Note: Descriptions are shown in the official language in which they were submitted.
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LIQUID DEGASER IN AN EBULLATED BED PROCESS
(D#78,996-F)
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an improved vapor-liquid
separator in an ebullated bed process. The separator comprises a
cup with a plurality of riser conduits. Specifically, the
invention relates to an additional separation stage comprising
directing flow discharged from the riser conduits circularly in
the cup.
2. Desc~ O _____ ther Relevant Methods ln the Field
The ebullated bed process comprises the passing of
concurrently flowing streams of liquids or slurries of liquids and
solids and gas through a ver~ically cylindrical vessel containing
catalyst. The catalyst is placed in random motion in the liquid
and has a gross volume dispersed through the liquid medium greater
than the volume of the mass when stationary. This technology has
found commercial application in the upgrading of heavy liquid
hydrocarbons or converting coal to synthetic oils.
The process is generally described in U.S. Patent No. Re
25,770 to E. S. Johanson. A mixture of hydrocarbon liquid and
hydrogen is passed upwardly through a bed of catalyst particles at
a rate such that the particles are forced into random motion as
the liquid and gas pass upwardly through the bed. The catalyst
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bed motion is controlled by a recycle liquid flow so that at
steady state, the bulk of the catalyst does not rise above a
definable level in the reactor. Vapors along with the liquid
which is being hydrogenated pass through that upper level of
catalyst particles into a substantially catalyst free zone and are
removed at the upper portion of the reactor.
In an ebullated bed process substantial amounts of
hydrogen qas and light hydrocarbon vapors rise through the
reaction zone into the catalyst free zone. Liquid is both
recycled to the bottom of the reactor and removed from the reactor
as product from this catalyst free zone. Vapor is separated from
the liquid recycle stream before being passed through the recycle
conduit to the recycle pump suction. The recycle pump (ebullation
pump) maintains catalyst bed expansion (ebullation) and random
motion of catalyst particles at a constant and stable level.
Gases or vapors present in the recycled liquid materially decrease
the capacity of the recycle pump as well as reduce the liquid
residence time in the reactor and limit hydrogen partial pressure.
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Reactors employed in a catalytic hydrogenation process
with an ebullated bed of catalyst particles are designed with a
central vertical recycle conduit which serves as the downcomer
for recycling liquid from the catalyst free zone above the
ebullated catalyst bed to the suction of a recycle pump to
recirculate the liquid through the catalytic reaction zone. The
recycling of liquid from the upper portion of the reactor serves
to ebullate the catalyst bed, maintain temperature uniformity
through the reactor and stabilize the catalyst bed.
U. S. Patent No. 4,221,653 to M. C. Chervenak et al~
describes an apparatus for separating vapor from liquid in an
ebullated bed process. The apparatus comprises a frusto-conical
cup in which are inserted a plurality of riser conduits. The
conduits are positioned in two concentric circles within the cup.
The generic term for the recycle gas-liquid separator apparatus
in an ebullating bed process is a recycle cup. The recycle cup
of the Chervenak et al. patent and those like it with a plurality
of riser conduits are referred to as a tubular recycle cup.
It is a critical feature of the recycle cup that the
upflowing liquid-gas mixture rising from the reaction zone passes
through the riser conduits of the separation apparatus and that
lower ends of all conduits are below the reactor liquid level.
After passage through the recycle cup, the gas portion rises to
the top of the reactor. Part of the liquid portion is returned
through a downcomer conduit and recycled to the reaction zone.
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The remaining liquid portion is withdrawn from the reactor as
liquid product. The returned liquid portion passes through the
recycle conduit to a recycle pump, then passes through a
liquid-gas distribution means, together with fresh liquid and
hydrogen feed to maintain uniform upward fluid flow through the
ebullated catalyst bed. The liquid and vapor effluent may be
withdrawn separately from the upper portion of the reactor. If
withdrawn ~eparately, a second interface between liquid and vapor
is established. Vapor is withdrawn from above the interface.
The liquid is withdrawn from a point in the reactor free of
vapor. If desired, liquid and vapor portions may be withdrawn
together through a single conduit extending into the reactor to a
position adjacent the separator apparatus.
U. S. Patent No. 4,151,073 to A. G. Comolli and U. S.
Patent No. 4,354,852 to P. H. Kydd recognize the advantages of
effecting the recycle liquid-vapor separation in an ebullated bed
process by feeding the fluid tangentially to a cylindrical
separator. By this method, the hot fluid is fed to the
cylindrical separator at conditions to prevent carbonaceous
particulate material from depositing on the interior surface of
the separator. These conditions include tangential injection of
feed to the separator, fluid temperature of 550F to 900F and a
separator length/diameter ratio of 20/1 to 50/1. The Kydd patent
additionally teaches that a liquid vortex in the cylindrical
separator reduces coke deposition.
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The design of liquid cyclone separators is well known in
the art. For example, U.S. Patent Nos. 3,668,116 to C. E. A~ams
et al. describe~ the use of a liquid cyclone in an ebullated bed
process. An essential feature of any cyclone is tangential feed
to a circumferential wall.
