Oil-free screw compressor

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

[0001] The present invention relates to an oil-free screw compressor.

[0002] If moisture-containing gas remains inside the compressor when it is out of operation, the drop in temperature of the gas can cause condensation. Condensation is not a problem in oil-lubricated compressors, in which oil is mixed into the compressed gas, but it can cause rust in oil-free compressors, in which 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.

[0003] As a technology for suppressing the occurrence of condensation during shutdown, Patent Document 1 discloses technology related to a multi-stage compressor including a low-pressure stage compressor main body and a high-pressure stage compressor main body. Specifically, the multi-stage compressor of Patent Document 1, when the compressor is shut down, aims to suppress the occurrence of condensation in a pipe connecting the discharge side of the low-pressure stage compressor main body and the suction side of the high-pressure stage compressor main body by supplying dry gas to the pipe.

[0004] Japanese Patent Application Publication No. 5-141350

[0005] An example of an oil-free compressor is a multi-stage screw compressor having multiple compressor bodies (compression stages). In this compressor, each compressor body generates compressed gas by rotating at high speed with the teeth of a pair of screw rotors, consisting of a male rotor and a female rotor, meshing with each other while maintaining a predetermined gap. In this compressor, in order to prevent gas leakage during compression, clearances within the compressor, including the gap, are kept extremely small (e.g., several tens of μm), which are smaller than the clearances of oil-lubricated screw compressors in which oil provides a sealing effect.

[0006] For this type of oil-free screw compressor, as in Patent Document 1, a dew point temperature sensor is installed in a pipe (referred to as a discharge pipe) connected to the discharge side of the high-pressure stage compressor main body, and dry gas is supplied to a pipe (referred to as an intermediate pipe) connecting the discharge side of the low-pressure stage compressor main body and the suction side of the high-pressure stage compressor main body according to the detected temperature.

[0007] First, as mentioned above, the gaps within an oil-free screw compressor are extremely small, making it difficult for compressed gas to travel 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 stopped. 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 likely to diverge. Furthermore, in Patent Document 1, the discharge pipe is opened to the atmosphere by opening the blow-off valve during shutdowns, which makes the humidity of the gas in the discharge pipe 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 may 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, the supply of dry gas may be stopped before the humidity of the gas in the intermediate pipe has sufficiently decreased. In other words, applying the configuration of Patent Document 1 to a screw compressor may not achieve the expected effect, and condensation may occur during shutdowns.

[0008] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an oil-free screw compressor that can suppress the occurrence of condensation in an intermediate pipe connecting two compressor bodies.

[0009] The present application includes a plurality of means for solving the above-described problems, and one example thereof 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 and 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 has an opening degree adjusted in accordance with the detection value of the sensor when the compressor is out of operation.

[0010] According to the present invention, it is possible to suppress the occurrence of condensation in the intermediate pipe connecting two compressor bodies in a multi-stage oil-free screw compressor. Problems, configurations, and effects other than those described above will become apparent from the description of the following embodiments.

[0011] Fig. 3 is a schematic diagram showing the configuration of an oil-free screw compressor according to a first embodiment of the present invention. 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. 5 is a plan sectional view of a compressor main body that can be used as the low-pressure stage compressor main body of Fig. 2. Fig. 6 is a sectional view taken along the arrows IV-IV of Fig. 3. Fig. 7 is a schematic diagram showing the configuration of an oil-free screw compressor according to a third embodiment of the present invention.

[0012] The configurations and operations of oil-free screw compressors according to first to third embodiments of the present invention will be described below with reference to the drawings. Note that the same reference numerals denote the same parts in each drawing. Also, "upstream" and "downstream" refer to the upstream and downstream in the flow direction of compressed gas.

[0013] 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.

[0014] An oil-free screw compressor (hereinafter, sometimes simply referred to as a compressor) 100 according to this embodiment is a device that compresses gas (e.g., air) without mixing lubricating oil into the gas. As shown in Fig. 1 , the compressor 100 includes 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 that is provided on the supply pipe 5.

