Multistage radial turbine

Abstract

A multistage radial turbine includes: a single rotating shaft; first-stage and second-stage bladed wheels mounted on the rotating shaft, each of the bladed wheels including an inlet into which a working fluid flows radially inward and an outlet out of which the working fluid flows in the axial direction; a first-stage nozzle row located around an outer circumference of the inlet of the first-stage bladed wheel; a working fluid supply system that includes feed inlets circumferentially arranged around an outer circumference of the first-stage nozzle row and feeds the working fluid into the first-stage nozzle row either through one of the feed inlets or through two or more of the feed inlets; a second-stage nozzle row located around an outer circumference of the inlet of the second-stage bladed wheel; and a connection flow path connecting the outlet of the first-stage bladed wheel to the inlet of the second-stage bladed wheel. The connection flow path includes a region extending from the outlet of the first-stage bladed wheel to the second-stage nozzle row, the region being circumferentially divided into parallel flow paths.

Description

Technical Field

[0001] The present disclosure relates to the structure of a multistage radial turbine.Background Art

[0002] Radial turbines are known as devices that convert fluid energy to extract the energy as drive power. A radial turbine is a type of radial-flow turbine into which a working fluid flows in a direction perpendicular to a rotating shaft and in which a high-speed swirling flow enters a bladed wheel from the outer circumference of the bladed wheel to rotate the bladed wheel. Such radial turbines can be used as expanders that expand gases into liquids. Turbines used for the liquefaction of LNG or hydrogen are often multistage radial turbines including multiple bladed wheels, since such turbines can extract a large amount of drive power from the fluid. Patent Literature 1 discloses an example of a uniaxial multistage turbine including multiple bladed wheels mounted on a single shaft.

[0003] The multistage radial turbine disclosed in Patent Literature 1 includes: a single rotating shaft; bladed wheels mounted on the rotating shaft and axially spaced apart from each other; and nozzles each of which is located upstream of a corresponding one of the bladed wheels to rotationally accelerate the fluid. The outlet of each bladed wheel is connected to the inlet of the next downstream nozzle by a connection flow path. In this multistage radial turbine, the working fluid discharged axially from one bladed wheel passes through the connection flow path and flows into the inlet of the next bladed wheel in a direction perpendicular to the rotating shaft. In this manner, the working fluid acts on the bladed wheels sequentially, thereby rotating the rotating shaft.Citation List Patent Literature

[0004] PTL 1: Japanese Laid-Open Patent Application Publication No. 2011-132877Summary of Invention Technical Problem

[0005] When a radial turbine is operating under rated conditions where the working fluid flows into the turbine at a designed flow rate, the ratio between inlet and outlet pressures of the working fluid is a design-point pressure ratio, and high turbine efficiency is achieved. In some cases, a radial turbine performs partial load operation under low flow rate conditions where the flow rate of the working fluid is lower than the designed flow rate. Even in partial load operation, the turbine is often required to run at a high pressure ratio close to the design-point pressure ratio. However, when operated under low flow rate conditions, a multistage radial turbine has difficulty continuing partial load operation with high efficiency while maintaining a sufficient level of pressure ratio.

[0006] The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide a uniaxial multistage radial turbine that can operate at a high pressure ratio close to a design-point level and achieve improved turbine efficiency even during partial load operation.Solution to Problem

[0007] To solve the above problem, a multistage radial turbine according to one aspect of the present disclosure includes: a single rotating shaft; first-stage and second-stage bladed wheels mounted on the rotating shaft and spaced apart from each other in an axial direction, each of the bladed wheels including an inlet into which a working fluid flows radially inward and an outlet out of which the working fluid flows in the axial direction; a first-stage nozzle row located around an outer circumference of the inlet of the first-stage bladed wheel; a working fluid supply system that includes feed inlets circumferentially arranged around an outer circumference of the first-stage nozzle row and that is switchable at each of the feed inlets between permitting and blocking feed of the working fluid into the first-stage nozzle row and feeds the working fluid into the first-stage nozzle row either through one of the feed inlets or through two or more of the feed inlets; a second-stage nozzle row located around an outer circumference of the inlet of the second-stage bladed wheel; and a connection flow path connecting the outlet of the first-stage bladed wheel to the inlet of the second-stage bladed wheel, wherein the connection flow path includes a region extending from the outlet of the first-stage bladed wheel to the second-stage nozzle row, the region being circumferentially divided into parallel flow paths. Advantageous Effects of Invention

[0008] The present disclosure can provide a uniaxial multistage radial turbine that can operate at a high pressure ratio close to a design-point level and achieve improved turbine efficiency even during partial load operation.Brief Description of Drawings

[0009] FIG. 1 is a schematic partial cross-sectional view showing a multistage radial turbine according to one embodiment of the present disclosure. FIG. 2 illustrates a working fluid supply system of the multistage radial turbine. FIG. 3 illustrates a working fluid supply system according to a variant of the multistage radial turbine. FIG. 4 is a schematic view showing a connection flow path of the multistage radial turbine as viewed in the axial direction from the side on which a second-stage bladed wheel is located. FIG. 5 is a schematic view showing a connection flow path according to a variant of the multistage radial turbine as viewed in the axial direction from the side on which a second-stage bladed wheel is located. Description of Embodiments

[0010] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. A multistage radial turbine according to one aspect of the present disclosure is a uniaxial multistage radial turbine. The multistage radial turbine is used, for example, as a turboexpander. The working fluid of the multistage radial turbine is a liquid, a gas, or a gas-liquid two-phase mixture.<<Configuration of multistage radial turbine 1>>

[0011] FIG. 1 is a schematic partial cross-sectional view showing a multistage radial turbine 1 according to one embodiment of the present disclosure. The multistage radial turbine 1 shown in FIG. 1 includes a casing 7, a rotating shaft 3 supported by the casing 7 via bearings, and bladed wheels 5 fitted around the rotating shaft 3. In FIG. 1, the letter C represents the centerline of the rotating shaft 3. The bladed wheels 5 are aligned in the axial direction X of the rotating shaft 3. The multistage radial turbine 1 according to the present embodiment includes two bladed wheels 5, one of which is a first-stage bladed wheel 5A and the other of which is a second-stage bladed wheel 5B. The number of bladed wheels 5 is not limited to two, and any greater number of bladed wheels 5 may be employed.

