This type of fresh water generator is based on two sets of shell and tube heat exchangers, one acting as evaporator or heater and other as condenser. Steam can also be used as a heat source instead of main engine jacket cooling water. The submerged tube type fresh water generator explained below uses the heat from main engine jacket cooling water to produce drinkable water by evaporating seawater due to the high vacuum, which enables the feed water to evaporate at a comparative low temperature.
This type of single effect plant is designed to give better economy than obsolete Boiling Evaporators. Hence using energy from a heating coil, and by reducing pressure in the evaporator shell, boiling can takes place at about 40 to 60 degree Celsius. The source of heat for the fresh water generator could be waste heat rejected by main engine jacket cooling water. By maintaining a low pressure, water can be boiled at low temperatures say 50 degree Celsius. Fresh Water Generator Working Principleīasic principle of all low pressure freshwater generator is that, boiling point of water can be reduced by reducing the pressure of the atmosphere surrounding it. In addition to this water ejector, ejector pump, distillate pump, salinity indicator, demister or mesh separator, solenoid valve and water flow meter are also fitted as accessories. The shell and tube freshwater generator consist of heat exchanger, separator shell and condenser. Submerged Tube Type Fresh Water Generator What ever type of plant is used, essential requirement of any fresh water generator is that it should produce fresh water as economically as possible. Submerged tube type fresh water generator.Various types of fresh water generators used on board ships are mainly: The equipment used on board for the production of freshwater from seawater is known as fresh water generator. It is statutory requirement to have a distillation plant for emergency use if otherwise ship has carried sufficient potable water. The stowage space that would have been used for fresh water can hence be utilized for fuel or extra space made available for cargo when fresh water generator is installed on a ship. It is common practice to take on only a minimum supply of potable water and make up the rest by distillation of sea water. But the quality of this water will be too poor for use in water tube boilers and for filling expansion tanks. Sufficient potable water may be taken on in port to meet crew and passenger requirement. In a steam ship (a ship whose main propulsion unit is steam turbine or a ship which is a large tanker having steam turbine driven cargo oil pumps) the consumption for the boiler can be as high as 30 tonnes/day.
The crew consumes an average 100 liter/head/day. A considerable amount of fresh water is consumed in a ship. Fresh water production from sea water for domestic and auxiliary purposes is an essential requirement aboard ships.
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