AU2016280925B2

AU2016280925B2 - Expansion turbine device

Info

Publication number: AU2016280925B2
Application number: AU2016280925A
Authority: AU
Inventors: Hidetsugu ISHIMARU; Daisuke Kariya; Yuichi Saito; Naoto Sakai; Tomohiro Sakamoto; Ryota Takeuchi
Original assignee: Kawasaki Jukogyo KK
Current assignee: Kawasaki Motors Ltd
Priority date: 2015-06-19
Filing date: 2016-06-15
Publication date: 2018-12-13
Anticipated expiration: 2036-06-15
Also published as: WO2016203768A1; CN107614836B; JP6616109B2; CN107614836A; AU2016280925A1; JP2017008776A

Abstract

This expansion turbine device is provided with a main body, a turbine impeller, a brake impeller, a rotation shaft, a hydrostatic gas bearing, a labyrinth seal, a gas supply path, and a mixed gas discharge path, wherein the pressure of the gas supplied midway in the labyrinth seal is lower than the inlet pressure of the expansion chamber and higher than the back pressure of the hydrostatic bearing.

Description

Title of Invention: EXPANSION TURBINE APPARATUS

Technical Field [0001] The present invention relates to an expansion turbine apparatus. Particularly, the present invention relates to a leakage prevention technique for the expansion turbine apparatus including hydrostatic gas bearings.

Background Art [0002] In general, a liquefying system which liquefies a raw material gas such as a hydrogen gas and a helium gas includes a feed line which sends the raw material gas, a refrigerant circulation line which circulates a refrigerant gas, and a heat exchanger which cools the raw material gas with a refrigerant. The refrigerant gas circulated through the refrigerant circulation line is compressed by a compressor, and then expanded in a heat insulating state by an expansion turbine, so that the temperature of the refrigerant gas is decreased. In the heat exchanger, the raw material gas is cooled by heat exchange with the refrigerant gas in a decreased temperature state.

[0003] A bearing which supports a rotary shaft is required for the expansion turbine. If a liquid bearing which uses lubricating oil is used as the bearing for the expansion turbine, the lubricating oil may flow into the refrigerant gas flowing through the expansion turbine. For this reason, a gas bearing which uses a gas with the same kind as that of the refrigerant gas is preferably used as the bearing. Among the gas bearings, a hydrostatic gas bearing is capable of suppressing friction between a bearing surface and the rotary shaft during start and stop of the liquefying system, and is suitable for a high-speed rotation. For this reason, the hydrostatic gas bearing is used as the bearing of the expansion turbine (e.g., see Patent Literature 1).

[0004] The expansion turbine which uses the hydrostatic gas bearing includes a bearing gas supply line which supplies to the hydrostatic gas bearing a bearing gas with the same kind as that of the refrigerant gas, and a bearing gas discharge line which discharges the bearing gas which has flowed through the hydrostatic gas bearing. A rotary shaft is inserted into a bearing chamber inside the expansion turbine, and the bearing gas supply line and the bearing gas discharge line are connected to each other. A turbine impeller provided at a first end (one end) of the rotary shaft is accommodated in the expansion chamber. The expansion chamber is provided with an expansion chamber entrance into

- 1 which the refrigerant gas flows, at an outer peripheral side of the turbine impeller, and an expansion chamber exit from which the refrigerant gas is discharged, at a center portion in an axial direction. A brake impeller provided at a second end (the other end) of the rotary shaft is accommodated in a braking gas chamber. The braking gas chamber is provided with a communication passage via which the exit and entrance of the braking gas chamber are in communication with each other, and thus a closed circuit including the brake impeller is formed.

[0005] A labyrinth seal is provided on the back surface of the turbine impeller of the expansion turbine to suppress leakage of the refrigerant gas with a low temperature from the expansion chamber to the bearing chamber (e.g., see Patent Literature 2).

Citation List

Patent Literature [0006] Patent Literature 1: Japanese-Laid Open Patent Application Publication No. 2000-55050

Patent Literature 2: Japanese-Laid Open Patent Application Publication No. Hei.

6-26301

Summary of Invention

Technical Problem [0007] However, there is a clearance between the labyrinth seal and the rotary shaft. Therefore, the labyrinth seal cannot perfectly prevent the leakage due to a seal differential pressure. If the amount of leakage of the low-temperature gas from the expansion chamber to the bearing chamber is increased, efficiency of the expansion turbine is reduced. In addition, due to cooling of the bearing chamber, the dimension of a clearance between the rotary shaft and a radial hydrostatic bearing is changed. Depending on the case, contact between the rotary shaft and the radial hydrostatic bearing occurs.

[0008] In view of the above, an object of the present invention is to suppress seal leakage of a low-temperature gas in an expansion turbine including hydrostatic gas bearings.

