U.S. patent application number 15/495611 was filed with the patent office on 2017-08-10 for membrane filter element with multiple fiber types.
The applicant listed for this patent is Cameron Solutions, Inc., Petronas Carigali SDN BHD. Invention is credited to Zalina Binti Ali, Faizal bin Mohamad Fadzillah, Hatarmizi Bin Hassan, Faudzi Mat Isa, Fatimah Binti A. Karim, George E. Mahley, III, Atsushi Morisato, Richard D. Peters, Wan Atikahsari Wan Zakaria.
Application Number | 20170226438 15/495611 |
Document ID | / |
Family ID | 42629774 |
Filed Date | 2017-08-10 |
United States Patent
Application |
20170226438 |
Kind Code |
A1 |
Peters; Richard D. ; et
al. |
August 10, 2017 |
Membrane Filter Element With Multiple Fiber Types
Abstract
A membrane filter element includes at least two
cylindrical-shaped, fiber bundles, one of the fiber bundles
containing first fibers fabricated to provide a selected first gas
selectivity, a selected first gas permeability, or a selected first
gas selectivity and permeability performance and arranged so a
first gas permeate exits the membrane element; another of the fiber
bundles containing second fibers fabricated to provide a selected
second, different gas selectivity, a selected second different gas
permeability, or a selected second gas selectivity and permeability
performance and arranged so a second different gas permeate exits
the membrane element. The different performance characteristics can
reduce the number of membrane elements required for gas separation
and to improve gas separation performance due to changing gas
composition as the gas travels through the membrane element.
Inventors: |
Peters; Richard D.; (Katy,
TX) ; Mahley, III; George E.; (Berkeley, CA) ;
Morisato; Atsushi; (Walnut Creek, CA) ; Karim;
Fatimah Binti A.; (Selangor, MY) ; Hassan; Hatarmizi
Bin; (Selangor, MY) ; Ali; Zalina Binti;
(Selangor Darul Ehsan, MY) ; Wan Zakaria; Wan
Atikahsari; (Selangor, MY) ; Isa; Faudzi Mat;
(Selangor, MY) ; Fadzillah; Faizal bin Mohamad;
(Kuala Lumpur, MY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Cameron Solutions, Inc.
Petronas Carigali SDN BHD |
Houston
Kuala Lumpur |
TX |
US
MY |
|
|
Family ID: |
42629774 |
Appl. No.: |
15/495611 |
Filed: |
April 24, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12706105 |
Feb 16, 2010 |
9630141 |
|
|
15495611 |
|
|
|
|
61154219 |
Feb 20, 2009 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
Y02C 10/10 20130101;
B01D 63/04 20130101; B01D 2257/504 20130101; C10L 3/103 20130101;
B01D 2053/224 20130101; B01D 53/227 20130101; C10L 2290/548
20130101; B01D 2319/06 20130101; B01D 2257/304 20130101; B01D 53/22
20130101; C10L 3/104 20130101; B01D 2258/06 20130101; Y02C 20/40
20200801; B01D 63/02 20130101; B01D 63/043 20130101 |
International
Class: |
C10L 3/10 20060101
C10L003/10; B01D 63/02 20060101 B01D063/02; B01D 53/22 20060101
B01D053/22 |
Claims
1. A membrane element comprising: at least two concentric,
cylindrical-shaped zones spanning a total height of the membrane
element and surrounding a central longitudinal axis of the membrane
element; one of the zones defined by first fibers fabricated to
provide a selected first gas selectivity and arranged so a first
gas permeate exits an end of the membrane element; another of the
zones defined by second fibers fabricated to provide a selected
second, different gas selectivity so a second different gas
permeate exits an end of the membrane element.
2. A membrane element according to claim 1 wherein the first fibers
are fabricated to provide a selected first gas permeability and the
second fibers are fabricated to provide a second, different gas
permeability.
3. A membrane element according to claim 2 wherein the first and
second fibers are fabricated to provide, relative to one another, a
different target CO.sub.2 permeability.
4. A membrane element according to claim 2 wherein the first and
second fibers are fabricated to provide, relative to one another, a
different target H.sub.2S permeability.
