WO2025181936A1 - Oil-free screw compressor - Google Patents

Abstract

The present invention comprises: a low-pressure stage compressor body (1); a high-pressure stage compressor body (2) that compresses a gas compressed by the low-pressure stage compressor body (1); intermediate piping (3) connecting the discharge side of the low-pressure stage compressor body (1) and the intake side of the high-pressure stage compressor body (2); a sensor (4) that detects the dew point or the humidity of gas in the intermediate piping (3); supply piping (5) that communicates with the intermediate piping (3) and supplies a drying gas into the intermediate piping (3); and a valve (6) that is provided to the supply piping (5) and in which the opening degree is adjusted in accordance with the detection value of the sensor (4) while compressor operation is stopped.

Description

Oil-free screw compressor

The present invention relates to an oil-free screw compressor.

If gas containing moisture remains inside the compressor when it is not in operation, condensation can occur as the temperature of the gas drops. Condensation is less of a problem in oil-lubricated compressors, where oil is mixed into the compressed gas, but it can cause rust in oil-free compressors, where oil is not mixed into the compressed gas. If the rust peels off and seeps into the compressor body when operation resumes, it can lead to reduced compressor performance or failure.

As a technology for suppressing condensation during shutdowns, Patent Document 1 discloses technology related to a multi-stage compressor comprising a low-pressure stage compressor main body and a high-pressure stage compressor main body. Specifically, when the compressor is shut down, the multi-stage compressor of Patent Document 1 attempts to suppress condensation within the piping by supplying dry gas to the piping connecting the discharge side of the low-pressure stage compressor main body and the suction side of the high-pressure stage compressor main body based on the temperature detected by a dew point temperature sensor installed in the discharge side piping of the high-pressure stage compressor main body.

Japanese Patent Application Publication No. 5-141350

Oil-free compressors include multi-stage screw compressors with multiple compressor bodies (compression stages). In these compressors, each compressor body generates compressed gas by rotating at high speed, with the teeth of a pair of screw rotors, consisting of a male and female rotor, meshing with each other while maintaining a specified gap. Furthermore, in these compressors, to prevent gas leakage during compression, the gaps within the compressor, including the gap mentioned above, are kept extremely small (for example, a few tens of microns), and these gaps are smaller than those in oil-lubricated screw compressors, where oil provides a sealing effect.

For this type of oil-free screw compressor, as in Patent Document 1, a dew point temperature sensor is installed in the piping connected to the discharge side of the high-pressure stage compressor main body (referred to as the discharge piping), and dry gas is supplied to the piping connecting the discharge side of the low-pressure stage compressor main body and the suction side of the high-pressure stage compressor main body (referred to as the intermediate piping) according to the detected temperature.

First, as mentioned above, because the gaps within an oil-free screw compressor are extremely small, it is difficult for compressed gas to move between the intermediate pipe and the discharge pipe during shutdowns when the rotation of the male and female rotors of the high-pressure compressor body is halted. In other words, the dew-point temperatures (temperature and humidity) of the gas in the intermediate pipe and the gas in the discharge pipe are maintained in a state in which they are prone to diverge. Furthermore, in Patent Document 1, the blow-off valve is opened to the atmosphere during compressor shutdowns, which makes it easy for the humidity of the gas in the discharge pipe to approach that of the atmosphere. As a result, the divergence between the dew-point temperatures of the gas in the intermediate pipe and the gas in the discharge pipe can become even greater. Therefore, if the timing of supplying dry gas to the intermediate pipe is determined based on the dew-point temperature of the gas in the discharge pipe, as in Patent Document 1, there is a risk that the supply of dry gas will be stopped before the humidity of the gas in the intermediate pipe has sufficiently decreased. In other words, even if the configuration of Patent Document 1 is applied to a screw compressor, the expected effects will not be achieved, and condensation may occur during shutdowns.

The present invention was made in consideration of the above circumstances, and its purpose is to provide an oil-free screw compressor that can suppress the occurrence of condensation in the intermediate piping connecting two compressor bodies.

The present application includes multiple means for solving the above problem, but one example includes a low-pressure stage compressor main body, a high-pressure stage compressor main body that compresses gas compressed by the low-pressure stage compressor main body, an intermediate pipe that connects the discharge side of the low-pressure stage compressor main body to the suction side of the high-pressure stage compressor main body, a sensor that detects the dew point or humidity of gas in the intermediate pipe, a supply pipe that communicates with the intermediate pipe and supplies dry gas into the intermediate pipe, and a valve that is provided in the supply pipe and whose opening is adjusted in accordance with the value detected by the sensor when the compressor is not operating.