Solution to Problem [0009] According to an aspect of the present invention, there is provided an expansion turbine apparatus including: a body formed with an expansion chamber, a braking gas chamber, and a shaft insertion hole inside the body, the shaft insertion hole being provided

-2in such a manner that the expansion chamber and the braking gas chamber are in communication with each other via the shaft insertion hole and a rotary shaft is insertable into the shaft insertion hole; a turbine impeller accommodated in the expansion chamber to expand a refrigerant gas; a brake impeller which is accommodated in the braking gas chamber, and braked by a braking gas with the same kind as that of the refrigerant gas; the rotary shaft inserted into the shaft insertion hole with a clearance between the rotary shaft and the shaft insertion hole, the turbine impeller being provided at a first end portion of the rotary shaft, the brake impeller being provided at a second end portion of the rotary shaft; a hydrostatic gas bearing which is provided in a bearing chamber formed inside the shaft insertion hole and supports the rotary shaft in such a manner that the rotary shaft is rotatable, by a static pressure of a bearing gas with the same kind as that of the refrigerant gas supplied from an entrance and discharged from an exit; a labyrinth seal provided in a region between the bearing chamber and the expansion chamber; a gas supply passage provided in the labyrinth seal to supply to a portion of the labyrinth seal a gas with the same kind as that of the refrigerant gas; and a mixture gas discharge passage, an upstream end of which is connected to a bearing chamber exit of the hydrostatic gas bearing, the mixture gas discharge passage being configured to discharge a mixture gas containing the bearing gas which has flowed through the hydrostatic gas bearing, the refrigerant gas which has leaked from the expansion chamber to the bearing chamber through the labyrinth seal, and the gas supplied to the portion of the labyrinth seal, wherein a pressure of the gas supplied to the portion of the labyrinth seal is lower than an entrance pressure of the expansion chamber and higher than a back pressure of the hydrostatic gas bearing. [0010] In accordance with this configuration, the gas with the pressure which is lower than the entrance pressure of the expansion chamber and higher than the back pressure of the hydrostatic gas bearing is supplied to a portion of the labyrinth seal. Therefore, the amount of the refrigerant gas which leaks from the expansion chamber to the mixture gas discharge passage through the labyrinth seal substantially depends on the supply pressure of the gas. This makes it possible to make the amount of the refrigerant gas which leaks, under a condition in which the back pressure of the hydrostatic gas bearing is equal, less in a case where the gas is supplied than in a case where the gas is not supplied. For example, in a case where the gas is not supplied, the bearing back pressure may be increased and the differential pressure of the labyrinth seal may be reduced, to reduce the

-3 amount of the refrigerant gas which leaks. However, in this case, bearing performance may be reduced. In contrast, in a case where the gas is supplied, in the above-described configuration, the amount of the refrigerant gas which leaks through the labyrinth seal can be reduced without increasing the bearing back pressure.

[0011] The expansion turbine apparatus may further comprise: a first pressure sensor which measures the pressure of the gas; a pressure control valve provided at the gas supply passage to control the pressure of the gas; a second pressure sensor which measures the entrance pressure of the expansion chamber; and a controller which controls the pressure control valve so that the pressure of the gas becomes lower than the entrance pressure of the expansion chamber and higher than the back pressure of the hydrostatic gas bearing.

[0012] In accordance with this configuration, since the controller controls the pressure control valve so that the pressure of the gas becomes lower than the entrance pressure of the expansion chamber and higher than the back pressure of the hydrostatic gas bearing, it is not necessary to increase the bearing back pressure to reduce the amount of the refrigerant gas which leaks. As a result, reduction of bearing performance due to an increase in the back pressure can be prevented.

[0013] The controller may control an initial pressure of the gas to be supplied to the portion of the labyrinth seal so that the initial pressure becomes approximately equal to the back pressure of the hydrostatic gas bearing, and control the pressure control valve so that the pressure of the gas is increased in a case where a temperature of the mixture gas flowing through the mixture gas discharge passage is reduced.

[0014] In a case where the amount of the refrigerant gas which leaks from the expansion chamber through the labyrinth seal is increased, the temperature of the mixture gas discharge passage is reduced. In accordance with the above-described configuration, the controller increases the pressure of the gas to be supplied to the labyrinth seal. This can secure equilibrium between the pressure of a region of the labyrinth seal which is closer to the turbine and the pressure of the gas. In theory, leakage of the low-temperature gas from the turbine can be prevented. Since the amount of leakage of the low-temperature gas flowing through a region close to the turbine can be reduced, a temperature decrease in a region in a room (normal) temperature state can be prevented.

-4Advantageous Effects of Invention [0015] In accordance with the present invention, it becomes possible to suppress seal leakage of a low-temperature gas in an expansion turbine apparatus including hydrostatic gas bearings. As a result, it becomes possible to suppress reduction of efficiency of a turbine and cooling of a bearing chamber.

[0016] The above and further objects, features and advantages of the present invention will more fully be apparent from the following detailed description of preferred embodiment with reference to accompanying drawings.

Brief Description of Drawings [0017] Fig. 1 is a partial cross-sectional view showing the configuration of an expansion turbine apparatus according to Embodiment 1.

Fig. 2 is a schematic view showing the configuration of a radial hydrostatic bearing of Fig. 1.

Fig. 3 is a schematic view showing the configuration of a thrust hydrostatic bearing of Fig. 1.

Fig. 4 is a schematic view showing the configuration of a labyrinth seal of Fig. 1.

Fig. 5 is a schematic view showing the overall configuration of the expansion turbine apparatus of Fig. 1.

Fig. 6 is a schematic view showing the configuration of an expansion turbine apparatus according to Embodiment 2.

Description of Embodiments [0018] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Throughout the drawings, the same or corresponding constituents are designated by the same reference symbols and will not be described in repetition.

