Note: Descriptions are shown in the official language in which they were submitted.
CA 02364881 2001-12-11
~1-
SF.,AL1NG MEANS FOR ROTARX PRESSURE SWING
ADSORPTION APPARATUS
F>ELD OF THE INVENTION
The present invention xelates to an apparatus for separating gas fractions,
from a gas
mixture having multiple gas fractions. In particular, the present invention
relates to a rotary
valve gas separation system having a plurality of rotating adsorbent beds
disposed therein for
implementing a pressure swing adsorption pxocess for separating out the gas
fiactions_
l0 BACKGROUND OF THE llWENTION
Pressure swing adsorption (PSA) and vacuum pressure swing adsorption (vacuum-
PSA)
separate gas fractions from a gas mixture by coordinaxiag pressure cycling and
Ilow reversals
over an adsorbent bed which preferentially adsorbs a more readily adsorbed
component relative
to a less readily adsorbed componentof the mixture. The total pressure of the
gas mixture in the
adsorbent bed is elevated whit a the gas mixture is flowing through the
adsorbent bed from a first
end to a second etrd thereof, and is reduced while the gas mixture is flowing
thmugh the
adsorbent from the second end back to the trst end. As the PSA cycle is
repeated, the less
readily adsorbed wmponent is concentrated adjacent the second end of the
adsorbent bed, while
the more readily adsorbed component is concentrated adj scent the first egad
of the adsorbent bed.
As a result, a "light" product (a gas fraction depleted in the more xeadily
adsorbed component and
enriched in the less ~readxly adsorbed component) is delivered fmm the second
end of the bed, and
a "heavy" product (a gas fraction enriched in the more strongly adsorbed
component) is
exhausted from the $rst end of the bed.
The conventional system for implementing pressure swing adsorption or vacuum
pressure
swing adsorption uses two ormore stationary adsorbent beds iriparallel, with
directional valuing
at each end of each adsorbent bed to connect the hods in alternating sequence
to pressure sources
and sinks. However, this system. is often di~cult and expensive to implement
due to the
complexity of the valuing required.
Furthermore, the conventional PSA system makes inefficient use of applied
energy,
because feed gas pressurization is provided by a compressor whose delivery
pressure is the
highest pressure of the cycle. Iri PS,A, energy expended an. compressing the
feed gas used for
pressurization is then dissipated in throttling over valves over the
instantaneous pressure
difference between the adsorber and the high pressure supply. Similarly, in
vacuum-PSA, whew
CA 02364881 2001-12-11
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the lower pressure of the cycle is established by a vacuum pw~np exhausting
gas at that pressure,
eneigy is dissipated in throttling ova valves during counteTciurentblawdown of
adsorbers whose
pressure is.being roduced. A further enertgy dissipation in both Systems
occurs in throttling of
light reflex gas used for purge, equalization, cocurrent blowdown and pmduct
pressurization or
backfill steps.
Numerous attempts have been made at ovateoming the deficiencios associated
with the
conventional PSA system, For examples, Siggelin (U.S. Patent No. 3,176,446),
Marries (CJ.S.
Patent No. 4,452,612), Davidaon and Lywood (U.S. Patent No. 4,758,253), Boudet
et al (U.S.
Patent No. 5,133,784), Petit et al (U.S. Patent No. 5,441,559) and Sehastz
(PCT publication WO
94/04249) disclose PSA devices using rotary distributor valves having rotors
fitted withmultiple
angularly sepata~d adsorb~t beds. Ports communicating with the tutor-mounted
adsorbent beds
sweep past fixed ports for feed admission, product delivery and pressure
equalization. However,
these prior art rotary distributor valves are impracticable for large PSA
units, owing to the weight
of the rotating assembly. Furthermore, since the valve faces are remote from
the ends of the
adsorbent beds, these rotary distributor valves have considerable dead volume
for flow
distribution and eollocti,,on. As a result; the prior art mtary distributor
valves have poor flow
distribution, particularly at high cycle frequencies.
Hay (U.S. Pat. No. 5,246,676) and Engler (U.S. Pat. No. 5,393,326) provide
examples
of vacuum pressure swing adsorption systems which reduce throttling losses in
an attempt to
improve the efficiency of the gas separation process system. The systems
taught by Hay and
Engler use a plurality of vacuum pumps to pump down the pressure of each
adsorbent bed
sequentially in turn, with the pumps operating at successively lower
pressw~es, so that each
vacuum pump reduces the pressure in each bed a predetermined amount. However,
with these
systems, the vacuum pumps ate subj acted to large pressure variations,
stressing the compression
machincsy and causing large fluctuations in overall;power demand. Because
centrifugal or axial
compression machix~eiy cannot operate under such unsteady conditions, rotary
lobe machines are
typically used in such systems. However, such machines have lower efficiency
than modern
centrifugal compressors/vacuum pumps worlang under steady conditions.
Accordingly, there re~naina a need for a PSA system which is suitable for high
volume
end high frequency production, while reducing the losses associated with the
prior art devices.
SL~N~tARY OF THE INVENTION
According to the invention, there is provided a P5A gas separation system
which
CA 02364881 2001-12-11
. ..
addresses the deficiencies of the prior art PSA systcuns.
The gas separation system, in accordance with the inve~don, comprises a stator
and a
tutor rotatably coupled to the stator. The stator includes a first stator
valve face, a socond stator
valve face, a number of first function compartments opening into the first
stafior valve face, and
a number of second function compartments opening into the second stator valve
face. 'The tutor
includes a first tutor valve surface is communication with the f rst stator
valve face, a second
tutor valve face in communication with the second stator valve face, and a
number of flow paths
fox receiving adsorbent material therein which preferentially adsorbs a first
gas component of a
feed gas mixture in response to increasing pressure in relation to a second
gas component of the
feed gas mixture. The rotor also includes a number of aporhlras provided in
the rotor valve faces
in communication with the function compartments and the onds of the flow
paths.
Compression machinery, which earl deliver and receive gas flow at a numbs of
discrete
pressure levels, is coupled to the function compartme;ats so as to maintain
uniformity of gas flow
through the function compartments. As a result, mechanical stresses an the
compression
machinery is reduced, allowing use of centrifltgal or axial compression
machinery.
The gas separation system includes a number of variable-gap clearance-type
valve seals
interposed between the first tutor valve face and the first stator valve face
and between the
second tutor valve face and the second stator valve face. Each variable-gap
clearance seal
includes a sealing face disposed adj scent a respective one of the rotor valve
faces and is pivotal
relative to the respective rotor valve face for varying the gas flow rate in
accordance with the
clearance distance between the sealing face and the respective rotor valve
face. Each variable-
gap clearance seal also includes an opposing face disposed adjacent the
respective stator valve
face, with the opposing face sad the respective stator valve face together
defining a passage
therebetween which communicates with one of the function compartments for
varying the
Z5 clearance distance in response to a pressure differential between the
passage and an adjacent
opposite end. In this way, the seal maintains a smooth pressure txansitiaa
profile as the flow
paths are switched between the function colxlparbments. As a result,
equilibrium is maintained
between the adsorbent material and the mass transfer front of the gas, and the
efficiency of the
gas sej78ratlOn pIOCeBS 15 CnhBnCed.
3 0 The gas separation system also includes a number of fixed-gap clearance-
type valve seals
interposed between the first rotor valve ;face and the first stator valve face
and between the
second rotor valve face and the second stator valve face for sealing
respective ends of the flow
paths. Each fixed-gap clearance seal is substantially identical to the
variable-gap clearance seal,
CA 02364881 2001-12-11
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including a sealing face disposed adjacent a respective one of the tutor valve
faces, an opposing
face disposed adj aceox the respective stator valve face, and a passa~c
between the opposing face
and tire stator valve face for pressurizing the sealing face against the rotor
valve fact. However,
the compartment does not communicate with any function compartment, and the
fixed-gap
clearance seal is fixed at at least one end thereof relative to the respective
rotor valve face so as
to restrict variations in the clearance gap and to prevent gas leakage from
each flow path end
passing the sealing face.
In one embodiment of the invention, each viable-gap clearance-type valve seal
is
positioned between adjacent blowdown function compartments and consists of as
elongate
slipper having a sealing face and an. opposing face extending between the ends
of the slipper.
Eacb slipper is pivotally coupled adjacent one of the respective slipper ends
to the respectiuc
tutor valve face, and includes a resilient biasing clement positioned
equidistantly between the
slipper ends and extending between the stator valve face and the respective
opposing slipper face.
Fin then each passage compzises a co;taparlment defined by the respective
stator valve face, the
opposing faces of adj anent sealing elements, and adj scent biasing elements,
and provides a linear
pressure transition profile, at the flow path ends, between the pressure of
one of the adjacent
blowdown compartments and the pressure ofthe other of the adj scent blowdown
coxnparanents.
Since each flow path end opens fully to one of the adjacent blowdown
compartments prior to
traversing the sealing face of the valve seal, the pressure at the end of each
flow path drops
linearly from the pressure it attained prior to traversing the sealing face to
the pressure of the
other of the adjacent blawdown compartments.
In another embodiment of the invention, each variablo-gap clearance-type valve
seal is
positioned between adj scent pressurization function compartments, includes a
resilient biasing
element positioned at each slipper end and extending between the stator valve
face and the
respective opposing slipper face. Each passage comprises a compartment defined
by the
respective stator calve face, the opposing faces of adjacent sealing elements,
sud the respective
biasing elements, and includes an aperture positioned equidistantly between
the slipper ends and
extending through the slipper between the respective sealing face and the
resp~tive opposing
face so as to provide a linear pressure transition profile, at the flow path
ends, betwreen the
pressure of one of the adjacent pressurization compartine~nts and the pressure
of the other ofthe
adja~eent pressurization compartments. Since each flow path ewd opens fully to
one of the
adjacent prcsSmization compartments prior to traversing the sealing face of
the valve seal, the
pressure at the end of each flow path increases linearly from the pressure it
attained prior to
CA 02364881 2001-12-11
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traversing the sealing Mace to the pressure of the other of the adjacent
pressurization
compartments,
In operation, a feed gas mixture, including a fixer gas component and a second
gas
component, is delivered to the rotor flow paths through the first rotor-stator
valve surface pair,
and the rotor is rotated at a frequency so ss to expose the gas mixture in
each rotor flow path to
cyclical changes in pressure ~d direction of flow, These cyclical changes
cause the more readily
adsorbed component of the feed gas to be exhausted as heavy product gas fmm
the first mtor-
stator valve surface pair and the less readily adsorbed component to be
delivered as light product
gas tram the second rotor-stator valve surface pair. To enhance gas
separation, Right reflex exit
gas is withdrawn from the second rotor-stator valve surface pair and is
returned after pressure
letdown to the second rotor-stator valve surface pair.