The present invention makes it possible to suppress the occurrence of condensation in the intermediate pipe connecting two compressor bodies in a multi-stage oil-free screw compressor. Issues, configurations, and effects other than those described above will become clear from the description of the following embodiments.

1 is a schematic diagram showing a configuration of an oil-free screw compressor according to a first embodiment of the present invention. FIG. FIG. 4 is a schematic diagram showing the configuration of an oil-free screw compressor according to a second embodiment of the present invention. FIG. 3 is a plan cross-sectional view of a compressor body that can be used as the low-pressure stage compressor body of FIG. 2 . 4 is a cross-sectional view taken along the line IV-IV in FIG. 3. FIG. 10 is a schematic diagram showing the configuration of an oil-free screw compressor according to a third embodiment of the present invention.

The following describes the configuration and operation of oil-free screw compressors according to first to third embodiments of the present invention, using the drawings. Note that the same symbols refer to the same parts in each drawing. Also, "upstream" and "downstream" refer to the upstream and downstream directions in the flow direction of compressed gas.

(First embodiment)
FIG. 1 is a schematic diagram showing the configuration of an oil-free screw compressor 100 according to a first embodiment of the present invention.

The oil-free screw compressor (hereinafter sometimes simply referred to as the compressor) 100 according to this embodiment is a device that compresses gas (e.g., air) without mixing lubricating oil into it. As shown in FIG. 1, the compressor 100 comprises a low-pressure stage compressor main body 1, a high-pressure stage compressor main body 2 that compresses the gas compressed by the low-pressure stage compressor main body 1, an intermediate pipe 3 that connects the discharge side of the low-pressure stage compressor main body 1 to the suction side of the high-pressure stage compressor main body, a sensor 4 that detects the dew point or humidity of the gas in the intermediate pipe 3, a supply pipe 5 that is connected to the intermediate pipe 3 and supplies dry gas into the intermediate pipe 3, and a valve 6 provided on the supply pipe 5.

The low-pressure stage compressor body 1 and the high-pressure stage compressor body 2 are capacity-controlled screw compressor bodies that generate compressed gas by meshing the teeth of a pair of screw rotors while maintaining a predetermined gap and rotating at high speed. The low-pressure stage compressor body 1 and the high-pressure stage compressor body 2 may be the same compressor body, or different compressor bodies may be used. Furthermore, this embodiment shows an embodiment of a two-stage compressor that has two compressor bodies, the low-pressure stage compressor body 1 and the high-pressure stage compressor body 2. However, this is not limited to this, and the compressor body may also be used in a multi-stage compressor in which the compressor bodies are connected in series.

Gas compressed in the low-pressure stage compressor main body 1 flows through the intermediate pipe 3, and this gas is introduced into the suction side of the high-pressure stage compressor main body 2.

The sensor 4 is preferably attached to the intermediate pipe 3.

The supply pipe 5 is a pipe for supplying dry gas from a dry gas supply source into the intermediate pipe 3. The supply pipe 5 is provided with a valve 6 for adjusting the amount of dry gas supplied to the intermediate pipe 3. The supply pipe 5 is preferably connected to the intermediate pipe 3 at a location downstream of the sensor 4 in the flow direction of the compressed gas on the intermediate pipe 3. Furthermore, it is preferable that the humidity of the dry gas be lower than that of the gas in the intermediate pipe 3 at the start of the shutdown of the compressor 100, and it is even more preferable that the pressure of the dry gas be equal to or higher than atmospheric pressure.

The opening of valve 6 is adjusted according to the detection value of sensor 4 when compressor 100 is out of operation with low-pressure stage compressor main body 1 and high-pressure stage compressor main body 2 stopped. For example, when the detection value of sensor 4 approaches a value indicating the occurrence of condensation in intermediate pipe 3 (the dew point temperature if sensor 4 is a dew point sensor, or 100% if it is a humidity sensor), valve 6 opens and dry gas is supplied to intermediate pipe 3 via supply pipe 5. On the other hand, when the detection value of sensor 4 moves away from that value, valve 6 is kept closed.

If the sensor 4 is a humidity sensor, it is preferable that the valve 6 be opened when the detected value of the humidity sensor 4 is equal to or greater than a first threshold value (e.g., 80%) and closed when the detected value of the humidity sensor 4 is less than a second threshold value (e.g., 50%) that is smaller than the first threshold value while the compressor 100 is out of operation. Alternatively, the valve 6 may be configured to be opened when the detected value of the humidity sensor 4 is equal to or greater than the first threshold value and closed when the detected value of the humidity sensor 4 is less than the first threshold value while the compressor 100 is out of operation.

