U.S. patent application number 11/153534 was filed with the patent office on 2005-11-24 for apparatus and method for separating fluids through a membrane.
This patent application is currently assigned to KVAERNER PROCESS SYSTEMS A.S.. Invention is credited to Dannstrom, Henrik, Falk-Pedersen, Olav, Gronvold, Marianne Soby, Ronning, Odd, Stuksrud, Dag Birger.
Application Number | 20050258091 11/153534 |
Document ID | / |
Family ID | 26244588 |
Filed Date | 2005-11-24 |
United States Patent
Application |
20050258091 |
Kind Code |
A1 |
Dannstrom, Henrik ; et
al. |
November 24, 2005 |
Apparatus and method for separating fluids through a membrane
Abstract
Apparatus for contacting first and second fluids at elevated
pressures with a membrane such that one or more components of one
of the fluids passes through the membrane into the other fluid,
comprising a housing e.g. a pressure vessel (4), and a membrane
module (20) housed in the pressure vessel and having a first fluid
inlet (8a) and a first fluid outlet (8b) and a second fluid inlet
(9a) and a second fluid outlet (9b), wherein a seal (61) extends
round the membrane module and seals between an outside wall of the
membrane module and an inside wall of the pressure vessel so as to
separate the first fluid inlet from the first fluid outlet.
Inventors: |
Dannstrom, Henrik;
(Sandefjord, NO) ; Falk-Pedersen, Olav;
(Toensberg, NO) ; Ronning, Odd; (Sandefjord,
NO) ; Stuksrud, Dag Birger; (Sandefjord, NO) ;
Gronvold, Marianne Soby; (Porsgrunn, NO) |
Correspondence
Address: |
BACON & THOMAS, PLLC
625 SLATERS LANE
FOURTH FLOOR
ALEXANDRIA
VA
22314
|
Assignee: |
KVAERNER PROCESS SYSTEMS
A.S.
Lysaker
NO
|
Family ID: |
26244588 |
Appl. No.: |
11/153534 |
Filed: |
June 16, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11153534 |
Jun 16, 2005 |
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10220263 |
Sep 6, 2002 |
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6926829 |
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10220263 |
Sep 6, 2002 |
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PCT/GB01/00964 |
Mar 6, 2001 |
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10220263 |
Sep 6, 2002 |
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60187051 |
Mar 6, 2000 |
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Current U.S.
Class: |
210/321.79 ;
210/321.72; 210/321.88 |
Current CPC
Class: |
B01D 61/30 20130101;
B01D 53/22 20130101; B01D 2313/14 20130101; B01D 63/06 20130101;
B01D 63/02 20130101; B01D 65/00 20130101; B01D 61/28 20130101 |
Class at
Publication: |
210/321.79 ;
210/321.72; 210/321.88 |
International
Class: |
B01D 063/06 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 3, 2000 |
GB |
0016368.3 |
Claims
1-17. (canceled)
18. Apparatus for contacting first and second fluids at elevated
pressures with a membrane such that one or more components of one
of the fluids passes through the membrane into the other fluid, the
apparatus being assembled from a housing and a membrane module, the
membrane module comprising a plurality of membrane tubes with
opposite axial ends which are potted to separate the shell sides of
the tubes from the tube sides of the tubes at the axial ends
thereof, and the membrane module being housed in the housing and
having a first fluid inlet and a first fluid outlet for fluid flow
on the shell side of the membrane tubes and, at the opposite axial
ends of the membrane tubes, a second fluid inlet and a second fluid
outlet for fluid flow on the tube side of the membrane tubes,
wherein the apparatus further comprises a first seal extending
round the membrane module and sealing between an outside wall of
the membrane module and an inside wall of the housing so as to
separate the first fluid inlet from the first fluid outlet, and a
pair of second seals each extending round the membrane module and
sealing between the outside wall of the membrane module and the
inside wall of the housing, the second seals being axially spaced
form the first seal and on opposite axial sides thereof, so as to
define a first fluid inlet region between the first seal and one of
the second seals and a first fluid outlet region between the first
seal and the other of the second seals, and said first seal and
said pair of second seals all permitting assembly into the housing,
in the axial direction, of said membrane module with its potted
membrane tubes.
19. Apparatus as claimed in claim 18, wherein the membrane module
has at least one lateral opening in its outside wall to form the
first fluid inlet and at least one lateral opening in its outside
wall to form the first fluid outlet.
20. Apparatus as claimed in claim 18, wherein first fluid inlet and
outlet are disposed axially inwardly of said opposite axial
ends.
21. Apparatus as claimed in claim 18, wherein the membrane module
has a cross-sectional shape corresponding substantially to that of
the housing so as to fit closely therein.