In order for the flowing gas streams entering or exiting the function
compartments to be
substantially uniform in pressure and velocity, the feed gas is delivered. to
the rotor flow paths,
through the clearance seals, at plurality of incremental feed gas.pressure
levels. Similarly, the
hoavy product gas is exhausted from the rotor flow paths as countercurrent
blowdown gas,
through the clearance seals, at a plurality of decnmental exhaust gas pressure
levels. Preferably,
the light reflex exit gas is withdrawn fi~om the rotor flow paths, through the
clearance seals, at
a pXurality of docremental light reflex exit pressure levels and is returned
to tile rotor flow paths
as light reflex return gas, through the clearance seals, at pressure levels
less than the respective
light reflex exit pressure level.
Preferably the rotor also has a large number of adsorbers such that several
adsorbers are
exposed to each pressure level at any given moment. Duringpressurization
andblowdown steps,
the pressures of the adsor'bers passing through each of these steps converge
to the nominal
pressure level of each step by a throttling pressure equalization" through the
clearance seals, from
the pressure Revel of the previous step experienced by the adsorbers. Flow is
provided to the
adsorbers in a pressurization step or withdrawn in a blowdown step by the
compression
machinery at the nominal pressure level of that step. Hence flow and pressure
pulsations seen
by the compression machinery at each intermediate pressure level are minimal
by averaging from
the several adsorbers passing through the step, although each adsorber
undergoes large cyclic
changes of pressure and flow.
BRIEF DESCRipTION OF T~iE DRAWTNQ~S
The preferred etabodiments of the presort invention will now be described, by
way of
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example only, vaith xef~ence to the drawings in which:
Fig. 1 is a sectional view of a rotary PSA module according to the present
invention,
showing the stator, the rotor and the adsorber situated in the rotor,
Fig. 2 is a sectional view of the module of Fig. 1, with the stator deleted
for clarity;
Fig. 3 is a sectional view of the stator shown in Fig. 1, with the adsorbers
deleted for
clarity;
Fig. 4 is an axial section of the module of Fig. 1;
Fig. 5 shows a typical PSA cycle attainable with the present inventian;
Fig. 6 shows one variation of the PSA cycle with heavyreflux, attainable with
the present
invention;
Fig. 7 shows a pressure swing adsorption apparatus according to the present
invention,
depicting the rotary module shown in Fig. 1 end a compression machine coupled
to the rotary
module;
Fig. 8 shows aradial-flow-con~&guredmtaryPSAmodule, with the
compressionmachine
deleted for clarify,
Fig. 9 shows an a~cial-flovrr-configured rotaryPSA module, with the
compressionmschine
deleted for clarity;
Fig. 10 shov~rs the first valve face of the rotary PSA module shown is Fig. 9;
Fig. 11 shov~rs the second valve face of the rotary PSA modules shown in Fig.
9;
Fig.12a is a sectional view of a self regulating clearance seal fox use with
the blowdown
compartments of an axial-flow-configured rotary PSA module, such as the PSA
module shown
in Fig. 9;
Fig. 12b is a schematic diagram showing various pressure transition profiles
of a flow
path end opening to a blowdown compartment, including the pressure transition
profile of a flow
path end fitted with the clearance seal shown in Fig. 12a;
Fig 13a is a sectional view of a self regulating clearance seal for use with
the
pressurization comparhnents of an axial-flow-confiigated rotary PSA module,
such as the PSA
module shown in Fig. 9;
Fig. 13b is a schematic diagram showing various pressure transition profiles
of a llovcr
path end opening to a pressurization comparhneir~t, including the pressure
transition profile of a
flow path end fitted with the clearance seal shown in Fig. 13a;
Fig. 14 is a sectional view of a radial-flow-configured rotary PSA module,
such as the
PSA module shown in Fig. 8, depicting the placement of the self regulating
clearance seals
CA 02364881 2001-12-11
employed therein;
Fig. 1 S is an unrolled view of the outer seal assambl~r frown Fig. 14; and
Figs. 16A and 16B are sectional views of the scat assembly shown in Fig_ 15.
Fig. 17 shows the fixer valve face of a simplified ~cial-flow-configured
rotary vacuum
PSA module as shown in Fig. 9,
Fig. 18 shows a perspective view of the first valve face of Fig. 17,
Fig. 19 shows a unitized seal for a rotor to engage with the valve face of
Fig. 17,
Fig. 20 and Fig. 21 acre sections of the seal of Fig_ 19 as installed in the
rotor of Fig. 9.
Fig. 22 is a sectional view of a cixcutnf~ential section of the module of Fig.
17
Fig. 23 shows a sketch of a rotor of the module in Fig. 17.
DETAILED DESCRI~'TION OF THE PREFF.R,i:ED EMBODIMENTS
Figs.l. 2. 3 sad 4
A rotary module 10 according to the present invention is shown in Figs. 1, 2,
3 and 4.
The module includes a rotor 11 revolving about axis 12 in the direction shown
by arrow 13
within stator 14. In general, the apparatus of the invention maybe configured
for flow through
the adsozber elements in the radial, axial or oblique conical directions
relative to the rotor axis.
However, for operation at high cycle fi~equency, radial ~low has the advantage
that the centripetal
acceleration will lie parallel to the flow path for most favourable
stabilization of buoyancy driven
free convection, as well as centrifugal clamping of granular adsorbent with
uniform flow
distribution.
As shown in Fig. 2, the rotor 11 is of annular section, having concentrically
to axis 12 an
outs cylindrical wall 20 whose extx~nal surface is first valve surface 21, and
~ inner cylindri cal
wall 22 whose internal surface is second valve surface 23. The rotor has (in
the plane of the
section defined by arrows 15 and 16 in Fig. 4) a total of "N" radial flow
adsorber elements 24.
An adjacent pair of adsorber elements 25 and 26 are separated by p~ition 27
which is
structurally and sealingly j oiaed to outer wall 20 and inner wall 22. Adj
ac:ent adsorbac elements
25 and 26 arc angularly spaced relative to axis 12 by an angle of [360°
/ N].
Adsorber element 24 has a first end 30 defined by support screen 31 and a
second end 32
defined by support screen 33. The adsorbe~r may be provided as granular
adsorbent, whose
pacl~ng voidage defines a flow path contacting the adsorbent between the first
and second ends
of the adsorber.
CA 02364881 2001-12-11
8 .
First aperture or orifice 34 provides flow communication from first valve
surface 21
through wall 20 to the first end 30 of adsoxber 24.. Second aperture or
rnifice 35 provides flow
communication from second valve surface 23 through wall 22 to the second end
31 of adsorber
24. Support screens 31 and 33 respectively provide flow distribution 32
between first apertwe
34 and first end 30, and between second aperture 35 and second end 32, of
adsorber element 24.
Support screen 31 also supports the centrifugal force loading of the
adsorbent.
As shown in Fig. 3, stator 14 is a pressure housing including an outer
cylindrical shell or
first valve stator 40 outside the annular rotor 11, and an inner cylindrical
shell or second valve
stator 41 inside the annular rotor 11. Outer shell 40 carries axially
extending strip seals (e.g_ 42
and 43) sealingly engaged with first valve surface 21, while inner shell 41
carries axially
extending strip seals (e.g. 44 and 45) soaliagly ongag~ with second valve
surface 23. The
azimuthal sealing width of the strip seals is greater than the disutetors or
azimuthal widths of the
first and second apertw~es 34 and 35 opening through the first and second
valve surfaces.
A act of first compartments in the outer shell each open in an angular sector
to the first
valve surface, arid each provide fluid communication between its angular
sector of the first valve
surface and a manifold external to the module_ The angular sectors of the
compa~aents are
much wider than the angular separation of the adsorbor elements. The first
compartments are
separated on the first sealing surface by the strip seals (e.g. 42).
Proceeding clockwise in Fig.
3, in the direction of rotor rotation, a first feed pressurization
conxpattment 46 communicates by
conduit 47 to first feed pressurization manifold 48, which is maintained at a
first intermediate
feed pressure. Similarly, a second feed pressurization compartment 50
communicates to second
feed pressurization manifold 51, which is maintained at a second intermediate
feed pressure
higher than the first intermediate feed pressure but less than the higher
working pressure.
For greater generality, module 10 is shown with provi area for sequential
admission oftwo
feed mixtures, the first feed gas having a lower concentration of the more
readily adsorbed
component relafiive to the second feed gas. First food compartment 52
communicates to first feed
manifold 53, which is maintained at substantially the higher working pressure.
Likewise, second
feed compartment 54 communicates to second feed manifold 55, which is
maintained at
substantially the higher worlang pressure. A first eountorcurr~nt blowdown
compartment 56
communicates to first countercurrent blowdown manifold 57, which is maintained
at a first
countercurrent blowdown intermediate pressure. A ' second countercurrent
blowdown
eomparlment 58 connmunicates to second countercurrent blowdown manifold 59,
which is
maintained at a second countercurrent blowdown intermediate pressure above the
lower working
CA 02364881 2001-12-11
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pressure. A heavy product compartment 60 communicates to heavy product exhaust
manifold
61. which is maintained at substantially the lower working pressure. It will
be noted that
compartment 58 is bounded by strip seals 42 and 43, and similarly all the
compartments are
bounded and mutually isolaxed by strip scats.
A set of second compartments in the inner shell each open is an angular sector
to the
second valve surface, and each provide fluid communication between its angular
sector of the
second valve surface and a manifold external to the module. The second
compartments are
separated on the second sealing surface bythe strip seals (e.g. 44).
Proceeding clockwise in Fig.
3, again in the direction of rotor rotation, light product compartment 70
communicates to light
product manifold 71, and receives light product gas at substantially the
higher working pressure,
less frictional pressure drops thmugh the adsorbers and the first and second
orifices. According
to the angular extension of compartment 70 relative to compartments 52 and 54,
the light product
may be obtained only from ad$orbers simultaneously receiving the first feed
gas from
compartment 52, or from adsorbexs receiving both the first and secoztd feed
gases_
A first light reflex exit compartment 72 communicates to first light reflex
exit manifold
73, which is maintained at a first light reflex exit pressure, here
substantially the higher working
pressure less frictional pressure drops. A first cocurreat blowd,own
compartment 74 (which, is
actually the.second light reflex exit compartment), communicates to s~ond
light reflex exit
manifold 75, which is maintained at a fast cocunreat blowdownt prossure less
than the higher
z0 working pressure. A second cocutrent blowdown compartment or third light
reflex exit
compartment 76 communicates to third light reflex exit manifold 77, which is
maintained at a
second eocurrent blowdown pressure less than the first cocutrent blowdown
pressure. A third
cocurrenx blowdown compartment or fourth light reflex exit compartment 78
communicates to
fourth light reflex exit manifold 79, which is maintained at a third cocurrent
blowdown pressure
- less than the second, coc~urent blowdown pressuto.
