Fluid Catalytic CrackingFluid Catalytic Cracking(FCC)(FCC)

Quak Foo, LeeQuak Foo, LeeChemical and Biological Chemical and Biological

EngineeringEngineeringThe University of British ColumbiaThe University of British Columbia

OutlineOutline What is FCC?What is FCC? Why use circulating Fluidized Bed Why use circulating Fluidized Bed

Reactor in FCC?Reactor in FCC? Operating CharacteristicsOperating Characteristics Description of the ProcessDescription of the Process Heat BalanceHeat Balance Pressure BalancePressure Balance ConclusionsConclusions

What is FCC?What is FCC? Primary conversion process in petroleum Primary conversion process in petroleum

refinery.refinery. The unit which utilizes a micro-The unit which utilizes a micro-

spherodial catalyst (zeolitic catalyst) spherodial catalyst (zeolitic catalyst) which fluidizes when properly aerated.which fluidizes when properly aerated.

The purpose is to convert high-boiling The purpose is to convert high-boiling petroleum fractions (gas oil) to high-petroleum fractions (gas oil) to high-value, high-octane gasoline and heating value, high-octane gasoline and heating oil.oil.

Why use Circulating Why use Circulating Fluidized Bed in FCC?Fluidized Bed in FCC?

Compared with Fixed Bed, Fluidized BedCompared with Fixed Bed, Fluidized Bed CFB – fast fluidization regimeCFB – fast fluidization regime CFB good for catalyst size < 0.2 mmCFB good for catalyst size < 0.2 mm Excellent in:Excellent in:

– Gas-solid effective contactGas-solid effective contact– Catalyst effectivenessCatalyst effectiveness– Catalyst internal temperature controlCatalyst internal temperature control– Catalyst regenerationCatalyst regeneration

Operating CharacteristicsOperating Characteristics

Particle Diameter = 150 Particle Diameter = 150 mm Geldart Classification = AGeldart Classification = A Temperature = 650 Temperature = 650 00CC Pressure = 100 kPaPressure = 100 kPa Superficial gas velocity = 10 m/sSuperficial gas velocity = 10 m/s Bed depth = 0.85 mBed depth = 0.85 m Fresh feed flow rate = 300,000 kg/hrFresh feed flow rate = 300,000 kg/hr Catalyst to oil ratio = 4.8Catalyst to oil ratio = 4.8

FCC Reactor-RegeneratorFCC Reactor-Regenerator

Description of the ProcessDescription of the Process ReactorReactor RiserRiser CyclonesCyclones StripperStripper RegeneratorRegenerator Standpipe and Slide ValveStandpipe and Slide Valve

Reactor PerformanceReactor Performance

Feed oil enters the riser near the base Feed oil enters the riser near the base Contacts the incoming regenerated catalystContacts the incoming regenerated catalyst Cracking reactions occur in the vapor Cracking reactions occur in the vapor

phase phase Expanded volume of vapors lift the catalyst Expanded volume of vapors lift the catalyst

and vaporized oil risesand vaporized oil rises Fast reaction, few seconds of contact timeFast reaction, few seconds of contact time

RiserRiser DimensionsDimensions

– Diameter: 1.2 m (4 ft)Diameter: 1.2 m (4 ft)– Height : 36.6 m (120 ft)Height : 36.6 m (120 ft)

Plug flow with minimum back-mixingPlug flow with minimum back-mixing Steam is used to atomize the feedSteam is used to atomize the feed

– Increases the availability of feedIncreases the availability of feed Outlet vapor velocity: 18 m/s (60 ft/sec)Outlet vapor velocity: 18 m/s (60 ft/sec) Hydrocarbon residence time: 2 secondsHydrocarbon residence time: 2 seconds

CyclonesCyclones Located at the end of riser to separate Located at the end of riser to separate

the bulk of the catalyst from the vaporthe bulk of the catalyst from the vapor Use a deflector device to turn catalyst Use a deflector device to turn catalyst

direction downwarddirection downward Two-stage cyclonesTwo-stage cyclones

– To separate the remaining of the catalyst To separate the remaining of the catalyst Return the catalyst to the stripper Return the catalyst to the stripper

through the diplegsthrough the diplegs The product vapors exit the cyclones The product vapors exit the cyclones

and flow to the main fractionator columnand flow to the main fractionator column

CyclonesCyclones

Riser

Stripping Bed

Stripping SectionStripping Section The spent catalysts falls into the stripperThe spent catalysts falls into the stripper Valuable hydrocarbons are absorbed Valuable hydrocarbons are absorbed

within the catalyst bedwithin the catalyst bed Stripping steam, at a rate of 4 kg per Stripping steam, at a rate of 4 kg per

1000 kg of circulating catalyst, is used to 1000 kg of circulating catalyst, is used to strip the hydrocarbons from the catalyststrip the hydrocarbons from the catalyst

