75. The Indian 1 MW OTEC Plant-Technological Challenges and Development Activities

Ocean Thermal Energy Conversion (OTEC) utilizes the thermal gradient available in the ocean to operate a heat engine to produce work output. The technology is mature enough to establish commercial power plants. India is geographically well placed as far the potential is concerned with a ∆T above 20^OC between sea surface water and 1000 m depth through out the year. Attractive locations suitable for land based as well as floating OTEC plants are available on the Indian coast and in the Island groups in Indian Ocean. Since 1998 National Institute of Ocean Technology was involved in the design, development and demonstration of a 1 MW (gross) OTEC floating plant – the largest of its kind. This is to be commissioned south east of Tuticorin, South India where an ocean depth of 1200 m available from 40 km off the main land. The computer analysis, model studies and site surveys were done in 1999. The basic power cycle design was completed within 4 months. The plant is based on the closed Rankine cycle with ammonia as the working fluid. The evaporators have a special steel coating on the ammonia side to enhance the nucleate boiling. An after condenser is introduced after laboratory studies to improve the power plant stability. A four-stage axial flow ammonia turbine was developed with a pressure ratio of 1.4. The plant was integrated on a floating barge with 3 moon pools acting as sump for sea water intake and discharge. The cold water sump is having 14 m depth locked on the deck to provide enough NPSH for the cold water pumps. The stage qualification tests were carried out in 2000–01 on sea water pumps at shallow waters and turbine-generator unit with compressed nitrogen gas. The floating barge is to be moored with single point mooring at 1200 m depth using the 1 m diameter HDPE pipe, which is the intake for the cold water. The power plant and sea water systems are ready and it is scheduled to be commissioned in January-February 2004. This paper is projecting the technological and economical aspects of the OTEC with an overview of the various studies and pre-commissioning tests carried out.