JPS6147288B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a turbine gland seal steam system for suppressing thermal stress in an intermediate pressure turbine packing portion, etc. when the output of the turbine changes.

As is well known, the grand seal steam system of a steam turbine uses grand seal steam to isolate the inside of the turbine from outside air, thereby preventing steam inside the turbine from leaking to the outside or outside air from flowing into the turbine.

In a high-to-intermediate pressure turbine, gland seal steam is normally supplied to the gland packing section during startup and low load, and is discharged as surplus steam to the gland seal steam system during high load. That is,
The supply and discharge of seal steam is determined by the relationship between the pressure inside the high-intermediate pressure turbine and the grand seal steam pressure. Seal steam is discharged from the high and intermediate pressure turbines 3 and 6 as shown schematically by broken lines. Conversely, if the grand seal steam pressure is higher than the pressure inside the high-intermediate pressure turbines 3 and 6, the seal steam will be supplied to the packing parts 11 and 12 (usually labyrinth packing) as shown by the solid line.

On the other hand, in the case of a low-pressure turbine, the grand seal steam pressure is always higher than the pressure inside the low-pressure turbine, and seal steam is constantly supplied.

As mentioned above, the supply and discharge of seal steam in the high and intermediate pressure turbines 3 and 6 is determined by the magnitude relationship between the pressure inside the turbines 3 and 6 and the grand seal steam pressure, so in some cases, even though supply is necessary, The gland seal steam pressure may be low and seal steam may not be supplied. In other words, at startup and under low load, there is insufficient gland seal steam.
As a supply steam source for this insufficient sealing steam, high-temperature, high-pressure and low-temperature, low-pressure steam from the main steam system or auxiliary steam system must be reduced to an appropriate pressure by a regulator to supply the insufficient sealing steam.

However, at times of high load, the surplus exhaust seal steam from the high-intermediate pressure turbine alone can cover the insufficient seal steam from the low-pressure turbine, and there is no need to supply the main steam or auxiliary steam. Note that during such high loads, when the amount of excess seal steam discharged from the high and intermediate pressure turbine is larger than the amount of seal steam necessary to be supplied to the low pressure turbine, the difference is calculated by the regulator 9a (see Figure 2, which will be explained later). It is recovered to a condenser, etc.

In the past, steam turbines were mainly operated under constant high-load operation, but recently, with changes in the electric power situation, so-called middle thermal power generation is progressing, and two-shift operation with high-load operation during the day and low-load operation at night, or From low to high loads, there is a trend towards variable pressure operation where only the pressure is changed while keeping the temperature constant to improve efficiency.

Next, a conventional grand seal steam system will be explained.

FIG. 1 shows an example of a prior art reheat turbine gland seal steam system. The flow of steam from the turbine passes through a main steam stop valve 1 and a steam control valve 2 sent from a boiler (not shown), enters a high-pressure turbine 3, performs work in the high-pressure turbine 3, and then passes through a low-temperature reheat pipe 4. and enters a reheater (not shown). The high temperature reheated steam reheated by the reheater passes through the reheat valve 5,
It enters the intermediate pressure turbine 6 and then the low pressure turbine 7.
The water works in the condenser 8 and is condensed in the condenser 8.

On the other hand, the sealing steam in the turbine packing section is as follows. As mentioned above, when the turbine is started and the load is low, there is a shortage of gland seal steam. High-temperature, high-pressure main steam is used as the insufficient sealing steam. This main steam passes through piping 15, is reduced in pressure to the optimal gland seal steam pressure by pressure regulator 9, and is then
and is led to each packing part 11, 12, 13, 14. During high load, as mentioned above, excess seal steam is discharged from the seal part 11 of the high pressure turbine 3 and the seal part 12 of the intermediate pressure turbine 6, and this surplus seal steam is discharged from the seal part 1 of the low pressure turbine 7.
3,14.

Next, the gland seal steam during the above-mentioned two-shift operation and variable pressure operation will be explained. In this type of operation, high-load operation and low-load operation are performed as described above, so as mentioned at the beginning, the sealing steam in the packing parts 11 and 12 of the high and intermediate pressure turbines 3 and 6 is Seal steam supply and discharge are repeated depending on the low load. Even if such repetition is performed, there is not much problem with the high pressure turbine 3. Since the seal steam in the packing part 11 of the high-pressure turbine 3 is discharged to a load lower than the above-mentioned low load operating range,
Even if this operation is performed, the seal part 11
This is because there is almost no temperature change and no thermal stress occurs.

