Flow regulated pressure swing adsorption system

Abstract

pressure swing adsorption (PSA) separation of a gas mixture is performed in an apparatus with a plurality of adsorbent beds. The invention provides rotary multiport distributor valves to control the timing sequence of the PSA cycle steps between the beds, with flow controls cooperating with the rotary distributor valves to control the volume rates of gas flows to and from the adsorbent beds in blowdown, purge, equalization and repressurization steps.

Description

This optimal ratio would take lower values of
(P_INT−P_L)/(P_H−P_L)=0.15 to 0.20
when the first component is more strongly adsorbed than nitrogen, as the case of hydrogen purification from a H₂/CO₂ mixture, with carbon dioxide the strongly adsorbed second component.

It will be seen from FIG. 7 that (P_INT−P_L)/(P_H−P_L)=0.2 at the value 267 of the time function, at which point the equalization and depressurization steps are each about 95% complete in approaching the terminal pressure of that step.

For identical step time intervals “t” of these steps, as is obtained with the cycle timing of FIGS. 5 and 6 (and also the timing of FIG. 9, but not for the timing of FIG. 4), the orifice areas “A” of orifices 96-98 should therefore be approximately equal. For FIGS. 5 and 6, it may be noted for each of the light reflux steps nominally

t=T/12,

since the step angular interval is 30°. The pressure drop resistance of each of the three light reflux steps should be substantially equal for the cycle of FIGS. 5 and 6 so that the desirable pressure transient curves of FIG. 7 will be attained with a nominal step time interval defined by time 267. Furthermore, equal adjustment of flow control valves 61-66 will not significantly upset the balance of pressure changes between the cocurrent and countercurrent blowdown steps in FIGS. 5 and 6.

Hence, the orifices 96-98 (once adjusted to approximately an equal effective area “A”) need not be further adjustable for the cycles of FIGS. 5 or 6, since flow control of light reflux steps can be provided by coordinated actuation of valves 61-66.

An important process embodiment of the present invention is thus to establish equal time intervals for each of the light reflux steps (equalization, cocurrent blowdown to purge, and product repressurization) by the porting of the second distributor valve, and then to provide coordinated actuation of flow controls (e.g. valves 61 to 66) between the second end of each bed and the second distributor valve, so as to achieve at any operating cycle frequency of the process substantial completion of the pressure equalization step while avoiding excessively rapid rate of pressure change, and while maintaining the ratio

0.1<(P_INT−P_L)/(P_H−P_L)<0.3, or preferably

0.15<(P_INT−P_L)/(P_H−P_L)<0.25.

With flow control valves 61-66 fully open, and orifices 96-98 also open with flow area “A”, the cycle of FIG. 5 can be operated at maximum cycle frequency for the given pressure ratio P_H/P_L to achieve pressure transient curves for the light reflux steps similar to FIG. 6. The cycle cannot be operated at higher frequency, except by lowering the pressure ratio P_H/P_L.

If the cycles of FIG. 5 or 6 are operated at lower frequency at the same pressure ratio PH/PL, the effective orifice flow area “A” must be adjusted in substantially inverse ratio to the step time interval “t” or cycle period “T”, so that the step time coefficient 267 is approximately constant. If the cycle period were increased by e.g. a factor of two without adjusting the effective “A” by a factor of ½, the cocurrent blowdown would be continued too far so P_INT would be much too low and the countercurrent blowdown step would be nearly eliminated, resulting in loss of purification and recovery performance for the light product.

Since the cycles of FIGS. 5 and 6 operate well with equal “A” for each light reflux step, it is immaterial to performance whether the effective “A” is controlled by adjusting the orifices 96-98 or the flow controls 61-66. In practice, the orifices 96-98 on the rotor within the second distributor valve are less conveniently controlled operationally, so flow controls 61-66 have been provided for more convenient operator control access. For these cycles, operational adjustability of orifices 96-98 may not be required, once the apparatus has been assembled with correct adjustments for a given application.

In the cycle of FIG. 4, the light reflux steps have unequal time intervals. The duration of the cocurrent blowdown step is twice as long (T/6) as the duration of the equalization and repressurization steps. Therefore, orifice 98 throttling the countercurrent blowdown step should have an effective flow area “A” (after lumped inclusion of other pressure drops between the second ends of beds exchanging gas in light reflux steps in the effective orifice area) only half the effective orifice flow area associated with orifices 97 and 96 throttling the equalization and repressurization steps respectively.

When the light reflux orifices are to be used for flow adjustment, it may be noted that the most critical adjustment is that of orifice 98 controlled countercurrent blowdown flow because maladjustment of that orifice for any operating cycle frequency will upset the desirable value of P_INT, so that the countercurrent blowdown may be too large or too small. If P_INT is too high because orifice 98 is too restrictive, the countercurrent blowdown will be relatively large while the resulting small cocurrent blowdown will release only a small volume of purge gas. If P_INT is too low because orifice 98 is too open, the countercurrent blowdown may be too small, compromising purity.

One simplification within the invention is to use fixed orifices 96 and 97 on the less critical equalization and repressurization steps, while using an adjustable orifice 98 to regulate the more critical countercurrent blowdown. This approach is especially suitable for the cycle of FIG. 4, having a slow countercurrent blowdown which is more sensitive to control as has been verified in experimental prototypes of the invention.

The above discussed control characteristics have been verified experimentally with prototypes, using six beds with valve timing according to FIG. 4 or FIG. 9. It was found that maladjustment of the flow controls could render the process inoperative, while satisfactory performance in hydrogen purification and oxygen concentration applications was demonstrated, with the orifices adjusted for each operating condition to achieve the pressure transients as depicted in FIG. 7.

FIGS. 8 and 9

FIG. 8 shows another embodiment 300 of a six bed PSA apparatus with several alternative features of the invention. Component numbering and nomenclature are similar to FIG. 1, except as noted below. Like FIG. 1, FIG. 8 schematically shows all bed ports and function ports of the first and second distributor valves, and likewise does not show the geometry of the ports relative to the axis of each valve. FIG. 9 shows timing diagrams and the pressure waveform for apparatus 300.

Apparatus 300 is configured to deliver the light product gas through the second distributor valve. Light product gas, enriched in the second component, is delivered by second function port 90, during the feed step of each adsorbent bed, and by light product delivery conduit 301 to optional light product compressor 302. Light product compressor with its downstream load provides means to regulate the pressure and flow of the light product gas. To avoid undesirable pressure reduction below the higher pressure of the light product gas, non-return valves 310-315 are provided in parallel with each of flow control valves 61-66. The non-return valves enable gas enriched in the second component to flow from the adsorbent beds to the second distributor valve with minimal pressure loss, while light reflux gas flowing back from the second distributor valve to the adsorbent beds may be throttled by the flow control valves 61-66.

