GB2090546A

GB2090546A - Apparatus containing membrane tubes embedded in a tube sheet

Info

Publication number: GB2090546A
Application number: GB8138902A
Authority: GB
Original assignee: Monsanto Co
Current assignee: Monsanto Co
Priority date: 1980-12-29
Filing date: 1981-12-24
Publication date: 1982-07-14
Also published as: JPS57136906A; AU7904081A; FR2497331A1; DK578181A; DE3151687A1; GB2090546B; CA1181699A; NL8105860A; IN154529B; IT8125862A0; IT1140190B; BE891634A; NO814445L; SU1134112A3; ZA818945B; BR8108400A

Abstract

In tube heat exchangers are in permeators (100) having hollow fiber membranes (116) suitable for fluid separations, the tubes or fibres are embedded in a tube sheet (120) and the tube sheet is positioned in a fluid tight relationship within a casing (102 by a cup seal (141). The cup seal comprises a polymeric ring which substantially surrounds and cooperates with a resilient member to provide both a pressure- actuated and self-actuated fluid tight seal. <IMAGE>

Description

SPECIFICATION Apparatus containing tubes embedded in a tube sheet This invention pertains to apparatus such as heat exchangers and permeators which contain tubes embedded in tube sheets. A particularly attractive aspect of this invention relates to improved permeators utilizing hollow fiber membranes in which the hollow fiber membranes are embedded in a tube sheet and the bores of the hollow fibers extend as fluid passageways through the tube sheet.

Apparatus, such as heat exchangers and permeators, have tubes positioned within a tubular shell with at least one end of each of the tubes embedded in a tube sheet. One purpose of the tube sheet is to secure the tubes in an essentially fluid tight relationship within the tube sheet. The tube sheet should provide a sufficiently strong barrier to fluid flow such that during operating conditions with often substantial differentials in pressure across the tube sheet, the tube sheet does not rupture or otherwise lose its integrity thereby allowing fluid to pass through the tube sheet.

Therefore, in many instances the tube sheet is of substantial thickness in order to ensure achieving a fluid tight relationship with the tubes and to ensure that the tube shes-t canwithstand any pressure differentials to which it may be subjected during operation.

The tube sheet may then be secured in an essentially fluid tight relationship in the apparatus such that fluid does not pass around the tube sheet between the sl1eli side and bore side of the tubes. Small leakages around the tube sheet can adversely affect the performance of a heat exchanger, and the effect on the performance of a permeator may often be even more serious since the non-permeating fluid can pass to the permeate exit side of the membranes and reduce the selectivity of separation of the membrane. This invention relates to improvements in providing a fluid tight relationship around the tube sheet.

In some operations, a tube sheet may be subjected to environments which tend to expand or contract the material of the tube sheet as well as potentially the materials of the tubes and shell. These expansions or contractions may be due to temperature and/or the presence of chemical species in the streams being processed in the apparatus which affect any of the materials of the tube sheets, tubes or shells. Any such expansions and/or contractions can pose several difficulties, especially since dissimilar materials are essentially always used for the tubes, tube sheet, and shell. For instance, a relative change in size (hereafter a "differential in expansion") between the tube sheet and shell may pose difficulties in ensuring a fluid tight seal.If, say, because of the operating environ ment, a tube sheet, which is positioned within a shell, expands to a greater extent than the shell, unduly large forces could be generated resulting in damage to the shell or tube sheet.

Also, similar differentials in expansion can occur between the tube sheet and the tube with similarly adverse effects. Moreover, since in many applications tube sheets often have two regions, for instance a region having a relatively high density of tubes and a concentric surrounding region having few, if any, tubes, each region may exhibit different expansion and contraction properties thereby increasing the risk that damage could occur within the tube sheet at the interface between these regions. Furthermore, one class of materials which have been found particularly attractive in lFabricating tube sheets and tubes, are resins, including synthetic and natural resins, which can be applied to the tubes or cast around the tubes as a liquid and then solidified, for instance, by curing.Such resinous materials, however, are often prone to exhibit substantial swelling in the presence of many chemical species which may be present in the streams being treated by the apparatus.

Hence, even greater problems of differentials in expansion may be posed.

One ivpe of apparatus which may be particularly affected by these prolblems of differentials in expansion are permeators. Permeators are utilized for separating at least one fluid from a fluid mixture containing at least one other component wherein the separation is effected by membranes. Separation effected by membranes can include gas-gas, gas-liquid, and liquid-liquid (including liquid-dissolved solids) separations. A fluid may pass through the membrane by interaction with the materials of the membrane or by flow in the interstices or pores present in the membrane.

In membrane separations, a permeable fluid in the fluid feed mixture passes, under the influence of a driving force such as concentration, partial pressure, total pressure, etc., (depending on the nature of the membrane separation operation) from a feed side of the membrane to a permeate exit side of the membrane. Usually, the driving force comprises maintaining a pressure differential across the membrane, and the greater the pressure differential, the greater the flux of the permeating fluid and the less membrane surface area which is required.

Membranes in a configuration of tubes, for instance, hollow fibers or hollow filaments, are particularly attractive in that the hollow fibers are generally self supporting, even at relatively high pressure differentials, and provide a greater amount of membrane surface area per unit volume of permeator than that which may otherwise be provided, for instance, by film membranes. Thusa, permeators containing hollow fibers may be attractive from the standpoint of convenience, size and reduced complexity of design. However, to be commercially attractive, the permeators must be able to withstand the operating conditions to which they may be subjected during separation operations and should be relatively noncomplex and easily assemblable to facilitate manufacturing inspection and repair.

