CA1181699A

CA1181699A - Apparatus with cup seals

Info

Publication number: CA1181699A
Application number: CA000393206A
Authority: CA
Inventors: Roger S. Otstot
Original assignee: Monsanto Co
Current assignee: Monsanto Co
Priority date: 1980-12-29
Filing date: 1981-12-24
Publication date: 1985-01-29
Also published as: ZA818945B; IT1140190B; SU1134112A3; GB2090546A; FR2497331A1; NL8105860A; AU7904081A; IN154529B; DK578181A; BR8108400A; DE3151687A1; JPS57136906A; NO814445L; BE891634A; IT8125862A0; GB2090546B

Abstract

APPARATUS WITH CUP SEALS ABSTRACT OF THE DISCLOSURE Permeators having hollow fiber membranes suitable for fluid separations embedded in a tube sheet, where the tube sheet is positioned in a fluid tight relationship within the permeator by a cup seal. 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.

Description

~ 6~ 36~04~

Th;s invention perta;ns to apparatus such as heat exchangers and permeators wh;ch contain tubes embedded ;n tube sheets.
particularly attractive aspect of this ;nvention relates to improved permeators utilizing hollow fiber membranes in which the hollow fiber membranes are embedded in a tube sheet and the bores of ~he hollow fibers extend as fluid passageways through the tube shee~.
Apparatus9 such as heat exchangers and oermeators, have tubes pos;t;oned with;n a tubular shell with at least one end of each of the tubes embedded in a tube sheet~ ~ne purpose of the tube sheet is to secure the tubes in an essentially flu;d tight relationship with;n the tube sheet. The tube sheet should provide a sufficiently stron~ barrier to fluid flow such that during operating condi~ions with often substantial d;fferen_;als ;n pressure across the tube sheet, the tube sheet does not rupture or otherwise lose its ;ntegr;ty thereby allow;n~ flu;d to pass through the tube sheet~
Therefore, in many ;nstances the ~ube sheet is of substantial th;ckness ;n order to ensure achieving a fluid tight relationsh;p with the tubes and to ensure that the tube sheet can withstand any pressure d;fferentials 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 shell side and bore side of the tubes. Small leakages around the tube sheet can adversely a~fect 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 ex;t s;de of the membranes and reduce the selectivity of separation of the membrane.
This invention relates to improvements in prov;ding a fluid tight relationsh;p around the tube sheet.
In some operations, a tube sheet may be subjected to env;ronments wh;ch tend to expand or contract the material of the

-2- 36-0448 tube sheet as well as potentially the materials of ~he 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 d;ff;culties, especially since diss;m;lar materials are essent;ally always used for the tubes, tube sheet, and shell. For instance, a relative change in size ~hereafter a "differential in expans;on") between the tube sheet and shell may pose difficult;es ;n ensur;ng a flu;d tight seal. If, say, because of the operating env;ronment, a tube sheet~ which is pos;t;oned within a shell, expands to 3 greater extent than the shell, unduly large forces could be generated resulting in damage to the shell or tube sheet. Also, similar d1fferentials in expansion can occur between the tube sheet and the tube with s;milarly adverse effects~ Moreover, since ;n many appl;cat;ons 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 w;th;n the tube sheet at the ;nterface between these reg;ons.
Furthermore~ one class of materials which have been found particularly attractive in fabricating 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 instance9 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 d;fferentials in expansion may be posed. -~
One type of apparatus which may be particularly affected by these problems of d;fferent;als ;n expans;on are permeators.
Permeators are utilized for separating at least one fluid from a flu;d mixture containing at least one other component wherein the separation ;s effected by membranes. Separation effected by membranes can include gas-gas, gas-liquid, and l;qu;d-liquid (includ;ng l;quid-dissolved solids) separat;ons. A fluid may pass through the membrane by interaction with the materials of the ~3~ 36-04~8 membrane or by flow in the interstices or pores present in the membrane. In membrane separat;ons, 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 dr;ving 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 con~iguration of tubes, for instance, hollow fibers or hollow filaments, are particularly attractive in that the hollow fibers are generally self support;ng, 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 provided9 for instance, by film membranes. Thus, 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 condit;ons to which they may be subjected dur;ng separation operations and should be relatively non-complex and eas;ly assemblable to facilitate manufacturing inspection and repa;r.
Permeators contain;ng hollow f;ber membranes have found acceptance for use in desalination, ultrafiltrat;on, and hemo-dia1ysis. In general, these separation operations provide environments wh;ch 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, ;n hemod;alys;s un;ts such as d;sclosed by Geen, - et al., in Un;ted States Patent No. 4,001,110, the tube sheet ;s s;mply 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.
Alternat;vely, a tube sheet having the hollow fiber membranes embedded there;n can be separately prepared and then inserted within a permeaeor shell. For instance, Mahon in United States Patent No.