Apparatus 300 illustrates alternative means of introducing a second feed gas, having a higher concentration in the first component than the feed gas. Instead of an external feed selector valve admitting alternating pulses of the feed and a second feed (or heavy reflux), a second feed supply conduit 326 introduces the second feed directly to second feed transfer chamber 327 between rotor 40 and stator housing 38. Transfer chamber 327 is isolated from feed transfer chamber 127 by rotary seal 328, and communicates to second feed port 350 on valve surface 45. Second feed port 350 follows feed port 50 in the timing sequence of first function ports 355 on first distributor valve timing diagram 360 of FIG. 9. Second feed port 350 corresponds to second feed port 226 in FIG. 6.

The second feed gas is admitted to the adsorbent beds in the latter portion of the feed step, or in a second feed step as provided in FIG. 6, after the admission of the feed gas less concentrated in the first component than the second feed gas. The sequential admission of feed gas increasingly concentrated in the first component helps to provide a rising concentration of the first component toward the first end of the adsorbent beds, and of the second component toward the second end of the adsorbent beds.

The process aspect here is supplying the feed gas mixture during the initial part of high pressure step (A) to the first end of the adsorbent bed, and then supplying a second feed gas with a greater concentration of the first component during the later part of step (A) to the first end of the adsorbent bed.

The second feed gas may be heavy reflux gas diverted from the exhaust gas and recompressed, as discussed for the embodiment of FIG. 1. Alternatively, the second feed gas may be another gas mixture, leaner in the second component than the first feed gas mixture. This principle may readily be generalized to a plurality of feed gases, each admitted in ascending order of concentration in the first component or declining order of concentration in the second component. Thus, in hydrogen recovery from refinery waste gases, there may be a multiplicity of feed gases with differing concentrations of hydrogen as the second component.

Apparatus 300 also includes provision in the second distributor valve for a second equalization step of the process. An additional light reflux withdrawal port 391 is provided, communicating through adjustable orifice 392 in rotor 80 to light reflux return port 394. The timing of ports 391 and 394 is shown in function port sequence 395 of second distributor valve timing diagram 396 of FIG. 9. The second equalization step includes depressurization of one bed from P_EQ1 to approach P_EQ2, exchanging light reflux gas as indicated by arrow 399 to another bed being pressurized from P_L to approach P_EQ2.

FIG. 10

As the adjustable orifices in the rotor of the second distributor valve are enclosed within a rotor and behind both dynamic and static seals, their operational adjustment presents challenges, particularly when the PSA system is purifying dangerous gases such as hydrogen. Hence the invention provides means for their adjustment.

FIG. 10 is a schematic drawing of an alternative second distributor valve 400 with control means for the adjustable orifices of the rotor as configured for embodiment 1 of FIG. 1. Adjustable orifices 96-98 are provided as throttle valves mounted in rotor 80, each with identical or similar external actuation means, described here in detail for adjustable orifice 97. Light reflux withdrawal port 91 communicates by conduit 401 to upstream valve chamber 402. Chamber 402 is penetrated by valve stem 405 with coaxial needle 406 aligned with valve seat 408. The adjustable throttle valve orifice is defined between needle 406 and seat 408, and provides fluid communication with downstream valve chamber 410 which in turn communicates by conduit 412 to light reflux return port 94.

Drive end 414 of valve stem 405 is isolated from process fluid by seal 415, and is provided with a drive pin 416 penetrating a drive slot 417 in rotor 80. Slot 417 has axial clearance for pin 416, sufficient for movement of stem 405 with needle 406 to adjust the orifice area between the needle and valve seat 408. Drive pin 416 projects clear of rotor 80 to roller 418 on drive pin 416, engaging circumferential thrust collar 420. Thrust collar 420 is slidably mounted for axial motion concentric to axis 83 in stationary guide 421, which is a coaxially concentric extension of stator housing 78 external of rotary seal 422. Actuation pin 424 on thrust collar 420 penetrates slot 425 in guide 421, and is coupled to linear actuator 430. Thus, linear motion of actuation pin 424 by actuator 430 is directly transmitted through thrust collar 420 and drive pin 416 to shift the valve stem.

Rotary seal 422 seals chamber 435 between rotor 80 and stator housing 78. Rotor 80 has a diameter 436 greater than the sealing diameter of rotary seal 422. Chamber 435 communicates with light reflux withdrawal port 90 so as to pressurize chamber 435 to substantially the higher pressure, thus providing gas loading means urging of rotor 80 onto valve surface 85. Mechanical valve loading means may also be provided by spring 438 loading thrust washer 439 onto rotor 80.

FIG. 11

An alternative embodiment 450 of the second distributor valve uses fluid transfer chambers between the rotor 80 and the stator housing 78, so that the adjustable orifices can be provided as throttle valves external to the stator housing.

On a common sealing diameter, rotary seals 451, 452, 453, 454 and 455 mutually isolate chamber 107 communicating in rotor 80 to light reflux withdrawal port 90 at substantially the higher pressure, transfer chamber 461 communicating to light reflux return port 93, transfer chamber 462 communicating to light reflux withdrawal port 91, transfer chamber 463 communicating to light reflux return port 94, transfer chamber 464 communicating to light reflux withdrawal port 92, and chamber 109 communicating to light reflux return port 95 at substantially the lower pressure. Adjustable orifice 96 is provided as throttle valve 471 communicating through stator housing 78 to chambers 107 and 461. Adjustable orifice 97 is provided as throttle valve 472 communicating through stator housing 78 to chambers 462 and 463. Adjustable orifice 98 is provided as throttle valve 473 communicating through stator housing 78 to chambers 464 and 109.

FIG. 12

Several refinements for providing flow control to minimize peak gas flow velocities, or to increase the average flow velocity in each step, are now discussed.

One such refinement is to oscillate the angular velocity of the first rotary distributor valve, to extend its open periods. With reference to FIG. 1, FIG. 12 provides an example of first valve drive means 41 and synchronizing linkage 152, here provided as a gear train 500 coupling motor 155 through variable speed drive 154 to shaft 42 turning rotor 40 in stator housing 38. Shaft 42 carries gear 501, driven by pinion 502 on lay shaft 503. The gear reduction ratio from shaft 503 to shaft 42 is 6:1 for the example of a PSA system with six adsorbent beds, or more generally N:1 for N adsorbent beds in parallel. Variable speed drive 154 drives output shaft 508, which is coupled to lay shaft 503 by a pair of noncircular or elliptical gears 505 and 506. Elliptical gears 505 and 506 have the same number of teeth.

By selecting readily available elliptical gears whose maximum pitch radius is twice the minimum pitch radius, constant rotary speed operation of shaft 508 will result in a variation of the instantaneous angular velocity of shaft 503 from half that of shaft 508 to twice that of shaft 508, or over a range of 4:1. Hence the instantaneous angular velocity of first rotary valve shaft 42 will also vary through a 4:1 ratio, with six maxima and six minima per complete revolution.

