U.S. patent application number 12/640458 was filed with the patent office on 2011-06-23 for liquid-liquid extraction tower having center feed inlet and process.
This patent application is currently assigned to E.I. DU PONT DE NEMOURS AND COMPANY. Invention is credited to Minye Liu, Donald Hugh Marlow.
Application Number | 20110147305 12/640458 |
Document ID | / |
Family ID | 43618256 |
Filed Date | 2011-06-23 |
United States Patent
Application |
20110147305 |
Kind Code |
A1 |
Marlow; Donald Hugh ; et
al. |
June 23, 2011 |
LIQUID-LIQUID EXTRACTION TOWER HAVING CENTER FEED INLET AND
PROCESS
Abstract
This invention relates to a liquid-liquid extraction tower
comprising a feed inlet and a plurality of stages and an area for
collection of the extract; at least one stage comprising a mixing
zone having a driven center horizontal impeller positioned between
a pair of horizontal annular shroud baffles having open centers,
the impeller having a center impeller plate; wherein the feed inlet
is positioned adjacent the center impeller plate. This invention
also relates to an improved liquid-liquid extraction process
comprising symmetrically introducing the feed adjacent the center
impeller plate.
Inventors: |
Marlow; Donald Hugh;
(Midlothian, VA) ; Liu; Minye; (Hockessin,
DE) |
Assignee: |
E.I. DU PONT DE NEMOURS AND
COMPANY
Wilmington
DE
|
Family ID: |
43618256 |
Appl. No.: |
12/640458 |
Filed: |
December 17, 2009 |
Current U.S.
Class: |
210/634 ;
422/259 |
Current CPC
Class: |
B29C 48/022 20190201;
B29C 48/04 20190201; B01D 11/0434 20130101; B01D 11/043 20130101;
B01D 11/043 20130101; B01D 11/0434 20130101 |
Class at
Publication: |
210/634 ;
422/259 |
International
Class: |
B01D 11/04 20060101
B01D011/04 |
Claims
1. A liquid-liquid extraction tower comprising: at least one feed
inlet, at least one extraction solvent inlet, at least one extract
outlet, and at least one raffinate outlet; wherein the tower
further has a plurality of stages and an area for collection of the
extract; at least one stage comprising a mixing zone having a
driven center horizontal impeller positioned between a pair of
horizontal annular shroud baffles having open centers, the impeller
having a center impeller plate; the stage further having openings
between the pair of horizontal annular shroud baffles and the side
of the tower; wherein the feed inlet is positioned adjacent the
center impeller plate.
2. The liquid-liquid extraction tower of claim 1, wherein the
vertical distance between the feed inlet and the center impeller
plate is one inch or less.
3. The liquid-liquid extraction tower of claim 1, wherein the feed
inlet is a sparger having vertical and/or angled orifices.
4. The liquid-liquid extraction tower of claim 1, wherein the feed
inlet is a substantially vertically-oriented tube located on the
centerline of the extraction tower.
5. The liquid-liquid extraction tower of claim 4, wherein the
vertical distance between the feed inlet and the center impeller
plate is less than one feed inlet tube diameter.
6. The liquid-liquid extraction tower of claim 1, wherein the feed
inlet is two or more tubes symmetrically distributed around the
centerline of the extraction tower.
7. The liquid-liquid extraction tower of claim 1, wherein the feed
inlet is two or more vertically-oriented tubes that are angled or
bent toward either the center of the mixing zone or the horizontal
impellers of the mixing zone.
8. The liquid-liquid extraction tower of claim 6, wherein the
vertical distance between the feed inlet and the center impeller
plate is less than one feed inlet tube diameter.
9. The liquid-liquid extraction tower of claim 1, wherein the
mixing zone including the pair of shroud baffles is positioned
between an additional set of annular flow baffles that direct flow
from the side of the tower.
10. In a process for liquid-liquid extraction of an extract from a
feed using an extraction solvent, using a liquid-liquid extraction
tower having at least one feed inlet, at least one extraction
solvent inlet, at least one extract outlet, and at least one
raffinate outlet; and wherein the tower further has a plurality of
stages and an area for collection of the extract; and at least one
stage having a mixing zone having a driven center horizontal
impeller positioned between a pair of horizontal annular shroud
baffles having open centers, the impeller having a center impeller
plate; the stage further having openings between the pair of
horizontal annular shroud baffles and the side of the tower; the
improvement comprising symmetrically introducing the feed adjacent
the center impeller plate.
