U.S. patent application number 13/536644 was filed with the patent office on 2013-01-03 for dual riser catalytic cracking process for making middle distillate and lower olefins.
This patent application is currently assigned to SHELL OIL COMPANY. Invention is credited to Weijian MO.
Application Number | 20130001130 13/536644 |
Document ID | / |
Family ID | 46516830 |
Filed Date | 2013-01-03 |
United States Patent
Application |
20130001130 |
Kind Code |
A1 |
MO; Weijian |
January 3, 2013 |
DUAL RISER CATALYTIC CRACKING PROCESS FOR MAKING MIDDLE DISTILLATE
AND LOWER OLEFINS
Abstract
A fluidized catalytic cracking process and system that provide
for the processing of hydrocarbon feedstocks to selectively produce
a middle distillate boiling range product and lower olefins. The
inventive process uses two riser reactors each having associated
therewith a separator/stripper for separating the cracked product
and cracking catalyst received from the respective riser reactor
and a single regenerator for regenerating coked or spent cracking
catalyst received from the separator/strippers. The two riser
reactors, two separator/strippers and regenerator are operatively
integrated to provide a process system for carrying out the process
of the invention.
Inventors: |
MO; Weijian; (Sugar Land,
TX) |
Assignee: |
SHELL OIL COMPANY
Houston
TX
|
Family ID: |
46516830 |
Appl. No.: |
13/536644 |
Filed: |
June 28, 2012 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61503209 |
Jun 30, 2011 |
|
|
|
Current U.S.
Class: |
208/79 |
Current CPC
Class: |
C10G 2400/04 20130101;
C10G 2400/08 20130101; C10G 11/18 20130101; C10G 2300/1037
20130101; C10G 2300/708 20130101; C10G 2400/06 20130101; C10G
2300/701 20130101; C10G 2400/20 20130101 |
Class at
Publication: |
208/79 |
International
Class: |
C10G 51/06 20060101
C10G051/06 |
Claims
1. A dual riser catalytic cracking process for making middle
distillate and lower olefins, wherein said process comprises:
catalytically cracking a first hydrocarbon feedstock within a first
riser reactor zone by contacting under first catalytic cracking
conditions within said first riser reactor zone said first
hydrocarbon feedstock with a combination of a clean spent catalyst
and a first portion of a regenerated cracking catalyst to yield a
first riser reactor product comprising a first cracked product and
a coked spent catalyst; catalytically cracking a second hydrocarbon
feedstock within a second riser reactor zone by contacting under
second catalytic cracking conditions within said second riser
reactor zone said second hydrocarbon feedstock with a second
portion of said regenerated cracking catalyst to yield a second
riser reactor product comprising a second cracked product and said
clean spent catalyst; passing said first riser reactor product to a
first separator/stripper providing means for separating said first
riser reactor product into a separated first cracked product and a
separated coked spent catalyst; passing said second riser reactor
product to a second separator/stripper providing means for
separating said second riser reactor product into a separated
cracked second cracked product and a separated clean spent
catalyst; using at least a portion of said separated clean spent
catalyst as said clean spent catalyst of said combination; and
passing said separated coked spent catalyst and a remaining portion
of said separated clean spent catalyst to a regenerator that
defines a regeneration zone and provides means for regenerating
said separated coked spent catalyst and said remaining portion of
said separated clean spent catalyst to yield said regenerated
cracking catalyst.
2. A process as recited in claim 1, which further comprises:
passing said separated first cracked product and said separated
second cracked product to a fractionator defining a fractionation
zone and providing fractionation means for separating either said
separated first cracked product or said separated second cracked
product, or both, into one or more product streams including a
naphtha product stream.
3. A process as recited in claim 2, which further comprises: using
at least a portion of said naphtha product stream as at least a
portion of said second hydrocarbon feedstock.
4. A process as recited in claim 3, wherein said first
separator/stripper defines a first separation zone that includes
first separation means for separating said first riser reactor
product into said separated first cracked product and said
separated coked spent catalyst, and wherein said first
separator/stripper further defines a first stripping zone, and
wherein within said first stripping zone said separated coked spent
catalyst is stripped of hydrocarbons.
5. A process as recited in claim 4, wherein said second
separator/stripper defines a second separation zone that includes
second separation means for separating said second riser reactor
product into said separated second cracked product and said
separated clean spent catalyst, and wherein said second
separator/stripper further defines a second stripping zone, and
wherein within said second stripping zone said separated clean
spent catalyst is stripped of hydrocarbons.
