This invention relates to the field of gas concentrators, and in particular to a miniaturized, portable gas concentrator and method of miniaturized gas concentration.
The pressure swing adsorption cycle was developed by Charles Skarstrom. FIGS. 1A and 1B describe the operation of the Skarstrom xe2x80x9cHeatless Dryerxe2x80x9d. In particular, ambient humid air is drawn into the system from an intake port, by a compressor. The pressurized air flows from the compressor through conduit 9 to a switching valve 4. With the valve in the shown position in FIG. 1A, pressurized air passes through conduit 5a to a pressure vessel 6a. The air feeds into the pressure vessel to a flow-restrictive orifice 1a. The effect of the restrictive orifice is to restrict the flow of gas escaping the pressure vessel. As the pressure builds up in the pressure vessel, water vapour condenses on the sieve material 8. Air with reduced humidity passes through orifice 1a to conduit 12. At conduit junction 11, some of the air is extracted for use from gas extraction port 2 while the remainder passes through conduit 13 to restrictive orifice 1b. The less humid air that passes through orifice 1b is used to blow humid air out of the unpressurized vessel 6b, through conduit 5b, through valve 4, to a vent port 7. When valve 4 switches to the position as shown in FIG. 1B, the opposite cycle occurs.
Thus, as valve 4 cycles from the position of FIG. 1A to the position of FIG. 1B, cyclically, there is a gradual reduction of humidity in the air as sampled at port 2. Likewise gases can be separated by adsorbing components of the gas on selective molecular sieves.
From laboratory observations, employing the Skarstrom cycle in the context of an oxygen separator or concentrator, wherein nitrogen is absorbed by molecular sieve beds to incrementally produce oxygen-enriched air, and using a precursor to the concentrator 10 arrangement of FIG. 2, it was observed that miniaturized (in this case nominal xc2xe inch NPT pipexc3x976 inch long) molecular sieve beds 12 and 14 could only reach a maximum of 30% concentrated or enriched oxygen detected at the gas extraction ports 11. It was thought that this was because the control valve of the laboratory arrangement was switching before all the nitrogen could be vented out of the molecular sieve beds and the exhaust lines. However, measurements from these places showed that the oxygen concentration was higher than normal. Therefore this was not the problem.
It was also observed that there was a lot of air flow coming out of the molecular sieve bed before the molecular sieve bed was completely pressurized. It seemed that the molecular sieve bed was saturated with nitrogen before the bed was finished pressurizing. FIG. 2B diagrammatically represents such a molecular sieve bed 16. Compressed air enters the bed in direction A through inlet passage 16a. A volume of air B is contained within the bed cavity. A proportion of the volume of air C escapes out through an outflow needle valve 18 while the molecular sieve bed pressurizes. It was thought that the volume of air C escaping could be a much larger volume than the volume of air B inside the bed 16. Thus the question became, what happens when the volume of the molecular sieve bed is decreased during miniaturization, but everything else stays the same?
Poiseauille""s Law was used in comparing the old bed volume B to the miniaturized bed volume to calculate the flow of a fluid that passes through a small hole such as needle valve 18 under a pressure difference.             1      )        ⁢          xe2x80x83        ⁢    Q    =                    r        4            ⁡              (                              p            InsideBed                    -                      p            OutsideBed                          )                    8      ⁢      η      ⁢              xe2x80x83            ⁢      L      
Where xe2x80x9cQxe2x80x9d is the fluid flow in meters cubed per second. xe2x80x9crxe2x80x9d is the radius of the small hole. xe2x80x9cplsideBedxe2x88x92pOutsideBedxe2x80x9d is equal to the pressure difference between inside the molecular sieve bed and outside the molecular sieve bed. xe2x80x9cxcex7xe2x80x9d is the fluid viscosity, and xe2x80x9cLxe2x80x9d is the depth of the small hole.
The flow rate, Q, in meters per second multiplied by the time the flow rate occurred is equal to the volume of flow in meters cubed.