[0012] Each bladed wheel 5 includes a hub 11 fitted around the rotating shaft 3 and blades 13 arranged circumferentially on the outer circumferential surface of the hub 11. Each blade 13 extends generally radially with respect to the rotating shaft 3. An inlet 21 into which the working fluid flows is located on the outer circumference of the bladed wheel 5. The inlet 21 is continuous circumferentially and opens radially. An outlet 23 out of which the working fluid flows is located at one end of the bladed wheel 5 in the axial direction X. The outlet 23 is continuous circumferentially and opens in the axial direction X. An inter-blade flow path 26 through which the working fluid flows from the inlet 21 toward the outlet 23 is defined between the adjacent blades 13 of the bladed wheel 5. During passage through the inter-blade flow path 26, the working fluid changes its flow direction from the radial direction to the axial direction X.

[0013] FIG. 2 illustrates a working fluid supply system 30 of the multistage radial turbine 1. As shown in FIGS. 1 and 2, a first-stage nozzle row 18 including circumferentially arranged nozzles is located around the outer circumference of the inlet 21 of the first-stage bladed wheel 5A. The first-stage nozzle row 18 is constituted by circumferentially arranged nozzle vanes, and the gaps between the nozzle vanes that are circumferentially adjacent to one another function as nozzles. The working fluid supply system 30 feeds the working fluid into the first-stage nozzle row 18.

[0014] The working fluid supply system 30 includes multiple sets of inlet flow paths 25, working fluid supply flow paths 28, and working fluid supply valves 29. The inlet flow paths 25 are arranged around the outer circumference of the first-stage nozzle row 18. For example, partition walls 32 extending radially may be arranged around the outer circumference of the first-stage nozzle row 18. The inlet flow paths 25 can be defined by dividing the space around the outer circumference of the first-stage nozzle row 18 using the partition walls 32. The partition walls 32 may be located in proximity to the first-stage nozzle row 18. Alternatively, as shown in FIG. 3, each of the partition walls 32 may be connected to a corresponding one of the nozzle vanes constituting the first-stage nozzle row 18. The working fluid supply system 30 according to the present embodiment includes six inlet flow paths 25, i.e., first to sixth inlet flow paths 25. The number of inlet flow paths 25 may be any value of two or more. The outlet of each inlet flow path 25 serves as a feed inlet 27 through which the working fluid is fed into the first-stage nozzle row 18. The circumferentially arranged feed inlets 27 face the outer circumference of the first-stage nozzle row 18. In the working fluid supply system 30 according to the present embodiment, the space around the first-stage nozzle row 18 is divided into six segments at the first to sixth feed inlets 27 corresponding to the first to sixth inlet flow paths 25.

[0015] Each inlet flow path 25 is connected to a working fluid source via a corresponding one of the working fluid supply flow paths 28. The working fluid supply valves 29 are located in the working fluid supply flow paths 28, respectively. Each working fluid supply valve 29 is a flow-regulating valve or an on-off valve. The working fluid supply system 30 includes first to sixth working fluid supply valves 29 in one-to-one correspondence with the first to sixth inlet flow paths 25, and each of the first to sixth feed inlets 27 can switch between permitting and blocking the feed of the working fluid independently of the other feed inlets 27. For example, when one of the first to sixth working fluid supply valves 29 is opened with the other working fluid supply valves 29 closed, the working fluid can be fed through one of the first to sixth feed inlets 27 while being blocked at the other feed inlets 27. In this case, the working fluid is fed into a one-sixth region of the first-stage nozzle row 18 and is not fed into the rest of the first-stage nozzle row 18. In this manner, in the multistage radial turbine 1, the working fluid can be fed either over the entire circumference of the first-stage nozzle row 18 or into a part of the first-stage nozzle row 18. In the case of partial feeding, the location and size of the region into which the working fluid is fed can be changed.

[0016] As shown in FIG. 1, the outlet 23 of the first-stage bladed wheel 5A and the inlet 21 of the second-stage bladed wheel 5B are connected by a connection flow path 90 defined by the casing 7 and a flow path structure 9. The connection flow path 90 includes: a bend portion 91 in which the fluid flowing out of the first-stage bladed wheel 5A in the axial direction X is redirected radially outward; a radial portion 92 through which the fluid flows radially outward; a U-turn portion 93 in which the fluid flowing radially outward is redirected radially inward; and a return portion 94 through which the fluid flows radially inward. The return portion 94 is connected to the inlet 21 of the second-stage bladed wheel 5B.

[0017] FIG. 4 is a schematic view showing the connection flow path 90 of the multistage radial turbine 1 as viewed in the axial direction X from the side on which the second-stage bladed wheel 5B is located. As shown in FIGS. 1 and 4, a second-stage nozzle row 19 including circumferentially arranged nozzles is located at the downstream end of the connection flow path 90, namely, in the return portion 94 and around the outer circumference of the inlet 21 of the second-stage bladed wheel 5B. The second-stage nozzle row 19 is constituted by circumferentially arranged nozzle vanes, and the gaps between the nozzle vanes that are circumferentially adjacent to one another function as nozzles. In the connection flow path 90 excluding its upstream and downstream end regions, partition plates 96 are circumferentially spaced apart from one another. Each partition plate 96 has an upstream end at a point in the bend portion 91 and a downstream end at a point in the return portion 94, and extends continuously from the point in the bend portion 91 to the point in the return portion 94 through the radial portion 92 and the U-turn portion 93. The upstream end of each partition plate 96 is slightly apart from the outlet 23 of the first-stage bladed wheel 5A to avoid interference between the partition plate 96 and the first-stage bladed wheel 5A. The downstream end of each partition plate 96 is in proximity to the outer circumference of the second-stage nozzle row 19. However, as shown in FIG. 5, the downstream end of each partition plate 96 may be connected to a corresponding one of the nozzle vanes constituting the second-stage nozzle row 19.

