Conceptual Design of Ocean Thermal Energy Conversion (OTEC) Power Plants In Sri Lanka

In 1994, NARA investigated the ocean thermal resources in the sea off Sri Lanka. In this paper, ten suitable sites within the sea off Sri Lanka are investigated and conceptual design for a 100-MW floating-type OTEC power plant is proposed. Optimum conditions are determined and plant specifications are computed using the ammonia as working fluid and plate type heat exchanger in evaporator and condenser. As a result, Rankine cycle efficiency is from 3.44 to 3.66 and a net power is about 70 % of the gross. INTRODUCTION The Ocean Thermal Energy Conversion system (OTEC) is a plant which converts heat energy in to electricity by operating a Rankine cycle using the temperature difference in the sea surface and depth (Uehara (1982)). A schematic diagram of the closed cycle OTEC power plant is shown in Fig. I. The warm seawater is used to evaporate a working fluid and cold seawater is used to condense the working fluid. The electricity is produced by running a turbine. Working fluid with a low boiling point is used e.g. freon or ammonia. Since the available temperature difference is small. The studies of OTEC have been done since the principle of OTEC was suggested by D'Arsonval (1881). In the OTEC system, since the temperature difference is small, the optimization should be considered not only on the individual systems like condenser and evaporator but also on the total system. Uehara and lkegami (1990) reported an optimization method for the OTEC considering the total system. One of the important points in constructing OTEC plant is the selection of the setting site. The selecting criteria are the sea temperature, the current velocity of seawater, the landform of the seabed, the consumption volume of electricity at setting area, the consumption volume of the drinking water and so on.