Abstract:
A system for delivering dry compressed gas is provided, the gas being separated from any entrained liquid lubricant and then passed through a moisture absorber column to interact with a moisture-removing fluid. The fluid is a liquid lubricant or is maintained in a separate closed circuit relative to the liquid lubricant. A moisture stripping device receives some of the gas from the absorber column, which is passed in moisture exchange relation with the fluid before the fluid enters the column. The column has a housing defining a vertical absorption zone, and partition plates each defining gas flow holes. The plates have at least one tube passing therethrough, with an open upper end above one plate, and a lower end adjacent the next lower plate. The fluid passes down the tubes and across a top surface of each plate, with the gas flow passing upwardly through the holes in the plates.

Description:
BACKGROUND OF THE INVENTION 
     1) Field of the Invention 
     The present invention relates to improvements in compressor systems adapted to provide clean dry compressed gas, particularly compressed air, at a discharge point therefrom, and an absorber configuration for use in such systems. 
     2) Description of Related Art 
     There is increasingly a need to provide moisture free pressurized gas, particularly compressed air, in many industries and applications. Such moisture free compressed gas or air is normally achieved by using separate add on gas drying equipment such as refrigeration driers. Such additional drying equipment is typically expensive to produce, and complicated and costly to operate. The objectives therefore of the present invention are to provide a simplified inexpensive system for producing clear pressurized gas including compressed air and an improved moisture absorber for use in such systems. 
     BRIEF SUMMARY OF THE INVENTION 
     Accordingly, the present invention provides in one aspect, a gas compressor system including a driven gas compressor means adapted to receive gas to be compressed and discharge compressed gas therefrom, said discharged compressed gas being delivered to a moisture absorber configured to receive and circulate therethrough a fluid capable of removing moisture from the compressed gas prior to the compressed gas being discharged as a dry compressed gas through filter means to remove any remaining said fluid therefrom, said fluid being circulated through a circuit including a moisture stripping means adapted to receive a portion of the dry compressed gas discharged from the moisture absorber and passing said portion of the dry compressed gas in moisture exchange relationship with said fluid prior to reintroducing said fluid into said moisture absorber, said fluid being heated after leaving said moisture absorber and before entering said moisture stripping means. With such an arrangement the fluid within the circuit need not be particularly hygroscopic in nature but improved performance may be expected if the fluid is in fact hygroscopic in nature, i.e. capable of absorbing or attracting moisture. It has been surprisingly found that by heating the fluid before it enters the moisture stripping means improves overall performance by minimizing the amount of dry compressed gas that needs to be diverted from the dry compressed gas discharge line from the system. Overall efficiency of the system is preferably improved by utilizing waste heat generated by the gas compression means. Alternatively, the fluid may be heated by an independent heater provided to heat the fluid before entering the moisture stripper. Preferably the discharged compressed gas from said gas compressor means is passed initially through a first cooler means to condense at least a portion of the moisture carried by the compressed gas which is collected and removed from the compressed gas flow prior to entering said absorber. 
     According to a second aspect of this invention, there is provided a gas compressor system including a driven gas compressor means adapted to receive gas to be compressed and discharge compressed gas therefrom, said discharged compressed gas being delivered to a moisture absorber configured to receive and circulate therethrough a fluid capable of removing moisture from the compressed gas prior to the compressed gas being discharged as a dry compressed gas through filter means to remove any remaining said fluid therefrom, said fluid being circulated through a circuit including a moisture stripping means adapted to receive a portion of the dry compressed gas discharged from the moisture absorber and passing said portion of the dry compressed gas in moisture exchange relationship with said fluid prior to reintroducing said fluid into said moisture absorber, said fluid being cooled after leaving said moisture stripping means and before entering said moisture absorber. Again performance is improved if the fluid has hygroscopic characteristics. 
     In accordance with a further aspect, the present invention also anticipates providing a drier for drying compressed gas, said drier being adapted to receive compressed gas to be dried from a gas compressor means, the compressed gas being delivered to a moisture absorber configured to receive and circulate therethrough a fluid capable of removing moisture from the compressed gas prior to the compressed gas being discharged as a dry compressed gas through filter means to remove any remaining said fluid therefrom, said fluid being circulated through a circuit including a moisture stripping means adapted to receive a portion of the dry compressed gas discharged from the moisture absorber and passing said portion of the dry compressed gas in moisture exchange relationship with said fluid prior to reintroducing said fluid into said moisture absorber, said fluid being heated after leaving said moisture absorber and before entering said moisture stripping means. 
