Oil-flooded screw compressor system and method for modifying the same

Abstract

An oil-flooded screw compressor system includes: a first lubricating oil supply system for supplying lubricating oil to screw parts; and a second lubricating oil supply system for supplying the lubricating oil to a bearing. The first lubricating oil supply system includes: a gas-liquid separator; a first supply flow passage; and a first supply path. The second lubricating oil supply system includes: a lubricating oil reservoir; a second supply flow passage; a second supply path; a first discharge flow passage; and a discharge path. It is possible to suppress dissolution of a gas to be compressed in lubricating oil and to suppress damage to a bearing due to deterioration of the performance of the lubricating oil, even in a case where the gas to be compressed is compatible with the lubricating oil.

Claims

1. An oil-flooded screw compressor system for compressing a gas to be compressed which is a compatible gas with lubricating oil, comprising: a screw compressor which includes: a male screw rotor and a female screw rotor each having a screw part and shaft portions formed on both ends of the screw part; a housing having a screw chamber accommodating the screw parts inside and a bearing chamber accommodating the shaft portions inside; and a bearing disposed in the bearing chamber, for rotatably supporting the shaft portions; a first lubricating oil supply system for supplying lubricating oil to the screw parts; and a second lubricating oil supply system for supplying the lubricating oil to the bearing, wherein the first lubricating oil supply system includes: a gas-liquid separator configured to introduce discharge gas of the screw compressor therein and to separate the lubricating oil from the discharge gas; a first supply flow passage formed through a housing wall which constitutes the housing, the first supply flow passage having an opening on an outer surface of the housing wall and being in communication with the screw chamber; and a first supply path connected to a lubricating-oil storage region of the gas-liquid separator and to the opening of the first supply flow passage, and wherein the second lubricating oil supply system includes: a lubricating oil reservoir; a second supply flow passage formed through the housing wall, the second supply flow passage having an opening on the outer surface of the housing wall and being in communication with the bearing chamber; a second supply path connected to the lubricating oil reservoir and to the opening of the second supply flow passage; a first discharge flow passage formed through the housing wall, the first discharge flow passage being in communication with the bearing chamber and having an opening on the outer surface of the housing wall; and a discharge path connected to the lubricating oil reservoir and to the opening of the first discharge flow passage, wherein a first branch discharge flow passage is formed so as to communicate with the first discharge flow passage and the screw chamber, wherein the first branch discharge flow passage and a part of the first discharge flow passage having an opening on the outer surface of the housing wall together constitute a linear through hole, and wherein the first branch discharge flow passage of the linear through hole is closed by a first closure member.

2. The oil-flooded screw compressor system according to claim 1, wherein a tapered female threaded hole is formed on a side of the opening of the first branch discharge flow passage which faces the first discharge flow passage, and wherein the first closure member has a tapered male thread formed thereon, the tapered male thread being engageable with the tapered female threaded hole.

3. The oil-flooded screw compressor system according to claim 1, wherein the lubricating oil reservoir is a sealed tank, and wherein the oil-flooded screw compressor system further comprises: a suction path connected to an inlet port of the screw compressor; a suction branch path branched from the suction path and connected to the lubricating oil reservoir; a return pipe connected to the lubricating oil reservoir and to a lubricating oil storage region of the gas-liquid separator; an open-close valve disposed in the return pipe; an oil-surface level sensor provided for the lubricating oil reservoir; and a controller which is configured to receive a detection value from the oil-surface level sensor and to open the open-close valve when the detection value is at most a threshold.

4. The oil-flooded screw compressor system according to claim 3, further comprising: a discharge gas path disposed in the housing; a temperature sensor for detecting a temperature of the discharge gas flowing through the discharge gas path; and a flow-rate adjustment valve disposed in the first supply path, wherein the controller is configured to receive a detection value of the temperature sensor and to adjust an opening degree of the flow-rate adjustment valve to adjust the temperature of the discharge gas.

