During a construction phase lasting around 6 months, Enns Power Station Staning was equipped with a new crane track for the portal crane above the weir system in the spring.
The renewal of the crane track corresponding to the state of the art turned out to be extremely complex owing to the lack of a weir bridge. A particular challenge involved handling the material and crane track supports, for which the existing portal crane was adapted with a special auxiliary structure, while using a load-lifting helicopter at the same time. The overall concept was developed jointly by the client with BHM INGENIEURE - Engineering & Consulting GmbH, the latter responsible for general planning.
The River Power Station Staning was constructed in the years 1941 to 1946 on the Enns river forming the border between Upper and Lower Austria. Five weir fields and a machine house extend over a length of more than 150 m. From 1983 to 1985, replacement of the impellers in the three Kaplan turbines plus renewal of the generators at the same time resulted in significantly improved efficiency. At a total flow rate of 345 m³/s and a drop height of 14.3 m, the machines installed vertically have since achieved a maximum output of 43.2 MW. The power station owned by Ennskraftwerke AG generates around 203 GWh of electricity during a normal year. To establish the best possible working conditions for future overall work, the operator commissioned a renewal of the around 36-year-old crane track system at the end of 2016.
The old crane system, consisting of steel girders located on the weir pillars above and below the water, was installed in 1981 as part of a measure to raise the water level. ‘Owing to signs of aging in the supports of the steel girders along with the outmoded structural design, we opted to provide a new crane track’, declares Project Manager at Ennskraftwerke AG, Gerhard Zarfl. The portal crane itself was left in its original state, apart from an adaptation during the conversion phase. Because the crane is only assigned the function of installing the inspection covers on the side above water, a complete renewal of the crane system would not have been expedient economically, continues Zarfl. ‘A modern structure for transporting and installing all cover parts and typically also used in the machine area, is not feasible owing to the existing facility concept at the Staning Power Station.’
The concept development together with the client and overall planning for the conversion were realised by the Linz branch of BHM INGENIEURE – Engineering & Consulting GmbH, which has already implemented several hydroelectric projects successfully for Ennskraftwerke AG. ‘The concept developed when the order was awarded in November 2016 involved using pontoons to “float” the new concrete supports along the waterway. This concept had to be rejected during the course of the tender for reasons of cost’, states BHM Project Manager Rudolf Kandler. Finally, an alternative concept was adopted in the spring of 2017, in which the construction work could be carried out with the existing infrastructure. In this solution, the portal crane was to be used by a corresponding adaptation for removing and installing the steel girders. The original concept of transporting the concrete via a pump line was also rejected. Instead, the decision was taken in favour of the solution proposed by the construction company BAYER Bauwerksinstandsetzung GmbH, to transport the old and fresh concrete entirely by air using a load-lifting helicopter.
Project implemented in 6 months
The project entered its implementation phase in July 2017 with establishment of the construction site and conversion of the portal crane. A projecting auxiliary structure was erected on both sides of the crane for this. While a hoist served for lifting the steel girders weighing several tonnes on one side, a counterweight acted as a load balance on the opposite side. Kandler stresses how the steelwork concept could be developed ready for implementation after the calculations of Linz-based civil engineer DI Matthias Parzer. Likewise, Bilfinger VAM Anlagentechnik GmbH from Upper Austria was able to prove its merit during practical implementation of the overall steel construction work. The disassembly of the disused steel girders on a weir field basis began on the Upper Austria side of the power station. Disassembly of the disused crane track was followed by removal of the old concrete base and subsequent concreting of the new support consoles on the weir pillars. ‘Transporting old and fresh concrete by helicopter worked really well during the project. We were able to realise the corresponding construction sections both rapidly and comparatively cheaply’, states Kandler. Like the dismantling of the old ones, the new girders could be reinstalled from the orographic left bank of the Enns.
All set for the next overhaul
The actual power station operation remained extensively unaffected by the renewal measures. When working on the weir fields, the weir gates were locked or blocked corresponding to the construction progress and the high water level at the plant lowered, above all for scaffolding work. After a construction phase lasting around 6 months, the renewal of the crane track could almost be completed in December 2017. Remaining work that still needs to be done, such as finalising the corrosion protection, will be carried out when the weather gets warmer in the spring. Kandler and Zarfl reiterate that the new construction of the crane track has led to a significant improvement for operation of the portal crane restored to its original state. Optimal preconditions for future overhauls of the power station are therefore in place.