Have you ever wondered how the crude oil ends up as gasoline and all of these other products that come from oil- crayons, plastics, heating oil, jet fuel, kerosene, synthetic fibers and tires etc;. Well, this is what this article focuses on. Here you will go through the various processes and technologies involved in refining crude oil to produce all of these different things.
Oil refining begins as simple distillation, going on to the complex series of processes to produce different products to meet the demands of the market. Let’s have a look at the crude oil first.
Crude oil, also known as "unprocessed" oil or petroleum, is a fossil fuel. Varying in color and viscosity, the crude oil can be clear to tar-black, and from water to almost solid. Crude oils contain hydrocarbons, which contain a lot of energy. Chemists find hydrocarbons very exciting, as they are very versatile and can be turned into everything from synthetic rubber to nylon to the plastic and more.
Crude oils are distinguished by their density and sulfur content. Less dense crude oils have a higher share of light hydrocarbons and higher value products. The denser crude oils produce a greater share of lower-valued products with simple distillation and require additional processing to produce the desired range of products. In addition to gravity and sulfur content, the type of hydrocarbon molecules and other natural characteristics become the other factors that may affect the cost of refining crude oil.Distillation
The first and basic process in refining crude oil is “Simple Distillation”. As crude oil is made up of a mixture of hydrocarbons, the distillation is aimed at separating the hydrocarbons in crude oil. As these products have different sizes and boiling ranges, chemists take advantage of these properties when refining oil. Crude oil is heated and put into a distillation column.
Different products boil off and are recovered at different temperatures. The lighter products like-liquid petroleum gases (LPG), and naphtha are recovered at the lowest temperatures. Jet fuel, kerosene, heating oil and diesel fuel come next as the middle distillates. The heaviest products -residuum or residual fuel oil are recovered at the highest temperatures of 1000 degrees F.Processing
Encompassing a variety of highly complex units designed for very different upgrading processes, some change the molecular structure of the fractions with chemical reactions, or in the presence of a catalyst, while in some cases with thermal reactions.
One fraction can be changed in to the other by one of three methods:
a) Cracking- breaking large hydrocarbons into smaller ones
b) Unification - combining smaller pieces to make larger ones
c) Alteration - rearranging various pieces to make desired hydrocarbons
The purpose of these processes is to take heavy, low-valued and convert it into lighter, higher-valued output. For example, a catalytic cracker uses the gasoil (heavy distillate) output from crude distillation and produces additional finished distillates (heating oil and diesel) and gasoline.
Sulfur removal is accomplished in a hydrotreater. A reforming unit produces higher octane components for gasoline from lower octane feedstock that was recovered in the distillation process. A Coker uses the heaviest output of distillation, the residue or residuum, to produce a lighter feedstock for further processing, as well as petroleum coke.Treating and Blending
Additional processing of the distillated and chemically processed fractions is required to remove impurities, such as organic compounds containing sulfur, nitrogen, oxygen, water, dissolved metals and inorganic salts.
A column of sulfuric acid removes unsaturated hydrocarbons, nitrogen compounds, oxygen compounds and residual solids like tars and asphalt. Water is removed using an absorption column filled with drying agents. Sulfur treatment and hydrogen-sulfide scrubbers removes sulfur and sulfur compounds.
After the treatment, the fractions are cooled and then blended together to make various products, like: gasoline of various grades, lubricating oils , kerosene , jet fuel, diesel fuel, heating oil and chemicals of various grades.
Depending on the refinery's equipment, the desired output mix, and the relative price of available crudes, refiners strive to run the optimal mix of crudes through their refineries. In recent years, there has been an increasingly demand of light products of higher quality by consumers and government mandates. With crude oil supply getting increasingly heavier, with higher sulfur content, the process of refining becomes difficult while the cost goes up.
Oil refining developed in consuming areas, as it was cheaper to move crude oil than to move product. Furthermore, it was easier to respond to shifting demands or to gauge seasonal shifts. So, while the Mideast is the largest oil producing region, the bulk of crude oil refining takes place in the United States, Europe or Asia. Today, North America has the largest concentration of oil refining capacity in the world.
Lately, the role of independent refiners has grown substantially, with the integrated companies largely seeking to streamline and realign their positions. Furthermore, with the independent refiners in a period of consolidation; the mergers and acquisitions are having a significant impact on refinery ownership.
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— Mikhail Khodorkovsky.