Air Compressor

Abstract

Provided is an air compression device comprising a buffer tank that is provided at a prescribed position of an air return pipe and temporarily stores return air.

Description

[Technical Field]

[0001] The present invention relates to an air compression device. [Background technology]

[0002] Patent Document 1 discloses an oil-free rotary compressor apparatus characterized in that a return gas pipe equipped with a flow control means is branched from the discharge gas pipe and connected to the suction side of the rotary compressor so that the discharge pressure can be increased while maintaining a predetermined compression ratio by returning a portion of the discharge gas to the suction side of the rotary compressor to increase the suction pressure (see paragraph 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 166785 / 1985 Summary of the Invention [Problem to be solved by the invention]

[0004] The air compressor described in Patent Document 1 returns a portion of the discharged air directly to the air intake side through a pipe, which makes the intake pressure unstable.

[0005] An object of the present invention is to stabilize the suction pressure in an air compressor. [Means for solving the problem]

[0006] An air compression device according to one aspect of the present invention is characterized by comprising: a compressor that compresses intake air drawn in from an intake port through an air intake pipe; a heat exchanger that cools the compressed air; an air return pipe that returns a portion of the cooled air to the air intake pipe as return air; and a buffer tank that is provided at a predetermined position on the air return pipe and that temporarily stores at least the return air. [Effects of the Invention]

[0007] According to one aspect of the present invention, it is possible to solve some or all of the above problems. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a diagram showing the configuration of an air compression device according to a first embodiment. [Figure 2] FIG. 4 is a flow chart of discharge air return control in the first embodiment. [Figure 3] FIG. 2 is a diagram showing the pressure, flow rate, temperature, and density at each location in the air compressor of the first embodiment. [Figure 4] FIG. 10 is a diagram showing the configuration of an air compression device according to a second embodiment. [Figure 5] FIG. 10 is a flow chart of discharge air return control in the second embodiment. [Figure 6] FIG. 10 is a diagram showing the pressure, flow rate, temperature, and density at each location in the air compressor of the second embodiment. [Figure 7] FIG. 10 is a diagram showing the configuration of an air compression device according to a third embodiment. [Figure 8] FIG. 10 is a flow chart of discharge air return control in the third embodiment. [Figure 9] FIG. 10 is a diagram showing the pressure, flow rate, temperature, and density at each location in the air compressor of the third embodiment. [Figure 10] FIG. 10 is a flow chart of another discharge air return control in the first and third embodiments. [Figure 11] FIG. 10 is a flow chart of another discharge air return control according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment will be described with reference to the drawings. [Example]

[0010] A first embodiment of the present invention will be described below with reference to FIGS. 1, 2 and 3. FIG.

[0011] FIG. 1 is a diagram showing the configuration of an air compressor according to a first embodiment, and solid lines in the figure indicate the air flow in the air compressor.

[0012] The area within the dashed line in 19 is the inside of the air compressor package. Outside air taken in through air intake 1 passes through air filter 2, check valve 3, and buffer tank 4 before being compressed by compressor 7 (the single-stage unit of the air compressor itself). The compressed, high-temperature air is cooled in intercooler (heat exchanger) 11 and further compressed to the target pressure by compressor 8 (the two-stage unit of the air compressor itself).

[0013] The compressed air is cooled in an aftercooler (heat exchanger) 12 and then discharged to the outside from a discharge port 14. A portion of the discharged air returns to the buffer tank 4 via an air return pipe 10. An orifice 9 and an adjustment valve 5 are attached to the air return pipe 10.

[0014] The suction pressure is measured by pressure gauge 6, the intermediate pressure by pressure gauge 16, the discharge pressure by pressure gauge 13, and the return air by pressure gauge 20, and the values ​​are acquired by control panel 15 via the control lines shown by the dashed dotted lines in the figure. The regulating valve 5 is controlled by control panel 15 via the control lines. Check valve 17 prevents the backflow of air from the customer side when unloading, and 18 is the air outlet when unloading.