Permeators containing hollow fiber membranes have found acceptance for use in desalination, ultrafiltration, and hemodialysis. In general, these separation operations provide environments which do not unduly swell the tube sheets. In view of the relatively mild operating environments which these permeators encounter in desalination, ultrafiltration and hemodialysis usage, tube sheets could be provided in a relatively non-complex manner.

For instance, in hemodialysis units such as disclosed by Geen, et al., in United States Patent No. 4,001,110, the tube sheet is simply cast in the shell such that the resinous material of the tube sheet adheres to the hollow fiber membranes and the interior surface of the shell.

Alternatively, a tube sheet having the hollow fiber membranes embedded therein can be separately prepared and then inserted within a permeator shell. For instance, Mahon in United States Patent No. 3,228, 877 discloses a permeator wherein the hollow fiber membranes are embedded in a cement material positioned within a coupling fitting and the cement material is in a fluid tight contact with the coupling fitting. The coupling fittings are then placed in a header end plate to assemble the permeator.

One commonly encountered means for securing a tube sheet within a shell is by the use of O-rings which are positioned around the tube sheet and contact the interior surface of the shell to provide the desired fluid tight relationship. The use of such O-rings is disclosed, for instance, by McLain in United States Patent No. 3,422,008; Caracciolo in United States Patent No. 3,528,553; McNa- mara, et al., in United States Patent No.

3,702,658; Clarke in United States Patent No. 4,061,574; and Teijin Limited in British patent publication 1,432,018.

The foregoing mentioned means for securing a tube sheet within a shell appear to provide no region for absorbing differentials in expansion and also appear to depend upon close tolerancing between the tube sheet and the shell such that O-rings or the like can provide the necessary fluid tight relationship.

Unavoidable differentials in expansions, for instance, due to changes in temperature, swelling agents in fluids being processed, etc., may therefore result in substantial difficulties.

In another proposal, Carey, et al., in United States Patent No. 3,760,949 diclose a tube sheet which is constructed of an elastomeric sealant and is in the form of a tapered plug with its narrowest point being proximate to the end. The elestomeric sealant is held within a mated reverse taper element which is inserted into the permeator shell. A porous plate is positioned at the end of the elastomeric sealant to constrain the sealant within the mated reverse taper element.While the elastomeric nature of the tube sheet may enable sufficient flowing of the tube sheet such that no undue problems caused by differentials in expansion exist, the elastomeric material of the tube sheet may not be able to impart the desired strength to the tube sheet and may increase difficulties in the handling of the tube sheet and the assembly of the permeator.

An improvement that provided the utilization of permeator technology in harsher environments, such as gaseous purge streams and liquid waste streams, which can contain species which may swell the material of the tube sheet, is disclosed by Bollinger, et al., in British Patent Publication 2,060,434, published 7 May 1981. In one aspect of their invention Bollinger, et al., disclosed a permeator in which tubes are embedded in a fluid tight relationship in a tube sheet. A tubular spacer substantially surrounds the tube sheet for at least a portion of the lateral surface of the tube sheet. The tubular spacer serves to position the tube sheet within the apparatus.

The tube sheet has at least one rise region intermediate the opposing bundle face and outer face and has an expanded zone with larger cross-sectional dimensions than the corresponding dimensions of the smaller of the faces. The rise region is adapted to abut the tubular spacer.

With the Bollinger, et al. apparatus differentials in expansion between the tube sheet and the shell can be accommodated while many taining the desired fluid tight relationship across the tube sheet. The apparatus is able to accommodate high pressure differentials across the tube sheet.

Bollinger, et al., however, used O-rings to provide the fluid tight relationship across the tube sheet, isolating the open bores of the hollow fiber terminating on the outer face of the tube sheet and the exterior surface of the hollow fibers. Often the O-rings are seated in an annular retaining slot, for instance, in the end closure cap or on the tube sheet abutting face of the tubular spacer.

While the use of a tubular spacer with a tube sheet minimized the effects of differential expansions among the tubes, shell, tube sheet and spacer, difficulties in maintaining the 0ring seal continue to exist in certain circumstances. For instance, the polymer material of the O-ring can be deteriorated by some environments such that the O-ring loses the resliency necessary to maintain a fluid tight relationship. The polymer material of the O-ring may also absorb sufficient quantities of fluid, such as gaseous species at high pressure, to undergo a change in dimensions. For instance, a swollen O-ring may be forced entiely or partially from a retaining slot so that the fluid tight relationship can not be maintained.

In some designs of permeators, such as those disclosed by Bollinger, et al., the tube sheet is slideable. This is often advantageous in that the arrangement can act as a safety valve to vent fluid at potentialy deleterious high pressure from the bore side of the hollow fibers to lower pressures onth shell side of the hollow fibers. This is accomplished by the differential in pressure causing the slideable tube sheet to lift from the O-ring seal. Such tube sheet lifting may also occur whenever there is a higher fluid pressure on the bore side of the hollow fiber membrane, as may frequently occur during routine or emergency shutdown of permeator operations. The O-ring can be dislodged from its seat, for instance, an annular retaining slot, when the tube sheet is lifted. Often the fluid tight relationship is not maintained when the tube sheet returns to contact with the O-ring.

By this invention apparatus containing tubes embedded in essentially fluid impermeable tube sheets are provided wherein difficulties in maintaining a fluid-tight seal around the tube sheet are minimized even when the slideable tube sheet is lifted to vent potentially deleterious high pressure and even in operating environments which may deteriorate the resiliency or dimensions of the sealing means.

These improvements in sealing are obtained in permeators having sufficient clearance between the tube sheet and other elements of the permeator, such as the shell and tubular spacer, such that significant differentials in expansion can be maintained.

