Note: Descriptions are shown in the official language in which they were submitted.
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APPARATUS AND PROCESS FOR MINIMIZING CATALYST
RESIDENCE TIME IN A REACTOR VESSEL
BACKGROUND OF THE INVENTION
[0001] This invention relates generally to processes for the quick separation
of particulate
solids from gases. More specifically, this invention relates to minimizing the
contact between
gaseous products and catalyst particles after reaction.
DESCRIPTION OF THE PRIOR ART
[0002] A fluidized catalytic cracking (FCC) process is a process that cracks
higher
molecular weight hydrocarbons down to gasoline and liquefied petroleum gas
(LPG) range
hydrocarbons. The FCC process is carried out by contacting hydrocarbonaceous
feed material
such as vacuum gas oil, residual crude, or another source of relatively high
boiling
hydrocarbons with a catalyst made up of finely divided or particulate solid
material in an
elongated conduit. Contact of the feed with the fluidized catalyst particles
catalyzes the
cracking reaction while coke is deposited on the catalyst. Catalyst exiting
the reaction zone is
spoken of as being "spent", i.e., partially deactivated by the deposition of
coke upon the
catalyst. Spent catalyst is traditionally transferred to a stripper that
removes adsorbed
hydrocarbons and gases from catalyst and then to a regenerator for purposes of
removing the
coke by oxidation with an oxygen-containing gas. Regenerated catalyst is
returned to the
reaction zone. Oxidizing the coke from the catalyst surface releases a large
amount of heat, a
portion of which leaves the regenerator with the regenerated catalyst. The FCC
processes, as
well as separation devices used therein are fully described in US 5,584,985
and US
4,792,437.
[0003] Spent catalyst still has catalytic activity. Prolonged contact between
spent catalyst
and cracked product can allow overcracking of desired products and additional
coke
deposition, thereby diminishing the recovery of desired product. Spent
catalyst and gas
products exiting the reactor conduit typically enter into a voluminous reactor
vessel in which
they may reside for prolonged times before separation, thereby allowing
additional cracking
to occur. Separation devices at the discharge end of the reactor conduit have
been used to
quickly separate much of the catalyst and gaseous product.
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[0004] US 4,397,738 and US 4,482,451 disclose an arrangement for making a
quick
separation by tangentially discharging a mixture of gaseous product and solid
catalyst
particles from a reactor conduit into a containment vessel. The centrifugal
force created by
the tangential discharge of the gases containing solid catalyst particles
forces the heavier
solids particles outwardly away from the lighter gases thereby allowing upward
withdrawal
of gases and downward collection of solids. The containment vessel has a
relatively large
diameter and generally provides a first separation of solids from gases. In
these arrangements
the initial stage of separation is typically followed by a second more
complete separation of
solids from gases in a traditional cyclone separator located in the reactor
vessel.
[0005] Cyclone separators usually comprise relatively small diameter cyclones
having a
tangential inlet on the outside of a cylindrical vessel that forms the outer
housing of the
cyclone. The tangential inlet imparts a tangential velocity to entering gases
and entrained
solids forcing outward and downward collection of solids and upward withdrawal
of the
lighter gases. The collected catalytic solids usually descend through a dipleg
into a catalyst
bed at bottom of the reactor vessel.
[0006] The catalyst bed is typically fluidized to facilitate entry of the
catalyst into a
stripper vessel. The reactor vessel contains a large volume of empty space in
which catalyst
can become entrained with gaseous product. Entrainment can occur when catalyst
is being
transferred between separator stages, transferred from the cyclone dipleg into
the catalyst bed
and fluidized in the catalyst bed. Typically, the reactor vessel is purged
with an inert gas,
such as steam, to suppress product gases from floating with entrained catalyst
particles in the
reactor vessel. However, catalyst particles entrained in the inert gas have
hydrocarbons
adsorbed thereon, which may continue to react until the catalyst enters the
stripping vessel.
Finally, in the stripping vessel a substantial proportion of the hydrocarbons
are desorbed and
separated from the catalyst particles. Consequently, catalyst and gaseous
product can be
together in the reaction vessel for a long period of time after the desired
reaction is complete
and the catalyst and gaseous product exit the reactor conduit.
[0007] US 4,220,623 discloses a reactor vessel for an FCC unit that is divided
from a
stripper vessel. Stripper vent lines extend from the stripper vessel upwardly
along the diplegs
of cyclones in the reactor vessel to a height above the dense bed in the
reactor vessel. The
arrangement purports to reduce the height of the reactor vessel. The reactor
conduit is not
directly connected to the cyclone separators in the reactor vessel.
