Working Principle of Fresh Water Generator on Board Ship

Fresh water generator(FWG) is one of the essential machineries on board ship, After-all a large amount of fresh water is utilized on ship every day. On board ship Fresh water is used for the most part by huge boilers having steam turbines as main propulsion or cargo pumps driven by turbines. They all in all record for 30+ Tons of fresh water every day separated from the day by day necessities of 10+ ton for crew consumption as drinking, cooking, washing,Tank cleaning and different utilities. Adequate consumable water might be taken up against the cargo load capacity in the port for satisfying crew and machinery necessity yet isn't prescribed to utilize shore water for boilers because of their low quality, so Fresh water generator is unavoidable on board ship.

But why do we need the FWG on board in first place?

In the middle of good old days people used to bring across lots of water in their ship. It was good however it expands the load on the ship and furthermore water lack issues were always there. Be that as it may, the nature of shore water will be extremely (too much) bad to be used in water tube boiler and filling (expansion) tanks. The storage space that could have been used for fresh water can as a result be used for fuel or added/more space for payload and products (that are bought and sold) when fresh water generator is installed on a ship. As you may know the first (or most important) concern for running a ship or any transportation business is to make money. Further more Boiler needs demineralized water to reduce overall scale development and corrosion issues. It is also normally used to build the general efficiency of the running machinery, mostly it uses the engine warmth/heat by Cooling The Hot Jacket Cooling Water At Around 85 Deg Celsius To 65 Deg Celsius.

Working Principal Of FWG?

Extremely important rule of all low weight freshwater generator is that, boiling point of water can be decreased by lessening the pressure of the air surrounding it. By keeping up a low pressure, water can be bubbled at low temperatures say 55 degree Celsius. The source of warmth for the fresh water generator could be waste heat rejected by generators and main engine jacket cooling water. This decrease In Saturation Temp lead to early vaporisation of water due to vacuum created within the chamber. It Is Created By The Help Of An Air Ejector, Which Extracts The Air From That compartment/chamber. An Air Ejector Works On Bernoulli's Rule and being used side by side with a brine ejector used to suck salt water from the chamber. The vacuum help disappear the water leaving behind the salt or salt water to be sucked by salt water ejector. It is then passed through the dimmister (A sort of punctured plate with very minute gaps) which traps any water or salt particle traveling through it. The evaporated water is then condensed together with the help of ocean water and after that tested for sality with the help of salino-meter.

Regulations Regarding Production of sea water on board ship:

1. Ship must be 12 nautical miles away from the nearest coastline to start the FWG.
2. Engine must be running at full ahead sea speed during start of FWG.
3. Ensure main engine parameters are normal.
4. Ship is not in congested water.
5. Ship is not maneuvering.
6. There is no oil/chemical spill reported in the visinity of the ship.

Safety Equipments on A Typical FWG:

1. Vacuum Breaker For Releasing Vacuum when we shut down the FWG.

2. Relief Valve For Releasing The Excess Pressure.

3. High Salinity Alarm: It Is Fitted To The Salinometer As It Measures Higher Salt Content In The Water Produced.

4. Temperature Gauge.

Starting Procedures for Fresh water generator:

• First we need to ensure that suction, discharge and overboard valves for ejector pumps are under open condition. Now once been checked, start the ejector pump.
• Close the vacuum breaker valve.
• Make Sure the S.W pressure at ejector (air) is not less than 3 bar. Now wait for 10-15 minutes to build vacuum in the generation chamber of fresh water generator. Wait until it shows more than 90% vacuum.
• Now open the sea water feed to the evaporator. Check for the sea water level in the shell through the sight glass and ensure it is at optimum level controlling feed through feed valve. Once the heating coils are fully submerged by the sea water open the J.C.W valves to the evaporator slowly.
• Purge out any air in the system by opening air vent at the top of the evaporator.
• Check for evaporation from the sight glass and then start the salinometer.
• Divert the outlet back to the feed water until the salinity is under the limit.
• When the salinity level is as per the desired or set value, open the discharge valve of distillate pump which sends the water to the fresh water holding tank through flow meter.
• Increase the evaporation rate and start the discharge pump. Check for the sytem to be stable.

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Author Amit                                                          Article requested by: NIÑO GONZALES

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Watch Keeping at sea for Marine Engineers | Step-by-step

Watch keeping is an integral part of marine engineer’s duties on board ship. The technicians perform tasks and routines for monitoring the ship's engine room. The clocks are divided into three periods of four hours and the following work must be carried out and checks carried out at sea.

