Abstract:
The present invention includes two beds of activated alumina or similar material, which can remove moisture during a PSA cycle. One bed is placed in series in each drive air line for the pressure intensifier or boost pump. The beds are sized such that there is sufficient material to adsorb the moisture contained in the volume of gas required to move the drive piston through a complete stroke.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a pressure swing adsorption dryer for a pneumatically driven pressure intensifier. More specifically, the present invention relates to a pressure intensifier used in a pressure swing adsorption system. The present invention also relates to a kit for retrofitting existing pneumatically driven pressure intensifiers. 
     2. Description of the Related Art 
     The use of concentrators of the pressure swing adsorber type to produce an enriched product gas is well known. Pressurized air is cyclically delivered to a plurality of beds of molecular sieve material and certain components of the air become adsorbed by the sieve while the chosen component passes through. The beds are sequentially vented to atmosphere and purged with product gas to discharge the adsorbed components from the molecular sieve, and in this manner, a continuous flow of enriched product gas can be generated. 
     In certain situations, the required pressure of the product gas is higher than the output pressure from the adsorber and a pressure booster may be used to increase the pressure of the product gas in order to meet system requirements. Booster compressors themselves are old in the art and may take several forms. Some are electrically driven but in certain situations a pneumatically driven booster provides advantages. The pneumatic booster may be driven in sync with the beds of the pressure swing adsorber and such a system is shown in U.S. Pat. No. 5,071,453 assigned to the assignee of the instant invention. 
     The pneumatically driven pressure intensifier utilizes low pressure drive air acting on a large piston to shuttle smaller pistons which in turn compress product gas to an elevated pressure. In addition, in some cases, the compressor size can be minimized by using air conservation techniques as described in U.S. Pat. No. 5,354,361, the disclosure of which is hereby incorporated by reference into the present specification in its entirety. The drive gas is separated from the product gas through a series of shaft and piston seals, which allow the pistons and drive shaft to move while providing pneumatic integrity. The drive air used to shuttle the pistons contains water vapor which can condense in the drive cylinder. The presence of water in the drive cylinder can have serious detrimental effects on the performance of the pressure intensifier. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a drying apparatus for use with a pressure intensifier for drying drive gas before the drive gas enters the pressure intensifier. 
     It is another object of the present invention to provide two activated beds and one or more valves between a pressurized air source and a pressure intensifier for drying drive gas before it enters the pressure intensifier. 
     Another object of the present invention is to provide a retrofit kit for retrofitting existing pressure swing adsorption systems with a drying apparatus for drying drive gas before the drive gas enters the pressure intensifier. 
     It is still another object of the present invention to provide a pressure swing adsorber and a pneumatically driven booster in which the timing of the valves which control the operation of the concentrator and the booster, and the plumbing between the concentrator and the booster are selected to control the timing of the transfer of gases which are admitted to the sieve beds. 
     These and other objects of the present invention are achieved by a drying apparatus for a pressure swing adsorption system including a pair of beds having molecular sieve material with each bed having an inlet and an outlet. A pressure intensifier increases the pressure of enriched product gas. The pressure intensifier includes a pneumatic drive cylinder which has opposed sides which are alternatively pressurized in order to drive the pressure intensifier. The pair of beds and the pneumatic drive cylinder are coupled to a source of compressed feed air. The drying apparatus includes a pair of moisture removing beds each connected to the source of compressed feed air. At least one valve is located between the source of compressed feed air and the pair of moisture removing beds. The pressure intensifier is alternatively pressurized with feed air via the pair of moisture removing beds. 
     The foregoing and other objects of the present invention are achieved by a method of drying gas used in a pneumatically driven pressure intensifier. The pressure intensifier is used in a pressure swing adsorption system. The pressure swing adsorption system includes a pair of molecular sieve beds each connected to a first and a second valve, respectively. The first and the second valves are each connected to a source of pressurized gas and an ambient vent line. The method comprises flowing pressurized gas to opposite sides of the pressure intensifier drive cylinder to position the pressure intensifier drive piston. Pressurized gas flows through a first activated bed to dry the gas and to pressurize one side of the pressure intensifier drive cylinder to shift the pressure intensifier to a first position. Gas is vented from the other side of the pressure intensifier drive cylinder through a second activated bed which desorbs moisture from the second bed. During the second stage of the pressure intensifier cycle, the side of the drive cylinder which was originally pressurized is vented to ambient through the first activated bed which desorbs moisture from the bed. Simultaneously, the other side of the drive cylinder is pressurized through the second activated bed. The second activated bed dries the gas entering the drive cylinder and shuttles the pressure intensifier piston to the other side. 
