Oil refineries convert crude oil into high-value products such as gasoline, diesel,
liquefied petroleum gas (LPG), and petrochemical feedstocks. After squeezing as
much salable product from the crude oil as possible, there remains a light gas stream
known as refinery fuel gas (RFG), which is too light for any of the high-value products.
The RFG (predominantly made up of a mixture of hydrogen, methane, and ethane) is
returned to the plant and used as fuel tofire the process heaters. At one time, a typical
plant did not make enough RFG to supply all of its heaters and was therefore required to
purchase a makeup fuel from a third-party supplier. In the United States, the purchased
fuel is usually natural gas, which is typically injected directly into the RFG manifold or
mix drum and represents what refiners call their“fuel gas cushion.”
Changes in refined product demand, environmental requirements and specifications,
and increasing emphasis on energy optimization over recent years have all changed the
refinery fuel gas balance. Hydrogen supply has become more important as both refined
product sulfur limits and reformer severities have been reduced, and lower emission
burners are limited in their tolerance for hydrogen in the fuel system. Environmental