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[0008] US 4,946,656 discloses a reactor conduit directly connected to a first
stage
cyclone separator, which is connected to a second stage cyclone separator by a
gas conduit.
The recovery conduit between the first and second stage cyclone separators is
open to the
reactor vessel. The diplegs of the first and second stage cyclone separators
descend into a
stripper zone through a frustoconical stripper cap. A circumference of the
stripper cap is
spaced from the inner sidewall of the reactor vessel by a maximum distance of
25% of the
inside radius of the reactor vessel. A vent conduit delivers gases from the
stripper zone to the
conduit between the first and second stage cyclone separators. The steam flow
rate necessary
to prevent product gases from passing from the stripper zone into the reactor
vessel though
the numerous openings in the stripper cap and to drive product gases upwardly
through the
vent conduit to the recovery conduit will be very large.
BRIEF SUMMARY OF THE INVENTION
[0009] We have discovered a way to minimize the time that catalyst and gaseous
products are in contact after exiting the discharge end of a reactor conduit
of an FCC unit.
The reactor conduit discharges into a disengaging chamber which is directly
connected to a
separator. A dipleg of the separator is directly connected to the disengaging
chamber or to an
intermediate chamber which is in direct communication with the disengaging
chamber.
Accordingly, catalyst never becomes entrained in the large open volume of the
reactor vessel.
Consequently, catalyst which makes it out of the disengaging chamber is
quickly returned
back to the disengaging chamber, thereby minimizing the time that catalyst and
gas products
are in contact after being discharged from the reactor conduit. Moreover, the
reactor vessel
may be purged with an inert gas such as steam to prevent any product gases
from ascending
upwardly in the reactor vessel.
[0010] Accordingly, it is an object of the present invention to provide an
apparatus and
process for minimizing the time that solid catalyst particles and gas products
are in contact
with each other after being discharged from a reactor conduit of an FCC unit.
[0011] Additional details and embodiments of the invention will become
apparent from
the following detailed description of the invention.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a schematic elevational view of an FCC unit arranged in
accordance with
this invention.
[0013] FIG. 2 is a schematic elevational view of an alternative FCC unit
arranged in
accordance with this invention.
[0014] FIG. 3 is an enlarged section of FIG. 2.
[0015] FIG. 4 is a schematic elevational view of an alternative partial FCC
unit arranged
in accordance with this invention.
[0016] FIG. 5 is a schematic elevational view of an alternative partial FCC
unit arranged
in accordance with this invention.
[0017] FIG. 6 is a schematic elevational view of an alternative partial FCC
unit arranged
in accordance with this invention.
[0018] FIG. 7 is an enlarged view of a section of FIG. 6.
DESCRIPTION OF THE INVENTION
[0019] The present invention can be used in any apparatus or process in which
solids and
gases must be separated. However, an FCC process always requires such
separations and will
be the most widespread application for the present invention. Hence, the
present invention
will be exemplarily described in an FCC application.
[0020] Looking first at more details of an FCC process in which the present
invention
may be used, 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. In
an
embodiment, the feed stream may consist of a mixture of hydrocarbons having
initial boiling
points, as determined by the appropriate ASTM test method, above 230 C (446
F), often
above 290 C (554 F) and typically above 315 C (600 F) and end points no more
than 566 C
(1050 F). The reaction zone of an FCC process is maintained at high
temperature conditions
which may generally include a temperature above 425 C (797 F). In an
embodiment, the
reaction zone is maintained at cracking conditions which include a temperature
of from 480
to 590 C (896 to 1094 F) and a pressure of from 69 to 517 kPa (ga) (10 to 75
psig) but
typically less than 275 kPa (ga) (40 psig). The catalyst-to-oil ratio, based
on the weight of
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catalyst and feed hydrocarbons entering the bottom of the riser, may range up
to 20:1 but is
typically 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 to
effect catalyst fluidization and feed dispersion. The average residence time
of catalyst in the
riser may be 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
zeolite base
material is preferred, but the older style amorphous catalyst may be used if
desired.
[0021] The catalyst regeneration zone is preferably operated at a pressure of
from 69 to
552 kPa (ga) (10 to 80 psig). The spent catalyst being charged to the
regeneration zone may
contain from 0.2 to 15 wt-% coke. This coke is predominantly comprised of
carbon and can
contain from 3 to 12 wt-% hydrogen, as well as sulfur and other elements. The
oxidation of
coke will produce the common combustion products: water, carbon oxides, sulfur
oxides and
nitrous oxides. As known to those skilled in the art, the regeneration zone
may take several
configurations, with regeneration being performed in one or more stages.
