Steam turbine

A steam turbine includes: a rotor; a casing; a thrust bearing; a steam inlet; a first pipe; a first regulation valve; a second pipe; a second regulation valve; and a control device. The control device estimates an exhaust flow rate of the steam turbine based on an operating point map which derives the exhaust flow rate of the steam turbine from an operating point of the steam turbine and estimates the thrust force applied to the thrust bearing based on the exhaust flow rate.

TECHNICAL FIELD

The present invention relates to a steam turbine.

BACKGROUND ART

A steam turbine includes a thrust bearing to receive a thrust force applied to a rotor during an operation of the steam turbine. Since there is a limit to a load capacity of the thrust bearing, it is necessary to perform a design in consideration of a thrust balance such that the thrust force applied to the rotor does not exceed the load capacity of the thrust bearing under any operating condition.

Patent Document 1 discloses a steam turbine in which a balance piston (dummy piston) is provided in a rotor and a thrust force (balance thrust force) in a direction opposite to that of a thrust force generated by an operation of the steam turbine is generated.

In the steam turbine disclosed in Patent Document 1, in order to regulate a pressure applied to the balance piston, a pressure adjusting valve is provided in a pipe which connects a chamber of the balance piston on a side opposite to a rotor blade side and a blade chamber in a turbine casing to each other. Accordingly, it is possible to regulate the thrust force acting on the balance piston.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

In the steam turbine disclosed in Patent Document 1, there is a problem that a regulation width of the balance thrust force is small. That is, a maximum balance thrust force is dependent to an internal pressure of the blade chamber to which the pipe is connected, and thus, there is a problem that it is not possible to cope with a case where it is necessary to generate a larger balance thrust force.

An object of the present invention is to provide a steam turbine capable of coping with a thrust force applied to a thrust bearing using a balance piston even in a case where the thrust force is largely changed.

Solution to Problem

According to a first aspect of the present invention, there is provided a steam turbine including: a rotor which has a rotor body extending along an axis, a plurality of stages of rotor blade rows, and a balance piston provided on one axial side of the plurality stages of rotor blade rows; a casing which covers the rotor from an outside in a radial direction relative to the axis and forms, between the casing and the rotor, a plurality of blade chambers corresponding to the rotor blade rows, a first chamber on the other axial side of the balance piston, and a second chamber on the one axial side of the balance piston; a thrust bearing which receives a thrust force applied to the rotor; a steam inlet through which steam is introduced into the first chamber; a first pipe which connects a second chamber and one blade chamber of the plurality of blade chambers to each other; a first regulation valve which is provided in the first pipe; a second pipe which connects the second chamber and another blade chamber of the plurality of blade chambers to each other, another blade chamber having an internal pressure different from that of the one blade chamber; a second regulation valve which is provided in the second pipe; and a control device which controls the first regulation valve and the second regulation valve based on a thrust force applied to the thrust bearing.

According to this configuration, it is possible to regulate a thrust force applied to the balance piston with a larger regulation width. Accordingly, even in a case where a thrust force applied to the thrust bearing is largely changed, it is possible to cope with the large change of the thrust force using the balance piston.

In the steam turbine, the control device may estimate an exhaust flow rate of the steam turbine based on an operating point map which derives the exhaust flow rate of the steam turbine from an operating point of the steam turbine, and may estimate the thrust force applied to the thrust bearing, based on the exhaust flow rate.

According to this configuration, in the estimation of the thrust force, a measurement device such as a device for measuring the temperature of the thrust bearing is not required, and thus, it is possible to operate the steam turbine at a low cost.

The steam turbine may further include a metal temperature measuring device which measures a metal temperature of the thrust bearing, and the control device may estimate the thrust force applied to the thrust bearing, based on the metal temperature of the thrust bearing.

For example, according to this configuration, it can be estimated that the thrust force is excessive in a case where the metal temperature of the thrust bearing is higher than a threshold value.

The steam turbine may include a load measuring device which measures a load applied to the thrust bearing and the control device may estimate the thrust force applied to the thrust bearing, based on the load applied to the thrust bearing.

According to this configuration, it is possible to directly estimate the thrust force by referring to the load applied to the thrust bearing.

Advantageous Effects of Invention

According to the present invention, it is possible to regulate a thrust force applied to the balance piston with a larger regulation width. Accordingly, even in a case where a thrust force applied to the thrust bearing is largely changed, it is possible to cope with the large change of the thrust force using the balance piston.

