SEPARATEUR RECTIFICATEUR A PLAQUES DE DISSIPATION POUR PROCEDE DE CRAQUAGE CATALYTIQUE FLUIDE

DISENGAGER STRIPPER CONTAINING DISSIPATION PLATES FOR USE IN AN FCC PROCESS

Abrégé anglais

A method and apparatus for an FCC process uses dissipator plates at the
outlet of a disengaging vessel to provide a quick separation of catalyst from
product
vapors and to prevent reentrainment of catalyst by stripping gas which is
passed into the
disengaging vessel. The process and apparatus use a riser for the conversion
of an FCC
feedstock and direct the effluent from the riser directly into a disengaging
vessel to
separate catalyst from the product vapors. Catalyst is directed downwardly out
of the
outlet of the disengaging vessel and through a series of dissipator plates
that eliminate
the tangential velocity that would be otherwise introduced by the vortex and
would lead
to reentrainment of catalyst. The dissipator plates are located in a stripping
vessel
positioned immediately below the disengaging vessel outlet to receive catalyst
as it
leaves the disengaging vessel.

Revendications

19
CLAIMS:
1. A fluid catalytic cracking apparatus comprising:
(a) a reactor vessel [19];
(b) a tubular riser [10] having an inlet end for receiving feed and catalyst
and
an outlet end;
(c) an elongated disengaging vessel [20] located in said reactor vessel [19]
having an upper end and a lower end, said upper end having a tangential
inlet in direct communication with said outlet end of said riser and a
central gas outlet [32] at the top of said disengaging vessel [20] and said
lower end having an open bottom [74] wherein the outermost portion of
said open bottom [74] is unoccluded to permit unobstructed fluid and
particulate flow:
(d) a stripping vessel [22] located directly below said disengaging vessel
[20], said stripping vessel having an inlet in open communication with
said open bottom [74] of said disengaging vessel [20] and an outlet [26]
for withdrawing catalyst from the stripping vessel [22];
(e) means [24] for adding stripping gas to said stripping vessel [22]; and,
(f) a segregation zone located in said stripping vessel [22] comprising at
least two vertical partition plates [80] space below said open bottom [74]
of said disengaging vessel [20].
2. The apparatus of claim 1 wherein a vortex stabilizer tube [76] extends
upward from said open bottom [74] into said disengagement vessel [20].
3. The apparatus of claim 2 wherein the diameter of said vortex stabilizer
[76] is less than 20% of the diameter of the open bottom [74] and said open
bottom is
unoccluded except for said vortex stabilizer.
4. The apparatus of claim 1, 2 or 3 wherein said vertical plates [80] extend
horizontally and vertically and border an unobstructed area located
immediately below said open
bottom [74] of said disengaging vessel [20].

20
5. The apparatus of any one of claims 1 to 4 wherein said stripper vessel [22]
has a larger diameter than the bottom of said disengaging vessel [20], said
vertical
plates extend from the wall of said stripping vessel [22] inwardly to define
at least two
circumferentially extended chambers located below and to the outside of said
open
bottom [74] of said disengaging vessel.
6. The apparatus of any one of claims 1 to 5 wherein said central gas outlet
[32] communicates with at least one cyclone [36], said cyclone has a dip leg
[42] for
returning catalyst to the reactor vessel [19] and a vapor outlet [40] for
discharging a
vapor product stream.
7. A process for the fluidized catalytic cracking (FCC) of an FCC
feedstream, said process comprising:
(a) passing FCC catalyst and said FCC feedstream to a riser reaction zone
[10] and therein contacting said feedstream with said FCC catalyst to
convert said feedstream to product vapors;
(b) discharging a mixture of said product vapors and spent FCC catalyst from
said riser directly to the inlet of a disengaging vessel [20] and directing
said mixture from said inlet tangentially into said disengaging vessel [20]
to form an inner and outer vortex;
(c) stabilizing the inner vortex with a vortex stabilizer [76] in said
disengaging
vessel [20];
(d) emptying catalyst particles in closed communication from the bottom of
said disengaging vessel [20] directly into the top of a subadjacent stripping
vessel [22];
(f) injecting a stripping gas into said stripping vessel [22] and contacting
said
catalyst particles with said stripping gas to desorb hydrocarbons from said
catalyst particles;

21
(g) discharging a gaseous stream of desorbed hydrocarbons and stripping gas
upwardly from said stripping vessel [22] through a plurality of vertical
dissipater plates [80] in said stripping vessel [22], through an open volume
[84] of said stripping vessel [22] located above a central portion [82] of
said dissipater plates [80] and below the bottom [74] of said disengaging
vessel [20] and out of the top of said stripping vessel (22] and into the
bottom of said disengaging vessel [20]:
(h) maintaining a relatively dense bed of catalyst in said stripping vessel
[22]
below said central portion [84] of said dissipater plates [80];
(i) withdrawing said product vapors and said gaseous stream from the top of
said disengaging vessel [20] through a central outlet [32];
(j) passing said product vapor and said gaseous stream from said central
outlet to a separator [36] to recover additional catalyst particles;
(k) recovering a product stream from said separator [36];
(l) transferring catalyst particles from said separator [36] to a lower
portion
of said stripping vessel [22];
(m) removing spent FCC catalyst from the lower end of said stripping vessel
[22] and transferring said spent catalyst to a regeneration zone [52];
(n) regenerating said FCC catalyst in said regeneration zone [52] by the
oxidative removal of coke; and,
(o) transferring FCC catalyst from said regeneration zone [22] to said riser
reaction zone [10].

