Screw compressor and gas compression facility

Abstract

A screw compressor includes: a screw rotor having a discharge-side end surface; a casing having a rotor facing surface facing the discharge-side end surface, and an opening disposed on the rotor facing surface and communicating with a discharge space into which a gas compressed by the screw rotor is to be discharged; a slide valve whose position in an axial direction of the screw rotor is variable so as to change an internal volume ratio; and a movable piece disposed along an edge of the opening of the casing and configured to be capable of blocking a part of the opening. The movable piece is configured to be movable between a first position where the movable piece forms a first contour of an axial discharge port together with the edge of the opening, and a second position farther away from the screw rotor in the axial direction than the first position. The screw compressor is configured such that when the movable piece is located at the second position, a second contour of the axial discharge port having an opening area larger than that of the first contour is formed by the opening.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a screw compressor and a gas compression facility.BACKGROUND

[0002] Positive displacement screw compressors generally have excellent advantages such as a simple structure and good durability, and are widely used.

[0003] As representative systems for capacity control in screw compressors, there are a rotational speed control system and a slide valve system, and it is common to adopt the slide valve system for capacity control in large-sized screw compressors.

[0004] In the slide valve system, by moving a slide valve that forms a rotor accommodating chamber together with a casing in the axial direction, the volume at the start of compression of a tooth groove space formed between a male rotor and a female rotor can be changed. Thereby, the gas volume to be compressed can be steplessly adjusted according to the load of the screw compressor.

[0005] On the other hand, the screw compressor has a volume ratio Vi (= suction volume V1 / discharge volume V2) suitable for operating conditions, and the positions and shapes of a suction port and a discharge port are determined so as to start discharging a compressed gas at a timing corresponding to the volume ratio Vi suitable for the operating conditions. In many existing screw compressors, since the internal volume ratio Vi is fixed, the discharge port is shaped to correspond to an average internal volume ratio.

[0006] However, in the screw compressor provided with the above-described slide valve, by moving the slide valve, the internal volume ratio (ratio of the volume at the start of compression (at the start of volume reduction) of the tooth groove space to the volume at the end of compression (at the end of volume reduction)) changes simultaneously.

[0007] Patent Document 1 describes a screw compressor provided with the above-described slide valve and capable of adjusting the internal volume ratio.Citation ListPatent Literature

[0008] Patent Document 1: WO2016 / 147467ASUMMARYProblems to be Solved

[0009] Here, when increasing the size of a screw compressor, if the size of the screw compressor is increased while maintaining the internal volume ratio of the discharge port, the area ratio of the discharge port to the displacement amount decreases, and the gas flow velocity in the discharge port increases. When the gas flow velocity in the discharge port increases in this manner, the pressure in the tooth groove space increases due to passage resistance in the discharge port, causing over-compression, which may increase discharge loss.

[0010] On the other hand, by increasing the area of the discharge port (low internal volume ratio), the increase in the gas flow velocity in the discharge port can be suppressed, so that the above-mentioned problem of increase in discharge loss is less likely to occur. However, in an operating region requiring a high internal volume ratio, due to insufficient compression, gas flowing back from the discharge side is re-compressed and discharged, so that the discharge loss may still increase.

[0011] In view of the above circumstances, an object of at least one embodiment of the present invention is to provide a screw compressor and a gas compression facility capable of suppressing discharge loss over a wide operating region (range of internal volume ratio).Solution to the Problems

[0012] A screw compressor according to at least one embodiment of the present invention includes: a screw rotor having a discharge-side end surface; a casing having a rotor facing surface facing the discharge-side end surface, and an opening disposed on the rotor facing surface and communicating with a discharge space into which a gas compressed by the screw rotor is to be discharged; a slide valve whose position in an axial direction of the screw rotor is variable so as to change an internal volume ratio; and a movable piece disposed along an edge of the opening of the casing and configured to be capable of blocking a part of the opening.

[0013] The movable piece is configured to be movable between a first position where the movable piece forms a first contour of an axial discharge port together with the edge of the opening, and a second position farther away from the screw rotor in the axial direction than the first position.

[0014] The screw compressor is configured such that when the movable piece is located at the second position, a second contour of the axial discharge port having an opening area larger than that of the first contour is formed by the opening.

[0015] Further, a gas compression facility according to at least one embodiment of the present invention includes: the above-described screw compressor configured to compress a gas; and an oil separator for separating the oil from a mixture of compressed gas and oil discharged from the screw compressor. Advantageous Effects

[0016] At least one embodiment of the present invention provides a screw compressor and a gas compression facility capable of suppressing discharge loss over a wide operating region (range of internal volume ratio).BRIEF DESCRIPTION OF DRAWINGS

[0017] FIG. 1 is a schematic diagram of a gas compression facility according to an embodiment. FIG. 2 is a schematic cross-sectional view of a screw compressor according to an embodiment in side view. FIG. 3 is a cross-sectional view of the screw compressor shown in FIG. 2 taken along line A-A. FIG. 4 is a schematic cross-sectional view showing the vicinity of an axial discharge port of a screw compressor according to an embodiment. FIG. 5 is a schematic diagram showing the contour of the axial discharge port shown in FIG. 4. FIG. 6 is a schematic cross-sectional view showing the vicinity of an axial discharge port of a screw compressor according to an embodiment. FIG. 7 is a schematic diagram showing the contour of the axial discharge port shown in FIG. 6. FIG. 8 is a schematic cross-sectional view showing the vicinity of an axial discharge port of a screw compressor according to an embodiment. FIG. 9 is a schematic diagram showing the contour of the axial discharge port shown in FIG. 8. FIG. 10 is a schematic cross-sectional view showing the vicinity of an axial discharge port of a screw compressor according to an embodiment. FIG. 11 is a schematic diagram showing the contour of the axial discharge port shown in FIG. 10. FIG. 12 is a schematic cross-sectional view showing the vicinity of an axial discharge port of a screw compressor according to an embodiment. FIG. 13 is a schematic cross-sectional view showing the vicinity of an axial discharge port of a screw compressor according to an embodiment. DETAILED DESCRIPTION