In order to adjust the opening degree in accordance with the detection value of sensor 4, it is preferable that valve 6 be a solenoid valve whose opening degree can be adjusted in accordance with an electrical command output from a control device (described below).

A discharge pipe 10 is connected to the discharge side of the high-pressure stage compressor main body 2, and the compressed gas discharged from the high-pressure stage compressor main body 2 is supplied to a tank (not shown) or a user, etc., via the discharge pipe 10.

[effect]
The oil-free screw compressor 100 of the above-described embodiment includes a low-pressure stage compressor main body 1, a high-pressure stage compressor main body 2 that compresses gas compressed by the low-pressure stage compressor main body 1, an intermediate pipe 3 that connects the discharge side of the low-pressure stage compressor main body 1 and the suction side of the high-pressure stage compressor main body 2, a sensor 4 that detects the dew point or humidity of the gas in the intermediate pipe 3, a supply pipe 5 that communicates with the intermediate pipe 3 and supplies dry gas into the intermediate pipe 3, and a valve 6 that is provided in the supply pipe 5 and has an opening degree adjusted in accordance with the detection value of the sensor 4 when the compressor is out of operation.

With the compressor 100 configured in this manner, the detection value of the sensor 4 is monitored while the compressor 100 is out of operation, and if there is no risk of condensation forming in the intermediate pipe 3, the valve 6 is kept closed. However, if there is a risk of condensation forming in the intermediate pipe 3, the valve 6 is opened to supply dry gas from the supply pipe 5 to the intermediate pipe 3. This makes it possible to prevent condensation from forming in the intermediate pipe 3 while the compressor is out of operation, and to prevent water droplets from being introduced into the high-pressure stage compressor main body 2 when operation is resumed. In other words, according to this embodiment, in a multi-stage oil-free screw compressor, it is possible to prevent condensation from forming in the intermediate pipe connecting two compressor main bodies while the compressor is out of operation.

Second Embodiment
2 is a schematic diagram showing the configuration of an oil-free screw compressor 100A according to a second embodiment of the present invention. The same components as those in the previous embodiment are designated by the same reference numerals, and the description of these components may be omitted.

Compressor 100A includes a low-pressure stage compressor main body 1, a high-pressure stage compressor main body 2, an intermediate pipe 3, a humidity sensor 4, a supply pipe 5, a solenoid valve 6, and a control device 7 that controls the opening degree of solenoid valve 6 based on the value detected by the humidity sensor 4.

The control device 7 is, for example, a computer equipped with a processing device and a storage device, and the storage device stores programs executed by the processing device and parameters (thresholds, etc.) used in the programs. The control device 7 is communicatively connected to the humidity sensor 4 and solenoid valve 6. The control device 7 calculates the humidity in the intermediate pipe 3 based on an input signal from the humidity sensor 4, and outputs an opening command to the solenoid valve 6 based on this calculated value. Although not shown in the figure, the control device 7 is communicatively connected to each part, including the motor 32, first air release valve 9, and second air release valve 12.

The low-pressure stage compressor body 1 and the high-pressure stage compressor body 2 are driven by a motor 32, which serves as a drive source. The motor 32 transmits power to the low-pressure stage compressor body 1, the high-pressure stage compressor body 2, and the oil pump 40 via multiple gears 34, 35, 36, 37, and 38 housed in a gear casing 31. A speed-increasing drive gear 34 and an oil pump drive gear 35 are attached to a motor output shaft 33 that protrudes from the motor 32 into the gear casing 31.

The speed-increasing drive gear 34 meshes with speed-increasing driven gears 36, 37, which are set at a predetermined gear ratio relative to the speed-increasing drive gear 34, and transmits driving force to the male rotors of the low-pressure stage compressor body 1 and the high-pressure stage compressor body 2 via the rotor shafts 14a of the low-pressure stage compressor body 1 and the high-pressure stage compressor body 2, which are connected to the speed-increasing driven gears 36, 37, respectively.

The oil pump drive gear 35 meshes with an oil pump driven gear 38, which is set at a predetermined gear ratio relative to the oil pump drive gear 35. The oil pump driven gear 38 is coupled to an oil pump shaft 39 that protrudes outside the gear casing 31, and transmits driving force to the oil pump 40. This allows lubricating oil to be supplied to bearings 15a, 15b, 16a, 16b (see Figure 3) and timing gears 17a, 17b (see Figure 3) via paths 21, 25, 30 (see Figure 4) of the low-pressure stage compressor body 1 and the high-pressure stage compressor body 2.

