Centrifugal compressor

Abstract

To achieve a reduction in the load on a rear stage side compression part.SOLUTION: A centrifugal compressor 10 includes five-or-more-stage compression parts 11, 14, a bull gear 19, and pinion shafts 21, 22. An outer diameter of the pinion shaft which drives the final stage compression part is smaller than an outer diameter of the pinion shaft 21 which drives the first stage compression part 11, and an outer diameter of an impeller of the final stage compression part is smaller than an outer diameter of an impeller 11a of the first stage compression part 11. A peripheral velocity Mach number of the impeller 11a is 1 to 1.5 both inclusive, and specific speed is 400 to 450 both inclusive. The peripheral velocity Mach number of the impeller of the final stage compression part is 0.5 inclusive to 1 exclusive, and the specific speed is 150 to 350 both inclusive.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a multi-stage centrifugal compressor with built-in gears. [Background technology]

[0002] In recent years, carbon dioxide is considered to have a large impact on global warming. Technologies such as carbon dioxide capture have attracted attention as an effective measure against this global warming problem. Incidentally, although it is not specifically a compressor for compressing carbon dioxide, a multi-stage centrifugal compressor with built-in gears is known, as disclosed in Patent Document 1. A multi-stage centrifugal compressor has multiple compression sections so that gas can be compressed in stages. Each compression section has an impeller, and each impeller is driven by a common bull gear via a corresponding pinion shaft. The pinion shaft is provided with a pinion gear, and the pinion shaft is arranged so that this pinion gear meshes with the bull gear. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-52492 Summary of the Invention [Problem to be solved by the invention]

[0004] In a multi-stage centrifugal compressor, the gas is pressurized sequentially, resulting in a smaller volumetric flow rate in the later compression sections. Therefore, the impellers in the later compression sections are relatively smaller. Accordingly, the pinion shaft (pinion gear) that drives the impeller also has a relatively small diameter, which means that the pinion gears that mesh with the bull gears in the later compression sections are likely to be subject to a greater load. In particular, when processing high-molecular-weight gases such as CO2, the processing load is likely to be greater than when processing low-molecular-weight gases.

[0005] However, Patent Document 1 only shows that the design period can be shortened by reducing the number of repeated evaluations when solving an optimization problem, and does not consider load distribution between compression units.

[0006] The present invention has been made in view of the above-mentioned problems, and has as its object to reduce the load on a rear-stage compression section in a multi-stage centrifugal compressor. [Means for solving the problem]

[0007] The centrifugal compressor according to the present invention is a multi-stage centrifugal compressor for processing a target gas having a molecular weight of 40 or more, and includes five or more compression sections that gradually increase the pressure of the target gas, a bull gear driven by a power source, and three or more pinion shafts that mesh with the bull gear directly or via idler gears and transmit power to the five or more compression sections. Each of the five or more compression sections includes an impeller and a scroll that recovers gas that has passed through the impeller. The outer diameter of the pinion shaft that drives the final compression section of the five or more compression sections is smaller than the outer diameter of the pinion shaft that drives the first compression section of the five or more compression sections, and the outer diameter of the impeller of the final compression section is smaller than the outer diameter of the impeller of the first compression section. In the first-stage compression section, the peripheral Mach number of the impeller is equal to or greater than 1 and equal to or less than 1.5, and the specific speed is equal to or greater than 400 and equal to or less than 500, and the peripheral Mach number and the specific speed of the first-stage compression section are the largest among the peripheral Mach numbers and specific speeds of the five or more stages of compression sections. In the final-stage compression section, the peripheral Mach number of the impeller is equal to or greater than 0.5 and less than 1, and the specific speed is equal to or greater than 150 and equal to or less than 350.

[0008] In the centrifugal compressor, the amount of work done in the first stage can be secured by increasing the peripheral Mach number and specific speed of the first stage compression section.

[0009] The peripheral Mach number and the specific speed in the final stage compressor section may be the smallest among the peripheral Mach numbers and specific speeds of the five or more compressor sections. In this aspect, the peripheral Mach number and the specific speed of the final stage compressor section are made the smallest, thereby reducing the load on the final stage compressor section.

