Krøll K1500L

Free Standing Capability

The main design difference on Krøll is that it uses steeply raised luffing jib that reduces the required overall tower height. In addition, this can be achieved with the need of a tie-back to the tower which allows the erection of a typical 170m tall 5 MW class wind turbine. This is an alternative to its another model, K1400-125 on a standard M40 tower system.

Ease of Transportation

The engineers have also found a solution to maintain the same outer dimensions of the crane tower from base to top. The M33 monoblock tower system is designed with road transportation dimensions in mind, keeping it in 3.3m x 3.3m x 7.8m.

For local transportation on a wind farm site, the A-frame can be folded back onto the machinery deck. Placing the winches inside instead on top of the platforms allows this to be possible.

For transportation on public roads, the A-frame can be removed to reduce the machinery deck weight from 82 ton to 55 ton. The removal of hoisting winch further reduces the weight of the heaviest crane component to 38 ton.

Shorter Erection Time at Cheaper Cost

Furthermore, it is also designed for fast climbing. Explained by Jorn Lorentzen, head of structural engineering department at Krøll, 7.8m long sections are optimised to reduce fewer masts to climb and bolting to be tightened, which in turn speeding up erection time. With two hydraulic rams integrated into the climbing frame, the crane can jack at a rate of one tower section per hour.

A separate winch mounted on the erection beam above the climbing frame is used to lift the tower masts into place at a possible winding speed of 15m per second. During the climbing process, the luffing jib balances the crane and inserted tower masts do not have to be bolted to the crane upper before picking up the next tower mast, saving time for each mast climb.

Re-inforcement are done only on the first four out of the twelve M33 mast sections. Outer dimensions are the same except that it is connected by eight screws instead of four per corner. With fewer connecting slug bolts, riggers are able to erect the tower in a more timely manner.

The luffing tower crane can climbing mast for erection thus greatly reduce the assist crane capacity needed for an erection. The complete upper body, with luffing jib and counterweight can be hoist as a single lift with special lugs designed on the machinery deck, eliminating the need of addition hoisting for the A-frame.

Krøll suggested using a 500-tonne capacity crane mobile crane as assist crane for the K1500L. With the complete machinery deck, including pre-assembled winches, A-frame, slewing ring support (82 ton in total), complete 70.1m boom (34 ton), it requires fewer hoisting operation for the cabin platform and counterweight blocks.

Challenges of K1500L for Wind Turbine Installation

Although luffing tower crane reduces the time for mast climbing process, there are still some challenges which the crane have to overcome. One of it was the steep boom angles during working which increases the risk of the gust of wind causing the crane to over hoist. Krøll countered this was a stiff A-frame with spring-loaded buffer system which touches the boom before reaching the minimum working radius.

With the rising of wind turbine tower, the risk of collision increases and Krøll has come out with a solution to manufacture rigid square outer section boom with wind sails to allow the 70.1m boom to be parked in a safe out of service position at 12.5m radius in adverse weather.

In addition, the crane is fitted with a proven AH Industries tagline system which two additional winches are mounted under the boom foot to guide sensitive loads like windmill blades using controlled tension.

A specially designed 16m x 16m cross base with height-adjustable cones at each corner. This cones can be adjusted to compensate of unbalanced ground that can go as much as 2% slope. Separate 150-tonne cylinders at each corner help to level the crane base. The cones sit on a 7m x 2.4m load distribution mats to spread the load-bearing to an estimated 20 ton / m2.

Krøll uses four falls reeving for all loads up to 125 ton. It can hoist up load by the 154 kW winch at 6m/min and hook without load lowering at 22m/min. Comparing with a conventional crawler crane, the luffing tower crane can hoist a turbine gondola to 179m hub height using half the time.

Milestones

Wind turbines specialist, TotalWind, has taken delivery of the first unit of K1500L. They choose the crane as it was a more economic alternative comparing the tower crane weighs 580 ton while the conventional 1200 ton capacity class crawler crane weighs more than 3 times in a full mobilisation. K1500L passed the initial field testing in a wind turbine site in Poland and was transfer to the next wind turbine site, taking only four days to dismantle, transport, re-erect and mast climbing procedure.