Molecular sieve abstract
An apparatus for generating high purity oxygen is described which
comprises a linear actuator, a dual acting air cylinder, two molecular
sieve beds, and valving. The linear actuator drives the air cylinder
back and forth, compressing air on both the forward and return stroke.
On each stroke, fresh air is compressed into one of the beds, generating
oxygen. Simultaneously, the opposite bed exhausts to ambient pressure
and the non-compressing side of the cylinder draws in fresh air.
The cylinder then reverses, which compresses air into the opposing
bed and allows the first bed to exhaust.
Molecular sieve claims
We claim:
1. An apparatus for producing oxygen, comprising:
(a) a dual acting air cylinder having a piston member comprising
an axial piston rod coupled to a piston slidably mounted in said
cylinder;
(b) an actuator coupled to said rod for retracting and extending
said piston in said cylinders thereby alternately compressing air
on a piston side and a rod side of said cylinder;
(c) first and second beds containing molecular sieve coupled to
said cylinder; and
(d) valving coupled to said cylinder and to said first and second
beds, said valving being operable in recurring cycles in which said
piston member is retracted and extended;
so that in each first half cycle of operation in which said piston
is being retracted, ambient air flows into said rod side of said
cylinder, pressurized air is simultaneously directed from said piston
side of said cylinder to said first bed to adsorb nitrogen and provide
a flow of oxygen gas from said first bed, and said second bed is
simultaneously depressurized and previously adsorbed nitrogen gas
is desorbed and exhausted from said second bed;
and in each second half cycle of operation in which said piston
is being extended, ambient air flows into said piston side of said
cylinder, pressurized air is simultaneously directed from said rod
side of said cylinder to said second bed to adsorb nitrogen and
provide a flow of oxygen gas from said second bed, and said first
bed is simultaneously depressurized and previously adsorbed nitrogen
gas is desorbed and exhausted from said first bed;
whereby by cyclically repeating said operation in which said piston
member is retracted and extended, a continuous stream of oxygen
is produced.
2. An apparatus as set forth in claim 1 wherein said valving comprises
a first set of valves coupled between said cylinder and said first
and second beds to control air flow to and from said cylinder and
nitrogen exhaust flow from said first and second beds and a second
set of valves coupled to said first and second beds to control oxygen
flow from said first and second beds.
3. An apparatus as set forth in claim 2 wherein said first set
of valves comprises first and second four way valves, said first
four way valve being operable to permit only the flow of compressed
air from said piston side of said cylinder to said first bed during
each said first half cycle of operation and to permit only the flow
of ambient air to said rod side of said cylinder and the exhaustion
of nitrogen gas from said second bed during each said second half
cycle of operation, and said second four way valve being operable
to permit only the flow of ambient air to said piston side of said
cylinder and the exhaustion of nitrogen gas from said first bed
during each said first half cycle of operation and to permit only
the flow of compressed air from said rod side of said cylinder to
said second bed during each said second half cycle of operation.
4. An apparatus as set forth in claim 2 wherein said second set
of valves comprises first and second two way valves, said first
two way valve being operable to permit the flow of oxygen gas from
said first bed only during each said first half cycle of operation
and said second two way valve being operable to permit the flow
of oxygen gas from said second bed only during each second half
cycle of operation.
5. An apparatus as set forth in claim 1 further comprising purge
means for regeneration of said first and second beds during depressurization
of said first and second beds.
Molecular sieve description
RIGHTS OF THE GOVERNMENT
The invention described herein may be manufactured and used by
or for the Government of the United States for all governmental
purposes without the payment of any royalty.
BACKGROUND OF THE INVENTION
The present invention relates generally to oxygen generators and,
more particularly, to a novel molecular sieve oxygen generator which
produces oxygen from compressed air without using an external compressor.
Molecular sieve oxygen generation systems (MSOGS) require a source
of compressed air in order to produce a supply of oxygen. These
devices typically employ a cylindrical adsorbent bed containing
a molecular sieve, which is an inert ceramic material designed to
adsorb nitrogen more quickly than oxygen. In operation, a stream
of compressed air (20-80 psig) is injected into the sieve bed. As
pressure builds in the bed, nitrogen molecules attach themselves
to the sieve while oxygen molecules pass through as the product
gas. Eventually, sieve in the bed becomes saturated with nitrogen
molecules and needs to be regenerated. This is done by venting the
pressure in the sieve tank to the atmosphere. The nitrogen molecules
previously attached to the sieve are released and within a few seconds
the sieve bed is ready to begin accepting the feed air supply and
producing oxygen again. The oxygen and air flows are controlled
automatically by electrically operated solenoid valves. The pressurization/depressurization
cycle does not degrade the sieve's adsorption capability. Therefore,
the system can be run indefinitely to produce a steady stream of
high purity (about 95%) oxygen.
