Hot dip galvanizing

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The Rietbergwerke setting sail

The use of renewable energies is being expanded. In this area, offshore wind farms are also being used. Due to the tough conditions at high see, operating them is very challenging, however. Our container technology has the necessary know-how for being able to survive in this area.

The wind whips over the waves of the North Sea. The air is cold, with sea spray. It isn't always pleasant at high sea. Yet these conditions are good, in fact very good. Since this strong, continuous wind is what makes offshore wind farms into extremely promising providers of electricity at the time of the energy transition.

By 2050, the German Federal Government wants to reduce greenhouse gas emissions by 80 percent below the 1990 levels. Its main approach here is expanding the use of renewable energy – and with offshore wind farms, the energy yield is higher than it is inland. The European Wind Energy Association (EWEA) estimates that by 2030, up to 150 gigawatts (GW) of offshore wind power could be installed in Europe. By the end of 2015, Germany will have around 3 GW of such power on its grid.

How an offshore wind turbine works
To operate these wind farms, specialist systems are required which can handle the harsh climatic conditions and protect the environment at the same time. Our container technology division in Rietberg has designed innovative containers for the company Adwen, which operates the Borkum and Global Tech I wind farms in the North Sea with 120 type AD5-116 turbines. These turbines are suitable for the transportation and refilling of fresh gear oil and offer decisive advantages.

To recognize the special attributes of our Quadro C 700 it is necessary to know how these offshore wind turbines are built. The main components are the tower, the nacelle, the rotor blades, the gear unit and the generator. The nacelle is attached to the tower and contains the gear unit and the generator. The gear unit transforms the slow turning of the rotor into a number of revolutions that is adapted to the generator. "The generator converts the rotary motion of the aerodynamically shaped rotor blades into electricity. Basically, it is similar to a bicycle dynamo, only that the turbine uses wind rather than muscle power." explains Peter Rogall, Service Support Mechanical at Adwen.

The efficiency of this gear unit is very high. Since the transmitted power with large wind turbines is enormous, the arising heat losses have to be discharged. Therefore, the gear oil is cooled in the so-called oil-water and/or oil-air heat exchangers, and the heat is emitted outwards.

"With its 700 litre capacity, the new specialist tank is just the right size for us: The crane capacity is not overloaded, but we can nevertheless take up enough oil to carry out the complete replacement in the nacelle."

Gear-unit operates with specialist oil
The oil has a similar consistency to honey. The colder it is, the thicker it is, and the temperatures outside in the North Sea are naturally rather low. This requires a particularly powerful pump, which does its duty reliably, even in harsh environments. In addition, the oil has to be very pure, since impurities would ultimately harm the gear unit, which would lead to output losses and high costs due to the damage. The oil contains special so-called additives, which are responsible for the lubrication of the gear unit. Over time, these are used up, which is why the oil must be regularly changed at specific maintenance intervals.

What sounds to a layman like a simple oil change, is actually a real challenge at high sea because of the special climate conditions, the heave of the sea and the strict environmental regulations. The crew, which must naturally also carry out other tasks during the deployment, will spend around a week at sea on assignments of this kind. If the waves are too choppy, for example, the crew will have to spend a day at sea waiting for the conditions to improve. The tank stays chained to the deck until the actual exchange can take place. "The Rietbergwerke have designed and built special containers for us that exactly meet with our requirements." explains Rogall. These are used after the old oil has been disposed of. In the future, Rietberg containers will also be used here with similar devices, although ones which are specially equipped for pumping the oil out.

Firstly, with a crane, the tank is moved from the ship to the external platform of the wind power plant approximately 25 meters above sea level. The employees climb up to the nacelle on site. They then open a hatch at the bottom through which the new oil tank is then lifted onto the nacelle platform with the help of the nacelle crane – at heights of 80 meters and more." explains Rogall. The actual refilling then begins. Once all of the oil has been pumped into the turbine, the container is returned to the external platform and then lowered back to the ship.

