US20100083683A1

US20100083683A1 - Refrigeration air dryer

Info

Publication number: US20100083683A1
Application number: US12/557,750
Authority: US
Inventors: Hideaki Aono
Original assignee: SMC Corp
Current assignee: SMC Corp
Priority date: 2008-10-03
Filing date: 2009-09-11
Publication date: 2010-04-08
Also published as: KR20100038138A; CN101711940A; DE102009043737A1; TW201020482A; JP2010088971A

Abstract

A refrigeration air dryer, which dehumidifies compressed air by cooling the air at a cooler by exchanging heat with a refrigerant, includes a first reheater and a second reheater. The first reheater has a configuration in which warm and moist primary air to be dehumidified is preliminarily cooled by exchanging heat between the primary air and low-temperature dehumidified air dehumidified by the cooler, and is transmitted to the cooler. At the same time, the temperature of the humidified air is raised, and the humidified air is transmitted to the second reheater. The second reheater has a configuration in which the humidified air having a temperature raised by the first reheater is again raised by exchanging heat with the high-temperature refrigerant compressed by the refrigerant compressor, following which the humidified air is externally discharged as secondary air.

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 moisture in the compressed air by cooling the compressed air.
2. Description of the Related Art
In an air compressor system employing solenoid valves, air cylinders, etc. in order to prevent trouble from occurring due to 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.
FIG. 2 shows a circuit of a refrigerant system and an air system in a conventional refrigeration air dryer. The refrigerant system in refrigeration air dryer includes a refrigerant compressor 10, a condenser 11 which condenses a 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, and a cooler 13 which again cools the air, which has been preliminarily cooled by a first reheater 14 included in the air system, using the low-temperature refrigerant transmitted from the expansion valve 12, so as to dehumidifies 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 air system includes: an air inlet 20 which allows primary air, which is warm and moist and which is to be dehumidified, to flow into the air system; the reheater 14 which preliminarily cools the primary air input via the air inlet 20 by heat exchanging with the low-temperature dehumidified air after the dehumidification processing; the cooler 13 which again cools the air thus preliminarily cooled by the reheater 14; and a drain separator 16 which performs drain separation processing for the air thus cooled again by the cooler 13, and transmits the air in a low-temperature dehumidified state to the reheater 14. The air system is configured such that heat exchange is performed at the reheater 14 between the dehumidified air and the primary air, thereby preliminarily cooling the primary air, and thereby raising the temperature of the low-temperature dehumidified air, following which the dehumidified air is externally discharged as secondary air.
Accordingly, the cooler 13 is connected to both the refrigerant system and the air system, and functionally connects the refrigerant system and the air system.
It should be noted that the drain separator 16, which performs the drain separation processing, includes a drain valve 15 which externally discharges resultant water drops.
In the 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. The temperature of the 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 to the reheater 14 via the air inlet 20, is 40° C. (rated temperature). The temperature of the air, which flows through the cooler 13 via the air pipe 24 after the air has been preliminarily cooled at the reheater 14, is approximately 25° C. The temperature of the dehumidified air, which is transmitted to the reheater 14 via the drain separator 16 after the dehumidified air has been again cooled at the cooler 13, is approximately 10° C. The temperature of the secondary air, which is externally discharged via the outlet pipe 21 after the temperature thereof has been raised at the reheater 14, is approximately 30° C.
It should be noted that 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 opening. The bypass refrigerant pipe 25 is provided in order to maintain the temperature of the low-temperature refrigerant such that it does not become equal to or smaller than a predetermined temperature, by mixing a portion of the high-temperature refrigerant flowing through the condenser 11 from the refrigerant compressor 10 into the low-temperature refrigerant in the low-temperature refrigerant pipe 23, by instructing the volume adjusting valve 17 to provide a suitable opening, thereby preventing the moisture included in the moist compressed air, which flows from the reheater 14 to the cooler 13 via the air pipe 24, 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.