The apparatus for “N” adsorbent beds in parallel has drive means including angular velocity variation means to vary the angular velocity of the rotor of the first distributor valve at a multiple “N” times the cycle frequency, so as to extend the time interval during which a function port is substantially fully open to each bed port, and to reduce the time interval during which that function port is substantially closed to any bed port, while maintaining the minimum angular velocity of the rotor to be greater than zero throughout the cycle so as to avoid excessive wear due to stopping and restarting rotation. The angular velocity variation means may be provided as a pair of noncircular gears in the drive train to the first distributor valve.

The angular phase of shaft 42 with respect to the angular velocity oscillations generated by the pair of elliptical gears will be set so that the angular velocity of rotor 80 is low while the first bed ports and first function ports are mutually opened, while the angular velocity will be high while the ports are closed and switching. Hence, the time during which the valve ports are nearly fully open will be maximized, while the time during which the valve ports are closed or nearly closed will be minimized. Since the minimum angular velocity of the rotor is well above zero, rapid wear due to stick-slip conditions (that would result from intermittent rotation with intervals of completely stopped rotation) is avoided.

By minimizing the duration of low flow valve switching time intervals, this feature enhances productivity of the adsorbent beds and of the distributor valve. It will be seen that the described gear train is means to vary the angular velocity of the valve rotor, so as to extend the time interval during which a function port is substantially fully open to each bed port, and to reduce the time interval during which that function port is substantially closed to any bed port, while maintaining a finite angular velocity of the rotor throughout the cycle.

It will be evident that other mechanisms could be used to vary the angular velocity of the distributor valve rotor, N times per cycle period, with correct phase to extend the duration of open intervals. This description has focused on the first distributor valve, whose function steps have an angular interval equal to the angular spacing between first bed ports. Oscillating the angular velocity of the second distributor valve is less advantageous, as some of its function steps may have much shorter angular interval than the bed port angular spacing. The first distributor valve typically must carry much larger flows than the second distributor valve, and hence can benefit substantially from the oscillatory angular velocity feature.

A further refinement is to adjust the phase relationship and angular velocity profile, so that the distributor valve opens relatively slowly and closes relatively quickly. This feature will provide increased throttling between partly open ports at the beginning of equalization, blowdown or repressurization steps. At the beginning of those steps, the driving pressure difference is greatest, so increased throttling then can usefully reduce peak velocities.

The principle of asymmetric throttling over the distributor valves, with stronger throttling at the beginning relative to the end of pressurization, equalization and blowdown steps, can also be achieved by shaping the valve ports. Thus, purge exhaust port 52 of FIG. 5 is shown with a narrow tapered leading edge 224, so that bed ports 30-35 will open gradually to port 52 with initially a small open orifice for relatively more intensive throttling, gradually opening to the maximum port orifice, and then after the open interval will close relatively abruptly. It can be seen from FIG. 6 that greater throttling at the early part of each step, progressively opening the valve ports to the fully open orifice area toward the end of the step, will make the flow more uniform through most of the step, except at the extreme beginning and end.

Another desirable refinement in larger scale applications is to make the lands between function ports somewhat narrower than the width of the bed ports, so that flow between the function port and bed ports is never completely closed. With a brief time interval of each function port being slightly open (with substantial throttling) to two beds, cross-port leakage between beds will be small, while flow pulsations and valve opening/closing time intervals will be reduced.

FIGS. 13 and 14

The rotary distributor valves discussed above have used gas pressure or compression spring (e.g. mechanical spring) loading systems concentric to the valve rotary axis, to ensure close contact between the rotor and stator at the valve surface. When the valve has N bed ports and its function ports spaced over 360°, so that one rotation of the rotor corresponds to one cycle of the process, it is unbalanced (as will be evident from FIGS. 2 and 3) because the higher and lower pressure function ports are on opposed sides of the axis. As a result of the imbalance, high contact pressures will be established between the rotor and the stator adjacent the lower pressure function ports. Radial balance is more important for the first distributor valve, as it is typically larger than the second distributor valve.

FIGS. 13 and 14 show an alternative embodiment 600 of the first distributor valve in which approximate radial balance of the contact pressure distribution on the valve surface 45 is achieved by communicating the pressure distribution on the valve surface to a plurality of axially aligned loading pistons 601-607 disposed in a coaxial annular ring around the axis 43 within the valve rotor at a radius approximately equal to or somewhat greater than the radius of the function ports. Each of the pistons 603-607 is pressurized by the local pressure at its axially projected position on the valve surface (typically corresponding to a function port), and is sealed by a piston ring 608 in a cylinder 613-617 in rotor 40, with each cylinder parallel to axis 43. The loading pistons are reacted on a rotating thrust plate 620, bearing against stationary thrust pad 621 of self-lubricating material. Thrust pad 621 is supported within stator housing 38, normal to the axis of rotation. Each of the loading pistons is located by a thrust socket 622 in thrust plate 620, thus forcing corotation of the thrust plate with the rotor.

FIG. 13 is a schematic drawing of valve embodiment 600, showing all of the bed ports and function ports, which would in fact be at a single radius from axis 43 as shown in FIG. 14. Likewise, FIG. 13 shows all of the loading pistons, which would be at a single radius substantially identical to or somewhat greater than the radius of the function ports from axis 43. FIG. 14 is section 623-624 of FIG. 13, and shows the annular pattern of the loading pistons at a somewhat greater radius and concentric with the function ports 50, 51 and 52. At the same radius as the function ports, pressure sensing ports 625, 626 and 627 (corresponding to positions in the valve surface lacking a function port) are positioned at 60° spacing from each other or from adjacent function port centers. Port 51 communicates to countercurrent blowdown flow control valve 132 via conduit 131 and transfer chamber 130, and by conduit 631 to cylinder 613. Port 625 communicates by conduit 634 to cylinder 614. Port 50 communicates by conduit 635 to cylinder 615, and to feed supply conduit 126 via transfer chamber 127. Port 626 communicates by conduit 636 to cylinder 616. Port 627 communicates by conduit 637 to cylinder 617. Purge exhaust port 52 communicates by conduit 640 to blank cylinder 641, communicating with chamber 642 between the rotor and the thrust plate 610, and thence to exhaust conduit 121, which by conduit 643 vents annular chamber 644 between the stator 36 and seal 112. No piston is needed in cylinder 641, since that cylinder is vented to the lower pressure.

Embodiment 600 of the first distributor valve is energized by the externally imposed pressure difference between the higher pressure in conduit 126 and the lower pressure in conduit 121. The axial thrust load exerted by the ring of annular pistons approximately balances the pressure distribution on the valve surface, so that excessively high contact pressures can be avoided.

FIG. 15

Another embodiment 700 of the distributor valves, here illustrated for a first distributor valve, uses a single eccentric loading device to achieve approximate radial balance of the rotor, while balancing the stator using loading pistons analogous to those used in the rotor of embodiment 600. Components common to first distributor valve 37 of FIG. 1 are denoted with equivalent reference numerals.