6. A dual riser cracking process for making middle distillate and
lower olefins, wherein said process comprises: catalytically
cracking a first hydrocarbon feedstock within a first riser reactor
zone by contacting under first catalytic cracking conditions within
said first riser reactor zone said first hydrocarbon feedstock with
a combination of a clean spent catalyst and a first portion of a
regenerated cracking catalyst to yield a first riser reactor
product comprising a first cracked product and a coked spent
catalyst; catalytically cracking a second hydrocarbon feedstock
within a second riser reactor zone by contacting under second
catalytic cracking conditions within said second riser reactor zone
said second hydrocarbon feedstock with a second portion of said
regenerated cracking catalyst to yield a second riser reactor
product comprising a second cracked product and said clean spent
catalyst; passing said first riser reactor product to a first
separator/stripper providing means for separating said first riser
reactor product into a separated first cracked product and a
separated coked spent catalyst; passing said second riser reactor
product to a second separator/stripper providing means for
separating said second riser reactor product into a separated
cracked second cracked product and a separated clean spent
catalyst; and passing said separated coked spent catalyst to a
regenerator and passing said separated clean spent catalyst to said
regenerator, wherein said regenerator defines a regeneration zone
and provides means for regenerating said separated coked spent
catalyst and said separated clean spent catalyst to yield said
regenerated cracking catalyst.
Description
[0001] This application claims the benefit of U.S. Provisional
Application No. 61/503,209 filed Jun. 30, 2011, the entire
disclosure of which is hereby incorporated by reference.
[0002] This invention relates to method and apparatus for the
manufacture of a middle distillate product and lower olefins from a
hydrocarbon feedstock by the use of a dual riser catalytic system
and process.
[0003] The fluidized catalytic cracking (FCC) of heavy hydrocarbons
to produce lower boiling hydrocarbon products, such as gasoline,
has been around since the 1940's. Typically, an FCC unit or process
system includes a single riser reactor, a catalyst separator and
stripper, and a regenerator. An FCC feedstock is introduced into
the riser reactor in which it is contacted with hot FCC catalyst
from the regenerator. The mixture of FCC feedstock and FCC catalyst
passes through the riser reactor and into the catalyst separator
wherein the cracked product is separated from the FCC catalyst. The
separated cracked product passes from the catalyst separator to a
downstream separation system and the separated catalyst passes to
the regenerator where the coke deposited on the FCC catalyst during
the cracking reaction is burned off the catalyst to provide a
regenerated catalyst. The resulting regenerated catalyst is used as
the aforementioned hot FCC catalyst and is mixed with the FCC
feedstock that is introduced into the riser reactor.
[0004] Many processes and systems are designed so as to provide for
a high conversion of the FCC feedstock to yield products having
boiling temperatures in the gasoline boiling range. But, some prior
art processes provide for the preferential conversion of a
hydrocarbon feedstock to a middle distillate product and lower
olefins. One such process is disclosed in the US Patent Publication
No. US 2006/0231461 of Mo et al. The process taught by Mo et al.
includes the use of a riser reactor in combination with a dense bed
reactor to process a gas oil feedstock and a gasoline feedstock in
a way to preferentially make middle distillate and lower olefins.
The disclosed process includes regenerating a spent cracking
catalyst and using the resulting regenerated catalyst in the dense
bed reactor. Used regenerated catalyst is passed from the dense bed
reactor and introduced into the riser reactor wherein it is used in
combination with regenerated catalyst in the fluidized catalytic
cracking of the gas oil feedstock.
[0005] Other publications disclose the use of a combination of
riser reactors or a combination of a dense fluid bed reactor with a
riser reactor to provide for recracking of a gasoline product from
the cracking of gas oil. U.S. Pat. No. 3,928,172 to Davis, Jr. et
al. discloses a number of alternative fluid catalyst systems and
processes that involve the recracking of cracked gasoline over a
zeolite-containing catalyst. It is asserted by Davis that the
zeolite catalyst is able to effect a degree of octane improvement
that was previously not possible with amorphous silica-alumina
catalysts.
[0006] One process and system disclosed by Davis uses a dense bed
reactor with a single riser reactor arranged in a catalyst flow
sequence such that the dense bed is placed between the regenerator
and riser. Davis further discloses a hydrocarbon upgrading process
that includes a first cracking zone in which gas oil is cracked and
a second cracking zone in which gasoline is cracked. The second
cracking zone may include a dense bed. In another disclosure of
Davis, gasoline is cracked within a dense bed reaction zone in
which freshly regenerated catalyst is introduced. Catalyst from the
dense bed reaction zone is then used for gas oil cracking in a
riser cracking zone.
[0007] In the article published by the Chinese Journal of Chemical
Engineering, 16(3) 394-400 (2008), entitled "Alternative Processing
Technology for Converting Vegetable Oils and Animal Fats to Clean
Fuels and Light Olefins," the authors Tian et al. disclose a
catalytic cracking process that utilizes two risers which share a
common disengager and regenerator. Fresh feedstock is introduced
into the first stage riser, and a recycle stream of gasoline or
heavy oil, or both, is introduced into the second stage riser.
