Off the Dutch coast an exciting test will soon commence that can bring a small revolution in the erection of offshore wind farms. Wind turbines need to be secured solidly in the seabed to prevent them from keeling over when exposed to the first light breeze. Many solutions have been developed for this purpose but one of the most common methods is driving down a large foundation pipe or pile into the seabed, add a transition piece and finally install the wind turbine generator at the very top, often more than 100 metres above the water surface.
The conventional piling operation causes underwater noise and exerts quite a large amount of stress on the foundation steel, but Dutch technology company Fistuca BV has now developed a novel type of hammer that uses water as the driving medium.
So far, the company has conducted successful small-scale tests onshore, for example on a mooring pile in a Dutch harbour, but during the summer of 2018 it takes the tests to a new level off the Dutch coast in a full-scale monopile driving test. Vattenfall sees a potential in the method and has joined a consortium of private and public stakeholders that will invest 3.2 million euro in the project and provide technical support, administration, hammer, monopile, installation vessels etc.
QUIETER, GENTLER AND MORE ENERGETIC
The system comprises a water tank and an open combustion chamber. The energy for driving the pile into the seabed is created with gas combustion that in a first blow drives the pile down and at the same time pushes a water column inside the tank upwards. As the water drops back to the bottom of the water tank, it decelerates and transfers the energy into the pile, driving it further down into the seabed. Due to the properties of water, this deceleration occurs over a longer time period than a conventional hydraulic hammer, providing a quieter, gentler but more energetic blow. According to Fistuca that reduces the number of hammering operations compared to conventional pile driving methods.
- Gas is fed into combustion chamber
- Gas combustion creates first blow and water flows out of the combustion chamber
- Combustion continues and water column moves up
- Water column continues to move upward
- Water column falls back and delivers second blow
- Exhaust gas is released through exhaust valve
Reducing noise and fatigue
The Blue Hammer is predicted to reduce underwater noise levels by up 20 dB and potentially reduce the fatigue damage on the pile from the hammering by up to 90 per cent, which would potentially make it possible to open up for “transition piece free” designs and pre-weld boat landing, ladders, internal platforms and other auxiliary parts to the monopile prior to the installation at the offshore wind farm.
Rene Schuster, project manager civil works and Vattenfall representative at the blue piling consortium, explains: “This is an extremely interesting project that could bring us much further in development with monopiles. We know how to work with monopiles, and instead of having to switch to more complex foundation structures as turbines become larger, this technology could push the boundaries for using monopiles. We also hope to save offshore time and thus money, if we can pre-weld much of the extra facilities on the monopiles and therefore avoid the second lift to install a transition piece”.
According to Schuster, it may furthermore be possible to eliminate the need for an additional vessel to install and operate the noise reducing bubble curtain, and fewer vessels and simpler logistics will make the whole operation safer and more environmentally friendly.
Vattenfall’s contribution to the consortium is driven by a wish to help new technologies into the market and secure a continuous development in the wind sector. Through the consortium, Vattenfall will also get exclusive insight into the data and the results and get access to participate in the tests.
Gunnar Groebler, Head of Business Area Wind, is also excited about the project: “The project offers potential improvements in three important areas – reduced costs, reduced environmental impact and increased technical knowhow. Based on 15 years’ experience and knowledge of developing, constructing and operating offshore wind in close cooperation with our suppliers, Vattenfall is already a cost leader in this field. We have proven this by three successful tenders in the past two years, but our commitment to be at the leading edge of technology and be more cost efficient and environmentally friendly is a continuous journey, and the BLUE piling technology could take us further along that road”.