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Air compressor arrangement - working principles and operational guideline

Use of compressed air for ships machinery
: The main aim of a compressor, as the name suggests, is to compress air or any fluid in order to reduce its volume. Some of the main applications of compressors onboard ships are main air compressor, deck air compressor, AC compressor and refrigeration compressor. Failure to start or control air compressor can be inconvenient, costly and can carry risks, which need to be managed.



Compressed air has many uses on board ship, ranging from diesel engine starting to the cleaning of machinery during maintenance. Ships compressed air systems are usually divided into one or more of the following: Low pressure (5-8 bar) air may be supplied by either individual compressors or pressure reducing valves fitted within the high pressure circuit.

High Pressure System

The Main and Auxiliary Engine starting air supply is to be monitored carefully for excess oil and water. Where compressors are fitted with cylinder lubrication then particular attention to the cylinder oil feed is required. Moisture traps and drain valves are to be blown down at regular intervals. Should the blowdown indicate excessive oil or moisture then the reason is to be immediately investigated.

All operating valves in the starting air system are to be operated slowly and with extreme caution. Do not stand directly in front of a high pressure valve when opening or closing. The Engine Room Staff are to be made fully aware by the Chief Engineer of the importance of correct operation and maintenance of the starting air compressors, and the effects of their failure during manoeuvring of the vessel. During manoeuvring of the main engine the starting air compressors are to be monitored locally for any sign of overheating or problem.


Low Pressure System

Compressed air equipment which supplies low pressure air for control or instrument purposes must be monitored constantly for moisture or other contaminants. Air, which is wet or contaminated, will have detrimental affects upon engine manoeuvring systems and process control.

All filters and moisture traps are to be cleaned and serviced as per the maker’s instructions or at intervals determined by operational experience. Short cycling of compressors indicated excessive consumption (leakage) must be investigated immediately. Long periods of compressor running are also to be investigated.


Dryers

For engine room service, refrigerant tap driers are normal practice. These units give long service with little maintenance, however manufacturer’s instructions must be adhered to. In some cases, absorption type driers are fitted which require strict change over routines.


Deck Service Compressors

Unwarranted use of these machines is to be avoided at all times. It is essential that any deck services are shut down when not required. Supply from the main starting compressors via reducing valves is not to be used for deck general service air supply unless an emergency exists.




Alarms

All compressor alarms, shut downs and measuring instruments are to be checked and calibrated at regular intervals and in line with the Planned Maintenance requirements. Emergency Air Compressors are to be tested as part of the weekly safety routines onboard.


Safety precautions

A recent case involving the failure of a control air compressor on board a ship illustrates how essential the control air system is to safe operations. The compressor in question provided compressed air to the main engine clutches. Failure of the air supply resulted in failure of the clutches. The ship sustained collision damage and subsequent delays.

The control air receiver was insufficiently topped up to re-engage the clutches. It is recommended that when one air compressor fails, the air receivers should be kept topped up at all times by the standby compressor.

Repair of the air compressor should be prompt. The engine room should operate a watch system and the Unattended Machinery Space notation should be considered suspended.

It is also recommended that the low air pressure alarm and set point be checked on a regular basis using currently calibrated gauges.


Related Info:

  1. Compressed Air Systems for various shipboard operations
  2. The main aim of a compressor, as the name suggests, is to compress air or any fluid in order to reduce its volume. Some of the main applications of compressors onboard ships are main air compressor, deck air compressor, AC compressor and refrigeration compressor. Failure to start or control air compressor can be inconvenient, costly and can carry risks, which need to be managed.....

  3. Marine air compressors working principles
  4. Control or instrument air supplies have particular requirements with regard to being moisture and oil free and without impurities. A special type of oil-free compressor may be used to supply control air or it may be treated after delivery from an ordinary air compressor. This treatment results in the air being filtered and dried in order to remove virtually all traces of oil, moisture and any atmospheric impurities.....

  5. Coolers at sea- Shell and tube type coolers and plate type coolers
  6. Heat exchangers on board ship are mainly coolers where a hot liquid is cooled by sea water. There are some instances where liquid heating is required, such as heavy fuel oil heaters and sea water heaters for tank cleaning. Although being heat exchangers, the main condenser for a steam ship and the evaporator/distiller are dealt with separately .....

  7. Distillation system- Production of distilled water for ships use - The evaporation process
  8. Distillation is the production of pure water from sea water by evaporation and re-condensing. Distilled water is produced as a result of evaporating sea water either by a boiling or a flash process. This evaporation enables the reduction of the 32000 parts per million of dissolved solids in sea water down to the one or two present in distilled water. The machine used is called an 'evaporator', although the word 'distiller' is also used.....

  9. Oily water separator and filter unit for 15 parts per million purity
  10. Oil/water separators are used to ensure that ships do not discharge oil when pumping out bilges, oil tanks or any oil-contaminated space. International legislation relating to oil pollution is becoming more and more stringent in the limits set for oil discharge.....

  11. Sewage treatment on board- biological and chemical sewage treatment plant
  12. The discharge of untreated sewage in controlled or territorial waters is usually banned by legislation. International legislation is in force to cover any sewage discharges within specified distances from land. As a result, and in order to meet certain standards all new ships have sewage treatment plants installed.....

  13. Incinerator for ships
  14. Stricter legislation with regard to pollution of the sea, limits and, in some instances, completely bans the discharge of untreated waste water, sewage, waste oil and sludge. The ultimate situation of no discharge can be achieved by the use of a suitable incinerator. When used in conjunction with a sewage plant and with facilities for burning oil sludges, the incinerator forms a complete waste disposal package.....



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 || Propellers || Power Plants || Starting air system || Steam turbines || Steering gear || Sulzer engine || Turbine gearing || Turbochargers || Two stroke engines || UMS operations || Drydocking & major repairs || Critical machinery || Deck machineries & cargo gears || Control and instrumentation ||Fire protection ||Engine room safety ||






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