[0022] FIG. 1 is the schematic illustration of an FCC unit embodying the
present
invention. The FCC unit includes an elongated riser or reactor conduit 10. Hot
catalyst is
delivered to a lower section of the reactor conduit 10 at which a fluidizing
gas from a
distributor 8 pneumatically conveys the catalyst particles upwardly through
the reactor
conduit 10. As the mixture of catalyst and conveying gas continues up the
reactor conduit 10,
a nozzle 40 injects hydrocarbonaceous feed and perhaps steam into the
catalyst. The contact
with hot catalyst vaporizes the hydrocarbons and further conveys the mixture
of gas and
catalyst through the reactor conduit 10 while cracking the hydrocarbons to
desirable lower
boiling products.
[0023] The reactor conduit 10 extends upwardly into a reactor vessel 12 as in
a typical
FCC arrangement. The reactor conduit 10 preferably has a vertical orientation
within the
reactor vessel 12 and may extend upwardly through a bottom of the reactor
vessel 12. The
reactor vessel 12 includes a disengaging chamber 16 defined by an outer
separating wall 24.
The outer separating wall 24 of the disengaging chamber 16 has sections, some
of which may
be cylindrical. The reactor conduit 10 terminates in the disengaging chamber
16 at exits
defined by the end of swirl arms 14. Each of the swirl arms 14 may be a curved
tube that has
an axis of curvature that may be parallel to the reactor conduit 10. Each
swirl arm 14 has one
end communicatively connected to the reactor conduit 10 and another open end
comprising a
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discharge opening 22. The swirl arm 14 discharges a mixture of gaseous fluids
comprising
cracked products and solid catalyst particles through the discharge opening
22. Tangential
discharge of gases and catalyst from the discharge opening 22 produces a
swirling helical
motion about the cylindrical interior of the disengaging chamber 16.
Centripetal acceleration
associated with the helical motion forces the heavier catalyst particles to
the outer portions of
the disengaging chamber 16. Catalyst particles from the discharge openings 22
collect in the
bottom of the disengaging chamber 16 to form a dense catalyst bed 38. The
gases, having a
lower density than the solid catalyst particles, more easily change direction
and begin an
upward spiral. The disengaging chamber 16 includes a gas recovery conduit 18
with an inlet
20 through which the spiraling gases ultimately travel. The gases that enter
the gas recovery
conduit 18 through the inlet 20 will usually contain a light loading of
catalyst particles. The
inlet 20 recovers gases from the discharge openings 22 as well as stripping
gases from a
stripping section 28 which may be located in the disengaging chamber 16 as is
hereinafter
described. The loading of catalyst particles in the gases entering the gas
recovery conduit 18
are usually less than 16 kg/m3 (1 lb/ft3) and typically less than 3 kg/m3 (0.2
lb/ft3). The gas
recovery conduit 18 of the disengaging chamber 16 includes an exit or outlet
26 contiguous
with an inlet or entrance 30 to one or more cyclones 32 that effect a
fi.trther removal of
catalyst particulate material from the gases exiting the gas recovery conduit
18 of the
disengaging chamber 16. The disengaging chamber 16, the gas recovery conduit
18 thereof
and the cyclones 32 are all directly connected, meaning that they are in fluid
communication
with each other and sealed against substantial leakage. Hence, substantially
all of the gases
and solids exiting the disengaging chamber 16 enter the cyclones 32.
[0024] The cyclones 32 create a swirl motion therein to establish a vortex
that separates
solids from gases. A product gas stream, relatively free of catalyst
particles, exits the
cyclones 32 through vapor outlet pipes 50 into a fluid-sealed plenum chamber
56. The
product stream then exits the reactor vessel 12 through an outlet 25. Each
cyclone 32 includes
an upper cylindrical barrel section 31 contiguous with the entrance 30. The
barrel section 31
is connected by a first frustoconical section 33 to a hopper section 35. The
hopper section 35
is contiguous with a second frustoconical section 37 which is contiguous with
a dipleg 34.
