WO1999006137A1

WO1999006137A1 - Pure oxygen by diffusion

Info

Publication number: WO1999006137A1
Application number: PCT/US1998/015604
Authority: WO
Inventors: Christiaan P. Van Dijk
Original assignee: Dijk Christiaan P Van
Priority date: 1997-07-30
Filing date: 1998-07-28
Publication date: 1999-02-11
Also published as: AU8666698A

Abstract

This invention relates to a process for preparing highly concentrated oxygen from air by repeated diffusion. This diffusion is preferably carried out at substantial pressure with take-off of several oxygen rich permeate streams in sequence. A three-stage diffusion suffices to obtain highly concentrated oxygen in high yield. The specific devices permit the take-off of several permeate streams.

Description

PURE OXYGEN BY DIFFUSION

The invention relates to a process for converting air into a highly concentrated oxygen stream, using membrane diffusion. On an industrial basis a highly concentrated oxygen product is made by either cryogenic techniques or by pressure swing absorption.

The cryogenic process is preferred for large-scale oxygen manufacture. It is based on achieving very low temperatures, thus liquefying part of the compressed and expanded air. Distillation then leads to high purity oxygen. In pressure-swing absorption (PSA) an absorbent is used, which preferentially absorbs one of the main components of the air. At high pressure nitrogen is commonly absorbed out of a pressurized air stream, thus leaving as a gas an oxygen stream with a purity of between 90 and 95 mole% oxygen which may be recovered. After oxygen recovery, swinging then to a lower pressure succeeds in liberating the nitrogen out of the absorbents used, after which the PSA unit is ready for another pass of compressed air to repeat the cycle of oxygen production and recovery followed thereafter by nitrogen liberation. It is also possible to use low pressure and liberate the nitrogen by reverting to vacuum. Pressure swing absorption is commonly used for smaller oxygen plants in the range of up to 200 to 300 metric tons per day (MTPD).

Making intermediate quantities of an oxygen concentrate, in a range between 40 and 50 mole% oxygen, has become possible with the use of membranes which have the characteristic that oxygen diffuses through them much faster than nitrogen. This membrane method had as a negative aspect the high compression duty of the air. In U.S. Patent 5,245,110 the present inventor, together with Mr. Lowell D. Fraley, described a use of a gas turbine which allowed for compressed air to be extracted from the air compressor unit of the gas turbine in order to produce an oxygen enriched gas stream which thereafter is used in a complex process which produces higher boiling carbon compounds as a final product after which the final tail gas stream from this process is used as the fuel for the gas turbine, thus returning to the gas turbine practically all the nitrogen contained in the compressed air stream initially taken from the gas turbine. This then is one way to lessen the negative aspect of a membrane method since the compression duties are fulfilled by the extra compressed air available from a gas turbine which services other needs in the overall process. While it has been understood that a first oxygen rich permeate of said between 40 and 50 mole% oxygen may be slightly recompressed and again passed through another diffusion membrane to lead to a considerably higher concentration of oxygen, like 65 to 80 mole% oxygen, this method has not been found attractive because the loss of oxygen to the second non-permeate stream is too high. One would surmise that perhaps one or more after steps of diffusion then would recover that oxygen in more valuable form. This would, however, call for use of higher pressure and a large number of diffusion steps.

Use of higher pressures for membrane diffusion would seemingly meet with substantial problems. The diffusion then is so fast for the desired higher oxygen containing product that it is difficult to stop the diffusion at that point. It should be born in mind that the membrane diffusion devices, particular for oxygen production, are normally hollow fibers which are contained in, for instance, polymer blocks at both ends of the fiber bundle. These polymer blocks both constrain the fiber bundle within its associated housing and also allows open passage into the bore of most of the individual fibers, which is the difficult and costly requirement for preparing hollow fiber membrane units. If, therefore, only a very small membrane amount is used for the initial stage of diffusion, still a substantial cost for such diffusion device is still encountered. Thus, the membrane cost can quickly become unacceptable.

