U.S. patent number 3,886,060 [Application Number 05/355,821] was granted by the patent office on 1975-05-27 for method for catalytic cracking of residual oils.
This patent grant is currently assigned to Mobil Oil Corporation. Invention is credited to Hartley Owen.
United States Patent |
3,886,060 |
Owen |
May 27, 1975 |
Method for catalytic cracking of residual oils
Abstract
A method and system for the fluid catalytic cracking of residual
and lower boiling oil streams is described which relies upon the
residual oil as a quench medium for limiting the conversion of a
recycle oil product thereof in a riser conversion zone. The overall
combination is enhanced by using a dual component cracking catalyst
of large and small pore size. Other virgin feeds requiring limited
conversion residence time may be used in the combination to obtain
restricted conversion of the residual oil feed.
Inventors: |
Owen; Hartley (Belle Mead,
NJ) |
Assignee: |
Mobil Oil Corporation (New
York, NY)
|
Family
ID: |
23398975 |
Appl.
No.: |
05/355,821 |
Filed: |
April 30, 1973 |
Current U.S.
Class: |
208/120.01;
208/77; 502/40; 208/74; 208/155 |
Current CPC
Class: |
C10G
11/05 (20130101); B01J 8/26 (20130101); C10G
11/18 (20130101) |
Current International
Class: |
C10G
11/05 (20060101); C10G 11/18 (20060101); C10G
11/00 (20060101); B01J 8/24 (20060101); B01J
8/26 (20060101); C01b 033/28 (); C10g 011/18 () |
Field of
Search: |
;208/120,74 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Gantz; Delbert E.
Assistant Examiner: Schmitkons; G. E.
Attorney, Agent or Firm: Huggett; Charles A. Farnsworth;
Carl D.
Claims
I claim:
1. A method for converting residual oils to lower boiling products
which comprises,
passing hot crystalline zeolite catalyst particles to the lower
portion of an elongated conversion zone, passing a recycle oil
product of residual oil cracking to the lower portion of said
conversion zone under conditions to form a suspension with said
catalyst particles at a temperature of at least 1,000.degree.F.,
passing said suspension through said conversion zone providing a
recycle oil charge residence time in the range of 0.5 to about 4
seconds, combining a residual oil feed with said suspension in said
conversion zone in an amount sufficient to quench said recycle oil
conversion, passing the suspension comprising said residual oil
feed through said conversion zone at lower temperature cracking
conditions for an additional hydrocarbon residence time in the
range of 0.5 to 6 seconds, cyclonically separating said suspension
into a hydrocarbon phase and a catalyst phase and separately
recovering said hydrocarbon phase and said catalyst phase.
2. The method of claim 1 wherein the residual oil is introduced to
said conversion zone at one or more spaced apart points.
3. The method of claim 1 wherein the catalyst comprises a dual
cracking component comprising a large pore crystalline zeolite of
the faujasite or mordenite type in combination with a smaller pore
crystalline zeolite such as erionite, offertite and ZSM-5 type
materials.
4. The method of claim 1 wherein the catalyst to oil ratio of the
suspension in the region of residual oil injection is adjusted by
adding additional hot catalyst to the suspension.
5. The method of claim 1 wherein the separated and recovered
catalyst phase is combined with additional regenerated catalyst
before stripping thereof of entrained hydrocarbons.
6. The method of claim 5 wherein the regenerated catalyst combined
with the recovered catalyst phase is relied upon to convert a low
severity reformate material to higher octane product.
7. The method of claim 1 wherein conversion of the residual oil is
restricted not to exceed about 50 volume percent of 400.degree.F.
ASTM boiling point material.
8. The method of claim 1 wherein gaseous materials selected from
the group comprising hydrogen, gaseous hydrocarbon products of more
severe gas oil cracking operations, mixtures of paraffins and
olefins and C.sub.1 to C.sub.3 hydrocarbons with or without
hydrogen are combined with the residual hydrocarbon feed to
suppress the effects of metal contaminants and coking
characteristics of the heavy feed.
9. The method of claim 1 wherein a separate second conversion zone
is provided for initially converting a heavy virgin naphtha or a
light virgin gas oil with suspended catalyst to gasoline boiling
product at a temperature of at least 1,000.degree.F. before
introducing residual oil to said second conversion zone as quench
and conversion thereof by contact with the catalyst suspension
provided therein.
