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Fresh Water Generator

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Fresh Water Generator by Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.

Fresh Water Generator by Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.

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  • 1. Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh. FRESH WATER GENERATOR 6/23/2014 1
  • 2. Fresh Water Generator Working Principle: - Water is generally produced on board using the evaporation method. - Fresh water is produced by evaporating sea water using heat from any of the heat source. - The evaporated sea water is then again cooled by the sea water and the cycle repeats. - Generally the heat source available is taken from the main engine jacket water, which is used for cooling the main engine components such as cylinder head, liner etc. -The temperature available from this jacket water is about 70°C. 6/23/2014 2 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 3. - But at this temperature the evaporation of water is not possible as we all know that the evaporation of water takes place at 100°C under atmospheric pressure. - Thus in order to produce fresh water at 70°C, we need to reduce the atmospheric pressure, which is done by creating a vacuum inside the chamber where the evaporation is taking place. - Also, as a result of the vacuum the cooling of the evaporated sea water will also take place at lower temperature. - This cooled water is collected and transferred to the tank. 6/23/2014 3 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 4. 6/23/2014 4 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 5. Function of All Parts of Shell & Tube Type FWG 6/23/2014 5 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 6. 6/23/2014 6 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 7. 6/23/2014 7 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 8. 6/23/2014 8 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 9. 6/23/2014 9 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 10. 6/23/2014 10 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 11. Vent Cock: It is used to break the vacuum after stopping. In idle condition and maintenance period, it is used for venting purpose. 6/23/2014 11 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 12. Relief Valve: It is used as a pressure-relief device . Vacuum Gauge: It is used to show the percentage of vacuum. 6/23/2014 12 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 13. 6/23/2014 13 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 14. Operation of a Shell & Tube Type FWG 6/23/2014 14 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 15. 6/23/2014 15 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 16. 6/23/2014 16 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 17. 6/23/2014 17 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 18. 6/23/2014 18 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 19. 6/23/2014 19 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 20. 6/23/2014 20 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 21. 6/23/2014 21 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 22. 6/23/2014 22 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 23. 6/23/2014 23 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 24. 6/23/2014 24 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 25. 6/23/2014 25 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 26. 6/23/2014 26 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 27. Fresh Water Generator Arrangement The main body of a fresh water generator on the ship consists of a large cylindrical body with two compartments. One of the compartments is the condenser and the other is the evaporator. The fresh water generator also consists of an educator which helps in generating the required vacuum. The fresh water pump and ejector pump helps in transfer of water to and from the fresh water generator. 6/23/2014 27 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 28. Starting the Fresh Water Generator 1. Before starting the fresh water generator we have to check that the ship is not in congested water, canals and is 20 nautical miles away from the shore. This is done because near the shore the effluents from factories and sewage are discharged into the sea can get into the fresh water generator. 2. Check whether engine is running above 50 rpm, the reason for this is that at low rpm the temperature of jacket water which is around 60 degrees and not sufficient for evaporation of water. 3. Check the drain valve present at the bottom of the generator is in close position. 4. Now open suction and discharge valves of the sea water pump which will provide water for evaporation, cooling and to the eductor for creating vacuum. 5. Open the sea water discharge valve from where the water is sent back to the sea after circulating inside the fresh water generator. 6. Close the vacuum valve situated on top of the generator. 6/23/2014 28 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 29. 7. Now start the sea water pump and check the pressure of the pump. The pressure is generally 3-4 bars. 8. Wait for the vacuum to build up. Vacuum should be at least 90% which can be seen on the gauge present on the generator. Generally the time taken for the generation of vacuum is about 10 minutes. 9. When vacuum is achieved open the valve for feed water treatment, this is to prevent scale formation inside the plates. 10. Now open hot water (jacket water) inlet and outlet valves slowly to about half. Always open the outlet valve first and then inlet valve. Slowly start to increase the opening of the valves to full open. 11. Now we can see that the boiling temperature starts increasing and the vacuum starts dropping. 12. The vacuum drop to about 85% which is an indication that evaporation is started. 13. Open the valve from fresh water pump to drain. 6/23/2014 29 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 30. 14. Switch on the salinometer if it has to be started manually. Generally it is on auto start. 15. Now start fresh water pump and taste the water coming out of the drain. 16. When fresh water starts producing it is seen that the boiling temperature drops again slightly and vacuum comes back to the normal value. 17. Check the water coming out of the salinometer is not salty and also check the reading of the salinometer. This is done to see if the salinometer is working properly or not and to prevent the whole fresh water from getting contaminated with salt water. The value of salinometer is kept below 10ppm. 18. After checking the taste of the water coming out of the salinometer, open valve for tank from the pump and close drain valve. 