JP4013752B2 - Centrifugal compressor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a centrifugal compressor, and more particularly to a centrifugal compressor that controls the flow rate using an inlet guide vane.
[0002]
[Prior art]
An example of a centrifugal compressor having a conventional inlet guide vane is described in Patent Document 1. In the centrifugal compressor described in this publication, the discharge air pressure is changed in order to change the surge line of the compressor by changing the inclination angle of the inlet guide vane according to the pressure change of the discharge compressed air, and to operate with high efficiency. A detector for detecting, a controller for obtaining a required inclination angle of the inlet guide vane, and an actuator driven by a signal of the controller are provided.
[0003]
Another example of a centrifugal compressor having a conventional inlet guide vane is described in Patent Document 2. The centrifugal compressor described in this publication has means for detecting the rotational speed and air temperature of the compressor, and drives the inlet guide vanes based on signals from these detection means to preliminarily convert the air flowing into the compressor. Swirl is given to change the flow rate characteristics of the compressor. Another example of a conventional compressor is described in Patent Document 3. In the centrifugal compressor described in this publication, one or more free rotors are provided between the inlet guide vane and the centrifugal impeller, and the flow energy is stored in the free rotor to further stabilize the operation of the compressor.
[Patent Document 1]
Japanese Patent Application Laid-Open No. 56-115897 (FIGS. 1 and 3)
[Patent Document 2]
JP 57-65898 A [Patent Document 3]
Japanese Patent Laid-Open No. 11-62894 [0004]
[Problems to be solved by the invention]
In the centrifugal compressors described in Patent Document 1 and Patent Document 2, by controlling the flow rate using an inlet guide vane, the performance of the centrifugal compressor can be improved, but the suction gas pressure of the centrifugal compressor increases. The case is not considered enough. That is, in a compressor in which the suction side pressure used in a chemical plant or the like is several times to 10 times or more of atmospheric pressure, the compressor may not be started unless the pressure difference between the upstream side and the downstream side of the inlet guide vane is large. . In this case, the pressure difference between the upstream side and the downstream side of the inlet guide vane increases, and the load applied to the blades of the inlet guide vane increases, which may cause damage to the inlet guide vane. However, the above patent documents do not consider the increase in load.
[0005]
In the centrifugal compressor described in Patent Document 3, the free rotor can store kinetic energy and prevent surging. However, there is no disclosure about the possibility that a large pressure difference may occur between the upstream and downstream of the inlet guide vane at the time of start-up when the suction pressure of the compressor becomes high, which may cause damage to the inlet guide vane. There is no description about eliminating.
[0006]
The present invention has been made in view of the above problems of the prior art, and its object is to avoid damage to the inlet guide vanes even when the suction pressure of the centrifugal compressor increases. Another object of the present invention is to improve the reliability of an inlet guide vane of a centrifugal compressor. Still another object of the present invention is to enable a centrifugal compressor to be operated with high efficiency. The present invention aims to achieve at least one of these objects.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, a feature of the present invention is that in a centrifugal compressor having an inlet guide vane arranged in a circumferential direction and having a variable orientation, a rotating shaft provided on the root side of the inlet guide vane is held. The inner diameter of the outer cylinder is made larger than the other parts at the inlet guide vane, and the outer diameter of the inner cylinder arranged on the inner diameter side of the inlet guide vane is made larger than the other parts at the inlet guide vane, Make the cross-sectional area perpendicular to the axis of the flow path at the inlet guide vane part larger than the cross-sectional area perpendicular to the axis of the flow path at the suction part end of the impeller, and increase the inner diameter of the outer cylinder from the increase of the outer diameter of the inner cylinder To reduce the maximum bending stress generated at the root portion of the inlet guide vane .
[0008]
And this feature smell Te, Lee emissions Rett guide vanes well to dispose a means for rotating the pressure of the working gas is sucked into the centrifugal compressor is more effective when it is 1MPa or more.