5. The oil-flooded screw compressor system according to claim 1, wherein the gas to be compressed is a hydrocarbon gas.

6. The oil-flooded screw compressor system according to claim 5, wherein the gas to be compressed is a hydrocarbon gas having a molar mass of at least 44.

7. An oil-flooded screw compressor, comprising: a male screw rotor and a female screw rotor each having a screw part and shaft portions formed on both ends of the screw part; a housing having a screw chamber accommodating the screw parts inside and a bearing chamber accommodating the shaft portions inside; a first supply flow passage formed through a housing wall which constitutes the housing so as to be in communication with the screw chamber and configured to supply a first oil to the screw chamber; a second supply flow passage formed through the housing wall so as to be in communication with the bearing chamber and configured to supply a second oil to the bearing chamber; a discharge flow passage formed through the housing wall so as to be in communication with the bearing chamber and configured to discharge the second oil from the bearing chamber; and a closure member disposed in a through hole penetrating the housing wall to radially extend to the screw chamber, wherein the discharge flow passage includes: a radial passage formed by a portion of the through hole positioned opposite to the screw chamber across the closure member; and an axial passage axially extending in the housing wall to intersect with the radial passage so as to be communicated with the bearing chamber and the radial passage.

8. A method of modifying an oil-flooded screw compressor which comprises: a male screw rotor and a female screw rotor each having a screw part and shaft portions formed on both ends of the screw part; a housing having a housing wall to form a screw chamber accommodating the screw parts inside and a bearing chamber accommodating the shaft portions inside; and an axial passage axially extending in the housing wall to be communicated with the bearing chamber, the method comprising: forming a through hole which penetrates the housing wall to radially extend to the screw chamber such that the through hole intersects with the axial passage at an intersection; and disposing a closure member in the through hole at a position between the screw chamber and the intersection such that a radial passage formed by a portion of the through hole positioned opposite to the screw chamber across the closure member constitutes a discharge flow passage for discharging oil from the bearing chamber together with the axial passage.

9. The method of modifying an oil-flooded screw compressor system according to claim 8, connecting the discharge flow passage to a lubricating oil reservoir for storing the oil to be supplied to the bearing chamber via a flow path.

10. The method of modifying an oil-flooded screw compressor system according to claim 9, wherein the lubricating oil reservoir is a tank inside of which is sealable, wherein the method further comprises: providing a suction branch path which branches from a suction path connected to an inlet port of the screw compressor and connects to the lubricating oil reservoir; providing a return pipe to be connected to the lubricating oil reservoir and to a lubricating-oil storage region of a gas-liquid separator configured to introduce discharge gas of the screw compressor therein and to separate the lubricating oil from the discharge gas, and providing an open-close valve for the return pipe; and providing an oil-surface level sensor disposed in the lubricating oil reservoir, and a controller for receiving a detection value of the oil-surface level sensor and opening the open-close valve when the detection value becomes at most a threshold.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a system diagram of an oil-flooded screw compressor system according to an embodiment.

(2) FIG. 2 is a front cross-sectional view taken along line II-II in FIG. 1.

(3) FIG. 3 is an enlarged cross-sectional view of section A in FIG. 1.

(4) FIG. 4 is an enlarged cross-sectional view of section B in FIG. 1.

(5) FIG. 5 is a system diagram of a typical oil-flooded screw compressor system.

(6) FIG. 6 is a flowchart of a modifying method according to an embodiment.

(7) FIG. 7 is a system diagram of another typical oil-flooded screw compressor system.

(8) FIG. 8 is an enlarged cross-sectional view of section C in FIG. 7.

DETAILED DESCRIPTION

(9) With reference the accompanied drawings, some embodiments of the present embodiments will be described. It is intended, however, that unless particularly specified, 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.

(10) For instance, 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.

(11) 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.

(12) Further, for instance, 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.

(13) On the other hand, an expression such as comprise, include, have, contain and constitute are not intended to be exclusive of other components.