Description

1
"DISENGAGER STRIPPER CONTAINING
DISSIPATION PLsTES FOR USE IN A_N FCC PROCESS"
This imrention relates generally to methods and apparatus for fluidized
catalytic cracking (FCC) units. More specifically this invention relates ~to
methods for
separating catalyst from product vapors in an FCC reaction zone.
The fluidized catalytic cracking of hydrocarbons is the main stay process for
the production of gasoline and light hydrocarbon products from heavy
hydrocarbons
1o such as vacuum gas oils. Large hydrocarbon molecules associated with the
heavy
hydrocarbon feed are cracked to break large hydrocarbon chains thereby
producing
lighter hydrocarbons. These lighter hydrocarbons are recovered as product and
can be
used directly or further processed to raise the octane barrel yield relative
to the heavy
hydrocarbon feed.
The basic equipment or apparatus for the fluidized catalytic cracking of
hydrocarbons has been in e~tistence since the early 1940's. The basic
component of the
FCC process include a reactor, a regenerator and a catalyst stripper. The
reactor
includes a contact zone where the hydrocarbon feed is contacted with a
particulate
catalyst and a separation zone where product vapors from the cracking reaction
are
2 o separated from the catalyst. Further product separation takes place in a
catalyst
stripper that receives catalyst from the separation zone and removes entrained
hydrocarbons from the catalyst by countercurrent contact with steam or another
stripping medium. The FCC process is carried out by contacting the starting
material,
whether it be vacuum gas oil, reduced crude or another source of relatively
high boiling
hydrocarbons with a catalyst made up of a finely divided or particulate solid
material.
The catalyst is transported like a fluid by passing gas or vapor through it at
sufficient
veloaty to produce a desired regime of fluid transport. The contact of the oil
with
fluidized material catalyses the cracking reaction. During the cracking
reaction coke is
deposited on the catalyst.
3 o Coke is comprised of hydrogen and carbon and can include other materials
in trace quantities such as sulfur and metals that enter the process with the
starting
material. Coke interferes with the catalytic activity of the catalyst by
blocking active

208097
sites on the catalyst surface where the cracking reactions take place.
Catalyst is
transferred from the stripper to a regenerator for purposes of removing the
coke by
oxidation with an oxygen-containing gas. An inventory of catalyst having a
reduced
coke content, relative to the catalyst in the stripper, hereinafter referred
to as
regenerated catalyst, is collected for return to the reaction zone. Oxidizing
the coke
from the catalyst surface releases a large amount of heat, a portion of which
escapes the
regenerator with gaseous products of coke oxidation generally referred to as
flue gas.
The balance of the heat leaves the regenerator with the regenerated catalyst.
The
fluidized catalyst is continuously circ~~lated from the reaction zone to the
regeneration
1o zone and then again to the reaction zone. The fluidized catalyst, as well
as providing a
catalytic function, acts as a vehicle for the transfer of heat from zone to
zone. Catalyst
exiting the reaction zone is spoken of as being spent, i.e., partially
deactivated by the
deposition of coke upon the catalyst. Specific details of the various contact
zones,
regeneration zones, and stripping zones along with arrangements for conveying
the
catalyst between the various zones are well known to those skilled in the art.
The rate of conversion of the feedstock within the reaction zone is controlled
by regulation of the temperature of the catalyst, activity of the catalyst,
quantity of the
catalyst (i.e., catalyst to oil ratio) and contact time between the catalyst
and feedstock.
The most common method of regulating the reaction temperature is by regulating
the
2 o rate of circulation of catalyst from the regeneration zone to the reaction
zone which
simultaneously produces a variation in the catalyst to oil ratio as the
reaction
temperatures change. That is, if it is desired to increase the conversion rate
an increase
in the rate of flow of circulating fluid catalyst from the regenerator to the
reactor is
effected. Since the catalyst temperature in the regeneration zone is usually
held at a
relatively constant temperature, significantly higher than the reaction zone
temperature, any increase in catalyst flux from the relatively hot
regeneration zone to
the reaction zone affects an increase in the reaction zone temperature.
The hydrocarbon product of the FCC reaction is recovered in vapor form
and transferred to product recovery facilities. These facilities normally
comprise a
3 o main column for cooling the hydrocarbon vapor from the reactor and
recovering a
series of heavy cracked products which usually include bottom materials, cycle
oil, and
heavy gasoline. Lighter materials from the main column enter a concentration
section
for further separation into additional product streams.

20809'4
The catalyst particles employed in an FCC process have a large surface area,
which is due to a great multitude of pores located in the particles. As a
result, the
catalytic materials retain hydrocarbons within their pores and upon the
external surface
of the catalyst. Although the quantity of hydrocarbon retained on each
individual
catalyst particle is very small, the large amount of catalyst and the high
catalyst
circulation rate which is typically used in a modem FCC process results .in a
significant
quantity of hydrocarbons being withdrawn from the reaction zone with the
catalyst.
Therefore, it is common practice to remove, or strip, hydrocarbons from
spent catalyst prior to passing it into the regeneration zone. It is important
to remove
1o retained spent hydrocarbons from the spent catalyst for process and
economic reasons.
First, hydrocarbons that entered the regenerator increase its carbon-burning
load and
can result in excessive regenerator temperatures. Stripping hydrocarbons from
the
catalyst also allows recovery of the hydrocarbons as products. Avoiding the
unnecessary
burning of hydrocarbons is especially important during the processing of heavy
(relatively high molecular weight) feedstocks, since processing these
feedstocks
increases the deposition of coke on the catalyst during the reaction (in
comparison to
the coking rate with light feedstocks) and raises the combustion load in the
regeneration zone. Higher combustion loads lead to higher temperatures which
at
some point may damage the catalyst or exceed the metallurgical design limits
of the
2 o regeneration apparatus.
The most common method of stripping the catalyst passes a stripping gas,
usually steam, through a flowing stream of catalyst, countercurrent to its
direction of
flow. Such steam stripping operations, with varying degrees of efficiency,
remove the
hydrocarbon vapors which are entrained with the catalyst and hydrocarbons
which are
adsorbed on the catalyst.
The efficiency of catalyst stripping is increased by using vertically spaced
baffles to cascade the catalyst from side to side as it moves down a stripping
apparatus
and countercurrently contacts a stripping medium. Moving the catalyst
horizontally
increases contact between the catalyst and the stripping medium so that more
3 o hydrocarbons are removed from the catalyst. In these arrangements, the
catalyst is
given a labyrinthine path through a series of baffles located at different
levels. Catalyst
and gas contact is increased by this arrangement that leaves no open vertical
path of
significant cross-section through the stripping apparatus. The typical
stripper
arrangement comprises a stripper vessel, a series of baffles in the form of
frusto-conical