[0015] The air compressor is provided with thermometer 21, thermometer 22, thermometer 23, and thermometer 24. Thermometer 21 measures the intake air temperature. Thermometer 22 measures the return air temperature. Thermometer 23 measures the first-stage discharge temperature. Thermometer 24 measures the discharge temperature.

[0016] The buffer tank 4 is where the air drawn in from the outside is mixed with a portion of the discharged air, and the pressurized intake air is stored. By temporarily storing air in the buffer tank 4, air with a stable pressure can be sent to the compressor 7 (single-stage compressor). This prevents chattering of the regulating valve 5. Here, chattering refers to the repeated fine opening and closing of the regulating valve 5 in an attempt to fine-tune the amount of return air due to changes in the amount of discharged air used or fluctuations in discharge pressure. Chattering can shorten the life of the regulating valve 5 and cause control errors.

[0017] In addition, a check valve 3 is attached to the inlet of the buffer tank 4 to prevent a portion of the discharged air sent into the buffer tank 4 from flowing back through the air intake port 1.

[0018] An adjustment valve 5 is attached to the air return pipe 10, which returns a portion of the discharged air, and the amount returned to the buffer tank 4 can be adjusted by opening and closing this adjustment valve 5. However, if the discharged air is sent directly to the adjustment valve 5, the valve will open and close while receiving high-pressure air, which can easily lead to deterioration or failure of the adjustment valve 5. To prevent this, an orifice 9 is attached to the air return pipe 10. The orifice 9 also serves to prevent the adjustment valve 5 from opening and closing too frequently in response to small fluctuations in the discharge pressure when controlling the return flow rate.

[0019] 2 shows the control flow of the adjusting valve 5 in the first embodiment. A series of controls of the adjusting valve 5 is performed by the control panel 15. The control flow will be explained below.

[0020] After the compressor is started (S201), the regulating valve 5 is closed and normal operation is performed (S202). d It is determined whether the pressure P is close to a preset target pressure (target value) (for example, within ±10% of the target pressure) (S203). d If the pressure is close to the target pressure (S203: Yes), normal operation S202 is continued, and P d is near the target pressure (S203).

[0021] If the result of the determination in S203 is that the pressure is not near the target pressure (S203: No), the adjustment valve 5 is adjusted (S204). Specifically, for example, if the pressure is 90% or less of the target pressure, the adjustment valve 5 is opened by a predetermined amount to increase the amount of compressed air returned to the buffer tank 4, and if the pressure is 110% or more of the target pressure, the adjustment valve 5 is closed by a predetermined amount to decrease the amount of compressed air returned to the buffer tank 4.

[0022] Compressed air returns to the buffer tank 4 by S204, and the first stage suction air pressure of the compressor 7 increases, and the air pressure (suction pressure P s ) is near a preset target pressure (target value) (for example, within ±10% of the target pressure) (S205).

[0023] If the pressure is not near the target pressure (S205: No), the adjusting valve 5 is further adjusted (S204). Specifically, for example, if the pressure is 90% or less of the target pressure, the adjusting valve 5 is opened by a predetermined amount to increase the amount of compressed air returned to the buffer tank 4, and if the pressure is 110% or more of the target pressure, the adjusting valve 5 is closed by a predetermined amount to decrease the amount of compressed air returned to the buffer tank 4, thereby adjusting the first-stage suction air pressure of the compressor 7 to be near the target pressure.

[0024] When the air pressure output from the buffer tank 4 measured by the pressure gauge 6 reaches a preset target value (S205: Yes), the compression ratio πi2 (ratio of intermediate pressure to discharge pressure: Pd / P1) of the compressor 8 (two-stage machine) is measured to determine whether it exceeds a preset reference value (S206). This is because if the compression ratio becomes too high, the compressed air will overheat, which could damage the compressor 8.

