Molecular sieve abstract
A valve assembly (B) cycles compressed gas from a compressor (A)
to a pair of molecular sieve beds (C) to perform a pressure swing
adsorption gas separation cycle. Each bed includes a peripheral
outer wall (20) and has a tubular member (30) extending down a central
axis thereof. An extensible sleeve (26) surrounds the central tube
and is in fluid communication therewith by way of an aperture (32).
A fluid amplifier (F) amplifies fluid pressure from system gases,
particularly the gases from the compressor, and uses the amplified
pressure to expand the extensible sleeve. Particles (22) of zeolite
material are inhibited from becoming fluidized and moving with fluid
flows by the clamping pressure between the extensible sleeve and
the peripheral wall of the bed.
Molecular sieve claims
Having thus described the preferred embodiments, the invention
is now claimed to be:
1. A pressure swing adsorption gas concentrating system comprising:
a means for cyclically supplying a gaseous mixture to and removing
an adsorbed gaseous component from at least one molecular sieve
bed over wide cyclic swings of pressures;
the sieve bed including:
a closed, generally cylindrical container having peripheral and
end walls, defining a first port through which the gaseous mixture
cyclically flows into the container and the adsorbed gases flow
in an opposite direction out of the container, defining a second
port through which separated gases flow out of the container, and
being substantially filled with a particulate molecular sieve material;
a radially extensible member disposed along the container generally
parallel to the peripheral wall;
an expanding means for radially expanding the member and maintaining
the member expanded over the wide swings of pressures, both as the
gaseous mixture flows into the container and as the adsorbed gases
flow out of the container to provide a compressive force between
the member and the peripheral wall which holds the particulate material
against becoming fluidized even as the gaseous mixture flows in
and the adsorbed gas flows out through the first port causing the
pressure in the sieve bed to undergo the wide swings.
2. The system as set forth in claim 1 wherein the expansible member
includes an inflatable sleeve and the expanding means includes means
for supplying fluid under pressure into an interior of the sleeve.
3. The system as set forth in claim 2 wherein the sleeve is cylindrical
with a major axis disposed parallel to a major axis of the closed
container.
4. The system as set forth in claim 3 further including a tubular,
central support extending centrally through the sleeve, the central
support being connected with the fluid pressure supplying means
and having at least one passage therethrough to provide fluid communication
with the sleeve interior.
5. The system as set forth in claim 4 further including first and
second screen assemblies disposed adjacent opposite ends of the
container and a means for fixing the screen assemblies against axial
separation.
6. The system as set forth in claim 2 wherein the means for supplying
fluid under pressure includes a pressure amplifier having an input
end operatively connected with the means for supplying fluid under
pressure for receiving fluid therefrom under pressure and an output
end for supplying the fluid under a higher pressure to the sleeve.
7. The system as set forth in claim 6 wherein the pressure amplifier
includes a low pressure chamber operatively connected with the supply
means for cyclically receiving the fluid under pressure therefrom
and a high pressure chamber connected through a first one way valve
means to the sleeve, and a second one way valve means operatively
connected between the fluid supply means and the high pressure chamber.
8. The system as set forth in claim 1 further including first and
second screen assemblies disposed adjacent opposite ends of the
container in a fixed axially spaced relationship.
9. A bed assembly which receives a nonconstant fluid flow cyclically
into and out of the bed in which fluid pressure within the bed cyclically
varies between high and low pressure extremes, the bed comprising:
a closed, generally cylindrical container having a cylindrical
peripheral wall and oppositely disposed end walls in a fluid sealing
relationship to the peripheral wall, a fluid access port being defined
adjacent each end wall, the container being substantially filled
with a particulate material;
a radially extensible member disposed along the container generally
parallel to a central axis of the cylindrical peripheral wall;
means for expanding the member with a substantially constant pressure
and holding the member expanded with the substantially constant
pressure over a multiplicity of cycles of the high and low fluid
pressure extremes.
