WO2013146674A1

WO2013146674A1 - Two-stage compression device

Info

Publication number: WO2013146674A1
Application number: PCT/JP2013/058563
Authority: WO
Inventors: 吉村　省二; 大祐和田
Original assignee: 株式会社神戸製鋼所
Priority date: 2012-03-30
Filing date: 2013-03-25
Publication date: 2013-10-03
Also published as: JP2013209953A

Abstract

Provided is a two-stage compression device which can adjust an internal compression ratio according to an external compression ratio. A two-stage compression device (1) has a low-stage compression unit (7) and a high-stage compression unit (8) and is configured in such a manner that the shaft of one of the screw rotors (5, 6) of the low-stage compression unit (7) and the high-stage compression unit (8) is connected thereto. A capacity adjustment means (14) is provided to the high-stage compression unit (8), and the volume ratio which is the ratio between a suction volume at the moment when a compression space is isolated from an intermediate flow passage (10) and a discharge volume at the moment when the compression space is connected to a discharge flow passage (11) is changed according to the ratio between the pressure in the intermediate flow passage (10) and the pressure in the discharge flow passage (11) by changing the discharge volume.

Description

Two-stage compressor

The present invention relates to a two-stage compression apparatus.

A pair of male and female screw rotors that mesh with each other is accommodated in a rotor chamber formed in the casing, and the space in the rotor chamber is divided by the screw rotor, and the volume decreases as the screw rotor rotates. A screw compressor that forms a compression space, sucks gas from the suction flow path into the compression space, compresses the gas, and discharges the gas into the discharge flow path is widely used.

Such a screw compressor has a gas back flow from the discharge flow path to the compression space or a gas in the discharge flow path when the pressure of the compression space at the moment of being connected to the discharge flow path is different from the pressure of the discharge flow path. Negative work such as expansion of the water occurs and efficiency decreases. The pressure of the compression space at the moment of being connected to the discharge flow path is the pressure of the compression space at the moment of being isolated from the suction flow path, that is, the pressure of the compression space at the moment of being isolated from the suction flow path to the pressure of the suction flow path. It is determined by the volume ratio that is the ratio of the volume and the volume of the compression space at the moment connected to the discharge flow path.

In general, the ratio between the pressure in the compression space at the moment isolated from the suction flow path and the pressure in the compression space at the moment connected to the discharge flow path is called the internal compression ratio, and the pressure in the suction flow path and the pressure in the discharge flow path Is called the external compression ratio. In order to improve the efficiency of the screw compressor, for example, as described in Patent Document 1, the volume ratio of the screw compressor is changed according to the pressure of the suction flow path and the pressure of the discharge flow path, and the internal compression ratio is changed. A mechanism such as a slide valve has been proposed for bringing the valve closer to the external compression ratio.

Also, a two-stage compression device in which two screw compressors are connected in series via an intermediate flow path is also used. Even in such a two-stage compressor, it is desirable to improve the efficiency by adjusting the internal compression ratio according to the external compression ratio. However, when two screw compressors of Patent Document 1 are connected in series, Adjusting the internal compression ratio of the stage-side compressor changes the pressure in the intermediate flow path, so the external compression ratio of the high-stage compressor also changes, and the internal compression ratio required for the high-stage compressor Will change. That is, when two screw compressors of Patent Document 1 are connected in series, the adjustment of the internal compression ratio of the two screw compressors interferes with each other, so that control is difficult.

Japanese Unexamined Patent Publication No. Sho 62-121848

In view of the above problems, an object of the present invention is to provide a two-stage compression device that can adjust the internal compression ratio according to the external compression ratio.

In order to solve the above problems, a two-stage compression apparatus according to the present invention compresses the gas sucked from the suction flow path and discharges it to the intermediate flow path, and compresses the gas sucked from the intermediate flow path. A pair of male and female screw rotors that engage with each other in a rotor chamber formed in the casing. And forming a compression space in the rotor chamber that is separated from each other by the screw rotor and decreases in volume as the screw rotor rotates, and is one shaft of the screw rotor of the low-stage compression unit. Are connected to one shaft of the screw rotor of the high-stage compression section, and the high-stage compression section is a suction volume that is an instantaneous volume isolated from the intermediate flow path of the compression space and the discharge flow. The volume ratio, which is the ratio of the discharge volume, which is the instantaneous volume connected to the, is adjusted according to the ratio of the pressure of the intermediate flow path and the pressure of the discharge flow path by changing the discharge volume It is assumed that capacity adjusting means is provided.

