CoC Oral Exam Preparation (Part – 20): OWS & Regulations

MARPOL Regulations of Discharging Machinery Bilge into the sea:

The rules and Regulations that govern the operation of an Oily Water Separator are under MARPOL  Annex I: “Prevention of pollution by oil”.

Regulation 14: Oil Filtering Equipment

  1. Vessels above 400 GT and less than 1000 GT shall have an oil filtering equipment
  • Approved by the Administration
  • Will ensure that any oily mixture discharged into the sea after passing through the equipment has an oil content not exceeding 15 ppm

2.  Vessels above 1000 GT shall have an oil filtering equipment

    • In addition to the above, shall be provided with alarm arrangements to indicate when the level cannot be maintained.
    • Also arrangements to ensure that any discharge of oily mixture is automatically stopped when the oil content of the effluent exceeds 15 ppm

Regulation 15: Control of discharge of Oil

A the provisions of regulation 4 (Exceptions) of this annex, any discharge into the sea of oil or oily mixtures from ships shall be prohibited.

A.  Outside special Area’s: (Regulation 15)

Any discharge into the sea of oil or oily mixtures from ships of 400 gross tonnage and above shall be prohibited except when all the following conditions are satisfied:

  1.  The ship proceeding is en route
  2. The oily mixture is processed through an oil filtering system
  3. The oil content of the effluent without dilution does not exceed 15ppm.
  4. Oily mixtures do not originate from the cargo pump room bilges in case of oil tankers
  5. Oily mixtures in case of oil tankers is not mixed with oil cargo residues

B.  In special Areas : (Regulation 15)

Any discharge into the sea of oil or oily mixtures from ships of 400 gross tonnage and above shall be prohibited except when all of the following conditions are satisfied:

  1. The ship proceeding is en route
  2. The oily mixture is processed through an oil filtering system
  3. The oil content of the effluent without dilution does not exceed 15ppm.
  4. When the vessel is in the special area the oil filtering system apart from having an alarm when the 15ppm cannot be maintained shall also be of a design where the oil filtering system shall stop automatically when the oil effluent exceeds 15ppm
  5. Oily mixtures do not originate from the cargo pump room bilges in case of oil tankers
  6. Oily mixtures in case of oil tankers is not mixed with oil cargo residues

C.   In respect of the Antarctic area, any discharge into the sea of oil or oily mixtures from any ship shall be prohibited.

Exceptions (Regulation 4)

  1. The discharge into the sea of oil or oily mixture necessary for the purpose of securing the safety of a ship or saving life at sea; or
  2. the discharge into the sea of oil or oily mixture resulting from damage to a ship or its equipment:
  3. provided that all reasonable precautions have been taken after the occurrence of the damage or discovery of the discharge for the purpose of preventing or minimizing the discharge; and
  4. except if the owner or the master acted either with intent to cause damage, or recklessly and with knowledge that damage would probably result; or
  5. the discharge into the sea of substances containing oil, approved by the Administration, when being used for the purpose of combating specific pollution incidents in order to minimize the damage from pollution. Any such discharge shall be subject to the approval of any Government in whose jurisdiction it is contemplated the discharge will occur.

Oily Water Separator (OWS)

ows

Fig: Oily Water Separator

Operation of Oily Water Separator:

1st Stage:

  • —The complete unit is first filled with clean water by opening the air vent.
  • The oily water mixture is then pumped through the separator inlet pipe into the coarse separating compartment. Here some oil, as a result of its lower density, will separate and rise into the oil collection space.
  • The remaining oil/water mixture now flows down into the fine separating compartment and moves slowly between the catch plates.
  • —More oil will separate out onto the underside of these plates and travel outwards until it is free to rise into the oil collecting space.
  • —The almost oil-free water passes into the central pipe and leaves the 1st Stage separator unit. The purity at this point will be 100 parts per million or less.
  • —An automatically controlled valve releases the separated oil to a storage tank.
  • Air is released from the unit by a vent valve.
  • —Steam or electric heating coils are provided in the upper and sometimes the lower parts of the separator, depending upon the type of oil to be separated.
  • Where greater purity is required, the almost oil-free water passes to a filter unit or 2nd Stage.

2nd Stage:

  • —The water flows in turn through two filter stages and the oil removed passes to oil collecting spaces.
  • —The first-stage filter removes physical impurities present and promotes some fine separation.
  • The second-stage filter uses coalescer inserts to achieve the final de-oiling. (—Coalescence is the breakdown of surface tension between oil droplets in an oil/water mixture which causes them to join and increase in size.)
  • The oil from the collecting spaces is drained away manually, as required, usually about once a week.
  • —The filter inserts will require changing, the period of useful life depending upon the operating conditions.
  • Current legislation requires the use of a monitoring unit which continuously records and gives an alarm when levels of discharge in excess of 15 parts per million occur.

OWS Monitor and Control Unit:

—Current regulations with respect to the discharge of oily water from ships set limits of concentration 15 parts per million.

  • —A monitor is required in order to measure oil content of processed discharging water through OWS and provide both continuous records and audio & visual alarm with auto stopping device where the permitted level is exceeded.

OWS Monitor

Fig: OWS Oil Monitor and Control Unit

Working Principle of Oil Monitor & Control Unit:

  • —The principle used is that of ultra-violet fluorescence.
  • —This is the emission of light by a molecule that has absorbed light.
  • —During the short interval between absorption and emission, energy is lost and light of a longer wavelength is emitted.
  • —Oil fluoresces more readily than water and this provides the means for its detection.
  • —A sample is drawn off from the overboard discharge and passes through a sample cell .
  • —An ultra-violet light is directed at the sample and the fluorescence is monitored by a photoelectric cell.
  • The measured value is compared with the maximum desired value in the controller/recorder. Where an excessive level of contamination is detected an audio and visual alarm is sounded and diverting valves are operated from overboard to bilge holding tank.
  • The discharging liquid is then passed to a Bilge holding Tank

(For details of MARPOL Regulations and requirement, please refer to www.imo.org or current edition of MARPOL 73/78 and read “A Short Notes on MARPOL Regulations”)

Written by Mohammud Hanif Dewan, IEng, IMarEng, MIMarEST, MRINA

Mohammud Hanif Dewan, IEng, IMarEng, MIMarEST, MRINA

Working as the Deputy Commandant at LMTI, Liberia and Assistant Consultant at IMO. Worked as the Lecturer at ALAM Malaysia, IMA & CMC Bangladesh. Sailed as Chief Engineer on board various types of Tankers in multinational companies. Also worked as a consultant for developing and preparation of new syllabuses of marine engineering pre-sea and post-sea courses of Department of Shipping, Bangladesh as per STCW 2010 Manila Amendments. Writer of maritime articles. Researcher on Energy Efficiency in Shipping Industry, UTM, Malaysia.

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