11. The process of claim 10, wherein the feed is introduced within
one inch or less of the center impeller plate.
12. The process of claim 10, wherein the feed is introduced within
one feed inlet tube diameter of the center impeller plate.
13. The process of claim 10, wherein the feed is introduced by use
of a sparger having vertical and/or angled orifices; a vertical
tube; or a plurality of vertically-oriented, angled, or bent
tubes.
14. The process of claim 10, wherein the feed is directed through
the open center of one of the horizontal annular shroud baffles and
into the annular inlet of the mixing zone.
15. The process of claim 14, wherein the feed is symmetrically
directed through the open center by use of a sparger having
vertical and/or angled orifices; a vertical tube; or a plurality of
vertically-oriented, angled, or bent tubes.
Description
BACKGROUND OF INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to a liquid-liquid extraction tower
and a method of operating the same. As used herein, the words
"tower" and "column" can be used interchangeably.
[0003] 2. Description of Related Art
[0004] Liquid-liquid extraction involves the transfer of mass from
one liquid phase into a second immiscible liquid phase. As defined
herein, a "feed" is a liquid supplied to the tower having
components that are to be separated, and can have as a major
component a feed solvent and as minor components, one or more
solutes. As defined herein, "extraction solvent" is the immiscible
liquid added to the tower for the purpose of extracting one or more
solutes from the feed. As defined herein, the "extract" is the
liquid removed from the tower containing the extraction solvent
plus the one or more solutes. As defined herein, the "raffinate" is
the liquid removed from the tower that contains primarily the feed
solvent; it is the remaining feed liquid after the one or more
solutes have been removed.
[0005] FIG. 1 is an illustration of a type of liquid-liquid
extraction tower based on the design of Scheibel. Various versions
of this general type of design are shown in, for example, U.S. Pat.
Nos. 2,493,265; 2,850,362; & 3,389,970 and pages 15-40 to 15-42
of Perry's Chemical Engineers' Handbook, Seventh Ed. (Copyright
1997).
[0006] The introduction of the feed into the side of the tower sets
up a large-scale circulation that can be deceptively significant
and can provide mixing and entrainment of the feed in the assumed
single phase extract leaving the tower. This impacts the quality of
the extract being removed from the tower. What is needed,
therefore, is an improved method of introducing the feed to the
tower such that large scale circulation in the area of collection
is reduced.
BRIEF SUMMARY OF INVENTION
[0007] In one embodiment, this invention relates to a liquid-liquid
extraction tower comprising at least one feed inlet, at least one
extraction solvent inlet, at least one extract outlet, and at least
one raffinate outlet; wherein the tower further has a plurality of
stages and an area for collection of the extract; at least one
stage comprising a mixing zone having a driven center horizontal
impeller positioned between a pair of horizontal annular shroud
baffles having open centers, the impeller having a center impeller
plate; the stage further having openings between the pair of
horizontal annular shroud baffles and the side of the tower;
wherein the feed inlet is positioned adjacent the center impeller
plate.
[0008] In another embodiment, this invention relates to an
improvement in the process for liquid-liquid extraction of an
extract from a feed using an extraction solvent, using a
liquid-liquid extraction tower having at least one feed inlet, at
least one extraction solvent inlet, at least one extract outlet,
and at least one raffinate outlet; and wherein the tower further
has a plurality of stages and an area for collection of the
extract; and at least one stage having a mixing zone having a
driven center horizontal impeller positioned between a pair of
horizontal annular shroud baffles having open centers, the stage
further having openings between the pair of horizontal annular
shroud baffles and the side of the tower;
the improvement comprising symmetrically introducing the feed
adjacent the center impeller plate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is an illustration of one type of liquid-liquid
extraction tower based on the design of Scheibel.
[0010] FIG. 2 is an illustration of the flows in the area of
collection of extract in the tower.
[0011] FIG. 3 is an illustration of one type of device for
symmetrically introducing the feed using a ring-type
distributor.
[0012] FIG. 4 is a perspective detail of the device for
symmetrically introducing the feed as shown in FIG. 3.
[0013] FIGS. 5A & 5 B are illustrations of alternative types of
devices for symmetrically introducing the feed utilizing a
plurality of open pipes angled to direct the feed either toward or
away from the centerline of the tower.