5. A membrane element according to claim 1 relative to one another,
a different target CO.sub.2 selectivity.
6. A membrane element according to claim 1 wherein the first and
second fibers are fabricated to provide, relative to one another, a
different target H.sub.2S selectivity.
7. A membrane element according to claim 1 wherein the first and
second fibers are fabricated to provide, relative to one another, a
different target water dew pointing performance.
8. A membrane element according to claim 1 wherein the first and
second fibers are fabricated to provide, relative to one another, a
different target hydrocarbon dew pointing performance.
9. A membrane element according to claim 1 wherein depth of the
zones differs from one another.
10. A membrane element according to claim 1 wherein at least one of
zones is an innermost zone or an outermost zone of the membrane
fiber element.
11. A membrane element according to claim 1 wherein the two zones
are located adjacent one another.
12. A membrane element according to claim 1 further comprising the
first and second fibers including hollow fibers.
13. A membrane element according to claim 1 wherein the first and
the second different gas permeates exit a same end of the membrane
element.
14. A membrane element according to claim 1 wherein the first and
second different gas permeates mix with one another after exiting
the same end.
15. A method of treating a gas, the method comprising: flowing the
gas through a membrane element containing at least two concentric,
cylindrical-shaped zones spanning a total height of the membrane
element and extending around the membrane element; wherein one of
the zones is defined by first fibers fabricated to provide a
selected first gas selectivity and arranged so a first gas permeate
exits an end of the membrane element; and wherein another of the
zones is defined by second fibers fabricated to provide a selected
second, different gas selectivity and arranged so a second
different gas permeate exits an end of the membrane element.
16. A method according to claim 15 wherein the first and second
fibers are fabricated to provide a selected first gas permeability
and the second fibers are fabricated to provide a second, different
gas permeability.
17. A method according to claim 15 wherein the first and second
fibers are fabricated to provide, relative to one another, a
different target water dew pointing performance.
18. A method according to claim 15 wherein the first and second
fibers are fabricated to provide, relative to one another, a
different target hydrocarbon dew pointing performance.
19. A method according to claim 15 wherein the first and second
fibers include hollow fibers.
20. A method according to claim 15 further comprising mixing the
first and second different gas permeates with one another after
exiting a respective end of the membrane element.
Description
CROSS-REFERENCE TO PENDING APPLICATIONS
[0001] This application is a continuation application of U.S.
patent application Ser. No. 12/706,105, filed Feb. 16, 2010, which
claimed the benefit of U.S. Provisional Patent Application No.
61/154,219, filed Feb. 20, 2009, the contents of which are hereby
incorporated by reference in their entirety.
BACKGROUND
[0002] Field
[0003] This disclosure relates generally to apparatuses used in the
treatment of gas. More particularly, the disclosure relates to
semi-permeable membranes used in gas separation processes to remove
acid gas and other components from a gas stream so that the gas may
be usable for fuel.
[0004] Description of the Related Art
[0005] Much of the world's produced natural gas contains
unacceptably high concentrations of acid gas--primarily CO.sub.2
and H.sub.2S--which must be removed before the gas is usable for
fuel. The utilization of semi-permeable membranes for
CO.sub.2/natural gas separation is well known and spiral wound and
hollow fiber membrane configurations have been used for this
purpose.
[0006] Commonly used membrane configurations include fiber
materials made of organic polymers and copolymers including
polysulfones, polycarbonates, cellulose acetates, cellulose
triacetates, polyamides, polyimides, and mixed-matrix membranes.
Regardless of the fiber material used, the membrane elements are
fabricated with the same type of fiber material throughout.
Therefore, these membranes are limited to a single and set range of
performance characteristics even though gas properties and volumes
change throughout the membrane as permeation occurs. Additionally,
current technology may require the operation of the membrane
elements in multiple stages, so that gas is passed through multiple
groups of membranes in series to partially compensate for the
inefficiencies in the performance of each individual membrane
stage. The result is additional equipment requirements and less
than optimal membrane separation performance.