-4- 36-0~48

3,Z28,877 discloses a permeator wherein the hollow fiber membr3nes are embedded in a cement material positioned within a coupling fitting and the cement material is in a fluid tight contact with the coupling fi~ting. The coupling f;ttings 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 posi~ioned 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 are disclosed, for instance, by McLain in United States ~atent No.
3,~22,~08; Caracciolo in United States Patent No~ 3,528,553;
MGNamara, et al., in United States Patent No. 3,702,658; Clar~e in United States Patent No. 4,061,574; and Te;jin Lim;ted in ~r;tish patent publication 1,432,018.
The foregoing mentioned means for securing a tube sheet with;n a shell appear to provide no region ~or absorbing differentials in expans;on and also appear to depend upon close toleranc;ng between the tube sheet anp the shell such that O-r;ngs or the l;ke can prov;de the necessary flu;d t;ght relationship. Unavoidable d;fferent;als ;n expans;ons, for ;nstance7 due to changes ;n temperaturej swell;ng agents ;n fluids being processed, etc., may therefore result in substantial difficult;es.
In another proposal, Carey, et al., in United States Patent No. 3,760,9~9 d;sclose a tube sheet wh;ch is constructed of an elastomer;c sealant and is in the form of a tapered plug with its narrowest po;nt be;ng proximate to the end. The elastomeric sealant ;s he1d w;thin a mated reverse taper element which is inserted into the permeator shell. A porous plate is pos;tioned at the end of the elastomer;c sealant to constrain the sealant w;th;n the mated reverse taper element. While the elastomeric nature of the tube sheet may enable suff;cient flowing of the tube sheet such that no undue problems caused by differentials in expansion ex;st~ the elastomeric mater;al of the tube sheet may not be able to impart the des;red strength to the tube sheet and may ;ncrease d;ff;culties ;n the handl;ng of the tube sheet and the assembly of the permeator.
An ;mprovement that provided the utilization of permeator technology in harsher environments, such as gaseous purge streams and liqu;d waste streams, wh;ch can conta;n species which may swell the mater;al of the tube sheet, is disclosed by ~ollinger, et al., in eritish Patent Publication 2~060,434, published 7 May 1981. In one aspect of their invention Bollinger, et al., disclosed a permeator in which tubes S are embed~ed in a fluid tight relationship in a tube sheet. A
twbular spacer substantially surrounds the tube sheet ~or at least a portion of the lateral surface of the tube sheet. The tubular spacer ser~es to posit;on 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-sect;onal d;mensions than the Gorresponding dimensions of the smaller of the faces. The rise region is adapted to abut the tubular spacer.
W;th the ~ollinger, et al. apparatus differentials in expans;on between the tube sheet and the shell can be accommodated wh;le mainta;ning the desired fluid tight relationship across the tube sheet. The apparatus is able to accommodate high pressure d;fferentials across the tube sheet.
aoll;nger, et al., however, used O-rings to prov;de the fluid t;ght relat;onsh;p across the tube sheet, isolating the open bores of the hollow fiber term;nating on the outer face of the tube sheet and the exter;or surface of the hollow f;bers. Often the O-rings are seated ;n an annular retaining slot, for instance, in the end closure cap or on the tube sheet abutting face of the tubular spacer.
Wh;le the use of a tubular spacer w;th a tube sheet m;nim;zed the effects of differential expansions among the tubes, shell, tube sheet and spacer, difficulties in maintaining the O-ring seal continue to exist in certain circumstances. For instance, the polymer mater;al of the O-ring can be deteriorated by some environments such that the O-ring loses the resiliency necessary to ma;ntain a flu;d tight relationsh;p. The polymer material of the O-ring may also absorb sufficient quantities of fluid, such as gaseous spec;es at high pressure, to undergo a change in dimens;ons. For ;nstanceg a swollen O-r;ng may be forced entirely or part;ally from a retain;ng slot so that the flu;d t;ght relat;onship can not be maintained.
In some designs of permeators, such as those d;sclosed by ~oll;nger, et 31., the tube sheet is slideable. This is often -6- 36-04~8 advantageous in that the arrangement can act as a safety valve to vent fluid at potent-,ally deleterious high pressure from the bore side of the hollow ~ibers to lower pressures on the shell side of the hollow fibers. This is accomplished by ~he differen~ial in pressure causing ~he slideable tube sheet to lift from ~he O-ring seal. Such tube sheet lifting may also occur whenever there is a h;gher flu;d pressure on the bore s;de 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 l;fted. Often the flu;d t;ght relationship ;s not maintained when ~he tube shee~ return to contact with the O-ring.
