Note: Descriptions are shown in the official language in which they were submitted.
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METI30D OF AND APPARATUS FOR SE;eARATING SOLVENT
IN A FEED OF SOLVENT AND DE,ASPHALTED OIL
FIELD OF THE INVENTION
This invention relates to a method of and apparatus
for separating solvent in a feed of solvent and
deasphalted oil produced by a deasphalting process.
BACKGROUND OF THE INVENTION
A by-product of refineries that process crude oil
into economically valuable light hydrocarbons, such as
gasoline, is a heavy viscous, hydrocarbon called
residual oil that often is further processed in a
solvent deasphalting plant. In such a plant, residual
oil is contacted with a solvent, su~~h as propane, i-
butane, n-butane, or pentane, under conditions of
temperature and pressure which separates the feed into
two liquid streams. One stream contains deasphalted oil
(DAO) and most of the solvent, and the other contains
asphaltene and the remainder of the solvent. The solvent
in the two streams produced by the separator is
recovered in a solvent recovery unit and used againa and
although the asphaltene product is of relatively limited
value, the DAO product is very valuable because it can
be cycled back to the refinery and converted into
gasoline or the like.
Some solvent recovery units operate under
conditions of temperature and pressure at which the
solvent in the stream of DAO and solvent is
supercritical. In its supercritical state, the solvent,
although a liquid, has a density much lower than that of
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the DAO, and behaves almost as a gas. As a consequence,
the stream of supercritical solvent and DAO acts as a
two-phase fluid.
Conventionally, a supercritical. solvent recovery
unit utilizes a pressure vessel that. receives the feed
of DAO and solvent through a nozzle which effects even
distribution of solvent and DAO across the cross-
sectional area of the vessel. Such distribution is often
accompanied by turbulence that causes mixing of the
supercritical solvent with the DAO, and complicates
separation and recovery of the solvent.
U.S. Pat. No. 4,479,875 discloses a nozzle for
introducing fluids of different densities into a calm
fluid in a vessel without causing excessive turbulence
and "carry-over" of high density fluid into the low
density fluid. While excessive turbulence and high
"carry-over" are eliminated, a significant pressure drop
is introduced and this results in a remixing of the two
phases.
The result is that the pressure vessel must be
sufficiently large to permit re-separation to occur so
that the solvent and DAO then can be drawn off
separately. Consequently, for a given through-put; the
separator vessel must be designed with a diameter
sufficiently large to permit the supercritical solvent
and DAO to again separate after the 'two-phase fluid is
introduced into the separator.
It is therefore an object of the present invention
to provide a new and improved method of and apparatus
for separating solvent in a feed of supercritical
solvent and deasphalted oil which is more efficient in
capital cost and physical size than conventional methods
and apparatus.
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BRIEF DESCRIPTION OF THE INVENTION
The present invention provides apparatus for
separating solvent in a feed of solvent and deasphalted
oil produced in a deasphalting process including a feed
line for receiving the feed and constructed and arranged
to produce a main stream of fluid containing
supercritical solvent and deasphalted oil. A
substantially horizontally disposed inlet line receives
the main stream of fluid and is designed to effect two
phase laminar flow at the outlet of the inlet line. The
two phase laminar flow of feed establishes a
substantially horizontally disposed interface that
divides the main stream into an upper part containing
the lighter supercritical solvent which floats on a
lower part containing the heavier deasphalted oil.
The invention also includes at least one divider
member at the outlet of said inlet :Line facing the
stream. This divider member has a tapered leading edge
whose apex can be located at substantially the same
elevation as the interface between supercritical solvent
and the deasphalted oil for mechanically separating the
main stream into an upper flow stream containing
essentially only supercritical solvent, and a lower flow
stream containing deasphalted oil with a significantly
reduced amount of solvent.
In one embodiment of the invention, at least one
substantially horizontal, axially extending tube is
provided. One end of this tube internally receives both
the upper and lower flow streams, a.nd the other end of
the tube is capped. The upper surface of_ the tube has
holes distributed axially along the length of the tube
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for effecting egress of fl~id (essentially all solvent)
from the upper flow stream, and the lower surface of
said tube is apertured for effecting' egress of fluid
(essentially all DAO) from the lower flow stream. The
lower surface of said tube may have holes distributed
axially along the length of the tube', or simply may have
a relatively large single aperture.