(14) FIGS. 1 to 4 are diagrams of an oil-flooded screw compressor system 10 according to at least one embodiment of the present invention.

(15) In FIG. 1, the oil-flooded screw compressor system 10 includes a pair of male and female screw rotors 12a and 12b, a housing 14 housing the screw rotors 12a and 12b, a screw compressor 11 including shaft portions 16a and 16b for rotatably supporting the screw rotors 12a and 12b, and a first lubricating oil supply system 18 and a second lubricating oil supply system 20 for supplying lubricating oil inside the housing 14.

(16) The male and female screw rotors 12a and 12b respectively include screw parts 22a and 22b, and suction-side shaft portions 24a, 24b and discharge-side shaft portions 26a, 26b formed on both ends of the screw parts 22a, 22b. The screw parts 22a and 22b have screw lobe surfaces formed thereon, engaging with each other to form a plurality of compression chambers in the axial direction.

(17) The housing 14 includes three casings: a screw casing 14a forming a screw chamber 27 that houses the screw parts 22a and 22b inside; a suction-side bearing casing 14b forming suction-side bearing chambers 28a and 28b that house the suction-side shaft portions 24a and 24b inside; and a discharge-side bearing casing 14c forming discharge-side bearing chambers 29a and 29b that house the discharge-side shaft portions 26a and 26b inside.

(18) As an exemplary configuration, the screw casing 14a, the suction-side bearing casing 14b, and the discharge-side bearing casing 14c are coupled to each other by bolts in series so as to be separatable.

(19) The bearing portions 16a and 16b have a radial bearing and a thrust bearing.

(20) In an exemplary configuration, journal bearings 31a and 31b are disposed around the suction-side shaft portions 24a, 24b and the discharge-side shaft portions 26a, 26b, as radial bearings. Further, for instance, angular contact ball bearings 32a and 32b are disposed in the discharge-side bearing chambers 29a and 29b, as thrust bearings. The angular contact ball bearing 32a is fit and fixed to the discharge-side shaft portion 26a of the male screw rotor 12a, while the angular contact ball bearing 32b is fit and fixed to the discharge-side shaft portion 26b of the female screw rotor 12b. The angular contact ball bearings 32a and 32b receive axial thrust loads (compression reaction forces) that occur from compression of the gas to be compressed in the compression chambers.

(21) Journal bearings 31a and 31b are provided to seal the gaps between the screw chamber 27 and the suction-side bearing chambers 28a, 28b or the discharge-side bearing chambers 29a, 29b.

(22) To reduce the axial thrust loads that act on the thrust bearings, a piston (balance piston) 34 is mounted to the suction-side shaft portion 24a of the male screw rotor 12a. A part of the suction-side bearing chamber 28a is defined as a cylinder (balance cylinder), and the balance piston 34 is housed inside the balance cylinder so as to be slidable in the axial direction of the male screw rotor 12a. The axial thrust loads are reduced by operating the balance piston 34 to adjust the pressure inside the balance cylinder.

(23) The first lubricating oil supply system 18 supplies lubricating oil to the screw parts 22a and 22b, and the second lubricating oil supply system 20 supplies lubricating oil to the bearing portions 16a and 16b.

(24) The first lubricating oil supply system 18 includes a gas-liquid separator 36, a first supply flow passage 38 formed through a wall of the housing 14, and a first supply path 40 connected to the gas-liquid separator 36 and the first supply flow passage 38.

(25) Discharge gas discharged from a discharge path 42 formed in the housing 14 is fed to the gas-liquid separator 36 via a discharge gas path 44. The discharge gas is separated from the lubricating oil when passing through a filter 37 inside the gas-liquid separator 36. The lubricating oil r separated from the discharge gas is accumulated in a lower section of the gas-liquid separator 36.

(26) The first supply flow passage 38 is formed through a housing wall of the screw casing 14a and has an opening on the outer surface of the housing wall, thus communicating with the screw chamber 27. In some embodiments, the first supply flow passage 38 may be formed on a capacity control valve 82 described below, via the housing wall. The first supply path 40 is connected to the opening of the first supply flow passage 38 and to the lower section of the gas-liquid separator 36 in which the lubricating oil is accumulated.