According to this configuration, the internal compression ratio of the low-stage compression unit is fixed and only the internal compression ratio of the high-stage compression unit is changed, so that control is easy and internal compression of the entire two-stage compression device High efficiency can be obtained by matching the ratio to the external compression ratio.

In the two-stage compression device of the present invention, the pressure in the discharge flow path of the low-stage compression section may be calculated from the pressure in the suction flow path.

According to this configuration, it is not necessary to detect the pressure inside the compression device, and the pressure can be detected in the front and rear pipes, so that the structure is not complicated.

Further, in the two-stage compression device of the present invention, the capacity adjusting means forms a part of the wall surface of the rotor chamber of the high-stage compression section, and advances and retreats in the axial direction of the screw rotor. It may be a slide valve that can change the opening position with respect to the discharge flow path.

According to this configuration, since the internal compression ratio can be continuously changed, high efficiency can be realized by matching the internal compression ratio with the external compression ratio.

Further, in the two-stage compression device of the present invention, the capacity adjusting means may be a bypass mechanism that opens a part of the wall surface of the rotor chamber of the high-stage compression section and communicates with the discharge flow path. .

According to this configuration, the efficiency can be improved by selecting two internal compression ratios while the configuration is simple and inexpensive.

Further, in the two-stage compression device of the present invention, the screw rotors of the low-stage compression section and the high-stage compression section may be driven by a motor capable of controlling the rotation speed.

According to this configuration, since the discharge flow rate can be adjusted by controlling the rotation speed while substantially maintaining the internal compression ratio of the entire stage compression apparatus, it is possible to prevent pressure fluctuations in the suction flow path and the discharge flow path.

As described above, according to the present invention, since only the internal compression ratio of the compression unit on the high stage side is changed in the two-stage compressor, the control is easy and the internal compression ratio of the entire two-stage compressor is externally changed. High efficiency can be obtained by matching the compression ratio.

It is a schematic block diagram of the two-stage compression apparatus of 1st Embodiment of this invention. It is a schematic block diagram of the two-stage compression apparatus of 2nd Embodiment of this invention. It is a figure which shows the change of the heat insulation efficiency in the two-stage compression apparatus of FIG.

Now, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a configuration of a two-stage compression apparatus 1 according to the first embodiment of the present invention. The two-stage compression apparatus 1 includes a low-stage compression section 7 and a high-stage compression section 8 that house a pair of male and

female screw rotors

5 and 6 that mesh with each other in

rotor chambers

3 and 4 formed in a casing 2. . The shaft of one screw rotor 5 of the low-stage compression unit 7 is integrally connected to the shaft of one screw rotor 6 of the high-stage compression unit 8.

The low-stage compression section 7 and the high-stage compression section 8 divide the

rotor chambers

3 and 4 by the

screw rotors

5 and 6 to form a plurality of compression spaces isolated from each other. The low-stage compression unit 7 sucks gas from the suction flow path 9 formed in the casing 2 in the compression space, compresses the gas by reducing the volume of the compression space with the rotation of the screw rotor 5, and The compressed gas is discharged into the formed intermediate flow path 10. The high stage compression unit 8 sucks the gas from the intermediate flow path 10 into the compression space, compresses the gas by the rotation of the screw rotor 6, and discharges the gas to the discharge flow path 11 formed in the casing 2.

The

screw rotors

5 and 6 are driven by a motor 13 that can adjust the rotation speed when electric power is supplied from the inverter 12. The high-stage compression unit 8 includes a slide valve 14 that constitutes a part of the inner wall of the rotor chamber 4 and is movable in the axial direction of the screw rotor 6. The slide valve 14 is driven by a hydraulic cylinder 15 and adjusts the position where the compression space of the high stage compression unit 8 communicates with the discharge flow path 11. That is, the slide valve 14 is a capacity adjusting means that can adjust the instantaneous volume when the compression space of the high-stage compression unit 8 is connected to the discharge flow path 11.

The two-stage compression device 1 has a hydraulic circuit 16 for driving the hydraulic cylinder 15. The hydraulic circuit 16 includes a four-way switching control valve 18 and a four-way switching control valve for switching the flow path so that pressure oil is supplied to the space before and after the piston 17 of the hydraulic cylinder 15 or oil is discharged from either space. And two

solenoid valves

19 and 20 for switching between supply and exhaust of compressed air for driving 18.