[0010] In the centrifugal compressor, a second-stage compression section among the five or more compression sections may be connected to a pinion shaft common to the first-stage compression section. In this case, the peripheral Mach number of the impeller in the second-stage compression section may be a value between the peripheral Mach number of the impeller in the first-stage compression section and the peripheral Mach number of the impeller in the final-stage compression section, and the specific speed may be a value between the specific speed of the first-stage compression section and the specific speed of the final-stage compression section. In this aspect, it is possible to prevent the load on the second-stage compression section from increasing more than on the first-stage compression section.

[0011] The compressor section next to the final stage among the five or more compressor sections may be connected to a pinion shaft common to the compressor section of the final stage. In this case, the peripheral Mach number of the impeller in the compressor section next to the final stage may be a value between the peripheral Mach number of the impeller in the second-stage compressor section and the peripheral Mach number of the impeller in the final-stage compressor section, and the specific speed may be a value between the specific speed of the second-stage compressor section and the specific speed of the final-stage compressor section.

[0012] The later the stage, the higher the pressure, and therefore the greater the gas density. If an impeller with a high specific speed is used in the compression section before the final stage, the radial height of the blades will increase, resulting in greater stress on the blades. In contrast, by reducing the specific speed, the radial height of the blades can be reduced, thereby suppressing stress.

[0013] The centrifugal compressor may further include a pre-stage compression section that takes in a target gas having a molecular weight of less than 40. In this case, the target gas may be dried by an external device and have a molecular weight of 40 or more, and the first-stage compression section may take in the target gas. [Effects of the Invention]

[0014] As described above, according to the present invention, it is possible to reduce the load on the rear-stage compression section in a multi-stage centrifugal compressor. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a diagram schematically illustrating a portion including first to fourth stage compression sections of a multistage centrifugal compressor according to an embodiment. [Figure 2] FIG. 3 is a diagram schematically illustrating a portion of the centrifugal compressor including fifth- and sixth-stage compression sections. [Figure 3] FIG. 2 is a perspective view partially showing the centrifugal compressor. [Figure 4] FIG. 10 is a diagram schematically illustrating a portion including fifth- to seventh-stage compression sections of a centrifugal compressor according to another embodiment. [Figure 5] FIG. 10 is a diagram schematically showing a portion including first to third stage compression sections of a centrifugal compressor according to another embodiment. [Figure 6] FIG. 10 is a diagram illustrating a portion of a centrifugal compressor according to another embodiment. [Figure 7] FIG. 1 is a cross-sectional view showing a part of a centrifugal compressor. DETAILED DESCRIPTION OF THE INVENTION

[0016] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0017] (First embodiment) A multi-stage centrifugal compressor is a compressor that processes gases with a molecular weight of 40 or more. Examples of gases to be processed (target gases) include carbon dioxide and propylene. Even in the case of a gas that is mainly composed of carbon dioxide and also contains moisture, if the carbon dioxide content is about 90%, the molecular weight of the gas may be about 40 in terms of molecular weight ratio, and such gases are also subject to processing.

[0018] As shown in FIGS. 1 and 2, the centrifugal compressor 10 includes six compression stages 11-16, a bull gear 19 driven by a motor 18 serving as a power source, and three pinion shafts 21-23.

[0019] The pinion shafts 21 to 23 each have a pinion 31 to 33 driven by the bull gear 19. The first pinion shaft 21 transmits the power of the bull gear 19 to the first stage compression section 11, which is the first stage compression section, and the second stage compression section 12, which is the second stage compression section. The second pinion shaft 22 transmits the power of the bull gear 19 to the third stage compression section 13, which is the third stage compression section, and the fourth stage compression section 14, which is the fourth stage compression section. The third pinion shaft 23 transmits the power of the bull gear 19 to the fifth stage compression section 15, which is the fifth stage compression section, and the sixth stage compression section 16, which is the sixth stage compression section.

[0020] The pinions 31 to 33 are provided at the middle portions of the pinion shafts 21 to 23, respectively, and each pinion 31 to 33 meshes with the bull gear 19. The pinions 31 to 33 are driven at a rotation speed that is increased from the rotation speed of the bull gear 19 in accordance with the ratio between the number of teeth of the pinions 31 to 33 and the number of teeth of the bull gear 19. The pinions 31 to 33 may mesh directly with the bull gear 19, or may mesh with the bull gear 19 via an idler gear (not shown).

