IL30906A - Apparatus for removing dissolved solids from a liquid by reverse osmosis - Google Patents

Description

APPARATUS FOR REMOVING DISSOLVED SOLIDS FROM A LIQUID BY REVERSE OSMOSIS n.B D'OBIB "D*P»I» ηκχιη5* τ n;i Π313Π nnoois The present invention resides in an apparatus for removing' dissolved solids from a liquid by reverse osmosis.

More specifically, the invention resides in a new and improved end seal in such apparatus utilizing the reverse osmosis principle.

It is also an object of the invention to provide a new and improved end seal which is easily effected, may be performed on site, which is unlikely to damage the membranes and which- provides a much more effective seal than heretofore known.

Because of the ever-increasing water shortage problem, considerable effort has been expended to develop economical methods and -apparatus for removing the salt from sea water or for purifying brackish water. Thus far, most success has been achieved by distillation methods or apparatus or by electrodialysis methods and apparatus. However, considerable promise also exists in the process of· reverse osmosis for economically providing potable water.

In order to purify salt water by reverse osmosis, sea water in contact with a semi-permeable membrane must be subjected to pressure in excess of the osmotic pressure of the sea water. For a typical concentration of salt, in sea, water, the osmotic pressure is on the order of 350 psig and accordingly, a pressure differential in excess of that figure must be maintained across the membrane. In this respect, it is not unusual to provide a pressure differential on the order of about 1000 psig and accordingly, it will be apparent that the membrane requires substantial support in order to resist rupture under such substantial pressures.

As a result, the prior art has resorted to the use 30908/2 ' · ■ · ■ . : . ' · figuration which are received within a rigid tube which supports the membrane when the liquid to be purified is di ected against the inner surface of the tubular membrane at high pressure. Potable water diffusing through the membrane to the interface of the membrane and the supporting tube is then directed through small apertures in the supporting tube to be collected for use. Because the supporting tubes and the membranes must be of finite length, it is necessary that a seal be provided at the ends of the membranes to preclude the water to be purified and directed to the interior of the tubular membrane from flowing to the interface between the membrane and the supporting tube where potable water is present.

According to currently known techniques, the required end seal is provided by softening the end of the tubular membrane by chemical means and flaring the thus-softened end with an inflatable rubber tool to form a sealing surface. Because the tubular membranes are extremely thin, the process of flaring the ends thereof is one which is extremely tedious and time consuming and which is unsatisfactory to the extent that the number of membranes split during the flaring process is relatively high and the reliability of the seal thus formed is relatively low. Furthermore, because the flaring process is a relatively exacting one, it is an extremely difficult operation to perform on the site of a desalinization apparatus utiliz- ing the reverse osmosis principle and as result, when membranes require replacement, oftentimes the entire apparatus must be disassembled and the supporting tubes shipped to a factory for replacement and flaring of membranes.

The present invention provides an apparatus for removing dissolved material from a liquid solution by reverse osmosis comprising a rigid tube, a unitary tubular structure disposed within the rigid tube and comprising an outer, porous tube, and an inner film of a semi-permeable membrane material bonded to the internal surface of the porous tube, said porous tube being relatively thin-walled and incapable of withstanding pressures on the order of the osmotic pressure of the liquid solution, and said tubular structure having a pottion communicating with an end of the rigid tube, conveying means communicating with the tubular structure for conveying the liquid solution to be processed to the interior of the tubular structure, and collecting means in fluid communication with the portion of the tubular structure for conveying processed liquid permeating the membrane film and flowing in the porous tube between the film and the rigid tube to a collection point.

Details and advantages of the invention will become apparent from the following description in conjunction with the accompanying drawings.

Figure 1 is a fragmentary sectional view of a portion of a reverse osmosis desallnization apparatus embodying an end seal made according to the invention] Figure 2 is a fragmentary sectional view of a desallnization apparatus embodying a modified form of end seal; and Figure 3 is a fragmentary sectional view of such an apparatus embodying still another form' of end seal.

One embodiment of a liquid purifying apparatus oper-ating on the principle of reverse osmosis and embodying the invention is illustrated in Figure 1 and is seen to comprise a header 10 which may Include a plurality of bores 12 (only one of which is shown) for receipt of the end 14 of a rigid support tube 16 . The rigid support tube 16 is formed to with-stand the relatively high pressure differentials customarily present in purifying equipment operating under the principle of reverse osmosis and the ends thereof may be grooved with the header 10 cast thereabout to provide a mechanical bond.

Within the support tube 16 is an expendable, mem-brane structure, generally designated 18. The membrane structure 18 is generally cylindrical in shape and includes a tubular film 20 that is generally cylindrical in shape and is formed of a semi-permeable membrane material as is known in the art.

Surrounding the tubular film 20 is a semi-rigid, porous tube 22 which has its ends (only one of which is shown) coated with a liquid impervious material 24 which serves to rigidlfy the same for sealing purposes as will be seen.