[0018] The partition plates 96 located within the connection flow path 90 define parallel flow paths 99 between the adjacent partition plates 96. In other words, the region from the outlet 23 of the first-stage bladed wheel 5A to the inlet 21 of the second-stage nozzle row 19 in the connection flow path 90 is circumferentially divided into the parallel flow paths 99. The connection flow path 90 is divided into the parallel flow paths 99 equally or unequally. Each of the parallel flow paths 99 includes the bend portion 91, the radial portion 92 connected to the bend portion 91, the U-turn portion 93 connected to the radial portion 92, and the return portion 94 connecting the U-turn portion 93 to the inlet 21 of the second-stage bladed wheel 5B. In the example shown in FIG. 4, the connection flow path 90 is divided by six partition plates 96 into six parallel flow paths 99; however, the number of the partition plates 96 is not limited to six. Although the numbers of the inlet flow paths 25 and the parallel flow paths 99 are equal in the present embodiment, the numbers of the inlet flow paths 25 and the parallel flow paths 99 may be different.

[0019] In the multistage radial turbine 1 according to the present embodiment, two bladed wheels 5 are coupled to a single rotating shaft 3; however, three or more bladed wheels 5 may be coupled to a single rotating shaft 3. In this case, the bladed wheels 5 adjacent to one another in the axial direction X are connected by connection flow paths 90, and the partition plates 96 may be omitted in the second and subsequent connection flow paths 90.<<Operarion mechanism of multistage radial turbine 1>>

[0020] The following describes the operation mechanism of the multistage radial turbine 1 configured as described above. First, depending on the flow rate of the working fluid, at least one or all of the working fluid supply valves 29 are opened, while the remaining supply valves 29 are closed. The feed inlets 27 connected to the working fluid supply flow paths 28 that include the opened working fluid supply valves 29 permit the feed of the working fluid. The working fluid is fed into the first-stage nozzle row 18 through the feed inlets 27 permitting the feed of the working fluid. The working fluid is rotationally accelerated by the first-stage nozzle row 18, forming a swirling flow which enters the inter-blade flow path 26 from the inlet 21 of the first-stage bladed wheel 5A. As the working fluid passes through the inter-blade flow path 26 of the first-stage bladed wheel 5A, the working fluid causes the first-stage bladed wheel 5A to rotate.

[0021] The working fluid exiting the outlet 23 of the first-stage bladed wheel 5A in the axial direction X enters the connection flow path 90. After entering the connection flow path 90, the working fluid is first redirected radially outward by the bend portion 91, flows radially outward through the radial portion 92 of the parallel flow path 99, is then redirected radially inward in the U-turn portion 93, flows radially inward through the return portion 94, and is fed into the second-stage nozzle row 19. The working fluid is rotationally accelerated by the second-stage nozzle row 19, forming a swirling flow which enters the inter-blade flow path 26 from the inlet 21 of the second-stage bladed wheel 5B. As it passes through the inter-blade flow path 26 of the second-stage bladed wheel 5B, the working fluid causes the second-stage bladed wheel 5B to rotate. The working fluid exiting the outlet 23 of the second-stage bladed wheel 5B is discharged outside the multistage radial turbine 1 through a discharge flow path 24.

[0022] When the multistage radial turbine 1 is operating under rated conditions, all of the working fluid supply valves 29 are opened, permitting the working fluid to be fed over the entire circumference of the first-stage nozzle row 18. During partial load operation, some (for example, half) of the working fluid supply valves 29 are opened, while the remaining working fluid supply valves 29 are closed. Accordingly, the feed of the working fluid is permitted at some of the feed inlets 27 and blocked at the other feed inlets 27. As a result, the area over which the working fluid is fed into the first-stage nozzle row 18 is narrower than that during feed over the entire circumference of the first-stage nozzle row 18. Since the working fluid is fed into the first-stage nozzle row 18 either through one of the feed inlets 27 or through two or more of the feed inlets 27, the working fluid flowing at a flow rate lower than the designed flow rate is fed into the inlet 21 of the first-stage bladed wheel 5A with a circumferential distribution of velocity, pressure, and temperature. The working fluid exiting the first-stage bladed wheel 5A is delivered to the second-stage bladed wheel 5B through the connection flow path 90. Within the connection flow path 90, the range of the circumferential movement of the working fluid is limited by the partition plates 96, and the working fluid reaches the second-stage nozzle row 19 through the parallel flow path(s) 99 that the working fluid has entered. In this manner, the working fluid passing through the connection flow path 90 is restricted from circumferentially diffusing, and is fed into the second-stage nozzle row 19 while preserving the distribution it had at the outlet 23 of the first-stage bladed wheel 5A. As a result, the working fluid passing through the second-stage nozzle row 19 acts on the second-stage bladed wheel 5B while retaining a suitable circumferential distribution of velocity, pressure, and temperature.[Summary]