However, the gasket 12 of the intermediate pressure turbine 6
In this case, the problem of thermal stress occurs. That is, as shown in FIG. 6, the supply and discharge of the seal steam from the packing portion 12 of the intermediate pressure turbine 6 are switched in the low load operating range. In FIG. 6, numeral 31 indicates the amount of gas leakage, the plus side indicates discharge, and the minus side indicates supply. This is as explained above. FIG. 7 shows the temperature characteristics of the packing portion 11 of the intermediate pressure turbine 6 when the sealing steam is switched. 33 indicates the supply seal temperature, and 32 indicates the discharge seal vapor. As described above, when the sealing steam moves from supply to discharge and from discharge to supply, an excessive temperature difference occurs in the packing portion 12 of the intermediate pressure turbine 6, and thermal stress is generated. In the above operating method, such operation is repeated, and as a result, there is a risk that the turbine will be destroyed, and reliability or safety will be significantly reduced.

Figure 2 shows the first
This is a system in which an auxiliary steam system 16 is added to the sealed steam system shown in the figure, and the pressure regulator 9a supplies auxiliary steam sent from an auxiliary boiler (not shown) or the like with priority over main steam. The auxiliary steam is mainly used for starting the turbine or warming up the turbine, so it is low-temperature and low-pressure steam. Figure 8 shows the temperature dynamics at the time of sealing steam switching when auxiliary steam is used as the insufficient sealing steam supply source.Similar to Figure 7, here the auxiliary steam is low temperature and low pressure, so the supply An excessive temperature difference occurs between the seal steam temperature 34 and the exhaust seal steam temperature 32. Therefore, similar to the main steam supply shown in FIG. 1, excessive thermal stress will occur when switching to seal steam.

FIG. 3 shows a system in which a desuperheater 17 is provided in the middle of the auxiliary steam system 16 shown in FIG. 2 to reduce the temperature of the steam. In the system shown in FIG. 3, in order to reduce the temperature difference when switching the seal steam, the auxiliary steam system 16
It is necessary to raise the steam temperature to a temperature that matches the exhaust seal steam temperature. However, if the auxiliary steam temperature is increased, an excessive temperature difference will occur in the gasket 12 during startup. Therefore, it is necessary to use the desuperheater 17 only during startup and not during low-load exercise. In this way, the desuperheater 17 installed to lower the auxiliary steam temperature is used only at startup, which is impractical, and the desuperheater 17
is very expensive and economically problematic.

As described above, in the conventional technology, there is a temperature difference between the supply and exhaust seal steam temperatures when switching the seal steam, and excessive thermal stress is generated in the packing portion, resulting in a disadvantage that the reliability or safety is significantly reduced. Furthermore, in order to improve this problem, if a desuperheater is provided in the middle of the auxiliary steam system, there is a drawback that the cost increases, and there is a need for a fundamental improvement measure to solve these problems.

The purpose of the present invention is to eliminate the drawbacks of the prior art described above, and to improve reliability by suppressing excessive thermal stress generated in the intermediate pressure turbine packing part etc. when output changes.
An object of the present invention is to provide a turbine gland seal steam system that can significantly improve safety and reduce equipment costs.

The features of the present invention are that a pipe for extracting steam at a temperature suitable for the gland seal metal temperature of the intermediate pressure turbine is connected in the turbine stage, and a steam supply valve is provided between the pipe and the gland seal steam system. The supply valve is equipped with a control unit that detects the pressure when the output of the turbine changes and opens the supply valve when there is a shortage of gland seal steam. In addition to extracting steam at approximately the same temperature as the steam, the control section opens the supply valve when the seal steam in the packing section of the intermediate pressure turbine is switched from discharge to supply. The present invention provides a turbine gland seal steam system that can suppress excessive thermal stress when external steam flows in, and does not increase equipment costs.

The present invention will be explained below based on the drawings.

An embodiment of the present invention is shown in FIGS. 4 and 5.

In this embodiment, the packing part 1 of the intermediate pressure turbine 6
Regarding 2, the piping 2 is configured to suppress the thermal stress that occurs when switching between the supply and discharge of seal steam, and the piping 2 for extracting steam to the low temperature reheat pipe 4 inserted in the middle of an arbitrary stage of the high pressure turbine 3. It is connected.

The low-temperature reheat pipe 4 is inserted in the middle of a stage where steam having a temperature suitable for the metal temperature of the packing part 12 of the intermediate pressure turbine 6 can be extracted.

