U.S. patent application number 11/617894 was filed with the patent office on 2007-09-06 for fcc dual elevation riser feed distributors for gasoline and light olefin modes of operation.
Invention is credited to Ismail B. Cetinkaya, Charles L. Hemler, SATHIT KULPRATHIPANJA, Daniel N. Myers, Paolo Palmas, Mark W. Schnaith, Peter J. Van Opdorp.
Application Number | 20070205139 11/617894 |
Document ID | / |
Family ID | 38470573 |
Filed Date | 2007-09-06 |
United States Patent
Application |
20070205139 |
Kind Code |
A1 |
KULPRATHIPANJA; SATHIT ; et
al. |
September 6, 2007 |
FCC DUAL ELEVATION RISER FEED DISTRIBUTORS FOR GASOLINE AND LIGHT
OLEFIN MODES OF OPERATION
Abstract
A fluid catalytic cracking process includes feeding hydrocarbon
into a riser in the presence of a catalyst, cracking the
hydrocarbon in the riser in the presence of the catalyst to form a
cracked stream, and separating the catalyst from the cracked
stream. When in a gasoline mode, the hydrocarbon is fed through a
first distributor into the riser, and when in a light olefin mode,
the hydrocarbon is fed through a second distributor into the riser.
The second distributor is positioned at a higher elevation than the
first distributor.
Inventors: |
KULPRATHIPANJA; SATHIT; (Des
Plaines, IL) ; Myers; Daniel N.; (Des Plaines,
IL) ; Palmas; Paolo; (Des Plaines, IL) ;
Schnaith; Mark W.; (Des Plaines, IL) ; Cetinkaya;
Ismail B.; (Des Plaines, IL) ; Van Opdorp; Peter
J.; (Des Plaines, IL) ; Hemler; Charles L.;
(Des Plaines, IL) |
Correspondence
Address: |
HONEYWELL INTELLECTUAL PROPERTY INC;PATENT SERVICES
101 COLUMBIA DRIVE, P O BOX 2245 MAIL STOP AB/2B
MORRISTOWN
NJ
07962
US
|
Family ID: |
38470573 |
Appl. No.: |
11/617894 |
Filed: |
December 29, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11365715 |
Mar 1, 2006 |
|
|
|
11617894 |
|
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Current U.S.
Class: |
208/113 |
Current CPC
Class: |
B01J 4/002 20130101;
C10G 11/18 20130101 |
Class at
Publication: |
208/113 |
International
Class: |
C10G 11/00 20060101
C10G011/00 |
Claims
1. A fluid catalytic cracking process, comprising: feeding
hydrocarbon into a riser in the presence of a catalyst; cracking
said hydrocarbon in said riser in the presence of said catalyst to
form a cracked stream, and separating said catalyst from said
cracked stream, wherein, when in a gasoline mode, said hydrocarbon
is fed through a first distributor into said riser, and when in a
light olefin mode, said hydrocarbon is fed through a second
distributor into said riser, wherein said second distributor is
positioned at a higher elevation than said first distributor.
2. The process of claim 1, wherein each one of said distributors
comprises a plurality of nozzles having substantially the same
elevation and being spaced radially around said riser.
3. The process of claim 1, wherein said separation of catalyst from
said cracked stream is performed in a swirl arm arrangement.
4. The process of claim 1, wherein the light olefin mode has
residence time of between about 0.5 second and about 2 seconds in
said riser.
5. The process of claim 1, wherein propylene-preferential mode has
residence time of about 1 to about 2 seconds in said riser.
6. The process of claim 1, wherein gasoline-making mode has
residence time of between about 2 seconds and about 5 seconds.
7. The process of claim 1, wherein said FCC process is changeable
from one mode to another without shutting the process down.
8. The process of claim 1, wherein said hydrocarbon and steam are
fed through same distributor nozzle.
9. The process of claim 1, wherein when in said gasoline mode, said
process produces a cracked stream having gasoline vol-% between
about 50 and about 70.
10. The process of claim 1, wherein, when in said light olefin
mode, said process produces a cracked stream having vol-% of
propylene between about 20 and about 40.
11. The process of claim 1, wherein said temperature at the outlet
of said riser is between about 490.degree. and about 630.degree.
C.