2080974
4
sections that direct the catalyst inwardly onto a baffle in a series of
centrally located
conical or frusto conical baffles that divert the catalyst outwardly onto the
outer baffles.
The stripping medium enters from below the lower baffle in the series and
continues
rising upward from the bottom of one baffle to the bottom of the next
succeeding baffle.
As the development of FCC units has advanced, temperatures within the
reaction zone were gradually raised. It is now commonplace to employ
temperatures of
about 975°F (525oC) . At higher temperatures, there is generally a loss
of gasoline
components as these materials crack to lighter components by both catalytic
and strictly
thermal mechanisms. At 525oC, it is typical to have 1% of the potential
gasoline
1o components thermally cracked into lighter hydrocarbon gases. As
temperatures
increase, to say 1025°F (SSOoC), most feedstocks can lose up to 6% or
more of the
gasoline components to thermal cracking. However, the loss of gasoline can be
offset
by the often more desirable production of light olefins.
One improvement to FCC units, that has reduced the product loss by thermal
25 cracking, is the use of riser cracking. In riser cracking, regenerated
catalyst and starting
materials enter a pipe reactor and are transported upward by the expansion of
the gases
that result from the vaporization of the hydrocarbons, and other fluidizing
mediums if
present upon contact with the hot catalyst. Riser cracking provides good
initial catalyst
and oil contact and also allows the time of contact between the catalyst and
oil to be
2 o more closely controlled by eliminating turbulence and backmixing that can
vary the
catalyst residence time. An average riser cracking zone today will have a
catalyst to oil
contact time of 1 to 5 seconds. A number of riser reaction zones use a lift
gas as a
further means of providing a uniform catalyst flow. Lift gas is used to
accelerate
catalyst in a first section of the riser before introduction of the feed and
thereby reduces
2 5 the turbulence which can vary the contact time between the catalyst and
hydrocarbons.
In most reactor arrangements, catalysts and conversion products still enter a
large chamber for the purpose of initially disengaging catalyst and
hydrocarbons. The
large open volume of the disengaging vessel exposes the hydrocarbon vapors to
turbulence and backmi~dag that continues catalyst contact for varied amounts
of time
3 o and keeps the hydrocarbon vapors at elevated temperatures for a variable
and extended
amount of time. Thus, thermal cxacking can be a problem in the disengaging
vessel. A
final separation of the hydrocarbon vapors from the catalyst is performed by
cyclone
separators that use centripedal acceleration to disengage the heavier catalyst
particles
from the lighter vapors which are removed from the reaction zone.

20809'4
s
In order to minimize thermal cracking in the disengaging vessel, a variety of
systems for directly connecting the outlet of the riser reactor to the inlet
of a cyclone
are suggested in the prior art. A majority of the hydrocarbon vapors that
contact the
catalyst in the reaction zone are separated from the solid particles by
ballistic and/or
centrifugal separation methods within the reaction zone. Directly connecting
the inlet
of a first cyclone and the outlet the first cyclone to the inlet of a second
cyclone in what
has been termed a "direct connected cyclone system" can greatly reduce thermal
cracking of hydrocarbons. Unfortunately in most cases direct connected
cyclones will
increase the complexity of operating an FCC unit. When the cyclones are
directly
1o connected to the riser any pressure surges that normally occur in the FCC
unit can
cause the cyclones to malfunction and lead to the carry-over of catalyst into
the main
column and separation facilities for the recovery of the product. A number of
different
riser and cyclone arrangements are shown in the prior art to increase the
reliability of
the cyclone operation when the riser is directly connected thereto.
One way in which to overcome the problem of pressure surges and catalyst
carry over is to connect a separation device having a large capacity to the
outlet of the
riser. Such a separation device is shown in Figure 8 of U.S: A-4,689,206. This
separation device provides a disengagement of the catalyst and product vapor
mixture
before the mixture enters the relatively small volume of an ordinary cyclone.
Due to its
2 0 large volume the separation device is not easily overloaded and ordinary
pressure
surges will not interrupt its operation. However such large separation devices
suffer
from low separation efficiencies that increase the particle load on the
downstream
cyclones or require the use of two stage cyclones or must have a relatively
long length to
provide a high separation efficiency. Reduced efficiencies are in large part
caused by
the reentrainment of catalyst particles with the gas as it flows out of the
separation
device. The present invention thus provides a unique solution to this problem
of direct
connection to cyclones.
It is an object of this invention to provide a catalyst separation system for
use
3 o inside a reactor vessel in an FCC unit which system will provide a quick
disengagement
between catalyst and product vapors and be simple and reliable to operate.
It is a second object of this im~ention to provide a disengaging system for
reactor products and catalysts in an FCC unit which system is not susceptible
to

2080974
overload from pressure surges and is relatively compact.
A third object of this invention is to provide a cyclone type separation
vessel
that can receive the entire effluent from an FCC reactor riser and provide a
high
separation efficiency without a susceptibility to overload from pressure
surges.
A fourth object of this invention is to provide an FCC process that provides a
quick separation of catalyst from product vapors and thus minimizes
overcracking and
is not susceptible to overload from pressure surges or changes in operation of
the
reactor system.
The objects of this invention are realized by a separation system that is
directly
connected to the outlet of the riser in an FCC unit and provides a high degree
of
separation by using a basic cyclone operation within a disengaging vessel and
partition
or dissipater plates below the disengaging vessel to improve catalyst
separation and
prevent catalyst reentrainment. These partitions or dissipaters are located
immediately
below the outer vortex that is formed in most cyclone operations. Ordinarily,
a
tangential velocity is introduced by the vortex, and if not dissipated will
create
turbulence that will reentrain free catalyst. Contact with the plates
dissipates these
tangential velocities and reduces turbulence immediately below the vortex. The
dissipater plates can also be arranged to trap catalyst particles as they fall
from the
vortex to reduce the particle velocity and prevent reentrainment.
2 o Accordingly, in one embodiment, this invention is a fluid catalytic
cracking
apparatus that includes a reactor vessel, a tubular riser having an inlet end
for receiving
feed and catalyst and an outlet end. An elongated disengaging vessel is
located in the
reactor vessel and has an upper and a lower end. The upper end of the
disengaging
vessel has a tangential inlet in direct communication with the outlet end of
the riser and
a central gas outlet at the top. The lower end has an open bottom wherein the
outermost portion of the open bottom is unoccluded to permit unobstructed
fluid and
particulate flow. A stripping vessel is located directly below the disengaging
vessel.
The stripping vessel has an inlet that communicates directly with the open
bottom of
the disengaging vessel and an outlet for withdrawing catalyst from the
stripping vessel.
3 o Means are provided for adding stripping gas to the stripping vessel. A
segregation zone
is located in the stripping vessel and includes at least two vertical
partition or
dissipation plates spaced below the open bottom of the disengaging vessel.

