JP2015048707A - Axial flow turbine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an axial flow turbine including tilting pad journal bearing capable of preventing or suppressing unstable vibration that is possibly generated in cases such as a case where a direction of a load acting on the tilting pad journal bearing is a direction other than a gravity direction or a case where the direction of the load changes due to the influence of a working fluid.SOLUTION: In one embodiment, a pad of a tilting pad journal bearing is arranged such that an action line of a resultant force 16 between a gravity-induced load acting on a turbine rotor and a load acting on the turbine rotor by which a working fluid is to displace the turbine rotor can pass through a pivot of one pad 1 of a plurality of pads.

Description

  Embodiments of the present invention relate to a technique for supporting a turbine rotor of an axial turbine using a tilting pad journal bearing.

  A tilting pad journal bearing is usually used as a bearing for supporting a rotating shaft of an axial turbine such as a steam turbine, for example, a journal of a turbine rotor. A general tilting pad journal bearing has a plurality of (in the illustrated example, five) swingable pads 1 as shown in FIG. Each pad 1 has a spherical back surface 5, and a pivot 6 that supports the pad 1 is embedded in the back surface 5. A pivot holder 7 is embedded in the bearing inner ring 2. The bearing inner ring 2 is fixed to an external structure via a bearing outer ring (not shown) fixed to a casing or a foundation (both not shown). The contact surfaces of the pivot 6 and the pivot holder 7 are both spherical surfaces. Therefore, each pad 1 can freely swing according to the movement of the journal 3.

  Usually, oil is used as a lubricant in a tilting pad journal bearing. The lubricating oil supplied to the inside of the bearing moves due to friction with the journal 3 generated for rotation, and is supplied to each pad 1. FIG. 2 shows an enlarged view of one pad 1. Here, a straight line 9 connecting the curvature center Ob of the inner surface of the bearing inner ring 2, the curvature center Op of the inner surface of the pad 1 and the center of gravity G of the pad 1 is drawn, and a line 10 perpendicular to the straight line 9 and passing through the pad center of gravity G is drawn. Set. Using this line 10 as a measurement standard for the pad inclination θ, a counterclockwise inclination (the same direction as the rotation direction 4 of the journal 3) is defined as a positive inclination, and a clockwise inclination is defined as a negative inclination.

  Lubricating oil is supplied to the gap 11 between the journal 3 and the pad 1. The lubricating surface 1d of the pad 1 is stationary, and the journal 3 is rotating at a very high peripheral speed. For this reason, since there is a very large speed difference between the journal side and the pad side of the lubricating oil filled in the gap 11, a shearing force acts on the lubricating oil and a viscous force is generated inside the lubricating oil. The wedge effect is generated by the viscous action and the inclination θ formed by the movement of the journal 3 and the pad 1, and an oil film pressure distribution is generated in the lubricating oil in the gap 11.

  When the oil film pressure distribution generated in each pad 1 is integrated over the entire circumference, it corresponds to the load applied to the journal 3. In a normal axial turbine, the load direction is constant with the direction of gravity acting on the journal 3, and therefore the pad 1 is arranged on the tilting pad bearing on the basis of the action line of gravity 8. As shown in FIG. 1, the pad 1 is arranged in a load in which each pad is arranged so that an action line of gravity 8 (corresponding to a two-dot chain line overlapping with gravity 8) passes through the center of a pivot 6 of one pad. In the on-pad type (hereinafter referred to as “LOP type”), as shown in FIG. 3, two adjacent pads 1 are arranged symmetrically with respect to the action line of gravity 8, in other words, two adjacent pads 1 There is a Rhodobit Wien type (hereinafter referred to as “LBP type”) in which an action line of gravity 8 passes through an intermediate position of the pivot 6.

  The pad 1 freely moves so that the contact point T1 between the pivot 6 and the pivot holder 7 is located vertically below the center point of the oil film pressure distribution that changes according to the rotation of the journal 3. Accordingly, the pad 1 receives the bearing load W in a self-aligning manner and as a whole, and prevents the generation of destabilizing force that causes whip or the like in the bearing. For this reason, the tilting pad journal bearing has a self-aligning function, is excellent in stability, and is particularly suitable for a high-speed rotating machine that requires high stability.

