US20110197890A1 - Ambulatory oxygen concentrator - Google Patents

Abstract

An oxygen concentrator provides ambulatory oxygen utilizing a vacuum swing adsorption (VSA) oxygen separator powered by a power pack. The separator has a plurality of nitrogen-selective adsorbent beds, each operating in VSA cycles including feed, evacuation and repressurization phases. The concentrator also contains a delivery system for receiving oxygen produced by the VSA separator.

Description

CROSS-REFERENCE TO RELATED APPLICATION
• This application claims priority as a continuation application under 35 U.S.C. §120 of earlier filed application Ser. No. 11/054,341 entitled “METHOD OF PROVIDING AMBULATORY OXYGEN”, Theodore W. Jagger et al., which is hereby incorporated by reference.
• Reference is hereby made to the following applications and patents which claim the same priority date of Feb. 9, 2005, with the present application: application Ser. No. 11/054,622 entitled “AMBULATORY OXYGEN CONCENTRATOR CONTAINING A POWER PACK”, Theodore W. Jagger et al. (now Abandoned); U.S. Pat. No. 7,604,005 entitled “ADSORBENT CARTRIDGE FOR OXYGEN CONCENTRATOR”, Theodore W. Jagger et al.; application Ser. No. 11/054,340 entitled “AMBULATORY OXYGEN CONCENTRATOR CONTAINING A THREE PHASE VACUUM SEPARATION SYSTEM”, Theodore W. Jagger et al.; U.S. Pat. No. 7,121,276 entitled “PERSONAL OXYGEN CONCENTRATOR”, Theodore W. Jagger et al.; U.S. Pat. No. 7,431,032 entitled “LOW POWER AMBULATORY OXYGEN CONCENTRATOR”, Theodore W. Jagger et al.; application Ser. No. 11/054,367 entitled “AMBULATORY OXYGEN CONCENTRATOR WITH HIGH EFFICIENCY ADSORBENT”, Theodore W. Jagger et al.; application Ser. No. 11/054,714, entitled “PORTABLE OXYGEN CONCENTRATOR WITH A DOCKING STATION”, Theodore W. Jagger et al. (now Abandoned); U.S. Pat. No. 7,766,010 entitled “METHOD OF CONTROLLING THE RATE OF OXYGEN PRODUCED BY AN OXYGEN CONCENTRATOR”, Theodore W. Jagger et al.; U.S. Pat. No. 7,171,963 entitled “PRODUCT PUMP FOR AN OXYGEN CONCENTRATOR”, Theodore W. Jagger et al.; U.S. Pat. No. 7,866,315, entitled “METHOD AND APPARATUS FOR CONTROLLING THE PURITY OF OXYGEN PRODUCED BY AN OXYGEN CONCENTRATOR”, Theodore W. Jagger et al.; U.S. Pat. No. 7,604,004, entitled “PERSONAL OXYGEN CONCENTRATOR”, Theodore W. Jagger et al.; application Ser. No. 11/595,602, entitled “PRODUCT PUMP FOR AN OXYGEN CONCENTRATOR”, Theodore W. Jagger et al., and application Ser. No. 11/595,603, entitled “OXYGEN CONCENTRATOR WITH A PRODUCT PUMP”, Theodore W. Jagger et al. (now Abandoned).
BACKGROUND
• The field of this invention relates to oxygen concentrators. In particular, the invention relates to wearable oxygen concentration systems utilizing vacuum swing adsorption for creating an oxygen stream for ambulatory respiratory patients.
• There is a need for home and ambulatory oxygen systems for use by patients. Supplemental oxygen is required for patients exhibiting symptoms from certain diseases and lung disorders; for example, pulmonary fibrosis, sarcoidosis, or occupational lung disease. For such patients, oxygen therapy is an increasingly beneficial prescription to help the patients live normal and productive lives. While not a cure for lung disease, prescriptive supplemental oxygen increases blood oxygenation, which reverses hypoxemia. Oxygen prescriptions prevent long-term effects of oxygen deficiency on organ systems, the heart, brain and kidneys. Oxygen treatment is also prescribed for Chronic Obstructive Pulmonary Disease (COPD), heart disease, AIDS, asthma, and emphysema.
• Currently, supplemental medical oxygen for therapy is provided to a patient from high pressure gas cylinders; cryogenic liquid in vacuum-insulated containers or thermos bottles commonly called “dewars”, and oxygen concentrators. Some patients require in-home oxygen only, while others require in-home as well as ambulatory oxygen depending on the prescription. The three systems are all used for in-home use. However, oxygen concentrators provide a special beneficial advantage because they do not require refilling of dewars or exchange of empty cylinders with full ones. Home oxygen concentrators, however, do have drawbacks. They consume relatively large amounts of electricity; are relatively large and heavy; emit excessive heat and are relatively noisy.
• There has been a need for an improved portable device for supplying oxygen to a patient. Only small high pressure gas bottles and small liquid dewars are truly portable enough to be used for ambulatory needs. Either system may be used for both in-home and ambulatory use. A patient using a stationary oxygen system at home (or even a portable system which cannot be readily transported), who travels must opt for small cylinders towed in a wheeled stroller or for portable containers that they carry, typically on a shoulder sling. Both of these options have significant drawbacks.
• A major drawback of the cylinder option is that small cylinders only provide oxygen for a short duration. Moreover, these cylinders are maintained at a high pressure, and thus their use is restricted due to safety considerations. Another drawback of the cylinders is the refill requirement after depletion of the contents of the cylinder. Empty cylinders must be refilled at specialized facilities, or in the patient's home using a commercial oxygen concentrator which extracts oxygen from the air. The latter option requires an on-site compressor to boost the output pressure of the concentrator to meet cylinder refill pressure requirements. Filling of cylinders with oxygen in the home is potentially dangerous due to the physics involved with compressing gas. Another detriment to cylinder usage is fire hazards associated with storage of large volumes of oxygen in the home environment.
• Convenience and safety issues are not the only drawbacks associated with the use of cylinders. Another drawback is the cost associated with cylinders. Cylinders require special care, and specialized materials are required for high pressure oxygen compatibility, which in turn drives up the cost of cylinder-based systems.
• The liquid oxygen storage system also has drawbacks. The primary drawback is the requirement of a base reservoir which necessitates refilling once a week or more from an outside source. Liquid oxygen is transferred from the base unit to a portable dewar, which is used by an ambulatory patient. However, there is substantial waste, as a certain amount of oxygen is lost during the transfer to the portable containers and from evaporation. Up to twenty percent of the contents of the base cylinder is lost in the course of two weeks because of losses in transfers and normal evaporation. Even without withdrawal by the patient, the base reservoir will typically boil dry over a period of one to two months.
• The aforementioned systems all require a refilling station. When the patient is out in public, such stations are not readily available. Upon running low (or out) of oxygen, the patient must return home to a specified place that can refill the system. Such a requirement detracts from the ambulatory usefulness of the systems.
• The industry has developed a set of recommendations for systems targeted to provide portable oxygen for ambulatory patients. The Fifth Oxygen Consensus Conference set forth the following standards for long-term oxygen therapy ambulatory equipment: 1) equipment must weigh less than 10 lbs., 2) equipment must provide the equivalent of 2 liter/min of continuous flow O₂, and 3) the flow rate must be maintained for four hours or more. Thus, ambulatory equipment, or personal oxygen systems (POS), are to be inconspicuous to the public as well as unrestricting to the patient. Cylinders and other liquid oxygen systems tend to be bulky, which interferes with normal daily activities. Similarly, cylinders and liquid oxygen systems are difficult to conceal from public view. Ideally, a POS is small, lightweight, quiet, and flexible which allows the device to be concealed from the public. The present invention, whereby oxygen rich gas is provided to a patient from a wearable oxygen concentrator, meets and exceeds these standards.
BRIEF SUMMARY OF THE INVENTION
• An oxygen concentrator provides ambulatory oxygen utilizing a vacuum swing adsorption (VSA) oxygen separator powered by a power pack. The separator has a plurality of nitrogen-selective adsorbent beds, each operating in VSA cycles including feed, evacuation and repressurization phases. The concentrator also contains a delivery system for receiving oxygen produced by the VSA separator.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a front view of a patient carrying the oxygen concentrator of the present invention.
• FIG. 2 is a front perspective view of the oxygen concentrator.
• FIG. 3 is a rear perspective view of the oxygen concentrator.
• FIG. 4 is a front perspective view of the oxygen concentrator and a docking station.
• FIG. 5 is a block diagram showing the components and connections of the oxygen concentrator.
• FIG. 6 is a diagram showing rotary valve timing.
• FIG. 7 is an exploded view of the oxygen concentrator in which the power pack and the adsorbent cartridge have been removed.
• FIG. 8 is a perspective view of the oxygen concentrator with a portion of the belt removed.
• FIG. 9 is a perspective view of the components of the oxygen concentrator without the belt.
• FIG. 10 is a perspective view of the components contained within the case portions of the modules and their associated pneumatic and electrical connections of the oxygen concentrator.
• FIG. 11 is a perspective view of the components contained within a battery module.
• FIG. 12ais a perspective view of an accumulator.
• FIG. 12bis a top view of the accumulator.
• FIG. 12cis a sectional view of the accumulator.
• FIG. 12dis another sectional view of the accumulator.
• FIG. 13 is a perspective view of a control module.
• FIG. 14 is a front view of the interior components of the control module.
• FIG. 15 is a perspective view of the cartridge contained within a cartridge module.
• FIG. 16 is an exploded view of columns and filters within the cartridge.
• FIG. 17 is a rear perspective view of the oxygen concentrator and the docking station.
• FIG. 18 is a front perspective view of the docking station.
• FIG. 19 is a chart showing the adsorption isotherms for two different adsorbent materials.
DETAILED DESCRIPTION
• The current invention relates to separation of gases using vacuum swing adsorption. Specifically, disclosed is an oxygen concentrator for a patient who requires a source of oxygen. The present invention is further explained with reference to the drawn figures in which like structures are referred to by like numerals throughout the several views.
Overview—Oxygen Concentrator100 (FIGS. 1-4)
• FIG. 1 is a front view showing patient P withoxygen concentrator100 andoxygen delivery tube102.Oxygen concentrator100 is a small unit which utilizes vacuum swing adsorption to separate oxygen from the ambient air around patient P. Oxygen concentrator100 is compact and light so as not to interfere with the ambulatory movement of patient P, and can produce a product stream of gas containing a range of eighty-five to ninety-five percent oxygen.
• Oxygen delivery tube102 is a polymer tube or similar oxidation resistant structure, which extends fromoxygen concentrator100 to the nose, mouth, or port into the upper airway ofpatient P. Tube102 allows delivery of oxygen to patient P for inhalation. InFIG. 1, patient P is about six foot tall to illustrate an approximation of the relative size ofoxygen concentrator100.
• FIG. 2 is a perspective view ofoxygen concentrator100.Oxygen concentrator100 is comprised ofbelt104,power module106 containingpower pack108,reservoir module110,control module112 containinguser interface114, andseparation cartridge module116.Oxygen concentrator100 is a portable oxygen separator used to provide an oxygen rich gas stream topatient P. Belt104 connects and carries themodules106,110,112, and116 ofoxygen concentrator100.Belt104 may contain belt loops (not illustrated), clips, or a pair of straps that contain a buckle and holes or like fastening device for securingoxygen concentrator100 to patient P. Alternatively,oxygen concentrator100 may be placed in a purse, fanny pack, or similar personal carrying device for transport with patient P.
• Power module106 provides the necessary power to operate the systems ofoxygen concentrator100. In the embodiment illustrated,power module106 containsreplaceable power pack108.Reservoir module110 stores oxygen rich gas that has been separated from ambient air bycartridge module116.Control module112 pilots and regulates the interaction of thepower module106,reservoir module110, andseparation cartridge module116 ofoxygen concentrator100.User interface114 oncontrol module112 is a console which allows patient P to adjust and monitoroxygen concentrator100.
• FIG. 3 is a perspective view of the opposite side ofoxygen concentrator100 as shown inFIG. 2. Illustrated inFIG. 3 arebelt104,power module106,reservoir module110,control module112, andseparation cartridge module116.Belt104 is constructed to containbelt segments120 formed byserrations118. This allows thebelt104 to be flexible and conform to patient P's body while wearingoxygen concentrator100.Belt104 is fabricated from a flexible material, such as textile or plastic and contains an inner padding such as foam. Belt104 also houses the electrical and pneumatic connections ofoxygen concentrator100.
• FIG. 4 is a perspective view of the front side of theoxygen concentrator100 ondocking station122. Illustrated areoxygen concentrator100 comprisingbelt104,power module106,reservoir module110,control module112, andseparation cartridge module116, along withdocking station122 containingpower pack chargers124aand124b.Belt104 is flexible and thus rests on the arc shapeddocking station122.Docking station122 containspower pack chargers124a(withpower pack108ainserted therein) and124b, as well asconcentrator dock126 which supports theoxygen concentrator100 while on thedocking station122.Docking station122 converts AC power to recharge power packs108.
Oxygen Concentrator100 System Components and Connections (FIG. 5)