[0021] The bull gear 19 is disposed in a gear case 35 (see FIG. 3), and a shaft 19a of the bull gear 19 is connected to a shaft 18a of the motor 18 via a coupling 37. The shaft 19a of the bull gear 19 is rotatably supported by the gear case 35. The first to third pinion shafts 21 to 23 are also rotatably supported by the gear case 35.

[0022] Each of the compression sections 11 to 16 includes an impeller 11a to 16a fixed to an end of a pinion shaft 21 to 23, a diffuser vane 11b to 16b for decelerating and pressurizing the target gas whose direction has been changed in the radial direction by the impeller 11a to 16a, and a scroll 12c, 13c for recovering the target gas that has passed through the diffuser vanes 11b to 16b. Note that while the scroll 12c of the second-stage compression section 12 and the scroll 13c of the third-stage compression section 13 are shown in Fig. 3, the scrolls of the compression sections of the other stages are not shown.

[0023] As shown in Fig. 1, the impeller 11a of the first-stage compression section 11 is fixed to one end of a first pinion shaft 21, and the impeller 12a of the second-stage compression section 12 is fixed to the other end of the first pinion shaft 21. The impeller 13a of the third-stage compression section 13 is fixed to one end of a second pinion shaft 22, and the impeller 14a of the fourth-stage compression section 14 is fixed to the other end of the second pinion shaft 22. As shown in Fig. 2, the impeller 15a of the fifth-stage compression section 15 is fixed to one end of a third pinion shaft 23, and the impeller 16a of the sixth-stage compression section 16 is fixed to the other end of the third pinion shaft 23.

[0024] The diffuser vanes 11b to 16b are fixed to the gear case 35. The diffuser vanes 11b to 16b are concentric with the corresponding impellers 11a to 16a and are arranged on the back side of the corresponding impellers 11a to 16a. The diffuser vanes 11b to 16b have outer diameters larger than the outer diameters of the corresponding impellers 11a to 16a and extend radially outward from the outer peripheries of the corresponding impellers 11a to 16a.

[0025] The diffuser vanes 11b to 16b have a number of blades arranged at intervals in the circumferential direction so that part of the kinetic energy imparted by the corresponding impellers 11a to 16a is converted into pressure energy.

[0026] As shown in Fig. 3, a casing 39 is coupled to the diffuser vanes 11b-16b, forming a space between the impellers 11a-16a and the diffuser vanes 11b-16b. A gas intake port 39a is formed in the casing 39. Between the impellers 11a-16a and the diffuser vanes 11b-16b, the casing 39 forms a space (acceleration space) in which the target gas drawn in through the intake port 39a is accelerated by the impellers 11a-16a, and a space (pressurization space) in which the accelerated target gas is pressurized by the diffuser vanes 11b-16b. Note that Fig. 3 only shows the casings 39 of the first-stage compression section 11 to the third-stage compression section 13, and does not show the casings of the other compression sections.

[0027] The target gas drawn in through the intake port 39a is given kinetic energy by the impellers 11a to 16a and flows circumferentially within the acceleration space. The target gas flows radially outward while flowing circumferentially, and is pressurized by the diffuser vanes 11b to 16b within the pressurization space.

[0028] The scrolls 12c and 13c form a flow path for collecting the target gas flowing in the circumferential direction in the pressurized space along the diffuser vanes 11b to 16b and flowing it in the spiral direction, and are connected to a casing 39.

[0029] The inlet port 39a of the casing 39 of the first-stage compression section 11 draws in the target gas flowing from the target gas supply source. The scroll of the first-stage compression section 11 is connected to the inlet port 39a of the casing 39 of the second-stage compression section 12 through a first connecting pipe 41 (see FIG. 1). The scroll 12c of the second-stage compression section 12 is connected to the inlet port of the casing 39 of the third-stage compression section 13 through a second connecting pipe 42 (see FIG. 1). The scroll 13c of the third-stage compression section 13 is connected to the inlet port of the casing of the fourth-stage compression section 14 through a third connecting pipe 43 (see FIG. 1). The scroll of the fourth-stage compression section 14 is connected to the inlet port of the casing of the fifth-stage compression section 15 through a fourth connecting pipe 44 (see FIG. 2). The scroll of the fifth-stage compression section 15 is connected to the inlet port of the casing of the sixth-stage compression section 16 through a fifth connecting pipe 45 (see FIG. 2). The scroll of the sixth stage compression section 16 is connected to a pipe 46 (see FIG. 2) that leads to the supply destination of the target gas.

