Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
BACKGROUND O~ THE INVENTION
The field of catalytic cracking and particularly fluid
catalyst operations have undergone significant development
improvements due primarily to advances in catalyst
technology and product distribution obtained therefrom.
With the advent of high activity catalyst and particularly
crystalline zeolite cracking catalysts, new areas of
operating technology have been encountered re~uiring even
further refinements in processing techniques to take
advantage of the high catalyst activity, selectivity and
operating sensitivity. The present invention therefore is
concerned with a combination operation comprising hydro-
carbon conversion and regeneration of the catalyst employed
therein. In a particular aspect the present invention is
concerned with improving the technique of using a low coke
producintg crystalline zeolite hydrocarbon conversion
catalyst.
SUMMARY OF THE INVENTION
The present invention relates to the conversion of
hydrocarbon feed materials in the presence of high activity
fluidizable crystalline zeolite containing catalyst partic-
les and the regeneration of the catalyst particles to
remove deactivating coke deposits by burning. In a more
particular aspect the present invention is concerned with
the method and system for separating fluidizable catalysc
particles from gasiform products and particularly from a
high activity crystalline zeolite cracking catalyst under
more efficient separating conditions reducing the over-
cracking of conversion products and promoting the recovery
of desired products of a hydrocarbon conversion operation.
In yet another aspect, the invention is concerned with a
particular relationship of operating parameters coupled in
a manner promoting a suspended catalyst phase removal of
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S~ '
deactivating deposits of carbonaceous material from high
activity hydrocarbon conversion catalyst particles and
heating thereof to an elevated temperature. In a more
particular aspect the invention is concerned with the
separation and recovery of entrained catalyst particles
from gasiform products of a short contact time riser
hydrocarbon conversion operation.
Thus, a main embodiment of the invention relates to
a method for separating a suspension of catalyst particles
and gasiform material following traverse of a riser contact
zone which comprises, discharging the suspension outwardly
through openings beneath the upper closed end of said riser
and beneath radially extending restricted catalyst collect-
ing passageways open on the bottom side thereof and provid-
ing a substantially confined stream of collected catalyst
particles generally separate from discharged gasiform
material, said catalyst collecting passageways curved
downwardly adjacent the outer end thereof to induce a
downward moment on said confined catalyst stream in said
passageway for discharge directly downwardly into the open
upper end of a restricted catalyst downcomer passageway
positioned to maintain catalyst so collected and directed
out of further contact with discharged gasiform material,
and recovering catalyst particles so collected from the
bottom of said passageway for further use as desired.
The hydrocarbon conversion catalyst employed is pref-
erably a high activity crystalline æeolite catalyst of
fluidizable particle size which is transferred in sus-
pended or dispersed phase condition generally upwardly
through one or more riser conversion zones providing a
hydrocarbon residence time in each conversion zone in the
range of 0.5 to about 10 seconds and more usually less
Q~
than a~out ~ seconds. High temperature riser hydrocarbon
conversions of at least 1000F at 0.5 to 4 seconds hydro-
carbon residence time ln contact with the catalyst in the
riser is desirable for some operations before initiating
separation of vaporous hydrocarbon product materials from
the catalyst. Rapid separation of catalyst from hydro-
carbons discharged from a riser conversion zone is partic-
ularly deslrable Eor restricting hydrocarbon conversion
time. During the hydrocarbon conversion step, carbonaceous
deposits accumulate on the catalyst particles and the par-
ticles entrain hydrocarbon vapors upon removal from the
catalyst conversion step. The entrained hydrocarbons are
subjected to further contact with the catalyst until removed
from the catalyst with mechanical means and stripping gas in
a separate catalyst stripping zone. Hydrocarbon conversion
products separated from the catalyst and stripped materials
are combined and passed to a product fractionation step.
Stripped catalyst containing deactivating amounts of carbon-
aceous material hereinafter referred to as coke is then
passed to a catalyst regeneration operation.
The dense fluid catalyst bed regeneration operation of
the present invention accomplishes the removal of coke or
carbonaceous material deposited on the catalyst particles
by burning in the presence of oxygen containing regener-
ation gas. The recovery of available heat through such a
coke removal operation is an essential part 03c the cracking
operation. The regeneration technique of this invention
relies upon introducing deactivated catalyst into a dense
fluid mass of catalyst fluidi~ed by upflowing oxygen con-
taining regeneration gas. This dense fluif mass of catalystis superimposed by a more dispersed catalyst phase. A
relatively high temperature profile is maintained in the
catalyst regeneration operationO The upwardly flowing
regeneration gas velocity fluidizing the mass of catalyst
being regenerated is maintained within the range of 1 to 3
ft./second to obtain the desired contact of catalyst with
oxygen regeneration gas in an upper portion thereof to
particularly accomplish combustion of carbon monoxide in
the combustion gases.
