Abstract:
A fractionator produces an oxygen enhanced gas for use in oxygen inhalation therapy. The fractionator includes an air source for supplying air, and a plurality of columns for containing an adsorbent material for adsorbing nitrogen gas. Each of the columns has first and second open ends. Air is directed from the air source to the column through the first open ends of the respective columns. A temperature sensor detects the temperature of the side wall of one of the columns. The fractionator changes the time for adsorption of nitrogen gas to the adsorbent material based on the detected temperature.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an improved apparatus for producing oxygen enhanced gas from air. 
     2. Description of the Related Art 
     Oxygen inhalation therapy has been employed as a most effective method of treatment for a malady of the respiratory system such as asthma, pulmonary emphysema or chronic bronchitis. In oxygen inhalation therapy, an oxygen enhanced gas, which is produced by separating nitrogen gas from air, is supplied to the patient. For this purpose, a fractionator or an apparatus for producing an oxygen enhanced gas from air has been developed. In particular, a compact fractionator is suitable for conducting oxygen inhalation therapy domestically. 
     WO 93/16876 discloses a fractionator for producing an oxygen enhanced gas by separating nitrogen gas from air. The fractionator has a plurality of columns filled with an adsorbent material and rotary valve for distributing air selectively to the columns. 
     The fractionator produces the oxygen enhanced gas with high efficiency when the temperature of the adsorbent material is within a temperature range. However, if the temperature of the adsorbent material is out of the range due to, for example change in the air temperature, the production of the oxygen enhanced gas is much reduced. 
     SUMMARY OF THE INVENTION 
     The invention is directed to solve the prior art problems, and to provide an apparatus for producing oxygen enhanced gas from air which is improved to maintain the production efficiency at a level in spite of changes in air temperature. 
     The invention provides an apparatus for producing an oxygen enhanced gas for use in oxygen inhalation therapy. The apparatus includes an air source for supplying air; a plurality of columns for containing an adsorbent material for adsorbing nitrogen gas, each of the columns having first and second open ends; means for directing the air from the air source to the column through the first open ends of the respective columns; an oxygen enhanced gas tank, fluidly connected to the second open ends of the respective columns, for receiving oxygen enhanced gas from the columns; a switching mechanism, provided adjacent to the first open ends of the columns, for sequentially selectively switching columns to which the air is supplied from the air source and columns from which the adsorbed nitrogen is released for regeneration of the adsorbent material so that the respective columns repeatedly adsorb nitrogen gas and release the adsorbed nitrogen gas according to an adsorption-regeneration cycle; a temperature sensor for detecting a temperature representing the temperature of the adsorbent material; and a controller for controlling the adsorption-regeneration cycle based on the representative temperature detected by the sensor. 
     The temperature sensor may be preferably attached to a side wall of one of the columns. 
     According to a preferred embodiment, the adsorbent material may include 13X type zeolite. In this case, the controller controls the adsorption-regeneration cycle to reduce the time for adsorption of the nitrogen gas when the representative temperature is not less than 20° C. 
     According to another embodiment, the adsorbent material may include 5A type zeolite. In this case, the controller controls the adsorption-regeneration cycle to reduce the time for adsorption of the nitrogen gas when the representative temperature is not more than 20° C. 
     According to another feature of the invention, the apparatus may include an air source for supplying air; a plurality of columns for containing an adsorbent material for adsorbing nitrogen gas, each of the columns having first and second open ends; means for directing the air from the air source to the inside of the column through the first open ends of the respective columns; an oxygen enhanced gas tank, fluidly connected to the second open ends of the respective columns, for receiving oxygen enhanced gas from the columns; a temperature sensor for detecting a temperature representing the temperature of the adsorbent material; and a temperature controller for controlling the temperature of the adsorbent material based on the representative temperature detected by the temperature sensor. 
     The preferred adsorbent material for this apparatus may include 5A type zeolite, and the temperature controller heats the columns to maintain the representative temperature within a temperature range 20 to 60° C. 
     The apparatus also may include a switching mechanism, provided adjacent to the first open ends of the columns, for sequentially selectively switching columns to which the air is supplied from the air source and columns from which the adsorbed nitrogen is released for regeneration of the adsorbent material so that the respective columns repeatedly adsorb nitrogen gas and release the adsorbed nitrogen gas according to an adsorption-regeneration cycle. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     These and other objects and advantages and further description will now be discussed in connection with the drawings in which: 
     FIG. 1 is an schematic illustration of a fractionator according to the first embodiment of the invention; 
     FIG. 2 is plan view of a stationary disk of a distributing mechanism; 
     FIG. 3 is plan view of a rotary disk of a distributing mechanism; 
     FIG. 4 is a graph showing the adsorption characteristics of zeolite relative to changes in the temperature thereof; 
     FIG. 5 is a graph showing experimental results of the fractionator shown in FIG. 1; 
     FIG. 6 is a graph showing other experimental results of the fractionator shown in FIG. 1; 
     FIG. 7 is an schematic illustration of a fractionator according to the second embodiment of the invention; and 
     FIG. 8 is a graph showing experimental results of the fractionator shown in FIG.  7 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to FIGS. 1-6, a first embodiment of the invention will be described below. 
