Multi-stage compressor

Abstract

To provide a multistage compressor capable of reducing thrust force with a simple structure.SOLUTION: A multistage compressor 1 comprises a low-stage impeller 3, and a high-stage impeller 5 that is provided on a common shaft 6 with the low-stage impeller 3 in a direction opposite to the low-stage impeller 3 and further compresses gas compressed by the low-stage impeller 3, where an inlet-side hub diameter D3 of the low-stage impeller 3 is larger than an inlet-side hub diameter D5 of the high-stage impeller 5.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a multi-stage compressor. [Background technology]

[0002] A conventional technique in this field is a multi-stage compressor described in Patent Document 1. This multi-stage compressor compresses gas in two stages using a low-stage impeller and a high-stage impeller, and employs a balance piston to reduce the thrust force of these impellers. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 5-263789 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in systems using balance pistons, the compressor structure tends to be complicated, requiring the provision of a labyrinth seal on the balance piston and a mechanism for sending gas into a pressure chamber that applies pressure to the balance piston. For this type of multi-stage compressor, a mechanism for more simply reducing thrust force is desired. An object of the present invention is to provide a multi-stage compressor that reduces thrust force with a simple structure. [Means for solving the problem]

[0005] The multi-stage compressor of the present invention is a multi-stage compressor comprising a low-stage impeller and a high-stage impeller that is provided on a common shaft with the low-stage impeller and faces in the opposite direction to the low-stage impeller, and that further compresses the gas compressed by the low-stage impeller, and the hub diameter on the inlet side of the low-stage impeller is larger than the hub diameter on the inlet side of the high-stage impeller.

[0006] The portion of the shaft extending from the inlet side of the hub of the low-stage impeller may have a larger diameter than the portion of the shaft extending from the inlet side of the hub of the high-stage impeller. Also, the diameter of the portion of the shaft extending from the inlet side of the hub of the low-stage impeller may be approximately equal to the hub diameter of the inlet side of the low-stage impeller. Also, the low-stage impeller may be located between the shaft rotation drive source and the high-stage impeller.

[0007] In addition, the low-stage impeller may be arranged with the rotary drive source side facing the inlet side, and the shaft may have a large diameter portion extending from the inlet side of the hub of the low-stage impeller and extending to the rotary drive source, and a small diameter portion extending from the inlet side of the hub of the high-stage impeller into which the low-stage impeller and high-stage impeller are inserted and attached, and the hub of the low-stage impeller may be abutted against a step portion at the boundary between the large diameter portion and the small diameter portion. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a multi-stage compressor that reduces thrust force with a simple structure. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view showing a multi-stage compressor of the present embodiment. [Figure 2] FIG. 2 is an enlarged cross-sectional view showing the vicinity of a low-stage impeller and a high-stage impeller of a multi-stage compressor. [Figure 3] 10A is a graph schematically showing the thrust force generated in the high-stage impeller, and FIG. 10B is a graph schematically showing the thrust force generated in the low-stage impeller. [Figure 4] FIG. 10 is an enlarged cross-sectional view showing the vicinity of a low-stage impeller and a high-stage impeller according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a compressor according to the present invention will be described in detail with reference to the drawings.

[0011] The multi-stage compressor 1 shown in Figure 1 is a two-stage compressor of a serial type having two centrifugal compressor sections. The multi-stage compressor 1 has a low-stage compressor section 2 that compresses gas, and a high-stage compressor section 4 that further compresses the gas compressed by the low-stage compressor section 2. A low-stage impeller 3 of the low-stage compressor section 2 and a high-stage impeller 5 of the high-stage compressor section 4 are attached to a common shaft 6. When the shaft 6 is rotated by a motor section 13 (described later) as a rotational drive source, the low-stage impeller 3, the high-stage impeller 5, and the shaft 6 rotate integrally around a rotation axis A within a housing 7 of the multi-stage compressor 1.

[0012] In the following description, when simply referring to the "axial direction," "circumferential direction," and "radial direction," they respectively mean the rotational axial direction of the shaft 6, the rotational circumferential direction of the shaft 6, and the rotational radial direction of the shaft 6. Furthermore, when using terms such as "rightward" and "leftward" in the following description, the motor unit 13 side will be referred to as the right side and the high-stage impeller 5 side as the left side, corresponding to the right and left in Figure 1.