It is presently proposed to use a multi-stage diffusion process with the characteristic that in several stages more than one permeate stream is sequentially evolved. This permits use of high pressure for the diffusion of the higher concentration oxygen streams of the later stages. In consequence thereof a much higher take-off pressure of the permeate streams, especially when at high oxygen concentrations, then becomes possible. A membrane device is described which allows such sequential take-off of permeate streams.

This device contains a standard hollow fiber bundle within a bundle housing wherein the hollow fiber bundle is constrained at each of the housing end within a polymer block, as presently is the common practice. However, in this invention the outside of the fiber mass within the bundle housing itself is separated in two or more zones, separated from one another. For this separation a low-cost polymer block can be used, but any other separation can be used. Preferably the zones within a given membrane unit increase progressively in the surface area of the fiber surface presented by the zone for diffusion from the bore of the hollow fiber to the permeate zone defined by the fiber exterior surface and the bundle housing. With a reasonable quality of membrane fibers a three-stage diffusion now suffices to prepare oxygen streams at higher than 85 or 90 mole% oxygen concentrations. At the same time the non-permeate streams can all be at an oxygen concentration of about 10 mole% or less. Thus the product oxygen recovery out of compressed air can be into the low 60% range. In comparison, use of a one-stage diffusion commonly will result in a 45 to 50 mole% oxygen concentration in the enriched air stream, coupled with an oxygen recovery from the compressed air feed in the 65 to 70% range. It is further preferred to feed the still pressurized non-permeate streams to an expander and most preferably to an expander of a gas turbine, this to recover as much of the energy of compression as possible. Using extraneous process heat to warm up the non-permeate streams fed to the expansion turbine of a gas turbine can be used to lower fuel use.

Figure 1 schematically illustrates a hollow fiber permeable membrane unit (hollow fibers per se not illustrated) wherein the unit is provided with a intermediate point blockage means which divides the permeate zone into two sections such that a first and second permeate stream can be taken off without comingling of the respective gas constituents therebetween. Figure 2 schematically illustrates a hollow fiber permeable membrane unit (hollow fibers per se not illustrated) wherein the unit is provided with two intermediate points of blockage means which divide the permeate zone into three sections.

Figure 3 schematically illustrates a three diffuser stage arrangement for production of an oxygen product stream wherein the middle or second diffuser stage is a membrane unit like that of Figure 2 and the third diffuser stage is a membrane unit allowing take-off of three separate permeate streams like that illustrated by Figure 4.

This invention comprises a process for producing a gas composition which is highly enriched in oxygen compared to air, comprising the steps of: diffusing pressurized gas compositions predominantly composed of oxygen and nitrogen through a sequence of two or three membrane units having hollow fiber membranes which are preferential for permeation of oxygen compared to nitrogen and wherein each successive membrane unit has a number of non- communicating permeate gas zones that is greater than the number of permeate gas zones of a preceding unit of the sequences such that the number of permeate gas composition streams increases progressively through the sequence. The first membrane unit produces a single permeate gas composition (IP) and a non-permeate gas composition (INP), the second membrane unit produces a first permeate gas composition (2P1), a second permeate gas composition (2P2) and a non-permeate gas composition (2NP) and a third membrane unit when present produces a first permeate gas composition (3P1), a second permeate gas composition (3P2), a third permeate gas composition (3P3) and a non-permeate gas composition (3NP).

In a two membrane unit sequence of operation, by compressing air in conjunction with heat exchange of such compressed air during and/or after its compression a compressed air stream of 110 F or less at a pressure substantially exceeding atmospheric pressure is formed as feed to a first membrane unit which operates to produce a permeate gas composition (IP) containing from about 45 to about 50 mole % oxygen, and a non-permeate gas composition (2ND) containing 12 mole% or less oxygen. By combining the first unit permeate gas composition (INP) with a second permeate gas composition (2P2) from a second membrane unit and compressing the combined permeate gas compositions in conjunction with heat exchange during and/or after compression an oxygen-nitrogen gas mixture at 110 F or less and at a pressure substantially exceeding atmospheric pressure is formed as feed for the second membrane unit which operates to produce a first permeate gas composition (2P1) containing from about 73 to about 80 mole% oxygen, a second permeate gas composition (2P2) containing from about 45 to about 50 mole% oxygen, and a non-permeate gas composition (2NP) containing 12 mole% or less oxygen.

