Abstract:
A gas dryer or condenser utilizes a two-stage insert, each stage containing a different moisture-removing material such as a combination of lava rock, gravel and a felt material, housed within a pressure vessel, to dry a stream of gas, such as air from an air compressor. Moisture-laden compressed air passing through sequentially through each of the two stages releases liquid in the air onto the surfaces of the materials and the separated liquid drains into a liquid collection area in the bottom of the pressure vessel.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention relates generally to apparatus for removing small amounts of liquids from a gas stream and more particularly to the removal of moisture from compressed gases such as air.  
       BACKGROUND OF THE INVENTION  
       [0002]     Downstream condensation can be a serious problem for equipment which rely upon a source of compressed air that contains even relatively small amounts of moisture for their operation.  
         [0003]     Typically, for use in drying gas flows in other industries such as the oil and gas industry, simple centrifugal separator vessels are implemented which are capable of gross removal but result in substantial moisture or liquid re-entrainment. Dehydrators are applied for the removal of water vapor from hydrocarbon gas streams. Dehydrators, such as those implementing glycol, are capable of greater moisture removal, however they are also associated with a large cost and negative environmental impact including a large energy cost associated with heating to separate water and glycol and the exhaust emissions. Such systems are too large and costly to be applied for use in most commercially available compressed air systems, and particularly those employed by the trades to operate air-powered tools or the like.  
         [0004]     More often, compressed air systems for use with tools are equipped with nothing at all to deal with moisture problems or are equipped with pressure vessels filled with dessicant materials which act to remove and accumulate the moisture in the pore spaces of the dessicant material. Typically, the systems are regenerative and have two dessicant filled pressure vessels fluidly connected to the compressed air source. As the desiccant in one pressure vessel becomes saturated with liquid removed from the compressed air, the system is switched to the second pressure vessel. The first pressure vessel is then regenerated by driving the moisture from the dessicant using heat, blowers and the like. Such systems are also relatively expensive and require a source of energy to power the regeneration system.  
         [0005]     Applicant has determined that there is a novel and simple approach to the removal of liquids from gas flows, such as compressed air, which demonstrates improved efficiency without the need for costly regenerative systems and additional energy consumption and which can be retrofit to existing compressed air systems.  
       SUMMARY OF THE INVENTION  
       [0006]     Apparatus are applied for the removal of liquids from gas streams including compressed air.  
         [0007]     A two-stage apparatus is provided for better liberating liquid from such gas streams so as to prevent downstream condensation in tools and the like, connected to the compressed air source.  
         [0008]     In one broad aspect the present invention comprises a pressure vessel for receiving the gas stream having an inlet at a top end, an outlet adjacent the top end and a liquid collection zone in a bottom end; a first stage adapted to be suspended in the pressure vessel above the liquid collection zone and having a bore, at least a portion of which is filled with a first moisture-removing material forming a tortuous pathway though which the gas stream passes, moisture being collected on a surface of the first moisture-removing material and flowing co-current with the gas stream, the liquid flowing to the liquid collection zone; and a second stage containing a second moisture-removing material for receiving a substantially drier gas stream from the first stage and removing residual moisture therefrom, the moisture being condensed to liquid which flows counter-current to the gas stream therein, the liquid flowing to the liquid collection zone and the substantially drier gas stream flowing to the gas outlet.  
         [0009]     In a second broad aspect the present invention comprises an insert, adapted to be suspended in a pressure vessel having cylindrical side walls, a bottom end, and gas inlet adjacent a top end, the insert comprising: a tubular first stage adapted to be suspended in the pressure vessel above the liquid collection zone and having a bore filled with a first moisture-removing material forming a tortuous pathway though which the gas stream may pass, moisture being condensed on a surface of the first moisture-removing material and flowing concurrent with the gas stream, the liquid flowing to the liquid collection zone; and a second stage formed in an annulus between the tubular first stage and the pressure vessel and containing a second moisture-removing material for receiving a substantially drier gas stream from the first stage and removing residual moisture therefrom, the moisture being condensed to liquid which flows counter-current to the gas stream therein, the liquid flowing to the liquid collection zone and the substantially drier gas stream flowing to the gas outlet.  
         [0010]     Applicant believes that moisture droplets are separated from the gas stream by the principles of impingement separation wherein liquid droplets or mist coalesce on the surface of the particulate or fiberous material and drain therefrom. Re-entrainment of the liquid into the gas flow is substantially prevented by the velocity of the gas stream, and the lack of contact of the gas stream with the separated liquids by diverting the flow of substantially dried gas away from the liquid collection zone in the bottom of the separator.  
