A new type of environmentally friendly pile driving system for foundations that is cheaper to use than conventional hammers is being tested offshore
In March 2018, the Carbon Trust announced the launch of a demonstration project, Blue Pilot, that aims to reduce the cost of installing foundations for offshore wind turbines and reduce underwater noise during construction.
Part of the Carbon Trust’s Offshore Wind Accelerator (OWA), the Blue Pilot project will see the deployment of the Blue Hammer, a new type of pile driver developed by Fistuca BV, a Dutch technology company founded as a spin-off from Eindhoven University of Technology.
The project is estimated to enable potential lifetime savings of €33-40M (US$40-48) for a 720 MW offshore windfarm, equal to a levelised cost of energy (LCOE) reduction of €0.9-1.2/MWh.
OWA partners Eon, EnBW, Ørsted, Statoil and Vattenfall, alongside industry partners Fistuca, Van Oord, Shell and Sif are contributing €3.2M in funding to the project. Due to the project’s ability to impact the cost of offshore wind, the Netherlands Enterprise Agency (RVO) has also granted public subsidies of over €2.5M.
The Blue Hammer is predicted to reduce underwater noise levels by up to 20 dB (SEL), and potentially reduce the fatigue damage during installation on the pile by up to 90%. This could not only remove the need for underwater noise mitigation, but also enable secondary steel to be prewelded to the monopile before installation, potentially unlocking ‘transition piece free’ designs. Furthermore, by reducing the amount of time and number of operations carried out offshore, the innovative piling method would improve health and safety and result in a significantly lower installation cost.
The Blue Pilot project aims to verify these predictions through installing a full-size monopile offshore, using measurement equipment and sensors to validate the predicted noise levels and fatigue damage. The tests will take place mid-year.
In the Blue Pilot project, the new pile driver will be tested offshore at a location in Dutch waters. Sif will provide the monopile, and Van Oord will support the installation logistics. The other industry partners will provide funding and strategic advice into the project to ensure its relevance to future commercial projects.
Fistuca’s founder and managing director Jasper Winkes told OWJ “We want to help the offshore wind industry to develop environmentally friendly installation methods and reduce the cost of installing foundations. Collaboration will help make this possible.”
Statoil’s technology director for wind and low carbon solutions, Rajnish Sharma told OWJ the company wants to reduce the environmental impact and cost of offshore wind projects. “Blue piling technology has the potential to be an important contributor in this work,” he said.
The OWA’s project engineer for foundations Michael Stephenson said he believed the Blue Pilot “has real potential” to reduce the levelised cost of energy of offshore wind projects. “We are excited to support this project to validate the hammer offshore and to support the integration of industry into the project, which will be vital to its success. It is great to see the whole supply chain involved in the project and collaborating towards the common goal of continuing the cost reduction in offshore wind,” he said.
Rather than hammering a monopile into the ground, the Blue Hammer concept developed by Fistuca uses acceleration of a water column by a gas mixture to provide the driving force – a mechanism that can deliver a large amount of energy without exciting undue vibration in a monopile.
Mr Winkes explained “The combustion of a gas mixture leads to an increase in pressure. This pressure creates an upward acceleration of the water and a downward force that pushes the pile into the seabed. Another powerful downward blow is delivered to the pile when the water mass falls. After the exhaust gases have been released, the cycle is repeated.”
‘Blue piling’ has several potential advantages compared to conventional impact hammers. Firstly, the hammer produces very low levels of noise compared to conventional hammers. This means that noise reduction measures – which can add significantly to the cost of piling operations – are much less likely to be required.
Secondly, compared to the impact of a conventional hammer, the duration of the impact from the Blue Hammer is much longer, which minimises fatigue damage to the monopile. Conventional hammers exert force over a short period of time, whereas the Blue Hammer delivers a blow over a period of more than 100 milliseconds. This makes the force delivered by the system more efficient. The water-based blows ensure a gradual build-up of force on the monopile, reducing tensile stresses in the pile and reducing acceleration levels. Fewer blows and lower stress levels reduce installation fatigue.
A third and increasingly important benefit of the Blue Hammer, given the rapid growth in the size of offshore wind turbines and in their foundations, is that it can drive large-diameter piles. As highlighted above, another advantage is that the concept is compatible with having secondary attachments mounted on the monopile before pile driving is undertaken. Lower acceleration levels allow piles to be partially pre-assembled prior to piling, reducing the loads on components such as flanges.
Apart from being able to drive larger-diameter monopiles, Blue Hammer is also well suited to doing so in deeper water. It is suitable for all types of conventional piling and foundation work using jacket (pin) piles as well as so-called XL monopiles. It interfaces with the pile in the same way as conventional piling technology, so the pile itself doesn’t need to be adapted.
In the first phase of the project the ‘blow profile’ of the hammer was analysed and modelled. This input was used to model the secondary steel on the pile and the expected underwater noise emissions. The next phase saw a test pile installed. In the third phase offshore piles were installed. Measurements on the hammer and pile will validate predicted fatigue loads on primary and secondary steel and underwater noise will be monitored. The final phases of the project will see the test pile fully decommissioned using water pressure and the findings of the tests summarised in a report made available to partners.
Foundation fabricator saved
Investment has been secured for offshore fabrication firm BiFab and its yards at Methil and Burntisland in Fife and Arnish in the Western Isles, Scotland’s First Minister Nicola Sturgeon has announced.
Canadian company JV Driver, through its subsidiary DF Barnes, has acquired BiFab as part of an agreement brokered by the Scottish Government to support new opportunities at the yards for fabrication and construction in the marine, renewables and energy sector. BiFab’s track record in the offshore wind industry includes work on the Beatrice, Alpha Ventus, Gwynt y Mor and Greater Gabbard windfarms.
Mono bucket technology tested in Japan
Universal Foundation and Hitachi Zosen have teamed up to undertake a feasibility study to assess the application of mono bucket foundation technology for a Japanese offshore wind project.
The project will use experience gained from commercial projects in Europe and the US and apply it to conditions and requirements relevant to the Japanese offshore wind market.
Hitachi Zosen Co is executing the work in partnership with Kyoto University and Toyo Construction Co.
The decision to engage Universal Foundation in the feasibility study was based on a comparative assessment of various foundation types for a windfarm with 15 turbines.
In an engineering, procurement, construction and installation cost assessment the mono bucket was concluded to be the most cost-effective solution and to have the potential to reduce the time it takes to build the windfarm.