The two-stage compressor 1 includes a suction pressure detector 21 that detects a suction pressure Ps that is a pressure in the suction flow path 9, and a discharge pressure detector 22 that detects a discharge pressure Pd that is a pressure in the discharge flow path 11. And a positioner 23 for detecting the position of the piston 17 of the hydraulic cylinder 15. Further, the two-stage compressor 1 includes an intermediate pressure calculation unit 24 that calculates an intermediate pressure Pm that is a pressure in the intermediate flow path 10 based on the suction pressure Ps detected by the suction pressure detector 21, and an intermediate pressure calculation unit 24. Based on the calculated intermediate pressure Pm and the discharge pressure Pd detected by the discharge pressure detector 22, a target position of the slide valve 14, that is, a valve target position calculator 25 for calculating the position of the piston 17 to be detected by the positioner 23; The valve position control unit 26 controls the

electromagnetic valves

19 and 20 of the hydraulic circuit 16 so that the detected value of the positioner 23 approaches the position calculated by the valve target position calculation unit 25.

Here, a method of calculating the intermediate pressure Pm in the intermediate pressure calculation unit 24 will be described. The stroke volume of the low-stage compression section 7 is Vt1, the stroke volume of the high-stage compression section 8 is Vt2, the volume efficiency of the low-stage compression section 7 is η1, the volume efficiency of the high-stage compression section 8 is η2, and the gas in the suction passage 9 The suction temperature that is the temperature of the gas is Ts, and the intermediate temperature that is the gas temperature in the intermediate flow path 8 is Tm. Then, the intermediate pressure Pm that is the pressure of the gas in the intermediate flow path 10 can be expressed as Pm = Ps × (Vt1 × η1 / Ts) / (Vt2 × η2 / Tm). Therefore, the external compression ratio of the low-stage compression unit 7 is Pm / Ps = (Vt1 × η1 / Ts) / (Vt2 × η2 / Tm) = (Vt1 / Vt2) × (η1 / η2) × (Tm / Ts) It becomes. Here, the stroke volumes Vt1 and Vt2 depend on the shape and size of the

screw rotors

5 and 6 and are proportional to the number of rotations of the motor 13, so (Vt1 / Vt2) is constant. Further, the volumetric efficiency η1, η2, the suction temperature Ts, and the intermediate temperature Tm may vary depending on external factors, but hardly change depending on the operation parameters of the two-stage compressor 1 itself. Therefore, the intermediate pressure Pm can be calculated based on the coefficient determined by the shape of the

screw rotors

5 and 6 and the suction pressure Ps detected by the suction pressure detector 21 regardless of the discharge pressure Pd.

Further, the suction volume that is the instantaneous volume isolated from the suction flow path 9 in the compression space of the low-stage compression unit 7 is Vs1, the discharge volume that is the instantaneous volume connected to the intermediate flow path 10 is Vd1, and the low-stage compression When the volume ratio, which is the ratio between the suction volume Vs1 of the part 7 and the discharge volume Vd1, is Vi1, and the low stage internal pressure Pd1 is the instantaneous pressure connected to the intermediate flow path 10 in the compression space of the low stage compression part 7, Based on the polytropic change formula, using the specific heat ratio κ, the relationship Ps × Vs1 ^κ = Pd1 × (Vs1 / Vi1) ^κ holds. Therefore, the low stage internal pressure Pd1 = Ps × Vi1 ^κ can be expressed.

Similarly, the suction volume that is the instantaneous volume isolated from the middle of the compression space of the high-stage compression unit 8 is Vs2, the discharge volume that is the instantaneous volume connected to the discharge flow path 11 is Vd2, and the high-stage compression unit 8 If the volume ratio, which is the ratio between the suction volume Vs2 and the discharge volume Vd2, is Vi2, and the high stage internal pressure, which is the instantaneous pressure connected to the discharge flow path in the compression space of the high stage compression section 8, is Pd2, the polytropic change Since Pm × Vs2 ^κ = Pd2 × Vd2 ^κ , Vs2 / Vd2 = (Pd2 / Pm) ^{1 / κ} (1).

If there is a difference between the discharge pressure Pd and the high-stage internal pressure Pd2, the backflow of gas from the discharge flow path 11 to the compression space, or the gas compressed excessively in the compression space causes instantaneous expansion in the discharge space, Incurs energy loss. Therefore, the two-stage compressor 1 calculates the target volume ratio Via of the volume ratio Vi2 of the high-stage compression section 8 such that the discharge pressure Pd and the high-stage internal pressure Pd2 are equal in the valve target position calculation section 25. More specifically, when Via = Vi2 = Vs2 / Vd2 and the polytropic change equation (1) is substituted for this, the target volume ratio Via = (Pd2 / Pm) ^{1 / κ} . Since the suction volume Vs2 of the high stage compression unit 8 is constant, the discharge volume Vd2 of the high stage compression unit 8 to be set by the slide valve 14 can be calculated and detected by the positioner 23 in order to achieve this target volume ratio Via. The position of the power piston 17 can be determined.

