ABS has issued its first Approval in Principle (AIP) for a new concept renewable energy design in which a moored spar uses ammonia in a closed-cycle process to produce electrical power for a commercial utility grid. Unlike wind, tidal or solar power the advanced design for this Ocean Thermal Energy Conversion (OTEC) system can deliver constant output 24 hours a day. “This concept combines proven offshore principles with off-the-shelf power, technology and proprietary innovations, all assembled in a unique way,” says Ian Simpson, ABS Director of Offshore Technology and Business Development, Americas Division. “The design application illustrates how ABS is able to use its novel concept approach and guidance to provide review of a concept within the framework of established safety standards.”
Developed by OTEC International (OTI) LLC of Baltimore, Maryland, the approach converts liquid ammonia into gas in a heat exchanger using warm ocean surface water. The ammonia gas then drives turbines that turn generators to produce electricity which is then exported through a submarine power cable to a land-based utility company. The ammonia is condensed back into a liquid phase using cold ocean water pumped from 3,000 feet below the water’s surface and the process begins again. The process is based upon the well-established thermodynamic Rankine cycle.
“OTI has integrated the OTEC power block into a large floating vessel, in this case a spar, for an economically and environmentally-efficient means of converting solar energy from the tropical oceans into affordable electricity,” explains Barry Cole, OTI’s Executive Vice President and Director of Technology Development.
Key elements evaluated by ABS include: spar hull sizing for the deep draft spar design; energy conversion equipment located in the spar; handling and storage of hazardous materials; deepwater mooring system; cold water pipe conduit suspended from the base of the spar; construction and attachment of the cold water pipe conduit; and power transmission cable with its securing, anchoring and suspension arrangements. ABS reviewed the design for an extended 30-year facility on-station life.
ABS has issued Approval in Principle for both the 25MW and 100MW designs; OTI could be eligible for ABS’ class notation A1, Floating Offshore Installation (FOI) Spar, SFA(30).