JP2003117330A - Apparatus for separating gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that the nitrogen gas producing efficiency of conventional nitrogen gas generating apparatus and the concentration of the produced nitrogen gas are obliged to be lowered because that the amount of compressed air to be supplied to an adsorption tank must be reduced when the moisture in a drier of a compressor is discharged in the condition that the compressor and the adsorption tank are communicated with each other and the compressed air is supplied to the adsorption tank. SOLUTION: The nitrogen gas producing efficiency is prevented from being lowered by discharging the moisture accumulated in the drier 4 by opening a drain discharging valve 4a of the drier 4 during the step to equalize the pressure of the compressor 3 to those of the adsorption tanks 1, 2 in the condition that the compressor 3 is blocked from the tanks 1, 2 by closing air supplying valves 8, 9 so that the pressure of each of the tanks 1, 2 is prevented from being lowered during the adsorption and withdrawal steps to produce nitrogen gas.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas separation device, and more particularly to a PSA (Pressure Swing Absorption) gas separation device, for example, a gas separation device suitable for use as a nitrogen generator or an oxygen generator.

[0002]

2. Description of the Related Art Generally, a PSA gas separation apparatus is one in which air is separated into nitrogen gas and oxygen gas using an adsorbent composed of molecular sieving carbon or zeolite, and one of them is taken out as a product gas for use. Is.

For example, in a PSA type nitrogen generator having a pair of adsorption tanks for producing nitrogen gas as a product gas, (a) Adsorption step: compression in a adsorption tank filled with an adsorbent by a compressor A step of introducing nitrogen and refluxing the nitrogen gas remaining in the product tank to the adsorption tank to pressurize the inside of the adsorption tank to adsorb oxygen molecules to the adsorbent using pressure, (b) Extraction step: Adsorption step From the compressor, continue to introduce compressed air from the compressor to the adsorption tank, and at the same time, take out the nitrogen gas separated and produced by the adsorbent from the adsorption tank, (c) pressure equalizing step: remain in the adsorption tank after completion of the taking step The residual gas with a high nitrogen concentration is supplied to the other adsorption tanks before the adsorption step to equalize the pressure between the adsorption tanks and improve the adsorption efficiency in the next adsorption step to obtain a higher purity nitrogen gas. The process for generating ) Regeneration step: step of regenerating the adsorbent by adsorption vessel after completion as equalization repressurization step to desorb the oxygen molecules adsorbed on the adsorbent under reduced pressure in the open air or vacuum pumps, but are sequentially performed.

Each of these steps (a) to (d) is repeated for each adsorption tank, and each device is controlled so that the steps in each adsorption tank are executed in cooperation with each other. That is, in a gas separation device having a pair of adsorption tanks, the pressure equalization step is performed after the adsorption step and the extraction step are completed in one adsorption tank and the regeneration step is completed in the other adsorption tank.

[0005]

However, in the gas separation device, nitrogen gas is separated and produced by repeating the steps (a) to (d), but an air supply for supplying compressed air to the adsorption tank is used. Drive of units (compressor, air tank, dryer) and control of water discharge of the dryer, and control of each process of the gas separation unit (adsorption tank, product tank, etc.) are performed independently of each other.

That is, the compressed air generated by the compressor is accumulated in the air tank, and the compressed air is supplied to the gas separation unit from the inside of the air tank through the dryer for removing the moisture of the compressed air during the adsorption process. It

At this time, the compressor performs a load operation (normal operation) when the pressure in the air tank is less than a predetermined pressure, and an unload operation (in no-load operation when the pressure in the air tank reaches a predetermined pressure). ). During the unloading operation, the drive motor of the compressor is still driven, but the air supply valve is held open and compressed air is not generated.

Further, in order to discharge the water separated from the compressed air, the dryer uses a control timer or the like, and a gas separation unit is used when a certain amount of water has accumulated in the air tank and when a certain amount of water is accumulated in the air tank. The water was exhausted under the control independent from.

Therefore, as in the case of supplying compressed air from the air supply unit to the gas separation unit in the adsorption process and the extraction process, the moisture in the dryer is discharged while the dryer and the gas separation unit are in communication with each other. In this case, the compressed air required to generate the nitrogen gas supplied to the adsorption tank is reduced, and the adsorption pressure in the adsorption tank is reduced.
There is a problem that the concentration of the generated nitrogen gas decreases.

