In addition to the higher severity operations of the FCCU, simple increases in FCCU
throughput can also impact the refinery’s fuel balance. Hot gas from the FCCU catalyst
regenerator is routed to a CO boiler, where its heat is used to generate steam. At higher
throughput, even if conversion remains the same, increased amounts of steam are
generated from waste heat in the CO boiler. Since FCCUs often generate steam at the
highest level in the refinery, this causes the refinery’s on-purpose boilers to reduce
production, thus reducing the demand for fuel gas.