Catalyst solids recovered by the cyclones 32 exit the bottom of the cyclone
through diplegs
34. The diplegs 34 comprise conduits that may have one or more sections. The
diplegs 34
extend downwardly in the reactor vessel 12 and extend through an opening 36 in
the outer
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separating wall 24 of the disengaging chamber 16. The dipleg 34 is thus
directly connected to
the disengaging chamber 16, meaning that the dipleg 34 is sealed against
leakage such that
substantially all of the solids and gases exiting the dipleg 34 enter into the
disengaging
chamber 16. The dipleg 34 shown in FIG. 1 includes a diagonal section that
extends into the
disengaging chamber 16. However, other configurations of the dipleg 34 are
embraced by the
invention, and it is not necessary that the dipleg 34 extend beyond the outer
wall 24 of the
disengaging chamber 16. Suitable devices, such as a slip joint or an expansion
joint, may be
used at the opening 36 to accommodate differential thermal expansion between
the dipleg 34
and the opening 36 in the outer wall 24 of the disengaging chamber 16.
Moreover, a suitable
valve, such as a trickle valve, may be used on the outlet of the dipleg 34 to
regulate catalyst
flow. If a slip joint is used between the dip leg 34 and the opening 36, an
inert gas, such a
steam, may be injected into the reactor vessel 12 by a distributor 42 to purge
the reactor and
prevent gases or solids from escaping the slip joint. If an expansion joint is
used at opening
36, no purge will be necessary to prevent gases or solids from escaping
through the opening
36 by the expansion joint. However, injection of an inert gas may be necessary
to purge other
gaps between piping in the reactor vessel 12.
[0025] The dipleg 34 delivers catalyst to the dense catalyst bed 38 in the
disengaging
chamber 16. Catalyst solids in the dense catalyst bed 38 enter the stripping
section 28 which
may be located in the disengaging chamber 16. Catalyst solids pass downwardly
through
and/or over a series of baffles 44 in the stripping section 28. A stripping
fluid, typically
steam, enters a lower portion of the stripping section 28 through at least one
distributor 46.
Counter-current contact of the catalyst with the stripping fluid over the
baffles 44 displaces
product gases adsorbed on the catalyst as it continues downwardly through the
stripping
section 28. Stripped catalyst from the stripping section 28 may pass through a
conduit 48 to a
catalyst regenerator 52. In the regenerator, coke deposits are combusted from
the surface of
the catalyst by contact with an oxygen-containing gas at high temperature.
Following
regeneration, regenerated catalyst particles are delivered back to the bottom
of the reactor
conduit 10 through a conduit 54.
[0026] FIG. 2 shows an alternative embodiment of the present invention shown
in FIG. 1.
FIG. 3 shows an enlarged section of FIG. 2. In FIGS. 2 and 3, the same
reference numerals
will be used to designate the same elements as in FIG. 1. However, elements
having a
different configuration in FIG. 2 than in FIG. 1 will be designated with the
same reference
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numeral as in FIG. 1 but marked with a prime symbol ('). Referring to FIG. 2,
the diplegs 34'
of the cyclones 32' do not extend all the way to the openings 36' in the outer
wall 24' of the
disengaging chamber 16'. However, the diplegs 34' extend at least to and in an
embodiment
through an opening 62 in an intermediate separating separating wall 60 in the
reactor vessel
12'. The intermediate separating separating wa1160 defines an intermediate
chamber 64 with
the wall of the reactor vessel 12' and the outer wall 24' of the disengaging
chamber 16'. FIG.
3 shows this arrangement in detail. The intermediate separating separating
wall 60 may be
secured to the inner surface of the outer wall of the reactor vessel 12' and
to the outer surface
of the outer wall 24'. An expansion joint may be provided between the opening
62 in the
intermediate separating separating wa1160 and the dipleg 34'. This arrangement
would
obviate the need for a purge to prevent escape of gases from intermediate
chamber 64 into the
open volume in the reactor vessel 12'. If a slip joint is provided between the
opening 62 in
the intermediate separating separating wa1160 and the dipleg 34', an inert gas
purge will be
necessary to prevent gases from escaping the intermediate chamber 64 through
opening 62.
The intermediate separating separating wall 60 may be made less robust than
the outer wall
24' or the wall of the reactor vessel 12'. If a pressure differential becomes
severe, the
intermediate separating separating wa1160 will fail or blow out before the
outer wall 24' of
the disengaging chamber 16' or the wall of the reactor vessel 12' fails, thus
preventing
pervasive damage to the disengaging chamber 16' or the reactor vessel 12'.
However, the
intermediate separating separating wall 60 is shown in FIGS. 2 and 3 to be
secured such as by
welding only to the outer surface of the outer wall 24' of the disengaging
chamber 16'.