[0015] 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. Also, in this embodiment, an embodiment of a two-stage compressor including two compressor bodies, the low-pressure stage compressor body 1 and the high-pressure stage compressor body 2, has been shown. However, the present invention is not limited to this, and can also be used in a multi-stage compressor in which compressor bodies are connected in series.

[0016] Gas compressed in the low-pressure stage compressor body 1 flows through the intermediate pipe 3 , and the gas is introduced into the suction side of the high-pressure stage compressor body 2 .

[0017] The sensor 4 is preferably attached to the intermediate pipe 3 .

[0018] 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 in communication with 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. The dry gas preferably has a lower humidity than the gas in the intermediate pipe 3 at the start of the shutdown of the compressor 100, and more preferably has a pressure equal to or higher than atmospheric pressure.

[0019] The opening degree of the valve 6 is adjusted in accordance with the detection value of the sensor 4 during the shutdown of the compressor 100 with the low-pressure stage compressor body 1 and the high-pressure stage compressor body 2 stopped. For example, when the detection value of the sensor 4 approaches a value indicating the occurrence of condensation in the intermediate pipe 3 (the dew-point temperature if the sensor 4 is a dew-point sensor, or 100% if the sensor 4 is a humidity sensor), the valve 6 is opened and dry gas is supplied to the intermediate pipe 3 via the supply pipe 5. On the other hand, when the detection value of the sensor 4 deviates from that value, the valve 6 is maintained in a closed state.

[0020] When the sensor 4 is a humidity sensor, the valve 6 is preferably 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 during an outage of the compressor 100. 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 during an outage of the compressor 100 and closed when the detected value of the humidity sensor 4 is less than the first threshold value.

[0021] From the viewpoint of adjusting the opening degree in accordance with the detection value of the sensor 4, it is preferable that the valve 6 is an electromagnetic valve whose opening degree can be adjusted in accordance with an electrical command output from a control device (described later).

[0022] A discharge pipe 10 is connected to the discharge side of the high-pressure stage compressor body 2, and compressed gas discharged from the high-pressure stage compressor body 2 is supplied to a tank (not shown) or a user, etc., via the discharge pipe 10.

[0023] [Effects] 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.

[0024] With the compressor 100 configured as described above, while the compressor 100 is out of operation, the detection value of the sensor 4 is monitored, and if there is no risk of condensation occurring in the intermediate pipe 3, the valve 6 is kept closed, whereas if there is a risk of condensation occurring 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 occurring 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 body 2 when the compressor is restarted. That is, according to this embodiment, in a multi-stage oil-free screw compressor, it is possible to prevent condensation from occurring in the intermediate pipe connecting two compressor bodies while the compressor is out of operation.

[0025] Second Embodiment Fig. 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 parts as those in the previous embodiment are denoted by the same reference numerals, and descriptions of these parts may be omitted.

[0026] The 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 the solenoid valve 6 based on the detection value of the humidity sensor 4.

[0027] 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, parameters (threshold values, etc.) used in the programs, etc. The control device 7 is communicably connected to the humidity sensor 4 and the solenoid valve 6. The control device 7 calculates the humidity of 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 the calculated value. Although not shown in the figure, the control device 7 is communicably connected to each part including the motor 32, the first air release valve 9, and the second air release valve 12.

[0028] The low-pressure stage compressor body 1 and the high-pressure stage compressor body 2 are driven by a motor 32, which is 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 a plurality of 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.

[0029] The speed-increasing drive gear 34 meshes with speed-increasing driven gears 36, 37 that are set to 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 that are connected to the speed-increasing driven gears 36, 37, respectively.

[0030] The oil pump drive gear 35 meshes with an oil pump driven gear 38 that 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 an oil pump 40. As a result, lubricating oil is supplied to the bearings 15a, 15b, 16a, 16b (see FIG. 3) and the timing gears 17a, 17b (see FIG. 3) via the paths 21, 25, 30 (see FIG. 4) of the low-pressure stage compressor body 1 and the high-pressure stage compressor body 2.