The piping 20 is provided with a steam supply valve 21 and an orifice 22, and when the supply valve 21 is opened, a sealing valve 21 and an orifice 22 are provided in the piping 20 to the sealing portion 12 through a piping 19 connected to the packing portion 12 of the gland seal steam system. It is now possible to supply steam.

A control section 23 is attached to the supply valve 21 .

The illustrated embodiment of the control section 23 includes a pressure switch 25 connected to the low temperature reheat pipe 4 through a pressure detection pipe 24, and an electromagnetic switching valve 27 connected to the pressure switch 25 through a wiring 26. There is.

The pressure switch 25 is set at a pressure higher than the pressure at which the state in which sealing steam is flowing from the intermediate pressure turbine 6 side to the packing part 12 to the state in which steam flows from the packing part 12 side toward the intermediate pressure turbine 6 is changed. The pressure is set slightly higher. Note that the pressure at the time of switching is predetermined at the time of designing the turbine plant. Also, when the pressure switch 25 is turned on, the electromagnetic switching valve 27 is opened, and the pressure switch 25 is turned on.
When the switch is turned OFF, the electromagnetic switching valve 27 is switched to close.

A pipe 28 connected to a fluid pressure supply source (not shown) is connected to the electromagnetic switching valve 27, and a pipe 29 for guiding the fluid pressure is connected between the electromagnetic switching valve 27 and the supply valve 21. A fluid pressure discharge pipe 30 is connected to the valve 27 . When the electromagnetic switching valve 27 is switched to open, the piping 28,
Fluid pressure is sent to the supply valve 21 through the electromagnetic switching valve 27 and piping 29 to open the supply valve 21, and when the electromagnetic switching valve 27 is switched to close, the fluid pressure is released through the piping 30. , the supply valve 21 is operated to close.

In FIG. 3, the same members as those shown in FIGS. 1 and 2 are designated by the same reference numerals.

Now, to explain the case of transition from high load operation to low load operation, as the load decreases as described above, the sealing steam of the packing part 12 of the intermediate pressure turbine 6 is switched from being discharged to being supplied.

During low load operation, the pressure inside the intermediate pressure turbine 6 decreases, so when this pressure becomes lower than the grand seal steam pressure, seal steam was previously discharged from the intermediate pressure turbine 26, but on the contrary, the seal steam is discharged from the intermediate pressure turbine 26. This is because the sealing steam is supplied to the intermediate pressure turbine 26 due to the increased steam pressure. In such a case, when the load changes from discharge to supply of seal steam, the pressure switch 25 is turned ON, the signal is led to the electromagnetic switching valve 27 via the wiring 26, the electromagnetic switching valve 27 is switched open, and the piping is switched on. 28 and 29 are connected to supply valve 2.
Fluid pressure is introduced into 1, the supply valve 21 is opened by the pressure, and a part of the steam extracted from the low temperature reheat pipe 4 passes through the supply valve 21, orifice 22, and piping 20, and is then transferred to the piping 19 of the sealed steam system. An appropriate amount of sealing steam, which is approximately the same temperature as the steam temperature of the intermediate pressure turbine 6, is delivered to the packing part 12 of the intermediate pressure turbine 6 through the
The packing portion 12 is sealed by being supplied in the same manner as in normal sealing steam supply.

When the seal steam in the packing part 12 of the intermediate pressure turbine 6 is in the discharge state, this steam is supplied to the packing parts 13 and 14 of the low pressure turbine 7,
When the load further decreases and the sealing steam in the packing part 12 of the intermediate pressure turbine 6 becomes insufficient, the piping 20
The supply seal steam will be supplied from.
As mentioned above, this steam temperature is approximately the same as the exhaust seal steam, so the gasket part 1 of the intermediate pressure turbine 6
No thermal stress occurs in No. 2.

Next, when transitioning from low load to high load,
The pressure in the low-temperature reheat steam pipe 4 increases as the load increases. Then, when the sealing steam in the sealing part 12 becomes a load that is switched from supply to discharge, the pressure switch 25 is turned OFF, contrary to when the load is reduced, and the signal is sent to the electromagnetic switching valve 2 through the wiring 26.
7, the electromagnetic switching valve 27 is switched to close,
The fluid pressure sent from the pipe 28 is released from the fluid pressure discharge pipe 30 through the electromagnetic switching valve 27, and the steam supply valve 21 is closed. Therefore, the supply of steam from the pipe 20 to the packing part 12 of the intermediate pressure turbine 6 is cut off, but at this time, the sealing steam in the packing part 12 has already been discharged as described above, and the temperature in the packing part 12 has increased. There is no change and no thermal stress occurs.