In a three membrane unit sequence of operation, by combining the first unit permeate gas composition (IP) with a second permeate gas composition (2P2) from the second membrane unit and with a third permeate gas composition (3P3) of a third membrane unit and compressing the combined permeate gas compositions in conjunction with heat exchange during and/or after compressing an oxygen-nitrogen gas mixture at 110 F or less and at a pressure substantially exceeding atmospheric pressure is formed as feed for the second membrane unit which operates to produce a first permeate gas composition (2P1) containing from about 73 to about 80 mole% oxygen, a second permeate gas composition (2P2) containing from about 45 to about 50 mole% oxygen, and a non-permeate gas composition (2NP) containing 12 mole% or less oxygen; thereafter by combining the first permeate gas composition (2P1) of the second membrane unit with a second permeate gas composition (3P2) of the third membrane unit and compressing the combined permeate gas compositions in conjunction with heat exchange during and/or after compressing an oxygen-nitrogen gas mixture at 110 F or less and at a pressure substantially exceeding atmospheric pressure is formed as feed for the third membrane unit which operates to produce a first permeate gas composition (3P1) containing from about 88 to about 93 mole% oxygen, a second permeate gas composition (3P2) containing from about 73 to about 80 mole% oxygen, a third permeate gas composition (3P3) containing from about 45 to about 50 mole% oxygen, and a non-permeate gas composition (3NP) containing 12 mole% or less oxygen. In the process embodiment of this invention wherein a highly O₂ enriched gas stream is to be produced by a three stage sequence, like that illustrated by Figure 3, ambient air (10) is compressed by one or more standard air compressors (12), preferably with inter-cooling (14) between compression stages, and this compressed air is fed to a membrane diffusion device (D) the membrane of which is preferential for permeation of oxygen compared to nitrogen to produce as a permeate (P) stream one which is significantly enriched in oxygen compared to air. The compression ratio of the compressed air after the final stage of compression is such that following diffusion of such compressed air through a semi-permeable membrane to produce a low pressure permeate (P) stream enriched in oxygen mole percent compared to air a non-permeate (NP) stream enriched in nitrogen mole percent compared to air remains which has a pressure slightly less of that pressure to which the air was initially compressed.

In either of the two or three membrane unit sequences of operation the respective oxygen- nitrogen gas mixtures which form the feed streams to a membrane unit may be compressed to a pressure of from about 8 to about 20 atmospheres absolute (ata). At lower compression levels a lesser compression duty is required but the heat exchange duties for interstage cooling of the compressed gas mixture increases somewhat on a relative basis and a somewhat greater fiber area is required to yield a final oxygen product gas of a slightly lower oxygen concentration. For example, in a three unit sequence, at a compression level of 8 ata for all feed streams, the permeate streams combined to form the feed for the second diffuser unit would be of about a 45.4%o oxygen concentration, the permeate streams combined to form the feed for the third diffuser unit would be of about a 70.9% oxygen concentration, and the first permeate stream from the third diffuser unit would be at about an 88.7% oxygen concentration and would represent a 54.3%) recovery of that oxygen in the initially compressed air. The non-permeate streams from each membrane unit would be of about an 11 % oxygen concentration. Conversely, at greater compression levels, although greater compression duties are required, one secures the benefits of a greater heat exchange efficiency for interstage cooling of the gases, a lesser area of fiber is required and a final product oxygen stream of a greater oxygen concentration and greater yield of recovered oxygen. For example, wherein all feed streams are compressed to 16 ata, the permeate streams combined to form the feed for the second diffuser unit have an about 48.36% oxygen concentration, the permeate streams combined to form the feed for the third diffuser unit have an about 77.17% oxygen concentration and the first permeate stream from the third diffuser unit which is the final product stream has an about 91.72% oxygen concentration and represents a 61.9%) recovery of oxygen from the initially compressed air.

