Crude Oil Storage Tank Cleaning Methods

By Harriett Crosby

Using crude oil tankers may seem easy, wait until the times comes to do the cleaning. There however are several procedures of Crude Oil Storage Tank Cleaning that have been used over the years and new improved methods that employed by some contractors. This process involves the removal of bottom sludge, separating it into oil and solid matter and the actual receptacle washing.

To start with the conventional methods, the sludge is manually removed from the tank bottom. This is done by trained personnel taking between three (3) to four (4) months. It involves both man and machines to complete the tedious process. When using solely remote operated machines, the process may take even double the time.

The second step in the conventional method is to treat the oil sludge. This involves separating the sludge into three components; recovered oil, solids and waste water. This is done inside the receptacle.

The third stage is to wash the tank since the sludge has been removed. By the use of high pressure cleaners, the floor and walls of storage chamber are thoroughly cleaned and de-rusted by use of sand blasting. It can take around 50 days if one team is working on it or about 30 days for two teams working simultaneously. To clean the external wall by sand blasting, the operators will take another 30 to 60 days based on the number of teams working on it. Another more efficient alternative which is more expensive is to use ultra-high pressure cleaning which combines de-rusting and de-painting in one process.

Another method of Crude Oil Tank Cleaning is to use one step tank washing technology. This scientifically developed and is way more efficient as it washes in one step. It involves the pumping of diesel through nozzles installed on the roof of the storage chamber. This diesel washes the sludge after which the mixture of diesel and sludge is pumped from the receptacle bottom.

Even though this method is more efficient than the conventional one, some sludge will still remain solid and stuck to the tank base. This may take up to four months to dissolve then the mixture is pumped out into another tank. This means that an extra receptacle is required to store the mixture before it I separated.

A two step washing technology is also in use. This is an advanced method and is very different from the first two. It cleans oil tanks in a matter of weeks as compared to the 4 months for the other processes. The first step involves the use of submerged rotary jet mixer to dissolve the sludge into the oil solutions, a process called re-suspension. Around 90% of the hydrocarbons can be recovered using this process. This only takes 10 days, 7 days for equipment installation and 3 days for cleaning.

The second step can be skipped if the client feels so. But if there is a need, then the residual sludge is removed. And since it is only 10%, the process will take way less time. And after the thorough and violent mixing, the remaining sludge is quite soft and easy to handle as compared to when using the conventional method of Crude Oil Storage Tank Cleaning.

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