Catalytic cracking unit with combined catalyst separator and stripper

A catalytic cracking apparatus is provided for cost-effectively separating and stripping hydrocarbon from catalyst while limiting the occurrence of undesired catalytic overcracking and thermal cracking reactions. The apparatus includes a reactor, a combined gross separator and catalyst stripping vessel, and a disengaging vessel. The combined vessel is positioned to quickly separate catalyst from reactor products, reduce catalytic overcracking and strip volatile hydrocarbon from coked catalyst in one unitary vessel. The disengager is designed to dampen the flow of grossly separated hydrocarbon, substantially separate catalyst fines from the grossly separated hydrocarbon, and convey the catalyst fines to the combined gross separation and catalyst stripping vessel.

BACKGROUND OF THE INVENTION 
1. Field of Invention 
This invention relates to an apparatus for the separation of catalyst from 
hydrocarbon in a fluid catalytic cracking unit (FCU). 
2. Background 
Gasoline and distillate liquid hydrocarbon fuels are the primary finished 
products for most petroleum refiners. These fuels boil in the range of 
about 100.degree. F. to about 650.degree. F. However, the crude oil from 
which these fuels are derived can often contain from 30 to 70 percent by 
volume hydrocarbon boiling above 650.degree. F. The process of fluid 
catalytic cracking breaks apart high boiling point, high molecular weight 
molecules into lower boiling point, lower molecular weight products that 
can be blended into gasoline and distillate fuels. 
Fluid catalytic cracking units operate through the introduction of a hot 
fluidized catalytic cracking catalyst into a high molecular weight feed at 
the upstream end of a riser reactor. Once contacted with the hot catalyst, 
the feed is vaporized, carrying a suspension of catalyst and hydrocarbon 
up through the riser reactor. The hot catalyst supplies all or a major 
portion of the heat necessary to vaporize the hydrocarbon feed and to 
carry out the endothermic catalytic cracking reaction. 
The suspension of catalyst and hydrocarbon vapor passes up the riser 
reactor at high velocity. However, due to the high activity of the 
catalyst, the cracking reaction generally proceeds to the desired extent 
prior to or upon reaching the upper or downstream end of the riser 
reactor. The cracked hydrocarbon must then be separated from the catalyst 
and further processed into upgraded products. The catalyst, which has 
accumulated coke in the cracking reaction, must be stripped to remove 
extraneous hydrocarbons and regenerated prior to reintroduction into the 
riser reactor. Apparatus improvements in this separation and stripping 
stage is the subject of this invention. 
Many catalytic cracking advancements have been made in the area of catalyst 
separation, catalyst stripping, and prevention of undesired catalytic 
reactions. Some catalytic cracking equipment had bed crackers with sloped 
risers. The sloped riser performed the function of carrying the oil and 
catalyst to the catalyst bed where most of the reaction occurred. Slower 
catalytic reaction times facilitated the operation of bed crackers and 
were a result of the lower activity catalyst prevalent at the time and 
lower reaction temperatures. Catalyst separation from hydrocarbon was 
performed in cyclones erected in the reaction vessel. Quick disengaging of 
catalyst from hydrocarbon was not as necessary to prevent undesired 
overcracking reactions due to the lower catalyst activity and reaction 
temperatures. Catalyst stripping was performed in a stripper section 
communicating with the catalyst bed. 
As crude costs increased, gasoline volume and octane requirements remained 
strong, and the phase out of lead from gasoline took effect, refiners 
stepped up cracking catalyst development efforts. High activity catalysts, 
particularly crystalline zeolite cracking catalysts, were developed, 
followed by processing techniques and equipment permitting higher reactor 
temperatures. However, as reaction temperatures and catalyst to oil ratio 
were increased, it was observed that much of the desired catalytic 
reaction was occurring in the riser. Refiners began building facilities 
that were designed to perform the cracking reactions in the riser. The 
fundamental change in apparatus featured longer, more vertically 
positioned riser reactors, which resulted in more effective catalyst to 
oil mixing. The vertical riser facilities reduced undesirable light gas 
production, increased conversion to light products, increased gasoline 
octane, and lowered undesirable coke production. 
