Patent Publication Number: US-2010107674-A1

Title: Refrigeration air dryer

Description:
BACKGROUND OF THE INVENTION 
     [1] Field of the Invention 
     The present invention relates to a refrigeration air dryer which dehumidifies compressed air by condensing the moisture in the compressed air by cooling the compressed air. 
     [2] Description of the Related Art 
     In air compressor system employing solenoid valves, air cylinders, etc., in order to prevent trouble from occurring due to the moisture included in compressed air to be supplied to the air compressor system, the moisture included in the compressed air is preferably removed beforehand. In order to remove such moisture, a refrigeration air dryer is employed. Such a refrigeration air dryer preferably controls the temperature of the compressed air at the outlet of the air dryer so as to again raise the temperature of the dehumidified compressed air in order to prevent occurrence of dew condensation at the secondary air pipe in the air dryer due to low-temperature compressed air dehumidified by cooling. 
       FIG. 3  shows a circuit of a refrigerant system and an air system in a conventional refrigeration air dryer which is capable of controlling the temperature of the compressed air at the outlet of the air dryer. The refrigeration system in the refrigeration air dryer includes a refrigerant compressor  10 , a condenser  11  which condenses the high-temperature refrigerant compressed by the refrigerant compressor  10  and transmitted via a high-temperature refrigerant pipe  22 , an expansion valve  12  which decompresses, by adiabatic expansion, the refrigerant thus condensed by the condenser  11  so as to lower the temperature of the refrigerant, and a cooler  13  which cools the moist compressed air, which has been input via the air inlet  20  of the air system, using the low-temperature refrigerant transmitted from the expansion valve  12 , so as to dehumidify the air. The refrigerant system is configured such that the refrigerant from the cooler  13  is returned to the refrigerant compressor  10  via a return refrigerant pipe  26 . 
     On the other hand, the aforementioned air system has a configuration in which, after the moist compressed air (primary air) input from the exterior via the air inlet  20  is cooled by the cooler  13 , drain separation processing is performed by a drain separator  16  so as to provide low-temperature dehumidified air, the dehumidified air is reheated by an electric heater  14 , and the dehumidified air thus reheated is transmitted as secondary air to an outlet pipe  21 . With such an arrangement, a temperature sensor  40  is provided to the outlet pipe  21 . The temperature of the secondary air detected by the temperature sensor  40  is input to a temperature controller  41 , and the temperature controller  41  controls the output of the electric heater  14 , thereby controlling the temperature of the secondary air at the outlet of the air dryer. Such an arrangement provides temperature control operation with relatively high precision. It should be noted that the drain separator  16 , which performs the aforementioned drain separation processing, includes a drain valve  15  which externally discharges resultant water drops. 
     In such a conventional refrigeration air dryer, the low-temperature dehumidified air, which has been dehumidified by cooling, is reheated by the electric heater  14 . Accordingly, such a conventional refrigeration air dryer requires great electric power, approximately the same as with the refrigerator. Accordingly, although the aforementioned conventional refrigeration air dryer is capable of controlling the temperature with high precision, such an arrangement has the disadvantage of great electric power consumption. 
     On the other hand, a technique has been known in which, instead of the electric heater  14 , a reheater is provided which exchanges heat between the warm primary air input via the air inlet  20  and the low-temperature dehumidified air transmitted via the cooler  13 , using the difference in temperature therebetween. With such an arrangement, by exchanging heat as described above, the primary air is preliminarily cooled, and the temperature of the dehumidified air is raised, following which the dehumidified air thus heated is output as secondary air. With such an arrangement including such a reheater, the primary air is preliminarily cooled, following which the primary air thus preliminarily cooled is again cooled by the cooler, thereby reducing the load to be applied to the refrigeration circuit. Furthermore, such an arrangement prevents occurrence of dew condensation at an air pipe by raising the temperature of the secondary air transmitted from the air dryer. Thus, such an arrangement effectively uses thermal energy. However, the temperature of the secondary air is dependent upon the temperature of the primary air. In a case in which the temperature of the primary air input via the air inlet  20  is low, in some cases, the secondary air discharged from the outlet pipe  21  cannot be raised up to a temperature at which dew condensation at the outlet pipe  21  can be prevented. It is difficult for such an arrangement to stably maintain the temperature in a required temperature range. 
