Around 1.75 billion euros for the ultimate power station

Mammoth project in the heart of the Alps: a new pumped storage facility is being built at an altitude of 1,700 metres

700,000 tons of blasted rock at an altitude of 1,700 metres in the heart of the Swiss Alps – the mammoth “Linthal 2015” project is by far the largest building project for Kraftwerke Linth-Limmern. The objective is to construct a pumped storage power station for the production of electricity. To achieve this, two underground caverns together with an extensive network of access tunnels and pressure shafts have been excavated for two years at a depth of up to 600 metres inside the mountain. 5.5 kilometres of conveyor belts are currently being used to take away the material. As dust emissions must be kept as low as possible, the company in charge is using special conveyor belt scrapers, which remove virtually 100% of the material from the belt thanks to the patented Twist-Swing® function and the dust load is thus reduced to a minimum.

Ten years ago the PM-10 standard was defined as a directive, which specifies the safety limits for inhaled dust and since then it has had to be taken into account in addition to the hitherto effective regulations. When it comes to conveying huge volumes of excavated material, as with the “Linthal 2015” project, the suppression of dust emissions plays an important role – especially as the workers are operating at a depth of up to 600 metres inside the mountain. The conveyor belts are therefore cleaned during ongoing operation around the clock with the help of the scrapers. This prevents material getting stuck to the belt and gradually crumbling off. In this case, the lost material would have to be removed manually with shovels.

Moreover, insufficiently cleaned belts lead to the soiling of the return rollers, which as a result can suffer damage in the long run and may have to be replaced. “If the scraping efficiency is poor, we have to clean the belts with water, but this makes the conveyed material muddy and thus difficult to transport,” explains Ernst Kuster, Project Manager at Marti Tunnelbau AG, which supplies the conveyor belts. Furthermore, self-extinguishing conveyor belts had to be used, in accordance with the regulations, where the rubber material is certainly less robust. However, in order to maximise their service life, good cleaning efficiency is essential.

Scrapers for reversible belt systems disengage automatically

One challenge with the “Linthal 2015” project was the restricted space and a gradient of 25 degrees, which made it particularly difficult to install the entire conveyor system. “To be able to install the belt scrapers in the confined space, we developed a smaller version on-site,” explains André Hanke, Sales Manager for Conveying Technology at conveying technology specialists Schulte Strathaus.

The segmented scrapers are used as both primary and secondary scrapers. Polyurethane feet with special rotatable mounted scrapers made of stainless steel with a carbide insert, which are fitted in the segment shaft, are used to remove the conveyed material.

The individual segments overlap so that none of the conveyed material can slip through. This ensures optimum cleaning of the belt.

The special shape and geometry of the polyurethane feet allow a high level of flexibility. This is a prerequisite for the patented Twist-Swing® function. The individual segments adapt excellently to the conveyor belt under the freely configurable contact pressure and swing with the movements of the belt. This not only achieves the best possible cleaning results, it also reduces wear and protects the belt. “Strip scrapers or inflexible scrapers that are usually used cannot cope with the unevenness of the belt and therefore always allow a certain amount of the conveyed material to fall through,” explains Hanke.

On account of the limited space at the “Linthal 2015” project, reversible belt systems are used, where the conveying direction can be changed as needed. They required special reversible belt scrapers, which automatically disengage when the direction of the belt changes. Auxiliary blades designed for the opposite direction immediately take over their function. This allows fast changes of direction without breaking the contact between the conveyor belt and the scraper. The system engages and disengages automatically as a result of the friction between the belt and the scraper segments, i.e. without any pneumatic, hydraulic or electrical support.

As optimum scraping efficiency, long services lives and easy maintenance are essential, particularly in tunnel applications, the scraper system under the brand name “Starclean®” has now become established as the standard for the majority of large tunnel projects worldwide. For instance, the largest construction sites in London, Hong Kong, Abu Dhabi, Ecuador, Panama, Madrid and Barcelona as well as the Ceneri and Gotthard tunnels are equipped with Schulte Strathaus technology.

Environmental protection: excavated material is recycled

Ever since the Gotthardt project, the conservation of natural resources has played an important role in Switzerland. Therefore, conservation and usage plans were drawn up in advance of the “Linthal 2015” project and environmental measures were defined in conjunction with representatives from the authorities and nature conservation organisations. These also include the recycling of the blasted raw material. As around 90% of the conveyed medium is scraped from the belt, the bulk of the excavated material can be reused. “80% of the blasted rock is further processed into concrete,” states Kuster. First the material is transported to a gravel works and processed there before it is sent to a nearby concrete plant.

Pumped storage power station secures peak loads and guarantees a reliable supply of electricity

It is estimated that the entire project will run for seven years. The first group of machines should be connected to the grid by the end of 2015. The objective is to optimise the existing plants and increase the current output of 480 MW to 1,480 MW with the new pumped storage power station. To do this, water will be flushed from the higher lying Muttsee Lake into a pressure system and drives the turbine, which in turn runs the motor generator. The electricity generated in the process is fed into the grid. The water from the turbine reaches the lower lying Limmernsee Lake, from where it is then pumped back up to the top. In this way, surplus electricity can be stored during off-peak periods and used during periods of peak consumption so that a reliable supply of electricitycan be guaranteed to meet consumer demand.

Kraftwerke Linth-Limmern AG is a partner company of the Swiss Canton of Glarus and Axpo AG. This in turn is a leading Swiss energy company that supplies electricity to around three million people. The Linth-Limmern power stations were built between 1957 and 1968 and in 2009 they were extended for the first time with a pumped storage facility. As a storage power station the company primarily covers peak loads and can therefore guarantee a reliable supply of electricity.

Marti Technik AG is part of Marti Holding AG with its headquarters in Moosseedorf in Switzerland. The company has specialised in construction logistics, formwork construction, plant engineering for the stone and quarrying industry, infrastructure plants and electrical engineering. The company is represented throughout Switzerland and also abroad.

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Schulte Strathaus GmbH & Co. KG