DESCRIPTION OF EMBODIMENTS

As shown inFIG. 1, a steam turbine1of the present embodiment is an external combustion engine which takes out energy of steam as a rotational power and is used for a generator or the like in a power plant.

The steam turbine1of the present embodiment is a steam turbine which has a high-pressure turbine2and a low-pressure turbine3and which can extract the steam from an intermediate state. The steam turbine1has a steam regulating valve4and an extraction regulation valve5. The steam regulating valve4increases or decreases a flow rate of high-pressure steam supplied to the high-pressure turbine2. The extraction regulation valve5increases or decreases a flow rate of steam supplied from the high-pressure turbine2to the low-pressure turbine3. In addition, the steam turbine1has a speed governor (electric governor, not shown) which controls the steam regulating valve4and the extraction regulating valve5according to a rotation speed of a rotor9or the like.

The steam turbine includes a casing7, a plurality of stationary blade rows8which are fixed to the casing7, a rotor9which extends along an axial direction Da, a thrust bearing10which receives a thrust force applied to the rotor9, journal bearings11which rotatably support the rotor9, and a control device12. The rotor9has rotor blade rows13which are disposed between the stationary blade rows8adjacent to each other in the axial direction Da.

The stationary blade rows8are formed at intervals in the axial direction Da. Each stationary blade row8includes a plurality of stationary blades provided at intervals in a circumferential direction.

Moreover, hereinafter, a direction in which an axis A of the rotor9extends will be referred to as an axial direction Da, a circumferential direction with respect to the axis A will be simply referred to as a circumferential direction, and a radial direction with respect to the axis A will be simply referred to as a radial direction. In addition, a left side inFIG. 1will be referred to as one axial side Da1and a right side inFIG. 1will be referred to as the other axial side Da2.

The high-pressure steam is introduced from the one axial side Da1(upstream side), flows to the other axial side Da2(downstream side), and is discharged.

A flow path of the steam is formed inside the casing7. The casing7covers the rotor9from an outside in the radial direction. The casing7has a high-pressure casing7awhich forms an outline of the high-pressure turbine2and a low-pressure casing7bwhich forms an outline of the low-pressure turbine3.

A steam inlet14is formed in the high-pressure casing7a, and the high-pressure steam is introduced from upstream sides of the stationary blade rows8and the rotor blade rows13into the high-pressure casing7athrough the steam inlet14. An extraction outlet15is formed in a downstream portion of the high-pressure casing7a, and the steam which has passed through the high-pressure casing7ais extracted through the extraction outlet15.

An exhaust outlet16is formed in a downstream portion of the low-pressure casing7b, and the steam which has passed through the low-pressure casing7bis exhausted through the exhaust outlet16.

The rotor blade rows13and the stationary blade rows8are alternately disposed in the axial direction Da. Each of the high-pressure turbine2and the low-pressure turbine3has three stages of rotor blade rows13and three stages of stationary blade rows8.

The rotor9has a rotor body18which extends along the axial direction Da, a thrust collar19, a balance piston20, a plurality of disks21, and a plurality of blade bodies22. The plurality of disks21are provided at intervals along the axial direction Da.

Each disk21is formed to extend radially outward from the rotor body18. The plurality of blade bodies22are provided on an outer peripheral surface of the disk21at intervals in the circumferential direction.

Each rotor blade row13includes the disk21and the plurality of blade bodies22. That is, the plurality of rotor blade rows13and the balance piston20are provided on the same rotor body18.

The rotor body18extends along the axis A to penetrate the casing7. An intermediate portion of the rotor body18in the axial direction Da is accommodated in the casing7, and both end portions of the rotor body18in the axial direction Da protrude to the outside of the casing7. Both end portions of the rotor9is rotatably supported around the axis A by the journal bearings11. The thrust bearing10which receives the thrust force applied to the rotor9is provided on the one axial side Da1of the journal bearing11on the one axial side Da1.

The thrust collar19is provided on an end portion on the one axial side Da1of the rotor9. The thrust collar19protrudes radially outward from an outer peripheral surface of the rotor body18. The thrust bearing10is provided to correspond to the thrust collar19which is formed on the rotor9.