The conventional air dryer shown in FIG. 2 has a problem in that the performance of the reheater drops depending upon the conditions of use. Specific description will be made. First, the purposes of employing the reheater 14 are as follows.
1. The compressed air input to the air dryer is preliminarily cooled by the reheater, thereby reducing the load applied to the refrigeration circuit (refrigerant system) (the load of the refrigerant circuit is reduced, thereby reducing energy consumption).
2. The temperature of the compressed air dehumidified by the air dryer is raised using the heat of the primary air input anew from the air inlet, thereby preventing occurrence of dew condensation at the secondary air pipe in the air dryer.
However, in a case in which the primary air has been input at a low temperature (approximately 20° C.) from the air inlet of the air dryer, in some cases, the performance of the reheater drops, leading to a situation in which the temperature of the secondary air, which is to be discharged via the outlet pipe 21, cannot be raised to a temperature at which dew condensation at the outlet pipe 21 can be prevented. This is a major problem of the conventional air dryers. That is to say, in general, the air pipes included in the air dryer are formed of iron (with zinc coating). Accordingly, such an air pipe can decay due to dew condensation water. Furthermore, the dew condensation water can lead to a puddle on the floor etc.. underneath the bottom of the pipe. Heat insulation of these pipes requires hard work and high costs.
An arrangement is conceivable in which the reheater is provided between the high-temperature refrigerant pipe 22, which transmits the refrigerant compressed by the refrigerant compressor 10 to the condenser 11, and the outlet pipe 21 via which the dehumidified air from the drain separator 16 is externally discharged, thereby enabling the temperature of the secondary air discharged from the outlet pipe 21 to be sufficiently raised. However, in this case, the air input via the air inlet 20 (primary air) cannot be preliminarily cooled. Accordingly, all of the thermal load is applied to the refrigeration circuit (refrigerant system), leading to reduction in the air throughput of the air dryer. In a case in which the air throughput is increased to that of the air dryer shown in FIG. 2, there is a need to increase the scale of the refrigeration circuit.
The methods for reducing energy consumption employed in such conventional refrigeration air dryers include: a method in which the capacity of the condenser is increased: a method in which the amount of the refrigerant for the condenser is increased; a method in which the temperature of the refrigerant thereof is lowered: etc. However, such methods leads to disadvantages, examples of which include: an increased scale of the dryer; an increased scale of refrigeration equipment (air conditioner, chiller, cooling tower, etc.), an increased energy consumption of the refrigeration equipment.
In order to reduce the energy consumption of the refrigeration air dryer, let us consider the relation of the input/output of energy among principal components in the conventional refrigeration air dryer shown in FIG. 2. With the heat exchanger duty of the cooler 13 (the heat is captured by the refrigeration circuit) as Q1, with the power consumption of the refrigerant compressor 10 (the work which is used by the refrigerant compressor to compress the refrigerant is converted into heat) as Q2, and with the heat exchanger duty of the condenser 11 (heat is discharged from the refrigeration circuit) as Q3, the following Expression (1) is satisfied.
Q3=Q1+Q2 (1)
In the condenser 11, the refrigerant is condensed by air cooling or water cooling. The lower the temperature of the refrigerant at the outlet of the condenser 11 is, the smaller the electric power consumption Q2 of the refrigerant compressor 10 is. Furthermore, the heat exchanger duty Q1 of the cooler 13 which corresponds to the refrigeration capacity of the refrigeration air dryer is predetermined. In the case of employing an air-cooled condenser, the ambient temperature around the condenser is predetermined, and in the case of employing a water-cooled condenser, the temperature of coolant water is predetermined. Accordingly, the capacity of the condenser 11 is predetermined. Assuming that the electric power consumption of the refrigeration air dryer approximately equals the electric power consumption of the refrigerant compressor 10, in a case in which the electric power consumption Q2 of the refrigerant compressor 10 is reduced by lowering the temperature of the refrigerant at the outlet of the condenser 11, there is only one method in which the heat exchanger duty Q3 of the condenser 11 is reduced.