[0007] For applications that require a significant amount of
CO.sub.2 removal, membrane element performance can be restricted by
these uniform performance characteristics. For example, a membrane
fiber that performs well in higher CO.sub.2 conditions may be less
effective at lower CO.sub.2 concentrations (and vice versa). As a
result, system design is often based on a compromise limited by the
performance characteristics of the membrane fiber. Because of less
than optimal membrane separation performance, additional equipment
and additional stages of membrane elements are required to remove
high percentages of CO.sub.2. In addition, the membrane separation
performance achieved with a single fiber type may be less efficient
overall, resulting in higher hydrocarbon losses to permeate.
[0008] In many applications, the inlet gas has a high percentage
(generally 10-95%) of inlet CO.sub.2 and membrane elements are used
to bulk remove CO.sub.2. As discussed previously, for high CO.sub.2
applications, the membrane elements often are configured to operate
in series with multiple stages of membranes in operation. This can
result in an inefficient configuration for equipment, which
requires interconnect piping between stages, thereby creating a
larger overall equipment footprint and higher equipment cost.
Having multiple stages of membranes may also result in difficulty
in balancing the flow rates and CO.sub.2 removal duties for each
stage of membranes, as the amount of membrane surface area
installed in each stage may have to be individually adjusted in
order to maintain the desired separation performance
characteristics.
[0009] Recent improvements in membrane manufacturing have led to
significant increases in membrane fiber surface area in a single
membrane element. For example, FIG. 1 shows older, prior art 5-inch
and 12-inch diameter CYNARA.RTM. membrane elements 10 (Cameron
International Corporation, Houston, Tex.) which have 500 and 2,500
square feet of active membrane fiber area, respectively. In
comparison, newer larger 16-inch and 30-inch diameter membranes
have been developed that have between 9,000 and 40,000 square feet
of active fiber area, respectively. In the prior art--and unlike
the embodiments disclosed herein--these larger diameter membranes
are single fiber type membranes. The shear surface area of these
larger diameter membranes provides greater capacity and allows for
fewer stages of processing when compared to the number of
processing stages needed when smaller diameter membranes are used.
However, these larger membranes experience a larger gradient in,
for example, CO.sub.2 concentration between the inlet and outlet
side of the membrane when compared to the smaller diameter
membranes. This larger gradient can reduce the effectiveness of
these larger diameter, single fiber type membrane elements.
[0010] For membrane gas separation applications, the relative
composition of the gas changes as the gas travels through the
membrane bundle and permeable components are separated from the
non-permeate components. At the same time, the inlet to
non-permeate gas volume is reduced as gas passes through the
membrane bundle and permeation occurs, with the inlet gas first
entering the membrane being higher in volume and permeable
components than the non-permeate gas exiting the membrane bundle.
In other words, the gas oftentimes undergoes significant and
non-uniform compositional changes as it travels through the
membrane. Therefore, a need exists for a membrane element that has
the requisite performance characteristics for improved gas
separation even as the gas volume and composition change as the gas
travels through the membrane.
SUMMARY
[0011] In general, disclosed herein are methods, systems, and
apparatuses for a membrane fiber element. In some embodiments, the
membrane element includes at least two concentric,
cylindrical-shaped zones spanning a total height of the membrane
element and extending around the membrane element. One of the zones
is defined by first fibers fabricated to provide a selected first
gas selectivity, a selected first gas permeability, or a selected
first gas selectivity and permeability performance and arranged so
a first gas permeate exits an end of the membrane element. Another
of the zones defined by second fibers fabricated to provide a
selected second, different gas selectivity, a selected second
different gas permeability, or a selected second gas selectivity
and permeability performance and arranged so a second different gas
permeate exits an end of the membrane element. A method of treating
a gas using the membrane element includes flowing the gas through
the membrane element in a single stage of processing.
[0012] In other embodiments of a membrane filter element at least
two different hollow fiber types are used. The hollow fiber types
are wrapped about a perforated non-permeate pipe located at the
center of the filter element to provide at least two
circumferential zones. The first circumferential zone includes the
first hollow fiber type and is located toward the inlet gas stream
(or feed) side of the element. The second (or any subsequent)
circumferential zone includes the second (or subsequent) hollow
fiber type and is located between the first zone and the perforated
non-permeate pipe. Because the hollow fiber types are fabricated to
differ from one another in targeted acid-gas selectivity and
permeability performance, and because the first and second hollow
fiber types are arranged in their respective zones, the selectivity
and permeability performance characteristics in the first zone
differ from those of the second zone as does the composition and
volume of the natural gas stream to which each zone is exposed.