     In FIG. 1, a fractionator  10  according to the embodiment of the invention includes a plurality of columns  12  for containing adsorbent material which adsorbs nitrogen gas much more than oxygen gas, top and bottom tanks  14  and  16  fluidly connected to the columns  12 , a rotary distributor (not shown in FIG. 1) provided within the bottom tank  16  and a rotary mechanism  26  such as an AC motor  26  for driving the rotary distributor. The columns  12  have top and bottom open ends for the fluid communication with the top and bottom tanks  14  and  16 . A controller  32  is provided for controlling the rotational speed of the AC motor  26  based on temperature detected by a temperature sensor  28  and output to the controller  32  via signal line  30 . The temperature sensor  28  is put on the side wall of one of the columns  12 . The controller  32  may include an inverter which changes the frequency of the alternating current supplied to the AC motor  26  based on the temperature detected by the temperature sensor  28 . The temperature detected by the sensor  28  is assumed to represent the temperature of the adsorbent material within the columns  12 . In this connection, the temperature detected by the sensor  28  is referred to the representative temperature. 
     The top tank  14  is fluidly connected to a nasal mask put on a patient through first and second conduits  38  and  42  between which a humidifier  40  is provided. The first conduit  38  includes a flow adjustment valve  34  and a flow setter  36 . The bottom tank  16  includes an air inlet port  18  and an exhaust port  20  through which nitrogen gas is discharged. The air inlet port  18  is fluidly connected to an air source or a blower  22  through an air conduit  24 . The blower  22  supplies air at a predetermined pressure, for example 1.0 atm-g. 
     With reference to FIGS. 2 and 3, the rotary distributing mechanism includes a stationary disk  44  which is connected to the bottom ends of the columns  12  and a rotary disk  46  disposed in contact with lower surface of the stationary disk  44 . The stationary disk  44  defines a plurality of orifices  44   1  to  44   12  which are arranged along a circle about the center of the stationary disk  44 . Each of the plurality of orifices  44   1  to  44   12  is fluidly connected to inside of the corresponding column  12  through the bottom open end thereof. 
     The rotary disk  46  is operatively connected to the shaft of the AC motor  26  to be rotated about its center relative to the stationary disk  44 . The rotary disk  46  includes three sets of channels and a central air inlet opening  48  which is fluidly connected to the air inlet port  18 . The three sets of channels consist of inlet channels  46   a  and  46   b , intermediate channels  46   c  and  46   d  and exhaust channels  46   e  and  46   f . Each of the inlet channels  46   a  and  46   b  is substantially formed into “T” shape having radial and peripheral portions and extends radially symmetrically to each other about the central air inlet opening  48 . The intermediate channels  46   c  and  46   d  are provided symmetrically about the inlet channels  46   a  and  46   b . The exhaust channels  46   e  and  46   f  are also provided symmetrically about the inlet channels  46   a  and  46   b.    
     The orifices  44   1  and  44   2 ,  44   7  and  44   8  are fluidly connected to the air inlet port  18 , the orifices  44   9  and  44   12 ,  44   3  and  44   6  are fluidly connected to each other through the intermediate channels  46   c  and  46   d , and the orifices  44   10  and  44   11 ,  44   4  and  44   5  are fluidly connected to outside of the bottom tank  16  or the atmosphere through the exhaust channels  46   e  and  46   f , when the rotary disk  46  is positioned relative to the stationary disk  44  so that inlet channels  46   a  and  46   b  are aligned with the orifices  44   1  and  44   2 ,  44   7  and  44   8 ; the intermediate channels  46   c  and  46   d  are aligned with the orifices  44   9  and  44   12 ,  44   3  and  44   6 ; and the exhaust channels  46   e  and  46   f  are aligned with the orifices  44   10  and  44   11 ,  44   4  and  44   5 . In this disposition, air is supplied through the inlet channels  46   a  and  46   b  and the orifices  44   1  and  44   2 ,  44   7  and  44   8  to the columns  12  disposed corresponding to the orifices  44   1  and  44   2 ,  44   7  and  44   8 , where the internal pressure of the columns increases and the large amount of nitrogen gas is separated by the adsorption to the adsorbent material and oxygen enhanced gas is produced and discharged into the top tank  14  through the top open ends of the columns. On the other hand, the internal pressure within the columns  12  disposed corresponding to the orifices  44   10  and  44   11 ,  44   4  and  44   5  decreases to the atmospheric pressure through the exhaust channels  46   e  and  46   h , and the adsorbed nitrogen gas is separated from the adsorbent due to the pressure drop. On the other hand, the internal pressure within the columns  12  disposed corresponding to the orifices  44   9  and  44   12 ,  44   3  and  44   6  are equalized to each other through the intermediate channels  46   c  and  46   d . Check valve mechanisms, for preventing the counter flow of the produced oxygen enhanced gas, may be provided on the top open ends of the respective columns  12 . 