22. Apparatus as claimed in claim 18, wherein the housing has at
least one full diameter flanged opening for insertion of the
membrane module.
23. Apparatus as claimed in claim 18, wherein the first seal is
received in a groove in the housing.
24. Apparatus as claimed in claim 23, wherein the groove is
provided in a separate member secured to two body portions of the
housing to form a connection therebetween.
25. Apparatus as claimed in claim 18, wherein the second seals
separate the first fluid from the second fluid.
26. Apparatus for contacting first and second fluids at elevated
pressures with a membrane such that one or more components of one
of the fluids passes through the membrane into the other fluid, the
apparatus being assembled from a housing and a membrane module, the
membrane module comprising a plurality of membrane tubes with
opposite axial ends which are potted to separate the shell sides of
the tubes form the tube sides of the tubes at the axial ends
thereof, and the membrane module being housed in the housing and
having a first fluid inlet and a first fluid outlet for fluid flow
on the shell side of the membrane tubes and, at the opposite axial
ends of the membrane tubes, a second fluid inlet and a second fluid
outlet for fluid flow on the tube side of the membrane tubes,
wherein the apparatus further comprises a first seal extending
round the membrane module and sealing between an outside wall of
the membrane module and an inside wall of the housing so as to
separate the first fluid inlet from the first fluid outlet and
obstruct the flow of the fluid, and a pair of second seals each
extending round the membrane module and sealing between the outside
wall of the membrane module and the inside wall of the housing, the
second seals being axially spaced from the first seal and on
opposite axial sides thereof, so as to define a first fluid inlet
region between the first seal and one of the second seals and a
first fluid outlet region between the first seal and the other of
the second seals, and said first seal and said pair of second seals
all assembled into the housing, in the axial direction, of said
membrane module with its potted membrane tubes.
27. Apparatus for contacting first and second fluids at elevated
pressures with a membrane such that one or more components of one
of the fluids passes through the membrane into the other fluid, the
apparatus being assembled from a housing and a membrane module, the
membrane module comprising a plurality of membrane tubes with
opposite axial ends which are potted to separate the shell sides of
the tubes from the tube sides of the tubes at the axial ends
thereof, and the membrane module being housed in the housing and
having a first fluid inlet and a first fluid outlet for fluid flow
on the shell side of the membrane tubes and, at the opposite axial
ends of the membrane tubes, a second fluid inlet and a second fluid
outlet for fluid flow on the tube side of the membrane tubes,
wherein the apparatus further comprises a first seal extending
round the membrane module and sealing between an outside wall of
the membrane module and an inside wall of the housing so as to
separate the first fluid inlet from the first fluid outlet and
obstruct the flow of the fluid, and a pair of second seals each
extending round the membrane module and sealing between the outside
wall of the membrane module and the inside wall of the housing, the
second seals being axially spaced from the first seal and on
opposite axial sides thereof, so as to define a first fluid inlet
region between the first seal and one of the second seals and first
fluid outlet region between the first seal and the other of the
second seals, and said first seal and said pair of second seals
being arranged so as to permit assembly into the housing, in the
axial direction, of said membrane module with its potted membrane
tubes.
Description
[0001] The invention relates to apparatus and methods for
separating one or more components from a fluid through a membrane,
at ambient or elevated pressures, and to modules containing such a
membrane. The basic principles of one type of separating process to
which the present invention is applicable is described in WO
98/04339.
[0002] In modern industry, mass and heat transfer processes are
among the most common processes. Mass transfer processes include
contacting columns and extraction processes. In a contacting column
such as an absorber or a desorber, a gas is contacted with a liquid
over a high surface area, allowing the desired chemical or physical
mass transfer processes to take place in a controlled manner.
Afterwards the gas and the liquid are separately and usually
continuously transported away from the column. Due to the intimate
contact between the fluids, a parallel heat transfer also takes
place in cases where the fluids have different temperatures.
[0003] Contacting devices can also simply be mixing devices with
subsequent separators, which is used in for example processes
involving two immiscible liquids. These processes include
liquid/liquid extraction.
[0004] Conventional equipment does however have certain limitations
and drawbacks. These include the limited gas to liquid ratios in
columns, requirements as to orientation and in most cases also the
fact that entrainment of one of the fluids in to the other often
takes place, causing nuisance in downstream equipment and/or loss
of product. For liquid/liquid extraction processes, the degree of
immiscibility is crucial.