[0014] FIGS. 6 & 7 are illustrations of other alternative types
of device for symmetrically introducing the feed utilizing either a
single pipe or a plurality of pipes that direct the feed vertically
around the center drive shaft of the tower.
[0015] FIG. 8 is an illustration of the liquid-liquid extraction
tower having device for symmetrically introducing the feed adjacent
the center impeller plate wherein the extract is taken from the
bottom of the tower.
[0016] FIG. 9 is an illustration of the liquid-liquid extraction
tower having a device for symmetrically introducing the feed
adjacent the center impeller plate wherein the extract is taken
from the top of the tower.
[0017] FIG. 10 is a detail from FIG. 9 showing an alternative type
of device for symmetrically introducing the feed utilizing a
plurality of pipes that direct the feed vertically around the
center drive shaft of the tower.
DETAILED DESCRIPTION OF INVENTION
[0018] This invention relates to a liquid-liquid extraction tower
comprising at least one feed inlet, at least one extraction solvent
inlet, at least one extract outlet, and at least one raffinate
outlet, and has a plurality of stages and an area for collection of
the extract. The tower has at least one stage comprising a mixing
zone having a driven center horizontal impeller having a center
impeller plate with the impeller positioned between a pair of
horizontal annular shroud baffles having open centers. The stage
further has openings between the pair of horizontal annular shroud
baffles and the side of the tower. The feed inlet is positioned
adjacent the center impeller plate. In a preferred embodiment, the
feed inlet is positioned in the area of collection such that the
feed is substantially symmetrically introduced adjacent the center
impeller plate such that large scale circulation in the area of
collection due to the introduction of the feed into the tower is
reduced.
[0019] FIG. 1 is a representation of the prior art liquid-liquid
extraction tower based on the design of Scheibel. The tower 10 has
an inlet for the feed 11, an inlet for the extraction solvent 12,
an outlet for the extract 14, and an outlet for the raffinate 15.
The tower also has a plurality of stages designated by the zones 20
and a plurality of mixing zones designated by 22. At either end of
the tower there are collection areas 21. Each mixing zone 22 has a
horizontal impeller 23a having a number of impeller blades attached
to impeller plate 23b and positioned between a pair of horizontal
annular shroud baffles 24 supported by suitable supports 24a, many
of which are not shown for clarity. The horizontal impeller is
driven by a center shaft 25. Each of the horizontal shroud baffles
has an open center 26 and another opening 27 between the baffles
and the side of the tower. The tower is also provided with a
plurality of annular flow baffles 28 that direct flow from the side
of the tower. An optional element that can be employed is the use
of packing or wire mesh 29 (not shown for clarity) in the areas of
A, B, or C.
[0020] FIG. 2 is a representation of a typical prior art
arrangement of a bottom collection area 21 of the tower of FIG. 1,
with an inlet for feed 11 located on the side of the tower and an
outlet for extract 14 located at the bottom of the tower. It is
typical for the inlet of the feed 11 to continuously discharge into
the bottom collection area 21 from the side of the tower, and the
extract in the form of one phase being continuously removed from
the bottom of the tower via extract outlet 14. Discharging the feed
into the side of the tower sets up an undesirable large-scale
circulation in the collection area. The lower density feed phase 11
immediately starts to rise and travel up the side of the tower as
shown by flow arrows 30 and 31. It has been found that the energy
imparted into the fluid in the collection area by the feed is
proportional to the distance the low density liquid in the feed
travels through the collection area. Also, if the volumetric rate
of feed to the tower is significant, the feed inlet can have a
horizontal flow component 32 that flows to the center of the
collection area and the open center 26 of the horizontal annular
shroud baffles 24. The combination of the upward and horizontal
flows set up a large-scale circulating flow in the collection area
as shown by flow arrows 33, 34, & 35. This circulating flow can
be deceptively significant and can provide mixing and entrainment
of undesirable low density material from the feed as small bubbles
in the second phase, which is the extract. This impacts the quality
of the extract being removed from the tower.
[0021] FIG. 2 illustrates an embodiment wherein the collection area
is at the bottom of the tower and the extract is the high density
phase. In other embodiments, the same principles would apply to the
mirror image of FIG. 2, wherein the collection is at the top of the
tower with the extract being the lower density phase. In either
case, undesirable circulating flow can provide mixing in the
collection area and entrainment of the undesired phase in the
desired phase of the extract.