10. The system as set forth in claim 9 wherein the extensible member
includes an inflatable sleeve and further including a means for
supplying fluid under pressure into an interior of the sleeve, whereby
inflating the sleeve compresses the particulate material and breaks
apart any particulate material bridges.
11. The system as set forth in claim 10 further including a tubular,
central support extending centrally through the sleeve, the central
support being connected with the fluid pressure supplying means
and having at least one passage therethrough to provide fluid communication
with the sleeve interior.
12. The system as set forth in claim 9 further including a means
for restraining the particulate material against motion in a direction
parallel to the central axis.
13. The system as set forth in claim 9 wherein the means for supplying
fluid under pressure includes a pneumatic pressure amplifier having
a low pressure and operatively connected with a means for cyclically
supplying a gaseous mixture to one of the fluid access ports and
a high pressure end for supplying fluid under a higher pressure
to the extensible member.
14. A gas concentrating system comprising:
a means for cyclically supplying a gaseous mixture to and removing
an adsorbed gaseous component from at least one molecular sieve
bed such that an interior of the bed is subject to a wide pressure
swing in each of a multiplicity of cycles;
the bed including:
a closed container substantially filled with a particulate molecular
sieve material;
an extensible member disposed generally centrally within the container;
and,
a means for continuously expanding the extensible member to compact
the particulate material continuously through each of the multiplicity
pressure swing of cycles between the extensible member and the container
to inhibit fluidization and cyclic abrasion of the particulate material.
15. The system as set forth in claim 14 further including a pneumatic
pressure amplifier having a low pressure side operatively connected
with the means for cyclically supplying the gaseous mixture and
a high pressure side for supplying the gaseous mixture under a higher
pressure to the extensible member.
16. The system as set forth in claim 15 further including a one
way valve means operatively connected between the high pressure
side of the amplifier and the extensible member.
17. A bed assembly for receiving a fluctuating fluid flow therethrough
whose pressure fluctuates between high and low pressure extremes,
the bed comprising:
a closed container having generally oppositely disposed fluid access
ports, the closed container being substantially filled with a particulate
material;
an extensible member disposed generally centrally within the container
such that expansion of the extensible member compacts the particulate
material between the extensible member and the container to inhibit
fluidization of the particulate materials;
a means for continuously expanding the member with a pressure at
least as high as the high pressure extreme even as the fluid flow
drops to the low pressure extreme.
18. The bed as set forth in claim 17 further including screen assemblies
disposed adjacent each fluid access port for holding the particulate
material in a spaced relationship thereto.
19. The bed as set forth in claim 17 wherein the extensible member
expands along two dimensions and further including a means for restraining
movement of the particulate materials along a third dimension.
20. The bed as set forth in claim 19 wherein the restraining means
includes a pair of screen assemblies disposed at opposite ends of
the container in a fixed, spaced relationship along the third dimension.
21. A pressure swing adsorption gas concentrating system comprising:
a means for cyclically supplying a gaseous mixture to and removing
an adsorbed gaseous component from at least one molecular sieve
bed with a cyclically changing pressure swing that causes the adsorbed
gaseous component to be adsorbed during a portion of each cycle
that the gaseous mixture is supplied and de-adsorbed during a portion
of each cycle in which the adsorbed gaseous component is removed;
the sieve bed including:
a closed, generally cylindrical container having a peripheral wall
and being substantially filled with a particulate molecular sieve
material;
an extensible member disposed along the container generally parallel
to the peripheral wall;
a liquid and vapor system in which a liquid and its vapor have
a relatively constant vapor pressure relationship independent of
the cyclically changing bed pressure, the liquid being disposed
in at least one of the extensible member and a reservoir in fluid
communication with the extensible member, the liquid and vapor system
being in vapor communication with the extensible member such that
the relatively constant vapor pressure expands the extensible member
against the particulate material with a relatively constant force
to hold the particulate material against cyclic fluidization and
abrasion.