Apurge compartment 80 communicates to afourthlightreflux retutn.manifold 81,
which
supplies the fourth light ref tux gas which has been expanded from the third
cocurrent blowdown
pressure to substantially the lower working pressure with an allowance for
frictional pressure
drops. The ordering of light zeflux pressurization steps is inverted from the
ordering or light
reflex exit or cocurrent blowdown steps, so as to maintain a desirable "last
out - first izi"
stratification of light reflex gas packets. Hence a. ftrst light reflex
presa~unization eoropattment
82 communicates to a third light retlux return manifold 83, which supplies the
third. light reflex
gas which has been expanded fmm the second eocurreat blowdown pressure to a
first light reflex
CA 02364881 2001-12-11
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presswization pressure greater than the lower woxidng pressure. A second light
reflex
pressurization comparbmertt 84 eammunicates to a second light retlux return
man~i~old 85, which
supplies the sacond light reflex gas which has been expanded from the first
cocurrent blowdown
pressuxe to a second light retlux pressurization pressure greater than the
first light reflex
pressurization pxessure. Finally, a third light reflex pressurization
compartunent 86
communicates to a first light reflex return manifold 87, which supplies the
first light reflex gas
which has been expanded from approximately the higher pressure to a third lift
reflex
pressurization pressure greater than the second light reflex pressurization
pressure, and in this
example less than the first feed pressurization pressure.
Additional details are shown in Fig. 4. Conduits 88 connect first compartment
60 to
manifold 61,, with muitiple conduits providing for good axial flow
distribution in compartment
60. Similarly, conduits 89 co~mect second compartment 80 to manifold 81.
Stator 14 has base
90 with bearings 91 and 92. The annular tutor 11 is supported on end disc 93,
whose shaft 94
is supported by bearings 91 and 92. Motor 95 is coupled to shaft 94 to drive
rotor 11. The rotor
t 5 could alternatively rotate as an annular drum. supported by rollers at
several angular positions
about its rim and also driven at its rim so that no shaft would be required. A
rim drive could be
provided by a ring gear attached to the rotor, or by a linear electromagnetic
'~noto~r whose stator
would engage an arc o~the rim. Outer circumferential seals 96 seal the ends of
outer strip seals
42 and the edges of first valve surface 21, while inner circumferential seals
97 seal the ends of
inner strip seals 44 and the edges of second valve surface 23. Rotor 11 has
access plug 98
between outer wall 20 and inner wall 22, which provides access for
installation and removal. of
the adsorbent in adsorbers 24.
Fins. 5 an 6 . .
Fig. 5 shows a typical PSA cycle which would be obtained using the gas
separation
system according to the invention, while Fig. 6 shows a sinniXar PSA cycle
with heavy reflex
recompression of a portion of the first product gas to pfmvide a second feed
gas to the process.
Ira Figs. 5 and 6, the vertical axis 150 indicates the working pressure in the
adsorbcrs and
the pressures in the first and second compartmazits. Pressure drops due to
flow within the
adsorber elements are neglected. The higher and lower working pressures are
respectively
3o indicated by dotted lines 15i and 152.
The horizontal axis 155 of Figs. 5 aad 6 indicates time, with the PSA cycle
period deFmcd
by the tame interval between points 156 and 157_ At times 156 and 157, the
working pressure
in a particular adsorber is pressure 158. Starting from time 156, the cycle
for a particular
CA 02364881 2001-12-11
-11'
adsorber (e.g. 24) begins as the first aperture 34 of that adsorber ie opened
to the first feed
pressurization comparimcnt 46, which is fed by first feed supply means 160 at
the first
intermediate feedpressure 161. The pressure in that adsorberrises from
pressure 158 at time 157
to the first intermediate feed pressure 161. .Proceeding ahead, first aperture
passes over a~seal
strip, first closing adsorber 24 to compar6ment 46 and then opening it to
second feed
pressurization compartment 50 which is feed by second feed supply mea~as 162
at the second
intermediate feed pressure 163. The adsorber pressure rises to the second
intermediate feed
pressure_
First apertuxe 34 of adsorber 24 is opened next to first feed compartment 52,
which is
maintained at substantially the higher pressure by a third food supply means
165. Once the
adsorber pressure has risen to substantiaXly the higher working pressure, its
second aperhue 35
(which has been closed to all second compartments since time 156) opens to
light product
compartment 70 and delivers light product 166.
Zn the cycle of Fig. 6, first aperture 34 of adsorber 24 is opened next to
second feed
comparratent 54, also maintained at substantially the higher pressure by a
fourth feed supply
means 167_ Tn general, the fourth feed supplymeans supplies a second food gas,
typically richer
in the more readily adsorbed component than the first feed gas provided by the
first, second and
third feed supply means. Iu the specific cycle ihuatrated in Fig. 6, the
fourth feed supply means
167 is a "heavy rcflux" compressor, recompressiag a portioA of the heavy
pmduct back into the
apparatus. In the cycle illustrated in Fig. 5, there is no fourth feed supply
means, and
compartment 54 could be eliminated or consolidated with compartment 52
extended over a wider
angular arc of the stator.
While feed gas is still being supplied to the first end of adsorbe~r 24 from
either
com~partm~ent 52 or 54, the second end of adsorber 24 is closed to light
product compartmaut 70
and opens to first light reflux exit compartment 72 while delivering "light
reflux" gas (enriched
in the less readily adsorbed component, similar to second product gas) to
first light reflex
pressure let-down means (or expander) 170. The first aperture 34 of adsorbct
24 is then closed
to all first compartments, urhile the second aperture 35 is opened
successively to (a) second light
reflex exit compartment 74, dropping the adsorbea pressure to the first
cocurreat blowdown
pressure 171 while delivering light reflex gas to second light reflex pressure
letdown nneans 172,
(b) third light reflex exit compartment 76, dropping the adsorber pressure to
the second coeurrent
blowdown pressure 173 while delivering light reflex gas to third light reflex
pressure letdown
means 174, and (c) fourth light reflex exit compartment 78, dropping the
adsorber pressure to
CA 02364881 2001-12-11
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the third cociurept blowdown pressure 175 while delivering light reflex gas to
fourth light reflex
pressure letdown means 176. Second aperture 35 is then closed for an interval,
until the light
reflex return steps following the countercurrent blowdown steps.
The light reflex pressure let-down means may be mechanical expanders or
expansion
stages for expansion energy rewvery, or may be rastrictox ori$ces or throttle
valves for
irreversible pressure let-down.
Either when the second aperture is closed after the final light reflex exit
step (as shown
in Figs. 5 and 6), or earlier while light reflex exit steps are still
underway, first aperture 34 is
opened to first countercurrent blowdown. compartment 56, dropping the adsorber
pressure to the
first countercurrent blowdown intermediate pressure 180 while releasing
"heavy" gas (enriched
in the more strongly adsorbed component) to first exhaust mesas I81. 'then,
first aperture 34
is opened to second counte~t~cuxrent blowdown compartment 58, dTOppit~g the
adsorberpressure
to the first countercurrent blowdown intermediate pressure 182 while releasing
heavy gas to
second exhaust means 183. Finally reaching the lower worlting pressure, first
aperhue 34 is
opened to heavy product compartment 60, dropping the adsorber pressure to the
lower pressure
152 while releasing heavy gas to third exhaust means 184, Once the adsorber
pressure has
substantially reached the lower pressure while first aperture 34 is open to
compartment 60, the
second aperture 3 5 opens to purge compartmant 80, which receives fourth light
reflex gas from
fourth light reflex pressure let-down means 176 in order to displace more
heavy gas into first
product com~parhment 60.
Ta Fig. 5, the heavy gas from the first, second and third exhaust means is
delivered as the
heavy product 185. Tn hig. 6, this gas is partly released as the heavy product
185, while the
balance is redirected as "heavy reflex" 187 to the heavy reflex compressor as
fourth feed supply
means 167. Just as light reflex enables as approach to high purity o~ the less
readily adsorbed
("light") component in the light product, heavy reflex enables an approach to
high purity of tine
more readily adsorbed ("heavy") component in the heavy product.
The adsorber is then repressuriaed by light reflex gas after the first and
second apertures
close to compartments 60 and 80. In succession, while the first aperture 34
remains closed at
least initially, (a) the second aperture 35 is opened to first Light reflex
pressurization
compartment 82 to raise the adsorberpressure to tho first light reflex
pressurization pressure I90
while receiving third light reflex gas from the third light reflex prassure
letdov~a means 174, (b)
the second aperture 35 is opened to second light reflex pressurization
compartment 84 to raise
the adsorber pressure to the second light reflex pressurization pressure 191
while receiving
CA 02364881 2001-12-11
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second light reflex gas fi~om the second light reflex pressure letdown means
172, and (c) the
second aperture 35 is opened to third light reflex gressurizatian compartment
86 to praise the
adsorber pressure to the third light reflex pressurization pressure 192 while
receiving first light
reflex gas from the first light reflex pressure letdown means 1?0. Unless feed
pressurization has
already been started while light reflex return for light reflex pressurization
is still underway, the
. process (as based on Figs. 5 and 6) begins feed pressurization for the next
cycle after time 157
as soon as the third light reflex pressurization step has been concluded.
The pressure variation waveform in each adsorber would be a rectangular
staircase if
there were no throttling is the first and second vales. In order to provide
balanced performance
of the adsorbers, preferably all of the apertures are closely identical to
each other.
The rate of pressure change in each pressurization or blowdown~ step will be
restricted
by throttling in ports (or in clearance ox labyrinth sealing gaps) of the
first and second valve
means, or by throttling in the apertures at first and second coda of the
adsorbers, resulting in the
typical pressure waveforni depicted in Figs. S and 6. Alternatively, the
aperhrres may be opened
1 S slowly by the seal strips, to provide flow restriction throttling between
the apertures and the seal
strips, which may have a senratod edge (e.g. with notches or tapered slits in
the edge of the seal
strip) so that the apertures are only opened to full flow gradually.