In another embodiment of the invention, the tube is
provided with an axially extending :>eparator baffle that
divides the tube into an upper chamber into which flows
said upper flow stream, and a lower chamber into which
flows said lower flow stream thus maintaining
segregation between the upper and lower streams. In such
ease, the upper and lower surfaces of the tube have
holes distributed axially along the length of the tube
for effecting egress of fluid from the upper flow
stream, and the lower surface of said tube is apertured
for effecting egress of fluid from the lower flow
stream.
In another embodiment of the invention, a first
substantially horizontally disposed axially extending
tube receives the upper flow stream, and a second
substantially horizontally disposed axially extending
tube receives the lower flow stream. The upper surface
of each tube has holes distributed axially along the
length of the tube for effecting egress of fluid, and
the lower surface of each tube is apertured for
effecting egress of fluid from the tube.
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According to a first broad aspect of an embodiment of the
present invention, there is disclosed apparatus for separating
solvent in a feed of lighter solvent and heavier deasphalted oil
produced in a deasphalting process, said apparatus comprising:'
a) a feed line for receiving said feed and
constructed and arranged to produce a main stream of
fluid containing supercritical solvent and deasphalted
oil;.
b) a substantially horizontally disposed inlet
line for receiving said main stream, and constructed and
arranged to produce a.t the outlet of said inlet line,
two phase laminar flow of said stream such that the
lighter supercritical solvent is substantially separate
from and floats on the heavier deasphalted oil.
According to a second broad aspect of an embodiment of the
present invention, there is disclosed apparatus for use with a
supercritical solvent recovery separator that is a part of a
deashphal.ting process which produces a fluid stream of
deasphalted oil and supercritical solvent, said apparatus
comprising:
a) an inlet line carrying said stream and
constructed and arranged to produce in said line,
two phase laminar flow of said stream such that the
lighter supercritical solvent is separate from and
floats on the heavier deasphalted oil;
b) a.nozzle in said separator having a
junction connected to said.inlet line;
c) said junction.being constructed and
arranged to separate said fluid into an upper flow
path containing essentially only supercritical
solvent, and a lower .flow path containing
essentially only deasphalted oil.
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BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the present invention are described
by way of example with reference to the accompanying
drawings wherein:
FIG. 2 is a schematic block diagram of a
conventional supercritical solvent f.easphalting plant
showing the conversion of a feed of residual oil from a
refinery, for example, into a product stream of
asphaltene and deasphalted oil;
FIG. 2 is a detail of the solvent recovery unit of
the plant shown in FIG. 1;
FIG. 3 is a schematic plan view of a supercritical
solvent recovery separator according to the present
invention showing a plurality of horizontally disposed
tubes that receives a feed of supercritical solvent and
deasphalted oil;
FIG. 3A is a sectional view taken along the line
3A--3A of FIG. 3;
FIG. 3B is a schematic diagram showing a control
system for maintaining a minimum amount of deasphalted
oil in the solvent output of the separator, and a
minimum amount of solvent in the deasphalted oil output;
FIG. 4 is a side elevation in :section of one of the
tubes shown in FIG. 3;
FIG. 5 is a side elevation in section of a
modification of the tube shown in F=CG. 4;
FIG. 6 is a side elevation in section of a further
modification of the tube shown in FIG. 4;
FIGS. 7 and 8 are side elevations of another
embodiment of the present invention,;
FIGS. 9-11 are side elevations of a further
embodiment of the present invention; and
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FIGS. 12-14 are side elevations of still a further
embodiment of the present invention;
DETAILED DESCRIPTION
Turning now to the drawings, reference numeral 100
designates a conventional supercritical solvent
deasphalting plant showing the canversion of feed 1 of
residual oil from a refinery, for example, into
20 asphaltene product stream 27 and deasphalted oil product
stream 41. Residual oil in line 1 is co~ibined with
solvent (e. g., propane) in line 4, for example,
producing in line 2, a stream of so:Lvent and residual
oil that is applied to asphaltene separator 5 which
typically operates slightly above, or slightly below the
critical pressure of the solvent and at temperature
which is in the range about 100°F. below to about 100°F.