  By the way, in the steam turbine, a so-called partial insertion structure is applied in order to suppress the secondary flow when the volume flow rate of the working fluid is small (see, for example, Patent Document 2). In a normal nozzle diaphragm of a steam turbine, a plurality of nozzles are arranged over the entire circumference of an annular opening formed between the outer ring of the diaphragm and the inner ring of the diaphragm, and the working fluid is substantially evenly downstream in the circumferential direction. To leak. On the other hand, the partial insertion is a structure in which a plurality of nozzles are arranged only in a partial area in the circumferential direction of the annular opening and the other areas are closed without providing nozzles. In this case, the blade height of the nozzle can be adjusted to be high by changing the ratio of the closed region of the annular opening. For this reason, even if the volume flow rate of the working fluid is small, it is possible to suppress the secondary flow and suppress the performance degradation of the steam turbine. Such a partial insertion structure is normally used suitably for the speed control stage of a steam turbine.

  However, due to the recent increase in size and speed of rotating machines, unstable vibrations are likely to occur even with tilting pad journal bearings. Furthermore, as a result of measures to improve the performance of steam turbines, the number of paragraphs, the reduction of leakage loss, and the trend toward higher temperatures and pressures are prominent. These include a reduction in the critical speed of the shaft system, a reduction in system damping, and an unstable sealing force. This increases the stability of the shaft system against vibrations.

Among them, unstable vibrations with the following characteristics have been confirmed.
-It depends on the load and does not occur at all while the load is small, or even if it occurs, the amplitude is small and does not matter. It becomes difficult to increase the load further.
-Also, there are many cases where the frequency is close to the primary natural frequency of the shaft system and the rotational speed of the shaft exceeds the primary critical speed, and the frequency is lower than the rotationally synchronized frequency.
The cause of such vibration is fluid force, which is referred to as destabilizing force. In order to suppress unstable vibration due to such destabilizing force, the bearing oil film and the bearing support portion of the journal 3 Measures have been reported to increase the anisotropy of the rigidity in the vertical and horizontal directions and increase the damping of the bearing oil film.

  However, when the partial insertion structure described above is applied, as shown in FIG. 4, the nozzle 12 includes a range 12 a in which fluid can be ejected and a partial insertion location 12 b (hatched portion) where the ejection is blocked. In the case shown in FIG. 4, the valve force 15 that is the force that lifts the turbine rotor from below is provided in the turbine rotor (fluid blade section) 14 where the fluid 13 injected from the range 12a works in a concentrated manner. Act on. When the valve force 15 as shown in FIG. 5 acts on the turbine rotor, that is, the journal 3 in the direction of displacing the turbine rotor, the resultant force 16 of the valve force 15 and the gravity 8 acting on the journal 3 is the tilting pad. This is the load on the journal bearing. At this time, when the action line of the resultant force 16 passes between the pad 1b and the pad 1c as shown in FIG. 5, the expected characteristics of the LOP type tilting pad journal bearing cannot be obtained. It becomes a characteristic like a mold.

  It is known that the use of LOP type bearings can provide stability against the unstable vibration caused by the load described above, and the bearing characteristics originally required for a turbine having this partial insertion structure cannot be obtained. This is not desirable from the viewpoint of ensuring device reliability.

JP2012-241758 JP-A-11-303608

  The embodiment of the invention prevents or suppresses unstable vibration that may occur when the load direction acting on the tilting pad journal bearing is a direction other than the direction of gravity or changes due to the influence of the working fluid. It is an object of the present invention to provide an axial turbine with a tilting pad journal bearing that can be made.

  According to an embodiment of the invention, a turbine rotor rotated by a working fluid, a stationary blade portion that forms a flow path of the working fluid in the axial direction of the turbine rotor, and a part of the flow path is blocked, Located on the downstream side of the stationary blade portion, provided in the turbine rotor and rotated by the working fluid guided by the flow path, and a plurality of pads forming a pad row along the circumferential direction. An axial turbine having a tilting pad journal bearing that supports the turbine rotor is provided by the oil film pressure generated in the lubricating oil between the pad and the turbine rotor. The plurality of pads forming the pad row are the combined force of the load due to gravity acting on the turbine rotor and the load that is generated when the working fluid that has passed through the flow path acts on the rotor blade portion to displace the turbine rotor. The action line is arranged to pass through the pivot of one of the plurality of pads.