The thrust bearing10has a first thrust bearing10awhich supports the thrust collar19from the other axial side Da2and a second thrust bearing10bwhich supports the thrust collar19from the one axial side Da1. The high-pressure steam flows from the upstream side to the downstream side, and thus, a thrust force acting on the rotor blade row13is supported by the first thrust bearing10a.

In addition, the thrust bearing10has a sensor which includes a temperature measuring device23which measures a metal temperature of the first thrust bearing10aand a load measuring device which measures a load applied to the first thrust bearing10a.

A plurality of blade chambers25are formed between the casing7and the rotor9inside the casing7. The steam turbines1has six blade chambers25from a first blade chamber25acorresponding to the rotor blade row13which is disposed on the most upstream side (one axial side Da1) to a sixth blade chamber25fcorresponding to the rotor blade row13fwhich is disposed on the most downstream side. While the steam turbine1is operated, an internal pressure in the first blade chamber25ais highest, and an internal pressure in the sixth blade chamber25fis lowest. That is, an internal pressure in the blade chamber decreases toward the downstream side.

The steam turbine1has a gland26which prevents the steam introduced from the steam inlet14from leaking from a rotor penetration portion of the casing7. For example, the grand26is constituted by a labyrinth ring.

In the steam turbine1, an HP gland26a, an MP gland26b, and an LP gland26care provided in this order from the other axial side Da2toward the one axial side Da1.

The balance piston20is provided inside the high-pressure casing7aand is provided on the one axial side Da1of the plurality of rotor blade rows13a. The balance piston protrudes radially outward from the outer peripheral surface of the rotor body18. That is, an outer diameter of the balance piston20is larger than an outer shape of the rotor body18.

In the casing7, a first chamber27which is formed on the other axial side Da2(rotor blade row13side) of the balance piston20and a second chamber28which is formed on the one axial side Da1of the balance piston20are provided between the casing7and the rotor9.

The balance piston20has a first surface20afacing the other axial side Da2(first chamber27) and a second surface20bfacing the one axial side Da1(second chamber28). An internal pressure of the first chamber27acts on the first surface20a. An internal pressure of the second chamber28acts on the second surface20b.

An outer peripheral surface of the balance piston20is sealed by the HP gland26.

The first chamber27and a fifth blade chamber25ecorresponding to a fifth rotor blade row13eare connected to each other by a first pipe29. A first regulation valve31is provided in the first pipe29.

The second chamber28and a second blade chamber25bcorresponding to the second rotor blade row13bare connected to each other by a second pipe30. A second regulation valve32is provided in the second pipe30.

That is, the second chamber28and the fifth blade chamber25ewhich is one blade chamber of the plurality of blade chambers25are connected to each other by the first pipe29, and the second chamber28and the second blade chamber25bwhich is another chamber having an internal pressure different from that of the fifth blade chamber25eare connected to each other by the second pipe30.

The second pipe30may branch off from the first pipe29.

In a case where the first regulation valve31is open and the second regulation valve32is closed, an internal pressure P2of the second chamber28is approximately the same as an internal pressure P4of the fifth blade chamber25e. Moreover, in a case where the first regulation valve31is closed and the second regulation valve32is open, the internal pressure P2of the second chamber28is approximately the same as an internal pressure P3of the second blade chamber25b.

The control device12has a bearing temperature determination unit12awhich performs a determination based on the metal temperature of the thrust bearing10and an exhaust flow rate determination unit12bwhich performs a determination based on an exhaust flow rate of the steam turbine1.

Next, an operation map of the steam turbine1will be described. In the present embodiment, the exhaust flow rate determination unit12bof the control device12of the steam turbine1can derive the exhaust flow rate of the steam turbine1with reference to the operating point map.

As shown inFIG. 2, in the operating point map, a horizontal axis indicates a turbine output (output of the steam turbine1) and a vertical axis indicates an inlet steam flow rate (a flow rate of the steam flowing in from the steam inlet14). According to a relative relationship therebetween, a scale is graduated in a vertical axis direction from 0% (line segment A1-A2inFIG. 2) to 100% (line segment A3-A4inFIG. 2) for an extraction flow rate, and a minimum exhaust operating point (line segment A4-A3inFIG. 2) and a maximum exhaust operating point (line segment A2-A5inFIG. 2) are shown for an exhaust flow rate.