[0019] (Embodiment 1)

Fig. 1 is a partial cross-sectional view showing the configuration of an expansion turbine apparatus according to Embodiment 1. As shown in Fig. 1, an expansion turbine apparatus 1 includes an expansion chamber 21, a braking gas chamber 20, and a shaft insertion hole 22, inside a body 10. The body 10 has, for example, a casing shape. The shaft insertion hole 22 is provided so that the expansion chamber 21 and the braking gas chamber 20 are in communication with each other via the shaft insertion hole 22, and a

-5 rotary shaft 13 is insertable into the shaft insertion hole 22.

[0020] The rotary shaft 13 is inserted into the shaft insertion hole 22 with a clearance between the rotary shaft 13 and the shaft insertion hole 22. A turbine impeller 11 is provided at a first end portion (one end portion) of the rotary shaft 13. A brake impeller 12 is provided at a second end portion (the other end portion) of the rotary shaft 13. The rotary shaft 13 extends vertically inside the body 10. The rotary shaft 13 is supported in such a manner that the rotary shaft 13 is rotatable around a vertical axis (axis extending vertically). The turbine impeller 11 is accommodated in the expansion chamber 21 and configured to expand a refrigerant gas. The turbine impeller 11 is provided at the lower end portion of the rotary shaft 13. The body 10 is provided with an expansion chamber entrance 24, a turbine nozzle 25, and an expansion chamber exit 26, in the lower portion of the body 10. The expansion chamber entrance 24 opens in the lower portion of the body 10. The turbine nozzle 25 is connected to the expansion chamber entrance 24 at a first end thereof, and is connected to the expansion chamber 21 at a second end thereof. The expansion chamber exit 26 opens in the lower portion of the center portion of the body 10. With this structure, the expansion chamber 21 accommodating the turbine impeller 11 is connected to an outside region of the body 10. The refrigerant gas flows into the expansion chamber entrance 24. The refrigerant gas is injected toward the turbine impeller 11 through the second end of the turbine nozzle 25. According to the rotation of the turbine impeller 11, the refrigerant gas is expanded and its temperature is decreased. After that, the refrigerant gas flows out of the body 10 through the expansion chamber exit 26.

[0021] The brake impeller 12 is accommodated in the braking gas chamber 20. The brake impeller 12 is braked by a braking gas with the same kind as that of the refrigerant gas. The brake impeller 12 is provided at the upper end portion of the rotary shaft 13. The body 10 is provided with a braking gas chamber entrance 27 and a braking gas chamber exit 29, in the upper portion of the body 10. In this structure, the braking gas chamber 20 accommodating the brake impeller 12 is connected to a braking line 15 disposed outside the body 10. The braking gas with a room (normal) temperature flows from the braking line 15 into the braking gas chamber entrance 27, and then flows toward the brake impeller 12. According to the rotation of the brake impeller 12, the braking gas is compressed and its pressure and temperature are increased. After that, the refrigerant

-6gas flows out of the braking gas chamber exit 29. Then, the braking gas flows through the braking line 15 and is returned to the braking gas chamber entrance 27.

[0022] A hydrostatic gas bearing 14 is provided in a bearing chamber 23 formed in the shaft insertion hole 22. The hydrostatic gas bearing 14 supports the rotary shaft 13 in such a manner that the rotary shaft 13 is rotatable, by a static pressure of a bearing gas with the same kind as that of the refrigerant gas which is supplied from the expansion chamber entrance 24 and discharged from the expansion chamber exit 26. The hydrostatic gas bearing 14 includes radial hydrostatic gas bearings 14a, 14d which support the rotary shaft 13 in a radial direction in such a manner that the rotary shaft 13 is rotatable, and thrust hydrostatic gas bearings 14b, 14c which support the rotary shaft 13 in an axial direction in such a manner that the rotary shaft 13 is rotatable. These hydrostatic gas bearings 14a to 14d have a substantially cylindrical shape and surround the outer periphery of the rotary shaft 13. In the bearing chamber 23, the first radial hydrostatic bearing 14d, the first thrust hydrostatic bearing 14c, the second thrust hydrostatic bearing 14b, and the second radial hydrostatic bearing 14a are arranged in this order, in a direction from the expansion chamber 21 toward the braking gas chamber 20. The second thrust hydrostatic bearing 14b and the first thrust hydrostatic bearing 14c are disposed to vertically sandwich a thrust collar 34 protruding in the radial direction from the vertical center portion of the rotary shaft 13.

[0023] Inside the body 10, a first common gas supply passage 35a, a second common gas supply passage 35b, and a common gas discharge passage 36 are provided. The first common gas supply passage 35a, the second common gas supply passage 35b, and the common gas discharge passage 36 are provided at different positions in a circumferential direction. The first common gas supply passage 35a is connected to a bearing gas inlet 49. The first common gas supply passage 35a is used to flow the bearing gas to be supplied to a clearance of the second radial hydrostatic bearing 14a and a clearance of the first radial hydrostatic bearing 14d. The second common gas supply passage 35b is connected to the bearing gas inlet 49. The second common gas supply passage 35b is used to flow the bearing gas to be supplied to a clearance of the second thrust hydrostatic bearing 14b and a clearance of the first thrust hydrostatic bearing 14c. Although in the present embodiment, the first common gas supply passage 35a and the second common gas supply passage 35b are independent of each other, they may be configured as a

-7common passage. The common gas discharge passage 36 is connected to a bearing gas outlet 50. The common gas discharge passage 36 is used to flow the bearing gas having been discharged from the clearances of the hydrostatic gas bearings 14a to 14d.

