Fluid Catalytic Cracking
Three major sections of FCC complex
a) Reactor – riser
b) Regenerator – flue gas separation
c) Distillation and recycling
Cracking in risers
• Function – to bring thorough contact between vapour and catalyst in
short time
• Contact time < 5 seconds
• Complexity of reaction increases as oil-catalyst move through riser
• Increasing cracking
• Deposition of coke
• Degradation in catalyst
activity
• Sharp increase in velocity
vapour
• Slip velocity – relative
velocity catalyst and oil
decreases
𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 𝑜𝑓 𝑣𝑎𝑝𝑜𝑢𝑟,𝑉𝑣
Slip velocity =
𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 𝑜𝑓 𝑐𝑎𝑡𝑎𝑙𝑦𝑠𝑡,𝑉𝑐
Regenerator – flue gas separation
• Cracked oil vapours escapes into separation system through inbuilt
cyclone system
• Disengaged catalyst falls into reactor and steam is stripped
• Catalyst regeneration – burning off coke in separate unit
Distillation and recycling
Fluidisation – dense phase and dilute phase
After regeneration and separation – catalyst recycling
Fluid Catalytic Cracking
• Designed by Texaco Development
Corporation
• Separate risers – fresh feed and
recycled feed
• Preheated stock mixed with catalyst
at bottom bend of fresh feed riser(1)
• Reactor space (3) – Product and
catalyst
• Cyclone system – vapors are freed
from catalyst dust
• Riser (2) – recycled stock enters,
mixes with regenerated catalyst
• Fresh feed riser – directs products
downwards into reactor space
• Vapours from risers – fractionation through
cyclones
• Regenerator (4) – spent catalyst from
reactor after steam stripping passes into
regenerator
• Coke burning – blast of air and flue gas
escapes through cyclone
FCC – Flexi cracking • High space velocities are maintained
– enhances the zeolite catalyst
activity
• Different feed stock handling
• Maximum liquid products – major
benefit
• Design of cyclones – plug flow of
catalyst
• Catalyst without back mixing with oil
• U bend design - abruptly changes
direction of catalyst and flow lines
• Smooth control in catalyst circulation
– side by side reactor and regenerator
• Increased recovery in catalyst
FCC – Flexi cracking • Pure transfer line configuration
• Cracking – transfer line
• Rapid termination of reaction -
disengaging oil from catalyst in
cyclone separator
• Space velocity – quality of the
feed
• Handling of different feed stocks
• Catalyst – silica- manganese,
natural catalyst with activated
earth
FCC – Kellog process
• Converting – heavy fractions to
valuable light olefins
• Temperature – 470 -500°C
• Pressure – 1.5 to 2.2 atm
• Regenerator temperature – 580-
610°C
• Pressure – 1.3 kg/cm2
• Catalyst/feed – 2.5 – 5 kgs/bbl
Naphtha cracking
Naphtha cracking
• Cracking process to produce olefins mainly ethylene and propylene
• Propane ethane are cracked/dehydrogenated to yield olefins
Naphtha cracking process