10. The method of claim 9 wherein catalyst is separated from each
conversion zone and stripped in a common stripping zone, the
stripped catalyst is combined with freshly regenerated catalyst and
passed upwards through a dispersed phase regeneration zone for
discharge into the dispersed catalyst phase above a dense fluid bed
of catalyst being regenerated, said discharged catalyst is passed
from said dispersed phase into said dense fluid bed of catalyst and
dense bed regenerated catalyst is passed to the inlet of each of
said conversion zones.
11. The method of claim 1 wherein conversion of the recycle oil
feed is restricted not to exceed 50 volume percent.
12. The method of claim 1 wherein conversion of the residual oil
feed is restricted to less than 45 volume percent.
Description
BACKGROUND OF THE INVENTION
It has been known for a long time that high octane gasoline product
can be obtained from various selected hydrocarbon oils by catalytic
cracking. However heavy oils such as residual oils have a large
percentage of very refractory components such as polycyclic
aromatics which are difficult to crack and cause an excessive
amount of coke to be deposited on the catalyst. Furthermore, metal
contaminants in the heavy oil feed poison or inactivate the
catalyst. Therefore it has been necessary in the prior art to
drastically reduce these components by different techniques such as
hydrogenation, thermal cracking and adsorption on particle material
of little or no cracking activity prior to disposal of the particle
material. Thus, mild thermal cracking and visbreaking operations to
produce more suitable feed materials for a catalytic cracking
operation has been the trend of the prior art processing
combinations.
Residual oil is a distress stock in the petroleum industry. A
substantial amount of residual oil is sold as fuel oil or thermally
processed to obtain lighter components and coke. Residual oils
contain large quantities of components having coke forming
tendencies and also metal components which exert adverse effects on
the stability and activity of cracking catalysts. For example,
residual oils contain carbon residue in excess of 0.6% by weight
and this characteristic, producing high additive coke in a cracking
operation, will operate to rapidly deactivate crystalline zeolite
cracking catalysts.
SUMMARY OF THE INVENTION
The present invention relates to an improved method for the
catalytic upgrading of residual oil. In a more particular aspect
the present invention is concerned with the catalytic upgrading of
residual oils in the presence of crystalline zeolite catalytic
materials to obtain gasoline, lower and higher boiling components
thereof.
A particular expedient of the processing concepts of the present
invention is concerned with providing a short contact time residual
oil catalytic conversion operation or operations at reasonable
cracking temperatures by effecting the cracking conversion
operation in the presence of a crystalline aluminosilicate
conversion catalyst. The process concepts of the present invention
are considerably different from present day fluid catalytic
cracking (FCC) operations in that feeds used in the operation will
be relatively cold (in the range of 100.degree. to about
350.degree.F.) and used in combination with a relatively high
catalyst to oil ratio as well as high catalyst circulation rates.
Furthermore since coke make will be in excess of that normally
required for a heat balanced operation, it will be expedient to
remove heat from the regenerators. The process concepts of the
present invention include using a recycle oil product stream of
cracking as the fresh feed for initially contacting suspended hot
highly active regenerated catalyst at an elevated temperature of at
least 950.degree.F. in a dispersed phase catalytic conversion zone
and thereafter injecting a heavy oil feed such as a residual oil
into a downstream portion of the dispersed phase suspension to
quench the cracking reaction initiated with the recycle oil. Thus
the fresh residual oil feed will be in contact with the regenerated
catalyst for only a limited residence time in the range of 0.5 to 6
seconds at temperature conditions herein identified and
particularly promoting the conversion thereof to lighter oil
components thereof before separation of the catalyst from
hydrocarbon material as by cyclonic separation means.