[0030] Therefore, the target gas sent from the supply source is sucked into the first-stage compression section 11 through the inlet 39a of the casing 39 of the first-stage compression section 11. In the first-stage compression section 11, the target gas is given kinetic energy by the impeller 11a driven by the bull gear 19, and is accelerated, compressed, and pressurized. This pressurized target gas is introduced into the second-stage compression section 12 through the first connecting pipe 41, where it is further pressurized. This target gas is further pressurized sequentially in the third-stage compression section 13 to the sixth-stage compression section 16, and the target gas discharged from the sixth-stage compression section 16 is sent to the supply destination through the pipe 46.

[0031] Here, the relationship between the specifications of the impellers 11a to 16a among the compression sections 11 to 16 and the relationship between the specifications of the pinion shafts 21 to 23 among the compression sections 11 to 16 will be described.

[0032] The impellers 11a to 16a of the compression sections 11 to 16 are set so that the outer diameters of the impellers 11a to 16a become smaller as they are positioned in the later compression sections 12 to 16. That is, the impeller 12a of the second compression section 12 has a smaller outer diameter than the impeller 11a of the first compression section 11, and the impeller 13a of the third compression section 13 has a smaller outer diameter than the impeller 12a of the second compression section 12. The same relationship applies to the fourth to sixth compression sections 14 to 16. For convenience, the impellers 11a to 16a are not depicted in FIGS. 1 and 2 in a manner that clearly shows this relationship.

[0033] Note that, as long as the outer diameter of the impeller 11a of the first-stage compression section 11 is the largest and the outer diameter of the impeller 16a of the sixth-stage compression section 16 (the final compression section) is the smallest among the six impellers 11a-16a, the above relationship does not need to be satisfied for all of the first to sixth stages. For example, between two consecutive compression sections 11-16, there may be compression stages in which the outer diameters of the impellers 11a-16a are the same. For example, the outer diameter of the impeller 13a of the third-stage compression section 13 and the outer diameter of the impeller 14a of the fourth-stage compression section 14 may be the same.

[0034] The rotation speed of the first pinion shaft 21 and the outer diameter of the impeller 11a are set so that the peripheral Mach number of the impeller 11a of the first-stage compression section 11 is equal to or greater than 1 and equal to or less than 1.5. The peripheral Mach number of the impeller 11a is the ratio (dimensionless quantity) of the peripheral speed of the impeller 11a to the sonic speed of the target gas. The peripheral speed of the impeller 11a is determined based on the rotation speed of the first pinion shaft 21 and the outer diameter of the impeller 11a. The rotation speed of the first pinion shaft 21 can be set by setting the rotation speed of the bull gear 19 and the gear ratio between the bull gear 19 and the pinion 31.

[0035] The rotation speed of the third pinion shaft 23 and the outer diameter of the impeller 16a are set so that the peripheral Mach number of the impeller 16a of the sixth-stage compression section (final-stage compression section) 16 is equal to or greater than 0.5 and less than 1. The peripheral Mach number of the impeller 16a is the ratio (a dimensionless quantity) of the peripheral speed of the impeller 16a to the sonic speed of the target gas. That is, in the sixth-stage compression section (final-stage compression section) 16, the peripheral speed of the impeller 16a is set to be less than the sonic speed of the target gas. Therefore, the occurrence of choked flow of the target gas is suppressed in the final-stage compression section, which has the highest pressure, and excessive load on the final-stage compression section can be prevented.

[0036] The peripheral speed of the impeller 16a is determined based on the rotation speed of the third pinion shaft 23 and the outer diameter of the impeller 16a. The rotation speed of the third pinion shaft 23 can be set by setting the rotation speed of the bull gear 19 and the gear ratio between the bull gear 19 and the pinion 33.