[0023] A multistage radial turbine 1 according to a first item of the present disclosure includes: a single rotating shaft 3; first-stage and second-stage bladed wheels 5A and 5B mounted on the rotating shaft 3 and spaced apart from each other in an axial direction X, each of the bladed wheels 5 including an inlet 21 into which a working fluid flows radially inward and an outlet 23 out of which the working fluid flows in the axial direction X; a first-stage nozzle row 18 located around an outer circumference of the inlet 21 of the first-stage bladed wheel 5A; a working fluid supply system 30 that includes feed inlets 27 circumferentially arranged around an outer circumference of the first-stage nozzle row 18 and that is switchable at each of the feed inlets 27 between permitting and blocking feed of the working fluid into the first-stage nozzle row 18 and feeds the working fluid into the first-stage nozzle row 18 either through one of the feed inlets 27 or through two or more of the feed inlets 27; a second-stage nozzle row 19 located around an outer circumference of the inlet 21 of the second-stage bladed wheel 5B; and a connection flow path 90 connecting the outlet 23 of the first-stage bladed wheel 5A to the inlet 21 of the second-stage bladed wheel 5B, wherein the connection flow path 90 includes a region extending from the outlet 23 of the first-stage bladed wheel 5A to the second-stage nozzle row 19, the region being circumferentially divided into parallel flow paths 99.

[0024] A multistage radial turbine 1 according to a second item of the present disclosure includes the features of the multistage radial turbine 1 according to the first item, wherein each of the parallel flow paths 99 includes: a bend portion 91 that causes the working fluid flowing out of the outlet 23 of the first-stage bladed wheel 5A in the axial direction to be redirected radially outward; a radial portion 92 that is connected to the bend portion 91 and that causes the working fluid to flow radially outward; a U-turn portion 93 that is connected to the radial portion 92 and that causes the working fluid flowing radially outward to be redirected radially inward; and a return portion 94 that connects the U-turn portion 93 to the inlet 21 of the second-stage bladed wheel 5B and that causes the working fluid to flow radially inward.

[0025] When the multistage radial turbine 1 according to the first or second item is operating under rated conditions, the working fluid is fed into the first-stage nozzle row 18 through all of the feed inlets 27. During partial load operation, the working fluid is fed into the first-stage nozzle row 18 through one or some of the feed inlets 27. Thus, during partial load operation, the working fluid can be introduced into the first-stage bladed wheel 5A with a circumferential distribution of pressure, flow velocity, and temperature. The working fluid flowing from the outlet 23 of the first-stage bladed wheel 5A into the parallel flow paths 99 of the connection flow path 90 is delivered to the second-stage nozzle row 19 while being restricted from diffusing circumferentially. Accordingly, the working fluid exiting the outlet 23 of the first-stage bladed wheel 5A is fed into the second-stage nozzle row 19 while preserving the circumferential distribution of physical quantities it had at the outlet 23 of the first-stage bladed wheel 5A. As a result, even during partial load operation, the multistage radial turbine 1 can maintain a high pressure ratio and efficiency close to design-point levels. Therefore, the multistage radial turbine 1 can achieve higher turbine efficiency during partial load operation than turbines that are not configured to restrict circumferential diffusion of the working fluid within the connection flow path 90.

[0026] A multistage radial turbine 1 according to a third item of the present disclosure includes the features of the multistage radial turbine 1 according to the first or second item, wherein the connection flow path 90 is divided into the parallel flow paths 99 by circumferentially arranged partition plates 96.

[0027] The partition plates 96 are stationary components and can restrict circumferential diffusion of the working fluid flowing through the connection flow path 90 with a simple structure. Since the use of the partition plates 96 eliminates the need for a movable component such as a variable nozzle to restrict circumferential diffusion of the working fluid flowing through the connection flow path 90, the partition plates 96 can be employed also when the working fluid used in the multistage radial turbine 1 is an extremely low-temperature fluid such as liquid hydrogen.

[0028] A multistage radial turbine 1 according to a fourth item of the present disclosure includes the features of the multistage radial turbine 1 according to the third item, wherein the second-stage nozzle row 19 includes circumferentially arranged nozzle vanes, and at least one of the partition plates 96 is connected to one of the nozzle vanes.

[0029] With this configuration, the multistage radial turbine 1 can prevent circumferential diffusion of the fluid through the gaps between the partition plates 96 and the nozzle vanes, thereby achieving higher performance.

[0030] The foregoing discussion on the present disclosure is merely illustrative and explanatory, and is not intended to limit the present disclosure to the modes described herein. For example, although the foregoing detailed description presents various features of the present disclosure together in a single embodiment in order to streamline the present disclosure, only some of the described features may be combined. The features disclosed herein may be combined into alternative embodiments, configurations, or aspects other than those discussed above.

Examples

Embodiment Construction

[0010]Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. A multistage radial turbine according to one aspect of the present disclosure is a uniaxial multistage radial turbine. The multistage radial turbine is used, for example, as a turboexpander. The working fluid of the multistage radial turbine is a liquid, a gas, or a gas-liquid two-phase mixture.

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[0011]FIG. 1 is a schematic partial cross-sectional view showing a multistage radial turbine 1 according to one embodiment of the present disclosure. The multistage radial turbine 1 shown in FIG. 1 includes a casing 7, a rotating shaft 3 supported by the casing 7 via bearings, and bladed wheels 5 fitted around the rotating shaft 3. In FIG. 1, the letter C represents the centerline of the rotating shaft 3. The bladed wheels 5 are aligned in the axial direction X of the rotating shaft 3. The multistage radial turbine 1 according to the present embodiment includes two bladed wheels 5, one ...

Technical Field

[0001] The present disclosure relates to the structure of a multistage radial turbine.Background Art

[0002] Radial turbines are known as devices that convert fluid energy to extract the energy as drive power. A radial turbine is a type of radial-flow turbine into which a working fluid flows in a direction perpendicular to a rotating shaft and in which a high-speed swirling flow enters a bladed wheel from the outer circumference of the bladed wheel to rotate the bladed wheel. Such radial turbines can be used as expanders that expand gases into liquids. Turbines used for the liquefaction of LNG or hydrogen are often multistage radial turbines including multiple bladed wheels, since such turbines can extract a large amount of drive power from the fluid. Patent Literature 1 discloses an example of a uniaxial multistage turbine including multiple bladed wheels mounted on a single shaft.