FIG. 9 shows the temperature characteristics of the sealing vapor of the present invention. In this figure, numeral 32 represents the discharge seal steam temperature, and numeral 35 represents the supply seal steam temperature. As is clear from this FIG. 9, according to the present invention, the temperature difference at the time of seal steam switching can be significantly reduced. I can do it.

As mentioned above, when transitioning from a high load to a low load or from a low load to a high load, when the sealing steam of the packing part 12 of the intermediate pressure turbine 6 is switched from discharge to supply, the low temperature reheat pipe 4 A part of the steam extracted in the gland seal steam system piping 1
9 to the packing part 12 of the intermediate pressure turbine 6, it is possible to compensate for the lack of sealing steam in the packing part 12, and also to reduce the temperature difference at the time of switching the sealing steam and reduce thermal stress. Therefore, it is possible to improve the lifespan and, in turn, improve reliability and safety.

Note that in the present invention, the control section 23 of the supply valve 21
The present invention is not limited to the above-mentioned embodiment, and the supply valve 21 may be an electric valve or a valve having an equivalent function, and the electromagnetic switching valve 27 may be omitted. In addition, the load detection may be performed not by the pressure switch 25, but by means for detecting the output of the generator, etc., and the pressure detection location may be any location as long as the pressure corresponding to the load can be detected.

The point where insufficient sealing steam is extracted from the sealing part 12 of the intermediate pressure turbine 6 varies depending on the type and type of turbine, and the point where the sealing steam of the sealing part 12 of the intermediate pressure turbine 6 is supplied is supplied with steam that matches the temperature at which the sealing steam is switched. The turbine stage is arbitrarily selected from the following turbine stages.

Further, the present invention provides a packing portion 12 of the intermediate pressure turbine 6.
Of course, the present invention is applicable not only to the seal of the present invention but also to all seals of the packing part where low steam temperature and high steam temperature alternate.

In addition, in FIGS. 1 to 4, the flow of the gland seal steam to the packing parts 11 and 12 of the medium and high pressure turbines 3 and 6 is shown representatively in the supply direction (flow toward the turbines 3 and 6). However, of course, as explained above, the flow is in the opposite direction at the time of discharge, and this is due to the
This is as explained using FIG.

The present invention has the configuration and operation described above.According to the present invention, when switching the seal steam, the thermal stress caused by the temperature difference of the seal steam can be significantly reduced, and as a result, the life of the turbine can be improved, and the turbine life can be improved. The reliability and safety of the system can be improved.

The present invention also has the advantage of reducing equipment costs compared to prior art techniques that use attemperators.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing an example of the conventional technology of a turbine gland seal steam system, Fig. 2 is an explanatory diagram showing another example of the conventional technology, Fig. 3 is an explanatory diagram showing another example of the conventional technology, 4 is a diagram showing an embodiment of the present invention, FIG. 5 is a detailed explanatory diagram of the main parts, and FIGS. 6 and 7.
8 and 8 are diagrams showing the seal steam temperature characteristics of the packing part of the intermediate pressure turbine in the prior art shown in FIGS. 1, 2, and 3, respectively, and FIG. 9 is the seal steam temperature characteristics in the present invention. FIG. FIG. 10 is a schematic diagram for explaining the discharge and supply of grand seal steam. 3...High-pressure turbine, 4...Low-temperature reheat pipe, 6...Intermediate-pressure turbine, 7...Low-pressure turbine, 11-14...Turbine packing part, 20...Low-temperature reheat pipe and gland seal connected to intermediate-pressure turbine packing part in the steam system 21... Steam supply valve, 2... Supply valve control unit,
24-30...Members constituting the control section.

Claims (1)

[Claims] 1. A pipe is connected in the middle of the turbine stage to extract steam at a temperature suitable for the gland packing metal temperature of the intermediate pressure turbine, and this pipe extracts steam at approximately the same temperature as the sealing steam from the intermediate pressure turbine. A steam supply valve is provided between the piping and the gland seal steam system, and a control unit is attached to the supply valve to detect the pressure when the output of the turbine changes and to open the supply valve when the gland seal steam is insufficient. A turbine gland seal steam system characterized in that a supply valve is opened when seal steam in a gasket of an intermediate pressure turbine is switched from discharge to supply by a control section.