PRECAUTION AGAINST ASPHALTENES IN BUNKER OIL

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Vessel face sometimes troubles while using residual fuels, even though fuel testing lab shows results to be in satisfactory condition.The root cause of such troubles is due to presence of asphaltenes.
      Asphaltenes are components of asphalt that are insoluble in petroleum naphtha but are soluble in carbon di sulfide. They are hard and brittle and are made up largely of high molecular weight poly nuclear hydrocarbon derivatives containing carbon, hydrogen, sulfur, nitrogen, oxygen and usually three heavy metals:- nickel, Iron, vanadium.
      As per fuel standards ISO 8217: 2010 carbon content limit is 18% m/m, whereas once the carbon content exceeds 15% m/m chances are higher for asphaltenes.
      Though asphaltenes are useful component of fuel oil but high level of asphaltenes can impair the combustion quality of the fuel oil, promoting increased  wear and fouling of engine components.
    Asphaltenes cause sludge formation and deposits in fuel tanks and oil lines. Asphaltenes should be kept soluble to prevent problem of sludge formation in centrifugal separation, filters and on tank bottoms. To minimize compatibility risks care should be taken to avoid mixing bunkers from different suppliers and sources in storage tanks on board.
   asphaltenes the most polar and heaviest compounds of oil, associate themselves in solution to form complex colloidal structures. This causes serious problems in diesel engines, fuel systems, oil recovery and oil carrying pipelines.
PRECAUTIONS:-

  1. Spot/ Drop test  introduced by Oliensis. Uniform spot represents an oil in which asphaltenes are stable whereas dark centered spot is diagnosis of unstable asphaltenes.
  2. There are asphaltene  dispersants and fuel stabilizer to disperse existing sediments and sludge and prevent new formation of sludge.
  3. Fuel homogenization--  This will help in reducing the size of the fuel.
  4. There are chemicals which can be added and they act on these concentrated aromatic carbons and break up into the very fine particles and help to disperse throughout the fuel oil system.
  5. The chemical helps to homogenization of the fuel by dispersing the heavy phase in the light phase.
  6. The smaller units burn more easily in the flame zone there by reducing the amount of unburned carbon residue in the combustion chamber, piston ring grooves, lubrication oil and in the flue gas.
  7. Fuel should be circulated from tank to tank on weekly basis to prevent sludge formation. 

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