Oil refining

Oil refinery in Iran

The refining of petroleum is a process that includes the fractioning and chemical transformation of petroleum to produce commercial derivatives.

In accordance with this objective, in general, these processes are carried out together in a refinery. The refinery is where the oil is treated to extract commercial fractions.

Oil is a mixture of different hydrocarbons, which must undergo a series of different treatments in order to be used in combustion engines and in various branches of industry. Very often, the quality of crude oil is highly dependent on its origin. According to its origin, color, viscosity, its sulfur content, the pour point or its mineral content. Therefore, refineries take these factors into account.

A refinery must be designed to handle a wide range of crudes. Of course, there are refineries designed to process only a single crude, but these are special cases where the estimated gross resource is very important.

There are simple and complex refineries. Simple refineries consist of only a few processing units while complex refineries have many more.

In the countries that have them, refineries are preferably installed on the coasts, to save transportation costs and the construction of oil pipelines.

Depending on where the refinery is located, as well as the nature of the crude oil processed (eg BTS or HTS crude, aromatic or naphthenic crude), the purpose and structure of the refinery is different; as well as depending on possible local needs, the refinery can be very simple or very complex. Often in Europe, in the United States and in general in areas where fuel needs are high, the structure of refineries is complex. By contrast, in developing countries, this structure is quite simple.

Once the crude oil arrives at the refinery, it is stored in large tanks. In general, crude oil is stored according to its sulfur content, low sulfur (BTS) is stored separately from high sulfur (HTS). The same is true in treatment. According to the market demand, the BTS is first treated in one cycle before treating one HTS cycle to avoid contamination of the BTS products by the HTS ones. If the opposite is the case, the products after a few hours after they are processed, if applicable, are directed to the HTS product containers for reprocessing.

Structure of a refinery

In refineries, oil is transformed, which is made up of thousands of hydrocarbons in fractions, with approximately constant composition and properties, which are distilled between two preset temperatures. Refineries have different complexities depending on the different plants installed. Its main products are gasoline, kerosene, gas oil, diesel and fuel oil.

Plants in an oil distillery (refinery)

Diagram of a refinery

A distillery should be designed to handle a fairly wide range of oils. In those places where the estimated crude oil reserves are projected to be similar in quality, the refineries are designed to treat only that type of crude. There are simple refineries (with a few processing units) and complex ones (with a large number of units).

• Vacuum distillation of topping residue

• Hydrodesulfuration Units (sulphur dioxide) of LPGs, Naftas, Kerosene and Gas oil to allow further reform

• Isomerization unit of light naphthas in high octane isoparaffins

• Treatment with nafta or kerosene soda (Merox unit)

• Unit for the reform of low octane heavy naphthas in high octane aromatic hydrocarbons

• The MTBE plant produces an additive to increase the octane of leadless naphtha

• Renting that produces lightweight with a higher number of octane

• Hydrocraqueo of oil gas resulting from the Empty Unit (in the presence of hydrogen and a catalyst) in gasoil of greater added value.

• Quotation to reduce surplus of low-value heavy fuel oil leaving almost pure carbon, called coke.

• Hydrogen Plant for hydrodesulfuration and hydrocraqueo processes

Types of crude oil

There are different types of crudes depending on their main components and their sulfur content:

• nafténicos,
• aromatic,
• very low sulfur content, SELV
• low sulfur content, BTS
• medium sulfur content, MTS
• high sulfur content, HTS
• very high sulfur content Thts

Refineries (processing units) are not always appropriate for the treatment of all these crudes because according to their construction, not all of them are designed to cover the entire range of crudes.