Valve embodiment 700 is shown in cross section, taken across the plane of bed conduits 20 and 23 connecting bed port 30 and 33 respectively to beds 2 and 5, which are not shown. Sealing connections between each of the bed conduits in housing 38 and corresponding bed ports in stator 36 are provided by fluid transfer sleeves, with fluid transfer sleeves 710 and 713 shown respectively for bed ports 30 and 33. The fluid transfer sleeves are sealed in the housing and stator by static seals 720 and 721. Compression springs 730 may optionally be provided to urge the fluid transfer sleeves toward the stator. The fluid transfer sleeves engage the stator against rotation relative to housing 38.

It will be evident that each fluid transfer sleeve exerts an axial thrust on the stator, corresponding to the pressure in that bed port acting on the axial area of each fluid transfer sleeve, plus the compression spring forces. Hence, the set of fluid transfer sleeves act like the loading pistons of embodiment 600, thrusting the stator to engage in sealing contact on sealing valve surface 45 against rotor 40. The force distribution will reflect the asymmetric pressure distribution in the bed ports at any instant, and will thus achieve partial balance with the pressure distribution across face 45.

Rotor 40 is rotated by shaft 42, sealed by shaft seal 116 with seal bushing 740. Thrust loads on rotor 40 from the pressure distribution on the valve surface 45 are reacted by a thrust slipper 750 against thrust plate 751 mounted on housing closure 752. The thrust slipper 750 is part of the rotor assembly. Thrust slipper 750 is enabled to move axially to contact thrust plate 751 by sliding or flexing of seal means 756 (which may be a piston ring seal, or a flexing diaphragm or bellows); and is thereby sealed to rotor 40, and is also urged against thrust plate 751 by compression spring 757 (which may be a metallic coil spring or an elastomeric spring, in the latter case possibly integral with a flexing diaphragm seal 756).

Feed port 50 on rotor 40 communicates to chamber 758 interior to thrust slipper 750, while exhaust port 52 communicates to interior chamber 759 of housing 38 external to piston 750. Chamber 758 communicates through the thrust plate 751 and end closure 752 to high pressure feed port 126, while chamber 759 communicates through housing 38 to low pressure exhaust port 121. Thrust plate 751 is secured to end closure 752 by dowels 761 and seal 762. End closure 752 is attached to housing 38 by capscrews 763.

Thrust slipper 750 acts as fluid transfer means to convey feed fluid from the stationary housing to the rotor. The thrust slipper also loads the rotor against the valve surface 45, and hence the diameter of thrust slipper seal 756 must be sufficient to provide an effective piston energized by feed pressure in chamber 758 for positive sealing of the valve surface. With the thrust slipper eccentrically positioned as shown in FIG. 15, radially offset from axis 43 so as to load the valve rotor toward the high pressure feed port and away from the low pressure exhaust port, approximate balance can be obtained of the present distribution in the valve surface. This feature allows the valve to be loaded less heavily than would otherwise be necessary, and thus to operate with smaller internal forces, and with less frictional power loss and heat dissipation.

It is within the scope of the invention to mount thrust slipper concentrically to axis 43. The concentric configuration requires a somewhat larger thrust force (e.g. greater diameter of thrust slipper seal 756) to ensure positive sealing in valve surface 45, and rotor 40 is subject to a greater radial force to be reacted by bushing 740 or other radial bearing.

The clearance space 770 between stator 36, housing 38 and the fluid transfer sleeves may be used as a fluid flow passage, e.g. of countercurrent blowdown gas, in order to achieve enhanced convective cooling of the valve stator and sealing surface.

It will be seen that loading means to establish fluid sealing contact between the rotor and stator is provided by axially aligned fluid transfer sleeves sealing each bed port of the stator and providing fluid communication to the corresponding adsorbent bed of each bed port, with the fluid transfer sleeves having enough axially projected area with optional assistance of compression springs, so as to thrust the stator against the rotor. Alternative or supplementary loading means to establish fluid sealing contact between the rotor and stator are provided by a thrust slipper engaged by axially compliant sealing means to the valve rotor so as to define a chamber pressurized by feed fluid to thrust the rotor against the valve sealing surface.

FIG. 16

Referring back to the embodiment of FIG. 1, flow controls 61 to 66 are adjusted by controller 164 if these flow controls or adjustable orifices are provided as throttle valves, and are to be adjusted continuously while the apparatus is operating, they should be actuated simultaneously so that these flow controls present substantially identical orifice restrictions to light reflux gas flow at any time. Hence, the flow controls 61 to 66 may be ganged together mechanically for simultaneous actuation by controller 164.

FIG. 16 shows a simplified embodiment 800 in which flow controls 61 to 66 are adjustable only between two discrete settings. This discretely adjustable flow control is illustrated for flow control 61, it being understood that the identical device would be applied to flow controls 62 to 66. The adjustable orifice of flow control 61 has a more restrictive setting defined by fixed orifice 801, and a less restrictive setting defined by the combination in parallel of fixed orifices 801 and 802. Orifices 801 and 802 are respectively in conduits 803 and 804 branching in parallel between conduit 55 and second end 14 of bed 2. A two-way selector valve 805 in conduit 804 is actuated by controller 164. When selector valve 805 is open or closed, flow control 61 is respectively at its less or more restrictive setting. With similar two-way selector valves in each of the discretely adjustable flow controls 61 to 66 to switch these flow controls between substantially identical more and less restrictive settings, and simultaneous actuation by controller 164 of all six selector valves, a simplified control is achieved compared to the alternative coordinated actuation of continuously adjustable throttle valves.

The use of two discrete settings for flow controls 61 to 66 will be particularly suitable for applications in which a two speed drive 154 or motor 155 is used to operate the rotary distributor valves at two cycle frequencies. The less restrictive setting of the flow controls would be used at the higher cycle frequency. For a wide range of flow control adjustment, more than two settings may be provided by providing additional orifices in parallel.

It will be appreciated that the above described device of discretely adjustable flow controls or adjustable orifices, with two or possibly more discrete settings established by selector valves opening and closing supplemental orifices in parallel, may be applied to any of the flow controls in the present invention, including flow controls 61 to 66; adjustable orifices 96, 97 and 98; or flow control valve 132.

INDUSTRIAL APPLICABILITY

The present invention is applicable to hydrogen separation, air separation, and to many other gas or vapour separations. The invention overcomes barriers to the technical simplification and economic scale-up of highly efficient and productive gas separation equipment.

An important application is hydrogen recovery from refinery offgases or low BTU syngas. PSA has previously been applied most successfully to purification of hydrogen from hydrogen rich feed streams (such as high BTU syngas generated by steam reforming of methane), typically available at high pressure. PSA has not previously been found economic for recovery of hydrogen from lean or very low pressure feed streams. Demand for hydrogen is rapidly increasing in the petroleum refining industry, while that industry continues to burn large amounts of hydrogen in waste fuel gas streams.