     Rotation of the rotary disk  46  moves the channels  46   a - 46   f  relative to the orifices  44   1  to  44   12  of the stationary disk  44 . If the rotary disk  46  rotates in the counter-clockwise direction by 30 degrees, which corresponds to the rotational angle between the adjacent orifices, the inlet channels  46   a  and  46   b  are aligned with the orifices  44   12  and  44   1 ,  44   6  and  44   7 , the intermediate channels  46   c  and  46   d  are aligned with the orifices  44   8  and  44   11 ,  44   2  and  44   5 , and the exhaust channels  46   e  and  46   f  are aligned with the orifices  44   9  and  44   10 ,  44   3  and  44   4 . Therefore, the orifices  44   12  and  44   1 ,  44   6  and  44   7  are fluidly connected to the air inlet port  18 , the orifices  44   8  and  44   11 ,  44   2  and  44   5  are fluidly connected to each other through the intermediate channels  46   c  and  46   d , and the orifices  44   9  and  44   10 ,  44   3  and  44   4  are fluidly connected to outside of the bottom tank  16  through the exhaust channels  46   e  and  46   f . In this disposition, air is supplied through the inlet channels  46   a  and  46   b  and the orifices  4   12  and  44   1 ,  44   6  and  44   7  to the columns  12  disposed corresponding thereto. The internal pressure within the columns  12  disposed corresponding to the orifices  44   9  and  44   10 ,  44   3  and  44   4  decreases to the atmospheric pressure through the exhaust channels  46   e  and  46   f , and the adsorbed nitrogen gas is separated from the adsorbent by the pressure drop. The internal pressure within the columns  12  disposed corresponding to the orifices  44   8  and  44   11 ,  44   2  and  44   5  are equalized to each other through the intermediate channels  46   c  and  46   d.    
     Thus, the rotation of the rotary disk  46  causes the adsorption-regeneration cycle of the respective columns  12  of the fractionator  10 . The nitrogen gas is separated from the air which is supplied to the columns  12 , disposed onto the inlet channels  46   a  and  46   b , by the adsorption to the adsorbent. The oxygen enhanced gas is produced and discharged from the columns  12  to the top tank  14 . The adsorbed nitrogen will be released from the adsorbent and discharged to the outside of the fractionator  10  when the corresponding columns  12  are relatively disposed onto the exhaust channels  46   e  and  46   f.    
     The adsorbent material adsorbs nitrogen gas much more than oxygen gas, and can include zeolite, in particular 13X type zeolite, which is available on the market as OXYSIV-5 or OXYSIV-7 from Union Carbide Corporation, located in Danbury, Conn. The zeolite adsorbent may be 5A type zeolite, which is also available on the market as 5AMG from Union Carbide Corporation. 
     FIG. 4 shows experimental results obtained, in terms of 13X type zeolite and 5A type zeolite, by using an experimental apparatus which includes a single column substantially identical to the above-described embodiment. In FIG. 4, the vertical axis is the volume fraction of the oxygen gas relative to the generated oxygen enhanced gas, and the horizontal axis is the temperature detected by the sensor attached to the side wall of the column. 
     As can be seen from FIG. 4, in case of 13X type zeolite, when the representative temperature is lower than 20° C., the oxygen concentration does not substantially change with a change in temperature. However, in the temperature range above 20° C., the oxygen concentration decreases with the increase in the temperature. This means that the nitrogen adsorption efficiency of 13X type zeolite is decreased in the temperature range above 20° C. On the other hand, in case of 5A type zeolite, when the representative temperature is lower than 20° C., the oxygen concentration increases with the increase in the temperature. However, in the temperature range above 20° C., the change in the oxygen concentration becomes flat. This means that the nitrogen adsorption efficiency of 5A type zeolite is decreased at the temperature range below 20° C. 