An apparatus of this invention comprises an elongated tubular shell having at least one open end; an essentially fluid impermeable end closure cap sealingly fastened to and covering said elongated tubular shell at the at least one open end, said closure cap having at least one fluid port; a plurality of hollow fibers which are generally parallel and extend longitudinally to form at least one bundle in the elongated tubular shell; an essentially fluid impermeable tube sheet in which the hollow fibers in said at least one bundle are embedded in a fluid tight relationship such that the bores of the hollow fibers provide fluid passageways through the tube sheet, said tube sheet having a bundle face from which the hollow fibers extend in said at least one bundle into the elongated tubular shell, an outer face on the surface of which the bores of the hollow fibers are open, and a lateral surface extending between said bundle face and said outer face; and a sealing means such that the bores of the hollow fibers providing fluid passageways through the tube sheet are in a fluid tight relationship around the exterior of the tube sheet with respect to the exterior of the hollow fibers extending from the tube sheet; wherein the sealing means comprises at least one cup seal comprising a polymeric ring having a concave surface and an external surface, said polymeric ring substantially surrounding and cooperating with a resilient member such that the resilient member can be compressed to provide an outward force on generally opposing portions of the external surface.

In one aspect of this invention the apparatus has a rigid tubular spacer substantially surrounding a lateral surface of the tube sheet for at least a portion of the distance between the outer face and bundle face of the tube sheet wherein said tubular spacer defines an opening adapted to receive said lateral surface of the tube sheet, said opening having a cross-section which is sufficiently large to provide space between the tubular spacer and the lateral surface of the tube sheet to accommodate differentials in expansion between tubular spacer and the tube sheet.

The sealing means in the apparatus of this invention provides a fluid tight relationship around the exterior of the tube sheet to isolate the exterior of the hollow fibers extending from the bundle face of the tube sheet from the bores of the hollow fibers which provide fluid passageways through the tube sheet.

The sealing means comprises at least one cup seal comprising a polymeric ring in cooperation with a resilient member where generally opposing portions of the external surface of the ring provide a fluid tight relationship around the tube sheet. For instance, portions of the external surface of the cup seal may be in sealing contact with the tube sheet and the shell, with the tube sheet and the end closure cap, or with the tube sheet and a tubular spacer, itself in fluid tight relationship with the rest of the permeator. Other arrangements for establishing sealing contact of the external surface of the cup seal are, of course, possible.

The polymeric ring of a cup seal useful in the permeators of this invention has a concave surface which generally substantially surrounds and cooperates with a resilient member to provide an outward directed force on generally opposing portions of the external surface of the polymeric ring. In some instances, it may be preferable to have the resilient member totally surrounded, that is encapsuated, by the polymeric ring. The resilient member may be an expander spring, for instance a metal expander spring, or may be an elastomer O-ring. Metal expander springs may be of any metal but corrosion resistant alloys are preferred. Such corrosion resistant alloys include stainless steels, such as 304 or 316 stainless steel; Inconel alloys, such as Inconel 718 or Inconel X-750; or Hastelloys, such as Hastelloy C.The metal expander springs may be of various configurations, such as U-shaped springs, which may be constructed from perforated or expanded metal. A preferred configuration is a metal helical wound flat wire spring. Elastomeric 0rings may be made of such materials as neoprene, silicone, fluorosilicone or Piton~.

The polymeric ring may comprise any polymeric material. A preferred polymeric material is chemically inert to the chemical species of the fluids being processed in the permeator and is functional over a wide range of temperatures, for instance, from about - 64'C. to about 1 27 C. Preferred materials include fluorocarbon polymers, such as Teflon~ TFE. Often the polymeric material may have a filler such as graphite, carbon/graphite, or fiberglass/molybdenum disulfide.

Preferred cup seals useful in the permeators of this invention are those spring-energized seals such as the Series 300 Omniseal supplied by the Flurocarbon Company. A preferred configuration of the Omniseal is a Teflon~ TFE ring partially encapsulating a helical wound flat wire spring of a stainless steel.

Such a polymeric ring substantially encompassing the resilient member is both a pressure-actuated and self-actuated sealing device.

The polymeric ring is generally installed between two sealing surfaces, for instance, between the shell and tube sheet of a permeator, where the distance between the sealing surface is generally less than the distance across opposing external surfaces of the ring.

In such an installation the polymeric ring is made to compress upon the resilient member thereby providing sufficient force at the generally opposing portions of the external surface of the polymeric ring to provide a self-actuated fluid-tight relationship between the sealing surfaces.

In most installations under operating conditions there will be a pressure differential across the polymeric ring. Where there is a fluid of higher pressure acting on the inner or concave surface of the ring an outward force component resulting from the differential pressure will act on at least a portion of the polymeric ring to promote a fluid tight relationship with those sealing surfaces in contact with the polymeric ring.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic representation of a longitudinal cross-section of a permeator in accordance with this invention having a cup seal located in a seal seat in the inside periphery of the shell providing a fluid tight seal between the shell and the tube sheet.

Figure 2 is a schematic representation of a partial view of the longitudinal cross-section of a permeator in accordance with this invention wherein the tubular spacer on a flange surrounds the tube sheet, and the tube sheet is in a fluid tight relationship with the tubular spacer.

Figure 3 is a schematic representation of a partial view of the longitudinal cross-section of a permeator in accordance with this invention wherein the tubular spacer is integral with the end closure cap. The end of the tube sheet also has shallow grooves to assist the venting of potentially deleterious high bore side pressure when the slideable tube sheet lifts from the abutting tubular spacer.

Figure 4 is a schematic representation of a partial view of a longitudinal cross-section of a permeator in accordance with this invention wherein the tubular spacer on a flange has a seal seat in the end surface abutting the tube sheet.

Figure 5 is a schematic representation of a partial view of a longitudinal cross-section of a permeator in accordance with this invention wherein the end closure cap has a seal seat for retaining a cup seal which contacts an extension of the external zone of the tube sheet.