[0025] If the determination result shows that the compression ratio πi2 exceeds the reference value (S206: No), the intermediate pressure is reduced by opening the regulating valve 5 (S204). If the determination result shows that the compression ratio πi2 does not exceed the preset reference value (S206: Yes), the process returns to normal operation in S202 while maintaining the open / closed state of the regulating valve 5.

[0026] As described above, by opening and closing the adjustment valve 5 according to the discharge air pressure Pd, the single-stage suction air pressure Ps, and the two-stage compression ratio πi2, it is possible to stabilize the suction pressure while protecting the compressor 8 with a simple configuration.

[0027] Next, a means for speeding up the process described in Fig. 2 will be described with reference to the control flow of Fig. 10. Here, a control panel 15 controls a series of adjustment valves 5.

[0028] This is almost the same as the control flow of the adjusting valve 5 shown in Fig. 2, except that step 206 is omitted. The other steps are almost the same as the control flow shown in Fig. 2, so their explanation will be omitted.

[0029] In the process of Figure 2, the opening and closing amount of the regulating valve 5 is set to a predetermined value, and there is a concern that it may take time to determine whether the pressure in each part has reached the target pressure after the regulating valve 5 has been opened or closed.

[0030] In particular, if the compression ratio πi2 exceeds the reference value and reaches the alarm value, an alarm is issued and the air compressor must be stopped to prevent damage to the compressor 8, so speeding up the processing is useful. Therefore, in the control flow of Figure 10, step 206 is omitted to speed up the processing.

[0031] By adopting this method, it is possible to calculate the amount of opening and closing of the adjustment valve 5 to bring the pressure in each part to the target pressure, eliminating the need to remeasure the pressure in each part after opening and closing the adjustment valve 5, thereby speeding up processing.

[0032] First, an example will be shown of how much of the discharge flow rate needs to be returned. Figure 3 shows the pressure P, volumetric flow rate Q, mass flow rate G, temperature T, and air density ρ at each position inside the air compressor package 19.

[0033] Since the first-stage suction flow rate is the sum of the suction flow rate and the return flow rate, it can be expressed by the following formula (1) based on Boyle's law.

[0034] Here, the calculation conditions are set as follows: suction air pressure Ps = 80 [kPa] (atmospheric pressure at an altitude of approximately 2000 m), and the first stage suction pressure Ps + r is increased to 100 [kPa] by return air.

[0035] [Formula 1] TIFF0007769136000001.tif1882 If we turn this equation (1) into an equation for the return flow rate Qr, it can be expressed as equation (2) below.

[0036] [Formula 2] TIFF0007769136000002.tif1797 Here, the suction air pressure is Qs = 80 kPa, the suction temperature is Ts = 303.15 K, and the density is ρs = 0.92 kg / m 3 , return air pressure Pr = 780 kPa, return temperature Tr = 423.15 K, density ρr = 6.43 kg / m 3 , First stage suction air pressure Ps+r=100kPa, First stage suction flow rate Qs+r=50m 3 / min, suction temperature Ts+r=303.15K, density ρs+r=1.15kg / m 3 Assuming that the intake air volume Qs and the intake air volume Qs+r of the first-stage air end are equivalent, the return flow rate Qr can be calculated using the following equation (3).

[0037] [Formula 3] TIFF0007769136000003.tif43170 Here, since the mass flow rate is constant regardless of temperature, the first-stage suction mass flow rate Gs+r is equivalent to the discharge mass flow rate Gd. It can be seen that the ratio of the return mass flow rate Gr to the first-stage suction mass flow rate Gs+r is the flow rate to be returned.

[0038] [Formula 4] TIFF0007769136000004.tif28170 From equation (4), it can be seen that the return mass flow rate Gr requires approximately 20% of the discharge mass flow rate Gd. Here, the control panel 15 stores in a memory unit (not shown) a table or formula that associates the opening / closing amount of the adjustment valve 5 with the return mass flow rate Gr, and it is possible to determine the opening / closing amount of the adjustment valve 5 required to return the required return mass flow rate Gr to the buffer tank 4.

