Screw compressor and gas compression facility

Abstract

A screw compressor according to the present invention comprises: screw rotors that have a discharge-side end surface; a casing that has a rotor-facing surface which faces the discharge-side end surface and an opening which is provided on the rotor-facing surface and which is in communication with a discharge space for discharging gas having been compressed by the screw rotors; a slide valve that has a position which is variable in the axial direction of the screw rotors to change the internal volume ratio; and a moveable piece that is provided along the edge of the opening of the casing and that is capable of partially closing the opening. The moveable piece is capable of moving between a first position at which the moveable piece and the edge of the opening together form a first contour of an axial discharge port and a second position which is further distanced from the screw rotors in the axial direction than the first position. When the moveable piece is at the second position, the opening forms a second contour of the axial discharge port, which is larger than the first contour in opening area.

Description

Screw compressors and gas compression equipment

[0001] The present disclosure relates to screw compressors and gas compression equipment.

[0002] Positive displacement screw compressors have the excellent advantages of simple structure and good durability, and are widely used. The representative methods for capacity control in screw compressors are the rotation speed control method and the slide valve method, and large screw compressors generally use the slide valve method for capacity control.

[0003] In the slide valve system, the volume of the tooth space formed between the male rotor and the female rotor at the start of compression can be changed by axially moving the slide valve, which forms a rotor chamber together with the casing. This allows for continuous adjustment of the compressed gas volume according to the load of the screw compressor. Meanwhile, screw compressors have a volume ratio Vi (= suction volume V1 / discharge volume V2) suitable for their operating conditions, and the positions and shapes of the suction port and discharge port are determined so that the discharge of the compressed gas begins at a timing corresponding to the volume ratio Vi suitable for the operating conditions. Most existing screw compressors have a fixed internal volume ratio Vi, and therefore have a discharge port shaped to select an average internal volume ratio. However, in screw compressors equipped with the above-mentioned slide valve, the internal volume ratio (the ratio of the volume at the start of compression of the tooth space (when volume reduction begins) to the end of compression (when volume reduction ends)) can also be changed by moving the slide valve.

[0004] Patent Document 1 describes a screw compressor that includes the above-mentioned slide valve and is capable of adjusting the internal volume ratio.

[0005] International Publication No. 2016 / 147467

[0006] However, when attempting to increase the size of a screw compressor while maintaining the internal volume ratio of the discharge port, the area ratio of the discharge port to the displacement decreases, and the gas flow velocity at the discharge port increases. When the gas flow velocity at the discharge port increases in this way, the pressure in the tooth groove space increases due to the passage resistance at the discharge port, causing overcompression, which may increase discharge loss.

[0007] On the other hand, by increasing the area of ​​the discharge port (low internal volume ratio), the increase in gas flow rate at the discharge port can be suppressed, making the problem of increased discharge loss less likely to occur. However, in an operating range requiring a high internal volume ratio, gas that flows back from the discharge side due to insufficient compression is recompressed and discharged, which may still increase discharge loss.

[0008] In view of the above circumstances, an object of at least one embodiment of the present invention is to provide a screw compressor and gas compression equipment that can suppress discharge loss over a wide operating range (range of internal volume ratio).

[0009] A screw compressor according to at least one embodiment of the present invention comprises: a screw rotor having a discharge side end face; a rotor opposing surface facing the discharge side end face; and a casing having an opening provided on the rotor opposing surface and communicating with a discharge space into which gas compressed by the screw rotor is discharged; a slide valve whose position in the axial direction of the screw rotor is variable so as to change the internal volume ratio; and a movable piece provided along the edge of the opening of the casing and configured to be able to block a portion 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 that is farther away from the screw rotor in the axial direction than the first position, and wherein when the movable piece is located at the second position, the opening forms a second contour of the axial discharge port having an opening area larger than the first contour.

[0010] Furthermore, a gas compression facility according to at least one embodiment of the present invention includes the above-described screw compressor configured to compress gas, and an oil separator for separating the oil from a mixture of compressed gas and oil discharged from the screw compressor.

[0011] According to at least one embodiment of the present invention, there is provided a screw compressor and gas compression equipment capable of suppressing discharge loss over a wide operating range (range of internal volume ratio).

[0012] FIG. 1 is a schematic diagram of a gas compression facility according to an embodiment. FIG. 2 is a schematic cross-sectional side view of a screw compressor according to an embodiment. FIG. 3 is a diagram showing an A-A cross section of the screw compressor shown in FIG. 2. 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 cross-sectional view 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 cross-sectional view 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. 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 cross-sectional view showing the vicinity of an axial discharge port of a screw compressor according to an embodiment.