Molecular sieve description
BACKGROUND OF THE INVENTION
The present invention relates to the art of restraining particulates
that are subject to the forces of gas or fluid flow. It finds particular
application in conjunction with restraining zeolite particles in
the adsorption beds of pressure swing adsorption (PSA) gas concentrators
and will be described with particular reference thereto. It is to
be appreciated, however, that the present invention may find utility
in conjunction with other types of gas concentrators and gas concentration
cycles as well as with other fluid treatment operations, such as
filters, catalysts, ion exchange systems, and the like.
Heretofore, pressure swing adsorption gas concentrators have commonly
included first and second molecular sieve beds connected by a cross
over valve to an air compressor. The beds are filled with particles
of a zeolite, carbon, or other material which adsorbed selected
component(s) of the air, e.g. nitrogen, received at an input port
while allowing other components, e.g. oxygen, to pass through the
bed to an output port. In some concentrators, the beds have layers
or strata of particulates with different characteristics.
The cross over valve cyclically supplied atmospheric air under
pressure to the input port of one of the beds while purging the
other bed by venting or drawing a vacuum on its input port. A small
part of the separated oxygen from the output port of the bed receiving
the air under pressure is fed back to the output port of the bed
being purged.
These changes in pressure and flow tend to cause an unwanted movement
of the zeolite particles. The movement rubs the particles together
abrading them. The abrading of the particles creates smaller particles
which are even more mobile, hence accelerating the abrading.
One prior art solution was to apply an axial compressive force
on the cylindrical molecular sieve beds. For example, the molecular
sieve bed was housed in a cylindrical housing in which one or both
of the ends could be moved axially. After the bed was filled with
zeolite, the ends were pressed together and locked. One of the problems
with axial pressure is that the effect of the clamping force was
dissipated and became ineffectual within a short distance. The particles
compact into a bridge that protects interior regions from the pressure.
Moreover, when the particles became smaller due to abrading, they
filled voids and packed more tightly, relieving the clamping pressure.
During normal use of a pressure swing adsorption system, the beds
receive various thermal forces, vibration, and the like, which tend
to cause undesirable movement of the particles. Moreover, the thermal
expansion, the abrading and settling of particles, the introduction
of compressed air, and the like tend to defeat or relieve the clamping
force.
The use of spring clamping systems to apply a continuing longitudinal
spring bias also tended to be ineffective. Again, the spring force
was dissipated within a short distance allowing the particles at
some distance from the spring to move. The particles under pressure
adjacent the spring would pack together and form a bridge which
blocked the spring force from reaching particles beyond the bridge
from the spring. Thus, the particles at the center of the cylinder
still abraded, packed together, formed voids, and thus increased
the mobility of the particles.
The present invention provides a new and improved particulate anchoring
system which overcomes the above referenced problems and others.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, a sieve
bed is provided. The sieve bed is a closed, generally cylindrical
container which has a peripheral wall and is substantially filled
with a particulate molecular sieve material. An elongated radially
extensible member is disposed through the container generally parallel
to the peripheral wall. A means is provided for selectively radially
expanding the radially expansible element to compress the particulate
material between the radially expansible element and the peripheral
wall.
In accordance with another aspect of the present invention, the
sieve bed is a closed container which has a peripheral wall and
is substantially filled with particles of molecular sieve material.
An expansible member is disposed generally centrally in the container.
A means is provided for expanding the expansible member to compress
the particulate material between the expansible member and the peripheral
wall.
In accordance with a more limited aspect of the present invention,
the sieve bed is incorporated in a pressure swing adsorption gas
concentrating system. A means is provided for cyclically supplying
a gaseous mixture to and removing an adsorbed gaseous component
from the sieve bed.
In accordance with a yet more limited aspect of the invention,
the means for expanding the expansible member derives pressure from
the cyclically supplied gaseous mixture. In this manner, the pressure
with which the expansible member is expanded is determined at least
in part by the pressure of the gaseous mixture. An increase in the
gaseous mixture pressure causes a corresponding increase in the
expansion pressure to maintain the compression of the particles.
A primary advantage of the present invention is that it immobilizes
granular materials through which fluid passes. The invention also
breaks apart particle bridging that might block particle immobilizing
forces.
