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Refrigeration of cargo spaces and storerooms
Refrigeration process system requirements:
Refrigeration is a process in which the temperature of a space or its
contents is reduced to below that of their surroundings. Refrigeration is used in the carriage of some liquefied gases and bulk chemicals
, in air conditioning systems, to cool bulk CO2 for fire
fighting systems and to preserve perishable foodstuffs during transport of foodstuff .
Ships refrigeration plant may vary from the small domestic refrigerating unit for provisions to large plant for reefer vessels.
The Chief Engineer is responsible for the correct temperatures being maintained, delegating the good operations and maintenance of the plant to the 2/E. Larger plants may have a Refrigeration Officer.
Machinery under ship's engineer responsibility may include:
All maintenance recommendations from the makers have to be carried out regularly and according to instructions, entered in the refrigeration maintenance log, together with the test of all cut outs, i.e. HP, LP, LO, HT, that have to be carried out at regular intervals, generally one month.
- Domestic ref. plant.
- Cargo ref. plants
- Air conditioning plants
- Ventilation and heating plants
- Cargo refrigerated containers
All adjustment must be made according to standard good practice and records of the same entered in the log.
Filter separators and driers should be regularly cleaned in order to have always the circuit moisture, dirty and oil free.
When shutting down a plant all refrigerant gas must be pumped in the liquid receiver or condenser.
How the system works ?
Refrigeration of cargo spaces and storerooms employs a system of
components to remove heat from the space being cooled. This heat is
transferred to another body at a lower temperature. The cooling of air
for air conditioning entails a similar process.
The transfer of heat takes place in a simple system: firstly, in the
evaporator where the lower temperature of the refrigerant cools the
body of the space being cooled; and secondly, in the condenser where
the refrigerant is cooled by air or water. The usual system employed for
marine refrigeration plants is the vapour compression cycle as shown in diagram here.
Fig: Vapour compression cycle
The pressure of the refrigerant gas is increased in the compressor and
it thereby becomes hot. This hot, high-pressure gas is passed through
into a condenser. Depending on the particular application, the
refrigerant gas will be cooled either by air or water, and because it is still
at a high pressure it will condense. The liquid refrigerant is then
distributed through a pipe network until it reaches a control valve
alongside an evaporator where the cooling is required. This regulating
valve meters the flow of liquid refrigerant into the evaporator, which is
at a lower pressure. Air from the cooled space or air conditioning system
is passed over the evaporator and boils off the liquid refrigerant, at the
same time cooling the air.
The design of the system and evaporator
should be such that all the liquid refrigerant is boiled off and the gas
slightly superheated before it returns to the compressor at a low
pressure to be recompressed.
Thus it will be seen that heat that is transferred from the air to the
evaporator is then pumped round the system until it reaches the
condenser where it is transferred or rejected to the ambient air or water.
It should be noted that where an air-cooled condenser is employed in
very small plants, such as provision storerooms, adequate ventilation is
required to help remove the heat being rejected by the condenser. Also,
in the case of water-cooled condensers, fresh water or sea water may be
employed. Fresh water is usual when a central fresh-water/sea-water
heat exchanger is employed for all engine room requirements. Where
this is the case, because of the higher cooling-water temperature to the
condenser, delivery temperatures from condensers will be higher than
that on a sea water cooling system.
Temperatures of domestic refrigerated rooms have to be corrected daily by the 2nd Engineer or delegated Officer, passed to the Chief Engineer and to the Master.
On larger plant suitable logs will be supplied in order to enter temperature of the cargo and all other relevant details.
- Refrigeration system components Centrifugal,reciprocating, or screw compressors. Modern Shell and tube type condensers.Various refrigerant types, refrigerant flow control valves & Ancillary fittings etc.....
- Modern refrigerants for cargo ships
In all refrigeration, heat is collected in a suitable fluid and this fluid is removed from the space substance being cooled carrying the heat with it. Such fluid known as refrigerant. All refrigerants using on board might be sub-divided into primary and secondary refrigerants.....
- Choice of refrigerants
Theoretically, almost any liquid can be used as a refrigerant if its pressure/temperature relationship is suitable for the conditions. Although no perfect refrigerant is known, there are certain factors which determine a refrigerant's desirability for a particular duty and the one selected should .....
- Cargo refrigeration procedure Refrigerated cargo vessels usually require a system which provides for various spaces to be cooled to different temperatures. The arrangements adopted can be considered in three parts: the central primary refrigerating plant, the brine circulating system, and the air circulating system for cooling the cargo in the hold.....
- How to troubleshoot refrigeration system faults
It is important that gas losses are minimized in systems. Gas used in this system is both expensive and a danger to health. The system is therefore to be kept in an absolutely gas-tight condition. On no account should the refrigerant be blown off to atmosphere. Before carrying out repairs the refrigerant should be pumped down to the liquid receiver or the condenser. The remaining gas should be vented off and the area well ventilated.....
- Safety precautions for refrigeration plant and refrigerated compartments Adequate information should be available on each vessel, laying down the operation and maintenance safeguards of the refrigeration plant, the particular properties of the refrigerant and the precautions for its safe handling.....
- Reefer container Individual containers with their own refrigeration plant are connected to the 440 or 220 a.c. sockets provided on deck. Systems designed for the cooling of refrigerated containers employ trunkings arranged so that containers stowed in stacks between built-in guide rails, can be connected to the suction and delivery air ducts of the ship's
refrigeration plant by bellows pieces operated pneumatically......
- Air conditioningSingle-duct & twin-duct marine air conditioning system - An air conditioning system aims to provide a comfortable working environment regardless of outside conditions. Satisfactory air treatment must involve a relatively 'closed' system where the air is circulated and
Marine machineries - Useful tags
Marine diesel engines ||Steam generating plant ||Air conditioning system ||Compressed air ||Marine batteries ||Cargo refrigeration ||Centrifugal pump ||Various coolers ||Emergency power supply ||Exhaust gas heat exchangers ||Feed system ||Feed extraction pump ||
Flow measurement || Four stroke engines || Fuel injector || Fuel oil system || Fuel oil treatment ||Gearboxes || Governor ||
Marine incinerator ||
Lub oil filters ||
MAN B&W engine ||
Marine condensers ||
Oily water separator ||
Overspeed protection devices ||
Piston & piston rings ||
Crankshaft deflection ||
Marine pumps ||
Various refrigerants ||
Sewage treatment plant ||
Starting air system ||
Steam turbines ||
Steering gear ||
Sulzer engine ||
Turbine gearing ||
Two stroke engines ||
UMS operations ||
Drydocking & major repairs ||
Critical machinery ||
Deck machineries & cargo gears
|| Control and instrumentation
||Engine room safety ||
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