[0013] Hereinafter, several embodiments of the present invention will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of components described as embodiments or shown in the drawings are merely illustrative examples and are not intended to limit the scope of the present invention.

[0014] 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.

[0015] The screw compressor 2 is configured to compress and discharge the gas that it has drawn in. In the drawing, the symbol Ps indicates the suction pressure of the screw compressor 2, and the symbol Pd indicates the discharge pressure of the screw compressor 2. Oil is supplied to the screw compressor 2 via an oil supply line 10 for cooling, lubrication, etc. The oil supplied to the screw compressor 2 is discharged together with the compressed gas.

[0016] The oil separator 4 is configured to separate oil from a mixture of compressed gas and oil discharged from the screw compressor 2. The oil separated in the oil separator 4 is supplied again to the screw compressor 2 via an oil supply line 10. Typically, the oil separated in the oil separator 4 is pressurized by a pump 8 and then supplied to the screw compressor 2 via 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 in the oil separator 4 may also be cooled in a cooler 6 and then pressurized by the pump 8.

[0017] (Configuration of screw compressor) Figure 2 is a schematic cross-sectional side view of a screw compressor according to one embodiment. Figure 3 is a view showing a cross section taken along line A-A of the screw compressor shown in Figure 2. As shown in Figures 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 that houses the pair of screw rotors.

[0018] The pair of rotor shafts 14, 16 are rotatably supported by a radial bearing 18 and a thrust bearing 20. Oil at a pressure Poil is supplied to each bearing via an oil supply line 10.

[0019] The male rotor 15 and the female rotor 17 have helical teeth that mesh with each other. The meshing of the teeth of the male rotor 15 and the female rotor 17 and the casing 12 form a plurality of tooth gap spaces along the axial direction of the rotor shafts 14, 16.

[0020] The rotor shaft 14 that constitutes the male rotor 15 is connected to the output shaft of a motor (not shown) and is configured to be rotationally driven by the motor. The female rotor 17 that meshes with the male rotor 15 is rotationally driven by the rotation of the male rotor 15. The female rotor 17 rotates in the opposite direction to the rotation of the male rotor 15. When the male rotor 15 and female rotor 17 rotate in their meshed state, the tooth groove space moves axially from the suction side to the discharge side.

[0021] A shaft seal 24 for suppressing gas leakage through the penetration portion of the casing 12, which is formed by the rotor shaft 14, is provided at the penetration portion. Oil at a pressure Poil may be supplied to the shaft seal 24 through the oil supply line 10.

[0022] The oil supplied to the bearings and shaft seal portion 24 is discharged from the casing 12 and returned to a relatively low-pressure space in the screw rotor accommodating portion of the casing 12 via a return line (not shown).

[0023] Gas is drawn into the tooth groove spaces from suction spaces 41 formed in the casing 12 via suction ports 40. When the male rotor 15 and the female rotor 17 rotate, the tooth groove spaces move axially from the suction side to the discharge side in accordance with the rotation of these screw rotors. During this process, when the volume of the tooth groove spaces reaches its maximum, the suction ports 40 are closed and the volume of the tooth groove spaces decreases, compressing the gas in the tooth groove spaces. When the tooth groove spaces reach the discharge ports 42 and are connected to the discharge spaces 43 formed in the casing 12, the compressed gas in the tooth groove spaces is discharged into the discharge spaces via the discharge ports 42. The discharge ports 42 will be described in detail later; however, the discharge ports 42 include radial discharge ports 46 for discharging the compressed gas from the tooth groove spaces in the radial direction, and axial discharge ports 44 for discharging the compressed gas from the tooth groove spaces in the axial direction.

[0024] As shown in FIG. 2 , the screw compressor 2 may include a balance piston 28 provided 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 provided on the suction side end of the rotor shaft 14 that constitutes the male rotor 15. Relatively high-pressure oil is supplied from the oil supply line 10 to a balance piston chamber 29 facing the suction side end face of the balance piston 28. As a result, a force (a force in the axial direction from the suction side to the discharge side) opposite to the thrust gas load acting on the rotor shaft 14 (a thrust load acting on the rotor shaft 14 in the axial direction from the discharge side to the suction side due to the 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 face of the balance piston 28. This reduces the load on the thrust bearing 20.

[0025] 2, the screw compressor 2 is provided with a slide valve 30 for adjusting the capacity in accordance with 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.