[0005] Membrane contactors provide means of carrying out the
processes mentioned above without these disadvantages. In a
membrane contactor, two (or more) fluids are exposed to each other
through a membrane. The membrane has the property to restrain one
or more components of each fluid, while allowing a relatively
higher proportion of selected components to pass through the
membrane. The membrane may also instead of being selective in
itself only provide such surface properties that for example
components in liquid form are not able to pass, but components in
gaseous form can. An-example of such a membrane is a (human) lung,
where blood is not able to pass through the lung "membrane", but
oxygen, water and CO.sub.2 are readily transported through driven
by the partial pressure difference of these on the two sides of the
lung.
[0006] For industrial applications the membrane provides a physical
barrier between the two fluids, thus eliminating problems related
to mixing of the fluids. The transport of a fluid is constrained to
either side of the membrane, thus allowing full flexibility in
terms of turndown (from zero to full flow) without affecting the
other side of the membrane. This also allows the orientation of the
unit to be arbitrary and independent of gravity.
[0007] The membrane used in each process is selected to have the
properties that are best suited for that particular
application.
[0008] In high pressure processes, the membrane contactor has to be
housed in a pressure vessel designed for the purpose. The
requirements to functionality, strength and corrosion resistance at
elevated pressure and temperature have to be met. A reliable and
suitable means of doing this is therefore required.
[0009] It is known from U.S. Pat. No. 5,916,647 and EP 941758 to
provide pressure vessels made of polyolefin and containing a bundle
of hollow fibre membrane contactors. The bundle has a hollow centre
via which shell side fluid flows into and out of the bundle, and
the hollow fibre ends are potted to provide for tube side fluid
flow into and out of the bundle. The pressure vessel is provided at
each end with inlet and outlet pipes disposed centrally so as to
mate in the hollow centre of the bundle in a manner sealed from the
tube side outlet and inlet. The assembly of the bundle into the
pressure vessel is therefore not simple. Moreover, the need for a
hollow centre in this type of membrane configuration reduces the
amount of active membrane area per unit volume.
[0010] From U.S. Pat. No. 5,264,171 it is known to provide
apparatus comprising a housing which receives a bundle of hollow
fibre membrane contactors with a type of inlet/outlet configuration
different from that described above. FIG. 1 of U.S. Pat. No.
5,264,171 shows a housing with a fluid inlet port and a fluid
outlet port at opposite axial ends for tube side flow, and a fluid
inlet port and a fluid outlet port for shell side flow which are
disposed axially inwardly of the axially opposite ends at the sides
of the housing. An impermeable wrapping means covers the exterior
cylindrical surface of the bundle of hollow fibre membrane
contactors. An opening is provided in the impermeable wrapping
means to communicate with the side inlet port of the housing, and a
corresponding opening is provided to communicate with the side
outlet port of the housing. The edges of the impermeable wrapping
means surrounding the openings are sealed to the housing side inlet
and outlet ports respectively, to prevent leakage from the shell
side space.
[0011] It is therefore necessary in this arrangement to fit the
bundle into the housing in such a way that the openings in the
impermeable wrapping means register with the housing side inlet and
outlet ports, with the edges of the openings properly sealing with
the ports. This tends to make the assembly of the apparatus
difficult, with a risk of unreliable sealing of the shell side
space in the region of the housing side inlet and outlet ports, for
example if exact rotational alignment about the longitudinal axis
between the bundle and the housing is not achieved.
[0012] Viewed from a first aspect the invention provides apparatus
for contacting first and second fluids at elevated pressures with a
membrane such that one or more components of one of the fluids
passes through the membrane into the other fluid, comprising a
housing, and a membrane module housed in the housing and having a
first fluid inlet and a first fluid outlet and a second fluid inlet
and a second fluid outlet, wherein a seal extends round the
membrane module and seals between an outside wall of the membrane
module and an inside wall of the housing so as to separate the
first fluid inlet from the first fluid outlet.
[0013] With such an arrangement, the assembly of the membrane
module into the housing can be relatively straightforward, in that
exact registration of the first fluid inlet and outlet with
respective inlet and outlet ports of the housing is not critical.
This may also enable the membrane module to be used in a
conventional housing. For example, the membrane module may be used
in a conventional pressure vessel without having to specially
design the pressure vessel. The membrane module may be retrofitted
to an existing housing, e.g. pressure vessel.
[0014] Various types of membrane may be used in the membrane
module, for example paste extruded membrane tubes or spirally wound
membranes. Preferably, a plurality of membrane tubes are provided.
In a preferred embodiment, the membrane module comprises a
plurality of membrane layers, each membrane layer comprising a
plurality of membrane tubes arranged side by side with connecting
portions connecting laterally adjacent membrane tubes, and the
membrane layers being stacked in alternation with spacers. Such an
arrangement can achieve a very effective mass transfer across the
membranes. The membrane layers are preferably as described in U.S.
Pat. No. 6,010,560.