[0039] Therefore, in S204 of FIG. 2, by opening and closing the adjustment valve 5 by the calculated opening and closing amount, the suction pressure can be stabilized more quickly. [Example]

[0040] A second embodiment of the present invention will be described below with reference to FIGS.

[0041] FIG. 4 is a diagram showing the configuration of an air compressor according to a second embodiment, and the solid lines in the figure indicate the air flow in the air compressor.

[0042] The second embodiment has a structure in which a part of the discharged air is returned between the compressor 7 (one-stage compressor) and the compressor 8 (two-stage compressor) (between the heat exchanger 11 and the second-stage intake port).

[0043] The configuration differs from the air compressor of Example 1 shown in Figure 1 in the arrangement of buffer tank 4 and check valve 3. Furthermore, Example 2 newly provides pressure sensor 25 and thermometer 26. Pressure sensor 25 is a sensor that measures second-stage suction pressure (Pc+r) and is connected to control unit 15 by a dashed-dotted line. Thermometer 26 is a thermometer that measures second-stage suction air temperature (Tc+r) and is connected to control unit 15 by a dashed-dotted line.

[0044] The air outlet from buffer tank 4 is provided between compressors 7 and 8, and buffer tank 4 temporarily stores the return air and sends it to compressor 8. In this case, check valve 3 is provided on the outlet side of buffer tank 4 to prevent the air cooled by heat exchanger 11 from flowing back into buffer tank 4.

[0045] By temporarily storing air in the buffer tank 4, air with a stable pressure can be sent to the compressor 8. This prevents chattering of the regulating valve 5.

[0046] The other configurations are almost the same as those of the air compressor of the first embodiment shown in FIG. 1, so detailed description thereof will be omitted.

[0047] FIG. 5 shows a control flow of the adjusting valve 5 in the second embodiment.

[0048] This is almost the same as the control flow of the adjusting valve 5 in the first embodiment shown in Fig. 2, except that the reference pressure after adjusting the adjusting valve 5 becomes the second-stage suction pressure P1+r (see S205). The other steps are almost the same as those in the first embodiment shown in Fig. 2, so the description thereof will be omitted.

[0049] Next, a means for speeding up the process described in Fig. 5 will be described with reference to the control flow of Fig. 11. Here, a series of control operations of the adjusting valve 5 are performed by a control panel 15.

[0050] This is almost the same as the control flow of the adjusting valve 5 shown in Fig. 5, except that step 206 is omitted. The other steps are almost the same as the control flow shown in Fig. 5, so their explanation will be omitted.

[0051] In the process of Figure 5, the opening and closing amount of the regulating valve 5 is set to a predetermined value, and there is a concern that it may take time to determine whether the pressure in each part has reached the target pressure after the regulating valve 5 has been opened or closed.

[0052] In particular, if the compression ratio πi2 exceeds the reference value and reaches the alarm value, an alarm is issued and the air compressor must be stopped to prevent damage to the compressor 8, so speeding up the processing is useful. Therefore, in the control flow of Figure 11, step 206 is omitted to speed up the processing.

[0053] Next, as in Example 1, an example will be shown of how much of the discharge flow rate needs to be returned. Figure 6 shows the pressure P, volumetric flow rate Q, mass flow rate G, temperature T, and air density ρ at each position. Since the first-stage suction flow rate is the sum of the suction flow rate and the return flow rate, it can be expressed by the following equation (5) based on Boyle's law.

[0054] Here, it is assumed that the intermediate pressure Pc+r is increased from 200 kPa to 250 kPa. From the calculation results, the return amount is 20% of the discharge. Tc is the outlet temperature of the intercooler (heat exchanger) 11.