     It should be noted that, in the aforementioned conventional refrigeration air dryer, in general, the temperature of the high-temperature refrigerant flowing into the condenser  11  from the refrigerant compressor  10  via the high-temperature refrigerant pipe  22  is approximately 90° C. On the other hand, the temperature of the low-temperature refrigerant, which flows into the cooler  13  via the low-temperature refrigerant pipe  23  after the adiabatic expansion provided by the expansion valve  12 , is approximately 5° C. Furthermore, the temperature of the primary air, which is input via the air inlet  20 , is 40° C. (rated temperature). The temperature of the dehumidified air transmitted from the cooler  13  to the electric heater  14  via the drain separator  16  is approximately 10° C. 
     It should be noted that, in the refrigeration air dryer, the high-temperature refrigerant pipe  22  that connects the refrigerant compressor  10  and the condenser  11  and the low-temperature refrigerant pipe  23  that connects the expansion valve  12  and the cooler  13  communicate with each other via a bypass refrigerant pipe  25  including a volume adjusting valve  17  which provides an adjustable aperture. As described above, the bypass refrigerant pipe  25  is provided in order to mix a portion of the refrigerant, which flows from the refrigerant compressor  10  to the condenser  11 , into the refrigerant flowing through the cooler  13 , so as to prevent the moisture included in the primary air flowing from the air inlet  20  to the cooler  13  from freezing due to excessive reduction in the temperature of the refrigerant flowing through the cooler  13 . 
     BRIEF SUMMARY OF INVENTION 
     It is a technical object of the present invention to provide a refrigeration air dryer which is capable of controlling the temperature of the secondary air in the outlet pipe with high precision as with an arrangement employing an electric heater, using a reheater employing heat occurring in the refrigerant system to raise the temperature of the secondary compressed air, by adjusting the flow rate of the refrigerant or air flowing through the reheater, without a need to heat the secondary air in the outlet pipe using an electric heater unlike the aforementioned conventional refrigeration air dryer. 
     In order to solve the aforementioned problem, a refrigeration air dryer is provided including: a refrigerant system which includes a refrigerant compressor, a condenser which condenses a high-temperature refrigerant compressed by the refrigerant compressor, a decompressing mechanism which decompresses, by adiabatic expansion, the refrigerant which has been condensed by the condenser, so as to lower the temperature thereof, and a cooler which cools moist compressed air input via the air inlet in an air system, using the low-temperature refrigerant transmitted from the decompressing mechanism, so as to dehumidify the air, and which is configured such that the refrigerant transmitted from the cooler is returned to the refrigerant compressor; and the air system which includes the air inlet which allows moist compressed air, which is input as primary air to be dehumidified, the cooler which cools the primary air input via the air inlet so as to obtain low-temperature dehumidified air, and a reheater which exchange heat between the low-temperature dehumidified air transmitted from the cooler and the high-temperature refrigerant transmitted from the refrigerant compressor included in the refrigerant system, and which outputs the dehumidified air, of which the temperature has been raised by the heat exchange at the reheater, is output as secondary air via the outlet pipe. With such an arrangement, the air dryer includes a temperature sensor which detects the temperature of the secondary air flowing through the outlet pipe, valve means which adjusts the flow rate of the dehumidified air or the refrigerant flowing through the reheater, and a temperature controller which adjusts the flow rate of the dehumidified air or the refrigerant by controlling the valve means based upon the detected temperature detected by the temperature sensor, so as to maintain the temperature of the secondary air at a constant level. 
     The air dryer according to the present invention is preferably configured such that the reheater is connected between the refrigerant compressor and the condenser, and the refrigerant transmitted from the refrigerant compressor is transmitted to the condenser via the reheater. 