     Therefore, in case of 13X type zeolite, with the fractionator  10  according to the embodiment shown in FIG. 1, the time for the nitrogen adsorption must be reduced in the temperature range above 20° C. in order to maintain the over-all nitrogen adsorption efficiency high. For this purpose, the rotational speed of the AC motor  26  is increased. On the other hand, in case of 5A type zeolite, the time for the nitrogen adsorption must be reduced in the temperature range below 20° C. For this purpose, the rotational speed of the AC motor  26  is increased. In this connection, in the specification, cycle time T c  is defined as follows: 
     
       
         T c =T/N 
       
     
     where 
     T: time for one rotation of the rotary disk 
     N: number of the orifices formed in the stationary disk 
     The increase or reduction of the time for the nitrogen adsorption is equivalent to the increase or reduction of the cycle time and also to the reduction or increase of the rotational speed of the rotary disk  46 . 
     FIGS. 5 and 6 show the other experimental results which were executed by using a fractionator shown in FIG.  1 . FIG. 5 shows the change in oxygen concentration of the oxygen enhanced gas relative to the representative temperature detected by the temperature sensor  28 , with 13X type zeolite filled in the columns  12 . As can be seen from FIG. 5, the operation with the cycle time of 2.0 sec provides better results than the operation with cycle time of 2.5 sec in the temperature range above 20° C. FIG. 6 is a graph similar to that of FIG. 5, with 5A type zeolite filled in the columns  12 . As can be seen from FIG. 6, the operation with the cycle time of 2.5 sec acquires better results than the operation with cycle time of 2.0 sec in the temperature range above 20° C. 
     With reference to FIG. 7, a second embodiment of the invention will be described below. 
     In FIG. 7, a fractionator  50  according to the embodiment of the invention includes a plurality of columns  52  for containing the adsorbent material the same as the first embodiment, top and bottom tanks  54  and  56  fluidly connected to the columns  52 , a rotary distributor the same as the first embodiment shown in FIGS. 2 and 3 and a rotary mechanism or an AC motor  66  for rotating the rotary distributor. 
     The top tank  54  is connected to a nasal mask put on a patient through first and second conduits  86  and  90  between which a humidifier  88  is provided. The first conduit  86  includes a flow adjustment valve  82  and a flow setter  84 . The bottom tank  56  includes an air inlet port  58  and an exhaust port  60  through which nitrogen gas is discharged. The air inlet port  58  is fluidly connected to an air source or a blower  62  through an air conduit  64 . 
     According to the second embodiment, the fractionator  50  further comprises a heating device for controlling the temperature of the columns  52 . The heating device includes a fan  78  for generating an air flow, an air duct  80  for directing the air flow to the blower  62  for cooling the blower  62  and a flow controller or a damper  76  provided on the air duct  80  for controlling the air flow rate through the air duct  80 . A controller  72  is provided for controlling the opening of the damper  76  via signal line  74 , based on the representative temperature detected by a temperature sensor  68  and output to the controller via signal line  70 . The temperature sensor  68  is put on the side wall of one of the columns  52 . 
     The air flow directed to the blower  62  is heated by heat exchange with the blower  62 . The duct  80  also directs the air flow from the blower  62  to the columns  52  to heat the columns  52 . 
     FIG. 8 shows experimental results executed by using an experimental apparatus substantially the same as the second embodiment with 5A type zeolite, except that the heating device of the experimental apparatus is an electric heater which can heat the columns  52  up to a desired temperature. In FIG. 8, the vertical axis is the oxygen gas concentration in the produced oxygen enhanced gas, and the horizontal axis is the representative temperature. The oxygen concentration was measured with the side wall temperature set to a predetermined value. As can be seen from FIG. 8, the oxygen gas concentration in the produced oxygen enhanced gas is not less than 90% when the representative temperature detected by the sensor  68  is 20-60° C., and it takes maximum value of 96% when the representative temperature is around 40° C. 
     Therefore, it is preferable that the controller  72  controls the opening of the damper  76  to maintain the representative temperature detected by the sensor  68  in the range 20-60° C. 
     Although the heating device utilizes the air flow used for cooling the blower  62  in FIG. 7, the heating device can include an electric heater for maintaining the representative temperature of the side walls of the columns  52 . In this case, the controller  72  controls the current supplied to the electric heater. 
     It will also be understood by those skilled in the art that the forgoing description is a preferred embodiment of the disclosed device and that various changes and modifications may be made without departing from the spirit and scope of the invention.