The method of converting residual oils and other hydrocarbon feed
materials contemplated by the present invention relies upon the
combination of initially forming a suspension of regenerated
catalyst with a low boiling hydrocarbon feed such as a recycle oil
product of cracking or other low boiling virgin feed herein
identified to provide a suspension at a temperature preferably in
the range of 1,000.degree. to about 1,300.degree.F. and a catalyst
to oil ratio in the range of 5 to 40. The suspension thus formed is
moved rapidly through a reaction zone such as a riser reaction zone
for a hydrocarbon residence time selected from within the range of
about 0.5 to about 4 seconds before the cracking reaction is
quenched at least 100.degree. and to a temperature in the range of
900.degree.F. to about 1,200.degree.F. by the injection of a
heavier hydrocarbon material such as the residual oil feed
material. To facilitate dispersion, the residual oil may be
combined with a diluent such as steam, low boiling gasiform
hydrocarbons or other suitable diluent material. The suspension
formed comprising catalysts, recycle oil conversion product and
injected residual oil is then separated after an additional
residence time in the range of 0.5 to about 6 seconds by cyclonic
means or by discharging into an upper dispersed catalyst phase for
gravity separation above a dense fluid bed of catalysts. The
separated hydrocarbon material is passed to a fractionation zone
for the separation recovery of various product fractions of the
conversion operation. The separated catalyst is collected in a
dense fluid bed of catalyst particles being stripped with stripping
gas or used for other conversion purposes. The thus separated
catalyst may be mixed with hot regenerated catalyst and thereafter
moved generally downwardly to and through a catalyst stripping zone
as provided below.
The method of the present invention contemplates combining freshly
regenerated catalyst with the catalyst separated from the riser
conversion zone to adjust the temperature thereof before further
contact with a light hydrocarbon feed material or by a stripping
gas. To accomplish this end, freshly regenerated catalyst may be
lifted through a separate riser reactor with relatively inert lift
gas or light hydrocarbons such as virgin naphtha or low severity
reformates may be used to convey the regenerated catalyst at an
elevated temperature of at least about 1,000.degree.F. into a bed
of catalyst separated from the heavier oil feed riser cracking
operation above discussed.
As provided herein the processing concepts of the present invention
contemplate varying the reaction residence time of the various
hydrocarbon components over a range of from a fraction of a second
up to several seconds and controlling this reaction residence time
by catalyst oil ratio and temperature through the concept of
multipoint quench oil injection in the riser and/or the addition of
regenerated catalyst to a downstream portion of the riser.
The processing concepts of the present invention lend themselves to
many different apparatus variations, two of which are specifically
discussed hereinafter. In one arrangement a side by side
reactor-regenerator system is employed which permits the use of
freshly regenerated cracking catalyst alone and in combination with
used catalyst to perform the various conversion reaction desired
under particularly selected temperature and catalyst to oil (C/O)
ratio reaction conditions. In yet another arrangement, a stacked
system is relied upon to accomplish the multiple hydrocarbon
conversion reactions desired which reactions are controlled
primarily as a function of temperature and hydrocarbon residence
time.
In the methods and systems of this invention, it is contemplated
using a relatively large diameter riser reactor for conversion of
the recycle oil and a smaller diameter riser reactor for converting
lower boiling hydrocarbon charge materials such as reformates,
heavy virgin or cracked naphtha and light virgin gas oils.
Furthermore, it is contemplated injecting the heavy quench oil in
the downstream portion of the recycle oil riser reactor at one or
more spaced intervals promoting the optimum desired conversion of
the recycle oil. Also the heavy quench oil injected in the light
hydrocarbon conversion riser reactor may be introduced at one or
more spaced intervals promoting the optimum upgrading of the light
hydrocarbon feed. Generally the recycle oil feed will require a
longer hydrocarbon conversion residence time.
The stacked regenerator-riser reactor system herein referred to
also lends itself to a regenerator system which improves upon the
recovery of available heat by effectively improving upon a first
stage of riser regeneration and a clean up stage of dense bed
catalyst regeneration by promoting the conversion of carbon
monoxide and the recovery of heat therefrom by the catalyst passed
to the first and second stages of catalyst regeneration. A better
understanding of the regeneration concepts of this invention will
be had by referring to the specific embodiments hereinafter
discussed.
The processing combination of the present invention contemplates
the use of catalyst compositions varying considerably in activity
and selectivity characteristics. That is, it is contemplated
employing as one of the catalyst compositions, a crystalline
zeolite of the X and Y faujasite type along or as the major
catalyst component with the other of said catalyst compositions
being an amorphous type cracking component of lower cracking
activity. On the other hand, the faujasite cracking component may
be combined with a smaller pore size crystalline zeolite having a
maximum pore opening not substantially in excess of about 9
Angstroms or smaller than about 4 Angstroms. It is contemplated
using with the large pore faujasite type crystalline zeolite
cracking catalyst and prepared from either X or Y type zeolites, a
crystalline zeolite of the erionite or offertite crystal structure
or preferably a crystalline aluminosilicate of the ZSM-5 type may
be employed with the larger pore crystalline zeolites. On the other
hand, the catalyst may be a mordenite type zeolite cracking
catalyst in combination with a ZSM-5 type of crystalline zeolite.
