Patent Publication Number: US-11660568-B2

Title: Compressed air drying unit

Description:
BACKGROUND 
     The present inventions relate generally to industrial air dryers for compressed air systems. 
     Compressed air is commonly used in factories to power pneumatic tools and to blow air onto various surfaces for cleaning, expanding bags, moving parts, etc. Typically, factories have a centralized compressed air system installed that feeds a network of compressed air piping that supplies numerous tools or stations with compressed air. Thus, one or more centralized air compressors may be used to supply an entire factory space with compressed air. 
     However, it is known that air compressors which draw air from the surrounding atmosphere also introduce moisture into the compressed air from the water vapor naturally contained in atmospheric air. Moisture within compressed air used in factories can cause numerous problems. For example, in the case of power tools that use compressed air as a power source, moisture within the supplied compressed air can cause corrosion of the internal components of the tool. In addition, where compressed air is blown onto surfaces, any moisture within the compressed air will also be blown onto the surface along with the blown air. This can be particularly problematic where it is a requirement that the surface remain dry, such as food packaging operations, and can also be a problem with delicate surfaces that might be damaged by water particles within the compressed air. 
     Due to the problems associated with moisture within compressed air systems, various types of air drying systems may be used in industrial factories to remove moisture contained within compressed air. While such systems are useful and adequately address the potential problems associated with moisture in compressed air, such systems can be large in size and are not always effective in matching the required compressed air demand. Thus, it would be desirable to provide improved air drying systems for industrial factories, including small and large applications where dried compressed air is needed. 
     SUMMARY 
     An air drying unit for compressed air systems is described. The air drying unit includes a precooler/reheater that cools compressed air flowing in from an air inlet and warms compressed air flowing out of an air outlet. The precooled air flows from the precooler/reheater to a main cooler which cools the compressed air with a coolant. Moisture which condenses from the compressed air due to cooling thereof is separated from the compressed air by a moisture separator to dry the compressed air. The dried air then flows back through the precooler/reheater to warm the compressed air before flowing out through the air outlet. The invention may also include any other aspect described below in the written description or in the attached drawings and any combinations thereof. 
    
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
       The invention may be more fully understood by reading the following description in conjunction with the drawings, in which: 
         FIG.  1    is a perspective view of an air drying unit; 
         FIG.  2    is another perspective view of the air drying unit from the reverse side; 
         FIG.  3    is a schematic view of the air drying unit showing compressed air flow through passages within the air drying unit; 
         FIG.  4    is a perspective view of multiple air drying units connected together; 
         FIG.  5 A  is an exploded view of a clamp; and 
         FIG.  5 B  is a cross section of a portion of the clamp of  FIG.  5 A . 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the figures, an air drying unit  10  is provided with three main components. That is, the air drying unit  10  has a precooler/reheater  12 , a main cooler  14  and a moisture separator  16 . In operation, compressed air from the air inlet  18  enters the precooler side  12 A of the precooler/reheater  12 . The air then exits the precooler/reheater  12  and enters the main cooler  14 . After cooling the compressed air, the air enters the moisture separator  16 . The moisture separator  16  may be within the main cooler  14  or may be a separate component located after the main cooler  14 . The air then reenters the precooler/reheater  12  on the reheater side  12 B, and thereafter, exits the air drying unit  10  through the air outlet  20 . 
     The precooler/reheater  12  is a heat exchanger  12  that exchanges heat between the incoming air flow and the outgoing air flow. That is, the incoming compressed air flow is warm relative to the outgoing compressed air flow. As described below, the air is cooled within the drying unit  10  to withdraw moisture from the air. Thus, the precooler/reheater  12  increases efficiency by cooling the incoming air with the outgoing air prior to additional cooling that occurs thereafter. Also, it is undesirable for the outgoing air to be too cool since this would cool the compressed air piping and cause condensation of water vapor on the exterior of the piping. Thus, the precooler/reheater  12  prevents this from happening by heating the outgoing compressed air using the warm incoming compressed air. The energy required to cool the compressed air in the main cooler  14  is also reduced. It is also possible to reduce the size of the main cooler  14  due to the precooling that is done to the compressed air. 
     The main cooler  14  is another heat exchanger  14  that performs the primary cooling of the compressed air. Cooling of the incoming compressed air by the main cooler  14  is necessary in order to cause gaseous moisture (i.e., humidity) within the air to condense to a fluid (e.g., water) in order to allow the moisture to be removed from the air. The main cooler  14  (which may be referred to as a chiller section) may cool the compressed air in various ways. In one embodiment, the main cooler  14  may use a liquid coolant, such as a glycol and water mixture, to cool the compressed air. In this case, the main cooler  14  is a liquid-air heat exchanger  14 . Alternatively, the main cooler  14  may use a refrigerant to cool the compressed air. Thus, in this case, the refrigerant side of the main cooler  14  may be considered to be an evaporator where the refrigerant evaporates and absorbs heat from the compressed air side of the main cooler  14 . It is also possible to have main coolers  14  that utilize a liquid coolant and a refrigerant. 