• FIG. 5 is a block diagram ofoxygen concentrator100illustrating power module106,reservoir module110,control module112, andseparation cartridge module116, along withdocking station122 and showing the components and connections among the modules anddocking station122.Oxygen concentrator100 components includes productgas outlet port103,adsorbent columns130a-130c(each containing a respective inlet port132a-132cand a respective outlet port134a-134c),air inlet port135,air inlet filter136, product gasfinal filter138,main valve140,drive reducer142,vacuum pump144, drive146, electric control module (ECM)148,breakthrough flow sensor150,valve position sensor152,product control pump154,check valve156,main storage reservoir158 containingpressure sensor159, dispensingvalve160, as well as previously identifiedcomponents tubing102,power pack108,user interface114, anddocking station122.
• As shown inFIG. 5,adsorbent cartridge module116 includesadsorbent columns130a-130ceach containing respective inlet ports132a-132cand outlet ports134a-134c,air inlet filter136, and product gasfinal filter138. Ambient air entersair inlet port135, passes throughair inlet filter136, and entersvalve140 for distribution toadsorbent columns130a-130c. Product gas passes throughfinal filter138 and productgas outlet port103 intotubing102 for delivery to patient P. Inlet ports132a-132cofadsorbent columns130a-130cconnect tovalve140 throughinlet lines164a-164c. Similarly, outlet ports134a-134cconnect tovalve140 through outlet lines166a-166c.
• Control module112 housesmain valve140,drive reducer142,vacuum pump144, drive146, electric control module (ECM)148,breakthrough flow sensor150,valve position sensor152, and containsuser interface114.Main valve140 is pneumatically connected toadsorbent columns130a-130c, as well asinlet filter136 viainlet line168,vacuum pump144 viavacuum inlet line170,product control pump154 viavacuum line172 andproduct gas line174, andmain reservoir158 viaproduct gas line176.Valve140 is actuated bydrive146 through amotor speed reducer142. Also,valve140 connects tobreakthrough flow sensor150 andvalve position sensor152 which sendelectrical inputs178 and180 toECM148.
• ECM148 is a logic control, such as a PLC (programmable logic controller), microprocessor, or similar structure which controls operation ofoxygen concentrator100.ECM148 contains the set of inputs and outputs associated with the modules for regulatingoxygen concentrator100.ECM148 also receives control setting inputs182 and184 fromuser interface114, anddocking station122, respectively, powerpack management input186 frompower pack108,reservoir pressure input188 frompressure sensor159 inmain reservoir158, andnasal pressure input190 from dispensingvalve160.ECM148 providesinterface output192 to the user interface114,interface output194 todocking station122,power management output196 topower pack108, dispensing valve timeopen output198 to dispensingvalve160, andmotor drive output200 to drive146.
• User interface114 contains physical controls such as dials, toggle switches, push button switches, and similar controls, for operatingoxygen concentrator100. The physical controls provide electrical control settings toECM148.ECM148 reads these settings asinputs182 and providesoutput192 to theuser interface114. The status is converted from electric signals to physical output by indicator lights, status display, and similar structures ofuser interface114.
• Powerpack management input186 andoutput196 control the charge and discharge of voltage frompower pack108 to drive146 viaECM148. Drive146 will activatevacuum pump144,valve140 throughdrive speed reducer142, and any other systems requiring power. Powerpack management output196 will also supply power to indicator lights, status display, audible alarm (if included), and other passive electrical system requirements onuser interface114 throughECM148.
• ECM148 controls and coordinates the steps of the vacuum swing adsorption cycle through its inputs and outputs. In one embodiment,breakthrough flow sensor150 provides an input178 intoECM148 by measuring air flow rates. The position ofvalve140 is detected byvalve position sensor152 to produceinput180.Reservoir158 contains a sensor to producereservoir pressure input188.Dispensing valve160 also contains a pressure sensor which providesnasal pressure input190 in response to differential pressure.ECM148 reads these inputs to control the cycle by changing outputs, such asmotor drive output200 fordrive146. Drive146 propelsvacuum pump144.Vacuum pump144 creates a vacuum that is communicated tovalve140 throughvacuum input line170, while dispelling nitrogen rich gas asexhaust177. Anotheroutput198 controls the time that dispensingvalve160 is open. In this embodiment, the inputs and outputs are connected to a PLC withinECM148 which is programmed to control the cycle ofoxygen concentrator100.
• Contained withinreservoir module110 is an oxygen-rich gasaccumulator comprising reservoir158,check valve156,product control pump154, andcheck valve153.Reservoir158 receives oxygen-rich gas produced byoxygen concentrator100 and stores it at a low pressure above ambient until it is required for use. A portion of the stored oxygen-rich gas is delivered back tovalve140 byproduct gas line176 for use in ordering the nitrogen content inadsorbent columns130a-130cby moving much of the residual nitrogen held after evacuation near the outlets134a-134ctoward inlets132a-132cof thecolumns130a-130c.Reservoir158 is in communication with dispensingvalve160 throughproduct gas line202.Check valve156 opens to allow oxygen intoreservoir158 and closes to prevent backflow of oxygen upon reaching the desired pressure inreservoir158.
• Product control pump154 is driven by vacuum provided by thevacuum pump144 throughvalve140 viavacuum line172.Product line174 is in communication fromseparation cartridge module116 to checkvalve153, which opens to allowproduct control pump154 to transport separated oxygen-rich gas toreservoir158.Product control pump154 delivers the product gas tomain reservoir158 throughcheck valve156.
• Dispensing valve160 andpower pack108 are contained withinpower module106.Dispensing valve160 is used to feed the flow of oxygen-rich gas to the patient P by delivery of the product gas through finalproduct gas line205 to productfinal filter138. The product gas is obtained from themain reservoir158 throughproduct gas line202.Power pack108 provides the power supply foroxygen concentrator100 as previously described.Power pack108 is rechargeable throughdocking station122 as represented by power connection204.
Vacuum Swing Adsorption (VSA) Process—Overview
• Oxygen concentrator100 operates using a vacuum swing adsorption process, which involves a series of cycles that include a feed step or phase, an evacuation step or phase, and a repressurization step or phase. Each of these three phases takes place in one of the threecolumns130a-130cat any given time. Eachcolumn130a-130cis in a different phase. For purposes of explanation, the VSA process will be described in reference to “column130”, which is representative of each of the threecolumns130a-130c.
• In the feed phase, a gas stream ofambient air162 enters inlet end132 ofcolumn130 while product gas containing concentrated oxygen is delivered from outlet end134 ofcolumn130. The slight vacuum incolumn130 drawsair162 intocolumn130 and through an adsorbent material (typically a zeolite) which preferentially retains specific components of air (nitrogen), allowing the desired product (oxygen) to pass through. A mass transfer zone (MTZ), which is a small region in which nitrogen is being adsorbed, is passing through the adsorbent material. The MTZ divides thecolumn130 into two segments: a nitrogen-rich segment where the MTZ has passed through, and an oxygen-rich segment ahead of the moving MTZ. The MTZ forms at the inlet132 at the start of the process and gradually moves through the column to the outlet134 as the process proceeds. Outlet end134 ofcolumn130 is connected tomain reservoir158 throughmain valve140,check valve153, andproduct control pump154, so that oxygen-rich product gas fromcolumn130 is pumped intoreservoir158.
• In the evacuation phase,column130 is brought to a stronger vacuum byvacuum pump144, causing the adsorbed component, i.e. nitrogen, to be desorbed. The nitrogen is evacuated fromcolumn130 throughmain valve140, and is discharged byvacuum pump144 aswaste exhaust177.
• In the repressurization phase, the previously evacuatedcolumn130 is returned to near 1 atm.Ambient air162 enterscolumn130 through inlet end132, and recycled product gas fromproduct line176 enterscolumn130 through outlet end134. The gases replace the vacuum that was previously drawn incolumn130 during the evacuation phase. Just prior tocolumn130 reaching about 1 atm, the repressurization phase ends and the feed phase of the cycle begins again.
• This constitutes the general principles of vacuum swing adsorption (VSA) for gas separation. All phases can be accomplished with a single column, or with a plurality of columns. If a plurality of columns are used, it is preferable to have a multiple of three (illustrated as130a-130cinFIG. 5) that are sequenced out of phase for the different cycle phases in order to maintain constant product flow.
The Feed Phase—Breakthrough Detection
• During the feed phase of the separation cycle, the position of the MTZ withinadsorbent column130 is monitored, determined, and beneficially used to control the termination of the feed phase. The control results in improvements in product purity and recovery with concomitant decrease in energy consumed, as well as system size and system weight for a given volume of product produced.
• Breakthrough is defined as the point when the MTZ reaches outlet134 ofadsorbent column130. At this point, feed gas begins to flow into the separated product gas stream. This is undesirable because the purity of the product stream is reduced by the feed stream gas if the feed is allowed to continue past this point. Conversely, if the feed phase is terminated before the MTZ nears outlet134 ofcolumn130, product recovery will be reduced because product gas contained incolumn130 between the MTZ and outlet134 ofcolumn130 will be subjected to the evacuation phase that follows the feed phase in the separation cycle, and much of this remaining product gas will be lost with the desorbed gas in the waste stream.
• For a particular column geometry, temperature, adsorbent type and condition, and cycle vacuum levels, there is an optimal time during the feed phase of the cycle to terminate the feed—before purity requirements are compromised, but after the maximum possible product has been recovered fromcolumn130. This optimal time is determined by the detection of the passage of the mass transfer zone through a specific position relative to outlet end134 ofcolumn130.
• For some combinations of system variables, the optimum feed termination time corresponds to the beginning of breakthrough when the leading edge of the MTZ has just reached outlet end134 ofcolumn130. This event can be detected by monitoring either or both of the gas flow rates at inlet132 or outlet134 tocolumn130. Before breakthrough, the outlet flow rate is less than the inlet flow rate by an amount equal to the rate of nitrogen gas adsorption ofcolumn130 from the feed gas flow. After breakthrough,column130 is no longer adsorbing nitrogen from the feed gas, so the inflow and outflow rates ofcolumn130 become equal. Any method of measuring gas flow rates to determine the point in time when these flow rates begin the transition toward equality can be used to detect this beginning of breakthrough.
• It has been determined that if the inflow rate of air tocolumn130 is maintained constant, a simple detection of a significant rise in slope of the outflow rate marks breakthrough. Conversely, if the outflow rate is held fairly steady, then a falling slope of the inflow rate marks the breakthrough. Monitoring the ratio of flow for the inlet and outlet and detecting a significant change in the ratio of flows toward a ratio of 1:1 can mark breakthrough in systems where inflow or outflow may not be steady enough to detect breakthrough by monitoring just one of the flow rates.
• For other combinations of system variables, the optimum feed termination time may correspond to the MTZ position prior to breakthrough. In these cases, it is beneficial for a specific amount of product to be intentionally left incolumn130 at the end of a feed phase. Detecting the position of the MTZ before breakthrough can be accomplished by additional methods.
• One method used determines the volume of gas passed into or out ofadsorbent column130 up to the point of breakthrough by integrating the flow rate during the time interval between an initial feed and breakthrough while using some breakthrough detection method as previously described. Volume of flow may also be directly measured by physical equivalent methods using displacements of known volumes. Once the volume of gas that passes the column up to the point of breakthrough is determined, the volume of gas flow can be monitored during subsequent feed phases and the feed terminated when the volume reaches a specific value less than that for breakthrough. At any time during the feed phase, the volume of gas passed throughcolumn130 since the beginning of feed divided by the volume of gas at breakthrough will be the same ratio as the position of the mass transfer zone divided by the length of column130 (assuming a constant cross sectional area along the length). Using this relationship, the position of the MTZ withincolumn130 can be adequately determined during the feed phase.
• The components ofoxygen concentrator100 as previously described are used to complete the cyclical phases of VSA to separate gases. The feed phase operates at a slight vacuum just below ambient (in the range of 0.9 to 1 atm). This provides just enough driving force to pullambient air162 intoadsorbent column130 throughinlet filter136. The vacuum is caused byproduct control pump154, which is driven by the vacuum drawn byvacuum pump144.Product control pump154 is a piston pump or similar structure that meters a volume of gas.Product control pump154 connects with a volume much greater than the piston displacement volume, such asmain reservoir158.