An unexpected penalty associated with higher catalyst activity and higher 
reactor temperatures was the occurrence of catalytic overcracking and 
thermal cracking. Unless the catalyst was quickly removed from the 
hydrocarbon, undesirable overcracking reactions would occur, reducing 
gasoline yield and increasing light gas production. Older prior art 
catalytic cracking units were not equipped to mitigate this condition. 
Newer facilities began to recognize the problems associated with 
overcracking and thermal cracking and included roughcut cyclone separation 
erected in close proximity to or communicating with the riser reactor to 
help reduce the problem. 
In some types of catalytic cracking units, the riser penetrates the center 
of the disengager vessel. These units afford quick separation of catalyst 
from oil by positioning an inverted can over the riser outlet. The 
catalyst and hydrocarbon is directed downwards where the catalyst is 
directed towards a stripping section positioned immediately below the 
disengaging section of the disengager vessel or to a separate stripper 
vessel. The hydrocarbon pressures back through the inverted can and is 
further separated from catalyst in secondary cyclones prior to exiting the 
disengager. The extended hydrocarbon flow pattern between the inverted can 
and the secondary cyclones permits undesirable thermal cracking reactions 
to occur at high reaction temperatures and detracts from the utility of 
center riser designs. 
The center riser facility also can have a completely enclosed internal 
"hot-wall" roughcut separator and secondary cyclones. Enclosed "hot-wall" 
roughcut separator designs translate into more costly and time-consuming 
maintenance. Prior art internal "hot-wall" vessels require more expensive 
metallurgy, thicker steel, exotic refractory and erosion protection, as 
well as more costly rigging to assemble the cyclone within another vessel 
than the external cyclone alternative. Moreover, internal cyclone failures 
in hot-wall vessels are difficult to visually detect. Repairs are also 
more difficult to perform, usually requiring unit shutdown as well as 
long, time-consuming preparation steps prior to and upon entry into the 
disengager vessel. 
Some prior art catalytic cracking units have an external positioned 
vertical riser with a closely connected external roughcut separator. Such 
units provide quick separation of catalyst from oil by the close proximity 
of the roughcut separator to the riser outlet. However, the apparatus is 
more expensive to build due to additional ductwork and plot space 
requirements. 
Other prior art catalytic cracking units have been employed to address many 
of the objectives and problems noted above, each with varying degrees of 
success and limitations. 
Anderson et al., U.S. Pat. No. 4,043,899, describes internal cyclones which 
have been modified to include cyclonic stripping of catalyst separated 
from hydrocarbon vapors from a center riser catalytic cracking unit. 
Parker et al., U.S. Pat. No. 4,455,220, describes a single vessel cyclone 
separator and stripper assembly having a vortex stabilizer mechanism 
separating the two vessel sections. The Parker design also has a secondary 
cyclone connected directly to the single vessel roughcut cyclone outlet 
without benefit of a disengaging space. While the design features less 
equipment and can be built for a lower cost, the generically nonuniform 
flow of riser reactors can pose difficulties for these systems. When the 
riser outlet flow surges upwards, roughcut separation efficiency is 
greatly reduced and excessive amounts of hydrocarbon can drop down to the 
stripper section while excessive amounts of catalyst spew out the top of 
the cyclone. This continuous cycling results in undesired overcracking in 
the roughcut cyclone hydrocarbon outlet and the potential for catalyst 
defeating the secondary cyclone and breaking through to downstream 
equipment. 
SUMMARY OF THE INVENTION 
It is an objective of this invention to provide an improved apparatus for 
reliably separating catalyst from hydrocarbon that capitalizes on the 
maintenance and reliablity advantages of external separation, reduces 
thermal cracking, compensates for the nonuniformity in flow from 
riser-reactors and the adverse effects of flow swings on cyclone 
performance, and achieves these results at minimum cost and complexity. 
It is an additional object of this invention to provide an improved 
apparatus for thoroughly and reliably stripping volatile hydrocarbon from 
coked catalyst, that provides adequate disengaging space and stripping gas 
access, while not requiring excessive facilities. 
The present invention achieves the above objectives by providing: a reactor 
which contacts a hydrocarbon feed with catalytic cracking catalyst at 
catalytic cracking conditions to produce a suspension of hydrocarbon 
product and coked catalyst; disengager means including a product inlet and 
a hydrocarbon gas outlet; and external means positioned outwardly of and 
communicating with the reactor and the disengager means. The external 
means include a separator means for grossly separating the coked catalyst 
from the hydrocarbon product and also include stripper means for 
substantially removing volatile hydrocarbon from the coked catalyst. 