U.S. Patent No. 4,443,551 to T. A. Lionetti et al.
teaches a distributor apparatus for delivering high velocity gas
from a gas distributor through a nozzle. The nozzles are
positioned to direct gas at specified angles in a fluid catalytic
cracking process regenerator.
5UMMARY OF THE INVENTION
The present invention provides in combination with a
high pressure reaction vessel adapted for the reaction of a fluid
hydrocarbon feed with a hydrogen rich gas at elevated temperatures
and pressures in the presence of a bed of a particulate solid
catalyst, said reaction being the type wherein the gas and
hydrocarbon feed are passed upwardly through the bed at velocities
whereby the hed is expanded to a volume greater than its static
volume and the particulate solid catalyst is put in a state of
random motlon and wherein the mixture of hydrocarbon feed, gas and
catalyst constitute a catalytic reaction zone wherein minimum
catalyst settling takes place, the upper portion of which is
defined by a liquid continuous, catalyst depleted zone
substantially free of catalyst the upper portion of which liquid
continuous, catalyst depleted zone is positioned;
a generally vertical recycle conduit having an enlarged upper
end of generally circular cross-section in fluid communication
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with a phase separation zone and a lower end in fluld
communication with means for recycling liquid from the catalyst
depleted zone to the lower end of the catalytic reaction zone and
a plurality of generally vertical riser conduits adapted for fluid
flow therethrough extending through the enlarged upper end having
lower ends in fluid communication with said catalyst depleted zone
and upper ends, the improvement to the recycle conduit comprising:
(a) means for directing flow from the upper end of the
riser conduit at an angle of 30 to 6C in the
horizontal plane from a line constructed between
the geometric center of the recycle conduit and the
geometric center of the riser conduit.
The present invention also provides in a high pressure
reaction vessel adapted for the reaction of a fluid hydrocarbon
feed with a hydrogen rich gas at elevated temperatures and
pressures in the presence of a hed of a particulate solid
catalyst, said reaction being the type wherein the gas and
hydrocarbon feed are passed upwardly through the bed at velocities
whereby the bed is expanded to a volume greater than its static
volume and the particulate solid catalyst is put in a state of
random motion and wherein the mixture of hydrocarbon feed, gas and
catalyst constitute a catalytic reaction zone, the upper portion
of which is defined hy a catalys~ depleted zone in which is
positioned; a generally vertical recycle conduit having an
enlarged upper end of circular horizontal cross-section in fluid
communication with a phase separation zone and a lower end in
fluid communication with means for recycling liquid from the
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catalyst depleted zone to the lower end of the catalytic reaction
~one and a plurality of generally vertical riser conduits
providing a plurality of vertical rectilinear fluid flows there
through, said riser conduits extending through the enlarged upper
end having lower ends in fluid communication wi~h said catalyst
depleted zone and upper ends, the improvement comprising: flow
directing means attached to said upper ends adapted to comhine the
plurality of rectilinear flows into a single circular flow in the
horizontal plane within said enlarged upper end.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a sectional elevated view of a reaction
vessel containing a tubular recycle cup vapor-liquid separation
apparatus.
Figure 2 is a cross-sectional view of a riser conduit
comprising a flow deflecting member.
Figure 3a is a plan view of flow deflecting members
oriented with a recycle conduit. Figure 3b is an enlarged plan
view of a deflecting member with orientation.
DETAILED DESCRIPTION OF THE DRAWINGS
In order to demonstrate and provide a better
understanding of the invention, reference is made to the drawings.
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The invention is further illustrated by reference to
Figure 1. Reaction vessel 10 is positioned with its long axis in
a vertical position and is generally of a circular cross section.
Although this Figure 1 drawing is schematic in order to show its
various features, it will be understood that the reactor is
constructed in such a fashion and from such materials that it is
suitable for reacting liquids, liquid-solid slurries, fluidized
solids and gases at elevated temperatures and pressures and in a
preferred embodiment for treating hydrocarbon liquids with
hydrogen at high pressures and high temperatures, e.g. 100 to
5000 psi and 300F to 1500DF. The reactor lO is fitted with a
suitable inlet conduit 12 for feeding heavy oil and a
hydrogen-containing gas. Outlet conduits are located in the
upper portion of reactor 10; outlet conduit 40 designed to
withdraw vapor and liquid, and optionally outlet conduit 24 to
withdraw mainly liquid product. The reactor also contains means
for introducing and withdrawing catalyst particles, which are
shown schematically as conduit 1~ through which fresh catalyst 16
is flowed and conduit 17 through which spent catalyst 14 is
withdrawn.
Heavy oil feedstock is introduced through conduit 11,
while hydrogen-containing gas is introduced through conduit 13,
and may be combined with the feedstock and fed into reactor 10
through conduit 12 in the bottom of the reactor. The incoming
fluid passes through grid tray 18 containing suitable fluid
distribution means. In this drawing, bubble caps 19 are shown as
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the fluid distribution means, but it is to be understood that any
suitable device known in the art which will uniformly distribute
the fluid coming from conduit 12 over the entire cross-sectional
area of reactor 10 may be utilized.