Another advantage of the present invention is that it extends zeolite
bed life in gas concentrating systems.
Yet another advantage of the present invention is that it is self
compensating for fluctuations in fluid pressure.
Still further advantages of the present invention will become apparent
to those of ordinary skill in the art upon reading and understanding
the following detailed description of the preferred embodiment.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention may take form in various components and arrangements
of components and in various steps and arrangements of steps. The
drawings are only for purposes of illustrating a preferred embodiment
and are not to be construed as limiting the invention.
FIG. 1 is a pressure swing adsorption gas concentrating system
incorporating the present invention;
FIG. 2 is a side sectional view of the zeolite bed in accordance
with the pressure invention;
FIG. 3 is a view taken through section 3--3 of FIG. 2; and,
FIG. 4 is a cross sectional view of an alternate pressure amplifier
for the system of FIG. 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
With reference to FIG. 1 a compressor A supplies a gaseous mixture,
such as atmospheric air, under pressure to a valving system B. The
valving system cyclically supplies the compressed gaseous mixture
to one or more molecular sieve beds C and vents or purges the other
bed or beds.
Each bed adsorbs one or more gases of the mixture, such as nitrogen,
while passing another gas, such as oxygen. During the purge cycle,
the interior of the bed is vented to atmosphere or connected to
a vacuum side of the compressor A to discharge the adsorbed gas
from the bed. Primary product gas, oxygen in the illustrated embodiment,
is passed from the beds to a primary product gas outlet D.
Each bed includes an anti-fluidization means E for inhibiting mobility
and fluidization of the zeolite particles within each bed. More
specifically to the preferred embodiment, a pressure amplifier F
amplifies the pressure of the gaseous mixture received from the
compressor. The amplified fluid pressure is connected with the anti-fluidization
means to provide the motive force for holding the zeolite particles
firmly against movement.
The valving means B includes a cross over valve means that includes
a bed inlet valve 10 for each bed and an exhaust valve 12 for each
bed. The inlet and exhaust valves are cycled alternately such that
one of the beds is connected with the inlet valve while the other
bed is connected with the exhaust valve.
With continuing reference to FIG. 1 and further reference to FIG.
2 each molecular sieve bed C includes an elongated, generally cylindrical
outer wall 20. Particles 22 of granular zeolite fill the space inside
the walls. The anti-fluidizing means E includes an air spring or
other radially extensible member 24 disposed axially along the center
of the cylindrical peripheral wall. The extensible member is urged
under pressure, e.g. pneumatic pressure, outward from a collapsed
or relaxed configuration. The outward radial expansion is inherently
anti-bridging. Any bridging is separated and distributed by the
radial expansion of the expansible member.
The illustrated embodiment, the expansible member includes a rubber
or other elastomeric bladder or sleeve 26 which expands radially
when subject to an internal pressure. Alternately, a non-elastomeric
bladder can be expanded from a folded or compressed configuration
back toward a less folded or relaxed configuration. The radial extension
presses the zeolite particles between the bladder and the peripheral
wall to lock them into a preselected position. The expansible bladder
may be selectively expanded and contracted during filing of the
bed to assist in compacting the zeolite.
The distance between the bladder and the outer wall is determined
by anticipated volumetric compaction or settling and the expansion
capacity of the bladder. The anticipated compaction of the particulate
zeolite should not exceed the ability of the extensible number to
expand. The bladder extends axially to within a half peripheral
wall diameter of the axial ends of the sieve material 22 to insure
that radial forces reach to the axial extremes of the sieve material.
Looking still to the preferred embodiment, a hollow rigid tube
30 extends centrally through the container or bed parallel to the
peripheral wall 20. The tube has one or more apertures 32 which
provide pressure communication from the inside of the tube to the
outside. The sleeve 26 surrounds the rigid tube and is sealed thereto
at opposite ends by a sealing means 34 such as radially compressive
clamps. The tube 30 may have peripheral grooves 36 to improve the
sealing interaction with the bladder. A shield 38 may be provided
between the radial clamp and the sleeve to inhibit the clamp from
cutting the sleeve or otherwise creating a situation which causes
premature failure. Numerous other sealing arrangements, such as
those in which internal sleeve pressure increases sealing with a
peripheral mounting element, are also contemplated.