• The feed phase is allowed to proceed until breakthrough is detected. Up to this point, the outflow gas fromadsorbent column130 has been a high purity oxygen/argon, low percent nitrogen mixture. The MTZ position is controlled to minimize nitrogen into the product gas mixture. The MTZ position is monitored bybreakthrough flow sensor150, which detects a large increase in flow rate associated with breakthrough when the nitrogen no longer is preferentially adsorbed byadsorbent column130. Breakthrough flow sensor is located near the column inlet132, column outlet134, or similar place where the flow rate being measured is accessible. When the increase MTZ flow is detected, a signal is sent toECM148, which also receives valve position signal180 from thevalve position sensor152. TheECM148 compares the timing of the MTZ breakthrough signal and the valve position signal and makes a minor adjustment tomotor speed200 based on lead, lag, or on-time status to keep the breakthrough time near the end of each feed phase. Alternately,ECM148 receives a signal frombreakthrough flow sensor150 and immediately terminates the current feed phase incolumn130 by signalingvalve140 to rotate to start the next phase. In yet another embodiment, the separation system contains a shut off valve that is signaled to close the feed ofambient air162 intocolumn130, or the delivery of product gas from the column upon breakthrough detection.
• In another embodiment, the method for determining the position of the mass transfer zone prior to breakthrough is accomplished by placing a small amount of non-adsorbing material withinadsorbent column130 at a particular position. When the mass transfer zone passes through this position, a flow change is detectable as the adsorption of gas is briefly interrupted by the non-adsorbing segment ofcolumn130. The resulting flow change is detectable using the same methods for breakthrough detection previously described.
• With larger columns and slower feed phases, the position of the mass transfer zone has been established by measuring temperature rise at positions of interest withincolumn130. Significant temperature increases result from the heat of adsorption at the MTZ and can be detected by thermistors or similar devices placed withincolumn130.
The Evacuation Phase
• The evacuation phase brings the gas inadsorbent column130 that was just in the feed phase to a vacuum state. At the end of the feed phase, theadsorbent column130 is in equilibrium with the air infeed mixture near 1 atm from column inlet132 up to the MTZ. Hence, if the ending position of the MTZ is established, and the nitrogen, oxygen, and argon isotherms for the chosen adsorbent mass are known, then the quantity of these gases present inadsorbent column130 at the end of each feed phase is known.Vacuum pump144 draws a vacuum onadsorbent column130. This vacuum level is determined and set to a state that will remove a large portion of the gas left incolumn130. In one embodiment, this is 0.2 to 0.3 atm. By percentage, the vast majority of gas discharged is nitrogen. The evacuated gas is discharged as waste fromexhaust177 ofvacuum pump144. The preferred embodiment uses a fixed displacement type ofvacuum pump144. During each evacuation phase, the adsorbed gas incolumn130 is expanded into a much larger volume made up of the column volume plus the fixed displacement volume ofpump144.
• The evacuate phase creates a self regulating effect that compensates for reductions in the amount of nitrogen adsorbed byadsorbent column130 as the adsorbent degrades (ages). If the adsorbent loses efficiency, less nitrogen will be present incolumn130 at the end of the phase, but the volume of the pump that the nitrogen expands into remains the same. A stronger vacuum will result that will remove more nitrogen and therefore allow more air to be fed during the next feed phase. A more constant breakthrough time results and provides a more robust product cycle.
• The evacuation is provided byvacuum pump144, which is controlled and activated bydrive146. The volume removed for each cycle of thevacuum pump144 will remain constant, but themotor drive output200 will be controlled by the rate of product gas used by patient P. The amount of oxygen used by patient P depends on the patient P's on-demand respiratory rate, which is sensed by the device and from a variable position switch which sends aninput192 fromuser interface114 toECM148, which in turn providesmotor drive output200 to drive146. This determines the speed of each successive phase and, therefore, the oxygen production rate.
• In one embodiment, a purge is applied at the very end of an evacuation phase. While still in the evacuation phase, a purge of product gas (mostly oxygen) introduced through outlet134 effectively drives out a portion of nitrogen incolumn130 through inlet132. Adding the purge gas of high purity oxygen/argon through outlet134 desorbs more nitrogen from outlet134 ofcolumn130, and pushes the nitrogen toward inlet132 ofadsorbent column130 and creates an ordering of the gases. The purge volume is a function of vacuum level and adsorbent characteristics. A purge portion of the evacuation phase is not a necessary phase for a functioning device, but allows high oxygen purity to be maintained with weaker vacuum levels.
The Repressurization Phase
• The repressurization phase brings adsorbent column130 (just previously evacuated and purged) up to the feed pressure. In one embodiment, the gas used for repressurization is from both the infeedambient air162 and a counter stream from the (oxygen-rich)product gas line176 from themain reservoir158. Alternately, the repressurization of product gas can be accomplished through valve design negating the need for a separate line. The product gas is dispensed from a stream of product gas from the adsorbent column that is in the feed phase through a vacuum break valve used during repressurization. Repressurization with product gas can be done before, simultaneously, or after partial pressurization with ambient air. Repressurization with product gas is done at the opposite end ofcolumn130 as repressurization withambient air162.
• The effect of adding the repressurization gas of high purity oxygen/argon through outlet134 creates a cleaning zone at outlet134 ofadsorbent column130 where, during the feed phase that follows next, any stray nitrogen can be preferentially adsorbed and not discharged as product gas. This improves the ordering of gases in theadsorbent column130. By repeating this phase during successive cycles, the purity will continue to increase in the product output. Weaker vacuums require more oxygen volume returned tocolumn130 during repressurization if high purity is desired. That is, a stronger vacuum must be drawn on thecolumn130 to effectuate the same purity of oxygen absent the use of oxygen-rich gas as a back flush for repressurization at the outlet134 ofcolumn130. At the end of repressurization, the feed phase will proceed.
Valve140 Timing (FIG. 6)
• The VSA cycle comprises three phases: evacuation, repressurization, and feed, which occur sequentially in eachcolumn130a-130c. For clarity,only column130awill be discussed, although each phase is performed (at different times during a complete cycle) in each ofcolumns130a-130c.
• Starting with the evacuation phase of the cycle, a small amount of oxygen (not illustrated) may flow intooutlet134aofadsorption column130ato purgeadsorption column130a, whilevacuum pump144 withdraws gas present atinlet134aof the column, i.e. nitrogen-rich gas.
• During the repressurization phase, an amount of previously separated oxygen flows intooutlet134aofadsorption column130afor a short time, and then air is allowed to enterinlet132aofcolumn130athat has been previously evacuated. There may be a slight overlap of the oxygen flow intooutlet134aofadsorption column130aand the air flow in the opposite direction intoinlet132a. Air freely flows intoinlet132aofadsorption column130aupon opening ofvalve140 asadsorption column130ahas been previously evacuated during the evacuation phase.
• During the feed phase, air continues to flow intoinlet132aofadsorption column130awhile oxygen is removed fromoutlet134aofcolumn130aby a pressure differential created byproduct control pump154. As the MTZ passes through the adsorption column and reaches a position at ornear outlet134a,vacuum pump144 will again begin to evacuateadsorbent column130aand restart with the evacuation phase. In the embodiment illustrated inFIG. 6, these phases are controlled bymain valve140.
• FIG. 6 is a diagram showing timing formain valve140, which is a rotary valve that moves 360° (one full revolution about a central axis) for each complete cycle of the VSA process. In the embodiment with threecolumns130a-130c, the timing for each phase of the cycle is 120°. Eachcolumn130a-130cis present in a different phase for each 120° of rotation ofvalve140 that is different from the other two columns to obtain a sequence that creates a steady flow of oxygen asvalve140 keeps rotating. As shown in the timing diagram,adsorption column130ais in the feed phase of the cycle at a start point of zero degrees. Air is being let in throughinlet filter136 andcolumn inlet132awhile separated gas consisting of highly concentrated oxygen is being removed throughcolumn outlet134a. A portion of the oxygen-rich product gas is used in the repressurization ofcolumn130b.Adsorption column130bis in the repressurization phase at a point ofrotary valve140 being in initial position zero degrees. Asvalve140 is turned,column outlet134bis fed with the oxygen-rich gas for a portion of the valve's rotation, preferably less than 120°. After the flow of oxygen-rich gas enterscolumn130bthrough thecolumn outlet134b, air repressurization through the opening ofcolumn inlet132bbegins. In the embodiment shown, this takes place at a point aftervalve140 has begun its rotation and ends before it reaches a third of its rotation, or a 120° rotation.
• Whilecolumn130ais in feed phase andcolumn130bis in the repressurization phase,column130cis in the evacuation phase. During the evacuation phase, a vacuum is drawn to remove adsorbed gas throughinlet132c, thereby regenerating it for the following feed phase.
• In the embodiment shown, eachcolumn130a,130b, and130c, is in a different phase of the cycle as one moves vertically down the diagram inFIG. 6. During the first one hundred twenty degrees of rotation of the rotary valve,column130ais in the feed phase. Simultaneously, from zero to one hundred twenty degrees of rotation,column130bis being repressurized, whilecolumn130cis being evacuated.
• For the next one hundred twenty degrees of rotation of valve140 (i.e., from 120° to 240°),adsorption column130ais in the evacuation phase. At this same time,column130bis in the feed phase, andcolumn130cis in the repressurization phase. Moving horizontally across the diagram forcolumn130a, during the final one hundred twenty degrees of rotation of valve140 (i.e., from 240° to 360°),column130ais repressurized first using separated gas, and then ambient air. Separated gas and ambient air are introduced to thecolumn130athroughcolumn inlet132aand column outlet174aat opposite ends ofcolumn130a. During the final one hundred twenty degrees of rotation (i.e. from 240° to 360°) ofmain valve140,column130bis in the evacuation phase, andcolumn130cis in the feed phase. Upon reaching three hundred sixty degrees,valve140 is back at its starting position (zero degrees), and the cycles for eachcolumn130a-130crestart from the zero degree position.
Oxygen Concentrator100 Physical Components (FIGS. 7-16)
• FIG. 7 shows an exploded view of theoxygen concentrator100, which includesbelt104,power module106 containingremovable power pack108,reservoir module110,control module112, andseparation cartridge module116 containingadsorbent cartridge206.Power pack108 has been removed fromreceptacle210 ofpower module106.Adsorbent cartridge206 has been removed fromreceptacle208 ofcartridge module116.Adsorbent cartridge206 andpower pack108 are easily removable to facilitate replacement.
• In this embodiment,power pack108 is a rechargeable battery.Receptacle210 contains electrical contacts (not illustrated) for connection topower pack108.Cartridge206 contains a quick-connect attachment (not illustrated) forinlet lines164a-164c, outlet lines166a-166c,inlet air line168, and final product gas line205 (not illustrated) withinreceptacle208. Also present oncartridge206 areair inlet ports135 which receiveambient air162 for separation.Adsorbent cartridge206 contains adsorbent material that deteriorates in efficiency as it is used and ages.
• FIG. 8 is a perspective view ofoxygen concentrator100. A portion ofbelt104 has been removed revealing backinterior surface211 and inner connections amongst the modules, includingutility tubes212,tube pathways214, module apertures216a-216d, and module sockets218a-218d.
• Utility tubes212 run between the adjacent modules and contain either electrical wiring or pneumatic lines, or comprise pneumatic lines and electrical wiring and associated connections.Tubes212 are constructed to be flexible and bend asbelt104 is manipulated. If thetubes212 contain electrical lines, the tubes are constructed from a dielectric material to insulate electrical wires, or similar material commonly used in electrical connections. If thetubes212 comprise pneumatic lines, they may be air tight, small diameter polyvinyl or PVC tubes to connect the various gas input, gas separation, and gas removal systems of theoxygen concentrator100.Tubes212 contain openings or connections as required for electrical and pneumatic communication with each module. The backinterior surface211 ofbelt104 containstube pathways214.Pathways214 fabricated on theinterior surface211 ofbelt104 allow theutility tubes212 to extend between themodules106,110,112, and116.Tube pathways214 create a semi-partitioned area on backinterior surface211 ofbelt104 which supporttubes212.
• Belt104 is fabricated to contain apertures216a-216dwhich allowmodules106,110,112, and116 to connectutility tubes212 ofbelt104 through sockets218a-218d. Apertures216a-216dand sockets218a-218dare fabricated as part ofmodules106,110,112, and116.Serrations118 can be seen between the upper andlower edges220 and222 ofbelt104. When fabrication ofbelt104 is completed, padding will be inserted betweenedges220 and222, and material will be wrapped around creatingserrations118 andbelt segments120 to completebelt104 as illustrated inFIG. 3. The padding is fabricated over the top oftubes212 andtube pathways214, or separately fabricated and fastened to backinterior surface211 during assembly ofbelt104. Individual modules allow the device to flex when mounted about a curved surface, such as a belt around patient P's waist. The construction ofbelt104 withtubes212 allows patient P to manipulate theoxygen concentrator100, such as by bendingbelt104 to wear around the waist, place ondocking station122, orfolding concentrator100 in half for transport in a carryall.
• FIG. 9 is a perspective view ofmodules106,110,112, and116 ofoxygen concentrator100. In this view,belt104 has been removed to illustrate the positions of sockets218a-218dcontaining apertures216a-216don eachrespective module106,110,112, and116. Eachrespective module106,110,112, and116 is constructed from a thermoplastic material such as acrylanitrile butadine styrene (ABS) or high density polyethylene (HDPE), or a lightweight metal or a similar rigid material that is oxidation resistant.