(27) The second lubricating oil supply system 20 includes a lubricating oil reservoir 46, a second supply flow passage 48 formed through a housing wall, a second supply path 50 connecting the lubricating oil reservoir 46 and the second supply flow passage 48, a first discharge flow passage 52 formed through the housing wall, a discharge path 54 connecting the lubricating oil reservoir 46 and the first discharge flow passage 52, and an oil pump 56 and an oil cooler 58 disposed in the second supply path 50.

(28) The second supply flow passage 48 is formed through housing walls of the screw casing 14a, the suction-side bearing casing 14b, and the discharge-side bearing casing 14c, and has an opening part having an opening on the outer surface of the housing wall of the discharge-side bearing casing 14c. Further, the second supply flow passage 48 branches to the suction-side bearing chamber 28a and to the discharge-side bearing chamber 29a to be in communication with the bearing chambers.

(29) The second supply path 50 is connected to the opening part of the second supply flow passage 48, and supplies lubricating oil stored in the lubricating oil reservoir 46 to the suction-side bearing chamber 28a and the discharge-side bearing chamber 29a. The suction-side bearing chamber 28a and the discharge-side bearing chamber 29a are in communication with the suction-side bearing chamber 28b and the discharge-side bearing chamber 29b via communication holes 30a, 30b, and 30c. The lubricating oil supplied to the suction-side bearing chamber 28a and the discharge-side bearing chamber 29a is supplied to the suction-side bearing chamber 28b and the discharge-side bearing chamber 29b via the communication holes 30a, 30b, and 30c.

(30) Accordingly, lubricating oil is supplied to the angular contact ball bearings 32a, 32b, the journal bearings 31a, 31b, and the balance cylinder, which are disposed in the suction-side bearing chambers 28a, 28b and the discharge-side bearing chambers 29a, 29b.

(31) The first discharge flow passage 52 is in communication with the suction-side bearing chamber 28b and the discharge-side bearing chamber 29b on the side of the female screw rotor 12b, and has an opening on the outer surface of the housing wall of the screw casing 14a. The discharge path 54 is connected to the opening of the first discharge flow passage 52 and to the lubricating oil reservoir 46.

(32) Further, a first branch discharge flow passage 60 (second discharge flow passage) is formed to communicate with the first discharge flow passage 52 and the screw chamber 27.

(33) As shown in FIG. 3, the first branch discharge flow passage 60 has a tapered female threaded hole 60a formed on a side of the opening into the first discharge flow passage 52. A closure plug 62 having a tapered male thread formed thereon is engaged with the female threaded hole 60a to close the first branch discharge flow passage 60. A flow passage 52a constituting a part of the first discharge flow passage 52 has an opening on the outer surface of the housing wall, and also constitutes a linear though hole (third discharge flow passage) in the axial direction with the first branch discharge flow passage 60.

(34) In an exemplary configuration of the present embodiment, the lubricating oil reservoir 46 is a closed tank with a closed space formed therein. Further, a suction path 66 is connected to an inlet port 64 of the screw compressor 11, and a suction branch path 68 branched from the suction path 66 is connected to the lubricating oil reservoir 46.

(35) Further, a return pipe 70 is connected to the lubricating oil reservoir 46 and to the lubricating oil storage region of the gas-liquid separator 36. An open-close valve 72 is disposed in the return pipe 70. Further, the lubricating oil reservoir 46 includes an oil-surface level sensor 74 for detecting a liquid level of lubricating oil, and a controller 76 that receives a detection value from the oil-surface level sensor 74 and opens the open-close valve 72 when the detection value becomes at most a threshold.

(36) A discharge pressure sensor 45 for detecting a pressure of discharge gas is disposed in the discharge gas path 44, and detection values of the discharge pressure sensor 45 are input into the controller 76.