     After the incoming compressed air has been cooled by the main cooler  14  (e.g., to below 5° C. and as low as 0° C.), the moisture separator  16  withdraws moisture from the compressed air. In the preferred embodiment, the moisture separator  16  is located below the main cooler  14 . Thus, gravity may be used to allow the condensed fluid to be removed through a drain  22 . In this arrangement, the compressed air which has been dried by removing moisture therefrom (and which may now be considered the outgoing compressed air) may change direction, e.g., a U-turn, and flow upwards from the moisture separator  16 . It is understood that where multiple drying units  10  are used together, the drains  22  of the units  10  may be connected together to provide a single drain system. 
     The outgoing compressed air then enters the reheater side  12 B of the precooler/reheater  12  and exits the drying unit  10  through the air outlet  20 . It is understood that air flow through the air drying unit  10  need not be separately forced or circulated therethrough, but instead may flow through the drying unit  10  as air is used by the compressed air demand and replaced by the compressed air supply. That is, any compressed air that flows to the compressed air demand from the compressed air supply must first pass through the drying unit  10  (or another drying unit  10  in the system) due to the location of the drying unit  10  between the supply and demand. 
     The drying unit  10  is designed to be compact and an integral unit. Thus, the unit  10  may be smaller than other conventional air dryers with equivalent capacity. That is, the precooler/reheater  12 , main cooler  14  and moisture separator  16  are all interconnected together in a unit  10  without being connected together with pipes and pipe couplers or fasteners. Instead, air flows between the precooler/reheater  12 , main cooler  14  and moisture separator  16  through internal passages  24  within the drying unit  10 . In order to contain the air within the unit  10 , it is necessary to ensure that the unit  10  is sealed sufficiently to contain compressed air (e.g., 100-200 psi). While the unit  10  may be made as a monolithic unit incorporating the precooler/reheater  12 , main cooler  14  and moisture separator  16 , it may be preferred that the components be welded (e.g., brazed) together so that the components are permanently connected together in sealed together (i.e., the internal passages  24  are sealed by the welds). For example, the precooler/reheater  12  may be welded  26  to the main cooler  14  and may be welded  28  to the moisture separator  16 . The main cooler  14  may also be welded  30  to the moisture separator  16 . 
     In order to make the drying unit  10  vertically compact, it may be desirable to partially overlap the precooler/reheater  12  vertically with the main cooler  14 . That is, the bottom end of the precooler/reheater  12  may be laterally adjacent the top end of the main cooler  14 . A more traditional arrangement would be to arrange the precooler/reheater  12  on top of the main cooler  14  so that the incoming compressed air flows downward from the precooler/reheater  12  to the main cooler  14 . However, in the preferred embodiment, the precooler/reheater  12  and main cooler  14  are offset from each other and partially overlapping in a side-by-side arrangement so that the incoming compressed air changes direction at the end of the precooler/reheater  12  to flow laterally from the precooler/reheater  12  to enter the main cooler  14 . As a result, the height of the drying unit  10  can be reduced. 
     In order to make the drying unit  10  modular and more easily used with multiple drying units  10  as described further below, the air inlet  18  and air outlet  20  may be pipes  18 ,  20  extending across the width of the unit  10 . In this arrangement, the axes of the pipes  18 ,  20  (which extend parallel to each other) extend in one direction across the unit  10 , but the compressed air must flow laterally with respect to the pipe axes in order to enter and exit the drying unit  10 . This may be accomplished by cutting a side opening through each pipe  18 ,  20  to fit the pipe  18 ,  20  against the drying unit  10  and welding  32  the pipe  18 ,  20  to the drying unit  10 . Thus, the compressed air flows laterally from or to the respective pipe  18 ,  20  to enter and exit the drying unit  10 . The openings  34  at the opposite ends of the pipes  18 ,  20  may be used to connect the drying unit  10  to the compressed air supply and compressed air demand. Preferably, the inlet pipe  18  and the outlet pipe  20  have equal lengths and are preferably longitudinally aligned with each other so that the end openings  34  of the two pipes  18 ,  20  extend out from the drying unit  10  the same length. It may be desirable to close one end  34  of each pipe  18 ,  20  with a plug or cap  36  when an additional drying unit  10  is not connected to the unit  10 . It is understood that the inlet and outlet pipes  18 ,  20  could be connected to the compressed air system of the facility on the same side of the drying unit  10  or on opposite sides as desired. It may also be desirable to provide pressure measurement taps in the air inlet and outlet pipes  18 ,  20  to measure pressure drop across the drying unit  10 . 