2) V=Qt
The variable for Q in equation 1 in this case is constant so
3) V=Kt
where K is some constant value.
Using this information to create a comparison of the Flows and Volumes of the original oxygen concentrator""s bed volume to the new bed volume may be described as.             4      )        ⁢          xe2x80x83        ⁢    R    =                    V        FlowNew                    V        BedVolumeNew                            V        FlowOld                    V        BedVolumeOld            
Since the time to pressurize the molecular sieve bed can be accurately timed using a programmable logic controller (PLC) timer, the following can be stated:                                                         5              )                        ⁢                          xe2x80x83                        ⁢            R                    =                                                                      Kt                  New                                                  V                  BedVolumeNew                                                                              Kt                  Old                                                  V                  BedVolumeOld                                                      ⁢                          xe2x80x83                        ⁢            or                          ⁢                  
                ⁢        6            )        ⁢          xe2x80x83        ⁢    R    =                              Kt          New                ⁢                  V          BedVolumeOld                                      Kt          Old                ⁢                  V          BedVolumeNew                      =                            t          New                ⁢                  V          BedVolumeOld                                      t          Old                ⁢                  V          BedVolumeNew                    
The ratio may then be calculated by inserting values using representative values for a prior art bed and a miniaturized bed (in this case xc2xe inch NPTxc3x976 inch long). Thus, for example:             7      )        ⁢          xe2x80x83        ⁢    R    =                              (          1          )                ⁢                  (          0.001885741          )                                      (          7          )                ⁢                  (          0.0000434375          )                      =    6.2  
From this it was concluded that the molecular sieve material of a nominal xc2xe inch NPT pipexc3x976 inch long molecular sieve bed (the example used in equation 7) has approximately 6.2 times the air passing through it during its pressurization cycle than the molecular sieve material of a prior art oxygen concentrator during its pressurization cycle.
As a consequence of the findings of this analysis it was found to be advantageous to pressurize and vent the molecular sieve beds in a different way than the prior art pressure swing adsorption (PSA) technique. In the method of the present invention the bed is not vented until the bed is substantially fully pressurized, hereinafter referred to as an air packet system or method.
In summary, the gas, such as oxygen, concentrator of the present invention for enriching a target component gas concentration, such as the oxygen concentration, and minimizing a waste component gas concentration, such as the nitrogen concentration, in a gas flow, includes an air compressor, an air-tight first container containing a molecular sieve bed for adsorbing the waste component gas, the first container in fluid communication with the compressor through a first gas conduit, and an air-tight second container in fluid communication with the first container through a second gas conduit. A gas flow controller such as PLC controls actuation of valves mounted to the gas conduits. The valves regulate air flow through the conduits so as to sequentially, in repeating cycles:
(a) prevent gas flow between the first and second containers and to allow compressed gas from the compressor into the first container during a first gas pressurization phase, whereby the first container is pressurized to a threshold pressure level to create a gas packet having an incrementally enriched target component gas concentration such as incrementally enriched oxygen-enriched air;
(b) prevent gas flow into the first container from the compressor and allow gas flow from the first container into the second container during a gas packet transfer phase, wherein the gas packet is transferred to the second container;
(c) prevent gas flow into the second container from the first container and allow gas to vent to atmosphere out from the first container through a vent valve of the first container;
(d) allow gas flow between the first and second containers from the second container into the first container during an air packet counter-flow phase, wherein the gas packet flows from the second container to the first container; and,
(e) prevent gas flow venting from the first container through the vent valve of the first container.
A gas flow splitter is mounted to the second gas conduit for diverting a portion of the gas packet into a gas line for delivery of target component gas, such as oxygen, enriched air for an end use, including use by an end user, downstream along the gas line.