         [0011]     Preferably, use of a moisture transporting material, such as gravel, in the bore of the first stage below the first moisture-removing material, aids in more quickly removing liquids from the moisture-removing material and transporting the liquids to the liquid collection zone.  
         [0012]     Natural materials may be used as the moisture-removing materials and particularly, lava rock and felt material which have large surface areas with tortuous and narrow passages through which the gas stream is directed for separation of liquids from the gas therein.  
         [0013]     The two-stage apparatus advantageously requires no regeneration of the moisture-removing materials and can be sized to accommodate the desired flow rates and to suit the relative humidity of the incoming gas stream.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is a longitudinal sectional view of an embodiment of a two-stage condenser apparatus having an insert according to an embodiment of the invention fit or retrofit therein;  
         [0015]      FIG. 2  is a partial sectional view of a mist distributor for distributing moisture-laden gas as a mist into a first stage of the insert according to  FIG. 1 ;  
         [0016]      FIG. 3  is a plan view of the insert according to  FIG. 1 ;  
         [0017]      FIG. 4  is a plan view of a top plate of the insert according to  FIG. 1 ; and  
         [0018]      FIG. 5  is a plan view of a bottom plate of the insert according to FIG.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0019]     Having reference to  FIG. 1 , a two-stage condenser or gas dryer  1 , according to an embodiment of the invention, is shown. Typically, in use, the two stage condenser  1  is connected downstream from a compressed gas source (not shown), such as an air compressor, and upstream from apparatus (not shown), such as air-powered tools, to prevent downstream condensation from occurring in the connected apparatus.  
         [0020]     The condenser  1  comprises an outer vessel  2 , typically a pressure certified vessel. The vessel  2  has an inlet  3  at a top end  4  for admitting a flow of moisture-laden compressed gas under pressure, typically air, and an outlet  5 , adjacent the vessel&#39;s top end  4  for releasing a flow of substantially moisture-free compressed gas therefrom. The inlet  3  is fluidly connected to an insert  10  suspended within the vessel  2 . The insert  10  comprises a tubular first stage  11  having a central bore  12 , a portion of which is filled with a first moisture-removing material  13  which has a large surface area and forms a plurality of surfaces and tortuous pathways therebetween capable of collecting moisture droplets thereon for removing moisture from the gas stream. The tubular first stage  11  is suspended above a bottom  6  of the vessel  2  creating a liquid collection zone  7  at the bottom of the vessel. As the moisture laden gas is flowed through the first moisture-removing material  13 , moisture droplets are retained on the surface of the material  13 , where the droplets are coalesce into a liquid flow which flows co-current with the gas, carried by the velocity of the flow and by gravity, to the bottom  6  of the vessel  2 .  
         [0021]     A top plate  14  ( FIG. 4 ), positioned adjacent the outlet  5  at the top  4  of the vessel  2  and a bottom plate  15  ( FIG. 5 ) positioned at a base  16  of the tubular first stage  11 , are fastened to the tubular first stage  11  and act to retain the first moisture-removing material  13  within the central bore  12 . A plurality of perforations  17  are formed in both the top  14  and bottom  15  plates to permit the flow of gas and liquid therethrough.  
         [0022]     Further, a plurality of perforations  18  are formed about a sidewall  19  of the tubular first stage  11 , adjacent and above the bottom plate  15 , to permit the flow of gas from the first stage  11  of the condenser  1  to a second stage  20  of the condenser  1 , situated in an annulus  21  formed between the tubular first stage  11  and the vessel  2 . Gas, having had a large portion of the liquid removed, flows from the tubular first stage  11  outwards through the sidewall perforations  18  and upwards into the second stage  20  of the condenser  1 , while heavier coalesced liquid droplets, removed in the first stage  11 , drain to the liquid collecting zone  7 . A drain  8  in the bottom  6  of the liquid collecting zone  7  is used to remove accumulated liquids from the condenser  1 .  
         [0023]     The second stage  20  of the condenser  1  is filled with a second moisture-removing material  22 . Gas flowing upward through the second moisture-removing material  22  releases a substantial portion of any residual moisture droplets retained therein. As the gas continues to rise, the collected liquids flow counter-current to the gas flow, gravity causing the liquid to flow downwards through the perforations  17  in the bottom plate  15  and into the liquid collection zone  7 . Substantially dry gas flows from the second stage  20  of the condenser  1  to the gas outlet  5  adjacent the top  4  of the vessel  2 .  
