Abstract:
This disclosure discusses devices to sweep the permeate side of fiber membrane permeators. Specifically, providing permeate side sweep wherein the fiber membranes comprise a bore; the feed fluid is in fluid communication with the outer surface of the fiber membrane; and the permeate is withdrawn from the bore of the fiber membrane. Permeate side sweep is used to increase the amount of permeate separated from a fluid mixture by the permeator device. The device of the subject invention includes a sweep chamber in fluid communication with the bore of the fiber membrane and in fluid communication with a suitable sweep fluid source. The sweep fluid is controllable and can be conditioned by devices known in the art.

Description:
CROSS-REFERENCES  
       [0001]     This application is related to and claims the benefit of U.S. Provisional Application No. 60/556,865, filed Mar. 26, 2004, entitled “Device To Enable Permeate Side Sweep (Internal and External) Of Hollow-fiber Gas Separation Membrane Modules.” 
     
    
     BACKGROUND  
       [0002]     Fluid separation fiber membrane permeators as described in U.S. Pat. Nos. 4,670,145 and 5,013,331 are used for industrial separation of components of fluid mixtures. These permeators comprise fiber membranes that selectively allow particular components of a fluid mixture to pass through the membrane. These fiber membranes comprise an inner bore and an outer surface, thus providing two regions for fluid mixture flow separated by the membrane. The initial fluid mixture, which will be separated, is the “feed fluid.” A component of the fluid passing through the fiber membrane is referred to as the “permeate,” while the remaining mixture is referred to as the “residue” fluid. The side of the membrane on which the feed mixture passes is referred to as the “feed side.” The side of the membrane on which the permeate exists is referred to as the “permeate side.” A “fiber membrane module” comprises one or more fiber membranes.  
         [0003]     For certain applications, the feed side and permeate side pressures are not substantially different. In these applications, a fiber membrane module with permeate side sweep as described in U.S. Pat. No. 5,314,528 can significantly enhance the amount of permeate recovered by the fiber membrane module. A permeate side sweep “sweeps” a fluid of relatively low permeate content on the permeate side, lowering the permeate partial pressure on the permeate side and causing the fiber membrane module to pass significantly more of the desired permeate, but at a lower purity than would occur without the permeate side sweep. A device utilizing a permeate side sweep with the feed fluid in communication with the bores of fiber membranes and a permeate side sweep of the outer surface of the hollow fibers is disclosed in U.S. Pat. No. 5,525,143.  
         [0004]     Previously disclosed permeate side sweep devices involve multiple-membrane fiber membrane modules in which feed is fed to the membrane bores (the feed side is the membrane bore), and the permeate side is the outer surface of the membranes. Additionally, such previously disclosed devices only provide a single permeate side sweep stage, allowing for higher permeate fluid yield only by operating at higher flow rates, which may be impractical, or by increasing the volume, and thus the relative size, of the fiber membrane module, which may also be impractical.  
         [0005]     However, it is desirable to provide a permeate side sweep with the membrane bores as the permeate side, because the membrane bores comprise a smaller relative volume than the volume around the outer surfaces of the membranes. Such an application may reduce the required volume of sweep fluid. Additionally, such smaller volumes may provide enhanced control of the partial pressures of the sweep fluid and the permeate. Further, providing a device with multiple stages of permeate side sweep can provide incrementally higher permeate fluid yield over existing devices.  
         [0006]     Accordingly, it is a goal of the invention to provide a permeate side sweep device allowing for use of the membrane bores as the permeate side, and to provide for control of the sweep fluid to such a device.  
         [0007]     It is a further goal of the invention to provide a device with multiple stages involving permeate side sweep to enhance the yield or flow rate of the permeate fluid.  
       SUMMARY  
       [0008]     The present invention is directed to a device that satisfies the need to feed sweep fluid to the bores of fiber membranes, control the sweep fluid feed, and feed the sweep fluid to multiple fiber membrane modules. A permeator device having features of the present invention comprises one or more fiber membranes, each of which comprises a bore, a feed fluid in partial fluid communication with the bores, a sweep chamber in fluid communication with the bore, and a sweep fluid source in fluid communication with the sweep chamber.  