[0003] The multistage radial turbine disclosed in Patent Literature 1 includes: a single rotating shaft; bladed wheels mounted on the rotating shaft and axially spaced apart from each other; and nozzles each of which is located upstream of a corresponding one of the bladed wheels to rotationally accelerate the fluid. The outlet of each bladed wheel is connected to the inlet of the next downstream nozzle by a connection flow path. In this multistage radial turbine, the working fluid discharged axially from one bladed wheel passes through the connection flow path and flows into the inlet of the next bladed wheel in a direction perpendicular to the rotating shaft. In this manner, the working fluid acts on the bladed wheels sequentially, thereby rotating the rotating shaft.Citation List Patent Literature

[0004] PTL 1: Japanese Laid-Open Patent Application Publication No. 2011-132877Summary of Invention Technical Problem

[0005] When a radial turbine is operating under rated conditions where the working fluid flows into the turbine at a designed flow rate, the ratio between inlet and outlet pressures of the working fluid is a design-point pressure ratio, and high turbine efficiency is achieved. In some cases, a radial turbine performs partial load operation under low flow rate conditions where the flow rate of the working fluid is lower than the designed flow rate. Even in partial load operation, the turbine is often required to run at a high pressure ratio close to the design-point pressure ratio. However, when operated under low flow rate conditions, a multistage radial turbine has difficulty continuing partial load operation with high efficiency while maintaining a sufficient level of pressure ratio.

[0006] The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide a uniaxial multistage radial turbine that can operate at a high pressure ratio close to a design-point level and achieve improved turbine efficiency even during partial load operation.Solution to Problem

[0007] To solve the above problem, a multistage radial turbine according to one aspect of the present disclosure includes: a single rotating shaft; first-stage and second-stage bladed wheels mounted on the rotating shaft and spaced apart from each other in an axial direction, each of the bladed wheels including an inlet into which a working fluid flows radially inward and an outlet out of which the working fluid flows in the axial direction; a first-stage nozzle row located around an outer circumference of the inlet of the first-stage bladed wheel; a working fluid supply system that includes feed inlets circumferentially arranged around an outer circumference of the first-stage nozzle row and that is switchable at each of the feed inlets between permitting and blocking feed of the working fluid into the first-stage nozzle row and feeds the working fluid into the first-stage nozzle row either through one of the feed inlets or through two or more of the feed inlets; a second-stage nozzle row located around an outer circumference of the inlet of the second-stage bladed wheel; and a connection flow path connecting the outlet of the first-stage bladed wheel to the inlet of the second-stage bladed wheel, wherein the connection flow path includes a region extending from the outlet of the first-stage bladed wheel to the second-stage nozzle row, the region being circumferentially divided into parallel flow paths. Advantageous Effects of Invention

[0008] The present disclosure can provide a uniaxial multistage radial turbine that can operate at a high pressure ratio close to a design-point level and achieve improved turbine efficiency even during partial load operation.Brief Description of Drawings

[0009] FIG. 1 is a schematic partial cross-sectional view showing a multistage radial turbine according to one embodiment of the present disclosure. FIG. 2 illustrates a working fluid supply system of the multistage radial turbine. FIG. 3 illustrates a working fluid supply system according to a variant of the multistage radial turbine. FIG. 4 is a schematic view showing a connection flow path of the multistage radial turbine as viewed in the axial direction from the side on which a second-stage bladed wheel is located. FIG. 5 is a schematic view showing a connection flow path according to a variant of the multistage radial turbine as viewed in the axial direction from the side on which a second-stage bladed wheel is located. Description of Embodiments

[0010] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. A multistage radial turbine according to one aspect of the present disclosure is a uniaxial multistage radial turbine. The multistage radial turbine is used, for example, as a turboexpander. The working fluid of the multistage radial turbine is a liquid, a gas, or a gas-liquid two-phase mixture.<<Configuration of multistage radial turbine 1>>

[0011] FIG. 1 is a schematic partial cross-sectional view showing a multistage radial turbine 1 according to one embodiment of the present disclosure. The multistage radial turbine 1 shown in FIG. 1 includes a casing 7, a rotating shaft 3 supported by the casing 7 via bearings, and bladed wheels 5 fitted around the rotating shaft 3. In FIG. 1, the letter C represents the centerline of the rotating shaft 3. The bladed wheels 5 are aligned in the axial direction X of the rotating shaft 3. The multistage radial turbine 1 according to the present embodiment includes two bladed wheels 5, one of which is a first-stage bladed wheel 5A and the other of which is a second-stage bladed wheel 5B. The number of bladed wheels 5 is not limited to two, and any greater number of bladed wheels 5 may be employed.

[0012] Each bladed wheel 5 includes a hub 11 fitted around the rotating shaft 3 and blades 13 arranged circumferentially on the outer circumferential surface of the hub 11. Each blade 13 extends generally radially with respect to the rotating shaft 3. An inlet 21 into which the working fluid flows is located on the outer circumference of the bladed wheel 5. The inlet 21 is continuous circumferentially and opens radially. An outlet 23 out of which the working fluid flows is located at one end of the bladed wheel 5 in the axial direction X. The outlet 23 is continuous circumferentially and opens in the axial direction X. An inter-blade flow path 26 through which the working fluid flows from the inlet 21 toward the outlet 23 is defined between the adjacent blades 13 of the bladed wheel 5. During passage through the inter-blade flow path 26, the working fluid changes its flow direction from the radial direction to the axial direction X.