A working system will often employ two such sieve beds and alternate
them between pressurization and depressurization. In a typical two-step
cycle, during step 1 of the cycle one bed receives high pressure
feed air which pressurizes the bed and establishes a product oxygen
flow. Simultaneously, the high pressure gas in the other bed is
vented to the atmosphere, and this depressurization serves to desorb
the nitrogen previously adsorbed during the high pressure phase
of the cycle. Also, a portion of the product gas from the high pressure
bed may be fed to the low pressure bed to flush the nitrogen-rich
gas from that bed. In step 2 of the cycle the adsorbent beds exchange
roles. This constant cycling results in a continuous product stream
of high purity oxygen.
One conventional method for supplying the sieve beds with the pressurized
source air is to use an external compressor. Air is drawn into the
compressor, pressurized and then held in a storage tank. The MSOGS
then runs off the compressed air from the tank. A limitation of
such a system lies in the size and complexity of the various components.
The external compressor is; usually large and heavy, and the tank
can be bulky as well. These physical constraints can limit the transportability
of the unit. Another method of supplying compressed air to MSOGS
used on board aircraft is to utilize engine bleed air. This source
of air is limited in quantity, can be filled with contaminants from
the engines, is not available when the engine is shut down, and
can sometimes be difficult to tap into.
It is therefore a principal object of the present invention to
provide a molecular sieve oxygen generator which operates without
an external compressed air source.
It is a further object of the invention to provide a compact, portable
oxygen generator.
It is an advantage of the present invention that it provides a
relatively simple apparatus for generating high purity oxygen.
Objects and advantages of the invention are set forth in part herein
and in part will be obvious herefrom, or may be attained by means
of instrumentalities and combinations pointed out in the appended
claims.
SUMMARY OF THE INVENTION
In accordance with the foregoing principles and objects of the
invention, an apparatus for generating high purity oxygen is described
which comprises a linear actuator, a dual acting air cylinder, two
molecular sieve beds, and valving. The air cylinder has a piston
slidably mounted therein. The linear actuator retracts and extends
the piston, compressing air on both the forward and return stroke.
On each stroke, fresh air is compressed into the first bed, adsorbing
nitrogen and providing a flow of oxygen. Simultaneously, the second
bed exhausts to ambient pressure, desorbing nitrogen, while the
non-compressing side of the cylinder draws in fresh air. The cylinder
then reverses, which compresses air into the second bed and allows
the first bed to exhaust. Valving controls oxygen and air flows.
A continuous stream of oxygen is produced by the cyclical repeating
of adsorption and desorption.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be clearly understood from the following detailed
description of preferred embodiments thereof read in conjunction
with the accompanying drawing wherein
FIG. 1 is a schematic view of the essential components of a representative
oxygen generator of the invention.
FIG. 2a illustrates a linear actuator coupled to an air cylinder
of the invention, the air cylinder being illustrated in cross section
to show a piston thereof in an extended position.
FIG. 2b illustrates a linear actuator coupled to an air cylinder
of the invention, the air cylinder being illustrated in cross section
to show the piston thereof in a retracted position.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to FIG. 1 shown therein is a schematic view of the
essential components of an oxygen generator 10 of the invention.
The invention includes a dual acting air cylinder 12 a linear actuator
14 two molecular sieve beds 16 18 and four valves 20 22 24
26.
As illustrated in FIG. 2a, air cylinder 12 has a piston member
28 comprising an axial piston rod 30 coupled to a piston 32 which
is slidably mounted in air cylinder 12. Preferably, the volume of
air cylinder 12 is approximately three times larger than the combined
sieve bed volumes. Preferably, air cylinder 12 is model 7012-DXP
manufactured by Bimba Manufacturin, Company of Monee, Ill., and
is provided with a 3 inch bore and 12 inch stroke.
As shown in FIG. 2 linear actuator 14 is coupled to piston rod
30 and operable to move piston 32 alternatively between retracted
and extended positions within air cylinder 12. As illustrated in
FIGS. 2a, 2b as piston 32 is retracted within cylinder 12 that
is, moved from an extended position as illustrated in FIG. 2a to
a retracted position as illustrated in FIG. 2b, air is compressed
on a piston side 34 of air cylinder 12. As piston 32 is extended
within cylinder 12 that is, moved from a retracted position as
illustrated in FIG. 2b to an extended position as illustrated in
FIG. 2a, air is compressed on a rod side 36 of air cylinder 12.
Preferably, linear actuator 14 is an electrically powered unit,
the speed and acceleration of which may be precisely controlled.
A linear actuator found useful in the present invention consists
of linear actuator model ACT2-B5-T1-N34-12 servo motor model 7ME175E,
servo amplifier model MHB5020HX and motion controller MP3-202HR2
all from DYNACT, Inc. of Orchard Park, N.Y. It should be understood,
however, that any device providing linear locomotion could be utilized
to operate air cylinder 12 whether or not electrically powered.
As shown in FIG. 1 first and second molecular sieve beds 16 18
are coupled to air cylinder 12 in a manner that will be further
explained. Preferably, beds 16 18 are stainless steel tubes with
flanged ends. Beds 16 18 are filled with a molecular sieve material,
which preferentially adsorbs nitrogen while allowing oxygen and
the other components of air, principally argon, to pass through.
Such molecular sieves are well known in the art. Preferably, beds
16 18 are filled with Oxysiv 5 a molecular sieve material which
is manufactured by UOP, Inc. of Des Plaines, Ill.