[0018] Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It is intended, however, that unless particularly identified, dimensions, materials, shapes, relative positions, and the like of components described in the embodiments shall be interpreted as illustrative only and not intended to limit the scope of the present invention.(Configuration of Gas Compression Facility)

[0019] FIG. 1 is a schematic diagram of a gas compression facility including a screw compressor according to some embodiments. As shown in the figure, the gas compression facility 1 includes a screw compressor 2, an oil separator 4, a cooler 6, and a pump 8.

[0020] The screw compressor 2 is configured to compress and discharge sucked gas. The reference character Ps shown in the figure indicates the suction pressure of the screw compressor 2, and the reference character Pd indicates the discharge pressure of the screw compressor 2. Oil is supplied to the screw compressor 2 through an oil supply line 10 for cooling, lubrication, and the like. The oil supplied to the screw compressor 2 is discharged together with compressed gas.

[0021] The oil separator 4 is configured to separate the oil from a mixture of compressed gas and oil discharged from the screw compressor 2. The oil separated by the oil separator 4 is supplied again to the screw compressor 2 through the oil supply line 10. Typically, the oil separated by the oil separator 4 is pressurized by the pump 8 and then supplied to the screw compressor 2 through the oil supply line 10. In this case, the pressure Poil of the oil supplied to the screw compressor 2 is higher than the discharge pressure Pd (Poil = Pd + α). The oil separated by the oil separator 4 may be cooled by the cooler 6 and then pressurized by the pump 8.(Configuration of Screw Compressor)

[0022] FIG. 2 is a schematic cross-sectional view of a screw compressor according to an embodiment in side view. FIG. 3 is a cross-sectional view of the screw compressor shown in FIG. 2 taken along line A-A. As shown in FIGs. 2 and 3, the screw compressor 2 includes a pair of screw rotors (a male rotor 15 and a female rotor 17) including a pair of rotor shafts 14, 16, and a casing 12 accommodating the pair of screw rotors.

[0023] The pair of rotor shafts 14, 16 are rotatably supported by radial bearings 18 and thrust bearings 20, respectively. Oil at pressure Poil is supplied to each bearing through the oil supply line 10.

[0024] The male rotor 15 and the female rotor 17 have helical teeth that mesh with each other. A plurality of tooth groove spaces are formed along the axial direction of the rotor shafts 14, 16 by meshing of the teeth of the male rotor 15 and the female rotor 17 together with the casing 12.

[0025] The rotor shaft 14 constituting the male rotor 15 is connected to an output shaft of a motor (not shown) and is configured to be rotationally driven by the motor. The female rotor 17 meshing with the male rotor 15 is rotationally driven by rotation of the male rotor 15. The female rotor 17 rotates in a direction opposite to the rotation direction of the male rotor 15. When the male rotor 15 and the female rotor 17 rotate in a meshed state, the tooth groove spaces move from the suction side to the discharge side in the axial direction.

[0026] A shaft seal part 24 is provided at a portion of the casing 12 through which the rotor shaft 14 passes to suppress leakage of gas through this portion. Oil at pressure Poil may be supplied to the shaft seal part 24 through the oil supply line 10.

[0027] The oil supplied to the bearings and the shaft seal part 24 is discharged from the casing 12 and returned to a relatively low-pressure space of a screw rotor accommodating portion of the casing 12 via a return line (not shown).

[0028] Gas is sucked into the above-described tooth groove space from a suction space 41 formed in the casing 12 via a suction port 40. When the male rotor 15 and the female rotor 17 rotate, the tooth groove space moves from the suction side to the discharge side in the axial direction with the rotation of these screw rotors. In this process, since the volume of the tooth groove space is reduced after the suction port 40 is closed upon reaching the maximum volume, the gas in the tooth groove space is compressed. When the tooth groove space reaches a discharge port 42 and the tooth groove space communicates with a discharge space 43 formed in the casing 12, the compressed gas in the tooth groove space is discharged to the discharge space via the discharge port 42. Although the discharge port 42 will be described in detail later, the discharge port 42 includes a radial discharge port 46 for discharging the compressed gas from the tooth groove space in the radial direction, and an axial discharge port 44 for discharging the compressed gas from the tooth groove space in the axial direction.

[0029] As shown in FIG. 2, the screw compressor 2 may include a balance piston 28 disposed on at least one of the pair of rotor shafts 14, 16. In the exemplary embodiment shown in FIG. 2, the balance piston 28 is disposed at a suction-side end portion of the rotor shaft 14 constituting the male rotor 15. Relatively high-pressure oil from the oil supply line 10 is supplied to a balance piston chamber 29 facing a suction-side end surface of the balance piston 28. Thereby, a force (a force in a direction from the suction side to the discharge side in the axial direction) opposite to a thrust gas load acting on the rotor shaft 14 (a thrust load in a direction from the discharge side to the suction side in the axial direction acting on the rotor shaft 14 due to a difference between the suction pressure Ps and the discharge pressure Pd of the screw compressor 2) acts on the rotor shaft 14 via the end surface of the balance piston 28. Thus, the load on the thrust bearing 20 can be reduced.