An intercooler 8 is provided in the intermediate pipe 3 to cool the gas compressed in the low-pressure stage compressor main body 1. The intercooler 8 is a device that cools the high-temperature compressed gas compressed in the low-pressure stage compressor main body 1. Cooling the high-temperature compressed gas compressed in the low-pressure stage compressor main body 1 using the intercooler 8 allows the gas to be compressed efficiently in the high-pressure stage compressor main body 2.

Furthermore, the gas cooled by the intercooler 8 becomes more humid. For this reason, it is preferable that the sensor 4 be provided in the intermediate pipe 3 so as to be located downstream of the intercooler 8 in the flow direction of the compressed gas.

Furthermore, a separator for separating water may be provided in the intermediate pipe 3, located downstream of the intercooler 8 and upstream of the sensor 4 in the flow direction of the compressed gas. This improves the cooling performance of the intercooler 8, allowing the gas to be compressed more efficiently in the high-pressure stage compressor main body 2.

Furthermore, a first air release valve 9 is provided in the intermediate pipe 3 so as to be located downstream of the low-pressure stage compressor main body 1 and upstream of the intercooler 8 in the flow direction of the compressed gas. The first air release valve 9 is a valve that releases the gas in the intermediate pipe 3 to the atmosphere, and is preferably closed when the compressor 100 is operating and opened when the compressor 100 is not operating.

As a result, when the compressor 100 is not operating, it can release compressed gas remaining in the intermediate pipe 3 to the atmosphere through the first air release valve 9, and fill the intermediate pipe 3 with dry gas supplied from the supply pipe 5. If the opening degree of the first air release valve 9 is controlled by the control device 7, it is preferable that the first air release valve 9 be a solenoid valve.

A gas tank 42 is connected to the supply pipe 5 as a source of dry gas. The gas tank 42 may be provided inside the casing of the compressor 100A or outside the compressor 100A. Furthermore, it is preferable that the supply pipe 5 communicate with the intermediate pipe 3 downstream of the sensor 4 in the flow direction of the compressed gas.

The discharge pipe 10 is provided with an aftercooler 11 that cools the gas compressed by the high-pressure stage compressor main body 2. Furthermore, the discharge pipe 10 is provided with a second air release valve 12 located downstream of the high-pressure stage compressor main body 2 and upstream of the aftercooler 11 in the flow direction of the compressed gas.

The second air release valve 12 is a valve that releases gas in the discharge pipe 10 to the atmosphere, and is closed when the compressor 100 is operating and open when the compressor 100 is not operating. Therefore, when the compressor 100 is not operating, it can release the compressed gas discharged from the high-pressure stage compressor main body 2 that remains in the discharge pipe 10 to the atmosphere through the second air release valve 12. In addition, the dry gas supplied from the supply pipe 5 to the intermediate pipe 3 leaks into the discharge pipe 10 through gaps in the high-pressure stage compressor main body 2, thereby reducing the humidity in the discharge pipe 10. Note that when the opening degree of the second air release valve 12 is controlled by the control device 7, it is preferable that the second air release valve 12 be a solenoid valve.

A check valve 41 is provided in the discharge pipe 10 downstream of the aftercooler 11 in the direction of compressed gas flow. A compressed gas discharge port 102 is provided downstream of the check valve 41 in the discharge pipe 10. The compressed air is supplied to the user, a tank, etc. via this outlet 102.

In this embodiment, the low-pressure stage compressor body 1 and the high-pressure stage compressor body 2 are driven by a single motor 32. However, this is not limited to this, and the low-pressure stage compressor body 1 and the high-pressure stage compressor body 2 may be driven by separate motors.

Figure 3 is a plan cross-sectional view of a compressor body that can be used as a low-pressure stage compressor body, and Figure 4 is a cross-sectional view taken along the line IV-IV in Figure 3.

As shown in Figure 3, the compressor body 50 has a pair of screw rotors 13 (13a, 13b) consisting of a male rotor 13a and a female rotor 13b. The male rotor 13a is fixed to the rotor shaft 14a, and the female rotor 13b is fixed to the rotor shaft 14b. It is preferable that the male rotor 13a and the rotor shaft 14a, and the female rotor 13b and the rotor shaft 14b are formed integrally.

Rotor shaft 14a and rotor shaft 14b are rotatably supported by bearings 15a and 15b on the intake side (right side in the figure) and bearings 16a and 16b on the discharge side (left side in the figure).

