Please don"t refer to the old books there they have shown the diagram of system which was used in 90 s .i have sailed on 2013 built ship and all modern ship nowadays uses this type of system which i will show you in my blog with practical explanation.
The corrosion and other problem associated with salt water circulation can be minimized by using central cooling system which uses a LT water which is a distilled water produced from fresh water generator with additives added in it.
NOW first take a look at S.W and service system on ship and then we will go into LT cooling water line diagram on ship.
The diagram shows a SW system on ship.
The sea water is drawn from( high sea chest when the ship is in port and from changeover to low sea chest when the ship sails away from port in high seas) sea chest through filter . The sea chest are incorporated with filter ,air vent for purging , MGPS (marine growth prevention system), drain hole. The all sea water system is on bottom platform .
From the sea water manifold the sea water is distributed for various purpose. Many pump such as
1.sea water pump for cooling.
2.ballast pump for ballasting and de ballasting .
3.fire and gs pump for fire fighting and deck washing.
4.fire and bilge pump for de ballasting aft peak tank , for pumping out bilges during an emergency (rare) and pumping out cargo hold bilges by the help of eductor
5. Ejector pump for fresh water generator.
In dia you can see all this pump are connected through a common manifold line
Now we are interested in sea water pump only ,we have two s.w pump which take suction from sea water common manifold with changeover arrangement. The sea water pump with a pressure of 3.5 bar approx send sea water to a height to
1. No 1 & No 2 F.W cooler or central cooler
2. Sewage treatment plant.
3. Atmospheric condensor.
And finally after cooling all this equipment it goes overboard.
Now lets talk about LT F.W cooling system line diagram.
As you can see in diagram the LT water i.e distilled water with additives is circulated all around the ship equipment to be cooled.
As the temperature of water is low around 35 to 50 degree than a HT water cooling system which is around 70 to 84 degree celcius ,so it is called low temperature cooling water system.
The low temperature water after cooling all equipment and machine onboard gets heated up and comes to LT F.w Cooler. Here the LT Water is cooled by heat exchanger by sea water on one side . A pneumatic controller continuosly control the LT Cooling water outlet temperature to around 40 degree. If suppose when the ship is in port only air condenser , reefer condensor ,air compressor , 1 generator is running ,so after cooling only this machinery the temperature of LT water will be less . In this case the bypassed to cooler valve is closed see dia.
When the ship is sailing all the machinery are running such as air cooler of ME, lube oil cooler ME , ME jacket cooling water , All the 3 generator etc. In this case the LT water temperature will be high enough, so the controller will open the bypass valve to cooler so that the LT water will be cooled by the LT FW COOLER.
Now lets talk about all the equipment which is to be cooled by LT water;
The LT water after LT F.W cooler passes to 3 pipeline:
They are
1.First pipeline goes to cool Engine control room condensor , main air compressor for intercooler, accomodation air conditioning, bridge control room condensor . All this after cooling meet at a point 3 as shown in figure.
2. Second pipeline is divided into again 3 pipeline. 1st pipeline for ME LO COOLER after cooling it ,it than goes to ME Jacket FW cooler (check my blog HT COOLING FW system). 2nd pipeline goes to cool ME air cooler and the 3rd pipeline goes to cool Intermediate shaft bearing. All this 3 after cooling meets at a point 1 as shown in figure.
3. The third pipeline goes to cool all the 3 generator on ship. The outlet then goes to LT expansion tank. After cooling in generator the outlet goes and meet at point 2 as shown in diag.
The outlet of LT expansion tank meets at point 4 in the diagram.
The LT cooler PUMP than suck the heated water from all 1 ,2 ,3 ,4 point and leads the water to LT FW cooler. This is how the circuits complete.
Note we do not have any controller in sea water cooling circuit.
Thus we can conclude there are 3 circuits
1) HT JCW FW COOLING
2)LT FW COOLING SYSTEM
3)SW COOLING SYSTEM.
ADVANTAGE OF ALL THIS SYSTEM LT/HT FRESH WATER COOLING ARE AS FOLLOWS;
1. Low maintenance cost -as the system runs with fresh water the cleaning ,maintenance and component replacement reduces .
2. Less corrosion
3. High speed of fluid hence better heat exchange . Higher speed is possible in fresh water system which results in reduced piping and low installation cost .
4. use of cheaper material since corrosion factor decreases, expensive material are not required for valves and pipelines.
5. Constant temperature level maintained -since the temperature controlled is irrespective of sea water temperature, stable temperature is maintained which helps in reducing machinery wear down ,due to thermal expansion if different maintained as for ex in sea water cooling system.
6. Less wear of engine parts - less wear of cylinder liner as the jacket is maintained warm avoiding cold corrosion.
7. Ideal for unmanned engine room the greater reliability and temperature controlling of the system offered by central cooling system.
DISADVANTAGE
1.high installation cost
2.limitation of low temperature
No comments:
Post a Comment