[0055] [Formula 5] TIFF0007769136000005.tif1883 As in the first embodiment, when this formula (5) is converted into a formula for the return flow rate Qr, it can be expressed as the following formula (6), and the return flow rate Qr can be calculated as the following formula (7). From formula (8), it can be seen that the return flow rate requires about 20% of the discharge flow rate, and as in the first embodiment, this can be used to determine the opening / closing amount of the adjustment valve 5 for adjusting the return flow rate in S204.

[0056] [Formula 6] TIFF0007769136000006.tif1797

[0057] [Formula 7] TIFF0007769136000007.tif44170

[0058] [Formula 8] TIFF0007769136000008.tif28170 [Example]

[0059] A third embodiment of the present invention will be described below with reference to FIGS.

[0060] FIG. 7 is a diagram showing the configuration of an air compressor according to a third embodiment, and solid lines indicate the air flow in the air compressor.

[0061] The main difference in configuration from the air compressor of the first embodiment shown in Fig. 1 is that the air compressor of the third embodiment does not have the compressor 8 (two-stage machine) and the heat exchanger 12 of the air compressor main body. In this way, the air compressor of the third embodiment is an air compressor of a single-stage configuration.

[0062] As shown in Figure 7, outside air is taken in through an air intake port 1, passes through an air filter 2, a check valve 3, and a buffer tank 4, and is then compressed by a compressor 7. The compressed, high-temperature air is cooled in a heat exchanger 11 and then discharged to the outside through a discharge port 14.

[0063] The other configurations are almost the same as those of the air compressor of the first embodiment shown in FIG. 1, and therefore the description thereof will be omitted.

[0064] FIG. 8 shows a control flow of the adjusting valve 5 in the third embodiment.

[0065] This is almost the same as the control flow of the adjusting valve 5 in the first embodiment shown in Fig. 2, except that the reference value of the compression ratio is πi1 (see S206). πi1 is the compression ratio of a single-stage compressor, and indicates the ratio Pd / P1 of the discharge pressure to the suction pressure. The other steps are almost the same as those in the first embodiment shown in Fig. 2, so a description thereof will be omitted.

[0066] Next, a description will be given of a means for speeding up the processing described in Fig. 8. The control flow is almost the same as the control flow in Fig. 2, so a description thereof will be omitted. Here, a series of control operations of the adjusting valve 5 is performed by a control panel 15.

[0067] In the process of Figure 8, the opening and closing amount of the regulating valve 5 is set to a predetermined value, and there is a concern that it may take time to determine whether the pressure in each part has reached the target pressure after the regulating valve 5 has been opened or closed.

[0068] In particular, if the compression ratio πi1 exceeds the reference value and reaches the alarm value, an alarm is sounded and the air compressor must be stopped to prevent damage to the compressor 8, so speeding up the processing is useful. Therefore, in the control flow of Figure 2, step 206 is omitted to speed up the processing.

[0069] Next, as in Example 1, an example will be shown of how much of the discharge flow rate needs to be returned. Figure 9 shows the pressure P, volumetric flow rate Q, mass flow rate G, temperature T, and air density ρ at each position. Since the first-stage suction flow rate is the sum of the suction flow rate and the return flow rate, it can be expressed by the following equation (9) based on Boyle's law.

[0070] Here, the calculation conditions are set as follows: suction air pressure Ps = 80 [kPa] (atmospheric pressure at an altitude of approximately 2000 m), and the suction pressure Ps + r is increased to 100 [kPa] by return air. The target discharge pressure Pd = Pr = 330 [kPa].

[0071] [Formula 9] TIFF0007769136000009.tif1782 As in the first embodiment, when this formula (9) is used as a formula for the return flow rate Qr, it can be expressed as the following formula (10), and the return flow rate Qr can be calculated as the following formula (11). From formula (12), it can be seen that the return flow rate requires about 20% of the discharge flow rate, and as in the first embodiment, this can be used to determine the opening / closing amount of the adjustment valve 5 for adjusting the return flow rate in S204.

