Crude oil washing (COW) is washing out the residue from the tanks of an oil tanker using the crude oil cargo itself. The oil dissolves the sediments and allows them to be recovered and sold. It replaced the load on top and seawater washing systems, both of which involved discharging oil-contaminated water into the sea. MARPOL 73/78 made this mandatory equipment for oil tankers of 20,000 tons or greater deadweight. A tanker is usually a vehicle carrying large amounts of liquid fuel. ... Ship Pollution is an abbreviated form of the Protocol of 1978 Relating to the International Convention for the Prevention of Pollution From Ships, 1973. ...

Seawater washing

Originally oil tankers used one set of tanks for cargo and about one third of the same tanks were for water ballast on their empty trips. High pressure, hot, sea water jets were used to clean the tanks and the mixture of sea water and residue called slops discharged into the sea, as was the oil-contaminated ballast water. The 1954 OILPOL Convention attempted to reduce the harm by prohibiting such discharges within 50 miles of most land and 100 miles of certain particularly sensitive areas. Ballast may mean : Something that improves stability Track ballast (gravel or cinders) forms the railroad or railway track-bed on which sleepers (ties) and track is laid. ... 1954 was a common year starting on Friday of the Gregorian calendar. ...

Load on top

The discharges from seawater washing were still considered a problem and during the 1960s the load on top approach began to be adopted. The mixture of cleaning water and residue was pumped into a slop tank and allowed to separate into oil and water during the journey. The water portion was then discharged, leaving only crude oil in the slop tank. This was pumped into the main tanks and the new cargo loaded on top of it, recovering as much as 800 tons of oil which was formerly discarded.

Crude oil washing

Even with load on top there is still some oil in the discharged water from the slop tank. Starting in the 1970s, equipment capable of using crude oil itself for washing began to replace the water-based washing, leading to the current techinque of crude oil washing. This eliminates the remaining deliberate discharge of oil-contaminated water and increases the amount of cargo discharged, providing a further benefit to the cargo owner.

Crude oil washing equipment became mandatory for new tankers of 20,000 tons or more deadweight with the 1978 Protocol to the 1973 MARPOL Convention. Revised specifications for the equipment were introduced in 1999. 1973 was a common year starting on Monday. ... Ship Pollution is an abbreviated form of the Protocol of 1978 Relating to the International Convention for the Prevention of Pollution From Ships, 1973. ... 1999 is a common year starting on Friday Anno Domini (or the Current Era), and was designated the International Year of Older Persons by the United Nations. ...

Modern tankers also use segregated ballast tanks and these remove the problem of discharge of ballast water,

External links

• International Maritime Organization description of Crude Oil Washing