[0022] In some embodiments, the feed inlet is a sparger having
vertical and/or angled orifices. FIG. 3 illustrates one embodiment
of a sparger 40 providing a feed inlet for the feed 11. The sparger
40 is positioned in the area of collection such that the feed is
substantially symmetrically introduced (as shown by flow arrows 41)
into the open center 26 of one of the pair of horizontal annular
shroud baffles 24, beneath and adjacent the center impeller plate
(not shown). Large scale circulation in the area of collection due
to the introduction of the feed into the tower is reduced. This
effectively introduces the feed substantially in mixing zone 22
rather than in the collection zone 21, and provides much less
circulation and entrainment of the feed in the extract 14.
[0023] In some embodiments, the sparger 40 or other device for
providing the feed adjacent the center impeller plate must be
positioned around or compensate for the center shaft 25 that drives
the horizontal impeller 23, that is positioned between the pair of
horizontal annular shroud baffles 24. If required, the sparger or
other device can be positioned around and/or attached to suitable
supports 24a for the horizontal annular shroud baffles.
[0024] FIG. 4 illustrates one embodiment of a sparger 40. In this
embodiment, the sparger is a circular ring having a plurality of
slots 41 for distributing the inlet flow in substantially a
symmetric manner. While a plurality of slots is shown, many
different various orifices could be used as long as they are
practical. For example one continuous circular slot could be used,
or the slots could be replaced with simple holes of either circular
or other shape. The orifices can be machined or positioned to cause
the flow to be essentially vertical, or could be angled towards the
centerline of the tower. Alternatively, in one preferred
embodiment, the orifices can be machined or positioned to cause the
flow to be angled away from the centerline of the tower and
directed towards the blades of the horizontal impeller, with the
feed inlet being either above or below the open center of the
horizontal annular baffle. In this case, in a preferred embodiment,
the flow is angled no more than about 80 degrees from the vertical,
while still being symmetrically distributed adjacent the center
impeller plate. In other embodiments, the flow is angled at least
40 degrees from the vertical, while still being symmetrically
distributed adjacent the center impeller plate.
[0025] Also, while the sparger in FIG. 4 is shown directing the
flow substantially vertically upward, as would be the case wherein
the collection area is at the bottom of the tower; a similar
sparger that directs the flow substantially vertically downward
could be used if the collection area is at the top of the tower. If
the collection area is at the bottom of the tower, "adjacent the
center impeller plate" means the feed inlet is below the nearest
center impeller plate; while if the collection area is at the top
of the tower "adjacent the center impeller plate" means the feed
inlet is above the nearest center impeller plate.
[0026] In some other embodiments, the feed inlet is two or more
tubes symmetrically distributed around the centerline of the
extraction tower. In some preferred embodiments, the two or more
vertically-oriented tubes are angled or bent toward either the
centerline of the tower or toward the horizontal impeller blades of
the mixing zone. FIGS. 5A and 5B are possible illustrations of such
devices made from a plurality of angled or bent tubes for
symmetrically providing the feed. Device 50 has at least two tubes
that direct the flow towards the center of the open center of the
horizontal annular baffle. Device 55 has at least two bent tubes
that direct the flow away the center of the open center of the
horizontal annular baffle but still into that open center. For
clarity, these are shown below the horizontal annular baffle,
however, it is understood these could and preferably would extend
through the open center of the horizontal annular baffle and into
the mixing zone.
[0027] In some embodiments, the feed inlet is a substantially
vertically-oriented tube located on the centerline of the
extraction tower. FIG. 6 illustrates this embodiment for
symmetrically providing the feed, wherein a single pipe 60 is used
that is specially adapted or sized to surround or compensate for
the center shaft 25 that drives the plurality of horizontal
impellers in the tower. In this embodiment, the center shaft is
actually inserted into the tube and serves the additional function
of helping to distribute the feed in an annularly symmetric manner
adjacent the center impeller plate. FIG. 7 illustrates still
another embodiment for symmetrically providing the feed, wherein a
plurality of vertical tubes 70 are used that are specially adapted
or positioned to compensate for the center shaft 25 and distribute
the feed in a symmetric manner adjacent the center impeller plate.
This illustrates the tubes extending through the open center of the
horizontal annular baffle.