12. The process of claim 1, wherein said catalyst is about 2 to
about 20 wt-% medium or smaller pore zeolite while operating in
said light olefin mode and less than 0.5 wt-% medium or smaller
pore zeolite while operating in said gasoline mode.
13. The process of claim 1, wherein said temperature in said
reactor in said light olefin mode is between about 550.degree. and
about 590.degree. C.
14. The process of claim 1, wherein said temperature in said
reactor in said gasoline-preferential mode is between about
500.degree. and about 550.degree. C.
15. The process of claim 1, wherein more steam is added to the
riser when operating in the light olefin mode than when operating
in the gasoline mode.
16. The process of claim 1, wherein a greater catalyst to feed
ratio is used when operating in the light olefin mode than when
operating in the gasoline mode.
17. The process of claim 1 further comprising the step of quenching
said cracked stream with a liquid after exiting said riser.
18. A fluid catalytic cracking process, comprising: feeding
hydrocarbon into a first region having a first predetermined
elevation in a riser in the presence of a catalyst, wherein said
thirst region and said first predetermined elevation are selected
to provide a greater yield of light olefins in a light olefin mode;
cracking said hydrocarbon in said riser in the presence of said
catalyst to form a cracked stream; separating said catalyst from
said cracked stream; and changing from said light olefin mode to a
gasoline mode by changing the location of the feed of said
hydrocarbon to a second region having a second predetermined
elevation lower than that of said first predetermined elevation to
produce a smaller yield of light olefins than when operated in the
light olefin mode.
19. A fluid catalytic cracking process, comprising: feeding
hydrocarbon into a riser in the presence of a catalyst; cracking
said hydrocarbon in said riser in the presence of said catalyst to
form a cracked stream; and separating said catalyst from said
cracked stream, wherein, when in a recracking mode, said
hydrocarbon is fed through a first distributor into a mixing
chamber below said riser.
20. The process of claim 19 further comprising the step of
introducing C.sub.8-feed into said mixing chamber below said riser.
Description
[0001] This application is a continuation-in-part of application
number Ser. No. 11/365,715, filed on Mar. 1, 2006.
BACKGROUND OF THE INVENTION
[0002] This invention relates generally to a process for catalytic
cracking of hydrocarbons.
DESCRIPTION OF THE PRIOR ART
[0003] Fluid catalytic cracking (FCC) is a catalytic conversion
process for cracking, heavy hydrocarbons into lighter hydrocarbons
accomplished by contacting the heavy hydrocarbons in a fluidized
reaction zone with a catalyst composed of finely divided
particulate material. Most FCC units use zeolite-containing
catalyst having high activity and selectivity. As the cracking
reaction proceeds, substantial amounts of highly carbonaceous
material referred to as coke are deposited on the catalyst, forming
spent catalyst. High temperature regeneration burns coke from the
spent catalyst. The regenerated catalyst may be cooled before being
returned to the reaction zone. Spent catalyst is continually
removed from the reaction zone and replaced by essentially
coke-free catalyst from the regeneration zone.
[0004] The basic components of the FCC process include a riser
(internal or external), a reactor vessel for disengaging spent
catalyst from product vapors, a regenerator and a catalyst
stripper. In the riser, feed distributor nozzles input the
hydrocarbon feed which contacts the catalyst and is cracked into a
product stream containing lighter hydrocarbons. Regenerated
catalyst and the hydrocarbon feed are transported upwardly in the
riser by the expansion of the lift gases that result from the
vaporization of the hydrocarbons, and other fluidizing mediums,
upon contact with the hot catalyst. Steam or an inert gas may be
used to accelerate catalysis in a first section of the riser prior
to or during introduction of the feed.
[0005] Riser residence time is one of the leading factors that
determine how effectively the heavy hydrocarbon feed is converted
to lighter, more valuable products. Increasing riser residence time
increases the percentage of heavy hydrocarbon feed that is
converted to lighter products. An average riser cracking zone has a
catalyst to oil (feed) contact time of 1 to 5 seconds. Generally, a
single elevation riser feed distributor is used for the process to
yield a single product slate. The elevation of an FCC feed
distributor may comprise one or a plurality of distributor nozzles
which determine the point of initial contact of feed with the
regenerated catalyst. The elevation of the feed distributor along
the riser determines the residence time in the riser. Varying
residence time determines the products yielded in the process.
