1. Fluid Catalytic Cracking (FCC)
Quak Foo, Lee
Chemical and Biological Engineering
The University of British Columbia

2. Outline What is FCC? Why use circulating Fluidized Bed Reactor in FCC?
Operating Characteristics
Description of the Process
Heat Balance
Pressure Balance
Conclusions

3. What is FCC? Primary conversion process in petroleum refinery.
The unit which utilizes a micro-spherodial catalyst (zeolitic catalyst) which fluidizes when properly aerated.
The purpose is to convert high-boiling petroleum fractions (gas oil) to high-value, high-octane gasoline and heating oil.

4. Why use Circulating Fluidized Bed in FCC?
Compared with Fixed Bed, Fluidized Bed
CFB – fast fluidization regime
CFB good for catalyst size < 0.2 mm
Excellent in:
Gas-solid effective contact
Catalyst effectiveness
Catalyst internal temperature control
Catalyst regeneration

5. Operating Characteristics
Particle Diameter = 150 m
Geldart Classification = A
Temperature = 650 0C
Pressure = 100 kPa
Superficial gas velocity = 10 m/s
Bed depth = 0.85 m
Fresh feed flow rate = 300,000 kg/hr
Catalyst to oil ratio = 4.8

6. FCC Reactor-Regenerator

7. Description of the Process
Reactor
Riser
Cyclones
Stripper
Regenerator
Standpipe and Slide Valve

8. Reactor Performance Feed oil enters the riser near the base
Contacts the incoming regenerated catalyst
Cracking reactions occur in the vapor phase
Expanded volume of vapors lift the catalyst and vaporized oil rises
Fast reaction, few seconds of contact time

9. Riser Dimensions Plug flow with minimum back-mixing
Diameter: m (4 ft)
Height : 36.6 m (120 ft)
Plug flow with minimum back-mixing
Steam is used to atomize the feed
Increases the availability of feed
Outlet vapor velocity: 18 m/s (60 ft/sec)
Hydrocarbon residence time: 2 seconds

10. Cyclones
Located at the end of riser to separate the bulk of the catalyst from the vapor
Use a deflector device to turn catalyst direction downward
Two-stage cyclones
To separate the remaining of the catalyst
Return the catalyst to the stripper through the diplegs
The product vapors exit the cyclones and flow to the main fractionator column

11. Cyclones
Riser
Stripping Bed

12. Stripping Section The spent catalysts falls into the stripper
Valuable hydrocarbons are absorbed within the catalyst bed
Stripping steam, at a rate of 4 kg per 1000 kg of circulating catalyst, is used to strip the hydrocarbons from the catalyst
The catalyst level provides the pressure head which allows the catalyst to flow into the regenerator

13. Inside Stripping Section
Catalyst Level
Steam
Reactor Riser
Reactor Stripper

14. Regenerator Two functions:
Restores catalyst activity
Supplies heat to crack the feed
Air is the source of oxygen for the combustion of coke
The air blower with 1m/s (3 ft/s) air velocity to maintain the catalyst bed in a fluidized state
14 kPa (2 psi) pressure drop in air distributors to ensure positive air flow through all nozzles

15. Inside Regenerator Catalyst (high carbon) Low Oxygen Dense Phase Bed
Air
Catalyst (low carbon)
High Oxygen

16. Standpipe & Slide Valve
Standpipe provides the necessary pressure head needed to circulate the catalyst around the unit
The catalyst density in standpipe is 642 kg/m3 (40 lbs/ft3)
Slide valve is used to regulate the flow rate of the regenerated catalyst to the riser
Slide valve function is to supply enough catalyst to heat the feed and achieve the desired reactor temperature

17. Heat Balance
A catalyst cracker continually adjusts itself to stay in heat balance.
The reactor and regenerator heat flows must be equal.
Heat balance performed around
the reactor
the stripper-regenerator
Use to calculate catalyst circulation rate and catalyst-to-oil ratio
overall heat balance

18. Heat Balance
The unit produces and burns enough coke to provide energy to:
Increase the temperature of the fresh feed, recycle, and atomizing steam from their preheated states to the reactor temperature.
Provide the endothermic heat of cracking.
Increase the temperature of the combustion air from the blower discharge temperature to the regenerator flue gas temperature.
Make up for heat losses from the reactor and regenerator to surroundings.
Provide for heat sinks, such as stripping steam and catalyst cooling.