2080974
In a more limited embodiment, this invention comprises a fluid catalytic
cracking apparatus that includes a reactor vessel and a tubular riser having
an inlet end
for receiving feed and catalyst and an outlet end. An elongated disengaging
vessel is
located in the reactor vessel and has upper and lower ends. The upper end of
the
disengaging vessel has a tangential inlet in direct communication with the
outlet end of
the riser and a central gas outlet at the top. The lower end has a vertically
extending
sidewall, an open bottom and a plurality of circumferentially spaced ports at
the bottom
of the vertically extending sidewall. A stripper vessel having an upper end
located in
the reactor vessel and into which the lower end of the disengaging vessel
extends is
located immediately below the disengaging vessel. At least two dissipator
plates are
located inside the stripper vessel. The dissipator plates extend inwardly from
the walls
of the stripper vessel with each dissipator plate lying in a common plane with
the
centerline of the stripper vessel. The dissipator plates have a central
portion, the top of
which is spaced below the lower end of the disengaging vessel. The stripper
vessel also
has a catalyst outlet at its lower end and at least one inner and at least one
outer
stripping baffle located between the top of the central portion of the
dissipator plates
and the catalyst outlet and means for introducing a stripping fluid into the
stripping
vessel. A vortex stabilizer extends into the lower end of the disengaging
vessel. Means
are provided for withdrawing gas from the open volume of the reactor vessel.
2 o In a yet more limited embodiment, this invention is a fluid catalytic
cracking
apparatus that includes a reactor vessel and a tubular riser having an inlet
end for
receiving feed and an outlet end. An elongated disengaging vessel is located
in the
reactor vessel and has an upper end and a lower end. The upper end has a
tangential
inlet in direct communication with the outlet end of the riser and a central
gas outlet at
the top of the disengaging vessel. The lower end has a vertically extending
sidewall, an
open bottom and a plurality of circumferentially spaced slots bordering the
bottom of
the vertically extending sidewall. A stripper vessel having upper and lower
sections is at
least partially located in the reactor vessel. The upper section of the
stripper vessel is
fixed to the lower end of the disengaging vessel and the lower section of the
stripper is
3o l5xed to the lower end of the reactor vessel. A slip joint between the
upper and lower
sections of the stripper vessel joins the two stripper sections. The stripper
vessel also
includes means for communicating the interior of the stripping vessel with the
interior
of the reactor vessel. The upper section of the stripping vessel also ha's a
larger
diameter than the lower end of the disengaging vessel and at least two
dissipator plates
extending inwardly from the walls of the stripper vessel with each dissipator
plate lying

200974
in a common plane with the centerline of the stripper vessel. The dissipater
plates have
a central portion spaced below the lower end of the disengaging vessel and an
outer
portion that extends vertically from the top of the central portion above the
open
bottom of the disengaging vessel. At least one stripping baffle is located at
the bottom
of the dissipater plates. The lower section of the stripping vessel has an
upper end
located in the reactor vessel and z~ lower end located outside of the reactor
vessel. The
lower end of the stripping vessel l~~srer section has a catalyst outlet and a
distributor for
adding stripping gas to the stripping vessel. The upper end of the lower
section has at
least one stripping baffle located therein. A vortex stabilizer extends into
the lower end
of the disengaging vessel. Means are provided for adding a fluidizing gas to
the bottom
of the reactor vessel. A cyclone separator receives product vapors and
catalyst from the
gas outlet of the disengaging vessel. The cyclone has a dip leg that returns
catalyst to
the reactor vessel. A first conduit communicates product vapors directly from
the gas
outlet to the cyclone separator. A second conduit communicates product vapors
from
the cyclone to product recovery facilities. The apparatus includes means for
venting
fluidizing gas out of the reactor vessel.
In an alternate embodiment this invention is a process for the fluidized
catalytic cracking of an FCC fsedstream which utilizes the FCC apparatus
described in
any of the previous embodiments. The process includes the steps of passing an
FCC
2 o catalyst and the FCC feedstream to a riser reaction zone and contacting
the feedstream
with the FCC catalyst in the riser reaction zone to convert the feedstream to
product
vapors, discharging a mixture of the product vapors and the spent FCC catalyst
from the
riser directly to the inlet of a disengaging vessel, and directing the mixture
from the
inlet tangentially into the disengaging vessel to form an inner and outer
vortex of
product gases in the disengaging vessel, stabilizing the inner vortex with a
vortex
stabilizer in the disengaging vessel, emptying catalyst particles from the
bottom of the
disengaging vessel directly into the top of a subadjacent stripping vessel.
The process
includes injecting a stripping gas into the stripping vessel and contacting
the catalyst
particles with the stripping gas to desorb hydrocarbons from the catalyst
particles,
3 o discharging a gaseous stream of desorbed hydrocarbons and stripping gas
upwardly
through the stripping vessel past a plurality of vertical disengaging plates
into the
disengaging vessel through an open volume of the stripping vessel located
above a
central portion of the disengaging plates and below the bottom of the
disengaging vessel
and out of the top of the stripping vessel and into the bottom of the
disengaging vessel;
maintaining a relatively dense bed of catalyst in the stripping vessel below
the central