[0028] As used herein, the term feed inlet means either the end of
the feed supply tubing or the surface of any sparger or other
device having holes or slots or other orifices where the liquid
feed flow is actually exiting the feed piping. In some preferred
embodiments the vertical distance between the feed inlet and the
bottom edge of the center impeller plate is one inch or less. In
some other preferred embodiments, the vertical distance between the
feed inlet and the open center of one of the horizontal annular
shroud baffles is less than one feed inlet tube diameter. In either
case, the vertical distance is measured from the closest point of
the end of feed tubing or the surface of any sparger or other
device to the plane of the horizontal annular shroud. It is
believed the feed inlet can be preferably be positioned as close as
0.25 inches (0.64 cm) vertically from the bottom edge of the center
impeller plate; any closer it thought to have the potential to
cause operability problems without added benefit.
[0029] By the term "symmetrically distributed" it is meant that if
there is a plurality of feed inlets, the inlets are uniformly
distributed in relation to the centerline of tower and are
symmetrically located; that is, at least one vertical plane can be
drawn through the centerline of the tower that shows symmetry of
the feed inlets. If there is a single feed inlet, at least one
vertical plane showing symmetry can be drawn through the centerline
of the tower and that inlet.
[0030] FIG. 8 illustrates one embodiment of a tower 80 including a
sparger or other device 81 for providing the feed adjacent the
center impeller plate, wherein the feed inlet and collection area
for the extract is in the bottom of the tower. For clarity, the
feed inlet is shown below the horizontal annular baffle, however,
it is understood this could and preferably would extend through the
open center of the horizontal annular baffle and into the mixing
zone. The tower has all the features as previously described,
including an inlet for the feed 11, an inlet for the extraction
solvent 12, an outlet for the extract 14, and an outlet for the
raffinate 15. The tower also has a plurality of stages and a
plurality of mixing zones as previously identified. Each mixing
zone has a horizontal impeller positioned between a pair of
horizontal annular shroud baffles as previously identified.
[0031] FIG. 9 illustrated another embodiment of a tower 90
including a sparger or other device 91 for providing the feed
adjacent the center impeller plate, wherein the feed inlet and
collection area for the extract is in the top of the tower. As
before, the feed inlet is shown above the horizontal annular
baffle, however, it is understood this could and preferably would
extend downward through the open center of the horizontal annular
baffle and into the mixing zone. The tower has all the features as
previously described, including an inlet for the feed 11', an inlet
for the extraction solvent 12', an outlet for the extract 14', and
an outlet for the raffinate 15'. The tower also has a plurality of
stages and a plurality of mixing zones as previously identified.
Each mixing zone has a horizontal impeller positioned between a
pair of horizontal annular shroud baffles as previously identified.
FIG. 10 is a detail of view 10-10 from FIG. 9. showing one possible
arrangement of the device 91, showing one possible arrangement for
positioning around or compensating for the center shaft 25 that
drives the pluarality of horizontal impellers in the tower.
[0032] In another embodiment, this invention relates to an
improvement in the process for liquid-liquid extraction of an
extract from a feed using an extraction solvent, using a
liquid-liquid extraction tower having at least one feed inlet, at
least one extraction solvent inlet, at least one extract outlet,
and at least one raffinate outlet; and wherein the tower further
has a plurality of stages and an area for collection of the
extract; at least one stage having a mixing zone having a driven
center horizontal impeller positioned between a pair of horizontal
annular shroud baffles having open centers, the impeller having a
center impeller plate; the stage further having an openings between
the pair of horizontal annular shroud baffles and the side of the
tower; the improvement comprising symmetrically introducing the
feed adjacent the center impeller plate.
[0033] In some preferred embodiments, the feed is introduced within
one inch or less of the center impeller plate. In some other
embodiments, the feed is introduced within one feed inlet tube
diameter of the center impeller plate. The feed can be introduced
directly into the mixing zone adjacent the center impeller plate by
use of a sparger having vertical and/or angled orifices; a vertical
tube; or a plurality of vertically-oriented, angled, or bent
tubes.
[0034] In some other embodiments, the feed is directed through the
open center of one of the horizontal annular shroud baffles and
into the annular inlet of the mixing zone. In some other
embodiments, the feed is symmetrically directed through the open
center by use of a sparger having vertical and/or angled orifices;
a vertical tube; or a plurality of vertically-oriented, angled, or
bent tubes.
* * * * *