[0031] An intercooler 8 that cools the gas compressed in the low-pressure stage compressor body 1 is provided in the intermediate pipe 3. The intercooler 8 is a device that cools the compressed gas that has been compressed in the low-pressure stage compressor body 1 and has reached a high temperature. When the compressed gas that has been compressed in the low-pressure stage compressor body 1 and has reached a high temperature is cooled by the intercooler 8, the gas can be efficiently compressed in the high-pressure stage compressor body 2.

[0032] Furthermore, the humidity of the gas cooled by the intercooler 8 increases. Therefore, the sensor 4 is preferably provided in the intermediate pipe 3 so as to be located downstream of the intercooler 8 in the flow direction of the compressed gas.

[0033] Note that a separator for separating water may be provided in the intermediate pipe 3 so as to be 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, and enables the gas to be compressed more efficiently in the high-pressure stage compressor body 2.

[0034] 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 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 while the compressor 100 is operating and opened while the compressor 100 is not operating.

[0035] As a result, during an operation shutdown of the compressor 100, the compressed gas remaining in the intermediate pipe 3 can be released to the atmosphere from the first air release valve 9, and the dry gas supplied from the supply pipe 5 can fill the intermediate pipe 3. When the opening degree of the first air release valve 9 is controlled by the control device 7, the first air release valve 9 is preferably a solenoid valve.

[0036] A gas tank 42 serving as a dry gas supply source is connected to the supply pipe 5. The gas tank 42 may be provided inside the casing of the compressor 100A or may be provided outside the compressor 100A. Furthermore, the supply pipe 5 preferably communicates with the intermediate pipe 3 downstream of the sensor 4 in the flow direction of the compressed gas.

[0037] An aftercooler 11 that cools the gas compressed by the high-pressure stage compressor body 2 is provided in the discharge pipe 10. Furthermore, a second air release valve 12 is provided in the discharge pipe 10 so as to be located downstream of the high-pressure stage compressor body 2 and upstream of the aftercooler 11 in the flow direction of the compressed gas.

[0038] 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 is open when the compressor 100 is not operating. Therefore, when the compressor 100 is not operating, the compressed gas discharged from the high-pressure stage compressor body 2 and remaining in the discharge pipe 10 can be released to the atmosphere through the second air release valve 12. Furthermore, the dry gas supplied from the supply pipe 5 to the intermediate pipe 3 leaks into the discharge pipe 10 from gaps in the high-pressure stage compressor 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, the second air release valve 12 is preferably a solenoid valve.

[0039] A check valve 41 is provided in the discharge pipe 10 downstream of the aftercooler 11 in the flow direction of the compressed gas. A compressed gas discharge port 102 is provided in the discharge pipe 10 downstream of the check valve 41. The compressed air is supplied to a user, a tank, or the like through the outlet 102.

[0040] In the present embodiment, the low-pressure stage compressor body 1 and the high-pressure stage compressor body 2 are driven by one motor 32. However, the present invention 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.

[0041] FIG. 3 is a plan sectional view of a compressor body that can be used as a low-pressure stage compressor body, and FIG. 4 is a sectional view taken along the line IV-IV in FIG.

[0042] 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 a rotor shaft 14a, and the female rotor 13b is fixed to a 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 integrally formed.

[0043] The rotor shaft 14a and the rotor shaft 14b are rotatably supported by bearings 15a and 15b on the intake side (right side in the drawing) and bearings 16a and 16b on the discharge side (left side in the drawing), respectively.

[0044] Timing gears 17a, 17b are provided on the rotor shafts 14a, 14b on the outer sides of the bearings 16a, 16b. The two timing gears 17a, 17b mesh with each other, and when the rotor shaft 14a is rotated by a drive source such as a motor, the rotor shaft 14b also rotates. As a result, the pair of screw rotors 13 rotate synchronously with each other, with a predetermined gap (for example, several tens of μm) between their teeth.

[0045] As the pair of screw rotors 13 rotate, gas drawn in through the intake port 1a shown in FIG. 4 is compressed in the compression chamber 18 and discharged from the discharge port 1b.