Excessively rapid rates of
pressure change would subject the adsorber to mechanical stress, while also
causing flow
transients which would tend to increase axial dispersion of the concentration
wavefroiit in the
adsorber. Pulsations of flow and pressure ate minimized by having a plurality
of adsorbers
simultaneously tte~nsiting each step of the cycle, and by providing enough
volume ire the fhnetion
compartments and associated manifolds so that they act effectively as surge
absorbers between
the compression machinery and the first and second valve means.
rt will be evident that the cycle could be generalized by having more or fewer
intermediate stages in each major step of feed pressurization, countercurrent
blowdown exhaust,
or light reflex. Furthermore, in air separation or air purification
applications, a stage of feed
ple58ul1aattOn (typically the first stage) could be performed by equalization
with atmosphere as
an intermediate pressure of the cycle. Similarly, a stage of countercurrent
blowdown could be
performed by equalization with atmosphere as an intermediate pressure of the
cycle_
Fig_ 7
Fig. 7 is a simplified schematic of a PSA system, in accordance with the
gresent
invention, for separating oxygen from air, using nitrogen selective zeolite
adsarbeats. The ligbt
product is concentrated oxygen, while the heavy product is nitrogen-enriched
air usually vented
CA 02364881 2001-12-11
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as waste. The cycle lower pressure 152 is nominally atmospheric pressure. Feed
air is
introduced, through filter intake 200 to a feed compressor 201. The feed
compressor includes
compressor fast stage 202, intcrcooler 203, compressor second stage 204,
second intercooler
205, compressor third stage 206, third intercooler 207, and compressor fourth
stage 208. The
feed compressor 201 as described may be a four stage axial compressor or
centrifugal compressor
with motor 209 as prime mover coupled by shaft 210, and the intetcoole~t~s are
optional_ With
reference to Fig. 5, the feed compressor first and second stages are the brat
feed supply means
160, delivering feed bas at the first intermediate feed pressure 161 via
conduit 212 and water
condensate separator 213 to first feed pressurization manifold 48. Feed
compressor third stage
206 is the second feed supply means 162, delivering feed gas at the second
intermediate feed
pressure 163 via conduit 214 and water condensate separator 215 to second feed
pressurization
manifold 51. Feed compressor fourth stage 208 is the third fend supply moans
165, delivering
feed gas at the higher pressure 151 via conduit 216 and worst condensate
separator 217 to feed
manifold 53. Lig.~tt product oxygen flow is delivered from light product
manifold 71 by conduit
218, maintained at substantially the higher pressure less frictional pressure
drops.
The apparatus of Fig. 7 includes energy recovery expanders, including light
reflu~t
expander 220 (here including four stages) and countercurrent blowdown expander
221 (here
including two stages), coupled to feed compressor 201 by shaft 222. The
expander stages may
be provided for example as radial inflow turbine stages, as full admission
axial turbine stages
with separate wheels, or as partial adm,isaion impulse turbine stages combined
in a single wheel.
Light reflex gas from first light reflex exit manifold 73 flows at the higher
pressure via
conduit 224 and heater 225 to first light pressure letdown means 170 which
here is first light
reflex expander stage 226, and then flows at the third light reflex
pressurization pressure 192 by
conduit 227 to the first light reflex return manifold 87. Light reflex gas
from second light reflex
exit manifold 75 flows at the first cocun: ent blvwdown pressure 171 via
conduit 228 and heater
225 to second light reflex pressure letdown means 172, here the second
expander stage 230, and
then flows at the second light reflex pressurization pressure 191 by conduit
231 to the second
light reflex return manifold 85. Light reflex gas firom third light reflex
exit maaifold 77 flows
at the second cocurrent blowdown pressure 173. via conduit 232 and heater 225
to third light
reflex pressure letdown means 174, here the third expander stage 234, and then
flows at the first
light reflex pressurization pressure 190 by conduit 235 to the third light
reflex return mannfold
83. Finally; light reflex gas from fourth light reflex exit manifold 79 flows
at the thud cocurreaat
blowdown pressure 175 via conduit 236 and heater 225 to fourth light reflex
pressure letdown
CA 02364881 2001-12-11
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means 176, here the fourth light reflex expander stage 238, and then flows at
substantially the
lower pressure 152 by conduit 239 to the fourth light reflex return manifold
81.
Heavy countercurrent blowdowa gas from first countercurrent blowdown manifold
57
Mows at first couatercurrent blowdown intermediate pressure 180 by conduit 240
to heater 241
and thence to first stage 242 of the countercurrent blowdown expander 221 as
first exhaust means
181, and is discharged from the expander to exhaust manifold 243 at
substanfiially the lower
pressure,152. Countercurrent blowdown gas from second countercurrcn~t blawdown
manifold
59 flows at secozid countercurrent blowdown intezmediate pressure 182 by
conduit Z44 to heater
241 and thence to second stage 245 of the countercurrent blowdown expander 221
as second
exhaust means 183, and is discharged from the expander to exhaust manifold 243
at substantially
the lower pressure 152. Finally, heavy gas from heavy product exhaust manifold
61 flows by
conduit 246 as third exhaust means 184 to exhaust manifold 243 delivering the
heavy product
gas 185 to be vented at substantially the lower pressure 152.
Heaters 225 and 241 raise the temperatures of gases entering expanders 220 and
221, thus
augmenting the recovery of expansion energy and increasing the power
transmitted by shaft 222
from expanders 220 and 221 to feed compressor 201, and reducing the power
required from
prime mover 209. While heaters 225 and 241 axe moans to pmvide heat to the
expanders,
intercoolers 203, 205 and 207 are means to remove heat from the feed
compressor and serve to
reduce the required power of the higher compressor stages_ The intercoolers
203, 205, 207 are
optional features of the invention.
If light reflex heater 249 operates at a su~ciantly high temperature so that
the exit
temperature ofthe light reflex expansion stages is higher than the temperature
at.which feed gas
is delivered to the feed sianifolds by conduits 212, 214 and 216, the
temperaature of the second
ends 35 of the adsoxbers 24 may be higher than the temperature of their first
ends 34. Hence, the
adsorbers have a thermal gradient along the flow path, with higher temperature
at their second
end relative to the first ea~d. This is an extension of the principle of
"thermally coupled pressure
swing adsorption" (TCPSA), introducedbyKeeferinU.S. PatentNo.4,702,903.
Adsorbcrrotor
11 then acts as~ a thermal rotary regenerator, as in reg~erative gas turbine
engines having a
compressor 201 and an expander 220_ Heat provided to the PSA process by heater
225 assists
powering the process according to a regenerative thermodynamic power cycle,
similar to
advanced regenerative gas turbine engines approximatelyrealizing the Enicsson
thermodynamic
cycle with intercooling on the compression side and intersta,ge heating on the
expansion side.
Ins the instance of PSA applied to oxygen separation from air, the total light
reflex flow is much
CA 02364881 2001-12-11
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less than the feed flow because of the strong bulk adsocptiorl of nitrogen.
Accordingly the Power
recoverable from the expanders is much less than the power required by the
compressor, but will
stih contribute significantly to enhanced ofi'xcieacy of oxygen pmductaiion.
If high energy efficiency is not of highest importance, the light reflex
expander stages and
tl~e eountercurtent blowdown expander stages may be replacod by rastrictor
orifices or throttle
valves for pressure letdown. The schematic of Fig. 7 shows a single shaft
supporting the
compressor stages, the countercurren~tblowdown of exhaust expander stages, and
the lightreflux
stages, as well as coupling the compressor to the prime mover. Howevor, it
should be understood
that separate shafts and even separate prinnc movers maybe used for the
distinct compression and
expansion stages within the scope of the present invention.
Fig. 8
Fig. 8 shows a radial flow rotary 1'SA module 300 in which the first and
second valve
surface 21, 23 are respectively provided as. hard-faced ported surfaces on the
first and second
valve stators 40 and 41. Sliding seals 380 are provided on rotor 11 between
each adsorbcr 2~4
and its neighbours, to engage both valve surfaces 21, 23 in Fluid sealing
contact. Seals 380 may
have a wear surface o~ a suitable composite material based on PTFE or carbon,
and should be
compliantly mounted on rotor 11 so as to compensate for wear, deflections and
misalignment.
Ports 381 may be sized, particularly at the leading ~igc of each compartment,
to provide
controlled throttling for smooth pressure equalization between adsorbess and
that compartment,
as each adsorber in turn is opened to that compartment.
Split stream vacuum pump 260 receives the countorcurrentt blowdowri and
exhaust flow
in three streams receiving exhaust gas at incrementally reduced pressures From
countercurrent
blowdown compartna~ent 56, compartment 58 and compartment 60. The combined
exliaust gas
is discharged as hoavyproduct gas. Znthis example, initial
feodpressurizationis performed from
atmosphere, so a first feed pressurization conduit 3 82 admits feed sir
directly from inlet $lter 200
to first Feed pressurization compartment 46 at substantially atmospheric
pressure. 'fhe first
discharge port of feed compressor 201 now communicates to second feed
pressurization
compartment 50. The compressor is shown as a split stage machine with inlet
391, and three
discharges 392, 393 and 394 at incrementally higher pressures.
To achieve light reflex pressure letdown with energy recovery, a split stream
light reflex
expander 220 is provided to provide pressure let-down of Four light re~lux
stages with energy
recovery. The light reflex expander 220 provides pressure let-down for e$ch of
four light reflex
stages. The stages znay opi~onally be compartxnmtalized within the ligk~t
reflex expander 220
CA 02364881 2001-12-11
_ 17-
to minimize mixing of gas concentration between the stages. 'The light product
purity will tend
to decline from tl~e light reflux stages of higher pressure fo those of lower
pressure, so that a
desirable stratification of the light reflex can be maintained if mining is
avoided.
Light reflex expander 220 is coupled to drive light product pressure booster
compressor
396. Compressor 396 receives the Iightproduct from compartment 70, and
delivers light product
(compressed to a delivery pressure above the higher pressure of the PSA cycle)
from delivery
conduit 218. Siaec the light reffux and light product are both enriched oxygen
streams of
approximately the same purity, expander 220 and light product compressor 396
may be
hezxnetically enclosed iri a single housing similar to a turbocharger.
Fig. 9
Fig. 9 is ~ axial sectional view of an axial flow rotary PSA module 600 for
small scale
oxygen production. The view is taken through compartineats 54 and 70 at the
higher pressure,
. and compartments 60 and 80 at the lov~rer pressure. The flow path in
adsorbers 24 is now parallel
to axis 601_ A better utxdessta~,ding will bo obtaio,ed from Figs. 10 and 11,
which are cross
sections ofmodule 600 in the planes respectively defined by arrows 602 - 603
and 604 - 605.
The adsorber tutor 11 contains the "N" adsorbers 24 in adsorber wheel 608, and
revolves
between the first valve stator 40 and the second, valve stator 41. Compressed
feed air is supplied
to compartment 54 as indicated by arrow 501, while nitrogen, enriched exhaust
gas is exhausted
from compartment 60 as i~adieated by arrow 502.
At the ends of rotor 11, circumfereatial seals 608 and 609 bound feat sealing
face 21, and
circumferential seals 610 and 611 bound second sealing face 23. The sealing
faces are flat discs.
The circumferential seals also define the ends of seals between the adsorbers,
or alteiaatively of
dynamic seals in the sealing faces between the stator compartments. Rotor 11
has a stub shaft
511 supported by bearing 512 in first beating housing 513, which is integral
with first valve
stator 40. Second valve stator 41 has a stub shaft engaging the rotor 11 with
guide bushing 612.
