have happened if the pipes had been damaged by falling rocks or something like that,” says Hellmuth Frasnelli,  commenting on the disaster hazard of open-air penstocks in the middle of an urban area. In intensive collaboration with the contracted planning offices of Studio G of Bruneck, project manager Dr Karl Pichler managed to develop the idea of using underground pipes into a workable project plan, which eventually won the full approval of the responsible officials during the contract awarding process.

UPHILL STRUGGLE FOR A PERMIT
But despite the decision, for Eisackwerk Mühlbach GmbH the project was far from being a done deal, as local authorities and political representatives kept criticizing the “radically innovative” character of the new concept. Until they finally were granted the required permission in November 2009, the two managing directors had to fight for approval all the way, including litigation in six cases against public offices and the provincial government. From the time when they submitted their planning documentation in 2005, the uphill struggle for the Pustertal power plant project went on for almost four years until all court cases were finally settled and the two innovators were granted permission for water power utilisation until 2040. With this hurdle cleared, they could concentrate fully on their ambitious power plant project for the Mühlbach region.

NEW INTAKE WITH PATENTED COANDA SYSTEM
The project plans called for the complete renewal of the existing (and still used) components of the motive water pipework in the upper section of the facilities. Renovation work began at the main intakes at the weir gates in Pfunders and Vals, which were completely renewed and fitted by Wild Metal of Ratschings with a new Grizzly trash rack. This patented intake system, which combines a Coanda screen with integrated protective rack, was installed in place of the original classic Tyrolean weirs. Gufler Metal of Moos in Passeier supplied and installed the other hydro steel structures for the project, including, among others, 26 barrier sluice gates with frame heights of up to 8 metres. The granted permit also authorised an increase in the design flow rate for the two new machine units in the central control cavern. This allowed the project operators to draw water at the Pfunderer Bach intake at 2.3  m3/sec (previously 2.0 m3/sec) for their electricity generating purposes. At the Valser Bach intake, the flow rate was increased to 1.9 m3/sec from previously 1.5 m3/sec. At the same time, however, the residual water flow at both streams had to be increased as well in order to preserve the ecologic qualities of the outflow reaches. Also, the weir facilities at the Valser Bach had to be fitted with a fish pass, which was implemented by the Studio G planners of Bruneck in the form of a pool pass with cross-wall notches and submerged orifices.

RAISE-BORING METHOD ENSURES PRECISION AND MANY BENEFITS
The main intakes are situated at different elevations: the Pfunders at 1,350 m above sea level, and Vals at 1,250 m.a.s.l. From there, the existing headrace tunnels lead to their respective pressure basins with surge tanks, which were completely refurbished as part of the overall renovation work. From these points onwards, the two pipes now run in parallel, not over-ground downhill towards Mühlbach as previously, but through a vertical pressure shaft – which was excavated using the so-called raise boring method – towards the power house cavern inside the mountain. “After 430 metres, the deviation of our pilot bore was only about 3 cm. For a 25 cm core bit, that is quite impressive”, explains Dr Karl Pichler in commenting the high-precision work of the tunnel excavation team. With the initial bore for the 2 penstocks and the breakthrough into the excavated cavern  complete, new core bits with diameters of 1,5 m and 1.8 m, respectively, were fitted to the turflange pipe and raised while in rotation, thus creating the required shaft. With this drilling method, the excavated material simply drops to the ground, where it can be collected and removed quite easily. This allowed for a steady progress of around 20 m a day. Raise boring has other advantages as well: the machinery can be operated safely outside the mountain, and the method allows for higher excavation speeds at low operating effort.

NEW PENSTOCK DIMENSIONS
Once the excavation work for the pressure shafts was finished, the engineers went on to insert and install the new steel penstock pipes. The 12 m pipe sections were welded together near the shaft entrance and lowered carefully into the mountainous depth. When the last pipe sections were installed, the total weight carried by the hydraulic lift amounted to more than 200 tons. “Once the pipework was in place the two shafts were bricked up, so everything should be maintenance-free  for the next hundred years, and that’s that!”, says Hellmuth Frasnelli emphatically, confirming the longevity of the steel penstock pipes. During the planning stage for the new penstock runs, the extension of the previous pipe diameters was a key issue, as it was essential for boosting the capacity of the new plant. “The old penstock for the machinery in Vals was a combination of DN600 and DN700 pipes. For the new pipework we used DN1100 pipes throughout. This way, we were able to reduce the hydraulic loss significantly, which means a higher net head and higher energy output,” explains DI (graduate engineer) Thomas Fiechter, project manager at hydropower specialist Troyer.

