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FEATURE SPONSOR


SPOTLIGHT ON IRELAND ORMONDE OFFSHORE WIND FARM


The Ormonde Offshore Wind Farm is located 10km off Barrow-In- Furness, in the Irish Sea. The wind farm comprises 30 RePower 5MW wind turbines producing 150MW of power, and 1 substation. This is sufficient to supply the equivalent of approximately 100,000 homes per year with clean power. The turbines cover an area of 8.7km2 in total.


FOUNDATION DESCRIPTION The 31 four-legged steel jackets were secured to the sea bed by their four main legs which were inserted into pre-driven piles. To form the connection between the leg and pre-driven piles, cement grout was injected into the annulus around the pile and stab-in-leg. Each leg had a primary and secondary grout line through which grout could be pumped.


Unlike the grout hose connection system on an oil & gas jacket, the Ormonde jackets’ grout connectors were located on the jacket transition deck, which made for speedier hose connections and disconnections when moving between the installations.


The Ormonde project was the first large- scale project of its kind in Europe to use jacket-type or space-frame foundations. The choice of a particular type of foundation is normally a decision based on a number of factors surrounding the site conditions and how the entire installed system interacts with these local conditions; this is one of the reasons why in some instances it is possible for one project to have a mix of foundation types.


ADVANTAGES


One consequence of adopting a space- frame design for the foundation is that it opens up the possibility of using an Ordinary Portland type cement. The advantages of using this type of cement, apart from its lower cost per tonne than the materials normally associated with offshore wind, is in its ability to be delivered and used offshore in silos. This delivery option will increase the efficiency of the offshore installation process through both faster mixing, and enabling the grouting vessel to stay on-site longer by storing more material. This is seen by FoundOcean, and generally accepted by the industry, as being a major factor in contributing towards the cost target of £100/MWh.


THE MIXING SYSTEM


The Ormonde project was the first project, later followed by Thornton Bank and then Borkum West II, where this opportunity presented itself. The cement was stored in 50-tonne bulk pressurised silos before being delivered to a surge tank above the mixer. Water was delivered to the mixer system from the vessel’s firemain.


ENGINEER’S PERSPECTIVE John Paul O’Sullivan, Senior Project Engineer at FoundOcean said, “It was exciting for FoundOcean to be a part of the Ormonde offshore wind farm, it was the first project of its kind to use multiple jacket foundations in European waters.


“At times the installation process was halted due to poor weather, but the crucial phase was completed within the timeframe and before the winter weather had a chance to affect the project. We grouted 123 of 124 annuli in accordance with offshore grouting procedures set by FoundOcean. One annulus was completed using standard contingency procedures.


We were pleased with the final outcome and the project went on to win the Large Project Award at the inaugural RenewableUK Energy Awards 2012. Together with Offshore Design Engineering Ltd, REpower and Vattenfall, we were recognised for our exceptional achievement in constructing the Ormonde Offshore Wind Farm.”


FoundOcean www.foundocean.com


Click to view more info = Click to view video


www.windenergynetwork.co.uk


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