Altematively, the intermediate separating separating wa1160 may be secured
only to the
dipleg 34' about the opening 62 or only to the inner surface of the outer wall
of the reactor
vessel 12'. In these cases, purge of inert gas from distributor 42 will be
necessary to prevent
gases from intermediate chamber 64 from escaping. In the event of a shutdown
or
malfunction which may precipitate a substantial pressure differential between
the disengaging
chamber 16' and the reactor vessel 12', the intermediate separating separating
wall 60 can
bend about its securement to permit equalization of the pressure differential.
The intermediate
separating separating wall 60 should have a small thickness compared to the
outer wall 24' of
the disengaging chamber 16' and/or the wall of the reactor vessel 12' to
facilitate bending or
blow out to relieve pressure. In an embodiment, the intermediate separating
separating wall
60 should be less than 1/8 of the thickness of the outer wall 24' or the wall
of the reactor
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vessel 12'. Edges of the intermediate separating wall 60 which are not secured
to an adjacent
surface define a gap therewith which is minimal and less than 25% of the
radius of the reactor
vessel 12'. The gap between the edges of the intermediate separating wall 60
and other walls
to which it is not secured should only be large enough to permit thermal
expansion so as to
reduce the load necessary to pump steam into the reactor vessel 12' and
prevent the escape of
product gases therefrom. Consequently, purge stream from the distributor 42
purges through
such gaps to prevent vapors in an intermediate chamber 64 from escaping to the
remainder of
the reactor vessel 12'. In an embodiment, the vapors in the intermediate
chamber 64 may
only escape through the openings 36' in the outer wall 24' of the disengaging
chamber 16'.
The openings 36' allow this dense catalyst bed 38 to form both within and
without of the
outer wall 24' of the disengaging chamber 16'. A distributor 66 may distribute
fluidizing gas,
such as steam, into the intermediate chamber 64 to facilitate entry of the
catalyst solids into
the disengaging chamber 16' through the openings 36'. If the level of the
dense catalyst bed
38 is designed to be higher than the openings 36', additional vent openings
(not shown) may
be made in the outer wall 24' of the disengaging chamber 16' to permit vapors
from the
intermediate chamber 64 to enter into the disengaging chamber 16'. Under such
a design, the
inert gas distributor 66 becomes more necessary. Such vapors from the
intermediate chamber
64 that enter the disengaging chamber 16' will mix with stripping gas from the
stripping
section 28 rising through the disengaging chamber 16' and vaporous product and
entrained
catalyst from the discharge openings 22 will ascend through the gas recovery
conduit 18 of
the disengaging chamber 16' through the cyclones 32' and out the vapor outlet
pipes 50 and
the outlet 25. However, product gas from the intermediate chamber 64 will not
be allowed to
mix in the reactor vessel 12', thereby reducing the residence time of gaseous
product
discharged from the discharge openings 22 from the reactor conduit 10. The
diplegs 34' in
FIGS. 2 and 3 are shown with counter-weighted flapper valves because the
bottom edge of
the dipleg 34' is generally horizontal. Other configurations of the outlet of
the dipleg may be
applicable, such as vertical or angled outlets. In those cases, trickle valves
or angled flapper
valves may be appropriate, respectively. Additionally, a vent (not shown) may
be provided in
the disengaging chamber 16' or in the gas recovery conduit 18 thereof to
equalize pressure
between the disengaging chamber 16' and the reactor vessel 12' and/or the
intermediate
chamber 64 in the event of a malfunction. The vent may comprise a piping
arrangement with
one end at a lower elevation in the reactor vessel 12' or in the intermediate
chamber 60 and
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another end in communication with the gas recovery conduit 18. Such an
arrangement may
be useful if a side stripper is employed.
[0027] FIG. 4 is a further alternate embodiment of the invention shown in FIG.
1.
Elements in FIG. 4 that have different configurations than the corresponding
elements in
FIGS. 1-3 will be designated with a reference numeral marked with a double
prime symbol
("). The outer separating wall 24" of the disengaging chamber 16" is expanded
around the
openings 36" to define an extended section 70. In an embodiment, the diplegs
34" of the
cyclones 32" include a diagonal section and extend to the opening 36" to
deliver gases and
solids to the dense catalyst bed 38 in the disengaging chamber 16". The
extended section 70,
in an embodiment, comprises a cylindrical band which has a diameter which is
greater than
the diameter of the disengaging chamber 16". Vents 72 in the dipleg 34" serve
to vent purge
gas from the distributor 42 through the dipleg 34", the opening 36" and into
the disengaging
chamber 16". The embodiment in FIG. 4 contemplates sealing the circumference
of the
dipleg 34" to the outer separating wall 24" of the disengaging chamber 16".