VISIONARY SOLUTION WITH STRUCTURALLY IDENTICAL TURBINES BY TROYER
Wherever the name Troyer is mentioned, one usually does not have to look far for the turbines by the renowned family-owned manufacturer of the South Tyrolean town of Sterzing. In the power house of the new Mühlbach hydropower facilities, two nearly identical four-jet Pelton turbines have replaced the original machinery, which remains in the old power house 700 m away. Describing the new turbines as “structurally identical” may sound slightly confusing at first, considering that they are not only designed for different design flow rates, but also work with different water heads: 622 m in the case of the Pfunders machine, and 487 m for the one in the Valsertal. “But to keep things easy for the customer in terms of replacement parts, the machine in Pfunders is operated at 1,000 revolutions per minute, and its ‘almost identical’ twin in Vals at 750 rpm,” reports Troyer’s project manager Thomas Fiechter.

NEW HYDROPOWER PLANT GENERATES 20% MORE OUTPUT
Both of the high-grade, air-cooled synchronous generators were provided by Lloyd Dynamowerke of Bremen (Germany); they can achieve output efficiency levels of up to 98%. The operating heat of the generators is dissipated through a closed cooling system into the used motive water, which is carried into the Mühlbach reservoir by way of two concrete pipes installed at the bottom of the 850 m cavern access tunnel. As a result of the comprehensive modernisation, the output of the new facility is more than 20% higher, thanks to the increased design flow rate, the higher output efficiency, optimised partialload behaviour of the new 4-jet turbines, and the improved, widened pipe hydraulics. In effect, these improvements translate into an increase in installed capacity from the old facility’s 16 MW to 20.7 MW.

RECORD-LENTH UNDERGROUND HIGHVOLTAGE CABLE
To be able to feed the expected annual energy output of 100 million kWh into the grid, Troyer – which also supplied the entire medium- voltage and protection technology – transported the transformer from the old power house at the Mühlbach reservoir to its new destination at the entrance to the cavern access tunnel. The transformer station located there, together with another, smaller transformer, now convert the generators’ 15,000 V output power to 132,000 V before it is carried via a 800 m underground high-voltage cable to the transmission line at the old power house. Troyer kept the old power station operational until 2012, when it was finally time to switch
over to the machinery at the new Mühlbach cavern power plant.

SOUTH TYROLEAN VALUE CHAIN
When the second machine was connected to the grid on November 16, 2012, the two project organisers could finally breathe a huge sigh of relief, take a step back and look at their  achievement with a certain sense of pride. “We made a conscious decision to award all project contracts to South Tyrolean firms,” says Hellmuth Frasnelli, thus confirming the essentially regional character of the entire project. Of the 26 million euros that he and his business partner Karl Pichler invested into the project, they provided 20 % themselves, the remaining 80% were contributed by Unit Credit Leasing, with an expected amortisation period of 18 years. But there is another thing the two private operators want the locals to profit from: Eisackwerk GmbH intends to grant 50% discounts, for up to 1,800 kWh per year, to all households in the Mühlbach community that have 3.3 kW mains connections. In case this is not possible for legal reasons, the operators intend to donate an equivalent amount to charitable causes in the region. This generous offer is the final highlight that underscores this ambitious and thoroughly successful model project in the South Tyrolean energy supply industry.

GUFLER METALL KG FACES SPECIAL TASKS AT THE MÜHLBACH POWER PLANT

Gufler Metall KG, based in the South Tyrolean Moos in Passeier, Italy, has been a big player in the field of hydraulic steel engineering for over 20 years. Originally it was a blacksmith and locksmith business.