Furthermore, timing gears 17a and 17b are provided on the outside of bearings 16a and 16b on rotor shafts 14a and 14b. The two timing gears 17a and 17b mesh with each other, and when rotor shaft 14a is rotated by a drive source such as a motor, rotor shaft 14b also rotates. As a result, the pair of screw rotors 13 rotate synchronously with their teeth maintaining a predetermined gap (for example, several tens of μm).

As the pair of screw rotors 13 rotate, gas drawn in through the intake port 1a shown in Figure 4 is compressed in the compression chamber 18 and discharged from the discharge port 1b.

Two shaft seals 19 (19a, 19b) and 20 (20a, 20b) are provided on the intake side of the rotor shafts 14a, 14b between the male and female rotors 13a, 13b and the bearings 15a, 15b.

The shaft seal 20 is an annular air seal (air seal 20a (male side), 20b (female side)). The gap between the shaft seal 20 and the rotor shafts 14a, 14b is maintained at, for example, several tens of microns, which prevents compressed gas from leaking from the compression chamber 18 to the intake side.

The shaft seal 19 is a thread seal that prevents the lubricating oil supplied to the bearings 15a, 15b from the lubricating oil path 21 shown in Figure 4 from entering the compression chamber 18. The inner surface of the thread seals 19a, 19b has a spiral angular groove, and the thread seals 19a, 19b are assembled so that they do not come into contact with the rotor shafts 14a, 14b and maintain a small gap. When the rotor shafts 14a, 14b rotate, the thread seals 19a, 19b generate sealing pressure in the grooves on their inner diameters, which acts to push the lubricating oil back toward the bearings 15a, 15b.

Furthermore, grooves 14aa and 14ba are formed in the circumferential direction on the outer peripheral surfaces of rotor shafts 14a and 14b between shaft seal portion 19 and shaft seal portion 20, and holes 22 are formed in the compressor main casing radially outside grooves 14aa and 14ba.

Hole 22 is a through-hole that penetrates from the inner circumferential surface of the through-hole provided in the compressor main casing, into which rotor shafts 14a and 14b are inserted, to the outside of the compressor main casing. Hole 22 functions as a gas vent hole, and gas that leaks from compression chamber 18 to the intake side is discharged from hole 22 into the atmosphere of compressor main body 50.

In addition, an oil drain port 24 is formed in the compressor main casing between the screw seals 19a, 19b and the bearings 15a, 15b to recover the lubricating oil supplied to the bearings 15a, 15b and return it to the oil reservoir 23 in the gear casing 31. Therefore, no lubricating oil flows into the compression chamber 18, and the gas is compressed without oil supply.

On the discharge side of the rotor shafts 14a, 14b, shaft seals 26 (26a, 26b) and 27 (27a, 27b) are provided between the male and female rotors 13a, 13b and the bearings 16a, 16b.

The shaft seal portion 27 is an annular air seal (air seal 27a (male side), 27b (female side)) with a gap of approximately several tens of μm between it and the rotor shafts 14a and 14b, preventing compressed gas from leaking from the compression chamber 18 to the discharge side.

The shaft seal 26 is a thread seal that prevents the lubricating oil supplied to the bearings 16a, 16b from the path 25 shown in Figure 4 from entering the compression chamber 18. The inner surface of the thread seals 26a, 26b has a spiral angular groove, and they are assembled so as to maintain a small gap without contacting the rotor shafts 14a, 14b. When the rotor shafts 14a, 14b rotate, the thread seals 26a, 26b generate sealing pressure in the grooves on their inner diameters, which acts to push the lubricating oil back toward the bearings 16a, 16b.

Furthermore, grooves 14ab and 14bb are formed in the circumferential direction on the outer peripheral surfaces of rotor shafts 14a and 14b between shaft seal portion 26 and shaft seal portion 27, and holes 28 are formed in the compressor main casing radially outside grooves 14ab and 14bb.

Hole 28 is a through-hole that penetrates from the inner circumferential surface of the through-hole provided in the compressor main casing, into which rotor shafts 14a and 14b are inserted, to the outside of the compressor main casing. Hole 28 functions as a gas vent hole, and gas that leaks from compression chamber 18 to the discharge side is discharged through hole 28 into the atmosphere of compressor main body 50.

Three bearings 16a, 16b are arranged on each of the male and female rotor shafts. A passage 25 is formed in the compressor main casing somewhere between these three bearings 16a, 16b to supply lubricating oil from above.

The compressor main casing is also provided with an oil drain port 29 that recovers lubricating oil from a position between the bearings 16a, 16b and the screw seals 26a, 26b. The lubricating oil supplied to the bearings 16a, 16b from the path 25 is recovered from the oil drain port 29. Therefore, no lubricating oil flows into the compression chamber 18, and the gas is compressed without oil supply.