• Check the colour of  exhaust emission from funnel.
• Check the Economizer temperatures, pressure drop and the system for any leakage.
• Check the oil fired boiler water level, blow through gauge glass and check pressure.
• Check the boiler circulating pump for operating pressure, vibration, noise, gland leakage and bearing oil level.
• Check and confirm normal operation of incinerator if running.
• Check the waste oil tank level and temperature, drain off water.
• Check Main & Aux. engine header tank levels, if they require filling record the quantity of water added.
• Check the temperatures and pressure of the fuel valve cooling system. Examine the level of the F. V. C  header tank, check for contamination and confirm through flow.
• Check stern tube header tank level, return flow, sump, pump and oil condition.Examine M. E cylinder tops for leakage, movement, overheating and any temperature or pressure outside the normal parameters.
• Check for exhaust gas leaks.Examine turbo charger oil levels, pump operation, temperatures, pressures and differentials, whilst checking also for any unusual noise or vibration.
• Monitor air cooler pressure drop, and ensure Makers operating parameters are adhered to with regard to dew point temperature.
• Check cylinder oil day tank level and individual lubricators for level, flow and function.
• Check all bunker fuel tanks for level, temperature and drain for water.
• Check fuel fine filter differential.Examine fuel pumps for leakage or unusual noises.Ensure oil mist detector is functioning correctly and test alarm.
• Check ME governor oil level and fuel pump racks.
• Examine auxiliary blower if running and scavenge belt to ensure that scavenge and air cooler drains are clear.
• Feel over scavenge belt.Test air line drains for water.
• Check all standby pumps are on auto mode and ready to start.
• Check air compressor  oil level, and the temperatures and pressures whilst  running.
• Check fresh water generator for normal operation & also chemical dosing to feed line.
• Check sewage treatment plant for normal operation.
• Examine A/E and check all running parameters are within limits. Fuel leakage, non fitting of double skin pipes and removed  protection or insulation from exhaust manifolds to be rectified immediately .
• Check A/E bilge’s for leakage.
• Confirm that an alternator engine is on standby in the control room and that the L. O priming pumps are on Auto.
• Checking drinking and domestic water hydrophore systems for levels, and leakage. Ensure that the Calorifier, circulating pump and UV Sterilizer are operating satisfactorily.
• Examine boiler feed water system for normal pump operation and check the cascade tank for temperature and level. Also check that there is no hot well contamination with fuel oil due fuel oil heating coil leaks.
• Examine air reservoirs and check the drains for water, ensure that control and service air reducing valves are functioning correctly and that the control air dehydrator is operating normally.
• Examine the purifier room for leakage, ensure that running purifiers and operating normally with regard to oil levels, flow rates, temperatures and pressures. 
• Ensure lowest throughput for L O purifiers.Check Calorifier.
• Examine Booster pumps, flow-meter and heaters for normal operation without leakage.
• Ensure that all main engine pumps are running normally and that standby pumps are ready for Auto operation.
• Check HFO Serv & Sett tanks levels and temp. Drain off water.
• Check all running purifiers for normal operation. Check gear case oil level, Separated Oil temperature and feed rate, motor load etc.
• Skim off sludge from recycle tank.
• Check F. O booster p/p, check F. O temperature.
• Check JCW pump and motor for normal operation.
• Check M/E Lubricating Oil Pressure (Bearing), X-Head Oil Pressure and Piston Cooling.Check piston cooler and L. O cooler in/out temp.
• Check sounding of all sludge tanks, bilge storage tanks, compare with previous sounding.
• Check M/E L O pump discharge filter Pressure drop.
• Check M/E L O pump/motor for normal operation.
• Check thrust bearing L. O temperature Fwd/Aft.
• Check E/R bilge level with special attention under the flywheel.
• Check L. O levels and temps of intermediate shaft bearings.
• Check stern tube L. O sump level, oil pressure, temp and return flow.
• Check M/E L. O sump sounding. compare with earlier soundings recorded.
• Check and confirm L. O purifier is operating normally note L. O temperature.
• Check piston cool leak off tank, open skimming v/v to skim off oil from top.
• Check piston cooling water tank level top up if required.
• Check and confirm main S. W p/p, motor and auxiliary  S. W pump/motor working normally.
• Check piston cooling p/p pressure and in/out temp of all units check flow.
• Check A/E load and winding temp. Do a function test on alarm panel. Reconfirm all running parameters of M/E and A/E.
• See the Chief Engineer’s standing instruction book and also notice board for daily instruction and guidance. Discuss with outgoing watch keeping engineer if there have been any special operations problems during his watch or any change in status of running machinery Function and lamp test of Alarm panel.
• Check no alarms are inhibited.Ensure no alarms indicating abnormal condition are active.
• Ensure air and water on deck shut if not required.
• Log down all parameters in log book
• Check for following hazards and rectify :-
• No Fuel, L. O or water  leaks.
• No loosely stowed equipment.
• Gas bottles shut and welding plant shut down.
• Fuel high pressure pipes for M/E & A /E’s secure and no leaks.
• No abnormal vibrations of any type.
• No water tight openings open unnecessary.
• Ensure that the welding equipment is off.Double check additional A/E on standby, and Emergency Generator on Auto.
• Double check M. E controls on Bridge and max speed limit set as per Chief Engineer’s instructions
• Check no alarms have been isolated, unless authorized by C/E and E/O. Note there are no existing alarm condition, unless a valid reason and C/E and E/O aware of.