The catalyst level provides the pressure The catalyst level provides the pressure head which allows the catalyst to flow head which allows the catalyst to flow into the regeneratorinto the regenerator

Inside Stripping SectionInside Stripping Section

Steam

Reactor Stripper

Catalyst Level

Reactor Riser

RegeneratorRegenerator Two functions:Two functions:

– Restores catalyst activity Restores catalyst activity – Supplies heat to crack the feedSupplies heat to crack the feed

Air is the source of oxygen for the combustion Air is the source of oxygen for the combustion of cokeof coke

The air blower with 1m/s (3 ft/s) air velocity to The air blower with 1m/s (3 ft/s) air velocity to maintain the catalyst bed in a fluidized statemaintain the catalyst bed in a fluidized state

14 kPa (2 psi) pressure drop in air distributors 14 kPa (2 psi) pressure drop in air distributors to ensure positive air flow through all nozzlesto ensure positive air flow through all nozzles

Inside RegeneratorInside Regenerator

Catalyst (low carbon)

Catalyst (high carbon)

High Oxygen

Low Oxygen

Dense Phase Bed

Cat

alys

t

A

ir

Standpipe & Slide ValveStandpipe & Slide Valve Standpipe provides the necessary Standpipe provides the necessary

pressure head needed to circulate the pressure head needed to circulate the catalyst around the unitcatalyst around the unit

The catalyst density in standpipe is 642 The catalyst density in standpipe is 642 kg/mkg/m33 (40 lbs/ft (40 lbs/ft33))

Slide valve is used to regulate the flow Slide valve is used to regulate the flow rate of the regenerated catalyst to the rate of the regenerated catalyst to the riserriser

Slide valve function is to supply enough Slide valve function is to supply enough catalyst to heat the feed and achieve the catalyst to heat the feed and achieve the desired reactor temperaturedesired reactor temperature

Heat BalanceHeat Balance A catalyst cracker continually adjusts A catalyst cracker continually adjusts

itself to stay in heat balance.itself to stay in heat balance. The reactor and regenerator heat The reactor and regenerator heat

flows must be equal.flows must be equal. Heat balance performed around Heat balance performed around

– the reactorthe reactor– the stripper-regeneratorthe stripper-regenerator

Use to calculate catalyst circulation rate and Use to calculate catalyst circulation rate and catalyst-to-oil ratiocatalyst-to-oil ratio

– overall heat balanceoverall heat balance

Heat BalanceHeat Balance The unit produces and burns enough coke to provide The unit produces and burns enough coke to provide

energy to:energy to:– Increase the temperature of the fresh feed, recycle, and Increase the temperature of the fresh feed, recycle, and

atomizing steam from their preheated states to the reactor atomizing steam from their preheated states to the reactor temperature.temperature.

– Provide the endothermic heat of cracking.Provide the endothermic heat of cracking.– Increase the temperature of the combustion air from the Increase the temperature of the combustion air from the

blower discharge temperature to the regenerator flue gas blower discharge temperature to the regenerator flue gas temperature.temperature.

– Make up for heat losses from the reactor and regenerator Make up for heat losses from the reactor and regenerator to surroundings.to surroundings.

– Provide for heat sinks, such as stripping steam and Provide for heat sinks, such as stripping steam and catalyst cooling.catalyst cooling.

FCC Heat BalanceFCC Heat BalanceRegenerator Reactor

Spent CatalystFlue gas

Heat losses

Regeneration Air Feed Preheater

Recycle

Fresh Feed

Products

Heat LossesHeat of Coke Combustion

Heat of Reaction

Regenerated Catalyst

FCC Heat BalanceFCC Heat BalanceRegenerator Reactor

Spent CatalystFlue gas

Heat losses

Regeneration Air Feed Preheater

Recycle

Fresh Feed

Products

Heat LossesHeat of Coke Combustion

Heat of Reaction

Regenerated Catalyst

Heat Balance Heat Balance Around Stripper-Around Stripper-

RegeneratorRegenerator Heat to raise air from the blower discharge Heat to raise air from the blower discharge

temperature to the regenerator dense temperature to the regenerator dense phase temperature. (108 phase temperature. (108 10 1066 Btu/hr) Btu/hr)

Heat to desorb the coke from the spent Heat to desorb the coke from the spent catalyst. (39.5 catalyst. (39.5 10 1066 Btu/hr) Btu/hr)

Heat to raise the temperature of the Heat to raise the temperature of the stripping steam to the reactor temperature. stripping steam to the reactor temperature. (4.4 (4.4 10 1066 Btu/hr) Btu/hr)

Heat to raise the coke on the catalyst from Heat to raise the coke on the catalyst from the reactor T to the regenerator dense the reactor T to the regenerator dense phase T. (3.7 phase T. (3.7 10 1066 Btu/hr) Btu/hr)