[0030] As shown in FIG. 2, the screw compressor 2 includes a slide valve 30 for adjusting the capacity according to the load of the screw compressor 2. In the illustrated embodiment, the slide valve 30 is driven by a hydraulic piston 32, and its position in the axial direction can be changed.

[0031] When the slide valve 30 is moved from the suction side to the discharge side in the axial direction, a bypass passage opens facing the tooth groove space in the compression stroke, and the gas in the tooth groove space is returned to a suction chamber with the rotation of the screw rotor, and compression in the tooth groove space starts from where the bypass passage is closed. As the slide valve moves toward the discharge side, the tooth groove space volume at the start of compression becomes smaller. In this way, by changing the position of the slide valve 30 in the axial direction, the volume Vs at the start of compression of each tooth groove space (that is, at the start of volume reduction of each tooth groove space, when the suction port 40 is closed) is changed. Accordingly, the internal volume ratio Vi of the screw compressor 2 (a ratio Vs / Vd of the volume Vs at the start of compression in the tooth groove space to the volume Vd at the end of compression (at the end of volume reduction of the tooth groove space, when the discharge port 42 opens)) is changed. That is, the closer the slide valve 30 is located to the discharge side, the smaller the tooth groove space volume Vs at the start of compression is. Therefore, the positioning of the slide valve 30 closer to the discharge side is a factor that decreases the internal volume ratio Vi (= Vs / Vd).

[0032] As described above, the discharge port 42 includes the radial discharge port 46 and the axial discharge port 44.

[0033] The radial discharge port 46 is formed by a notch 31 of the slide valve 30. The opening area of the radial discharge port 46 is maximum when the slide valve 30 is located most on the suction side in the axial direction, and decreases as the position of the slide valve 30 becomes closer to the discharge side. When the slide valve 30 reaches a predetermined axial position, the radial discharge port 46 is closed, and the opening area of the radial discharge port 46 becomes zero. The smaller the opening area of the radial discharge port 46, the smaller the volume Vd at the timing when the discharge port 42 opens for each tooth groove space. Therefore, the decrease in the opening area of the radial discharge port 46 by moving the slide valve 30 toward the discharge side is a factor that increases the internal volume ratio Vi (= Vs / Vd).

[0034] The axial discharge port 44 is at least partially formed by an opening 52 (see FIG. 3) provided on an end surface of the casing 12. The opening 52 is disposed on a rotor facing surface 50 (end surface of the casing 12) of the casing 12 facing a discharge-side end surface 48 of the screw rotor (the male rotor 15 and the female rotor 17) so as to communicate with the discharge space 43.

[0035] Here, FIGs. 4 and 6 are schematic cross-sectional views showing the vicinity of the axial discharge port 44 of the screw compressor according to an embodiment, corresponding to cross-section B-B of FIG. 3. FIGs. 5 and 7 are schematic views showing the contour of the axial discharge port 44 shown in FIGs. 4 and 6, respectively. FIGs. 8 to 11 are views showing the vicinity of the axial discharge port 44 of the screw compressor according to another embodiment, corresponding to FIGs. 4 to 7, respectively. FIGs. 4, 6, 8, and 10, and FIGs. 12 and 13 described later are cross-sectional views in the vicinity of the discharge port 42 on the male rotor 15 side, and hatched lines shown in the screw rotor in these figures indicate tooth tips of the screw rotor around the axial discharge port. That is, these figures show how the volume of the tooth groove space decreases toward the discharge port 42.

[0036] As shown in FIG. 3, and FIGs. 4, 6, 8, and 10, in some embodiments, the screw compressor 2 includes a movable piece 54 disposed along an edge of the opening 52 provided in the above-described casing 12. The movable piece 54 is capable of blocking a part of the opening 52.

[0037] The movable piece 54 includes a first end surface 54a and a second end surface 54b which are both end surfaces in the axial direction. The first end surface 54a is an end surface facing the discharge-side end surface 48 of the screw rotor (the male rotor 15 and the female rotor 17), and the second end surface 54b is an end surface opposite to the first end surface 54a in the axial direction.

[0038] In the exemplary embodiments shown in FIGs. 4 to 11, the movable piece 54 includes a piston 56 capable of advancing and retreating in the axial direction. The piston 56 is inserted into a hole 68 extending along the axial direction provided in the casing 12, and is prevented from coming out of the hole 68 by a plug 66.

[0039] In the exemplary embodiments shown in FIGs. 4 to 7, the first end surface 54a and the second end surface 54b of the above-described movable piece 54 are formed by both end surfaces of the piston 56.

[0040] In the exemplary embodiments shown in FIGs. 8 to 11, the movable piece 54 includes, in addition to the piston 56 capable of advancing and retreating in the axial direction, a plate-like member 78 attached to an end portion of the piston 56 on the suction side in the axial direction. The first end surface 54a of the movable piece 54 is formed by an end surface of the plate-like member 78 on the suction side in the axial direction, and the second end surface 54b of the movable piece 54 is formed by an end surface of the piston 56 on the discharge side in the axial direction.

[0041] The movable piece 54 is configured to be movable between a first position in the axial direction (see FIGs. 4 to 5 and FIGs. 8 to 9) and a second position farther away from the screw rotor in the axial direction than the first position (see FIGs. 6 to 7 and FIGs. 10 to 11). That is, the movable piece 54 at the second position is located on the discharge side in the axial direction relative to the movable piece 54 at the first position.