     In accordance with a still further aspect, the present invention also anticipates providing a drier for drying compressed gas, said drier being adapted to receive compressed gas to be dried from a gas compressor means, the compressed gas being delivered to a moisture absorber configured to receive and circulate therethrough a fluid capable of removing moisture from the compressed gas prior to the compressed gas being discharged as a dry compressed gas through filter means to remove any remaining said fluid therefrom, said fluid being circulated through a circuit including a moisture stripping means adapted to receive a portion of the dry compressed gas discharged from the moisture absorber and passing said portion of the dry compressed gas in moisture exchange relationship with said fluid prior to reintroducing said fluid into said moisture absorber, said fluid being heated after leaving said moisture absorber and before entering said moisture stripping means, said fluid being cooled after leaving said moisture stripping means and before entering said moisture absorber. 
     According to yet another aspect of this invention, a novel form of moisture absorber column is proposed for use in compressor systems of the above discussed types. According to this aspect, the present invention provides a moisture absorber column including an outer housing defining a vertically disposed absorption zone, a plurality of vertically spaced partition members traversing the absorption zone and each having a plurality of gas flow openings formed therein, at least one conduit member extending through an aperture in each said partition member to have a first portion extending upwardly from the partition member and a second portion extending downwardly towards the next adjacent said partition member located below said partition member, the conduit member having liquid flow means at or adjacent a lower end arranged to allow liquid flow from within the conduit member across the partition member located beneath said conduit member, said absorber column having liquid inlet means arranged to deliver liquid to the uppermost said partition member and liquid outlet means to withdraw liquid from a region below the lowermost said partition member, gas inlet means arranged to deliver gas to the region below the lowermost said partition member whereby said gas flows upwardly through the gas flow openings fanned therein, and gas outlet means arranged to withdraw gas from the absorption zone above the uppermost said partition member. Conveniently, the absorber liquid travels downwardly through the absorption zone as the gas travels upwardly through the absorption zone of the column. The liquid flows initially over or across the uppermost partition member and gas flowing upwardly through the gas flow openings formed therein causes the liquid to bubble or froth upwardly and into the upper ends of the conduit member or members to flow downwardly to the next adjacent partition member below where the process is repeated. In this way maximum contact is established between the gas flow and the liquid flow such that moisture from the gas flow can be collected by the liquid flow to effectively dry the gas flow. In some situations, it may be desirable to maintain a pool of liquid in the absorber through which the gas is bubbled before it reaches the partition members. In this manner, it is ensured that there is always some contact between the liquid and gas, even at start up of the system. Conveniently the pool of liquid is maintained below the lowermost absorber partition member. 
     In accordance with a still further preferred aspect of this invention, it is proposed to provide a novel module for use in constructing an absorber column as aforesaid. Absorber columns intended for use in gas compressor systems may typically be essentially constructed from an upright cylindrical casing of a relatively small diameter, of the order of 4 to 8 inches. This makes the internal construction of the absorber somewhat difficult and therefore costly. According to this aspect, it is desired to provide a module for use in constructing a moisture absorber column, the module including a partition plate member having a plurality of spaced gas flow openings formed therein, and at least one conduit member extending through an aperture in the partition plate member whereby a first portion extends upwardly from the partition plate member and a second portion extends downwardly below the partition plate member, the second portion having a closed lower end with one or more liquid flow openings located at or adjacent the closed lower end. Modules of this type may simply be positioned, one after the other in a cylindrical outer casing making the construction of same relatively simple. Moreover, the form of construction allows easy adjustment by permitting repositioning of the conduit members relative to the partition plate members to particular applications prior to fixing same into a desired optimum position. 
     The present invention also anticipates providing a gas compressor system including a driven gas compressor means adapted to receive gas to be compressed and discharge compressed gas therefrom, said discharged compressed gas being passed to a moisture absorber column as described above. 
     Still further, the present invention also anticipates providing a compressed gas drier including a moisture absorber column as described above adapted to receive compressed gas to be dried from a gas compressor means and deliver said compressed gas to said gas inlet means of the moisture absorber column, said liquid outlet means communicating with a moisture stripping column through which the liquid discharged from said moisture absorber column is passed with moisture picked up by said liquid being at least partially stripped from said liquid by a part of the dry compressed gas flow exiting the gas outlet means of the absorber column being diverted through said moisture stripping column, the liquid after passing through said moisture stripping column being delivered to the liquid inlet means of the moisture absorber column. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       Various preferred embodiments and features of aspects of this invention will become clearer from the following description given in relation to the accompanying drawings, in which: 
         FIG. 1  schematically illustrates a first preferred embodiment of a gas compressor system according to the present invention; 
         FIGS. 2 and 3  schematically illustrate two further preferred embodiments of similar gas compressor systems; 
         FIG. 4  illustrates a still further embodiment of a gas compressor system while also illustrating features of a preferred absorber construction; 
         FIG. 5  illustrates the preferred absorber construction shown in  FIG. 3  with a common gas receiver vessel; and 
         FIG. 6  illustrates in partial side view, further features of the preferred absorber construction; 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring first to  FIG. 1 , the illustrated compressor system includes a rotary compressor unit  10  driven by a motor  11  which receives a gas (typically air) to be compressed at  12  via an inlet valve  7 . The rotary compressor unit  10  may be a screw compressor of any known configuration or in fact any other form of rotary compressor. The system further includes a separator vessel  13  receiving compressed gas and entrained lubricant via line  14  with a preliminary separation of gas and lubricant occurring therein. The lubricant is collected in a lower region of the vessel  13  and returned via line  15  and a lubricant cooler  16  to a lower pressure region of the compressor unit  10 . Compressed gas leaves the vessel  13  via a preliminary filter means  17  and a minimum pressure valve  18 . The compressor system thus described is essentially conventional in nature and within the context of this invention might be substituted by any other known similar rotary compressor system. 
