Petroleum refining processes introduction
Petroleum refining processes are the chemical engineering processes and other facilities used in petroleum refineries (also referred to as oil refineries) to transform crude oil into useful products such as liquefied petroleum gas (LPG), gasoline or petrol, kerosene, jet fuel, diesel oil and fuel oils
Although all fractions of petroleum find uses, the greatest demand is for gasoline. One barrel of crude petroleum contains only 30-40% gasoline. Transportation demands require that over 50% of the crude oil be "converted" into gasoline. To meet this demand some petroleum fractions must be converted to gasoline.
This may be done by :
Generally, the simplest refineries consist of crude, vacuum, reforming and some hydrotreating capacity. The next level of complexity adds cat cracking and some additional hydrotreating. The most complex refineries add coking, more hydrotreating and hydrocracking.
Refining separates crude oil into components used for a variety of purposes, from high-performance fuels to plastics.
This may be done by :
- Cracking — breaking down large molecules of heavy heating oil and resids
- Isomerization — rearranging the atoms in a molecule so that the product has the same chemical formula but has a different structure, such as converting normal butane to isobutene.
- reforming — changing molecular structures of low quality gasoline molecules
Generally, the simplest refineries consist of crude, vacuum, reforming and some hydrotreating capacity. The next level of complexity adds cat cracking and some additional hydrotreating. The most complex refineries add coking, more hydrotreating and hydrocracking.
Refining separates crude oil into components used for a variety of purposes, from high-performance fuels to plastics.
Distillation
Distillation starts by pumping crude oil into pipes running through hot furnaces and heating the oil to vaporize it. The resulting vapors and liquids are discharged into distillation towers , the tall, narrow columns that give refineries their distinctive skylines.
Inside the towers, the liquids and vapors separate into components or fractions according to their density and boiling point. The lightest fractions, including gasoline and liquid petroleum gas (LPG), vaporize and rise to the top of the tower, where they condense back to liquids. Medium-weight liquids, including kerosene and diesel oil, stay in the middle. Heavier liquids, called gas oils, separate lower down. The heaviest fractions with the highest boiling points settle at the bottom. These tar-like fractions, called residuum, are literally the "bottom of the barrel."
The various fractions are then piped to different stations or plants within the refinery. Some fractions require relatively little additional processing to become road asphalt or jet fuel. However, fractions destined to become high-value products, such as gasoline, typically require much more additional processing.
Conversion: Cracking and rearranging molecules
Conversion is where fractions from the distillation towers are transformed into streams (intermediate components) that eventually become finished products. This also is where a refinery makes money, because only through conversion can most low-value fractions become gasoline.
The most widely used conversion method is called cracking, which uses heat and pressure to literally "crack" heavy hydrocarbon molecules into lighter ones. A cracking unit consists of one or more tall, thick-walled, bullet-shaped containers, called reactors, and a network of furnaces, heat exchangers, and other vessels.
Fluid catalytic cracking, or "cat cracking," is the basic gasoline-making process. Using intense heat (about 1,000 degrees Fahrenheit), low pressure and a powdered catalyst (a substance that accelerates chemical reactions), the cat cracker can convert most relatively heavy fractions into smaller gasoline molecules.
Hydrocracking applies the same principles but uses a different catalyst, slightly lower temperatures, much greater pressure and hydrogen to obtain chemical reactions. Although not all refineries employ hydrocracking, Chevron is an industry leader in using this technology to cost-effectively convert medium- to heavyweight gas oils into high-value streams. The company's patented hydrocracking process, which takes place in the Isocracker unit, produces mostly gasoline and jet fuel.
The most widely used conversion method is called cracking, which uses heat and pressure to literally "crack" heavy hydrocarbon molecules into lighter ones. A cracking unit consists of one or more tall, thick-walled, bullet-shaped containers, called reactors, and a network of furnaces, heat exchangers, and other vessels.
Fluid catalytic cracking, or "cat cracking," is the basic gasoline-making process. Using intense heat (about 1,000 degrees Fahrenheit), low pressure and a powdered catalyst (a substance that accelerates chemical reactions), the cat cracker can convert most relatively heavy fractions into smaller gasoline molecules.
Hydrocracking applies the same principles but uses a different catalyst, slightly lower temperatures, much greater pressure and hydrogen to obtain chemical reactions. Although not all refineries employ hydrocracking, Chevron is an industry leader in using this technology to cost-effectively convert medium- to heavyweight gas oils into high-value streams. The company's patented hydrocracking process, which takes place in the Isocracker unit, produces mostly gasoline and jet fuel.
Fluid catalytic cracking, or "cat cracking," is the basic gasoline-making process. Using intense heat (about 1,000 degrees Fahrenheit), low pressure and a powdered catalyst (a substance that accelerates chemical reactions), the cat cracker can convert most relatively heavy fractions into smaller gasoline molecules.
Hydrocracking applies the same principles but uses a different catalyst, slightly lower temperatures, much greater pressure and hydrogen to obtain chemical reactions. Although not all refineries employ hydrocracking, Chevron is an industry leader in using this technology to cost-effectively convert medium- to heavyweight gas oils into high-value streams. The company's patented hydrocracking process, which takes place in the Isocracker unit, produces mostly gasoline and jet fuel.
Treatment: Adding the finishing touches
Treament is the final step before tanker trucks and railroad cars head out of the refinery to deliver gasoline to our local gas station.A major part of modern refining involves blending, purifying, fine-tuning and otherwise improving products to meet these requirements.
To make gasoline, refinery technicians carefully combine a variety of streams from the processing units. Among the variables that determine the blend are octane level, vapor pressure ratings, and other special considerations, such as whether the gasoline will be used at high altitudes. Technicians also add patented performance additives, and dyes to distinguish the various grades of fuel.
To make gasoline, refinery technicians carefully combine a variety of streams from the processing units. Among the variables that determine the blend are octane level, vapor pressure ratings, and other special considerations, such as whether the gasoline will be used at high altitudes. Technicians also add patented performance additives, and dyes to distinguish the various grades of fuel.