[0015] It will be appreciated that the word "tube" used herein in
relation to the membrane is not intended to be limiting as to the
diameter size of the tube and should therefore be understood to
cover various diameters of tube, including tubes in the form of
fibres.
[0016] The seal extending round the membrane module is preferably
positioned at an intermediate location along the membrane module,
spaced from axial ends thereof.
[0017] Preferably, a pair of second seals each extend round the
membrane module and seal between the outside wall of the membrane
module and the inside wall of the housing, the second seals being
axially spaced from the first-mentioned seal and on opposite axial
sides thereof. Such second seals can in effect define isolated
inlet and outlet regions, namely an inlet region between the first
seal and one of the second seals and an outlet region between the
first seal and the other of the second seals.
[0018] Appropriate sealing arrangements may be provided for the
second fluid inlet and outlet. It is however preferred and
advantageous for the second seals additionally to serve to separate
the first fluid inlet or outlet from the second fluid inlet or
outlet.
[0019] The housing may be a pressure vessel or pipe spool or other
form of housing. In a preferred embodiment, the housing has
respective inlet and outlet ports cooperating with the fluid inlets
and outlets of the membrane module. In a particularly preferred
arrangement: a first fluid inlet port of the housing is arranged to
supply the first fluid to the first fluid inlet, which is provided
in the outside wall of the membrane module; a first fluid outlet
port of the housing is arranged to receive the first fluid from the
first fluid outlet, which is provided in the outside wall of the
membrane module; a second fluid port of the housing is arranged to
supply the second fluid to the second fluid inlet of the membrane
module, which is provided at an axial end of the membrane module;
and a second fluid outlet port of the housing is arranged to
receive the second fluid from the second fluid outlet of the
membrane module, which is provided at the opposite axial end of the
membrane module. Preferably, the first inlet and outlet ports for
the first fluid are disposed axially inwardly of opposite axial
ends of the housing, preferably being laterally directed, and the
second inlet and outlet ports for the second fluid are provided at
the axially opposite ends of the housing, preferably being axially
directed.
[0020] The housing may have more than one first fluid inlet port
and more than one first fluid outlet port. For example, the housing
may have a pair of diametrically opposed first fluid inlet ports
and a pair of diametrically opposed first fluid outlet ports.
[0021] In the case where a plurality of membrane tubes are used, it
is preferred for the first fluid to flow on the shell side of the
tubes and for the second fluid to flow on the tube side. Thus, in
the preferred arrangement discussed above, the first inlet and
outlet ports of the housing, and the corresponding first inlet and
first outlet of the membrane module, are provided for shell side
flow; whilst the second inlet and outlet ports of the housing, and
the corresponding second inlet and second outlet of the membrane
module, are provided for tube side flow.
[0022] It will be appreciated that by arranging a second seal
axially between an end port and a lateral port of the housing,
these ports may be sealingly separated from each other. Thus, the
first seal and the pair of second seals can advantageously isolate
the four housing ports from each other by sealing between the
outside wall of the membrane module and the inside wall of the
housing. Four inlet and outlet regions can effectively be defined
at the point when the membrane module is inserted, e.g. axially,
into the housing.
[0023] It is desirable to use the available space in the housing
and thus optimise the performance of the apparatus relative to its
size. Preferably, therefore, the membrane module has a
cross-sectional shape corresponding substantially to that of the
housing so as to fit closely therein.
[0024] The membrane module is most conveniently assembled into the
housing in the axial direction. The housing may therefore have at
least one full diameter flanged opening for insertion of the
membrane module. In some circumstances, such as for slender
membrane modules, both ends may have a full diameter flange.
Flanges do however add to the cost and weight of the housing and
alternatively therefore an end cap may be welded to the housing to
close an end thereof, after insertion of the membrane module. If
necessary, such a welded end cap can be burned off if the membrane
module needs to be changed after a period of service.
[0025] It is preferred for the first-mentioned seal to be placed in
the housing before insertion of the membrane module into the
housing. This is because the seal is ideally located and retained
by a groove and in general it is easier to provide a groove in the
housing than in the membrane module. Preferably, therefore, the
seal is received in a groove in the housing. It is particularly
preferred to provide the groove in a separate member which is
secured to a main body of the housing, e.g.. by welding. This avoid
having to form a groove directly in the main body, the inside of
which, particularly in the case of a long slender housing, may be
difficult to access.
[0026] The separate member may be secured inside a single main body
of the housing. However, if welding is used, the welding stresses
may cause distortion and prevent proper sealing. This problem can
be solved by providing the housing with two body portions to each
of which the separate member is secured to form a connection
between the body portions. The separate member may then be of
greater external diameter than the body portions thereby providing
a strengthening flange which is not significantly distorted during
the securing process.
