1. Click to edit Master title style Click to edit Master text styles – Second level Third level – Fourth level » Fifth level 1 Anglo-Eastern Maritime Academy ©  Anglo-Eastern Maritime Academy Fresh water generator

2. Click to edit Master title style Click to edit Master text styles – Second level Third level – Fourth level » Fifth level 2 Anglo-Eastern Maritime Academy ©  Anglo-Eastern Maritime Academy 2 ©  Anglo-Eastern Maritime Academy 2 Average shipboard water consumption is taken as 100 litres per person per day On a steam ship or a large tanker with steam driven COPs, the boiler fresh water consumption can be as high as 30 tonnes per day. Sea water salinity: approx: 32000 ppm varies from place to place Fresh Water Generator can generate upto 1 ppm of fresh water considered as distilled water

3. Click to edit Master title style Click to edit Master text styles – Second level Third level – Fourth level » Fifth level 3 Anglo-Eastern Maritime Academy ©  Anglo-Eastern Maritime Academy 3 ©  Anglo-Eastern Maritime Academy 3 FRESH WATER STORAGE IN A 47,000 DWT CHEMICAL TANKER

4. Click to edit Master title style Click to edit Master text styles – Second level Third level – Fourth level » Fifth level 4 Anglo-Eastern Maritime Academy ©  Anglo-Eastern Maritime Academy 4 ©  Anglo-Eastern Maritime Academy 4 It is now common practice to take on only a minimal supply of potable water in port and to make up the rest by distillation of sea water. The saved storage capacity for water, is available for cargo and increases the earning power of the ship. A vessel which carries sufficient potable water for normal requirements is required, if ocean-going, to carry distillation plant for emergency use.

5. Click to edit Master title style Click to edit Master text styles – Second level Third level – Fourth level » Fifth level 5 Anglo-Eastern Maritime Academy ©  Anglo-Eastern Maritime Academy 5 ©  Anglo-Eastern Maritime Academy 5 Low pressure (operating under vacuum conditions) 1.Control over type of scale formed, i.e. mainly calcium carbonate which is soft and easy to remove. 2.Heating medium supplied can be at a relatively low temperature e.g. diesel cooling water or waste steam. 3.Improved heat transfer across the heating element. This is due to higher temperature differences for lower pressures than higher pressures.

6. Click to edit Master title style Click to edit Master text styles – Second level Third level – Fourth level » Fifth level 6 Anglo-Eastern Maritime Academy ©  Anglo-Eastern Maritime Academy This is supplied with diesel engine cooling water as the heating medium. Vapour evolved at a very rapid rate by boiling of the sea-water feed, tends to carry with it, small droplets of salt water The demister of knitted monel metal wire collects the salt- filled water droplets as they are carried through by the air.

7. Click to edit Master title style Click to edit Master text styles – Second level Third level – Fourth level » Fifth level 7 Anglo-Eastern Maritime Academy ©  Anglo-Eastern Maritime Academy 7 ©  Anglo-Eastern Maritime Academy 7 Evaporation of part of the sea water leaves a brine the density of which must be controlled by continual removal through a brine ejector or pump. Air and other gases released by heating of the sea water, but which will not condense, are removed by the air ejector. The evaporator shown has a single combined ejector for extraction of both brine and air. Scale is not a major problem where submerged heating coils reach a temperature of only 60°C.

8. Click to edit Master title style Click to edit Master text styles – Second level Third level – Fourth level » Fifth level 8 Anglo-Eastern Maritime Academy ©  Anglo-Eastern Maritime Academy 8 ©  Anglo-Eastern Maritime Academy 8 LIMITATIONS Cannot be used in ports, anchorages and closer to shore than 12 nm because of domestic sewage and industrial effluents. Unfit as potable water because: -Not sterilised -Tasteless -Slightly acidic in nature -Devoid of any minerals requried for human body.