BRIEF SUMMARY OF INVENTION

Basically, it is a technical purpose of the present invention to provide high dehumidification performance with small electric power consumption by reducing the heat exchanger duty Q3 of the condenser in the refrigeration air dryer, i.e., the heat quantity discharged from the condenser, effectively using energy in the conventional refrigeration air dryer, thereby providing an energy-saving refrigeration air dryer.
More specifically, it is a technical purpose of the present invention to provide a refrigeration air dryer which exhibits stable dehumidification performance even in a case in which the load of the compressed air to be dehumidified is great (in a case in which the temperature, the humidity, or the flow of the compressed air is great, etc.), and which is capable of preventing occurrence of dew condensation in a sure manner at the outlet pipe via which the dehumidified secondary air is externally discharged even in a case in which the temperature of the primary air is low.
In order to solve the problem, a refrigeration air dryer according to the present invention 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 again cools the air, which has been preliminarily cooled by a first reheater 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 an air inlet which allows warm and moist compressed air, which is to be dehumidified, to be input as primary air, the first reheater which preliminarily cools the primary air and raises the temperature of the dehumidified air by exchanging heat between the primary air input via the air inlet and low-temperature dehumidified air transmitted from the cooler, and the cooler which again cools the primary air thus preliminarily cooled by the first reheater so as to dehumidify the primary air, thereby obtaining the low-temperature dehumidified air. Furthermore, the refrigeration air dryer further includes a second reheater which exchange heat between the dehumidified air, of which the temperature has been raised at the first reheater by exchanging heat with the primary air, and the high-temperature refrigerant compressed by the refrigerant compressor. The refrigeration air dryer is configured such that the dehumidified air, of which the temperature has been again raised by heat exchange at the second reheater, is output as secondary air via an outlet pipe.
With the present invention, the second reheater is preferably connected between the refrigerant compressor and the condenser. Furthermore, the refrigerant transmitted from the refrigerant compressor is preferably transmitted to the condenser via the second reheater.
Also, an arrangement may be made in which a high-temperature refrigerant pipe which connects the refrigerant compressor and the second 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 so as to communicate with each other via a bypass refrigerant pipe including a volume adjusting valve which provides an adjustable opening, thereby allowing a portion of the high-temperature refrigerant compressed by the refrigerant compressor to directly flow into 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 refrigeration air dryer preferably includes a drain separator in a flow channel from the cooler up to the first reheater, which is used to perform drain separation processing for the air again cooled by the cooler.
The refrigeration air dryer having the above-described configuration employs a combination of the first reheater which exchanges heat between the primary air input via the air inlet and the low-temperature dehumidified air transmitted via the cooler and the second reheater which exchanges heat between the refrigerant which has become high temperature by compression at the refrigerant compressor and the dehumidified air of which the temperature has been raised by being subjected to the preliminary cooling of the primary air at the first reheater.
Thus, such an arrangement provides high dehumidification performance with small electric power consumption by reducing the heat exchanger duty Q3 of the condenser in the refrigeration air dryer, i.e., the heat quantity discharged from the condenser. For example, this reduces the thermal load to be applied to a cold source such as an air conditioner for an air-cooled condenser, a cooling tower or a chiller for a water-cooled condenser, etc., thereby providing energy-saving operation. Furthermore such an arrangement exhibits stable dehumidification performance even in a case in which the load of the compressed air to be dehumidified is great. In addition, such an arrangement is capable of preventing occurrence of dew condensation in a sure manner at the outlet pipe via which the dehumidified compressed air is externally discharged, even in a case in which the temperature of the compressed air is low.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a circuit diagram which shows a refrigeration circuit and a compressed air circuit of a refrigeration air dryer according to an embodiment of the present invention.

FIG. 2 is a circuit diagram which shows a refrigeration circuit and a compressed air circuit of a conventional refrigeration air dryer.