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The high temperature profile of the regeneration
operation is promoted by mixing hot catalyst comprising
carbonaceous material recovered from a stripping operation
with a portion of a dense fluid bed of regenerated
catalyst so that upon contact with preheated oxygen
containing regeneration gas such as air, combustion of
carbonaceous deposits is rapidly promoted.
A significant observation contributing to the
operational concepts of this invention is the further
finding that a carbon monoxide oxidation promoter may be
added to the catalyst to be regenerated to promote the
recovery of available heat by promoting the burning of
carbon monoxide to carbon dioxide. In either a single
zeolite catalyst conversion operation or one employing
both a large and smaller pore crystalline zeolite,
the oxidation promoter may be charged to the catalyst in any
one of several different methods. In one arrangement the
oxidation promoter may be admixed with the smaller pore zeolite
component alone. The oxidation promoter may be added to
a stream of catalyst separated from a catalyst stripping zone,
in a riser contact zone maintained in the upper portion of the
stripper zones to a make up stream of catalyst, directly
to the coked catalyst in the stripping zone of the hydrocarbon
conversion operation. I~ is further contemplated maintaining
the temperature of any one of the above separated catalyst
streams below about 500F when contacted with the oxidation
promoter. It is also contemplated adding the oxidation promoter
in a relatively dilute liquid form by spraying it directly into
the bed of catalyst in the regeneration zone. The combination
5~
operation of the present invention lends itself particularly
well to obtaining a good mixing of the oxidation promoter by
adding it to an area of relatively high turbulence promoting
good mixing such as found immediately downstream or in the
throat of the spent catalyst flow control valve in the spent
catalyst standpipe. The oxidation component added may be one
selected from the group of metals and compounds thereof such
as copper, nickel, chromium, manganese oxide, copper chromite
and platinum group metals such as platinum, palladium, iridium,
osmium, rhodium, ruthenium and rhenium. The amount of promoter
added will vary with the component selected. It is preferred
that a relatively small amount of oxidation promoter be added
and the component selected should be one which does not undesirably
affect the hydrocarbon conversion operation. A particularly
useful component which may be added in small amounts for promoting
the combustion of carbon monoxide in an oxidizing atmosphere
is one of either platinum or palladium. When a small pore
crystalline zeolite such as a ZSM-5 crystalline zeolite is
employed with a larger pore zeolite such as a faujasite
2~ crystalline zeolite cracking component, the metal oxidation
promoter may be added to the mixture or to the small pore
crystalline zeolite alone with beneficial results since it does
not coke deactivate as readily as the larger pore zeolite. It
is important to use the metal carbon monoxide oxidation
promoter in a manner which will expose it to carbon monoxide
formed during burning of the carbonaceous deposits with the
oxygen containing regeneration gas. One suitable method for
accomplishing this purpose is to apply the oxidation promoter
directly to the coked surface of the deactivated or spent
.
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568
catalyst prior to introduction thereof to the regeneration zone.
This may be accomplished by any one of the methods identified
above,it being preferred to add the promoter to a cool stream
of catalyst passed to regeneration. The addition of an oxidation
promoter may be in amounts within the range of 0.1 to 100 parts
per million of oxidation metal component based on the final
catalyst composition employed. ~or platinum group metals
it is preferred to employ less than 10 parts per million of the
oxidation promoter based on the catalyst composition. The
platinum group metal may be added to or present with the
cracking catalyst as the metal, oxide, sulfide, halide, sulfate
or carbide form.
The regeneration zone or regeneration vessel
may take on substantially any shape generally cylindrical
f large diameter in a bottom portion and tapered to a smaller
diameter in an upper portion to provide a generally upflowing
catalyst regeneration operation. The regeneration zone is
preferably one which will provide the operating parameters
herein defined.