The present invention has been tested experimentally for purification of hydrogen generated by steam reforming of methanol or partial oxidation of methane, and for hydrogen recovery from refinery hydrotreater offgases as well as from tail gas of conventional PSA systems.

A small industrial pilot plant according to the embodiment of FIG. 1 has been operated with a methanol reformer to produce hydrogen of 99.999% purity at flow rates sufficient for a 6 kilowatt fuel cell. A variable speed drive was used to operate the rotary distributor valves. Using the flow controls of FIG. 1, satisfactory operation was established with varying methanol reformate feed flow and pressure over a 4:1 range of cycle frequencies.

The present invention enables the use of simple multiport rotary distributor valves and cooperating flow controls, with adsorbent beds cycled at relatively high frequency, to recover hydrogen from lean and low pressure petroleum refinery offgases.

Typical application objectives are to recover hydrogen from a hydrotreater purge gas containing 30% hydrogen, supplied at a pressure of 8 atmospheres, while discharging tail gas depleted of hydrogen at 2 atmospheres total pressure. With adsorbent beds approximately 1.5 meters deep, containing 8/12 mesh pellets of suitable adsorbent (e.g. 13X zeolite, with a guard layer of alumina dessicant at the first end of the adsorbent beds), it is found that the apparatus of the invention can deliver high purity hydrogen at cycle periods of 20 to 30 seconds. High cycle frequency enables low adsorbent inventory. Having relatively shallow adsorbent beds, this apparatus can be delivered to an application site as a fully assembled modular skid. The small adsorbent inventory and simplified controls enable competitive performance and economics.

The invention may also be applied to concentrate oxygen from atmospheric air, using a zeolite adsorbent on which nitrogen is more readily adsorbed than oxygen at ambient temperature. The higher pressure of the process will be above atmospheric, and the lower pressure may be atmospheric or subatmospheric. Suitable adsorbents include zeolite 13X or 10X. The typically six bed cycles of the present invention achieve higher product recovery than conventional PSA or VSA air separation cycles, while high cycle frequency again enables a low adsorbent inventory.

It will be understood that the different aspects of the present invention may be expressed with much diversity and in many combinations other than the specific examples described above, under the scope of the following claims.

Claims

1. Process for separating first and second components of a feed gas mixture, the first component being more readily adsorbed under increase of pressure relative to the second component which is less readily adsorbed under increase of pressure over an adsorbent material, such that a gas mixture of the first and second components contacting the adsorbent material is relatively enriched in the first component at a lower pressure and is relatively enriched in the second component at a higher pressure when the pressure is cycled between the lower and higher pressures at a cyclic frequency of the process defining a cycle period; providing for the process a number “N” of substantially similar adsorbent beds of the adsorbent material, with said adsorbent beds having first and second ends; and further providing for the process a first rotary distributor valve connected in parallel to the first ends of the adsorbent beds and a second rotary distributor valve connected in parallel to the second ends of the adsorbent ends, with flow controls cooperating with the first and second distributor valves; introducing the feed gas mixture at substantially the higher pressure to the first distributor valve; and rotating the first and second distributor valves so as to perform in each adsorbent bed the sequentially repeated steps within the cycle period of:

(A) supplying a flow of the feed gas mixture at the higher pressure through the first distributor valve to the first end of the adsorbent bed during a feed time interval, withdrawing gas enriched in the second component from the second end of the adsorbent bed, and delivering a portion of the gas enriched in the second component as a light product gas,

(B) withdrawing a flow of gas enriched in the second component as light reflux gas from the second end of the adsorbent bed through the second distributor valve, so as to depressurize the adsorbent bed from the higher pressure toward an equalization pressure less than the higher pressure, while controlling the flow so that the pressure in the bed approaches the equalization pressure within an equalization time interval,

(C) withdrawing a flow of light reflux gas enriched in the second component from the second end of the adsorbent bed through the second distributor valve, so as to depressurize the adsorbent bed from approximately the equalization pressure to an intermediate pressure less than the equalization pressure and greater than the lower pressure, while controlling the flow so that the pressure in the bed reaches approximately the intermediate pressure within a cocurrent blowdown time interval,

(D) withdrawing a flow of gas enriched in the first component from the first end of the adsorbent bed through the first distributor valve, so as to depressurize the adsorbent bed from approximately the intermediate pressure to approach the lower pressure, while controlling the flow so that the pressure in the bed approaches the lower pressure within a countercurrent blowdown time interval,

(E) returning a low of light reflux gas enriched in the second component from the second distributor valve to the second end of the adsorbent bed at substantially the lower pressure, while withdrawing gas enriched in the first component from the first end of the adsorbent bed and through the first distributor valve over a purge time interval, said flow of gas enriched in the second component from the second distributor valve being withdrawn from another of the adsorbent beds which is undergoing cocurrent blowdown step (C) of the process,

(F) returning a flow of light reflux gas enriched in the second component from the second distributor valve to the bed, so as to repressurize the adsorbent bed from approximately the lower pressure to approach the equalization pressure, while controlling the flow so that the pressure in the bed approaches the equalization pressure within an equalization time interval, said flow of gas enriched in the second component from the second distributor valve being withdrawn from another of the adsorbent beds which is undergoing equalization step (B) of the process,

(G) admitting gas to the adsorbent bed, so as to further repressurize the adsorbent bed from the equalization pressure toward the higher pressure, while controlling the flow so that the presence in the bed approaches the higher pressure within a repressurization time interval,

(H) cyclically repeating steps (A) to (G).

2. The process of claim 1, further varying cycle frequency so as to achieve desired purity, recovery and flow rate of the light product gas.

3. The process of claim 1, in step (G) returning a flow of light reflux gas enriched in the second component from the second distributor valve to the bed, so as to repressurize the adsorbent bed to approach the higher pressure, while controlling the flow so that the pressure in the bed approaches the higher pressure within a repressurization time interval, the flow of gas enriched in the second component from the second distributor valve being withdrawn from another of the adsorbent beds which is undergoing feed step (A) of the process.

4. The process of claim 1, in step (G) admitting feed gas from the first distributor valve to the bed, so as to repressurize the adsorbent bed to approach the higher pressure, while controlling the flow so that the pressure in the bed approaches the higher pressure within a repressurization time interval.

5. The process of claim 1, supplying the feed gas mixture during the initial part of step (A) to the first end of the adsorbent bed, and then supplying a second feed gas with a greater concentration of the first component during the later part of step (A) to the first end of the adsorbent bed.

6. The process of claim 5, recompressing a portion of the gas enriched in the first component withdrawn from the first end of an adsorbent bed during step (D) or preferably (E) to substantially the higher pressure, and supplying this portion of the gas enriched in the first component as the second feed gas through the first distributor valve to the first end of the adsorbent bed in the latter part of the feed time interval in step (A).