9. Click to edit Master title style Click to edit Master text styles – Second level Third level – Fourth level » Fifth level 9 Anglo-Eastern Maritime Academy ©  Anglo-Eastern Maritime Academy 9 ©  Anglo-Eastern Maritime Academy 9 Two stage Flash evaporator

10. Click to edit Master title style Click to edit Master text styles – Second level Third level – Fourth level » Fifth level 10 Anglo-Eastern Maritime Academy ©  Anglo-Eastern Maritime Academy 10 Anglo-Eastern Maritime Academy ©  Anglo-Eastern Maritime Academy 10 Sea water is pumped through the control valve A to the second, then the first stage, vapour condensers wherein it increases in temperature before final heating to 80°C in the steam supplied heat exchanger. The pressurised, heated sea water flows through an orifice into the first flash chamber whose low pressure corresponds to a saturation temperature less than that of the incoming heated sea water. Hence some of the water must be evaporated, in order that its temperature can fall to around that which corresponds to the pressure in the chamber. Unevaporated water flows through an orifice-which maintains pressure difference-into the second chamber where more water is evaporated since the pressure is lower than in the first chamber.

11. Click to edit Master title style Click to edit Master text styles – Second level Third level – Fourth level » Fifth level 11 Anglo-Eastern Maritime Academy ©  Anglo-Eastern Maritime Academy 11 Anglo-Eastern Maritime Academy ©  Anglo-Eastern Maritime Academy 11 A brine pump extracts low density unevaporated water and discharges the bulk overboard. Some however may return to the suction side of the supply pump through the auto-valve B to maintain the feed inlet temperature at about 30°C irrespective of how low the sea water temperature may be. The vapour and non-condensible gases in each of the chambers pass through the demisters then over and down through the vapour condensers. Distillate flows from the first stage to the second through an orifice then it is extracted by the distillate pump and delivered to the storage tank. A salinity detector controls the distillate pump, if the density is too high the pump stops and the distillate passes over the double loop seal to the brine pump suction to be discharged overboard. Non-condensible gases are extracted by the ejector which maintains the high vacuum condition in the chambers

12. Click to edit Master title style Click to edit Master text styles – Second level Third level – Fourth level » Fifth level 12 Anglo-Eastern Maritime Academy ©  Anglo-Eastern Maritime Academy Salinometer Pure distilled water may be considered a non-conductor of electricity. The addition of impurities such as salts in solution increases the conductivity of the water, and this can be measured. Since the conductivity of the water is, for low concentrations, related to the impurity content, a conductivity meter can be used to monitor the salinity of the water.

13. Click to edit Master title style Click to edit Master text styles – Second level Third level – Fourth level » Fifth level 13 Anglo-Eastern Maritime Academy ©  Anglo-Eastern Maritime Academy 13 Anglo-Eastern Maritime Academy ©  Anglo-Eastern Maritime Academy 13 Drinking Water Treatment Filtration – to remove any solid particulate matter – using carbon filter, membrane filter etc. Sterilisation – to remove bacteria – through chlorination, UV treatment, ozonisation etc. Neutralisation – to neutralise acidic nature – add calcium or magnesium carbonate Mineralisation – to add minerals required for human body by dosing calcium or magnesium carbonate

14. Click to edit Master title style Click to edit Master text styles – Second level Third level – Fourth level » Fifth level 14 Anglo-Eastern Maritime Academy ©  Anglo-Eastern Maritime Academy Drinking water treatment The low operating temperature of the evaporator is not sufficient to sterilize. Harmful organisms may enter with the sea water and pass through to the domestic water tank. There is a likelihood that while in the domestic tank, water may become infested with bacteria. Sterilization by the addition of chlorine, is recommended.

15. Click to edit Master title style Click to edit Master text styles – Second level Third level – Fourth level » Fifth level 15 Anglo-Eastern Maritime Academy ©  Anglo-Eastern Maritime Academy Chlorine sterilization and conditioning The distillate is passed through a neutralite unit containing magnesium and calcium carbonate. Some absorption of CO2 from the water and the neutralizing effect of these compounds, removes acidity. The addition of hardness salts also gives the water a better taste. The sterilizing agent chlorine, being a gas, is carried into the water as a constituent of sodium hypochlorite (a liquid) or in granules of calcium chloride dissolved in water. The addition is set to bring chlorine content to 0.2 ppm. The passage of water from storage tanks to the domestic system, is by way a carbon filter which removes the chlorine taste.

16. Click to edit Master title style Click to edit Master text styles – Second level Third level – Fourth level » Fifth level 16 Anglo-Eastern Maritime Academy ©  Anglo-Eastern Maritime Academy Reverse osmosis Osmosis is the natural process which occurs when water spontaneously flows from a purer solution, through a semi-permeable membrane into a more concentrated solution. In A, the semi-permeable membrane will allow water to pass through it but not salt. In B, the height will increase until the pressure of the column of salt water is so high that it causes the water flow to stop. The difference in the water levels on the two sides is the “Osmotic Pressure”. In Reverse Osmosis the natural osmosis forces are overcome by applying an external pressure to the concentrated solution. Thus the flow of water is reversed and pure water is removed from the feed solution, leaving a more concentrated salt solution.