The ZSM-5 type component of the catalyst may be retained as a
separate particle in a support matrix material in combination with
separate particles of the larger pore size cracking component.
Furthermore the weight percent of ZSM-5 component may be less than
or equal to the other crystalline cracking component of the dual
component catalyst. The dual component catalyst disclosed in
copending application Ser. No. 135,783, filed Apr. 20, 1971, now
U.S. Pat. No. 3,748,251, may be employed with preference in the
process of the present invention.
The processing concepts of this invention are concerned with
adjusting and optimizing the temperature of the various catalyst
streams employed and particularly that separated from the residual
oil contact step and collected as a dense fluid bed of catalyst.
Thus as discussed above, provision is made for adding high
temperature regenerated catalyst to the dense fluid bed of
catalyst. In addition a light hydrocarbon gasiform fluid material
may be added to the bed of catalyst for conversion thereof by the
small pore crystalline aluminosilicate compound of the catalyst.
Thus depending upon the extent of quench effected with the residual
oil feed and the temperature desired in the collected dense fluid
bed of catalyst, the small pore crystalline zeolite, such as a
ZSM-5 type material, may be maintained at substantially any
temperature within the range of 300.degree.F. up to
1,000.degree.F., it being preferred to select temperatures, which
upgrade the light hydrocarbons to useful products by the ZSM-5
catalyst component. Preferred temperatures will be in the range of
500.degree.F. to about 950.degree.F.
The dense fluid bed of catalyst collected and temperature adjusted
as above described is stripped of entrained vaporous hydrocarbon
material before passing thereof to a catalyst regeneration zone.
The processing combinations herein identified will be a producer
carbonaceous deposits on the catalyst which will generate in many
cases an excess amount of heat during combustion thereof in the
regeneration zone. Therefore it is proposed when required to
provide steam coils or other means in combination with the
regeneration operation to develop process steam or a source of
process heat for use in the process or in other adjacent operations
of the refinery.
In pursuing the processing concepts of this invention it is
contemplated restricting conversion of the residual oil injected to
relatively low levels so that a relatively mild cracking of the
residual oil will be effected and produce a gas oil product
considerably less contaminated with metal contaminants and additive
carbon components.
Thus conversion of the residual oil may be restricted to less than
about 45 volume percent (vol.%) of 400.degree.F. ASTM boiling point
material and lighter but conversion may go as high as 70 vol.
percent. The cycle stock product thereof will be subjected to
temperatures, catalyst to oil ratios and space velocity conditions
in an initial portion of the riser reactor commensurate with
obtaining significant conversion thereof to a lighter oil product
boiling in the range of 90.degree. to 700.degree.F. Thus conversion
of recycle oil to gasoline boiling range products will normally be
restricted not to exceed about 50%.
It is contemplated injecting gaseous materials into the dense fluid
bed of catalyst collected as above identified as well as with the
recycle feed and/or the residual oil feed passed to the hydrocarbon
conversion zone. Gaseous materials which may be used with the heavy
hydrocarbon feed to suppress the adverse effects of metal
contaminants and additive coke characteristics of the feed on the
catalyst in the conversion zone include hydrogen, gaseous
hydrocarbon products of more severe gas oil cracking operations,
mixtures of paraffin and olefin, C.sub.1 -C.sub.3 hydrocarbons,
with or without hydrogen combined therewith. It is also
contemplated as suggested above of lifting hot regenerated catalyst
from the regeneration zone into the collected dense fluid bed of
catalyst with straight run or other low octane naphtha boiling
range products including reformate to obtain a high temperature
zeolite cracking catalyst octane improvement thereof before
discharge into the dense fluid bed of catalyst. This of course can
be used as a means for controlling the temperature of the catalyst
thus employed. Thus by the use of diluent materials as above
identified with the heavy residual oil and recycle oil feeds, the
effects of hydrocarbon partial pressure on the conversion operation
can be considerably altered.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. I shows diagrammatically in elevation a side-by-side
arrangement of vessels with interconnecting transfer conduits for
effecting regeneration of a hydrocarbon conversion catalyst,
conversion of hydrocarbons and the transfer of catalyst particles
within the system.
