Floating Powerplant Offshore to Support Submerged Operations
Authors: Edwards Russell N. , Zupanick Joseph E. 
Published: October 2008

The exploitation of the offshore environment for petroleum, mining and scientific purposes will lead to submerged power requirements of several thousand kilowatts in the next decade. The deep submergence nuclear powerplants may fill these requirements at the higher power levels. Air breathing floating powerplants, using established gas turbine driven alternators, are applicable to early operational requirements.

Environmental limitations of the airbreathing floating powerplant are not extreme, although the ingestion of salt-water spray must be minimized. A wave-riding spray 4 feet in diameter and less than 30 feet tall, excluding the air intake stack, will survive hurricane conditions and operate successfully for more than 90% of the time in most parts of the world.

The floating powerplant includes a "marinized" version of an aircraft turbo-shaft engine driving a group of aircraft alternators through a gear reduction unit. The buoy houses the power train, command and control, air intake processing, mechanical termination, electrical connectors and cables to the submerged sea-terminal.

The cable to the sea-terminal provides for mooring and power and fuel transmission. The system can operate using fuel stored in a submerged cache or natural gas obtained from a producing oil or gas well. The seaterminal contains apparatus for fuel and electrical power conditioning and command and and control systems. Life support equipment makes it possible to carryon maintenance of this equipment under shirt-sleeve environment within the sea-terminal pressure vessel.

The combination of an air-breathing floating powerplant and a maintainable submerged sea-terminal provides an efficient and flexible power source for a wide variety of undersea systems. All adaptations to the submerged operational requirements are provided in the sea terminal which meets the deep-ocean interface requirements.

INTRODUCT ION

Increased production of oil from offshore fields has focused attention on the need for improved operational capabilities. A key element of these capablities is the source of power for operation of submerged equipment at remote offshore locations. The timely availability of economical power supplies is essential to competitive submerged offshore production.

Several types of power supply; platform diesel generators, electrical cables from shore, floating powerplants and submerged nuclear systems, will have application to offshore production. The key parameters affecting the selection of the most cost effective system are 1) distance from shore, 2) depth of producing sea bed, 3) power level, and 4) total operating life. Consideration of these factors shows that floating powerplants offer significant life-cycle economies when distance from shore exceeds about 20 miles, the sea floor depth is greater than 300 fe.et, and the life-time energy requirement is well below the 100,000 kilowatt year level of an economical nuclear powerplant.

Electrical cable system costs increase parabolically with transmission distance in ideal systems. Offshore platform costs increase exponentially with depth. Nuclear system costs are high at power levels of 1,000 KW but rise only about as the cube root of the power level, leading to relatively modest costs at high power levels. The moored floating powerplant, in contrast, is relatively independent of operating depth and distance from shore and scales almost linearly in cost as a function of power level.