Figures 6, 7 and 8 are schematic representations of radial cross-sections of cup seals.

In the embodiments depicted in Figs. 1 through 5, the tube sheet is positioned inside the shell. Clearly, in the permeators of this invention, the tube sheet may extend at least partially out of the shell, or, if desired, it may reside outside the shell at the open end, for instance, within a separate head enclosure.

This invention is particularly useful for providing permeators. The permeators may be of suitable design for effecting fluid separations and may be single ended or double ended permeators. A single ended permeator has a tube sheet at only one end (such as depicted in Fig. 1), and one or both ends of the tubes (generally referred to as hollow fibers in the permeator art) are embedded in the tube sheet. When only one end of each of the hollow fibers is embedded in the tube sheet, the other end must be plugged or otherwise closed. In a souble ended permeator, a tube sheet is provided at each end of the shell and the hollow fibers may extend from one tube sheet to the other tube sheet, or the permeators may contain at least two distinct bundles of hollow fibers where at least one bundle extends into only one tube sheet.

The permeator may be operated in any desired manner, for instance, the fluid feed mixture may be introduced into the shell and initially contact the shell side of the hollow fibers, or it may be introduced into the bores of the hollow fibers. The flow pattern of the fluid on the shell side of the hollow fibers may be primarily transverse to the longitudinal orientation of the hollow fibers or may be primarily axial to the orientation of the hollow fibers. When the flow on the shell side of the hollow fibers is axial, it may be generally concurent or countercurrent with the flow in the bores of the hollow fibers.

Hollow fiber membranes may be fabricated from any suitable synthetic or natural material suitable for fluid separation or for the support of materials which effect the fluid separations.

The selection of the material for the hollow fiber may be based on heat resistance, chemical resistance, and/or mechanical strength of the hollow fiber as well as other factors dictated by the intended fluid separation for which it will be used and the operating conditions to which it will be subjected. The material for forming the hollow fibers may be inorganic, organic or mixed inorganic and organic. Typical inorganic materials include glasses, ceramics, cermets, metals and the like. The organic materials are usually polymers.

Typical polymers which may be suitable for hollow fiber membranes include substituted and unsubstituted polymers selected from polysulfones, including polyether sulfones and polyaryl-sulfones; polystyrenes; cellulose polymers; polyurethanes; polyesters, polymers from monomers having apha-olefinic unsaturation such as polyethylene, polyvinyls, and polyvinylidenes; polyhydrazides, etc.

The cross-sectional dimensions of the hollow fibers utilized in the permeators of this invention may be selected over a wide range; however, the hollow fibers should have sufficient wall thickness to provide adequate strength, and the bore (lumen) should be sufficiently large as to not result in an unduly high pressure drop to fluids passing in the bore. Frequently, the hollow fibers exhibit some flexibility over their lengths to accommodate any expansions or contractions which may occur under expected operating conditions. The outside diameter of the hollow fiber is at least about 20, say, at least about 30 microns, and the same or different outside diameter fibers may be contained in a bundle.

Often the outside diameter of hollow fiber membranes does not exceed about 800 or 1000 microns since such larger diameter hollow fibers may provide less desirable ratios of hollow fiber surface area per unit volume of the permeator. However, larger diameter hollow fibers up to 10,000 microns or more in diameter, may be particularly desirable. Preferably, the outside diameter of hollow fiber membranes is about 50 to 800 microns.

Generally, the wall thickness of the hollow fibers is at least about 5 microns, and in some hollow fibers, the wall thicknesses may be up to about 200 or 300 microns, say, about 50 to 200 microns. With hollow fibers fabricated from materials having lesser strength, it may be necessary to employ larger hollow fiber diameters and wall thicknesses to impart sufficient strength to the hollow fiber. The walls of the hollow fibers may be essentially solid or may contain a substantial void volume. When voids are desired, the density of the hollow fiber can be essentially the same throughout its wall thickness, that is, the hollow fiber is isotropic; or the hollow fiber can be characterized by having at least one relatively dense region within its wall thickness in barrier flow relationship in the wall of the hollow fiber, that is, the hollow fiber is anisotropic.

Generally, shells for permeators have a circular cross-sectional configuration due to availability, handling convenience, and strength; however, shells of other cross-sectional configurations, for instance, rectangular, may be highly suitable for many permeators.

Often, the shells have a major cross-sectional dimension of at least about 0.1 or preferably at least about 0.2 meter, say, up to about 1 or 2 or more meters. The length of the shell containing the hollow fibers is frequently at least about 0.5 meter and may be up to 10 or more meters.

The hollow fibers are generally parallelly arranged in the form of one or more bundles in the shell. Generally, at least about 10,000 and often substantially greater numbers, for instance, up to 1 million or more hollow fibers are contained in a permeator. The fibers in the bundle, for instance, may be relatively straight, or they may be spirally wound such as disclosed by McLain in United States Patent No. 3,422,008. In many instances, a single bundle of hollow fibers is employed in a permeator and at least one end of the hollow fibers in the bundle is embedded in a tube sheet. The opposite end of the hollow fibers may be looped back, for instance, the bundle is generally in a ''U"shape, and embedded in the same tube sheet, or the opposite end of the hollow fibers may be plugged or embedded in another tube sheet.When the hollow fibers in the bundle are in a "U"shape, the ends may be segmented such that different regions on the tube sheet contain each end of the hollow fibers. Each of these region on a tube sheet can be maintained in an essentially fluid impermeable relationship such that the fluid communication between the regions can only occur by passage of fluid through the bores of the hollow fibers.

A tube sheet useful in the permeators of this invention may have any general configuration suitable for use in a permeator containing bundles of hollow fibers. Since these permeators frequently have circular cross-sections, the tube sheet in such instances generally has a circular cross-section.