2~8~97~
9
portion of the dissipator plates; withdrawing the product vapors and the
gaseous stream
from the top of the disengaging vessel through a central outlet; passing the
product
vapor and the gaseous stream from the central outlet to a separator to recover
additional catalyst particles; recovering a product stream from the separator;
transferring ~talyst particles from the separator to a lower portion of the
stripping
vessel; removing spent catalyst from the lower end of the stripping vessel and
transferring spent catalyst to a regeneration zone; regenerating the FCC
catalyst in the
regeneration zone by the oxidative removal of coke; and transferring FCC
catalyst from
the regeneration zone to the riser reaction zone.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a sectional elevation of a reactor riser, reactor vessel and
regenerator arrangement that incorporates the separation system of this
invention.
Figure 2 is an enlarged detail of the separation section located in the
reactor
vessel of Figure 1.
Figure 3 is a section of the enlarged separation section taken across lines
3/3
of Figure 2.
Figure 4 is a detailed cross-section of a secondary stripper section shown in
Figure 1.
Figure 5 is an enlarged view of the upper section of the reactor shown in
2 o Figure 1.
The typical feed to an FCC unit is a gas oil such as a light or vacuum gas
oil.
Other petroleum-derived feed streams to an FCC unit may comprise a diesel
boiling
range mixture of hydrocarbons or heavier hydrocarbons such as reduced crude
oils. It is
preferred that the feed stream consist of a mixture of hydrocarbons having
boiling
points, as determined by the appropriate ASTM test method, above about 230 C
and
more preferably above about 290 C. It is becoming customary to refer to FCC
type
units which are processing heavier feedstocks, such as atmospheric
reduced~crudes, as
residual crude cracking units, or residual cracking units. The process and
apparatus of
3 o this invention can be used for either FCC or residual cracking operations.
For

2080974
to
convenience, the remainder of this specification will only make reference to
the FCC
process.
The chemical composition and structure of the feed to an FCC unit will
affect the amount of coke deposited upon the catalyst in the reaction zone.
Normally,
the higher the molecular weight, Conradson carbon, heptane insolubles, and
carbon/hydrogen ratio of the feedstock, the higher will be the coke level on
the spent
catalyst. Also, high levels of combined nitrogen, such as found in shale-
derived oils, will
increase the coke level on spent catalyst. Processing of heavier feedstocks,
such as
deasphalted oils or atmospheric bottoms from a crude oil fractionation unit
(commonly
1o referred to as reduced crude) results in an increase in some or all of
these factors and
therefore causes an increase in the coke level on spent catalyst. As used
herein, the
term "spent catalyst" is intended to indicate catalyst employed in the
reaction zone
which is being transferred to the regeneration zone for the removal of coke
deposits.
The term is not intended to be indicative of a total lack of catalytic
activity by the
catalyst particles.
The reaction zone, which is normally referred to as a "riser", due to the
widespread use of a vertical tubular conduit, is maintained at high
temperature
conditions which generally include a temperature above 427°C.
Preferably, the
reaction zone is maintained at cracking ~nditions which include a temperature
of from
2 0 480°C to 590°C and a pressure of from 65 to 601 kPa but
preferably less than 376 kPa.
The catalyst/oil ratio, based on the weight of catalyst and feed hydrocarbons
entering
the bottom of the riser, may range up to 20:1 but is preferably between 4:1
and 10:1.
Hydrogen is not normally added to the riser, although hydrogen addition is
known in
the art. On occasion, steam may be passed into the riser. The average
residence time
of catalyst in the riser is preferably less than 5 seconds. The type of
catalyst employed
in the process may be chosen from a variety of commercially available
catalysts. A
catalyst comprising a zeolitic base material is preferred, but the older style
amorphous
catalyst can be used if desired. Further information on the operation of FCC
reaction
zones may be obtained from U.S: A-4,541,922 and U.S: A-4,541,923.
3o An FCC process unit comprises a reaction zone and a catalyst regeneration
zone. This im~ention may be applied to a~ configuration of reactor and
regeneration
zone that uses a riser for the oom~ersion of feed by contact with a finely
divided
fluidized catalyst maintained at an elevated temperature and at a moderate
positive
pressure. In this invention, contacting of catalyst with feed and conversion
of feed takes

~0809'~4
11
place in the riser. The riser comprises a principally vertical conduit and the
effluent of
the conduit empties into a disengaging vessel. One or more additional solids-
vapor
separation devices, almost invariably a cyclone separator, is normally located
within and
at the top of the large separation vessel. The disengager vessel and cyclone
separate
the reaction products from a portion of catalyst which is still carried by the
vapor
streann. One or more conduits vent the vapor from the cyclone and separation
zone.
After initial separation the spent catalyst passes through a stripping zone
that is located
directly beneath the disengaging vessel. It is essential to this invention
that the
stripping vessel is located below the disengaging zone and that the upper
portion of the
1 o stripping vessel contain means for dissipating turbulence at the outlet of
the disengaging
vessel. After the catalyst has passed through the stripping zone it can be
transferred to
the reactor vessel or pass through one or more additional stages of stripping.
Once stripped, catalyst flows to a regeneration zone. In an FCC process,
catalyst is continuously circulated from the reaction zone to the regeneration
zone and
z5 then again to the reaction zone. The catalyst therefore acts as a vehicle
for the transfer
of heat from zone to zone as well as providing the necessary catalytic
activity. Catalyst
which is being withdrawn from the regeneration zone is referred to as
"regenerated"
catalyst. The catalyst charged to the regeneration zone is brought into
contact with an
oxygen-containing gas such as air or oxygen-enriched air under conditions
which result
2 o in combustion of the coke. This results in an increase in the temperature
of the catalyst
and the generation of a large amount of hot gas which is removed from the
regeneration zone and referred to as a flue gas stream. The regeneration zone
is
normally operated at a temperature of from 600°C to 800°C.
Additional information
on the operation of FCC reaction and regeneration zones may be obtained from
U.S:
25 A-4,431,749; U.S: A-4,419,221 and U.S: A-4,220,623.
The catalyst regeneration zone is preferably operated at a pressure of from
136 to 601 kPa. The spent catalyst being charged to the regeneration zone may
contain
from 0.2 to 5 wt.% coke. This coke is predominantly comprised of carbon and
can
contain from 3 to 15 wt.% hydrogen, as well as sulfur and other elements. The
3 0 oxidation of coke will produce the common combustion products: carbon
dioxide,
carbon monoxide, and water. The regeneration zone may take several
configurations,
with regeneration being performed in one or more stages. Further variety in
the
operation of the regeneration zone is possible by regenerating fluidized
catalyst in a
dilute phase or a dense phase. The term "dilute phase" is intended to indicate
a