FIG. II shows diagrammatically in elevation a stacked arrangement
of vessels with interconnecting transfer conduits for effecting the
catalytic conversion of different hydrocarbon feed materials and
regeneration of catalyst particles used for that purpose.
DISCUSSION OF SPECIFIC EMBODIMENTS
Referring now to FIG. I by way of example, there is shown a
side-by-side reactor-regenerator system with product fractionator
for converting different hydrocarbon feed materials in the presence
of catalyst compositions comprising crystalline aluminosilicate
conversion catalysts. In the arrangement of FIG. I, a regenerator 2
containing a bed of finely divided catalyst particles in maintained
in a fluidized condition by regeneration gas introduced to the
bottom portion of the fluid bed by conduit 6 and communicating with
a regeneration gas distributor grid 8. Coils 10 for generating
process steam are provided in the regeneration zone. Cyclone
separators 12 with diplegs 14 are provided in the upper portion of
the regenerator for separating and returning to the catalyst bed
entrained catalyst fines from regeneration flue gas. The separated
flue gases pass into plenum chamber 16 and are withdrawn therefrom
by conduit 18. During regeneration of the catalyst in fluid bed 4,
carbonaceous material deposits on the catalyst are removed by
burning in the presence of oxygen containing regeneration gas
thereby raising the temperature of the catalyst about
1,000.degree.F. and more usually to a temperature in the range of
1,200.degree.F. up to about 1,400.degree.F. Regeneration of the
catalyst may be accomplished in many different processing systems,
it being important to select a system which will accomplish a
desired heating of the catalyst during burning removal of
carbonaceous deposits in an efficient manner.
Regenerated catalyst obtained at an elevated temperature of about
1,300.degree.F. is withdrawn from bed 4 by withdrawal conduit 20
provided with a catalyst flow control valve 22 for passage to the
inlet of riser 24. Lift gasiform material which may be inert or a
hydrocarbon reactant is introduced to the bottom of riser 24 by
conduit 26. In riser 24 a suspension is formed comprising catalyst
and lift gasiform material which is conveyed under elevated
temperature conditions upwardly therethrough for deposit in a dense
fluid bed of catalyst 28 obtained as hereinafter described. As
indicated herein before the light gasiform material used in riser
24 may be relatively inert or it may be a reactant material which
undergoes elevated temperature conversion reactions during contact
with the hot catalyst transferred through the riser. Thus the
gasiform material used may comprise C.sub.1 -C.sub.3 hydrocarbons
which are converted by the ZSM-5 component of the catalyst mixture;
a naphtha boiling range material may be used which is then provided
with a high temperature octane boost primarily by the faujasite
component of the catalyst; or a relatively inert gaseous material
may be used to convey the catalyst. Other materials identified
above may be used.
Regenerated catalyst is also withdrawn from bed 4 by withdrawal
conduit 30 provided with catalyst flow control valve 32 for passage
to the inlet of riser reactor 34.
The processing concepts of the present invention are particularly
concerned with the relationship of conditions for converting
distress stocks of high coke producing characteristics and
comprising metal contaminates known as residual oils. Generally
residual oils are high boiling hydrocarbon materials having an
initial boiling point in excess of about 950.degree.F. and more
usually at least about 1,000.degree.F. Thus to accomplish the
catalytic conversion of such residual oil distress stocks, the
present invention employs the procedure of initially contacting
freshly regenerated catalyst at an elevated temperature of at least
900.degree.F. with a recycle oil product fraction of the cracking
step introduced by conduit 36 to riser 34 to provide a recycle oil
reaction residence time in the presence of suspended catalyst
passing up the riser in the range of 1 to 5 seconds and thereafter
injecting a residual oil in a downstream portion of riser 34 by
conduit 38 connected to a plurality of separate spaced apart
injection conduit 38. The residual oil at a temperature in the
range of 100.degree. to 300.degree.F. is used as a quench fluid to
the catalyst oil suspension and products formed with the recycle
feed. The introduction of residual oil is sufficient to quench the
suspension to a temperature within the range of 850.degree. to
1,000.degree.F. before separation thereof preferably by cyclonic
means in separators 40 provided. The suspension is separated in
separators 40 into a hydrocarbon phase and a catalyst phase. The
hydrocarbon phase is withdrawn from the separators by conduit 42
and then passed by conduit 44 to a product fractionator 46 wherein
products of conversion are separated into a bottom fraction
withdrawn by conduit 48, a heavy oil recycle fraction withdrawn by
conduit 50, a light oil recycle fraction withdrawn by conduit 52, a
heavy gasoline fraction withdrawn by conduit 54 and materials
boiling below the separated gasoline fraction withdrawn by conduit
56. The vaporous material withdrawn by conduit 56 is passed to a
condenser wherein reflux material is separated for return to the
tower as reflux by conduit 58.