[0013] FIG. 2 illustrates a working fluid supply system 30 of the multistage radial turbine 1. As shown in FIGS. 1 and 2, a first-stage nozzle row 18 including circumferentially arranged nozzles is located around the outer circumference of the inlet 21 of the first-stage bladed wheel 5A. The first-stage nozzle row 18 is constituted by circumferentially arranged nozzle vanes, and the gaps between the nozzle vanes that are circumferentially adjacent to one another function as nozzles. The working fluid supply system 30 feeds the working fluid into the first-stage nozzle row 18.

[0014] The working fluid supply system 30 includes multiple sets of inlet flow paths 25, working fluid supply flow paths 28, and working fluid supply valves 29. The inlet flow paths 25 are arranged around the outer circumference of the first-stage nozzle row 18. For example, partition walls 32 extending radially may be arranged around the outer circumference of the first-stage nozzle row 18. The inlet flow paths 25 can be defined by dividing the space around the outer circumference of the first-stage nozzle row 18 using the partition walls 32. The partition walls 32 may be located in proximity to the first-stage nozzle row 18. Alternatively, as shown in FIG. 3, each of the partition walls 32 may be connected to a corresponding one of the nozzle vanes constituting the first-stage nozzle row 18. The working fluid supply system 30 according to the present embodiment includes six inlet flow paths 25, i.e., first to sixth inlet flow paths 25. The number of inlet flow paths 25 may be any value of two or more. The outlet of each inlet flow path 25 serves as a feed inlet 27 through which the working fluid is fed into the first-stage nozzle row 18. The circumferentially arranged feed inlets 27 face the outer circumference of the first-stage nozzle row 18. In the working fluid supply system 30 according to the present embodiment, the space around the first-stage nozzle row 18 is divided into six segments at the first to sixth feed inlets 27 corresponding to the first to sixth inlet flow paths 25.

[0015] Each inlet flow path 25 is connected to a working fluid source via a corresponding one of the working fluid supply flow paths 28. The working fluid supply valves 29 are located in the working fluid supply flow paths 28, respectively. Each working fluid supply valve 29 is a flow-regulating valve or an on-off valve. The working fluid supply system 30 includes first to sixth working fluid supply valves 29 in one-to-one correspondence with the first to sixth inlet flow paths 25, and each of the first to sixth feed inlets 27 can switch between permitting and blocking the feed of the working fluid independently of the other feed inlets 27. For example, when one of the first to sixth working fluid supply valves 29 is opened with the other working fluid supply valves 29 closed, the working fluid can be fed through one of the first to sixth feed inlets 27 while being blocked at the other feed inlets 27. In this case, the working fluid is fed into a one-sixth region of the first-stage nozzle row 18 and is not fed into the rest of the first-stage nozzle row 18. In this manner, in the multistage radial turbine 1, the working fluid can be fed either over the entire circumference of the first-stage nozzle row 18 or into a part of the first-stage nozzle row 18. In the case of partial feeding, the location and size of the region into which the working fluid is fed can be changed.

[0016] As shown in FIG. 1, the outlet 23 of the first-stage bladed wheel 5A and the inlet 21 of the second-stage bladed wheel 5B are connected by a connection flow path 90 defined by the casing 7 and a flow path structure 9. The connection flow path 90 includes: a bend portion 91 in which the fluid flowing out of the first-stage bladed wheel 5A in the axial direction X is redirected radially outward; a radial portion 92 through which the fluid flows radially outward; a U-turn portion 93 in which the fluid flowing radially outward is redirected radially inward; and a return portion 94 through which the fluid flows radially inward. The return portion 94 is connected to the inlet 21 of the second-stage bladed wheel 5B.

[0017] FIG. 4 is a schematic view showing the connection flow path 90 of the multistage radial turbine 1 as viewed in the axial direction X from the side on which the second-stage bladed wheel 5B is located. As shown in FIGS. 1 and 4, a second-stage nozzle row 19 including circumferentially arranged nozzles is located at the downstream end of the connection flow path 90, namely, in the return portion 94 and around the outer circumference of the inlet 21 of the second-stage bladed wheel 5B. The second-stage nozzle row 19 is constituted by circumferentially arranged nozzle vanes, and the gaps between the nozzle vanes that are circumferentially adjacent to one another function as nozzles. In the connection flow path 90 excluding its upstream and downstream end regions, partition plates 96 are circumferentially spaced apart from one another. Each partition plate 96 has an upstream end at a point in the bend portion 91 and a downstream end at a point in the return portion 94, and extends continuously from the point in the bend portion 91 to the point in the return portion 94 through the radial portion 92 and the U-turn portion 93. The upstream end of each partition plate 96 is slightly apart from the outlet 23 of the first-stage bladed wheel 5A to avoid interference between the partition plate 96 and the first-stage bladed wheel 5A. The downstream end of each partition plate 96 is in proximity to the outer circumference of the second-stage nozzle row 19. However, as shown in FIG. 5, the downstream end of each partition plate 96 may be connected to a corresponding one of the nozzle vanes constituting the second-stage nozzle row 19.

[0018] The partition plates 96 located within the connection flow path 90 define parallel flow paths 99 between the adjacent partition plates 96. In other words, the region from the outlet 23 of the first-stage bladed wheel 5A to the inlet 21 of the second-stage nozzle row 19 in the connection flow path 90 is circumferentially divided into the parallel flow paths 99. The connection flow path 90 is divided into the parallel flow paths 99 equally or unequally. Each of the parallel flow paths 99 includes the bend portion 91, the radial portion 92 connected to the bend portion 91, the U-turn portion 93 connected to the radial portion 92, and the return portion 94 connecting the U-turn portion 93 to the inlet 21 of the second-stage bladed wheel 5B. In the example shown in FIG. 4, the connection flow path 90 is divided by six partition plates 96 into six parallel flow paths 99; however, the number of the partition plates 96 is not limited to six. Although the numbers of the inlet flow paths 25 and the parallel flow paths 99 are equal in the present embodiment, the numbers of the inlet flow paths 25 and the parallel flow paths 99 may be different.

