Dry gas is defined as the C2 and lighter gases that are produced in the FCC unit. Often the fuel gas stream leaving the sponge oil or secondary absorber tower is also referred to as “dry gas” despite its containing H2S, inert gases, and C31 components. Once the gas is amine-treated for the removal of H2S and other acid gases, it is usually blended into the refinery fuel gas system. Depending on the volume percent of hydrogen in the dry gas, some refiners will recover this hydrogen using processes such as cryogenics, pressure-swing absorption, or membrane separation. This recovered hydrogen is typically used in hydrotreating processes.