There is no disclosure, however, of the use of multiple catalyst
separators or strippers nor is there any disclosure of the
selective separation or stripping of catalyst taken from each of
the two risers and the separate or selective recycle thereof.
[0008] One of the objects of this invention is to provide method
and apparatus for the preferential conversion of a hydrocarbon
feedstock to a middle distillate product and lower olefins.
[0009] Accordingly, provided is a dual riser cracking process for
making middle distillate and lower olefins, wherein said process
comprises: catalytically cracking a first hydrocarbon feedstock
within a first riser reactor zone by contacting under first
catalytic cracking conditions within said first riser reactor zone
said first hydrocarbon feedstock with a combination of a clean
spent catalyst and a first portion of a regenerated cracking
catalyst to yield a first riser reactor product comprising a first
cracked product and a coked spent catalyst; catalytically cracking
a second hydrocarbon feedstock within a second riser reactor zone
by contacting under second catalytic cracking conditions within
said second riser reactor zone said second hydrocarbon feedstock
with a second portion of said regenerated cracking catalyst to
yield a second riser reactor product comprising a second cracked
product and said clean spent catalyst; passing said first riser
reactor product to a first separator/stripper providing means for
separating said first riser reactor product into a separated first
cracked product and a separated coked spent catalyst; passing said
second riser reactor product to a second separator/stripper
providing means for separating said second riser reactor product
into a separated cracked second cracked product and a separated
clean spent catalyst; using at least a portion of said separated
clean spent catalyst as said clean spent catalyst of said
combination; and passing said separated coked spent catalyst and a
remaining portion of said separated clean spent catalyst to a
regenerator that defines a regeneration zone and provides means for
regenerating said separated coked spent catalyst and said remaining
portion of said separated clean spent catalyst to yield said
regenerated cracking catalyst.
[0010] FIG. 1 is a process flow schematic illustrating certain
aspects of one embodiment of the inventive process.
[0011] The invention includes process and apparatus that provide
for the processing of hydrocarbon feedstocks to selectively or
preferentially produce a middle distillate boiling range product
and lower olefins. The inventive process uses two riser reactors
each having associated therewith a separator/stripper for
separating the cracked product and cracking catalyst received from
the respective riser reactor and a single regenerator for
regenerating coked or spent cracking catalyst received from the
separator/strippers. The two riser reactors, two
separator/strippers and regenerator are operatively integrated to
provide a process system for carrying out the process of the
invention.
[0012] In the inventive process, a first hydrocarbon feedstock is
introduced into the bottom of a first riser reactor zone that is
defined by a first riser reactor. Hot cracking catalyst (e.g., the
first portion of the regenerated cracking catalyst, as defined
below, and, optionally, at least a portion of, or, alternatively, a
remaining portion of, the separated clean spent catalyst, as they
are defined below) is also introduced into the first riser reactor
zone, wherein it is mixed and contacted with the first hydrocarbon
feedstock under suitable first catalytic cracking conditions to
provide for catalytically cracking the first hydrocarbon
feedstock.
[0013] A second hydrocarbon feedstock is introduced into the bottom
of the second riser reactor zone that is defined by a second riser
reactor. Regenerated catalyst (e.g., the second portion of
regenerated cracking catalyst, as defined below) is also introduced
into the second riser reactor zone, wherein it is mixed and
contacted with the second hydrocarbon feedstock under suitable
second catalytic cracking conditions to provide for catalytically
cracking the second hydrocarbon feedstock.
[0014] The fresh catalytic cracking catalyst used in the inventive
process and circulated within the process system can be any
suitable cracking catalyst known in the art to have cracking
activity under the catalytic cracking conditions contemplated by
the invention. Preferred catalytic cracking catalysts for use in
the inventive process include fluidizable cracking catalysts
comprised of a molecular sieve having cracking activity dispersed
in a porous, inorganic refractory oxide matrix or binder.
[0015] The term "molecular sieve" as used herein refers to any
material capable of separating atoms or molecules based on their
respective dimensions. Molecular sieves suitable for use as a
component of the cracking catalyst include pillared clays,
delaminated clays, and crystalline aluminosilicates. Normally, it
is preferred to use a cracking catalyst that contains a crystalline
aluminosilicate. Examples of such aluminosilicates include Y
zeolites, ultrastable Y zeolites, X zeolites, zeolite beta, zeolite
L, offretite, mordenite, faujasite, and zeolite omega. The
preferred crystalline aluminosilicates for use in the cracking
catalyst are X and Y zeolites with Y zeolites being the most
preferred.
