Petroleum refining processes

Petroleum refinery in Anacortes, Washington, United States

Petroleum refining processes are the chemical engi-neering processes and other facilities used in petroleumrefineries (also referred to as oil refineries) to transformcrude oil into useful products such as liquefied petroleumgas (LPG), gasoline or petrol, kerosene, jet fuel, dieseloil and fuel oils.[1][2][3]

Petroleum refineries are very large industrial complexesthat involve many different processing units and auxiliaryfacilities such as utility units and storage tanks. Each re-finery has its own unique arrangement and combinationof refining processes largely determined by the refinerylocation, desired products and economic considerations.There are most probably no two refineries that are iden-tical in every respect.Some modern petroleum refineries process as much as800,000 to 900,000 barrels (127,000 to 143,000 cubicmeters) per day of crude oil.

1 History

Prior to the nineteenth century, petroleum was knownand utilized in various fashions in Babylon, Egypt, China,Persia, Rome and Azerbaijan. However, the modern his-tory of the petroleum industry is said to have begun in1846 when Abraham Gessner of Nova Scotia, Canadadiscovered how to produce kerosene from coal. Shortlythereafter, in 1854, Ignacy Lukasiewicz began produc-ing kerosene from hand-dug oil wells near the town ofKrosno, now in Poland. The first large petroleum refinerywas built in Ploesti, Romania in 1856 using the abundantoil available in Romania.[4][5]

In North America, the first oil well was drilled in 1858by James Miller Williams in Ontario, Canada. In theUnited States, the petroleum industry began in 1859whenEdwin Drake found oil near Titusville, Pennsylvania.[6]The industry grew slowly in the 1800s, primarily produc-ing kerosene for oil lamps. In the early twentieth century,the introduction of the internal combustion engine andits use in automobiles created a market for gasoline thatwas the impetus for fairly rapid growth of the petroleumindustry. The early finds of petroleum like those in On-tario and Pennsylvania were soon outstripped by large oil“booms” in Oklahoma, Texas and California.[7]

Prior to World War II in the early 1940s, most petroleumrefineries in the United States consisted simply of crudeoil distillation units (often referred to as atmosphericcrude oil distillation units). Some refineries also hadvacuum distillation units as well as thermal cracking unitssuch as visbreakers (viscosity breakers, units to lower theviscosity of the oil). All of the many other refining pro-cesses discussed below were developed during the war orwithin a few years after the war. They became commer-cially available within 5 to 10 years after the war endedand the worldwide petroleum industry experienced veryrapid growth. The driving force for that growth in tech-nology and in the number and size of refineries worldwidewas the growing demand for automotive gasoline and air-craft fuel.In the United States, for various complex economic andpolitical reasons, the construction of new refineries cameto a virtual stop in about the 1980s. However, many ofthe existing refineries in the United States have revampedmany of their units and/or constructed add-on units in or-der to: increase their crude oil processing capacity, in-crease the octane rating of their product gasoline, lowerthe sulfur content of their diesel fuel and home heatingfuels to comply with environmental regulations and com-ply with environmental air pollution and water pollutionrequirements.

2 Processing units used in refiner-ies

• Crude Oil Distillation unit: Distills the incomingcrude oil into various fractions for further process-ing in other units.

• Vacuum distillation unit: Further distills the residueoil from the bottom of the crude oil distillation unit.

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2 4 THE CRUDE OIL DISTILLATION UNIT

The vacuum distillation is performed at a pressurewell below atmospheric pressure.

• Naphtha hydrotreater unit: Uses hydrogen to desul-furize the naphtha fraction from the crude oil distil-lation or other units within the refinery.

• Catalytic reforming unit: Converts the desulfurizednaphtha molecules into higher-octane molecules toproduce reformate, which is a component of the end-product gasoline or petrol.

• Alkylation unit: Converts isobutane and butylenesinto alkylate, which is a very high-octane componentof the end-product gasoline or petrol.

• Isomerization unit: Converts linear molecules suchas normal pentane into higher-octane branchedmolecules for blending into the end-product gaso-line. Also used to convert linear normal butane intoisobutane for use in the alkylation unit.

• Distillate hydrotreater unit: Uses hydrogen to desul-furize some of the other distilled fractions from thecrude oil distillation unit (such as diesel oil).

• Merox (mercaptan oxidizer) or similar units: Desul-furize LPG, kerosene or jet fuel by oxidizing unde-sired mercaptans to organic disulfides.

• Amine gas treater, Claus unit, and tail gas treatmentfor converting hydrogen sulfide gas from the hy-drotreaters into end-product elemental sulfur. Thelarge majority of the 64,000,000 metric tons of sul-fur produced worldwide in 2005 was byproduct sul-fur from petroleum refining and natural gas process-ing plants.[8][9]

• Fluid catalytic cracking (FCC) unit: Upgrades theheavier, higher-boiling fractions from the crude oildistillation by converting them into lighter and lowerboiling, more valuable products.

• Hydrocracker unit: Uses hydrogen to upgrade heav-ier fractions from the crude oil distillation and thevacuum distillation units into lighter, more valuableproducts.

• Visbreaker unit upgrades heavy residual oils fromthe vacuum distillation unit by thermally crackingthem into lighter, more valuable reduced viscosityproducts.

• Delayed coking and fluid coker units: Convert veryheavy residual oils into end-product petroleum cokeas well as naphtha and diesel oil by-products.