Further, when the compressor and the pipe of the adsorption tank are shut off by a solenoid valve as in the pressure equalizing step, the pressure in the air tank rises, and when the pressure exceeds a predetermined pressure, the compressor switches to unloading operation. Will end up. In this case, there is a problem that the compressor is not loaded until the pressure becomes lower than a predetermined pressure, the ability to supply compressed air to the gas separation device decreases, and the nitrogen gas generation efficiency decreases.

Therefore, an object of the present invention is to provide a gas separation device that solves the above problems.

[0012]

Means for Solving the Problems In order to solve the above problems, the present invention has the following features. Claim 1
In the invention, an adsorption step of supplying compressed air, which is compressed by a compressor and dewatered by a dehumidifying means, to an adsorption tank filled with an adsorbing means and pressurizes the inside of the adsorption tank to generate a product gas, , A step of taking out the product gas generated in the adsorption tank from the adsorption tank and a pressure equalizing step of equalizing the pressure in the adsorption tank with the pressure in another adsorption tank are sequentially performed. In the gas separation device, when the shut-off means provided between the compressor and the adsorption tank is shut off, the drain discharge valve provided in the dehumidifying means is opened and the compressed air is dehumidified by the dehumidifying means. The water accumulated in the dehumidifying means is discharged.

Further, in the second aspect of the invention, in the gas separation apparatus of the first aspect, during the pressure equalizing step, the drain discharge valve provided in the dehumidifying means is opened and compressed by the compressor. It is characterized in that the water accumulated in the dehumidifying means generated when the air is dehumidified by the dehumidifying means is discharged.

Further, in the invention of claim 3, the compressed air compressed by the compressor having the unloading operation function and dewatered by the dehumidifying means is supplied to the adsorbing tank filled with the adsorbing means to adsorb the compressed air. An adsorption step of raising the pressure in the tank to generate a product gas, an extraction step of taking out the product gas generated in the adsorption tank from the adsorption tank, and a pressure in the adsorption tank equal to that in another adsorption tank. In a gas separation device configured to sequentially perform a pressure equalizing step of pressure-izing, a pressure gauge is provided between the compressor and the adsorption tank, and the pressure measured by the pressure gauge reaches a set predetermined pressure. At this time, the drain discharge valve provided in the dehumidifying means is opened to discharge the water accumulated in the dehumidifying means generated when the compressed air compressed by the compressor is dehumidified by the dehumidifying means. It is what

Further, the invention of claim 4 is the gas separating apparatus according to claim 3, wherein in the gas separating apparatus, the pressure in the air tank of the compressor is switched to the unloading operation of the compressor. When the pressure set in the air tank reaches a preset pressure lower than the preset pressure, the drain discharge valve provided in the dehumidifying means is opened when the pressure in the air tank reaches the set pressure for moisture discharge, and the compression compressed by the compressor is performed. It is characterized in that the water accumulated in the dehumidifying means generated when the air is dehumidified by the dehumidifying means is discharged.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing an overall configuration of a PSA type nitrogen generator which is a first embodiment of the present invention.

In FIG. 1, reference numerals 1 and 2 denote first and second adsorption tanks, respectively.
The adsorption tanks 1 and 2 are filled with molecular sieving carbons 1A and 2A as adsorption means, respectively.

Reference numeral 3 denotes a compressor serving as a compressed air supply source. The compressor 3 produces compressed air, and the compressed air is stored in a tank 3a, and a refrigerating dryer 4, a pipe 6, which is a dehumidifying means.
The air is supplied alternately to the adsorption tanks 1 and 2 via the air supply valves 7. Therefore, in the middle of the pipes 6 and 7, the air supply valves 8 and 9 as shut-off means composed of electromagnetic valves, respectively. Is provided.

Further, the refrigeration dryer 4 is provided with a drain discharge valve 4a for discharging the water accumulated in the refrigeration dryer 4.

Reference numerals 10 and 11 denote pipes for discharging gas from the adsorption tanks 1 and 2 when desorbing oxygen molecules from the adsorbent, and are connected to a silencer 12 for reducing exhaust noise. In the middle of the pipes 10 and 11, the adsorption tank 1,
Exhaust gas exhaust valves 13 and 14 that are electromagnetic valves that alternately discharge the desorbed exhaust gas in 2 every half cycle (from one adsorption tank to the pressure equalization step to the pressure equalization step) are provided.