[0042] For example, as shown in FIGs. 4 to 5 and FIGs. 8 to 9, a first contour 101, which is the contour of the axial discharge port 44 when the movable piece 54 is at the first position, is formed by the movable piece 54 and the edge of the opening 52 provided in the casing 12 (see FIGs. 5 and 9). That is, the movable piece 54 at the first position blocks a part of the opening 52 in the casing 12, and therefore, the opening area of the axial discharge port 44 when having the first contour 101 is smaller than the opening area of the opening 52 of the casing 12. When the movable piece 54 is at the first position, the first end surface 54a of the movable piece 54 is flush with the rotor facing surface 50 of the casing 12.

[0043] Further, for example, as shown in FIGs. 6 to 7 and FIGs. 10 to 11, when the movable piece 54 is at the second position, a second contour 102, which is the contour of the axial discharge port 44, is formed by the edge of the opening 52 provided in the casing 12 (see FIGs. 7 and 11). That is, the opening area of the axial discharge port 44 when having the second contour 102 is larger than the opening area of the axial discharge port 44 when having the first contour 101. When the movable piece 54 is at the second position, the first end surface 54a of the movable piece 54 is located on the discharge side in the axial direction relative to the rotor facing surface 50 of the casing 12.

[0044] In the exemplary embodiments shown in FIGs. 4 to 7, when the movable piece 54 is at the first position, the end surface of the piston 56 on the suction side in the axial direction (the first end surface 54a of the movable piece 54) is flush with the rotor facing surface 50 of the casing 12 (see FIG. 4), and the piston 56 forms a part of the first contour 101 (see FIG. 5).

[0045] In the exemplary embodiments shown in FIGs. 8 to 11, when the movable piece 54 is at the first position, the end surface of the plate-like member 78 on the suction side in the axial direction (the first end surface 54a of the movable piece 54) is flush with the rotor facing surface 50 of the casing 12 (see FIG. 8), and the plate-like member 78 forms a part of the first contour 101 (see FIG. 9).

[0046] In the above-described embodiments, the movable piece 54 disposed along the edge of the opening 52 of the casing 12 forming the axial discharge port 44 is movable between the first position in the axial direction and the second position farther away from the screw rotor (the male rotor 15 and the female rotor 17) than the first position. When the movable piece 54 is at the second position, the opening area of the axial discharge port 44 is larger than when it is at the first position. Therefore, under operating conditions where the internal volume ratio Vi of the screw compressor 2 is relatively high (for example, when the slide valve 30 is located relatively on the suction side in the axial direction), by positioning the movable piece 54 at the second position, the opening area of the axial discharge port 44 is made relatively large, whereby an increase in gas flow velocity at the discharge port 42 can be suppressed, and an increase in discharge loss can be suppressed. Further, under operating conditions where the internal volume ratio Vi of the screw compressor 2 is relatively low (for example, when the slide valve 30 is located relatively on the discharge side in the axial direction), by positioning the movable piece 54 at the first position, the opening area of the axial discharge port 44 is made relatively small, whereby an increase in discharge loss due to insufficient compression can be suppressed. Therefore, according to the above-described embodiments, by switching the position of the movable piece 54 between the first position and the second position according to the internal volume ratio Vi, discharge loss can be suppressed over a wide operating region (internal volume ratio Vi).

[0047] In the above-described embodiments, the movable piece 54 includes the piston 56 capable of advancing and retreating in the axial direction. That is, since the movable piece 54 (piston 56) advances and retreats in a direction perpendicular to the discharge-side end surface 48 of the screw rotor, interference between the movable piece 54 and the screw rotor is unlikely to occur, and damage due to contact between them or the like can be suppressed.

[0048] In the exemplary embodiments shown in FIGs. 4 to 7, when the movable piece 54 including the piston 56 is at the first position, the end surface of the piston 56 (the first end surface 54a of the movable piece 54) is flush with the rotor facing surface 50 of the casing 12, and the piston 56 itself forms the contour (first contour) of the axial discharge port 44. Thus, the screw compressor 2 including the above-described movable piece 54 can be achieved with a simple configuration.

[0049] In the exemplary embodiments shown in FIGs. 8 to 11, when the movable piece 54 including the plate-like member 78 attached to the end portion of the piston 56 is at the first position, the end surface of the plate-like member 78 (the first end surface 54a of the movable piece 54) is flush with the rotor facing surface 50 of the casing 12, and the plate-like member 78 forms the contour (first contour) of the axial discharge port 44. Here, since any shape can be used for the plate-like member 78, by making the shape of the plate-like member 78 appropriate, the shape of the first contour of the axial discharge port 44 can be easily optimized according to the tooth profile of the screw rotor or the like.

[0050] In some embodiments, as shown in FIGs. 4, 6, 8, and 10, the piston 56 has a first portion 58, and a second portion 60 adjacent to the first portion 58 in the axial direction, located on the discharge side of the first portion 58 in the axial direction, and having a diameter larger than that of the first portion 58. A stepped portion 61 is formed between the first portion 58 and the second portion 60 in the axial direction, and the movement of the piston 56 in a direction from the second position toward the first position (that is, a direction from the discharge side to the suction side in the axial direction) is restricted by the stepped portion 61.

[0051] In the illustrated embodiment, the casing 12 is provided with a position regulating surface 76 facing the discharge side in the axial direction, and the position of the piston 56 in the axial direction is restricted by contact between a surface of the second portion 60 of the piston 56 forming the stepped portion 61 and the position regulating surface 76.