Heat BalanceHeat BalanceAround Stripper-Around Stripper-

RegeneratorRegenerator Heat to raise the coke products from the Heat to raise the coke products from the

regenerator dense temperature to flue regenerator dense temperature to flue gas temperature. (2.17 gas temperature. (2.17 10 1066 Btu/hr) Btu/hr)

Heat to compensate for regenerator heat Heat to compensate for regenerator heat losses. ( 19.3losses. ( 19.3 10 1066 Btu/hr) Btu/hr)

Heat to raise the spent catalyst from the Heat to raise the spent catalyst from the reactor temperature to the regenerator reactor temperature to the regenerator dense phase. (305.5 dense phase. (305.5 10 1066 Btu/hr) Btu/hr)

Reactor Heat BalanceReactor Heat Balance Hot-regenerated catalyst supplies Hot-regenerated catalyst supplies

the bulk of the heat required to the bulk of the heat required to vaporize the liquid feedvaporize the liquid feed

To provide the overall endothermic To provide the overall endothermic heat of crackingheat of cracking

To raise the temperature of To raise the temperature of dispersion steam and inert gases to dispersion steam and inert gases to the reactor temperaturethe reactor temperature

Reactor Heat BalanceReactor Heat Balance Heat into the reactor Heat into the reactor

– Regenerated catalyst = 1186 Regenerated catalyst = 1186 10 1066 Btu/hrBtu/hr

– Fresh feed = 267 Fresh feed = 267 10 1066 Btu/hr Btu/hr– Atomizing steam = 12 Atomizing steam = 12 10 1066 Btu/hr Btu/hr– Heat of absorption = 35 Heat of absorption = 35 10 1066

Btu/hrBtu/hr Total heat in = 1500 Total heat in = 1500 10 1066 Btu/hr Btu/hr

Reactor Heat BalanceReactor Heat Balance Heat out of the reactorHeat out of the reactor

– Spent catalyst = 880 Spent catalyst = 880 10 1066 Btu/hr Btu/hr– To vaporize feed = 513 To vaporize feed = 513 10 1066 Btu/hr Btu/hr– Heat content of steam = 15 Heat content of steam = 15 10 1066

Btu/hrBtu/hr– Loss to surroundings = 6 Loss to surroundings = 6 10 1066 Btu/hr Btu/hr– Heat of reaction = ?Heat of reaction = ?

Total heat out = 1414 Total heat out = 1414 10 1066 Btu/hr Btu/hr + Heat of reaction+ Heat of reaction

Reaction Heat BalanceReaction Heat Balance Calculation of Heat of ReactionCalculation of Heat of Reaction Total heat out = Total heat inTotal heat out = Total heat in Total heat in = 1500 Total heat in = 1500 10 1066 Btu/hr Btu/hr Total heat out = 1414 Total heat out = 1414 10 1066 Btu/hr + Btu/hr +

Heat of reactionHeat of reaction Therefore, Overall Endothermic Heat Therefore, Overall Endothermic Heat

of Reaction = 86 of Reaction = 86 10 1066 Btu/hr Btu/hr

Pressure BalancePressure Balance Deals with the hydraulics of catalyst Deals with the hydraulics of catalyst

circulation in the reactor and circulation in the reactor and regenerator circuit.regenerator circuit.

The incremental capacity come from The incremental capacity come from increased catalyst circulation or from increased catalyst circulation or from altering the differential pressure altering the differential pressure between reactor-regenerator.between reactor-regenerator.

Pressure Balance ResultsPressure Balance Results In spent catalyst standpipe:In spent catalyst standpipe:

– Pressure buildup = 27 kPa (4 psi)Pressure buildup = 27 kPa (4 psi)– Catalyst density = 658 kg/mCatalyst density = 658 kg/m33

– Optimum pressure to circulate more Optimum pressure to circulate more catalystcatalyst

In regenerated catalyst standpipe:In regenerated catalyst standpipe:– Pressure buildup = 55 kPa (8 psi)Pressure buildup = 55 kPa (8 psi)– Catalyst density = 642 kg/mCatalyst density = 642 kg/m33

ConclusionsConclusions Circulating Fluidized Bed is used in Circulating Fluidized Bed is used in

FCC unit.FCC unit. Stripping steam of 4 kg per 1000 kg Stripping steam of 4 kg per 1000 kg

circulating catalyst is required.circulating catalyst is required. Overall endothermic Heat of Overall endothermic Heat of

Reaction is 86 MBtu/hr.Reaction is 86 MBtu/hr. Pressure buildup in spent catalyst Pressure buildup in spent catalyst

standpipe is 27 kPa (4 psi).standpipe is 27 kPa (4 psi). Pressure buildup in regenerated Pressure buildup in regenerated

catalyst standpipe is 55 kPa (8 psi).catalyst standpipe is 55 kPa (8 psi).