         [0009]     Feeding a sweep fluid down the bores of fiber membrane permeators increases the amount of permeate exiting the permeator device. In this application, a fiber membrane permeator refers to a permeator device comprising at least one fiber membrane comprising a bore. In the preferred embodiment, a fiber membrane permeator additionally comprises a seal, a permeate chamber, a permeate port, and a residue port. Typically, but not necessarily, the fiber membrane module comprises a plurality of permeable fiber membranes of a type well known in the art comprising an outer surface and a bore. The seal, for example a tubesheet, prevents fluid in communication with the outer surfaces of the fiber membranes from flowing into the bores of the fiber membranes. One skilled in the art knows how to construct various configurations of fiber membrane permeators or fiber membrane modules with the components above as shown in U.S. Pat. Nos. 4,670,145 and 4,080,296.  
         [0010]     The present invention comprises a fiber membrane module, a feed fluid in partial fluid communication with the bore of the fiber membrane, a sweep chamber in fluid communication with the bore of the fiber membrane, and a sweep fluid source in fluid communication with the sweep chamber. The feed fluid is a multi-component feed stock which is separated into a desired permeate and a residue. The partial fluid communication of the feed fluid with the bore of the fiber membrane separates the permeate, which passes through the wall of the fiber membrane into the bore of the fiber membrane.  
         [0011]     The apparatus is used to increase the amount of permeate separated from the feed fluid by passing sweep fluid, of relatively low permeate content, to the permeate side (that is, the bore) of the fiber membrane. The fiber membrane selectively allows the permeate into the bore. However, the rate at which permeate can reach the bore is determined by the relative permeate partial pressure on either side of the fiber membrane. As permeate enters the bore through the membrane, the relative permeate partial pressure increases until a steady state is reached. If the permeate partial pressure within the bore is high, that is, when the permeate within the bore is of high purity, flow of permeate across the fiber membrane into the bore is limited. Introducing sweep fluid, such as residue fluid, into the bore lowers the partial pressure of the permeate in the bore and allows a higher rate of permeate flow across the fiber membrane into the bore.  
         [0012]     The permeate and sweep fluids are withdrawn through the permeate port. In the preferred embodiment, the sweep fluid source is controllable, so that the amount or flow rate of the sweep fluid through the bore can be adjusted. Additionally, the sweep fluid may be conditioned in a conditioning system before being fed to the sweep chamber. Conditioning may comprise filtering, treating, changing the composition of, or otherwise modifying the sweep fluid by placing various devices, such as filters, separators, or other devices in fluid communication with the sweep conduit.  
         [0013]     Because fiber membrane permeators often contain a number of fiber membrane modules in one device, various embodiments of the invention may comprise various combinations of sweep fluid sources, conditioning of the sweep fluid, or controlling the sweep fluid to each fiber membrane module individually, to all fiber membrane modules jointly, or any combination of individual and joint sweep fluid feed depending on the needs of the application.  
         [0014]     The apparatus has the advantage of providing a simple and economical apparatus for implementing a permeate side sweep of a fiber membrane permeator in which the permeate is in fluid communication with the bore of the fiber membrane and the feed fluid is in fluid communication with the outer surface of the fiber membrane. Preferred embodiments provide the advantages of conditioning or controlling the sweep flow, thus controlling the quantity and purity of permeate fluid exiting the fiber membrane permeator. By increasing the amount of sweep fluid (through increasing the flow rate or pressure of the sweep fluid), the fiber membrane permeator typically produces a larger quantity of permeate, but at a lower purity level.  
         [0015]     Alternately, reducing the amount of sweep fluid typically causes the fiber membrane permeator to produce less permeate at a higher purity.  
         [0016]     One embodiment of the device includes the ability to feed sweep fluid to each fiber membrane module individually. Feeding fiber membrane modules individually allows the practitioner maximum flexibility to optimize the amount and purity of permeate withdrawn from the fiber membrane permeator. The practitioner can vary the sweep flow to the individual fiber membrane modules, provide different sweep fluid sources to different fiber membrane modules, or condition the sweep fluid differently to different fiber membrane modules.  
