Created by Ankur Sharma, Gurudayal Srivastava, Vikram Vikram Singh, Sanket Sank et Tamhane Tamhane 1. Vaccum loss occurred in fresh water generator. How will you come to know without pressure gauge? We can check through the sight glass that water is not getting boiled or the b oiling is not that efficient at the same jacket water temerature or we can ut our finger on the vaccum cock attached to the generator casing! "f finger is not getting sucked, it shows fresh water generator is not creating vaccum! 2. Fresh water generator principle? The saturation temerature of water is directly roortional to the vaor ressure of the li#uid! As the ressure decreases, the saturation temerature of water decreases, thereby if we reduce the ressure well below vaor ressure of the li#uid at certain temerature, evaoration takes lace! $ressure and temerature are related by Gay%&ussac' Ga y%&ussac'ss law( $)*T)+$*T 3. Start the fresh water generator, principle of fresh water generator and working of eector? Starting the Fresh !ater "enerator
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-efore starting starting the the fresh water generator generator we we have to check that the the shi shi is not in in congested congested water, water, canals and is .
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! !
Check whether whether engine engine is running above /. /. rm, the reason reason for this is is that at low rm the temerature of jacket jacket
water which is around 0. degrees and not sufficient for evaoration of water! 1!
Check the drain valve resent at the bottom of the the generator is in close osition!
2!
3ow oen oen suction and discharge discharge valves of the the sea water um which will rovide water for for evaoration, evaoration, cooling
and to the eductor for creating vacuum! /!
4en the the sea water discharge discharge valve from from where the water water is sent back back to the sea sea after circulating inside the fresh fresh
water generator! 0!
Close the vacuum valve situated on to of the generator!
5!
3ow start start the sea sea water water um um and check the ressure of the um! The ressure is generally 1%2 bars!
6!
Wait Wa it for the vacuum to build u! Va Vacuum cuum should be at least 7.8 which can be seen on the gauge resent on the
generator! Generally Generally the time taken for the generation of vacuum is about ). minutes! 7!
When vacuum is achieved achieved oen the valve for feed water treatment, this is to revent revent scale formation inside the
lates! ).!
3ow oen hot water 9jacket water: inlet and outlet valves slowly to about half! Always oen oen the outlet outlet valve first
and then inlet valve! Slowly start to increase the oening of the valves to full oen! ))!
3ow we can see that that the boiling temerature temerature starts increasing and the vacuum starts droing! droing!
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The vacuum dro to about 6/8 which is an indication indication that evaoration is is started!
)1!
4en the valve from fresh water um to drain!
)2!
Switch on the salinometer if it has to be started manually! Generally it is on auto start!
)/!
3ow start fresh water um and taste the water coming out of the drain!
)0!
When fresh water starts roducing it is seen that the boiling temerature dros again slightly and vacuum comes
back to the normal value! )5!
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 roerly or not and to revent the whole fresh water from getting contaminated with salt water! The value of salinometer is ket below ).m! )6!
After checking the taste of the water coming out of the salinometer, oen valve for tank from the um and close
drain valve!
Stopping#
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Close the jacket water inlet valves! Generally inlet is closed first and then the outlet valve!
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Close the valve for feed water treatment!
1!
Sto fresh water um!
2!
Switch off the salinometer!
/!
Sto sea water um 9also known as ejector um:!
0!
4en vacuum valve!
5!
Close sea water suction valve and overboard valve! This is generally not re#uired as they are non% return valves!
;owever, in case of valve leaking or damage, these valves are to be closed without fail!
!orking of eector# •
Air Ejector Theory "t works on the rincile of convergent *divergent no<
$)%ressure of the fluid entering the no<ivergent no<
>% >ivergent 3o<iffuser $oint!
•
Air Ejector
$. How will you start fresh water generator? Covered above! %. Fresh water generator working, air eector working, salinometer working? !orking of the F!"
The hot jacket water from the diesel engine is assed through the evaorator's heated nest! The sea water enters the evaorator through the flow meter and due to the low ressure of the chamber? it boils and gets converted to steam! Generally the feed of the seawater is ket half the stated #uantity to facilitate ade#uate boiling of sea water! The steam then asses through a steam searator, in which the water articles in the steam are searated and collected! The steam then enters the condenser, where it cools down to form fresh water! "t is then removed from the condenser with the hel of a distillate um! The remainder sea water articles or the brine which gets collected at the bottom is drawn out with the hel of an ejector um!
&ir eector working already co'ered. Salinometer working#
Water urity, in terms of the absence of salts, is essential where it is to be used as boiler feed! $ure water has a high resistance to the flow of electricity whereas salt water has a high electrical conductivity! A measure of conductivity, in Siemens, is a measure of urity! The salinity measuring unit shown in @igure )/!) uses two small cells each containing a latinum and a gunmetal electrode! The li#uid samleasses through the two cells and any current flow as a result of conductance is measured! Since conductivity rises with temerature a comensating resistor is incororated in the measuring circuit! The insulating lunger varies the water flow in order to correct values to .C for a convenient measuring unit, the microsiemens*cm1 or dionic unit! A de%gassifier should be fitted ustream of this unit to remove dissolved carbon dioBide which will cause errors in measurement! (. F!" not producing 'accum)reasons? )! ;ole in the chamber, ejector or the ieline con necting chamber to ejector! ! "f there is a crack in chamber body! 1! "f the vaccum releasing cock is not holding! 2! "f the line from chamber to ejector is choked! /! "f the sea water ejector um is not creating sufficient ressure! *. Fresh water generator working and pro+lems? . -rinciple of fresh water generator, re'erse osmosis? -rinciple of e'erse /smosis
As the name suggest, this methods works on reversing the osmosis rincile! When a chemical solution is searated from ure water b y a semi ermeable membrane 9allowing assage of water not salt: then the ure water flows through the me mbrane until all the ure water has assed through or until the hydrostatic ressure head of the salt solution is sufficiently big enough to arrest or sto the rocess! everse osmosis is the use of this henomenon in reverse direction! This results in water being forced through the membrane from the concentrated solution toward the more dilute one! This is achieved b y alying ressure of the osmotic ressure of the concentrated solution!
!orking
The osmotic ressure of sea water is 6 bars but to overcome system losses and the fact that the sea water concentration increases as it asses through the length of the membrane, much higher ressure around 2.%5. bar, deending uon the lant si