[0016] U.S. Pat. No. 3,130,007, the disclosure of which is hereby
incorporated by reference in its entirety, describes Y-type
zeolites having an overall silica-to-alumina mole ratio between
about 3.0 and about 6.0, with a typical Y zeolite having an overall
silica-to-alumina mole ratio of about 5.0. It is also known that
Y-type zeolites can be produced, normally by dealumination, having
an overall silica-to-alumina mole ratio above about 6.0. Thus, for
purposes of this invention, a Y zeolite is one having the
characteristic crystal structure of a Y zeolite, as indicated by
the essential X-ray powder diffraction pattern of Y zeolite, and an
overall silica-to-alumina mole ratio above 3.0, and includes Y-type
zeolites having an overall silica-to-alumina mole ratio above about
6.0.
[0017] The stability and/or acidity of a zeolite used as a
component of the cracking catalyst may be increased by exchanging
the zeolite with hydrogen ions, ammonium ions, polyvalent metal
cations, such as rare earth-containing cations, magnesium cations
or calcium cations, or a combination of hydrogen ions, ammonium
ions and polyvalent metal cations, thereby lowering the sodium
content until it is less than about 0.8 weight percent, preferably
less than about 0.5 weight percent and most preferably less than
about 0.3 weight percent, calculated as Na.sub.2O. Methods of
carrying out the ion exchange are well known in the art.
[0018] The zeolite or other molecular sieve component of the
cracking catalyst is combined with a porous, inorganic refractory
oxide matrix or binder to form a finished catalyst prior to use.
The refractory oxide component in the finished catalyst may be
silica-alumina, silica, alumina, natural or synthetic clays,
pillared or delaminated clays, mixtures of one or more of these
components and the like. Preferably, the inorganic refractory oxide
matrix will comprise a mixture of silica-alumina and a clay such as
kaolin, hectorite, sepiolite and attapulgite.
[0019] A preferred finished catalyst will typically contain between
about 5 weight percent to about 40 weight percent zeolite or other
molecular sieve and greater than about 20 weight percent inorganic,
refractory oxide. In general, the finished catalyst may contain
between about 10 to about 35 weight percent zeolite or other
molecular sieve, between about 10 to about 30 weight percent
inorganic, refractory oxide, and between about 30 to about 70
weight percent clay.
[0020] The crystalline aluminosilicate or other molecular sieve
component of the cracking catalyst may be combined with the porous,
inorganic refractory oxide component or a precursor thereof by any
suitable technique known in the art including mixing, mulling,
blending or homogenization. Examples of precursors that may be used
include alumina, alumina sols, silica sols, zirconia, alumina
hydrogels, polyoxycations of aluminum and zirconium, and peptized
alumina.
[0021] In a preferred method of preparing the cracking catalyst,
the zeolite is combined with an alumino-silicate gel or sol or
other inorganic, refractory oxide component, and the resultant
mixture is spray dried to produce finished catalyst particles
normally ranging in diameter between about 40 and about 80 microns.
If desired, however, the zeolite or other molecular sieve may be
mulled or otherwise mixed with the refractory oxide component or
precursor thereof, extruded and then ground into the desired
particle size range. Normally, the finished catalyst will have an
average bulk density between about 0.30 and about 0.90 gram per
cubic centimeter and a pore volume between about 0.10 and about
0.90 cubic centimeter per gram.
[0022] The first hydrocarbon feedstock may be any suitable
hydrocarbon feedstock that is chargeable to a fluidized catalytic
cracking unit or that will result in providing a particularly
desired product mix. In one preferred embodiment of the inventive
process, the first hydrocarbon feedstock is a gas oil. Hydrocarbon
mixtures boiling in the range of from 345.degree. C. (653.degree.
F.) to 760.degree. C. (1400.degree. F.) can suitably be used as the
first hydrocarbon feedstock of the invention. Examples of the types
of refinery feed streams that can make suitable gas oil feedstocks
include vacuum gas oils, coker gas oils, straight-run residues,
thermally cracked oils and other hydrocarbon streams.
[0023] The catalytic cracking conditions can be defined by such
parameters as the average residence time of the hydrocarbons in a
particular riser reactor, the catalyst-to-oil ratio, and the riser
reactor temperature.
[0024] The first catalytic cracking conditions at which the first
riser reactor zone is operated can include an average residence
time of the hydrocarbons (e.g., first hydrocarbon feedstock) in the
first riser reactor zone that is generally in the range of upwardly
to about 5 to 10 seconds, but, usually, it is in the range of from
0.1 to 5 seconds. The weight ratio of catalyst (e.g., the first
portion of regenerated cracking catalyst, as defined below, and,
optionally, at least a portion of, or, alternatively, a remaining
portion of, the separated clean spent catalyst, as defined below)
to first hydrocarbon feedstock (i.e., the catalyst/oil ratio)
introduced into the first reactor zone generally can be in the
range of from about 2 to about 100 and even as high as 150. More
typically, the catalyst-to-oil ratio can be in the range of from 5
to 100. The temperature in the first riser reactor zone generally
can be in the range of from about 400.degree. C. (752.degree. F.)
to about 600.degree. C. (1112.degree. F.). More typically, the
first riser reactor temperature can be in the range of from
450.degree. C. (842.degree. F.) to 550.degree. C. (1022.degree.