     A similar arrangement may be used for the coolant pipes  38 ,  40  as well. The inlet  38  and outlet  40  coolant pipes allow the coolant to flow into and out of the main cooler  14 . Preferably, the coolant pipes  38 ,  40  are cut and shaped to the side of the main cooler  14  and are welded  42  to the main cooler  14 . Like the air inlet and outlet pipes  18 ,  20 , the coolant flows laterally from the respective pipe  38 ,  40  to enter and exit the main cooler  14 . The coolant pipes  38 ,  40  are also preferably the same length and aligned with each other so that the end openings  44  of the two pipes  38 ,  40  extend out from the drying unit  10  the same length. It is understood that various arrangements may be used for the coolant pipes  38 ,  40  depending on the particular application and depending on whether a liquid coolant or a refrigerant is used. 
     One advantage of the drying unit  10  is that it may be chained together with multiple drying units  10  to increase capacity. It is understood that because the air drying units  10  have a common design manufacturing the units  10  may be more efficient. Also, performing maintenance on the units  10  in operation may be easier due to their commonality. Because adding each additional unit  10  increases capacity in an additive fashion, compressed air demand can also be matched more closely and capacity may be added to a factory at a later time if needed merely be adding additional drying units  10 . 
     By connecting the air inlet pipes and air outlet pipes of multiple drying units  10  together, the drying units  10  are arranged in parallel with each other between the compressed air supply and the compressed air demand. In other words, when multiple air drying units  10  are connected together and operating simultaneously, the compressed air flow from the supply is split into separate portions that flow through separate drying units  10 . Thus, where there are two drying units  10  connected together, the compressed air flow will be divided in half due to the pressure differences so that half the compressed air flows from the air inlets  18  through each drying unit  10 . The portions are then recombined at the air outlets  20  after flowing through the multiple drying units  12  in order to be supplied to the compressed air demand. Therefore, by connecting the air inlet pipes  18  together and the air outlet pipes  20  together of multiple units  10 , the connected pipes  18 ,  20  act as a common inlet header and a common outlet header. The air inlet and outlet pipes  18 ,  20  can be connected to a coupling or fitting, such as a tee, elbow or straight pipe section which may act as a central pipe carrying compressed air to the assembly. The tee, elbow or straight pipe may be used to connect to the compressed air system of the facility. An inlet filter and/or outlet filter with the same type of grooved connection or flanged connection may also be connected to the drying unit  10  assembly to filter the compressed air entering and exiting the assembly. 
     The air inlet pipes  18  and the air outlet pipes  20  are preferably each connected together with a clamp  46  that wraps around the ends  34  of two adjacent pipes  18 ,  20 . Thus, the units  10  are not connected together with intervening pipes, but are located directly adjacent each other with a single clamp  46  connecting two adjacent pipe ends  34  together. As shown in  FIGS.  5 A- 5 B , the clamps  46  may have rigid (e.g., metal) half round clamp members  52  with a circular groove  56  therein. A flexible round seal (e.g., plastic)  54  may be located in the central groove  56  of the clamp members  52 . The seal  54  may have ends  58  that are pressed into corresponding grooves  60  in the air inlet and outlet pipes  18 ,  20 . Bolts  62  and nuts  64  may be used to tighten the two clamp members  52  together and squeeze the seal  54  against the ends  34  of the pipes  18 ,  20 . 
     A similar connection may be made with the coolant inlet pipes  38  and the coolant outlet pipes  40 . Thus, the coolant pipes  38 ,  40  may be directly connected to corresponding adjacent coolant pipes  38 ,  40  with a pipe coupler (e.g., a swivel connector) without intervening pipes. Like described above, this results in the coolant pipes  38 ,  40  acting as common headers where the coolant is split evenly between the main coolers  14  of the units  10  so that equal portions flow from the coolant inlet pipes  38  into the main coolers  14 , and the coolant is recombined in the coolant outlet pipes  40  after flowing through the main coolers  14 . This arrangement would be particularly useful where a liquid coolant is used in contrast to a refrigerant which would preferably be fed directly to each main cooler separately. 
     Therefore, it can be seen that the air drying units  10  can be easily added together to satisfying increased compressed air demand while providing a compact package and common design. In addition to connecting the drying units  10  together with the pipes  18 ,  20 ,  38 ,  40  and connecting fasteners  46 ,  48 , it may also be desirable to provide additional structural supports  50  that are connected to multiple drying units  10  to securely connect the units  10  together. 
     While preferred embodiments of the inventions have been described, it should be understood that the inventions are not so limited, and modifications may be made without departing from the inventions herein. While each embodiment described herein may refer only to certain features and may not specifically refer to every feature described with respect to other embodiments, it should be recognized that the features described herein are interchangeable unless described otherwise, even where no reference is made to a specific feature. It should also be understood that the advantages described above are not necessarily the only advantages of the inventions, and it is not necessarily expected that all of the described advantages will be achieved with every embodiment of the inventions. The scope of the inventions is defined by the appended claims, and all devices and methods that come within the meaning of the claims, either literally or by equivalence, are intended to be embraced therein.