FIG. 3 is a cross-sectional view (in a direction perpendicular to the axis) in the transverse direction schematically showing the configuration of the LOP type tilting pad journal bearing. The enlarged view of one pad shown in FIG. FIG. 3 is a transverse cross-sectional view schematically showing a configuration of an LBP type tilting pad journal bearing. The schematic perspective view which shows a part of turbine for demonstrating a partial insertion structure. The transverse direction sectional view of a tilting pad journal bearing for explaining change of bearing load by a partial load structure. FIG. 3 is a transverse cross-sectional view schematically showing the configuration of the first embodiment of the tilting pad journal bearing. The axial direction fragmentary sectional view which shows the structure of 2nd Embodiment of a tilting pad journal bearing. The figure which developed the inner peripheral surface of the bearing inner ring | wheel on the plane for demonstrating arrangement | positioning of the pad of each row | line | column in 2nd Embodiment, and showed it with the pad. The transverse direction sectional view of the tilting pad journal bearing for explaining arrangement of the pad of A row in a 2nd embodiment. The transverse direction sectional view of the tilting pad journal bearing for explaining arrangement of the pad of B row in a 2nd embodiment. The transverse direction sectional view of the tilting pad journal bearing for explaining one modification of a 2nd embodiment. The transverse direction sectional view of the tilting pad journal bearing for explaining other modifications of a 2nd embodiment. The expanded view similar to FIG. 8 for demonstrating the further another modification of 2nd Embodiment. The axial direction sectional view showing roughly the composition of the axial flow turbine provided with the tilting pad journal bearing concerning a 2nd embodiment.

  Embodiments will be described below with reference to the accompanying drawings. In the description of the embodiment, the same or substantially the same members as those shown in FIGS. 1 to 5 for explaining the background art are denoted by the same reference numerals, and redundant description will be omitted. In FIGS. 6, 9, 10, 11, and 12, two orthogonal auxiliary lines indicated by alternate long and short dash lines indicate a horizontal direction and a vertical direction.

[First Embodiment]
The first embodiment will be described with reference to FIG. In FIG. 6, a white arrow indicated by a reference numeral 16 indicates a load (in this example, “steam”) acting on the turbine rotor that causes the turbine rotor, that is, the journal 3 to be displaced (in this example, the background art). The “valve force 15” described in the section) and the resultant force of the gravity load acting on the turbine rotor, that is, the journal 3, in accordance with the weight of the turbine rotor.

  The tilting pad journal bearing according to the present embodiment has a plurality of (in the illustrated example, five) pads 1 arranged so as to form a single pad row along the circumferential direction. The pads 1 are arranged at equal intervals in the circumferential direction, and the center of the pivot 6 of one of the plurality of pads 1 is on the line of action of the resultant force 16 (two-dot chain line overlapping with the resultant force 16 in the figure). Is located. That is, the pad 1 has an LOP type arrangement with respect to the resultant force 16. The “action line” means a half line extending in the direction of the resultant force 16 from the center of the turbine rotor, that is, the journal 3 which is the center of gravity of the journal 3 in the cross section of FIG.

  The direction of the resultant force 16 can vary depending on the operating conditions of the axial turbine. For example, the valve force varies depending on the amount of introduced steam. Therefore, it is preferable that the resultant force 16 considered as a reference for the arrangement of the pad 1 is a resultant force under operating conditions where stability is most desired. The operating condition for which stability is most desired is, for example, rated load operation of an axial turbine.

  According to the first embodiment, the pads 1 are arranged in the LOP type in correspondence with the resultant force 16 that appears under certain specific operating conditions (for example, at rated load operation), so that Generation of unstable vibration due to the destabilizing force can be prevented or reduced.

[Second Embodiment]
Next, a second embodiment will be described with reference to FIGS. In the second embodiment, one tilting pad journal bearing is composed of two rows of pad rows (A row and B row). In each pad row, the pads 1 are arranged in an LOP type with respect to forces (loads) in different directions. For example, in the row A, the pads 1 are arranged in an LOP type with respect to the resultant force 16 during rated load operation (see FIG. 9), as in the first embodiment described above, and the row B is a turbine rotor ( That is, the pads 1 are arranged in an LOP shape corresponding to only gravity so that the center of the pivot 6 of one pad 1 is positioned on the line of gravity acting on the journal 3) (see FIG. 10). . Therefore, the array phase (array angle position) is shifted by a predetermined angle between the pad 1 in the A row and the pad 1 in the B row.

  Each pivot holder 7 (or a piston coupled thereto) is slidably accommodated in a cylinder chamber 2 a formed in the bearing inner ring 2. A pressure control mechanism 17 is provided in an oil passage that connects a hydraulic source (not shown) and the cylinder chamber 2a. By increasing or decreasing the hydraulic pressure applied to the cylinder chamber 2 a by the pressure control mechanism 17, the pad 1 can be advanced and retracted in the radial direction of the journal 3 via the pivot holder 7.