[0006] A problem presented by the prior art is that changing
operation of an FCC unit, such as from olefin production mode to
gasoline production mode, by substantially changing riser residence
time may require the unit be shut down for equipment changes to be
made. Shutting down an FCC process stops the production of the
valuable products and disrupts the desired steady state of
operations. Changing equipment prolongs the down time. Therefore,
changing modes of operation in this way may be undesirable for
several reasons, including effects on productivity, efficiency and
cost.
SUMMARY OF THE INVENTION
[0007] An FCC process which may include a dual elevation riser feed
distributor and may vary the residence time requirement for
multiple modes of operation. One aspect of the invention may be the
ability to shift operation for the unit to different modes of
operation without shutting down the unit. In accordance with the
invention, an FCC process may utilize a dual elevation riser feed
distributor rather than a single elevation feed distributor. The
dual elevation riser feed distributor may enable the refiner to
operate the unit in one mode of operation, such as a gasoline mode,
with a first elevation feed distributor or in a second mode of
operation, such as a light olefin mode, with a second, higher,
elevation feed distributor. In a preferred embodiment, both sets of
feed distributors may be generally identical except for their
positions vertically with respect to each other within the riser,
and they may have generally the same number, size, and arrangement
of nozzles, or the equivalents thereof, in order to provide the
refiner with additional flexibility and options for running the new
and improved FCC process.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is an elevational diagram showing an FCC unit.
[0009] FIG. 2 is a cross section taken along segment A-A in FIG.
1.
[0010] FIG. 3 is a cross section taken along segment B-B in FIG.
1.
[0011] FIG. 4 is an elevational diagram showing a feed distributor
nozzle.
DETAILED DESCRIPTION OF THE INVENTION
[0012] This invention relates generally to an improved FCC process.
Specifically, this invention may relate to an improved elevation
riser distributor and may be useful for FCC operators to more
efficiently shift modes to yield different products as dictated by
the market. The process and apparatus aspects of this invention can
be used in the design of new FCC units or to modify the operation
of existing FCC units.
[0013] As shown in FIG. 1, an FCC system 10 may be utilized in the
FCC process, which may include feeding hydrocarbon into a riser 20
in the presence of a catalyst. Hydrocarbon may be cracked in the
riser 20 in the presence of catalyst to form a cracked stream. A
reactor vessel 30, with a separation chamber 32, separates spent
catalyst particles from the cracked stream. A stripping zone 40
removes residual adsorbed hydrocarbon from the surface of the
catalyst optionally as the catalyst travels over baffles 42. Spent
catalyst from the stripping zone 40 is regenerated in a regenerator
46 having one or more stages of regeneration. Regenerated catalyst
from the regenerator 46 re-enters the riser 20 to continue the
process.
[0014] FCC feedstocks, suitable for processing by the method of
this invention, include conventional FCC feeds and higher boiling
or residual feeds. The most common of the conventional feeds is a
vacuum gas oil which is typically a hydrocarbon material having a
boiling range of from 343.degree. to 552.degree. C. (650.degree. to
1025.degree. F.) and is prepared by vacuum fractionation of
atmospheric residue. Heavy or residual feeds, i.e., boiling above
499.degree. C. (930.degree. F.), are also suitable. The FCC process
of the present invention is suited best for feed stocks that are
heavier than naphtha range hydrocarbons boiling above about
177.degree. C. (350.degree. F.). Hydrocarbon feed may be modified
to other feeds with appropriate modifications such as understood by
those of ordinary skill in the art.
[0015] Looking then at FIG. 1, the riser 20 provides a conversion
zone for cracking of the feed hydrocarbons. The vertical riser 20
may have a smaller diameter than a mixing chamber 90, so that
catalyst accelerates as it passes out of the mixing chamber 90 into
the riser 20. The riser typically operates with dilute phase
conditions above the point of feed injection wherein the density is
usually less than 320 kg/m.sup.3 (20 lb/ft.sup.3) and, more
typically, less than 160 kg/m.sup.3 (10 lb/ft.sup.3). Feed is
introduced into the riser 20 by either a first feed distributor 52
at a relatively lower elevation or a second feed distributor 54 at
a relatively higher elevation between a riser inlet 28 and a riser
outlet 24. Volumetric expansion resulting from the rapid
vaporization of the feed as it enters the riser further decreases
the density of the catalyst within the riser to typically less than
160 kg/m.sup.3 (10 lb/ft.sup.3). Before contacting the catalyst,
the feed will ordinarily have a temperature in a range of from
150.degree. to 370.degree. C. (302.degree. to 698.degree. F.).
