Common process units found in a refinery

• Desalter unit washes out salt from the crude oil before it enters the atmospheric distillation unit.
• Atmospheric distillation unit distills crude oil into fractions. See Continuous distillation.
• Vacuum distillation unit further distills residual bottoms after atmospheric distillation.
• Naphtha hydrotreater unit uses hydrogen to desulfurize naphtha from atmospheric distillation. Must hydrotreat the naphtha before sending to a Catalytic Reformer unit.
• Catalytic reformer unit is used to convert the naphtha-boiling range molecules into higher octane reformate (reformer product). The reformate has higher content of aromatics and cyclic hydrocarbons). An important byproduct of a reformer is hydrogen released during the catalyst reaction. The hydrogen is used either in the hydrotreaters or the hydrocracker.
• Distillate hydrotreater unit desulfurizes distillates (such as diesel) after atmospheric distillation.
• Fluid catalytic cracker (FCC) unit upgrades heavier fractions into lighter, more valuable products.
• Hydrocracker unit uses hydrogen to upgrade heavier fractions into lighter, more valuable products.
• Visbreaking unit upgrades heavy residual oils by thermally cracking them into lighter, more valuable reduced viscosity products.
• Merox unit treats LPG, kerosene or jet fuel by oxidizing mercaptans to organic disulfides.
• Alternative processes for removing mercaptans are known, e.g. doctor sweetening process and caustic washing.
• Coking units (delayed coking, fluid coker, and flexicoker) process very heavy residual oils into gasoline and diesel fuel, leaving petroleum coke as a residual product.
• Alkylation unit produces high-octane component for gasoline blending.
• Dimerization unit converts olefins into higher-octane gasoline blending components. For example, butenes can be dimerized into isooctene which may subsequently be hydrogenated to form isooctane. There are also other uses for dimerization.
• 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 store propane and similar gaseous fuels at pressure sufficient to maintain them in liquid form. These are usually spherical vessels or bullets (horizontal vessels with rounded ends.
• Storage tanks store crude oil and finished products, usually cylindrical, with some sort of vapor emission control and surrounded by an earthen berm to contain spills.
• Slug catcher used when product (crude oil and gas) that comes from a pipeline with two-phase flow, has to be buffered at the entry of the units.
• Amine gas treater, Claus unit, and tail gas treatment convert hydrogen sulfide from hydrodesulfurization into elemental sulfur.
• Utility units such as cooling towers circulate cooling water, boiler plants generates steam, and instrument air systems include pneumatically operated control valves and an electrical substation.
• Wastewater collection and treating systems consist of API separators, dissolved air flotation (DAF) units and further treatment units such as an activated sludge biotreater to make water suitable for reuse or for disposal.
• Solvent refining units use solvent such as cresol or furfural to remove unwanted, mainly aromatics from lubricating oil stock or diesel stock.
• Solvent dewaxing units remove the heavy waxy constituents petrolatum from vacuum distillation products.