Catalyst particles separated from hydrocarbon vapors in cyclone
separators 40 are conveyed by diplegs 60 to a collected dense fluid
bed of catalyst 28 therebelow.
The catalyst employed in the processing sequence of the present
invention is a dual cracking component catalyst comprising a ZSM-5
type of crystalline aluminosilicate as one of the cracking
components. The other cracking component of the composition is
preferably a faujasite type of zeolite with the Y type being
preferred. To take full advantage of the conversion potential of
the ZSM-5 type of crystalline zeolite in the catalyst mixture, a
light hydrocarbon feed is introduced by conduit 62 to a lower
portion of the dense fluid bed of catalyst 28 and above the
catalyst entrance to a catalyst stripping zone therebelow. The
light hydrocarbon feed may be a mixture of C.sub.1 -C.sub.3
hydrocarbons alone or in combination with a light naphtha boiling
range material. In the dense fluid bed 28 and riser 24, utilization
of the ZSM-5 type catalyst component is particularly promoted and
this is enhanced by maintaining the catalyst bed, for example, at a
temperature in the range of from about 500.degree.F. up to about
900.degree.F. The fluid bed of catalyst 28 is caused to move
generally downwardly into and through a catalyst stripping zone in
countercurrent contact with stripping gas such as steam introduced
to a lower portion thereof by conduit 64. Stripped hydrocarbon
products and stripping gas are removed from the upper portion of
fluid bed 28 and pass through one or more cyclone separators
represented by separator 66. Separated catalyst is returned to the
catalyst bed as by dipleg 68 with the separated vaporous material
passing into a plenum chamber 70 from which the vapors are
withdrawn by conduit 44.
Stripped catalyst obtained as above defined is then passed by
conduit 72 provided with catalyst flow control valve 74 to a bed of
catalyst 4 in the regeneration zone, thus completing the primary
circulation of catalyst through and between the regeneration zone
and the hydrocarbon conversion zones. However, as shown in the
drawing, additional catalyst may be withdrawn from regenerator
catalyst bed 4 as by conduit 80 containing flow control valve 82
for admixture with the suspension passing upwardly through riser 34
in a region for residual oil injection.
Provision is made for adding a diluent material with the recycle
oil as by conduit 76. An injection conduit 78 is also provided in
the lower portion of riser 34 for introducing recycle hydrocarbon
material initially or in addition to for admixture with catalyst
particles flowing upwardly through the riser. For example, it is
contemplated initially lifting the catalyst introduced to the
bottom of riser 34 with gasiform material alone as identified
hereinbefore to form a suspension which is contacted with recycle
oil feed introduced by conduit 78. On the other hand the recycle
feed may be split so that a portion is introduced by conduit 36
with or without gasiform materials with another portion of the
recycle oil feed being introduced by conduit 78. In any of these
arrangements, the conversion of the recycle oil feed may be
controlled as by catalyst to oil ratio employed to maximize
production of gasoline boiling range product or be restricted in
favor of producing product boiling above gasoline. Also the
conversion of the residual oil feed may be restricted over a
relatively wide range, depending upon the conversion conditions
selected for converting the recycle oil in the riser beneath the
residual oil injection point. In addition, the processing concepts
of this invention may be enhanced by subjecting the recycle oil
feed to a prehydrogenation treatment prior to the cracking thereof
in riser 34. Prehydrogenation of the recycle oil will operate to
reduce the coke forming characteristics of the oil charge by
hydrogenating polycyclic aromatics in the charge. Also the
prehydrogenation of the oil feed will reduce to a considerable
extent metal contaminants in the oil feed.