• Eachmodule106,110,112, and116, comprises acase portion224,226,228, and230, defining the outer volume of each respectively.Bottom padding232,234,236, and238, covers the lower base portion of eachmodule106,110,112, and116, respectively. Similarly,top padding240 extends around the top perimeter ofpower module106, whiletop padding242 and244 covers the top portions ofmodules110 and112. Power packtop padding246 covers the top portion ofpower pack108 andcartridge top padding248 covers the top ofseparation cartridge206. Padding222-248 is a foam or similar lightweight material that adds protection to the modules as well as acts to reduce vibration ofoxygen concentrator100 felt by patient P. Alternately,oxygen concentrator100 is enclosed in soft, flexible material to further increase comfort and maintain flexibility. In one embodiment, padding232-248 is fabricated separately from themodules106,110,112, and116,power pack108 andcartridge206. In assembling theoxygen concentrator100, padding232-248 andcase portions224,226,228, and230, are merged and secured either using fasteners, adhesives, or a manufacturing process such as ultrasonic welding.
• Case portions224,226,228, and230, of each of themodules106,110,112, and116, contain sockets218a-218dfabricated on the surface thatcontacts belt104. Socket218a-218dfor each module is constructed to havesupport paths250 for electrical wiring and pneumatic tubing similar to those contained withinbelt104 represented bytube pathways214. Sockets218a-218dare constructed so thatsupport paths250 on sockets218a-218dalign withtube pathways214 inbelt104 when eachindividual module106,110,112, and116, is connected to belt104. In one embodiment, sockets218a-218dare constructed to allow eachindividual module106,110,112, and116, to snap ontobelt104 or attach in a similar quick connect fashion.Utility tubes212 comprise quick connects at module apertures216a-216d. Apertures216a-216dare openings in thecase portions224,226,228, and230, provided for connection ofutility tubes212 to components contained within eachmodule106,110,112, and116. This allows for removal of asingle module106,110,112, or116 should a specific component require maintenance or replacement. Sockets218a-218dare constructed from the same material as thecase portions224,226,228, and230.
• FIG. 10 is a perspective view of the components contained withinmodules106,110,112, and116, and the associated pneumatic and electrical connections ofoxygen concentrator100. Illustrated arepower pack108,valve140,drive reducer142,vacuum pump144, drive146, oxygen accumulator252 (comprisingproduct control pump154,check valves153 and156, and reservoir158), dispensingvalve160 connected to nasalpressure sensor line190 and dispensing valveopen line198,column inlet lines164a-164c, column outlet lines166a-166c, product controlpump vacuum line172, product controlpump inlet line174,product gas line202, finalproduct gas line205,adsorbent cartridge206, and mainelectrical cable254.
• Mainelectrical cable254 contains a set of electrical wires that carryinputs178,180,182,188, and190,outputs192 and198, andpower lines186,198, and200 shown inFIG. 5. Mainelectrical cable254 extends frompower pack108 to ECM148 (not visible inFIG. 10). Dispensing valve timeopen output198 and nasalpressure sensor input190 are wires that extend betweenECM148 and dispensingvalve160. Similarly, the other inputs and outputs are wired to the appropriate system components as illustrated inFIG. 5 (although not specifically illustrated inFIG. 10.)
• Product gas line202 connects dispensingvalve160 withreservoir158 ofaccumulator252. Finalproduct gas line205 connects dispensingvalve160 to productgas outlet port103 for connection todelivery tube102 after passing throughfinal filter136 located inadsorbent cartridge206 to provide patient P with oxygen rich product gas. Product controlpump inlet line174 extends frommain valve140 toproduct control pump154, which pumps separated oxygen rich gas intoreservoir158.Vacuum line172 connectsproduct control pump154 throughvalve140 to a vacuum drawn byvacuum pump144, and provides the actuation forproduct control pump154.Column inlet lines164a-164cand column outlet lines166a-166cconnectmain valve140 with column inlet ports132a-132cand column outlet ports134a-134cofcolumns130a-130c, respectively (not illustrated).Inlet air line168 transportsambient air162 fromseparation cartridge206 tomain valve140, whilevacuum inlet line170 connectsvacuum pump144 tomain valve140. Alllines164a-164c,166a-166c,168,170,172,174,176,202, and205, are pneumatic lines or similar structures that allow for the isolated flow of gases between system components.
• FIG. 11 is a perspective view of the components contained within power module106: power pack108 (comprisingcells256,outer wall258, and power pack life indicator260) and dispensingvalve160. In the embodiment illustrated,power pack108 is a lithium-ion battery pack comprised of fivecells256.Individual cells256 are contained withinouter wall258, part of which has been removed to showcell256.Power pack108 is a battery that is rechargeable and removable frompower module106. Although illustrated as a trapezoid containing five cylindrical cells, the shape and number of cells will vary depending on the shape ofpower module106 and power requirements ofoxygen concentrator100.
• Power pack108 is a lithium based battery pack capable of being recharged in a recharging socket or station that connects to an external power supply. Alternatively,power pack108 comprises a battery or fuel cell. In one embodiment,power pack108 is a lithium ion battery pack that is constructed from several interconnected lithium-ion batteries.Oxygen concentrator100 uses a maximum of fifteen watts of power. This results in a battery weight of less than 0.7 pounds (0.3 kg). In this embodiment, patient P taking twenty breaths per minute at a setting of 2 liters per minute equivalent can useoxygen concentrator100 for a minimum of four hours on a fully charged battery.Power pack108 is easily exchanged with another similar battery pack, and can be removed with a simple pulling or tugging motion. In another embodiment (not illustrated),oxygen concentrator100 contains a jack for receiving a power cord which can then be plugged into either a110 volt wall outlet or a 12 volt power supply system (such as a car utility plug) so thatpower pack108 can be charged in place inoxygen concentrator100.
• Powerpack life indicator260 displays the amount of time left that the power pack will operate theoxygen concentrator100. As illustrated, powerpack life indicator260 is a display, such as a liquid-crystal display (LCD) or light emitting diode (LED) screen, with numeric output of expected life in hours. The LCD or LED screen may also contain a series of bars that act as indicators. Alternately, powerpack life indicator260 is a light or series of lights.
• Dispensing valve160 is contained withinpower module106 and is used to feed the flow of oxygen to patientP. Dispensing valve160 is a valve activated by a change in pressure, such as that caused when a person is inhaling. A sensor in the dispensing valve circuit monitors pressure, and opens dispensingvalve160 when a drop in pressure is sensed.ECM148 communicates with dispensingvalve160 throughinput190 and output198 (seeFIG. 5).Dispensing valve160 is in communication withreservoir158 throughproduct gas line202.Reservoir158 is kept at a slight pressure above ambient. Thus, when dispensingvalve160 is opened, oxygen rich gas will flow fromreservoir158 through finalproduct gas line205,final product filter138, and productgas outlet port103 for delivery to patient P throughtubing102. The flow of gas is further assisted by the pressure drop created by patient P's inhaling.Dispensing valve160 can be set to deliver oxygen rich gas to patient P for the beginning portion of a breath when patient P first inhales rather than the whole breath.
• Dispensing valve160 provides for operatingoxygen concentrator100 in one of two possible modes: pulse flow or continuous flow. When patient P is using theoxygen concentrator100 in the pulse flow mode, dispensingvalve160 will open intermittently in response to inhalation and will stay open for a pulse time according to the setting of the controls as set by patient P. If continuous flow is desired, dispensingvalve160 is maintained at an open or partially opened state. The product is dispensed to patient P thoughoxygen delivery tube102 at a continuous rate, typically in the range of 1-1.5 lpm (liters per minute). The pressure difference corresponding to a dispensing orifice indelivery tube102 will accommodate the flow rate from thereservoir158.
• FIGS. 12a-12dare various views of components contained inside ofreservoir module110.FIG. 12ais a perspective view ofaccumulator252.FIG. 12bis a top view of accumulator12b.FIGS. 12cand12dare sectional views corresponding to the section lines in12b. Contained withinreservoir module110 is oxygen accumulator252 (comprisingreservoir158,check valves153 and156, and product control pump154),inlet port261, andoutlet port263.Accumulator252 receives separated product gas throughinlet port261. Product inlet line174 (shown inFIG. 10) is connected toinlet port261 and linksproduct control pump154 toseparation cartridge206 throughmain valve140 to transport oxygen rich gas separated bycartridge206.Inlet port261 connects to checkvalve153 which allows product gas intoproduct control pump154.
• Product control pump154 includespiston262, actuated byspring264 withinpump chamber265, which pushes separated oxygen-rich product gas intoreservoir158.Check valve156 opens to allow oxygen into thereservoir158 and closes to prevent back flow of oxygen-rich gas when the desired pressure inreservoir158 is attained. The low pressure ofreservoir158 exerts a force oncheck valve156 to keepvalve156 closed.Reservoir158 takes oxygen-rich gas produced byoxygen concentrator100 and stores it at a low pressure above ambient until the product is required for use by patient P.
• Product control pump154 is driven by vacuum. Product controlpump vacuum line174 is connected to the vacuum drawn byvacuum pump144 throughmain valve140. When a vacuum is drawn, the force drawspiston262 down to compressspring264 which expandspump chamber265, and causescheck valve153 to open. Oxygen-rich gas fromseparation cartridge206 flows throughcheck valve153 and enterspump chamber265 in the volume created by the displacement ofpiston262. At the appropriate time in the cycle,valve140 will interrupt the vacuum toproduct control pump154, andspring264 will forcepiston262 upwards. The movement ofpiston262 will force oxygen rich gas inpump chamber265 throughcheck valve156 and intoreservoir158. At the same time,check valve153 closes to prevent more gas from enteringpump154. With this embodiment, no additional drive (other than the vacuum to pullpiston262 down and the spring force to move it up) is required forproduct control pump154 which adds to the overall efficiency of the system.
• In one embodiment,reservoir158 has a capacity that is about four times larger than the size of the largest pulse provided byoxygen concentrator100. In one embodiment, extra volume is included to account for separated oxygen used as a back flow inadsorbent columns130a-130c. Specifically,main storage reservoir158 foroxygen concentrator100 can be designed according to the flow rates listed in Table 1.Storage reservoir158 is 100 cc (cubic centimeters) to 400 cc in volume.Main storage reservoir158 is maintained at a low pressure to provide delivery of the product gas to patient P throughoutlet263 which is connected to finalproduct dispensing line202. In one embodiment, the pressure is between 1 atm (ambient) and 1.5 atm. Also acceptable are pressures less than eight psi (55,158 Pa), with a pressure of two and one half to five psi (17,236 to 34,473 Pa) preferred. The low pressure ofreservoir158 allowsoxygen concentrator100 to be used in most areas where high pressure oxygen is banned. Also, low pressure requires less energy to fillreservoir158, which adds to the efficiency of the system by requiring a simpler pressurizing mechanism compared to high pressure systems.
• Reservoir158 contains pressure sensor159 (such as a piezoresistive or capacitive sensor) that sends reservoir pressure signal188 to ECM148 (seeFIG. 5).ECM148 adjusts the speed of the motor ofdrive146 based onreservoir pressure signal188 in combination with the current settings onuser interface114. As patient P's respiratory rate increases for the current setting, more oxygen-rich gas fromreservoir158 is dispensed thus lowering the pressure ofreservoir158. The drop in pressure is sensed and the system will react by increasing the production of product gas. Similarly, a decrease in the respiratory rate of patient P at the current setting ofoxygen concentrator100 raises the pressure inreservoir158. The rise in pressure is sensed andECM148 adjusts drive146 accordingly to maintain a preset pressure range inreservoir158. Thus, only the amount of oxygen used by patient P is produced byoxygen concentrator100.
• FIG. 13 is a perspective view of thecontrol module112. Illustrated are thecase228 containingaperture216candsocket218c, andpadding236 and234.Control module112 containsuser interface114 comprisingpower switch266, flow level indicator lights268,flow setting switches270aand270b,boost switch272, andindicator lights274 and276.Power switch266 is an ordinary toggle or push button switch capable of turningoxygen concentrator100 on and off.
• Flow settings are dually controlled by patient P utilizing flow setting switches270. First, continuous or pulse mode is selected by patient P. In a continuous flow mode, oxygen is dispensed at a continuous flow rate such as one to one and a half liters per minute. Ifoxygen concentrator100 is set in a pulse mode for controlling flow,oxygen concentrator100 utilizes dispensingvalve160 to provide pulse dispensing of product gas. The pulse mode is set to meet patient P's needs for the equivalent of one to five liters per minute of continuous oxygen flow. In one embodiment, a dial containing settings of one to five is utilized. In the embodiment illustrated inFIG. 13, flow setting switches are used to adjust the flow rate between various stepped levels. Each setting corresponds to the specific value for continuous flow, or a corresponding pulse volume. For example, settings for a pulse mode are contained in the table below.

