In addition to the units that directly process hydrocarbons, a refinery will have a number of supporting units providing utilities and other services. These typically include:
Gas processing - Separation of light ends (propane, butane) from fuel gas coming from distillation and all of the conversion units
Acid gas recovery - Separation of H2S and CO2 from refinery gas
Sulfur recovery - Conversion of H2S to elemental sulfur
Hydrogen production - Generation of hydrogen from natural gas or other hydrocarbons for use in hydrotreaters and hydrocracker
Hydrogen capture - Extraction of hydrogen from conversion unit gas
Steam production - Generation of steam for process units
Cooling water - Cooling water used in process units
Waste water treating - Removal of contaminants from process and runoff water