The valve position control unit 26 controls the hydraulic circuit 16 so that the volume ratio Vi2 of the high-stage compression unit 8 approaches the target value Via. Typically, the discharge volume Vd <b> 2 of the high stage compression unit 8 changes in proportion to the position of the slide valve 14. In this case, the volume ratio Vi2 of the high stage compression unit 8 is proportional to the position of the piston 15 detected by the positioner 21 because the suction volume Vs2 of the high stage compression unit 8 is constant. Therefore, when the volume ratio Vi2 calculated from the detection value of the positioner 21 is larger than the target value Via by a predetermined allowable deviation α, for example, greater than 0.1 (Vi2−Via> α). By setting the solenoid valve 19 to the exhaust position and the solenoid valve 20 to the compressed air supply position, the hydraulic cylinder 15 is extended to increase the opening of the slide valve 14 and to reduce the volume ratio Vi2. Conversely, when the detected volume ratio Vi2 is smaller than the target value Via by a predetermined allowable deviation α, for example, more than 0.1 (Vi2−Via <−α), the valve position control unit 26 reverses the solenoid valve 19. Is set to the compressed air supply position, and the electromagnetic valve 20 is set to the exhaust position, thereby shortening the hydraulic cylinder 15 and reducing the opening of the slide valve 14.

As described above, the two-stage compression device 1 adjusts the volume ratio Vi2 of the high-stage compression section 8 by changing the discharge capacity Vd2 of the high-stage compression section 8, thereby adjusting the internal compression ratio of the high-stage compression section 8. The external compression ratio (Pd / Pm) of the high-stage compression unit 8 is substantially matched. That is, since the internal compression ratio of the entire two-stage compression device 1 is adjusted to the external compression ratio (Ps / Pd) of the entire two-stage compression device 1 by adjusting the volume ratio Vi2 of the high-stage compression unit 8, power loss is reduced. Less efficient.

In addition, since the two-stage compressor 1 is driven by the motor 13 whose frequency is controlled by the inverter 12, the internal compression ratio of the low-stage compressor 7 and the high-stage compressor 8 is substantially maintained while meeting the demand. The discharge amount of the compressed gas can be adjusted. For this reason, the pressure fluctuation of the suction flow path 9 and the discharge flow path 11 can be prevented.

Subsequently, FIG. 2 shows a two-stage compressor 1a which is a second embodiment of the present invention. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and redundant description is omitted.

In the two-stage compression device 1a of the present embodiment, the slide valve 14a is arranged at one of two positions on the suction side and the discharge side in the axial direction of the screw rotor 6 by a spring return type hydraulic cylinder 15a. The slide valve 14 a has a communication hole 27, and moves to the discharge side to open a part of the outer wall of the rotor chamber 4 and communicate with the discharge flow path 11 through the communication hole 27. That is, the slide valve 14a is a capacity adjusting means that changes the volume ratio Vi2 of the high stage compression unit 8 in two stages. For this reason, the hydraulic circuit 16a is a simple one having only one solenoid valve 28 that can be switched between an oil supply position for supplying pressure oil to the hydraulic cylinder 15a and an oil discharge position for discharging oil from the hydraulic cylinder 15a. is there.

Further, the two-stage compression apparatus 1a has an intermediate pressure detector 29 that directly detects the intermediate pressure Pm in the intermediate flow path 10. Therefore, the intermediate pressure detector 29 directly determines the position of the slide valve 14a from the detection value Pm and the detection value Pd of the discharge pressure detector 22, and the electromagnetic valve 28 of the hydraulic circuit 16 is set to the position of the slide valve 14a. It has a valve position determination unit 30 that switches to a corresponding oil supply position or oil discharge position.

FIG. 3 shows a change in the heat insulation efficiency with respect to the external compression ratio depending on the position of the slide valve 14a. As shown in the figure, there is an external compression ratio πa in which the heat insulation efficiency is the same when the slide valve 14a is located on the suction side and when it is located on the discharge side. Therefore, the position of the slide valve 14a may be switched with the external compression ratio πa at which the heat insulation efficiency becomes equal.