[0009]
Another feature of the present invention to achieve the above object is to provide a centrifugal compressor having a plurality of circumferentially arranged inlet guide vanes whose directions are variable, and a rotary shaft provided on the root side of the inlet guide vanes. The inner diameter of the outer cylinder to be held is made larger than the suction end of the impeller at the inlet guide vane, and the inlet guide vane is positioned radially corresponding to each inlet guide vane on the inner diameter side of the inlet guide vane. A split vane to be connected is provided, the outer cylinder rotatably holds the inlet guide vane, the inner cylinder rotatably holds the split vane, and the inner cylinder has one end held in the inner cylinder. Spring (24), piston (23) to which the other end of the spring is connected, rack (28) attached to the piston, and pinio meshing with the rack (27) and a sleeve (25) for slidably holding the piston are housed, and holes (21) and (22) for guiding the working gas to the both axial ends of the piston are formed in the inner cylinder. The working gas on the downstream side of the inlet guide vane is led from one hole (21), the working gas on the upstream side of the inlet guide vane is led from the other hole, and the working gas pressure on the upstream side and the downstream side are guided. When the pressure difference from the working gas pressure is small, the spring force acting on the piston acts on the rack, the rack is moved in the axial direction of the impeller, and the pinion that meshes with the rack rotates to separate the divided vanes. pressed against the inlet guide vane, when the pressure difference between the pressure of the working gas pressure and the downstream side of the working gas on the upstream side is large, work in the inlet guide vane away split vane from the inlet guide vane Bending stress is shall be reduced.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Several embodiments of the centrifugal compressor according to the present invention will be described below with reference to the drawings. 1 and 2 are views of an embodiment of a centrifugal compressor, FIG. 1 is a longitudinal sectional view, and FIG. 2 is a view taken along the line AA. A main shaft 100a of a centrifugal compressor is connected to a shaft of a driving machine (not shown) directly or via a speed increaser. A centrifugal impeller 11a is attached to the tip of the main shaft 100a. On the downstream side of the centrifugal impeller 11a, a diffuser 101 formed by a side surface of the housing 103a and a side surface of an outer cylinder whose details will be described later is provided. The housing 103a houses a bearing for holding the main shaft 100a and shaft sealing means. The diffuser 101 may be a diffuser with a rib in which blades having a slight height in the flow path width direction as shown in the figure are arranged at intervals in the circumferential direction, a diffuser with blades, or a diffuser without blades. A spiral scroll 102 is disposed downstream of the diffuser 101.
[0011]
The scroll 102 is formed by the back surface of the diffuser 101 that forms part of the outer cylinder 14 a and the casing 42. On the suction side of the impeller 11a, a cylindrical suction flow path is formed by the inner peripheral surface of the outer cylinder 14a. An inner cylinder 13a supported by a stay 15a is disposed at the center of the suction flow path. The tip of the inner cylinder 13a is streamlined to reduce flow path resistance. The outer peripheral side of the stay 14a is fixed to the outer cylinder 14a. A plurality of stays 15a are arranged at substantially equal positions in the circumferential direction.
[0012]
An inlet guide vane 12a is disposed in a suction flow path between the stay 15a and the impeller 11a and corresponding to the intermediate portion of the inner cylinder 13a. In this embodiment, there are 11 inlet guide vanes 12a, which are arranged at equal intervals in the circumferential direction. A rotating shaft 31 is provided on the base side of the inlet guide vane 12a. The rotary shaft 31 is rotatably supported by a bearing 20a held by the outer cylinder 14a. A rotating shaft 17a extending outside the casing 42 is connected to the rotating shaft 31 of one inlet guide vane among the plurality of inlet guide vanes 12a, 12a,..., And is rotated by a bearing 16c held in the casing 42. Supported as possible.
[0013]
An arm 19a extending in the radial direction is attached to an end of the rotating shaft 17a that extends outside the casing 42. On the other hand, an arm 20a extending in the direction perpendicular to the axis is attached to an axially intermediate portion of each of the rotary shafts 31, 31,. The end of the arm 20a is connected to the ring 18a via another arm 32. When the arm 19a outside the casing 42 is rotationally driven using a pneumatic power device or the like (not shown), the arm 20a attached to the rotary shaft 31 rotates the ring 18a around the rotary shaft of the impeller 11a. As the ring 18a rotates around the impeller shaft, the arm 32 of each inlet guide vane attached to the ring 18a moves. Then, the rotating shafts 31 connected to the arm 32 are simultaneously rotated by the same angle in the same direction as the rotating shaft 17a. Thereby, the angle of all the inlet guide vanes 12a is changed by the same amount.
[0014]
Using the inlet guide vane 12a configured as described above, the working gas is caused to flow into the impeller 11a at a predetermined flow angle. The working gas compressed by the impeller flows into the scroll 102 through the diffuser 101. During steady operation without flow control, the inlet guide vane 12a is fully opened. At this time, the inlet guide vane 12a faces the flow direction. At the start of the compressor, the inlet guide vane 12a is rotated so that the working gas has a swirling component. At this time, the suction flow path is narrowed.