[0024] The first common gas supply passage 35a is divided into a first gas supply passage 37 and a second gas supply passage 38. The second common gas supply passage 35b is divided into a third gas supply passage 43 and a fourth gas supply passage 44.

The first gas supply passage 37 is used to flow the bearing gas to be supplied to the clearance of the second radial hydrostatic bearing 14a. The second gas supply passage 38 is used to flow the bearing gas to be supplied to the clearance of the first radial hydrostatic bearing 14d. The third gas supply passage 43 is used to flow the bearing gas to be supplied to the clearance of the second thrust hydrostatic bearing 14b. The fourth gas supply passage 44 is used to flow the bearing gas to be supplied to the clearance of the first thrust hydrostatic bearing 14c.

[0025] The common gas discharge passage 36 is connected to a first gas discharge passage 39, a second gas discharge passage 40, a third gas discharge passage 41, and a fourth gas discharge passage 42. The first gas discharge passage 39 is used to flow the bearing gas having been discharged in an upward direction from the clearance of the second radial hydrostatic bearing 14a. The second gas discharge passage 40 is used to flow the bearing gas having been discharged in a downward direction from the clearance of the second radial hydrostatic bearing 14a and the bearing gas having been discharged in the upward direction from the clearance of the second thrust hydrostatic bearing 14b.

The third gas discharge passage 41 is used to flow the bearing gas having been discharged in the downward direction from the clearance of the first thrust hydrostatic bearing 14c and the bearing gas having been discharged in the upward direction from the clearance of the first radial hydrostatic bearing 14d. The fourth gas discharge passage 42 is used to flow the bearing gas having been discharged in the downward direction from the clearance of the first radial hydrostatic bearing 14d. The refrigerant gas which has leaked from the expansion chamber 21 to a portion of the bearing chamber 23 corresponding to the first radial hydrostatic bearing 14d through the first labyrinth seal 30 flows into the fourth gas discharge passage 42.

[0026] Fig. 2 schematically shows the cross-section of the configuration of the first radial hydrostatic bearing 14d. As shown in Fig. 2, a bearing member 51 with a

-8substantially cylindrical shape is provided to surround the outer periphery of the rotary shaft 13. The bearing member 51 has a clearance between the bearing member 51 and the rotary shaft 13. The bearing member 51 has a plurality of nozzle holes (bearing entrances) 51a formed in the circumferential direction. The bearing gas flowing through the second gas supply passage 38 which branches from the first common gas supply passage 35a of Fig. 1 is injected to the rotary shaft 13 through the nozzle holes 51a. A bearing membrane (indicated by dotted lines) of the first radial hydrostatic bearing 14d is formed between the inner peripheral surface of the bearing member 51 and the outer peripheral surface of the rotary shaft 13. The bearing gas (indicated by dotted-line arrows) having been discharged in the upward direction from a first end (bearing exit) of the clearance of the first radial hydrostatic bearing 14d is discharged through the third gas discharge passage 41 and then the common gas discharge passage 36 of Fig. 1. The bearing gas (indicated by dotted-line arrows) having been discharged in the downward direction from a second end (bearing exit) of the clearance of the first radial hydrostatic bearing 14d is discharged through the fourth gas discharge passage 42 and then the common gas discharge passage 36 of Fig. 1. The second radial hydrostatic bearing 14a of Fig. 1 has a structure similar to that of the first radial hydrostatic bearing 14d. The bearing membrane is formed by the bearing gas in the second radial hydrostatic bearing 14a. The bearing gases having been discharged in the upward direction and the downward direction from the both ends (bearing exit) of the clearance of the second radial hydrostatic bearing 14a are guided to the common gas discharge passage 36 through the first gas discharge passage 39 and the second gas discharge passage 40.

[0027] Fig. 3 schematically shows the cross-section of the thrust hydrostatic bearings 14b, 14c. As shown in Fig. 3, the rotary shaft 13 and the thrust collar 34 are disposed with a clearance inside the body 10. The third gas supply passage 43 branches from the second common gas supply passage 35b of Fig. 1. The third gas supply passage 43 is used to flow the bearing gas to be supplied to the clearance of the second thrust hydrostatic bearing 14b. The fourth gas supply passage 44 branches from the second common gas supply passage 35b. The fourth gas supply passage 44 is used to flow the bearing gas to be supplied to the clearance of the first thrust hydrostatic bearing 14c. [0028] The bearing gas flowing through the third gas supply passage 43 is injected through a nozzle hole (bearing entrance) 43 a. A bearing membrane (indicated by dotted

-9lines) of the second thrust hydrostatic bearing 14b is formed between the lower end surface of an inner wall 22a of the shaft insertion hole 22 and the upper end surface of the thrust collar 34. The bearing gas flowing through the fourth gas supply passage 44 is injected through a nozzle hole 44a. A bearing membrane (indicated by dotted lines) of the first thrust hydrostatic bearing 14c is formed between the upper end surface of the inner wall 22a of the shaft insertion hole 22 and the lower end surface of the thrust collar 34. The bearing gas (indicated by dotted-line arrows) having been discharged in the upward direction from a first end (bearing exit) of the clearance of the second thrust hydrostatic bearing 14b is discharged through the second gas discharge passage 40 and then the common gas discharge passage 36 of Fig. 1. The bearing gas (indicated by dotted-line arrows) having been discharged in the downward direction from a second end (bearing exit) of the clearance of the first thrust hydrostatic bearing 14c is discharged through the third gas discharge passage 41 and then the common gas discharge passage 36 of Fig. 1. The bearing gas (indicated by dotted-line arrows) having been discharged in the downward direction from a first end (bearing exit) of the clearance of the second thrust hydrostatic bearing 14b and the bearing gas (indicated by dotted-line arrows) having been discharged in the upward direction from a second end (bearing exit) of the clearance of the first thrust hydrostatic bearing 14c are discharged through the common gas discharge passage 36.