A pair of screen assemblies 40 are mounted at opposite ends of
the bed to the bed or central shaft. The screen assemblies function
as a means for restraining the zeolite particulate from movement
along the central axis. The screen assemblies also hold the zeolite
particulate away from a top end wall 42 and a bottom end wall 44
to provide a ready air passages 46 48 to inlet and outlet ports
50 52. Each of the screen assemblies include at least one layer
of a stiff, structurally strong material that withstands pressure
from the zeolite due to the compression thereof, and a fine screen
which holds the zeolite material in place. In the illustrated embodiment,
a plurality of bolts clamp two layers of the structurally strong
material with relatively large apertures together with a fine mesh
screen in between.
One of the end wall and the screen assembly includes a stand-off
means for maintaining the spaces between the screen assemblies and
the end walls. A top stand-off means may also include stops 54 in
the peripheral wall which limit outward axial movement of the top
screen assembly. Complementary stops 56 on the peripheral wall 20
interact with the stops 54 to fix the position of the top screen
assembly. Further to the illustrated embodiment, an arched configuration
of the bottom wall 44 provides the stand-off means for the lower
screen assembly. Alternately, the screen assemblies may be held
in position by tube 30. The center tube may also support the end
caps 42 44 function as a structured support for the bed, provide
a convenient mounting assembly for mounting the bed to associated
structures, or the like.
In the preferred embodiment, the central shaft 30 is threaded at
each end to receive an upper mounting plug 60 and exterior lower
nut 62. The nut fixes the tube and screen assemblies to the lower
wall 44. In the illustrated embodiment, the lower nut 62 directly
engages the lower wall, which in turn engages the lower screen assembly
to fix the screens such that they restrain movement of the sieve
and contain the pressure. The center tube 30 may be eliminated if
unnecessary to a differing structural configuration.
The expansible member enables the zeolite to be sufficiently compacted
during filling that axial compression is unnecessary. After the
bed is filled and tamped, the member is expanded to compress the
zeolite against the outer wall. The bladder may be expanded under
constant pressure or pulsed. When the member is deflated the annular
gap around the center is filled with more zeolite. This radial compaction
and fill cycle is repeated as needed. This compaction of the zeolite
before installation of the top screen and end caps not only simplifies
zeolite loading but also facilitates screen and top cap installation.
The screens need only be positioned against the zeolite with sufficient
firmness to restrain it under various pressures and mechanical forces.
It is unnecessary to apply the mechanical force required to effect
significant axial compression of the zeolite.
Other extensible systems may also be utilized. For example, if
the height and width of the tank are substantially the same, a generally
spherical bladder may be disposed in the center of the bed to apply
compressive forces along three dimensions. As yet another option,
the bladder may be two flat sheets of a flexible material which
substantially span one dimension of the bed. Under internal pressure,
the sheets may move outward to apply compressive forces substantially
perpendicular to their surfaces, i.e. along one dimension. In this
manner, the bladder may apply a one dimensional rather than two
or three dimensional compressive force. Other air springs, expansible
bladders, extensible members, and the like may be utilized to provide
one, two, and three dimensional compressive forces relative to the
end and side walls of the bed.
The central tube 30 of each bed includes a Schrader valve 70 in
an inlet end or a connection with a pressure amplifier means F.
With reference to FIG. 1 more specifically, a check valve 72 connects
the inlets of the expansible members with a high pressure chamber
74 of a piston cylinder assembly 76. The check valve allows high
pressure to flow from the pressure amplifier into the bladder but
prevents flow in the opposite direction. The pressure amplifier
includes a cylinder 76 in which a piston 78 is slidably mounted.
The cylinder has a larger surface area facing a low pressure chamber
80 and a smaller surface area facing the high pressure chamber 74.