The gear casing 31 has a lubricating oil passage 30 formed therein for supplying lubricating oil above the timing gears 17a and 17b. After being supplied to the timing gears 17a and 17b, the lubricating oil flows from the oil drain port 24 formed below into the oil drain port 29 and is then collected in the oil reservoir 23.

[Operation]
Next, the operation of the compressor 100A according to this embodiment will be described. In the following, it is assumed that the opening degrees of the solenoid valve 6, the first air release valve 9, and the second air release valve 12 are controlled by electrical signals output from the control device 7.

<1. Compressor operation>
During operation, the compressor 100A operates as follows: That is, the control device 7 drives the motor 32 to close the solenoid valve 6, the first air release valve 9, and the second air release valve 12.

When the motor 32 is driven, the low-pressure stage compressor body 1 draws in gas from the suction port 101 through the gas suction pipe 103 and compresses it. The compressed gas is discharged from the discharge side of the low-pressure stage compressor body 1 to the intermediate pipe 3. The compressed gas discharged to the intermediate pipe 3 is cooled by the intercooler 8.

Similarly, the high-pressure stage compressor main body 2 takes in compressed gas cooled by the intercooler 8, further compresses it, and discharges it into the discharge pipe 10. The compressed gas discharged into the discharge pipe 10 is cooled in the aftercooler 11 and supplied to the user, etc. from the compressed gas discharge port 102 via the check valve 41.

When the solenoid valve 6 and first air release valve 9 are closed, dry gas is not supplied to the intermediate pipe 3 from the supply pipe 5, and compressed gas discharged from the low-pressure stage compressor main body 1 to the intermediate pipe 3 is not released into the atmosphere.

When the second air release valve 12 is closed, the compressed gas discharged from the high-pressure stage compressor main body 2 into the discharge piping 10 is not released into the atmosphere.

<2. Operation during compressor shutdown>
Next, the compressor 100A operates as follows when it is out of operation.

When compressor 100A is shut down, control device 7 stops motor 32 and opens first air release valve 9 and second air release valve 12.

When the motor 32 stops, the low-pressure stage compressor body 1 and the high-pressure stage compressor body 2 cease compression operations. As a result, gas compressed by the low-pressure stage compressor body 1 and cooled by the intercooler 8 remains in the intermediate pipe 3 and the high-pressure stage compressor body 2.

When the first air release valve 9 is opened, the gas in the intermediate pipe 3 can be released to the atmosphere, and the pressure inside the intermediate pipe 3 becomes atmospheric. As a result, when dry gas is supplied from the supply pipe 5 to the intermediate pipe 3, if the pressure of the dry gas is made higher than atmospheric pressure, the dry gas can be easily supplied into the intermediate pipe 3. Furthermore, since the gas in the intermediate pipe 3 is released to the atmosphere while the first air release valve 9 is open, the intermediate pipe 3 can be easily and quickly filled with dry gas.

When the second air release valve 12 is opened, the pressure between the high-pressure stage compressor main body 2 and the aftercooler 11 in the discharge piping 10 is maintained at approximately atmospheric pressure, making it easier to discharge gas remaining in the high-pressure stage compressor main body 2 into the discharge piping 10.

Generally, when gas is compressed, the amount of water vapor per volume increases, and there is a risk that the water vapor that cannot be completely dissolved in the gas will condense. Furthermore, when gas containing water vapor is cooled, the humidity increases, and there is a risk that the water vapor will condense. In other words, condensation can occur inside the intermediate piping 3 when operation is suspended. If condensation occurs, for example, rust that has formed inside the intermediate piping 3 can peel off when operation is resumed and enter the high-pressure stage compressor main body 2, which can lead to a decrease in compressor performance or failure.

In this embodiment, the compressor 100A monitors the humidity inside the intermediate pipe 3 using the humidity sensor 4 while the compressor is out of operation. If the humidity detected by the humidity sensor 4 is equal to or higher than a first threshold value (e.g., 80%), the controller 7 determines that there is a risk of condensation and opens the solenoid valve 6 to supply dry gas from the supply pipe 5 to the intermediate pipe 3. This prevents condensation from occurring in the intermediate pipe 3. Note that, because the first air release valve 9 is open and the pressure inside the intermediate pipe 3 is maintained at approximately atmospheric pressure, dry gas can be easily supplied to the intermediate pipe 3 by maintaining the pressure of the dry gas in the gas tank 42 at or above atmospheric pressure.

