Exploring the feasibility of placing a wind turbine on top of an FPSO

Abstract

Changing the way of power production on a Floating, Production, Storage, and Offloading (FPSO)
system by using renewable power can contribute to reducing an FPSO’s carbon footprint while operating. Bluewater Energy Services is interested in the use of a wind turbine placed on top of an
FPSO, to power the FPSO’s internal electricity grid. This suggested configuration of a wind turbine and FPSO results in many different challenges that are new to the offshore industry. Therefore, this thesis considers the following research question: ‘To what extent is placing a 5 MW wind turbine on top of an FPSO feasible?’

To answer this question this research is split into two parts. The first part consists of a literature
research, in which two reference FPSOs, Bleo Holm and Haewene Brim, are introduced, and the decision of considering a 5 MW horizontal axis wind turbine is made. A wind turbine with this capacity can deliver approximately 75% of the FPSO’s required power during its normal operations. This information is used as input for a hazard identification (HAZID), in which a group of experts was challenged to brainstorm on possible hazards concerning the topic. The second part introduces the first design concept and focuses on the assessment of feasibility. Both technical feasibility and non-technical feasibility are evaluated. For technical feasibility, topics such as vessel stability, vessel strength, vibrations, the system’s motions, and wind turbine use during operational events on the FPSO are considered. From the non-technical feasibility, additional focus is put on the health, safety, and environmental (HSE) aspects of the project, and the project’s business case.

From the technical evaluation of the chosen design configuration a motion analysis, which consists of a diffraction analysis in HydroStar and a time domain simulation in OrcaFlex, identified a limitation in the wind turbine’s nacelle acceleration. This motion analysis was limited by the unavailability of a wind turbine model consisting of a yaw control system. In operations, the limit for nacelle acceleration is exceeded, which can be mitigated by performing more frequent wind turbine shutdowns. In extreme conditions for the vessel’s fully loaded condition, this mitigation is not an option. Recommended is an improvement of the design, to reduce the nacelle’s acceleration, with options such as reducing the wind turbine tower height or increasing the tower’s bending stiffness. Also, the found result is linked to the location of the Haewene Brim in the central North Sea, which is generally considered a site with rough environmental conditions. A different location with calmer waters is likely to still facilitate this concept. The considerable HSE-related risks that have been identified are related to the risk of a wind turbine’s dropped objects onto the FPSO, which can occur from different causes such as fire, structural failure, or lightning. This risk comes with a low probability, while its impact can be high. The business case of the project shows the potential of saving 250,000 tonnes of CO2 emissions during a typical wind turbine’s lifetime of 20 years. Also, it is estimated that a positive return on investment can be made in case the capital expenditures are less than €64.3 million. However, this result is sensitive to changes in, among other parameters, the wind turbine’s power production.

Based on the findings described above the conclusion to the question: ‘To what extent is placing a
5 MW wind turbine on an FPSO feasible?’ is that it can be considered feasible in case a design concept is found for which the nacelle acceleration is no longer an issue. However, future research is recommended on comparing this concept to other renewable power alternatives for the FPSO, based on their risks and financials, to see if the safety risks are worth the financial gain. On top of that, the development of a wind turbine yaw-controlled model is suggested to capture the interaction between weathervaning FPSO and yaw-operating wind turbine. In addition, research can be done on the installation method for a wind turbine on an FPSO.