     The foregoing and other objects of the present invention are achieved by a drying kit for retrofitting a pressure intensifier used in a pressure swing adsorption system. The pressure intensifier has a first side and a second side. The pressure swing adsorption system has a pair of molecular sieve beds and a first valve connected to a source of pressurized gas and to one of the pair of molecular sieve beds and a second valve connected to the source of pressurized gas and to the other of the pair of molecular sieve beds. The drying kit includes a first activated bed connectable to the source of pressurized gas and to the first side of the pressure intensifier and a second activated bed connectable to the source of pressurized gas and to the second side of the pressure intensifier. At least one valve is provided to selectively connect said first activated bed to the source of pressurized gas and to selectively connect the second activated bed to the source of pressurized gas. 
     The foregoing and other objects of the present invention are achieved by a pressure swing adsorption system having a pressure intensifier including a drying apparatus. The pressure swing adsorption system includes a pair of beds having molecular sieve material each having an inlet and an outlet. A pneumatic drive cylinder has opposed sides which are alternatively pressurized in order to drive the pressure intensifier. The pair of beds are coupled to a source of compressed feed air. The pair of moisture removing beds are each connected to the source of compressed feed air. The pressure intensifier is alternatively pressurized with feed air via the pair of moisture removing beds. At least one valve is located between the source of compressed feed air and the pair of moisture removing beds. 
     The present invention provides a method and apparatus for drying drive gas before it enters the drive cylinder. The present invention includes two beds of activated alumina or similar material, which can remove moisture during a PSA cycle. One bed is placed in series in each drive gas line for the pressure intensifier or boost pump. The beds are sized such that there is sufficient material to adsorb the moisture contained in the volume of gas required to move the drive piston through a complete stroke. During operation as one side of the cylinder is pressurized the gas entering the cylinder is dried by the activated alumina bed. The gas from the other side of the piston is vented back to ambient through the other bed which regenerates the activated alumina in that bed due to the desorption caused by the drop in pressure. The present invention is usable as a drying apparatus for a pressure intensifier in a pneumatic circuit for a conventional PSA system. The present invention is also usable as a drying apparatus for a pressure intensifier in a pneumatic circuit for a system utilizing the gas conservation scheme described in U.S. Pat. No. 5,354,361. Advantageously, activated beds can be incorporated into the drive cylinder body or the drive caps to eliminate extra components and minimize weight and size. The present invention can also be provided as a kit to retrofit a drying apparatus to an existing pressure swing adsorption system having a pressure intensifier. 
     It is still another object of the present invention to provide a pressure swing adsorber and a pneumatically driven booster in which the timing of the valves which control the operation of the concentrator and the booster, and the plumbing between the concentrator and the booster are selected to control the timing of the transfer of gases which are admitted to the sieve beds. 
     Still other objects and advantages of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein the preferred embodiments of the invention are shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description thereof are to be regarded as illustrative in nature and not as restrictive. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention is illustrated by way of example, and not by limitation, in the figures of the accompanying drawings, wherein elements having the same reference numeral designations represent like elements throughout and wherein: 
     FIG. 1 is a schematic view of a combination pressure swing adsorber using air conservation techniques and booster compressor using the drying apparatus according to an embodiment of the present invention with the valves shown in a de-energized position; 
     FIG. 2 is a graph showing the timing of the valves used to control the pressure swing adsorber and the booster compressor; 
     FIG. 3 is a schematic view of a combination pressure swing adsorber and booster compressor using the drying apparatus in accordance with an embodiment of the present invention; 
     FIGS. 4A-4C are illustrations of dryer beds incorporated into the drive cylinder; and 
     FIG. 5 is a pressure intensifier drive cylinder head with integral dryer on each cap. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 depicts a combination of a pressure swing adsorber or concentrator and a pressure intensifier or boost pump generally designated by the reference numeral  10 . It should be understood that terms such as “left” and “right” are used for purposes of explanation only. Example concentrators usable with the present invention are described in U.S. Pat. No. 5,858,062, entitled “Oxygen Concentrator”, issued Jan. 12, 1999 and U.S. Pat. No. 5,549,736, entitled “Modular Stackable Pressure Swing Adsorption Concentrator”, issued Aug. 27, 1996, both of which are hereby incorporated by reference in their entirety into the present specification. The concentrator comprises a pair of three-way solenoid valves  12  and  13  which are coupled by inlet lines  14  and  15  respectively to a common node  17 . The node  17  is coupled to a feed air inlet  18  which receives air from a compressor. The outlets of the valves  12  and  13  are coupled to inlet lines  20  and  21 , respectively, for the sieve beds  22  and  23 . Each sieve bed  22  and  23  can have an inlet restriction  24  and  25  located immediately adjacent the inlet to the bed although not necessary. The outlets  26  and  27  of the sieve beds  22  and  23  are coupled to nodes  34  and  35  which are coupled to check valves  28  and  29  and to one another through a restrictor  36 . The outlets of the check valves  28  and  29  are coupled to a node  31  which is coupled on the side of the pressure intensifier. 
