ABSTRACT:

Low Temperature Thermal Desalination (LTTD) process utilizes the temperature gradient between two water bodies to evaporate the warmer water at low pressures and condense the resultant fresh using the colder water to obtain high quality fresh water. National Institute of Ocean Technology (NIOT) has been working extensively on LTTD process since 2004. A land based 100m3/day capacity desalination plant was established in 2005 in Kavaratti Island, 400 km off the west coast of India, to demonstrate the utility of the process for the islands. An experimental floating barge mounted 1000m3/day desalination plant was established in 2007, about 40km off Chennai coast to demonstrate the utility of the process for the mainland applications. Another land based 150m3/day capacity desalination plant is established in 2009 in North Chennai Thermal Power Station (NCTPS) to demonstrate the utility of the process for any coastal thermal power plant that discharges huge amounts of condenser reject water into the near by sea. The paper discusses the salient features of these plants. Apart from the potable water, the process can also provide the intangible benefits, like aqua culture if used in the context of the ocean thermal gradient and reduction of thermal pollution if used in the context of power plant discharge. A review of various aspects of the process is also presented in the paper.

INTRODUCTION

Thermal gradient between different layers of the ocean water column provides huge reservoirs of warm and cold water that can effectively be utilized for power generation, desalination and air-conditioning. The deep ocean cold water is rich in nutrients and is highly beneficial for aquaculture. The available thermal gradient between warmer surface water and colder deep seawater is utilized by flash evaporating the warm water at low temperatures and condensing the resultant vapour with cold water.

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