Preferably a tube sheet is rigid; that is, a tube sheet exhibits sufficient strength that it retains its integrity and configuration under stress. Often, the material of the tube sheet exhibits a Shore A hardness (ASTM D 2240) of at least about 60, most frequently at least about 70 or 75, say, at least about 80 or 90.

Suitable materials for forming a tube sheet include settable liquid resins (natural or synthetic), and particularly resinous compositions which cross-link during setting. Frequently the cross-linking (or curing) increases the strength of the tube sheet as well as increases the resistance of the tube sheet to chemicals.

Suitable resins for tube sheets often include epoxies, phenolics, acrylics, urea urethanes, and the like.

The tube sheet may be formed in any suitable manner, for instance, by casting a resinous material around the end of the bundle of tubes such as disclosed by Fritzsche, et al., in British Patent Publication 2,066,697 published on 15 July 1981, or by impregnating the ends of the tubes with resinous material while assembling the tubes to form a bundle such as disclosed in United States Patent No. 3,455,460 (Mahon) and 3,690,465 (McGinnis, et al.) The length (in the axial direction) of the tube sheet is generally sufficient to provide suitable strength for withstanding total pressure differentials to which the tube sheet may be subjected in operations. Thus, the length employed may depend upon the strength of the resin.Also, the tube sheet should be sufficiently thick that ample contact is provided between the hollow fibers and the resin such that an essentially fluid tight relationship is ensured. Consequently, the adherence between the hollow fibers and the material of the tube sheet will also affect the desired lengths of the tube sheets. Often, tube sheets are at least about 2 centimeters in length and may be up to about 50 centimeters in length.

The bores of the hollow fibers are exposed at the outer face of the tube sheet to provide fluid passageways through the tube sheet.

Any suitable technique may be employed for providing exposed bores at the outer face of the tube sheet, and then after casting the tube sheet, the end of the casting can be severed to form the outer face of the tube sheet and expose the bores of the hollow fibers.

form the outer face of the tube sheet and expose the bores of the hollow fibers.

While tube sheets generally comprise at least one zone having hollow fibers, they may also comprise a concentric outer zone of enlarged cross-sectional dimensions substantially devoid of hollow fibers. Such a concentric outer zone may extend over part of, or all of, or more than, the length of the at least one zone having hollow fibers, depending on particular design preferences. Of course tube sheets can also be provided without a concentric outer zone. Such tube sheets are characterized as having a periphery defined by crosssectional dimensions only slightly larger than the cross-sectional dimensions of the periphery of the bundle of hollow fibers embedded in the tube sheet. In such an embodiment less material may be employed for embedding the hollow fibers in a fluid tight relationship than in tube sheets having concentric outer zones substantially devoid of hollow fibers.Accordingly, there may be advantages of minimized swelling and minimized expansion or contraction of the tube sheet. There may also be advantages in casting such tube sheets where the material comprising the tube sheet is cured by exothermic reaction; that is, since the mass of the material forming the tube sheet is minimized, potentially deleterious temperatures from exothermic curing reactions can be avoided.

On the other hand it may be more advantageous to manufacture tube sheets comprising a concentric outer zone devoid of hollow fibers. In such configurations the differences in cross-sectional dimensions between the tube sheet and say that shell of the permeator are not as critical particularly where the fluid tight seal is made on an axial face of the outer zone. Such an application may also involve locating the seal at a rise region between the periphery of a zone having hollow fibers and a concentric outer zone devoid of hollow fibers, particularly where said rise region abuts a tubular spacer.

Such a tubular spacer may extend sufficiently to contact the end closure cap. Often the tubular spacer may abut the end closure cap in a fluid tight relationship. The tubular spacer may even be integral with the end closure cap, for instance, the tubular spacer and end closure cap may be from the same casting.

Alternatively, the tubular spacer may be welded or fastened to the end closure cap in a fluid tight relationship.

In another embodiment the tubular spacer can have flange, for instance, at one end of the spacer proximate to the end closure cap.

Such flange can conveniently be inserted between flanges on the end closure cap and the shell in a fluid tight relationship. Gaskets, for instance, such as O-rings, installed on opp6s- ing faces of the tubular spacer flange allow the tubular spacer to be maintained in a fluid tight relationship with the shell and/or end closure cap of a permeator. A tubular spacer having such a flange is a significant improvement over other tubular spacer configurations, such as loose tubular spacers, or tubular spacers abutting end closure caps in a fluid tight relationship.

The tubular spacer has a bore having a sufficiently large cross-section to provide sufficient space between the tubular spacer and the tube sheet to accommodate differentials in expansion transverse to the axis of the tube sheet. Desirably, the tubular spacer also allows for differentials in expansion in an axial direction. The tubular spacer can advantageously serve to position the tube sheet within the shell. The tubular spacer can also provide support to the tube sheet and, in some instances, can assist in effecting a fluid tight relationship across the tube sheet. For instance, seal seats for holding the cup seal can be located in the tubular spacer. Convenient locations are the inside peripheral surface of the spacer or on the end surface abutting the rise region of the tube sheet.

In general, the tubular spacer can often be more readily machined to close tolerances than can a tube sheet. Accordingly, the tubular spacer can be closely toleranced to fit within the shell, but yet, enable use of tube sheets which are not so closely toleranced and which otherwise may be unacceptable to provide a fluid tight relationship directly with the shell. Addtionally, the tubular spacer may be prepared from the same material as the shell, or alternatively the same material as the tube sheet, to minimize differentials in expansion with either the shell or the tube sheet and thereby facilitate maintaining a fluid tight relationship over widely varying operating conditions. Suitable materials for fabricating the tubular spacer may include polymeric materials such as epoxies, phenolic resins, etc.; metals such as aluminum, steel, etc.; and the like.