The disengager means desirably comprises a substantially upright 
disengaging vessel for dampening the swings in flow of roughly separated 
hydrocarbon and substantially disengaging and separating coked catalyst 
from the hydrocarbon product. The disengaging vessel desirably contains at 
least one internal cyclone separator. 
Preferably, a hydrocarbon quench injector is provided on the roughcut 
cyclone hydrocarbon outlet to the disengager vessel. In the preferred 
embodiment, the quench comprises light catalytic cycle oil and/or a heavy 
catalytic cycle oil. 
In the preferred form, the external means comprises a single unitary vessel 
having an upper external roughcut cyclone separation section with a 
roughcut cyclone and a lower catalyst stripping section spaced below the 
upper cyclone separation section. The upper external roughcut cyclone 
separation section has a product outlet and a coked catalyst outlet to the 
catalyst stripping section. The lower catalyst stripping section is 
positioned to strip volatile hydrocarbon from the coked catalyst from both 
the external roughcut cyclone separation section and the disengager 
vessel. 
The invention can be configured as an original installation or as a 
retrofit to an existing fluid catalytic cracking facility. 
A more detailed description of the invention is provided in the following 
specification and claims taken in conjunction with the accompanying 
drawing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention provides an improved catalytic cracking unit 
apparatus and process for cost-effectively and reliably separating and 
stripping hydrocarbon from catalyst to achieve a substantially 
catalyst-free hydrocarbon product while limiting the occurrence of 
undesired catalytic overcracking and thermal cracking reactions. 
The process of catalytic cracking and the present invention in particular 
begins with a high boiling catalytic cracker feedstock which generally 
comprises a mixture of distillate range material boiling between 
430.degree. F. and 650.degree. F., gas oil range material boiling between 
650.degree. F. and 1000.degree. F., and resid range material boiling at 
greater than 1000.degree. F. The feedstock, also referred to as 
hydrocarbon feed, high molecular weight feed, and gas oil feed is 
generally dominated by the gas oil fraction. The hydrocarbon feed line 1 
of the Figure connects at point 1A to vertical upright riser reactor 3. 
The riser reactor comprises a substantially vertical tubular riser 
reaction zone 3A. The hot regenerated fluidized catalytic cracking 
catalyst is supplied to the vertical riser reactor 3 from the regenerator 
4. Hot catalyst flows from the regenerator 4, through a catalyst feedline 
or standpipe 5, through two standpipe catalyst slide valves 6, and curved 
J-Bend 7, prior to entry into the vertical riser reactor 3. The catalyst 
is generally supplied at temperatures ranging from 1000.degree. F. to 
1500.degree. F. 
Suitable hydrocarbon cracking catalysts for use in the practice of this 
invention include those of the amorphous silica-alumina type having an 
alumina content of about 10 to about 50 weight percent. Catalysts of the 
silica-magnesia type are also suitable which have a magnesia content of 
about 20 weight percent. Preferred catalysts include those of the 
zeolite-type which comprise from about 0.5 to about 50 weight percent and 
preferably from about 1 to about 30 weight percent of a crystalline 
aluminosilicate component distributed throughout an amorphous matrix. 
Zeolite-type cracking catalysts are preferred because of their thermal 
stability, high catalytic activity and selectivity. 
Catalyst addition to the vertical riser reactor is controlled by the two 
catalyst slide valves 6. If desired, one catalyst slide valve can be used. 
Catalyst addition through the standpipe slide valve 6 is generally 
controlled to target a combined catalyst and oil vertical riser reactor 
outlet 8 temperature. To reach higher reactor temperatures, the ratio of 
catalyst to oil is generally higher, hydrocarbon conversion is increased, 
and the potential for undesirable catalytic overcracking and thermal 
cracking reactions is increased. At lower vertical riser reactor 
temperature targets, the standpipe slide valves 6 constrict, reducing the 
catalyst to oil ratio, lowering hydrocarbon conversion, and reducing the 
potential for undesirable catalytic overcracking and thermal cracking 
reactions. Conversion for the purpose of this patent application is 
defined as the percentage, by weight, of feed boiling over 430.degree. F. 
converted to products below 430.degree. F. and coke. 