  As shown in FIGS. 9 and 10, one pressure control mechanism 17 is provided for each pad 1. The operation of each pressure control mechanism 17 is controlled by a controller (not shown) so that the pads 1 belonging to the same pad row simultaneously move in the same direction (inward or outward in the radial direction). Each pressure control mechanism 17 and a controller (not shown) constitute a switching mechanism that selectively functions one of the A row and the B row as a bearing.

  The force by which the working fluid acting on the turbine rotor tries to displace the turbine rotor, that is, the journal 3, depending on the load state of the axial flow turbine. Here, when the magnitude (and / or direction) of the valve force changes, the direction of the resultant force 16 changes. Change. When the direction of the valve force is small enough to be ignored, for example, when operating at a much lower load than the rated operation, only the B row pad 1 exerts the bearing function so that the B row pad 1 Pressure is applied to the associated cylinder chamber 2a, that is, pressure is applied to the back surface of the pad 1 in the B row, and the gap between the pad 1 in the B row and the journal 3 is reduced. Further, for example, during rated load operation of the axial turbine, pressure is applied to the back surface of the A row pad 1 to reduce the gap between the A row pad 1 and the journal 3. In any case, when pressure is applied to the back surface of the pad 1 in one row, the pressure is released from the back surface of the pad 1 in the other row, and the gap between the pad 1 and the journal 3 in the other row is set. Pressure control is performed to increase the pressure.

  According to the second embodiment, by changing the pad that functions in response to the change in the direction of the bearing load due to the load condition, the unstable vibration due to the destabilizing force from the working fluid regardless of the change in the load condition. Can be prevented or reduced.

  In the second embodiment, the portion related to the A row and the portion related to the B row of one tilting pad journal bearing may be mechanically separated (for example, a till having only the A row). Or a part of the bearing inner ring 2 for the A row and the bearing inner ring 2 for the B row (for example, an integration of the bearing inner ring 2 for the A row and the bearing inner ring 2 for the B row). ).

  In the second embodiment, as shown in FIG. 11, in the plurality of pads 1 constituting one row of pads, the gap between the pad 1 and the journal 3 positioned on the action line of the resultant force 16 is different from that of the other pads 1. The pressure control mechanism 17 may be controlled so as to be smaller than the gap with the journal 3. That is, for example, a relatively large pressure is applied to the back surface of the pad 1 (1a) located on the line of action of the resultant force 16, and a relatively small pressure is applied to the back surface of the other pads 1.

  In order to ensure the stability of the rotor against the load, there is a measure to increase the load ratio between the load direction and its vertical direction (hereinafter referred to as “anisotropic”) for the rigidity, which is one of the bearing characteristics. As shown in FIG. 11, by reducing the gap only in the pad 1a, the bearing load applied to the pad 1a is increased and the displacement with respect to the force is reduced, so that the rigidity in the same direction is increased, so that the rigidity anisotropy is increased and the load is stable. Increases nature. Thereby, stability of a tilting pad journal bearing can be improved more.

  In the second embodiment, the pad row (B row) that functions during low-load operation is an LOP-type arrangement with respect to the gravity action line, but is not limited to this, and FIG. As shown, it may be an LBP type arrangement with respect to the line of gravity. The above-mentioned LOP type can provide a very good effect on the stability of the turbine in a high load (for example, rated load) state. However, in the case of a low load state, depending on the conditions, the LBP type pad arrangement is better. However, there is a case where a large damping in the bearing characteristics is obtained, and a more stable operation state may be possible.

  In the second embodiment, one tilting pad journal bearing has two pad rows. However, the present invention is not limited to this, and as shown in FIG. Three or more different pad rows may be provided. According to this, it can respond flexibly by the change of load conditions, and can enable more stable turbine operation.

  A plurality of tilting pad journal bearings having a double row structure according to the second embodiment can be provided in order to support the journals 3 provided at a plurality of locations in one turbine rotor. Thereby, a more stable operation of the turbine can be achieved.

  FIG. 14 schematically shows the structure of an axial turbine having a tilting pad journal bearing. The axial turbine has a turbine casing 21. In the turbine casing 21, a plurality of nozzle diaphragms (not shown in detail) fixed to the turbine casing 21 and a plurality of moving blade rows (not shown in detail) provided on the turbine rotor 22 are alternately arranged in the axial direction. One turbine stage 23 is constituted by one nozzle diaphragm (static blade portion) and a moving blade row (moving blade portion) on the downstream side thereof. A working fluid supplied from the working fluid supply pipe 24, for example, steam passes through a plurality of turbine stages 23 to perform work on the moving blades, the turbine rotor 22 is rotationally driven, and a generator connected to the turbine rotor 22. The load is rotated. The working fluid that has passed through the moving blade row in the final paragraph is discharged to the outside of the turbine casing 21 through the working fluid discharge passage 25. The journals 3 provided at both ends of the turbine rotor 22 can be supported by a tilting pad journal bearing according to the first or second embodiment indicated by reference numeral 26 in FIG.

