Since mid-May last year, the two Kaplan turbines at the newly built Danzermühl power plant on the Traun river in Upper Austria have been turning.

The plant started regular operation at the end of June. In around two and a half years, the construction project, which had to overcome considerable structural challenges especially at the beginning, was completed on schedule. With the two modern Kaplan turbines from Voith Hydro, the new power station in Laakirchen will from now on generate around 43 GWh in a standard year, 125 percent more than the old plant. The electricity generated is entirely consumed in the neighbouring Laakirchen Papier AG; the paper mill is, like the power plant, part of the Heinzel Group.

The construction of the Danzermühl hydropower plant in Laakirchen dates back to 1880. It’s a power plant with a long history which has been regularly modernised, expanded, and adapted over the decades of its existence. Most recently, four Francis turbines have been installed, which supply around 16.5 GWh of electricity in a normal year. The plant had already been serving Laakirchen Papier AG for many years, enabling the company to cover part of its own electricity requirements. In 2011, in the course of the required construction of a fish ladder, the company commissioned the renowned engineering company BHM INGENIEURE to draw up a rehabilitation concept in which different variants were examined. At the end of the evaluations, however, the result was not a rehabilitation concept, but a concept for a new replacement building. Christoph Heinzel, managing director of Kraftwerk Laakirchen GmbH, comments “None of the proposed rehabilitation options promised a sustainable solution. That’s why we decided to build a replacement.” Christian Hufnagel, project manager at Kraftwerk Laakirchen GmbH, adds “Rehabilitation of the old power station would not have been economically feasible. Moreover, the old weir with its wooden superstructure would definitely not have been approved in future water rights negotiations.”

MODEL FOR UNDERWATER DEEPENING OPTIMISED FOR AQUATIC ECOLOGY
With the replacement of the Danzermühl power plant, it should be possible to achieve several advantages at once. Not only was there the prospect of an immense increase in electricity yield, but the habitat of fish and water organisms in the Traun reservoir area was also to be improved by merging the two existing weirs. There was also a marked improvement in flood protection. In the end, by removing the Kohlwehr weir, which was located about 700 m downstream, an obstacle that had previously been impassable for aquatic life was removed from the course of the river and the free flow of the Traun was extended. The bottom sill has been broken off and a deepening of the riverbed has been carried out up to the power station,” explains Gerhard Schönhart, chief planner of BHM INGENIEURE, who adds “To this end, a terrain model was even created for the underwater deepening, which was optimised in terms of aquatic ecology. Areas with predatory trees, deadwood zones and special shallow water zones were created. It was also important to us that we leave almost all the material removed during the underwater deepening in the river bed.” A fish ladder in the form of a vertical slot pass was installed at the new weir, and an additional fish ladder was integrated into the system.

IMPROVED FLOOD PROTECTION
Due to the elimination of the old weir system and the lowering of the weir sill, water drainage has also been made easier in the event of flooding. The new, fully automatically controlled weir system also plays an important role in this. “Today even smaller floods can be controlled very well. The power plant can easily drain a 100-year flood,” explains Gerhard Schönhart.
The weir system consists of two weir sections with flap gates and a lower outlet section equipped with a segmental gate with top flap. A fine horizontal screen with a total screen area of 240 m² was installed in front of the inlet of the works water. The entire hydraulic steel construction was built by Braun Maschinenfabrik. To protect the lateral seals from icing up at low temperatures, the side plates were equipped with self-regulating heating rods. The weir flaps are moved individually by a hydraulic lifting cylinder mounted on the side of the structure. A trash rack cleaning machine with hydraulic drive is used to remove debris from the horizontal protective rack. This is completed by a hydraulic crane arm including a polyp grab with which bulky debris can be removed from the intake area with manual operation.

SPEEDY PROJECT IMPLEMENTATION
Although the construction project was subject to EIA, it was implemented quickly. After the project was submitted towards the end of 2015, the necessary approvals were obtained after just over a year. Construction was able to begin in spring of 2017. By autumn, the construction work had progressed to the point that the pre-assembly of the turbines could begin. Two Kaplan bulb turbines are being used – they are practically predestined for these conditions. This design with axial flow offers several advantages: Losses are kept to a minimum by the almost straight inflow. The overall efficiency is very high over a very wide operating range, even at partial load. The arrangement of the turbine and generator on a shaft with only two bearing points means that the machine can be constructed to be extremely compact. This also means that the surrounding structure requires less space. The majority of the heat produced by the generator during operation is discharged directly into the process water via the surface of the housing around which it flows. The topic of sustainability also played a central role here. Therefore oil-free runners were ordered. This means that there is no lubricant that could leak into the water in the event of an incident. The impeller, impeller ring, and guide vanes are made of stainless steel, which of course increases their durability. The shaft seal concept was also influenced by the principle of sustainability: at the request of the operator, a seal water supply was installed to keep the process water away from the seal. Furthermore, there are precautions in place for early detection of the early signs of wear.

MACHINES MEET EXPECTATIONS
In concrete terms, the two identical turbines with their 4-bladed runners are designed for a gross head of 9.34 m and a flow rate of 60 m3/s each. Each of them achieves a rated output of 5,017 kW – triple that of the old electrical equipment. They drive the generator rotor, which is directly connected to the turbine shaft, at a rotational speed of 187.50 rpm. The generators deliver a rated output of 5,768 kVA at a rated voltage of 10,000 V.
In mid-April 2019 the time had finally come: the reservoir area was flooded and the water level reached the prescribed level. This enabled the machines to be turned on with the water of the Traun for the first time. One month later, in mid-May, the second machine unit was also put into operation. “The work went perfectly according to plan: both machines went into operation on schedule, and the first months of operation confirmed the first good impression,” says Gerhard Schönhart from BHM INGENIEURE.

PAPER MILL USES OWN RESOURCES
The operating company heinzelenergy, a subsidiary of the Heinzel Group, has invested around EUR 38.5 million in the replacement construction of the Danzermühl power plant. In the end, all of the planned objectives were achieved – from ecological improvement and improved flood protection to an increase in electricity yield. “Ecological paper production is firmly anchored in the corporate philosophy at Laakirchen Papier. By increasing our own energy production within the Heinzel Group we can now significantly reduce the share of external electricity from the public grid and thus make a positive contribution to achieving Austria’s climate targets,” emphasises Thomas Welt, CEO of Laakirchen Papier AG. All in all, the result today is a massive increase in yield, namely by 125 percent to around 43 GWh in a normal year. This enables the paper mill to cover around 10 percent of its own requirements.