The regeneration technique and system of this
invention is aided to some considerable extent by mixing
regenerated catalyst particles with coke deactivated catalyst
particles in a ratio particularly promoting coke burning
temperature conditions. A dense catalyst bed phase regeneration
system superimposed by a more dispersed phase of catalyst
particles may be relied upon for promoting the burning of coke
and formed C0 to C02. This is particularly desired along with
the recovery of heat thus generated by the catalyst particles
dispersed in upflowing combustion gas and products thereof.
In such an upflowing catalyst regenera~ion operation the
oxygen containing regeneration gas stream is introduced to
the bottom of catalyst bed for flow upwardly through the
mass of catalyst comprising both spent and regenerated
catalyst under carbon burning condi-tions in the dense bed
o~ catalyst. Secondary regeneration gas may be added, i
desired, to an llpper portion of the large dense mass of
catalyst or a dispersed phase thereabove in the regenera-
tion zone. Preheating of the regeneration gas stream is
particularly desirable before contact with the low coke
producing crystalline zeolite catalyst so that the regen-
erated catalyst will not be undesirably cooled and a com-
bustion temperature of at least 1175F in the dense fluld
bed of catalyst in the regenerator will be rapidly
attained.
In the arrangement of the present inventionl it is con-
templated supplementing residual carbonaceous material such
,~,
as coke transferred to the regeneration system by the
introduction of torch oil thereto. In a particular aspect
it is contemplated adding torch oil alone or in admixture
with an oxidation promotor discussed above to the spent
catalyst passed to the regenerator or directly into the
dense fluid bed of catalyst in the regenerator. It is also ~ -
contemplated adding the torch oil to a regeneration air
line burner exit to aid with vaporization of the torch oil.
It will be recognized from the discussion herein
provided that a relatively delicate balance in operating
parameters is maintained to obtain desired burning of
available coke in either the dense or dispersed catalyst
phases, burning of carbon monoxide in the combustion flue
gases and the recovery by the catalyst of the available
heat thus generated in the operation. The operating
restrictions and parameters herein identified are dictated
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in substantial measure by the hydrocarbonaceous material
containing spent catalyst obtained from the hydrocarbon
conversion operation herein described.
In the hydrocarbon conversion portion oE the combina-
tion operation of this invention, it is desired to employ
a high activity crystalline zeolite conversion catalyst
such as a faujasite "Y" zeolite containing cracking
catalyst alone or in admixture with a smaller pore zeolite
such as a ZSM-5 class of crystalline zeolites. The hydro-
carbon conversion operation is preferably a dispersedcatalyst phase riser conversion operation of limited
hydrocarbon contact time between catalyst and hydrocarbon
reactant selected to particularly promote the formation
of desired products including gasoline boiling range
materials as well as lighter and higher boiling product
materials. Thus it is contemplated practicing the con-
version of gas oil feeds and higher boiling hydrocarbon
materials in a single riser reactor employing temperatures
in excess of 900~F and as high as 1050 or 1100F. In such
~0 hydrocarbon conversion operations, the catalyst-hydrocarbon
residence time in a riser reaction zone is usually restric-
ted to less than 15 seconds and is desirably restricted
depending on reaction temperature and feed composition
to within the range of 0.5 to about 8 seconds hydrocarbon
residence time. For the high temperature operations it
is preferred to restrict the hydrocarbon residence time in
contact with catalyst within the range of 2 to 5 seconds
and to minimize overcracking of desired products by effect-
ing a rapid separation of the suspension substantially
immediately upon discharge from the riser conversion zone~
Thus an important aspect of this invention is concerned
particularly with an apparatus modification and operating
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technique or method for obtaining a rapid separation of
a hydrocarbon catalyst suspension discharged from a high
temperature riser cracking zone.
The present invention is concerned with separating
a suspension discharged from a riser contact zone under
conditions restrictively collecting the catalyst particles
in a zone separate from discharged gasiform material and
altering the flow direction of the collected catalyst
particle to flow out of contact with gasiform material as
a downwardly confined stream. The collected and confined
catalyst particles stream thus separated as for example
from hydrocarbon products of catalytic conversion are dis-
charged into an open ended restricted downflow passageway
wherein the catalyst particles are maintained out of con-
tact with hydrocarbon vapors. The downflow passageway
referred to herein as a restricted downcomer collected
catalyst zone is positioned beneath the catalyst separ-
ation and collection means so that the separated and
confined catalyst stream is maintained out of further
contact with discharged hydrocarbon conversion vapors
during transfer to a catalyst stripping zone. By employ-
ing the concepts of this invention a vessel means housing
the upper end of the riser reactor or riser catalyst
regeneration may be reduced in cross section since the
catalyst arm separating arrangement herein described will
occupy less space then cyclonic separators attached to
the end of the riser reactor. In the arrangement of this
invention, the downcomer zone of restricted cross sectional
dimensions may be attached adjacent to the wall of the
riser, to the wall of the housing vessel or in some cases
positioned intermediate therebetween. In any of the
arrangements selected it is important to bear in mind
that minimizing the
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size of the housing vessel minimizes catalyst hold up.