(37) The pressure inside the lubricating oil reservoir 46 communicating with the suction branch path 68 is as low as that in the suction path 66. On the other hand, the pressure inside the gas-liquid separator 36 communicating with the discharge path 42 is as high as the discharge path 42. Thus, when the open-close valve 72 is opened, the lubricating oil inside the gas-liquid separator 36 automatically flows into the lubricating oil reservoir 46. Accordingly, it is possible to ensure the amount of lubricating oil in the lubricating oil reservoir 46.

(38) Furthermore, in an exemplary configuration, a temperature sensor 43 for detecting a temperature of discharge gas passing through the discharge path 42 is provided, and a flow-rate adjustment valve 78 is disposed in the first supply path 40. The controller 76 receives detection values from the temperature sensor 43 and is capable of adjusting the temperature of the discharge gas by adjusting the opening degree of the flow-rate adjustment valve 78.

(39) Further, in an exemplary configuration, as shown in FIG. 2, a capacity control device 80 is provided. The capacity control device 80 includes the capacity control valve 82, which is housed in a cylinder (capacity control cylinder) defined inside the housing 14. The capacity control cylinder extends along the screw chamber 27 and is in communication with the discharge path 42. An end portion of the capacity control cylinder on the side of the discharge path 42 constitutes a radial communication part that is in communication with the compression chambers in the radial direction. Accordingly, the gas compressed in the compression chambers can flow into the discharge path 42 through the radial communication part of the discharge port and the radial communication part of the capacity control cylinder.

(40) The capacity control valve 82 is disposed slidably in the axial direction of the male screw rotor 12a and the female screw rotor 12b. The capacity control valve 82 is coupled to the hydraulic cylinder 84 that serves as a drive unit. The first supply path 40 is connected to the hydraulic cylinder 84, and working oil is supplied to the hydraulic cylinder 84 from the first supply path 40. The capacity control valve 82 is caused to reciprocate inside the capacity control cylinder by the hydraulic cylinder 84.

(41) The capacity control device 80 operates the hydraulic cylinder 84 to adjust the position of the capacity control valve 82, and thereby it is possible to adjust the length of the compression chambers in the axial direction, which is, in other words, the starting time of compression in the compression chambers, and to adjust the capacity of the screw compressor 11.

(42) As shown in FIGS. 1 and 4, the connection part between the discharge path 54 and the screw casing 14a includes a coupling 55 and a pipe 90 connected to the coupling 55. A flange 92 is fixed to an end of the pipe 90, and is connected to the screw casing 14a with a plurality of bolts 94. Accordingly, the discharge path 54 is in communication with the first discharge flow passage 52.

(43) Further, the first supply path 40 includes an oil pump 86 and an oil cooler 88 for feeding lubricating oil r that accumulates in the lower section of the gas-liquid separator 36 to the first supply flow passage 38.

(44) With the above configuration, the discharge-side shaft portion 26a of the male screw rotor 12a is rotated by a power source (e.g. electric motor), and the female screw rotor 12b rotates in synchronization by engagement between the screw parts 22a and 22b.

(45) In the first lubricating oil supply system 18, the lubricating oil r accumulated in the lower section of the gas-liquid separator 36 is cooled by the oil cooler 88, and is supplied to the screw chamber 27 via the first supply path 40 and the first supply flow passage 38. The lubricating oil lubricates the screw parts 22a and 22b in the screw chamber 27, and returns with the discharge gas to the gas-liquid separator 36 through the discharge path 42 and the discharge gas path 44.

(46) In the second lubricating oil supply system 20, the lubricating oil inside the lubricating oil reservoir 46 is fed to the second supply path 50 by the oil pump 56 to be cooled by the oil cooler 58, and is supplied to the bearing portions 16a and 16b through the second supply flow passage 48. The lubricating oil after lubricating the bearing portions 16a and 16b flows through the first discharge flow passage 52 and the discharge path 54 and returns to the lubricating oil reservoir 46.