3 Auxiliary facilities required inrefineries

• Steam reformer unit: Converts natural gas into

hydrogen for the hydrotreaters and/or the hydroc-racker.

• Sour water stripper unit: Uses steam to remove hy-drogen sulfide gas from various wastewater streamsfor subsequent conversion into end-product sulfur inthe Claus unit.[10]

• Utility units such as cooling towers for furnishingcirculating cooling water, steam generators, instru-ment air systems for pneumatically operated controlvalves and an electrical substation.

• Wastewater collection and treating systems consist-ing of API separators, dissolved air flotation (DAF)units and some type of further treatment (such as anactivated sludge biotreater) to make the wastewaterssuitable for reuse or for disposal.[10]

• Liquified gas (LPG) storage vessels for propane andsimilar gaseous fuels at a pressure sufficient to main-tain them in liquid form. These are usually spheri-cal vessels or bullets (horizontal vessels with roundedends).

• Storage tanks for crude oil and finished products,usually vertical, cylindrical vessels with some sortof vapour emission control and surrounded by anearthen berm to contain liquid spills.

4 The crude oil distillation unit

The crude oil distillation unit (CDU) is the first processingunit in virtually all petroleum refineries. The CDU distillsthe incoming crude oil into various fractions of differentboiling ranges, each of which are then processed furtherin the other refinery processing units. The CDU is oftenreferred to as the atmospheric distillation unit because itoperates at slightly above atmospheric pressure.[1][2][11]

Below is a schematic flow diagram of a typical crude oildistillation unit. The incoming crude oil is preheated byexchanging heat with some of the hot, distilled fractionsand other streams. It is then desalted to remove inorganicsalts (primarily sodium chloride).Following the desalter, the crude oil is further heated byexchanging heat with some of the hot, distilled fractionsand other streams. It is then heated in a fuel-fired furnace(fired heater) to a temperature of about 398 °C and routedinto the bottom of the distillation unit.The cooling and condensing of the distillation tower over-head is provided partially by exchanging heat with theincoming crude oil and partially by either an air-cooledor water-cooled condenser. Additional heat is removedfrom the distillation column by a pumparound system asshown in the diagram below.As shown in the flow diagram, the overhead distillatefraction from the distillation column is naphtha. The frac-

6.2 Middle distillates 3

tions removed from the side of the distillation column atvarious points between the column top and bottom arecalled sidecuts. Each of the sidecuts (i.e., the kerosene,light gas oil and heavy gas oil) is cooled by exchangingheat with the incoming crude oil. All of the fractions(i.e., the overhead naphtha, the sidecuts and the bottomresidue) are sent to intermediate storage tanks before be-ing processed further.

Schematic flow diagram of a typical crude oil distillation unit asused in petroleum crude oil refineries.

5 Flow diagram of a typicalpetroleum refinery

The image below is a schematic flow diagram of a typicalpetroleum refinery that depicts the various refining pro-cesses and the flow of intermediate product streams thatoccurs between the inlet crude oil feedstock and the finalend-products.The diagram depicts only one of the literally hundredsof different oil refinery configurations. The diagram alsodoes not include any of the usual refinery facilities pro-viding utilities such as steam, cooling water, and electricpower as well as storage tanks for crude oil feedstock andfor intermediate products and end products.[1][2][12]

6 Refining end-products

The primary end-products produced in petroleum refin-ing may be grouped into four categories: light distillates,middle distillates, heavy distillates and others.

6.1 Light distillates

• Liquid petroleum gas (LPG)

A schematic flow diagram of a typical petroleum refinery.

• Gasoline (also known as petrol)

• Heavy Naphtha

• Light Naphtha

6.2 Middle distillates

• Kerosene

• Automotive and rail-road diesel fuels

• Residential heating fuel

• Other light fuel oils

•

6.3 Heavy distillates

• Heavy fuel oils

• Bunker fuel oil and other residual fuel oils

7 References

This article incorporates material from theCitizendium article "Petroleum refining pro-cesses", which is licensed under the CreativeCommons Attribution-ShareAlike 3.0 UnportedLicense but not under the GFDL.

4 7 REFERENCES

[1] Gary, J.H. and Handwerk, G.E. (1984). Petroleum Refin-ing Technology and Economics (2nd Edition ed.). MarcelDekker, Inc. ISBN 978-0-8247-7150-8.

[2] Leffler, W.L. (1985). Petroleum refining for the nontech-nical person (2nd Edition ed.). PennWell Books. ISBN978-0-87814-280-4.

[3] James G, Speight (2006). The Chemistry and Technologyof Petroleum (Fourth Edition ed.). CRC Press. 0-8493-9067-2.

[4] 150 Years of Oil in Romania

[5] WORLD EVENTS: 1844-1856 www.pbs.org

[6] “Titusville, Pennsylvania, 1896”. World Digital Library.1896. Retrieved 2013-07-16.

[7] Brian Black (2000). Petrolia: the landscape of America’sfirst oil boom. JohnsHopkinsUniversity Press. ISBN978-0-8018-6317-2.

[8] Sulphur production report by the United States GeologicalSurvey

[9] Discussion of recovered by-product sulphur

[10] Beychok, Milton R. (1967). Aqueous Wastes fromPetroleum and Petrochemical Plants (1st Edition ed.).JohnWiley & Sons. Library of Congress Control Number67019834.

[11] Kister, Henry Z. (1992). Distillation Design (1st Editioned.). McGraw-Hill. ISBN 978-0-07-034909-4.

[12] Refinery flowchart from the website of Universal OilProducts

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