The vertical riser reactor 3 is where most of the catalytic cracking 
reaction substantially takes place. Hydrocarbon feed is substantially 
vaporized upon contact with the hot catalyst and the catalyst and vapor 
suspension catalytically react as the hydrocarbon stream proceeds up the 
vertical riser reactor 3 to produce an upgraded catalyst-laden product 
stream of catalytically cracked hydrocarbon (oil vapors) and coked spent 
cracking catalyst comprising larger coked cracking catalyst particulates 
and smaller coked cracking catalyst fines. The catalyst accumulates coke 
in the process of converting the hydrocarbon to lighter products. 
Not all industry fluid catalytic crackers feature vertical riser designs. 
Some refiners are still using sloped riser bed crackers. Vertical risers 
are generally preferred by most refiners since vertical risers improve 
catalyst and hydrocarbon mixing, reduce coke production, and reduce the 
period of hydrocarbon vaporization increasing reaction time available in 
the riser for the desired cracking reactions. Vertical risers also result 
in lower riser wall temperatures which reduces undesired light hydrocarbon 
gas production and prolongs riser life. 
Upon reaching the top 8 of the vertical riser reactor 3, the coked catalyst 
and vapor suspension passes through a horizontal linkage line 9 to 
external means comprising an external elongated, upright combined unitary 
stripper and cyclone vessel 10. The horizontal linkage line 9 length is 
minimized to reduce the coked catalyst in oil resonance time to 
substantially eliminate undesired catalytic overcracking and thermal 
cracking reactions. 
The external elongated upright combined unitary vessel 10 includes an upper 
external roughcut or grosscut separation section 11 providing a gross 
separation means with a roughcut gross cyclone, also referred to as a 
grosscut cyclone, in the upper portion of the vessel 10 and a lower coked 
catalyst stripping section 12 providing stripping means with a stripper in 
the lower portion of the vessel 10. The roughcut gross cyclone grossly 
separates the coked catalyst particulates from the catalyst-laden product 
stream, as well as from recycled volatile hydrocarbon products as 
explained below, to produce a grossly separated particulate lean stream of 
hydrocarbon and a grossly enriched stream of coked catalyst particulates. 
The horizontal linkage line 9 communicates with the roughcut cyclone 
section 11 tangentially to create swirling action necessary for 
particulate separation. The stripper removes and strips volatile 
hydrocarbon from the grossly separated particulate enriched stream of 
coked catalyst particulates as well as from the disengaged coked catalyst 
fines, as explained below, by directing the coked catalyst along a 
convoluted path in the presence of stripping steam, leaving volatile 
hydrocarbon products and stripped coked catalyst. 
Since the external roughcut cyclone section 11 is combined with stripper 
section 12, it is important that the vortex action of the cyclone does not 
conflict with the operation of the stripper section. Should the tail of 
the vortex extend to the coked catalyst dense bed phase 13, coked catalyst 
could be fluidized back into the external roughcut cyclone section, 
reducing cyclone efficiency. Extension of the vortex tail could also 
disrupt the dense bed coked catalyst level 14. This level must remain 
steady since it is often utilized to control at least one of the two 
stripper slide valve positions 15. 
The unitary vessel 10 provides a dual function external means which is 
designed to accommodate both separation and stripping functions by proper 
dimensioning of the vessel itself, the cyclone separator design, and the 
horizontal linkage line. It is important to provide sufficient distance 
between the tail of the vortex and the stripper section dense bed level in 
order to maintain cyclone performance and hold a steady dense bed coked 
catalyst level 14. The following formula provides the calculation for 
vortex length and the design parameters available to ensure sufficient 
space between the vortex tail and the coked catalyst dense bed level. 
Vortex Length=2.3 DE(DC.sup.2 /(AB)).sup.1/3 where: 
DE is the cyclone hydrocarbon outlet diameter 
DC is the cyclone diameter 
A is the cyclone inlet duct width 
B is the cyclone inlet duct height. 