Numerals 15 and 16 are extraction pipes for extracting nitrogen gas as a product gas from the adsorption tanks 1 and 2, and 17 is an extraction pipe connected to the extraction pipes 15 and 16, and the extraction pipe 1
In the middle of 5 and 16, extraction valves 18 and 19 which are electromagnetic valves that are alternately opened under the control of a control circuit 100 described later for half cycles are provided. The take-out pipe 17 is connected to the product tank 20.

Reference numeral 21 is a pipe for connecting the adsorption tanks 1 and 2 with each other.
Reference numeral 2 is a pressure equalizing valve made up of a solenoid valve provided in the middle of the pipe 21, and the pressure equalizing valve 22 is opened for a predetermined few seconds just before the end of the half cycle by the adsorption tanks 1 and 2, and the adsorption tanks 1 and 2 are To equalize pressure (equalizing process).

Reference numeral 23 is a product gas extraction pipe connected to the product tank 20, and a product gas extraction valve 24 composed of an electromagnetic valve is provided in the middle thereof.

Reference numeral 25 is a densitometer, which is connected to a branch pipe 26 which branches from the product gas extraction pipe 23. The densitometer 25 measures the nitrogen gas concentration of the gas taken out from the product tank 20 through the product gas taking-out pipe 23.

Reference numeral 50 denotes a branch pipe for discharging a product gas. The branch pipe 50 is opened for a predetermined time only when the apparatus itself is started based on a valve opening signal from a control means 100 described later, and then closed. A product gas discharge valve 51 formed of a solenoid valve, and a variable throttle that keeps the discharge amount of nitrogen gas in the product tank 20 discharged from the branch pipe 50 outside by opening the product gas discharge valve 51 constant. 52 is provided.

Next, the control circuit 100 will be described.
The control circuit 100 is supplied with a valve control circuit 101 for controlling the opening and closing of each solenoid valve to generate nitrogen gas, and an oxygen gas concentration measurement signal output from the concentration meter 25 described above. The product tank 20 from the value of the measurement signal
A nitrogen gas concentration detection circuit 104 that detects the nitrogen gas concentration in the inside and outputs the nitrogen gas concentration to the concentration abnormality detection circuit 102 and the performance deterioration determination circuit 103 as abnormality detection means.
It consists of and.

Next, the operation of the valve control circuit 101 of the nitrogen generator constructed as described above will be explained. First, the basic operation of the nitrogen generator is shown in FIGS.
Will be explained. In FIG. 3, (B) shows the state of the adsorption tank 1, and (C) shows the state of the adsorption tank 2. here,
When the nitrogen generator is activated, each solenoid valve operates under the control of the valve control circuit 101 of the control circuit 100, and nitrogen gas (product gas) is generated.

First, as shown in FIGS. 2 and 3, first,
In the second adsorption tank 2, the operations of the adsorption step, the extraction step, and the pressure equalizing step are performed, and in the first adsorption tank 1, the regeneration step is performed between and, and at that time, A pressure equalization process is performed.

In the adsorption process of the second adsorption tank 2 in FIG. 2, the air supply valve 9 and the extraction valve 19 on the second adsorption tank 2 side.
Open. As a result, the compressed air as the raw material gas is supplied from the compressor 3 to the second adsorption tank 2. Further, the nitrogen gas in the product tank 20 flows backward through the extraction pipes 16 and 17, and is returned from the upper portion (downstream side) into the adsorption tank 2. As a result, the second adsorption tank 2 is in a pressurized state due to the compressed air from the compressor 3 and the nitrogen gas in the product tank 20 flowing in from above and below, and oxygen is adsorbed by the molecular sieve carbon 2A. It

On the other hand, in the first adsorption tank 1, the exhaust gas discharge valve 13 is opened to reduce the pressure, and the adsorbed oxygen is desorbed and discharged.

Next, in the process of taking out the second adsorption tank 2 in FIG. 2, the air supply valve 9 and the take-out valve 19 on the side of the second adsorption tank 2 are kept open after the adsorption process. Since the compressed air is continuously supplied to the second adsorption tank 2, the pressure in the second adsorption tank 2 becomes higher than the pressure in the product tank 20, and the nitrogen gas in the second adsorption tank 2 is taken out. Become. At this time, the first adsorption tank 1 is still in the decompression state of the regeneration process in which the exhaust gas discharge valve 13 is opened, and is ended by closing the pressure equalizing valve 22.

