What are methods of oil supply in C.O.W or crude oil washing ? |

What are methods of oil supply in C.O.W or crude oil washing ?

There are basically three wash oil supplying methods so called ―

  1. Bleed-off System.
  2. Closed Cycle
  3. Open Cycle
  1. Semi-open Cycle System:-
    • Wash oil is introduced from a tank being discharged and drained oil is discharged into the aftermost centre tank or slop tank.
    • Precaution:- The tank be used as a source of crude oil washing (Driving Oil) should be first discharged at least one metre in depth before supplying as a washing medium to suppress electrostatic charges.
  2. Closed Cycle System (re-circulation method):-

Wash oil is supplied from the aftermost centre tank or slop tank and drained oil is collected in the same tank, i.e., the same tank is used for both purposes

  1. Slop tanks loaded by the ―Load-on-Top‖ procedure should be discharged entirely and then filled with fresh oil (crude oil free from water and residue) prior to COW.
    • It is considered better to discharge Driving Oil in Slop tank after washing a few tanks, not more than six tanks, and replace to fresh oil again as it may avoid the Driving oil to be sludge-full.


  1. Bleed-off System (Open Cycle System):- A method in which a part of the oil being discharged is branched off to the tank cleaning line. Some terminals call this system in which cargo is discharged simultaneously with COW.


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