Sunday, December 22, 2013

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.

In the conventional method, the sludge is removed from storage chamber's bottom, a process that can take between 90 to 120 days. This is done with experienced personnel and machines and with more operators, the stage can take less like 2 to 3 months. And when using receptacle cleaning machines that are remotely operated will take double the time as compared to human operators.

The removed sludge is then treated in the second step. It is separated into oil, solid wastes and water. The process is done right in the storage chamber before pumping it out of system.

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.

There is a one step cleaning method that has been developed and used by some companies. In this process, diesel is pumped through nozzles in a jet fixed on the receptacle's roof. This washes the sludge dissolving it after which the sludge/diesel mixture is pumped out of the storage chamber.

Even though this method is efficient and faster, some sludge still remains at the bottom of the storage chamber and requires time to dissolve. This may takes around 4 months to dissolve for a 100,000KL tank. It also requires a temporary storage tank to handle the diesel/sludge mixture pumped out of the chamber in order to clean the receptacle.

Other than these methods, there is a two step procedure. It is quite advanced and cleans tanks in a matter of weeks compared to the months it takes to clean with the other methods. In the first step, a submerged rotary jet mixer violently and thoroughly mixes the sludge dissolving it into a suspended mixture, a process referred to as re-suspension. Here, about 90% of the oil is recovered for recycling and use. This only requires 7 days to set up the machine and 3 days to do the mixing.

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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