A flanged cover plate 615 is provided for structural connection and fluid
sealing
enclosure betycreea the first valve stator 40 and the second valv~ stator 41.
Rotor 11 includes seal
carrier 618 attached at joint 619 to adsorber wheel 608, and extending between
the back of
second valve stator 41 and cover plato 615 to sealing face 621 which is
contacted by dynamic
seal 625. Seal 625 prevents contamination of the light product gas by leakage
from chamber 626
adjacent the fu~st valve sealing face 21 to chamber 62? adjacent the second
valve sealing face 23.
Seal 625 needs to be tight against leakage that could compromise product
purity. By
manufacturing this seal to a smaller diameter than the valve faces outer
diameter, frictional
CA 02364881 2001-12-11
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torque from this seal is greatly reduced than if this seal were at the full
rotor diameter. The
cucumfcrential perimeter exposed to leakage is also reduced. As in Fig. 8, a
split stream light
reflex expander 220 with close~oupled light pmduct compressor 396, may be
installed maids
the light valve stator.
Figs. 10 ands
Fig. 10 shows the first valve face 21 of the axial flow rotary PSA module 600
shown in
Fig. ~9, at section 602 - 603, with fluid;connections to a split stream feed
compressor 201 and a
split stream countercurrent blowdown expander 221. Fig. l l shows the second
valve face 23 of
the axial flow rotary PSA module 600 sbown in Fig. 9, at section 604 - 605,
with fluid
connections to a split stream light roflua expander 220 and light product
booster coanpressor 396.
Arrow 670 indicates the direction of rotation by adsorber rotor 11. The open
area of
. valve face 21 ported to the feed and exliaust compartments is indicatedby
clear angular segments
46, 50, 52, 56, 58, 60 corresponding to those compartments, between
circumfcaential seals 608
and 609. The closed area of valve face 21 between compartments is indicated by
cross-hatched
sectors 675 and 676. Similarly, the open area of valve face 23 ported to the
light reflex exit and
return compartments is indicated by clear angular segments 70, 72, 74, 76, 78,
80, 82, 84, 86
corresponding to those compartments, while the closed are of valve face 23
bctwreen the light
reflex and return compartments is indicated by the cross-hatched sectors.
Typical closed sector 675, shown in Fig. 10, provides a transition for an
adsorbcr,
between being open to compatt~nent 56 and open to compartment 58. Gradual
opening is
pro~nided at the leading edges 677 and 678 of compartments, so as to achieve
gentle pressure
equalization of an adsorberbeing opened to a new compartment. Much wider
closed sectors (e. g.
676) are provided to substantially close flow to or from one end of the
adsorbers when
pressurization or blowdown is being performed fi'om the other end
Sealing between compartments at typical closed sectors (e.g. 675) may be
provided by
rubbing seals on either stator or rotor against a ported hard-faced sealing
counter face on the
opposing rotor or stator, or by narrow gap clearance seals on the stator with
the area of the
narrow sling gap defined by the cross hatched area of the nominally closed
surface. Rubbing
seals may be provided as radial strip seals, with a self lubricating solid
material such as suitable
PTFE compounds or graphite, or as brush seals in which a tightly packed brush
of compliant
fibers rubs against the counter face.
If the rubbing seals are on the rotor (between adjacent adsorbcrs), cross-
hatched sectors
675 and 676 would be non ported portions of the hard-faced sealing counter
face on the stator.
CA 02364881 2001-12-11
-19-
If the rubbing seals are on the stator, the ported hard-faced counter face is
on the rotor valve face.
Those rubbing seals could be provided a8 full sector strips for narrow closed
sectors (e.g. 67S).
For the wider closed sectors (e.g. 676), narrow radial rubbing seals may be
used as the edges 678
and 679, and at intervals between those edges, to reduce friction in
comEparison with rubbing
engagement across the full area of such wide sectors.
Cleatxance seals are sth~active, especially for larger scale modules with a
very large
number "N" of adsorbars in parallel. The leakage discharge coe~ciez~t to or
from the clearance
gap varies according to the angular position of the adsorber, thus providing
gentle pressure
equalization as desired. The clearance gap geometry is optimized in typical
nominally closed
sectors (e_g. 675) so that the leakage in the clearance gap is mostly used for
adsorber pressure
equalization, thus munimizing fihmngh leakage between compartments.
Preferably, the clearance
gap is tapered in such sectors 675 to widen the gap toward compaztments being
opened, so that
the rate of pressure change in pxessuro equalization is close to linear and
rubbing friction is
reduced- For wide closed sectors (e.g. 676) the clearance gap would be
relatively narrow to
. minimize flows at that end of adsorbers passing through those sectors.
For all types ~of valve face seals described above, it is preferable that
consistent
performance be achieved over time, and that all '2V" adsorbers experience the
same flow pattern
after all perturbations from seal imperfections. This consideration favours
placing rubbing seals
on the stator so that any imperfections are experienced similarlyby all
adsorbers. If the seals are
mounted on the rotor between adsorbers, it is preferable that they are closely
identical arid highly
reliable to avoid upsetting leakages between adjacent adsorbers.
To compensate for misalignment, thermal distortion, structural deflections and
wear of
seals and bearings, the sealing system should have a suitable self aligning
suspension. Thus,
rubbing seal or clearance seal elements may be supported on elastomeric
supports, bellows or
2S diaphragms to provide the self aligning suspension with static seating
behind the dynamic seal
elements. Rubbing seals may be energized into sealing contact by a combination
of elastic
preload and gas pressure loading.
Clearance seals require extreiaely accurate gap control, which may be
established by
rubbing guides. However, in the p~teferred embodiments, discussed below, gap
control for
blowdown compartr~nents is achieved through a self ~'egulating seal in which
the connect gap is
nr~aintained by a balance between gas pressure in the gap of a clearance seal
segment, acrd the
pressures of adjacent blowdown compartments loading the seal behind that
segment. For
pressurization compartments, gap control is achieved through a self regulating
seal in which the
CA 02364881 2001-12-11
-20-
correct gap is maintained by a balance between gas pressure in the gap of a
cleataaee seal
segment, and an intermediate pressure loading the seal behind that segment,
with the
intermediate pressure being the average of the pressure of the flow paths
approaching the
clearance seal segment and the pressure of flow paths leaving the clearance
seal segment. The
preferred etnbodimeats of the self xegulating clearance seals are discussed
below. .
F~'gs.12a,12b
Fig. 12a shows a self regulating clearance soal 700 for use with the counts .
' t
blowdov~rn comparirnents 56, 58, 60 and the cocurrent blowdown compartments
72, 74, 76, 78
of an axial-flow-configured rotary PSA module, such as the PSA module 600 ahoy
in Fig. 9.
The self regulating clearance seal 700 comprises a sealing element 702, acrd a
resilient biasing .
element 704 coupled to the sealing element 702. The sealing element 702 is
interposed between
the first valve face 21 of the rotor.ll and the corresponding stator valve
face of the stator 14, .
when used in conjunction with counterc~urent blowdown compartments 56, 58, 60,
or is
interposed between the second valve face 23 of the rotor 11 and the
coxtesponding stator salve
face of the stator 14, when used in conjunetion with the cocurrent blowdown
campattmettts 72,
74, 76, 78 . Sealing elements 702 are positioned along the stator valve face,
with each sealing
element 702 being positioned bciween a pair of adjacent blowdown compartment,
such as
between the blowdown compartments 56, 58 shown in Fig. 12a. However, it should
be
understood that the sealing element 702 xnay be positioned between any
blowdown
compartments, or proximate to any first gas ~low conduit which facilitates
pressure blowdown
of a second gas flow conduit moving past the first gas flow conduit.
Each scaling element 702 comprises an elongate slipper having fixer and second
opposite
ends 706a, 706b, a substantially planar sealing face 708 extending be~tweca
the opposite ends
706, and an opposing second face 710 also extending between the apposite ends
706 but
positioned opposite the sealing face 708. The sealing element 702 is
positioned between the
rotor vale face 21 (or the rotor valve face 23) and the corresponding stator
valve face, with the
first end 706a being positioned adjacent one of the blowdown compartments,
such as the
blowdown compartment 56, and with the second end 706b being proximate to the
adjacent
blowdown con~parGment, such as the blowdown compartment 58.
The ixrst end 706a of the sealing element 702 is pivotally coupled to the
rotor valve face
21 (or rotor valve face 23) through a bearing 712 positioned adj scent one
aide edge of the sealing
element 702, and which extends laterally outwards from the sealing element 702
and engages a
corresponding race on the rotor 11. A sinnilar beating 712 (not shown) is
positioned an the
CA 02364881 2001-12-11
-21 -
opposite side odge of the sealing element 702 arid engages a con~pondin~g race
on the tutor 11.
As will be described below, with this amaagement, a variable clearance gap 714
is maintained
between the sealing face 708 and the rotor valve face 21 (or rotor valve face
23) so as to allow
the gas flow rate'tluough the apertures 34 (or the apertures 35) of the rotor
11 to vary as the
height of the clearance gap 714 between the sealing face 708 and the mto;r
valve face is varied.
However, the clearance gap 714 at the first end 706a is maintained
substantially constant, and
is sized to minimize gas flows between adjacent blowdown compartments, such as
between the
blowdown compartment 56 and the blowdown compartment 58.
As will be appreciaxed, by providing bearings 712 at the first end. 706a of
the sealing
X10 element 702, the clearance gap 714 at the first eud 706a of the sealing
element 702 is
substantially independent of the degree of roundness of the tutor valve face.
As a result, friction
bet~reen the sealing face 708 and the rotor valve face 2I, 23 is less than if
the first eed 706a
actually contacted the rotor valve face 21, 23. However, the bearings 712 ~e
not essential
features of the invention. For instance, in one variation (not shown), the
seaaing element 702
includes apair ofprotubesanees integrally foamed with the scaling element 702
andwhich extend
laterally outwards from the side edges of the sealing element 702 for
engagement witb the
bearing races on the rotor 11. Yn another variation (not shown), the bearings
712 are replaced
with a single rod which extends through the sealing element 702 between the
side edges for
lications where reeise control
engagement with the bearing races on the rotor 11. Further, in app P
over the clearance gap 714 at the first end 706a is not critical, or where the
rotor valve face is
precisiozt machined, the first end 706a may be coupled to the stator 14.