19. FCC Heat Balance Regenerator Reactor Flue gas Spent Catalyst Products
Heat of Coke Combustion
Heat Losses
Heat losses
Heat of Reaction
Recycle
Regenerated Catalyst
Fresh Feed
Regeneration Air
Feed Preheater

20. FCC Heat Balance Regenerator Reactor Flue gas Spent Catalyst Products
Heat of Coke Combustion
Heat Losses
Heat losses
Heat of Reaction
Recycle
Regenerated Catalyst
Fresh Feed
Regeneration Air
Feed Preheater

21. Heat Balance Around Stripper-Regenerator
Heat to raise air from the blower discharge temperature to the regenerator dense phase temperature. (108  106 Btu/hr)
Heat to desorb the coke from the spent catalyst. (39.5  106 Btu/hr)
Heat to raise the temperature of the stripping steam to the reactor temperature (4.4  106 Btu/hr)
Heat to raise the coke on the catalyst from the reactor T to the regenerator dense phase T (3.7  106 Btu/hr)

22. Heat Balance Around Stripper-Regenerator
Heat to raise the coke products from the regenerator dense temperature to flue gas temperature. (2.17  106 Btu/hr)
Heat to compensate for regenerator heat losses. ( 19.3 106 Btu/hr)
Heat to raise the spent catalyst from the reactor temperature to the regenerator dense phase. (305.5  106 Btu/hr)

23. Reactor Heat Balance
Hot-regenerated catalyst supplies the bulk of the heat required to vaporize the liquid feed
To provide the overall endothermic heat of cracking
To raise the temperature of dispersion steam and inert gases to the reactor temperature

24. Reactor Heat Balance Heat into the reactor
Regenerated catalyst = 1186  106 Btu/hr
Fresh feed = 267  106 Btu/hr
Atomizing steam = 12  106 Btu/hr
Heat of absorption = 35  106 Btu/hr
Total heat in = 1500  106 Btu/hr

25. Reactor Heat Balance Heat out of the reactor
Spent catalyst = 880  106 Btu/hr
To vaporize feed = 513  106 Btu/hr
Heat content of steam = 15  106 Btu/hr
Loss to surroundings = 6  106 Btu/hr
Heat of reaction = ?
Total heat out = 1414  106 Btu/hr + Heat of reaction

26. Reaction Heat Balance Calculation of Heat of Reaction
Total heat out = Total heat in
Total heat in = 1500  106 Btu/hr
Total heat out = 1414  106 Btu/hr + Heat of reaction
Therefore, Overall Endothermic Heat of Reaction = 86  106 Btu/hr

27. Pressure Balance
Deals with the hydraulics of catalyst circulation in the reactor and regenerator circuit.
The incremental capacity come from increased catalyst circulation or from altering the differential pressure between reactor-regenerator.

28. Pressure Balance Results
In spent catalyst standpipe:
Pressure buildup = 27 kPa (4 psi)
Catalyst density = 658 kg/m3
Optimum pressure to circulate more catalyst
In regenerated catalyst standpipe:
Pressure buildup = 55 kPa (8 psi)
Catalyst density = 642 kg/m3

29. Conclusions Circulating Fluidized Bed is used in FCC unit.
Stripping steam of 4 kg per 1000 kg circulating catalyst is required.
Overall endothermic Heat of Reaction is 86 MBtu/hr.
Pressure buildup in spent catalyst standpipe is 27 kPa (4 psi).
Pressure buildup in regenerated catalyst standpipe is 55 kPa (8 psi).