[0026] When the slide valve 30 is moved axially from the suction side to the discharge side, a bypass passage opens facing the tooth gap space during the compression stroke. As the screw rotor rotates, the gas in the tooth gap space is returned to the suction chamber, and compression in the tooth gap space begins when the bypass passage is closed. The more the slide valve is moved toward the discharge side, the smaller the tooth gap space volume at the start of compression. In this way, changing the axial position of the slide valve 30 can change the volume Vs of each tooth gap space at the start of compression (i.e., when the volume of each tooth gap space starts to decrease and the suction port 40 is closed). This changes the internal volume ratio Vi of the screw compressor 2 (the ratio Vs / Vd of the volume Vs of the tooth gap space at the start of compression to the volume Vd at the end of compression (when the volume of the tooth gap space ends to decrease and the discharge port 42 is opened)). That is, the more the slide valve 30 is positioned toward the discharge side, the smaller the tooth gap space volume Vs at the start of compression. Therefore, the positioning of the slide valve 30 closer to the discharge side is a factor in the reduction of the internal volume ratio Vi (=Vs / Vd).

[0027] The discharge ports 42 include the radial discharge ports 46 and the axial discharge ports 44 as described above.

[0028] The radial discharge port 46 is formed by the notch 31 in the slide valve 30. The opening area of ​​the radial discharge port 46 is largest when the slide valve 30 is positioned closest to the suction side in the axial direction, and decreases as the position of the slide valve 30 approaches 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 reduction in the opening area of ​​the radial discharge port 46 by moving the slide valve 30 to the discharge side is a factor in increasing the internal volume ratio Vi (= Vs / Vd).

[0029] The axial discharge port 44 is at least partially defined by an opening 52 (see FIG. 3 ) provided in the end face of the casing 12. The opening 52 is provided in a rotor-opposing surface 50 (end face of the casing 12) of the casing 12 that faces the discharge-side end faces 48 of the screw rotors (the male rotor 15 and the female rotor 17) so as to communicate with the discharge space 43.

[0030] Here, FIGS. 4 and 6 are schematic cross-sectional views showing the vicinity of the axial discharge port 44 of a screw compressor according to one embodiment, corresponding to the cross section B-B in FIG. 3. FIGS. 5 and 7 are schematic views showing the contours 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 a screw compressor according to another embodiment, corresponding to FIGS. 4 to 7, respectively. Note that FIGS. 4, 6, 8, and 10, as well as FIGS. 12 and 13, which will be described later, are cross-sectional views of the vicinity of the discharge port 42 on the male rotor 15 side. In these figures, the oblique lines in the screw rotor indicate the tooth tips of the screw rotor around the axial discharge port. In other words, these figures show how the volume of the tooth gap space decreases toward the discharge port 42.

[0031] 3, 4, 6, 8, and 10, in some implementations, the screw compressor 2 includes a movable piece 54 provided along the edge of the opening 52 provided in the casing 12. The movable piece 54 is capable of blocking a portion of the opening 52.

[0032] The movable piece 54 includes a first end face 54a and a second end face 54b, which are both end faces in the axial direction. The first end face 54a is an end face facing the discharge-side end faces 48 of the screw rotors (the male rotor 15 and the female rotor 17), and the second end face 54b is an end face opposite the first end face 54a in the axial direction.

[0033] 4 to 11, the movable piece 54 includes a piston 56 that is movable back and forth in the axial direction. The piston 56 is inserted into a hole 68 that is provided in the casing 12 and extends along the axial direction, and is prevented from slipping out of the hole 68 by a plug 66.

[0034] In the exemplary embodiment shown in FIGS. 4 to 7, the first end surface 54 a and the second end surface 54 b of the movable piece 54 are formed by both end surfaces of the piston 56 .

[0035] 8 to 11 , the movable piece 54 includes a piston 56 that is movable back and forth in the axial direction, as well as a plate-like member 78 attached to an end of the piston 56 on the suction side in the axial direction. A 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 a 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.

[0036] The movable piece 54 is configured to be movable between a first position in the axial direction (see FIGS. 4 to 5 and 8 to 9) and a second position (see FIGS. 6 to 7 and 10 to 11) that is farther away from the screw rotor in the axial direction than the first position. That is, the movable piece 54 in the second position is located closer to the discharge side in the axial direction than the movable piece 54 in the first position.

[0037] 4-5 and 8-9, for example, a first contour 101, which is the contour of the axial discharge port 44 when the movable piece 54 is in 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 in the first position blocks a portion of the opening 52 provided in the casing 12, and therefore the opening area of ​​the axial discharge port 44 when it has the first contour 101 is smaller than the opening area of ​​the opening 52 in the casing 12. Note that when the movable piece 54 is in 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.