     Also, an arrangement may be made in which a high-temperature refrigerant pipe which connects the refrigerant compressor and the reheater and a low-temperature refrigerant pipe which connects the decompressing mechanism and the cooler or a return refrigerant pipe which connects the cooler and the refrigerant compressor are connected such that they communicate with each other via a bypass refrigerant pipe including a volume adjusting valve which provides an adjustable aperture, thereby allowing a portion of the high-temperature refrigerant compressed by the refrigerant compressor to directly flow through the low-temperature refrigerant pipe or the return refrigerant pipe in a case in which the load of the cooler has become small. 
     With the present invention, the valve means preferably comprises a three-way flow adjusting valve having one inlet port and two outlet ports. With such an arrangement, the three-way flow adjusting valve preferably allows a portion of the dehumidified air or the refrigerant, which is to be transmitted to the reheater, to flow bypassing the reheater. 
     In this case, also, an arrangement may be made in which a bypass pipe that bypasses the reheater is connected to the dehumidified air pipe which transmits the dehumidified air from the cooler to the reheater and the outlet pipe which outputs the secondary air transmitted from the reheater, and the three-way flow adjusting valve is arranged at a branching node at which the bypass pipe is provided branching from the dehumidified air pipe or at a junction of the bypass pipe and the outlet pipe. 
     Also, an arrangement may be made in which a refrigeration bypass pipe that bypasses the reheater is connected to a high-temperature refrigerant pipe which connects the refrigerant compressor and the reheater and an intermediate refrigerant pipe which connects the reheater and the condenser, and the three-way flow adjusting valve is arranged at a branching node at which the refrigeration bypass pipe is provided branching from the high-temperature refrigerant pipe or at a junction of the refrigerant bypass pipe and the intermediate refrigerant pipe. 
     With the refrigeration air dryer according to the present invention having the above-described configuration, the flow rate of the dehumidified air to be transmitted to the reheater after drain separation processing, or the flow rate of the refrigerant from the refrigerant compressor is controlled based upon the temperature of the dehumidified air flowing through the outlet pipe such that the temperature thereof is maintained at a constant level. Accordingly, the refrigeration air dryer is capable of controlling the flow rate thereof with relatively high precision using electric means. Thus, the refrigeration air dryer employing such a reheater is capable of controlling the temperature of the compressed air in the outlet pipe with high precision as with an arrangement employing an electric heater. 
     The above-described refrigeration air dryer according to the present invention employs the reheater to use heat that occurs in the refrigerant system to raise the temperature of the compressed air at the outlet pipe, instead of employing an electric heater to heat the dehumidified air at the outlet pipe, unlike the aforementioned conventional refrigeration air dryers. By adjusting the flow rate of the fluid that flows through the reheater, such an arrangement controls the temperature of the compressed air at the outlet pipe with high precision as with an arrangement employing an electric heater. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a circuit diagram which shows a refrigeration system and an air system of a refrigeration air dryer according to a first embodiment of the present invention. 
         FIG. 2  is a similar circuit diagram which shows a refrigeration air dryer according to a second embodiment of the present invention. 
         FIG. 3  is a circuit diagram which shows a refrigeration system and an air system of a conventional refrigeration air dryer. 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
       FIG. 1  shows a first embodiment of a refrigeration air dryer according to the present embodiment, and  FIG. 2  shows a second embodiment of a refrigeration air dryer according to the present embodiment. In these embodiments, the same components as those of a conventional refrigeration air dryer shown in  FIG. 3  are denoted by the same reference numerals shown in  FIG. 3 . 
     Roughly, the refrigeration air dryer according to the first embodiment shown in  FIG. 1  includes a refrigerant system, an air system, and a control system which controls the flow rate of dehumidified air or the flow rate of a refrigerant flowing through a reheater  18  connected to the refrigerant system and the air system, so as to maintain the temperature of the secondary air output from the refrigeration air dryer. 