The low pressure permeate stream which is enriched in oxygen mole percent compared to air is fed to a further oxygen concentration device, as in Figure 1 , by a further series of stage compressions may be recompressed to a higher pressure such that the recompressed oxygen-enriched gas stream would form the feed for a second diffusion device. In the case of recompression and feed of a first permeate oxygen-rich gas stream to a second diffusion device, the still higher oxygen level then produced in the permeate stream resulting from the second diffusion device would permit a low cost further concentration of oxygen from this second permeate gas stream by feeding this second permeate gas stream now further enriched in oxygen mole percent relative to nitrogen through a third series of recompressions to be followed by a third diffusion step, as in Figure 2.

The non-permeate gas stream obtained from one or more of the diffusion devices is of a pressure slightly less than of that of the initially compressed air. These non-permeate gas streams will have an oxygen content of less than 12 and preferably less than 10 mole%. Preferably, a non-permeate gas stream is fed to the combustion system of the gas turbine for mixture with the combustion gases. From the combustion system the combined gas mixture flows to the expansion turbine increasing the mass flow which expands therethrough thus resulting in a greater output power by the gas turbine. To the extent that the non-permeate gas stream is at a temperature lower than the compressed air supplied by the air compressor of the gas turbine for use as gas for cooling the combustion gases to the desired TIT. the non-permeate gases will require warming up to at least this same temperature. If waste or extra heat is already available within the unit operation, it may be used through appropriate heat exchanges as a medium for a pre-warmup of the non-permeate gas stream to a higher temperature. If such extra heat is inadequate or even unavailable, then the burner of the gas turbine combustion system may, by the addition of a further quantity of fuel, be operated to supply a combustion gas with a further quantity of heat as is required for the warmup of the non-permeate gas stream as it mixes with the combustion gases supported by the burner.

In this repeated diffusion process use of a special diffuser device (as illustrated in Figure 1) is preferred in which several diffused streams can be taken off sequentially through the existence of barriers in the area where the diffused gas stream is being generated. Figure 1 illustrates a hollow-fiber membrane unit wherein a blockage against permeate gas comingling has been provided at a intermediate point between the gas receiving and gas outlet ends of the hollow fiber bundle within the membrane housing 30. This blockage may readily be created during fabrication of the membrane unit by injecting a polymerizable liquid into the bundle housing to occupy the interstitial space between individual fibers of the bundle then polymerizing this liquid. In Figure 1 this interstitial space blockage is illustrated as shade space 32. Fiber end binders 34 and 36 secure the fiber bundle ends within housing 30. In the configuration illustrated pressured inlet gas 40 is supplied to the bores of the hollow fibers and permeates to the interstitial space between the hollow fibers wherein it may be taken from the housing by appropriate exit ports as a first permeate (PI) and a second permeate (P2) stream and the residual gas or non-permeate (NP) stream is taken from the outlet end 36 of the unit.

As is known in the industry, compression of the first about 50% oxygen or enriched air permeate obtained to only a modest level of several atmospheres suffices to allow permeation of this composition through another membrane unit to achieve another permeate stream of a considerably higher oxygen concentration. However, the second resulting non-permeated mixture then still has a high oxygen concentration, which results in a poor oxygen yield, compared to the oxygen content of the enriched air stream of say 45 to 50% oxygen concentration that is used as the feed for a second membrane unit. The approach proposed in this application is to compress the first O₂ enriched permeate stream to a much higher pressure, actually of the same order as the initially compressed air stream, say 14 to 20 ata, and then diffuse this recompressed O₂-rich first permeate stream through a modified membrane system, like that illustrated by Figure 1. In this modified system it is made possible to extract several permeates streams without contaminating one with the other. At the high inlet pressure the membrane amount for achieving the first highly concentrated oxygen stream is quite limited. Then continuing the diffusion, the still high pressure allows diffusion of a second, still interestingly high oxygen content enriched air stream, while the final unitary non-permeated stream is reduced to an oxygen content of about 10% or less. This device, from which several diffusate streams can be taken off, has a blockage around the fiber mass, which prevent co-mingling of the different permeate streams that issue from the membrane of this device.