[0029] The body 10 of Fig. 1 includes the bearing gas inlet 49 and the bearing gas outlet 50. The bearing gas inlet 49 is connected to the first common gas supply passage 35a and the second common gas supply passage 35b. The bearing gas outlet 50 is connected to the common gas discharge passage 36. Through the bearing gas inlet 49, the bearing gas with a high pressure (in a high-pressure state) is supplied to the hydrostatic gas bearings 14a to 14d inside the body 10 of the expansion turbine apparatus 1. In the present embodiment, as the bearing gas, a hydrogen gas with the same kind as that of the refrigerant gas and with a room (normal) temperature is used. By supplying the bearing gas with the high-pressure to the clearances of the hydrostatic gas bearings 14a to 14d, the rotary shaft 13 can be rotatably supported inside the body 10, and a radial load and a thrust load of the rotary shaft 13 can be sufficiently borne. During start-up and stop of the expansion turbine apparatus 1, no friction is generated between the outer peripheral surface of the rotary shaft 13 and the inner peripheral surfaces of the hydrostatic gas

- 10bearings 14a to 14d. As a result, the lives of the expansion turbine apparatus 1, and the radial hydrostatic bearings 14a to 14d can be extended.

[0030] A first labyrinth seal 30 is provided in a region between the bearing chamber 23 and the expansion chamber 21 (see Fig. 1). A second labyrinth seal 31 is provided in a region between the end of the bearing chamber 23, the end being closer to the braking gas chamber 20 and a portion of the bearing chamber 23 at which the radial hydrostatic bearing 14a which is closer to the brake impeller is disposed (see Fig. 1). The first labyrinth seal 30 and the second labyrinth seal 31 are disposed to surround the outer periphery of the rotary shaft 13. In the present embodiment, a gas supply passage 55 is provided in the first labyrinth seal 30 to supply to a portion of the first labyrinth seal 30 a gas with a room (normal) temperature and with the same kind as that of the bearing gas. [0031] Fig. 4 is a schematic view showing the configuration of the first labyrinth seal 30. As shown in Fig. 4, the first labyrinth seal 30 has an inner peripheral surface surrounding the outer periphery of the rotary shaft 13 with a gap between the inner peripheral surface and the outer periphery of the rotary shaft 13. The inner peripheral surface of the first labyrinth seal 30 has a plurality of seal teeth. These seal teeth are provided along the outer periphery of the rotary shaft 13. Although in the present embodiment, the seal teeth are provided on a stationary side (first labyrinth seal 30), they may be provided in the rotary shaft 13. Hereinafter, one seal tooth and one tooth groove will be referred to as one stage. In an ideal case, after the refrigerant gas has flowed into the expansion chamber entrance 24 and then through the turbine nozzle 25, all of the refrigerant gas flows to the expansion chamber exit 26. However, a part of the refrigerant gas leaks to the first labyrinth seal 30 located on the back surface of the turbine impeller 11 (see Fig. 1). Whenever the refrigerant gas having leaked passes through each stage of the first labyrinth seal 30, a pressure of the refrigerant gas gradually decreases. In the present embodiment, the gas supply passage 55 penetrates the inside of the first labyrinth seal 30 in such a manner that a first end of the gas supply passage 55 opens in the outer peripheral surface of the first labyrinth seal 30 and a second end thereof opens in the inner peripheral surface of the first labyrinth seal 30. Although in the example of Fig. 4, the first end of the gas supply passage 55 is configured to supply the gas from right and left sides of Fig. 4 to the rotary shaft 13 through the inside of the first labyrinth seal 30, the configuration of the gas supply passage 55 is not limited to that shown in Figs. 1 and 4 so long as the gas supply

- 11 passage 55 is configured to supply to a portion of the first labyrinth seal 30, the gas with the room temperature and with the same kind as that of the refrigerant gas.

[0032] Fig. 5 is a schematic view showing the overall configuration of the expansion turbine apparatus 1 of Fig. 1. Hereinafter, the constituents already described above will not be described in repetition. As shown in Fig. 5, the expansion turbine apparatus 1 includes the body 10, the braking line 15, the turbine line 16, a bearing gas supply line 17, a bearing gas discharge line 18, the gas supply passage 55, a first pressure sensor 60, a second pressure sensor 70, a third pressure sensor 80, a pressure control valve 90, a controller 100, and a temperature sensor 110.