     The aforementioned refrigerant system includes: a refrigerant compressor  10 ; a high-temperature refrigerant pipe  22  which transmits a refrigerant, which has been compressed by the refrigerant compressor  10  so as to have a high temperature, to the reheater  18 ; a condenser  11  which condenses the refrigerant transmitted from the reheater  18  via an intermediate refrigerant pipe  27 ; an expansion valve  12  which decompresses, by adiabatic expansion, the refrigerant thus condensed by the condenser  11  so as to lower the temperature of the refrigerant; and a cooler  13  which cools the moist compressed air, which has been input via the air inlet  20  of the air system, using the low-temperature refrigerant transmitted from the expansion valve  12 . The refrigerant system is configured such that the refrigerant transmitted from the cooler  13  is returned to the refrigerant compressor  10  via a return refrigerant pipe  26 . 
     It should be noted that the expansion valve  12  has been illustrated as an example of the decompressing mechanism. Also, capillary tubes or the like may be employed instead of the expansion valve, for example. 
     On the other hand, the air system of the refrigeration air dryer includes: an air inlet  20  via which warm and moist compressed air (with rated temperature of 40° C.) to be dehumidified is input as primary air from the exterior: the cooler  13  which condenses the moisture by cooling the primary air input via the air inlet  20 : a drain separator  16  which dehumidifies the compressed air, which has been cooled by the cooler  13 , by performing drain separation processing: and the reheater  18  which exchanges heat between the low-temperature dehumidified air thus subjected to drain separation processing by the drain separator  16  and the high-temperature refrigerant compressed by the refrigerant compressor  10  included in the refrigerant system. The air system is configured such that the temperature of the low-temperature dehumidified air is raised by the heat exchange operation at the reheater  18 , and the dehumidified air with a raised temperature is transmitted as secondary air to the outlet pipe  21 . 
     Accordingly, the aforementioned cooler  13  and the reheater  18  are connected to both the refrigerant system and the air system, and functionally connect the refrigerant system and the air system. 
     It should be noted that the drain separator  16 , which performs the aforementioned drain separation processing, includes a drain valve  15  which externally discharges resultant water drops. 
     The aforementioned control system, which maintains the temperature of the secondary air flowing through the outlet pipe  21 , includes a three-way flow adjusting valve  30  connected in a dehumidified air pipe  28  that connects the drain separator  16  and the reheater  18 . The three-way flow adjusting valve  30  has one inlet port  30   a  and two outlet ports  30   b  and  30   c,  and is configured such that the dehumidified air input via the inlet port  30   a  is distributed and the dehumidified air thus distributed is output from two outlet ports  30   b  and  30   c.  The inlet port  30   a  is connected to an upstream portion  28   a  of the dehumidified air pipe  28  which communicates with the drain separator  16 . The outlet port  30   b,  which is one of the outlet ports, is connected to a downstream portion  28   b  of the dehumidified an pipe  28  which communicates with the reheater  18 . A bypass pipe  29  is connected between the branching outlet port  30   c  and the outlet pipe  21 . 
     The bypass pipe  29  allows a portion of the dehumidified air flowing through the dehumidified air pipe  28  to bypass the reheater  18 , and to directly flow toward the outlet side of the reheater  18 . The bypass pipe  29  allows the flow rate of the dehumidified air flowing through the reheater  18  to be adjusted. 
     Furthermore, the aforementioned control system includes a temperature sensor  40  which is connected to the outlet pipe  21 , and which detects the temperature of the secondary air flowing through the outlet pipe  21 . The temperature sensor  40  and the three-way flow adjusting valve  30  are connected to a temperature controller  42 . The temperature controller  42  controls the three-way flow adjusting valve  30  based upon the detected temperature of the secondary air thus detected by the temperature sensor  40 , thereby controlling the flow rates of the dehumidified air passing through the reheater  18  and of the dehumidified air bypassing the reheater  18 . 
     The temperature controller  42  makes a comparison between the temperature target value set beforehand and the actual detected temperature thus detected by the temperature sensor  40 , and controls the aperture of the three-way flow adjusting valve  30  such that the difference therebetween becomes zero, i.e., so as to maintain the temperature of the secondary air in the outlet pipe  21  thereby controlling the flow rate of the dehumidified air flowing the bypass pipe  29  and the flow rate of the dehumidified air flowing through the reheater  18 . 