~ y this invent;on apparatus conta;ning tubes embedded in essent;ally flu;d impermeable ~ube sheets are prov;ded where;n d;fficult;es in main~a;n;ng a flu;d-tight seal around the tube sheet are minim;zed even when the sl;deable tube sheet ;s lifted to vent potent;ally deleterious high pressure and even in opera~ing environments wh;ch may deter;orate the res;liency or d;mensions of the sealing means. These improvements in sealing are obtained in permeators hav;ng suff;c;ent clearance between the tube sheet and other elements of the permeator, such as the shell and tubular spacer, such that s;gn;f;cant different;als ;n expansion can be ma;nta;ned.
An apparatus of th;s ;nvent;on compr;ses an elongated tubular shell hav;ng at least one open end; an essent;ally fluid impermeable end closure cap sealingly fastened to and covering sa;d 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 long;tud;nally to form at least one bundle ;n the elongated tubular shell; an essent;ally fluid ;mpermeable tube sheet ;n wh;ch the hollow f;bers ;n sa;d at least one bundle are embedded ;n a flu;d tight relat;onship such that the bores of the hollow fibers prov;de flu;d passageways through the tube sheet, sa;d tube sheet hav;ng 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 wh;ch the bores of the hollow f;bers are open, and a lateral surface extend;ng between sa;d bundle race and sa;d outer face; and a sealing means such that the ~7~ 36-0~8 bores of the hollow f;bers prov;ding flu;d passageways ~hrough the tube shee~ are in a fluid t;ght relationship around the exter;or 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 naving 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 invent;on the apparatus has a rigid tubular spacer subs~antially 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 def;nes 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 prov;des a fluid tight relationship around the exterior of the tube sheet to isolate the exterior of the hollow f;bers extend;ng from the bundle face of the tube sheet from the bores of the hollow fibers wh;ch provide flu;d passageways through the tube sheet. The sealing means comprises at least one cup seal comprising a polymeric ring in 2S cooperat;on w;th a resil;ent member where generally oppos;ng portions of the external surface of the ring prov;de a fluid tight relation-sh;p around the tube sheet. For instance, portions of the external surface of the cup seal may be in sealing contact w;th the tube sheet and the shell, w;th the tube sheet and the end closure cap, or w;th the tube sheet and a tubular spacer, itself in flu;d t;gh~
relat;onship w;th the rest of the permeator. ~ther arrangements for establ;sh;ng seal;ng contact of the external surface of the cup seal are, of course, possibleO
The polymer;c r;ng of a cup seal useful in the permeators of this ;nvention has a concave surface which generally substantially surrounds and cooperates with a resilient member to provide an outward directed -8- 36-04~8 force on generally oppos;ng portions of the external surface of the polymeric rlng. In some instances, it may be preferable to have the resilient member totally surrounded, that is encapsulated, by the polymeric ring. The resilient member may be an expander spring, for instance a netal 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 ~astelloy C~ The metal expander springs may be of var;ous configura-tions, such as U-shaped springs, wh;ch may be constructed from perforated or expanded~metal. A preferred configuration is a metal helical ~ound flat wire spring. Elastomeric O-rings may be made of such mater;als as neoprene, silicone, fluorosilicone or Viton~.
The polymer;c r;ng may compr;se 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 w;de range of temperatures~ for instance, from about -64C. to about127 C. Preferred materials include fluoro-carbon polymers, such as Teflon~ TFE. Often the polymeric material may have a filler such as graphite, carbontgraphite, 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 Fluorocarbon Company~ A preferred configuration of the Omniseal is a Teflon~ TFE ring partially encapsulating a hel;cal wound flat wire spring of a stainless steel.
Such a polymeric ring substantially encompassing the resilient member is both a pressure-ac~uated 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 r;ng. In such an installation the polymer;c r;ng is made to compress upon the resil;ent 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 ;nner 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 t;ght relationsh;p with ~hose sealing surfaces in contact with the polymer;c r;ng.