[0013] The different performance characteristics may be a function
of intentional differences in bore size, wall thickness, material,
manufacturing process, or some combination thereof between the
multiple hollow fiber types. For example, in an embodiment, the
hollow fiber types differ in permeability (capacity or flux) and
selectivity (separation or alpha). Or, the hollow fiber types may
differ in CO.sub.2 and H.sub.2S removal capacity or hydrocarbon
removal capacity. Additionally, the hollow fiber types may differ
in water dew pointing or hydrocarbon dew pointing performance.
[0014] Embodiments include a single membrane filter element that
effectively accomplishes a range of separation from high CO.sub.2
to low CO.sub.2 (or vice versa). The membrane filter element can be
optimized to two or more distinct separation functions including
but not limited to CO.sub.2 and H.sub.2S separation or CO.sub.2 and
hydrocarbon dewpointing to the membrane filter element can provide
for improved membrane efficiency and a better overall separation
and capacity and simplify process control by reducing the number of
filtering stages that require monitoring and eliminating the need
for plant operators to rebalance flow rates between multiple stages
of membrane filter elements or to change the relative loading
between these stages. to the membrane filter element may provide
for increased flexibility in accommodating changes in inlet gas
composition over time. The membrane filter element can create more
resistance to bypass or gas channeling and, therefore, eliminate
the need for internal baffles or other gas distribution
mechanisms.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] So that the manner in which the above recited features can
be understood in detail, a more particular description may be had
by reference to embodiments, some of which are illustrated in the
appended drawings, wherein like reference numerals denote like
elements. It is to be noted, however, that the appended drawings
illustrate various embodiments and are therefore not to be
considered limiting of its scope, and may admit to other equally
effective embodiments.
[0016] FIG. 1 compares membrane filter element sizes--ranging in
diameter from about 5 to 30 inches. For the purpose of this
disclosure, the two smaller diameter membrane filter elements 10
are examples of prior art single fiber type filter elements. In
many applications, several of these single fiber elements must be
deployed in series or stages to treat an incoming natural gas
stream. In some embodiments, a membrane element with a diameter
greater than 12 inches is used for producing the multiple fiber
membrane filter element of this disclosure. However, because of the
greater bundle depth recently provided by large membrane elements,
multiple fiber types may be used effectively in a single filter
element, eliminating the need for several single fiber filter
elements and multiple processing stages. Therefore, for the purpose
of this disclosure, the two larger diameter membrane filter
elements 20 are non-limiting examples of a multiple fiber type
filter element.
[0017] FIG. 2 is a graphical depiction of the hollow fibers that
make up the multiple fiber membrane filter element 20 of FIG. 1.
The hollow fibers are arranged about a perforated non-permeate
pipe. Optionally, the fibers may be arranged in bundles and then
wrapped about the pipe.
[0018] FIG. 3 is a graphical depiction of the several hollow fibers
of one of the bundles of FIG. 2. The fibers are isolated to
indicate the size of the individual fibers.
[0019] FIG. 4 is an end view of one of the hollow fibers of FIG. 3
as it might appear under magnification. The multiple fiber membrane
filter element includes many hundreds of thousands of these hollow
fibers.
[0020] FIG. 5 is an end view of the multiple fiber membrane filter
element 20 of FIG. 1 as it experiences an outside-in gas flow. The
fiber types are generally arranged in two circumferential zones.
Bundles located in the first circumferential zone include hollow
fibers of one type and bundles located in the second zone hollow
fibers of another type. Because the hollow fiber types are
intentionally fabricated to differ from one another and provide a
different target selectivity and permeability, the first zone
exhibits different performance than does the second zone.
Alternatively, gas flow could occur "inside out," flowing first
through the second zone and then through the first zone.
[0021] FIG. 6 is a schematic illustrating a prior art process that
makes use of single fiber filter elements arranged in series, or
two different single fiber type membranes with one fiber type used
in Stage 1 and the second fiber type used in Stage 2.