[0037] The impeller 12a of the second-stage compression section 12 is set to have a peripheral Mach number between the peripheral Mach number of the impeller 11a of the first-stage compression section 11 and the peripheral Mach number of the impeller 16a of the sixth-stage compression section 16. In this embodiment, the first-stage compression section 11 and the second-stage compression section 12 are connected to a common pinion shaft, the first pinion shaft 21, so that the impeller 11a of the first-stage compression section 11 and the impeller 12a of the second-stage compression section 12 have the same rotation speed. Therefore, the outer diameter of the impeller 12a of the second-stage compression section 12 is smaller than the outer diameter of the impeller 11a of the first-stage compression section 11. As a result, the peripheral Mach number of the impeller 12a of the second-stage compression section 12 is smaller than the peripheral Mach number of the impeller 11a of the first-stage compression section 11.

[0038] The impeller 15a of the fifth-stage compression section 15 is set to have a peripheral Mach number between the peripheral Mach number of the impeller 12a of the second-stage compression section 12 and the peripheral Mach number of the impeller 16a of the sixth-stage compression section 16. In this embodiment, the fifth-stage compression section 15 and the sixth-stage compression section 16 are connected to a third pinion shaft 23, which is a common pinion shaft, so that the impeller 15a of the fifth-stage compression section 15 and the impeller 16a of the sixth-stage compression section 16 have the same rotation speed. Therefore, the outer diameter of the impeller 15a of the fifth-stage compression section 15 is larger than the outer diameter of the impeller 16a of the sixth-stage compression section 16. As a result, the peripheral Mach number of the impeller 15a of the fifth-stage compression section 15 is larger than the peripheral Mach number of the impeller 16a of the sixth-stage compression section 16.

[0039] The first stage compression section 11 is set to have a specific speed of 400 or more and 450 or less, and the sixth stage compression section 16 is set to have a specific speed of 200 or more and 300 or less. The second stage compression section 12 is set to have a specific speed that is a value between the specific speeds of the first stage compression section 11 and the sixth stage compression section 16, and the fifth stage compression section 15 is set to have a specific speed that is a value between the specific speeds of the second stage compression section 12 and the sixth stage compression section 16.

[0040] Specific speed is an index that shows the similarity as a fluid machine, and means the rotational speed required to pump a unit flow rate of gas by the amount of head, and is expressed by the following equation (1). In other words, specific speed is a dimensionless quantity.

[0041]

number

[0042] where n s :Specific speed (sec -1 , m 3 / sec, m), n: rotation speed (sec -1 ), Q: Flow rate (m 3 / sec), g: Gravitational acceleration (m / sec), g: Gravitational acceleration (m / sec) 2 ), H: head or height (m).

[0043] Therefore, the rotational speeds required to increase the pressure of a unit flow rate of target gas by a predetermined amount are set to decrease in the order of the first stage compression section 11, the second stage compression section 12, the fifth stage compression section 15, and the sixth stage compression section 16. The specific speed of the first stage compression section 11 and the specific speed of the second stage compression section 12 may be set to the same value. The specific speed of the fifth stage compression section 15 and the specific speed of the sixth stage compression section 16 may be set to the same value.

[0044] The pinion shafts 21-23 are set so that the outer diameter of the pinion shafts 21-23 connected to the later-stage compression sections 11-16 becomes smaller. That is, the outer diameter of the second pinion shaft 22 is smaller than the outer diameter of the first pinion shaft 21, and the outer diameter of the third pinion shaft 23 is smaller than the outer diameter of the second pinion shaft 22. Therefore, the outer diameter of the pinion shaft 23 that drives the sixth-stage compression section (final-stage compression section) 16 is smaller than the outer diameter of the pinion shaft 21 that drives the first-stage compression section 11.

[0045] As described above, according to this embodiment, the peripheral Mach number and specific speed of the first compression stage 11 are greater than those of the other compression stages, so it is possible to ensure the amount of work in the first compression stage 11. Furthermore, the peripheral Mach number and specific speed of the sixth compression stage (final compression stage) 16 are the smallest, so it is possible to reduce the load on the sixth compression stage 16, where the target gas reaches the highest pressure.

[0046] Furthermore, in this embodiment, the peripheral Mach number and specific speed in the second stage compression section 12 are set to values ​​between the peripheral Mach number and specific speed in the first stage compression section 11 and the peripheral Mach number and specific speed in the sixth stage compression section 16. Therefore, it is possible to prevent the load in the second stage compression section 12 from increasing more than in the first stage compression section 11.