It is important, however, to provide space adjacent the
riser outlet and beneath the disengager arm sufficient
for discharged hydrocarbon vapors to rapidly disassociate
anfl separate Erom suspended catalyst forming the confined
collected catalyst stream discharged into the downcomer
zone. The continued contact of hydrocarbon vapors with
catalyst discharged from the riser is avoided to some
considerable extent by the separakion and catalyst
collecting arrangement of this invention. The separation
can be further improved by the proper use of stripping
gas. For example, stripping gas may be passed upwardly
through areas of catalyst concentration as well as in the
areas relied upon for effecting the separation of hydro-
carbon vapors from catalyst immediately after discharge
from the riser. The arrangement of separation apparatus
of this invention tends to minimize the downward thrust
of separated hydrocarbon vapors and this can be further
offset by the use of upflowing stripping gas. Therefore,
it is contemplated employing stripping gas adjacent the
catalyst inlet to the downcomer zone for flow in the free
space between the downcomer zone and the riser reactor
outlet. Stripping gas employed as herein discussed is
recovered from the stripping zone and passes upwardly
through the housing vessel and into the cyclonic separa-
tors through which hydrocarbon vapors are recovered and
positioned in the upper part of the vessel above the riser
discharge.
In the drawings which illustrate this invention:
Figure 1 is a diagrammatic elevation of one embodiment
of the invention,
~l~Q56~ :
Fig~re 2 is a diagramrnatic elevation of a discharge
arrangement; and
Figure 3 is a top cross--sectional view of a riser.
Referring now to the Figure I, a hydrocarbon feed such
as gas oi] aLone or in admixture with a hi~her or lower
boiling feed material is introduced by conduit 2 to the
bottom of a riser conversion zone 4. Hot regenerated
catalyst in conduit 5 provided with flow eontrol valve 8
enters the bottom portion of riser 4 for admixture with
the oil feed to form a catalyst-oil suspension at an
elevated eonversion temperature of at least about ~00F.
and more usually at least 980F. or 1000F. The suspen-
sion formed is passed upwardly through the riser eonversion
zone 4 under elevated temperature hydrocarbon conversion
eonditions preferably at least 980F. promoting the erack- .
ing of the oil feed to lower and higher boiling products
including depositing earbonaceous material on the catalyst.
The gasiform produets inelude gasoline, boiling hydroear
bons, fuel oils and normally gaseous hydrocarbon products.
The gasiform hydrocarbon material with suspended catalyst
- particles may be maintained in the riser eonversion zone
for a hydrocarbon residence time within the range of 0.5
to 10 seconds. However, a hydrocarbon residence time
within the range of 0.5 to about 4 seconds may be employed
with particular advantage when using hydrocarbon convers-
ion temperatures of at least 1000F and up to about 1150F.
The suspension passed upwardly in the riser is discharged
from the upper end of the riser conversion zone through
peripheral openings positioned beneath two or more horizon-
tally radiating catalyst collecting arms 6. The arms areprovided with a curved inner surface promoting cyclonic
separation of catalyst particles from hydrocarbon vapors.
-12-
s~
A further modification to this discharge arrangement is
particularly shown in Figures II and III. Radial extending
arms 6 provided with a curved inner surface and catalyst
particle confining sidewalls is arranged to impart a cyclonic
concentration of catalyst particles promoting a forced
separation from hydrocarbon vapors discharged as a suspension
from the riser conversion zone. Thiscyclonic collection and
concentration of catalyst particles is used to reverse the
flow of the separated catalyst such that it is concentrated
as a downwardly flowing confined stream which discharges
generally downwardly and into the open upper end o~ a catalyst
downcomer chamber 8. In the arrangement of Figure I, chamber 8
is shown positioned adjacent to the wall of vessel lO. The
downcomer chamber 8 may be cylindrical, rectangular, semi-
cylindrical or any other suitable shape which will separately
retain the downwardly discharged catalyst stream in the confined
zone comprising the downcomer chamber and out of significant
further contact with hydrocarbon vapors. In the arrangement
shown, it is essential that adequate vapor disengaging space
be provided beneath arms 6 at the riser outlet and adjacent
the area of catalyst centrifugal separation which will
particularly promote the removal of separated vapors from out
of contact with discharged catalyst.
