A number of process units focus an improving the quality of a hydrocarbon stream without changing the product mix of the refinery. Typically this involves injecting hydrogen or extracting trace amount of contaminants.
This category of process units includes:
Hydrotreater - used to treat a variety of hydrocarbons, using hydrogen under pressure to remove contaminants and/or saturate hydrocarbons
Merox - Treats keosene by oxidizing trace amounts of mecaptans