In the present context, the world is pursuing the development of renewable energies. One promising solution is marine renewable energy. In this field, Ocean Thermal Energy Conversion (OTEC) has the opportunity of becoming an essential contributor in using the temperature gradient between warm sea surface and cold deep sea water to run a heat engine and/or air conditioning (SWAC). Actually, those technologies are only at their beginning and there is room for major improvements thus major advantages can be highlighted compared to existing solutions.
Bardot Group is a renowned world Polymer specialist for subsea solutions. Our new concepts based on polymer materials allow significant cost reductions and efficient solutions for OTEC & SWAC technologies.
Bardot Group experience relies on a solid knowledge of the HDPE (High Density Polyethylene) material, based upon 10 years of subsea projects and in house laboratory material qualification.
Bardot Group has also developed and delivered its own Water Intake Riser (WIR) for cold water pumping for production process.
Nowadays our design is based on a mix of structural and hydrodynamic analysis. In the past of the industry, studies remained focused in modelling the pipe/riser behaviour under waves and current mainly for steel structure.
The use of HDPE pipes for SWAC and OTEC now brings new challenges that leads to develop specific material behaviour programs.
The aim of this paper is to present, in the first part, our testing program on HDPE mechanical properties. As a second part the paper will present the innovative Bardot concept for pumping cold water for Offshore systems and its applications to OTEC and SWAC.
For HDPE Pipes, specific material tests have been developed to assess the following mechanical properties:
* Abrasion tests to demonstrate the possible friction between two riser intakes or with the seabed.
* Ageing process in seawater to model the variation of mechanical behaviour
* Tensile uniaxial fatigue
* Flexure fatigue
A full-scale test program is also scheduled to define:
* Full-scale impact tests in case of interference with another material
* Axial stiffness test
* Hoop stress tests
In 2015, Bardot has developed a HDPE Water Intake Riser for the Total/Saipem Kaombo FPSO project (built in Singapore). The aim of the WIR is to use cold water for the FPSO process and to reduce the use of heat exchanger.
Thanks to using HDPE Riser, the loads applied on the hull and during the installation of the system are significantly reduced compared to steel Riser. Intensive hydrodynamic FEA on the global HDPE structure have been carried out. These FEA analysis showed that the HDPE light weight and low stiffness allows to decrease stress, moment reaction and impact in the line. Furthermore, our test campaign have also qualified the HDPE concept in fatigue using our SN Curve for HDPE.
Bardot is now exploring deep WIR for process cooling solutions.
Indeed today, HDPE material appears like a competitive solution also for OTEC.
The main challenge in OTEC system is pumping water into deep water.
Based on our experience and bringing our test campaign solutions, Bardot Group is developing innovative concepts for OTEC and SWAC system. Our knowledge gained on WIR is applied onto more important flow rates and deeper water depth for OTEC. HDPE riser also presents all necessary characteristics (low weight to reduce tension in top structure, good capacity in flexure...).
At last, Bardot is applying its technology also to SWAC system including pipeline stabilisation system but also anti friction devices.
As a conclusion, the HDPE technology for designing, building and installing a deep water and large diameter riser for water pumping is a key element in the success of OTEC, SWAC and WIR.
The proper material definition but also tests are key milestones in the development of this technology. Association of polymer specialist, hydrodynamic and use of HDPE can move OTEC/SWAC from research to industrial and competitive solutions.