Denmark-based Krøll Cranes manufactures the world's biggest tower cranes, up to 25,000 tonne-metres. As a custom crane builder, Krøll provides tower crane lifting solutions for the specialised segments of shipbuilding, conventional and nuclear power-plant construction, bridge building, heavy construction and, now, the wind-energy sector.
Krøll Cranes has developed an innovative solution to cater for the higher erection levels and heavier nacelle weight requirements of the wind turbine construction industry. Krøll Cranes has adapted and developed its high, free-standing heavy-lifting crane
designs, and has recently supplied cranes for installation projects in Europe and Asia.
Krøll has successfully entered a market previously dominated by heavy crawler and all-terrain mobile cranes, proving that large-capacity free-standing tower cranes are an effective - and, in many cases, the only - solution for wind-turbine construction.
In conditions of restricted and limited access, small hardstands, high construction heights and large nacelle weights, Krøll cranes have provided effective, alternative solutions in conditions where crawler and mobile cranes could not be applied.
Current Krøll tower-crane models for the wind industry offer lift capacities of 95-150t and under-hook heights of 157-195m.
Multiple Model K760L Krøll cranes were used in recent projects in Thailand. 70 Vestas wind turbines reaching 140m tall were erected in 20 weeks, showing the clear advantages of the Krøll tower-crane solution. On this project, an optimised cycle time of four days an installation was achieved. This included tower crane erection, wind turbine installation and tower crane dismantling, all in single-shift operations.
Krøll's free-standing mast designs require no tie-in to the turbine tower, and impose no loads on the tower either. The resulting time savings and increased safety during installation, erection and dismantling are very significant. Designers of wind turbine towers are also not restricted by the need to accommodate the additional forces of an erection crane.
Operational functionality of the tower crane at full erection height can be maintained in wind conditions up to 20m/s, and 15m/s under full load.
Transportation logistics for Krøll cranes are similarly minimised, with the maximum load width being 3.5m; maximum weights, subject to the preferred degree of dismantling, can range from 24 to 46t.
Low initial erection heights prior to commencing self-telescoping allow for attendant service cranes for erection and dismantling to be sized in the capacity range of 200-400t, depending on the model of the Krøll crane.
With a choice of foundation configurations between embedded bolts and reusable cross bases, the application of Krøll tower cranes also adapts easily to small hardstands, thus minimising the construction and access footprint. This gives rise to very substantial savings in civil ground-works costs, as well as assistance in meeting local environmental regulations and restrictions.
Given the ease of transportation, rapid erection times, minimised service-crane requirements and full free-standing capability, the Krøll tower cranes are well suited for long-term post-construction wind-turbine service works. Returning a Krøll tower crane to site for future blade or nacelle maintenance is very cost-effective and can be achieved with minimal disturbance.