Next, the pressure equalizing step in FIG.
2 is opened and the air supply valve 9, the extraction valve 19, and the exhaust gas discharge valve 13 are closed, and the space between the adsorption tanks 1 and 2 and the compressor 3 and between the adsorption tanks 1 and 2 and the product tank 20 are changed. The space between them is cut off, and the adsorption tanks 1 and 2 are communicated with each other. As a result, the nitrogen gas remaining in the second adsorption tank 2 is recovered in the first adsorption tank 1, and the pressure in each of the adsorption tanks 1 and 2 becomes equal. The pressure equalizing step is usually 1 to 5 seconds.

As a result, the first half of the one cycle shown in FIG. 3A is completed, and the air supply valve 8, the extraction valve 18, and the exhaust gas discharge valve 14 are opened. By the above, as shown in FIGS. 3 (B) and 3 (C), the cycle is switched to the latter half cycle shown by to in FIG. 2 and these steps are repeated.

In the latter half of the cycle, the first
In the adsorption tank 1, the adsorption step, the extraction step, and the pressure equalization step are performed, in the second adsorption tank 2, the regeneration step is performed between and, and in the adsorption tank 1, the pressure equalization step of the adsorption tanks 1 and 2.

As described above, the valve control circuit 101 repeats the above cycle to convert the raw material gas supplied from the compressor 3 into nitrogen gas and other gas (oxygen gas) in the adsorption tanks 1 and 2. The nitrogen gas separated and separated in the adsorption tanks 1 and 2 is stored in the product tank 20. Along with this, the nitrogen gas in the product tank 20 is returned to the adsorption tanks 1 and 2, so that the gases other than the nitrogen gas contained in the nitrogen gas are removed in the adsorption tanks 1 and 2 and the product is again produced. By being supplied into the tank 20, the product tank 20
The nitrogen gas concentration itself can also be made higher.

The valve control circuit 101 also controls the opening and closing of the product gas extraction valve 24 and the product gas discharge valve 51, in addition to the control of the above-mentioned electromagnetic valves. That is, at the time of starting the nitrogen generator, the valve control circuit 101 does not output the valve opening signal to the product gas extraction valve 24 in parallel with the control of the above-mentioned electromagnetic valves for performing the above-mentioned basic operation. Gas extraction valve 24
While the valve is closed, a valve opening signal is output to the product gas discharge valve 51, and the concentration meter 25 measures the nitrogen concentration of the product gas. Then, the product gas discharge valve 51 is opened to supply the nitrogen gas having a low nitrogen concentration in the product tank 20 to the branch pipe 5
The starting operation control in the starting operation state in which the state of discharging from 0 is continued until the nitrogen concentration of the product gas reaches a predetermined concentration after the present apparatus is started is performed.

After the start-up operation control is completed (after the lapse of the predetermined time), the product gas discharge valve 51 is closed and the product gas extraction valve is maintained while the basic operation of the valve control circuit 101 is maintained. A normal operation state in which a valve opening signal is output to 24 to open the product gas extraction valve 24 to supply the nitrogen gas in the product tank 20 to the supply target device (not shown) through the product gas extraction pipe 23. The normal operation control is performed.

In the normal operation control after the start-up operation control in this embodiment, for example, the supply of electricity to the nitrogen generating device itself is cut off, or an operation switch (not shown) provided in the device itself. It is performed until OFF is operated.

Next, the water discharge control of the refrigerating dryer 4 which is the point of the present invention will be described.

During the pressure equalizing step described above, the control circuit 100
Sends a signal to the valve control circuit 101 to open the pressure equalizing valve 22 and to close the extraction valve 18 and the air supply valve 8 or the extraction valve 19 and the air supply valve 9, and at the same time, the refrigeration dryer 4
A valve opening signal for discharging water is sent to the drain discharge valve 4a. The drain discharge valve 4a discharges the water accumulated in the refrigeration dryer 4 discharged from the compressed air supplied from the compressor during the pressure equalizing step, and at the same time when the pressure equalizing step is completed, the water of the refrigeration dryer 4 is discharged. Also ends.