     The pressure booster  40  comprises a first stage compression cylinder  42 , a second stage compression cylinder  43  and a driving cylinder  44 . A driving piston  46  is positioned in the driving cylinder  44  and reciprocates to either end thereof. The driving piston  46  is connected to a drive shaft  47  having a first stage piston  48  at one end and a second stage piston  49  at the other end. Product gas from the concentrator outlet line  38  is coupled to the inlet  51  of the first stage cylinder  42  through a check valve  52 , control valve  37 , line  33  and plenum  32 . The outlet  53  of the first stage cylinder is coupled through a check valve  54  to an intercooler  56 . The intercooler is coupled through a second check valve  58  to the inlet  59  of the second stage compression cylinder  43 . The outlet  61  of the second stage cylinder  43  is coupled through a check valve  62  to an outlet conduit  63  which is coupled to the point of use (not shown) of the compressed product gas. 
     Gas which is used to drive the driving piston  46  is supplied to either side of the driving cylinder  44  by the two inlet lines  64  and  65 . The inlet lines  64  and  65  are coupled to the outlets of the three-way solenoid valves  12  and  13  at nodes  66  and  67 , respectively, and thus receive air from the feed air inlet  18  in a timed sequence which is controlled by the valves  12  and  13 . 
     The drying apparatus according to the present invention is advantageously placed in inlet lines  64  and  65  as depicted in FIG.  1 . Advantageously, the present invention can either be retrofitted to an existing pressure swing adsorption system or can be used in a new pressure swing adsorption system. As depicted schematically in FIG. 1, a first dryer bed  80  is inserted in the inlet line  64  upstream from a two-way valve  82 . Similarly, a second dryer bed  90  is inserted in the inlet line  65  upstream from a two-way valve  92 . The two-way valves  82  and  92  are open when the pressure intensifier is operating and closed when it is not operating. The dryer beds  80 ,  90  include a drying material such as an activated alumina or other similar material for removing moisture from the source of feed air. 
     FIG. 2 shows the timing sequence for solenoid valve  12 , valve  13 , valve  82  and valve  92  for a PSA system utilizing the energy conservation techniques described in U.S. Pat. No. 5,354,361. As shown, valve  82  and valve  92  are open while the pressure intensifier  44  is operating. At time T 0 , valve  12  is open to the compressed air line  18  and valve  13  is venting to ambient through the vent line  19 . At time T 1 , valve  13  switches to the compressed air line  18  which allows bed  23  which is at very low pressure to be pressurized by the compressor and the gas contained in bed  22 , dryer  80  and the right hand side of the drive cylinder  44 . At time T 2 , valve  12  switches to the vent line  19  which completes venting of bed  22 , dryer  80  and the right hand side of the drive air cylinder  44 . Valve  13  remains switched to the compressed air line  18 . At time T 3  valve  12  switches the compressed air line  18  which allows bed  22  which is at a very low pressure to be pressurized by the compressor and the gas from bed  23 , dryer  90  and the left hand side of the drive cylinder  44 . At time T 4 , valve  13  switches to the vent line  19  which completes venting of bed  23  dryer bed  90  and the left hand side of the drive cylinder  44 . At time T 5 , valve  13  switches back to the. compressed air line and at time T 6 , valve  12  switches to again be open to the compressed air line  18 . 
     At the beginning of a typical pneumatic cycle with the pressure intensifier operating, valve  12  is open to the compressed air inlet  18 , bed  22 , dryer bed  80  and the right side of the intensifier  44  are pressurized. Valve  13  is open to the vent line  19  and bed  23 , dryer bed  90  and the left side the drive cylinder  44  are vented to atmosphere through the vent line  19 . In the next step of the cycle valve  13  switches to the compressed air line. This allows the high pressure gas from bed  22 , dryer bed  80  and the right side of the pressure intensifier  44  to flow into bed  23  which is at a low pressure through valve  12  in addition to the compressed feed air which flows through valve  13 . At the end of this period, valve  12  switches to the vent line  19  allowing bed  22 , dryer bed  80  and the right side of the pressure intensifier to vent to atmosphere. At this time valve  13  remains open to the feed air line allowing bed  23 , dryer bed  90  and the left side of the pressure intensifier  44  to continue to pressurize. In the last step of the pneumatic cycle valves  12  and  13  are both switched to the compressed air feed line  18 . This allows the high pressure gas from bed  23 , dryer bed  90  and the left side of the pressure intensifier to flow into bed  22  which is at a low pressure through valve  13  in addition to the feed air which flows through valve  12 . This cycle is repeated allowing both the molecular sieve beds and the dryer beds to adsorb and desorb the unwanted components from the gas stream in a regenerative process. 