[0022] FIG. 7 is a schematic illustrating a process that makes use
of a filter element embodiment. The multiple fiber type filter
element allows for single-stage processing.
DETAILED DESCRIPTION
[0023] In the following description, numerous details are set forth
to provide an understanding of some embodiments of the present
disclosure. However, it will be understood by those of ordinary
skill in the art that the system and/or methodology may be
practiced without these details and that numerous variations or
modifications from the described embodiments may be possible.
[0024] In the specification and appended claims: the terms
"connect", "connection", "connected", "in connection with", and
"connecting" are used to mean "in direct connection with" or "in
connection with via one or more elements"; and the term "set" is
used to mean "one element" or "more than one element". Further, the
terms "couple", "coupling", "coupled", "coupled together", and
"coupled with" are used to mean "directly coupled together" or
"coupled together via one or more elements". As used herein, the
terms "up" and "down", "upper" and "lower", "upwardly" and
downwardly", "upstream" and "downstream"; "above" and "below"; and
other like terms indicating relative positions above or below a
given point or element are used in this description to more clearly
describe some embodiments of the disclosure
[0025] Embodiments of a membrane element that has multiple hollow
fiber types will now be described by making reference to the
drawings and the following elements illustrated in the
drawings:
TABLE-US-00001 10 Single fiber membrane element 20 Multiple fiber
membrane element 21 Hollow fiber 23 Wall of 21 25 Bore of 21 27
Fiber bundle 29 Bundle depth 31 First circumferential zone of
fibers 33 Second circumferential zone of fibers 35 Perforated
non-permeate pipe 37 Central longitudinal axis of 20 & 35 41
Gas inlet or feed side of 20 43 Outlet or non-permeate side of 20
45 Membrane division
[0026] Referring now to FIG. 1, two prior art, single fiber
membrane elements 10 are shown. Because membrane elements that have
a diameter greater than 12 inches are useful for producing a
multiple fiber membrane element, the larger diameter membranes of
FIG. 1 are labeled as membrane 20. Membrane element 20 takes
advantage of manufacturing improvements that have enabled the
production of much larger diameter semi-permeable membrane filter
elements for CO.sub.2/natural gas separation. Single fiber membrane
elements 10 are available in sizes similar to that of membrane
element 20, but membrane element 20 as disclosed herein is not a
prior art membrane element. The cylindrical-shaped membrane 10, 20
is typically housed within a pressure vessel connected by way of
piping to an inlet gas stream (not shown) and may be configured for
an "outside in" flow or "inside out" flow. Regardless of the
direction of flow, as the inlet gas stream travels through the
membrane 10, 20, acid gas and other undesirable components are
removed to the permeate.
[0027] For the purpose of comparison with multiple fiber membrane
element 20, single fiber membrane element 10 may be generally less
than 15 inches in diameter and from about 24 inches to about 48
inches in height. Because membrane 10 does not have sufficient
depth to minimize bypass--and because it employs a single fiber
type that cannot account for the changes in gas volume and
composition as the gas stream travels through the membrane 10--two
or more membranes 10 must be arranged in series (see FIG. 6) with
separation being performed in at least two stages. Selection of the
fiber type for use in membrane 10 at each stage typically involves
a trade-off between permeability (known as flow capacity or flux)
and selectivity (called permeation rate or alpha). By way of
example, as permeability increases in a polymeric membrane fiber,
selectivity decreases (and vice versa).
[0028] Because of the trade-off between permeability and
selectivity, some membrane fibers are better suited to higher
concentrations of permeable components, while others are better
suited to higher grade separations at lower concentrations of
permeable components. Membrane fibers that exhibit better
hydrocarbon separation attributes (higher selectivity) and lower
permeability may be selected for use in membrane 10 at the first
stage of processing. Conditions at this stage are typically
characterized by higher gas flow rates and higher CO.sub.2
concentrations. For hydrocarbon/CO.sub.2 separation applications,
the majority of CO.sub.2 is permeated in this first stage, and the
majority of "hydrocarbon losses" occur in this stage. Although the
higher alpha fibers selected for use have a slightly lower flux,
the fibers still operate efficiently due to the high CO.sub.2
concentrations. At the second stage, however, membrane fibers that
exhibit higher permeability and lower selectivity may be used.