[0013] The low-stage impeller 3 is located between the motor section 13 and the high-stage impeller 5, and the low-stage impeller 3 and the high-stage impeller 5 are attached to the shaft 6 in opposite directions so that their hub back surfaces face each other. In other words, the low-stage impeller 3 is oriented so that the motor section 13 side is its inlet side, and the high-stage impeller 5 is oriented so that the side opposite the motor section 13 side is its inlet side. The gap between the wall separating the low-stage impeller 3 and the high-stage impeller 5 and the shaft 6 is sealed by a labyrinth seal 11.

[0014] The housing 7 is formed with an intake port 2a for introducing gas into the low-stage impeller 3 of the low-stage compressor section 2, and a diffuser 2b for discharging gas from the low-stage impeller 3. Similarly, the housing 7 is formed with an intake port 4a for introducing gas into the high-stage impeller 5 of the high-stage compressor section 4, and a diffuser 4b for discharging gas from the high-stage impeller 5. In addition, a connecting pipe 8 is provided outside the housing 7, connecting the diffuser 2b and the intake port 4a.

[0015] Furthermore, a motor unit 13 is provided inside the housing 7 around the shaft 6. The motor unit 13 includes a rotor 13r fixed to the shaft 6 and a stator 13s fixed to the housing 7. When a current is supplied to the motor coil of the stator 13s, the rotor 13r and the shaft 6 rotate, and the low-stage impeller 3 and the high-stage impeller 5 rotate. In this manner, the multi-stage compressor 1 is a direct-drive compressor in which the rotational force of the motor unit 13 is directly transmitted to the low-stage impeller 3 and the high-stage impeller 5. Inside the housing 7, two radial magnetic bearings 19a, 19b that support the shaft 6 in the radial direction with the motor unit 13 sandwiched therebetween, and one thrust magnetic bearing 21 that supports the shaft 6 in the axial direction are provided. Note that, although magnetic bearings (19a, 19b and the thrust magnetic bearing 21) are used as bearings in this embodiment, bearings other than magnetic bearings may also be used.

[0016] Gas flowing into the low-stage compressor section 2 from the intake port 2a of the housing 7 is accelerated radially by the rotating low-stage impeller 3, and then decelerated and pressurized by the diffuser 2b. The gas discharged from the diffuser 2b is introduced into the high-stage compressor section 4 from the intake port 4a via the connecting pipe 8. A cooler for cooling the gas may be provided along the connecting pipe 8. The gas introduced from the intake port 4a is accelerated radially by the rotating high-stage impeller 5, and then decelerated and pressurized by the diffuser 4b, and then supplied to the outside as compressed gas. In this way, the multi-stage compressor 1 compresses gas in two stages: the low-stage compressor section 2 including the low-stage impeller 3, and the high-stage compressor section 4 including the high-stage impeller 5.

[0017] FIG. 2 is an enlarged cross-sectional view showing the vicinity of the low-stage impeller 3 and the high-stage impeller 5. The low-stage impeller 3 has a hub 3a and blades 3b provided on the front side of the hub 3a. Similarly, the high-stage impeller 5 has a hub 5a and blades 5b provided on the front side of the hub 5a. The low-stage impeller 3 and the high-stage impeller 5 are attached to the shaft 6 as follows. The left end of the shaft 6 has a smaller diameter than the motor unit 13 side. That is, the shaft 6 has a large-diameter portion 6a and a small-diameter portion 6b. Furthermore, a male thread is formed on the left end of the small-diameter portion 6b. The low-stage impeller 3 is inserted into the small-diameter portion 6b with the motor unit 13 side (the right side in FIG. 2) facing inward, and the front end face 3c of the hub 3a abuts against a step portion 6c at the boundary between the large-diameter portion 6a and the small-diameter portion 6b.

[0018] The high-stage impeller 5 is further stacked on top of the low-stage impeller 3 and inserted into the small diameter portion 6b with the side opposite the motor portion 13 facing the inlet side. The end face on the back side of the hub 5a is abutted against the end face on the back side of the low-stage impeller 3. Then, bolts 23 are screwed and tightened into the small diameter portion 6b that protrudes leftward from the inlet side of the hub 5a of the high-stage impeller 5, whereby the low-stage impeller 3 and the high-stage impeller 5 are sandwiched and fixed between the stepped portion 6c and the bolts 23.

[0019] An inlet hub diameter D3 of the low-stage impeller 3 is larger than an inlet hub diameter D5 of the high-stage impeller. Furthermore, a diameter D63 of a large diameter portion 6a extending rightward from the inlet side of the hub 3a of the low-stage impeller 3 and extending to the motor unit 13 is larger than a diameter D65 of a small diameter portion 6b of the shaft 6 extending leftward from the inlet side of the hub 5a of the high-stage impeller 5. Furthermore, in this embodiment, the diameter D63 of the large diameter portion 6a is approximately equal to the inlet hub diameter D3 of the low-stage impeller 3.