[0027] The second seals may also be placed in the housing before
insertion of the membrane module. However, in the case of a long
slender module proper axial alignment can be difficult to control.
Hence, the second seals may preferably be placed after insertion of
the membrane module into the housing, before closing off the
housing with end caps, with or without flanges.
[0028] Flow of one of the fluids may be at an angle, such as a
right angle, to the membrane surface (this would be shell side flow
in the case of conventional membrane tubes or hollow fibres). Such
crossflow is commonly used in membrane separating processes.
Preferably, however, a first fluid flow path is defined along one
surface of the membrane and a second fluid flow path is defined
along an opposite surface of the membrane, wherein the direction of
flow of the first and second fluids along their respective paths is
substantially parallel to said surfaces of the membrane. The first
and second fluid flows are ideally in directions opposite to each
other. These arrangements have been found to work particularly well
in the preferred embodiments of the invention.
[0029] The membrane module preferably has at least one lateral
opening in its outside wall to form the first fluid inlet and at
least one lateral opening in its outside wall to form the first
fluid outlet. It may be preferred to arrange for the lateral
opening(s) to be positioned on the side of the pressure vessel
remote from the inlet/outlet port thereof, in order to obtain a
more even flow into the membrane module and avoid excessive flow
velocities. In such circumstances, a degree of rotational alignment
will be necessary but it may not have to be exact.
[0030] Preferably, however an even flow into the membrane module
without excessive flow velocities is obtained by arranging the
first fluid inlet to permit flow of the first liquid laterally into
the membrane module substantially around its entire periphery. This
arrangement is considered to be of independent patentable
significance, as discussed further below.
[0031] In known systems, multiple membrane tubes are arranged in an
axially extending bundle with their ends potted so that the fluid
for tube side flow can be directed into the axial end of the bundle
and the fluid for shell side flow can be directed into the sides of
the bundle inwardly of the axial ends. Efforts have been made in
the art to optimize the efficiency of fluid to membrane contact but
the known systems still suffer from a lack of use of the maximum
available membrane surface area. In particular, shortcomings in the
design of the inlet and outlet arrangements for shell side flow
often mean that there are membrane portions in dead spaces where
little or no shell side flow takes place. For example, in the case
of U.S. Pat. No. 5,264,171 mentioned above, the external housing of
the membrane contactor apparatus has a single fluid inlet port
which feeds into a single opening in the impermeable wrapping means
in sealed registration with that port, with the result that the
membranes on the side of the housing opposite the port may be in
dead space as far as shell side flow is concerned.
[0032] The known systems are therefore not as efficient as they
could be, in that not all of the membrane surface area is providing
contact between the tube and shell side fluid flows. We have
invented an inlet arrangement for a membrane bundle which improves
the shell side flow in the inlet region and therefore maximises the
use of the available membrane surface area.
[0033] Viewed from another aspect, therefore, the invention
provides membrane contactor apparatus comprising a bundle of
axially extending membrane tubes arranged for a first fluid to flow
outside of said tubes and for a second fluid to flow axially inside
said tubes from an axial end of the bundle to an opposite axial end
thereof, such that one or more components of one of the fluids
passes through walls of the membrane tubes into the other fluid,
the apparatus further comprising inlet means disposed axially
inwardly of one of said axial ends of the bundle for introducing
said first fluid into the bundle, wherein the inlet means extends
peripherally round the bundle and is arranged to permit flow of
said first fluid laterally into the bundle substantially around its
entire periphery.
[0034] This arrangement can reduce dead spaces and maximise the
axial length of membrane tubes available for fluid contacting.
Moreover, it is generally desirable for the bundle to be provided
in a mechanically rigid form, particularly where it is to be
inserted in a housing. Thus the bundle may be provided as part of a
membrane module, as discussed above, having an outside wall. By
arranging the first fluid inlet means to extend peripherally round
the bundle, it is possible to avoid the use of a single large
opening in the outside wall which would result in a non-symmetrical
load bearing capacity and potential adverse bending during
installation of the bundle or even leakage past the seals caused by
distortion.
[0035] The inlet means may comprise one continuous inlet opening in
the periphery of the bundle. However this may not always be
practical from a mechanical integrity point of view and there may
be intervals between plural openings in the periphery of the
bundle. Preferably, the inlet means comprises a plurality of
circumferentially spaced inlet openings in the periphery of the
bundle. The periphery of the bundle may be defined by an
impermeable outside wall around the bundle, such as the outside
wall of a membrane module.
[0036] In a preferred embodiment, the membrane tubes are arranged
in a plurality of layers extending laterally across the bundle, for
example of the type shown in U.S. Pat. No. 6,010,560. Flow within
the bundle is generally easier parallel to the layers than passing
from one layer to another (although this is usually allowed for by
suitable holes in the layers and spacers if provided).