         [0017]     As indicated above, another advantage of the apparatus is the ability to place the sweep chambers in fluid communication with different sweep fluid sources. The preferred sweep fluid source is the residue exiting the permeator. However, significant advantages can be obtained using other fluid streams available to the practitioner for the sweep fluid source that result in higher permeate production, greater overall system efficiencies, or lower operating costs. For instance, the practitioner may have a separate or related process from which there is an excess of a stream low in permeate content that can be used as the sweep fluid source. Furthermore, feeding each fiber membrane module individually provides an advantage by allowing the practitioner to further optimize the permeation process by feeding residue fluid to some of the fiber membrane modules, while feeding a sweep fluid from another source to other fiber membrane modules. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0018]      FIG. 1  is a sectional view of one embodiment of a fiber membrane permeator of the present invention.  
         [0019]      FIG. 1A  is a side view of segment A-A′ of  FIG. 1 , showing detail of the fiber membrane module.  
         [0020]      FIG. 2  is a sectional view of a multi-module embodiment of the present invention.  
         [0021]      FIG. 3  is a sectional view of an alternative embodiment of the multi-module embodiment of  FIG. 2 .  
         [0022]      FIG. 4  is a sectional detail view of one embodiment of a sweep fluid source of the present invention. 
     
    
     DESCRIPTION  
       [0023]     Referring to  FIGS. 1 and 1 A, one embodiment of a fiber membrane permeator  10  with permeate side sweep of the fiber membrane bores comprises a fiber membrane module  12  with a seal  14 , a permeate chamber  16 , a permeate port  18 , a residue port  20 , a sweep chamber  22 , a sweep conduit  24  and a sweep fluid source  26 . The permeate chamber  16  is sealingly engaged with the seal  14  and in fluid communication with the bores  28  of the fiber membranes  30 . The sweep chamber  22  comprises a chamber cap  32  sealingly engaged with the seal  14  of the fiber membrane module  12  to create a sealed volume in fluid communication with the bores  28  of the fiber membranes  30 . The sweep conduit  24  is in fluid communication with the sweep fluid source  26  and the sweep chamber  22 .  
         [0024]     One skilled in the art will recognize that there are various configurations of supplying feed fluid  34  to the fiber membrane permeator  10 . For example, in the preferred embodiment of  FIG. 2 , the fiber membrane modules  12   a,b,c  are in a housing  36  and the feed fluid  34  is in fluid communication with a feed port  38  of the housing  36 . It is also possible to place the fiber membrane permeator  10  directly in a reservoir of feed fluid (not shown) exposing the outer surface  40  of the fiber membrane  30  directly to the feed fluid  34 . This invention is applicable to any configuration wherein the feed fluid  34  is in fluid communication with the outer surface  40  of the fiber membrane  30 .  
         [0025]     Referring again to  FIG. 1 , the permeate port  18  is in fluid communication with the permeate chamber  16  and in fluid communication with the permeate conduit  42  allowing withdrawal of the permeate from the fiber membrane permeator  10 . The residue port  20  is in partial fluid communication with the feed fluid  34 . As depicted in  FIG. 1 , the residue port  20  is in the annulus of a round bundle of fiber membranes  30 . However, other configurations may be used without departing from the spirit of the invention. The residue port  20  is in fluid communication with the residue conduit  44 . The residue conduit  44  allows withdrawal of the residue from the fiber membrane permeator  10 .  
         [0026]     Still referring to  FIG. 1 , fluid communication between the sweep chamber  22  and the sweep fluid source  26  is via a sweep conduit  24 . The sweep fluid source  26  is any suitable source of fluid. The preferred sweep fluid source  26  has a content of the permeated component that is lower than the content of the permeate exiting the fiber membrane permeator  10 . In the preferred embodiment of  FIG. 2 , the sweep fluid source  26  is the residue ports  20   a,b,c . The sweep chamber  22  is in fluid communication with the residue ports  20   a,b,c  via a sweep conduit  24  that is in fluid communication with the residue conduit  44 .  