12 2080974
catalyst/gas mixture having a density of less than 320 kg/m3. In a similar
manner, the
term "dense phase" is intended to mean that the catalyst/gas mixture has a
density equal
to or more than 320 kg/m3. Representative dilute phase operating conditions
often
include a catalyst/gas mixture having a density of 15 to 150 kg/m3.
Figu~~e 1 shows a traditional stacked FCC reactor/regenerator arrangement
that has been modified to incorporate the separation system of this invention.
In its
basic operation, feed enters the lower end of a riser 10 through a nozzle 12
where it is
contacted with fresh regenerated catalyst from a regenerated catalyst conduit
14. A
valve 16 controls the rate of catalyst addition to riser 10. Steam may also be
added with
1o the feed through nozzle 12 in order to achieve the desired feed velocity
and help the
dispersion of feed into the stream of catalyst particles. Feed hydrocarbons
are cracked
by contact with the catalyst in the riser and spent catalyst and product
vapors exit the
upper end of riser 10 through a horizontal pipe section 18. Pipe section 18
discharges
the catalyst and product vapor mixture directly into a disengaging vessel 20.
A reactor
vessel 19 contains stripping gas, spent catalyst and product vapors. Catalyst
disengaged
from the stripping gas and product vapors in disengager 20 pass downwardly
into a
stripping vessel 22. Steam entering stripping vessel 22 through a nozzle 24
countercurrently contacts catalyst particles to strip additional hydrocarbons
from the
catalyst. Catalyst exits stripping vessel 22 through nozzle 26 and enters a
second
2 o catalyst stripper 28. Steam entering stripping vessel 28 through nozzle 30
again
countercurrently contacts the catalyst particles to remove additional
hydrocarbons from
the catalyst. Stripping gas and separated hydrocarbons rise upwardly through
stripping
vessels 28 and 22 and are withdrawn in a manner hereinafter more fully
described
through disengaging vessel 20 and a central gas outlet 32. A manifold 34
conducts
stripping fluid and product vapors into cyclones 36 that effect a further
separation of
catalyst particles from the stripping fluid and product vapors. A manifold 38
collects
stripping fluid and product vapors from the cyclone 36 which are removed from
the
reactor vessel by conduits 40. Product vapor and stripping fluid are taken
from
manifold 38 to product separation facilities of the type normally used for the
recovery
3 0 of FCC products.
All of the spent catalyst from the reactor section is directed into the
regenerator. Spent catalyst collected by cyclones 36 drops downwardly throup~h
dip legs
42 and collects as a dense bed 44 in a space between the wall of reactor
vessel 19 and
the outside of stripping vessel 22. A plurality of ports 46, hereinafter more
fully

CA 02080974 2003-O1-20
13
described, transfer catalyst from bed 44 to the interior of stripping vessel
22. Spent catalyst
stripped of hydrocarbons is withdrawn from the bottom of vessel 28 through
spent catalyst
conduit 48 at a rate regulated by control valve 50.
In a regenerator 52 the catalyst is regenerated by oxidizing coke from the
surface of the
catalyst particles and generating flue gas that contains H,O, CO and CO, as
the products of
combustion. The catalyst enters regenerator 52 through a nozzle 54 and is
contacted with air
entering the regeneration vessel through a nozzle >6. This invention does not
require a specific
type of regeneration system. The regeneration vessel pictured in Figure 1
ordinarily operates
with a dense bed 58 in its lower section. Some form of distribution device
across the bottom
of the regeneration vessel distributes air over the entire cross-section of
the vessel. A variety
of such distribution devices are well known to those skilled in the art.
Alternatively, this
invention can be practiced with a regeneration zone that provides multiple
stages of coke
combustion. Furthermore, the regeneration zone can achieve complete CO
combustion or
partial CO combustion. In the dense bed operation, as depicted in Figure 1,
flue gas and
entrained catalyst particles rise up from bed 58. A f first stage cyclone 60
collects flue gas and
performs an initial separation of the catalyst particles which are returned to
bed 58 by dip leg
62 and the flue gas which is transferred by a conduit 64 to a second cyclone
66. A further
separation of catalyst from the flue gas takes place in cyclones 66 with the
catalyst particles
returning to bed 58 via a dip leg 68 and the Clue gas leaving the upper end of
cyclone 66 and the
regeneration vessel via a collection chamber 70 and a flue gas conduit 72.
A more complete understanding of the operation and arrangement of disengaging
vessel
20 and stripping vessel 22 is obtained by reference to Figure 2. Figure 2
shows disengaging
vessel 20 located completely within reactor vessel 19. Disengaging vessel 20
operates with the
mixture of spent catalyst and product vapors entering the upper end of
disengaging vessel 20
tangentially through horizontal conduit 18. 'Tangential entry of the gases and
solids into
disengaging vessel 20 forms the well-known double helix flow pattern through
the disengaging
vessel that is typically found in the operation of traditional cyclones.
Catalyst and gas swirls
downwardly in the first helix near the outer wall of vessel 20 and starts back
upwardly as an
inner helix that spirals through the center of disengaging vessel 20 and exits
the top of the
disengaging vessel through central gas outlet 32. The spinning action of the
gas and catalyst
mixture concentrates the solid particles near the wall of vessel 20. Gravity
pulls the particles