WHEN IN DOUBT DO NOT HESITATE TO CALL CHIEF ENGINEER

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Author Amit                                                                            

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Comparison between shell and plate type Heat Exchangers

Both the Shell and Tube and Plate Type heat exchangers work with the same principles, exchanging heat between two fluids through thermal conduction, but with very different construction methods. Both plate type and shell and tube heat exchangers are normally used on ships and have their advantages and disadvantages.

Plate Type Heat Exchanger

Advantages

1. Simple and compact in size.
2. Heat transfer efficiency is more.
3. Can be easily dismantled for cleaning.
4. No extra space is required for dismantling.
5. Capacity can be increased by introducing plates in pairs.
6. Leaking plates can be removed in pairs, if necessary without replacement.
7. Maintenance – cleaning is difficult (as surface is visible).
8. Turbulent flow help to reduce deposits which would interfere with heat transfer.

Disadvantages
1. Initial cost is high since Titanium plates are expensive.
2. Finding leakage is difficult since pressure test is not as easy as tube coolers.
3. Bonding material between plates limits operating temperature of the cooler.
4. Pressure drop caused by plate cooler is higher than tube cooler.
5. Careful dismantling and assembling to be done.
6. Over tightening of the clamping bolts result in increased pressure drop across the cooler.
7. Joints may be deteriorated according to the operating conditions.
8. Since Titanium is a noble metal, other parts of the cooling system are susceptible to corrosion.

Shell and Tube Heat Exchanger

Advantages
1. Less expensive as compared to Plate type coolers.
2. Can be used in systems with higher operating temperatures and pressures.
3. Pressure drop across a tube cooler is less.
4. Tube leaks are easily located and plugged since pressure test is comparatively easy.
5. Tubular coolers in refrigeration system can act as receiver also.
6. Using sacrificial anodes protects the whole cooling system against corrosion.
7. Tube coolers may be preferred for lubricating oil cooling because of the pressure differential.


Disadvantages
1. Heat transfer efficiency is less compared to plate type cooler.
2. Dismantling for maintenance is difficult since a tube cooler requires enough clearance at one end to remove the tube nest / accommodate the lancing tool and the end covers are relatively large & heavy.
3. Capacity of tube cooler cannot be increased.
4. Requires more space in comparison to plate coolers.

REFERENCE SOURCE: 

“General Engineering Knowledge” by H.D. McGeorge

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Guest Author Name: Aditya Malik
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Short Bio: Trainee marine engineer opting for m.tech in marine engineering in U.K.



* The following article is partly produced as it is from Reference source for better understanding. Nor the blog owner or other permanent authors are responsible for any copyright claims. Inform us if you have any problem with the content.

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Conventional fresh water cooling system | Explaned

The machines installed on ships are designed to work with maximum efficiency and performance for long hours. The heating energy should be so reduced or heat transfer be increased by a cooling means to avoid a malfunction or a machine failure to prevent. For this reason the cooling water systems are installed on ships.

While there is an abundance of seawater available, marine diesel engines do not use it directly to keep the hottest parts of the engine cool. Instead, the water flows to the engine is fresh water, which is then cooled by seawater.

The engine cooling is achieved by circulating a cooling fluid around the internal passages in the engine. Therefore, the coolant is heated and itself cooled by a cooling flow of seawater. Without adequate cooling, parts of the engine, which are exposed to very high temperatures can be damaged so fast. The engine cooling allows metals to maintain their mechanical properties. The lubricating oil is sometimes used for cooling the piston, as a leak in the crankcase will not cause any problems.

Here a cooling system with fresh water  for low diesel engine speed is displayed. It is divided into two separate systems, one for the cooling coats of cylinders, cylinder heads and turbo blowers; The other for piston cooling.

The cooling water of the cylinder, after leaving the engine via a seawater cooler and circulation pump then turn the water circulation. Then pumped around the cylinder body, cylinder heads and turbo blowers/chargers. A head cap or expansion tank allows water to expand and system make-up. Venting openings are driven by the engine to the head of the reservoir for water from air exhaust cooling. A heater in the circuit facilitates the engine pre-heat in front of the hot water circuit.

The cooling system uses components similar to pistons, except that the drain tank is used instead of a head tank, and vent openings are performed at high points in the engine room. A piston cooling system
Only used to limit the contamination of the piston piston cooling glands.

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Author Amit                                                                                      Article Requested By: Alice

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* Various sources has been refereed before producing this post both online and offline but no part is reproduced except for the image (for reference purposes only).

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