  When the two journals 3 of the turbine rotor are each supported by the tilting pad journal bearing having a double row structure according to the second embodiment (see FIG. 14), the pad row that operates in the rated load state (row A) Should be positioned axially inside. That is, it is preferable that the axial interval between the A rows be smaller than the axial interval between the B rows. It is known that when the rotor is supported by two bearings, the stability is improved if the distance between the bearings is shortened, and the stability in the rated load state is reduced by reducing the distance between the bearings in the rated load state. Can be improved.

  Although the embodiments of the present invention have been described above, the embodiments are illustrative, and the scope of the present invention is not limited to the above-described embodiments, and does not depart from the spirit of the present invention. Various changes are possible. The description of the embodiment has been made on the assumption that it is applied to an axial flow steam turbine having a partial insertion structure. However, the present invention is not limited to this, and the turbine rotor supported by the tilting pad journal bearing described above is, for example, It may be a rotor of a gas turbine. Further, the force for displacing the turbine rotor is not limited to that generated from the partial insertion structure, and may be generated from a mechanism to which the turbine rotor is connected, for example.

1 Pad 3 Journal 6 Pivot 7 Pivot Holder 15 Valve Force (Force to Displace Turbine Rotor)
16 resultant force 17 pressure control mechanism (switching mechanism)

Claims (9)

A turbine rotor rotated by a working fluid;
Forming a flow passage in the turbine rotor axial direction of the working fluid, and a stationary blade portion in which a part of the flow passage is blocked;
Located on the downstream side of the stationary blade portion, provided on the turbine rotor and rotated by the working fluid guided by the flow path,
A tilting pad journal bearing that has a plurality of pads forming a pad row along a circumferential direction, and supports the turbine rotor by an oil film pressure generated in lubricating oil between the pads and the turbine rotor;
In an axial turbine with
The plurality of pads forming the pad row try to displace the turbine rotor generated by the load due to gravity acting on the turbine rotor and the working fluid that has passed through the flow path acting on the moving blade portion. An axial flow turbine characterized by being arranged so that a line of action of a resultant force with a load to be passed passes through a pivot of one of the plurality of pads. The tilting pad journal bearing has at least one sub pad row adjacent to the main pad row in the axial direction and along the circumferential direction in addition to the main pad row as the pad row according to claim 1. Is a double row structure tilting pad journal bearing having a plurality of pads,
The angular position where the pad of the sub pad row is arranged is shifted by a predetermined angle with respect to the angular position where the pad of the main pad row is arranged,
The tilting pad journal bearing having the double row structure is provided with a switching mechanism that selectively functions as one of the primary pad row and the secondary pad row as a bearing depending on a load state of a turbine. The axial flow turbine according to claim 1.   The axial flow turbine according to claim 2, wherein a plurality of the sub pad rows are provided, and angular positions at which the pads are arranged in the sub pad rows are different from each other for each pad row.   The axial flow turbine according to claim 2 or 3, wherein a plurality of journals of the turbine rotor are provided with tilting pad journal bearings having the double row structure.   In the tilting pad journal bearing of the double row structure provided in each of two journals spaced apart in the axial direction, the main pad row provided in one journal and the main pad provided in the other journal The shaft according to claim 2 or 3, wherein an axial distance between the rows is smaller than an axial distance between the sub pad row provided in one journal and the sub pad row provided in the other journal. Flow turbine.   The gap between one pad and the journal through which the action line passes through the pivot in the main pad row is smaller than the gap between the other pad and the journal. Axial flow turbine.   The said subpad row | line | column WHEREIN: The action line of the gravity which acts on the said turbine rotor is arrange | positioned so that it may pass through the pivot of one pad of several pads. An axial turbine according to the item.   7. The gravity line acting on the turbine rotor is arranged so as to pass between two adjacent pads in the sub-pad row, according to claim 2. Axial turbine.   9. The primary pad row is used when the turbine is in a rated load state, and the secondary pad row is used when the turbine is in a lower load state than the rated load. The axial flow turbine as described in any one of Claims.

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