David K Creber, Alcan International Ltd., and
Alistair Johnson, GEC-Marconi
Closed-cycle OTEC systems convert thermal gradients in the ocean into useable power by use of a Rankine cycle. This paper describes the technology, design, sizing and performance expectations of a 100 kWe (nominal) system scheduled for construction in 1994 at the NELHA in Keahole Point, Hawaii. The relative merits of this system are compared to a similarly sized open-cycle OTEC system.
Because of the small temperature difference of 15-23¢XC, large water flows and large heat exchangers are required for this system. Thus, the practical application of this technology depends on the use of low cost heat exchangers. For this pilot plant, aluminum plate type heat exchangers (Roll-bond) will be used. The heat transfer characteristics of these panels, along with the corrosion performance in seawater predict successful, long term operation of this system. Based on thermal performance tests, a thermodynamic model has been developed and used to design the 100 kWe pilot project. Using this model, a sensitivity analysis has been carried out to determine the consequences of system design changes on performance. As well the effect of seasonal variations in the ocean thermal gradients on system performance is considered.
A key feature in the design of this system is its integration into the ongoing mariculture operations at the NELHA site. Consideration of the effect of any changes in the water quality on these operations which might occur because of the operation of the OTEC plant has been evaluated by NELHA.
The applicability of the closed-cycle OTEC technology to industrial power generation has been previously demonstrated at Alcan's sea cooled U.K. power station (DT1 Project DT1/FTR/3). The 100 kWe OTEC design analysis follows this work and is now used to demonstrate a near term commercial future in this field as well as the potential of larger, 5 MWe OTEC systems.