Sufficient space should generally be provided between the tubular spacer and the tube sheet to accommodate differentials in expansion between the tubular spacer and the tube sheet and to permit relative movement between the tubular spacer and the tube sheet under operating conditions such that differentials in expansion can be tolerated. It is often preferable that contact between the tube sheet and tubular spacer therefore be a moveable contact.

With respect to surfaces of the tube sheet and tubular spacer, which surfaces are not capable of freely moving with respect to each other, in order to dissipate differentials in expansion (e.g., parallel surfaces which are in turn parallel to the axis of the tube sheet), an ample distance should be provided between the tube sheet and tubular spacer that the expected differentials in expansion during operation do not result in contact between the tubular spacer and the tube sheet. Frequently, this distance is less than about 2 centimeters, say, less than about 1 centimeter, e.g., about 0.05 to 0.5 centimeter. A cup seal may be positioned between the tube sheet and the spacer in order to position the tube sheet within the tubular spacer and provide a fluid tight seal between the tube sheet and the tubular spacer.

The following embodiments are provided to further assist in the understanding of the invention and are not provided as limitations to the invention.

The permeator depicted in Fig. 1 is gener ally designated by the numeral 1 ü0.100. Permea- tor 100 comprises shell 102 (only the head and tail ends are depicted) which is adapted to receive a tube sheet at one end. Shell 102 may be comprised of any suitable, fluid impervious material such as metals and plastics. In many permeators, metals such as steel are employed due to their ease of fabrication, durability, and strength. The shell may be in any suitable cross-sectional configuration; however, generally circular cross-sections are preferred. Shell 102 has a head end of in creased diameter. The head end has head end flange 104 and fluid communication port 108. Port 108 can provide for fluid communi cation with the interior of the shell.While only a single port 108 is depicted, it should be understood that a plurality of ports 108 may be positioned around the periphery of shell 102. End cap 112 is positioned at the tail end of shell 102 and is fastened by bolts (not shown) to rail flange 110. Gasket 114 is positioned between end cap 112 and tail flange 110 to provide an essentially fluid impermeable seal. End cap 11 2 is provided with port 11 5 for fluid óarîmunication through the end cap.

Within shell 102 is positioned bundle 1 16 (not shown in cross-section) which is com posed of a plurality of hollow fiber mem branes. Often the bundle comprises over 10,000 hollow fibers and, with smaller diam eter hollow fibers or large diameter shells, there may 13e an excess of 100,000 or even an excess of 1 million fibers. As depicted, the bundle has essentially the same cross-sec tional eonfiguration as the shell. One end of each of the hollow fibers is embedded in plug 1 18 (not shown in cross-section).The bores of the hollow fibers do not communicate through plug 118. Alternatively, the ends of the hollow fibers may be closed and the fibers joined together by heat, for instance by pass ing a hot wire through the bundle of hollow fibers.

The other end of bundle 11 6 passes through plenum 106 having fluid distribution ports (not shown). Plenum 106 is positioned within the head end of the shell 102 and serves to distribute fluid passing to or from fluid communication port 108. Bundle 116 is terminated at the head end with tube sheet 120 (not shown in cross-section). The bores of the hollow fibers provide passageways through tube sheet 120 to the open end of shell 102.

A seal seat 141 is cut into the wall of shell 102. A cup seal 140 is seated in the seal seat 141 and contacts sealing surfaces on tube sheets 120 and on the shell 102 within seal seat 141 to provide a fluid tight relationship across tube sheet 1 20. Among the preferred configurations fsr cup seal 140 are those exemplified as in cross section, in Figs. 6, 7 and 8, as cup seal 60, 70 or 80 comprising resilient members 61, 71 or 81 substantially surrounded by, and in contact with the con cave surface of, polymeric rings 62, 72 and 82, respectively.

End closure cap 1 24 is adapted to cover the open end of the shell and is securely fastened to shell 102 by the use of bolts (not shown). A gasket 1 26 is positioned between the end closure cep 124 and head end flange 104 such that when end closure cap 124 having fluid comnQunication pox 130 is securely attached to the shell, a fluid tight relationship is achieved.Circular boss 128 extends from the end closure cap 1124 to contact the periphery of phe outer face of tube sheet 1 20 forcing the Sulbe sheet 120 to compress against spring 122. A plura#ity of springs 122 located between plenum 106 and tube sheet 120 serve to provide an outward directed Free on the tuba sheet. By selecting springs of appropriate si2e and number, a desired spacing and flexibility can be achieved.Accordingly, suitable forces can be obtained without concern for close toleraneTng of the length of the tube sheet.

Springs sheet.122 are optional in this permeator configuration. With the fluid tight seal made on the lateral surface of the tube sheet, the tube sheet can be allowed to be say slideu- ble between plenum 106 and boss 128.

In an operation of permeator 100, a fluid feed mixture may be introduced into the shall side of the permeator through pert 1 1 o#or, pre- ferably, port 108, with the non perm@ating fluid being removed front the shell IIside of the permeatorthroug the other port ernzeatinq3 fluid enters the bores of the hollow fibers and passes within the bores through the tube sheet 1 20 and is exhausted from the permea- tor through port 130 in heed end closure cap 124.

Fig. 2 illustrates the head portion of a permeator generally designated by the numeral 200. Permeator 200 comprises a shell 202 which has a circular cross-sectional configuration. Shell 202 is pro#ided with head end flange 204 and fluid communication port 208. Within shell 202 is positioned bundle 216 (not shown in cross-section) which is composed of a plurality of hollow fibers. The bundle has the same general transverse crnss- sectional configuration as the interior of the shell. Bundle 216 is terminated at the head end with tube sheet 220 (not shown in croeis- section).As depicted, tube sheet 220 has a cylindrical expanded zone 221, a rise region 222 perpendicular to the axis of the tube sheet and a concentric cylindrical portion 223 extending to the end face.