FIGU~E 1 ;s a schematic representation of a long;tud;nal cross-1~ section of a permeator in accordance with this ;nvention hav;ng a cup seal located in a seal seat in the ;nside per;phery of the shell providing a fluid tight seal between the shell and the ~ube sheet.
FIGURE 2 is a schematic representation of a part;al 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 flu;d tight relationship with the tubular spacer~
FIGURE 3 is a schematic representation of a partial view of the long;tudinal 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 h;gh bore side pressure when the sl;deable tube sheet l;fts 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 surfac~ 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 C3p 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 Figures l through 5, the tube sheet ;s pos;t;oned ;nside the shell~ Clearly, in the permeators of this ;nvention, the tube sheet may extend at least partially out of the shell, or, if desired, ;t may reside outs;de the shell at the open end, for ;nstance, w;th;n a separate head enclosure.

10- 36-04~8 This in~ention is particularly useful for providing permeators.
The permeators may be of su;table design for effecting fluid separa~ions and may be single ended or double ended permeators. A
single ended permeator has a tube sheet at only one end (such 3S
depicted ;n F;gure 1), and one or both ends of the tubes (generally referred to as hollow f;bers 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 otherw;se closed. In a double 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 f;bers where at least one bundle extends into only one tube sheet.
The permeator may be operated ;n any des;red manner, for instance, the flu;d feed mixture may be introduced into the shell and initially contact the shell s;de of the hollow f;bers, or it may be ;ntroduced into the bores of the hollow fibers. The flow pattern of the fluid on the shell s;de of the hollow fibers may be pr;mar;ly transverse to the long;tud;nal or;entat;on of the hollow Z0 f;bers or may be pr;mar;ly ax;al to the or;entat;on of the hollow f;bers. When the flow on the shell s;de of the hollow f;bers is ax;al, it may be generally concurrent or countercurrent w;th the flow ;n the bores of the hollow f;bers.
Hollow fiber membranes may be fabricated from any su;table synthetic or natural material suitable for flu;d separat;on or for the support of mater;als wh;ch effect the flu;d separations. The select;on of the mater;al for the hollow fiber may be based on heat res;stance, chem;cal res;stance, and/or mechanical strength of the hollow f;ber as well as other factors d;ctated by the ;ntended flu;d separat;on for wh;ch ;t w;ll be used and the operat;ng conditions to which ;t w;ll be subjected. The mater;al for forming the hollow f;bers may be inorgan;c, organ;c or m;xed inorganic and organ;c~ Typ;cal inorgan;c mater;als ;nclude glasses, ceram;cs, cermets, metals and the l;ke. The organ;c mater;als are usually polymers.
Typ;cal polymers wh;ch may be su;table for hollow f;ber membranes include subst;tuted and unsubst;tuted polymers selected from polysulfones, ;ncluding polyether sulfones and polyaryl--11- 36-0~48 sulfones7 polystyrenes~ cellulose polymers; polyurethanes; polyesters, polymers from monomers having alpha~olefinic unsaturat;on such as polyethylene, polyvinyls, an~ polyvinylidenes; polyhydrazides, etc.
The cross-sectional dimensions of the hollow fibers utilized ;n the permea~ors of this invention may be selected over a wide range; however, the hol10w 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 exh;b;t some flex;bility over their lengths to accommodate any expans;ons or contract;ons wh;ch may occur under expected operating condit;ons. The outs;de d;ameter of the hollow fiber is at least about ~0, say, at least about 30 microns~ and the same or d;fferent ou~s;de d;ameter fibers may be conta;ned ;n a bundle. Often the outside dia~neter of hollow f;ber membranes does no~ exceed about 80U or 1000 m;crons since such larger diameter hollow ~ibers may provide less desirable ratios of hollow fiber surface area per un;~
volume of the permeator. However, larger diameter hollow fibers up to 10,000 microns or more in diameter, may be particularly desirable4 Preferably~ the outside d;ameter of hollow f;ber membranes is about 50 to 800 microns~ Generally, the wall thickness of the hollow fibers is at least about S microns, and in some hollow fibers, the wall thicknesses may be up to about 200 or 3ûO microns, say, about 50 to 200 microns. With hollow f;bers fabr;cated from mater;als hav;ng lesser strength, ;t may be necessary to employ larger hollow f;ber diameters and wall thicknesses to impart suff;cient 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 th;ckness in barr;er flow relationship in the wall of the hollow fiber, that ;s~ 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 -12- 36-0~8 permeators. ~ften, the shells have a major cross-sect;onal dimension of at least about O.l or preferably at least about 3.2 meter, say, up to about l 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 lû or more meters.
The hollow fibers are generally parallelly arranged ;n the form of one or more bundles in the shell. Generally, at least about lO,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 Pa~ent No. 3,42Z,008. In many instances, a single bundle of hollow f;bers ;s employed in a permeator and at least one end of the hollow f;bers in the bundle ;s embedded in a tube sheet. The oppos;te 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~ ~he ends may be segmented such that different regions on the ~ube sheet contain each end of the hollow fibers. Each o~ 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 o~ fluid through the bores of the hollow fibers.