DETAILED DESCRIPTION OF INVENTION

FIG. 1 shows an embodiment of a refrigeration air dryer according to the present invention. The refrigeration air dryer according to the embodiment includes a refrigerant system and an air system in which several components are the same as those in the conventional refrigeration air dryer shown in FIG. 2. Accordingly, in FIG. 1, the same components as those in FIG. 2 are denoted by the same reference numerals. The major difference between the embodiment and the conventional refrigeration air dryer shown in FIG. 2 is that the embodiment employs a first reheater 18 and a second reheater 19 in order to reduce electric power consumption while maintaining the stable operation of the refrigeration air dryer.
The refrigerant system in the refrigeration air dryer shown in FIG. 1 includes a refrigerant compressor 10, a condenser 11 which condenses a high-temperature refrigerant which has been compressed by the refrigerant compressor 10 and has been transmitted from a high-temperature refrigerant pipe 22 via the second reheater 19, 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 again cools the air, which has been preliminarily cooled by the first reheater 18 in 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 20.
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 which allows warm and moist primary air (rated temperature of 40° C.), which is to be dehumidified, to flow into the air system; the first reheater 18 which preliminarily cools the primary air and raises the temperature of the dehumidified air by exchanging heat between the primary air input via the air inlet 20 and the low-temperature dehumidified air transmitted from the cooler 13; the cooler 13 which again cools, using the refrigerant, the air thus preliminarily cooled by the first reheater 18 so as to condense the moisture; a drain separator 16 which performs drain separation processing for the air thus cooled again by the cooler 13, and transmits the air in a low-temperature (approximately 10° C.) and dehumidified state to the first reheater 18; and the second reheater 19 which again raises the temperature of the humidified air, of which the temperature has been raised by exchanging heat with the warm primary air at the first reheater 18, by exchanging heat with the high-temperature refrigerant. The air system is configured so as to allow the dehumidified air, of which the temperature has been again raised by the second reheater 19, to be externally discharged as the secondary air via the outlet pipe 21.
Accordingly the cooler 13 and the second reheater 19 are connected to both the refrigerant system and the air system, and functionally connect the refrigerant system and the air system.
The drain separator 16, which performs the drain separation processing, includes a drain valve 15 which externally discharges resultant water drops.
The reheater 19 is provided between the refrigerant compressor 10 and the condenser 11, and is a component which again raises the temperature of the dehumidified air by exchanging heat between the high-temperature refrigerant compressed by the refrigerant compressor 10 and the dehumidified air, of which the temperature has been preliminarily raised by the first reheater 18 and which has been transmitted via the air pipe 28, using the difference in temperature therebetween. Accordingly, the second reheater 19 includes the high-temperature refrigerant pipe 22 via which the refrigerant, of which the temperature has been raised by the refrigerant compressor 10, is transmitted to the second reheater, and the outlet pipe 21 via which the dehumidified air having a temperature raised by exchanging heat with this refrigerant is externally discharged.
The temperatures of the refrigerant and the compressed air at each component in the refrigerant system and the air system in the refrigeration air dryer are almost the same as those in the conventional refrigeration air dryer shown in FIG. 2, except that the temperature of the compressed air (secondary air) at the outlet pipe 21 is approximately 45° C. However, there is a great difference in the stability of these temperatures therebetween.
The high-temperature refrigerant pipe 22 that connects the refrigerant compressor 10 and the second reheater 19 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 opening. The bypass refrigerant pipe 25 is provided in order to maintain the temperature of the low-temperature refrigerant such that it does not become equal to or smaller than a predetermined temperature, by mixing a portion of the high-temperature refrigerant from the refrigerant compressor 10 into the low-temperature refrigerant in the low-temperature refrigerant pipe 23, bypassing the second reheater 19, the condenser 11, and the expansion valve 12, by instructing the volume adjusting valve 17 to provide a suitable opening, thereby preventing the moisture included in the moist air, which flows from the first reheater 18 to the cooler 13 via the air pipe 24, 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 adjusts the flow rate of the refrigerant flowing through the second reheater 19, the condenser 11, and the expansion valve 12. By adjusting the flow rate, such an arrangement is capable of preventing a situation in which the temperature of the dehumidified air is excessively raised in the reheating step at the reheater 19.
It should be noted that the bypass refrigerant pipe 25 may be connected to the high-temperature refrigerant pipe 22 and the return refrigerant pipe 26 which connects the cooler 13 and the refrigerant compressor 10. In this case, the flow rate of the refrigerant flowing through the cooler 13 is reduced, thereby providing the same advantage as that provided by the above-described arrangement, i.e., the advantage of preventing the moisture included in the air, which is cooled by the cooler 13, from freezing.
In order to make a comparison with the relation of the input/output of energy among principal components in the conventional refrigeration air dryer shown in FIG. 2, the relation of the input/output of energy is represented with respect to the embodiment shown in FIG. 1 in the same way.
In FIG. 1, using the same Q1 through Q3 as those in FIG. 2, with the heat exchanger duty of the second reheater 19 (heat is discharged from the refrigeration circuit to the compressed air) as Q4, the following Expression (2) is satisfied.
Q3+Q4=Q1+Q2
Q3=Q1+Q2−Q4 (2)
Making a comparison between the Expression (1) and Expression (2), the refrigeration air dryer shown in FIG. 1 provides the heat quantity Q3 which is smaller by the heat quantity Q4 than that in the conventional refrigeration air dryer shown in FIG. 2. This also reduces the heat quantity Q2, thereby reducing energy consumption.
It should be noted that the heat discharged from the refrigeration air dryer is processed by temperature management equipment such as an air conditioner, cooling tower, chiller, etc.
The refrigeration air dryer having such a configuration reduces energy consumption as described above, thereby exhibiting high humidification performance with small electric power consumption. Specifically, such an arrangement is capable of reducing the heat exchanger duty of the condenser (heat quantity discharged from the condenser), thereby reducing the thermal load to be applied to a cold source (air conditioner for an air-cooled condenser, cooling tower or chiller for a water-cooled condenser). Furthermore, even in a case in which the load of the supplied moist compressed air is great, such an arrangement provides stable dehumidification. This improves the capacity of the refrigeration air dryer, thereby providing an increased critical load, which is used by an protection relay circuit to stop the operation of the refrigerator in a case in which the load becomes great. Furthermore, such an arrangement prevents occurrence of dew condensation at the secondary air pipe in the air dryer in a sure manner.