[0033] The braking line 15 is a pipe which circulates the braking gas to be supplied to the brake impeller 12. A first end (one end) of the braking line 15 is connected to the braking gas chamber entrance 27 of the braking gas chamber 20 of Fig. 1, while a second end (the other end) of the braking line 15 is connected to the braking gas chamber exit 29 of the braking gas chamber 20. A heat exchanger 53 is provided in a portion of the braking line 15. The heat exchanger 53 serves to decrease the temperature and pressure of the braking gas circulated through the braking line 15. The braking gas circulated through the braking line 15 is compressed, and thereby its temperature and pressure are increased, while flowing through the brake impeller 12. However, the braking gas flows through the heat exchanger 53 and thereby its temperature and pressure are decreased. The braking gas is maintained at a room (normal) temperature.

[0034] The turbine line 16 is a pipe used to supply the refrigerant to the turbine impeller 11. A first end of the turbine line 16 is connected to the expansion chamber entrance 24 of the expansion chamber 21 of Fig. 1. A second end of the turbine line 16 is connected to the expansion chamber exit 26 of the expansion chamber 21. The refrigerant with a low temperature and a high pressure which has been compressed by a compressor (not shown) at an upstream side of the expansion chamber entrance 24 of the expansion chamber 21 is led to the turbine impeller 11. The turbine impeller 11 decreases the temperature and pressure of the refrigerant with the low temperature and the high pressure by heat insulative expansion.

[0035] The bearing gas supply line 17 is configured to supply the bearing gas with the high pressure to the hydrostatic gas bearings 14a to 14d. A first end of the bearing gas supply line 17 is connected to, for example, a feed line which sends the raw material gas

- 12of the liquefying system. A second end of the bearing gas supply line 17 is connected to the bearing gas inlet 49 of the body 10 (see Fig. 1). The bearing gas supply line 17 is configured to supply the bearing gas to each of the second radial hydrostatic bearing 14a, the second thrust hydrostatic bearing 14b, the first thrust hydrostatic bearing 14c, and the first radial hydrostatic bearing 14d. The bearing gas supply line 17 is connected to the first common gas supply passage 35a and the second common gas supply passage 25b of Fig. 1. The bearing gas is supplied to the second radial hydrostatic bearing 14a and the first radial hydrostatic bearing 14d through the first gas supply passage 37 and the second gas supply passage 38, respectively, which branch from the first common gas supply passage 35 a. The bearing gas is supplied to the first thrust hydrostatic bearing 14c and the second thrust hydrostatic bearing 14b through the third gas supply passage 43 and the fourth gas supply passage 44, respectively, which branch from the second common gas supply passage 35b (see Fig. 1).

[0036] The bearing gas discharge line 18 is a mixture gas discharge passage, the upstream end of which is connected to the exit of the bearing chamber 23 corresponding to the hydrostatic gas bearings 14a to 14d, and which is configured to discharge a mixture gas containing the bearing gas which has flowed through the hydrostatic gas bearings 14a to 14d, the refrigerant gas which has leaked from the turbine line 16 (expansion chamber) to the bearing chamber 23 through the first labyrinth seal 30, and the gas supplied to a portion of the first labyrinth seal 30. In the present embodiment, the bearing gas discharge line 18 includes the first gas discharge passage 39, the second gas discharge passage 40, the third gas discharge passage 41, the fourth gas discharge passage 42, and the common gas discharge passage 36 (see Fig. 1).

[0037] The gas supply passage 55 is a pipe used to supply the gas with the same kind as that of the refrigerant to the first labyrinth seal 30. The first end of the gas supply passage 55 branches from the bearing gas supply line 17. The gas supply passage 55 penetrates the inside of the first labyrinth seal 30 in such a manner that the first end of the gas supply passage 55 opens in the outer peripheral surface of the first labyrinth seal 30 and the second end thereof opens in the inner peripheral surface of the first labyrinth seal 30 (see Fig. 1).

[0038] The first pressure sensor 60 is provided at the gas supply passage 55 and configured to measure a pressure Pi of the gas. The first pressure sensor 60 is configured

- 13 to output the measured pressure information to the controller 100.

[0039] The second pressure sensor 70 is configured to measure an entrance pressure P2 of the expansion chamber 21 in the turbine line 16. The second pressure sensor 70 is configured to output the measured pressure information to the controller 100.

[0040] The third pressure sensor 80 is provided at the bearing gas discharge line 18 and configured to measure a bearing gas back pressure P3 of the bearing gas discharge line 18. The third pressure sensor 80 is configured to output the measured pressure information to the controller 100.

[0041] The pressure control valve 90 is provided at the gas supply passage 55 and configured to control (adjust) the pressure Pi of the gas. The pressure control valve 90 is configured to control (adjust) the opening degree of the valve in accordance with a command from the controller 100.

[0042] The temperature sensor 110 is provided at the bearing gas discharge line 18 and configured to measure a bearing discharge gas temperature T1 of the bearing gas discharge line 18. The temperature sensor 110 is configured to output the measured temperature information to the controller 100.