A tube sheet use-ful in the permeators of this invention may have any general configuration suitable for use in a permeator containing bundles of hollow fibersO Since these permeators frequently have circular cross-sec~ions, the tube sheet in such instances generally has a circular cross-section.
Preferably a tube sheet is rigid; that is, a tube sheet exhibits sufficien~ strength ~hat it retains its integrity and configuration under stress. Often~ the material of the tube sheet exhibits a Shore A hardness (ASTM D 2Z40) 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 wh;ch- cross-l;nk during setting. Frequently the cross-linking (or cur;ng) increases the strength of the tube sheet as well -13- 36-~4~8 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 ~rit;sh 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 3,690,405 (McG;nnis~ et al.) The length (in the axial direction) of the tube sheet is generally suff;cient to provide suitable strength for withstanding total pressure differentials to wh;ch the tube sheet may be subjected ;n operations.
Thus, the length employed may depend upon the s~rength of the resin.
Also, the tube sheet should be suf-fic.iently 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 o, the hollow fibers are exposed a~ 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 ou~er face of the tube sheet. For instance, the bores of the hollow fibers may be plugged prior to casting the tube sheet, and then after cast;ny 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.
While tube sheets generally comprise at least one zone having hollow fibers, they may also compr;se a concentric outer zone of enlarged cross-seotional d;mensions substantially devoid of hollow f;bers. Such a concentr;c 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 6~5~
-14- 36-0~8 cross-sect;onal d;mensions only s1ightly 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 rela~;onship than in tube sheets having concentr;c 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 mater;al comprising the tube sheet is cured by exothermic reaction; that is, s;nce the ~ass of the material forming the tube sheet is minimized, potentially deleterious temperatures from exothermic curing reactions can be avoidedO
0n the other hand it may be more advantageous to manufacture 1S tube sheet~ compr;sing a concentric outer zone devoid of hollow fibers. In such configurations the differences in cross-sectional dimensions between the tube sheet and say the shell of the permeator are not as critical particularly where the flu;d tight seal is made on an ax;al face of the outer zoneO Such an application may also involve locating the seal at a r;se region between the periphery of a zone having hollow fibers and a concentric outer zone devoid of hollow f;bers, part;cularly where sa;d rise reg;on abuts a ~ubular spacer.
Such a tubular spacer may extend suff;ciently to contact the end closure cap~ Often the tubular spacer may abut the end closure cap in a fluid tight relationship~ rhe tubular spacer may even be integral w;th the end closure cap, for instance, the tubular spacer and end closure cap may be from the same casting. Alternat;velyg 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, fcr instance, at one end of the spacer prox;mate to the end closure cap.
Such flange can conven;ently be inserted between flanges on the end closure cap and the shell in a fluid tight relationship. Gaskets~
for ;nstance, such as 0-rings, ;nstalled on oppos;ng faces of the tubular spacer flange allow the tubular spacer to be maintained in a fluid tight relat;onship w;th the shell and/or end clcsure cap of a permeatar. A tubular spacer having such a flange ;s a significant -15~ 36-0~8 ;mprovement over other tubular spacer configurat;ons, such as loose ~ubular spacers5 or twbular spacers abutt;ng end closure caps ;n a fluid tight relat;onship.
The tubular spacer has a bore having a sufficiently large cross-section to provide sufficien~ space between the tubular spacer andthe tube sheet to accommodate d;fferentials in expansion transverse to the axis of the tube shee~ 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 w;thin the shell. The tubular spacer can also provide support ~o the tube sheet and, in some ;nstances~ can assist in effecting a flu;d tight relationsh;p across the tube sheet. For instance, seal seats for hold;ng the cup seal can be located in the tubular spacer.
Conven;ent locations are the ;nside peripheral surface of the spacer or on the end surface abutting the r;se region of the tube sheet.
In general, the tubular spacer can often be more read;ly machined to close tolerances than can a tube sheet. Accord;ngly, the tubular spacer can be closely toleranced to fit w;th;n the shell, but yet, enable use of tube sheets which are not so closely toleranced and wh;ch otherw;se may be unacceptable to provide a flu;d t;ght relationship directly with the shell. Add;tionally, the tubular spacer may be prepared from the same material as the shell, or alternatively the same material as the tube sheet, to minimize different;als in expansion with e;ther the shell or the tube sheet and thereby facilitate maintaining a fluid tight relationship over widely vary;ng operating conditions. Suitable materials for fabr;cat;ng 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 prov;ded between the tubular spacer and the tube sheet to accommodate d;fferentials in expansion between the tubular spacer and the tube sheet and to permit relative movement between the tubular spacer and the tube sheet under operat;ng conditions such that d;fferent;als ;n expans;on can be tolerated. It is often preferable that contact between the tube sheet and tubular spacer therefore be a moveable contact.