17. Click to edit Master title style Click to edit Master text styles – Second level Third level – Fourth level » Fifth level 17 Anglo-Eastern Maritime Academy ©  Anglo-Eastern Maritime Academy Reverse Osmosis (RO) is the finest level of filtration available. Reverse Osmosis is a membrane process that acts as a molecular filter to remove 95 to 99% of dissolved salts and inorganic molecules, as well as organic molecules with a molecular weight greater than 100. The Reverse Osmosis membrane also removes more than 98% of residual biological and colloidal matter from the feed water, resulting in a highly purified product stream.

18. Click to edit Master title style Click to edit Master text styles – Second level Third level – Fourth level » Fifth level 18 Anglo-Eastern Maritime Academy ©  Anglo-Eastern Maritime Academy For production of large amounts of pure water, the membrane area must be large and it must be arranged in a configuration which makes it strong enough to withstand the very high pump pressure needed. The pump delivery pressure for a reverse osmosis system of 60 bar calls for a robust reciprocating or gear pump. The system must be protected by a relief arrangement.

19. Click to edit Master title style Click to edit Master text styles – Second level Third level – Fourth level » Fifth level 19 Anglo-Eastern Maritime Academy ©  Anglo-Eastern Maritime Academy Membrane material used for sea-water purification is produced in the form of flimsy polyamide or polysulphonate sheets, which without backing would not be strong enough. It is done by making up spirally wound cartridges. The core of the cartridge is a porous tube to which are attached the open edges porous tube for water which is squeezed through the membranes. The envelopes are separated by coarse gauze sheets. The finished cartridge is produced by rotating the actual central tube, so that envelopes and separators are wrapped around it in a spiral, to form a cylindrical shape. Cartridges with end spacers, are housed in tubes of stainless steel or other material.

20. Click to edit Master title style Click to edit Master text styles – Second level Third level – Fourth level » Fifth level 20 Anglo-Eastern Maritime Academy ©  Anglo-Eastern Maritime Academy 20 Anglo-Eastern Maritime Academy ©  Anglo-Eastern Maritime Academy 20 One problem with any filtration system, is that deposit accumulates and gradually blocks the filter. Design of the cartridges is therefore such that the sea-water feed passes through the spiral windings and over the membrane sheets with a washing action that assists in keeping the surfaces clear of deposit. A dosing chemical, sodium hexametaphosphate, is also added to assist the action. There is also a back flushing system to remove the deposits.

21. Click to edit Master title style Click to edit Master text styles – Second level Third level – Fourth level » Fifth level 21 Anglo-Eastern Maritime Academy ©  Anglo-Eastern Maritime Academy 21 Anglo-Eastern Maritime Academy ©  Anglo-Eastern Maritime Academy 21 Pre-treatment and post-treatment Sea-water feed for reverse osmosis plant, is pretreated before being passed through. The chemical sodium hexametaphosphate is added to assist the wash through of salt deposit on the surface of the elements and the sea water is sterilized to remove bacteria which would otherwise become resident in the filter. Chlorine is reduced by the compressed carbon filter while solids are removed by the other filters. Treatment is also necessary to make the water product of reverse osmosis potable. The method is much the same as for water produced in low temperature evaporators.

22. Click to edit Master title style Click to edit Master text styles – Second level Third level – Fourth level » Fifth level 22 Anglo-Eastern Maritime Academy ©  Anglo-Eastern Maritime Academy 22 Anglo-Eastern Maritime Academy ©  Anglo-Eastern Maritime Academy 22 Domestic water tanks Harmful organisms in drinking water storage tanks have caused major health problems. To eliminate this problem, water storage tanks should be pumped out at six-month intervals and the surfaces should be hosed to down clean them. At the 12-month inspection, recoating may be needed in addition to the cleaning. Washing with a 50 ppm solution of chlorine is done. Super-chlorinating when the vessel is drydocked, consists of leaving a 50ppm chlorine solution in the tank over a four hour period, followed by flushing with clean water. The steel tank surfaces may be prepared for coating by wire brushing and priming. Subsequently a cement wash is applied or an epoxy or other coating suitable for use in fresh water tanks.