Additional amounts of feed may be added downstream of the initial
feed point.
[0016] The blended catalyst and reacted feed vapors are then
discharged from the top of the riser 20 through the riser outlet 24
and separated into a cracked product vapor stream and a collection
of catalyst particles covered with substantial quantities of coke
and generally referred to as "coked catalyst." This invention can
use any arrangement of separators to remove coked catalyst from the
product stream quickly. In particular, a swirl arm arrangement 29,
provided at the end of the riser 20 can further enhance initial
catalyst and cracked hydrocarbon separation by imparting a
tangential velocity to the exiting catalyst and cracked product
vapor stream mixture. The swirl arm arrangement 29 is located in an
upper portion of the separation chamber 32, and the stripping zone
40 is situated in the lower portion of the separation chamber 32.
Catalyst separated by the swirl arm arrangement 29 drops down into
the stripping zone 40. The cracked product vapor stream comprising
cracked hydrocarbons including gasoline and light olefins and some
catalyst exit the separation chamber 32 via a gas conduit 36 in
communication with cyclones 33. The cyclones 33 remove remaining
catalyst particles from the product vapor stream to reduce particle
concentrations to very low levels. The product vapor stream then
exits the top of the reactor vessel 30 through a product outlet 35.
Catalyst separated by the cyclones 33 return to the reactor vessel
30 through diplegs into a dense bed 39 where it will enter the
stripping zone 40 through openings 37. The stripping zone 40
removes adsorbed hydrocarbons from the surface of the catalyst by
counter-current contact with steam over the optional baffles 42.
Steam enters the stripping zone 40 through a line 41.
[0017] A first portion of the coked catalyst is returned to the
riser 20 without first undergoing regeneration while a second
portion of the coked catalyst is regenerated in the regenerator 46
before it is delivered to the riser 20. The first and second
portions of the catalyst may be blended in the mixing chamber 90
before introduction to the riser 20. The recycled catalyst portion
may be withdrawn from the stripping zone 40 for transfer to the
mixing chamber 90. A recycle conduit 22 transfers the first portion
of the coked catalyst stripped of hydrocarbon vapors exiting the
stripping zone 40 back to the mixing chamber 90 as the recycled
catalyst portion at a rate regulated by a control valve. The second
portion of the coked, stripped catalyst is transported to the
regenerator 46 through a coked catalyst conduit 23 at a rate
regulated by a control valve for the removal of coke.
[0018] On the regeneration side of the process, coked catalyst
transferred to the regenerator 46 via the conduit 23 undergoes the
typical combustion of coke from the surface of the catalyst
particles by contact with an oxygen-containing gas. The
oxygen-containing gas enters the bottom of the regenerator 46 via a
distributor 48 and passes through a dense fluid zing bed of
catalyst. Flue gas consisting primarily of N.sub.2, H.sub.2O,
O.sub.2, CO.sub.2 and perhaps containing CO passes upwardly from
the dense bed into a dilute phase of the regenerator 46. A
separator, such as cyclones 49 or other means, remove entrained
catalyst particles from the rising flue gas before the flue gas
exits the vessel through an outlet 50. Combustion of coke from the
catalyst particles raises the temperatures of the catalyst which is
withdrawn by a regenerator standpipe 18.
[0019] The regenerator standpipe 18 passes regenerated catalyst
from the regenerator 46 into the mixing chamber 90 at a rate
regulated by a control valve where it is blended with recycled
catalyst from the stripping zone 40 via the recycle conduit 22.
Fluidizing gas such as steam passed into the mixing chamber 90 by a
distributor 26 contacts the catalyst and maintains the catalyst in
a fluidized state to blend the recycled and regenerated catalyst.
The regenerated catalyst which is relatively hot is cooled by the
unregenerated, coked catalyst which is relatively cool to reduce
the temperature of the regenerated catalyst by 28.degree. C. to
83.degree. C. (50.degree. to 150.degree. F.) depending upon the
regenerator temperature and the coked catalyst recycle rate.