     It should be noted that the three-way flow adjusting valve  30  is not restricted to a single valve. Also, a combination of multiple valves may be employed as long as it is capable of controlling the flow rate of the dehumidified air flowing through the bypass pipe  31  and the flow rate of the dehumidified air flowing through the reheater  18  based upon a signal received from the temperature controller  42 . 
     By detecting the temperature of the secondary air flowing through the outlet pipe  21  by the temperature sensor  40 , and by controlling the flow rate of the dehumidified air flowing through the bypass pipe  29  and the flow rate of the dehumidified air flowing through the reheater  18  based upon the temperature thus detected, the refrigeration air dryer having such a configuration according to the first embodiment is capable of controlling the temperature of the secondary air output via the outlet pipe  21  using the reheater  18  with high precision as with a conventional arrangement employing an electric heater. 
     Next, in comparison with the above-described first embodiment, description will be made regarding a refrigeration air dryer according to a second embodiment of the present invention with reference to  FIG. 2 . In the refrigerant system according to the second embodiment, a three-way flow adjusting valve  32 , which is controlled by the temperature controller  42 , is provided within the high-temperature refrigerant pipe  22  that connects the refrigerant compressor  10  and the reheater  18 . The three-way flow adjusting valve  32  is the same as that employed in the above-described first embodiment, and has one inlet port  32   a  and two outlet ports  32   b  and  32   c.  The inlet port  32   a  is connected to an upstream portion  22   a  of the high-temperature refrigerant pipe  22  which communicates with the refrigerant compressor  10 . The outlet port  32   b,  which is one of the outlet ports, is connected to a downstream portion  22   b  of the high-temperature refrigerant pipe  22  which communicates with the reheater  18 , and the other outlet port  32   c,  which is a branching port, is connected to one terminal of the refrigerant bypass pipe  31 . The other terminal of the refrigerant bypass pipe  31  is connected to the intermediate refrigerant pipe  27  which connects the outlet of the reheater  18  and the condenser  11 . The refrigerant bypass pipe  31  allows a portion of the refrigerant flowing through the high-temperature refrigerant pipe  22  to bypass the reheater  18 , and to directly flow toward the outlet side of the reheater  18 . 
     The other configurations of the refrigeration air dryer according to the second embodiment are substantially the same as those of the refrigeration air dryer according to the first embodiment. Accordingly, description of such common configurations will be omitted. 
     The three-way adjusting valve  32  is controlled by the temperature controller  42  such that the temperature of the secondary air in the outlet pipe  21  detected by the temperature sensor  40  equals the target value set for the temperature controller  42 . This control operation is substantially the same as the control operation of the three-way flow adjusting valve  30  according to the first embodiment. 
     The three-way flow adjusting valve  32  according to the second embodiment is not restricted to a single valve, as with the three-way flow adjusting valve  30  according to the first embodiment. Also, a combination of multiple valves may be employed as long as it is capable of controlling the flow rate of the dehumidified air flowing through the bypass pipe  31  and the flow rate of the dehumidified air flowing through the reheater  18  based upon a signal received from the temperature controller  42 . 
     On the other hand, the air system according to the second embodiment is configured such that all of the low-temperature dehumidified air subjected to drain separation processing by the drain separator  16  is transmitted to the reheater  18  via the dehumidified air pipe  28 , unlike the air system of the refrigeration air dryer according to the first embodiment. However, the other configurations except for this difference are substantially the same as those of the refrigeration air dryer according to the first embodiment. 
     With the second embodiment, as described above, by providing the three-way adjusting valve  32  within the high-temperature refrigerant pipe  22  that connects the refrigerant compressor  10  and the reheater  18 , and by controlling the flow rate of the high-temperature refrigerant flowing through the reheater  18 , the temperature of the secondary air in the outlet pipe  21  detected by the temperature sensor  40  can be controlled such that it attains the target value set for the temperature controller  42 , as with the first embodiment. It should be noted that, in  FIG. 2  showing the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals. 
     In the first embodiment described above, the bypass pipe  29  is provided branching from the dehumidified air pipe  28  via which the dehumidified air flows into the reheater  18 , and the three-way flow adjusting valve  30  is provided at a junction of these pipes  28  and  29 . Also, instead of this junction, the three-way flow adjusting valve  30  may be arranged at a junction of the bypass pipe  29  and the outlet pipe  21 . 
