The oil industry is facing a major problem with the large amount of oil residue generated in the tanks that store and process crude oil or its products. In the oil industry there are various types of tanks, vessels and pits that store or process fluids which contain oil in their composition. One of them is the crude oil tank,used for storage of crude oil. A crude oil tank can be a bolted steel tank (API 12 B), a welded steel tank (API 1 F BS 2654), a flat-sided (API 620) or a field welded (API 12 D – API 650 ) tank. It is usually made of carbon steel which is capable of external and or internal painting, galvanized coating or polymeric coating for corrosion protection. The tank type, dimensions and material vary depending on the storage conditions of the oil (pressure, temperature), the properties of the crude (composition, toxicity) and the amount of storage required. Its main parts are the shell, bottom, roof (fixed and floating), nozzles, pipelines and instruments, cathodic protection system and steel structures for the service of the staff.
The roof can be fixed or floating. The floating roof may be internal in combination with a fixed roof(occurring in cases of increased snow fall or rainfall long periods of time that burden the floating roof exposed to the environment) or external. The floating roof floats on the oil inside the tank with the help of pontoons that exists outside the perimeter . Isolation of oil with the environment is achieved by sealing the perimeter between roof and the shell with a double sealing system, which prevents the oil from leaving the tank and the entry of any fluid or solid into the tank but allows the roof to move freely up and down. The main advantage of a floating roof is that it comes in direct contact with the oil inside the tank, thereby reducing vapor formation, and also reduces the risk of fire and corrosion caused by the presence of air. The remaining parts of the floating roof are the supports, the vents,the drains, the manholes and the gauges. Attached to the shell there are several nozzles servicing various needs, such as filling and emptying, cleaning, installation of equipment (agitators, valves and gauges), manholes for staff entry, etc. There is also a fire safety network installed on the roof of the tank in case of fire. A cathodic protection system is also installed on the tank bottom to prevent the galvanic corrosion.
Cleaning of Industrial Oil Tanks
Cleaning industrial tanks, vessels and pits containing petroleum residues is an inevitable process in the industry that companies must deal with. The main reason for cleaning is the residues created over time by the settling of the heavier elements contained in petroleum. These residues occupy considerable space in the tanks, reducing their capacity and altering the quality of the products. Apart from everything else we mentioned, there is also the need for some scheduled inspections which are required by the operating regulations. These activities cannot be carried out with the presence of residues inside the tank. Companies have focused on finding cleaning methods aimed at staff safety, cleaning efficiency, time/money savings and environmental protection. The methods that could be used to clean a tank could be manual, automatic (mechanical) and robotic.
In most cases, staff entry inside the tank is required to complete the job, but the time spent in the tank and the number of people varies according to the procedure. Some of the goals for an effective clean-up are to reduce the number of staff entering a permit-required confined space because exposure to hazardous environments carries a number of risks, with studies showing an increased rate of accidents in recent years. Also, the need to reduce cleaning costs and increase safety has focused on more automated methods that require less labour and have proven safer. Another major goal is to recover the oil contained in large percentages in the sludge residues that have been deposited at the bottom of the tank. A lot of case studies have shown that the revenue generated by oil recovered from sludge outweighs the costs of the cleaning operation. Moreover, with environmental regulations becoming stricter every year, the safe transportation and storage of the sludge, inside a closed loop circuit, and other cleaning waste from the tank to a specific site and from there to the waste treatment plants is also an important factor in an effective cleaning method.
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