F.).
[0025] The second hydrocarbon feedstock may be any suitable
hydrocarbon feedstock that is chargeable to a fluidized catalytic
cracking unit or that will provide the particularly desired product
mix. In a preferred embodiment of the inventive process, the second
hydrocarbon feedstock include hydrocarbon mixtures boiling in the
naphtha or gasoline boiling temperature range. Generally, gasoline
feedstocks comprise hydrocarbons boiling in the temperature range
of from about 32.degree. C. (90.degree. F.) to about 204.degree. C.
(400.degree. F.). Examples of refinery streams that may be used as
the naphtha or gasoline feedstock of the inventive process include
straight run gasoline, straight run naphtha, catalytically cracked
gasoline, and coker naphtha.
[0026] The second catalytic cracking conditions at which the second
riser reactor zone is operated can include an average residence
time of the hydrocarbons (e.g., second hydrocarbon feedstock) in
the second riser reactor zone generally in the range upwardly to
about 20 seconds, but usually the average residence time is in the
range of from 0.1 to 10 seconds. The weight ratio of catalyst
(e.g., the second portion of regenerated cracking catalyst, as
defined below) to second hydrocarbon feedstock (i.e., the
catalyst/oil ratio) can generally be in the range of from about 2
to about 100 and even as high as 150. More typically, the
catalyst-to-oil ratio can be in the range of from 5 to 100. The
temperature in the second riser reactor zone generally can be in
the range of from about 482.degree. C. (900.degree. F.) to about
871.degree. C. (1600.degree. F.). More typically, the second riser
reactor zone generally can be in the range of from 538.degree. C.
(1000.degree. F.) to 732.degree. C. (1350.degree. F.).
[0027] The hot cracking catalyst that is introduced into the first
riser reactor zone along with the first hydrocarbon feedstock
includes a first portion of regenerated cracking catalyst taken
from the regenerator. In another embodiment of the inventive
process, at least a portion of the separated clean spent catalyst
is introduced into the first riser reactor zone along with the
first hydrocarbon feedstock and the first portion of the
regenerated cracking catalyst. The remaining portion of separated
clean spent catalyst, which is the portion that is not introduced
into the first riser reactor zone, is passed and introduced into
the regenerator. In an alternative embodiment of the invention, at
least a portion of the separated clean spent catalyst is, instead,
passed and introduced into the regenerator; and, then the remaining
portion of the separated clean spent catalyst, which is the portion
that is not introduced into the regenerator, is passed and
introduced into the first riser reactor zone.
[0028] The clean spent catalyst is referred to herein as being
"clean" because it is derived from the product of the second riser
reactor zone that is defined by a second riser reactor. The second
riser reactor zone of the process is operated under suitable second
catalytic cracking conditions that are more severe than the
reaction conditions under which the first riser reactor zone is
operated. The second hydrocarbon feedstock charged to the second
riser reactor zone is, preferably, a lighter feedstock than the
first hydrocarbon feedstock charged to the first riser reactor
zone, thus resulting in less coke yield.
[0029] Due to the cracking of a lighter feedstock, the used
cracking catalyst yielded from the product of the second riser
reactor zone has a lower concentration of coke than the spent or
coked spent catalyst yielded from the product of the first riser
reactor zone. Thus, the used cracking catalyst from the second
riser reactor product is referred to herein as being "clean" for
the purpose of distinguishing it from the spent or coked spent
catalyst yielded from the first riser reactor product.
[0030] Yielded from the first riser reactor zone is a first riser
reactor product that comprises a first cracked product and a coked
spent catalyst. The first riser reactor product is passed to the
first separator/stripper associated with the first riser reactor.
The first separator/stripper provides means for separating the
first riser reactor product into a separated first cracked product
and a separated coked spent catalyst.
[0031] The separated coked spent catalyst has a coke content,
generally, in the range of from about 0.5 to about 5 weight percent
(wt. %), based on the total weight of the catalyst and the carbon.
More typically, the coke content on the separated coked spent
catalyst is in the range of from or about 0.5 wt. % to or about 1.5
wt. %.
[0032] A second riser reactor product is yielded from the second
riser reactor zone and comprises a second cracked product and a
clean spent catalyst. This second riser reactor product is passed
to the second separator/stripper that is associated with the second
riser reactor. The second separator/stripper provides means for
separating the second riser reactor product into a separated second
cracked product and a separated clean spent catalyst.
[0033] The separated clean spent catalyst has a coke content that
is typically lower than the coke content of the separated coked
spent catalyst. Generally, the coke content of the separated clean
spent catalyst is in the range of from about 0.1 to about 1 weight
percent (wt. %), based on the total weight of the catalyst and the
carbon. More typically, the coke content on the separated clean
spent catalyst is in the range of from or about 0.1 wt. % to or
about 0.6 wt. %.