         [0024]     In one embodiment of the invention, the first moisture-removing material  13  is a particulate material which when packed in the bore  12  has a large surface area and the ability to collect and coalesce liquid droplets from the gas as it passes through the tortuous pathways between the particulates and subsequently permits the coalesced liquid to flow therethrough. It is believed that the liquid is separated from the gas stream by the principles of impingement separation wherein liquid droplets or mist coalesce on the surface of the particulate material  13  and drain therefrom with minimum to no re-entrainment of the liquid into the gas flow.  
         [0025]     Typically, in impingement separation, re-entrainment is prevented by the velocity of the gas flow, the ratio of the liquid to the gas and preventing the gas from contacting the liquid once separated. In the case of the present invention, the velocity of the gas flow in the pressure vessel  2  is maximized by the velocity of the input from the compressor and the restricted nozzle-like inlet  3 . Moisture in the compressed gas flow is minimized as much as possible through conventional compressor technology and the gas flow is prevented from contacting the larger volumes of collected liquid in the liquid collection zone  7  by diverting the flow of the substantially dried gas outwards through the sidewall perforations  18  of the first stage  11  substantially above the liquid collection zone  7 . Advantageously, regeneration of the moisture-removing materials is not required, as the interaction at the surface does not alter or exhaust the materials ability to remove liquids, over time.  
         [0026]     Examples of the first moisture-removing material  13  are broken solids such as brick, tile, rock and stone and further include, gravel and lava rock, lava rock being preferred. In the case where lava rock is used as the first moisture-removing material  13 , a layer of gravel  23  is placed at the base  16  of the first stage  11 , below the lava rock and adjacent the sidewall perforations  18  of the tubular first stage  11  and the bottom plate  15  to aid in transporting liquid collected on the lava rock  13  to the liquid collection zone  7 . In an embodiment of the invention, the layer of lava rock  13  is approximately 6 inches, the remainder of the central bore  12  being filled with gravel  23 .  
         [0027]     The second moisture-removing material  22  is a relatively finer pore material than the first moisture-removing material  13  to ensure remaining moisture in the gas flow is contacted as it passes therethrough to ensure maximum collection and moisture removal. One such material  22  is a felt material, preferably a fine density felt material. It is believed that, much like conventional fiber mist eliminators, the felt, a randomly oriented fiber bed having tortuous and narrow pathways formed therethrough, acts to collect droplets on the fibers by inertial impaction and direct interception, while even smaller droplets are collected on the fibers by brownian diffusion. As the droplets coalesce into larger droplets, the larger droplets are flowed by gravity, counter-current to the gas flow, and to the liquid collection zone  7 .  
         [0028]     As shown in  FIGS. 1 and 3 , dividers  30  are connected between the insert  10  and the vessel  2  at intervals throughout the annulus  21  to ensure the second moisture-removing material  22  is kept in place in the second stage  20 .  
         [0029]     The insert  10 , including the top and bottom plates  14 , 15 , can be manufactured from corrosion resistant materials such as stainless steel, galvanized steel, PCV plastic, ABS plastic or the like.  
         [0030]     Having reference to  FIGS. 1 and 2 , the inlet  3  is typically a pipe connected to a port  24  in a top  4  of the vessel  2  which is connected, at an outside end  25 , to a gas compressor (not shown). The insert  10  is suspended in the vessel  2 , typically by threading the inlet pipe  3  into the port  24  in the top  4  of the vessel  2 . Further, the inlet  3  extends through the top plate  14  and is connected to a mist distributor  40  at an inside end  41 . The mist distributor  40  is fluidly connected to the inlet  3  and positioned beneath the top plate  14 , in the bore  12  of the first stage  11 . The mist distributor  40  acts to ensure that moisture in the gas flow is formed into mist prior to loading the gas flow into the first stage  11  of the insert  10  to ensure optimal contact of the moisture with the material therein.  
         [0031]     As shown in greater detail in  FIG. 2 , one embodiment of the mist distributor  40  comprises a circular housing  42  which is adapted to be fastened to an underside  43  of the top plate  14 , fluidly connected to the inside end  41  of inlet pipe  3  and having a solid bottom plate  44  and a perforated sidewall  45 . Moisture-laden gas, from a compressor (not shown), entering the mist distributor  40  through the restricted inlet  3  has a significant velocity, which causes the entrained moisture to strike the bottom plate  44  and deflect through the perforations  46  in the sidewall  45 , creating a mist which is subsequently carried through the first stage  11  by the velocity of the gas flow, as well as by gravity.  