At the rise region 222 of tube sheet 220 is positioned tubular spacer 234. The tubular spacer has seal seat 241 cut into its inside wall. Cup seal 240 is postioned at the opposite end in seal seat 241 to provide a fluid tight relationship between tubular spacer 234 and tube sheet 220. Tubular spacer 234 is attached to the spacer flange 232 which is held in position between head end flange 204 and end closure cap 224 by the use of bolts (not shown).

End closure cap 224 is adapted to cover the open end of the shell and is securely fastened to shell 202 by the use of bolts (not shown). Gaskets 226 and 227 are positioned between the end closure cap 224, the spacer flange 232 and head end flange 204 such that when the end closure cap 224 having a fluid communication port 230 is securely attached to the shell, a fluid tight relationship is achieved.

Tubular spacer 234 serves to position tube sheet 220 within the shell. The expanded zone 221 of the tube sheet can therefore be maintained a sufficient distance away from the interior surface of shell 202 that any differentials in expansion between the shell and the tube sheet can be accommodated.

Tubular spacer 234 surrounds only the smaller rliameter portion of tube sheet 220 which portion is only slightly larger than the zone through which the hollow fibers pass.

Since this portion of the tube sheet will exhibit less absolute expansion than the ex pander zone of the tube sheet, the distance between the tubular spacer and the tube sheet can be easier to maintain than that between the shell and the expanded zone of the tube sheet. Hence, the fluid tight seal around the tube sheet provided by cup seal 240 is facilitated. Also, cup seal 240 enables relative axial movement of the tube sheet between the tubular spacer and the plenum 206.Furthermore, since the contact between the tubular spacer and the tube sheet is essentially only at rise region 222, the tubular spacer does not restrict expansions or contractions of the tube sheet. Since concentric cylindrical portion 223 of the tube sheet has a diameter only slightly larger than the diameter of the bundle passing through the tube sheet, the expansions and contractions of the tube sheet due to the operating environments to which the permeator may be subjected, may not be ot sufficient magnitude to hinger achieving fluid tight seal by cup seal 240.

Fig. 3 illustrates the head portion of a permeator generally designated by the nu- meral 300. Permeator 300 comprises shell 302 which has a circular transverse crosssectional configuration. Shell 302 is provided with head end flange 304 and fluid communication port 308. Within shell 302 is positioned bundle 316 5not shown in cross-section) which is composed of a plurality of hollow fibers. The bundle has the same general transverse cross-sectional configuration as the shell. Bundle 316 is terminated at the head end with tube sheet 320 (not shown in cross-section). Tubular spacer 334 surrounds the extended cylindrical section of tube sheet 320 and abuts rise region 322. Tubular spacer 334 is sealingly attached to end closure cap 324. T his is achieved, for instance, by welding tubular spacer 334 to end closure cap 324, by machining an end closure cap having a tubular spacer from unitary casting or by any other convenient means. Seal seat 341 is provided in the interior circumferential surface of the tubular spacer to retain cup seal 340 which provides a fluid tight relationship around the tube sheet. It is often convenient for ease of installation of the cup seal that the tubular spacer comprise a washer portion 335 attached, for instance, by bolts 336 to the portion of the spacer having the seal seat 341. Gasket 326 is provided between the end closure cap 324 and head end flange 304 to provide a fluid tight seal.The end closure cap is also provided with port 330 for fluid communication with the bores of the hollow fibers.

Differentials in expansion between the tube sheet and the tubular spacer can be accommodated by the gap between them and the resiliency of cup seal 340. Also, relative movement between the tube sheet and tubular spacer may occur in a direction substantially parallel to the axis of the tube sheet. In one aspect of this exemplification of applicant's permeator the extended cylindrical portion of the tube sheet has shallow grooves 350 extending a short length from the end of the tube sheet such that the shallow grooves 350 do not extend to the cup seal 340 when the rise region 322 of tube sheet abuts the tubular spacer.

In an advantageous mode of operation of the permeator of this configuration the axis of the shell of permeator is maintained in a vertical orientation with the tube sheet end of the permeator down. The fluid feed mixture is introduced to the shell side of the hollow fibers. Since the fluid feed mixture is generally at a higher total pressure than the pressure of the permeating fluid, the pressure differential from the shell side to the bore side assists not only in maintaining the fluid tight relationship at the cup seal but also assists in forcing the slideable tube sheet to an abutting relationship with the tubular spacer. With the tube sheet abutting the tubular spacer the shallow grooves extend below, and are not in contact with, the cup seal. This mode of operation can advantageously provide a safety valve feature to protect the hollow fiber membranes.For example, if the shell side total pressure were decreased without a decrease in the bore side total pressure, a substantially higher pressure may exist inside the bores of the hollow fibers which could deleteriously affect the hollow fiber membranes. However before such deleterious effect on the hollow fiber membranes this higher pressure may be sufficient to force the slideable tube sheet toward the retaining boss 306 such that the area having shallow grooves 350 slides into proximity with the cup seal to eliminate the fluid tight relationship around the tube sheet and thereby releating the pressure on the bore side of the hollow fiber membranes.

Fig. 4 and 5 illustrate embodiments of this invention where the cup seal is oriented so that the opening to concave surface faces radially outward in the plane of the cup seal.