Referring now to FIG. II there is shown a stacked fluid cracking
system employing a plurality of riser reactors to effect conversion
of a recycle oil product of residual oil conversion and lower
boiling hydrocarbon straight run feed materials. In the arrangement
of FIG. II, a first riser reactor 1 is provided with hot
regenerated catalyst in the lower portion thereof by conduit 3
containing flow control valve 5. A hydrocarbon feed material such
as a recycle oil product of cracking a residual oil is introduced
to the riser by conduit 7 to form a suspension with the introduced
catalyst. A suspension of desired catalyst to oil ratio is formed
having a preselected conversion temperature designed to accomplish
conversion primarily to gasoline boiling products or to products
boiling above gasoline. The suspension formed as above identified
then passes upwardly through riser 1 under velocity conditions
providing a hydrocarbon reaction residence time within the range
herein identified. In a downstream portion of riser 1 provisions
are made for introducing a heavy hydrocarbon material such as a
residual oil in an amount to effect quenching of the conversion of
the recycle oil feed and its products of reaction. The heavy
hydrocarbon is introduced by conduit 9 to a manifold 11 providing
the plurality of spaced apart injection points for the quench oil.
Thus the residual quench oil may be introduced throughout the
length of riser 1 to provide the recycle oil with reaction
conversion residence time in the range of 1 to 6 seconds. The
suspension comprising catalyst and hydrocarbon material in riser 1
is discharged directly into cyclonic separation means 13 positioned
in the upper portion of a vessel 15. Vessel 15 is primarily a
catalyst collection and stripping hopper within which cyclone
separation means are retained. Catalyst separated in 13 is
withdrawn by dipleg 17 and passed to a dense fluid bed of catalyst
particles 19 therebelow. Hydrocarbon material separated from the
catalyst is withdrawn from separator 13 by conduit 21 and conveyed
to chamber 23 from whence it is withdrawn by conduit 25 for passage
to a product fractionator not shown.
A riser reactor 27 supplied with hot regenerated catalyst in a
lower portion thereof by conduit 29 containing flow control valve
31 is provided. A hydrocarbon feed is introduced to the lower
portion of riser 27 by conduit 33. The hydrocarbon feed introduced
by conduit 33 is preferably either a heavy virgin naphtha or a
light virgin gas oil. The feed thus introduced is combined with
introduced catalyst to form a suspension at a temperature in the
range of 1,000.degree.F. to about 1,200.degree.F. of desired
catalyst to oil ratio. The suspension then passes upwardly through
riser 27 under velocity conditions designed to achieve high
temperature octane improvement of the virgin naphtha and in the
case of light virgin gas oil a conversion thereof to gasoline
boiling range products. To control these conversions within the
limits desired, provision is made for introducing a heavy
hydrocarbon such as a residual oil to that portion of the riser as
quench to secure the desired conversion result. For example, quench
fluid is introduced by conduit 35 to a manifold provided with a
plurality of spaced apart injection conduits 37. Thus it will be
seen that conversion of the naphtha or light gas oil may be
obtained under very short reaction residence time before the quench
fluid is introduced and itself converted under the limited
conversion conditions as herein defined. The suspension thus
obtained is caused to move through riser 27 to a cyclone separator
39 positioned in the upper portion of vessel 15. Catalyst separated
in separator is conveyed by dipleg 41 to catalyst bed 19 and
hydrocarbon vaporous material is conveyed by conduit 43 to chamber
23. The risers used in the arrangement of FIG. II may be of the
same diameter or of different diameter. For example, riser 1 used
for converting the recycle oil feed may be of a larger diameter
than riser 27 used for converting the much lighter virgin feed
materials.
The catalyst collected in bed 19 is caused to move generally
downward through a stripping zone and countercurrent to stripping
gas introduced by conduit 45. A plurality of baffles 47 are
provided in the stripping zone comprising the lower portion of
vessel 15. The stripped catalyst is withdrawn by standpipe 49 and
conveyed to the lower portion of a riser regeneration zone. In this
embodiment the bottom open end of the standpipe is in matching
engagement with an adjustable plug valve 51 provided with stem 53
for adjusting the vertical height of the plug valve and thus the
rate of discharge of catalyst from standpipe 49.