7. The process of claim 6, providing a feed selector valve to alternatingly direct the feed gas mixture or the heavy reflux gas through the first distributor valve to the first end of the adsorbent bed, and switching the feed selector valve at a frequency “N” times the cycle frequency.

8. The process of claim 1, exchanging light reflux gas enriched in the second component between a bed undergoing step (B) and another bed undergoing step (F) directly through the second distributor valve in substantially identical equalization time intervals for those steps (B) and (F).

9. The process of claim 8, in which the cycle period is approximately the sum of the feed time interval, twice the equalization time interval, the cocurrent blowdown time interval, the purge time interval, and the repressurization time interval.

10. The process of claim 1, further providing adjustable orifices interposed between the second end of each adsorbent bed and the second distributor valve as flow controls cooperating with the second distributor valve, one adjustable orifice being provided for each bed and the orifices being adjusted simultaneously so as to have substantially identical settings at any time, and adjusting the orifices so as to control the flow at the second ends of the adsorbent beds in steps (B), (C), (E), (F) and (G).

11. The process of claim 10, further providing a product delivery check valve for each adsorbent bed communicating from the second end of that adsorbent bed to a light product manifold, and delivering the light product through the product delivery check valves.

12. The process of claim 10, in which the time intervals of steps (B), (C) and (F) are substantially equal, so that the intermediate pressure remains substantially constant as the orifices are adjusted.

13. The process of claim 10, in which the orifices are adjusted by switching between discrete settings.

14. The process of claim 1, further delivering the light product gas through the second distributor valve.

15. The process of claim 1, further providing an adjustable orifice in the second distributor valve as a flow control cooperating with the second distributor valve, and adjusting the orifice so as to control the flow in step (C).

16. The process of claim 1, further providing adjustable orifices in the second distributor valve as flow controls cooperating with the second distributor valve, and adjusting the orifices so as to control the flow at the second ends of the adsorbent beds in steps (B), (C), (E), (F) and (G).

17. The process of claim 1, further providing a flow control cooperating with the first distributor valve to control the flow in step (D) so as to establish the intermediate pressure relative to the higher and lower pressures, such that the ratio of the difference between the intermediate pressure and the lower pressure to the difference between the higher pressure and the lower pressure is in the range of approximately 0.15 to 0.25.

18. The process of claim 1, further controlling the flow in step (A) by establishing the volumetric flow of the feed gas mixture at the higher pressure.

19. The process of claim 1, further controlling the flow in step (A) by regulating the pressure at which the product gas is withdrawn.

20. The process of claim 1, further controlling the flow in each step so as to avoid damaging the adsorbent by transient high flow velocity in the adsorbent bed.

21. The process of claim 1, further controlling the flow velocities in steps (B), (C), (D), (F) and (G) so that the ratio of the peak flow velocity to the average flow velocity in those steps will not exceed approximately 2:1.

22. Apparatus for separating first and second components of a feed gas mixture, the first component being more readily adsorbed under increase of pressure relative to the second component which is less readily adsorbed under increase of pressure over an adsorbent material, such that a gas mixture of the first and second components contacting the adsorbent material is relatively enriched in the first component at a lower pressure and is relatively enriched in the second component at a higher pressure when the pressure is cycled between the lower and higher pressures at a cyclic frequency of the process defining a cycle period, the apparatus including

(a) a number “N” of substantially similar adsorbent beds of the adsorbent material, with said adsorbent beds having first and second ends defining a flow path through the adsorbent material;

(b) light product delivery means to deliver a light product flow of gas enriched in the second component from the second ends of the adsorbent beds;

(c) a first rotary distributor valve connected in parallel to the first ends of the adsorbent beds; the first distributor valve having a stator and a rotor rotatable about an axis; the stator and rotor comprising a pair of relatively rotating valve elements, the valve elements being engaged in fluid sealing sliding contact in a valve surface, the valve surface being a surface of revolution coaxial to the axis, each of the valve elements having a plurality of ports to the valve surface and in sequential sliding registration with the ports in the valve surface of the other valve element through the relative rotation of the valve elements; one of said valve elements being a first bed port element having N first bed ports each communicating to the first end of one of the N adsorbent beds; and the other valve element being a first function port element having a plurality of first function ports including a feed port, a countercurrent blowdown port and a purge exhaust port; with the bed ports spaced apart by equal angular separation between adjacent ports; and with the first function ports and first bed ports at the same radial and axial position on the valve surface so that each first function port is opened in sequence to each of the N first bed ports by relative rotation of the valve elements;

(d) a second rotary distributor valve connected in parallel to the second ends of the adsorbent beds and cooperating with the first distributor valve; the second distributor valve having a stator and a rotor rotatable about an axis; the stator and rotor comprising a pair of relatively rotating valve elements, the valve elements being engaged in fluid sealing sliding contact in a valve surface, the valve surface being a surface of revolution coaxial to the axis, each of the valve elements having a plurality of ports to the valve surface and in sequential sliding registration with the ports in the valve surface of the other valve element through the relative rotation of the valve elements; one of said valve elements being a second bed port element having N second bed ports each communicating to the second end of one of the N adsorbent beds; and the other valve element being a second function port element having a plurality of second function ports including a plurality of light reflux withdrawal ports and light reflux return ports, with each light reflux return port communicating through the second function element to a light reflux withdrawal port; with the bed ports spaced apart by equal angular separation between adjacent ports; and with the function ports and bed ports at the same radial and axial position on the valve surface so that each function port is opened in sequence to each of the N bed ports by relative rotation of the valve elements;

(e) drive means to establish rotation of the rotors, and hence relative rotation of the bed port elements and the function port elements of the first and second distributor valves, with a phase relation between the rotation of the rotors and angular spacing of the function ports of the first and second distributor valves so as to establish for each adsorbent bed communicating to corresponding first and second bed ports the following sequential and cyclically repeated steps at a cycle frequency for those bed ports;

(i) the first bed port is open to the feed port, while light product gas is delivered by a light product delivery means,

(ii) the second bed port is open to a light reflux withdrawal port,

(iii) the first bed port is open to the countercurrent blowdown port,

(iv) the first bed port is open to the purge exhaust port, while the second bed port is open to a light reflux return port;

(f) countercurrent blowdown flow control means cooperating with the first distributor valve;

(g) light reflux flow control means cooperating with the second distributor valve;

(h) feed supply means to introduce the feed gas mixture to the feed port of the first distributor valve at substantially the higher pressure; and

(i) exhaust means to remove gas enriched in the first component from the purge exhaust port of the first distributor valve.