14 2080974
downward along the wall of vessel 20 and out through a lower outlet 74. The
efficiency
of the disengager is improved by controlling the positioning of the double
helix with a
vortex stabilizer 76 that is located in the center of disengaging vessel 20.
More than
95% of the solids passing through conduit 18 are removed by disengaging vessel
20 so
that the gas stream that exits through conduit 32 contains only a light
loading of catalyst
particles. The vortex shape is also enhanced by giving disengaging vessel 20 a
slight
fr~mto-conical shape such that the upper section has a larger diameter than
the lower
section. It is also preferred that disengaging vessel 20 be designed such that
the bottom
of the outer helix ends at or about the bottom of opening 74. This design
differs from
1 o traditional cyclones which are designed such that they will have a much
longer length
than the outer helix length. The required space for disengaging vessel 20 has
been
reduced by designing it such that the bottom of the outer helix extends to or
only
slightly below the outlet 74. The length of the disengager required for a
specific helix
configuration will depend on its size and the gas velocity. For disengagers of
average
size, those ranging from 5 to 10 feet (1.5 to 3 m) in diameter, the length of
the
disengager from the bottom of the gas and catalyst inlet to the outlet 74 will
be 2 to 3
times the largest diameter of the disengaging vessel.
As the solids leave disengaging vessel 20 through outlet 74, it tends to be
reentrained by gas that is circulating near opening 74 or entering disengaging
vessel 20
2 o through opening 74. Locating the outlet 74 near the bottom of the outer
helix of the
disengaging vessel can create turbulence that will reentrain additional
catalyst.
Stripping gas and stripped hydrocarbons flowing upwardly from the stripping
vessel into
the disengaging vessel can also reentrain catalyst particles. In one
embodiment of this
invention, a portion of catalyst particles exit outlet 74 radially through a
series of slots
or ports 78 that extend circumferentially around the lower portion of outlet
74.
Typically, the outlet will have 8 to 24 of such slots spaced around the
outside. These
slots will usually vary from 12 to 24 in (305 to 610 mm) in height and
approximately 3
to 6 in (76 to 152 mm) in width. The slots improve the separation efficiency
by
containing the vortex that is near the outlet 74 while allowing catalyst
particles to spray
3 o outwardly under the influence of the vortex into the outer portion of
stripping vessel 22,
thereby clearing the central portion of outlet 74 for the influx of gas.
Disengaging vessel 20 opens directly into the top of stripping vessel 22.
Swirling gas flow associated with the cyclonic vortex and the countercurrent
flow of gas
upvvardly from the stripping vessel 22 normally would create a long zone of
turbulence

is 2080~'~4
below outlet 74. The effect of any turbulence is reduced by a set of plates 80
that
function to dissipate any turbulence associated with the swirling action of
the helical gas
flows. These plates are spaced below the bottom of opening 74 such that an
open area
84 provided between the top 82 of the central portion of the dissipater or
partition
plates 80, and the bottom of outlet 74. The length of this space is indicated
by
Dimension A and will preferably be equal to approximately half the diameter of
the
outlet 74. This space is provided and the top 82 of plates 80 is not brought
all the way
up to the bottom of opening 74 in order to reduce the velocity of the
descending vortex
before it contacts the dissipater plates.
1o The dissipater plates 80 are attached to the inner walls of stripper 22 and
extend inwardly to the center line of vessel 22. Plates 80 are preferably
arranged
vertically. In most cases at least four dissipater plates will extend inwardly
from the
walls of vessel 22 and divide the cross-section of the stripper vessel in the
region of the
dissipater plates into four quadrants. Plates 80 dissipate any horizontal
components of
i5 gas flow that extend below the open area 84. The plates 80 also provide a
convenient
means of locating and supporting vortex stabilizer 76 and stripper baffle 88.
The
vertical orientation of plates 80 obstruct any tangential or horizontal
components of gas
velocity such that the effects of any vortex does not extend past upper plate
section 82.
In addition, the horizontal momentum of any catalyst particles that extend
below plate
2 o boundary 82 is stopped by plate 80 so that the particles have a more
direct downward
trajectory and the total distance traveled by the particles through the
stripping vessel is
reduced. Reducing the travel path of the particles through stripping vessel 22
lessens
the tendency of catalyst reentrainment. In a preferred arrangement, at least
one
dissipater plate bisects the cross-section of the stripping vessel 22. At
minimum, the
25 Diameter B of the dissipater plates about the central portion 82 should be
at least equal
to the diameter of outlet 74. The effectiveness of the dissipater plates is
increased by
having the Diameter B at least slightly larger than the diameter of outlet 74.
The
stripping vessel can be arranged such that its outer wall has a diameter equal
to
Dimension B. The effectiveness of the dissipater plates can be further
increased by
3 o increasing the diameter of stripping vessel 22 relative to Dimension B and
providing the
dissipater plates with an outer section 86 that extends outwardly to the
region beyond
Dimension B and above the central portion 82 of the plates. Outer section 86
preferably extends above outlet 74 and more preferably above the top of slots
78. The
additional plate area provided by sections 86 of the dissipater plates 80
serves to further
35 reduce tangential gas velocity components and moreover to provide a
relatively