Founded by Gothard Gufler in 1991 it developed over the years into a hydropower specialist focusing on metal construction, hydraulic steel engineering and penstock welding. Gufler’s proud references include almost all new hydropower plants built in South Tyrol in the last few years. Therefore it comes as no surprise that Gufler Metall KG was commissioned to provide the special hydraulic steel engineering and welding works at the new Mühlbach power plant.

In the course of the renovation of various water catchments of the Mühlbach power plant in the South Tyrolean Puster Valley, Gufler Metall delivered and installed numerous hydraulic steel components, including a total of 26 gate valves with a frame height of up to 8 meters. These valves were installed in the water catchments on the Pfundererbach Creek, Valserbach Creek and Eiterbach Creek, as well as in the surge chambers of Pfunders and Vals. Furthermore Gufler Metall KG was responsible for supplying and installing the penstock protection valves of a dimension of DN1200 and a pressure rating of PN10, as well as the bellmouth and the supply and return air ventilation ducts of the two surge chambers.

SPECIALISED IN WELDING OF PENSTOCKS
The welding specialists of South Tyrolean hydraulic steel engineering company Gufler were even assigned the welding of the new penstocks from the two surge chambers to the passage into the vertical shaft. These tasks were performed partly on steep and challenging grounds. The highly qualified personnel employed by Alfred and Gothard Gufler are constantly kept up to date regarding the newest technology and operation processes. This guarantees Gufler Metall KG’s high-quality products and the company’s consistent success.

GRIZZLY MODULE SYSTEM: TREND-SETTING WATER CATCHMENT TECHNOLOGY

The new operator of the Mühlbach
hydropower plant, Eisackwerk Mühlbach
GmbH, hired Wild Metal, a company
based in South Tyrol, Italy, to supply
and install the entire hydraulic steel
engineering components in the course of
the modification works of the plant.
Grizzly rake modules for water intakes
turned out to be the ideal solution for
an efficient and low-maintenance
discharge of process water. This system,
patented by Wild Metal, combines an
integrated protective rack with a
Coanda screen and skims off the smallest
sediments and debris. The water
catchment on the Pfundererbach Creek
is equipped with a Grizzly 2300,
which is the largest Grizzly module
ever used in power plants.

Adapting the water catchment to stateof-
the-art technology was an important
stage of the modification project
of the Mühlbach power plant. This is why the
operators decided on a new and highly efficient
rack cleaner system, which guarantees
the highest screen capacity and the lowest
maintenance requirements: the Grizzly by
Wild Metal. Its patented catchment concept,
which is constantly revisited by the manufacturer
based in Ratschings, South Tyrol, combines
a robust, hot dip galvanized protective
screen with a Coanda screen placed underneath
it. To significantly increase the functionality of
the catchment on the Valser Bach Creek, its
existing structures were adapted by installing
14.5 elements of the Grizzly rake modules.
The water catchment on the Pfundererbach
Creek is a clearly larger version with 18 integrated
modules of the Grizzly 2300. With a
breadth of 20 meters it is the largest water
catchment with a Coanda system in the
Alpine region. It is designed for a guaranteed
capacity of 3,000 liters per second. The extrastrong
protective rack was designed to divert
even a heavy bed load of a few tons safely over
the catchment during high water periods.

MINIMIZING CONSTRUCTION COSTS WITH
THE GRIZZLY SYSTEM
The patented Grizzly rack module is a truly
innovative development by Wild Metal. The
basic technical improvements in comparison
to a Tyrolean weir are the shorter gap spacing
of the Coanda screen and the integrated protective
rack. The gap spacing of the Coanda
screens used at the catchment of the Mühlbach
power plant is 0.5 mm. This means that
only particles with a grain diameter of less
than 0.3 mm can enter the process water
system. Consequently the grit chamber is
smaller in dimension and in that way saves
construction costs. Pine needles, leaves, twigs
and other debris is washed over the catchment
and floats off. The design of the module
offers an extraordinarily simple and quick
installation. Another characteristic of the
Grizzly rack is its low height. Together with
the newest development of coarse rack bars
expanding towards the bottom, it represents
the most maintenance-friendly rack cleaner
system for water catchments currently available
in the hydropower market.