The Fluid Catalytic Cracking Unit (FCCU)
This cracking process is among the oldest in the oil industry. Although developed in
the mid-1920s, it first came into prominence during the Second World War as a
source of high-octane fuel for aircraft. In the early 1950s its prominence as the
major source of octane was somewhat overshadowed by the development of the
catalytic reforming process with its production of hydrogen as well as high-octane
material. The prominence of the fluid catalytic cracking unit (FCCU) was
reestablished in the 1960s by two developments in the process. These were:
• The use of highly active and selective catalysts (Zeolites)
• The establishment of riser cracking techniques
These two developments enabled the process to produce higher yields of betterquality distillates from lower-quality feedstocks. At the same time catalyst inventory and consumption costs were significantly reduced.
The process consists of a reactor vessel and a regenerator vessel interconnected
by transfer lines to enable the flow of finely divided catalyst powder between
them. The oil feed (typically high-vacuum gas oil, HVGO, from the crude
vacuum unit) is introduced to the very hot regenerated catalyst stream leaving
the regenerator en route to the reactor. Cracking occurs in the riser inlet to the
reactor due to the contact of the oil with the hot catalyst. The catalyst and oil are
very dispersed in the riser so that contact between them is very high exposing a
large portion of the oil to the hot catalyst. The cracking is completed in the
catalyst fluid bed in the reactor vessel. The catalyst fluidity is maintained by
steam injection at the bottom of the vessel. The cracked effluent leaves the top of
the reactor vessel as a vapor to enter the recovery section of the plant. Here the
distillate products of cracking are separated by fractionation and forwarded to
storage or further treating. An oil slurry stream from this recovery plant is
returned to the reactor as recycle.
The catalyst from the reactor is transferred to the regenerator on a continuous
basis. In the regenerator the catalyst is contacted with an air stream which maintains
the catalyst in a fluidized state. The hot carbon on the catalyst is burned off by
contact with the air and converted into CO and CO 2 . The reactions are highly
exothermic rising the temperature of the catalyst stream to well over 1,000
F and
thus providing the heat source for the oil cracking mechanism.
Products from this process are:
• Unsaturated and saturated LPG
• Light cracked naphtha
• Heavy cracked naphtha
• Cycle oil (mid distillate)
• Slurry
Introduction to Crude Oil and Petroleum Processing
37
This cracking process is among the oldest in the oil industry. Although developed in
the mid-1920s, it first came into prominence during the Second World War as a
source of high-octane fuel for aircraft. In the early 1950s its prominence as the
major source of octane was somewhat overshadowed by the development of the
catalytic reforming process with its production of hydrogen as well as high-octane
material. The prominence of the fluid catalytic cracking unit (FCCU) was
reestablished in the 1960s by two developments in the process. These were:
• The use of highly active and selective catalysts (Zeolites)
• The establishment of riser cracking techniques
These two developments enabled the process to produce higher yields of betterquality distillates from lower-quality feedstocks. At the same time catalyst inventory and consumption costs were significantly reduced.
The process consists of a reactor vessel and a regenerator vessel interconnected
by transfer lines to enable the flow of finely divided catalyst powder between
them. The oil feed (typically high-vacuum gas oil, HVGO, from the crude
vacuum unit) is introduced to the very hot regenerated catalyst stream leaving
the regenerator en route to the reactor. Cracking occurs in the riser inlet to the
reactor due to the contact of the oil with the hot catalyst. The catalyst and oil are
very dispersed in the riser so that contact between them is very high exposing a
large portion of the oil to the hot catalyst. The cracking is completed in the
catalyst fluid bed in the reactor vessel. The catalyst fluidity is maintained by
steam injection at the bottom of the vessel. The cracked effluent leaves the top of
the reactor vessel as a vapor to enter the recovery section of the plant. Here the
distillate products of cracking are separated by fractionation and forwarded to
storage or further treating. An oil slurry stream from this recovery plant is
returned to the reactor as recycle.
The catalyst from the reactor is transferred to the regenerator on a continuous
basis. In the regenerator the catalyst is contacted with an air stream which maintains
the catalyst in a fluidized state. The hot carbon on the catalyst is burned off by
contact with the air and converted into CO and CO 2 . The reactions are highly
exothermic rising the temperature of the catalyst stream to well over 1,000
F and
thus providing the heat source for the oil cracking mechanism.
Products from this process are:
• Unsaturated and saturated LPG
• Light cracked naphtha
• Heavy cracked naphtha
• Cycle oil (mid distillate)
• Slurry
Introduction to Crude Oil and Petroleum Processing
37