[0047] In a multi-stage centrifugal compressor 10, gas pressure increases with increasing stage, resulting in an increase in gas density. Therefore, if an impeller with a high specific speed is used in the compression section (fifth-stage compression section 15) before the final stage, the height of the blades of the impeller in a direction perpendicular to the rotation axis at the suction-side end (hereinafter referred to as the "radial height" of the impeller blades. The radial height is, for example, height r1 shown in FIG. 7 . That is, the radial height r1 of the blade 50 is the height from the hub outer surface 51 at the suction-side end of the blade 50 in a direction perpendicular to the rotation axis 52) increases, resulting in increased stress on the blades. In contrast, by using an impeller 15a with a lower specific speed in the fifth-stage compression section 15 than that of the second-stage compression section 12, the radial height of the blades can be reduced, thereby suppressing stress on the blades.

[0048] The disclosed embodiments are illustrative in all respects and should not be considered limiting. The present invention is not limited to the above-described embodiments, and various modifications and improvements are possible without departing from the spirit and scope of the present invention. For example, the centrifugal compressor 10 of this embodiment is a compressor having a six-stage compression section, but is not limited to a six-stage compressor. The centrifugal compressor 10 may be a compressor having a seven-stage compression section or an eight-stage compression section, as long as it has at least five compression sections. FIG. 4 shows the fifth to seventh compression sections 15-17 when the centrifugal compressor 10 is configured as a seven-stage compressor, and in addition to the configuration of FIG. 2, a fourth pinion shaft 24 is added. A pinion 34 is provided on the fourth pinion shaft 24, and this pinion 34 meshes with the bull gear 19. The pinion 34 may mesh with the bull gear 19 directly or via an idler gear (not shown). Furthermore, an eighth-stage compression section (not shown) may be provided at the other end of the fourth pinion shaft 24.

[0049] An impeller 17a of the seventh-stage compression section 17, which is the final-stage compression section, is fixed to one end of the fourth pinion shaft 24. The seventh-stage compression section 17 is also provided with a diffuser vane 17b. The scroll of the sixth-stage compression section 16 is connected to the intake port of the casing of the seventh-stage compression section 17 through a sixth connecting pipe 47. The scroll of the seventh-stage compression section 17 is connected to a pipe 46 leading to a supply destination of the target gas.

[0050] The outer diameter of the impeller 17a of the seventh-stage compression section 17 is smaller than the outer diameter of the impeller 11a of the first-stage compression section 11 and the outer diameter of the impeller 16a of the sixth-stage compression section 16. The rotation speed of the fourth pinion shaft 24 and the outer diameter of the impeller 17a of the seventh-stage compression section (final-stage compression section) 17 are set so that the peripheral Mach number is 0.5 or more and less than 1.

[0051] The impeller 12a of the second-stage compression section 12 is set to have a peripheral Mach number between the peripheral Mach number of the impeller 11a of the first-stage compression section 11 and the peripheral Mach number of the impeller 17a of the seventh-stage compression section 17. The impeller 16a of the sixth-stage compression section 16 is set to have a peripheral Mach number between the peripheral Mach number of the impeller 12a of the second-stage compression section 12 and the peripheral Mach number of the impeller 17a of the seventh-stage compression section 17. The seventh-stage compression section 17 is set to have a specific speed of 200 or more and 300 or less. The specific speed of the sixth-stage compression section 16 is set to have a value between the specific speed of the second-stage compression section 12 and the specific speed of the seventh-stage compression section 17.

[0052] In the above embodiment, a compression section is provided at each end of first pinion shaft 21, but the present invention is not limited thereto. For example, as shown in FIG. 5 , first-stage compression section 11 may be provided at one end of first pinion shaft 21, while second-stage compression section 12 may be provided on second pinion shaft 22 instead of first pinion shaft 21. In this case, third-stage compression section 13 is provided at the other end of second pinion shaft 22, and fourth-stage compression section 14 and fifth-stage compression section 15 are provided on third pinion shaft 23. Note that instead of providing a compression section at only one end of first pinion shaft 21, a compression section may be provided at only one end of second pinion shaft 22, or a compression section may be provided at only one end of third pinion shaft 23.