On the other hand, if the humidity detected by the humidity sensor 4 falls below a second threshold value (e.g., 50%), it is determined that there is no longer any risk of condensation, and the control device 7 closes the solenoid valve 6 to stop the supply of dry gas from the supply pipe 5 to the intermediate pipe 3. This makes it possible to prevent excessive supply of dry gas into the intermediate pipe 3.

In this case, from the perspective of control stability, the solenoid valve 6 is opened when the humidity detected by the humidity sensor 4 is equal to or greater than the first threshold, and is closed when the humidity detected by the humidity sensor 4 falls below the second threshold while the solenoid valve 6 is open. However, instead of this control, control may be adopted in which the solenoid valve 6 is opened when the detected humidity is equal to or greater than the first threshold, and closed when the detected humidity is below the first threshold.

<3. Operation when compressor restarts>
When the compressor 100A resumes operation, the control device 7 keeps the solenoid valve 6, the first air release valve 9, and the second air release valve 12 closed, and restarts the motor 32. This stops the supply of dry gas into the intermediate pipe 3, and compression by the compressor bodies 1 and 2 starts in a state in which the release of gas into the intermediate pipe 3 and the discharge pipe 10 to the atmosphere is stopped.

[effect]
The oil-free screw compressor 100A of the present embodiment preferably includes a control device 7 that, during an operation shutdown of the compressor 100, opens the solenoid valve 6 when the detection value of the humidity sensor 4 is equal to or greater than a first threshold value and closes the solenoid valve 6 when the detection value of the humidity sensor 4 is less than a second threshold value. As a result, the compressor 100 of the present embodiment opens the solenoid valve 6 to supply dry gas into the intermediate pipe 3 when the detection value of the humidity sensor 4 provided in the intermediate pipe 3 is equal to or greater than the first threshold value, thereby making it possible to suppress the occurrence of condensation in the intermediate pipe 3. Furthermore, the compressor 100 of the present embodiment closes the solenoid valve 6 when the detection value of the humidity sensor 4 provided in the intermediate pipe 3 is less than the second threshold value, making it possible to suppress an excessive supply of dry air into the intermediate pipe 3.

In the oil-free screw compressor 100A of this embodiment, it is preferable that the dry gas has a lower humidity than the gas in the intermediate pipe 3 at the start of the compressor 100A's shutdown. As a result, the compressor 100A of this embodiment can reduce the humidity in the intermediate pipe 3 by opening the valve 6 to supply gas from the supply pipe 5 into the intermediate pipe 3.

The oil-free screw compressor 100A of this embodiment preferably further comprises an intercooler 8 provided in the intermediate piping 3 to cool the gas compressed in the low-pressure stage compressor main body 1. This allows the high-temperature gas compressed in the low-pressure stage compressor main body 1 to be cooled and reduced in volume, allowing the gas to be efficiently compressed in the high-pressure stage compressor main body 2.

Furthermore, it is preferable that the sensor 4 is provided in the intermediate pipe 3 so as to be located downstream of the intercooler 8 in the flow direction of the compressed gas. This allows the sensor 4 to detect the dew point or humidity of the gas that has been cooled by the intercooler 8 and has increased in humidity, thereby further suppressing the occurrence of condensation.

Furthermore, it is preferable that the supply pipe 5 communicates with the intermediate pipe 3 downstream of the sensor 4 in the flow direction of the compressed gas. In this way, the supply pipe 5 supplies dry gas to the gas with increased humidity downstream of the intercooler 8, further suppressing the occurrence of condensation.

The oil-free screw compressor 100A of this embodiment comprises a first air release valve 9 which is provided in the intermediate piping 3 so as to be located downstream of the low-pressure stage compressor main body 1 and upstream of the intercooler 8 in the flow direction of the compressed gas, and which releases the gas in the intermediate piping 3 to the atmosphere; a discharge piping 10 connected to the discharge side of the high-pressure stage compressor main body 2; an aftercooler 11 which is provided in the discharge piping 10 and cools the gas compressed in the high-pressure stage compressor main body 2; and a second air release valve 12 which is provided in the discharge piping 10 so as to be located downstream of the high-pressure stage compressor main body 2 and upstream of the aftercooler 11 in the flow direction of the compressed gas, and which releases the gas in the discharge piping 10 to the atmosphere; and it is preferable that the first air release valve 9 and the second air release valve 12 are closed when the compressor 100A is operating and open when the compressor 100A is not operating. As a result, the compressor 100A can release compressed gas from the intermediate pipe 3 and the discharge pipe 10 to the atmosphere through the first air release valve 9 and the second air release valve 12 while the compressor 100A is out of operation. This makes it easy to fill the intermediate pipe 3 and the discharge pipe 10 with dry gas, further suppressing the occurrence of condensation.