-16- 3~-0448 W;th respect to surfaces of the tube sheet and tubular spacer, wh;ch 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 ~ube sheet), an ample distance should be provided bet~een 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 O.S centimeter. A cup seal may be positioned between the tube sheet and the spacer in order to posit;on the tube sheet within the tubular spacer and provide a fluid tight seal between the ~ube sheet and the tubular spacer.
The following embodiments are provided to further assist ;n the understanding of the ;nvention and are not provided as limitations to the invention.
The permeator depicted in Figure 1 is generally designated by the numeral 100. Permeator 100 comprises shell 102 (only the head ànd ta;l ends are dep;cted) which is adapted to receive a tube ZO sheet at one end. Shell 102 may be compr;sed of any su;table, flu;d impervious mater;al such as metals and plasticsO In many permeators, metals such as steel are employed due to their ease of fabr;cat;on, durab;l;ty, and strength. The shell may be in any suitable cross sect;onal conf;guration; however, generally circular cross-sections are preferred. Shell 102 has a head end of increased d;ameter. The head end has head end flange 104 and fluid commun;cat;on port 108. Port 108 can provide for fluid communication w;th the ;nterior of the shell. Wh;le only a s;ngle port 108 is depicted, it should be understood that a plurality of ports 108 may be pos;tioned around the periphery of shell 102~ End cap 112 ;s positioned at the tail end of shell 102 and is fastened by bolts (not shown) to tail flange 110. Gasket 114 is positioned between end cap 112 and tail flange 110 to provide an essentially fluid ;mpermeable seal. End cap 112 ;s prov;ded w;th port 115 for flu;d commun;cat;on through the end cap.
W;th;n shell 102 is positioned bundle 116 (not shown in cross-sect;on) wh;ch ;s composed of a plurality of hollow fiber membranes~
Often the bundle comprises over 10,000 hollow f;bers and, with -17- 36-04~