[0038] 6 to 7 and 10 to 11, when the movable piece 54 is in 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 it has the second contour 102 is larger than the opening area of ​​the axial discharge port 44 when it has the above-mentioned first contour 101. Note that when the movable piece 54 is in the second position, the first end surface 54a of the movable piece 54 is located closer to the discharge side in the axial direction than the rotor-facing surface 50 of the casing 12.

[0039] In the exemplary embodiment shown in Figures 4 to 7, when the movable piece 54 is in the first position described above, the axial end face of the piston 56 on the intake side (first end face 54a of the movable piece 54) is flush with the rotor-facing surface 50 of the casing 12 (see Figure 4), and the piston 56 forms part of the first contour 101 (see Figure 5).

[0040] In the exemplary embodiment shown in Figures 8 to 11, when the movable piece 54 is in the first position described above, the axial end face of the plate-like member 78 on the intake side (first end face 54a of the movable piece 54) is flush with the rotor-facing surface 50 of the casing 12 (see Figure 8), and the plate-like member 78 forms part of the first contour 101 (see Figure 9).

[0041] In the above-described embodiment, the movable piece 54, which is provided along the edge of the opening 52 of the casing 12 that forms the axial discharge port 44, is movable between a first position in the axial direction and a second position that is farther away from the screw rotors (the male rotor 15 and the female rotor 17) than the first position. When the movable piece 54 is located at the second position, the opening area of ​​the axial discharge port 44 is larger than when the movable piece 54 is located at the first position. Therefore, under operating conditions in which the internal volume ratio Vi of the screw compressor 2 is relatively high (for example, when the slide valve 30 is located relatively closer to the suction side in the axial direction), positioning the movable piece 54 at the second position relatively increases the opening area of ​​the axial discharge port 44, thereby suppressing an increase in the gas flow velocity at the discharge port 42 and thereby suppressing an increase in discharge loss. Furthermore, 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 positioned relatively closer to the discharge side in the axial direction), the opening area of ​​the axial discharge port 44 is relatively small by positioning the movable piece 54 in the first position, thereby suppressing an increase in discharge loss due to insufficient compression. Therefore, according to the above-described embodiment, by switching the position of the movable piece 54 between the first position and the second position in accordance with the internal volume ratio Vi, discharge loss can be suppressed over a wide operating range (internal volume ratio Vi).

[0042] In the above-described embodiment, the movable piece 54 includes a piston 56 that can move back and forth in the axial direction. That is, the movable piece 54 (piston 56) moves back and forth in a direction perpendicular to the discharge end face 48 of the screw rotor, so interference between the movable piece 54 and the screw rotor is unlikely to occur, and damage due to contact between the two can be suppressed.

[0043] Furthermore, in the exemplary embodiment shown in FIGS. 4 to 7 , when the movable piece 54 including the piston 56 is in the first position, the end face of the piston 56 (first end face 54 a 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, so that the screw compressor 2 including the above-mentioned movable piece 54 can be realized with a simple configuration.

[0044] 8 to 11 , when the movable piece 54 including the plate-like member 78 attached to the end of the piston 56 is in the first position, the end face of the plate-like member 78 (the first end face 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, any shape can be used for the plate-like member 78, and therefore, by selecting an appropriate shape for the plate-like member 78, it becomes easier to optimize the shape of the first contour of the axial discharge port 44 according to the tooth shape of the screw rotor, etc.

[0045] 4 , 6 , 8 , and 10 , the piston 56 has a first portion 58 and a second portion 60 that is adjacent to the first portion 58 in the axial direction, is located on the discharge side of the first portion 58 in the axial direction, and has a larger diameter than the first portion 58. A step portion 61 is formed between the first portion 58 and the second portion 60 in the axial direction, and this step portion 61 restricts movement of the piston 56 in the direction from the second position toward the first position (i.e., the axial direction from the discharge side toward the suction side).

[0046] In the illustrated embodiment, the casing 12 is provided with a position control surface 76 that faces the discharge side in the axial direction, and the position of the piston 56 in the axial direction is controlled by the surface of the second part 60 of the piston 56 that forms the step portion 61 abutting against the position control surface 76.

[0047] By providing the above-mentioned step portion 61, movement of the piston 56 in the direction from the second position toward the first position is restricted, and it is therefore possible to prevent the end face of the piston 56 (the first end face 54a of the movable piece 54) from protruding toward the screw rotor from the position of the rotor-facing surface 50 of the casing 12. This makes it possible to suppress contact between the piston 56 and the discharge-side end face 48 of the screw rotor.