     On the other hand, in the above-described second embodiment, the refrigerant bypass pipe  31  is provided branching from the high-temperature refrigerant pipe  22  which transmits the refrigerant from the refrigerant compressor  10  to the reheater  18 , and the three-way flow adjusting valve  32  is arranged at the junction thus formed. Also, instead of this junction, the three-way flow adjusting valve  32  may be arranged at the junction of the refrigerant bypass pipe  31  and the intermediate refrigerant pipe  27  arranged on the outlet side of the reheater  18 . 
     It is needless to say that, in such modifications in which the three-way flow adjusting valve is arranged at such a pipe junction, the flow rate of the dehumidified air or the refrigerant flowing through the reheater  18  and the bypass pipe  29  or  31  is controlled according to a control signal received from the temperature controller  42 . 
     The three-way flow adjusting valve arranged at the junction is not restricted to a single valve. Also, a combination of multiple valves may be employed as long as it is capable of controlling the flow rate of the dehumidified air or the refrigerant flowing through the reheater  18  and the bypass pipe  29  or  31  according to a control signal received from the temperature controller  42 . 
     It should be noted that, in the above-described first and second embodiments, the high-temperature refrigerant pipe  22  that connects the refrigerant compressor  10  and the reheater  18  and the low-temperature refrigerant pipe  23  that connects the expansion valve  12  and the cooler  13  are connected so as to communicate with each other via the bypass refrigerant pipe  25  including the volume adjusting valve  17  which provides an adjustable aperture. The bypass refrigerant pipe  25  is provided in order to mix a portion of the high-temperature refrigerant transmitted from the refrigerant compressor  10  into the low-temperature refrigerant in the low-temperature refrigerant pipe  23 , bypassing the reheater  18 , the condenser  11 , and the expansion valve  12 , by instructing the volume adjusting valve  17  to provide a suitable aperture, so as to maintain the temperature of the low-temperature refrigerant such that it does not become equal to or smaller than a predetermined temperature, thereby preventing the moisture included in the moist primary air, which flows from the air inlet  20  to the cooler  13 , from freezing due to excessive reduction in the temperature of the refrigerant flowing from the expansion valve  12  to the cooler  13  via the low-temperature refrigerant pipe  23 , in a case in which the load of the cooler  13  has become small. Accordingly, the bypass refrigerant pipe  25  is a component which provides a function of adjusting the flow rate of the refrigerant flowing through the reheater  18 , the condenser  11 , and the expansion valve  12 . 
     The bypass refrigerant pipe  25  may be connected to the high-temperature refrigerant pipe  22  and the return refrigerant pipe  26  that connects the cooler  13  and the refrigerant compressor  10 . In this case, by reducing the flow of the refrigerant flowing through the cooler  13 , such an arrangement provides the same advantage as with the above-described arrangement, i.e., the advantage of preventing the moisture included in the air cooled by the cooler  13  from freezing. 
     The temperature of the refrigerant or the compressed air at each component in the refrigerant system and the air system in the refrigeration air dryer according to the first and second embodiments as described above are almost the same as those in the conventional refrigeration air dryer shown in  FIG. 3 , except for the temperature of the secondary air at the outlet pipe  21 . However, with each of the above-described embodiments, the temperature of the secondary air in the outlet pipe  21  is controlled, thereby providing stable temperature thereof. Furthermore, the flow rate of the dehumidified air which has been subjected to the drain separation processing and which is to be transmitted to the reheater  18 , or the flow rate of the refrigerant from the refrigerant compressor  10  is controlled such that the temperature of the secondary air flowing through the outlet pipe  21  is maintained at a constant level based upon the temperature thereof. Thus, such an arrangement is capable of controlling the flow rate thereof with relatively high precision by electric means. Thus, such an arrangement employing the reheater  18  is capable of controlling the temperature of the secondary air in the outlet pipe  21  with high precision, as with an arrangement employing an electric heater.