[0020] A dual elevation riser feed distributor may provide more
efficient operation of an FCC process, as shown in FIG. 1. The time
duration for the stream of hydrocarbon to pass through the riser
20, also known as residence time, affects the selectivity of the
conversion of hydrocarbon feed to lighter olefins. We have found
that selectivity to lighter olefins is increased when riser
residence time is decreased relative to the residence time typical
for FCC operation which has greater selectivity to gasoline. The
location of the feed distributor along the riser 20 affects the
residence time in the riser. Varying residence time may affect the
products yielded in the process.
[0021] In one embodiment of the invention, when an FCC process is
in a first mode, such as a gasoline operation mode, hydrocarbon
feed is fed through a first feed distributor 52. When the FCC
process is in a second mode, such as a light olefin mode,
hydrocarbon feed is fed through the second feed distributor 54
which is higher in elevation than first feed distributor 52. The
first feed distributor 52 is located along the riser 20 in a
position to input feed upstream of the second feed distributor 54.
Hydrocarbon fed through the first feed distributor 52 thereby has a
longer residence time in the riser 20 than hydrocarbon fed through
the second feed distributor 54. The difference in residence time
for hydrocarbon fed through the first feed distributor 52 from
hydrocarbon fed through the second feed distributor 54 results in
an FCC process that may yield different products. For example, an
FCC process designed to maximize gasoline selectivity has a longer
residence time than an FCC process designed to maximize light
olefin yield.
[0022] In an embodiment of the invention, hydrocarbon feed may be
fed through the first feed distributor 52 at suitable position
along the riser 20 to produce a substantial yield of gasoline in
preference to other products. Preferably, residence time for
hydrocarbon fed through the first feed distributor 52 may have a
residence time between about 2 seconds and about 5 seconds to
maximize gasoline yield. Residence time is the time it takes for
the hydrocarbon to travel from the distributor 52, 54 to the riser
outlet 24. Hydrocarbon may be fed through the second feed
distributor 54 at suitable position along the riser 20 to produce a
substantial yield of light olefins with greater selectivity to
light olefins than in the gasoline mode in which feed is
distributed through the first feed distributor 52. Preferably,
residence time for hydrocarbon fed through the second feed
distributor 54 may be between about 0.5 seconds and about 2 seconds
to maximize the yield of light olefins. More preferably, residence
time for hydrocarbon fed through the second feed distributor 54 may
be about 1 to about 2 seconds.
[0023] As shown in FIGS. 2 and 3, each feed distributor 52, 54 may
comprise one or more individual feed distributor nozzles 60.
Preferably, a plurality of the feed distributor nozzles 60 may be
utilized for each feed distributor 52, 54. In a preferred
embodiment of the invention, two, three, four or more feed
distributor nozzles 60 may be arranged generally uniformly around
the riser 20. In a still more preferred embodiment, as shown in
FIG. 2, four feed distributor nozzles 60 may be arranged radially
around the riser 20. Each feed distributor 52, 54 may have
different numbers of the nozzles 60.
[0024] When in gasoline operation mode, the process produces a
cracked stream having gasoline vol-% between about 50 and about 70.
Preferably, producing a cracked stream having gasoline vol-%
between about 55 and about 65. When in light olefin operation node,
the process may produce a cracked stream having light olefin vol-%
between about 20 and about 50. Preferably, producing a cracked
stream having light olefin vol-% between about 25 and about 40.
[0025] Regenerated catalyst from the regenerator standpipe 18 will
usually have a temperature in a range from 677.degree. to
760.degree. C. (1250.degree. to 1400.degree. F.) and, more
typically, in a range of from 699.degree. to 760.degree. C.
(1290.degree. to 1400.degree. F.). In an embodiment, stripped
catalyst from the stripping zone 40 may be recycled to the riser 20
without undergoing regeneration. The mixing chamber 90 may be used
to blend spent and regenerated catalyst for sufficient time to
achieve substantially thermal equilibrium. The temperature of the
recycled catalyst portion will usually be in a range of from
510.degree. to 621.degree. C. (950.degree. to 1150.degree. F.). The
relative proportions of the recycled and regenerated catalyst will
determine the temperature of the blended catalyst mixture that
enters the riser. The blended catalyst mixture will usually range
from about 593.degree. to 704.degree. C. (1100.degree. to
1300.degree. F.).