[0034] Each separator/stripper of the inventive fluidized catalytic
cracking process system includes a vessel that defines a separation
zone and a stripping zone. Within the separation zone there may be
one or more cyclones that define one or more cyclone separation
zones. The cyclones may be operated in series flow or in parallel
flow and they provide means for receiving a riser reactor effluent
and for separating spent catalyst and catalytically cracked
vaporous hydrocarbons of the riser reactor effluent. The separated
vaporous hydrocarbon product exits the cyclones and the
separator/stripper apparatus to pass downstream for further
processing such as with a main fractionator of the fluidized
catalytic cracking unit. The separated spent catalyst passes from
the cyclones through diplegs into the stripping zone or section of
the separator/stripper apparatus. The separated spent catalyst is
stripped of hydrocarbons within the stripping zone, typically, by
the use of stripping steam that is introduced into the stripping
section of the separator/stripper apparatus. Stripped catalyst is
removed from the stripping section of the stripping section of the
separator/stripper apparatus by way of a catalyst standpipe
conduit.
[0035] The first riser reactor product is received into first
separation means of the first separator/stripper which defines a
first separation zone. First separation means provides for
separating the first riser reactor product into a separated first
cracked product and a separated coked spent catalyst.
[0036] The second riser reactor product is received into second
separation means of the second separator/stripper which defines the
second separation zone. Second separation means provides for
separating the second riser reactor product into a separated second
cracked product and a separated clean spent catalyst.
[0037] Any suitable means known in the art may be used as either
first separation means or second separation means, but, typically,
and preferably, such means include cyclone separators that utilize
centrifugal flow and gravity to provide for the separation of
hydrocarbon gases and catalyst particles. Many of the various types
or designs of suitable cyclone separators and their uses are known
to those skilled in the art.
[0038] The separated first cracked product and separated second
cracked product that are respectively yielded from the first
separator/stripper and second separator/stripper pass to the
downstream where they may further be processed. It is preferred for
the separated first cracked product and the separated second
cracked product to pass either separately or in combination to one
or more fractionators, but, typically, a combined stream is passed
to a main fractionator.
[0039] The main fractionator defines a fractionation zone and
provides means for separating the separated first cracked product
or the separated second cracked product, or a combination of both,
into one or more product streams including a naphtha product
stream. Other product streams may include a lower olefins stream, a
cracked gasoline stream, and a cracked gas oil stream.
[0040] The first separator/stripper further defines a first
stripping zone generally contained within the bottom section of the
first separator/stripper. In the operation of the first
separator/stripper, the separated coked spent catalyst falls from
first separation means into the first stripping zone, wherein it is
stripped of hydrocarbons. Any suitable stripping fluid may be used
to strip the hydrocarbons from the separated coked spent catalyst,
but, the preferred stripping fluid is steam, which may, in general,
be introduced into the bottom of the first stripping zone or
section of the first separator/stripper. The stripped hydrocarbons
will pass to downstream along with the separated first cracked
product for further processing and the separated coked spent
catalyst passes from the first stripping zone to be introduced into
the regeneration zone of the regenerator.
[0041] The second separator/stripper further defines a second
stripping zone generally contained within the bottom section of the
second separator/stripper. In the operation of the second
separator/stripper, the separated clean spent catalyst falls from
second separation means into the second stripping zone, wherein it
is stripped of hydrocarbons. As with the first separator/stripper,
any suitable stripping fluid may be used to strip the hydrocarbons
from the separated clean spent catalyst with the preferred
stripping fluid being steam. The stripped hydrocarbons will pass to
downstream along with the separated second cracked product for
further processing.
[0042] The separated clean spent catalyst passes from the second
stripping zone and at least a portion of the separated clean spent
catalyst including up to the entire flow of the separated clean
spent catalyst from the second separator/stripper is introduced
into the regeneration zone of the regenerator. In another
embodiment of the invention, the remaining portion of the separated
clean spent catalyst that is not introduced into the regenerator is
further passed to and introduced in combination or along with a
first portion of the regenerated cracking catalyst into the riser
reactor zone of the first riser reactor. In still another
embodiment of the inventive process, at least a portion of the
separated clean spent catalyst, instead, is introduced, in
combination or along with a first portion of a regenerated cracking
catalyst, into the first riser reactor zone of the first riser
reactor wherein the catalyst is contacted with the first
hydrocarbon feedstock. A remaining portion of the separated clean
spent catalyst, which is that portion of the separated clean spent
catalyst that is not passed to and introduced into the first riser
reactor zone, is introduced into the regeneration zone of the
regenerator.