"Our steel container is specially coated on its exterior, and therefore protected very well against corrosion, despite the harsh climatic conditions at sea."

Efficiency and reliability are important
The accommodation of the bulky pump with its extra-large suction connection was especially difficult during the construction. However, the spacious stowage box of the series was sufficient to accommodate everything safely. The pump has optimized connections, so that its output can be fully utilized. Because of the crane capacity, it was important that the tank wasn't too big. But it was also important that it wasn't too small either, so that sufficient oil for the gearbox can be transported into the nacelle. Of the various available sizes, a container with a total weight of less than one tonne was ultimately chosen. The new container has enabled Adwen to achieve a much more efficient working sequence, because the offshore experts no longer have to complete the arduous task of pumping the fresh oil on site into small individual containers to take it up to the nacelle – they can simply use the container for this task instead. In this way, several work steps are combined and a lot of time is saved.

"Our Quadro-C 700 holds about 670 litres and is made of steel. The sturdy crane lugs mean it is possible to move the tank by crane when it is full – which is the safest way to reach the nacelles of the turbines at sea." reports Guido Röttgers from the Rietbergwerke sales team. The container is also double-walled, with an energy-independent vacuum leak monitoring system on both walls. This means that it can be stored without additional collecting troughs, even in a water conservation area. Furthermore, the penetration of water in the tank is effectively prevented, which in turn ensures the purity of the oil. The tanks of the Quadro series are approved for an unlimited period as a transport container (IBC) for the transport of dangerous goods at sea (IMDG), by road (ADR), railway (RID) and inland waterways (ADN). In addition, they have technical approval for the storage of hazardous materials from the German Institute for Building Technology.

A tank that survives in tough conditions
It was also important for Adwen for the tank to be very sturdy. It has been specially coated on its outside, which ensures long-term protection against corrosion, even during storms, vibrations and contact with salty water. This tank can therefore cope with the harsh climate at sea without any problems. "We also offer additional protection for our customers: Yellow bumpers encase the tank and prevent the tower of the wind turbine getting damaged when the tank is lifted up." highlights Röttgers. "If the external shell were to be damaged during this task, the salty seawater would cause corrosion very quickly. And it would be difficult and very expensive to have to paint the tower at sea."

In addition, the container is not only equipped with a particularly strong pump, but also with a special heating system. The warmer the oil is, the less viscous it is – which speeds up the refuelling process. True to the well-known phrase: time is money. Since the oil should not be heated too much, however, a powerful heating system has been installed, in which the energy for the heating is limited to the extent that the oil is not damaged.

The oil container was not ordered in the usual hot dip galvanized version which is normal with mobile tanks, because the additives in the oil can react with the zinc.

For supplying the diesel at sea, Adwen ordered a standard diesel tank, which was galvanized in our galvanizing plant in Rietberg. It is well equipped for use at sea by nature, and has been used in its galvanized version for decades at sea.

In addition to these offshore tanks, the Rietbergwerke build a variety of vessels for the purposes of supply and disposal. The provision of emergency generators both in and on wind turbines is also a frequent requirement, for which specially customized systems in a wide range of sizes are available. For supplying oil to engines, the Rietbergwerke are the only company to offer tanks which can be used with engine oil at up to 95° Celsius, for example. These tanks help biogas plants to last longer, for instance, and can even make the stoppages for oil changes unnecessary. For the area of disposal, in turn, we also have a variety of concepts for liquids that are hazardous to water and flammable in our product range. Moreover, the Rietbergwerke also specializes on offering tanks for mobile and stationary refuelling with diesel, petrol and AdBlue. When equipping the tanks, we focus entirely on the individual needs of our customers. Thanks to our in-house hot dip galvanizing, our containers are way ahead in terms of their robustness and durability.

Further references of the Seppeler Group

Bilster Berg Drive Resort

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