     FIG. 3 is similar to FIG. 1 except that line  164  is connected directly to the feed air line at node  117  which is upstream from the valve  12 . A four-way valve  302  is positioned in line  164  and is connected to the first dryer bed  170 . A line  166  connects the four-way valve  302  to the first dryer bed  170 . A line  168  connects the four-way valve  302  to the second dryer bed  172 . In turn, the first dryer bed  170  is connected to the right side of the drive cylinder  44  by a line  176  and the second dryer bed  172  is connected to the left side of the drive cylinder  44  by a line  178 . The operation of the second embodiment in FIG. 3 is similar to the FIG. 1 embodiment except that the four-way valve  302  does the switching rather than the two-way valves. In this system operation of the pressure intensifier  44  is independent of the timing cycle of the beds  22 ,  23 . The gas in the drive cylinder  44  and dryer beds  170 ,  172  does not vent back through the molecular sieve beds  22 ,  23 . 
     As depicted schematically in FIGS. 1 and 3, the dryer beds  170 ,  172  are separate from the drive cylinder  44 . However, in either embodiment depicted in FIGS. 1 and 3, the dryer beds can be incorporated into the drive cylinder  44  and more specifically into the drive cylinder housing  144  as depicted in FIGS. 4A-4C and  5  and discussed in detail below. 
     As depicted in FIG. 1, the drive cylinder  44  has a central housing  144  and two end plates  146 ,  148 . The central housing  144  is cylindrical and is mounted at opposite ends to the drive caps  146 ,  148 . 
     Turning now to FIGS. 4A-4C, the dryer beds  80 ,  90  from FIG. 1 or  3  embodiments  170 ,  172  can be incorporated into the central housing  144  of the drive cylinder  44 . For example, as depicted in FIGS. 4A-4C, dryer beds  80 ,  90  or  170 ,  172  can be co-extensive with the overall length of the central housing  144  by forming hollow sections  402 ,  404  on the outer periphery of the drive cylinder  144 . These hollow sections can then be filled with the activated alumina material  426 . Tube fittings  406 ,  408 ,  410 ,  412  are located at opposite ends of the hollow cylinders  402 ,  404  and serve to keep the activated alumina in the hollow cylinders  402 ,  404 . Each bed includes a filter  420 , a perforated plate  422  and a spring  424 , such as a wave spring, at opposite ends of the hollow sections. The filter  420 , perforated plate  422  and the spring  424  serve to retain the activated alumina  426 . Advantageously, by having the dryer beds incorporated into the drive cylinder, space is utilized effectively. This advantageously eliminates extra components and minimizes weight, size and costs. 
     Refer now to FIG. 5 where one of the dryer beds  80 ,  90 ;  170 ,  172  is incorporated into an end cap  146 . The end cap  146  can be modified to include a hollow portion  502  which is located radially outwardly from the center line of the end cap  146 . The hollow portion  502  is in communication with the inner volume of the drive cylinder  44  so that the air flowing through the bed is dried before reaching the inner volume of the drive cylinder  44 . The bed assembly includes a screen  510  made of a mesh screen material and a filter  512  for preventing particulates from entering the inner volume. At an opposite end of the hollow cylinder is another screen  514  and a filter  516 . A wave spring  518  is located at the distal end of the hollow cylinder for compressing the activated alumina  520  which is centrally located between the screens  512 ,  514 . A tube fitting is also located at the distal end for connection to an air line which is then connected to either a two-way valve  82 ,  92  or to the four-way valve  302 . 
     It should now be apparent that a drying apparatus has been described which is useful for eliminating moisture from drive air for driving a pressure intensifier. 
     It will be readily seen by one of ordinary skill in the art that the present invention fulfills all of the objects set forth above. After reading the foregoing specification, one of ordinary skill will be able to affect various changes, substitutions of equivalents and various other aspects of the invention as broadly disclosed herein. It is therefore intended that the protection granted hereon be limited only by the definition contained in the appended claims and equivalents thereof.