[0015]
By the way, the inlet guide vane 12a used for controlling the flow rate of the centrifugal compressor has advantages in that it has high efficiency other than the normal operating point and can relatively reduce the torque at the time of starting. This inlet guide vane 12a swirls the gas sucked into the centrifugal compressor in addition to the flow rate control. When the suction gas has a swirling component, the work amount of the impeller 11a changes. That is, the head Δh that the impeller gives to the working gas is the circumferential speed component of the absolute speed of the working gas at the impeller outlet, where u _{2 is} the peripheral speed of the impeller 11a outlet, u _{1 is} the peripheral speed of the impeller 11a inlet. v _u2 , the circumferential component of the absolute velocity of the working gas at the impeller inlet is represented by v _u1 , and the gravitational acceleration is represented by g.
Δh = (1 / g) · (u ₂ v _u2 −u ₁ v _u1 )
It becomes.
[0016]
Here, when the inlet guide vane 12a is not equipped, the absolute velocity direction of the gas at the inlet of the impeller 11a is the radial direction. As a result, v _u1 = 0. When the inlet guide vane 12a swirls the gas flow, v _u1 ≠ 0 and the work amount of the impeller 11a can be increased or decreased.
[0017]
Furthermore, when the inlet guide vane 12a is used, the torque at the time of starting can be reduced. When the centrifugal compressor is driven by an induction motor that can be operated only at a constant speed, it may be necessary to reduce the torque at the start of the centrifugal compressor due to limitations on the current value and voltage value. For example, in a compressor used in a chemical reaction plant, the gas inlet temperature, gas pressure, and density may be higher at startup than during steady operation. In this case, the starting torque must be reduced. When the inlet guide vane is used, the sectional area of the inlet of the inlet guide vane is reduced in addition to turning the working gas, so that the mass flow rate is reduced and the load on the impeller is reduced. As a result, the compressor can be started.
[0018]
When the inlet guide vane 12a is provided, the compressor can be started even if the suction gas temperature and pressure are high, but the pressure at the impeller inlet is smaller than the suction pressure. As a result, a pressure difference is generated between the upstream side and the downstream side of the inlet guide vane 12a, and a load corresponding to this pressure difference is applied to the inlet guide vane 12a. In the case of an atmospheric pressure suction air compressor, the pressure difference between the upstream side and the downstream side of the inlet guide vane is at most 1 atm, and the load applied to the inlet guide vane is relatively small. However, in a centrifugal compressor having a suction pressure several times to 10 times the atmospheric pressure, the pressure difference between the upstream side and the downstream side of the inlet guide vane increases as a result of restricting the inlet guide vane portion to start the compressor. The load on the inlet guide vane increases dramatically.
[0019]
Therefore, in this embodiment, instead of making the outer cylinder 14a and the inner cylinder 13a into a cylindrical shape having a constant radius, which has been used in the past, the diameters of both the outer cylinder 14a and the inner cylinder 13a of the inlet guide vane 12a are set to other parts. Larger diameter. At the same time, both the outer cylinder 14a and the inner cylinder 13a are smoothly reduced in outer diameter from the large diameter portion to the impeller entrance. Compared to the case where the radii of the outer cylinder 14a and the inner cylinder 13a remain the same in the flow direction, the present embodiment in which the flow path cross-sectional area is increased by the outer cylinder 14a and the flow path cross-sectional area is decreased by the inner cylinder 13a, The channel cross-sectional area is increasing.
[0020]
In addition, when changing a flow-path cross-sectional shape with the said method, the increase amount of the diameter of the outer cylinder 14a can be made smaller than the increase amount of the diameter of the inner cylinder 13a. For example, consider a case where the inner diameter d and outer shape D of the flow path are changed without changing the flow path cross-sectional area S. If the subscript 1 before the change and the subscript 2 after the change, S = π (D ₁ ² −d ₁ ² ) / 4 = π (D ₂ ² −d ₂ ² ) / 4, The difference Δ between the inner and outer diameters is Δ ₂ <Δ1 when D ₂ > D ₁ . Therefore, the radial length L of the inlet guide vane 12a obtained by subtracting the inner diameter of the inner cylinder 13a from the inner diameter of the outer cylinder 14a can be shortened. Since the length L of the inlet guide vane 12a is shortened, the strength of the inlet guide vane 12a can be set to a strength range that can withstand the pressure difference between the upstream and downstream of the inlet guide vane 12a that is necessary when starting the compressor. The reason for this is as follows.
