Abstract:
A method and apparatus for reducing the moisture content of a gas stream is provided. The apparatus includes a shell having a least one tube disposed therein and a condensate trap attached to the shell. A gas stream inlet and outlet are provided so that the gas stream may flow through tubes or shell, and preferably through the tubes although it is contemplated to flow the gas stream through the shell side. The drying apparatus further includes a coolant and/or volatile fluid inlet and outlet to flow a fluid such as, but not limited to, water, alcohol, or acetone to cool the gas stream and condense moisture contained therein. The drying apparatus and method of the present invention may further include a vaporization unit for vaporizing the volatile fluid with a stream of gas such as air to form a cool vapor cloud to pass through the drying apparatus.

Description:
This application is a non-provisional application claiming priority to provisional application No. 60/133,959 filed on May 13, 1999 and provisional application No. 60/168,042 filed on Nov. 30, 1999, pursuant to 35 U.S.C. 119. Provisional applications Nos. 60/133,959 and 60/168,042 are included herein in there entirety by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates in general to methods and apparatus for removing excess moisture from air streams and in particular to a method and apparatus that removes excess moisture from compressed air streams through a unique cooling and condensation process. 
     BACKGROUND 
     Compressed air systems are utilized in a wide variety of applications and industries ranging from repair shops, construction sites, manufacturing, and dry cleaning facilities to home use. In areas where relative humidity is high, water build up in air lines can cause severe problems. Water in the air lines can shorten the life of air tools, clump media in sandblasting operations, ruin delicate parts during air jet cleaning processes, damage air driven components within machinery or produce inferior painted surfaces. Excessive water and water buildup in the air storage tanks corrodes and damages tanks prematurely. 
     There are a number of methods and devices on the market intended to remove free moisture from compressed air streams. There are two primary types of prior art dryers, refrigerant and media dryers. Refrigerant dryers commonly utilize are refrigerant such as fluorocarbons that are expensive and detrimental to the environment. Media type dryers typically include desiccants which must be replaced or regenerated periodically. The bulk of these prior art devices are very expensive, large, exhibit environmental concerns, and are maintenance intensive and operationally sensitive. 
     It would be a benefit therefore to have a method and apparatus which removes excess water from an air stream and that is easily installable in an air system. It would be a still further benefit to have a method and apparatus for removing excess moisture from an air stream that utilizes material which is readably available and environmentally safe. It would be a still further benefit to have a method and apparatus for removing excess moisture from an air stream that is inexpensive and relatively maintenance free. 
     GENERAL DESCRIPTION 
     Accordingly, a method and apparatus for reducing the moisture content of a gas stream is provided. The apparatus includes a shell having a least one tube disposed therein and a condensate trap attached to the shell. A gas stream inlet and outlet are provided so that the gas stream may flow through tubes or shell, and preferably through the tubes although it is contemplated to flow the gas stream through the shell side. The drying apparatus further includes a coolant and/or volatile fluid inlet and outlet to flow a fluid such as, but not limited to, water, alcohol, or acetone to cool the gas stream and condense moisture contained therein. The drying apparatus and method of the present invention may further include a vaporization unit for vaporizing the volatile fluid with a stream of gas such as air to form a cool vapor cloud to pass through the drying apparatus. 
     An apparatus for reducing the moisture content of a gas stream is provided that includes a shell and tube exchanger having a gas inlet and gas outlet, a coolant inlet and coolant outlet, a condensate trap, and a condensate drain, wherein the gas inlet is connectable within a gas stream whereby the gas stream is routed through the inlet, the tubes and discharged through the gas outlet; and a coolant transmitted through the coolant inlet, through the shell, and by the tubes and discharged through the coolant outlet. The coolant may be any type fluid and may be water which is available and most sites and may be a vapor. The gas stream may be formed of substantially any gas including air. 
     The drying apparatus may include a vaporization forming a mixing nozzle and connected to the coolant inlet. A source of coolant or volatile fluid such as, but not limited to, water, alcohol, or acetone connected to the fluid inlet in communication with the mixing nozzle, and a source of charged air passing through an air nozzle in connection with the mixing nozzle of the vaporization unit to form a cool vapor within the drying unit when the volatile fluid flash vaporizes. Additionally, micro-droplets may be formed in the vapor to aid in thermal coupling with the tubes to condense the moisture in the gas stream. 
     The foregoing has outlined the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic drawing of an embodiment of the compressed air drying system of the present invention. 
     FIG. 2 is a partial cross-sectional view of a shell and tube exchanger of the present invention. 
     FIG. 3 is a schematic drawing of another embodiment of the compressed air drying system of the present invention. 
     FIG. 4 is a partial cross-sectional view of the air dryer shown in FIG.  1 . 
     FIG. 5 is a partial cross-sectional view of an embodiment of the vaporization cooling unit of the present invention. 
     FIG. 6 is a partial cross-sectional view of another embodiment of the vaporization cooling unit of the present invention. 
    
    
     DETAILED DESCRIPTION 
     Refer now to the drawings wherein depicted elements are not necessarily shown to scale and wherein like or similar elements are designated by the same reference numeral through the several views. 