Advantageously, therefore, the inlet openings are arranged in the
periphery of the bundle so that each membrane layer is exposed to
at least one of the inlet openings.
[0037] If the circumferential spacing between adjacent lateral
openings in the outside wall is too small, this can undesirably
weaken the mechanical integrity of the wall. It is therefore
advantageous to provide at least two rows of circumferentially
spaced inlet openings in the periphery of the bundle, with the
centres of inlet openings in adjacent rows being circumferentially
offset. With such an arrangement, every membrane layer can be
exposed to a respective inlet opening whilst an adequate
circumferential spacing between the openings in the same row is
provided for mechanical strength.
[0038] In the case of a membrane layer, it is possible to expose
the layer to a respective inlet opening at only one side of the
layer. This means that a membrane layer exposed on one side need
not be exposed on the other side, so that the circumferential
spacing between adjacent inlet openings in the periphery of the
bundle on that other side may be greater, allowing mechanical
rigidity and strength to be retained. Thus, in this arrangement,
some of the membrane layers are exposed to a respective inlet
opening at only one side of the respective layer.
[0039] As discussed above in relation to the first aspect of the
invention, the bundle may be housed in a housing having an inlet
port for the first fluid. In such an arrangement, one way of
providing for flow laterally into the bundle substantially around
its entire periphery is to provide an inlet chamber arranged to
receive the first fluid from the inlet port and extending round the
periphery of the bundle. In the case of the preferred bundle of
circular cross-sectional shape, the inlet chamber will be
annular.
[0040] In order to avoid a high pressure drop and mechanical forces
on the bundle, the first fluid flow speed should decrease from the
inlet port to the periphery of the bundle. This can be achieved
across the width of the inlet chamber, providing the width is
greater than a certain size. Preferably, the width of the inlet
chamber, measured between an inside wall of the housing and the
periphery of the bundle, is greater than or equal to one quarter of
the width of the inlet port.
[0041] It will be appreciated that the features described above in
relation to the inlet means of the bundle are generally applicable
also to appropriate outlet means of the bundle. Thus the apparatus
may comprise outlet means disposed axially inwardly of the axial
end of the bundle remote from the inlet means, the outlet means
extending peripherally round the bundle and being arranged to
permit flow of the first fluid laterally out of the bundle
substantially around its entire periphery. The outlet means may
comprise a plurality of circumferentially spaced outlet openings in
the periphery of the bundle, and/or an outlet chamber extending
round the periphery of the bundle, the outlet openings and the
outlet chamber being analogous respectively to the inlet openings
and the inlet chamber.
[0042] The invention also extends to a membrane module for use in
apparatus as described herein and to mass transfer processes using
such apparatus.
[0043] Certain preferred embodiments of the invention will now be
described by way of example and with reference to the accompanying
drawings, in which:
[0044] FIG. 1 is a side view of a membrane module;
[0045] FIG. 2a is a cross-section on lines A-A of FIG. 1;
[0046] FIG. 2b is a cross-section on lines B-B of FIG. 1;
[0047] FIG. 3 is a side view of a housing in the form of a pressure
vessel for containing the membrane module;
[0048] FIG. 4 shows the pressure vessel in an open condition for
insertion of the membrane module;
[0049] FIG. 5 is a side view of the pressure vessel showing the
membrane module contained within;
[0050] FIG. 6 is a view, to an enlarged scale, of part of a
modified housing.
[0051] The membrane module 20 comprises a bundle 1 of membrane
tubes contained in a canister 2 made of a plastics composite
material or metal. The bundle 1 consists of several layers, each
membrane layer comprising a plurality of membrane tubes la arranged
side by side with connecting portions 1b connecting laterally
adjacent membrane tubes, the membrane layers being stacked in
alternation with spacers 1c. The membrane layers are of the type
shown in U.S. Pat. No. 6,010,560. As seen in FIG. 2, the layers are
arranged such that substantially the entire cross section of the
tubular canister 2 is occupied.
[0052] The membrane tubes are potted at the opposite ends of the
canister by potting 3. A thermosetting polymeric material is used
as matrix material in between the individual membrane tubes. In
addition to ensuring that inlet/outlet flow may only pass through
the membrane tubes, i.e. tube side flow, the potting ensures
adhesion, load bearing and mechanical stability to the membrane
bundle. Axially inwardly of the potted ends, but adjacent thereto,
the canister is provided with a set of openings 7a, 7b for inlet
and outlet flow on the membrane shell side. Each set of openings
7a, 7b comprises a pair of longitudinally spaced rows, the openings
in each row being circumferentially spaced from each adjacent
opening. As shown, the centres of the openings in one row are
circumferentially offset from those in the other row. Thus, the
openings of the pair of rows are arranged so that every membrane
layer is exposed to at least one opening.