(47) According to the above embodiment, the first lubricating oil supply system 18 and the second lubricating oil supply system 20 form independent circulation systems from each other, and thus lubricating oil supplied from the second lubricating oil supply system 20 to the bearing chamber is not supplied to the screw chamber 27. Thus, it is possible to reduce the amount of lubricating oil supplied to the screw chamber 27. Accordingly, it is possible to suppress cooling of the gas to be compressed in the screw chamber 27 and increase the temperature of the gas to be compressed at the discharge side of the compressor, which makes it possible to suppress condensation of the gas to be compressed and the amount of dissolution of the gas to be compressed in the lubricating oil.

(48) Furthermore, the lubricating oil supplied to the bearing chambers does not make contact with the gas to be compressed having a high discharge pressure, and thus it is possible to reduce the size of the oil cooler 58 for cooling lubricating oil to be supplied to the bearing chamber.

(49) Still further, slight leakage of lubricating oil between the screw chamber 27 and the bearing chambers is allowable, and thus it no longer necessary to provide a costly seal structure as described in Patent Document 1. Thus, it is possible to reduce the size and costs of the seal structure.

(50) Further, while the first branch discharge flow passage 60 is formed in communication with the first discharge flow passage 52 and the screw chamber 27, the above described typical oil-flooded screw compressor has a passage similar to the first branch discharge flow passage 60, formed through the housing wall. Such a typical oil-flooded screw compressor can be modified into the screw compressor 11, by simply closing the first branch discharge flow passage 60 with the closure plug 62, and forming the flow passage 52a with an opening on the outer surface of the housing wall communicating with the first discharge flow passage 52.

(51) Further, when the amount of lubricating oil inside the lubricating oil reservoir 46 decreases, it is possible to recover the lubricating oil r inside the gas-liquid separator 36 automatically to the lubricating oil reservoir 46 by opening the open-close valve 72 with the controller 76, due to the pressure difference between the lubricating oil reservoir 46 and the gas-liquid separator 36. Accordingly, it is possible to ensure the amount of lubricating oil in the lubricating oil reservoir 46 constantly.

(52) While the lubricating oil stored in the gas-liquid separator contains gas to be compressed, the gas to be compressed is separated from the lubricating oil when the lubricating oil enters the lubricating oil reservoir 46 having a low pressure, and is discharged through the inlet port 64 of the screw compressor 11 via the suction branch path 68 and the suction path 66. Thus, the amount of gas to be compressed in the lubricating oil stored in the lubricating oil reservoir 46 decreases.

(53) Further, the controller 76 adjusts the opening degree of the flow-rate adjustment valve 78 in accordance with the detection value of the temperature sensor 43, and thus it is possible to adjust the temperature of the discharge gas to a desired temperature. Accordingly, it is possible to increase the temperature of the gas to be compressed, which makes it possible to suppress condensation of the gas to be compressed and the amount of dissolution of the gas to be compressed in the lubricating oil.

(54) Further, the gas to be compressed does not enter the second lubricating oil supply system 20 except for the minute amount of gas to be compressed that leaks from the screw chamber 27 to the suction-side bearing chambers 28a, 28b and the discharge-side bearing chambers 29a, 29b. Thus, even in a case where the gas to be compressed is a gas that is highly compatible with the lubricating oil, such as a hydrocarbon gas, particularly a hydrocarbon gas having a molar mass of at least 44 (e.g. a hydrocarbon gas having a greater molar mass than propane gas), it is possible to suppress a decrease in the viscosity of lubricating oil supplied to the bearing chamber, and to suppress damage to the bearing portions 16a and 16b.

(55) Next, with reference to FIGS. 5 to 8, an embodiment of a method for modifying a typical oil-flooded screw compressor system to obtain the second oil-flooded screw compressor system according to the present invention will be described.

(56) FIG. 5 is a diagram of a typical oil-flooded screw compressor system 100A. The oil-flooded screw compressor system 100A includes a screw compressor 102A.