An annular frusto conical deflector 16 is provided as an additional barrier 
between the vortex tail and the coked catalyst dense bed level 14. The 
annular deflector 16 comprises a tubular frusto conical baffle with an 
upwardly slanted converging sidewall 16A designed to channel volatile 
hydrocarbon upwardly through a central opening (hole) from the stripping 
section 12 and recycle the hydrocarbon back through the center of the 
cyclone 11. Channeling hydrocarbon concentrically through the cyclone 
center minimizes disturbance to coked catalyst flowing downward the 
cyclone inner wall 17. The downwardly diverging flared sidewalls 16B of 
the annular deflector 16 provide a skirt which is spaced from and 
cooperates with the cyclone inner wall 17 to form an annular catalyst 
passageway therebetween for annularly passing and dispersing the catalyst 
downwardly and outwardly at an angle of inclination ranging from 15 
degrees to 75 degrees relative to the vertical axis of the vessel 10 and 
in a diverging manner into the baffled stripper section 12. The stripped 
volatile hydrocarbon product is channeled and passed upwardly through the 
central opening of the deflector 16 in countercurrent flow relationship to 
the downwardly passing grossly separated annular particulate-enriched 
stream of coked catalyst particulates, so as to pass and be recycled to 
the grosscut cyclone in the upper separation section 11 of the vessel 10. 
The upward stream of hydrocarbon product flows generally along and about 
the vertical axis of the vessel 10 and is substantially concentric to and 
annularly surrounded by the downward flow of the grossly separated 
particulate-enriched stream of coked catalyst particulates along and 
outwardly of the skirt of the deflector 16. 
Some prior art catalytic cracking units have gross cyclone separation 
sections which are designed to be internal to the disengager vessel. 
Internal gross cyclone separation sections can be used for quick 
separation of coked catalyst from the oil upon exiting the riser outlet. 
The present invention provides for quick coked catalyst separation while 
not incurring the penalties of an internal separator design. 
Internal separator designs translate into more costly and time-consuming 
maintenance. Internal "hot-wall" vessels require more expensive 
metallurgy, thicker steel, exotic refractory and erosion protection, as 
well as more costly rigging to assemble the cyclone within another vessel 
than the external cyclone alternative. Moreover, internal cyclone failures 
in hot-wall vessels are difficult to visually detect. Repairs in hot-wall 
vessels are also more difficult to perform, usually requiring shutdown as 
well as long, time-consuming preparation steps prior to and upon entry 
into the disengager vessel. 
The stripper section 12 is also contained in the combined unitary vessel 10 
comprising the external means. The stripper section 12 is positioned at 
the bottom portion of the vessel 10 below the upper external roughcut 
cyclone separation section 11. In the preferred embodiment, the stripper 
section 12 has an array of internals comprising alternating tiers of 
conical baffles 20 with the peaks of the conical baffles facing upwards. 
The baffle design causes the coked catalyst to follow a convoluted flow 
path increasing contact and countercurrent exposure between the stripping 
gas and the coked catalyst, effecting a more thorough removal of volatile 
hydrocarbon product from coked catalyst. The stripping section has an 
upper dilute phase stripping area 21 located between the annular deflector 
16 and the dense bed coked catalyst level 14 and a lower dense bed 
stripping area 22 located below the dense bed coked catalyst level 14. 
Stripping gas can be injected by one or more stripping gas injectors 23 at 
any level within the lower dense bed stripping area 22, although the 
preferred embodiment features a stripper gas injector 23 located below the 
bottom conical baffle 41. The preferred stripping gas is steam for best 
results. 
The upper external roughcut cyclone separator hydrocarbon product outlet 
19, also referred to as cyclone product outlet and tubular crossover, 
extends upwardly from the vessel 10, looping back down via an inverted 
semicircular U-shaped section 19A to a substantially horizontal tubular 
duct section 19B, prior to entering an upright vertical disengager vessel 
18. The inverted semicircular U-shaped loop 19A is provided as a means of 
accommodating expansion at temperatures that often exceed 1000.degree. F. 
Connected to the cyclone product outlet 19 is the quench injector 24 which 
is provided to inject a cycle oil quench, such as light catalytic cycle 
oil (LCCO) or heavy catalytic cycle oil (HCCO), into the product stream 
after gross separation of coked catalyst therefrom so as to reduce the 
occurrence of thermal cracking reactions in the hydrocarbon product. This 
is achieved by positioning the quench injection line (injector) 24 at a 
location on the downward bend of the downstream leg of the inverted 
U-shaped loop 19A to permit operation at high riser temperatures and 
higher resultant catalyst to oil ratios while concurrently quenching the 
cyclone product outlet stream immediately after rough catalyst removal and 
before substantial undesired thermal cracking reactions can occur. 