[0053] The centrifugal compressor 10 may be provided with pre-compression sections 81 and 82 upstream of the first-stage compression section 11, as shown in FIG. 6. Although two pre-compression sections 81 and 82 are provided in FIG. 6, the number of pre-compression sections 81 and 82 may be any number other than two. The pre-compression sections 81 and 82 suck in a target gas (gas A) having a molecular weight of less than 40 (for example, 25) and supply it to an external device 9 of the centrifugal compressor 10. The target gas (gas A) is dried in the external device 9 to become a target gas (gas B) having a molecular weight of 40 or more. The target gas (gas B) having a molecular weight of 40 or more is discharged from the external device 9 and sucked into the first-stage compression section 11. The pre-compression sections 81 and 82 may be compression sections having impellers 81 a and 82 a that rotate by the driving force of a bull gear 19. [Explanation of symbols]

[0054] 10: Centrifugal compressor 11: First stage compression section 11a: Impeller 11b: Diffuser vane 12: Second stage compression section 12a: Impeller 12b: Diffuser vane 12c: Scroll 13: Third stage compression section 13a: Impeller 13b: Diffuser vane 13c: Scroll 14: Fourth stage compression section 14a: Impeller 14b: Diffuser vane 15: 5th stage compression section 15a: Impeller 15b: Diffuser vane 16: 6th stage compression section 16a: Impeller 16b: Diffuser vane 17: 7th stage compression section 17a: Impeller 17b: Diffuser vane 18: Motor 19: Burgia 21: First pinion shaft 22: Second pinion shaft 23: Third pinion shaft 24: 4th pinion shaft 31: Pinion 32: Pinion 33: Pinion 34: Pinion

Claims

1. A multi-stage centrifugal compressor for treating a target gas having a molecular weight of 40 or more, a compression section having five or more stages for stepwise pressurization of the target gas; a bull gear driven by a power source; three or more pinion shafts that mesh with the bull gear directly or via idler gears and transmit power to the five or more compression stages; Equipped with Each of the five or more stages of compression units is The impeller and a scroll for recovering gas that has passed through the impeller; Equipped with an outer diameter of a pinion shaft that drives a final-stage compression section among the five or more stages of compression sections is smaller than an outer diameter of a pinion shaft that drives a first-stage compression section among the five or more stages of compression sections; an outer diameter of the impeller of the final stage compression section is smaller than an outer diameter of the impeller of the first stage compression section, In the first-stage compression section, the peripheral Mach number of the impeller is equal to or greater than 1 and equal to or less than 1.5, and the specific speed is equal to or greater than 400 and equal to or less than 500, and the peripheral Mach number and the specific speed in the first-stage compression section are the largest among the peripheral Mach numbers and the specific speeds of the five or more compression sections, a peripheral Mach number of the impeller in the final stage compression section being equal to or greater than 0.5 and less than 1, and a specific speed being equal to or greater than 150 and less than 350.

2. 2. The centrifugal compressor according to claim 1, wherein the peripheral Mach number and the specific speed in the final stage compression section are smallest among the peripheral Mach numbers and the specific speeds in the five or more stages of compression sections.

3. a second-stage compression unit among the five or more stages of compression units is connected to a pinion shaft common to the first-stage compression unit, In the second stage compression section, The peripheral Mach number of the impeller is a value between the peripheral Mach number of the impeller in the first stage compression section and the peripheral Mach number of the impeller in the final stage compression section, and 3. The centrifugal compressor according to claim 1, wherein the specific speed is a value between the specific speed of the first stage compressor section and the specific speed of the final stage compressor section.

4. a compression unit one stage before a final stage among the five or more compression units is connected to a pinion shaft common to the compression unit of the final stage, In the compression section one stage before the final stage, The peripheral Mach number of the impeller is a value between the peripheral Mach number of the impeller in the second-stage compression section and the peripheral Mach number of the impeller in the final-stage compression section, and 4. The centrifugal compressor according to claim 3, wherein the specific speed is a value between the specific speed of the second stage compression section and the specific speed of the final stage compression section.

5. Further provided is a pre-compression section that takes in a target gas having a molecular weight of less than 40, 3. The centrifugal compressor according to claim 1, wherein the first stage compression section takes in the target gas that has been dried by an external device and has a molecular weight of 40 or more.

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