[0026] In an embodiment, the temperature in the reactor vessel 30
in light olefin operational mode may be between about 490.degree.
and about 630.degree. C. at the riser outlet 24. More preferably,
the reactor temperature may be between about 550.degree. and about
590.degree. C. The reactor temperature is typically less in
gasoline mode than in light olefin mode. The temperature in the
reactor vessel 30 in gasoline operation mode may be between about
460.degree. and about 600.degree. C. More preferably, reactor
temperature may be between about 500.degree. and about 550.degree.
C.
[0027] The recycle of spent catalyst to the riser bypassing
regeneration enables the FCC unit to be run at higher ratios of
catalyst to feed without impacting the heat balance of the unit.
The light olefin mode can be run at higher catalyst to feed ratios
than the gasoline mode to produce more light olefins. The catalyst
to feed ratio in the riser 20 when in light olefin mode may be 15
or greater. Whereas, the catalyst to feed ratio in the riser may be
less than 15 while operating in gasoline mode.
[0028] Reactor pressure in kPa may be between about 93 and about
113. Lower hydrocarbon partial pressure in the riser 20 operates to
favor the production of light olefins. Low hydrocarbon partial
pressure can be achieved by using steam or other inert gas as a
diluent. In light olefin mode, 5 to 25 wt-% steam relative to the
hydrocarbon feed may be added to reduce hydrocarbon partial
pressure. Typically in gasoline mode, FCC units are operated with
0.5 to 5 wt-% steam to disperse the feed and purge stagnant zones.
Hence, light olefin mode is operated with higher steam rates than
gasoline mode. Only the fluidizing gas distributor 26 is shown in
the drawings. However, other steam distributors may be provided
along the riser and elsewhere in the FCC unit.
[0029] The zeolitic molecular sieves used in typical FCC gasoline
mode operation have a large average pore size. Typically, molecular
sieves with a large pore size have pores with openings of greater
than 0.7 nm in effective diameter defined by greater than 10 and
typically 12 membered rings. Pore Size Indices of large pores are
above about 31. Suitable large pore molecular sieves include
synthetic zeolites such as X-type and Y-type zeolites, mordenite
and faujasite. Y zeolites with low rare earth content are
preferred. Low rare earth content denotes less than or equal to
about 1.0 wt-% rare earth oxide on the zeolitic portion of the
catalyst.
[0030] Catalyst additive may be added to the catalyst composition
when operating in the light olefin mode. Catalyst additive includes
a medium or smaller pore zeolite catalyst exemplified by ZSM-5,
ZSM-11, ZSM-12, ZSM-23, ZSM-35, ZSM-38. ZSM-48, and other similar
materials. U.S. Pat. No. 3,702,886 describes ZSM-5. Other suitable
medium or smaller pore zeolites include ferrierite, erionite, and
ST-5, developed by Petroleos de Venezuela, S.A. The medium or
smaller pore zeolite may be dispersed on a matrix comprising a
binder material such as silica or alumina and an inert filer
material such as kaolin. The catalyst additive may also comprise
some other active material such as beta zeolite. These catalyst
additives have a crystalline zeolite content of 10 to 40 wt-% or
more and a matrix material content of 60 to 90 wt-% or less.
Catalysts containing 25 wt-% crystalline zeolite are typical.
Medium and smaller pore zeolites are characterized by having an
effective pore opening diameter of less than or equal to 0.7 nm,
rings of 10 or fewer members and a Pore Size Index of less than
31.
[0031] When in light olefin operation mode, the cracking step may
be conducted in the presence of an effective amount of medium or
smaller pore zeolitic catalyst such as ZSM-5 shape-selective
catalyst. Preferably, in light olefin mode, the cracking step may
be conducted in the presence of 2 to 20 wt-% of medium or smaller
pore zeolite. More preferably, the cracking step may be conducted
in the presence of an additional 3 to 10 wt-% medium or smaller
pore zeolite. Fresh catalyst is added periodically to the FCC unit
to make up for catalyst loss in the product outlet 35 and flue gas
from the regenerator outlet 50. When switching to gasoline mode
from light olefin mode, no small or medium pore zeolite should be
added to allow the inventory to purge itself of this additive.
Eventually, the catalyst inventory in the FCC unit will have less
than 0.5 wt-% additive. When switching to light olefin mode from
gasoline mode a large amount of medium or smaller pore zeolite may
be added all at once or in increments to bring the additive level
in the catalyst inventory up to that desired for light olefin
mode.