Separation of hydrocarbon vapors from the riser
discharged suspension is aided in considerable measure by
enlarging the riser peripheral discharge opening beneath arm 6
referred to above so that its cross-sectional area is at
least 1.5 times the cross-sectional area of the riser conduit.
Thus the combination of the inverted channel members open on
- its bottom side forming arm 6 with the enlarged vapor disengaging
5G8
space beneath the disengaging arm particularly facilitates the
rapid separation of vaporous hydrocarbon material from
suspended catalyst partlcles.
In the arrangement of Figure I, the catalyst collected
in downcomer chamber 8 is caused to flow to the lower portion
of the housing vessel or chamber 10 wherein a mass of
separated catalyst 12 is collected. This mass of collected
catalyst may be fluidized with a stripping gas such as steam
introduced to a bottom portion of the vessel by means not
shown or the mass of catalyst may be caused to flow inko a
separate external but adjacent stripping vessel 14 as shown in
Figure I. I~ is contemplated as shown in Figure II of introducing
stripping gas to a lower portion of the downcomer chamber 8 for
upflow therethrough. Stripping chamber 14 is particularly
provided and supplied with stripping gas by conduit 16. The
stripping charnber is provided with a plurality of downwardly
sloping baffle members which provide a tortuous path
for downflow of catalyst countercurrent to upflowing stripping
gas. Depending on the riser conversion temperature the catalyst
in stripping zone 14 is stripped at a temperature which is
from 50 to about 150 degrees below the riser conversion temperature.
It is preferred that stripping of the catalyst occur
at an elevated temperature which is less than 100 degrees
below the riser discharge temperature. The stripped catalyst
is passed downwardly through a pressure building standpipe 18
containing flow control valve 20 to a catalyst regeneration zone
22. In the arrangement of Figure I, the regeneration zone
is shown positioned substantially vertically below housing
vessel 10 which may or may not be on a common vertical axis
-14-
as desired. In any event, the standpipe 18 discharges into
a bed of' catalyst maintained in the lower portion of regenerati.on
zone 22 wherein it is maintained as a fluid bed of catalyst 24
ln a lower bottom portion of the regeneration vessel. Regeneration
gas such as air or an oxygen supplemented gas stream is introduced
by conduit 26 to a regeneration gas distributor manlfold 28
positioned cross-sectionally in a lower portion of the dense
fluid bed of catalyst in the regeneration zone. In the arrangement
shown, the stripped catalyst is discharged into an upper portion
of the fluid bed of catalyst for admixture with hot regenerated
catalyst therein. The stripped catalyst may be introduced
tangentially with respect to the regenerator cross-section and
preferably above an intermediate portion of the bed of catalyst.
In some arrangements it may be desirable to introduce it to
the bed of catalyst at its interface with a more dispersed phase
of catalyst thereabove. During regeneration the carbonaceous
material contaminated catalyst stripped of entrained hydrocarbon
vapors is heated by admixture with regenerated catalyst and
raised to a temperature sufficient to initiate burning of
carbonaceous material thereby producing carbon monoxide
as well as carbon dioxide containing flue gases. Carbon
monoxide formed during the combustion of carbonaceous deposits
by oxygen is desirably further oxidized to improve the heat
recovery by the catalyst in the regeneration operation. The
combustion of carbonacecus deposits will occur at a temperature
above about 1150F and the regenerated catalyst will be heated
during such combustion operations to a temperature within the
range of 1300 to 1400F. It is particularly desired to accomplish
the above oxidation reactions comprising catalyst regeneration
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56~3
in the dense fluid phase of catalyst particles as well as in the
more dispersed fluid phase of catalyst particles thereabove.
It is particularly desired to minimize carbon monoxide combustion
in the regenerator cyclone separators 30 and 32 in the upper
portion of the regeneration zone 22 by effecting complete
combustion of combustibles in the dense and dispersed catalyst
phases. Cyclonic separators 30 and 32 are sequentially
arranged for flow of flue gas therethrough. The flue gas
separated from catalyst fines in each cyclone separator
passes into a plenum chamber 34 before being withdrawn by
conduit 36. Catalyst fines separated in the cyclonic separators
are returned to the dense fluid bed of catalysts by suitably
provided catalyst diplegs.
