In a refinery, hydrogen gas is an important feedstock to many process units, which use it to remove impurities (e.g., hydrotreaters) and to saturate cracked components (e.g., hydrocrackers).

Within a refinery, the big users of hydrogen are the various hydrotreaters and the hydrocracker. 

Hydrogen production

Hydrogen is generated as a by product of the reforming process and is also made on purpose in the hydrogen plant.

Reformer - the reformer produces hydrogen as it removes a hydrogen molecule from cyclic compounds (naphthenes) to form aromatics. Reformer hydrogen is produces in a mixture with other gases and has to be purified for use in other refining process units.

• SMR - steam methane reforming is the most common provess for making on-purpose hydrogen in a refinery.  Typically methane (natural gas) is used as a feedstock.

• PO - partial oxidation reacts methane with a small amount of oxygen to result in partial oxidation of the methane to CO and hydrogen 

• ATR - autothermal reforming is a combination of the SMR and PO processes

• Electrolisis - hydrogen can also be produced from electrolisis of water.  This is more expensive than conventional processes but is seeing growing interest as a means to producing low-carbon hydrogen 

Low-carbon hydrogen

Hydrogen is also seen as a potential path to decarbonization both by switching to greener sources of hydrogen and by using greener hydrogen as an alternative fuel directly or as a feedstock to making alternative fuels.

Hydrogen has been given color designation based on the perceived level of carbon intensity of the different paths to production:

• Gray hydrogen - conventional hydrogen produced from natural gas

• Black hydrogen - hydrogen from coal or other fossil sources that result in higher CO2 emissions than conventional hydrogen

• Blue hydrogen - hydrogen produced in the conventional way but with carbon capture for the CO2 produced in the process

• Green hydrogen - produced from electrolysis of water using renewable power or from a bio-based feedstock

• Turquoise hydrogen - hydrogen produced from pyrolisis of methan to form hydrogen and solid carbon

• Pink/Purple/Red hydrogen - hydrogen from electrolisis of water using nuclear power