Improvements In Crude Oil Storage Tank Cleaning Of Tankers

By Rachael Gutierrez

The procedures in crude oil storage tank cleaning, also known as Crude Oil Washing (COW), is a process of cleaning the storage using the fuel itself. Before environmental regulations were enacted, these tankers were cleaned by spraying seawater into the containers. Initially, water was also stored in these same tanks to level the ships and ensure that the propellers will be below sea level, until ballast tanks were introduced.

Overtime, multiple regulations were introduced to ensure proper disposal of waste from the process of cleansing the tanker after trips. Private institutions also found ways to take advantage of these changes by using readily available fluids and by lessening waste of their products, which equates to additional savings for the company. We will be covering the changes and improvements for the past decades that led to the regulations being followed today.

Petroleum is delivered by tanker vessels every day from oil platforms to refineries to be processed. With this line of business, cost efficiency is very important to ensure the profitability of each trip. One of the easiest ways to decrease cost is to have regular cleansing of these containers. Once a container is left without this procedure, the oil will form a sticky layer on the walls and will add unnecessary weight to the ship when it is returning to the platform for another delivery.

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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