Claims

1. A refrigeration air dryer including:

a refrigerant system including 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 again cools the air, which has been preliminarily cooled by a first reheater 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 including an air inlet which allows warm and moist compressed air, which is to be dehumidified, to be input as primary air, the first reheater which preliminarily cools the primary air and raises the temperature of the dehumidified air by exchanging heat between the primary air input via the air inlet and low-temperature dehumidified air transmitted from the cooler, and the cooler which again cools the primary air thus preliminarily cooled by the first reheater so as to dehumidify the primary air, thereby obtaining the low-temperature dehumidified air,

wherein the refrigeration air dryer further includes a second reheater which exchange heat between the dehumidified air, of which the temperature has been raised at the first reheater by exchanging heat with the primary air, and the high-temperature refrigerant compressed by the refrigerant compressor,

and wherein the dehumidified air, of which the temperature has been again raised by heat exchange at the second reheater, is output as secondary air via an outlet pipe.

2. A refrigeration air dryer according to claim 1, wherein the second reheater is connected between the refrigerant compressor and the condenser,

and wherein the refrigerant transmitted from the refrigerant compressor is transmitted to the condenser via the second reheater.

3. A refrigeration air dryer according to claim 2, wherein a high-temperature refrigerant pipe connecting the refrigerant compressor and the second reheater and a low-temperature refrigerant pipe connecting the decompressing mechanism and the cooler or a return refrigerant pipe connecting the cooler and the refrigerant compressor are connected so as to communicate with each other via a bypass refrigerant pipe including a volume adjusting valve which provides an adjustable opening, thereby allowing a portion of the high-temperature refrigerant compressed by the refrigerant compressor to directly flow into the low-temperature refrigerant pipe or the return refrigerant pipe in a case in which the load of the cooler has become small.

4. A refrigeration air dryer according to any one of claim 1 to claim 3, further including a drain separator in a flow channel from the cooler up to the first reheater, which is used to perform drain separation processing for the air again cooled by the cooler.