In one embodiment of the present invention, both the first and second containers contain molecular sieve beds for adsorbing the waste component gas, in which case the second container is also in fluid communication with the compressor; for example through a third conduit. Also, in that case, the gas flow controller, following the air packet transfer phase and following preventing gas flow into the second container from the first container, allows compressed gas from the compressor into the second container during a second gas pressurization phase, whereby the second container is pressurized to the threshhold pressure level. The gas flow controller, following preventing the gas flow from venting from the first container through the vent valve of the first container and following preventing gas flow between the first and second containers during the first gas pressurization phase, allows gas to vent to atmosphere out from the second container through a vent valve of the second container and prevents gas flow into the second container from the compressor.
The gas flow controller may be a processor cooperating with the compressor so as to shut off the compressor when gas flow from the compressor into both the first and second containers is prevented. The processor and the compressor may be powered by a battery. The first and second containers, the conduits, the valves, the processor, the compressor and the battery may be mounted in a housing.
The first and second containers may be elongate hollow conduits. The molecular sieve beds may, where the waste component gas is nitrogen, include Zeolite as the molecular sieve material. The first and second containers may be generally parallel and mounted in the housing in parallel array. They may be spaced apart laterally relative to the length of the containers so as to define a channel therebetween. The processor and the compressor may be mounted in the channel. A valve and manifold housing may also be mounted in the channel, the valves mounted to the valve and manifold housing. The valve and manifold housing includes interconnecting manifolds for interconnecting the valves to the first and second containers and the compressor via the gas conduits.
A gas reservoir may be provided, for example formed as part of the valve and manifold housing, in fluid communication with the gas flow splitter. The reservoir is for containing a reserve of, for example, the oxygen-enriched air for delivery to the end use. One of the valves is a demand valve cooperating between the gas line and the reservoir for release of the reserve into the gas line upon a triggering event triggering actuation of the demand valve. In one embodiment, a pressure sensor cooperates with the gas line, and the triggering event is a drop in pressure in the gas line sensed by the pressure sensor. The pressure sensor provides a triggering signal to trigger the actuation of the demand valve upon detecting the drop in pressure, for example to a pre-set lower threshold pressure, below which the pressure sensor provides the triggering signal.
In one embodiment, the compressor is run intermittently upon actuation signals from the processor so as to only run when required, including during the pressurization phase.
In the embodiments in which the end use is for example oxygen supply to an end user such as a patient, the first and second containers may be elongate and curved along their length so as to conform to a body shape of the end user when the gas concentrator is worn by the end user. In any event, when the end use is oxygen supply to an end user, it is intended that the gas concentrator may be adapted to be worn by the end user.
Thus the method of the present invention includes the sequential steps, in repeating cycles, of:
(a) preventing gas flow between the first and second containers and allowing compressed gas from the compressor into the first container during a first gas pressurization phase, whereby the first container is pressurized to a threshold pressure level to create a gas packet having incrementally enriched target component gas concentration;
(b) preventing gas flow into the first container from the compressor and allowing gas flow from the first container into the second container during a gas packet transfer phase, wherein the gas packet is transferred to the second container;
(c) preventing gas flow into the second container from the first container and allowing gas to vent to atmosphere out from the first container through a vent valve of the first container;
(d) allowing gas flow between the first and second containers from the second container into the first container during an air packet counter-flow phase, wherein the gas packet flows from the second container to the first container; and,
(e) preventing gas flow venting from the first container through the vent valve of the first container.
Where the gas concentrator further includes a molecular sieve bed for adsorbing the waste component gas in the second container and wherein the second container is in fluid communication with the compressor through a third conduit, the method of the present invention further includes the steps of:
(a) following the gas packet transfer phase and following preventing gas flow into the second container from the first container, the gas flow controller allowing compressed gas from the compressor into the second container during a second gas pressurization phase, whereby the second container is pressurized to the threshold pressure level; and
(b) following preventing the gas flow from venting from the first container through the vent valve of the first container and following preventing gas flow between the first and second containers during the first gas pressurization phase, the gas flow controller allowing gas to vent to atmosphere out from the second container through a vent valve of the second container and preventing gas flow into the second container from the compressor.