petroleum refining

1. Older FCC Unit Configurations
• Typical FCC unit configurations:
•One of the most important
process different in FCC units
relates to the location and control
of the cracking reaction.
•Until 1965, most units were
designed with a discrete dense-
phase fluidized-catalyst bed in the
reactor vessel.
•Most of the cracking occurred in
the reactor bed.
•The extent of cracking was
controlled by varying reactor bed
depth (time) and temperature.
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2. Older FCC Unit Configurations
• Although it was recognized that cracking occurred in the
rise feeding the reactor because the catalyst activity and
temperature were at their highest, no significant attempt
was made to regulate the reaction by controlling riser
conditions.
• After more reactive zeolite catalysts were adopted by
refineries, amount of cracking occuring in the rise
(transfer line) increased to levels requiring operational
changes in existing units.
• As a result, most recently constructed units have been
designed to operate with a minimum bed level in the
reactor and with control of the reaction being
maintained by a varying catalyst circulation rate. 2

3. Older FCC Unit Configurations
• Many older units have been modified to
maximize and control riser tracking.
• Unit are also operate with different
combinations of feed-riser and dense-bed
reactors, including:
- feed-riser followed by dense-feed
- feed riser in parallel with dense-feed
- parallel feed-riser lines (one for fresh feed and
the other for recycle)
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4. Improvement
• Improvements in catalysts and to get more
efficient contact of heavy feedstocks with
catalysts particles.
• The results – higher conversion levels with
better selectivity (higher gasoline yields at
given conversion levels).
• Shorter and better controlled reaction times
(1-3 sec)
• Improved feed distribution systems
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5. Operations
• Fresh feed & recycle streams are preheated by heat
exchangers or a furnace and enter the unit at the base of
feed riser where they are mixed with the hot regenerated
catalyst.
• The heat from catalyst vaporizes the feed and brings it up to
the desired reaction temperature.
• Mixture of catalyst and hydrocarbon vapor travels up the
riser into reactors.
• Cracking reaction start when the feed contacts the hot
catalyst in the riser and continues until the oil vapors are
separated from the catalyst in reactor.
• The hydrocarbon vapors are sent to synthetic crude
fractionator for separation into liquid and gaseous
products.
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6. 6

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8. New Design of FCC Units
• Newer units are designed to incorporate up to
25% reduced crude in FCC unit feed.
1. FLEXICRACKING IIIR design by Exxon Research
& Engineering
2. Indmax FCC (I-FCC) Process developed by
Indian Oil Corporation (IOCL)
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9. FLEXICRACKING IIIR
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10. FLEXICRACKING IIIR
• FLEXICRACKING IIIR technology includes process design,
hardware details, special mechanical and safety features,
control systems, flue gas processing options and a full range of
technical services and support.
• The reactor (1) incorporates many features to enhance
performance, reliability and flexibility, including a riser (2)
with patented high-efficiency close-coupled riser termination
(3), enhanced feed injection system (4) and efficient stripper
design (5).
• The reactor design and operation maximizes the selectivity of
desired products, such as naphtha and propylene.
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11. FLEXICRACKING IIIR
• The technology uses an improved catalyst circulation
system with advanced control features, including cold-
walled slide valves (6). The single vessel regenerator (7)
has proprietary process and mechanical features for
maximum reliability and efficient air/catalyst
distribution and contacting (8).
• Either full or partial combustion is used. With
increasing residue processing and the need for
additional heat balance control, partial burn operation
with outboard CO combustion is possible, or KBR dense
phase catalyst cooler technology may be applied.
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12. Indmax FCC (I-FCC) Process
• This process overcomes the drawbacks or
limitations of just adding ZSM-5 (zeolite).
• It employs a riser reactor system along with
catalyst stripper and catalyst regenerator (just
like a conventional FCCU)
• Catalyst formulation is unique & very different
from what has been used before, it specific to
each operation and depends on feedstock
characteristics.
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13. Indmax FCC (I-FCC) Process
• The process utilises a higher riser reactor temp.
(530 – 600 degree C), a higher catalyst to oil ratio
(12-20) and lower hydrocarbon partial pressure
to achieve high conversion and selectivity.
• Lummus Technology: Micro jet feed injectors,
riser design, reaction termination device (RTD),
modular grid catalyst stripper.
• I-FCC process’s catalyst formulation, hardware
design and operating strategy can upgrade heavy
feeds for high yield of light olefins.
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14. FCC Regenerator
• FCC regenerator is a key part of an FCC unit to
recover solid catalyst activity by burning off
the coke deposit on the catalyst surface
• The spent catalyst (that leave the reactor) and
contains hydrocarbon adsorbed on its internal
and external surfaces as well as the coke
deposited by the cracking.
• Adsorbed hydrocarbon removed by stripping
before the catalyst enters the regenerator.
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15. 56 – Fluidized catalyst bed
82 – Dip leg
80 – 2 stage cyclones
Flue gas to CO Boiler
Regeneration air
from blower
Regenerated catalyst
to reactor-riser
Air grid
Plenum Chamber
*CO boiler
(Steam
generating
boiler)
Spent catalyst from reactor
Typical FCC Regenerator diagram
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16. FCC Regenerator
• In regenerator, coke is burned from the
catalyst with air.
• Regenerator temperature and coke burn-off
are controlled by varying the air flow rate.
• Heat of combustion raises the catalyst temp.
to 620 – 845 degree C.
• Regenerated catalyst contains from 0.01 to 0.4
wt% residual coke.
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17. FCC Regenerator – Old vs New
• Older units
- designed to burn CO to minimize blower capital and
operating cost – because only about half as much air
had to be compressed to burn to carbon monoxide
rather than to CO2.
• Newer units
- designed and operated to burn the coke to CO2 in the
regenerator because they can burn to a much lower
residual carbon level on the generated catalyst.
- Gives more reactive & selective catalyst in the riser and
a better product distribution results at the same
equilibrium catalyst activity and conversion level.
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18. FCC Regenerator – CFD Model
• The next video shows the model of a full-scale fluidized
catalytic cracking (FCC) regenerator using the Eulerian-
Lagrangian CPFD (computational particle fluid dynamics)
method.
• This is a simulation of an actual operating unit in at a U.S.
refinery.
• This is the first simulation of its kind known to exist for an
entire FCC regenerator with the coke-burning chemistry
included. T
• he purpose of the simulation was to determine root causes
for afterburn in the unit (undesirable temperature rise
between the top of the bed and the discharge), which has
been present in unit for over 70 year and has never before
successfully been addressed. 18