The biasing element 704 coz~aprises a resilient element including a brat side
wall 716x,
and a second side wall 716b opposite the first side wall 716x. 'fhe biasing
element 704 is
positioned equidi .stantly between the first and second ends 706a, 706b and
extends between the
opposing face 710 and the stator valve face between adjacent blowdown
compartments. The
biasing element 704 prevents the sealing element 702 from rotati:tig with the
rotor 11 as the
aperhires 34 (or the apertures 35) of the rotor 11 mope past the sealing face
708, and urges the
sealing face 708 towards the rotor valve face. 'Further, since the gas flour
rate through the
apertures 34, 35 of the rotor 11 is dependent upon the height of the clearance
gap 714, the first
side wall 716a of the resilient biasing element 704 is concave so to allow the
height of the
clearance gap 714 to be varied. However, to roduce friction between the sface
708 and.
the rotor valve face, preferably the biasing element 704 does not press the
sealing face 708
' against the rotor valve face. The biasing element 704 is sized so the
sealing face 708 tapers away
CA 02364881 2001-12-11
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from the rotor valve face from the first end 706a towards the second end 706b,
so that the
clearance gap 714 is greater adjacent the second end 706b than adjacent the
first end 706x. As
will become apparent, this feature allows for a gradual pressure letdown for
the gas flowing ~rom
the flow path cnd.R 30, 32 of the adsorbers 24'as the corresponding apertures
34, 35 of the rotor
11 t~rraverse the sealing face 708.
A first compartment 718a is provided between the first side wall 716a of each
biasing
element 704, the portion of the stator valve face extending between the first
side wall 716a and
the blowdown compartment immediately adjacent thereto (blowdown compatb~nent
56), at~d the
portion of the opposing face 710 extending between the first side wall 716a
and the first end
0 706x. A second compartment 718b is provided between the second side wall
716b of each
biasing element 704, the portion of the stator vale face extending between the
second side wall
716b and the blowdown compartment immediately adjacent thereto (blowdown
compartment
58), and the portion of the opposing face 710 extending between the second
side wall 716b ~d
the second end 706b. The second compatkraent 71 Sb communicates with a first
compartment
718a associated with the adjacent sealing element_ The operation of the
clearance seal 700 will
now be described with reference to Figs 12a, 12b.
In operation, the rotor rotates in the direction of the arrow denoted by
reference numeral
720. Since clearance seals 700 are positioned along the circumference of
the,stator valve face
between adjacent blowdown compartments, the first end 706a of each sealing
~elemet~t 702 will
be maintained at the pressure level of one of the blowdown compartments, and
the second and
706b of each scaling element 702 will be maintained at the pressure level of
the adjacent
blowdown compartment. In the example shown in Fig. 12a, the f rst ~d 706a is
maintained at
the pressure level of the blowdown compartment 56, and the second end 706b is
maintained at
the pressure level of the blowdown compa~ment 58. Accordingly, when an
aperture 34, 35
approaches the first end 706a of the sealing element 702, the gas flowing ~rom
the ape~ue 34,
35 is equalized to the pressure of the blo~uvdown compartment 56. As the
apertures 34, 35 pass
the first end 706a and approach the second end 706b, the clearance gap 714
increases, thereby
allowing the rate of gas flow from the aperture 3~4, 35 to increase and th'e
pressure at the
corresponding flow path end 30, 32 of the adsorber 24 to decrease.
30 ~ Preferably, the pressure transition profile between the first blowdowa
compartment
(blowdown comparhment 56) and the second blowdown compartment (blowdown
compartment
58) is substantially linear so as to maintain equilibrium between the
adsorbent material and the
mass transfer front of the gas. However, as discussed above, the rate of gas
how (and houce the
CA 02364881 2001-12-11
23 -
rate of pressure blowdown) depends on the height of the clearance gap 714. For
instance, in a
conventional clearance seal, ifthe clearance gap 714 increasod too rapidly,
the~prcssure transition
profile ~crould normally have the concave shape (denoted by reference numeral
722) shown in
Fig. 12b, whereas if the clearance gap 714 increased too slowly, the pressure
transition profile
would nomnally have the convex shape (denoted by reference numeral 7z4).
However, as will
now be explained, with the present invention, the height of the clearance gap
714 automatically
adjusts to obtain the linear pressure trardsition profile (denoted by
reference numeral 726).
Since each biasing element 704 xs positioned equidistantly between the,first
and second
ends 706x, 706b, the first and second comparhnnents 718 are of equal si2e_
Therefore; as the
0 clearance seals 700 are positioned along the stator valve fact between
adjacent blowdown
compartments, the pressure acting against the opposing face 710 at the
position occupied by the
biasing element 704 is equal to the average ofthe pressure ofthe bloardown
compartment 56 and
the blowdown compartment 58 (as shown by the reference numeral 728). As a
result, if the
clearance gap 714 increased too rapidly, the pressure (as shown byreference
numeral 730) at the
5 sealing face 708 at the same position will be less than the average pressure
728, causing a
moment to be developed about the first end 706a tondimg to force the clearance
gap 714 to
narrow. The narrowing of the clearance gap 714 will cause a flattening of the
pressure transition
profile. The clearance gap 714 (and the eagle between the sealing face 708 and
the rotor fact)
will continue to narrow in response to the pressure differential between the
eomparlments 716
and the apertures 34, 35 until the pressure 728 equals the pressure 728, at
which point a linear
pTe55uTe transition profile will be obtained.
Conversely, if the clearance gap 714 increased too slowly, the pressure (as
shown by
refea~encc numeral 732) at the sealing face 708 at the position of the biasing
element 704 will be
greater than the average pressure 728, causnz~g an opposite moment to be
developed about the
5 ' first end 706a tending to force the clearance gap 714 to widen. The
widening of the clearance
gap 714 again will cause a flattening of the pressure transition profile. Tlxe
clearance gap 714
(and the angle between the sealing face 708 at~d the rotor face) will
conti~rtue to widen in response
to the pressure differential between. the compartments 718 and the apertures
34, 35 until the
pressure 732 equals the pressure 728, at wl,,;ich point a linear pressure
tra~asition profile again vnill
0 , be obtained.
Numerous variations of the foregoing clearance seal will be apparcsit. In one
such
variation, shown in Fig. 12a, the sealing face 708 includes a plurality of
passages, provided as
a labyrinth, for increasing the flow resistance for a given channel gap 714
height_ In another
CA 02364881 2001-12-11
-24-
variation (not shown), rather than fihe sealing face 708 being planar, the
sealing face 708 includes
a plurality of planar stepped portions,. so that the sealing face 708 tapers
away from the rotor face
o~rex a plurality of steps and the flow resistance is increased for a given
angle of deflection of the
sealing element 702. Itt yet another variation, the biasing element 704 is
positioned at an off
centre position so as to pmvide a controlled non linear pressure transition
profile.
In still another variation, the clearance seals 700 are used to provide
sealing far closed
sectors, such as the closed axial flow settoxs 675, 676 shown in Fig. 10. In
this latter variarion,
the bearings 712 are replaced with fasteners which rigidly secure the first
end 706a of the sealing
element 702 to a race on the rotor valve face 21 (or rotor valve face 23) so
as to prevent
variations in the height of the clearance gap 714. Further, the first and
second comparhnents
718a, 718b do not communicate r~rith any blowdown compartments, but are
pressurized to the
pressure of the apertures 34, 35. As a result, the soalixxg faces ?08 are
urged towards the rotor
face so as to limit the gas flow through the apertures 34, 35.
Figs. 13a.13b
Fig_ I3a shows a seX~ regulating clearance seal 800 for use with the
pressurization
compartments 46, 50, 52, 54 or the light reflex return compartments 82, 84, 86
of an axial-flow
configured rotary PSA module, such as the PSA module 600 shown in Fig. 9. The
clearance seal
800 may even be used in connection with heavy reflex return compartments if
desired.
The self regulating seal 800 is substantially similar to the self regulating
seal 700,
comprising a sealing element 802, and first and second resilient biasing
elements 804a, 804b
coupled to the sealing clement 802. The scaling element 802 is interposed
between the first
valve face 21 of the rotor 11 and the eorrcspondittg stator valve face of the
stator 14, when used
in conjunction with pressurizatiotr compartments 46, 50, 52, 54, or ie
interposed between the
second valve face 23 of the rotor 11 and the corresponding stator valve face
of the stator 14,
when used in conjunction with the light reflex return compartments 82, 84, 86.
Sealing elements
802 are positioned along the stator valve face, with each sealing element 802
being positioned
betvcreen a pair of adjacent pressurization or reflex retwtr~ compartment,
such as betwoen the
pressurization compartments 50, 52 shown in Fig.12a. However, the sealing
elements 702 may
be positioned between any pressurization compartments, or proximate to any
fast gas flow
conduit which facilitates pressurization of a second gas flow conduit moving
past the first gas
flow conduit. Alte~natcly, the clearance seals 800 may be used without any
pressurization
compartments, to provide sealing for closed sectors.
CA 02364881 2001-12-11
- 25 -
Each sealing element $02 com~pzises ate elongate slippethaving ~~xst and
second opposite
ends 806x, 806b, a substantially planar sealing face 808 extending between the
opposite ends
806, and an opposing second face 810 also extending betweec~ the opposite ends
806 but
positioned opposite the sealing face 808. 'The sealing elmnet~t $02 is
positioned between ~e
S rotor valve face 21 (or the rotor valve face 23) and the corresponding
stator valve face, with the
f rat end 806a being positioned adjacent one of the pressurization/ reflex
return compartments,
such as the pressurization compartment 50, and with the second end 806b being
proximate to the
adj scent pressurization/reflux return compartment, such as the pressurization
compartment 52.
The first end 806a of the sealing element 802 is pivotally coupled to the
rotor valve face a1 (ox
rotor valve face 23) through bearings 812, as with the self regulating seal
700.
Each biasing element 804 comprises a resilient element including a first aide
wall 816a,
and a second side wall 816b opposite ithe first side wall S l tin. The biasing
elements 804 are
positioned at opposite ends of the sealing element 802, with the first biasing
element 804a being
positioned adjacent the first end 806a,; and the second biasing element 804b
being positioned
adj scent the second er~d 806b. Each pair of biasing elements 804a, 804b
extend between the
opposing face 810 and the stator .valve face between a pau of adjacent
pressurization/reflux
return compartments. The biasing elemea~ts 804 prevent the Sealing element 802
from rotating
with the rotor 11 as the apertures 34 (or the apertures 35) of the rotor 11
move past the seavng
face 808, and urge the sealing face 808 towards the tutor valve face. Further,
since the gas flow
rate through the apertures 34, 35 of the rotor 11 is dependent upon the height
of the clearance gap
814, the second side wall 816b of each resilient biasing element 804 is
concave so to allow the
height o~ the clearance gap 81.4 to be varied. However, to reduce friction
between the scaling
face 808 and the rotor valve face, preferably the biasing dements 804 do not
press the sealing
face 808 against the rotor valve face. The biasing elements 804 are also sized
so the sealing face
808 tapers away from the rotor valve face from the ~xxet end 806a towards the
second end 806b,
so that the clearance gap 814 between the sealing ~ace 808 and the rotor face
is gfeater adjacent
the second end 806b than adj ace~t the first end 806a. As will be apparent,
this feature provides
a gradual pressure increase for the gas; flowing into the flow path ends 30,
32 of the adsorbers
24 as the correspondiixg apertures 34, 35 of the rotor 11 tiraverse the
sealing face 808.