Regenerated catalyst at a temperature of at least
about 1300F is withdrawn from a lower portion of the dense
fluid bed of catalyst 24 as by conduit 38 provided with a
catalyst flow control valve 8. The withdrawn regenerated
catalyst is passed to the bottom lower portion of riser 4
for use as discussed herein before. The outlet to catalyst
withdrawal standpipe 38 is shown positioned above manifold 28.
However, the inlet may be positioned in another portion of the
dense fluid bed of catalyst which will provide regenerated
catalyst of desired characteristics for withdrawal therefrom.
Provisions may be provided although not shown for adding a
secondary regeneration gas stream to the fluid bed
cf catalyst above manifold 28 to assist with the removal
of carbonaceous material from the catalyst particularly when
discharging the catalyst adjacent the upper dense fluid
catalyst bed interface. In any of the arrangements herein
discussed it is important to promote the oxidation of
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carbon monoxide and this may be accomplished by the addition
of a carbon monoxide oxidation catalyst promoter
as herein described. The upper portion of vessel 10 is
provided with sequentially arranged cyclonic separators 40
and 42 communicating with withdrawal conduit 44 for passing
hydrocarbon vapors to a product fractionator not shown.
The present invention is particularly concerned
with apparatus arrangements and concepts for effecting
a rapid separation of a gasiform hydrocarbon material-catalyst
suspension discharged from a riser conversion zone.
The concepts of this invention find particular application
in riser reactor and riser regenerator arrangements of the
most recent and modern design particularly concerned with
minimizing catalyst inventory in the system or apparatus
employed as well as the contact time between gasiform reactant
and catalyst. In such systems, the vessels and interconnecting
piping are sized to accommodate a given capacity operation
within the operating constraints desired and such a system
of modern design often limits any excess space for additional
separating equipment. The present invention is concerned with
such systems and the arrangement of apparatus for particularly
accomplishing a rapid separation of a suspension discharged
from a riser reactor zone.
Figure II shows one expanded specific arrangement
of apparatus in elevation for effecting separation of a
suspension discharged from a riser zone into a hopper vessel
of restricted dimensions. It is not essential that the hopper
vessel be so restricted in cross-sectional dimensions since
the concepts of this invention may be broadly employed with
: ;
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equal advantage also in larger vessels.
In the arrangement of Figure II there is shown
diagrammatically the upper end of a riser hydrocarbon conversion
zone 50 extending upwardly into a hopper vessel 52. The riser
terminates in an upper intermediate portion of vessel 52 with a
horizontal and shaped cross member arm referred to as a cross
arm disengager means 54. The disengager arm means 54 is
preferably a combination of two or more arms such as 2 plurality
of arms extending generally horizontally outward from the
upper capped end 68 of the riser. The disengager arm
shaped as shown in Figures II and III extends outwardly from
the riser above opening 56 in the upper periphery of the
riser. The bottom side of the disengager arm is in open
communication with vapor disengaging space therebelow and opposite
outlets 56. The arms are provided with a downwardly sloping
curved surface area 58 adjacent the outer ends thereof.
Positions beneath and spaced apart or adjacent the disengager
arm is an open ended catalyst collecting vessel 60 of cross-
sectional dimensions adequate to retain the separated catalyst
stream for unrestricted downflow therethrough. On the other hand
vessel 60 may be provided with a plurality of stripping
trays 62. Stripping trays 62 may be solid baffle members or
perforated baffle members to allow stripping gas to pass upwardly
through or around the trays into contact with the catalyst. Conduit
means 64 and 66 are provided for introducing stripping gas
such as steam to a lower portion of the catalyst collecting
vessel 60. As shown in the drawing the upper open end of the
vessel 60 is enlarged to provide a funnel shaped collecting zone
for catalyst discharged downwardly from the disengaging arm.
-18-
This funnel arrangement should not be so large as to encourage
entrainment of hydrocarbon vapors.
When using the apparatus cr Figure II, a suspension of
fluidizable catalyst particles in gasiform material such as
hydrocarbon vapors ls caused to flow upwardly through riser 50
and outwardly through openlng 56 beneath the disengaging arm 54.