The mixture of liquid and gas flows upwardly, and the
catalyst particles are thereby forced into an ebullated movement
by the gas flow and the liquid flow delivered by recycle pump 20
(ebullation pump) which may be either internal or external to the
reactor 10. The upward liquid flow delivered by this recycle
pump 20 is sufficient to cause the mass of catalyst particles in
catalytic reaction zone 22 (catalyst bed) to expand by at least
10~ and usually by 20 to 100% over the static volume, thus
permitting gas and liquid flow as shown by direction arrow 21
through reactor 10. Due to the upwardly directed flow provided
by the pump and the downward forces provided by gravity, the
catalyst bed particles reach an upward level of travel or
ebullation while the lighter liquid and gas continue to move
upward beyond that level. In this drawing, the upper level of
catalyst or catalyst-liquid interface is shown as interface 23,
and the catalytic reaction zone 22 extends from grid tray 18 to
level 23. Catalyst particles in catalytic reaction zone 22 move
randomly and are uniformly distributed through the entire zone in
reactor 10.
At steady state, few catalyst particles rise above
catalyst-liquid interface 23. The catalyst depleted zone 29,
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above the interface 2~, is filled with liquid and entrained gas
or vapor. Gas and vapor are separated from liquid in the recycle
cup 30 to collect and recycle a liquid with a substantially
reduced gas and vapor content through recycle conduit 25 of
generally circular cross-sectional area. A substantially liquid
product may be withdrawn separately from gas and vapor through
conduit 24, in which event conduit 40 terminates in a vapor space
and is used to withdraw vapor alone. Alternatively gases,
vapors, and liquids may be withdrawn together through conduit 40.
The enlarged upper end of recycle conduit 25 is the
recycle cup 30 of horizontally circular cross-section. A
plurality of vertically directed riser conduits 27 and 28
provides fluid communication between catalyst depleted
zone 29 and phase separation zone 39. Gas-entrained liquid moves
upwardly through the riser conduits 27 and 28, and upon leaving
the upper ends of these riser conduits, a portion of the fluid
reverses direction and flows downward through recycle conduit 25
in the direction of arrow 31 to the inlet of recycle pump 20 and
thereby is recycled to the lower portion of reactor 10 below grid
tray 18. Gases and vapors which are separated from the liquid,
rise to collect in the upper portion of reactor 10 and are
removed through outlet conduit 40. The gases and vapors removed
at this point are treated using conventional means to recover as
much hydrogen as possible for recycle to conduit 13.
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Reference is made to Figure 2. Figure 2 is a
cross-sectional view of the Figure 1 configuration of a single
riser conduit 28 which is positioned in recycle cup 30 in
reactor lQ. Gas-entrained liquid 41, represented as a flow arrow
coincident with the geometric center 28a of riser conduit 28,
moves upwardly into riser conduit 28 where it contacts helical
member 42. Helical member 42 imparts a tangential velocity
component to the gas-entrained liquid 41 and directs it
tangentially toward cyclone separator 50. Cyclone separator 50
effects a vapor-liquid separation. Separated vapor 65 is
redirected through directing member 55 through an angle of 30 to
to 90 preferably 30 to 60 most preferably 45 to become
redirected vapor 65a to a relatively vapor rich zone such as a
vapor zone if a vapor-liquid interface exists within reactor 10.
Separated liquid 45 flows downward along the surface toward
recycle conduit 25 in the direction of arrow 31.
Reference is made to Figure 3a and Figure 3b.
Figure 3a is a plan view of a plurality of deflecting members 55
oriented with respect to the geometric center 25a of the recycle
conduit 25 and with respect to the recycle cup 30. Figure 3b is
an enlarged plan view of a single deflecting member 55 with
orientation. Deflecting member 55 is oriented such that when a
line 80 is constructed between the geometric center 25a of the
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recycle conduit 25 and the geometric center 2~a of the riser
conduit 28, flow is deflected along flow line 99 at an angle of
to 60 preferably 45 in the horizontal plane to the
constructed line.
It is found that the deflection of riser conduit flow in
the angle of 45 in the horizontal plane and ~5 in the vertical
plane takes greatest advantage of the circularity of the recycle
cup 30. As seen in Fig. 3a, these angles are effective in
combining the plurality of vertical rectilinear flow through the
riser conduits into a single coherent circumferential flow in the
horizontal plane. The circular cross-section of both the recycle
cup 30 and reactor vessel 10 are utilized to greater advantage.
The induced tangential flow enhances liquid-vapor separation by
creating a second stage of cyclonic separation within the recycle
cup and above the recycle cup within the upper portion of the
reactor vessel. The existing equlpment is therefore u~ilized to
better process advantage.
While particular embodiments of the invention have been
described, it is well understood that the invention is not limited
thereto since modifications may be made. For example, elevation
angle is adjusted with liquid level in the recycle cup to optimize
separation efficiency. It is therefore contemplated to cover by
the appended claims any such modifications as fall within the
spirit and scope of the claims.
