Central Cooling System:
One of the most common systems is central cooling. Fresh water is here used in a closed circuit to cool down the engine room machineries. The fresh water returning from the heat exchanger after cooling the machineries is further cooled by sea water in seawater cooler.
In central cooling systems the seawater is used as a cooling media in large seawater cooled heat exchangers to cool the fresh water of the closed circuit. They are the central coolers of the system.
The fresh water system can be a mixed system; the heat from all the different machineries and other components that need cooling is mixed together in one flow. This is the easiest system to install and regulate, but needs some more cooling area than a split system.
In a split system the low temperature (LT) circuit is used for low temperature zone; hence its temperature is lower than the high temperature (HT) circuit. The LT circuit comprises of all auxiliary systems. The HT circuit mainly comprises of jacket water system of the main engine where the temperature is quite high.
High Temperature Circuit:
Fresh water pump pumps the water from the main engine and the auxiliary engine jacket. Water is taken at the outlet (some are by orifice) from the engines to the fresh water generator. From the outlet of the fresh water generator, the water is led back to the pumps. The inlet temperature to the engine is about 65˚C and the outlet about 80˚C. Whatever high temperature goes to the central coolers.
Low Temperature Circuit:
Temperature of 35˚C. Distributed to two groups of auxiliaries connected in series. Within each group, the components are connected in parallel. 1st group - air compressors, air-con plant, condenser for fresh water generator, 2nd group - the air and lube oil coolers for the main engine. The air and lube oil coolers for the auxiliary engines are also connected. The bulk of the fresh water is then fed back to the central fresh water coolers.
Temperature Control:
The heat absorbed by the fresh water in the high temperature circuit will be transferred to the low temperature circuit at the junction. The temperature regulated valve mixes water of about 45˚C from the low temperature circuit with warmer water of about 55˚C from the engines and fresh water generator outlet to a suitable level for the inlet to the engines.
Fresh Water Cooling System:
Ø A clean system with reduced requirements regarding cleaning and maintenance.
Ø Less “wear” of pipes and valves, therefore less maintenance cost.
Ø Less investment of cost as pipes need not be made for seawater usage.
Ø Reduced number of valves made of expensive materials.
Ø Constant to near constant temperature level of cooling medium means easier temperature control of air and lube oil coolers for main and auxiliary engines.
Ø No condensate on air side, reducing air fouling, owing to the higher and constant temperature for main engine air coolers. Cleaner air coolers compensate for higher cooling water temperature.
Ø No cold starting of main engine, since the whole system is kept at warm temperature when the ship is in port.
Ø Constant running condition for the main engine as regards to cooling water, lube oil and air.
Ø Less wear of cylinders liners, as consequences of running condition – no cold corrosion/startup.
Ø Greater reliability of services offered by the central cooling system is important for an unmanned engine room.
Disadvantages:
Ø Initial high cost.
Ø Limitation of lower temperature, especially for main engine air cooler, also during high sea water temperature.
Central Cooling System:
One of the most common systems is central cooling. Fresh water is here used in a closed circuit to cool down the engine room machineries. The fresh water returning from the heat exchanger after cooling the machineries is further cooled by sea water in seawater cooler.
In central cooling systems the seawater is used as a cooling media in large seawater cooled heat exchangers to cool the fresh water of the closed circuit. They are the central coolers of the system.
The fresh water system can be a mixed system; the heat from all the different machineries and other components that need cooling is mixed together in one flow. This is the easiest system to install and regulate, but needs some more cooling area than a split system.
In a split system the low temperature (LT) circuit is used for low temperature zone; hence its temperature is lower than the high temperature (HT) circuit. The LT circuit comprises of all auxiliary systems. The HT circuit mainly comprises of jacket water system of the main engine where the temperature is quite high.
High Temperature Circuit:
Fresh water pump pumps the water from the main engine and the auxiliary engine jacket. Water is taken at the outlet (some are by orifice) from the engines to the fresh water generator. From the outlet of the fresh water generator, the water is led back to the pumps. The inlet temperature to the engine is about 65˚C and the outlet about 80˚C. Whatever high temperature goes to the central coolers.
Low Temperature Circuit:
Temperature of 35˚C. Distributed to two groups of auxiliaries connected in series. Within each group, the components are connected in parallel. 1st group - air compressors, air-con plant, condenser for fresh water generator, 2nd group - the air and lube oil coolers for the main engine. The air and lube oil coolers for the auxiliary engines are also connected. The bulk of the fresh water is then fed back to the central fresh water coolers.
Temperature Control:
The heat absorbed by the fresh water in the high temperature circuit will be transferred to the low temperature circuit at the junction. The temperature regulated valve mixes water of about 45˚C from the low temperature circuit with warmer water of about 55˚C from the engines and fresh water generator outlet to a suitable level for the inlet to the engines.
Fresh Water Cooling System:
Ø A clean system with reduced requirements regarding cleaning and maintenance.
Ø Less “wear” of pipes and valves, therefore less maintenance cost.
Ø Less investment of cost as pipes need not be made for seawater usage.
Ø Reduced number of valves made of expensive materials.
Ø Constant to near constant temperature level of cooling medium means easier temperature control of air and lube oil coolers for main and auxiliary engines.
Ø No condensate on air side, reducing air fouling, owing to the higher and constant temperature for main engine air coolers. Cleaner air coolers compensate for higher cooling water temperature.
Ø No cold starting of main engine, since the whole system is kept at warm temperature when the ship is in port.
Ø Constant running condition for the main engine as regards to cooling water, lube oil and air.
Ø Less wear of cylinders liners, as consequences of running condition – no cold corrosion/startup.
Ø Greater reliability of services offered by the central cooling system is important for an unmanned engine room.
Disadvantages:
Ø Initial high cost.
Ø Limitation of lower temperature, especially for main engine air cooler, also during high sea water temperature.
Few Figure for Easy Understanding:
----------------------------------------------------------------------------------------------------
Links:
Thank you so much. But can you update the photo of HT Circuit, LT Circuit, Temp Controle section? Some photos are not showing.
ReplyDelete