In the preferred embodiment, this surface area differential is achieved
with a cylinder rod 82 which extends from the high pressure side
of the piston to reduce the surface area facing the high pressure
chamber. The pressure amplification is generally in proportion to
the ratio of the surface areas of the piston facing the high and
low pressure chambers. Thus, by enlarging the diameter of the piston
rod, the pressure amplification can be increased.
The low pressure chamber 80 is connected with the cross over valving
means B to receive the compressed gaseous mixture therefrom. More
specifically, the low pressure chamber is connected with the input
port of one, but not both of the beds. In this manner, each time
that bed is connected with the compressor, the low pressure chamber
80 is pressurized, causing the high pressure chamber 74 to pump
higher pressure fluid past check valve 72 into the extensible members.
The check valve 72 holds the extensible members at the high pressure
when the low pressure chamber 80 is depressurized on the purging
portion of each cycle. Another check valve 84 connects the high
pressure chamber with the input of the other bed. When the first
bed is being purged and the low pressure chamber is vented, the
check valve 82 allows the gaseous mixture being pumped into the
second bed to be diverted in part to the high pressure chamber.
This replenishes any gas which might leak through the extensible
member, fittings, valves, or tubing portions of the assembly.
It will be noted that if the pressure of the gaseous mixture increases,
then the pressure in the low pressure chamber 80 will also increase.
This higher pressure will be amplified by the same proportion raising
the pressure into the expansible members accordingly. In this manner,
the pressure exerted by the air springs to hold the particulate
materials against fluidization increases with increases in the pressure
of the fluid moving through the beds or reservoirs. If the pressure
of the gases flowing into the beds is decreased, the operating pressure
for the expansible members will also decrease with time due to bladder
and system leakages.
A pressure gauge 90 is connected with the high pressure side of
the extensible members to provide an observable reading of the gas
pressure therein. A differential pressure switch 92 prevents operation
of the system when the extensible members are not pressurized to
a preselected level. For example, switch 92 may prevent cycling
of cross over valves 10 and 12 until the expansible members are
fully pressurized. A check valve controlled fill port 94 provides
an auxiliary access to the expansible members or gas springs to
enable them to be filled manually from an outside pressure source.
With reference to FIG. 4 other pressure amplifiers may, of course,
be utilized. For example, the low pressure chamber 80 may be defined
in a first rolling diaphragm 100 and the high pressure chamber may
be defined in a second rolling diaphragm 102. A push rod 104 interconnects
the two diaphragms to transfer force from one to the other. The
low pressure diaphragm is larger in diameter than the high pressure
diaphragm by an amount selected in accordance with the desired pressure
ratio. The rolling diaphragm embodiment is advantageous in that
a very low friction and leakage are encountered. A vent 106 assures
that a negligible and common pressure is provided between the two
diaphragms by venting any build up of pressure which might tend
to negate pressure intensification or to invert the diaphragms.
Optionally, direct fluid communication tubing and valves may be
provided for connecting the pressure amplifier F directly with the
compressor A or another source of pressure. If high pressure is
always available, e.g. directly from the compressor A then the source
of higher pressure may be connected directly to the check valve
72. A pressure regulator valve, when supplied with adequate pressure,
may replace check valve 72 and amplifier means F. As yet another
alternative, the pressure amplifier may maintain a tank or reservoir
at the higher pressure. The check valve 72 or the pressure regulator
valve connects the high pressure tank with a check valve.
With reference again to FIG. 2 as yet another alternative, a tank
110 or the extensible member itself, may contain a gas-vapor-liquid
medium which supplies its vapor at such pressure as to accomplish
the desired restraint. Such a liquid vapor system serves to provide
a considerable reserve against leakage, while maintaining an essentially
constant, though temperature dependent, pressure as long as any
liquid phase remains.
The invention has been described with reference to the preferred
embodiments. Obviously, further modifications and alterations will
occur to others upon reading and understanding the preceding specification.
It is intended that the invention be construed as including all
such alterations and modifications insofar as they come within the
scope of the appended claims or the equivalents thereof. |