     The compressed gas flow leaving the separator vessel  13  is conveniently cooled in a gas cooler device  19  such that at least a portion of the moisture is cooled, condensed, collected and drained away at  20  from the system. The cool humid compressed gas flow is then passed via line  21  to an absorption column  22  where a shower of cool dry hygroscopic fluid is falling. As the compressed gas flow passes upwardly through this shower, moisture is absorbed into the hydroscobic fluid flow conveniently originates via diverting a portion of the lubricant flow in line  15  through a line  23  and thereafter passing same through a further lubricant cooler  24  prior to delivering same to the absorption column  22 . In an alternative arrangement the diverted flow might be after the cooler  16  with or without further cooling. 
     The lubricant falls to the bottom of the absorption column  22  where it is collected and conveniently passed via line  25  back to line  15  or some other lower pressure region of the compressor circuit including the compressor unit  10 . This lubricant flow then mixes with the main lubricant flow where it is heated and the absorbed moisture flashes into vapour. This vapour is subsequently condensed in the gas after cooler device  19  and at least partially drained away at  20 . 
     The cool dry compressed gas flow leaving the absorption column  22  passes through a final filter means  26  so that no droplets of coolant can escape with the clean dry compressed gas discharge at  27 . Conveniently lubricant purge lines  3 , 3 ′ are operatively associated with each of the filter means  17  and  26  to return any collected lubricant back to a lower pressure portion of the compressor system such as the compressor unit  10  itself. Further possible changes to the system may include integrating the absorption column  22  into the separator vessel  13  whereby a secondary vessel is not required. Alternatively, the absorption column  22  might be integrated into the air receiver tank as shown in FIG.  5 . 
     Referring now to  FIGS. 2 and 3 , there is illustrated a compressor system  9  including a gas compression device  8  which in the illustration is a rotary compressor device similar to that described in the foregoing with reference to FIG.  1 . It should, however, be recognised that any other form of gas compressor devices including reciprocating devices could be used. 
     Similar to the system described with reference to  FIG. 1 , the compressed gas flow leaving the separator vessel  13  may be conveniently cooled in a gas cooler device  19  such that at least a portion of the moisture contained within the gas is cooled, condensed, collected and drained away at  20  from the system. The cool humid compressed gas flow is then passed via line  21  to an absorber column  22 , preferably in the form of an upright column where a shower of cool dry hygroscopic fluid is falling. As the compressed gas flow passes upwardly through this shower, moisture is absorbed into the hygroscopic fluid flow. It should be appreciated that any other form of absorber might be used. 
     The lubricant falls to the bottom of the absorber column  22  where it is collected and conveniently passed via line  25  in a closed circuit  6  back to the absorber column  22  via a heat exchanger  28  and line  29 . The heat exchanger  28  may take up heat from the returning hot lubricant in line  15  from the separator vessel  13 . Alternatively, an electric coil  31  might be used to heat the liquid in the aforementioned closed circuit. A still further alternative may be to use heat from the exiting compressed gas in the cooler  19  as shown in dashed outline. Such heating of the fluid conveniently minimizes the amount of dry compressed gas that needs to be diverted from the dry compressed gas discharge line as described hereinafter. 
     The cool dry compressed gas flow leaving the absorber column  22  passes through a final filter means  26  so that no droplets of absorber liquid can escape with the clean dry compressed gas discharge at  27  possibly to a gas/air receiver tank. Conveniently a lubricant purge line  3  is operatively associated with the filter means  17  to return any collected lubricant back to a lower pressure portion of the compressor system such as the compressor unit  10  itself. Further possible changes to the system may include integrating the absorber column  22  into the separator vessel  13  whereby a secondary vessel is not required. Alternatively, the absorber column  22  might be integrated into the air receiver tank  32  as shown in FIG.  5 . 
     The compressor system of  FIG. 3  is essentially similar to that of  FIG. 2  except that in  FIG. 2  the compressor system  9  is constructed as a common support platform  9  whereas in  FIG. 3 , the absorber may be constructed as a support platform  5  different to the support platform  4  of the compressor  8  thus providing a separate gas drier assembly. 