According to the present invention, the capacity adjusting means can change the volume ratio Vi2 of the high-stage compression unit 8 in addition to the slide valve 14a having the slide valve 14 of the first embodiment and the communication hole 27 of the second embodiment. Anything may be used. For example, a valve mechanism such as a piston valve that can provide an opening in the axial end surface of the rotor chamber 4 and allow the opening to communicate with the discharge flow path 11 may be employed as the capacity adjusting means.

In the first embodiment, the intermediate pressure Pm may be detected by an intermediate pressure detector instead of being calculated from the suction pressure Ps. In the second embodiment, the intermediate pressure Pm may be calculated from the suction pressure Ps instead of being detected by the intermediate pressure detector.

DESCRIPTION OF SYMBOLS 1, 1a ... Two-stage compression apparatus 2 ...

Casing

3, 4 ...

Rotor chamber

5, 6 Screw rotor 7 ... Low stage compression part 8 ... High stage compression part 9 ... Suction flow path 10 ... Intermediate flow path 11 ... Discharge flow path 12 ... Inverter 13 ...

Motor

14,14a ...

Slide valve

15,15a ...

Hydraulic cylinder

16,16a ... Hydraulic circuit 21 ... Suction pressure detector 22 ... Discharge pressure detector 23 ... Positioner 24 ... Intermediate pressure calculation unit 25 ... Valve target position calculation 26: Valve position control unit 27: Communication hole 29 ... Intermediate pressure detector 30 ... Valve position determination unit

Claims

A low-stage compression section that compresses the gas sucked from the suction flow path and discharges it to the intermediate flow path, and a high-stage compression section that compresses the gas sucked from the intermediate flow path and discharges it to the discharge flow path,
The low-stage compression section and the high-stage compression section each contain a pair of male and female screw rotors that mesh with each other in a rotor chamber formed in a casing, and are separated from each other by the screw rotor in the rotor chamber. To form a compression space whose volume is reduced as the screw rotor rotates,
One shaft of the screw rotor of the low-stage compression unit and one shaft of the screw rotor of the high-stage compression unit are coupled,
The high-stage compression unit has a volume ratio that is a ratio of a suction volume that is an instantaneous volume isolated from the intermediate flow path of the compression space and a discharge volume that is an instantaneous volume connected to the discharge flow path. A two-stage compression device comprising capacity adjusting means for adjusting the discharge volume according to a ratio between the pressure of the intermediate flow path and the pressure of the discharge flow path by changing the discharge volume.
2. The two-stage compression apparatus according to claim 1, wherein the pressure in the discharge flow path of the low-stage compression section is calculated from the pressure in the suction flow path.
The capacity adjusting means forms a part of the wall surface of the rotor chamber of the high-stage compression portion, and slides to advance and retract in the axial direction of the screw rotor to change the opening position of the rotor chamber with respect to the discharge flow path. The two-stage compressor according to claim 1, wherein the two-stage compressor is a valve.
The capacity adjusting means forms a part of the wall surface of the rotor chamber of the high-stage compression portion, and slides to advance and retract in the axial direction of the screw rotor to change the opening position of the rotor chamber with respect to the discharge flow path. The two-stage compression apparatus according to claim 2, wherein the two-stage compression apparatus is a valve.
2. The two-stage compression according to claim 1, wherein the capacity adjusting means is a bypass mechanism that opens a part of a wall surface of the rotor chamber of the high-stage compression section and communicates with the discharge flow path. apparatus.
3. The two-stage compression according to claim 2, wherein the capacity adjusting means is a bypass mechanism that opens a part of a wall surface of the rotor chamber of the high-stage compression section and communicates with the discharge passage. apparatus.
2. The two-stage compression device according to claim 1, wherein the screw rotors of the low-stage compression section and the high-stage compression section are driven by a motor capable of controlling the rotation speed.
The two-stage compression device according to claim 2, wherein the screw rotors of the low-stage compression section and the high-stage compression section are driven by a motor capable of controlling the rotation speed.
The two-stage compression apparatus according to claim 3, wherein the screw rotors of the low-stage compression section and the high-stage compression section are driven by a motor capable of controlling the rotation speed.
The two-stage compression apparatus according to claim 4, wherein the screw rotors of the low-stage compression section and the high-stage compression section are driven by a motor capable of controlling the rotation speed.
The two-stage compression device according to claim 5, wherein the screw rotors of the low-stage compression section and the high-stage compression section are driven by a motor capable of controlling the rotation speed.
The two-stage compression device according to claim 6, wherein the screw rotors of the low-stage compression section and the high-stage compression section are driven by a motor capable of controlling the rotation speed.