[0043] The regenerator of the inventive process or system provides
means for regenerating the separated coked spent catalyst and the
at least a portion or the remaining portion of the separated clean
spent catalyst to yield regenerated cracking catalyst. The
regenerator defines a regeneration zone into which the separated
coked spent catalyst and the at least a portion, or the remaining
portion, of the separated clean spent catalyst are introduced and
wherein deposited carbon is burned to provide the regenerated
cracking catalyst having a reduced carbon content. The regenerator,
typically, is a vertical vessel of any suitable configuration that
defines the regeneration zone and wherein the separated coked spent
catalyst and the remaining portion, or at least a portion, of the
separated clean spent catalyst is maintained as a fluidized bed by
the upward passage of an oxygen-containing regeneration gas, such
as air.
[0044] The regeneration temperature within the regeneration zone
is, in general, maintained in the range of from about 621.degree.
C. (1150.degree. F.) to 760.degree. C. (1400.degree. F.), and more
typically, in the range of from 677.degree. C. (1250.degree. F.) to
715.degree. C. (1320.degree. F.).
[0045] The pressure within the regeneration zone typically is in
the range of from about atmospheric to about 345 kPa (50 psig),
and, preferably, from about 34 to 345 kPA (5 to 50 psig).
[0046] The residence time of the separated coked spent catalyst and
the at least a portion, or the remaining portion, of the separated
clean spent catalyst within the regeneration zone is in the range
of from about 1 to about 6 minutes, and, typically, from or about 2
to or about 4 minutes.
[0047] The coke content on the regenerated cracking catalyst is
less than the coke content on the separated coked spent catalyst
and the at least a portion, or remaining portion, of the separated
clean spent catalyst that are introduced into the regeneration zone
of the regenerator. The coke content of the regenerated cracking
catalyst will, thus, generally be in the range of from or about
0.01 wt. % to or about 0.5 wt. %. It is preferred for the coke
concentration on the regenerated cracking catalyst to be less than
0.1 wt. % and, it will preferably be in the range of from 0.01 wt.
% to 0.1 wt. %.
[0048] The regenerated cracking catalyst yielded from the
regenerator is used as a hot cracking catalyst that is introduced
into the first riser reactor zone and the second riser reactor zone
for contacting with the respective hydrocarbon feedstocks. Thus, a
first portion of the regenerated cracking catalyst is introduced
into the first riser reactor zone wherein it is contacted with the
first hydrocarbon feedstock, and a second portion of the
regenerated cracking catalyst is introduced into the second riser
reactor zone wherein it is contacted with the second hydrocarbon
feedstock.
[0049] Now referring to FIG. 1 which presents a process flow
schematic representing certain aspects of the inventive process 10.
In process 10, a first hydrocarbon feedstock, which preferably is a
gas oil feedstock, is passed by way of conduit 12 and introduced
into first riser reactor zone 14 that is defined by first riser
reactor 16.
[0050] First riser reactor 16 is an elongated conduit that extends
vertically. The first hydrocarbon feedstock is introduced into
first riser reactor zone 14 at or near the bottom of first riser
reactor 16, wherein it is mixed or contacted with hot catalyst. The
mixture of first hydrocarbon feedstock and hot catalyst passes
through first riser reactor zone 14, which is operated under
suitable first catalytic cracking conditions so as to provide a
first riser reactor product.
[0051] The first riser reactor product, which comprises a first
cracked product and a coked spent catalyst, is yielded from first
riser reactor zone 14 and passes by way of conduit 18 from outlet
20 of first riser reactor 16 to be introduced into first
separator/stripper 22 through inlet 24.
[0052] The sources of hot catalyst introduced into first riser
reactor zone 14 include a first portion of the regenerated cracking
catalyst taken from regenerator 26, and, in an alternative
embodiment of the invention, at least a portion, or, in another
alternative embodiment of the invention, a remaining portion, of
the separated clean spent catalyst taken from second
separator/stripper 30. Thus, a first portion of the regenerated
cracking catalyst passes from regenerator 26 by way of conduit 32
and is introduced into first riser reactor zone 14. Or, a first
portion of the regenerated cracking catalyst in combination with at
least a portion of the separated clean spent catalyst is introduced
into first riser reactor zone 14. Or, a first portion of the
regenerated cracking catalyst in combination with a remaining
portion of the separated clean spent catalyst is introduced into
first riser reactor zone 14. The at least a portion of the
separated clean spent catalyst is introduced into first riser
reactor zone 14 by way of conduit 34. The remaining portion of the
separated clean spent catalyst, likewise, is introduced into first
riser reactor zone 14 by way of conduit 34.
[0053] First separator/stripper 22 includes and defines first
separation zone 36 and first stripping zone 38. One or more
cyclones (not shown) may be included within first separation zone
36 to provide first separation means for separating the first riser
reactor product into a separated first cracked product and a
separated coked spent catalyst. Provided within first stripping
zone 36 are baffles or trays (not shown) that provide for enhanced
contact between the falling catalyst and a stripping fluid, such as
steam, that is introduced into the first stripping zone by way of
conduit 40, so as to assist in the stripping of the hydrocarbons
from the falling catalyst. The separated coked spent catalyst
passes from first stripping zone 38 by way of conduit 44 to be
introduced into regeneration zone 46 of regenerator 26.