A compartment 818 is provided between the secQad side wall 816b of the first
biasing
element 804x, the first side wall 8 I 6~ of the second biasing elentterrt
$04a, and the portions of the
stator valve face and the opposing face 810 extending thcrebetween. The
compartment 818
communicates with the pressurization/i~eBux return compartment adjacent the
second end 806b
CA 02364881 2001-12-11
-26-
(pressurization compartment 52) through an aperture 820 provide in the sealing
element 802_
The aperture 820 is positioned. equidistantly betweon the first and second
ends 806x, 806b and
extends between the sealing face 808 and the opposing face 810. The operatian
of the clearance
sear 800 will now be described with ,reference to Figs 13a, 13b.
In operation, the rotor rotates in the direction of the aztow denoted by
reference numeral
822. Since clearance seals 800 are positioned along the circumfet~e~nce of the
stator valve face
between adjacent pressurization/reflux return compartments, the first end 806a
will be exposed
to a pressure from one of the pressurizationlrcflux return compartmec~ts, and
the second end 806b
will be exposed to a greaterpressure from the adjacent pressurization/reflux
return compartment.
In the example shown in Fig. 13a,, the first end 806a is exposed to a pressure
from the
pressurization compartment 50, and the second end 806b~is exposed to a greatex
pressure from
the pressurization compartment 52. Accordingly, when an aperture 34, 35
approaches the ftxst
end 806a of the sealing clement 802, the gas entering the aperture 34, 35 is
equalize to the
pressure of the pressurization compartment 50. As the apertures 34, 35 pass
the first end 806a
and approach the second end 806b, the clearance gap 814 ineroases, thereby
allowing the rate of
gas flow into the aperture 34, 35 to increase and the pxessure at the
corresponding flow path end
30, 32 of the adsorber 24 to increase.
Preferably, the pressure transition profile between the first
pressurization/re#lux return
compartment (pressurization compartnnent 50) arid the second
pressurization/reflux return
compartment (pxessurization eomp~.rrtment 52) is substantially linear so as to
maintain
equilibrium between the adsorbent material and the mass transfer front of the
gas. However, as
discussed above, the rate of gas flow (and hence the rate of pxossure
blowdown) depends on the
height of the clearance gap 814. For instance, ix~ a conventional clearance
seal, if the clearance
gap 814 increased too rapidly, the pressure transition profile would normally
have the convex
shape (denoted by reference numeral 824) shown in Fig. 13b, whereas if the
clearance gap 814
increased too slowly, the pressure transition profile would normally have the
concave shape
(denoted by reference numeral 82t7.~ However, as will stow be explained, with
the present
invention, the height of the clearance gap 814 automatically adjusts to obtain
the linear pressure
transition profile (denoted by reference numeral 828).
Since the compartment 818 communicates with the pressurization/reBuX return
compartment adjacent the second end 806b through a passage 820 positioned
equidistantly
between the first and second eeds 806a, 806b, the compartment 818 of each
sealing element 802
will be maintained at a pressure level which is equal to the pressure of the
sealing face 808 at the
CA 02364881 2001-12-11
-27-
equidistant position. If the clearance gap 814 increases too rapidly, the
pressure (as shown by
reference numeral 830) in the compardment 818 will be greater than the
average(dcnoted by
reference numexal 831) of the pressure of the pressurization compartment 52
and the pressure
of the pressurization compartment 54; Since the pressure exorted against the
sealing face 808
between the first end 806a and the position of the passage 820 will be
significantly less than the
'
pressure 830, and the pressure exerted;againat the sealing face 808 between
the second end 806a
and the position of the passage 820 will ouy be slightly greater than the
pressure 830, a moment
' will be developed about the first end 8068 tending to force the cloarance
gap 814 to narrow. The
narrowing of the clearance gap 814 will cause a flattening of the pressure
tranBition profile. The
clearance $ap 814 (and the angle betwoan the sealing faco 808 and the rotor
face) will continue
to narrow in response to the pressure differential between the compartment 818
and the apertures
34, 35 until the pressure 830 equals the average of the pressure of the
pressurization
compartment 52 and the pressurization compartment 54, at which point a linear
pressure
transition profile will be obtained.
Conversely, if the clearance gap 814 increased too slowly, the pressure (as
shown by
reference numeral 83Z) in the compartment 818 will'be less than the average of
the pressure of
the pressurization compartment 52 and the pressurization compartment 54. Since
the~pressuxe
exerted against the sealing face 808 between the second end 806a and the
position of the passage
820 will be significantly greater than the pressure 832, and the pressure
exerted against the
sealing faco 808 between the first end 806a and the positio~a o~ the passage
820 will only be
slightly less than the pressure 832, a moment will be developed about the
first end 806a tending
to force the clearance gap 814 to widen The widening of the clearance gap 814
will cause a
flattening of the pressure izansition p~file. The clearance gap 814 (and the
angle betwe~ the
sealing face 808 and the rotor face) wiXl continue to widen in response to the
pressure differential
_ betwexn the coropariment 818 and the, apertures 34, 35 until the pressure
832 equals the average
of the pressure of the pressurization compartment 52 and the pressurization
comparbmeat 54, at
which point a linear pressure transition profile will be obtained.
Numerous variations of the foregoing clearance seal, will be apparent. In one
such
variation, shown in Fig_ 13a, tlZe sealing face 808 includes a plurality of
passages, provided as
' 30 a labyrinth, for increasing the flow resistance for a given channel gap
814 heigtxt. Tn another
variation (not shown), rather than the sealing fact 808 being planar, the
sealing face 808 includes
a plurality of planar stepped portions, so that the sealing face $08 tapers
away from the rotor face
over a plurality of steps and the flow resistance is increased for a given
angle of deflection of the
CA 02364881 2001-12-11
I i
i _2g_ . . .
seating element 802. 1n yet another variation, the aperture 820 is positioned.
at an off centre
position so as to provide a controlled non-linear pressuro transition profile.
i
In still another variation, the dlearanee seals 800 are used to provide
sealing for closed
sectors; such as the closed axial flow sectors 675, 676 shown in Fig. 10. In
this latter variation,
the beavrmgs 812 are replaced with fasteners which rigidly secure the first
cud; 806a of the sealing
dement 802 to a race on the stattor valve face 40 (or stator valve face 41) so
as to prevent
variations in the height ofthe clearance gap 814. Further, the first and
second'compartments 818
do not communicate with any blowdown compartments, but are pressurized to the
pressure of
the apertures 34, 35. As a result, the sealing faces 808 are urged towards the
rotor face sa as to
Limit the gas flow through the apertures 34, 35.
r . 14
Fig. 24 shows self regulatingl clearance seals 700', 800' respectively for use
with the
blowdownandpressurizatior~compardmentsofaxadial-flowconfiguxed.mtatyPSAmodule.
The
blowdown clearance seals 700' are shown positioned between the stator and
rotor valve faces for
use witty the countezcurrent blowi3own compartments 56, 58, b0 and the
cocurrent blowdown
compartments 72, 74, 76, 78. Similarly, the pressurization eloarance seals
800' are shown
positioned between the stator and rotor valve faces for use with the
pressurization compartments
46, 50, 52, and the light reflux return compartments 82, 84, 86. In addition,
Fig. 24 shows self
regulating blowdown clearance scale 700", identical to clearance seals 70f,
but being used
without blowdowa compartrne~nts for sealing closed radial flow sectoxs,
simxXax to the closed
a~iaX flow sectors 675, 676 shown in Fig. 10. Alternately, pressurization
seals 800", identical
to clearance seals 700", may be used without pxessuxi2ation compattanents for
sealing closed
radial ~low sectors. ' .
The clearance seals 70f, 800' are respectively substantiallyideatical to the
clearance seals
.25 700, 800. Unlike the clearance seals 700, 800, however, the clearance
seals 70f, 80f
I '
respectively have areuate sealing faces 708', 808' and arcuate opposed faces
710', 810' instead
ofthe substantia11yp1anat sealing faces 708, 808 and the substantiallyplanar
opposed faces 710,
810 to allow the clearance seals 700'; 800' to regulate the flow of radial gas
flow through the
rotary PSA module. However, as discussed above with respect to the clearance
seals 700, 800,
! r
the clearance seals 700', 800' are not limited for use with rotary PSA
modules. Rather, the
clearance seals 700' may be used to regulate the pressure letdown of radial
flow of gas between
any first gas slow conduit and any second gas flow conduit moving past the
first gas flow
CA 02364881 2001-12-11
-29-
conduit. Similarly, the clearance seals 800' may be used to regulate the
pressurization, from a
first gas flow conduit, of a second gas conduit which moves past t6c first gas
flow conduit.
Figs.l5.16A and 1GB
Fig. 15 is an tmrolled view ofi the first valvo face seals from Fig. 14, with
the view split
arbitrarily at feed pressurization comlisrtment 46. Figs.16A and 16B are
sections 901- 902 and
903 - 904 respectively of Fig. 15.
Circumferentisl seals 905 and 906 provide sealing bthe stator 14 and tutor 11
at
the ends thereof, to bound the first' sealing face 21 at each cnd while
closing the function
compartments (as well as pressure balancing compathnents that have no intended
through flow
function)betweeneachadjacentpairofcleararucesea1s700',700",800' and$00".
Sea1s905and
906 are attached to stator 14 in order] to maintain the seals in position
while reacting frictional
torques. Seals 905 and 906 may be solid or split rings. In the case of split
ring cx~rcunaferentyal
seals, the split should be at a point of the circumferenco where the working
pressure most closely
roaches acternal ambient
app pressure,, and may be an aztchox point fox tensile or pin connections
to the casing . Hinges 712 and 812 of respectively the blowdown and
pressurization clearance
seals are attached to the cireumferential seals which thus hold the clearance
soak in place. The
l
clearance seals through their hinge connections may also desirably serve as
struts to control the
relative spacing of the circumfcrential seals to resist lateral deflections
under pressure loading.
Flexible static seals 911 and 912 are provided with the appropriate curvature
to flex in
. tension for the portions of the circumf~ential seals respoctively sealing
compartments at positiYe
working pressure and vacuum (if any. Static seals 911 and 912 may be
substantially idonticaX
in section and material of construction to the biasing elements 704, 804a and
804b of the
clearance seals. The section and iaaterial should provide ~ adequate
compliance to absorb
deflections due to manufacturing tolerances, initial misalignment, pressure
and thermal. loads,
and wear of the seal surfaces. As shov~ra by the dashed lines on Fig.15,
static seals 911 and 912
and biasing elcanents 704, 804a and 804b are jointed at the corners of the
function compartments
(and supplementary pressure balancing compartments 913) to maintain static
sealing of those
compartments behind the clearance and circumferential seals.