Since the top of the riser is capped by a solid member 68,
the catalyst portion of the suspension is concentrated in the
end thereof and caused to flow outwardly through arm 54 from
opening 56. The discharged catalyst is particularly confined
within the limits of the inverted "U" shaped disengaging arm 54
thereby forcing a separation of catalyst from hydrocarbon vapors.
The abrupt change in direction of the suspension from vertical
upflow to horizontal flow and then to a downPlow pattern by internal
curved surface 58 establishes a centrifugal moment of
catalyst flow on the discharged catalyst thereby concentrating
the catalyst particles on the upper side of arm 54 and along
the curved surface 58 for discharge downwardly into the open
upper end of vessel 60. The gasiform part of the suspension
comprising hydrocarbon vapors thus centrifugally separated from
entrained catalyst particles in the disengaging space provided
in conjunction with centrifugal disengagement means moves
out from under the open disengager arm into a lower velocity
region and in~o an upper portion of the vessel of reduced gas
velocity. The vapors thus separated pass upwardly to the
inlet of cyclonic separating equipment 70 and 72 shown
positioned in the upper part of vessel 52. Cyclone separators
70 and 72 may be single stages of cyclone separator or sequentially
arranged primary and secondary stages of cyclonic separating
equipment such as shown in Figure I. Separated vaporous
19 -
or gasiform material is withdrawn and passed to fractionation
(not shown) by conduit 78. The cyclones may be located within
the vessel as shown or outside the vessel if space is at a
premium. The cyclones are provided with catalyst carrying
diplegs which extend downwardly into a lower or bottom portion
of vessel 52. The bottom open end of the dipleg may be immersed
in a bed o~ catalyst particles collected in the lower portion
of the vessel or they may terminate above the normal angle of
repose of a bed of collected catalyst and be provided with
spaced apart baffle means 80 supported by rod means 82 or flap
valve means which retard the flow of catalyst and significant
amounts of gasiform material passing upwardly through the
downcomer. Catalyst particles collected in the lower portion
of vessel 52 as a bed of catalyst may be withdrawn by side
conduit means 74 as shown for passage to a stripping zone as
shown in Figure I. Vessel 52 may be modified in a bottom
portion thereof to provide an elongated annular stripping
zone about the riser before withdrawing stripped catalyst
for passage to a catalyst regeneration zone. The arrangement
of Figure II is particularly concerned with providing
separating means for reducing the contact time encountered
between catalyst and hydrocarbon vapors after discharge from
a riser conversion zone. The apparatus of Figure II promotes
the separation of catalyst from gasiform hydrocarbon vapors,
the separate confinement of separated catalyst out of contact
with hydrocarbon vapors and the removal of vaporous material from
the segregated catalyst. This serves to significantly reduce
undesired extended overcracking of products of the riser
cracking zone.
-20~
In the combination operation of this invention
the efficient separa~on of catalyst from gasiform
materials in the cyclonic separators is enhanced by
employing gas velocities of at least 50 ft./sec. and
preferably gas velocities of at least 60 ft./sec~ The
suspension separation arrangement at the riser outlet
contributes in substantial measure to achieving the results
desired as expressed above. Thus it is contemplated employing
two or more disengaging arms, such as three or four equally
spaced apart radially extending arms from the upper end of
the riser. Also, the catalyst collecting or downcomer
chamber may be an annular chamber when several disengaging
arms are employed on a separate chamber associated with each
arm is positioned to maximize the recovery of separated
catalyst particles to the substantial exclusion of gasiform
hydrocarbon product of riser conversion. The open ended
catalyst collecting vessel is preferably hung with respect
to the downwardly thrust catalyst stream to maximize vapor
disengaging space adjacent the riser wall. Adequate vapor
disengaging space provided below arms 56 and intermediate
the dowrlcomer vessel and the riser wall promotes the
separation particularly desired. The particular location
of the downcomer will depend on the length of the disengaging
arm and the diameter of the hopper vessel about the upper end
of the riser. In the arrangements herein identified substantial
hydrocarbon vapor disengaging space is provided beneath
the catalyst disengager arm, the top of the catalyst collecting
chamber and the wall of the riser conversion zone so that the
flow characteristics of the separated vaporous material may be
substantially changed in direction and velocity from further
contact with the catalyst.
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56~3
Figure III shows a top cross sectional view of the
riser 50 of Figure II with two horizontally positioned disengager
arms 54 in relationship to cylindrical catalyst collector downcomer
vessels 60 positioned beneath the outer extremity of the
disengager arm.
Havlng thus generally the concepts 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.