(Third embodiment)
5 is a schematic diagram showing the configuration of an oil-free screw compressor 100B according to a third embodiment of the present invention. The same components as those in the previous embodiment are denoted by the same reference numerals.

The compressor 100B according to this embodiment differs from the compressor 100 according to the first embodiment mainly in that the compressor 100B further includes a tank 242 in which compressed gas compressed by the high-pressure stage compressor main body 2 is stored. In other words, the discharge end of the discharge pipe 10 of the compressor 100B is connected to the tank 242. The supply pipe 5 is also connected to the tank 242, and the compressed gas in the tank 242 can be supplied to the intermediate pipe 3 as dry gas.

[effect]
In the compressor 100B of this embodiment, the compressed gas in the tank 242 compressed by the high-pressure stage compressor main body 2 is used as the dry gas, so there is no need to generate dry gas using other equipment, and energy savings can be achieved.

In each of the above embodiments, a two-stage compressor having two compressor bodies has been exemplified, but the number of stages in the compressor body may be three or more.

Furthermore, the present invention is not limited to the above-described embodiments, and includes various modifications. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and are not necessarily limited to those that include all of the configurations described. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

1...Low-pressure stage compressor body, 2...High-pressure stage compressor body, 3...Intermediate piping, 4...Sensor, humidity sensor, 5...Supply piping, 6...Valve, solenoid valve, 7...Control device, 8...Intercooler, 9...First air release valve, 10...Discharge piping, 11...Aftercooler, 12...Second air release valve, 100, 100A, 100B...Oil-free screw compressor, 242...Tank

Claims (7)

a low-pressure stage compressor body;
a high-pressure stage compressor main body that compresses the gas compressed by the low-pressure stage compressor main body;
an intermediate pipe connecting a discharge side of the low-pressure stage compressor main body and a suction side of the high-pressure stage compressor main body;
a sensor for detecting a dew point or humidity of a gas in the intermediate pipe;
a supply pipe that is connected to the intermediate pipe and that supplies a dry gas into the intermediate pipe;
a valve provided in the supply pipe, the opening of which is adjusted in accordance with the detection value of the sensor while the compressor is out of operation. 2. The oil-free screw compressor according to claim 1,
the sensor is a humidity sensor;
the valve is a solenoid valve;
an oil-free screw compressor, further comprising a control device that opens the solenoid valve when a detection value of the humidity sensor is equal to or greater than a first threshold value during an operation shutdown of the compressor, and closes the solenoid valve when the detection value of the humidity sensor is less than a second threshold value that is smaller than the first threshold value. 2. The oil-free screw compressor according to claim 1,
The oil-free screw compressor is characterized in that the dry gas has a lower humidity than the gas in the intermediate pipe at the start of a shutdown of the compressor. 2. The oil-free screw compressor according to claim 1,
The compressor further includes a tank for storing compressed gas compressed by the high-pressure stage compressor body,
The supply pipe is connected to the tank, and the compressed gas in the tank is supplied to the intermediate pipe as the dry gas. 2. The oil-free screw compressor according to claim 1,
an intercooler provided in the intermediate piping to cool the gas compressed by the low-pressure stage compressor body,
the sensor is provided in the intermediate pipe so as to be located downstream of the intercooler in a flow direction of the compressed gas,
The oil-free screw compressor is characterized in that the supply pipe is in communication with the intermediate pipe downstream of the sensor in the flow direction of the compressed gas. 6. The oil-free screw compressor according to claim 5,
a first air release valve that is provided in the intermediate pipe so as to be located downstream of the low-pressure stage compressor body and upstream of the intercooler in a flow direction of compressed gas, and that releases gas in the intermediate pipe to the atmosphere;
a discharge pipe connected to the discharge side of the high-pressure stage compressor body;
an aftercooler provided in the discharge piping and configured to cool the gas compressed by the high-pressure stage compressor body;
a second air release valve that is provided in the discharge piping so as to be located downstream of the high-pressure stage compressor body and upstream of the aftercooler in a flow direction of the compressed gas, and that releases the gas in the discharge piping to the atmosphere,
The oil-free screw compressor, wherein the first air release valve and the second air release valve are closed when the compressor is operating and are opened when the compressor is not operating. 2. The oil-free screw compressor according to claim 1,
the sensor is a humidity sensor;
the valve is a solenoid valve;
an oil-free screw compressor, further comprising a control device that opens the solenoid valve when a detection value of the humidity sensor is equal to or greater than a predetermined value and closes the solenoid valve when the detection value of the humidity sensor is less than the predetermined value during shutdown of the compressor.