[0046] On the intake side of the rotor shafts 14a, 14b, two shaft seals 19 (19a, 19b) and 20 (20a, 20b) are provided between the male and female rotors 13a, 13b and the bearings 15a, 15b.

[0047] 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, about several tens of μm, which prevents the compressed gas from leaking from the compression chamber 18 to the intake side.

[0048] 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 is formed with a spiral angular groove, and the thread seals 19a, 19b are assembled so as to maintain a minute gap without contacting the rotor shafts 14a, 14b. The thread seals 19a, 19b generate sealing pressure in the grooves on the inner diameter due to the rotation of the rotor shafts 14a, 14b, and operate to push the lubricating oil back toward the bearings 15a, 15b.

[0049] In addition, grooves 14aa and 14ba are formed circumferentially on the outer surfaces of the rotor shafts 14a and 14b between the shaft seal portions 19 and 20, and holes 22 are formed in the compressor main casing radially outside the grooves 14aa and 14ba.

[0050] The holes 22 are through-holes that extend from the inner circumferential surface of the through-holes, into which the rotor shafts 14 a, 14 b provided in the compressor main casing are inserted, to the outside of the compressor main casing. The holes 22 function as gas vent holes, and gas that leaks from the compression chambers 18 to the intake side is discharged from the holes 22 to the atmosphere of the compressor main body 50.

[0051] Additionally, an oil drain port 24 is formed in the compressor main body 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.

[0052] On the discharge sides of the rotor shafts 14a, 14b, shaft seals 26 (26a, 26b) and shaft seals 27 (27a, 27b) are provided between the male and female rotors 13a, 13b and the bearings 16a, 16b.

[0053] The shaft seal portion 27 is an annular air seal (air seal 27a (male side), 27b (female side)) that has a gap of about several tens of μm with the rotor shafts 14a, 14b, preventing compressed gas from leaking from the compression chamber 18 to the discharge side.

[0054] The shaft seals 26 are thread seals that prevent the lubricating oil supplied to the bearings 16a, 16b from entering the compression chambers 18 through the path 25 shown in Figure 4. The inner surfaces of the thread seals 26a, 26b are formed with spiral grooves, and the thread seals 26a, 26b are assembled so as to maintain a small gap without contacting the rotor shafts 14a, 14b. The thread seals 26a, 26b generate sealing pressure in the grooves on the inner diameters as the rotor shafts 14a, 14b rotate, and operate to push the lubricating oil back toward the bearings 16a, 16b.

[0055] In addition, grooves 14ab and 14bb are formed circumferentially on the outer surfaces of the rotor shafts 14a and 14b between the shaft seal portions 26 and 27, and holes 28 are formed in the compressor main casing radially outside the grooves 14ab and 14bb.

[0056] The holes 28 are through-holes that extend from the inner circumferential surfaces of through-holes provided in the compressor main casing, into which the rotor shafts 14 a, 14 b are inserted, to the outside of the compressor main casing. The holes 28 function as gas vent holes, and allow gas that leaks from the compression chambers 18 to the discharge side to be discharged into the atmosphere of the compressor main body 50.

[0057] Three bearings 16a, 16b are arranged on each of the male and female rotor shafts. A passage 25 for supplying lubricating oil from above is formed in the compressor main body casing at a position somewhere between these three bearings 16a, 16b.

[0058] The compressor main body casing is also provided with an oil drain port 29 that recovers lubricating oil from a position between the bearings 16a, 16b and the thread 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.

[0059] A lubricating oil passage 30 for supplying lubricating oil above the timing gears 17 a, 17 b is formed in the gear casing 31. After being supplied to the timing gears 17 a, 17 b, the lubricating oil flows from an oil drain port 24 formed below into an oil drain port 29 and is then collected in the oil reservoir 23.

[0060] [Operation] Next, the operation of the compressor 100A according to this embodiment will be described. Note that, hereinafter, 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.

[0061] 1. Operation of the Compressor During Operation The compressor 100A operates as follows during operation: 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.