During the pressure equalizing step, the air between the refrigerating dryer and the adsorption tanks 1 and 2 is shut off by the air supply valves 8 and 9, so that even if the moisture in the refrigerating dryer 4 is discharged, the adsorption tank is removed. Since the pressure in 1 and 2 does not decrease and the pressure in the entire gas separation device does not decrease, the nitrogen gas can be efficiently supplied even after the pressure equalization process is completed, and the nitrogen gas generation efficiency is decreased. There is nothing to do.

Further, since the compressor 3 and the adsorption tanks 1 and 2 are shut off during the pressure equalizing step, conventionally, as shown in FIG. Tank 3
Although the pressure in a rises and exceeds the predetermined pressure in the tank 3a, it switches to unloading operation, but by discharging water during each pressure equalizing step for about 1 to 5 seconds, the compressor 3 Since there is only a slight increase in the pressure from the chiller to the refrigeration dryer 4, there is no need to switch to unload operation, and the decrease in the ability to supply compressed air to the gas separation device due to unload operation and switching to load operation. It is possible to prevent a decrease in product gas generation efficiency without taking time.

Next, a second embodiment will be described with reference to FIG. In the second embodiment, a pressure gauge 6 is provided between the compressor 3 and the air supply valve 8 or 9 of the first embodiment.
0 is provided. When the pressure measured by the pressure gauge 60 becomes higher than a predetermined pressure, the water accumulated in the refrigerating dryer 4 is discharged, and the pressure becomes equal to or lower than the predetermined pressure. Stop draining water. As a result, before switching to the unload operation, an increase in the pressure between the compressor 3 and the refrigeration dryer 4 is suppressed, and the ability to supply compressed air in the gas separation device due to the unload operation decreases and It does not take time to switch to operation.

Here, if the predetermined pressure is set higher than the pressure for switching to the unloading operation, the adsorption tank 1,
The compressor 3 which supplies compressed air to 2 switches to the unloading operation before the pressure in the air tank 3a exceeds the predetermined pressure. Therefore, the predetermined pressure (moisture discharge pressure) that determines the timing of discharging the water accumulated in the refrigeration dryer 4 is set lower than the pressure for switching to this unloading operation, and the pressure in the air tank 3a is The water is discharged when the set predetermined pressure is reached. This suppresses an increase in pressure between the compressor 3 and the refrigeration dryer 4 before switching to the unload operation, reduces the pressure in the gas separation device due to the unload operation, and switches to the load operation. It doesn't take much time.

In this embodiment, the drain discharge valve 4a
Although the timing for discharging the moisture from the dryer 4 by opening the valve is described in the pressure equalizing step in which the air supply valves 8 and 9 as the shutoff means are shut off, the present invention is not limited to this. When the air supply valves 8 and 9 are opened before the completion of the take-out step as shown by the dotted lines (D) and (E) in FIG. During this time, the drain discharge valve 4a may be opened during the extraction process to discharge the moisture in the dryer 4.

In the present embodiment, the drainage of water only from the refrigeration air dryer 4 has been described, but the moisture stored in the tank 3a may be drained at the same timing.

Further, in the present embodiment, the description has been made by using the refrigerating dryer as the dryer, but the present invention is not limited to this.
A dryer using a desiccant or the like may be used as long as it can dehumidify the water content of the compressed air.

In the first and second embodiments, the PSA type nitrogen generator having a pair of adsorption tanks has been described, but the invention is not limited to this, and the compressor and the adsorption tank are shut off from each other. It may have a single adsorption tank or two or more adsorption tanks as long as it has a blocking means.

Further, in the present embodiment, the starting operation control is explained by measuring the product gas concentration by the densitometer 25 and controlling the product gas discharge valve 51 according to the concentration.
The present invention is not limited to this, and the product gas discharge valve 51 may be controlled by measuring the time after the gas separation device is activated and elapse of a predetermined time.

[0050]

As described above, the first aspect of the present invention is
Since the air between the compressor and the adsorption tank is cut off, the water accumulated in the dehumidifying means is discharged when it is not necessary to supply compressed air to the adsorption tank, so the degree of pressure rise in the adsorption tank is not reduced. It is possible to prevent the production efficiency of the product gas generated in the adsorption tank from decreasing.