above the critical temperature of the solvent. In the
separator, the residual oil separates into a mixture of
lighter deasphalted oil and heavier asphaltene. A
lighter stream of deasphalted oil and most of the
solvent passes out the overhead of the separator into
line 6, and a heavier stream of asphaltene and solvent
passes out the bottom of the separator in line l7. Valve
26 in line 17 regulates the operation of separator 5.
Heat exchangers 7 and 9 further heat the stream in
lines 6 and 8 causing the solvent in the stream to reach
a temperature and pressure at which the solvent is in
supercritical condition. Although in a liquid state, the
supercritical solvent behaves as if_ it were a gas; and
the stream of supercritical solvent. and DAO exiting heat
exchanger 9 is a two-phase flow that is applied to
supercritical solvent recovery sep<~rator 12 via feed
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line 10. within separator 11, the solvent coalesces
separately from the DAO, and mostly liquid solvent comes
out the top of the separator into line 12, and DAO and
some solvent comes out the bottom of the separator into
line 28. Heat exchangers 7 and 9 and separator 11
substantially comprise a supercritical solvent recovery
unit of the solvent deasphalting plant.
The supercritical hot solvent in line 12 is
returned to separator 5 after first removing heat from
the solvent to return it to its sub<:ritical state. This
is achieved by first passing the supercritical solvent
through heat exchanger 7 where some of the heat is given
up to the solvent and DAO mixture in line 5, and then
passing the cooled solvent through cooler 14.
The mixture of mostly DAO and solvent in line 28 is
applied to stripper 29 wherein steam from line 40
vaporizes the solvent. Vaporized solvent exits the
stripper at the top in line 30, and DAO that remains is
drawn off at the bottom of the stripper in line 36. Some
of the DAO is cycled back to the stripper via lines 37
and 39 after being reheated at 38 i:n order to further
reduce the amount of residual solvent in the DAC. The
balance of the DAO, substantially free of solvent, is
drawn off as product in line 41. This valuable product
may be cycled back to a refinery where it can be
converted into gasoline or the like.
Asphaltene in the mixture of asphaltene and solvent
that passes out of the separator in. line 17 is recovered
by first heating the mixture at 28 and then applying the
mixture to stripper 20 which operates essentially like
stripper 29 producing vaporized solvent in line 21 and
substantially solvent free asphaltene product in line
27.
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Finally, vaporized solvent in line 21 produced by
asphaltene stripper 20 and vaporized solvent in line 30
produced by DAC stripper 29 are combined at 31, cooled
and condensed in condenser 32, and returned to solvent
drum 34 via line 33. Sour water in the solvent drum from
condensed steam is removed at 35, and line 16 provides
make-up solvent to separator 5.
In order to establish a supercritical condition for
the solvent in the DAO and solvent feed in line 10, a
feedback arrangement like that shown in FIG. 2 can be
utilized. That is to say, temperature sensor 22 in line
10 senses the temperature of the fluid in the line and
adjusts flow control valve 23 which controls the mass
flow of thermal fluid 42 from heat exchanger 43 through
heat exchanger 9 for transferring heat to fluid entering
heat exchanger 9 via line 8. The set-point temperature
of sensor 22 corresponds to a temperature which is at or
slightly above the critical temperature of the solvent;
and in this manner, the solvent flowing in line 10
enters separator 21 at critical conditions.
Separator 21 is a pressure vessel within which a
nozzle (not shown) connected to feed line 10 evenly
distributes the lower density supercritical solvent and
the higher density DAO across a horizontal cross-section
of the separator. In this way, the lower density
supercritical solvent separates from the higher density
DAO permitting each fluid to be piped away
independently.
As indicated above, nozzles of the prior art
introduce turbulence into the fluid in separator 11
which results in mixing of the supercritical solvent
with the DAO. This problem is substantially eliminated
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with the nozzle configurations of the present invention
described below.