(57) The screw compressor 102A includes a lubricating oil flow passage (second discharge flow passage) including the first discharge flow passage 52 and the first branch discharge flow passage 60 and being in communication with the suction-side bearing chambers 28b and the discharge-side bearing chamber 29b and the screw chamber 27. Such a compressor housing that includes the above lubricating oil passages is made by casting, for instance.

(58) The oil-flooded screw compressor system 100A includes the second supply path 50 which does not have the lubricating oil reservoir 46. The second supply path 50 is connected to the first supply path 40 in the vicinity of the gas-liquid separator 36, and supplies lubricating oil r of the gas-liquid separator 36 to the second supply flow passage 48. Further, the screw compressor 102A includes the first branch discharge flow passage 60 and the first discharge flow passage 52, and the lubricating oil flow passage (second discharge flow passage) is in communication with the suction-side bearing chambers 28b and the discharge-side bearing chamber 29b and the screw chamber 27.

(59) The rest of the configuration is the same as that of the oil-flooded screw compressor system 10, and the same features are associated with the same reference numerals.

(60) In the oil-flooded screw compressor system 100A, lubricating oil discharged from the suction-side bearing chamber 28b and the discharge-side bearing chamber 29b is supplied to the screw chamber 27 through the first discharge flow passage 52 and the first branch discharge flow passage 60. The lubricating oil lubricates the screw parts 22a and 22b, and returns with the discharge gas to the gas-liquid separator 36 through the discharge path 42 and the discharge gas path 44. The lubricating oil r is separated from the discharge gas in the gas-liquid separator 36, and then is supplied to the second supply flow passage 48 via the second supply path 50.

(61) The oil-flooded screw compressor system 100A is modified into the oil-flooded screw compressor system 10 by the modification process shown in FIG. 6.

(62) In FIG. 6, a flow passage 52a (third discharge flow passage) is formed through a housing wall (screw casing 14a), the flow passage 52a communicating with the second discharge flow passage including the first discharge flow passage 52 and the first branch discharge flow passage 60, and having an opening on the outer surface of the screw casing 14a and the screw chamber 27 together with the second discharge flow passage (the first step S10). The third discharge flow passage is a linear through hole.

(63) Next, a discharge path 54 is connected to the opening of the third discharge flow passage on the outer surface of the housing (the second step S12). For example, the pipe 90 is fixed as shown in FIG. 4, and the discharge path 54 is connected to the pipe 90 via the coupling 55 to bring the flow passage 52a and the discharge path 54 into communication.

(64) Next, as shown in FIG. 3, the first branch discharge flow passage 60 is closed by the closure plug 62 (the third step S14).

(65) Further, the second supply path 50 is connected to the lubricating oil reservoir 46, and the discharge path 54 is connected to the lubricating oil reservoir 46 (the fourth step S16).

(66) In the present embodiment, the following exemplary steps are added. In this case, the lubricating oil reservoir 46 includes a tank that can be sealed tightly.

(67) A suction branch path 68 is provided, which is branched from the suction path 66 connected to the inlet port 64 of the screw compressor 11, and is connected to the lubricating oil reservoir 46 (the eighth step S18). Next, a return pipe 70 is provided, which is connected to the lubricating oil reservoir 46 and to the lubricating oil storage region of the gas-liquid separator 36, and an open-close valve 72 is provided in the return pipe 70 (the ninth step S20). Further, an oil-surface level sensor 74 is provided for the lubricating oil reservoir 46, and a controller 76 is provided, which receives a detection value from the oil-surface level sensor 74 and opens the open-close valve 72 when the detection value becomes at most a threshold (the tenth step S22).

(68) With the above steps, it is possible to modify a typical oil-flooded screw compressor, easily and at low costs, to the oil-flooded screw compressor system 10 including the first lubricating oil supply system 18 for supplying lubricating oil to the screw chamber 27, and the second lubricating oil supply system 20 for supplying lubricating oil to the bearing chambers, independent and separate from the first lubricating oil supply system 18.

