Enhancement Of Crude Oil Storage Tank Cleaning Of Tanker Vessels

By Rachael Gutierrez

Crude oil storage tank cleaning, or commonly called Crude Oil Washing (COW), is mainly the process of cleaning the storage using the oil itself. Prior to strict environmental regulations, tankers were cleaned using jets that sprayed seawater inside the containers. Also, before ballast tanks were introduced in ship design, water had to be stored in order for the propeller to be properly immersed at sea.

Many regulations have been in effect after concerns were raised in the wastes produced in the cleaning process after every trip of tankers. Companies themselves have used these changes to their benefit, as it also decreases the oil that is thrown away and reused on their next trip. Many of these advancements will be discussed to understand how these processes changed in a few decades time.

Every day, a great number of tanker vessels carry petroleum to refineries from oil platforms for processing. Thus, it is ideal to make sure that there is profit on every trip and to decrease cost whenever possible. One commonly followed procedure for cost efficiency in the industry is the regular cleaning of the tanks storing the fuels. If this is skipped, the petroleum will form a sticky layer from the walls that would add unnecessary weight to the vessel when emptied for its return trip.

One of first methods used in cleansing was to pump heated seawater and were then sprayed to remove the layers of oil on the walls, and were then discharged from the ship. This resulted in great amounts of discharged petroleum into the sea and were highly concentrated in docks where these took place.

The introduction of Oil Pollution Convention (OILPOL) in 1954 mandated that discharged wastes should only be done when beyond 50 miles from the nearest land. In cases where that specific land raised great concerns on irreparable environmental impact, the distance was extended for up to 100 miles.

Due to the pollution that was still being produced by the OILPOL adaption, a new process was introduced where the tanks were still cleaned using pressurized heated water, but instead of disposing the waste, it is first placed into a special slop tank. While the ship is on its return voyage, the oil, which is lighter than water, would eventually float on top. The water, which settled at the bottom, will be returned to the sea. This process is called the Load on Top.

An estimated amount of 8 million tons of petroleum were prevented from being discharged back into the sea. The remaining fuel from this process can then be reused by mixing with a fresh batch of crude oil, which resulted in higher profit margins by cutting losses.

The crude oil storage tank cleaning process was once again improved by using pressurized crude oil and was sprayed onto the sediments sticking on the tank walls. This process, that eliminated the need for slop tanks, was named Crude Oil Washing. This resulted in a cleaning procedure that eliminated the possibility for waste water and only involved the fuels that were also being delivered.

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