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A lifting revolution: Wessel Helmens on Mammoet’s wind turbine cranes

PMV Middle East catches up with Wessel Helmens, Mammoet’s director of innovations, to discuss the heavy lifter’s radical new proposal for wind turbine work

The first of Mammoet’s new concepts, the WTA 250, or ‘Wind Turbine Assembly’ crane, can lift 250 tonnes and is being developed in close cooperation with MECAL.
The first of Mammoet’s new concepts, the WTA 250, or ‘Wind Turbine Assembly’ crane, can lift 250 tonnes and is being developed in close cooperation with MECAL.
The logistics of bringing the wind turbine components to site remain the same. Here, Mammoet delivers the tallest wind turbine in the world, at 234m, in Denmark.
The logistics of bringing the wind turbine components to site remain the same. Here, Mammoet delivers the tallest wind turbine in the world, at 234m, in Denmark.

The heavy lifting industry is a can-do business environment where work ultimately go to those operators that demonstrate that they have the ingenuity necessary to solve any problem.

And when a challenge arises that is beyond the capacities of current lifting equipment, there’s no quitting; it’s just back to the drawing board to build a bigger and better machine.

The Netherlands-based Mammoet is one such heavy lifting and transportation company whose impressive exploits around the world are testament to this skill set. Through trial and error, the firm’s apparent knack for coming up with the lifting solutions for the most unconventional and challenging projects have positioned it as a global leader in the industry.

The company’s latest and most extravagant project was conducted last year, and saw the firm lift, skid and install a 36,200-tonne arched shelter over the Chernobyl Nuclear Plant site. Neither was that the first nuclear clean-up for Mammoet, which also raised Russian nuclear submarine, the Kursk, from the seabed in 2001.

In 2017, however, Mammoet’s sights are trained on a more conventional challenge: wind turbine erection — but true to form, the company is proposing two solutions for assembly and maintenance that are just as innovative in their design and hold potentially momentous implications for wind energy.

The first, the WTA 250, is designed for assembly operations, and will climb wind turbines using a guide rail built into the mast structure, while the second, the WTM 100, is designed for maintenance operations, and will use hoists eyes — again built into the mast structure — to pull itself up to a turbine’s hub height to deliver new parts to the nacelle.

Both will use the mast of a wind turbine as their primary support, which in turn allows them to lift and lower heavy components to the height of a wind turbine’s hub, or nacelle, with much greater efficiency than a conventional lattice boom crawler or mobile crane setup.

The development work is being led by Wessel Helmens, the company’s director of innovations and a veteran of the offshore and heavy lifting industries. He has two decades of experience with Mammoet, and it began with the Kursk.

The concept

He tells PMV Middle East that the idea for such a concept has been a long time coming: “We started on this idea in 1996. It came to mind because you’re building a tower, and then beside that tower you’re erecting a separate crane — so instead of doing that, you could also use the tower to climb it.  At that time, the towers were only 70m or 80m high — so not as high — and the operations were still possible with existing cranes. It was therefore never a goer, and we moved on to other opportunities.

“But what you now see in the wind industry is that that the structures are going higher and higher, and the cranes that are necessary to reach the nacelles are getting bigger and bigger, — to the point where it is no longer logical to carry out lifting operations from the ground.”

Helmens highlights how, above the 200m point in particular, the feasibility of wind turbine operation drops off dramatically — not due to technical limitations, but due to the cost and risk factors involved.

He notes: “The plans for 200m turbines are on the design table, and they will go higher and with even bigger turbines on top and then there’s a huge cost impact, because you need very big cranes with very long booms.”

And then there’s the time factor, he notes, because larger cranes have longer setup times, and once a lifting operation is completed, take longer to dismantle again — “so you’re losing a lot of time there,” he adds.

Meanwhile, during the operation itself, larger cranes have larger wind profiles, produce a greater sail effect and therefore present a greater level of risk during windy conditions.

Given that wind farms are invariably situated in windy locations with high average wind speeds, larger cranes as a consequence have narrower windows of operation — presenting a two-fold challenge for the industry given both the rising scale and number of wind turbines.

These problems come to a head with the lifting of the rotor blades, as Helmens explains: “The rotor blades are always a critical lift: the weight is not very high, but they’re a wind catcher like the sail of a ship: you always have to be very careful that the rotor blade does not take the whole crane with it. With our cranes you are more in control of the load, since the cranes are always positioned where you have to install something — and if the structure is moving in the wind, you’re moving with it.

“It will also allow our cranes to handle more load and to go higher. By virtue of being attached to the tower, the lifting height of our crane will be almost unlimited, and it will also for sure be safer to operate. They will also be cheaper to build and have a shorter erection time — and so have better workability.”

