LOW TEMPERATURE THERMAL DESALINATION (LTTD)
ABSTRACT
Fresh water is an essential requirement of mankind for drinking, agriculture & Industrial purpose & is amongst one of the most important input for man™s survival. The rapid increase of world™s population and non uniform distribution of potable water has forced mankind to develop new techniques to generate potable water. Fresh water rivers, lakes & other natural sources are not able to meet the over growing demand of potable water forcing the scientists to look towards the sea to fulfill the need of fresh water. Sea water is available in abundance; however, its conversion to fresh water is limited & restricted due to high cost of conversion. Various processes are being developed to reduce the salinity of sea water so as to make it fit for human consumption and use. The most popular processes presently being used are Distillation, Reverse Osmosis & Electro dialysis. Scientists all over the world are constantly working on developing economical process so as to generate fresh water on large and economical sales. The new process developed by Indian Scientists known as the process of Low Temperature Thermal Desalination (LTTD). 0.1 Million Liters per day pilot plant on LTTD process has already been commissioned and is in operation since May 2005 which was designed, fabricated & installed by Indian Scientists at Kavaratti in Lakshadweep. In LTTD method the energy requirement for the evaporation of water are taken from sea which makes the process eco-friendly and uses renewable source of energy. LTTD uses the temp difference which exists between the surface layer water (28°-30°C) & deep sea layer water (7°-10°C) existing in an ocean to produce potable water. The surface sea water at about 28°C “ 30°C is pumped into flash chamber which is maintained under low pressure of about 25 mbar absolute (below the saturated vapour pressure of water). The warm sea water in the flash chamber evaporates due to low pressure being maintained, taking latent heat of evaporation from the warm water stream itself. The evaporated water vapours move towards the shell & tube condenser and the return water, loosing temp by about 7°C is returned back to the sea. The main condenser has a circulation of cold sea water at a temp of 12°-13°C, pumped from the lower layers of sea & is used for the condensation of the evaporated water vapour. The condensate thus produced is fresh drinking water fit for human consumption.