[0062] When the motor 32 is driven, the low-pressure stage compressor body 1 takes 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.

[0063] Similarly, the high-pressure stage compressor body 2 takes in compressed gas cooled by the intercooler 8, further compresses it, and discharges it to the discharge pipe 10. The compressed gas discharged to the discharge pipe 10 is cooled by the aftercooler 11 and supplied to a user or the like from a compressed gas discharge port 102 via a check valve 41.

[0064] When the solenoid valve 6 and the first air release valve 9 are closed, dry gas is not supplied to the intermediate pipe 3 from the supply pipe 5, and the compressed gas discharged from the low-pressure stage compressor main body 1 to the intermediate pipe 3 is not released into the atmosphere.

[0065] When the second air release valve 12 is closed, the compressed gas discharged from the high-pressure stage compressor body 2 into the discharge pipe 10 is not released into the atmosphere.

[0066] <2. Operation of Compressor During Outage> Next, the compressor 100A operates as follows during outage.

[0067] When the compressor 100A is stopped, the control device 7 stops the motor 32 and opens the first air release valve 9 and the second air release valve 12 .

[0068] When the motor 32 stops, the compression operations of the low-pressure stage compressor body 1 and the high-pressure stage compressor body 2 are suspended. As a result, the 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.

[0069] 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.

[0070] 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.

[0071] 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. That is, there is a possibility that condensation will occur inside the intermediate piping 3 while the operation is suspended. If condensation occurs, for example, rust that has formed inside the intermediate piping 3 will peel off when operation is resumed and enter the high-pressure stage compressor main body 2, which may lead to a decrease in performance or a malfunction of the compressor.

[0072] Therefore, the compressor 100A of this embodiment monitors the humidity in the intermediate pipe 3 while the compressor is out of operation using the humidity sensor 4. If the humidity detected by the humidity sensor 4 is equal to or higher than a first threshold value (e.g., 80%), it is determined that condensation may occur, and the control device 7 opens the solenoid valve 6 to supply dry gas from the supply pipe 5 to the intermediate pipe 3. This makes it possible to suppress the occurrence of condensation in the intermediate pipe 3. Note that, because the first air release valve 9 is open and the pressure in 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.

[0073] On the other hand, when the humidity detected by the humidity sensor 4 becomes less than a second threshold value (for example, 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.

[0074] From the viewpoint of control stability, the solenoid valve 6 is opened when the humidity detected by the humidity sensor 4 is equal to or greater than a first threshold, and is closed when the humidity detected by the humidity sensor 4 falls below a second threshold while the solenoid valve 6 is open. However, instead of this control, it is also possible to adopt a control in which the solenoid valve 6 is opened when the detected humidity is equal to or greater than the first threshold, and is closed when the detected humidity is below the first threshold.

[0075] <3. Operation when compressor operation is restarted> When the compressor 100A restarts 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 main bodies 1 and 2 is started in a state in which release of gas into the intermediate pipe 3 and the discharge pipe 10 to the atmosphere is stopped.

[0076] [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 and closes the solenoid valve 6 when the detection value of the humidity sensor 4 is less than a second threshold. 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, 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, making it possible to suppress an excessive supply of dry air into the intermediate pipe 3.

[0077] In the oil-free screw compressor 100A of the present 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 shutdown of the compressor 100A. Thus, the compressor 100A of the present 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.

[0078] The oil-free screw compressor 100A of the present embodiment preferably further includes an intercooler 8 that is provided in the intermediate pipe 3 and cools the gas compressed in the low-pressure stage compressor body 1. This allows the gas that has been compressed in the low-pressure stage compressor body 1 and has become hot to be cooled and reduced in volume, allowing the gas to be efficiently compressed in the high-pressure stage compressor body 2.

[0079] Furthermore, the sensor 4 is preferably 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 cooled by the intercooler 8 and having increased humidity, thereby further suppressing the occurrence of condensation.

[0080] 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. This allows the supply pipe 5 to supply dry gas to the gas with increased humidity downstream of the intercooler 8, thereby further suppressing the occurrence of condensation.