smaller diameter hollow fibers or large diameter shells9 there may be an excess of 100,000 or even an excess of 1 million fibersO As depicted, the bundle has essentially the same cross-sectional configuration as the shell. One end of each of the hollow fibers is embedded ;n plug 118 (not shown ;n cross-sect;on). 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 passing a hot wire through the bundle of hollow fibers.
The other end of bundle 116 passes through plenum 106 having fluid d;stribution ports (not shown). Plenum lû6 is positioned within the head end of the shell lOZ and serves to distribute fluid passing to or from flu;d commun;cat;on port 108. Bundle 116 is term;nated at the head end with tube shee~ 120 (not shown in cross-sect;on). The bores of the hollow fibers provide passageways through tube sheet 120 to the open end of shell lOZ.
A seal seat 141 ;s cut into the wall of shell 102. A cup seal 140 ;s seated ;n the seal seat 141 and contacts seal;ng surfaces on tube sheets 120 and on the shell lOZ w;th;n seal seat 141 to prov;de a flu;d t;ght relat;onsh;p across tube sheet 120. Among the preferred conf;gurations for cup seal 140 are those exempl;fied as ;n cross-sect;on, ;n Figures 6, 7 and 8, as cup seal 60, 70 or 80 compr;s;ng resil;ent members 61, 71 or 81 subs~ant;ally surrownded by, and ;n contact w;th the concave surface of, polymer;c r;ngs 62, 72 and 8Z, respect;vely.
End closure cap 124 ;s adapted to cover the open end of the shell and ;s securely fastened to shell 102 by the use of bolts ~not shown). A gasket 126 ;s pos;t;oned between the end closure C3p 124 and head end flange 104 such that when end closure cap 124 hav;ng fluid communication port 130 is securely attached to -the shell, a flu;d tight relationship ;s achieved. Circular boss 128 extends from the end closure cap 124 to contact the periphery of the outer face of tube sheet 120 forcing the tube sheet 120 to compress against spring 122. A plurality of springs 122 located between plenum lOo and tube sheet 120 serve to prov;de an owtward d;rected force on the tube sheet. ay selecting spr;ngs of appropriate size and number, a desired spacing and flex;bility can be achievedO
Accordingly, suitable forces can be obta;ned wi~hout concern for close tolerancing of the length of the tube sheet.
Springs 122 are optional in this permeator configuration. ~ith the fluid tight seal made on the 1ateral surface of the tube sheet, the tube sheet can be allowed to be freely slideable betwe~n plenum 106 and boss128.
In an operation of permeator 100, a fluid feed mi~ture may be ;ntroduced into the shell side o~f the permeator through port 115 or7 preferably, port 108, with the non-permeating fluid being removed from the shell side of the permeator through the other port~
Permeating fluid enters the bores of the hollow fibers and passes w;thin the bores through the tube sheet 120 and is exhausted from the permeator through port 130 in head end closure cap 124.
F;gure-2 illustrates the head portion of a permeator generally designated by the numeral 200. Permeator 200 comprises a shell 20Z
wh;ch has a circular cross-sectional configuration. Shell 202 is provided with head end flange 204 and fluid communication port 20~.
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 cross-sectional configurat;on as the interior of the shell. 8undle 216 is terminated at the head end w;th tube sheet 220 (not shown ;n cross-section). As depic~ed, tube sheet 220 has a cylindrical expanded zone 221, a rise region 222 perpendicular to the ax;s of the tube sheet and a concentric cylindr;cal portion 223 extending to the end face.
At the r;se reg;on 222 of tube sheet 220 is positioned tubular spacer 234. The tubular spacer has seal seat 241 cut ;nto its ;ns;de wall. Cup seal 240 is posit;oned 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 ~lange 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 ;s securely fastened to shell 202 by the use of bolts (not shown). Gaskets 226 and 227 are pos;tioned 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 ;s securely attached to the shell, a fluid ~ight relationship is achieved.