• TABLE 1
  	Total		Pulse
  	Volume	Trigger	Flow	Pulse	Peak
  	Pulse Range	Time	Ramp	Duration	Pulse
  Setting	(cc/pulse)	(sec)	Rate (sec)	Max (sec)	Flow (LPM)
  1	10 to 12	.001 to .02	.03 to .07	.15	14
  2	20 to 24	.001 to .02	.03 to .07	.20	14
  3	30 to 36	.001 to .02	.03 to .07	.25	15
  4	40 to 48	.001 to .02	.03 to .07	.30	16
  5	50 to 60	.001 to .02	.03 to .07	.35	17

• When the unit is set in pulse mode, product gas is dispensed only at the beginning of inhalation. In one embodiment,product dispensing valve160 is only opened between zero and 0.4 seconds of the beginning of a breath of patient P. This controls the amount of oxygen removed fromreservoir158. In another embodiment,oxygen concentrator100 is shut off if no pressure drop is sensed bynasal pressure sensor190 for a set amount of time, such as two minutes, which in turn closes dispensingvalve160.
• Patient P can temporarily increase (or “boost”) the flow rate of oxygen by actuatingboost control switch272 onuser interface114. Whenboost switch272 is activated,oxygen concentrator100 increases the flow rate of oxygen for a set period of time, such as 10 minutes. After timing out,oxygen concentrator100 returns to the previous setting. The boost function will not work ifoxygen concentrator100 is already operating at the maximum flow rate.
• Indicator light274 indicatespower pack108 is running low.Indicator light276 indicates that there is a problem withseparation cartridge206, such as a bad connection withreceptacle208. In one embodiment,oxygen concentrator100 contains three different colored lights: red, yellow, and green. The green light indicates that there are no problems detected withoxygen concentrator100. A yellow flashing light or a yellow non-flashing light indicates a condition has been sensed that should be addressed. An example of such a condition is a low battery. A red flashing light indicates that a condition has been detected that requires an immediate response. A red non-flashing light indicates thatoxygen concentrator100 has failed, and has shut down. For example, ifoxygen concentrator100 fails to produce a stream of separated gas of eighty-five percent oxygen,oxygen concentrator100 will detect this problem viabreakthrough flow sensor150.ECM148 shuts offmain valve140 so noambient air162 is being submitted to thegas separation cartridge206. Product gas is no longer being supplied toreservoir158. After a few breaths,reservoir158 will empty, triggering reservoir pressure sensor output188 (shown inFIG. 5), which communicates toECM148 to shut downoxygen concentrator100, and display the red warning light. This signals patient P that maintenance is needed. In addition to the aforementioned indicator lights, the unit may also contain a boost indicator light to indicate when a boost function is in operation. Similarly, an audible alarm may be included inoxygen concentrator100 to indicate failure.
• FIG. 14 is a front view of the interior components ofcontrol module112. Illustrated aredrive146,vacuum pump144,drive speed reducer142, andvalve140. Drive146 includes a DC motor, driven bybattery power pack108, which supplies the necessary power to operatevacuum pump144. The motor draws a maximum of 15 watts of power.Vacuum pump144 is a positive displacement pump. In this embodiment, drive146 runs bothvacuum pump144 andvalve140.Vacuum pump144 is run by the motor at one speed, whilevalve140 is run off the same motor but at a reduced speed. The reduction in speed is accomplished with gears that comprisedrive speed reducer142 between the motor ofdrive146 andvalve140.
• Valve140 is a valve containing a minimum number of ports equal to two times the number of adsorbent beds (columns) inseparation cartridge206. Additionally,main valve140 contains other ports for the inlet ofambient air162, vacuum provided byvacuum pump144, and recycling of product gas used to purgecolumns130a-130cduring repressurization. In the preferred embodiment,valve140 is a rotary valve, but may also be a solenoid valve, directional control valve, or series of individual valves in communication with each other and each connected to anadsorbent column130a-130c.
• In an alternate embodiment, drive146 may contain an independent motor for operatingvalve140. Ifvalve140 is run by an independent motor, that motor is powered bypower pack108 and synchronized with the other motor(s) ofdrive146 byECM148. As illustrated, drive146 contains a single motor andvalve140 is connected to a system of gears that comprisedrive speed reducer142. Alternately,drive speed reducer142 can be any common power transmission components such as pulley and belts, or gears and sprockets.
• FIG. 15 is a perspective view ofseparation cartridge206 contained withinseparation cartridge module116. Illustrated are inlet ports132a-132c, outlet ports134a-134c, andcasing230. In the embodiment illustrated, three adsorption columns are contained withincasing230 with one inlet port132a-132c, and one outlet port134a-134c, for eachadsorption column130a-130c. Eachadsorption column130a-130cis a hermetically sealed container containing a bed of adsorption material, preferably a zeolite capable of adsorbing nitrogen gas, such as lithium low silica 13× zeolite. Each bed contains between five and twenty-five cubic centimeters of material, and in one embodiment contains fifteen (plus or minus one) cubic centimeters of material. The adsorbent bead size is a thirty by sixty mesh, wherein thirty mesh is equal to 0.0234 inches (0.0594 cm) and sixty mesh is equal to 0.01 inches (0.0254 cm).
• Column inlet ports132a-134care connected to receive eitherambient air162 or vacuum, while outlet ports134a-134cexpel product gas or receive purge gas. This arrangement promotes ordering of gases within thecolumns130a-130cby having oxygen rich gas always present at one end of the column. This results in improved efficiency as air flow through thecolumns130a-130ccreates an oxygen rich zone continuously at one end, which allows the vacuum to evacuate and desorb the previously adsorbed nitrogen where it is contained in the greatest concentration.
• FIG. 16 is a perspective view of thecolumns130a-130cand thefilters136 and138 withincasing230 ofseparation cartridge206. Illustrated arefinal product filter138 connected to productgas outlet port103 which connects totubing102,inlet air filter136, andadsorbent columns130a-130ceach comprising spin inducers280a-280f, adsorbent material282a-282c, porous filters284a-284f, and springs286a-286c. Springs286a-286care coil springs that hold each adsorbent column incompression130a-130cin place withincasing230 ofseparation cartridge206 to prevent movement of adsorbent beads. Spin inducers280a-280fhelp force even distribution of gases throughcolumns130a-130c, which helps to keep the MTZ well defined for more accurate detection.
• Adsorbent material282a-282cis the same as that previously described.Filters136 and138 are constructed of common filtering materials and are used to remove dust and other large particulate matter from the air streams to assure that the flow of oxygen out to patient P is free of such materials. Porous filters284a-284fare a small section of material commonly used as a particle filter provided at each end ofcolumns130a-130c. Porous filters284a-284fact to prevent adsorbent particles from contacting the mechanisms and valving ofconcentrator100.
Docking Station122 (FIGS. 17-18)
• FIG. 17 is a perspective view of the back side ofoxygen concentrator100 ondocking station122. Illustrated areoxygen concentrator100 comprisingpower module106,reservoir module110,control module112, andseparation cartridge module116,belt104, anddocking station122 containingstatus display288.Status display288 is an LED, LCD, or similar digital display used to provide information to patient P such as time of day, time the concentrator has been used, time of recharging forpower pack108, or similar information. Additionally,docking station122 may contain other controls (not illustrated) including a boost setting while the concentrator is docked, a mode switch for switching between pulse and continuous flow of oxygen, and indicator lights to show expected battery life, adsorbent column life, gas input, gas output, or gas separation system malfunctions, or other similar items that were previously described as part ofuser interface114.
• FIG. 18 is a perspective view of thedocking station122 withoxygen concentrator100 removed.Concentrator dock126 is visible ondocking station122 withoxygen concentrator100 removed.Concentrator dock126 may optionally contain electrical connections (not illustrated) to chargepower pack108 contained withinpower module106 whileoxygen concentrator100 is docked. Additionally,docking station122 contains a power cord (not illustrated) available to connect to a wall socket or other power source such as a car utility plug.Docking station122 uses power provided through the power cord to operateoxygen concentrator100 and/or recharge power packs108.Docking station122 contains aflat bottom290 to rest on a level surface and allowoxygen concentrator100 to be in the docking station without moving. Alternately,docking station122 is mountable to a wall in one embodiment, and is a free standing device that is set on a generally flat surface in another embodiment.
• In one embodiment,docking station122 comprises indicator lights and control power switch (not illustrated) in addition tostatus display288,power pack chargers124aand124b, andconcentrator dock126. Indicator lights provide information to patient P utilizingoxygen concentrator100. Indicator lights will indicate ifoxygen concentrator100 is functioning properly, requires maintenance, or has failed. Control switch is a master switch for supplying or terminating power or controlling the setting of flow foroxygen concentrator100. Status display128 is an LED, LCD or similar digital display that can be used to indicate various information to patient P such as time of day,time oxygen concentrator100 has been docked, time of recharging for the power pack, or similar information.
• Docking station122 also containspower pack chargers124aand124bandconcentrator dock126.Docking station122 contains a power cord (not illustrated) available to plug into a wall socket or a similar power pack.Docking station122 converts AC power to rechargepower pack108 inpower pack chargers124aand124b.Power pack chargers124aand124bcontain contacts that are used to transfer power topower pack108 while recharging. Alternatively, apower pack108 placed incharger124aor124bis inductively coupled to recharge thepower pack108. Similarly, power is provided tooxygen concentrator100 itself while ondocking station122, and to recharge of the power pack108 (seeFIG. 4) still attached to theoxygen concentrator100.Concentrator dock126 is shaped to provide a place to setoxygen concentrator100 while docked, as well as facilitate easy removal ofoxygen concentrator100 for ambulatory use.
• In one embodiment,docking station122 performs several functions withoxygen concentrator100 docked. First,oxygen concentrator100 is allowed to run without utilizingpower pack108 while it is docked. Second, a boost setting is available to increase the delivery rate of oxygen whileoxygen concentrator100 is docked.Boost switch272 is located on user interface114 (SeeFIG. 13). In an alternate embodiment, a boost switch is located ondocking station122. Upon removal ofoxygen concentrator100 fromdocking station122, the boost setting is removed andoxygen concentrator100 operates at a set delivery rate in either a continuous or pulse mode.
• Oxygen concentrator100 contains flow setting switch270 (FIG. 13), and a mode switch (not illustrated). The mode switch allows patient P to select continuous or pulse flow. In one embodiment, patient P is allowed to adjust the setting ofoxygen concentrator100 only while docked. That is, patient P can reprogram by changing a pulse setting (e.g., from 2 to 3), or continuous flow mode (e.g., from 1.0 to 1.5 liters per minute), only whileoxygen concentrator100 is ondocking station122. Patient P wishing to adjust settings will be required to hold the control switch while adjusting the flow setting dial or mode switch. In another embodiment,docking station122 contains a switch automatically activated by placingoxygen concentrator100 indocking station122 which allows patient P to adjust flow setting. The requirement that settings can only be changed during docking prevents accidental switching of the flow mode ofoxygen concentrator100 during ambulatory use. For example, there is no change in flow ifflow setting switch130 is bumped, which would normally increase oxygen flow. Ifoxygen concentrator100 can only be reprogrammed indocking station122,oxygen concentrator100 will remain in the preset mode set atdocking station122 and will not increase or decrease flow by a change of the setting. In one embodiment, the flow setting switch and mode switch are located on a user interface located directly ondocking station122.
• Another function ofdocking station122 is to provide diagnostic features of the system.Docking station122 may indicate expected battery life, adsorbent column life, or pump malfunctions through the use of indicator lights, or status display128, or a combination of both. Alternatively, these items are located onuser interface114, or at a combination of locations ofuser interface114 anddocking station122. For example,battery life indicator142 is located directly onpower pack108 that comprises the battery itself, and battery problem warning light274 is onuser interface114 also. Similarly, adsorbentcartridge warning light276 is located onuser interface114, but may also be on either thecartridge module116 ordocking station122 as well.
Concentrator Efficiency
• Oxygen concentrator100 can produce a stream of product gas containing a range of 85-95 percent oxygen which provides up to 5 liters per minute pulsed equivalent of product gas. By utilizing vacuum swing adsorption, the separation process phases are all performed at less than 1 atm.