As illustrated in FIG. 1 a first end of bed 16 is connected to
a port 38 on piston side 34 of air cylinder 12 via air tubing 40.
A first four-way valve 20 directs air flow between air cylinder
12 bed 16 and the atmosphere. A suitable four-way valve is model
Mark IV available from Numatics, Inc of Highland, Mich. A second
end of bed 16 is coupled via air tubing 42 to product gas collection
means (not shown). A first two-way valve 24 controls the flow of
the product gas out of bed 16. A suitable two-way valve is model
IOS2CD8SG manufactured by Allenair Corp of Mincola, N.Y.
A first end of bed 18 is connected to a port 44 on rod side 36
of air cylinder 12 via air tubing 46. A second four-way valve 22
directs air flow between air cylinder 12 bed 18 and the atmosphere.
A second end of bed 18 is coupled to product gas collection means
(not shown) via air tubing 48. A second two-way valve 26 controls
the flow of the product gas out of bed 18. A pressure regulator
50 and flow controller 52 maintain pressure within beds 16 and 18
in a manner well known in the art.
The operation of the above described embodiment will now be explained
in detail by reference to FIG. 1. Oxygen generator 10 operates in
recurring cycles. The operation of the system during each first
and second half cycle of operation will be described.
In each first half cycle of operation, piston 32 is retracted within
air cylinder 12 by actuator 14 thereby compressing air on piston
side 34 of cylinder 12. Simultaneously, four-way valve 20 operates
to direct pressurized air from piston side 34 of cylinder 12 to
first bed 16 wherein nitrogen gas is adsorbed. At the same time,
two-way valve 24 operates to permit the flow of oxygen gas from
first bed 16. Four-way valve 22 simultaneously operates to allow
ambient air to flow into rod side 36 of cylinder 12 and to depressurize
second bed 18 thereby allowing previously adsorbed nitrogen gas
to be desorbed. Thus, during each first half cycle, four-way valve
20 permits only the flow of compressed air from cylinder 12 to first
bed 16 whereas four-way valve 22 permits only the flow of ambient
air to cylinder 12 and the exhaustion of nitrogen gas from second
bed 18. Two-way valve 26 remains closed during each first half cycle.
During the second half cycle of operation, previous actions are
reversed. Thus, in each second half cycle of operation, piston 32
is extended within air cylinder 12 by actuator 14 thereby compressing
air on rod side 36 of cylinder 12. Simultaneously, four-way valve
22 operates to direct pressurized air from rod side 36 of cylinder
12 to second bed 18 wherein nitrogen gas is adsorbed. At the same
time, two-way valve 26 operates to permit product oxygen gas to
be collected from second bed 18. Four-way valve 20 simultaneously
operates to allow ambient air to flow into piston side 34 of cylinder
12 and to depressurize first bed 16 thereby allowing previously
adsorbed nitrogen gas to be desorbed. Thus, during each second half
cycle, four-way valve 22 permits only the flow of compressed air
from cylinder 12 to second bed 18 whereas four-way valve 20 permits
only the flow of ambient air to cylinder 12 and the exhaustion of
nitrogen gas from first bed 16. Two-way valve 24 remains closed
during each second half cycle.
By cyclically repeating the operation of adsorption and desorption,
a continuous stream of oxygen from first and second beds 16 and
18 is thereby produced.
Because speed and acceleration of linear actuator 14 may be precisely
controlled, the flow rate and pressure of the compressed air entering
beds 16 18 may also be carefully controlled. Slowing down this
initial pressure wave may improve performance of the system by giving
the molecular sieve more time to adsorb nitrogen.
As illustrated in FIG. 1 oxygen generator 10 may also include
purge means for regeneration of beds 16 18 during the depressurization
phases of the cycle. Preferably, purge means consist of a purging
tube 54 which connects beds 16 and 18 and which is used to feed
a portion of the product oxygen gas from the high-pressure bed to
the low pressure bed in order to flush out excess nitrogen in preparation
for the next high pressure cycle. Such purging improves the efficiency
of MSOGS devices in a manner that is well known in the art.
Because the oxygen generator of the present invention uses a dual
acting air cylinder to inject compressed air into the sieve beds,
the present requirement for bulky storage tanks or an external compressor
is eliminated. Air is compressed only as needed. The embodiment
described herein requires only electrical power to operate and may
be packaged into a compact, transportable unit capable of generating
a steady stream of 95% oxygen. Inventors' apparatus may be used
by pilots and aircrew operating in high altitude or high gravity
environments to help prevent hypoxia. The invention may also be
used for medical purposes in field hospitals or for home therapeutic
purposes.
The invention therefore provides a novel molecular sieve oxygen
generator which produces high purity oxygen without an external
compressed air source. It is understood that modifications to the
invention may be made as might occur to one with skill in the field
of the invention within the scope of the appended claims All embodiments
contemplated thereunder which achieve the objects of the invention
have therefore not been shown in complete detail. Other embodiments
may be developed without departing from the spirit of the invention
or from the scope of the appended claims. |