23. The apparatus of claim 22, in which the second function ports of the second distributor valve include light reflux withdrawal ports to withdraw light reflux gas enriched in the second component from beds undergoing feed, equalization depressurization and cocurrent blowdown steps; light reflux return ports to supply gas enriched in the second component to beds undergoing purge, equalization pressurization and repressurization steps; and each light reflux withdrawal port communicates to a light reflux return port through an orifice; so as to establish by rotation of the distributor valve rotors the following sequential and cyclically repeated steps for the adsorbent bed of:

(A) the first bed port is open to the feed port, while the second bed port is open to a light reflux withdrawal port communicating through an orifice to a light reflux return port open to repressurize another bed undergoing step (F) below, and light product gas is delivered from the second end of the adsorbent bed by a light product delivery valve;

(B) the second bed port is open for pressure equalization to a light reflux withdrawal port communicating through an orifice to a light reflux port open to another bed undergoing step (F) below, so as to equalize the pressures of the beds;

(C) the second bed port is open for countercurrent blowdown to a light reflux withdrawal port communicating through an orifice to a light reflux port open for purging to another bed undergoing step (E) below;

(D) the first bed port is open to the countercurrent blowdown port, so as to depressurize the bed to the lower pressure;

(E) the first bed port is open to the purge exhaust port, while the second bed port is open to a light reflux return port so as to receive light reflux gas from another bed undergoing step (C) above;

(F) the second bed port is open to a light reflux return port so as to receive light reflux gas from another bed undergoing step (B) above for pressure equalization; and

(G) the second bed port is open to a light reflux return port so as to receive light reflux gas from another bed undergoing step (A) above for repressurization.

24. The apparatus of claim 23, in which the first bed port is opened to the feed port before light product gas is delivered from the second end of the adsorbent bed by the light product delivery valve, so that repressurization of the adsorbent bed is achieved at least in part by feed gas.

25. The apparatus of claim 23, in which each light reflux withdrawal port communicates to a light reflux return port through an orifice which is an adjustable orifice, provided as light reflux flow control means.

26. The apparatus of claim 23, in which the first bed port element is the stator, and the first function port element is the rotor, of the first distributor valve; and the second bed port element is the stator, and the second function port element is the rotor, of the second distributor valve.

27. The apparatus of claim 26, in which each light reflux withdrawal port communicates to a light reflux return port through an orifice which is an adjustable orifice within the rotor, provided as light reflux flow control means.

28. The apparatus of claim 26, with actuator means to control the adjustable orifice from outside the rotor while the rotor is revolving.

29. The apparatus of claim 28, in which the adjustable orifice is provided as a throttle valve within the rotor, and the actuator means is coupled to the throttle valve through a mechanical linkage.

30. The apparatus of claim 26, in which each light reflux withdrawal port communicates to a light reflux return port through an adjustable orifice which is a throttle valve external to the rotor, with transfer chambers having rotary seals providing fluid communication between the throttle valve and the light reflux withdrawal port, and between the throttle valve and the light reflux return port.

31. The apparatus of claim 26, in which the light reflux control means includes an adjustable orifice or throttle valve interposed between the second end of each adsorbent bed and the second distributor valve, and means to adjust the orifices or throttle valves simultaneously such that each of the adjustable orifices will have substantially identical settings at each time.

32. The apparatus of claim 31, in which each of the adjustable orifices is provided by at least two fixed orifices in parallel, with one of the fixed orifices always open to flow, and another orifice being opened or closed to flow by a selector valve so as to establish respectively less restrictive and more restrictive discrete settings of the adjustable orifice.

33. The apparatus of claim 31, in which the light product delivery means for each adsorbent bed is provided as a check valve enabling flow from the second end of that adsorbent bed to a product delivery manifold.

34. The apparatus of claim 31, in which the light product delivery means is the second distributor valve, provided with a light product delivery port; and a check valve is provided in parallel with each adjustable orifice or throttle valve so as to permit unrestricted flow from the second end of each bed to the second distributor valve.

35. The apparatus of claim 22, with the drive means being a variable speed drive controlled by a cycle frequency controller.

36. The apparatus of claim 22, with the drive means including angular velocity variation means to vary the angular velocity of the rotor of the first distributor valve at a multiple “N” times the cycle frequency, so as to extend the time interval during which a function port is substantially fully open to each bed port, and to reduce the time interval during which that function port is substantially closed to any bed port, while maintaining the minimum angular velocity of the rotor during the cycle to be greater than zero.

37. The apparatus of claim 36, in which the angular velocity variation means is provided as a pair of noncircular gears in the drive train to the first distributor valve.

38. The apparatus of claim 22, in which a function port is shaped so as to provide a gradually opening orifice so as to impose relatively intensive throttling at the beginning of a blowdown, pressurization or equalization step.

39. The apparatus of claim 22, in which the valve surface of a distributor valve is a flat disc normal to the axis of that valve, and with loading means to establish fluid sealing sliding contact between the stator and rotor of that distributor valve.

40. The apparatus of claim 39, in which the loading means is in part provided by compression springs.

41. The apparatus of claim 39, in which the loading means includes a plurality of axially aligned loading pistons disposed in a coaxial annulus within the valve rotor at substantially the radius of the function ports, with each piston communicating to the local gas pressure at its axially projected position in the valve surface, and the pistons reacting against a rotating thrust plate so as to achieve approximate radial balance.

42. The apparatus of claim 39, in which the loading means to establish fluid sealing contact between the rotor and stator is provided by axially aligned fluid transfer sleeves for each bed port of the stator and providing sealed fluid communication to the corresponding adsorbent bed of each bed port, with the fluid transfer sleeves having enough axially projected area so as to thrust the stator against the rotor in sealing contact, with optional assistance of compression springs.

43. The apparatus of claim 42, in which a clearance space between stator and the fluid transfer sleeves may be used as a fluid flow passage to achieve enhanced convective cooling of the valve.

44. The apparatus of claim 39, in which the loading means to establish fluid sealing contact between the rotor and stator is provided by a thrust slipper reacting against a stationary thrust plate and engaged by axially compliant sealing means to the valve rotor so as to define a chamber pressurized by feed fluid to thrust the rotor against the valve sealing surface.

45. The apparatus of claim 44, in which the thrust slipper provides fluid transfer means to convey feed fluid from a stationary housing to the rotor.

46. The apparatus of claim 44, in which the thrust slipper is eccentrically positioned and radially offset from the axis of said rotor toward the high pressure feed port and away from the low pressure exhaust port, so as to balance approximately the pressure distribution in the valve sealing surface.