[0032] In the process of the present invention, as shown in FIG. 4,
hydrocarbon and steam may be introduced through the same feed
distributor nozzle. Other types of feed distributor nozzles may be
suitable. A distributor barrel 62 for each distributor nozzle 60
receives steam from a steam inlet pipe 68. A barrel body flange 64
secures the distributor barrel 62 to a riser nozzle 70 in the
reactor riser 20 by bolts and may be oriented such that the bolt
holes straddle a radial centerline of the riser 20. An oil inlet
pipe 76 delivers hydrocarbon feed to an internal oil pipe 78. An
oil inlet barrel flange 66 secures the oil inlet pipe 76 to the
distributor barrel 62 by bolts. Vanes 83 in the internal oil pipe
82 cause the oil to swirl in the oil pipe before exiting. The
internal oil pipe 78 distributes swirling oil to the distributor
barrel 62 where it mixes with steam and is injected from orifices
80 in the face of a distributor tip 74 extending into the riser 20.
Distributor metallurgy, except for the internal oil pipe 78 and the
distributor tip 74 may be a high chromium steel alloy, preferably 9
Cr-1 Mo. Distributor metallurgy for the internal oil pipe 78 and
the distributor tip 74 may be a cobalt-based alloy, preferably
Cobalt Alloy 6 (AMS 5387).
[0033] In one embodiment of this invention, a hydrocarbon stream is
introduced through a third feed distributor 56, as shown in FIG. 1.
Preferably, the third, alternate, feed distributor 56 may introduce
feed into the mixing chamber 90. The FCC unit may be run in a
recracking mode in which feed is introduced through the third feed
distributor 56 lower than and upstream of the feed distributors 52,
54 solely without or in conjunction with feed being distributed
through one or both of the feed distributors 52, 54. In one
embodiment, a C.sub.8-hydrocarbon feed stream comprising molecules
predominantly having less than eight carbons may be introduced
through the third, alternate feed distributor 56. In another
embodiment, a C.sub.6+ hydrocarbon feed stream is introduced
through the third, alternate feed distributor 56. The feed may be
obtained from an outside source but is preferably derived from
products recovered from the product outlet 35 and further processed
to yield a cut of intermediate product that can be further
upgraded. Upwards of about 30 wt-% of C.sub.8-hydrocarbons may be
cracked in the mixing chamber 90 to more valuable products. Steam
introduced in the mixing chamber 90 to fluidize the chamber and
facilitate mixing of spent and regenerated catalyst may be utilized
to adjust superficial velocity and catalyst density to achieve a
fast fluidized flow regime. Weight hourly space velocity of the
hydrocarbons and residence time may also be influenced. Additional
steam also may be introduced in the riser 20 below the feed
distributor nozzles 60 to adjust the velocity in the riser 20 prior
to the introduction of the conventional FCC feed.
[0034] In one embodiment of this invention, the FCC process may
include injecting a fluid such as light cycle oil (LCO) through an
injector 34 to quench cracked product vapors in the gas conduit 36
from the riser outlet 24. The quench from the injector 34 may
reduce the outlet temperature. Reducing the temperature helps to
minimize post riser thermal cracking and to maintain the yields and
selectivity of desired products from the riser 20. Furthermore, the
refiner thereby possesses greater flexibility in controlling the
reactor outlet temperature. The quench process of this embodiment
of the invention may reduce temperatures by about 28.degree. C. to
about 56.degree. C. (50.degree. F. to about 100.degree. F.). The
quench fluid may be derived from products exiting product outlet
35.
EXAMPLE
[0035] In an example of one embodiment of this invention, an FCC
process of the present invention was simulated to run in gasoline
mode under the conditions given for the present invention which
produced a gasoline selectivity of 60 vol-% and a propylene
selectivity of 8 vol-%. When the present invention was simulated to
run in light olefin mode under the conditions given for the present
invention it produced a gasoline selectivity of 33 vol-% and a
propylene selectivity of 32 vol-%.
[0036] While the foregoing written description of the invention
enables one of ordinary skill to make and use what is considered
presently to be the best mode thereof, those of ordinary skill will
understand and appreciate the existence of variations,
combinations, and equivalents of the specific exemplary embodiments
thereof. The invention is therefore to be limited not by the
exemplary embodiments herein, but by all embodiments within the
scope and spirit of the appended claims.
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