Whereas in 1980 a wind turbine only had an output of 50 kW and a rotor diameter of 15 metres, current offshore wind turbines have reached 11 MW and a rotor diameter of 200 metres – and the trend is rising.
Esbjerg (70,000 inhabitants) is the centre of Danish offshore wind power activities in the North Sea. Liebherr lattice boom cranes from the successful LR-series therefore play a major role in Esbjerg. Their task is to assemble the tower elements into a tower reaching 110 metre high. The fully wired tower is erected on a special platform by the LR 11350 and is being lifted on board by the erection vessel's on-board crane. Four wind power plants i.e. 12 rotor blades, four turbines and four towers are taken on each trip.
“We are safe up to a wind speed of 13.5 m/s,” states Thomsen. In addition to the LICCON system, which constantly monitors the wind, BMS also uses its own app, which allows those responsible to access the wind data at any time. “This is very important,” says Crane Supervisor Michael Leonard, who normally coordinates installations for BMS in Scotland. “I keep a close eye on the wind and weather and also coordinate with the installation company Fairwind and the wind turbine manufacturer - we only do the lift when we say together that it will be pulled. A tower element weighing 100 tonnes must under all circumstances not be allowed to start swinging.”
The Liebherr crawler cranes in the 1,400-tonne-class used by BMS are permanently upgraded and ballasted with 400 tonnes on the superstructure. For heavy lifts, an additional 260 tonnes of suspended ballast is added. The lifts are complicated and often have to be carried out on special crane tracks with. These are very precisely levelled so that the LR´s centre of gravity is always perfectly positioned, which is digitally displayed to the driver in real time by the LICCON.
Michael Leonard remarks: “I know all of our Liebherr cranes because I operated them. I interpret every sound during operation and am in constant radio contact with our operators. BMS drivers check the four large LR crawler cranes daily before commissioning - fixed teams of drivers are assigned to the machines - work is carried out in two shifts of 12 hours each. Even fog, rain or darkness do not hinder the work. Cameras on the hook and at the tip of the boom give the driver a perfect view of the hook, ropes and load. Other cameras monitor the winding and unwinding of the ropes, as is usual with large LR cranes.
The fact is that the LR 11350s will reach the end of its performance in the not-too-distant future. BMS and other rental companies with a focus on the offshore wind industry are on constant dialog with Liebherr in Ehingen, because the turbines are becoming heavier, the towers higher and there is no end in sight - a spiral that, according to BMS, is closely coordinated between wind turbine manufacturers and the crane manufacturer.
One thing is certain for BMS, which operates a fleet of over 100 lattice boom crawler cranes worldwide from Taiwan to Australia, America and Arabia: “The Liebherr products are top-class machines - especially the erection and the fast dismantling and the excellent LICCON control system make our work easy” states Thomsen. Operators of the super-heavy giants work their way up at BMS from the two-axle LTM 1040-2.1 to large telescopic cranes and crawler cranes.
From February to December, the 106 wind turbines are assembled and loaded in Esbjerg - the next orders in Denmark's only North Sea port are already lined up. A power station and a large transhipment site for building materials are disappearing on the neighbouring port area - all for wind power all for BMS.