         [0027]     Referring again to the preferred embodiment of  FIG. 1 , the fluid communication between the sweep fluid source  26  and the sweep chamber  22  is controllable by a sweep control device  46 . The sweep control device  46  can be by any device or method known to one skilled in the art. The sweep control device  46  is in fluid communication with the sweep conduit  24  that is in fluid communication with the sweep fluid source  26  and the sweep chamber  22 . Another embodiment (not shown) would use a method of calculating the size of the sweep conduit  24  to control the flow of sweep fluid to the sweep chamber  22  by the pressure drop of the fluid in the sweep conduit  24 .  
         [0028]     The preferred embodiment of  FIG. 2  shows a plurality of fiber membrane modules  12   a,b,c  stacked to form a multi-module fiber membrane permeator  48 . One skilled in the art can construct a multi-module fiber membrane permeator  48  comprising a plurality of fiber membrane modules  12   a,b,c . Typically, but not necessarily, the permeate side of the fiber membrane modules  12   a,b,c  are in fluid communication with a plurality of permeate ports  18   a,b,c  that are in fluid communication with a permeate conduit  42 . The residue side of the fiber membrane modules  12   a,b,c  are in fluid communication with a common residue conduit  44  through their respective residue ports  20   a,b,c.    
         [0029]     Still referring to  FIG. 2 , a plurality of the sweep chambers  22   a,b,c  are in fluid communication with a common sweep conduit  24  and sweep fluid source  26 . A common sweep conduit  24  is in fluid communication with the residue conduit  44 . Thus the residue conduit  44  is the sweep fluid source  26 . A common sweep control device  46  in fluid communication with the sweep conduit  24  controls the sweep fluid to all sweep chambers  22   a,b,c.    
         [0030]     In the preferred embodiment of  FIG. 3 , a plurality of sweep chambers  22   a,b,c , are in fluid communication with a plurality of sweep fluid sources  26   a,b,c . There are separate sweep control devices  46   a,b,c  in each sweep conduit  24   a,b,c . The sweep control devices  46   a,b,c  control the fluid communication between the sweep chambers  22   a,b,c  and the sweep fluid sources  26   a,b,c  individually. One skilled in the art will recognize many combinations wherein some of the sweep chambers  22   a,b,c  are in fluid communication with individual sweep fluid sources  26   a,b,c  as shown in  FIG. 3 , and some of the sweep chambers  22   a,b,c  are in fluid communication with a common sweep fluid source  26  as shown in  FIG. 2 .  
         [0031]     The preferred embodiment of  FIG. 4  comprises a fiber membrane module  12  with a permeate chamber (not shown) in fluid communication with the bores  28  of the fiber membranes  30 . The embodiment further comprises a permeate port (not shown), a residue port  20 , and a sweep chamber  22 . The sweep chamber  22  comprises a chamber cap  32  sealingly engaged with the seal  14  of the fiber membrane module  12  to create a sealed volume in fluid communication with the bores  28  of the fiber membranes  30 . An orifice  50  provides the fluid communication between the sweep fluid source  26  and the sweep chamber  22 . Thus the sweep fluid source  26  is in fluid communication with the residue port  20 .  
         [0032]     Although the present invention has been described in considerable detail with reference to certain preferred versions thereof, other versions are possible. For example, a permeator may contain single or multiple fiber membrane modules in arrangements other than the arrangements shown. Likewise, the device may or may not contain a sweep conduit. Furthermore, a sweep conduit, if provided, may vary in construction such as piping, tubing, or conduits integral to a permeator housing. There are also a variety of devices known in the art to control the flow or pressure of the sweep fluid such as self contained regulators, pressure control valves, flow orifices, flow control valves, or flow valves mounted in flow conduits integral to a permeator housing. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained herein.  
         [0033]     All the features disclosed in this specification (including any accompanying claims, abstract, and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.