In this proposed scheme, since all diffused streams have to be compressed up to a considerable pressure, it is important to keep the number of those streams limited. It is therefore proposed to compress the about 50%) oxygen stream, diffuse it in the modified membrane system to yield a first permeate stream of about a 75 to 80% oxygen content stream and a second permeate stream of about 50% oxygen content after which a non-permeated stream results containing less than 10% oxygen. Repeating this with the 75 to 80% oxygen content stream by recompression and diffusion through a third membrane unit (like that illustrated by Figure 2) results in obtaining three different diffusates, now respectively at about 90 to 93%, at about 75 to 80% and at about 50% oxygen content. Again the final non-permeated stream contains less than 10% oxygen.

Based on air a one-stage diffusion normally recovers about 65-70%) of the oxygen content at a concentration of oxygen of about 45 to 50%, while the above three-stage diffusion process results in an oxygen recovery of about 60 to 63%, resulting in a final product of about 90 mole% oxygen concentration.

In the following examples ambient air is deemed to be 21 mole% oxygen and 79 mole% nitrogen at a pressure of 14.7 psia (lata) and be of a 60% relative humidity; lb-moles/hr is abbreviated as MPH; pressure is reported as atmospheres absolute (ata); and the oxygen and/or nitrogen contents of given streams are reported on a mole% basis.

EXAMPLES Example 1

1000 MPH of ambient air (assumed to be 21% oxygen and 79% nitrogen) is compressed in three stages of electrical powered air compressors to a final pressure of 16 atmospheres absolute (ata) with cooling to 100 F after each compression stage. The cool compressed air is diffused through a set of MG-Generon membrane units to produce a permeate stream at 1 ata of 286.76 MPH of 48.36 mole%> oxygen comprising 138.68 lb-moles/hour (MPH) of oxygen (equivalent to 48.3 MTPD). Also produced is a non-permeate stream at about 14 ata of 713.24 MPH, containing 10 mole% or 71.32 MPH of oxygen. The oxygen recovery in the permeate stream is 138.68/(1000 x 0.21) = 66.04%. Example 2

In this example two stages of gas permeation are employed. The first gas permeation is conducted as an Example 1 to produce a permeate stream and a non-permeate stream as therein described. For the second stage of diffusion, diffuser units are used that allow two permeate streams to be taken off sequentially. The two-stage device is illustrated by Figure 1 hereof.

In operation, the second stage is fed with 286.76 MPH of a compressed 48.36 mole% oxygen-containing stream and it produces a first permeate stream of a concentration of 77.17 mole% oxygen and a second permeate stream of a concentration of 48.36 mole%> oxygen, while the non-permeate stream produced contains about 6 mole% oxygen. The second permeate stream is cycled back into combination with the permeate stream produced by the first membrane unit and this combined oxygen-nitrogen mixture is compressed with interstage cooling to form a stream of 16ata pressure and 100 F temperature and is fed to the second membrane unit. Example 3

In this example three stages of gas permeation are employed. The first gas permeation stage is conducted as described in Example 1 to produce a permeate stream and a non-permeate stream as therein described.

A second diffuser unit is employed which is like that described and illustrated by Fig. 1 hereof, and provides for a first and second point of permeate stream take-off such that the gas constituents of the first and second permeate streams will not comingle one with another. The non-permeate stream composition resulting as a product of the take-off of a first and a second permeate stream from this second diffuser device do comingle and exit the device as a unitary non-permeate stream.

Following the second diffuser unit, a third diffuser is provided which is a membrane unit like Fig. 2 take-off of three permeate streams. In operation, as illustrated in Figure 3, the feed to the second diffusers unit comprises the permeate stream taken from the first diffuser unit as in Example 1 - namely the 48.36% oxygen enriched air comprising 138.68 MPH oxygen and 148.08 MPH nitrogen at about 1 ata — together with the second permeate stream taken from the second diffuser unit and the third permeate stream taken from the third diffuser unit. The three permeate streams, being of a pressure of about 1 ata are first combined and then compressed in stages with interstage cooling to 100 F. to a final pressure of about 16 ata and this mixture is then fed to the second diffuser unit.