• Utilizing a vacuum to exhaust unwanted gas fromadsorbent columns130a-130cimproves efficiency of theoxygen concentrator100. Less power is required than pressure swing adsorption (PSA) or vacuum-pressure swing adsorption (VPSA), which results in a smaller battery and thus a lighter weight product.Oxygen concentrator100 as disclosed weighs less than 3 pounds (1.4 kg) and occupies less than 1 liter of volume. Also, the efficiency of the system allows foroxygen concentrator100 to operate for at least three hours while producing up to 5 liters per minute pulsed equivalent of product gas without requiring patient P to attend to the unit, e.g. changing the battery. Further, the low energy consumption causes less heat transfer. The product gas is discharged from the separation system at a temperature of ±six degrees Celsius from that of the ambient air. This eliminates the need for heat exchangers which add to the overall weight and reduces system efficiency. The amount of heat generated causes no discomfort to patient P wearing and utilizing theoxygen concentrator100. Also, upon startingoxygen concentrator100, the flow of product gas will increase from 21 percent oxygen (ambient) to 85 percent or more oxygen in under two minutes.
• Improvements over the prior art are attained by regulating the device to only separate the amount of oxygen needed by patient P at any given time. The prior art separates a flow of oxygen and delivers that rate to patient P as a steady flow. Patient P is only inhaling this oxygen during about ⅓ of the normal breathing cycle. Within the inhalation portion of the breathing cycle, the volume of gas inhaled last stays in the dead space of the airways and is not presented to the alveoli. Therefore if oxygen is dispensed to patient P only during the early part of inhalation, less than1/3 the steady flow is actually required. Moreover, prior art devices do not adjust the flow based on a patient P's needs, but operate at the same steady flow. The present concentrator slows down its entire cycle rate producing only the amount of oxygen needed. Thus,oxygen concentrator100 retains a high oxygen recovery percentage at all product flow rates while minimizing energy consumption and maximizing adsorbent life. Patient P's actual needs vary with real time changes in activity. This causes a corresponding variation in breathing rate.Oxygen concentrator100 tracks patient P's breathing rate and adjusts oxygen separation and delivery rates proportionally. In combination, these two features allowoxygen concentrator100 to separate oxygen only at the rate it is being consumed, resulting in a reduction in the amount of oxygen needing to be separated for patient P.
• Another improvement over the prior art involves reducing the waste of separated oxygen in the various adsorb and desorb cycle phases. This is typically referred to as maximizing product recovery. The primary system components become larger or smaller as the amount of oxygen separated increases or decreases. Therefore, a dramatic reduction in size and weight of the concentrator requires use of as much separated oxygen as possible by delivering it to patient P rather than losing it to the waste stream. The prior art works by using the Skarstrom cycle well known to those skilled in the art.
• During one phase of the Skarstrom cycle in PSA or VPSA, air is pumped into one end of a column of adsorbent pressurizing it above atmospheric pressure while oxygen is flowing out of the opposing end. Nitrogen is being adsorbed as the MTZ propagates toward the oxygen outlet end of the column. This phase is terminated before the MTZ breaks through into the oxygen stream so that oxygen purity is not diluted by the nitrogen rich air trailing the MTZ. If it is terminated earlier than necessary to maintain purity there will be substantial separated oxygen left in the column in front of the MTZ that is not passed to the patient. During the next cycle phase the column pressure is reduced to a lower cycle pressure desorbing the nitrogen that was adsorbed during the separation phase and it is passed to the waste stream. Some of the oxygen left in the column at higher pressure will also be passed to the waste stream as gas flows from the column when pressure is reduced. Recovery of separated oxygen can therefore be maximized by stopping the previous separation phase just short of breakthrough, leaving minimal oxygen in the column to be lost to the waste stream during the reduced pressure evacuation phase. The position of the MTZ needs to be accurately known to terminate the separation phase for optimal recovery without compromising purity. This position cannot be accurately estimated because its propagation rate is a function of many variables including product oxygen flow rate, high and low cycle pressures, temperature, adsorbent water content and the amount of other contaminants accumulated in the adsorbent. Prior art systems stop the separation phase well short of breakthrough to encompass worst case operating conditions without sacrificing purity and thereby waste separated oxygen in the evacuation phases during most typical non-worst case operating conditions.
• Oxygen concentrator100 determines the position of the MTZ just prior to breakthrough and terminates the flow from outlet134 for the remainder of the feed phase or adjusts the motor speed, as previously described. Additional oxygen is left in the column at the end of a feed phase and is wasted during the evacuation phases. This is oxygen adsorbed by the adsorbent combined with oxygen present in the interstitial and dead spaces of the adsorbent and column. All adsorbents used in oxygen separators adsorb nitrogen, and also oxygen to some extent. The adsorbent used inoxygen concentrator100 presents a very high ratio of adsorbed nitrogen to adsorbed oxygen. As the amount of oxygen adsorbed is minimized through the choice of an adsorbent with a low affinity for oxygen, the amount of adsorbent needed to separate a given amount of nitrogen during a separation phase will decrease as its affinity for nitrogen increases. The less adsorbent needed to adsorb a given amount of nitrogen, the less adsorbent there is to adsorb oxygen and the smaller the column can be with less interstitial and dead space.
• For example, a LiLSX adsorbent referred to as Oxysiv MDX from UOP Corporation has a very high ratio of adsorbed nitrogen to adsorbed oxygen in the operating pressure range ofoxygen concentrator100. The Skarstrom cycle of the prior art uses a purge phase in which separated oxygen is fed back into the product end of the column while nitrogen rich gas is passing out of the opposing end of the column into the waste stream as the pressure transitions to the lower cycle pressure. While this purge can enhance product purity, some of the purge oxygen passes all the way through the column and is lost to the waste stream.Oxygen concentrator100 using VSA achieves a measured 60% oxygen recovery rate, compared to a typical recovery rate of 30% for the prior art utilizing PSA.
• Another improvement over the prior art concerns the choice of adsorbent and operating pressure range. The energy required by the separation process directly defines the weight and size of major components such as the battery, motor and gas pump of a concentrator. Minimizing the amount of adsorbent minimizes the amount of energy needed to separate a given amount of oxygen. Each adsorbent has a characteristic pair of isotherms that show the amount of oxygen and nitrogen a given mass of adsorbent will hold at equilibrium over a range of pressures and vacuums for these gasses at a constant temperature. The cycle phases of the system necessarily include the pumping of gas contained in volumes of adsorbent to produce a change in nitrogen partial pressure between a chosen higher pressure and a chosen lower pressure. The pneumatic energy a pump must deliver in the process of cycling a given volume of gas between a higher and a lower level is in direct proportion to the volume of gas pumped multiplied by the difference between the high and low vacuum levels. The isotherms for various adsorbent candidates specify the amount of nitrogen contained in a fixed mass of adsorbent at a fixed temperature as a function of nitrogen partial pressure.
• An example of the isotherm for the LiLSX adsorbent Oxysiv MDX along with the isotherm for a typical 13× type adsorbent used in the prior art is shown inFIG. 19. Having minimized the amount of oxygen needed to be separated from air and having maximized the recovery percent of oxygen as previously disclosed, along with knowing the percentage of oxygen present in air prescribes a specific minimum amount of air that must be moved into the system to produce the needed oxygen. This minimum amount of air minus the maximized separated oxygen must pass out of the system as a minimized volume of waste gas.Oxygen concentrator100 acts to minimize the flow rates of the air feed stream and the waste stream. This flow must be pumped across a pressure difference defined by the choice of high and low operating pressures requiring a pumping energy that is proportional to both the flow rate and the pressure difference. The gas streams are pumped into or out of the adsorbent during each complete cycle to produce the needed swing in pressure between high and low cycle pressure levels allowing the separation of nitrogen from oxygen. Minimizing the amount of gas being pumped through the system reduces the pumping energy in proportion to reductions in the difference between chosen high and low pressure points that the gas must be pumped across. The isotherm for nitrogen shows that nitrogen is transferred in or out of the adsorbent with the smallest change in pressure where the slope of the isotherm is the steepest. Using typical PSA, a ratio of high to low pressure levels in these systems needs to be 3:1 or greater to maintain the desired oxygen purity. Lower pressure ranges, i.e. sub-atmospheric or vacuum ranges used in VSA, allow this ratio to be maintained with less total difference between the high and low pressure levels.
• For example, prior art operates between 1 and 3 atmospheres for a 3:1 ratio and a pressure difference between high and low levels of 2 atmospheres.Oxygen concentrator100 using VSA operates between 0.3 atmospheres and 1 atmosphere. A ratio of about 3.3:1 is achieved with a pressure difference of only 0.7 atmospheres. Operating on this range of the isotherm as seen inFIG. 19 allows just as much nitrogen to be passed in and out of the LiLSX adsorbent with a 0.7 atmosphere pressure range as a PSA system does with 13× adsorbent and a 2.0 atmosphere pressure range. The LiLSX adsorbent allows a cycle pressure range that is nearly ⅓ that of a PSA system with a proportional reduction in pumping energy.
• Oxygen concentrator100 is a quiet device. Whenoxygen concentrator100 is running, it produces a noise level in the range of ten to thirty decibels. Further, with the compact size of the parts,vacuum pump144 is running continuously and there is very little vibration to affect a person using it docked or wearing it as an ambulatory device. The device of the present invention with the described components weighs less than three pounds (1.36 kg). The compact size (less than about 61 cu. in. (1000 cc)) allows for easy portability. Similarly, the small size does not disrupt counter space or storage when used at home. The device does give off some heat, however the outer case is less than 6 degrees Celsius higher than ambient whenoxygen concentrator100 is running on battery power. The device may emit more heat while it is docked and operating on AC power to charge thepower pack108, but is still less than 15 degrees Celsius above ambient.
• Based on the foregoing embodiments, the efficiency of the concentrator can be determined. One measure of efficiency is the ratio of oxygen produced to the amount of adsorbent material used to obtain the oxygen, represented by the following:
• 
  Qp=Liter/min O₂produced
• 
  Madsorbent=Kg of Adsorbent Material
• for example, the disclosed embodiments includeadsorbent columns130a-130c, with each column containing 15 cubic centimeters (cc) of adsorbent material with a density of 0.66 gm/cc. That is:
• $\left(3\mathrm{columns}\right)\left(\frac{15{\mathrm{cm}}^3}{\mathrm{column}}\right)\left(\frac{0.66\mathrm{gm}}{{\mathrm{cm}}^3}\right)=30\mathrm{gms}$
• for the system.
  The following flow rates (Qp) were obtained by the above disclosed concentrator:
• 
  Qpmax=1.5 L/min
• 
  Qpmin=0.14 L/min
• This results in a range for kilograms of adsorbent material to oxygen flow rate of:
• $0.020<\frac{\mathrm{Madsorbent}}{\mathrm{Qp}}<0.214$
• Similarly, flow rates (Qp) were determined for a system that contains three adsorption columns, each column containing 15 cc of adsorbent material. The separation completed in a range of 0.3 atm to 0.95 atm. Values were calculated for breakthrough time, work, battery life, and flow rate. The volume of gas contained in a column at the end of a feed phase was 150 cc. These constants were used to determine the following measures of efficiency:
• Work per evacuation cycle or pneumatic power requirements were determined based on the following calculations:
• 
  W(work)=(volume moved)*(vacuum differences);
• The vacuum differences are calculated as the vacuum pump is continuously changing gas out, and as vacuum progresses to end point. From this:
• V_H=Vacuum upper level
• V_L=Vacuum lower level
• Vol=Volume of gas in the column at end of feed phase
• 
  W=Vol*(V_H−V_L)*(1+(V_H/(V_H−V_L))*ln(V_L/V_H)+ln(V_H/V_L)
• Inserting the above constants and converting to joules (multiply by 100.32 to get L*atm to joules) yields:
• 
  W=4.81 joules
• Thus, 4.81 joules is required to evacuate the gas which desorbs during the evacuation phase. From experimentation, the following flow rates (LPM is liters per minute) and cycle times were recorded:

• 	Qp (flow rate)	Low = .14 LPM
  		Med = .720 LPM
  		High = 1.5 LPM
  	Cycle time	Low = 5.6 sec.
  		Med = 1.12 sec.
  		High = .54 sec.

  
  Power consumption can be determined by calculating work divided by the time of the cycle.
• 
  Low flow power=4.81 joule/5.6 sec=0.85 watts
• 
  Medium Flow power=4.81 joule/1.12 sec=4.29 watts
• 
  High flow power=4.81 joule/0.54 sec=8.9 watts
• From the above, a measure of energy consumed to the flow rate can be made and used as an indicator of the system efficiency:
• $\mathrm{Low}\text{:}\frac{\mathrm{.85}w}{\mathrm{.14}\mathrm{LPM}}=6.07w\text{/}\mathrm{LPM}$$\mathrm{Medium}\text{:}\frac{4.29w}{\mathrm{.72}\mathrm{LPM}}=5.95w\text{/}\mathrm{LPM}$$\mathrm{High}\text{:}\frac{8.9w}{1.5\mathrm{LPM}}=5.93w\text{/}\mathrm{LPM}$
• Another measure of efficiency is the ratio of mass of the power pack (Mpowerpack) compared to the amount of oxygen produced (Qp) over time:
• $\frac{\mathrm{Mpowerpack}}{\mathrm{QpT}\left(\mathrm{time}\right)}$
• The following constants are used in the calculation: the battery cell is a type 18650 lithium ion battery with 7.4 watts-hrs, measuring 42 g; motor efficiency is 90 percent; and vacuum pump efficiency is 80 percent.
  Pneumatic work=6 W/L/min. Thus,
• $\mathrm{Electric}\mathrm{power}=\frac{6W\text{/}\mathrm{LPM}}{\left(\mathrm{.9}\right)\left(\mathrm{.8}\right)}=8.3W\text{/}\mathrm{LPM}$
• Battery mass compared to energy consumption is:
• $\frac{42g}{7.4\left(\mathrm{watt}\right)\left(\mathrm{hr}\right)}\left(\frac{1\mathrm{Kg}}{1000g}\right)\frac{8.3\mathrm{watt}}{\mathrm{LPM}}=0.47\frac{\mathrm{Kg}}{\mathrm{LPM}\left(\mathrm{HR}\right)}$
• Total battery mass for the power pack can be determined from this equation. For example, if a patient requires the concentrator to run for four hours at setting of “3” and takes 20 breaths per minute (the medium flow rate):
• $\left(4\mathrm{hr}\right)*\frac{\mathrm{.047}\mathrm{kg}}{\mathrm{LPM}\left(\mathrm{hr}\right)}\mathrm{.72}\mathrm{LPM}=\mathrm{.135}\mathrm{kg}$
• The mass of the batteries needed is 0.135 Kg. Assuming each battery cell is 42 g as previously stated, the number of batteries for the power pack can be calculated:
• $\mathrm{.135}\mathrm{kg}\left(\frac{1000\mathrm{<figure-callout\; label="g"\; filenames="US20110197890A1-20110818-D00004.png,US20110197890A1-20110818-D00012.png"\; state="\{\{state\}\}">g</figure-callout>}}{1\mathrm{kg}}\right)\frac{\mathrm{battery}\mathrm{cell}}{42g}=3.2\mathrm{battery}\mathrm{cells}$
• Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. For example, larger flow rates may be achieved by scaling the concentrator components to achieve desired flow rates at the disclosed efficiencies.