The catalyst discharged from standpipe 49 is combined with hot
regenerated catalyst as more fully discussed below in an amount to
raise the temperature of the spent catalyst and promote the
combustion of carbonaceous deposits on the catalyst. Regeneration
gas such as air introduced by conduit 55 is passed to separate air
distributor means 57 and 59 for admixture with the catalyst in zone
61 and the conveyance thereof as a suspension upwardly through an
annular regeneration zone 63. The suspension in zone 63 may be
varied in density considerably by adjustment of air rates and/or
catalyst feed rate to zone 61. It is contemplated passing the
suspension upwardly through zone 63 as a relatively dilute catalyst
phase suspended in regeneration gas under catalyst regeneration
conditions of at least 1,000.degree.F. The suspension may also be
considerably more dense depending upon the amount of recycled
regenerated catalyst combined with the spent catalyst passed
upwardly through the annular regeneration zone. The suspension
discharged from the upper end of the annular regeneration zone is
separated into a catalyst phase and a combustion gas or flue gas
phase. Separation is effected by gravity and cyclonic means with
cyclonic separation being particularly relied upon when high
velocities are used in zone 63 for regenerating a relatively dilute
catalyst phase. Cyclonic separation is effected in a plurality of
suitable separators 65 provided with a dipleg 67. The catalyst
particles separated by cyclonic means and by gravity are collected
in an annular bed of catalyst 69 maintained in a relatively dense
fluid phase condition. Regeneration gas is introduced to the lower
portion of bed 69 by conduits 71 and 73. Regenerated catalyst is
withdrawn from the bottom of catalyst bed 69 by conduits 75 and 77
provided with flow control valves 79 and 81. Thus catalyst mix zone
61 is provided with hot regenerated catalyst by conduits 75 and 77
in an amount sufficient to raise the temperature of the spent
catalyst discharged from standpipe 49 up to a catalyst regeneration
temperature of at least 1,000.degree.F. Regeneration of the
catalyst is completed in fluid bed 69 with flue gases discharged
from the upper portion thereof mixing with catalyst and flue gas
discharged from the upper end of the annular riser regeneration
zone. Thus in the dispersed catalyst phase of the regenerator
between the riser outlet and the inlet to the cyclone separators
65, the conversion of carbon monoxide (CO) to carbon dioxide
(CO.sub.2) is promoted thereby heating the flue gases to an
elevated temperature and providing heat exchange with catalyst
particles in direct contact therewith before and during cyclonic
separation in separators 65. Thus the regeneration combination of
steps lends itself to the type of operation providing a relative
rapid circulation of catalyst through the riser regeneration stage,
the cyclonic separation stage, the dense fluid bed catalyst
regeneration stand and recycle of regenerated catalyst therefrom to
the riser regeneration step.
The combination of the present invention lends itself to the
processing of various hydrocarbon feed materials in addition to
those disclosed above to improve the product composition and/or the
product material for conversion to more desired products. For
example, in the arrangement of FIG. I it is contemplated initially
cracking a heavy catalytic naphtha in the lower portion of riser 78
before quench of the conversion reaction. On the other hand,
conversion of heavy naphtha may be accomplished alone in riser 24.
In the arrangement of FIG. II, heavy catalytic naphtha may be
subjected to a high temperature short contact recracking in either
riser 1 or riser 27 or in both risers before quench of the
conversion reaction with a heavier hydrocarbon feed material.
Cracking of such heavy naphtha product of cracking will provide an
octane improvement, a reduction in the product sulfur level, a
reduction in olefin content and generally improve the volatility of
the gasoline product.
On the other hand, a light hydrocarbon feed material in the C.sub.3
to C.sub.4 boiling range may be initially converted under selected
high temperature short contact time conversion conditions in the
riser reactors comprising 1, 27, 34 and 24 to form light olefins,
free radicals and aromatics. The light olefins and free radicals
that do not combine to form aromatics in the presence of the ZSM-5
catalyst component may undergo reaction with the heavier
hydrocarbon material charged to a downstream portion of the riser
and conversion products thereof.
It is also contemplated charging low octane light virgin naphtha,
atmospheric gas oil and heavy virgin naphtha to the risers above
identified to form alkylate feed material in addition to producing
high octane gasoline during high temperature cracking (of at least
1,000.degree.F.) of these feed materials. For example, the high
catalyst to oil ratios in combination with high catalyst
temperature and relatively short hydrocarbon residence time before
introduction of residual oil feed to the riser is particularly
suitable for accomplishing the results desired. It is also
contemplated charging coker naphtha or low octane reformate
material (such as 90 to 95 R+O (Research clear) octane material) to
such a high temperature riser cracking zone to raise the octane
level thereof in combination with producing alkylate feed
material.
Having thus provided a general discussion of the improved methods
and systems of the present invention and described specific
examples in support thereof, it is to be understood that no undue
restrictions are to be imposed by reason thereof except as defined
by the following claims.
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