Apparatus according to the present invention for
separating solvent in a feed of lighter solvent and
heavier deasphalted oil produced in a deasphalting
process is shown in FIG. 3 and designated by reference
numeral 50. Apparatus includes a feed line (not shown)
like line 10 in FIG. 1, and heat exchangers (not shown)
like heat exchangers 7 and 9 in FIG. 1, for receiving
the feed and producing a main stream of fluid containing
supercritical solvent and deasphalted oil. The feed line
is connected to inlet line 10A that is substantially
horizontally disposed and receives the main stream.
Inlet line 20A is constructed and arranged to produce at
outlet 51 of line 10A, two phase laminar flow of the
main stream. Such a flow is established by ensuring that
the cross-sectional area of line 10A is large enough for
the flow of supercritical solvent and DAO to be in the
laminar flow region. As a consequence of having a two-
phase laminar flow in line 10A, the lighter
supercritical solvent is separate from and floats on the
heavier deasphalted oil establishing interface 51A lying
in a horizontal plane as indicated in FIG. 3A.
The apparatus includes at least one wedge shaped
divider member 52 (see Fig. 3A) at outlet 51 of line
10A, the member facing the stream o:E supercritical
solvent and DAO and having tapered leading edge 53 whose
apex 54 can be located at the same level as interface
51A. As shown in FIG. 3A, apex 54 divides the stream of
supercritical solvent and DAO into 'upper flow stream 55
containing essentially only supercritical solvent, and
lower flow stream 56 containing deasphalted oil with a
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significantly reduced amount of solvent (refer to Fig. 2
as well).
The apparatus also includes a substantially
horizontal, axially extending tube 57 located in
pressure vessel 11A and having one end 58 for internally
receiving the upper flow stream of supercritical solvent
and the lower flow stream of DAO. Opposite end 58,A of
tube 57 is capped at 59. Upper surface 60 of the tube
has holes 61, see Figs. 4 and 5, distributed axially
along the length of the tube for effecting egress of
supercritical solvent in upper flow stream 55. Lower
surface 62 of the tube is apertured for effecting egress
of DAO in lower flow stream 56.
In one arrangement, of the of the supercritical
solvent separator shown in Fig. 3 and in Fig. 3A (a
sectional view), as shown in FIG. 4, lower surface 62 of
the tube has holes 63 distributed axially along the
length of the tube. In another arrangement, as shown in
FIG. 5, axially extending, horizontally disposed baffle
64 in the tube downstream of member 52 divides the tube
into upper chamber 65 into which upper stream 55 flows,
and lower chamber 66 into which lower stream 56 flows.
Preferably, in each of the arrangements shown in
FIGS. 4 and 5, lower surface 62 of the tubes has holes
63 distributed axially along the length of the tube.
Alternatively, in further_arrangement of the
supercritical solvent separator showri in Fig. 3 and in
Fig. 3A (a sectional view), lower surface 62 of the
tube may be apertured as indicated at 68 in FIG. 6 for
effecting egress of fluid from the tube.
In a preferred arrangement, apparatus 50 includes
three additional tubes like tube 57, namely tubes 69,
'70, and 71 arranged at a 90. degree. angle to each other
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and intersecting at outlet 51 of line 10A as shown in
FIG. 3. Outlet 51 is axially located within vessel 11A
and forms a common inlet to each of the tubes which
extend radially in a common plane from outlet 51 toward
the walls of the vessel. A wedge-like divider member is
associated with each tube at the inlet thereof for
directing the supercritical solvent toward the top of
each tube, and the DAO toward the bottom. Preferably,
holes 61 in the top surface of each tube, through which
the supercritical salvent exits, are evenly distributed
along the length of the tube. Egress of the DAO from the
tubes can be at either axial end, ox° uniformly along the
length.
While four tubes are shown in FIG. 3, more than or
less than four tubes can be used. Moreover, in another
alternative arrangement (not shown), a hollow,
cylindrical, horizontally disposed disk-like member
whose horizontal cross-section substantially fills the
pressure vessel may be used instead of separate tubes.