     In  FIGS. 2 and 3  a moisture stripper  32 , preferably in the form of a column, is provided cooperatively working with the absorber column  22 . Fluid exiting from the column  22  may pass via line  25  through the heat exchanger  28  or, in an alternative embodiment may pass via line  33 , to the moisture stripper column  32 . A portion of dry compressed gas may be taken from the discharge line  27  and delivered via line  34  to the stripper column  32  such that it may pass in contact with the fluid in the circuit  6  after it has left the absorber column  22  where it has picked up moisture. The dry air or gas delivered to the stripper column  32  effectively dries the fluid passing through the stripper column  32  before it enters the absorber column  22 . Moisture picked up by the gas/air passing through the stripper column is discharged via line  35  as vapour. Diverting dry compressed gas from the discharge line  27  in this way provides an inefficiency in the system and therefore it is desirable to minimize the amount of dry gas diverted from the line  27 . Liquid moisture absorber medium entering the absorber  22  should be cool for proper operation and accordingly, a cooler  70  may be provided in the line  23  following the pump  30  leading to the absorber  22 . The pump  30  may be any known type including electrically driven or air driven pumps utilizing compressed air from the discharge  27 . As a possible alternative to the cooler  70 , a heat exchanger  71  may be provided between the line  23  and the line  29 . 
     With arrangements as illustrated in  FIGS. 2 and 3 , the liquid within the substantially closed circuit  6  need not be particularly hygroscopic in nature but improved performance may be achieved if it was hygroscopic in nature. Glycol based fluids may be suitable for this application including glycol based lubricants such as Ingersoll Rand&#39;s ULTRA™ type coolant and Kluber-Summit&#39;s SUPRA™ type coolant. 
       FIG. 4  illustrates a preferred construction of absorber for use in compressor systems as described above, or in fact for any other application. The compressor system  9  is similar in nature to that shown in  FIGS. 1 and 2  except that the preliminary cooler  19  has been omitted and the line  35  is directed to the inlet gas flow  12  to the compressor  10 . Like features in the earlier embodiments have been given the same reference numerals in FIG.  4 . 
     The absorber column  22  has an outer upright cylindrical shell or casing  36  closed at an upper end by plates  37 ,  38  and at a lower end by plate  39 . Located within the outer casing  36  are a plurality of plates  40  each with a plurality of small gas flow holes  41  in a predetermined array. The plates  40  each have three vertical tubes  42  or conduits passed through apertures in the plates  40  such that the position of the tubes  42  can be adjusted relative to the plates prior to being fixed in an adjusted position. As best seen in  FIG. 6 , the tubes  42  are closed at the bottom by end caps  43  each having a reduced foot portion  44  to allow liquid flow around the foot portion. It will of course be appreciated that, depending on performance requirements, the number of tubes  42  per plate  40  can be varied depending on allowed space. Each tube  42  has at least one opening  45  adjacent the lower end caps  43  as well as at least one reduced volume flow opening adjacent their upper edges. The reduced volume flow openings may be one or more apertures  46  or notches  47  as illustrated in FIG.  6 . To enable an absorber column to be built of any desired capacity, a selected number of modules  48  consisting of a plate  40  and one or more tubes  42  can be stacked one on another within an outer cylindrical casing of desired length. Compressed gas may enter the absorber column  22  via line  21  and a port  49  in the lower end plate  39 . The gas essentially travels upwardly through the absorption zone  50  within the casing  36  by passing successively through the holes  41 . 
     Dry liquid is delivered, as shown in  FIGS. 4 and 5 , via line  51  from the pump  30  to a port  52  in the upper end plates  38 ,  37 . The liquid travels down the tube  53  in the absorber column  22  to be discharged onto the uppermost plate  40 . Gas travelling up through the holes  41  (as shown in  FIG. 6 ) in this plate causes the liquid to bubble or froth up and flow eventually into the upper ends of the tubes  42  to flow down these tubes to the next lower plate  40 . This process is repeated in a cascade fashion until the liquid is collected in the lower chamber  56  and discharged therefrom via a port  55  in the lower plate  39  to line  29  or lines  29 ,  33  returning to the moisture stripper  32 . In some applications it may be desired to keep a pool of liquid in the lower chamber  56  so that gas entering this chamber must pass through the liquid before reaching the lowermost plate  40 . Compressed gas leaving the absorber  22  may conveniently pass through a coalescent type final filter means to remove any liquid picked up via the drying process in the absorber. The filter means  26  may be mounted from one of the plates  37 ,  38  to be positioned within the absorber. In some applications, a minimum pressure valve (mpv)  18  may be provided mounted to the gas outlet port  57  ( FIG. 4 ) or be separated therefrom (FIG.  3 ).