(69) Further, with the additional steps S18 to S22, when the oil-surface level of lubricating oil inside the lubricating oil reservoir 46 decreases, it is possible to return the lubricating oil r inside the gas-liquid separator 36 automatically to the lubricating oil reservoir 46 by opening the open-close valve 72, due to the pressure difference between the lubricating oil reservoir 46 and the gas-liquid separator 36. Accordingly, it is possible to ensure the amount of lubricating oil inside the lubricating oil reservoir 46 constantly.

(70) Next, with reference to FIGS. 7 and 8, an embodiment of a method for modifying a typical oil-flooded screw compressor to the third oil-flooded screw compressor according to the present invention will be described.

(71) FIG. 7 is a diagram of a typical oil-flooded screw compressor system 100B. The oil-flooded screw compressor system 100B includes a screw compressor 102B.

(72) The screw compressor 102B includes the second supply path 50 which does not have the lubricating oil reservoir 46. The second supply path 50 is connected to the first supply path 40 in the vicinity of the gas-liquid separator 36, and supplies lubricating oil r of the gas-liquid separator 36 to the second supply flow passage 48. The screw compressor 102B includes a lubricating oil flow passage (second discharge flow passage) including the first discharge flow passage 52 and the first branch discharge flow passage 60 and being in communication with the suction-side bearing chambers 28b and the discharge-side bearing chamber 29b and the screw chamber 27. Further, the screw compressor 102B has the flow passage 52a (third discharge flow passage) communicating with the first branch discharge flow passage 60 and having an opening on the outer surface of the housing wall of the screw casing 14a, and also forming a linear through hole in the axial direction with the first branch discharge flow passage 60.

(73) The rest of the configuration is the same as that of the oil-flooded screw compressor 10, and the same features are associated with the same reference numerals.

(74) In a case where the first branch discharge flow passage 60 is formed by machining, it is necessary to form a hole with a drill from the outer surface of the housing wall. Thus, the screw compressor 100B has the flow passage 52a that forms a linear through hole in the axial direction with the first branch discharge flow passage 60. Further, the opening of the flow passage 52a on the outer surface of the housing wall is closed.

(75) For example, as shown in FIG. 8, the opening of the flow passage 52a is closed by a blind flange 96 fixed to the screw casing 14a with a plurality of bolts 98.

(76) In the oil-flooded screw compressor system 100B, lubricating oil discharged from the suction-side bearing chamber 28b and the discharge-side bearing chamber 29b is supplied to the screw chamber 27. The lubricating oil lubricates the screw parts 22a and 22b, and returns to the gas-liquid separator 36 through the discharge path 42 and the discharge gas path 44 with the discharge gas. The lubricating oil r is separated from the discharge gas in the gas-liquid separator 36, and then is supplied to the second supply flow passage 48 via the second supply path 50.

(77) Similarly to the oil-flooded screw compressor system 100A, the oil-flooded screw compressor system 100B undergoes steps S12 to S16 of the modification process shown in FIG. 6. Further, for example, steps S18 to S22 are added.

(78) With the above steps, it is possible to modify a typical oil-flooded screw compressor, easily and at low costs, to the oil-flooded screw compressor system 10 including the first lubricating oil supply system 18 for supplying lubricating oil to the screw chamber 27, and the second lubricating oil supply system 20 for supplying lubricating oil to the bearing chambers, separate and independent from the first lubricating oil supply system 18.

(79) With the above additional steps S18 to S22, it is possible to achieve the same advantageous effects as the modifying steps according to the above embodiment.

INDUSTRIAL APPLICABILITY

(80) According to at least one embodiment of the present invention, it is possible to provide an oil-flooded screw compressor system whereby it is possible to suppress dissolution of gas to be compressed in lubricating oil and to suppress damage to bearings disposed in bearing chambers, even in a case where the gas to be compressed is compatible with the lubricating oil, which can be provided by making a simple modification to a typical oil-flooded screw compressor system.