16 20809'4
stagnant area for collecting catalyst particles that accumulate on the outside
wall of
stripper vessel 22. Plate sections 86 function to further direct catalyst
particles, that
would otherwise become entrained in the upflowing stripping gas and swirling
gas
associated with the cyclonic separation, to flow downwardly into the stripping
vessel.
As the catalyst flows downwardly, it is countercurrently contacted with the
stripping gas from nozzle 24. In order to improve the stripping efficiency,
conical
baffles are provided to increase the contact between the solid particles and
the stripping
gas in the middle or lower sections of the stripping vessel. These stripping
baffles have
the usual cone arrangement that is ordinarily found in FCC strippers. In one
particular
1o arrangement, an uppermost inner cone type baffle 88 is attached to
partition plates 80
and a lower outer cone 90 is attached to the wall of stripping vessel 22.
These baffles
can be of any ordinary design well known to those skilled in the art and
commonly used
in FCC strippers. Preferably, the stripper baffles will be provided with
skirts that
depend downwardly from the lower conical portion of the baffle. It is also
known that
such skirts can be perforated to increase the contacting efficiency between
the stripping
fluid and the catalyst particles.
Figure 2 depicts an arrangement of the stripping vessel wherein an upper
portion 22' is located in the reactor vessel 19 and a lower portion 22"
extends below the
interior of reactor vessel 19. This arrangement facilitates the location of
nozzle 26 for
2 o the withdrawal of spent catalyst from the stripping vessel.
The stripping vessel and the disengaging vessel may be supported from the
reactor vessel 19 in any manner that will allow for thermal expansion between
disengaging vessel 20 and reactor vessel 19. One support arrangement uses a
solid
stripping vessel fixed to the bottom shell of reactor vessel 19 and a
disengaging vessel
2~ fixed rigidly thereto. In such an arrangement, thermal expansion of the
disengaging
vessel and the upper portion 22' of the stripping vessel is provided by
expansion joints in
the conduit 18 and the central outlet 32 or the manifolds located thereabove.
Figure 2 shows an arrangement wherein the upper portion 22' is fixed to the
bottom of disengaging vesxl ZO and a slip joint is provided between the upper
portion
3 0 22' and the lower portion 22" of the stripping vessel.

CA 02080974 2003-O1-20
17
Catalyst bed 44 surrounds the location of stripper section 22'. The lower
portion of
reactor vessel 19 must have a catalyst inlet to transfer catalyst from bed 44
to stripper vessel 22.
In the arrangement of Figure 2, catalyst drains into the stripper vessel
through the slots 46 in the
manner previously described. Fluidizing gas, which is generally steam,
distributed to the bottom
of bed 44 by distributor 98 facilitates the transport of catalyst into the
stripping vessel through
slots 46 and strips the catalyst discharged from the dip legs of the reactor
cyclones.
In addition to the slots for catalyst passage, the slip joint arrangement of
Figure 2 shows
additional slots in the upper portion of lower stripper section 22'. These
slots provide clearance
for the dissipater plates as the disengaging vessel and upper stripper section
22 grow downward
with respect to the lower stripper section 22'.
The slots are sized to maintain a bed of dense catalyst in the bottom of the
reactor vessel.
This bed prevents stripped vapors from entering the open volume of the reactor
vessel. Figure
3 depicts the dissipater plates, upper stripper baffle, slip joint and slots
in plan view. Looking
at Figure 3, four dissipater plates are shown spaced apart and extending from
the outer wall of
the upper stripper section 22' to the outside of vortex stabilizer 76. Vortex
stabilizer 76 is
centrally supported from the dissipater plates. The slots 92 spaced about the
upper end of
section 22" lie directly beneath the dissipater plates 80 to prevent
interference between the
bottom of the dissipater plates and the top of section 22". Slots 46 are
spaced regularly about
the lower periphery of section 22'. Four to sixteen of such slots 46 are
usually provided. The
slots are sized to maintain a catalyst level in bed 44 and prevent the leakage
of gas outwardly
from the stripping vessel into the open area of reactor vessel 19 as shown in
Figure 2. For a
typical arrangement, the slots 46 will be 500 to 1000 mm in height and from
300 to 400 mm
wide. Slots 92 are sized as necessary to provide adequate clearance for the
dissipater plates; for
an ordinary arrangement, slots approximately 250 mm x 250 mm will provide
adequate
clearance.
Catalyst that leaves the stripping vessel through nozzle 26 enters the
secondary stripping
vessel 28. Stripping vessel 28, shown in more detail by Figure 4, operates in
a conventional
manner. Catalyst passes downwardly through the stripper and is cascaded
side/side through a
3(> series of inner baffles 100 and outer baffles 102. Catalyst is withdrawn
through ports 104 in a
lower portion of a support conduit 106 to which inner stripper baffles 100 are
attached. Ports
104 direct the catalyst into conduit 48 for transfer into regenerator vessel
52 in the manner
previously described. Stripping baffles 100 and 102 may again be provided with
dependent

CA 02080974 2003-O1-20
18
skirts and orifices to increase the contact between catalyst and steam that
enters the stripping
vessel through nozzle 30. Steam or other stripping fluid that contacts the
spent catalyst rises
countercurrently to the catalyst and flows out of stripping vessel 28 through
nozzle 26.
All of the stripping steam as well as displaced hydrocarbons flow upwardly
through the
upper stripping vessel and into the disengaging vessel where they are
withdrawn with product
vapors through the central gas tube 32. Figure 5 shows the upper portion of
reactor vessel 19.
The top of disengaging vessel 20 extends into the upper section of reactor
vessel 19. The
disengaging vessel is supported by support lugs (not shown) which are attached
to the wall of
vessel 19. Central gas nozzle 32 extends upwardly and branches into a manifold
that provides
transfer conduits having arms 110. Each of arms 110 is connected to a cyclone
inlet 112 for
cyclones 36. The upper section of the manifold arms and cyclones are supported
by gas outlet
tubes 40. An expansion joint 114 is provided in the branch arms to accommodate
differential
thermal expansion between the gas tube and branch arms and the shell of
reactor vessel 19.
All of the product vapors, stripped hydrocarbons, stripping fluid and
fluidizing gas enter
central gas outlet 32 from the disengaging vessel in the manner previously
described. Pressure
equalizer ports 116 are provided in the sides of central gas tubes 32 and
communicate the open
area of the reactor vessel with the interior of the gas tube to vent
fluidizing gas from the open
area of the reactor vessel. The ports 116 are sized to maintain a suitable
pressure drop usually
less than 0.7 kPa between the open area of the reactor vessel and the central
gas conduit 32. Of
course, venting of gases from the open area of the reactor can be provided by
a vent located in
the branch arms 110, the cyclone inlets 1 12, or even a separate cyclone
vessel located within or
outside of the reactor vessel 19. In addition, it is clear to those skilled in
the art that this
invention can be used with any number of secondary cyclones 36.

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