Hence, the dipleg
34" is equipped with the vents 72 to purge the outlet of the dipleg and to
allow for pressure
relief in the event of unit malfunction. In this embodiment, the diplegs 34"
can be equipped
with slip joints to allow for differential thermal expansion but these are not
shown in FIG. 4.
Purge gas will also flow through slip joints to prevent product gas from
escaping into the
reactor vessel 12". Alternatively, the diplegs 34" may be completely sealed
against fluid
communication with the reactor vessel 12" but allow for thermal expansion, as
is known in
the art by use of an expansion joint. Under this alternative, the distributor
42 and the vents 72
would be omitted. Moreover, the diplegs 34" are equipped with a trickle valve,
which may be
omitted or another type of outlet valve for the dipleg may be used. The
cylindrical extended
section 70 is defined by an outer cylindrical separating wall 74 and top and
bottoms walls
which connect the expanded cylindrical separating wall 74 to the outer wall
24" of the
disengaging chamber 16".
[0028] FIG. 5 is an alternative embodiment to the expanded disengaging
chamber.
Reference numerals in FIG. 5 which refer to elements which have a different
configuration
than in any of the FIGS. 1-4 are marked with a triple prime symbol ("'). In
the embodiment
in FIG. 5, the disengaging chamber 16"' is expanded to divide the extended
section 70"'
which circumferences the disengaging chamber 16"'. In an embodiment, the
annular
separating wall 74"' extends diagonally from the outer wall 24"' of the
disengaging
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chamber 16"' to join the shell of the reactor vessel 12"', thereby defining
the extended
section 70"'. The diplegs 34"' of the cyclones 32"' extend through the
openings 36"' in the
extended separating wall 74"' of the outer wall 24"' of the disengaging
chamber 16"'.
Consequently, the diplegs 34"' omit the diagonal section. In an embodiment,
the dipleg is
sealed to the expanded separating wall 74"' with an expansion joint, so that
no vapors from
outside the extended section 70"' come in or come out through the separating
wall 74"'
except through the dipleg 34"'. Under such conditions, the purge gas from a
distributor may
be omitted. Alternatively, in another embodiment, the distributor of purge gas
may be
retained, although not shown in FIG. 5, and either the dipleg 34"' is coupled
by a slip joint to
the separating wall 74"' or a vent opening is provided somewhere in the outer
wall 24"' of
the disengaging chamber 16"' or in the gas recovery conduit 18 to allow purge
gas
therethrough. The dipleg 34"' is shown without any outlet valve and extending
through the
expanded separating wall 74"'. However, appropriate outlet valves may be
provided and the
dipleg 34"' may be designed to extend not more than to the expanded separating
wall 74"'.
[0029] FIG. 6 shows a further embodiment of the present invention. FIG. 7
shows a
partial expanded view of a portion of FIG. 6. In FIGS. 6 and 7, reference
numerals which
designate elements that have different configurations from corresponding
elements in FIGS.
1-5 are marked with a quadruple prime (""). In this embodiment, the
disengaging chamber
16"" is equipped with reception tubes 78 extending from the outer wall 24"" of
the
disengaging chamber 16"". The diplegs 34"" of the cyclones 32"" extend through
the
opening 36"" in a separating wall 74"" of the reception tubes 78. The
reception tubes 78
together define the extended section 70" " which receive the lower section of
the diplegs
34"". A slip joint is provided in the opening 36"" to allow differential
thermal expansion
between the dipleg 34"" and the separating wall 74"" of the reception tubes
78. Hence,
purge gas from the distributor 42 in the reactor vessel 12"" may purge through
a gap (not
shown) between the inner diameter of the opening 36.... in the separating wall
74.... and the
outer diameter of the dipleg 34..... The flow rate of purge gas from the
distributor 42 is set so
that purge gas can only go through the opening 36"" into the extended section
70"" but
gases and entrained catalyst within the extended section 70"" cannot exit
therefrom through
the opening 36"". Alternatively, the dipleg 34"" may connected by an expansion
joint to
the reception tubes 78 obviating the need for inert gas purge. In a further
alternative, the
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extended section 70"" may comprise a unitary annular section comprising a
plurality of the
openings 36"" which circumferences all or a portion of the disengaging chamber
16"".
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