For example, the turbine output is 70% and the extraction flow rate is 75%, an operating point A7is determined on the operating point map, and the inlet steam flow rate and the exhaust flow rate can be derived at the operating point A7.

Here, the turbine output corresponds to a rotation speed control output signal of the rotor9, the inlet steam flow rate corresponds to an operation signal of the steam regulating valve4, and the extraction flow rate corresponds to an operation signal of the extraction regulating valve5. Accordingly, for example, the rotation speed control output signal of the rotor9may be referred instead of the turbine output. In addition, the inlet steam flow rate may be obtained from a flow rate of steam flowing through the extraction outlet15and a flow rate of steam flowing through the exhaust outlet16.

In this manner, a method of deriving the exhaust flow rate of the steam turbine1with reference to the operating point map is not limited to the turbine output and the extraction flow rate, and can use various parameters.

Next, a control method of the steam turbine1of the present embodiment will be described.

As shown inFIG. 3, the control method of the steam turbine1includes a normal operation mode setting step S1of setting the first regulation valve31and the second regulation valve32to normal operation modes, a bearing temperature determination step S2of estimating the thrust force based on a metal temperature T of the first thrust bearing10a, an exhaust flow rate determination step S3of deriving the exhaust flow rate based on the operating point map in a case where the metal temperature T is equal to or more than a threshold value T1and estimating the thrust force based on the exhaust flow rate, and an emergency mode setting step S4of setting the regulating valves31and32to emergency modes in a case where the exhaust flow rate derived with reference to the operating point map is equal to or more than a threshold value F1.

If the high-pressure steam is introduced via the steam inlet14from a boiler (not shown) or the like, the steam flows into the blade chamber25of the high-pressure chamber2and the blade chamber25of the low-pressure turbine3, and the temperature and the pressure of the steam decrease while the steam applies a rotation force to the rotor9. After the steam finishes the work, the steam is discharged to the outside of the steam turbine1via the exhaust outlet16.

During the operation of the steam turbine1, the thrust force toward the other axial side Da2is generated in the rotor9. For example, the thrust force toward the other axial side Da2is generated by a differential pressure generated between the blade body22and the disk21. The thrust force is supported by the first thrust bearing10a.

On the other hand, a thrust force (balance thrust force) toward the one axial side Da1is generated in the balance pinion20by a differentia pressure between the first chamber27and the second chamber28. The steam turbine1of the present embodiment is configured such that the thrust force and the balance thrust force balance with each other by communicating the second blade chamber25bwith the second chamber28each other and by making the internal pressure of the second blade chamber25band the internal pressure of the second chamber28approximately the same.

In the normal operation mode setting step S1, the control device12sets the steam turbine1to the normal operation mode after the steam turbine1starts. In the normal operation mode, the second regulation valve32is set to the open state, and the first regulation valve31is set to the closed state.

Here, an internal pressure in the first chamber27will be referred to as P1, an internal pressure in the second chamber28will be referred to as P2, a pressure in the second blade chamber25bwill be referred to as P3, and a pressure in the fifth blade chamber25ewill be referred to as P4.

At the time of the normal operation of the steam turbine1, the second regulation valve32is open and the first regulation valve31is closed. Accordingly, the internal pressure P2of the second chamber28and the internal pressure P3of the second blade chamber25bare approximately the same as each other.

Therefore, the thrust force and the balance thrust force balance with each other, and forces acting on the entire rotor9in the axial direction Da balance with each other. That is, the thrust force applied to the first thrust bearing10ais within a load capacity range of the first thrust bearing10a.

The bearing temperature determination step S2is a step of monitoring the metal temperature of the first thrust bearing10aduring the operation of the steam turbine1. The bearing temperature determination unit12aof the control device12determined whether or not the metal temperature of the first thrust bearing10ais equal to or more than the threshold value T1. For example, the threshold value T1can be set to 100° C.

The bearing temperature determination unit12aof the control device12continues the normal operation mode in a case (NO) where the metal temperature T of the first thrust bearing10ais lower than the threshold value T1.

On the other hand, in a case (YES) where the metal temperature T of the first thrust bearing10ais equal to or more than the threshold value T1, the exhaust flow rate determination step S3is performed. The exhaust flow rate determination step S3is a step of deriving the exhaust flow rate of the steam turbine1based on the operating point map and estimating the thrust force based on the exhaust flow rate.