19. FCC Regenerator – CFD Model
• http://www.youtube.com/watch?v=RHrrNRC3rjo
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20. Process variables
• Major operating variables effecting the
conversion and product distribution:
Activity : ability to crack a gas oil to lower
boiling fractions
catalyst/oil ratio (C/O) = lb catalyst/lb feed
conversion = 100 (volume of feed – volume of
cycle stock)/ volume of feed
Efficiency = (% gasoline) x conversion
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21. Process variables
-recycle ratio = volume recycle/ volume fresh
feed
Selectivity : the ratio of the yield of desirable
products to the yield of undesirable products
(coke and gas)
Cycle stock: portion of catalytic-cracker
effluent not converted to naphtha and lighter
products
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22. Operating Conditions & Design Features
• Designed to provide balance of reactor and
regenerator capabilities.
• Usually operate to one or more mechanical limits,
common limit is capacity to burn carbon from the
catalyst
if air compressor capacity is limit, capacity may
be increased at feasible capital cost.
If regenerator metallurgy is limit, design changes
can be formidable.
Regenerator cyclone velocity limit
Slide valve ∆P limit
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23. Product Yields
• Produces high yields of liquids and small amounts
of gas and coke
-mass liquid yields are usually 90% - 93%; liquid
volume yields are often more than 100%
• The yield pattern is determined by complex
interaction of feed characteristics and reactor
conditions that determine severity of operation.
• Conversion defined relative to what remains in
the original feedstock boiling range
• Conversion = 100% - (gas oil yield)
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24. Health and Safety Considerations
-Fire Prevention and Protection
 Liquid hydrocarbons in the catalyst or entering the heated combustion air
stream should be controlled to avoid exothermic reactions.
 Because of the presence of heaters in catalytic cracking units, the
possibility exists for fire due to a leak or vapor release.
 Fire protection including concrete or other insulation on columns and
supports, or fixed water spray or fog systems where insulation is not
feasible and in areas where firewater hose streams cannot reach, should
be considered.
 In some processes, caution must be taken to prevent explosive
concentrations of catalyst dust during recharge or disposal.
 When unloading any coked catalyst, the possibility exists for iron sulfide
fires. Iron sulfide will ignite spontaneously when exposed to air and
therefore must be wetted with water to prevent it from igniting vapors.
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25.  Regular sampling and testing of the feedstock, product, and recycle streams should
be performed to assure that the cracking process is working as intended and that no
contaminants have entered the process stream.
 Corrosives or deposits in the feedstock can foul gas compressors.
 Inspections of critical equipment including pumps, compressors, furnaces, and heat
exchangers should be conducted as needed.
 When processing sour crude, corrosion may be expected where temperatures are
below 900° F. Corrosion takes place where both liquid and vapor phases exist, and at
areas subject to local cooling such as nozzles and platform supports.
 When processing high-nitrogen feedstock, exposure to ammonia and cyanide may
occur, subjecting carbon steel equipment in the FCC overhead system to corrosion,
cracking, or hydrogen blistering.
 Inspections should include checking for leaks due to erosion or other malfunctions
such as catalyst buildup on the expanders, coking in the overhead feeder lines from
feedstock residues, and other unusual operating conditions.
Health and Safety Considerations
-Safety
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26.  Because the catalytic cracker is a closed system, there is normally little
opportunity for exposure to hazardous substances during normal
operations. The possibility exists of exposure to extremely hot (700° F)
hydrocarbon liquids or vapors during process sampling or if a leak or
release occurs.
 In addition, exposure to hydrogen sulfide and/or carbon monoxide gas
may occur during a release of product or vapor.
 Catalyst regeneration involves steam stripping and decoking, and produces
fluid waste streams that may contain varying amounts of hydrocarbon,
phenol, ammonia, hydrogen sulfide, mercaptan, and other materials
depending upon the feedstock, crudes, and processes.
 Safe work practices and/or the use of appropriate personal protective
equipment may be needed for exposures to chemicals and other hazards
such as noise and heat; during process sampling, inspection, maintenance
and turnaround activities; and when handling spent catalyst, recharging
catalyst, or if leaks or releases occur.
Health and Safety Considerations
-Health
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