[0021]
The portion where the maximum stress is generated in the inlet guide vane 12a is the root portion of the inlet guide vane 12a. The maximum bending stress at this portion is proportional to the cube of the radial length L of the inlet guide vane 12a and inversely proportional to the cube of the thickness of the inlet guide vane 12a. When the thickness of the inlet guide vane 12a is increased, the suction flow of the compressor is disturbed, and a non-uniform flow flows into the impeller 11a. Therefore, the length L of the inlet guide vane 12a is shortened without increasing the thickness of the inlet guide vane 12a. If the length L of the inlet guide vane 12a is shortened, the natural frequency of the inlet guide vane 12a is inversely proportional to the square of the length L, so that the natural frequency of the inlet guide vane 12a is also increased.
[0022]
Another embodiment of the centrifugal compressor according to the present invention will be described with reference to the longitudinal sectional view shown in FIG. This embodiment is suitable when the pressure difference between the working gas before and after the inlet guide vane is larger than the embodiment shown in FIG. That is, it is used when there is a possibility that the bending stress acting on the inlet guide vane is increased only by changing the flow path inner / outer diameter ratio of the inlet guide vane portion, and the inlet guide vane cannot withstand the pressure difference.
[0023]
The difference of this embodiment from the above embodiment is that the inlet guide vane is divided into a plurality of pieces in the radial direction instead of changing the shape of the suction passage of the impeller. Further, in the vicinity of the shut-off of the inlet guide vane, a portion communicating from the upstream to the downstream is formed in a part of the cross section perpendicular to the axis of the suction flow path by the divided inlet guide vane. As a result, a required pressure difference can be generated before and after the inlet guide vane at the time of startup, and the strength of the inlet guide vane can withstand this pressure difference.
[0024]
A split vane 12c is disposed on the inner diameter side of the inlet guide vane 12b. When the inlet guide vane 12b and the divided vane 12c are integrated, the axial perpendicular projection becomes a fan shape as shown in FIG. During steady operation, both the inlet guide vane 12b and the divided vane 12c are positioned along the flow direction Fin as shown in FIG. On the other hand, at the time of activation, the inlet guide vane 12b is rotated to the angle at which the suction flow path is closed. However, the divided vane 12c is rotated at an angle different from that of the inlet guide vane 12b.
[0025]
Here, the division | segmentation vane 12c is attached to the inner cylinder 13b. A rotating shaft 26 extending in a direction perpendicular to the rotating shaft 100a of the impeller 11a is disposed around the piston 23 inside the inner cylinder 13b. A pinion 27 is attached to the rotating shaft 26. The center position in the flow direction of the rotating shaft 26 is matched with the center position in the flow direction axis of the inlet guide vane 12b. A rack 28 that meshes with the pinion 27 is attached to the piston 23. The end of the piston 23 on the impeller 11a side is fitted to a sleeve 25 disposed in the inner cylinder 13b. The suction side end of the piston 23 is restrained by the inner cylinder by a spring 24. A hole 21 is formed in the wall surface of the inner cylinder 13b corresponding to the end of the sleeve 25 on the impeller 11a side so as to communicate the suction flow path with the inside of the inner cylinder. Similarly, a hole 22 is formed in the wall surface of the inner cylinder 13b corresponding to the spring 24 so as to communicate the suction flow path with the inside of the inner cylinder. These holes 21 and 22 are formed on the upstream side and the downstream side in the flow direction with the divided vane 12c interposed therebetween. A pivot receiver is formed at the center of the inner peripheral surface of the inlet guide vane 12b, and a pivot that is fitted to the pivot receiver is formed at the center of the outer peripheral surface of the divided vane 12c. As for these, the pressure of the gas in the suction flow path upstream of the inlet guide vane 12b from the hole 22 is loaded on the piston 23. From the hole 21, the pressure of the gas in the suction channel on the downstream side of the inlet guide vane 12 b is applied to the piston 23. The space between the piston 23 and the sleeve 25 is sealed, and the working gas does not come and go. When the pressure difference between the upstream side gas pressure and the downstream side gas pressure of the inlet guide vane 12b is small, the spring 24 force acting on the piston 23 acts on the rack 28 and the rack 28 in the axial direction of the impeller 11a. Move. When the rack 28 moves, the pinion 27 meshing with the rack 28 rotates and presses the divided vane 12c against the inlet guide vane 12b. That is, the inlet guide vane 12b and the divided vane 12c are in a combined state in the state of steady operation of the compressor, and the inlet guide vane 12b and the divided vane 12c rotate in the same direction.
[0026]
At the time of starting the compressor, the inlet guide vane 12b is driven to rotate as shown in FIG. Since the inlet guide vane 12b is closed, a pressure difference is generated between the upstream and downstream of the inlet guide vane 12b. A force corresponding to the pressure difference is generated by the working gas flowing in from the hole 22 and the hole 21 and moves the piston 23 against the force of the spring 24.