[0048] 4, 6, 8, and 10, the screw compressor 2 includes a communication passage 74 that connects a back space 72, to which the second end surface 54b of the movable piece 54 is exposed, with the discharge space 43. In the illustrated embodiment, the back space 72 is formed between the second end surface 54b of the movable piece 54 and the plug 66.

[0049] As shown in Figures 4, 6, 8 and 10, a biasing member 62 (e.g., a spring) may be provided between the movable piece 54 (piston 56) and the plug 66 in the axial direction to apply a preload to the movable piece 54 in the direction from the discharge side to the suction side (i.e., the direction from the movable piece 54 to the screw rotor).

[0050] According to the above-described embodiment, the first end surface 54a of the movable piece 54 faces the tooth groove space immediately before 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 that communicates with the discharge space 43. Therefore, the movable piece 54 can be automatically driven by the pressure difference between the tooth groove space immediately before the axial discharge port 44 and the discharge space 43.

[0051] That is, under operating conditions where the internal volume ratio Vi is relatively low, the pressure in the tooth gap space immediately before the axial discharge port 44 is equal to or lower than that of the discharge space 43, and at this time, the movable piece 54 is located at the first position due to the difference in pressure acting on both end faces (the first end face 54a and the second end face 54b). On the other hand, under operating conditions where the internal volume ratio Vi is relatively high, the pressure in the tooth gap space immediately before the axial discharge port 44 is higher than that of the discharge space 43, and therefore a force from the first end face 54a toward the second end face 54b acts on the movable piece 54 due to the difference in pressure acting on the first end face 54a and the second end face 54b, and so the movable piece 54 is located at the second position.

[0052] As described above, according to the embodiment described above, the movable piece 54 can be automatically and appropriately driven in accordance with the difference in pressure acting on both end faces (the first end face 54a and the second end face 54b) of the movable piece 54 so that the movable piece 54 is positioned at the first position when the internal volume ratio Vi is relatively low, and is positioned at the second position when the internal volume ratio Vi is relatively high. This makes it possible to suppress discharge loss over a wide operating range (internal volume ratio Vi).

[0053] Figures 12 and 13 are schematic cross-sectional views showing the vicinity of the axial discharge port 44 of a screw compressor according to one embodiment, and show modified examples of the embodiment shown in Figures 4 to 11. Note that Figures 12 and 13 correspond to Figure 4 (figures including the movable piece 54 positioned in the first position), and figures including the movable piece 54 positioned in the second position (figures corresponding to Figure 6) are omitted. In Figures 12 and 13, descriptions of elements that are assigned the same reference numerals as those shown in Figures 4 to 11 will be omitted to avoid repetition.

[0054] 12 and 13 does not include the above-described communication passage 74. Instead, the screw compressor 2 according to this embodiment includes a high-pressure line 82 for introducing a high-pressure fluid having a higher pressure than the discharge space 43 into the back space 72 facing the second end surface 54b of the movable piece 54, and a valve 84 provided on the high-pressure line 82. In the illustrated embodiment, the high-pressure fluid from the high-pressure line 82 is introduced into the back space 72 via an internal flow path 80 provided in the casing 12.

[0055] In one embodiment, oil pressurized by the pump 8 in the oil supply line 10 (pressure Poil: Pd+α) may be supplied to the rear side space 72 via a high-pressure line 82.

[0056] In the above-described embodiment, by appropriately operating the valve 84, high-pressure fluid can be introduced via the high-pressure line 82 into the rear space 72 where the second end surface 54b of the movable piece 54 is exposed. This allows the movable piece 54 to be forcibly moved from the second position to the first position.

[0057] For example, even when the load on the screw compressor 2 is relatively high and the pressure in the tooth groove space immediately before the axial discharge port 44 is relatively high, the valve 84 can be appropriately operated as needed to introduce high-pressure fluid from the high-pressure line 82 into the back side space 72 and forcibly move the movable piece 54 from the second position to the first position, thereby narrowing the opening area of ​​the axial discharge port 44 and increasing the internal volume ratio Vi.

[0058] The exemplary embodiment shown in FIG. 12 further includes an orifice 88 that connects the rear space 72 and the discharge space 43 .

[0059] In the above-described embodiment, the rear space 72 and the discharge space 43 are connected via the orifice 88. Therefore, while the valve 84 is open and high-pressure fluid is supplied from the high-pressure line 82 to the rear space 72, the rear space 72 can be maintained at an appropriate pressure higher than the discharge space 43, and the movable piece can be maintained at the first position. The high-pressure oil in the rear space 72 is appropriately released to the discharge space 43 via the orifice 88. Furthermore, while the valve 84 is closed and the supply of high-pressure fluid from the high-pressure line 82 to the rear space 72 is stopped, the pressure in the rear space 72 becomes equal to the pressure in the discharge space 43. Therefore, as already described, the movable piece 54 can be automatically driven to move between the first position and the second position by the pressure difference between the tooth groove space immediately before the axial discharge port 44 and the discharge space 43 (i.e., the pressure difference acting on the first end face 54a and the second end face 54b of the movable piece 54).