[0019] In the multistage radial turbine 1 according to the present embodiment, two bladed wheels 5 are coupled to a single rotating shaft 3; however, three or more bladed wheels 5 may be coupled to a single rotating shaft 3. In this case, the bladed wheels 5 adjacent to one another in the axial direction X are connected by connection flow paths 90, and the partition plates 96 may be omitted in the second and subsequent connection flow paths 90.<<Operarion mechanism of multistage radial turbine 1>>

[0020] The following describes the operation mechanism of the multistage radial turbine 1 configured as described above. First, depending on the flow rate of the working fluid, at least one or all of the working fluid supply valves 29 are opened, while the remaining supply valves 29 are closed. The feed inlets 27 connected to the working fluid supply flow paths 28 that include the opened working fluid supply valves 29 permit the feed of the working fluid. The working fluid is fed into the first-stage nozzle row 18 through the feed inlets 27 permitting the feed of the working fluid. The working fluid is rotationally accelerated by the first-stage nozzle row 18, forming a swirling flow which enters the inter-blade flow path 26 from the inlet 21 of the first-stage bladed wheel 5A. As the working fluid passes through the inter-blade flow path 26 of the first-stage bladed wheel 5A, the working fluid causes the first-stage bladed wheel 5A to rotate.

[0021] The working fluid exiting the outlet 23 of the first-stage bladed wheel 5A in the axial direction X enters the connection flow path 90. After entering the connection flow path 90, the working fluid is first redirected radially outward by the bend portion 91, flows radially outward through the radial portion 92 of the parallel flow path 99, is then redirected radially inward in the U-turn portion 93, flows radially inward through the return portion 94, and is fed into the second-stage nozzle row 19. The working fluid is rotationally accelerated by the second-stage nozzle row 19, forming a swirling flow which enters the inter-blade flow path 26 from the inlet 21 of the second-stage bladed wheel 5B. As it passes through the inter-blade flow path 26 of the second-stage bladed wheel 5B, the working fluid causes the second-stage bladed wheel 5B to rotate. The working fluid exiting the outlet 23 of the second-stage bladed wheel 5B is discharged outside the multistage radial turbine 1 through a discharge flow path 24.

[0022] When the multistage radial turbine 1 is operating under rated conditions, all of the working fluid supply valves 29 are opened, permitting the working fluid to be fed over the entire circumference of the first-stage nozzle row 18. During partial load operation, some (for example, half) of the working fluid supply valves 29 are opened, while the remaining working fluid supply valves 29 are closed. Accordingly, the feed of the working fluid is permitted at some of the feed inlets 27 and blocked at the other feed inlets 27. As a result, the area over which the working fluid is fed into the first-stage nozzle row 18 is narrower than that during feed over the entire circumference of the first-stage nozzle row 18. Since the working fluid is fed into the first-stage nozzle row 18 either through one of the feed inlets 27 or through two or more of the feed inlets 27, the working fluid flowing at a flow rate lower than the designed flow rate is fed into the inlet 21 of the first-stage bladed wheel 5A with a circumferential distribution of velocity, pressure, and temperature. The working fluid exiting the first-stage bladed wheel 5A is delivered to the second-stage bladed wheel 5B through the connection flow path 90. Within the connection flow path 90, the range of the circumferential movement of the working fluid is limited by the partition plates 96, and the working fluid reaches the second-stage nozzle row 19 through the parallel flow path(s) 99 that the working fluid has entered. In this manner, the working fluid passing through the connection flow path 90 is restricted from circumferentially diffusing, and is fed into the second-stage nozzle row 19 while preserving the distribution it had at the outlet 23 of the first-stage bladed wheel 5A. As a result, the working fluid passing through the second-stage nozzle row 19 acts on the second-stage bladed wheel 5B while retaining a suitable circumferential distribution of velocity, pressure, and temperature.[Summary]

[0023] A multistage radial turbine 1 according to a first item of the present disclosure includes: a single rotating shaft 3; first-stage and second-stage bladed wheels 5A and 5B mounted on the rotating shaft 3 and spaced apart from each other in an axial direction X, each of the bladed wheels 5 including an inlet 21 into which a working fluid flows radially inward and an outlet 23 out of which the working fluid flows in the axial direction X; a first-stage nozzle row 18 located around an outer circumference of the inlet 21 of the first-stage bladed wheel 5A; a working fluid supply system 30 that includes feed inlets 27 circumferentially arranged around an outer circumference of the first-stage nozzle row 18 and that is switchable at each of the feed inlets 27 between permitting and blocking feed of the working fluid into the first-stage nozzle row 18 and feeds the working fluid into the first-stage nozzle row 18 either through one of the feed inlets 27 or through two or more of the feed inlets 27; a second-stage nozzle row 19 located around an outer circumference of the inlet 21 of the second-stage bladed wheel 5B; and a connection flow path 90 connecting the outlet 23 of the first-stage bladed wheel 5A to the inlet 21 of the second-stage bladed wheel 5B, wherein the connection flow path 90 includes a region extending from the outlet 23 of the first-stage bladed wheel 5A to the second-stage nozzle row 19, the region being circumferentially divided into parallel flow paths 99.

[0024] A multistage radial turbine 1 according to a second item of the present disclosure includes the features of the multistage radial turbine 1 according to the first item, wherein each of the parallel flow paths 99 includes: a bend portion 91 that causes the working fluid flowing out of the outlet 23 of the first-stage bladed wheel 5A in the axial direction to be redirected radially outward; a radial portion 92 that is connected to the bend portion 91 and that causes the working fluid to flow radially outward; a U-turn portion 93 that is connected to the radial portion 92 and that causes the working fluid flowing radially outward to be redirected radially inward; and a return portion 94 that connects the U-turn portion 93 to the inlet 21 of the second-stage bladed wheel 5B and that causes the working fluid to flow radially inward.