[0020] Next, the effects of the multi-stage compressor 1 will be described.

[0021] FIG. 3(a) is a graph showing a schematic representation of the thrust force generated by the high-stage impeller 5. Reference numeral 5 in the graph shows half of the outline of a cross section of the high-stage impeller 5 (i.e., a cross section taken along a plane including the rotation axis). Corresponding to the left and right sides of FIG. 1, the left side is the front side of the high-stage impeller 5, and the right side is the rear side of the high-stage impeller 5. The vertical axis of the graph shows the radial position based on the rotation axis of the high-stage impeller 5. Reference numeral 5a in the graph shows the area of ​​the hub 5a as viewed from the front side of the high-stage impeller 5, and reference numeral 5b shows the area of ​​the blades 5b as viewed from the front side of the high-stage impeller 5. Graph S1 shows the pressure distribution on the front side of the high-stage impeller 5, and graph S2 shows the pressure distribution on the rear side of the high-stage impeller 5. A rightward force F1 based on the pressure of graph S1 and a leftward force F2 based on the pressure of graph S2 act on the high-stage impeller 5.

[0022] Similarly, Figure 3(b) is a graph schematically showing the thrust force generated by the low-stage impeller 3. The symbol 3 in the graph schematically shows half of the cross-sectional profile of the low-stage impeller 3. Corresponding to the left and right sides of Figure 1, the right side is the front side of the low-stage impeller 3 and the left side is the rear side of the low-stage impeller 3. The vertical axis of the graph indicates the radial position based on the rotation axis of the low-stage impeller 3. The symbol 3a in the graph indicates the area of ​​the hub 3a as seen from the front side of the low-stage impeller 3, and the symbol 3b indicates the area of ​​the blades 3b as seen from the front side of the low-stage impeller 3. The graph T1 shows the pressure distribution on the front side of the low-stage impeller 3, and the graph T2 shows the pressure distribution on the rear side of the low-stage impeller 3. A leftward force G1 based on the pressure of the graph T1 and a rightward force G2 based on the pressure of the graph S2 act on the low-stage impeller 3.

[0023] The difference between forces F1 and F2 generates a leftward thrust force on the high-stage impeller 5. Similarly, the difference between forces G1 and G2 generates a rightward thrust force on the low-stage impeller 3. And because the leftward thrust force generated on the high-stage impeller 5 is greater than the rightward thrust force generated on the low-stage impeller 3, ultimately a leftward thrust force is generated on the shaft 6. Forces F1 and G2 are factors that increase the rightward thrust force on the shaft 6, and forces F2 and G1 are factors that increase the leftward thrust force on the shaft 6. Note that the space behind the high-stage impeller 5 and the space behind the low-stage impeller 3 are separated by the aforementioned labyrinth seal 11 (Figure 1), creating a pressure difference between them, so forces F2 and G2 are generated independently with little or no influence on each other.

[0024] Here, in the graph of FIG. 3(b), a cross section of a conventional low-stage impeller 3' is shown by a dashed line as a comparative example. The area of ​​the hub 3a as seen from the front side of the low-stage impeller 3' is designated by the symbol 3a', and the area of ​​the blades 3b as seen from the front side of the low-stage impeller 3' is designated by the symbol 3b'. In the low-stage impeller 3' of the comparative example, the area width of the hub 3a' as seen from the front side is equal to the area width of the hub 5a as seen from the front side of the high-stage impeller 5. That is, in the low-stage impeller 3' of the comparative example, the inlet hub diameter D3 (see FIG. 2) is approximately equal to the inlet hub diameter D5 (see FIG. 2) of the high-stage impeller 5. In a two-stage compressor in which the low-stage impeller and the high-stage impeller are mounted on a common shaft, it is a common design practice to make the inlet hub diameter of the low-stage impeller and the inlet hub diameter of the high-stage impeller approximately equal, as described above.

[0025] Consider the case where the low-stage impeller 3' is replaced with a low-stage impeller 3 with an enlarged inlet hub diameter D3 (see FIG. 2). In a centrifugal compressor impeller, the pressure in the hub region (reference numerals 3a and 3a') is constant and lowest, while the pressure in the blade region (reference numerals 3b and 3b') increases toward the outer periphery. Therefore, if the low-stage impeller 3' is replaced with the low-stage impeller 3, the hub region with low pressure expands from 3a' to 3a, and the pressure distribution on the front side of the low-stage impeller changes from graph T1' to graph T1. As a result, the pressure on the front side of the low-stage impeller decreases overall, and the force G1 decreases. In this way, the force G1, which is a factor that increases the leftward thrust force, decreases, and as a result, the leftward thrust force acting on the shaft 6 decreases. For the above reasons, the multi-stage compressor 1 of this embodiment reduces the thrust force acting on the shaft 6. That is, in the multi-stage compressor 1 of this embodiment, the thrust force acting on the shaft 6 is reduced by a simple configuration in which the inlet hub diameter D3 of the low-stage impeller 3 is made larger than the inlet hub diameter D5 of the high-stage impeller 5, and as a result, the load on the thrust magnetic bearing portion 21 (Figure 1) can be reduced.