[0060] 13 , the screw compressor 2 includes a low-pressure line 90 connected to a low-pressure source having a lower pressure than the discharge space 43. The valve 84 is configured to be able to switch the connection destination of the rear space 72 between the high-pressure line 82 and the low-pressure line 90.

[0061] The low-pressure source may be a gas having a suction pressure Ps, and the low-pressure line 90 may be branched off from a suction line (not shown) for introducing suction gas (pressure: Ps) into the screw compressor 2. The valve 84 may include a three-way valve provided between the rear space 72 and the high-pressure line 82 and low-pressure line 90.

[0062] In the above-described embodiment, by appropriately operating the valve 84, the connection destination of the back side space 72, to which 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, 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. By connecting the back side space 72 to the low-pressure line 90, low-pressure fluid from a 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, 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 depending on the operating status of the screw compressor 2, 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 and makes it easier to suppress discharge loss over a wide operating range (internal volume ratio).

[0063] As described above, according to the exemplary embodiment shown in FIGS. 12 and 13, the screw compressor 2 can be operated more flexibly, and the discharge loss can be easily suppressed over a wide range of operating ranges (internal volume ratios).

[0064] The contents described in each of the above embodiments can be understood, for example, as follows.

[0065] [1] A screw compressor (2) according to at least one embodiment of the present invention comprises: 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 opposing surface (50) facing the discharge side end surface and an opening (52) provided on the rotor opposing surface and communicating with a discharge space (43) from which gas compressed by the screw rotor is discharged; a slide valve (30) whose position in the axial direction of the screw rotor is variable so as to change the internal volume ratio; and a movable piece (54) provided along an edge of the opening of the casing and configured to be able to block 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 (101) of an axial discharge port (44) together with the edge of the opening, and a second position that is farther away from the screw rotor in the axial direction than the first position, When the movable piece is located at the second position, the opening forms a second contour (102) of the axial discharge port having an opening area larger than that of the first contour.

[0066] In the configuration [1] above, a movable piece provided along the edge of the opening of the casing that forms the axial discharge port is movable between a first position in the axial direction and a second position that is farther from the screw rotor than the first position. When the movable piece is in the second position, the opening area of ​​the axial discharge port is larger than when the movable piece is in the first position. Therefore, under operating conditions where the internal volume ratio of the screw compressor is relatively high, positioning the movable piece in the second position relatively increases the opening area of ​​the axial discharge port, thereby suppressing an increase in gas flow velocity at the discharge port and thereby suppressing an increase in discharge loss. Furthermore, under operating conditions where the internal volume ratio of the screw compressor is relatively low, positioning the movable piece in the first position relatively reduces the opening area of ​​the axial discharge port, thereby suppressing an increase in discharge loss due to insufficient compression. Therefore, according to the configuration [1] above, by switching the position of the movable piece between the first and second positions depending on the internal volume ratio, discharge loss can be suppressed over a wide operating range (internal volume ratio).

[0067] [2] In some embodiments, in the configuration of [1] above, the movable piece includes a piston (56) that is movable forward and backward in the axial direction.

[0068] According to the configuration [2] above, it is possible to realize a screw compressor including the movable piece described in the above [1] with a simple configuration using a piston that can advance and retreat in the axial direction.

[0069] [3] In some embodiments, in the configuration of [2] above, the screw compressor is configured such that, when the movable piece is in the first position, an end face of the piston in the axial direction (e.g., a first end face 54a of the movable piece 54) is flush with the rotor-facing surface of the casing, and the piston forms part of the first contour.

[0070] According to the configuration [3] above, when the movable piece including the piston is in the first position, the end face 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, so that a screw compressor including the movable piece described in [1] above can be realized with a simple configuration.

[0071] [4] In some embodiments, in the configuration of [2] above, the movable piece includes a plate-like member (78) attached to an end of the piston in the axial direction, and the screw compressor is configured such that, when the movable piece is in the first position, an end face of the plate-like member in the axial direction (e.g., a first end face 54a of the movable piece 54) is flush with the rotor-facing surface of the casing, and the plate-like member forms part of the first contour.

