Understanding Oil Storage
An Oil Terminal (also called a Tank Farm, Oil Installation or Oil Depot) is an industrial facility for the storage of oil, petroleum and petrochemical products, and from which these products are transported to end users or other storage facilities. An oil terminal typically has a variety of above or below ground tankage; facilities for inter-tank transfer; pumping facilities; loading gantries for filling road tankers or barges; ship loading/unloading equipment at marine terminals; and pipeline connections. Oil terminals may be located close to, or be part of, oil refineries; or be located in coastal locations where marine tankers can discharge or load cargo. Some terminals are connected to pipelines from which they draw or discharge their products. Terminals can also be served by rail, barge and road tanker (sometimes known as "bridging"). Oil terminals are also located near cities from which road tankers transport products to petrol stations or other domestic, commercial or industrial users.
In most oil terminals there is no processing or other product transformation on site. The products from a refinery which are stored in the terminal are in their final form suitable for delivery to customers. Blending of products may be undertaken, and additives may be injected into products, but there is usually no manufacturing plant on site. Modern terminals have a high degree of site automation. Marine oil terminals have jetties to provide a deep water mooring for tankers. Jetties have loading/unloading arms for transferring cargo to/from ship to shore. Facilities for vapor recovery may be provided. Some oil terminals receive crude oil production from offshore installations. Crude oil received by pipeline may have been ‘spiked’ with natural gas liquids (NGL), and is known as live crude. Such oil needs to be processed or stabilized to remove the lighter fractions such as ethane, propane and butane to produce a dead or stabilized crude that is suitable for storage and transport. Such oil terminals may include processing facilities to treat the oil to achieve an oil Reid vapor pressure (RVP) of 10 to 12 psi (70 to 82 kPa). The process facilities include oil heaters to warm the oil which then routed to separator vessels. In the separators the lighter fractions flash off from the oil and are further processed to separate them into their individual components. The now stabilized oil can be routed to storage and then sold or sent for further processing.
The storage tanks at an oil terminal may includes fixed roof tanks, internal floating roof tanks and external floating roof tanks. Floating roof tanks are generally used for more volatile products to reduce evaporation loss. Fixed roof tanks which have a vapor space above the product and which breathes in or out as the product is removed or the tank is filled. Some tank may be fitted with internal heating coils using hot water or steam to keep the contents warm. This reduces the viscosity of the product to ease transfer and pumping. Terminals may also have ‘Horton spheres’ which are used to store liquefied petroleum gases such as propane and butane.