Claims (20)

1. An oxygen concentrator which produces a product gas containing at least about eighty-five percent oxygen by utilizing a vacuum swing adsorption (VSA) process comprising:

a gas input system for supplying ambient air;

a VSA gas separation system in communication with the gas input system to receive the ambient air, the gas separation system comprising a cartridge containing an adsorbent material for producing oxygen;

a delivery system for receiving oxygen produced by the gas separation system;

a drive which actuates the delivery system and the gas separation system;

a power pack connected to the drive; and

wherein the oxygen concentrator has a weight of less than 2.3 kg and a volume of less than 1 liter.

2. The oxygen concentrator ofclaim 1 wherein the VSA gas separation system further comprises a vacuum pump which evacuates nitrogen rich gas from the adsorbent material.

3. The oxygen concentrator ofclaim 1 wherein the power pack comprises a battery.

4. The oxygen concentrator ofclaim 1 wherein the delivery system includes an oxygen conserver.

5. A method of providing oxygen separated from ambient air to a patient, the method comprising:

performing vacuum swing adsorption cycles in each of a plurality of adsorbent beds containing an adsorbent selective for nitrogen, each cycle including a feed phase, an evacuation phase, and a repressurization phase; wherein the pressure throughout the vacuum swing adsorption cycles does not rise above that of ambient air; and

delivering product gas containing oxygen separated by the vacuum swing adsorption cycles to the patient.

6. The method ofclaim 5 wherein vacuum levels in the beds during cycles are between about 0.1 atm and about 1.0 atm.

7. The method ofclaim 5 wherein each of the beds has a first end and a second end.

8. The method ofclaim 7 wherein during the feed phase ambient air at about 1.0 atm is introduced into the first end of the bed and product gas is removed from the bed through the second end of the bed.

9. The method ofclaim 8 wherein the feed cycle is terminated when a mass transfer zone has reached a specific position in the column.

10. The method ofclaim 7 wherein during the repressurization phase, the bed is partially repressurized by product gas introduced through the second end.

11. The method ofclaim 10 wherein during the repressurization phase the bed is repressurized to near 1.0 atm with ambient air introduced through the first end.

12. The method ofclaim 5 and further comprising:

controlling cycle rate of the vacuum swing adsorption cycles as a function of the product gas delivered to the patient.

13. The method ofclaim 5 wherein delivering product gas comprises delivering a pulse of product gas in response inhalation by the patient.

14. The method ofclaim 5 wherein plurality of adsorbent beds comprises at least two adsorbent beds, each in a different phase at any given instant.

15. The method ofclaim 12 wherein the adsorbent is LiLSX adsorbent.

16. An oxygen concentrator comprising:

a portable power pack;

a vacuum swing adsorption (VSA) oxygen separator powered by the power pack and having a plurality of nitrogen-selective adsorbent beds, each bed operating in VSA cycles including feed, evacuation and repressurization phases, the VSA cycles operating with vacuum levels within in a range between about 0.1 atm and about 1.0 atm, wherein the pressure throughout the VSA cycles does not exceed about 1.0 atm; and

a delivery system for receiving oxygen provide bye the gas separation system.

17. The oxygen concentrator ofclaim 16 wherein the power pack, the VSA oxygen separator, and the delivery system have a combined mass of less than 2.3 kg.

18. The oxygen concentrator ofclaim 16 wherein the VSA oxygen separator comprises:

an ambient air inlet;

a vacuum pump; and

a valve for selectively connecting the ambient air inlet, the vacuum pump and the delivery system to the adsorbent beds during different phases of the VSA cycles.

19. The oxygen concentrator ofclaim 16 wherein the VSA oxygen concentrator further comprises:

a motor for driving the valve and the vacuum pump.

20. The oxygen concentrator ofclaim 16 wherein the adsorbent beds comprise an LiLSX adsorbent.

Images