Hydrocarbon quench is most effective when injected immediately after 
roughcut catalyst separation since less reaction time is provided for the 
undesired thermal cracking reactions to occur. In addition, less quench 
volume is required to perform an equivalent magnitude of quenching when 
the hot catalyst has been removed first. Excessive quench volume, beyond 
that necessary to substantially eliminate undesired thermal cracking 
reactions is energy inefficient and can limit downstream fractionator 
capacity. A direct enclosed hydrocarbon conduit such as the external 
roughcut cyclone outlet 19 in the present invention, is the preferred 
structure for quench injection since this injection point is external, 
accessible, and substantially contains the entire hydrocarbon product 
stream immediately after roughcut separation. The preferred conduit 19 can 
also be cost-effectively retrofitted with quench injectors on stream or on 
unit shutdown. 
The quench itself can include light catalytic cycle oil (LCCO), heavy 
catalytic cycle oil (HCCO), heavy catalytic naphtha, light coker gas oil, 
coker still distillates, kerosene, hydrotreated distillate, virgin gas 
oil, heavy virgin gas oil, decanted oil, resid and water. The quench 
stream is preferably HCCO and most preferably LCCO for best results. 
The upper external roughcut cyclone separator 11 is designed to accommodate 
a high coked catalyst loading. While the external roughcut cyclone 
separator 11 substantially removes about 96 to 98 percent of the larger 
coked catalyst particles, at a size of generally greater than 50 microns, 
it is not as efficient separating the smaller coked catalyst particles, at 
a size generally ranging from 20-50 microns, also known as coked catalyst 
fines, from the cyclone product outlet. 
Loss of roughcut cyclone efficiency can also be caused by the generally 
unsteady, pulsating flow of the riser reactor 3. When the riser reactor 3 
intermittently produces surges of hydrocarbon and catalyst, the 
temporarily higher catalyst loading can result in the breakthrough of 
coked catalyst particles and more so of smaller catalyst fines into the 
cyclone product outlet 19 and into the disengaging vessel 18. 
The disengager vessel 18 is spaced laterally and apart from the riser 3 and 
the external unitary vessel 10 and designed to substantially remove the 
remaining coked catalyst fines from the cyclone outlet product. The 
disengager vessel 18 itself performs the function of dampening and 
absorbing the intermittent surges in flow initiated in the riser 3 so as 
to dampen the flow of the cooler quenched stream of hydrocarbon, creating 
a steadier flow of hydrocarbon and coked catalyst fines. 
The disengager vessel 18 has an upper dilute phase portion, area, or zone 
25 and a lower dense phase portion, area, or zone 26 which are separated 
by the interface of the dense phase zone 27, also known as the disengager 
catalyst bed level. Inside the disengager vessel 18 are positioned at 
least one, and in the preferred embodiment, at least two internal cyclone 
separators 28, also known as internal secondary cyclones to separate the 
coked cracking catalyst fines from the steadier flow of cooled quenched 
hydrocarbon to produce an effluent product catalyst lean stream of 
upgraded hydrocarbon and a concentrated stream of disengaged coked 
catalyst fines. The secondary cyclones 28 can be in series or in parallel 
as pictured in the Figure. A parallel secondary cyclone configuration 
comprises splitting the steady flow of cooler quenched hydrocarbon into at 
least two streams, independently cyclone-separating at least two of the 
streams, and recombining the streams to produce the effluent product 
catalyst lean stream of upgraded hydrocarbon. The secondary cyclones are 
positioned in the upper dilute phase 25 where the hydrocarbon outlets of 
the secondary cyclones are connected to a plenum 29, which is secured to 
the roof 32 or top of the disengager vessel 18. The plenum 29 is connected 
to the outlet or disengaged product exit of the disengager 30, discharging 
the effluent product, comprising a catalyst fine-lean stream or 
substantially catalyst-free upgraded product stream of hydrocarbon, out of 
the disengager vessel for further processing. The bottom of the secondary 
cyclones 28 are connected to catalyst diplegs 31, which transport 
separated catalyst fines into the lower dense phase zone 26. 