As take-off streams the second diffuser unit produces a first permeate stream at 1 ata of 182.54MPH of 77.17% oxygen enriched air comprising 140.86 MPH oxygen and 41.67 MPH nitrogen; a second permeate stream at 1 ata of 118.26 MPH of 48.36% oxygen enriched air comprising 57.19 MPH oxygen and 61.07 MPH nitrogen; and a non-permeate stream at about 14 ata of 6% oxygen comprising 7.45 MPH oxygen and 116.69 MPH nitrogen.

The first permeate stream of the second diffuser unit is combined with the second permeate stream of the third diffuser unit, is compressed to about 16 ata with interstage cooling to 100 F, and then fed to the third diffuser unit to produce as a first permeate stream 141.70 MPH of 91.72% oxygen enriched air comprising 129.97 MPH oxygen and 11.73 MPH nitrogen. The second permeate stream from this third diffuser unit is produced at a total of 30.74 MPH as a 77.16%) oxygen enriched air comprising 23.72 MPH oxygen and 7.02 MPH nitrogen. The third permeate stream from this third diffuser unit is produced at a total of 19.92 MPH as a 48.36% oxygen enriched air comprising 9.63 MPH oxygen and 10.29 MPH nitrogen. The non-permeate stream from this third diffuser is produced at 14 ata in a total of 20.92 MPH as a 6% oxygen stream comprising 1.25 MPH oxygen and 19.67 MPH nitrogen.

The non-permeate gas compositions of the diffuser units are combined and the so combined non-permeate stream comprising 858.30 MPH total (80.02 MPH oxygen and 778.27 MPH nitrogen) at 14 ata is fed to a gas expansion turbine wherein the expansion through the expansion turbine produces 2,681 BHP of output power.

In this Example the compression duties required in the oxygen generation process are 1663 BHP for initial compression of 1000 MPH air as feed for the first diffuser unit; 707 BHP for recompression of the three permeate streams which form the total feed to the second diffuser unit; and 355 BHP for recompression of the two permeate streams which form the feed to the third diffuser unit. Total compression duties are thus 2725 BHP. The additional output power generated by expansion of the combined non-permeate streams of the first and second diffuser units through the expansion turbine is 2,681 BHP. The third stage is fed with a pressurized 77.17 mole%> oxygen containing stream. It produces three permeate streams, respectively, from the second and the third stage. This combined stream is also compressed to abut 16 ata.

The following Table 1 shows the size of the different streams. The final 91.72 mole% oxygen stream contains 141.70 MPH of gas, containing 129.98 MPH oxygen or 61.89%) of the total oxygen in the original compressed air feed stream. Also given in Table 1 is the compression duties required as brake horsepower (BHP) values.

Table 1

The foregoing disclosure and description of the invention are illustrative and explanatory thereof, and various changes in the details of the illustrated apparatus and construction and method of operation may be made without departing from the spirit of the invention.

Claims

CLAIMS What is claimed is:

1. A process for producing a gas composition which is highly enriched in oxygen compared to air, comprising the steps of: diffusing pressurized gas compositions predominantly composed of oxygen and nitrogen through a sequence of at least two membrane units having hollow fiber membranes which are preferential for permeation of oxygen compared to nitrogen and wherein each successive membrane unit has a number of non-communicating permeate gas zones that is greater than the number of permeate gas zones of a preceding unit of the sequences such that the number of permeate gas composition streams increases progressively through the sequence whereby the first unit produces one permeate gas composition (IP) and a non-permeate gas composition (INP) and the second unit produces a first permeate gas composition (2P1), a second permeate gas composition (2P2) and a non- permeate gas composition (2NP) wherein by compressing air in conjunction with heat exchange of such compressed air during and/or after it compression a compressed air stream of 1 10 F or less at a pressure substantially exceeding atmospheric pressure is formed as feed to a first membrane unit which operates to produce a permeate gas composition (IP) containing from about 45 to about 50 mole % oxygen, and a non-permeate gas composition (2ND) containing 12 mole% or less oxygen; combining the first unit permeate gas composition (IP) with a second permeate gas composition (2P2) from the second membrane unit and compressing the combined permeate gas compositions in conjunction with heat exchange during and/or after compressing to form an oxygen-nitrogen gas mixture at 110 F or less and at a pressure substantially exceeding atmospheric pressure as feed for the second membrane unit which operates to produce a first permeate gas composition (2P1) containing from about 73 to about 80 mole%> oxygen, a second permeate gas composition (2P2) containing from about 45 to about 50 mole% oxygen, and a non-permeate gas composition (2NP) containing 12 mole% or less oxygen.