Fig. 4 illustrates the head portion of the permeator generally designated by the numeral 400. Permeator 400 comprises shell 402 which has a circular cross-sectional configuration. Shell 402 is provided with head end closure flange 404 and fluid communication port 408. The end closure cap 424 is adapted to close the open end of shell 402 and is secured to head end flange 404 by bolts (not shown). Within shell 402 is positioned bundle 41 6 (not shown in cross-section) which is composed of a plurality of hollow fibers. The bundle has the same general transverse crosssectional configuration of the interior of the shell. Bundle 41 6 is terminated at the head end with tube sheet 420 (not shown in crosssection). The tube sheet comprises two concentric zones surrounding the bundle embedded in the tube sheet, where one zone is expanded.Rise region 421 extends between the concentric zones providing part of the boundary to the expanded zone. A tubular spacer 434 extends from the rise region of tube sheet 420 toward the end closure cap 424. The tubular spacer has a flange section 432 which assists in positioning the tubular spacer within the shell. Gaskets, for instance O-rings, 426 and 427 are positioned between the end closure cap 424, the flange section 432 and the head end closure flange 404 to provide a fluid tight seal when the flanges are secured. A seal seat 441 is located on the tube sheet abutting end of the tubular spacer to hold a cup seal 440 which provides a fluid tight relationship around the tube sheet when the tube sheet abuts the stubular spacer.A plurality of springs 422 are positioned between the bundle face of the expanded zone of the tube sheet and the plenum 406 to provide a force directed axially outward from the head end of the shell which forces the tube sheet to abut tubular spacer thereby establishing a fluid tight relationship with the cup seal.

In a preferred mode of operation the fluid feed mixture is introduced to the shell side of the permeator, say, through port 408. Since often the fluid feed mixture at the shell side is at a higher total pressure than the pressure of the permeating fluid on the above side of the hollow fibers, the pressure differential across the tube sheet (from the shell side to the tube side) will assist in maintaining the fluid tight relationship as the tube sheet is forced to compress the cup seal. This pressure differential also operates on the cup seal with the higher fluid pressure in contact with the concave surface providing an expanding force on the cup seal thereby promoting the fluid tight relationship.

A similar fluid tight relationship is achieved in permeator 500. Fig. 5 illustrates the head portion of a permeator generally designated by the numeral 500. Permeator 500 comprises shell 502 which has a circular trans verse cross-sectional configuration. Shell 602 is provided with a head end flange 504 and fluid comunication port 508. With this shell 502 is positioned bundle 51 6 (not shown in cross-section) which is composed of a plurality of hollow fibers. The bundle has the same general transverse cross-sectional configura-.

tion as the shell. Bundle 516 is terminated at the head end with the tube sheet 520 (shown in partial cross-section) which is in the configuration of a cylinder having a concentric central zone characterized by the presence of hollow fiber membranes embedded in and passing through the tube sheet and by a concentric outer zone characterized by the absnece of hollow fiber membranes. The outer zone is further characterized in that it extends for a greater length at the open end of the tube sheet away from the bundle than does the concentric inner zone.

A plurality of springs 522 cooperate between the retaining boss 506 and the bundle face of the tube sheet to force the tube sheet in an axial direction toward end closure cap 524. The end closure cap is equipped with a permeate effluent port 530, the flange portion of the end closure cap can be provided in a fluid tight relationship with the head end flange 504 of the shell by the presence of gasket 526 when the flanges are joined together, for instance by bolts (not shown). End closure cap also has a seal seat 541 which retains cup seal 540 in a position proximate to the extended end face of the concentric outer zone of the tube sheet.

Claims

1. An apparatus comprising: (a) an elongated tubular shell having at least one open end; (b) an essentially fluid impermeable end closure cap sealingly fastened to and covering said elongated tubular shell at the at least one open end,said end closure cap having at least one fluid port; (c) a plurality of hollow fibers which are generally parallel and extend longitudinally to form at least one bundle in the elongated tubular shell;; (d) an essentially fluid impermeable tube sheet in which the hollow fibers in said at least one bundle are embedded in a fluid tight relationship such that the bores of the hollow fibers provide fluid pasageways through the tube sheet, said tube sheet having a bundle face from which the hollow fibers extend in said at least one bundle into the elongated tubular shell, an outer face on the surface of which the bores of the hollow fibers are open, and a lateral surface extending between said bundle face and said outer face; (e) a sealing means such that the bores of the hollow fibers providing fluid passageways through the tube sheet are in a fluid tight relationship around the exterior of the tube sheet with respect to the exterior of the hollow fibers extending from the tube sheet; wherein the sealing means comprises at least one cup seal comprising a polymeric ring having a concave surface and an external surface, said polymeric ring substantially surrounding and cooperating with a resilient member such that the resilient member can be compressed to provide an outward force on generally opposing portions of the external surface.

2. Apparatus of Claim 1 wherein the cup seal is positioned between the shell and the tube sheet.

3. Apparatus of claim 1 wherein the cup seal is positioned between the end closure cap and the tube sheet.

4. Apparatus of claim 1 wherein a rigid tubular spacer substantially surrounds a lateral surface of the tube sheet for at least a portion of the distance between the outer face and bundle face of the tube sheet wherein said tubular spacer defines an opening adapted to receive said lateral surface of the tube sheet, said opening having a cross-section which is sufficiently large to provide space between the tubular spacer and the lateral surface of the tube sheet to accommodate differentials in expansion between tubular spacer and the tube sheet.

5. Apparatus of claim 4 wherein the cup seal is positioned between the tubular spacer and the tube sheet.

6. Apparatus of claim 4 wherein the spacer is sealingly joined to the end closure cap.

7. Apparatus of claim 6 wherein the cup seal is positioned between the tubular spacer and the tube sheet.

8. Apparatus of claim 1 or 4 wherein the polymeric ring comprises a fluorocarbon polymer.

9. Apparatus of claim 1 wherein the resilient member comprises a metal helical wound flat wire spring.

10. An apparatus of Claim 1 substantially as hereinbefore described with reference to and as illustrated in any of the accompanying Drawings.