     FIG. 1 is a schematic drawing of a preferred embodiment of a compressed air drying system  13  including an air dryer  10  of the present invention. Compressed air system  13  includes a compressor  12 , a compressed air reservoir tank  14 , and air dryer unit  10 . 
     Compressed air system  13  as shown is a common air compressor found in gas stations, homes, at construction sites, and in manufacturing facilities. Compressor  12  mechanically pressurizes air which is then transmitted to tank  14  or directly to a tool for operation. Tank  14  is not necessary although a common and beneficial part of the compressed air system. Typically in a compressed air system moisture will be contained in the air stream which is pressurized resulting in damage to tools and equipment associated with the system. To alleviate the problems with moisture in the compressed air it is desired to dry the air. The present invention includes an air dryer  10  which may be connected within an existing air compressor system or constructed as a unitary part of an air compressor system. 
     Air dryer  10  includes a shell and tube heat exchanger  18  having a condensate trap  20 , an air inlet  22 , a dry air outlet  24 , a coolant inlet  26 , a coolant outlet  28 , and a drain  30 . Air dryer  10  is in fluid connection between compressor  12  and tank  14  or operating tools such as a pneumatic wrench or sand blaster. Air dryer  10  is further in operational connection with a coolant source  32  such as a reservoir containing water or a mixture of fluid such as, but not limited to, water and ethylene glycol. 
     As shown in FIG. 1, compressed air which is heated during the compression phase is transmitted into air dryer  10  at inlet  22  and exits dryer  10  at outlet  24  to tank  14  or an tool for operation. A coolant, such as water, is circulated from reservoir  32  through coolant inlet  26 , through shell and tube exchanger  18  and discharged from coolant outlet  28  back to reservoir  32  or an appropriate disposal site. As compressed air and coolant pass through air dryer  10  excess moisture is condensed from the compressed air, collected in trap  20  for discharge through drain  30 . 
     FIG. 2 is a partial cross-sectional view of shell and tube exchanger  18  of the present invention. Tube and shell exchanger  18  includes a plenum  38 , tubes  40  which are connected between an upper tube plate  44  and a lower tube plate  46 , and condensate trap  20 . A baffle  42  may be included adjacent the exit ends of tubes  40  to prevent condensate  48  from exiting outlet  24  with dried compressed air  34 . 
     With reference to FIGS. 1 and 2, compressed air  34 , heated and laden with moisture, is discharged from compressor  12  and transmitted to air dryer  10  via inlet  22 . Compressed air  34  enters tubes  40  at plenum  38  and passes through tubes  40  into condensate trap  20  where it exits at outlet  24  and is transmitted to tank  14  or to tools. Coolant  36 , such as water, enters dryer  10  through inlet  26  and passes through shell and tube exchanger  18  on the shell side passing across tubes  40  and exits outlet  28 . As coolant  36  passes across tubes  40  through which compressed air  34  is passing heat is transferred from air  34  to coolant  36  condensing moisture out of air  34 . The condensate  48  drops into trap  20  where it can be drained at intervals. 
     FIG. 3 is a schematic drawing of another embodiment of the compressed air drying system of the present invention. Air dryer  13  as shown in FIG. 3 further includes a vaporization cooling unit  100 . Compressed air  34  is transmitted through air inlet  22  into shell and tube exchanger  18  and exits air outlet  24  for transmission to tank  14  or tools. Coolant  36 , which maybe water from a water tap  32  or other fluids such as acetone, alcohol or the like, is introduced into shell and tube exchanger  18  through inlet  26  via vaporization cooler  100 . Additionally, pressurized charge air  50  is introduced into vaporization unit  100  with coolant  36 . In this embodiment charge air  50  is transmitted from tank  14  to vaporization unit  100 , although other sources of charge air  50  may be utilized. 
     FIG. 4 is a partial cross-sectional view of air dryer  10  as shown in FIG.  3 . Compressed, moist air  34  is introduced to shell and tube exchanger  18  through inlet  22 , passing through tubes  40  and exits outlet  24  after releasing condensate  48 . Water is condensed from air  34  by passing a cooled vapor cloud  52  through the shell side of exchanger  18  so as to cool air  34  in tubes  40  forming a condensate. Cooled vapor cloud  52  is formed by mixing a coolant  36  such as water in a liquid form with charge air  50  in vapor unit  100 . Vapor cloud  52  enters exchanger  18  at coolant inlet  26  and passes over tubes  40  exiting at coolant outlet  28 . One of the benefits of the present invention is the ability to dispose of coolant  36  in a environmentally safe manner without any treatment of the exiting coolant. 
     FIG. 5 is a partial cross-sectional view of an embodiment of vaporization cooling unit  100  of the present invention. Vaporization cooling unit  100  includes a mixing nozzle  110  formed therein and a fluid inlet  102  and fluid nozzle  106 , and a charged air inlet  104  and charged air nozzle  108  all in operational communication with mixing nozzle  100 . Vaporization cooling unit  100  is connected to coolant inlet  26  at the larger diameter end of mixing nozzle  110 . Charged air  50  line is connected to charged air inlet  104  with charged air nozzle  108  in fluid communication with mixing nozzle  110 . A fluid  36  line is connected to fluid inlet  102  with fluid nozzle  106  in fluid communication with mixing nozzle  110 . 