According to a second aspect of the present invention, dehumidification of water accumulated in the dehumidifying means during the pressure equalizing step which does not require the supply of compressed air to the adsorption tank in which the compressor and the adsorption tank are shut off from each other. Since this is performed, it is possible to prevent the production efficiency of the product gas generated in the adsorption tank from decreasing without reducing the degree of pressure increase in the adsorption tank.

Further, according to claims 3 and 4 of the present invention, since the water accumulated in the dehumidifying means is dehumidified when the pressure in the air tank reaches a predetermined pressure, the pressure in the tank is prevented from rising rapidly. Therefore, it is possible to prevent the compressor from being switched to the unloading operation, and prevent the product gas generation efficiency from decreasing.

[Brief description of drawings]

FIG. 1 is a diagram showing an overall configuration of a gas separation device according to first and third embodiments of the present invention.

FIG. 2 is a diagram showing a situation of supply and exhaust in each step (basic operation) of the adsorption tanks 1 and 2 of the gas separation device.

FIG. 3 is a diagram showing a time chart of each step (basic operation) of the adsorption tanks 1 and 2 of the gas separation device.

FIG. 4 is a diagram showing a pressure change in an air tank of the gas separator according to the present invention and the related art.

FIG. 5 is a diagram showing an overall configuration of a gas separation device according to a second embodiment of the present invention.

[Explanation of symbols]

1, 2 adsorption tank 3 compressor 3a tank 4 freezing dryer 4a drain discharge valve 8,9 Air supply valve 18, 19 Extraction valve 20 product tanks 22 Pressure equalizing valve 100 control circuit 101 valve control circuit

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Manabu Manabu             1116 Kozono, Ayase-shi, Kanagawa Tokiko stock             Company Sagami Factory F term (reference) 4D012 CA05 CA06 CB16 CD07 CG01                       CH10 CJ01 CJ10                 4D052 AA01 BA04 FA09 GA01 GB08                 4G042 BA15 BB02

Claims (4)

[Claims] 1. An adsorption step of supplying compressed air, which has been compressed by a compressor and whose moisture has been removed by a dehumidifying means, to an adsorption tank filled with an adsorbing means to raise the pressure in the adsorption tank to generate a product gas. And a step of taking out the product gas generated in the adsorption tank from the adsorption tank and a pressure equalizing step of equalizing the pressure in the adsorption tank with the pressure in another adsorption tank. In the gas separation device, when the shut-off means provided between the compressor and the adsorption tank is shut off, the drain discharge valve provided in the dehumidifying means is opened to dehumidify the compressed air by the dehumidifying means. A gas separation device, characterized in that the generated water accumulated in the dehumidifying means is discharged. 2. The gas separation device according to claim 1,
The dehumidifying means generated when the drain discharge valve provided in the dehumidifying means is opened and the compressed air compressed by the compressor is dehumidified by the dehumidifying means during the pressure equalizing step in which the shutoff means shuts off. A gas separation device, which discharges the water accumulated inside. 3. Compressed air compressed by a compressor having an unloading operation function and having moisture removed by dehumidifying means,
An adsorption step of supplying the adsorption gas to the adsorption tank filled with the adsorption means and increasing the pressure in the adsorption tank to generate a product gas; a step of taking out the product gas generated in the adsorption tank from the adsorption tank; In a gas separation device configured to sequentially perform a pressure equalizing step for equalizing the internal pressure with the pressure in another adsorption tank, a pressure gauge is provided between the compressor and the adsorption tank, and the pressure is measured by the pressure gauge. When the set pressure reaches a set predetermined pressure, the drain discharge valve provided in the dehumidifying means is opened, and the dehumidification generated when the compressed air compressed by the compressor is dehumidified by the dehumidifying means. A gas separation device, characterized in that water accumulated in the means is discharged. 4. The gas separation device according to claim 3,
The moisture discharge pressure for opening the drain discharge valve is set to a pressure lower than a predetermined pressure for unloading operation for switching to the unloading operation of the compressor, and when the pressure of the pressure gauge reaches the moisture discharge pressure, The drain discharge valve provided in the dehumidifying means is opened to discharge the water accumulated in the dehumidifying means generated when the compressed air compressed by the compressor is dehumidified by the dehumidifying means. Gas separation device.