[0043] The controller 100 is configured to control the pressure control valve 90 based on the pressure Pi of the gas, the entrance pressure P2 of the expansion chamber 21, the back pressure P3 of the hydrostatic gas bearings 14a to 14d, and the bearing discharge gas temperature Tp In the present embodiment, the controller 100 has a function of controlling the compressor and other devices, as well as the expansion turbine apparatus 1. The controller 100 is, for example, a microcomputer configured to mainly include CPU, ROM, and an input/output interface. Process data such as measurement values of the pressure Pi of the gas, the entrance pressure P2 of the expansion chamber 21, the back pressure P3 of the bearing gas discharge line 18, and the bearing discharge gas temperature Ti, and a turbine rotational speed are input to the input side of the controller 100. The pressure control valve 90, a supply valve, a discharge valve, and others are connected to the output side of the controller 100. The CPU executes control programs stored in the ROM. The CPU controls the pressure control valve 90 so that the pressure Pi of the gas, the entrance pressure P2 of the expansion chamber 21, and the bearing back pressure P3 become set values while monitoring the temperature measurement value of the process data. The controller 100 sets an initial pressure of the gas pressure Pi so that it is

- 14approximately equal to the bearing back pressure P3 and controls the pressure control valve 90 so that the pressure Pi of the gas is increased in a case where the bearing discharge gas temperature T1 falls below a reference value Ts. The reference value T_s of the temperature is a predetermined value or a specified range value in a normal state. [0044] During the operation (running) of the expansion turbine apparatus 1, the bearing gas with a high pressure is supplied from the bearing gas supply line 17 to the clearances of the hydrostatic gas bearings 14a to 14d of the turbine body 10. Thus, the rotary shaft 13 is rotatably supported inside the body 10, and the radial load and thrust load of the rotary shaft 13 are borne. The bearing gas of the hydrostatic gas bearings 14a to 14d is discharged from the bearing gas discharge line 18. The turbine nozzle 25 reduces the pressure P2 of the expansion chamber entrance 24. Most of the refrigerant in the turbine line 16 (expansion chamber) is expanded in a heat insulating manner at the turbine impeller 11 and then flows toward the expansion chamber exit 26. The first labyrinth seal 30 is provided in a region between the end of the bearing chamber 23, the end being closer to the expansion chamber 21 accommodating the turbine impeller 11, and a portion of the bearing chamber 23 at which the radial hydrostatic bearing 14d is disposed. Some of the refrigerant gas leaks from the turbine line 16 (expansion chamber) to the bearing through the first labyrinth seal 30. Therefore, the mixture gas containing the bearing gas and the refrigerant gas having leaked exits in the bearing gas discharge line 18. At this time, the amount of the refrigerant gas which leaks from the turbine line 16 (expansion chamber) to the bearing chamber 23 through the first labyrinth seal 30 depends on a differential pressure between an entrance pressure P4 of the first labyrinth seal 30 and an exit pressure of the first labyrinth seal 30. It is difficult to attach a sensor on an entrance or an exit of the first labyrinth seal 30, and it is difficult to accurately measure a pressure. The exit pressure of the first labyrinth seal 30 is almost equal to the bearing back pressure P3.

[0045] In the present embodiment, the gas with the pressure Pi which is lower than the entrance pressure P2 of the expansion chamber 21 and higher than the back pressure P3 of the hydrostatic bearing is supplied to a portion of the first labyrinth seal 30. In other words, the amount of the refrigerant gas which leaks from the expansion chamber 21 to the bearing gas discharge line 18 through the first labyrinth seal 30 substantially depends on the supply pressure Pi of the gas. This makes it possible to make the amount of the

- 15 refrigerant gas which leaks, under a condition in which the back pressure of the hydrostatic gas bearing is equal, less, in a case where the gas is supplied than in a case where the gas is not supplied. For example, in a case where the gas is not supplied, the bearing back pressure may be increased and the differential pressure of the labyrinth seal may be reduced, to reduce the amount of the refrigerant gas which leaks. However, in this case, bearing performance may be reduced. In contrast, in a case where the gas is supplied, like the present embodiment, the amount of the refrigerant gas which leaks through the first labyrinth seal 30 can be reduced without increasing the bearing back pressure.

[0046] In actuality, the entrance pressure of the labyrinth seal is lower than the entrance pressure of the expansion chamber. Therefore, if the gas with a pressure lower than the entrance pressure of the expansion chamber and higher than the entrance pressure of the labyrinth seal is supplied, the gas flows back and the normal-temperature gas flows to the expansion chamber. In view of this, the supply pressure Pi of the gas is desirably set lower than the entrance pressure P4 of the first labyrinth seal 30. The entrance pressure P4 of the first labyrinth seal 30 is almost equal to the exit pressure of the turbine nozzle 25 of Fig. 1. This makes it possible to prevent the room-temperature gas from flowing from the entrance of the first labyrinth seal 30 into the expansion chamber 21.

[0047] In a case where the amount of the refrigerant gas which leaks from the turbine line 16 (expansion chamber) to the bearing through the first labyrinth seal 30 is increased, the temperature of the bearing gas discharge line 18 which is measured by the temperature sensor 110 is reduced. In a case where the bearing discharge gas temperature T1 becomes lower than the reference value T_s, the controller 1100 controls the pressure control valve 90 so that the pressure Pi of the gas to be supplied to the first labyrinth seal 30 is increased. This can secure equilibrium between the entrance pressure of a region of the first labyrinth seal 30 which is closer to the turbine and the pressure Pi of the gas. In theory, leakage of the low-temperature gas from the turbine can be prevented. As a result, reduction of turbine performance can be prevented, and reduction of the temperature in a region in a room temperature state can be prevented.