Conditions at this stage are typically characterized by lower gas
flow rates and lower CO.sub.2 concentrations. Therefore, element 10
can exhibit higher permeability at this stage in order to minimize
the amount of membrane area and associated equipment required.
[0029] Turning now to FIGS. 5 & 7, a multiple fiber membrane
element 20 replaces multiple single fiber membranes 10 and multiple
stages of separation processing. The improved processing
performance provided by membrane 20 is due in part to the use of
different types of hollow fibers 21 in different zones 31, 33 of
the membrane 20 and the increased surface area and bundle depth 29
provided by membrane 20. For example, in one embodiment membrane 20
is about 30 inches in diameter and 72 inches in height. Compared to
a 12-inch diameter single fiber membrane 10, multiple fiber
membrane filter element 20 generally has about 10 times the surface
area and about 3 times the bundle depth 29 as that of membrane
10.
[0030] Referring now to FIGS. 2 to 5, membrane 20 includes hundreds
of thousands of two or more different types of hollow fibers 21.
The fibers 21 are wrapped about a perforated non-permeate tube or
pipe 35 that shares a central longitudinal axis 37 with membrane
20. Alternatively, the fibers 21 may be arranged in bundles 27 and
wrapped about pipe 35. Fibers 21 are arranged so permeate that
permeates the wall 23 and enters the bore 25 of the hollow fibers
21 may exit through the top and bottom of membrane 20. Membrane 20
is fabricated as a divided membrane element with two distinct
circumferential zones 31, 33, with line 45 indicating the division
between the two zones. Fibers 21 located in a first circumferential
zone 31 of the membrane 20 have a different type (or types) of
hollow fibers 21 than fibers 21B located in a second
circumferential zone 33. The performance characteristics of each
zone 31, 33 differ because the hollow fibers 21 or combination of
hollow fibers 21 fabricated and selected for use in zone 31 have
been fabricated to achieve, for a composition and volume of the
natural gas stream flowing through the zone 31, a different
selectivity and permeability than the hollow fibers 21B or
combination of hollow fibers 21B in zone 22 for the composition and
volume of the natural gas stream flowing through the zone 33.
[0031] The hollow fibers 21 in each zone 31, 33 are selected in
order to maximize the overall capacity and separation performance
of membrane 20 as a gas stream passes through it, thereby reducing
or eliminating the need for multiple processing or separation
stages (see FIG. 7). For example, a higher separation, lower
permeability hollow fiber 21 may be located nearest to the inlet or
feed side 41 of the membrane 20, in circumferential zone 31, where
maximum permeation flow volumes occur, in order to reduce the
hydrocarbon losses to the permeate. A higher permeability but lower
separation hollow fiber 21 may be located nearest to the outlet or
non-permeate side 43 of the membrane 20, in circumferential zone
33, to improve capacity where CO.sub.2 is lower. Alternatively, a
first hollow fiber 21 having a higher permeation of one component
(e.g. H.sub.2S) may be bundled with a second hollow fiber 21 having
higher permeation of another component (e.g. CO.sub.2 or
hydrocarbon dewpointing) or vice versa.
[0032] Configuring membrane 20 with multiple types of hollow fibers
21 can optimize performance by taking advantage of the performance
characteristics of the different types of hollow fibers 21 included
in each zone 31, 33 relative to the gas composition and more than
two zones 31, 33 may be deployed. For example: [0033] 1. Combining
larger bore hollow fibers 21 on the high CO.sub.2 zone nearest the
feed gas side 41 of element 20 and smaller bore fibers 21 on the
low CO.sub.2 zone nearest the non-permeate side 43 of element 20 to
add more relative surface area in low CO.sub.2 conditions. [0034]
2. Combining hollow fibers 21 that have greater CO.sub.2 partial
pressure resistance in the zone nearest the feed gas side 41 with
hollow fibers 21 having higher flux in the zone nearest the
non-permeate side 43. [0035] 3. Combining hollow fibers 21 that
exhibit different separations, such as combining a hollow fiber 21
for dehydration with a fiber 21 for CO.sub.2/hydrocarbon separation
or combining a fiber 21 for CO.sub.2 removal with a fiber 21 for
H.sub.2S removal or for hydrocarbon dewpointing.