     A method of utilizing air dryer  10  and vaporization unit  100  of FIG. 3 is described with reference to FIGS. 3 through 5. A volatile fluid  36 , such as water, is introduced to refrigerator  100  via a volatile fluid feed hose, volatile fluid feed port  102 , and a volatile fluid nozzle  106 . Charged air  50  is introduced to refrigerator  100  via an air feed line, air feed port  104 , and air nozzle  108 . Volatile fluid  36  is flash vaporized as it is introduced into the air stream via the vacuum created by a venturi effect. Volatile fluid feed  36  is sufficient to allow micro-droplets  54  to form in the cloud discharge  52 . The droplets  54  adopt the same temperature as the cloud discharge  52  and assure good thermal coupling to the heat exchanger tubes  40 . The expansion of cloud discharge  52  is controlled via an expansion cone  110  formed in refrigerator body  100 . 
     FIG. 6 is a partial cross-sectional view of another embodiment of vaporization cooling unit  100  of the present invention. FIG. 6 is a vaporization cooling unit  100  similar to that as shown in FIG. 5 further including an emulsification cavity  112  and cover air port  114 . Emulsification cavity  112  is formed by unit  10  so as to be in fluid communication between mixing nozzle  110  and fluid inlet and fluid nozzle  106 . Cover air port  114  is a conduit formed between emulsification cavity  112  and an exterior of unit  100  to allow cover air  116  to enter cavity  112 . 
     A method of utilizing unit  100  as shown in FIG. 6 is described with reference to FIGS. 3 through 6. Volatile fluid  36  is introduced into refrigerator  100  via a volatile fluid  36  line, volatile fluid feed port  102 , and volatile fluid nozzle  106 . Charged air  50  is introduced to refrigerator  100  via an air feed line, air feed port  104 , and air nozzle  108 . Cover air  116  and volatile fluid  36  are drawn up through the emulsification cavity  112  via the vacuum created by a venturi effect. Cover air  116  is drawn through cover air port  114 . As volatile fluid  36  and cover air  116  are drawn through the emulsification cavity  112  volatile fluid  36  is emulsified. The emulsified volatile fluid is flash vaporized as it is introduced into air stream  50  via the vacuum created by a venturi effect. The volatile fluid feed  36  is sufficient to allow micro-droplets  54  to form in the cloud discharge  52 . The droplets  54  adopt the same temperature as the evaporated cloud discharge  52  and assure good thermal coupling to the heat exchanger tubes  40 . The expansion of the cloud discharge  52  is controlled via an expansion cone  110  incorporated into refrigerator body  100 . 
     EXAMPLE: With reference to FIGS. 3 through 6, utilizing seven 23.5 inch, 0.25 inch outside diameter tubes having a wall thickness of 0.35 inches, in a 1.25″ schedule  40  shell in conjunction with a five and ten horsepower compressors. 
     Charge air  50  is introduced into air nozzle  108  at pressure of 120 PSI. Air nozzle  108  will dictate a flow rate of 1.2 CFM@120 PSI. The discharge of air nozzle  108  is approximate the small end of the 20° cone  110 . The air enters the 20° cone  110  and expands at a controlled rate until the pressure has dropped to atmospheric pressure @10.2 CFM. Water  36  is introduced into a 0.015 inch nozzle  106  at a pressure of 40 PSI. Fluid nozzle  106  will dictate a flow rate of 0.07 GPM. Fluid nozzle  106  is positioned to introduce the water flow into the air stream. As the water comes in contact with the air stream, it is atomized and flash vaporized forming a 35° F. vapor cloud  52 . The water flow is sufficient to produce a saturated cloud and micro-droplets of water  54 . The droplets  54  adopt the same temperature as the vapor cloud  52  and aid the thermal coupling to the heat exchanger tubes  40 . 
     Compressed air  34  with a temperature between 35° and 450° F., relative humidity between 20% and 100%, pressure between 35 and 250 PSI, and a flow rate between 5 and 17 CFM is introduced to exchanger  18  and through tubes  40 . The outside of the exchanger tubes  140  are cooled to 35° F. by the refrigerated vapor cloud  52  and, in turn, the air inside of the exchanger tubes is cooled to 38° F. As the air is cooled, water vapor is condensed and forms droplets  38  on the inside wall of the exchanger tubes  40 . These droplets  38  run down the exchanger tubes  40  and drip into condensate trap  20 . The dry air  34  flows around the bottom of the aspiration baffle  42  and is discharged through outlet  24 . The dripping condensate  38  is captured in condensate trap  20  and must be periodically drained. The cooled cloud  52  is discharged through the discharge port  28 . The discharge may be in the form of a vapor cloud and/or liquid. 
     Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made wherein, such as drying a gas stream other than compressed or utilizing fluids such as but not limited to water, alcohol, and acetone without departing from the spirit and scope of the invention as defined by the appended claims.