[0053] Three annular seal surfaces 61, 62 and 63 are provided
around the outside of the canister 2. A first annular seal surface
61 is disposed at a position axially intermediate of the canister
ends, the other two annular seal surfaces 62, 63 being axially
spaced from the first annular seal surface 61 towards the
respective canister ends.
[0054] FIG. 3 shows a pressure vessel 4. At one end this has a full
size flange opening 5, enabling easy insertion of the membrane
module 20 as shown in FIG. 4. In a modification, a flange opening 5
is provided at both ends and an additional flange opening 5 is
therefore shown in dotted lines. At its axial ends the pressure
vessel has an inlet port 8a and an outlet port 8b. Axially inwardly
of the ends, but adjacent thereto, the pressure vessel 4 has a
sideways facing inlet port 9a and a sideways facing outlet port 9b.
In a further modification, a pair of inlet ports 9a and a pair of
outlet ports 9b are provided and these are shown in dotted lines.
Each port of a pair is diametrically opposite the other port of the
pair. The ports 8a, 8b are provided for tube side flow, whilst the
ports 9a, 9b are provided for shell side flow.
[0055] A back pressure regulator 10 is provided downstream of the
outlet port 8b and is arranged to receive a reference signal 11
indicative of the pressure at inlet port 9a. The back pressure
regulator 10 is arranged to ensure that the differential pressure
across the membranes does not exceed a predetermined amount,
thereby ensuring that the membranes are not damaged in use.
[0056] FIG. 4 shows three annular seals 61a, 62a and 63a provided
inside the pressure vessel for sealing engagement respectively with
the three annular seal surfaces 61, 62 and 63. At the flanged
opening 5, each flange has a bevelled edge so as to form a V-shaped
groove when the end cap closes the pressure vessel 4. The seal 63a
is installed after the membrane module 20 has been inserted into
the pressure vessel 4. When the flanges are tightened together, the
end seal 63a is compressed.
[0057] Intermediate seal 61a is supported in an annular groove
formed in a separate member in the form of a ring 30 welded inside
the pressure vessel to the inside of its cylindrical wall 32. In
the modification shown in FIG. 6 the pressure vessel is formed as
two body portions to each of which a ring 30 incorporating a radial
outer flange is secured to form a connection between the body
portions. The ring is welded to the body portions by outer welds 34
and inner welds 36. The ring 30 shown in FIG. 6 also has an annular
groove for supporting seal 61a.
[0058] End seal 62a is, like intermediate seal 61a, supported in an
annular groove in a separate member where no flanged opening is
provided at that end. Both seals 61a and 62a are sufficiently
flexible to give little resistance during installation of the
membrane module into the pressure vessel. If an additional flanged
opening is provided at the end where seal 62a is located, then the
arrangement will be the same as provided for end seal 63a.
[0059] FIG. 5 shows the membrane module 20 contained in the
pressure vessel 4. It will be seen that once the membrane module is
inserted in the pressure vessel, the annular seals 61a, 62a, 63a
ensure the separation of the pressure vessel inlet and outlet ports
as required. The three annular seals effectively create four
isolated inlet and outlet regions within the pressure vessel.
Between seal 61a and seal 62a an annular outlet chamber
communicates with the pressure vessel outlet port 9b. Between the
seal 61a and the seal 63a an annular inlet chamber communicates
with the pressure vessel inlet port 9a. Inlet port 8a is located to
the left of seal 62a and this seal ensures that inlet 8a is
separated from outlet 9b. Outlet 8b is disposed to the right of
seal 63a and this seal ensures that outlet 8b is separated from
inlet 9a.
[0060] The provision of the three annular seals in this way means
that there is no need for any particular rotational alignment of
the membrane module and the pressure vessel in embodiments such as
that illustrated where openings 7a, 7b are provided at equal
intervals around the entire membrane module circumference.
[0061] The width of the annular inlet and outlet chambers is shown
as W and the diameter of the inlet and outlet ports 9a,9b is shown
as D. The width W is preferably greater than or equal to one
quarter of the diameter D, in order to allow for the desired
reduction in flow velocity downstream of the inlet port 9a and
increase in flow velocity upstream of the outlet port 9b.