[0072] According to the configuration [4] above, when the movable piece including the plate-shaped member attached to the end of the piston is in the first position, the end face of the plate-shaped member is flush with the rotor-facing surface of the casing, and the plate-shaped member forms the contour (first contour) of the axial discharge port. Here, since any shape of plate-shaped member can be used, it is easy to optimize the shape of the first contour of the axial discharge port according to the tooth shape of the screw rotor, etc.

[0073] [5] In some embodiments, in any of the configurations [2] to [4] above, the piston has a first portion (58) and a second portion (60) that is provided on the opposite side of the screw rotor in the axial direction, sandwiching the first portion, and has a larger diameter than the first portion, and 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 step portion (61) formed by the first portion and the second portion.

[0074] According to the configuration [5] above, the step portion of the piston restricts the movement of the piston from the second position toward the first position, so that the end face of the piston can be prevented from protruding toward the screw rotor from the position of the rotor-facing surface of the casing, thereby suppressing contact between the piston and the end face of the screw rotor.

[0075] [6] In some embodiments, in any of the configurations [1] to [5] above, the movable piece has a first end face (54a) facing the screw rotor and a second end face (54b) opposite the first end face in the axial direction, and the screw compressor has a communication passage (74) that connects a back side space (72) to which the second end face is exposed and the discharge space.

[0076] According to the configuration [6] above, the first end face of the movable piece faces the tooth groove space immediately before the axial discharge port (i.e., the tooth groove space immediately before discharge), and the second end face of the movable piece faces the back side space that communicates with the discharge space, so that the movable piece can be automatically driven by the pressure difference between the tooth groove space and the discharge space. That is, the movable piece can be automatically and appropriately driven in accordance with the pressure difference so that the movable piece is located at the first position when the internal volume ratio is relatively low, and at the second position when the internal volume ratio is relatively high.

[0077] [7] In some embodiments, in any of the configurations [1] to [5] above, the movable piece has a first end face (54a) facing the screw rotor and a second end face (54b) opposite the first end face in the axial direction, and the screw compressor includes: a high-pressure line (82) for introducing a high-pressure fluid having a higher pressure than the discharge space into a back side space (72) to which the second end face is exposed; and a valve (84) provided between the back side space and the high-pressure line.

[0078] According to the configuration [7] above, by appropriately operating the valve, high-pressure fluid can be introduced via the high-pressure line into the back space where the second end face of the movable piece is exposed, thereby forcibly moving the movable piece from the second position to the first position. Therefore, even when the load on the screw compressor is relatively high and the pressure in the tooth groove space immediately before the axial discharge port is relatively high, the valve can be operated to introduce high-pressure fluid into the back space as needed to forcibly move the movable piece from the second position to the first position, thereby narrowing the opening area of ​​the discharge port and increasing the internal volume ratio. This enables more flexible operation of the screw compressor and makes it easier to suppress discharge loss over a wide operating range (internal volume ratio).

[0079] [8] In some embodiments, in the configuration of the above [7], an orifice (88) is provided that connects the rear side space to which the second end surface is exposed and the ejection space.

[0080] According to the configuration [8] above, since the rear space and the discharge space are connected via an orifice, while the valve is open and high-pressure fluid is supplied from the high-pressure line to the rear space, the pressure in the rear space is maintained at an appropriate level higher than the discharge space, and the movable piece can be maintained in the first position. Also, while the valve is closed and the supply of high-pressure fluid from the high-pressure line to the rear space is stopped, the pressure in the rear space becomes equal to the pressure in the discharge space, so that the movable piece can be automatically driven by the pressure difference between the tooth groove space immediately before the axial discharge port and the discharge space, as explained in [6] above.

[0081] [9] In some embodiments, in the configuration of [7] above, a low-pressure line (90) connected to a low-pressure source having a lower pressure than the discharge space is provided, and the valve is configured to be able to switch the connection destination of the rear side space between the high-pressure line and the low-pressure line.

[0082] According to the configuration [9] above, by appropriately operating the valve, the connection of the back 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 space to the high-pressure line, high-pressure fluid can be introduced into the back space, forcing the movable piece to move from the second position to the first position. By connecting the back space to the low-pressure line, low-pressure fluid from a low-pressure source can be introduced into the back space, forcing the movable piece to move from the first position to the second position. That is, by operating the valve to switch the connection of the back space between the high-pressure line and the low-pressure line depending on the operating conditions of the screw compressor, 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 range (internal volume ratio).

