An oil refinery or petroleum refinery is an industrial process plant where crude oil is transformed and refined into useful products . The products are such as petroleum naphtha, gasoline, diesel fuel, asphalt base, heating oil, kerosene, liquefied petroleum gas, jet fuel and fuel oils.
Petrochemicals feed stock like ethylene and propylene can also be produced directly by cracking crude oil . It do not e need of using refined products of crude oil such as naphtha.
The crude oil feedstock has typically been processed by an oil production plant. There is usually an oil depot at or near an oil refinery for the storage of incoming crude oil feedstock as well as bulk liquid products. According to the Oil and Gas Journal, on 31 December 2014, a total of 636 refineries operated worldwide with a total capacity of 87.75 million barrels (13,951,000 m3).
The crude oil distillation unit (CDU) is the first processing unit in virtually all petroleum refineries. The CDU distills the incoming crude oil into various fractions of different boiling ranges. Each of which is then processed further in the other refinery processing units.
The CDU is often referred to as the atmospheric distillation unit because it operates at slightly above atmospheric pressure.
Products of oil refineries
- Diesel fuel
- Fuel oils
- Liquid petroleum gas (LPG)
- Lubricating oils
- Paraffin wax
Common process units found in a refinery
- Desalter Unit (washes out salt from the crude oil before it goes into the atmospheric distillation unit)
- Atmospheric Distillation Unit (distills crude oil into fractions)
- Vacuum Distillation Unit (further distills residual bottoms after atmospheric distillation)
- Naphtha Hydrotreater Unit (desulfurizes naphtha from atmospheric distillation. Must hydrotreat the naphtha before sending to a Catalytic Reformer Unit.)
- Catalytic Reformer Unit (contains catalyst used to convert the naphtha-boiling range molecules into higher octane reformate (reformer product). The reformate has higher content of aromatics, olefins, and cyclic hydrocarbons). An important byproduct of a reformer is hydrogen released during the catalyst reaction. The hydrogen is used either in the hydrotreaters and hydrocracker.)
- Distillate Hydrotreater Unit (desulfurizes distillate (diesel) after atmospheric distillation)
- Fluid Catalytic Cracking (FCC) Unit (upgrades heavier fractions into lighter, more valuable products)
- Hydrocracker Unit (upgrades heavier fractions into lighter, more valuable products)
- Coking unit (processes asphalt into gasoline and diesel fuel, leaving coke as a residual product)
- Alkylation unit (produces high octane component for gasoline blending)
- Dimerization Unit
- Isomerization Unit (converts linear molecules to higher octane branched molecules for blending into gasoline or feed to alkylation units)
- Steam reforming Unit (produces hydrogen for the hydrotreaters or hydrocracker)
- Liquified gas storage units for propane and similar gaseous fuels at pressure sufficient to maintain in liquid form – these are usually spherical or bullets (horizontal cylinder with rounded ends).
- Storage tanks for crude oil and finished products, usually cylindrical, with some sort of vapor enclosure and surrounded by an earth berm to contain spills
- Utility units such as cooling towers for circulating cooling water, boiler plants for steam generation, and wastewater collection and treating systems to make such water suitable for reuse or for disposal.