[0072] [Formula 10] TIFF0007769136000010.tif18100

[0073] [Formula 11] TIFF0007769136000011.tif44170

[0074] [Formula 12] TIFF0007769136000012.tif39170 As shown in Examples 1 to 3 above, regardless of whether the machine is a single-stage or two-stage machine or the air return position, it is possible to increase the pressure by returning the amount of discharge air calculated, thereby maintaining the target discharge air pressure.

[0075] According to the above embodiment, the suction pressure can be increased stably by returning a portion of the discharged air to the buffer tank installed on the suction side. Furthermore, chattering of the adjusting valve 5 attached to the air return pipe can be prevented. [Explanation of symbols]

[0076] 1 Air intake 2. Intake filter 3. Check valve 4 Buffer Tank 5 Flow control valve 6 Suction pressure sensor 7 Compressor (single stage) 8 Compressor (two-stage) 9 Orifice (pressure reducing valve) 10 Air return pipe 11 Intercooler 12 Aftercooler 13 Discharge pressure sensor 14 Discharge port 15 Control Panel 16 Intermediate pressure sensor 17 Check valve 18 Blow piping

Claims

1. a compressor that compresses intake air drawn in from an intake port through an air intake pipe; a heat exchanger for cooling the compressed air; an air return pipe that returns a portion of the cooled air to the air intake pipe as return air; a buffer tank provided at a predetermined position on the air return pipe for temporarily storing at least the return air; an orifice provided at a predetermined position in the air return pipe; An air compression device comprising:

2. The buffer tank is 2. The air compressing device according to claim 1, wherein the intake air drawn through the air intake pipe and the return air are temporarily stored, and mixed air obtained by mixing the intake air and the return air is sent to the compressor.

3. The buffer tank is provided on the inlet side of the compressor, The heat exchanger comprises:

2. The air compressing device according to claim 1, wherein the compressor is provided on an outlet side of the compressor.

4. an adjusting valve provided at a predetermined position on the air return pipe; a control panel for controlling the adjusting valve; The control panel includes:

2. The air compressor according to claim 1, wherein the flow rate of the return air to the buffer tank is adjusted by opening and closing the adjusting valve.

5. 2. The air compressor according to claim 1, further comprising a check valve provided at a predetermined position in the air intake pipe to prevent the return air stored in the buffer tank from flowing back into the air intake pipe.

6. a first compressor that compresses air drawn in through an air inlet; a second compressor that further compresses the air compressed by the first compressor; a first heat exchanger that cools the air compressed by the first compressor; a second heat exchanger that cools the air compressed by the second compressor; an air return pipe for returning a portion of the air cooled by the second heat exchanger to the air intake side as return air; a buffer tank connected to the air return pipe for temporarily storing at least the return air; an orifice provided at a predetermined position in the air return pipe; An air compression device comprising:

7. The buffer tank is The compressor is provided on the inlet side of the first compressor, 7. The air compression device according to claim 6, wherein the intake air taken in through the air intake port and the return air are temporarily stored, and mixed air obtained by mixing the intake air and the return air is sent to the first compressor.

8. 8. The air compressor according to claim 7, further comprising a check valve provided on the inlet side of the buffer tank to prevent the return air from flowing back to the air intake side.

9. The buffer tank is The compressor is provided between the first compressor and the second compressor, 7. The air compression device according to claim 6, wherein the return air is temporarily stored and then sent to the second compressor.

10. 10. The air compression device according to claim 9, further comprising a check valve provided on an outlet side of the buffer tank to prevent the air cooled by the first heat exchanger from flowing back into the buffer tank.

11. an adjusting valve provided at a predetermined position on the air return pipe; a control panel for controlling the adjusting valve; The control panel includes:

7. The air compressor according to claim 6, wherein the amount of return air returned to the buffer tank is adjusted by opening and closing the adjustment valve.

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