47. A rotary distributor valve comprising:

a stator housing having a stator housing face, wherein the stator housing face comprises at least three fluid port openings, and a central axis of rotation;

a rotor having a rotor face, wherein the rotor face comprises at least two fluid port openings and a central axis of rotation disposed coaxially with the axis of rotation of the stator housing face;

an intermediate valve element having first and second faces, a central axis of rotation disposed coaxially with the axes of rotation of the stator housing and rotor faces, and a plurality of fluid ports extending between the first and second faces, which fluid ports are aligned with the fluid port openings in one of the stator housing face or the rotor face, wherein the first face of the intermediate valve element faces the rotor face and is in fluidly sealing contact with the rotor face, and the second face of the intermediate valve element faces the stator housing face and is in fluidly sealing contact with the stator housing face; and

loading means operable to exert a sealing force on the rotary valve, which urges the stator housing face and the rotor face towards each other to promote fluidly sealing contact between the rotor and stator housing faces and the first and second faces of the intermediate valve element respectively;

wherein the stator housing face and the rotor face are rotatable relative to each other about their common coaxial axis of rotation;

wherein the rotor additionally comprises at least one fluid passage connecting a first fluid port opening in the rotor face to a second fluid port opening in the rotor face; and

wherein the loading means comprises gas pressure loading means, and the gas pressure loading means is operable to exert distributed variable sealing force around a sealing face of the rotary distributor valve, said distributed variable sealing force being responsive to the distribution of pressure in the fluid port openings in the stator housing face.

48. A rotary distributor valve comprising:

a stator housing having a stator housing face, wherein the stator housing face comprises at least three fluid port openings, and a central axis of rotation;

a rotor having a rotor face, wherein the rotor face comprises at least two fluid port openings and a central axis of rotation disposed coaxially with the axis of rotation of the stator housing face; and

an intermediate valve element having first and second faces, a central axis of rotation disposed coaxially with the axes of rotation of the stator housing and rotor faces, and a plurality of fluid ports extending between the first and second faces, which fluid ports are aligned with the fluid port openings in one of the stator housing face or the rotor face, wherein the first face of the intermediate valve element faces the rotor face and is in fluidly sealing contact with the rotor face, and the second face of the intermediate valve element faces the stator housing face and is in fluidly sealing contact with the stator housing face;

wherein the stator housing face and the rotor face are rotatable relative to each other about their common coaxial axis of rotation;

wherein the rotor additionally comprises at least one fluid passage connecting a first fluid port opening in the rotor face to a second fluid port opening in the rotor face; and

wherein the rotor additionally comprises flow control means to control fluid flow within the at least one fluid passage.

49. The rotary distributor valve according to claim 47 wherein the intermediate valve comprises a stator secured to the stator housing face.

50. The rotary distributor valve according to claim 47 wherein the intermediate valve element fluid ports are aligned with the fluid port openings in the stator housing face, and the intermediate valve element remains rotationally stationary relative to the stator housing face during relative rotation of the stator housing face and the rotor face.

51. The rotary distributor valve according to claim 47 additionally comprising rotary drive means operable to rotate the rotor face and stator housing face relative to each other.

52. The rotary distributor valve according to claim 51 wherein the rotary drive means is operable to vary the speed of relative rotation between the rotor face and stator housing face.

53. The rotary distributor valve according to claim 47 wherein the stator housing face and rotor face comprise metal materials, and the intermediate valve element comprises polymeric or carbon materials.

54. The rotary distributor valve according to claim 47 wherein the valve is a rotary pressure swing adsorption distributor valve.

55. The rotary pressure swing adsorption distributor valve according to claim 54 additionally comprising flow control means to control fluid flow within the at least one fluid passage.

56. The rotary pressure swing adsorption distributor valve according to claim 55 additionally comprising rotary drive means operable to rotate the rotor face and stator housing face relative to each other.

57. The rotary pressure swing adsorption distributor valve according to claim 56 wherein the rotary drive means is operable to vary the speed of relative rotation between the rotor face and stator housing face.

58. The rotary pressure swing adsorption distributor valve according to claim 56 additionally comprising loading means operable to exert a sealing force on the rotary valve, which urges the stator housing face and the rotor face towards each other to promote fluidly sealing contact between at least one of the rotor and stator housing faces and the first and second faces of the intermediate valve element respectively.

59. The rotary pressure swing adsorption distributor valve according to claim 56 wherein the intermediate valve comprises a stator secured to the stator housing face.

60. The rotary pressure swing adsorption distributor valve according to claim 56 wherein the intermediate valve element fluid ports are aligned with the fluid port openings in the stator housing face, and the intermediate valve element remains rotationally stationary relative to the stator housing face during relative rotation of the rotor face and stator housing face.

61. The rotary distributor valve according to claim 60 wherein the intermediate valve element is fixedly attached to the stator housing face.

62. The rotary pressure swing adsorption distributor valve according to claim 56 wherein the stator housing face, rotor face and first and second intermediate valve element faces are configured as surfaces of revolution.

63. The rotary pressure swing adsorption distributor valve according to claim 62 wherein the stator housing face, rotor face and first and second intermediate valve element faces are configured as discs.

64. The rotary pressure swing adsorption distributor valve according to claim 63 wherein the intermediate valve element is a plate.

65. A rotary distributor valve comprising:

a stator housing having a stator housing face, wherein the stator housing face comprises at least three fluid port openings, and a central axis of rotation;

a rotor having a rotor face, wherein the rotor face comprises at least two fluid port openings and a central axis of rotation disposed coaxially with the axis of rotation of the stator housing face;

an intermediate valve element having first and second faces, a central axis of rotation disposed coaxially with the axes of rotation of the stator housing and rotor faces, and a plurality of fluid ports extending between the first and second faces, which fluid ports are aligned with the fluid port openings in one of the stator housing face or the rotor face, wherein the first face of the intermediate valve element faces the rotor face and is in fluidly sealing contact with the rotor face, and the second face of the intermediate valve element faces the stator housing face and is in fluidly sealing contact with the stator housing face;

wherein the stator housing face and the rotor face are rotatable relative to each other about their common coaxial axis of rotation;

wherein the rotor additionally comprises at least one fluid passage connecting a first fluid port opening in the rotor face to a second fluid port opening in the rotor face;

wherein the valve is a rotary pressure swing adsorption distributor valve;

flow control means to control fluid flow within the at least one fluid passage;

rotary drive means operable to rotate the rotor face and stator housing face relative to each other; and

loading means operable to exert a sealing force on the rotary valve, which urges the stator housing face and the rotor face towards each other to promote fluidly sealing contact between at least one of the rotor and stator housing faces and the first and second faces of the intermediate valve element respectively;

wherein the loading means comprises distributed gas pressure loading means, the stator housing face and rotor face each comprise at least six fluid port openings, the intermediate valve element comprises at least six fluid ports, and the rotary drive means comprises an electric rotary drive motor.

66. The rotary pressure swing adsorption distributor valve according to claim 65 wherein the electric rotary drive motor is a variable speed electric rotary drive motor.

67. The rotary pressure swing adsorption distributor valve according to claim 66, wherein the stator housing face and rotor face comprise metal materials, and the intermediate valve element comprises at least one polymeric material.

68. The rotary pressure swing adsorption distributor valve according to claim 67 wherein the intermediate valve element comprises at least one carbon material.