Presentation on theme: "Fluid Catalytic Cracking (FCC)"— Presentation transcript:
1 Fluid Catalytic Cracking (FCC) Quak Foo, LeeChemical and Biological EngineeringThe University of British Columbia
2 Outline What is FCC? Why use circulating Fluidized Bed Reactor in FCC? Operating CharacteristicsDescription of the ProcessHeat BalancePressure BalanceConclusions
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 BedCFB – fast fluidization regimeCFB good for catalyst size < 0.2 mmExcellent in:Gas-solid effective contactCatalyst effectivenessCatalyst internal temperature controlCatalyst regeneration
7 Description of the Process ReactorRiserCyclonesStripperRegeneratorStandpipe and Slide Valve
8 Reactor Performance Feed oil enters the riser near the base Contacts the incoming regenerated catalystCracking reactions occur in the vapor phaseExpanded volume of vapors lift the catalyst and vaporized oil risesFast 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-mixingSteam is used to atomize the feedIncreases the availability of feedOutlet vapor velocity: 18 m/s (60 ft/sec)Hydrocarbon residence time: 2 seconds
10 CyclonesLocated at the end of riser to separate the bulk of the catalyst from the vaporUse a deflector device to turn catalyst direction downwardTwo-stage cyclonesTo separate the remaining of the catalystReturn the catalyst to the stripper through the diplegsThe product vapors exit the cyclones and flow to the main fractionator column
12 Stripping Section The spent catalysts falls into the stripper Valuable hydrocarbons are absorbed within the catalyst bedStripping steam, at a rate of 4 kg per 1000 kg of circulating catalyst, is used to strip the hydrocarbons from the catalystThe catalyst level provides the pressure head which allows the catalyst to flow into the regenerator
14 Regenerator Two functions: Restores catalyst activitySupplies heat to crack the feedAir is the source of oxygen for the combustion of cokeThe air blower with 1m/s (3 ft/s) air velocity to maintain the catalyst bed in a fluidized state14 kPa (2 psi) pressure drop in air distributors to ensure positive air flow through all nozzles
16 Standpipe & Slide Valve Standpipe provides the necessary pressure head needed to circulate the catalyst around the unitThe 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 riserSlide valve function is to supply enough catalyst to heat the feed and achieve the desired reactor temperature
17 Heat BalanceA catalyst cracker continually adjusts itself to stay in heat balance.The reactor and regenerator heat flows must be equal.Heat balance performed aroundthe reactorthe stripper-regeneratorUse to calculate catalyst circulation rate and catalyst-to-oil ratiooverall heat balance
18 Heat BalanceThe 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 CombustionHeat LossesHeat lossesHeat of ReactionRecycleRegenerated CatalystFresh FeedRegeneration AirFeed Preheater
20 FCC Heat Balance Regenerator Reactor Flue gas Spent Catalyst Products Heat of Coke CombustionHeat LossesHeat lossesHeat of ReactionRecycleRegenerated CatalystFresh FeedRegeneration AirFeed 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 BalanceHot-regenerated catalyst supplies the bulk of the heat required to vaporize the liquid feedTo provide the overall endothermic heat of crackingTo raise the temperature of dispersion steam and inert gases to the reactor temperature
25 Reactor Heat Balance Heat out of the reactor Spent catalyst = 880 106 Btu/hrTo vaporize feed = 513 106 Btu/hrHeat content of steam = 15 106 Btu/hrLoss to surroundings = 6 106 Btu/hrHeat 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 inTotal heat in = 1500 106 Btu/hrTotal heat out = 1414 106 Btu/hr + Heat of reactionTherefore, Overall Endothermic Heat of Reaction = 86 106 Btu/hr
27 Pressure BalanceDeals 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/m3Optimum pressure to circulate more catalystIn 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).