[0054] Regenerator 26 defines regeneration zone 46 and provides
means for regenerating the separated coked spent catalyst by
contacting the separated coked spent catalyst with an
oxygen-containing gas, such as air, under carbon burning conditions
to remove carbon therefrom. The oxygen-containing gas is introduced
into regeneration zone 46 through conduit and the combustion gases
pass from regeneration zone 46 by way of conduit 50 to downstream
for further handling or processing.
[0055] Second riser reactor 54 is an elongated conduit that extends
vertically. The second hydrocarbon feedstock, which is preferably a
naphtha or gasoline feedstock, is introduced by way of conduit 55
into second riser reactor zone 56 at or near the bottom of second
riser reactor 54, wherein it is mixed or contacted with a second
portion of regenerated cracking catalyst. The second portion of
regenerated cracking catalyst passes from regenerator 26 by way of
conduit 58 and is introduced into second riser reactor zone 56 by
way of conduit The mixture of second hydrocarbon feedstock and the
second portion of regenerated cracking catalyst passes through
second riser reactor zone 56, which is operated under suitable
second catalytic cracking conditions so as to provide a second
riser reactor product.
[0056] The second riser reactor product, which comprises a second
cracked product and a clean spent catalyst, is yielded from second
riser reactor zone 56 and passes by way of conduit 60 from outlet
64 of second riser reactor 54 to be introduced into second
separator/stripper 30 through inlet 66.
[0057] Second separator/stripper 30 provides means for receiving
the second riser reactor product by way of conduit 60 and through
inlet 66. Second separator/stripper 30 includes and defines second
separation zone 68 and second stripping zone 70. One or more
cyclones (not shown) may be included within second separation zone
68 to provide second separation means for separating the second
riser reactor product into a separated second cracked product and a
separated clean spent catalyst. Provided within second stripping
zone 70 are baffles or trays (not shown) that provide for enhanced
contact between the falling catalyst and a stripping fluid, such as
steam, that is introduced into the second stripping zone by way of
conduit 72, so as to assist in the stripping of the hydrocarbons
from the falling catalyst.
[0058] The separated clean spent catalyst, which may be introduced
into regeneration zone 46 of regenerator 26, passes from second
stripping zone 70 by way of conduit 74. At least a portion of the
separated clean spent catalyst up to and including the entire
portion or flow of the separated clean spent catalyst can be
introduced into regeneration zone 46 by way of conduit 76. Then,
the remaining portion of the separated clean spent catalyst that is
not introduced into regenerator 26 passes by way of conduit 34 for
introduction into first riser reactor zone 14. Or, in another
alternative embodiment of the invention, a remaining portion of the
separated clean spent catalyst, which is that portion of the
separated clean spent catalyst not passed to first riser reactor
zone 14 through conduit 34, can be introduced into regeneration
zone 46 by way of conduit 76. In this embodiment, at least a
portion of the separated clean spent catalyst is passed by way of
conduit 34 to be introduced into first riser reactor zone 14.
[0059] Regenerator 26 further provides means for regenerating the
separated coked spent catalyst and the separated clean spent
catalyst that are charged to it. Thus, regenerator 26 defines a
regeneration zone 46 and provides means for regenerating separated
coked spent catalyst and a remaining portion, or at least a
portion, of separated clean spent catalyst to yield regenerated
cracking catalyst.
[0060] A separated first cracked product passes from first
separator/stripper 22 by way of conduit 80. A separated second
cracked product passes from second separator/stripper 30 by way of
conduit 82. Either the separated first cracked product or separated
second cracked product, or a combination of the two streams, may be
passed to a main fractionation column or system (not shown). The
main fractionation column or system may be any separation system
know to those skilled in the art for recovering and separating
cracked product streams into various FCC products, such as, for
example, cracked gas, cracked gasoline, cracked gas oils and cycle
oil that respectively pass from main fractionation column. A main
fractionation system may include such systems as absorbers and
strippers, fractionators, compressors and separators or any
combination of known systems for providing recovery and separation
of the cracked products that may make up the separated first
cracked product or the separated second cracked product, or both.
In a preferred embodiment of the process, a combination of the
separated first cracked product and the separated second cracked
product passes to a main fractionation column which provides means
for their separation into one or more product streams, as indicated
above, including the cracked gasoline or a naphtha product
stream.
[0061] In one embodiment of the inventive process, at least a
portion of the cracked gasoline or naphtha product stream passing
from the main fractionation system is recycled and utilized as the
second hydrocarbon feedstock introduced into second riser reactor
zone 34 by way of conduit 44.
* * * * *