An oil refinery is an industrial separation and production aggregation of processes where crude oil which comes from the ground (from drilling process) is transformed and refined into more useful products such as petroleum, light and heavy naphtha, diesel, and others useful and needful compounds or fuels. Oil refinery plants are huge, sprawling industrial complexes with extensive piping carrying feeds, gas, steam, and other fluids between large chemical processing units, such as distillation columns, reactors, and storage tanks. Each refinery has its own unique arrangement and combination of dedicated refining processes and units mostly determined from the refinery location and economic constraints.
Raw (unprocessed) crude oil is not useful in an industrial or any other application. Therefore, the crude oil consisted of hundreds of different hydrocarbon molecules is separated in a refinery into components that can be used as fuels, lubricants, and feedstocks in petrochemical and other processes which manufacture products such as plastics, detergents, solvents, elastomers, and fibers. Different boiling points (vaporization temperatures) allow the hydrocarbons to be separated by the distillation (separation) process. Since crude oil contains hydrocarbons of varying molecular masses, forms, and lengths (paraffins, aromatics, cycloalkanes, alkenes, dienes, and alkynes). The differences in the structure of these hydrocarbon molecules make their physical and chemical properties varying. This variety of physical and chemical properties is what makes crude oil useful in a broad range of applications. Oil refineries also produce various products such as:
- Hydrogen, light hydrocarbons, reformate and pyrolysis gasoline used for further blending or processed further on-site.
- Sulfur which is sold to the chemical industry.
- Different shares of petroleum products which are typically sorted in four categories: light distillates (LPG, gasoline, naphtha), middle distillates (kerosene, jet fuel, diesel), heavy distillates and residuum (heavy fuel oil, lubricating oils, wax, asphalt) usually used as an engine fuel or in construction.
- Petrochemical organic compounds that are the ingredients for the chemical industry and pharmaceuticals.
- Heat and electricity
Oil refineries are large scale plants, processing about a hundred thousand to several hundred thousand barrels of crude oil a day. Because of the high capacity, many of the units operate continuously, as opposed to processing in batches, at steady state or nearly steady state for months to years. The high capacity also makes process optimization and advanced process control very desirable.