In such case, the disk-like member would be apertured
uniformly on the top and bottom, and be provided with a
centrally located plate that divides the member into
upper and lower chambers for respectively receiving the
separated supercritical solvent and DAO.
In accordance with the present invention, the
dimensions of tubes 57, 69, 70, and 71, as well as the
dimensions of the horizontally disposed disk-like member
previously mentioned, should be large enough for the
flow of supercritical solvent and the DAO to be in the
laminar regime.
In the event of variations in the elevation of
interface 51A (refer to Figs. 3A and 5) between the
supercritical solvent and DAO in inlet line 10A, due,
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for example, to variations in throughput, the leading
edge of member 53, or of baffle 64, may become
misaligned with interface 51A. This will cause diversion
of some DAO into upper chamber 65 of a tube (or the
upper chamber of the disk-like member), or the diversion
of some of the supercritical solvent into the lower
chamber 66 of a tube (or the lower chamber of the disk-
like member). Small diversions do not affect the
operation of the invention; but in the event the
variations in elevation are large, the approach shown in
FIG. 3B can be employed. to minimize the effect of such
variations.
In FIG. 3B, sensor 75 monitors the interface level
in inlet line 10A using, for example, a differential
pressure transmitter, a sonic level detector, a float-
type level detector, or a nuclear-based level detector.
Sensor 75 generates a signal indicative of the magnitude
and direction of the difference between a set point
level and the actual level. Such signal is used to
control valve 76 in the DAO line at the bottom on vessel
11A. Thus, if the interface level drops below edge 54 of
member 53 (refer to Fig. 3A), sensor 75 would signal
valve 76 to reduce the flow of DAO, etc.
Embodiment 80 of the invention shown in FIG. 7
includes inlet tube 10A that contains the main stream of
supercritical solvent and DAO flowing in a two phase
regime with the lighter supercritical solvent floating
on the heavier DAO. Interface 51A between supercritical
solvent and the DA0 is substantially aligned with apex
81 of wedge-shaped divider member 82 positioned at the
outlet of tube 10A and divides the flow into upper
stream 83 containing substantially only supercritical
solvent and lower stream 84 contai:nirig substantially
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only DAO. Upper stream 83 flows in conduit 85 to
substantially horizontally disposed axially extending
tube 86 that projects into vertical separator column 11B
which functions like separator 11A previously described;
and lower stream 84 flows in conduit 87 to substantially
horizontally disposed axially extending tube 88 that
projects into separator column 118.
Any DAO in the fluid flowing in tube 86 will
separate from the supercritical solvent and flow below
the solvent; and any supercritical solvent in the fluid
flowing in tube 88 will separate from the DAO and flow
above the DAO. The upper surface of each of tubes 86 and
88 have holes 89 distributed axially along the length of
the tube for effecting egress of supercritical solvent,
and the lower surface of each tube has apertures 89 for
effecting egress of DAO from the tube. Any DAO in stream
83 will separate from the solvent as the stream flows in
tube 86, and will flow downwardly through apertures 90.
Any solvent in stream 84 will separate from the DAO as
the stream flows in tube 88, and will flow upwardly
through apertures 90. Although tubes 86 and 88 may be
positioned at substantially the same elevation in
separator column 118, it is preferred that the tubes be
positioned at different elevations as shown in FIG. 7.
Embodiment 90A shown in FIG. 8 is a modification of
embodiment 80 tshown in Fig. 7? and is ideally suited
for a situation in which the elevation of interface 51A
is below apex 81 ensuring that only supercritical
solvent flows in conduit 85A. In such case, a two phase
flow of solvent and DAO will flow via conduit 87A to
tube 88 with the solvent exiting through holes 89 and
the DAO exiting though apertures 90. The solvent in
column 11B can be combined with the solvent in conduit
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85A and returned to the asphaltene separator after
suitable cooling as shown in FIG. 1.,
The embodiments shown in FIGS. 9 and 10 eliminate
the need for a wedge-shaped divider member for dividing
the two-phase flow of supercritical solvent and DAO into
separate flow paths. Embodiment 100A in FIG. 9 includes
feed line 101 which contains the feed stream of
supercritical solvent and DAO flowing in a two phase
regime. Line 101 is connected, though sonically shaped
transition 102 to inlet line 203 which has a cross-
section much larger than the cross-section of feed line
201. Specifically, apex 104 of sonically shaped
transition 102 portion is connected to feed line 101,
apex 104 lying in alignment with the axes of feed line
101 and inlet line 103 which is cy7_indrical. In this
embodiment, the axis of line 103 is horizontal. Because
the cross-section of line 203 is much larger than the
cross-section of feed line 201, the flow of fluid in the
inlet line is slowed, and is laminar. Separation of the
flow into two phases occurs in line 103.