6/23/2014 30 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 31. Stopping the Fresh water Generator 1. Close the jacket water inlet valves. Generally inlet is closed first and then the outlet valve. 2. Close the valve for feed water treatment. 3. Stop fresh water pump. 4. Switch off the salinometer. 5. Stop ejector pump. 6. Open vacuum valve. 7.Close sea water suction valve and overboard valve. This is generally not required as they are non- return valves. However, in case of valve leaking or damage, these valves are to be closed without fail. 6/23/2014 31 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 32. 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. 6/23/2014 32 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 33. SALINOMETER ALARM UNIT 6/23/2014 33 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 34. 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 6/23/2014 34 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 35. 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. 6/23/2014 35 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 36. 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. 6/23/2014 36 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 37. REVERSE OSMOSIS Reverse Osmosis (RO) is one of the methods which are used on board for generating fresh water. Generally this is used on passenger vessels wherein there is a large requirement of fresh water production. However, in merchant ships the evaporation method is used as reverse osmosis is costly and includes large maintenance cost for membrane.
  • 38. Working Principle Of RO: Osmosis describes the process whereby a fluid will pass from a more dense to a less dense solution through a semi-permeable membrane. It is very important to the water absorbtion processes of plants. RO is a process which uses a semi- permeable membrane which retains both salt and impurities from sea water while allowing water molecules to pass. Filtration of up to 90% is possible thus making the produced water unsuitable for boiler feed without further conditioning. Improved quality is possible using a two or more pass system. 6/23/2014 38 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 39. An experiment to determine this osmotic head is shown.6/23/2014 39 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 40. The parchment paper acts as the semi-permeable membrane and allows the water molecules to pass but not the larger salt molecules.6/23/2014 40 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 41. Operation of Reverse Osmosis Plant: - Reverse osmosis is the process whereby a pressure greater than the osmotic head pressure is applied to a solution of high density. - Fluid is forced from the high density side to the less dense side. - For desalination plants the pressure is applied to sea water and the water is forced through the semi-permeable membrane. 6/23/2014 41 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 42. 6/23/2014 42 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 43. Operation of Reverse Osmosis Plant (cont’d) - Design of the cartridges is therefore such that the sea water feed passes over the membrane sheets so that the washing action keeps the surfaces clear of deposits. - A dosing chemical is also injected to assist the action. 6/23/2014 43 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 44. Operation of Reverse Osmosis Plant (cont’d) - The two membranes sealed on the outer three edges, enclose porous under-layer through which the permeate spirals to central collecting tube. - Pressurized feed water passes lengthways through the tubular spiral wound membrane element. - Freshwater permeate travels through the membrane layers as directed along a spiral bath in-out a central perforated tube, while brine is discharged out the end of the membrane element. 6/23/2014 44 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 45. Operation of Reverse Osmosis Plant (cont’d) - The fluid could be water and the solutions sea water. Under normal conditions the water would pass from the less saline solution to the more saline solution until the salinity was the same. - This process will cease however if the level in the more saline side raises to give a difference greater than the Osmotic height. - For practical use to allow the generation of large quantities of water. It is necessary to have a large surface area of membrane which has sufficient mechanical strength to resist the pressurized sea water. 6/23/2014 45 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 46. Operation of Reverse Osmosis Plant (cont’d) - One problem with any filtration system is that deposits accumulate and gradually blocks the filter. - The sea water is supplied at a pressure of 60bar, a relief valve is fitted to the system. - The Osmosis production plant is best suited to the production of large quantities of water rather than smaller quantities of steam plant feed quality. SEMI PERMEABLE MEMBRANE: The semi permeable membrane which is typically made of polyamide membrane sheets wrapped in a spiral form around a perforated tube resembling a loosely wound like a toilet paper roll. The material used for sea water purification is spirally wound polyamide or polysulphonate sheets. 6/23/2014 46 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 47. 47 REVERSE OSMOSIS SEAWATER TO POTABLE WATER SEAWATER 6/23/2014 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 48. Pretreatment and post treatment Sea water feed for reverse osmosis plant is pretreated before being passed through. The chemical sodium hexa- phosphate is added to assist wash through of salt deposits on the surface of the elements and the sea water is steriliazed to remove bacteria which could otherwise become resident in the filter. Chlorine is reduced by compressed carbon filter while solids are removed by other filters. Treatment is also necessary to make the water drinkable. 6/23/2014 48 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 49. 49 REVERSE OSMOSIS 6/23/2014 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 50. 50 REVERSE OSMOSIS 6/23/2014 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 51. 51 RO FILTER MODULE 6/23/2014 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 52. 52 RO FILTER MODULE 6/23/2014 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.
  • 53. ANY QUESTION? THANK YOU! 6/23/2014 Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh. 53