2. A process for producing a gas composition which is highly enriched in oxygen compared to air, comprising the steps of: diffusing pressurized gas compositions predominantly composed of oxygen and nitrogen through a sequence of three membrane units having hollow fiber membranes which are preferential for permeation of oxygen compared to nitrogen and wherein each successive membrane unit has a number of non-communicating permeate gas zones that is greater than the number of permeate gas zones of a preceding unit of the sequences such that the number of permeate gas composition streams increases progressively through the sequence whereby the first unit produces one permeate gas composition (IP) and a non-permeate gas composition (INP), the second unit produces a first permeate gas composition (2P 1 ), a second permeate gas composition (2P2) and a non- permeate gas composition (2NP) and the third unit produces a first permeate gas composition (3P1), a second permeate gas composition (3P2), a third permeate gas composition (3P3) and a non-permeate gas composition (3NP), wherein by compressing air in conjunction with heat exchange of such compressed air during and/or after it compression a compressed air stream of 110 F or less at a pressure substantially exceeding atmospheric pressure is formed as feed to a first membrane unit which operates to produce a permeate gas composition (IP) containing from about 45 to about 50 mole % oxygen, and a non-permeate gas composition (2ND) containing 12 mole%> or less oxygen; combining the first unit permeate gas composition (IP) with a second permeate gas composition (2P2) from the second membrane unit and with a third permeate gas composition (3P3) of the third membrane unit and compressing the combined permeate gas compositions in conjunction with heat exchange during and/or after compressing to form an oxygen-nitrogen gas mixture at 110 F or less and at a pressure substantially exceeding atmospheric pressure as feed for the second membrane unit which operates to produce a first permeate gas composition (2P1) containing from about 73 to about 80 mole% oxygen, a second permeate gas composition (2P2) containing from about 45 to about 50 mole%> oxygen, and a non-permeate gas composition (2NP) containing 12 mole% or less oxygen; combining the first permeate gas composition (2P1) of the second membrane unit with a second permeate gas composition (3P2) of the third membrane unit and compressing the combined permeate gas compositions in conjunction with heat exchange during and/or after compressing to form an oxygen-nitrogen gas mixture at 110 F or less and at a pressure substantially exceeding atmospheric pressure as feed for the third membrane unit which operates to produce a first permeate gas composition (3P1) containing from about 88 to about 93 mole% oxygen; a second permeate gas composition (3P2) containing from about 73 to about 80 mole%> oxygen; a third permeate gas composition (3P3) containing from about 45 to about 50 mole%> oxygen; and a non-permeate gas composition (3NP) containing 12 mole%> or less oxygen.

3. The process of claim 1 wherein said gas compositions of oxygen and nitrogen that are compressed are compressed to a pressure of from about 8 to about 20 ata.

4. The process of claim 2 wherein said gas compositions of oxygen and nitrogen that are compressed are compressed to a pressure of from about 8 to about 20 ata.

5. A device comprising: a hollow fiber bundle within a bundle housing, wherein the hollow fiber bundle is constrained at each end of said housing within a polymer block so as to provide for gas to bores of the fiber bundle, and further comprising at one or more intermediate points between said ends of the housing a blockage within said housing which occupies interstitial spaces between individual fibers of said bundle to segregate the interior space of said housing into two or more zones to prevent comingling of permeate gases therebetween.