         [0032]     While typically used in a vertical configuration, the condenser  1  of the present invention is also operable in a substantially prone position, provided the condenser  1  is positioned at a slight angle, preferably not less than  4  degrees, to permit drainage. In a prone configuration, liquids released as a result of condensation in both the first  11  and second  20  stages fall to the sidewall  19  of the tubular first stage  11  or the sidewall of the pressure vessel  2  respectively and flow therealong to the liquid collection area  7 .  
         [0033]     Embodiments of the insert  10  of the invention may be manufactured separately for use to retrofit pre-manufactured pressure vessels  2 , which are already pressure certified, to make condensers  1  according to embodiments of the present invention. Alternatively, the complete condenser  1  including the pressure vessel  2  and the insert  10  may be manufactured and subsequently be pressure certified. The size of the condenser  1  may be customized for the use to which it is to be put, taking into consideration the pressure, the flow rates of gas produced by the compressor, the flow rate required downstream and the initial humidity of the gas  6  flow.  
       EXAMPLE 1  
       [0034]     As shown in  FIG. 1 , a 48 inch long, prior art, certified pressure vessel having a diameter of approximately 8 inches was used to house a 36 inch long insert  10  according to an embodiment of the invention. The insert  10  was suspended from the inlet  3  such that a liquid collection zone  7  of approximately 8 inches was formed below the bottom plate  15  and a space of approximately 4 inches was formed between the top  4  of the pressure vessel  2  and the top plate  14  of the insert  10 . The gas outlet  5  was located in the pressure vessel  2 , approximately 1 inch above the top plate  14 . Dividers  30 , shown in  FIG. 3 , were connected to the first stage  11  at 12 inch intervals above the bottom plate  15  to support ½″ to 2″ thick layers of felt material  22  therebetween. The dividers  30  were 1″×1×⅛″ plates connected between the sidewall  19  of the tubular first stage  11  and the vessel  2 . The perforations  18  in the sidewall  19  of the tubular first stage  11  are about ¼ inch in diameter and are located in a 2 inch band about the circumference of the first stage  11 , extending from approximately 2 inches to approximately 4 inches above the bottom plate  15 . A 2 inch layer of gravel  23  is positioned at the base  16  of the first stage  11 , the remainder of the bore  12  being filled with lava rock  13 .  
         [0035]     The mist distributor  40  is a 2″ pipe, approximately ¾ inch long and having a double row of ⅜ inch holes formed therebout. The inlet pipe  3  is a 1 inch pipe extending from the top  4  of the vessel  2  to the top plate  14  where it is fluidly connected to the mist distributor  40  position therebeneath.  
         [0036]     As shown in  FIG. 4 , an outer portion  50  of the top plate  14  is perforated with 32⅜ inch holes  51  which coincide with the annulus  21  of the insert  10  to permit dry gas flowing upwards through the annulus  21  to pass through to the gas outlet  5 . The reminder of the top plate  14 , save holes  52  provided for bolting to the tubular first stage  11 , is solid, acting to cover the mist distributor  40 .  
         [0037]     Having reference to  FIG. 5 , the bottom plate  15  is perforated with a plurality of ⅜ inch drain holes  53 , predominately in a central portion  54  adjacent the base  16  of the first stage  11  to permit liquids to drain through to the liquid collection zone  7  situated below. Holes  55  are also formed about a periphery  56  to permit any liquids draining from the second stage  20  to enter the liquid collection zone  7 .  
         [0038]     In use, the condenser  1 , connected to an air compressor operating at approximately 160 psi with an output of approximately 35 cfm, produced approximately 16 oz of liquid every 5 days, consistently reducing the relative humidity of the compressed air from 23% to 8% and sometimes as low as 6%.  
       EXAMPLE 2  
       [0039]     A small, one horsepower air compressor was connected to a condenser according to an embodiment of the invention, the compressor being operated for approximately 2 hours. The output of the compressor was approximately 7.5 cfm and the moisture output, while small at only 8-10 drops over the two hour period, was sufficient to drop the relative humidity of the air from an input relative humidity of approximately 23% to an output relative humidity of approximately 10%.  
         [0040]     Application of the apparatus disclosed herein results in significant savings over known drier technology and significantly improves performance and life of tools where a small, economical gas dryer was not previously available.