[0027]
The rack 28 attached to the piston 23 moves and the pinion 27 rotates to separate the divided vane 12c from the inlet guide vane 12b. As a result, the suction flow path is slightly spaced from the deadline. Since the gap is formed in the suction flow path, the pressure difference between the working gas upstream and downstream of the inlet guide vane 12b is reduced, and the bending stress acting on the inlet guide vane 12b is reduced. In this embodiment, the spring force of the spring 24 connected to the piston 23 needs to be set appropriately. When the pressure difference before and after the inlet guide vane 12b exceeds the pressure difference that can start the compressor, the spring force of the spring 24 is set to move the piston.
[0028]
【The invention's effect】
According to the present invention, since the bending stress due to the pressure of the working gas acting on the inlet guide vane is reduced, the reliability of the centrifugal compressor can be improved even if the suction pressure is high. Further, surging of the centrifugal compressor can be avoided.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of an embodiment of a centrifugal compressor according to the present invention.
FIG. 2 is an AA arrow view of FIG.
FIG. 3 is a longitudinal sectional view of another embodiment of the centrifugal compressor according to the present invention.
4 is a cross-sectional view taken along arrow B in FIG. 3;
5 is a cross-sectional view taken along arrow B in FIG.
[Explanation of symbols]
11a ... impeller, 12a, 12b ... inlet guide vane, 13a, 13b ... inner cylinder, 14a, 14b ... outer cylinder, 15a ... stay, 16a ... bearing, 17a ... rotating shaft, 18a ... ring, 19a, 20a ... arm, 21, 22 ... hole, 23 ... piston, 24 ... spring, 25 ... sleeve, 26 ... rotary shaft, 27 ... pinion, 28 ... rack, 31 ... rotary shaft, 32 ... arm, 42 ... casing, 100a ... main shaft, 101 ... Diffuser, 102 ... Scroll.

Claims (5)

In a centrifugal compressor having a plurality of circumferentially arranged inlet guide vanes whose orientation is variable, the inner diameter of the outer cylinder holding the rotating shaft provided on the root side of the inlet guide vane is the other portion in the inlet guide vane portion. The outer diameter of the inner cylinder arranged on the inner diameter side of the inlet guide vane is made larger than that of the other portions at the inlet guide vane, and the cross-sectional area perpendicular to the axis of the flow path at the inlet guide vane is set. Generated at the root of the inlet guide vane by making it larger than the cross-sectional area perpendicular to the axis of the flow path at the suction section end of the impeller and making the increase in the inner diameter of the outer cylinder smaller than the increase in the outer diameter of the inner cylinder A centrifugal compressor characterized by reducing the maximum stress of bending.   The centrifugal compressor according to claim 1, further comprising means for changing the direction of the inlet guide vane.   The centrifugal compressor according to claim 1 or 2, wherein the pressure of the working gas sucked into the centrifugal compressor is 1 MPa or more. In a centrifugal compressor having an inlet guide vane arranged in a plurality in the circumferential direction and having a variable orientation, the inner diameter of the outer cylinder holding the rotating shaft provided on the root side of the inlet guide vane is set at the inlet guide vane portion of the impeller. A split vane that is radially connected to the inlet guide vane is provided at a position corresponding to each inlet guide vane on the inner diameter side of the inlet guide vane with a larger diameter than the suction end, and the outer cylinder has an inlet guide vane. The inner cylinder holds the divided vane rotatably, and a spring (24) having one end held by the inner cylinder is connected to the inner cylinder and the other end of the spring is connected to the inner cylinder. A piston (23), a rack (28) attached to the piston, a pinion (27) meshing with the rack, and a slide for holding the piston slidably. The inner cylinder is formed with holes (21) and (22) for guiding the working gas to both ends of the piston in the axial direction. From one hole (21), When the working gas on the downstream side of the inlet guide vane is led and the working gas on the upstream side of the inlet guide vane is led from the other hole, and the pressure difference between the upstream working gas pressure and the downstream working gas pressure is small The spring force acting on the piston acts on the rack, moves the rack in the axial direction of the impeller, the pinion that meshes with this rack rotates , and presses the divided vane against the inlet guide vane, and the upstream working gas pressure centrifugation and is large pressure difference between the pressure of the working gas downstream, characterized that you reduce the bending stress acting on inlet guide vanes away split vane from the inlet guide vane Compressor.   The centrifugal compressor according to claim 4, wherein the divided vanes are set at an angular position different from the inlet guide vanes when the compressor is started.

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