In terms of the capacity of Mammoet’s first new concepts, the WTA 250, or ‘Wind Turbine Assembly’ crane, can lift 250 tonnes and is being developed in close cooperation with MECAL, another Netherlands-based firm that specialises in wind turbine engineering.

MECAL is working on the design for concrete masts that will incorporate the guide rail that the WTA crane needs to climb the structure.

The methodology

After the initial placement of the base section of a mast, the WTA 250 is installed and uses the base section as a support to place the second section, before sliding up the guide rail on to the second section for the lifting of the third section, and so on. This continues until the unit reaches the top of the mast, from where it can install the nacelle and rotor blades.

Once construction has been completed, the guiderail can either be removed, or remain in place to facilitate easy access in the case of future maintenance operations.

The second concept, the WTM 100, or ‘Wind Turbine Maintenance’ crane, has a capacity of 100 tonnes, but operates in quite a different manner. It is being designed to attach to hoisting eyes at the top of a turbine mast that it then uses to pull itself up into a lifting position. Once at height, the WTM 100 has a set of claw-like braces that it fastens around the tower to secure itself in a working position.

Current wind turbines do not have hoisting eyes, but Mammoet and MECAL are similarly working on incorporating these fixed positions into turbine masts in a way that could see them included as standard in future designs.

“It’s a shame,” Helmens comments, that there are no hoists eyes or fastening points on existing turbines, but the company is also working on a workaround for previous designs.

He adds: “In maintenance scenarios, the current methodology is even worse. If you have to replace the gearbox, you have erect a whole crane on site for a simple lift of 35 tonnes or so, and then break down the crane — so the huge mobilisation and demobilisation is huge.”

The smaller size of the new concepts also yields further advantages when it comes to transportation, as Helmens notes: “Both cranes are compact: the WTM can easily fit into two standard-sized containers, and the WTA only needs two transport trailers to be moved on site. This makes them much more efficient than conventional alternatives.

“More importantly, both cranes eliminate the height restrictions for turbines and render both the assembly and replacement process faster and more cost-effective.”

Mammoet’s aim with the WTA 250 machines is to be able to carry out the entire turbine erection operation — including installation, assembly, and de-installation — within the space of two days. With the WTM, meanwhile, a replacement part could be delivered and installed in the nacelle within a day. In contrast, a conventional assembly can go on for weeks.

The benefits continue, as Helmens notes: “The tower-based design also puts the crane and the operator closer to the work area, rendering assembly and maintenance both safer and easier.”

He adds that, “because the cranes are attached to the tower, they have no footprint” — making the need for additional ground reinforcements virtually redundant.

So, he concludes: “You win on erecting time and your workability window is better. It requires no or very little ground preparation. There is also none of the risk associated with travelling a crawler crane from one site to another, and the total operational cost picture is that you save a lot of money. So there are a lot of pros, and we don’t see that many cons.”

The reception

Not everybody is going to be happy about this. Mammoet’s plans make grim reading for the major crane manufacturers that have, up until now, only had to compete with like product in the segment. In recent months, this played out with both Terex Cranes and Liebherr launching similar extension kits for their most popular crawler cranes for wind turbine erection.

Helmens notes: “These companies are not interested in machines like ours, because they would be killing their own market — and so they would never come with ideas like ours. It has to come from a company like Mammoet, because we are a crane company, of course, but we are not building cranes for a third party; we are a project company, and we are doing the execution of the job, so we are users.”

Global wind energy developers, are also sitting up and paying attention, and Mammoet is already in advanced discussions with two of the largest companies in the business, with a view to rolling out the product in a year’s time.

Helmens notes: “We are in contact with a lot of builders, and they are very interested. Worldwide, there has been a lot of reaction, and it all depends on that — maybe we will have to speed it up. We will see.”

In the Middle East, where installed capacity is still modest — but where many countries have ambitious plans — Mammoet’s concept offers the possibility of rapidly deploying new wind farms in a much more cost efficient and safer way than was previously possible.

Helmens adds: “We have offices all over the globe, and we are looking at markets and our contacts worldwide, especially in those regions where they don’t have a lot of those cranes.

Beyond assembly, the wind industry is very conscious of the fact that many wind turbines are now ageing, as Helmens notes: “There are going to be more and more windmills requiring maintenance, and this is just starting. Over the last 20 years a lot of windmills have been built, and the first generation of windmills, especially, are not as good as today’s — so there will be a lot of additional costs coming.”

He adds that there are other systems in the market for maintenance operations that take a few days to set up, but they have limitations and still do not represent a good solution.

The company is also working on 250-tonne and 40-tonne maintenance cranes, and bigger assembly cranes. But for now, Mammoet has set its flag, and in a year we will see the results.

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