Tubular spacer Z34 serves to position tube sheet 220 within the shellO The expanded zone 221 of the tube shee~ can therefore be ma;ntained a suff;c;ent distance away from the inter;or surface of shell 202 that any differentials in expansion between the shell and the tube sheet can be accommoda~ed. Tubular spacer 234 surrounds only the smaller diameter 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 expans;on than the expanded zone of the tube sheet, the d;stance between the tubular spacer and the ~ube 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 prov;ded by cup seal 240 ;s fac;liated. Also, cup seal 240 enables relat;ve axial movement of .he 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 r;se reg;on 222, the ~ubular spacer does not restrict expansions or contractions of the tube sheet~ Since concentr;c 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 of sufficient magnitude to h;nder achieving fluid tight seal by cup seal 240.
F;gure 3 il1ustrates the head portion of a permeator generally z5 des;gnated by the numeral 300. Permeator 300 compr;ses shell 302 wh;ch has a c;rcular transverse cross-sect;onal configuration. Shell 302 ;s prov;ded w;th head end flange 304 and flu;d commun;cat;on port 308. Within shell 302 is positioned bundle 316 (not 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. ~undle 316 is tPrm;nated at the head end w;th tube sheet 320 (not shown in cross-sect;on~. Tubular spacer 334 surrounds the extended cyl;ndrical section of tube sheet 320 and abuts r;se region 322. Tubular spacer 334 ;s sealingly attached to end closure cap 3Z4. Th;s is achieved, for instance, by welding tubular spacer 334 to end closure cap 324, by mach;ning an end closure cap hav;ng a tubular spacer from un;tary casting or by any other convenient means.
Seal seat 341 is provided in the interior circumferential surface of -20- 36-0~8 -the tubular spacer to retain cup seal 3~0 which provides a fluid tight relationship around the tube sheetn It is often convenient for ease of ins~allation of the GUp seal that the tubular spacer comprise a washer portion 335 attached, for instance9 by bolts 336 to the portion of the spacer having the seal seat 341. Gasket 326 is provided between the end closure cap 32~ and head end flange 30~ to provide a fluid tight seal.
The end closure cap is also provided with port 330 for fluid communica-tion 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 ax;s of the tube sheet. In one aspect of this exemplif;cat;on of appl;cant's permeator the extended cylindrical portion of the tube sheet has shallow grooves 3;0 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 ax;s of the shell of permeator is maintained in a vertical orientation with the tube sheet end of the permeator downO
The fluid feed mixture is introduced to the shell side of the hollow fibers. S;nce 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 ma;nta;ning the fluid tight relationship at the cup seal but also assists in forcing the slideable tube sheet to an abutting relation-ship w;th 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 ;n the bore s;de total pressure, a substantially higher pressure may exist inside the bores of the hollow fibers which could deleter;ously effect the hollow fiber membranes. However before such deleter;ous effect on the hollow fiber membranes this higher pressure may be sufficient to force the slideable tube sheet taward 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 f~
~21- 36-04~8 side o~ the hollow fiber membranes.
Figure 4 and 5 illustrate embodiments of this invention where the cup seal ;s oriented so that the opening to concave surface faces radially outward in ~he plane of the cup seal.
Figure 4 illustrates the head portion of the permeat~or generally designated by the numeral 400. Permeator 400 ccmprises 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 416 (not shown in cross-section) which is composed of a plurality of hollow fibers.
The bundle has the same general transverse cross-sectional configuration of the interior of the shell. Bundle 416 is termina~ed a~ the head end with tube sheet 420 (not shown in cross-section).
The tube sheet comprises two concentr;c zones surround;ng the bundle embedded in the tube sheet, where one zone is expanded. Rise region 4Z1 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 ass;sts in pos;t;on;ng the tubular spacer w;th;n the shell. Gaskets, for instance 0-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 ~h;ch provides a flu;d tight relationship around the tube sheet when the tube sheet abuts the tubular spacer. A plurality of spr;ngs 422 are positioned between the bundle face of the expanded zone of the tube sheet and the plenum 4û6 to orovide a force d;rected axially outward from the head end of the shell wh;ch forces the tube sheet to abut tubular spacer thereby establish;ng a flu;d t;ght 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 3 higher total pressure than the pressure of the permeat;ng fluid on the above side of the hollow f;bers, the pressure d;fferent;al across the tube sheet ~from the shell s;de to the tube side) will assist in 3~
-2~- 30-0448 mainta;ning the fluid t;ght relationship as the tube sheet is forced to compress the cup seal. This pressure d;fferential also operates on the cup seal with the higher fluid pressure ;n contact with the concave surface providing an expandiny force on the cup S seal thereby promoting the fluid tight relationsh;p~
A sim;lar fluid tight relat;onship is ach;eved in permeator 500.
F;gure 5 illustrates the head portion of a permeator generally des;gnated by the numeral 500. Permeator 500 comprises shell 502 which has a circular transverse cross-sectional configuration.
Shell 502 is prov;ded w;th a head end flange 504 and flu;d communication port 508. With th;s shell 502 is positioned bundle 51S (not 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 516 is term;nated at the head end w;th the tube sheet 520 ~shown ;n part;al cross-sect;on) 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 absence of hollow fiber membranes.
The outer zone is further character;zed 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 plur31ity of springs 522 cooperate between the retaining boss S06 and the bundle face of the tube sheet to force the tube sheet in an ax;al direction toward end closure cap 524~ The end closure cap is equ;pped w;th 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 20ne of the tube sheet~

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In 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 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;
(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.
the improvement 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.