In operation, a liquid containing dissolved solids to be removed such as sea water is conveyed to the interior of it's osmotic pressure and as a result., the liquid will diffuse through the tubular film 20 in a purified form and flow through the porous, semi-rigid tube 22 to the interface between the membrane structure 18 and the rigid tube 16. In the embodiment illustrated in Figure 1, the rigid tube 16 is provided with a plurality of apertures 26 extending through the walls thereof so that a purified liquid at the above-mentioned interface may exit from the rigid tube 16 via the apertures 26 for subsequent collection.

Of course, for the above-mentioned process to take place, liquid to be purified must be conveyed to the interior of the tubular film 20 and the same must be precluded from mixing with the purified liquid at the interface between the rigid tube 16 and the membrane structure 18. Accordingly, adjacent the outermost end of the bore 12 and the header 10 is an annular groove 28 which receives a gasket 30 which may be in the nature of a conventional 0-rlng having a radial extent greater than that of the membrane structure. Additionally, in order to direct the liquid to be purified to the interior of the tubular film 20, an end cap 32 having a channel 3 is tightly clamped by any suitable means to the header 10 in such a way that the channel 3 will be in fluid communication with the interior of the tubular film 20.

The channel 3 is constructed such that its boundary, generally designated 36, at the channel's point of emergence from the end cap 32 will sealingly engage the gasket 30 and somewhat compress the same against the outer edge of the annular groove 28, the end of the rigid tube l6 and the water impervious coating 24 on the membrane structure 18. As a result, fluid communication between the channel 34 and the Interface 'precluded except for purified liquid which diffuses through the tubular film 20.

Turning now to Figure 2, a second embodiment of a liquid purifying apparatus utilizing the principle of reverse osmosis and embodying the invention is illustrated. For the sake of convenience, elements in the- Figure 2 embodiment corresponding to the same elements in Figure 1 will be designated by the same reference numerals appearing in the latter except that they are primed.

A header 10 ' is provided which includes a bore 12 ' which receives an end 14 ' of a rigid support tube 16 ' . The support tube 16 ' Includes apertures (not shown) corresponding to the apertures 26 in the embodiment illustrated in Figure 1.

Within the rigid support tube 16 ' is a membrane structure, generally designated 18 ' which, in all respects is identical to the membrane structure 18 except that the coating 24 is omitted. That is, the membrane structure l8 " consists entirely of a tubular film 20 ' and a semi-rigid porous tube 22 ' Interrelated in the same manner as the tubular film 20 and semi-rigid porous tube 22.

Again, an, end cap 32 ' including a channel 34 ' having a boundary 36 ' is provided and a gasket 30 ' sealingly engages the end 14 ' of the rigid tube 16 ' , the membrane structure .181 and the boundary.36 ' at the point of emergence of the channel 34 ' from the end cap 32 ' .

The gasket 30 ' differs somewhat from the gasket 30 in that the former includes a major portion 38 ar*d a minor portion 40. The major portion 38 is. generally circular in shape and has a greater radial extent than the membrane struc-ture 18 ' . The minor portion 40 is generally cylindrical in extent of the inner surface of the tubular film 20' and extends inwardly into the membrane structure 18' to sealingly engage the end of the tubular film 20 .

The major portion 38 of the gasket 30' Is located In a gap formed by the end 14' of the rigid tube 16' , the wall of the bore 12' and the boundary 36' of the channel 34""* in the end cap 32' and the arrangement is such that a sealing engagement is obtained between the major portion 38 of the gasket 30' , the end 14' of the rigid tube 16· and the boundary 36' of the channel 34'. As pointed out above, a sealing engagement is also formed between the minor portion 40 of the gasket 30· and the membrane structure 18' at the end of the tubular film 20' , In order to insure a positive seal at the last named location, a generally cylindrical ferrule 42 is located within the gasket 30' to embrace the radially inner surface thereof along its entire length and thereby hold the minor portion 40 in tight engagement with the inner surface of the end of the tubular film 20' .

Turning now to Figure 3 another embodiment of a liquid purifying apparatus utilizing the principle of reverse osmosis is illustrated. The apparatus of Figure 3 utilizes a membrane structure, generally designated 18'', in all respects identical to the. membrane structure utilized in the embodiment Illustrated in Figure 1/ and accordingly, it is not believed necessary to further describe the membrane structure 18''.

The apparatus illustrated in Figure 3 like the apparatus illustrated in Figures 1 and 2 includes a header 10' ' including a bore 12' ' which receives an end 14' ' of a rigid support tube l6 . The support tube 16'", unlike the support does not require the use of apertures for permitting the liquid accumulating at the interface between the support 16' 1 and the membrane structure 18' » to be collected.

Rather, advantage is taken of the porous character-istic of the semi-rigid tube 22' 1 which allows water diffusing through the tubular film 20» 1 to flow laterally to a collection space defined by a narrow neck 44 of the bore 12'' at the outer end of the latter as will be seen.

The apparatus illustrated in Figure 3 also includes an end cap 3211 including a channel 34·' which has a boundary 36' ' at the point of emergence of the channel 34 ' ' from the end cap 32' 1 and which is defined by an annular groove 46 in the end cap 32''. Within the annular groove 46 there is received a gasket 30' 1 having a greater radial extent than the membrane structure 181 ' and which provides a seal between the boundary 36' 1 and the coating 24' 1 on the membrane structure 18' ' while permitting liquid to be purified within the channel 34' 1 to flow to the interior of the tubular film 201'.