[0048] (Embodiment 2)

Next, Embodiment 2 will be described with reference to Fig. 6. Hereinbelow, the same constituents as those of Embodiment 1 will not be described, and only the

- 16constituents different from those of Embodiment 1 will be described.

[0049] Fig. 6 is a schematic view showing the configuration of an expansion turbine apparatus 1A according to Embodiment 2. As shown in Fig. 6, the expansion turbine apparatus 1A is different from the expansion turbine apparatus 1 according to Embodiment 1 in that the expansion turbine apparatus 1A further comprises a back pressure control valve 120 provided at the bearing gas discharge line 18 to control the back pressure P₃ of the hydrostatic gas bearings 14a to 14d, and the controller 100 controls the back pressure control valve 120 so that the back pressure P₃ of the hydrostatic gas bearings 14a to 14d is increased in a case where the temperature of the mixture gas flowing through the bearing gas discharge line 18 is reduced. In accordance with this configuration, by increasing he back pressure P₃ of the hydrostatic gas bearings 14a to 14d, leakage of the low-temperature gas from the turbine can be more effectively suppressed, compared to Embodiment 1.

[0050] Although in the present embodiment, only the back pressure P₃ of the hydrostatic gas bearings 14a to 14d is controlled to be increased, the expansion turbine apparatus 1A may further comprise a constituent (not shown) for controlling the pressure of the bearing gas supply line 17, to prevent reduction of the differential pressure between the entrance and the exit of the bearings.

[0051] Numerous modifications and alternative embodiments of the present invention will be apparent to those skilled in the art in view of the foregoing description. Accordingly, the description is to be construed as illustrative only, and is provided for the purpose of teaching those skilled in the art the best mode of conveying out the invention. The details of the structure and/or function may be varied substantially without departing from the spirit of the invention.

Industrial Applicability [0052] The present invention is effectively used in an expansion turbine including hydrostatic gas bearings.

Reference Signs List [0053] 1, 1A expansion turbine apparatus turbine body turbine impeller brake impeller rotary shaft hydrostatic gas bearing

14a second radial hydrostatic bearing (braking gas chamber side) 14b second thrust hydrostatic bearing (braking gas chamber side) 14c first thrust hydrostatic bearing (expansion chamber side) 14d first radial hydrostatic bearing (expansion chamber side) braking line turbine line bearing gas supply line bearing gas discharge line (mixture gas discharge passage) braking gas chamber expansion chamber shaft insertion hole bearing chamber expansion chamber entrance turbine nozzle expansion chamber exit braking gas chamber entrance braking gas chamber exit first labyrinth seal (expansion chamber side) second labyrinth seal (braking gas chamber side) first pressure sensor second pressure sensor third pressure sensor pressure control valve

100 controller

110 temperature sensor

120 back pressure control valve

Claims

1. An expansion turbine apparatus including:

a body formed with an expansion chamber, a braking gas chamber, and a shaft insertion hole inside the body, the shaft insertion hole being provided in such a manner that the expansion chamber and the braking gas chamber are in communication with each other via the shaft insertion hole and a rotary shaft is insertable into the shaft insertion hole;

a turbine impeller accommodated in the expansion chamber to expand a refrigerant gas;

a brake impeller which is accommodated in the braking gas chamber, and braked by a braking gas with the same kind as that of the refrigerant gas;

the rotary shaft inserted into the shaft insertion hole with a clearance between the rotary shaft and the shaft insertion hole, the turbine impeller being provided at a first end portion of the rotary shaft, the brake impeller being provided at a second end portion of the rotary shaft;

a hydrostatic gas bearing which is provided in a bearing chamber formed inside the shaft insertion hole and supports the rotary shaft in such a manner that the rotary shaft is rotatable, by a static pressure of a bearing gas with the same kind as that of the refrigerant gas supplied from an entrance and discharged from an exit;

a labyrinth seal provided in a region between the bearing chamber and the expansion chamber;

a gas supply passage provided in the labyrinth seal to supply to a portion of the labyrinth seal a gas with the same kind as that of the refrigerant gas; and a mixture gas discharge passage, an upstream end of which is connected to a bearing chamber exit of the hydrostatic gas bearing, the mixture gas discharge passage being configured to discharge a mixture gas containing the bearing gas which has flowed through the hydrostatic gas bearing, the refrigerant gas which has leaked from the expansion chamber to the bearing chamber through the labyrinth seal, and the gas supplied to the portion of the labyrinth seal, wherein a pressure of the gas supplied to the portion of the labyrinth seal is lower than an entrance pressure of the expansion chamber and higher than a back pressure of the hydrostatic gas bearing.

2. The expansion turbine apparatus according to claim 1, further comprising:

a first pressure sensor which measures the pressure of the gas;

a pressure control valve provided at the gas supply passage to control the pressure of the gas;

a second pressure sensor which measures the entrance pressure of the expansion chamber; and a controller which controls the pressure control valve so that the pressure of the gas becomes lower than the entrance pressure of the expansion chamber and higher than the back pressure of the hydrostatic gas bearing.

3. The expansion turbine apparatus according to claim 2, wherein the controller controls an initial pressure of the gas to be supplied to the portion of the labyrinth seal so that the initial pressure becomes approximately equal to the back pressure of the hydrostatic gas bearing, and controls the pressure control valve so that the pressure of the gas is increased in a case where a temperature of the mixture gas flowing through the mixture gas discharge passage is reduced.