[0052] By providing the stepped portion 61, the movement of the piston 56 in the direction from the second position toward the first position is restricted, so that the end surface of the piston 56 (the first end surface 54a of the movable piece 54) can be prevented from protruding toward the screw rotor from the position of the rotor facing surface 50 of the casing 12. Therefore, contact between the piston 56 and the discharge-side end surface 48 of the screw rotor can be suppressed.

[0053] In some embodiments, as shown in FIGs. 4, 6, 8, and 10, the screw compressor 2 includes a communication passage 74 communicating the discharge space 43 with a back-side space 72 where the second end surface 54b of the movable piece 54 is exposed. In the illustrated embodiment, the back-side space 72 is formed between the second end surface 54b of the movable piece 54 and the plug 66.

[0054] As shown in FIGs. 4, 6, 8, and 10, a biasing member 62 (e.g., a spring) for applying a preload to the movable piece 54 in a direction from the discharge side to the suction side in the axial direction (that is, a direction from the movable piece 54 toward the screw rotor) may be provided between the movable piece 54 (piston 56) and the plug 66 in the axial direction.

[0055] According to the above-described embodiments, the first end surface 54a of the movable piece 54 faces the tooth groove space immediately upstream of the axial discharge port 44 (i.e., the tooth groove space immediately before discharge), and the second end surface 54b of the movable piece 54 faces the back-side space 72 communicating with the discharge space 43. Therefore, the movable piece 54 can be automatically driven by the pressure difference between the tooth groove space immediately upstream of the axial discharge port 44 and the discharge space 43.

[0056] Specifically, under operating conditions where the internal volume ratio Vi is relatively low, the pressure in the tooth groove space immediately upstream of the axial discharge port 44 is equal to or lower than the pressure in the discharge space 43. At this time, the movable piece 54 is located at the first position due to the difference in pressure acting on both end surfaces (the first end surface 54a and the second end surface 54b). On the other hand, under operating conditions where the internal volume ratio Vi is relatively high, the pressure in the tooth groove space immediately upstream of the axial discharge port 44 is higher than the pressure in the discharge space 43. Therefore, a force directed from the first end surface 54a toward the second end surface 54b acts on the movable piece 54 due to the difference in pressure acting on the first end surface 54a and the second end surface 54b, so that the movable piece 54 is located at the second position.

[0057] Thus, according to the above-described embodiment, the movable piece 54 can be automatically and appropriately driven according to the difference in pressure acting on both end surfaces (the first end surface 54a and the second end surface 54b) of the movable piece 54 such that the movable piece 54 is located at the first position when the internal volume ratio Vi is relatively low, and the movable piece 54 is located at the second position when the internal volume ratio Vi is relatively high. As a result, discharge loss can be suppressed over a wide operating region (internal volume ratio Vi).

[0058] FIGs. 12 and 13 are schematic cross-sectional views showing the vicinity of an axial discharge port 44 of a screw compressor according to an embodiment, respectively, showing modifications of the embodiment shown in FIGs. 4 to 11. FIGs. 12 and 13 are views corresponding to FIG. 4 (views including the movable piece 54 at the first position), and views including the movable piece 54 at the second position (views corresponding to FIG. 6) are omitted. In FIGs. 12 and 13, elements denoted by the same reference numerals as those shown in FIGs. 4 to 11 are not described to avoid repetition.

[0059] In the exemplary embodiments shown in FIGs. 12 and 13, the above-described communication passage 74 is not provided. Instead, the screw compressor 2 according to the present embodiments includes a high-pressure line 82 for introducing a high-pressure fluid having a pressure higher than that of the discharge space 43 into the back-side space 72 which the second end surface 54b of the movable piece 54 faces, and a valve 84 disposed in the high-pressure line 82. In the illustrated embodiments, the high-pressure fluid from the high-pressure line 82 is introduced into the back-side space 72 via an internal passage 80 disposed in the casing 12.

[0060] In an embodiment, the oil pressurized by the pump 8 in the oil supply line 10 (pressure Poil: Pd + α) may be supplied to the back-side space 72 through the high-pressure line 82.

[0061] In the above-described embodiments, by appropriately operating the valve 84, the high-pressure fluid can be introduced through the high-pressure line 82 into the back-side space 72 where the second end surface 54b of the movable piece 54 is exposed. Thus, the movable piece 54 can be forcibly moved from the second position to the first position.

[0062] For example, even when the load of the screw compressor 2 is relatively high and the pressure in the tooth groove space immediately upstream of the axial discharge port 44 is relatively high, by appropriately operating the valve 84 to introduce the high-pressure fluid from the high-pressure line 82 into the back-side space 72 and forcibly moving the movable piece 54 from the second position to the first position as necessary, the opening area of the axial discharge port 44 can be narrowed to increase the internal volume ratio Vi.

[0063] The exemplary embodiment shown in FIG. 12 further includes an orifice 88 connecting the back-side space 72 and the discharge space 43.

[0064] In the above-described embodiment, since the back-side space 72 and the discharge space 43 are connected via the orifice 88, while the valve 84 is opened and the high-pressure fluid is supplied from the high-pressure line 82 to the back-side space 72, the inside of the back-side space 72 can be maintained at an appropriate pressure higher than the discharge space 43 to maintain the movable piece at the first position. The high-pressure oil in the back-side space 72 is appropriately discharged to the discharge space 43 through the orifice 88. Further, while the valve 84 is closed and the supply of the high-pressure fluid from the high-pressure line 82 to the back-side space 72 is stopped, the pressure in the back-side space 72 becomes equal to the pressure in the discharge space 43. Therefore, as already described, the movable piece 54 can be automatically driven by the pressure difference between the tooth groove space immediately upstream of the axial discharge port 44 and the discharge space 43 (that is, the difference in pressure acting on the first end surface 54a and the second end surface 54b of the movable piece 54) to be moved between the first position and the second position.

