Process units

A refinery is a plant that includes a number of different processing units. Each of these plays a role in the overall process of converting crude oil into finished petroleum products. A typical refinery will have a dozen or more of these processing units. These fall into four broad categories:

• Separation units - Some process units separate a hydrocarbon mixture into its components through distillation or extraction. The most common separation units are atmospheric distillation and vacuum distillation
• Conversion units - Conversion units take individual hydrocarbon streams and convert them to other hydrocarbons by changing their size and chemical structure. Examples are the coker, FCC, and alkylation unit
• Treating units - A number of process unites improve a hydrocarbon stream by removing impurities and changing some chemical properties, but without changing the refinery's product yield. Good examples of this are the hydrotreaters
• Supporting process units - This includes utilities and and other non-hydrocarbon processing units

Typical process units in a refinery include:

• Crude desalting - Removes salt and other contaminants from crude oil before it is sent to atmospheric distillation for separation
• Atmospheric distillation - The first major process unit in a refinery. Separates crude oil into its component distillation fractions
• Vacuum distillation - Secondary distillation that separates the heaviest fractions into VGO and vacuum resid
• Coker - Thermal conversion process that converts the heaviest distillation fraction (vacuum resid) into lighter fractions
• Visbreaker - Mild thermal conversion process that lower the viscosity of vacuum resid
• Resid hydrocracker - Catalytic conversion process that converts vacuum resid to lighter fractions while injecting hydrogen
• RCC - Catalytic cracking process that converts atmospheric resid to lighter fractions; similar to an FCC but with heavier feed
• De-asphalting - Solvent extraction process that removes asphaltenes from vacuum resid
• FCC - Catalytic conversion process that converts VGO to lighter fractions
• Hydrocracker - Catalytic conversion process that converts VGO to lighter fractions (especially distillates) while injecting hydrogen)
• Thermal cracker - Non-catalytic process for converting VGO to lighter fractions
• Reformer - Increases the octane value of heavy naphtha
• Alkylation - Combines light olefins with isobutane to make gasoline
• Dimersol - Converts propylene into a higher-value gasoline blend stock
• Polymerization - Converts light olefins into a higher-value gasoline blend stock
• MTBE
• ETBE  
• TAME 
• Iso-octene 
• C5/C6 isomerization - Improves the octane value of light naphtha
• C4 isomerization - Converts butane into isobutane as feed to the alkylation unit
• Hydrogen production - Generates hydrogen for other process units from methane or other hydrocarbon feedstocks
• Hydrogen purification - Extracts hydrogen from refinery gas streams
• Naphtha hydrotreater - Catalytic process to remove sulfur and other contaminants from naphtha by injecting hydrogen
• Kerosene hydrotreater - Catalytic process to remove sulfur and other contaminants from kerosene by injecting hydrogen
• Distillate hydrotreater - Catalytic process to remove sulfur and other contaminants from distillate by injecting hydrogen
• FCC gasoline hydrotreater - Catalytic process to remove sulfur and other contaminants from FCC gasoline by injecting hydrogen
• VGO hydrotreater - Catalytic process to remove sulfur and other contaminants from VGO by injecting hydrogen
• Resid hydrotreater - Catalytic process to remove sulfur and other contaminants from resid by injecting hydrogen
• Asphalt plant - Creates asphalt from vacuum resid
• Base oil plant - Collection of processes that extracts base oil from VGO and vacuum resid 
• BTX plant - Collection of processes that extracts aromatics (benzene, toluene, xylene) from reformate
• Sat gas plant - Collection of processes that separates components in saturated refinery gas and removes impurities
• Unsat gas plant - Collection of processes that separate components in unsaturated (cracked) refinery gas and remove impurities
• Sulfur plant - Converts H2S into solid sulfur
• Calciner - Processes pet coke for use as a specialty product
• Acid regeneration
• Tail gas recovery