[0026] 2, in the multi-stage compressor 1, the diameter D63 of the portion (large diameter portion 6a) of the shaft 6 extending from the inlet side of the hub 3a of the low-stage impeller 3 is approximately equal to the inlet hub diameter D3 of the low-stage impeller 3. With this configuration, the outer circumferential surface of the shaft 6 and the outer circumferential surface of the hub 3a are approximately flush. As a result, gas introduced from the intake port 2a (FIG. 1) smoothly flows into the blades 3b of the low-stage impeller 3 while coming into contact with the almost step-free outer circumferential surface of the shaft 6 and the outer circumferential surface of the hub 3a. In this way, the flow of gas in the low-stage compressor section 2 is smoothed, and compression efficiency is improved.

[0027] As described above, the multi-stage compressor 1 employs an impeller arrangement in which the motor section 13, the low-stage impeller 3, and the high-stage impeller 5 are arranged in this order. By arranging the low-stage impeller 3, which has a large inlet hub diameter (i.e., is relatively large), closer to the motor section 13 than the high-stage impeller 5 in this manner, the rotational stability of the shaft 6 is further ensured.

[0028] The present invention can be implemented in various forms, including the above-described embodiment, with various modifications and improvements based on the knowledge of those skilled in the art. Furthermore, it is also possible to configure modified examples by utilizing the technical matters described in the above-described embodiment. The configurations of the respective embodiments may be used in appropriate combination.

[0029] For example, in the embodiment, the diameter D63 of the portion of the shaft 6 (large diameter portion 6a) extending from the inlet side of the hub 3a of the low-stage impeller 3 is approximately equal to the inlet hub diameter D3 of the low-stage impeller 3, but this configuration is not essential. That is, as shown in Fig. 4, in a structure in which the low-stage impeller 3 is inserted into the small diameter portion 6b and the front end face 3c of the hub 3a abuts against the stepped portion 6c, the diameter D63' of the large diameter portion 6a may be smaller than the inlet hub diameter D3 of the low-stage impeller 3. [Explanation of symbols]

[0030] 1 Multi-stage compressor 3 Low-stage impeller 5 High-stage impeller 6 shafts 6a Large diameter part 6b Small diameter section 6c Step 13 Motor section (rotation drive source) D3 Inlet hub diameter D5 inlet hub diameter D63 Diameter of large diameter part D65 Diameter of small diameter part

Claims

1. A multi-stage compressor comprising: a low-stage impeller; and a high-stage impeller provided on a common shaft with the low-stage impeller in an opposite direction to the low-stage impeller, for further compressing gas compressed by the low-stage impeller, The hub diameter of the inlet side of the low-stage impeller is larger than the hub diameter of the inlet side of the high-stage impeller, the low-stage impeller is located between the rotational drive source of the shaft and the high-stage impeller, the low-stage impeller is disposed with the rotary drive source side facing the inlet side, The shaft a large diameter portion extending from an inlet side of the hub of the low-stage impeller and extending to the rotary drive source; and a small diameter portion extending from the inlet side of the hub of the high-stage impeller into which the low-stage impeller and the high-stage impeller are inserted and attached, a hub of the low-stage impeller abutting against a step portion at a boundary between the large diameter portion and the small diameter portion, The end face of the high-stage impeller on the rear side is abutted against the end face of the low-stage impeller on the rear side. Multi-stage compressor.

2. 2. The multi-stage compressor according to claim 1, wherein the portion of the shaft extending from the inlet side of the hub of the low-stage impeller has a larger diameter than the portion of the shaft extending from the inlet side of the hub of the high-stage impeller.

3. 3. The multi-stage compressor according to claim 2, wherein the diameter of the portion of said shaft extending from the inlet side of the hub of said low-stage impeller is equal to the diameter of the hub on the inlet side of said low-stage impeller.

4. 4. The multi-stage compressor according to claim 1, wherein the low-stage impeller is positioned between the rotational drive source of the shaft and the high-stage impeller.

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