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.

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&#39;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. 2 a  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. 2 b  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. 2 a , 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. 2 a ,  2   b  as piston  32  is retracted within cylinder  12 , that is, moved from an extended position as illustrated in FIG. 2 a  to a retracted position as illustrated in FIG. 2 b , 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. 2 b  to an extended position as illustrated in FIG. 2 a , 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&#39; 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.