A BSTRA CT
Floating platforms housing hydrogen plants operated with IOO MW of OTEC-generated electricity have been conceptualized. These plantships, deployed throughout the tropical oceans, could provide a significant source of energy in the form of liquid hydrogen. Large suspended pipes would transport cold seawater from depths of 1000 m to the heat exchangers onboard.
A 285 O00-tonne ship-shaped vessel isfirst proposed. It provides deck space for the OTEC plant, hydrogen plant, storage, and crew quarters. A length of 250 m and a beam of 60 m are sufficient to accommodate five seawater sumps. The operational draught is 20 m. Four 3000 hp thrusters permit grazing at one-half knot and some maneuvering capability.
A more compact plantship jet-propelled by the momentum flux of the OTEC discharge is also presented. The length is reduced to 200 m, for a displacement of 225 000 tonnes. Only one sump is required, and warm seawater is fed through lateral openings.
Key words." OTEC, ocean energy, hydrogen, platform, plantship. on how work is extracted in the system's turbine. For larger plants, Closed-Cycle OTEC is the configuration of choice: an auxiliary working fluid, such as ammonia, circulates in a closed loop, and undergoes phase changes in an evaporator and a condenser on either side of the turbine. The two heat exchangers are fed by warm and cold seawater streams, respectively. The theoretical thermal efficiency of OTEC power cycles is low, but the energy resource employed is renewable and environmental impact is minimal.
The ideas of generating OTEC power from a floating offshore structure on the one hand, and to use a material energy carrier to transmit OTEC power to shore on the other hand, have already been proposed. This paper represents a particular update of these two complementary concepts in the light of recent theoretical and experimental work. Emphasis is laid on the design of an offshore platform capable of supporting a 100 MW OTEC power plant and a hydrogen production facility.
Following his ground-breaking experiments in Matanzas, Cuba, the OTEC pioneer Claude, in the thirties, shifted his interest from landbased OTEC plants to platforms. ~ Moreover, he planned to utilize OTEC power to produce ice offshore. The very costly experiment which he organized off the coast of Brazil, after refurbishing the 10 000-tonne ship Tunisia, failed in 1935 because the design of the 2-5-m diameter, 700-m long Cold Water Pipe (CWP) was far beyond the state-of-knowledge in ocean engineering at that time. Financially, Claude was also coping with the World's worst economic crisis.
Deep-sea oil exploitation brought the concept of large offshore platforms into reality about forty years later. At the same time, renewed interest in OTEC, prompted by an escalation ofoil prices in 1974, led to significant design efforts and to some landmark experimental studies in the United States. In particular, a model basin test of a floating 40 MW closed-cycle OTEC platform, at 1:110 scale, was completed in 1981 under the supervision of NOAA. 2 In 1983, a more ambitious phase of the 40 MW OTEC platform project followed, under the leadership of the Hawaiian Dredging and Construction Company (HDCC), which consisted of the at-sea test of the 1:3 scale CWP suspended from a barge, in Hawaiian waters. The analysis of the results is presented in Ref. 3.
Because of the progress achieved in the field of heat exchangers, reported for example by Stevens et al., 4 the baseline 100 MW net power production would correspond to a CWP about 10 m in diameter, similar to the conduit selected in 1981 for the 40 MW US project. Consequently, a significant ocean engineering data base is directly applicable here, with minor modifications. The heat-and-mass balance for the closed-cycle