The disengager vessel 18 also includes a disengaged catalyst outlet 33 to 
discharge a concentrated stream of disengaged coked catalyst fines to a 
catalyst conduit 34 comprising a catalyst recycle line for conveying and 
passing the catalyst fines to the external means stripping section dense 
bed phase 13 in the bottom portion of the vessel. In the preferred 
embodiment, the disengaged catalyst outlet 33 operates as a catalyst 
overflow line such that the level of the interface of the dense phase zone 
27 is determined by the elevation of the catalyst outlet 33 adjusted for 
hydraulic considerations between the stripper section 13 of the external 
means and the disengager catalyst outlet 33. The level of the interface of 
the dense phase zone can also be controlled by a control valve on the 
catalyst conduit 34 along with the appropriate level control 
instrumentation. 
It is the preferred embodiment of this invention to provide a first 
supplemental stripping steam injector 35 on the catalyst recycle line 34. 
It is also a preferred embodiment to provide a second supplemental steam 
injector 36 into the disengager lower dense phase zone 27. The 
supplemental stripping steam injectors can be used to reduce hydrocarbon 
carryover to the regenerator 4 as well as for catalyst fluidization. The 
total stripping steam provided through injector 23 and supplemental 
injectors 35 and 36 will generally be in a range of 1 to 15 pounds of 
steam per ton of catalyst circulated. Additional steam injection would be 
inefficient; reduced steam usage may result in excessive hydrocarbon 
breakthrough to the regenerator 4. 
The entry position of the catalyst conduit 34 on the stripper section 12 in 
the preferred embodiment 37 is in the stripper section dense bed phase 13 
above the topmost baffle 42. The entry position should be kept below the 
dense bed coked catalyst level 14. Entry above the dense bed coked 
catalyst level 14 could create catalyst level disturbances that can 
disrupt roughcut separator efficiency and stripper slide valve 15 
operation. Entry above the topmost baffle 42 can beneficially subject the 
catalyst fines to additional stripping gas exposure which can reduce 
hydrocarbon carryover to the regenerator 4. In some circumstances, it may 
be desirable to adjust the entry position to a lower location on the 
stripper section 12 or into the stripper outlet line 38. 
An advantage of the disengager 18 and secondary cyclone 28 tandem is that 
the tandem ensures effective particulate removal from hydrocarbon product 
under extraordinary stripping conditions. Should a special need exist to 
substantially increase catalyst stripping, such as a regenerator 
temperature excursion, stripping steam may be increased to the first 35 
and second 36 supplemental stripping steam injectors with substantially no 
detrimental effect. Additional stripping steam may be added to a third 
location in the combined unitary vessel stripping section, if desired, 
since the disengager and secondary cyclone tandem can recover coked 
catalyst that is not recovered in the roughcut cyclone. 
The stripper outlet line 38 conveys stripped coked catalyst through the two 
stripper slide valves 15 for return to the regenerator vessel 4. The 
preferred embodiment includes two slide valves 15, although in some 
circumstances only one slide valve need be used. The stripper slide valves 
15 are often controlled to maintain the dense bed coked catalyst level 14. 
The coked catalyst is dropped into the catalyst return line 39 for 
conveying back to the regenerator vessel 4. The coked catalyst is carried 
back to the regenerator 4 with a carrier gas injected through carrier line 
40. The carrier stream in the preferred embodiment is compressed, air but 
other gases may be utilized, including steam. 
The coked catalyst is conveyed back to the regenerator vessel 4 where the 
catalyst is contacted with an oxygen-containing gas stream, preferably 
air, containing an amount of molecular oxygen in excess of that necessary 
for substantially complete combusion of the coke accumulated on the 
catalyst in the cracking reaction and for substantially complete 
combustion of carbon monoxide to carbon dioxide. The regenerator 4 
operates at a temperature in the range of 1000.degree. F. to 1500.degree. 
F., providing the hot catalyst supplied to the standpipe 5 and completing 
the process cycle. 
Other embodiments of the invention will be apparent to those skilled in the 
art from a consideration of this specification or from practice of the 
invention disclosed herein. It is intended that this specification be 
considered as exemplary only with the true scope and spirit of the 
invention being indicated by the following claims.