[0065] In the exemplary embodiment shown in FIG. 13, the screw compressor 2 includes a low-pressure line 90 connected to a low-pressure source having a pressure lower than that of the discharge space 43. Further, the valve 84 is configured to be capable of switching a connection destination of the back-side space 72 between the high-pressure line 82 and the low-pressure line 90.

[0066] The above-described low-pressure source may be gas at the suction pressure Ps, and the low-pressure line 90 may be branched from a suction line (not shown) for introducing a suction gas (pressure: Ps) into the screw compressor 2. Further, the above-described valve 84 may include a three-way valve disposed between the back-side space 72, and the high-pressure line 82 and the low-pressure line 90.

[0067] In the above-described embodiment, by appropriately operating the valve 84, the connection destination of the back-side space 72 where the second end surface 54b of the movable piece 54 is exposed can be switched between the high-pressure line 82 and the low-pressure line 90. By connecting the back-side space 72 to the high-pressure line 82, the high-pressure fluid can be introduced into the back-side space 72 to forcibly move the movable piece 54 from the second position to the first position. Additionally, by connecting the back-side space 72 to the low-pressure line 90, the low-pressure fluid from the low-pressure source can be introduced into the back-side space 72 to forcibly move the movable piece 54 from the first position to the second position. That is, according to the operating status of the screw compressor 2, by operating the valve 84 to switch the connection destination of the back-side space 72 between the high-pressure line 82 and the low-pressure line 90, the position of the movable piece 54 can be appropriately changed between the first position and the second position. This enables more flexible operation of the screw compressor 2, making it easier to suppress discharge loss over a wide operating region (internal volume ratio).

[0068] As described above, the exemplary embodiments shown in FIGs. 12 and 13 enable more flexible operation of the screw compressor 2, making it easier to suppress discharge loss over a wide operating region (internal volume ratio).

[0069] The contents described in the above embodiments would be understood as follows, for instance. [1] A screw compressor (2) according to at least one embodiment of the present invention includes: a screw rotor (e.g., a male rotor 15 and a female rotor 17) having a discharge-side end surface (48); a casing (2) having a rotor facing surface (50) facing the discharge-side end surface, and an opening (52) disposed on the rotor facing surface and communicating with a discharge space (43) into which a gas compressed by the screw rotor is to be discharged; a slide valve (30) whose position in an axial direction of the screw rotor is variable so as to change an internal volume ratio; and a movable piece (54) disposed along an edge of the opening of the casing and configured to be capable of blocking a part of the opening.

[0070] The movable piece is configured to be movable between a first position where the movable piece forms a first contour (101) of an axial discharge port (44) together with the edge of the opening, and a second position farther away from the screw rotor in the axial direction than the first position.

[0071] The screw compressor is configured such that when the movable piece is located at the second position, a second contour (102) of the axial discharge port having an opening area larger than that of the first contour is formed by the opening.

[0072] In the above configuration [1], the movable piece disposed along the edge of the opening of the casing forming the axial discharge port is movable between the first position in the axial direction and the second position farther away from the screw rotor than the first position. When the movable piece is located at the second position, the opening area of the axial discharge port is larger than when it is located at the first position. Therefore, under operating conditions where the internal volume ratio of the screw compressor is relatively high, by positioning the movable piece at the second position, the opening area of the axial discharge port is made relatively large, whereby an increase in gas flow velocity at the discharge port can be suppressed, and an increase in discharge loss can be suppressed. Further, under operating conditions where the internal volume ratio of the screw compressor is relatively low, by positioning the movable piece at the first position, the opening area of the axial discharge port is made relatively small, whereby an increase in discharge loss due to insufficient compression can be suppressed. Therefore, with the above configuration [1], by switching the position of the movable piece between the first position and the second position according to the internal volume ratio, discharge loss can be suppressed over a wide operating region (internal volume ratio).

[0073] [2] In some embodiments, in the above configuration [1], the movable piece includes a piston (56) capable of advancing and retreating in the axial direction.

[0074] With the above configuration [2], the screw compressor including the movable piece described in [1] above can be achieved with a simple configuration using the piston capable of advancing and retreating in the axial direction.

[0075] [3] In some embodiments, in the above configuration [2], the screw compressor is configured such that when the movable piece is at the first position, an end surface of the piston in the axial direction (e.g., the first end surface 54a of the movable piece 54) is flush with the rotor facing surface of the casing, and the piston forms a part of the first contour.

[0076] With the above configuration [3], when the movable piece including the piston is at the first position, the end surface of the piston is flush with the rotor facing surface of the casing, and the piston itself forms the contour (first contour) of the axial discharge port. Thus, the screw compressor including the movable piece described in [1] above can be achieved with a simple configuration.

[0077] [4] In some embodiments, in the above configuration [2], the movable piece includes a plate-like member (78) attached to an end portion of the piston in the axial direction.

[0078] The screw compressor is configured such that when the movable piece is at the first position, an end surface of the plate-like member in the axial direction (e.g., the first end surface 54a of the movable piece 54) is flush with the rotor facing surface of the casing, and the plate-like member forms a part of the first contour.