[0083]

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

[0084] In the configuration

[10] above, a movable piece provided along the edge of the opening of the casing forming the discharge port is movable between a first position in the axial direction and a second position that is farther from the screw rotor than the first position. When the movable piece is in the second position, the opening area of ​​the axial discharge port is larger than when the movable piece is in the first position. Therefore, under operating conditions where the internal volume ratio of the screw compressor is relatively high, positioning the movable piece in the second position relatively increases the opening area of ​​the axial discharge port, thereby suppressing an increase in gas flow velocity at the discharge port and thereby suppressing an increase in discharge loss. Furthermore, under operating conditions where the internal volume ratio of the screw compressor is relatively low, positioning the movable piece in the first position relatively reduces the opening area of ​​the axial discharge port, thereby suppressing an increase in discharge loss due to insufficient compression. Therefore, according to the configuration

[10] above, by switching the position of the movable piece between the first and second positions depending on the internal volume ratio, discharge loss can be suppressed over a wide operating range (internal volume ratio).

[0085] The above describes an embodiment of the present invention, but the present invention is not limited to the above-described embodiment, and also includes forms in which the above-described embodiment is modified, or forms in which these forms are appropriately combined.

[0086] In this specification, expressions expressing relative or absolute arrangements, such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial," not only strictly express such arrangements, but also express a state in which there is a relative displacement with a tolerance or an angle or distance to the extent that the same function is obtained. For example, expressions expressing that things are in an equal state, such as "identical," "equal," and "homogeneous," not only express a state in which there is a strict equivalence, but also express a state in which there is a tolerance or a difference to the extent that the same function is obtained. Furthermore, in this specification, expressions expressing shapes such as a rectangular shape or a cylindrical shape not only express shapes such as a rectangular shape or a cylindrical shape in the strict geometric sense, but also express shapes including concave and convex portions, chamfered portions, etc., to the extent that the same effect is obtained. Furthermore, in this specification, the expressions "comprise," "include," or "have" a component are not exclusive expressions that exclude the presence of other components.

[0087] REFERENCE SIGNS LIST 1 gas compression equipment 2 screw compressor 4 oil separator 6 cooler 8 pump 10 oil supply line 12 casing 14 rotor shaft 15 male rotor 16 rotor shaft 17 female rotor 18 radial bearing 20 thrust bearing 24 shaft seal portion 28 balance piston 29 balance piston chamber 30 slide valve 31 notch 32 hydraulic piston 40 suction port 41 suction space 42 discharge port 43 discharge space 44 axial discharge port 46 radial discharge port 48 discharge side end face 50 rotor opposing surface 52 opening 54 movable piece 54a first end face 54b second end face 56 piston 58 first portion 60 second portion 61 step portion 62 biasing member 66 plug 68 hole 72 Rear space 74: Communication passage 76: Position restriction surface 78: Plate-like member 80: Internal flow passage 82: High-pressure line 84: Valve 88: Orifice 90: Low-pressure line 101: First contour 102: Second contour Pd: Discharge pressure Ps: Suction pressure

Claims

1. A screw compressor comprising: a screw rotor having a discharge side end face; a rotor opposing surface opposing the discharge side end face; and a casing having an opening provided on the rotor opposing surface and communicating with a discharge space into which gas compressed by the screw rotor is discharged; a slide valve whose position in the axial direction of the screw rotor is variable so as to change the internal volume ratio; and a movable piece provided along an edge of the opening of the casing and configured to be able to block 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 which is farther from the screw rotor in the axial direction than the first position, and wherein when the movable piece is located at the second position, the opening forms a second contour of the axial discharge port having an opening area larger than the first contour.

2. The screw compressor according to claim 1, wherein the movable piece includes a piston that is movable back and forth in the axial direction.

3. The screw compressor according to claim 2, wherein, when said movable piece is in said first position, an end face of said piston in said axial direction is flush with the rotor-opposing surface of said casing, and said piston forms a part of said first contour.

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

5. A screw compressor as claimed in any one of claims 2 to 4, wherein the piston has a first portion and a second portion having a larger diameter than the first portion, the second portion being disposed on the opposite side of the screw rotor in the axial direction with the first portion between them, and wherein movement of the piston in a direction from the second position towards the first position is restricted by a step portion formed by the first portion and the second portion.

6. A screw compressor as claimed in any one of claims 1 to 4, wherein the movable piece has a first end face facing the screw rotor and a second end face opposite the first end face in the axial direction, and is provided with a communication passage that connects a rear space to which the second end face is exposed and the discharge space.

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

8. The screw compressor according to claim 7, further comprising an orifice connecting the rear space to which the second end face is exposed and the discharge space.

9. The screw compressor according to claim 7, further comprising a low pressure line connected to a low pressure source having a lower pressure than the discharge space, and the valve is configured to be able to switch the connection destination of the rear space between the high pressure line and the low pressure line.

10. A gas compression installation comprising: a 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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