[0036] Membrane 20 results in fewer stages of membrane elements
because it performs a much greater CO.sub.2 removal duty than its
single fiber predecessor membrane 10. A greater amount of CO.sub.2
can be removed in membrane 20 because there is more permeation of
CO.sub.2, which results in a greater differential between inlet
CO.sub.2 and exiting non-permeate CO.sub.2 inside of membrane 20.
Because of this, the gas passing through membrane 20 now has a
higher percentage of CO.sub.2 on the feed side 41 of membrane 20
than it does in the middle or on the exiting non-permeate side
43.
[0037] By way of example, consider an inlet gas stream entering
membrane 20 that contains about 50% inlet CO.sub.2. As the gas
passes through membrane 20 and travels toward the inner core or
central longitudinal axis 37, CO.sub.2 is permeated. As a result,
the hollow fibers 21 located closer to the central longitudinal
axis 35 of element 20 (that is, the non-permeate side 43) are
presented with gas having successively lower and lower amounts of
CO.sub.2. For example, depending on the type of hollow fibers 21
selected for use, non-permeate gas may exit the membrane 20 with
about 10% CO.sub.2. In this example, although the removal of
CO.sub.2 through the membrane 20 is a continuous process, for
simplification purposes zone 31 is a labeled a high-CO.sub.2 zone
where CO.sub.2 is removed from about 50% to 25%. The hollow fibers
21 located farther away from the feed side 41 and toward the
non-permeate side 43 reside in zone 33 or the low-CO.sub.2 zone,
where CO.sub.2 is removed from about 25% to 10%. Again, these
values are simply illustrative ones.
[0038] A membrane 20 can provide a number of benefits. Because of
the increased fiber bundle depth 29, the larger membrane 20 may
replace two stages of smaller conventional membranes 10. Equivalent
scale-up is not possible with spiral wound membrane elements due to
the restriction in gas flow paths between layers of the membrane.
CO.sub.2 is selectively separated within the membrane element 20 as
the flowing mixed CO.sub.2/hydrocarbon gas comes in contact with
the fibers 21. CO.sub.2 passes through the wall 23 of each fiber 21
into the bore 25 of each fiber 21 and exits through the ends of the
membrane element 20 as permeate gas. The inlet gas is reduced in
CO.sub.2 as the gas travels through membrane 20, resulting in the
exiting non-permeate gas having a lower CO.sub.2 concentration than
the inlet gas.
[0039] As gas passes through membrane element 20, each successive
array of fibers 21 actually processes gas with progressively lower
and lower CO.sub.2 content. The actual CO.sub.2 content that each
individual hollow fiber 21 is exposed to depends on the position of
the fiber 21 in the membrane 20 relative to the feed gas side 41,
with fibers 21 located near the inlet operating on higher CO.sub.2
gas than fibers 21 that are located downstream, nearer to the gas
outlet or non-permeate side 45. The larger bundle depth 29 thus
enables the use of multiple fiber types in a single membrane
element 20 and provides separation performance similar to that
which previously required gas to pass through two or more membranes
10 in series. Furthermore, within membrane 20 there is a greater
change in gas volume and composition due to permeation than with
previous smaller membranes 10. Therefore, membrane 20 is not only
processing more gas but is also operating with a greater
differential in gas composition between the feed gas side 41 and
the non-permeate side 43 enabling the use of multiple fiber types.
With current single fiber membranes 10, the resulting membrane
performance over the range of gas conditions present in the
membrane 10 may be sub-optimal.
[0040] While a membrane filter element having multiple fiber types
and a method for its use has been described with a certain degree
of particularity, many changes may be made in the details of
construction and the arrangement of components and steps without
departing from the spirit and scope of this disclosure. A filter
element and method according to this disclosure, therefore, is
limited only by the scope of the attached claims, including the
full range of equivalency to which each element thereof is
entitled.
* * * * *