Suitable materials for static seals and biasing elements may be elsstomers,
thermoplastics
or thin metal foil according to working temperatures and compatibility with
pmeess gas
components. Suitable materials for the rubbing circumferential seals include
PTFE composites
for operation near ambient temperature. A refinement for reduced fnictional
loads and longer
service life is to include pressure balancing grooves 920 extending
circumferentialiyin segments
CA 02364881 2001-12-11
-30-
over limited angular arcs at a central point of the rubbing surface of the
circumferential seals.
The angular arc of each segment will corrcapond to an angular sector (e.g.
adjacent a function
compartment) of the seal which is sealing a substantially constant worlo'tntg
pressure over that
angular arc. At one or a few locations for each such segment, a vent passage
is provided between
the groove and the higher pressure side of the seal. The vent passage is sized
so that the normal
design leakage flow across the seal in that angular arc would only cause a
small pressure drop
between the higherpressuxe side of the seal and the groove if substantially
all that design leakage
flow were flowing through the vent passage. Hence, the portion of the seal
upstream of the
groove (e. g. the higher pressure side of the seal) will be nearly pressure
balanced and hence under
low frictional loading as long as leakage across the seal in this sector
remains within the design
flow. In normal operation, the sealing load will thus be carried. primarily on
the downstream side
of the circurrtfetential seals. If the seal is damaged or wears severely so
that leakage on the
downstream side increases, increased flow thmugh the vent paxsage will result
in greater pressure
chop in the pressure balancing groove, so that the entire width of the seal
will be more heavily
loaded to reduce overall leakage albeit with greater frictianel loading dicing
extended service
life until the seals is replaced.
Fiss. 17_ 18 and 22
Fig. 17 shows the stator valve face 41 of a simplified axial-flow-configured
rotary
vacuum PSA module as shown in Fig. 9. Fig.18 shows a perspective view of the
first valve face
of Fig. 17 to better indicate the naaow gap flow control feature. In Fig. 17,
a single stage feed
blower 201 delivers compressed air to feed port 918 in compartment 52, while a
single stage
vacuum pump withdraws nitrogen enriched exhaust gas from exhaust port 919 in
compartm~t
60_
The stator valve face 41 of Figs. 17 and 18 has a first closed sector 676
corresponding
to the light reflex exit steps, and a second closed sector 676' corresponding
to the light reflex
return stops, of the vacuum PSA cycle. In sectors 676 attd 676', fluid flow in
the valve face is
minimi2ed by maintaining a narrow sealing gap between rotor and stator faces
of no more than
about 50 microns and preferably between 0 and about 25 microns.
The stator valve face 41 of Figs. 17 and 18 also has a feed pressurization
sector 920
exuding from angular position 921 adjoining closed sector 676' to angular
position 922
opening into compartment 52. A flowv control clearance gap between and
substantially across
the tutor and stator faces is established between angular positions 921, and
922, opening from 0
- 50 microns at position 92I to about 50 - 500 microns at position 922 so as
to provide flow
CA 02364881 2001-12-11
-31-
restriction to control the rate of pressurization of adsorbs progressing from
angular positions
921 to 922. A sei~ regulating clearance seal as shown in Fig.13 a may be used
in pressu~zation
sector 920, ox alternatively the clearance gap array harre a fixed geometry.
The stator valve face 41 of Figs. 17 and 18 also has a countercurrent blowdown
sector
S 923 extending from angular position 924 adjoining closed sector 676 to
angular position 925
opening into compartment 60. A flow control clearance gap botween the rotor
and stator faces
is established. between angular positions 924 and 925 and substantially acmas
the rotor and stator
faces, opening from 0 - 50 microns at position 924 to about 50 - 500 microns
at position 925 so
as to provide flow resitiction to control the rate of depressurization of
adsorbers progressing fronn
angular positions 924 to 925. A self regulating clearance seal as shown in
Fig. 12a maybe used
in counteacusent blowdown sector 923, or alternatively the clearance gap may
have a fixed
geometry.
Fig. 22 shows a sectional vaiew of a circumferential sectiio;n of tt~a module
of Fig. 17,
using the sealing member 930 illustrated in Figs. 19, 20 and 21, As is clearly
evidrut, the
clearance gap defined by th,e space between the opposing rotor and stator
valvo faces 21 and 41
widens towards the compartment being opened (such as heavy product
compertrnent 60, which
is illustrated), to effectively obtain progressive opening of an orifice (i.e.
a throttling effect) to
dampen the raft of pressure decrease as countercurrent blowdown takes place in
sector 923 and
gas exits thxough compartment 60. The same effect can be obtained for purposes
of
pressurization o~the absorbers.
pigs. I9. 20 and 21
Figs. l9 arid 20 Shaw a unitized sealing member orrotor seal 930 for sealing
engagemeant
with the stator valve face 41 and rotor valve face 21 of the axial flow rotary
pressure swing
adsorption apparatus of Fig. 17, with "N" adsorbent beds ox adsarbers 24. In
the specific
embodiment illustrated, N ~ 16. The sealing member 930 is disposed between the
rotor valve
face 21 and the stator valve ~ace 41 to maintain sealing eagagernent with the
rotor valve face 21
and the stator valve face 41 _ Manufacturing tolerances, misalig»nrtent,
differential theanal
expansion, and operational wear preseet challenges for maintaining proper
sealing beivween the
tutor and stator of a rotary pressure swing adsorption apparatus. In order to
maintaizt sealing
engagement with the rotor valve ~ace 21 and the stator valve face 41 despite
these imperfections,
sealing member 930 is configured for transverse movement relative to the valve
faces 21 and 23.
CA 02364881 2001-12-11
-32-
The rotor seal includes an outer cirr,-umferrutial 8ea1 ping 931, an inner
circumferential
seal ring 933, and a set of "N" laterally extending seal elements or spokes
933 a~ngulu~ly
separating adjacent pairs of the '21" adsorbers, e.g. adsorbers 25 and 26. The
seal spokes 933
extend laterally between outer seal ring 931 and inner seal ring 932. In one
embodiment, the seal
spokes extend rudially between, outer seal ring 931 and inner seal ring 932.
Tn one embodiment, the seal spokes 933 are rigidly attached to rind 931 and
932. rn
another embodiment, the spokes may be separate components engage by notches
into rings 931
and 932. In either case, the rotor seal 930 is of unitary construction whereby
spokes 933 join
rings 931 and 932.
The materials for rotor seal 930 and stator valve face 41 are selected for
compatibility in
rubbing contact to achieve low friction and low wear. Seal 930 may be
fabricated from (or faced
with) a PTFE compotmd, while fact 41 may be fabricated from or coated with a
metal alloy or
ceramic of higb hardness and with a smooth surface finish..
Fig. 20 and Fig. 21 are sections of the seal of Fig. 19 as installed in the
rotox of Fig. 9.
Fig. 20 is the section of a spoke indicated by arrows 940 arid 941 in Figs. 19
and 21, while Fig.
21 is a radial section indicated by arrows 942 and 943 in Fig. 19_
Referring to Fig. 20, rotor seal 930 is aligned for engagement to faces
prese~ated by each
of partition 27, inner wall 970, arid outer wall 972 of rotor 1 ~1. Partitions
27 extend radially
(lateralay) between inner welt 970 and outer wall 972, and join inner wall 970
to outer wall 972,
to thereby define a plurality of flow paths exteading between first and second
rotor ends 1003,
1005.
Referring to Fig. 20, spoke 933 is aligned with and engaged to partition 27,
,and has a
sealing face 950 which engages stator valwe face 41. The spoke 933 has a
static sealing web 951
disposed in a groove 952. Groove 952 is defined by flanges 953 and 954
extending from
shoulder 955 of partition 27 between typical adsorbers 25 and 26, portions of
which are shown
in Fig. 20. Spoke 933 has slxoulders 956 and 957 to achieve a desired angular
sealing width.
During operation, spoke 933 is retainedwithin groove 952 and is disposed in
sealing engagement
with partition 27 (flange 954) by frictional drag caused by seal 930 rnov~ing
against stator valve
CA 02364881 2001-12-11
- 33 -
surface 41. Alternatively, such sealing engagement is msintainad by pressure
di~'crontials
between flowpaths. Simultaneously, spoke 933 is permitted to move transversely
(in this case
axially) relative to valve surfaces 21 and 41 to ensure sealing engagement is
maintained with
stator valve st~'ace 4l .
,A. pteloading elenaet~t or resilient member 960 is d~xablyprovided or
captured in groove
952 to energize or bias (or urge) spoke 933 against stator face 41. In one
embodiment, resilient
member 960 is keyed into groove 952. Preloading clement 960 is more resilient
or compliant
than spoke 933. In. one embodiment, preloadiag element 960 is characterized by
a lower elastic
modulus than sealing member 930. Ia this respect, preloading element 960 may
be an
elastomeric seal (e.g. as O-ring as shown) which also provides static sealing
to minimize leakage
past steps 956 and 957 between adsorbers 25 and 26. Alternatively, preloadi~g
dement 960 may
be a metallic spring (e.g. a wave spring, or an elliptical coil spring).
Fig, 21 shows the typical spoke 933 attached to z~gs 931 and 932. Static seals
961 and
962 cooperate with preloadirng element 960 to enable some axial movement
between the seal 930
and rotor l1, to accommodate manufacturing tolerances, misalignment,
differential thermal
expansion, and wear of the seal 930 or the stator valve face 41. Outer ring
931 engages the outer
wall 970 of rotor 11 with a compliant static seal 971, and inner ring 932
engages the inner wall
972 ofrotor 11 with a compliant static seal 973. Static seals 971 and 973 are
more resilient, and
characterized by higher elastic modulus than rings 931 and 932. An outer
annular gap between
static seals 971 and 962, and similarly an inner annular gap befiween static
seals 973 and 961,
may be pressurized e.g. with compressed feed air so as to energize seal 930
against first valve
face 41.
It will be appreciated that a similar seal arrangement to that shown for the
first valve faces
21 and 41 at first rotor end 1001 in Figs 17 - 21 may be provided for the
second valve faces 23
and 43 at second rotor end 1003.
The foregoing description of the preferred embodixuents o~the invention is
intended to
be illustrative of the present invention. Those of ordinary skill will be envi
sage Certain additions,
deletions or modifications to the described embodiments without departing fzvm
the spirit or
scope of the in~rez~tion as defined by the appended daixus.