[0062] With larger values of W, the flow velocities into or out of
the membrane module are reduced, thereby reducing the likelihood of
membrane damage. On the other hand, by minimising W, the diameter
of the membrane module 20 can be maximised for a given diameter of
pressure vessel 4, and hence greater use of available space can be
achieved. These conflicting requirements can be balanced if W is
equal to one quarter of D, in which case the flow area of the port
is equal to the cross-sectional area of the respective annular
chamber. This produces good flow conditions, without excessive flow
velocities which might damage the membranes, whilst making
efficient use of the available space in the pressure vessel. More
preferably, therefore, W is approximately equal to one quarter of
D, for example within .+-.20% of one quarter of D. Where additional
inlet and outlet ports 9a, 9b are used, as shown in dotted lines in
FIG. 4, then the diameter D of the ports can be reduced and the
required width W of the annular chambers can be reduced by the same
ratio.
[0063] The canister does not need to be designed for the same
pressure as the pressure vessel, only to withstand the differential
pressure equal to the pressure drop between the tube and the shell
side of the membranes at any point. A larger pressure variation,
which may harm the membranes or the module, is prevented by the
membrane protection system, 10,11, which is external of the
pressure vessel. Additional reinforcement of the canister may
however be necessary in the region of the seals for these regions
to achieve sufficient back pressure on the seals, so that the seals
can function properly.
[0064] The canister is substantially rigid to facilitate its
assembly into the pressure vessel. It may be made of metal or fibre
reinforced plastics. In the latter case, the canister may be made
by filament winding. The winding may be effected with rods in the
mandrel to achieve the desired openings without reducing the
mechanical strength of the canister.
[0065] The flange opening 5 allows for both easy installation and
retraction of the canister as shown in FIG. 3. Retraction of the
canister can preferably be done with two textile straps glued into
the potting or wound into the canister tube if composite material
is selected. For more slender canisters or a narrow annulus, where
it might be more complicated to assemble the canister into the
pressure vessel, both ends may have a full diameter flange.
[0066] The seals in the annulus around the membrane module help to
achieve the correct flow pattern. The seals at each end, 62a and
63a, of the module prevent mixing of tube side fluid and shell side
fluid in the vessel. The mid section seal 61a prevents an
undesirable shortcut of the shell side fluid. In both cases the
pressure difference over the seals will not be higher than the
pressure drop along the module plus any additional contribution
from the surrounding process system. These seals should preferably
be made of an inert material and according to a design suitable for
the purpose, and will in a preferred case be simple O-rings or more
compressible spring loaded lip seals. Where some axial movement,
due to thermal expansion are foreseen square profiles such as
provided by James Walker might be used. A "D" profile, which is
stable against twisting, may be used.
[0067] The seal 61a at the mid section of the annulus may be an
inflatable seal type to ease the assembly. Such a seal can allow a
wider gap and will be inflated after assembly. Such seals are
available from Seal Master Corporation or Mechanical Research &
Design Inc. Inflatable seals are of greatest use at ambient or low
pressure applications, it not being generally practical to
pressurise a seal to a pressure greater than natural gas
pressure.
[0068] The membrane module should have a shell side feed arranged
in such a way that an even distribution of shell side fluid can be
ensured so as to protect the membranes from harmful inlet flow,
such as high velocity flows which might cause cavitation. This can
be prevented by adding a reducer after the feed port, e.g. nozzle,
or a bigger annulus in this section of the pressure vessel. A
preferred solution is to use a baffle inside the pressure vessel or
to place the inlet opening(s) of the canister on the opposite side
of the pressure vessel inlet port.
[0069] The canister tube should preferably have multiple openings
7a, 7b arranged to secure an even distribution of the flow into the
membranes or it could have one elliptical slot. The optimised
design will be different for each particular case. The openings
should be located axially as close to the membrane potting as
possible, in order to allow for a counter current flow over a
maximum axial length through the membrane module.
[0070] The tube side inlet and outlet of the membrane module are
provided at the potted ends thereof which communicate with the
inlet and outlet ports 8a,8b of the pressure vessel. Shell side
inlet and outlet ports 9a, 9b of the pressure vessel are arranged
such that they communicate with the corresponding openings 7a, 7b,
when the module is installed in the pressure vessel. The shell side
feed could also be through multiple nozzle connections, or through
a ring chamber if further improved distribution on the shell side
is required.
[0071] The total area of the ports should be such that the fluid
velocity on entrance into the membrane bundle, preferably does not
exceed 500 mm/s for a liquid and 5000 mm/s for a gas, or creates a
too high pressure drop.
[0072] There are many mass transfer processes in which the present
invention may be applied, as is known in the art. The invention is
particularly suitable for removing carbon dioxide, hydrogen
sulphide and water from natural gas, but this is just one possible
use.
[0073] Although the use of a pressure vessel renders the apparatus
suitable for mass transfer processes at elevated pressures, the
apparatus can also be used at ambient pressures. Typical elevated
pressures at which the apparatus is useful are those in excess of
10 bar g (10.sup.6 N/m.sup.2 above atmospheric pressure).
* * * * *