The exhaust flow rate determination unit12bof the control device12drives the exhaust flow rate of the steam turbine1with reference to the operating point map. Next, the exhaust flow rate determination unit12bof the control device12determines whether or not an exhaust flow rate F of the steam turbine1is equal to or more than the threshold value F1. If the maximum exhaust operating point is set to the exhaust flow rate 100% and the minimum exhaust operating point is set to the exhaust flow rate 0%, the threshold value F1can be set to the exhaust flow rate 90%.

In a case where the exhaust flow rate F is smaller than the threshold value F1, the exhaust flow rate determination unit12bof the control device12continues the normal operation mode. This is because it is considered that an increase in the metal temperature T of the first thrust bearing10ais a phenomenon due to wear of the thrust bearing10or a phenomenon due to deterioration of oil properties. That is, in a case where it is considered that the increase in the metal temperature T is not improved even if the differential pressure before and after the balance piston20is regulated, the normal operation mode continues.

On the other hand, in a case where the exhaust flow rate F is equal to or more than the threshold value F1, it is considered that the thrust force is excessive according to the increase in the exhaust flow rate F. Accordingly, the exhaust flow rate determination unit12bof the control device12sets the mode to an emergency mode in order to decrease the load of he first thrust bearing10a. In the emergency mode, the second regulation valve32is set to the closed state and the first regulation valve31is set to the open state.

Therefore, the internal pressure P2of the second chamber28is approximately the same as the internal pressure P4of the fifth blade chamber25e. The internal pressure P4of the fifth blade chamber25eis lower than the internal pressure P3of the second blade chamber25b, and thus, the internal pressure P2of the second chamber28decreases, and the balance thrust force increases toward the one axial side Da1. Accordingly, the load of the first thrust bearing10adecreases.

According to the above-described embodiment, switching is performed between the first pipe29and the second pipe30according to the thrust force applied to the rotor9, and thus, the thrust force applied to the balance piston20can be regulated with a larger regulation width. Accordingly, even in a case where the thrust force applied to the thrust bearing10is largely changed, it is possible to cope with the large change of the thrust force using the balance piston20.

In addition, the thrust force is estimated using the operation point map in addition to the metal temperature T of the thrust bearing10, and thus, it is possible to more accurately estimate the state of the thrust bearing10.

In addition, in the above-described embodiment, the bearing temperature determination unit12aestimates the thrust force based on the metal temperature T. However, the present invention is not limited to this. The thrust force may be estimated based on a load measured by a load measuring device24having a sensor. Accordingly, it is possible to more directly estimate the thrust force.

Hereinbefore, the embodiment of the present invention is described in detail with reference to the drawings. However, specific configurations are not limited to this embodiment, and design changes or the like within a scope which does not depart from the gist of the present invention are included.

For example, in the above-described embodiment, two pipes which communicate with the second chamber28and the blade chamber25are provided. However, the present invention is not limited to this, and for example, three or more pipes may communicate with the second chamber28such that a set range of the internal pressure P2of the second chamber28is widened.

Moreover, in the above-described embodiment, the regulating valves31and32are opened or closed based on the exhaust flow rate F of the steam turbine1estimated by the metal temperature T of the thrust bearing10and the operating point map. For example, the regulating valves31and32may be controlled based on only the operating point map. That is, in a case where it is estimated that the exhaust flow rate F is 90% of the maximum exhaust operating point by the operation point map, the regulating valves31and32are switched. In addition, the regulating valves31and32are controlled based on only the metal temperature T of the thrust bearing10, or the regulating valves31and32are controlled based on only the load applied to the thrust bearing10.

In addition, in the above-described embodiment, the regulating valves31and32are completely opened or closed. However, the present invention is not limited to this, and opening degrees of the regulating valves31and32may be regulated so as to regulate the internal pressure P2of the second chamber28.

REFERENCE SIGNS LIST

4: steam regulating valve

5: extraction regulating valve

8: stationary blade row

11: journal bearing

12: control device

12a: bearing temperature determination unit

12b: exhaust flow rate determination unit

13(13a,13b,13c,13d,13e,13f): rotor blade row

20a: first surface

20b: second surface

22: blade body

23: temperature measuring device

27: first chamber

28: second chamber

29: first pipe

30: second pipe

31: first regulation valve

32: second regulation valve

Da1: one axial side

Da2: the other axial side