Many refineries must generate hydrogen on purpose to supply all the needs of the hydrotreaters and hydrocrackers.

Refineries with a reformer typically generate a large portion of the hydrogen they need, but often this must be supplemented with on-purpose hydrogen generation, especially when making ultra-low sulfur fuels or when using a hydrocracker for conversion.

There are three major process options to make hydrogen, using either light ends or fuel oil as a feed:

• Steam methane reforming (SMR) - a catalytic process for making hydrogen from steam and a light hydrocrabon (usually methane, but can also use ethane or propane)

• Partial Oxidation (PO) - a process for generating hydrogen through partial combustion of a hydrocarbon (methane or  fuel oil) to CO and injection of steam to force production of H2

• Autothermal reforming (ATR) - a combination fo the SMR and PO processes

Hydrogen is also recovered from the off gas from other process units by a number of different processes.

• Pressure swing adsorption (PSA) - This processes uses and adsorption medium to capture impuritities. This can be a stand alone unit dedicated to handling off gas or part of the SMR process where it is also handling the output stream from the SMR reactor

• Membrane process - this process uses a hydrogen selective membrane to separate hydrogen from impurities

• Cryogenic process - this process uses low temperatures to crystallize impurities and seaparate from the hydrogen