Downstream end 107 of inlet line 103 connects to
column 11B and is thus considered to be closed. First
outlet line 105 near the top of downstream end 207
serves to effect egress of supercritical solvent from
line 103, and second outlet line 106 near the bottom of
downstream end 107 serves to effect egress of DAO.
Embodiment 110 in FIG. 10 is a modification of
embodiment 100A tshown in Fig. 9) and is the same except
that the axis of inlet line 103A is inclined relative to
the horizontal instead of being horizontal as is the
case with inlet line 103 in FIG. ~. Specifically, the
flow path of fluid in inlet 103A i.s tilted downwardly.
Preferably, the angle of inclination is 5°-15°.
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Embodiment 120 in FIG. 11 is a further modification
of embodiment 100A (shown in Fig. 9) in that means are
provided for raising solvent in feed line 101 to its
supercritical state. Specifically, embodiment 120
includes heat exchanger 121 in the form of shell 122
that surrounds feed line 101. Shell 122 contains a heat
transfer fluid that serves to add sufficient heat to the
mixture of solvent and DAO flowing in feed Line 201 so
that the solvent becomes supercritical. Heat exchanger
121 thus functions like heat exchangers 7 and 9 in FIG.
1.
In the previously described embodiments, the feed
line. and inlet line to the separator are horizontally
disposed. In the embodiments of FIGS. 12-14, still
further arrangements of the supercritical solvent
separator shown in Fig. 3 and in Fig. 3A (a sectional
view), the feed line is vertically oriented. In
embodiment 150 shown in FIG. 12, feed line 151 is
vertical; and a mixture of solvent and DAO is heated by
heat exchanger 152 using hot thermal fluid in line 153.
The temperature of the mixture iscontrolled by the set
point of regulator 154 as described in connection with
FIG. 2.
Embodiment 150 includes about 90° elbow 155 that
connects vertical feed line 151 to horizontally disposed
inlet line 156 that functions like inlet line 51 of the
previously described embodiment. Specifically,
embodiment 150 includes outlet line 157 connected to the
bottom of inlet line 156, but downstream of elbow 155,
and further outlet line 158 connected to the top of the
inlet line also downstream of the elbow. Auxiliary
conduit 159 connected to inlet line 151 at the outlet of
heat exchanger 152 carries supercritical solvent to
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separator column 11C, while any DAO in conduit 159
separates and travels downwardly in column 12C joining
DAO that exits inlet line 156 via outlet line 157.
A modification of embodiment 150 (shown in Fig. 12)
is shown at 160 in FIG. 13. In embodiment 160, auxiliary
line 161 is connected to the top of inlet line 156
downstream of elbow 155 instead of to feed line 151 as
in embodiment 150.
Embodiment 170 shown in FIG. 14 is a further
20 modification of embodiment 150 in that the auxiliary
line in embodiment 150 has been eliminated. In
embodiment 170, inlet line 156A connected to elbow 155
serves to effect laminar flow of the supercritical
solvent and DAO such that two-phase separation takes
place. The lighter solvent is drawn off at the top of
the outlet 158, and the heavier DAO is drawn off though
line 157 at the bottom of inlet line 156A.
The advantages and improved results furnished by
the method and apparatus of the present invention are
apparent from the foregoing description of the preferred
embodiment of the invention. Various changes and
modifications may be made without departing from the
spirit and scope of the invention as described in the
appended claims.
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