[0025] When the multistage radial turbine 1 according to the first or second item is operating under rated conditions, the working fluid is fed into the first-stage nozzle row 18 through all of the feed inlets 27. During partial load operation, the working fluid is fed into the first-stage nozzle row 18 through one or some of the feed inlets 27. Thus, during partial load operation, the working fluid can be introduced into the first-stage bladed wheel 5A with a circumferential distribution of pressure, flow velocity, and temperature. The working fluid flowing from the outlet 23 of the first-stage bladed wheel 5A into the parallel flow paths 99 of the connection flow path 90 is delivered to the second-stage nozzle row 19 while being restricted from diffusing circumferentially. Accordingly, the working fluid exiting the outlet 23 of the first-stage bladed wheel 5A is fed into the second-stage nozzle row 19 while preserving the circumferential distribution of physical quantities it had at the outlet 23 of the first-stage bladed wheel 5A. As a result, even during partial load operation, the multistage radial turbine 1 can maintain a high pressure ratio and efficiency close to design-point levels. Therefore, the multistage radial turbine 1 can achieve higher turbine efficiency during partial load operation than turbines that are not configured to restrict circumferential diffusion of the working fluid within the connection flow path 90.

[0026] A multistage radial turbine 1 according to a third item of the present disclosure includes the features of the multistage radial turbine 1 according to the first or second item, wherein the connection flow path 90 is divided into the parallel flow paths 99 by circumferentially arranged partition plates 96.

[0027] The partition plates 96 are stationary components and can restrict circumferential diffusion of the working fluid flowing through the connection flow path 90 with a simple structure. Since the use of the partition plates 96 eliminates the need for a movable component such as a variable nozzle to restrict circumferential diffusion of the working fluid flowing through the connection flow path 90, the partition plates 96 can be employed also when the working fluid used in the multistage radial turbine 1 is an extremely low-temperature fluid such as liquid hydrogen.

[0028] A multistage radial turbine 1 according to a fourth item of the present disclosure includes the features of the multistage radial turbine 1 according to the third item, wherein the second-stage nozzle row 19 includes circumferentially arranged nozzle vanes, and at least one of the partition plates 96 is connected to one of the nozzle vanes.

[0029] With this configuration, the multistage radial turbine 1 can prevent circumferential diffusion of the fluid through the gaps between the partition plates 96 and the nozzle vanes, thereby achieving higher performance.

[0030] The foregoing discussion on the present disclosure is merely illustrative and explanatory, and is not intended to limit the present disclosure to the modes described herein. For example, although the foregoing detailed description presents various features of the present disclosure together in a single embodiment in order to streamline the present disclosure, only some of the described features may be combined. The features disclosed herein may be combined into alternative embodiments, configurations, or aspects other than those discussed above.

Examples

Embodiment Construction

[0010]Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. A multistage radial turbine according to one aspect of the present disclosure is a uniaxial multistage radial turbine. The multistage radial turbine is used, for example, as a turboexpander. The working fluid of the multistage radial turbine is a liquid, a gas, or a gas-liquid two-phase mixture.

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[0011]FIG. 1 is a schematic partial cross-sectional view showing a multistage radial turbine 1 according to one embodiment of the present disclosure. The multistage radial turbine 1 shown in FIG. 1 includes a casing 7, a rotating shaft 3 supported by the casing 7 via bearings, and bladed wheels 5 fitted around the rotating shaft 3. In FIG. 1, the letter C represents the centerline of the rotating shaft 3. The bladed wheels 5 are aligned in the axial direction X of the rotating shaft 3. The multistage radial turbine 1 according to the present embodiment includes two bladed wheels 5, one ...

Claims

1. A multistage radial turbine comprising: a single rotating shaft; first-stage and second-stage bladed wheels mounted on the rotating shaft and spaced apart from each other in an axial direction, each of the bladed wheels including an inlet into which a working fluid flows radially inward and an outlet out of which the working fluid flows in the axial direction; a first-stage nozzle row located around an outer circumference of the inlet of the first-stage bladed wheel; a working fluid supply system that includes feed inlets circumferentially arranged around an outer circumference of the first-stage nozzle row and that is switchable at each of the feed inlets between permitting and blocking feed of the working fluid into the first-stage nozzle row and feeds the working fluid into the first-stage nozzle row either through one of the feed inlets or through two or more of the feed inlets; a second-stage nozzle row located around an outer circumference of the inlet of the second-stage bladed wheel; and a connection flow path connecting the outlet of the first-stage bladed wheel to the inlet of the second-stage bladed wheel, wherein the connection flow path includes a region extending from the outlet of the first-stage bladed wheel to the second-stage nozzle row, the region being circumferentially divided into parallel flow paths.

2. The multistage radial turbine according to claim 1, wherein each of the parallel flow paths includes: a bend portion that causes the working fluid flowing out of the outlet of the first-stage bladed wheel in the axial direction to be redirected radially outward; a radial portion that is connected to the bend portion and that causes the working fluid to flow radially outward; a U-turn portion that is connected to the radial portion and that causes the working fluid flowing radially outward to be redirected radially inward; and a return portion that connects the U-turn portion to the inlet of the second-stage bladed wheel and that causes the working fluid to flow radially inward.

3. The multistage radial turbine according to claim 1 or 2, wherein the connection flow path is divided into the parallel flow paths by circumferentially arranged partition plates.

4. The multistage radial turbine according to claim 3, wherein the second-stage nozzle row includes circumferentially arranged nozzle vanes, and at least one of the partition plates is connected to one of the nozzle vanes.

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