[0079] With the above configuration [4], when the movable piece including the plate-like member attached to the end portion of the piston is at the first position, the end surface of the plate-like member is flush with the rotor facing surface of the casing, and the plate-like member forms the contour (first contour) of the axial discharge port. Here, since any shape can be used for the plate-like member, the shape of the first contour of the axial discharge port can be easily optimized according to the tooth profile shape of the screw rotor or the like.

[0080] [5] In some embodiments, in any one of the above configurations [2] to [4], the piston has: a first portion (58); and a second portion (60) disposed opposite to the screw rotor across the first portion in the axial direction and having a diameter larger than that of the first portion.

[0081] The screw compressor is configured such that movement of the piston in a direction from the second position toward the first position is restricted by a stepped portion (61) formed by the first portion and the second portion.

[0082] With the above configuration [5], since the movement of the piston in the direction from the second position toward the first position is restricted by the stepped portion of the piston, the end surface of the piston can be prevented from protruding toward the screw rotor from the position of the rotor facing surface of the casing. Therefore, contact between the piston and the end surface of the screw rotor can be suppressed.

[0083] [6] In some embodiments, in any one of the above configurations [1] to [5], the movable piece has a first end surface (54a) facing the screw rotor, and a second end surface (54b) opposite to the first end surface in the axial direction.

[0084] The screw compressor includes a communication passage (74) communicating the discharge space with a back-side space (72) where the second end surface is exposed.

[0085] With the above configuration [6], the first end surface of the movable piece faces the tooth groove space immediately upstream of the axial discharge port (i.e., the tooth groove space immediately before discharge), and the second end surface of the movable piece faces the back-side space communicating with the discharge space. Therefore, the movable piece can be automatically driven by the pressure difference between the above-described tooth groove space and the discharge space. That is, according to the above-described pressure difference, the movable piece can be automatically and appropriately driven such that the movable piece is located at the first position when the internal volume ratio is relatively low, and the movable piece is located at the second position when the internal volume ratio is relatively high.

[0086] [7] In some embodiments, in any one of the above configurations [1] to [5], the movable piece has a first end surface (54a) facing the screw rotor, and a second end surface (54b) opposite to the first end surface in the axial direction.

[0087] The screw compressor includes: a high-pressure line (82) for introducing a high-pressure fluid having a pressure higher than that of the discharge space into a back-side space (72) where the second end surface is exposed; and a valve (84) disposed between the back-side space and the high-pressure line.

[0088] With the above configuration [7], by appropriately operating the valve, the high-pressure fluid can be introduced through the high-pressure line into the back-side space where the second end surface of the movable piece is exposed, whereby the movable piece can be forcibly moved from the second position to the first position. Therefore, for example, even when the load of the screw compressor is relatively high and the pressure in the tooth groove space immediately upstream of the axial discharge port is relatively high, by operating the valve to introduce the high-pressure fluid into the back-side space as necessary and thereby forcibly moving the movable piece from the second position to the first position, the opening area of the discharge port can be narrowed to increase the internal volume ratio. This enables more flexible operation of the screw compressor, making it easier to suppress discharge loss over a wide operating region (internal volume ratio).

[0089] [8] In some embodiments, in the above configuration [7], the screw compressor includes an orifice (88) connecting the discharge space and the back-side space where the second end surface is exposed.

[0090] With the above configuration [8], since the back-side space and the discharge space are connected via the orifice, while the valve is opened and the high-pressure fluid is supplied from the high-pressure line to the back-side space, the inside of the back-side space can be maintained at an appropriate pressure higher than the discharge space to maintain the movable piece at the first position. Further, while the valve is closed and the supply of the high-pressure fluid from the high-pressure line to the back-side space is stopped, the pressure in the back-side space becomes equal to the pressure in the discharge space. Therefore, similarly to the description in [6] above, the movable piece can be automatically driven by the pressure difference between the tooth groove space immediately upstream of the axial discharge port and the discharge space.

[0091] [9] In some embodiments, in the above configuration [7], the screw compressor includes a low-pressure line (90) connected to a low-pressure source having a pressure lower than that of the discharge space.

[0092] The valve is configured to be capable of switching a connection destination of the back-side space between the high-pressure line and the low-pressure line.

[0093] With the above configuration [9], by appropriately operating the valve, the connection destination of the back-side space where the second end surface of the movable piece is exposed can be switched between the high-pressure line and the low-pressure line. Here, by connecting the back-side space to the high-pressure line, the high-pressure fluid can be introduced into the back-side space to forcibly move the movable piece from the second position to the first position. Additionally, by connecting the back-side space to the low-pressure line, the low-pressure fluid from the low-pressure source can be introduced into the back-side space to forcibly move the movable piece from the first position to the second position. That is, according to the operating status of the screw compressor, by operating the valve to switch the connection destination of the back-side space between the high-pressure line and the low-pressure line, the position of the movable piece can be appropriately changed between the first position and the second position. This enables more flexible operation of the screw compressor, making it easier to suppress discharge loss over a wide operating region (internal volume ratio).

[0094]

[10] A gas compression facility (1) according to at least one embodiment of the present invention includes: the screw compressor (2) according to any one of [1] to [9] configured to compress a gas; and an oil separator (4) for separating the oil from a mixture of compressed gas and oil discharged from the screw compressor.