[0081] The oil-free screw compressor 100A of this embodiment includes: a first air release valve 9 that 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, and that releases the gas in the intermediate pipe 3 to the atmosphere; a discharge pipe 10 that is connected to the discharge side of the high-pressure stage compressor main body 2; an aftercooler 11 that is provided in the discharge pipe 10 and that cools the gas compressed in the high-pressure stage compressor main body 2; and a second air release valve 12 that is provided in the discharge pipe 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 that releases the gas in the discharge pipe 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 in operation, and are opened when the compressor 100A is out of operation. As a result, the compressor 100A can release the compressed gas in the intermediate pipe 3 and the discharge pipe 10 to the atmosphere from the first air release valve 9 and the second air release valve 12 while the compressor 100A is out of operation. Therefore, the intermediate pipe 3 and the discharge pipe 10 can be easily filled with dry gas, and the occurrence of condensation can be further suppressed.

[0082] Third Embodiment Fig. 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.

[0083] 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 that stores compressed gas compressed by the high-pressure stage compressor main body 2. That is, the discharge side end of the discharge pipe 10 of the compressor 100B communicates with the tank 242. The supply pipe 5 is connected to the tank 242, and is capable of supplying the compressed gas in the tank 242 to the intermediate pipe 3 as dry gas.

[0084] [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 can be saved.

[0085] Although the above-described embodiments have been described with reference to a two-stage compressor including two compressor bodies, the number of stages of the compressor body may be three or more.

[0086] 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 including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or 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.

[0087] 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

1. An oil-free screw compressor comprising: 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 connecting the discharge side of the low-pressure stage compressor main body and 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 has an opening that is adjusted in accordance with the detection value of the sensor when the compressor is out of operation.

2. An oil-free screw compressor according to claim 1, wherein the sensor is a humidity sensor, the valve is a solenoid valve, and the compressor further comprises a control device which, during periods when the compressor is out of operation, opens the solenoid valve when the detection value of the humidity sensor is equal to or greater than a first threshold value, 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.

3. An oil-free screw compressor according to claim 1, wherein the dry gas has a lower humidity than the gas in the intermediate pipe at the start of a compressor shutdown.

4. An oil-free screw compressor according to claim 1, further comprising a tank for storing compressed gas compressed by the high-pressure stage compressor body, the supply pipe being connected to the tank and supplying the compressed gas in the tank as the dry gas to the intermediate pipe.

5. An oil-free screw compressor as claimed in claim 1, further comprising an intercooler provided in the intermediate pipe for cooling the gas compressed in the low-pressure stage compressor body, the sensor being provided in the intermediate pipe so as to be located downstream of the intercooler in the flow direction of the compressed gas, and the supply pipe communicating with the intermediate pipe downstream of the sensor in the flow direction of the compressed gas.

6. An oil-free screw compressor as claimed in claim 5, comprising: a first air release valve provided in the intermediate pipe so as to be located downstream of the low-pressure stage compressor main body and upstream of the intercooler in the flow direction of compressed gas, the first air release valve releasing gas in the intermediate pipe to the atmosphere; a discharge pipe connected to the discharge side of the high-pressure stage compressor main body; an aftercooler provided in the discharge pipe so as to cool the gas compressed by the high-pressure stage compressor main body; and a second air release valve provided in the discharge pipe so as to be located downstream of the high-pressure stage compressor main body and upstream of the aftercooler in the flow direction of compressed gas, the second air release valve releasing gas in the discharge pipe to the atmosphere, the first air release valve and the second air release valve being closed when the compressor is operating and being open when the compressor is not operating.

7. An oil-free screw compressor according to claim 1, wherein the sensor is a humidity sensor, the valve is a solenoid valve, and the compressor further comprises a control device which, when the compressor is out of operation, opens the solenoid valve when the detected value of the humidity sensor is equal to or greater than a predetermined value, and closes the solenoid valve when the detected value of the humidity sensor is less than the predetermined value.

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