MCE HAS COMPLETED ONE OF THE MOST DIFFICULT ORDERS IN ITS HISTORY — THE REHABILITATION OF THE CLEUSON-DIXENCE HYDROELECTRIC POWER STATION IN SWITZERLAND. THE COMPANY HAS BEEN PART OF THE BILFINGER BERGER GROUP SINCE 2009.
The road gets narrower and narrower, winding ever upward in steep curves. There are no guardrails. “Just don’t look down,” Walter Pölz grins. He keeps the Toyota 4 x 4 headed for the top, slithers in the snow, drives on. And stops. “We’re here.” He points up the slope: “Just over there, that’s where the leak occurred.” For a moment all is silent, the snow swallows every sound. The city of Sion and the river Rhône are far down in the valley.
PRESSURE SHAFT INSIDE THE MOUNTAIN
It was inside this mountain in December 2000 that a steel pipe more than three meters in diameter ruptured 70 meters from the surface. It carried water from the Lac des Dix reservoir nearly 17 kilometers away at an altitude of 2,300 meters or more down to the Bieudron power station in the valley, one of the four stations that comprise the Cleuson- Dixence hydroelectric complex.
For the first 16 kilometers, the water passes through a horizontal tunnel. Then the shaft dips down, dropping at an angle of 34 degrees to emerge at the Bieudron station at a height of just 481 meters. Inside this steeply sloping, 4.3-kilometer pressure shaft, the water picks up the speed required to drive Bieudron’s three mighty turbines. For nine years the turbines stood still because the repairs needed to the shaft were so extensive. The power station finally reopened in January 2010.
“NO OTHER COMPANY IN EUROPE COULD DO THAT”
Walter Pölz was in charge of the works to repair Bieudron’s pressure pipes. The job was so demanding that MCE was the only company that could meet the technical requirements for the project. “The client wanted the new pipes to be manufactured and erected by one and the same company. We were the only company in Europe capable of doing that. The engineering came from Andritz Hydro.”
The 63-year-old Pölz is an unassuming man. He never forgets to make the point that it was teamwork that made the job a success. In the course of the project he had about 150 men under his command. Workers constantly had to be replaced. “It wasn’t everyone’s cup of tea,” says Pölz.
New pipes had to be laid inside the old ones. The workers descended into the depths in special cars lowered down the angled pressure shaft on a steel cable. “Down in the pipe it was hot and the air was bad. We also had to avoid a chimney effect and stop the draft so conditions would be right for the welds,” Pölz explains.
THE TIME PRESSURE WAS INCREDIBLE
MCE was awarded the contract in October 2006: the largest and most extensive hydroelectric project in the company’s history. The repair work in Sion had to begin just six months later. During this time all of the erection sequences had to be planned down to the last detail, while at the same time the manufacture of more than 400 steel pipes began in the Austrian towns of Wels and Linz.
The pipes, each up to twelve meters long and between two and a half and three meters in diameter, were brought by train from Austria to Switzerland. In Sion they were then offloaded onto semi-trailers and hauled up to the site. “It was an epic journey just getting the pipes up the mountain,” Walter Pölz recalls. “The trucks had to come up here, even in winter, carrying 60 tonnes of steel pipe, just imagine it,” he continues, pointing down the narrow road. “And the pipe sections needed at the very top were brought up by an aerial ropeway.”
To reach the more than four-kilometer long pressure shaft, four access tunnels were blasted into the mountain. Work proceeded at all four sites at the same time. The semitrailers had to reverse into the tunnels. The heavy steel pipes were then transferred onto wagons that took them by rail deeper into the mountain where cranes were waiting to lift and tilt them. Then, little by little, they were winched inside the old pipes and lowered down into the depths, ready to be welded in place. “That was precision work. The new pipes are only 30 centimeters smaller in diameter than the old ones.” After welding, the voids were filled with concrete.
“Not only was it a masterpiece of logistics just to move 400 steel pipes up the mountain,” says Walter Pölz. “We also had to design special equipment to install the pipes once they had arrived.” For example, MCE developed a jig that used hydraulic cylinders to precisely center the pipes as they were lowered down the existing shaft.
TEN DAYS FOR ONE PIPE
“Sometimes it could take days before a pipe was in the right position,” Pölz continues. “The very first pipe that had to be lowered to a depth of almost a kilometer took us nearly ten days. It was only twelve hours before it reached the bottom, but the welding went on for nine days.“ The deeper down a pipe is located, the greater the pressure exerted on it by the water. For this reason the pipes right at the bottom are eighty millimeters thick, and welding takes a proportionately long time. “By lowering one tube down, welding it, then lowering the next one, we worked our way from bottom to top from all four access tunnels at the same time.”
A UNIQUE FEAT OF ENGINEERING
And then there was the “bend” in the shaft: When the original pipe burst the rock was so badly damaged that a bypass had to be built. This reaches vertically downward for 73 meters, then turns at right angles and runs for 90 meters horizontally until it meets the old pressure shaft. MCE was faced with the difficult task of routing the pressure pipes round the bend in the bypass. Once again special cranes were developed with which to move the tonnes of pipe and join them together in a perfect fit. “That was a unique feat of engineering; nothing like that had ever been done before,” says Pölz. There were nights when he couldn’t sleep a wink for worrying about the tight schedule, the technical challenges and the dangers to his men manipulating massive loads in the dark confines of the shaft. “Especially on sites like this, men can be very badly injured; that worried me a lot. Thank goodness everyone was very careful and nothing happened,” he continues.
A POWER STATION WITH THREE WORLD RECORDS
Since January 2010 the water from the Lac des Dix has once again been flowing through the tunnels and pipes. It takes 50 minutes to travel almost 17 kilometers from the dam wall to the Bieudron power station—a huge cavern inside the mountain, larger than the nave of the Cologne cathedral. The water pours out of the pressure pipe into the blades of the mighty Pelton turbines at a rate of 75 cubic meters per second.
The power station holds three world records: for the 1,883 meter fall of the water, for the 423 megawatt output of each turbine and for the 35.7 megavolt amperes at each pole of the alternating current generators. “We gave Bieudron its water back; without us nothing here would be working,” says Walter Pölz, gazing with satisfaction at the powerful generators. “That was by far the most difficult project in my entire career.”
ADDED MUSCLE FOR THE SERVICES BUSINESS - MCE INTEGRATED INTO BILFINGER BERGER
The Cleuson-Dixence contract is a high-profile project for industrial and power services provider MCE, which was acquired by Bilfinger Berger in 2009. Of MCE’s total output volume, € 730 million was allocated to the Industrial Services division and around € 130 million to Power Services. Bilfinger Berger is broadening the scope of its services for the energy and process industries and consolidating its presence in Austria and Germany in particular. The acquisition was financed through a capital increase. (si)
HYDROELECTRICITY - ENDLESS ENERGY — BUT NOT IN GERMANY
Hydroelectric power supplies 17 percent of the world’s electricity needs, making it the most important source of renewable energy. Advantages include the fact that water can be stored until it is needed, energy is generated with no harmful emissions, the technology requires low maintenance and the efficiency exceeds 90 percent.
And yet hydroelectricity accounts for only 4 percent of the power generated in Germany, and the proportion is unlikely to increase. Why? Because nearly all suitable waterways have been exploited. In Austria and Switzerland the geography is more generous. In these countries 50 to 60 percent of the electricity is generated by water. (si)
Text: Oliver Link, Photos: Eric Vazzoler, MCE, Essencedesign.com
Bilfinger Berger Magazine 1/2010
Walter Pölz tells about the most difficult project he's ever had.