The end cap 3211 is secured to the header 10' ' by means of a bolt 48 which passes through aligned boie s 50 and 52 in the end cap 32'· and header 10' ' , respectively, to impale a nut 54. Around the edges of the interface of the end cap 32' 1 and the header 30' ' there is provided a sealing gasket. 56 which, together with a spacing washer 58 defines a collec-tlon channel whereby purified liquid from the collection space 44 may flow to a point of collection. I%re specifically, the spacing washer 58 includes an outer surface 60 which sealingly engages the gasket 30' 1 and tends to hold the same within the annular groove 46. The smooth outer surface 60 also engages the inner surface 62 of the end cap 32 ' ' to support the same in The inner surface of the spacing washer 58 is defined by a plurality of grooves 64 separated by lands 66, the latter being engaged with the outer surface 68 of the header 10 ' ·. As a result, liquid within the collection space 44 may flow through the grooves 64 to a space, generally designated 70, between the end cap 32 ' ' and the header 10 ' ' . The space 70 in turn is in fluid communication with a bore 72 in the end cap 32 ' · so that liquid may flow through the bore 72 to a point of collection for subsequent use.

From the oregoing, it will be appreciated that an apparatus for purifying liquid utilizing the principle of reverse osmosis made according to the invention provides a significant advantage over those heretofore known in that membrane structures do not require flaring in order to insure an ade-quate seal between the membrane material and the support tubes therefore. As a result, an apparatus constructed according to the invention may be easily disassembled on site for replacement of the membrane structure, a factor which minimizes down time, inventory costs and transportation expenditures.

Furthermore, when an apparatus according to the invention, and more specifically, according to the teaching utilized in the embodiments of Figures 1 and 3, is constructed, it will be appreciated that tolerances with respect to length of the membrane structures may be relatively loose in that ex-cess length of the same is easily accommodated within the channels. Accordingly, the necessity of precise fitting of the membrane structures in their respective support tubes is done away with.

Finally, apparatus embodying the invention, because of the positive nature of the seals, has a much higher reli , in l , process efficiency and thus the cost of purifying the liquid is significantly more economically advantageous and down time required to locate faulty seals is minimized.

Having described specific embodiments of the invention we do not wish to be limited to the precise details but rather, to have the invention construed according to the fol- lowing claims.

Claims (7)

30906/4

1. An apparatus for removing dissolved material from a liquid solution by reverse osmosis comprising a rigid imperforate support tube, a unitary tubular structure disposed within the support tube and comprising a semi-rigid porous tube and a film of a semi-permeable membrane material bonded to the internal surface of the porous tube, said porous tube being relatively thin-walled and incapable of withstanding pressures on the order of the osmotic pressure of the liquid solution, means for supporting the rigid tube, conduit means communicating with the interior of the tubular structure for conveying the liquid solution to be processed to the interior of the tubular structure through an end thereof, sealing means adjacent the ends of the tubular structure for preventing flow of the liquid solution to the interface between the support tube and the membrane film, and collecting means in fluid communication with the interface between the rigid tube and the membrane film for conveying processed liquid permeating the mem-brane film to a collection point.

2. The apparatus according to claim 1, wherein said conduit means comprises an end cap having a channel therein, an annular groove in the end cap surrounding the channel, a liquid impervious coating adjacent the ends of the porous tube, said sealing means comprising a gasket received in the groove with the liquid impervious coating on the porous tube extending into the channel and into sealing engagement with the gasket. 30906/4 ft v

3. The apparatus according to claim 2, wherein the gasket is spaced from the end of the rigid tube, and said collecting means including a receiving space for the processed liquid between the gasket and the end of the rigid tube.

4. The apparatus according to claim 2 or 3, including a washer surrounding the porous tube and interposed between the end cap and the support means, said washer abutting both the end cap and the gasket and forming a plurality of openings for flow of the processed liquid permeating through the tubular film for the receiving space to the collection point.

5. The apparatus according to claim 1, wherein the support means comprises a header having a bore for reception of the rigid tube, the end of the bore together with the end of the rigid tube defining a space for. receipt of the sealing means, said conduit means comprising an end cap having a channel therein, said sealing means comprising a gasket sealingly engaging the end cap about the boundary of the channel at is point of emergence from .A the end cap, a liquid impervious coating adjacent the ends of the porous tube, and the tubular structure extending from the rigid tube a sufficient distance so that the liquid impervious coating sealingly engages the gasket.

6. The apparatus according to claim 1, wherein the sealing means comprises a gasket having an inwardly directed minor portion having a radial extent' substantial 30906/ the tubular film, said minor portion sealingly engaging the interior surface at an end of the tubular film, and a ferrule within the gasket for holding the minor portion in sealing engagement with the tubular film. •

7. A reverse osmosis apparatus constructed and adapted to operate substantially as herein described with particular reference to the embodiments illustrated in the accompanying drawing. S. HOROWITZ & CO. AGENTS FOR APPLICANTS