[0095] In the above configuration

[10] , the movable piece disposed along the edge of the opening of the casing forming the discharge port is movable between the first position in the axial direction and the second position farther away from the screw rotor than the first position. When the movable piece is located at the second position, the opening area of the axial discharge port is larger than when it is located at the first position. Therefore, under operating conditions where the internal volume ratio of the screw compressor is relatively high, by positioning the movable piece at the second position, the opening area of the axial discharge port is made relatively large, whereby an increase in gas flow velocity at the discharge port can be suppressed and an increase in discharge loss can be suppressed. Further, under operating conditions where the internal volume ratio of the screw compressor is relatively low, by positioning the movable piece at the first position, the opening area of the axial discharge port is made relatively small, whereby an increase in discharge loss due to insufficient compression can be suppressed. Therefore, with the above configuration

[10] , by switching the position of the movable piece between the first position and the second position according to the internal volume ratio, discharge loss can be suppressed over a wide operating region (internal volume ratio).

[0096] Embodiments of the present invention were described in detail above, but the present invention is not limited thereto, and various amendments and modifications may be implemented.

[0097] In the present specification, an expression of relative or absolute arrangement such as "in a direction", "along a direction", "parallel", "orthogonal", "centered", "concentric" and "coaxial" shall not be construed as indicating only the arrangement in a strict literal sense, but also includes a state where the arrangement is relatively displaced by a tolerance, or by an angle or a distance whereby it is possible to achieve the same function.

[0098] For instance, an expression of an equal state such as "same", "equal", and "uniform" shall not be construed as indicating only the state in which the feature is strictly equal, but also includes a state in which there is a tolerance or a difference that can still achieve the same function.

[0099] Further, an expression of a shape such as a rectangular shape or a cylindrical shape shall not be construed as only the geometrically strict shape, but also includes a shape with unevenness or chamfered corners within the range in which the same effect can be achieved.

[0100] On the other hand, an expression such as "comprise", "include", and "have" are not intended to be exclusive of other components.Reference Signs List

[0101] 1Gas compression facility 2Screw compressor 4Oil separator .6Cooler 8Pump 10Oil supply line 12Casing 14Rotor shaft 15Male rotor 16Rotor shaft 17Female rotor 18Radial bearing 20Thrust bearing 24Shaft seal part 28Balance piston 29Balance piston chamber 30Slide valve 31Notch 32Hydraulic piston 40Suction port 41Suction space 42Discharge port 43Discharge space 44Axial discharge port 46Radial discharge port 48Discharge-side end surface 50Rotor facing surface 52Opening 54Movable piece 54aFirst end surface 54bSecond end surface 56Piston 58First portion 60Second portion 61Stepped portion 62Biasing member 66Plug 68Hole 72Back-side space 74Communication passage 76Position regulating surface 78Plate-like member 80Internal passage 82High-pressure line 84Valve 88Orifice 90Low-pressure line 101First contour 102Second contour PdDischarge pressure PsSuction pressure

Claims

1. A screw compressor, comprising: a screw rotor having a discharge-side end surface; a casing having a rotor facing surface facing the discharge-side end surface, and an opening disposed on the rotor facing surface and communicating with a discharge space into which a gas compressed by the screw rotor is to be discharged; a slide valve whose position in an axial direction of the screw rotor is variable so as to change an internal volume ratio; and a movable piece disposed along an edge of the opening of the casing and configured to be capable of blocking a part of the opening, wherein the movable piece is configured to be movable between a first position where the movable piece forms a first contour of an axial discharge port together with the edge of the opening, and a second position farther away from the screw rotor in the axial direction than the first position, and wherein the screw compressor is configured such that when the movable piece is located at the second position, a second contour of the axial discharge port having an opening area larger than that of the first contour is formed by the opening.

2. The screw compressor according to claim 1, wherein the movable piece includes a piston capable of advancing and retreating in the axial direction.

3. The screw compressor according to claim 2, wherein the screw compressor is configured such that when the movable piece is at the first position, an end surface of the piston in the axial direction is flush with the rotor facing surface of the casing, and the piston forms a part of the first contour.

4. The screw compressor according to claim 2, wherein the movable piece includes a plate-like member attached to an end portion of the piston in the axial direction, and wherein the screw compressor is configured such that when the movable piece is at the first position, an end surface of the plate-like member in the axial direction is flush with the rotor facing surface of the casing, and the plate-like member forms a part of the first contour.

5. The screw compressor according to any one of claims 2 to 4, wherein the piston has: a first portion; and a second portion disposed opposite to the screw rotor across the first portion in the axial direction and having a diameter larger than that of the first portion, and wherein the screw compressor is configured such that movement of the piston in a direction from the second position toward the first position is restricted by a stepped portion formed by the first portion and the second portion.

6. The screw compressor according to any one of claims 1 to 4, wherein the movable piece has a first end surface facing the screw rotor, and a second end surface opposite to the first end surface in the axial direction, and wherein the screw compressor comprises a communication passage communicating the discharge space with a back-side space where the second end surface is exposed.

7. The screw compressor according to any one of claims 1 to 4, wherein the movable piece has a first end surface facing the screw rotor, and a second end surface opposite to the first end surface in the axial direction, and wherein the screw compressor comprises: a high-pressure line for introducing a high-pressure fluid having a pressure higher than that of the discharge space into a back-side space where the second end surface is exposed; and a valve disposed between the back-side space and the high-pressure line.

8. The screw compressor according to claim 7, comprising an orifice connecting the discharge space and the back-side space where the second end surface is exposed.

9. The screw compressor according to claim 7, comprising a low-pressure line connected to a low-pressure source having a pressure lower than that of the discharge space, wherein the valve is configured to be capable of switching a connection destination of the back-side space between the high-pressure line and the low-pressure line.

10. A gas compression facility, comprising: the screw compressor according to any one of claims 1 to 4 configured to compress a gas; and an oil separator for separating the oil from a mixture of compressed gas and oil discharged from the screw compressor.

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