JPH0475363B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a method of operating a reheat steam turbine plant, and particularly to a method of operating a reheat steam turbine plant from no load or low load to high load. Regarding.

[Technical background of the invention and its problems] In thermal and nuclear power plants, etc.
An operation method that maintains a steam generation source such as a boiler or a nuclear reactor in a constant operating state without following fluctuations in turbine load, that is, a turbine bypass operation method has been adopted.

In other words, this turbine bypass operation method is
When the load on the turbine is low or the turbine is stopped, the amount of steam generated by the boiler, etc. is kept constant, and the excess steam is collected by bypassing the turbine and returning to the condenser.
In recent years, it has been adopted by many power plants to flexibly follow power load fluctuations during the day and night.

This turbine bypass operation allows the boiler to continue operating, so it stops only the turbine at night when the power load is low, and restarts the turbine immediately when the power load demand increases, reducing the startup time of the turbine. It is possible to shorten the time. Furthermore, the startup time of the turbine can be shortened even when the turbine is tripped or under heavy load after load interruption.

Figure 1 shows a reheat steam turbine plant consisting of thermal power. In this reheat steam turbine plant, the main steam generated in the boiler 1 is transmitted through the main steam pipe 9, the main steam stop valve 10, or the main steam turbine that bypasses this. The steam is led to the high pressure turbine 2 via a steam stop valve bypass valve 11 and a steam control valve 12 .

After applying the thermal energy of the main steam to the high-pressure turbine 2, the main steam is exhausted from the high-pressure turbine 2, passes through the high-pressure exhaust check valve 13, is led back to the boiler 1 through the low-temperature reheat pipe 14, and is heated again. This reheated steam is passed through a high temperature reheat pipe 16 to a reheat stop valve 17.
The steam flows into the intermediate pressure turbine 3 via the intercept valve 18 or the intercept valve bypass valve 19, is further guided to the low pressure turbine 4, imparts effective thermal energy of the steam to the turbine, and is recovered in the condenser 6 and condensed. It is considered water.

In such a basic reheat cycle, the bypass system consists of two systems: high pressure and low pressure.

That is, a high-pressure bypass line 22 branches from the main steam pipe 9 upstream of the main steam stop valve 10, is depressurized and temperature-reduced by the high-pressure bypass device 15, and joins the low-temperature reheat pipe 14, and a high-pressure bypass line 22 branches upstream of the reheat stop valve 17. The low pressure bypass line 23 branches from the high temperature reheat pipe 16 at the high temperature reheat pipe 16, is depressurized by the low pressure bypass valve 20, is further reduced in temperature by the desuperheater 21, and is recovered to the condenser 6.

In turbine bypass operation using such a system, main steam flows into the low-temperature reheat pipe 14 through the high-pressure bypass line 22 before the turbine is started, and reheated steam flows into the low-pressure bypass line 2
3. It passes through the desuperheater 21 and flows into the condenser 6. As a result, both the high-pressure bypass line 22 and the low-pressure bypass line 23 have steam pressure, and the startup conditions for the turbine are different from those of a plant that does not have a bypass system.

In other words, in such a reheat steam turbine plant, when the turbine is started with high main steam and reheat steam pressures, the amount of steam passing through the high-pressure turbine 2 will decrease in the no-load state until the load is applied. is extremely small. As a result, there is a problem in that windage loss occurs due to the rotation of the high-pressure exhaust stage blades, the steam temperature rises, and the amount of heat is transmitted to the blades, rotor, etc., raising the temperature of the rotating body.

At this time, since the high-pressure exhaust has a certain level of pressure, there is a problem in that this phenomenon becomes even more pronounced.

Such a rise in the high pressure exhaust temperature is extremely significant, and especially in a warm start, the main steam temperature itself during turbine ventilation is high, and therefore the high pressure exhaust temperature becomes a fairly high value even in absolute value. This makes the conditions for the thermal stress of the rotor, the strength of the blades, etc. of the high-pressure exhaust stage stricter.

[Object of the Invention] The present invention has been made in response to such conventional circumstances, and is aimed at the turbine bypass operating state, that is,
This prevents the rise in high-pressure exhaust temperature that occurs when starting the turbine with high main steam and reheat steam pressure, and maintains the thermal stress of the rotor and the strength of the blades in the high-pressure exhaust stage at a sufficiently safe level. It is an object of the present invention to provide a method for operating a reheat steam turbine plant.

[Summary of the invention] That is, the present invention provides a boiler having a reheater;
A high-pressure turbine driven by main steam led from the boiler through a main steam pipe having a steam control valve; a low-temperature reheat pipe that leads exhaust gas from the high-pressure turbine to the reheater; a reheat steam turbine driven by reheat steam guided through a reheat pipe; a high-pressure bypass line branched from the main steam pipe, bypassing the high-pressure turbine and connected to the low-temperature reheat pipe; and the high-temperature reheat pipe. A low-pressure bypass line branched from the reheat steam turbine and connected to the condenser, and a steam dump line branched from the low-temperature reheat pipe and connected to the condenser. In the method of operating a reheat steam turbine plant, when the turbine is started, the supply of steam to the high pressure turbine is cut off, and the steam of the high pressure turbine is guided to the condenser through the steam dump line, and the inside of the high pressure turbine is brought into a vacuum state. After that, the reheat steam turbine is supplied with reheat steam to drive the reheat steam turbine, and then the valve opening degree of the steam dump valve is adjusted to prevent the high pressure turbine from overheating when the high pressure turbine takes a load. This is a method of operating a reheat steam turbine plant, characterized in that the control valve is closed as a reverse operation of the opening direction of the control valve.

[Embodiments of the invention] The details of the present invention will be explained below with reference to the drawings.

FIG. 2 shows a reheat steam turbine plant to which the reheat steam turbine plant operating method of the present invention is applied, and in the figure, reference numeral 31 indicates a boiler. The steam generated in the boiler 31 passes through the main steam pipe 32 and passes through the main steam stop valve 33 and the steam control valve 34.
It flows into the high-pressure turbine 35 through the. The steam exhausted from the high-pressure turbine 35 passes through the check valve 37 of the low-temperature reheat pipe 36, is guided to the reheater 38, and is heated again. The steam passing through the reheater 38 is transferred to a high temperature reheating pipe 39
through the reheat steam stop valve 40 and reheat steam control valve 41
The steam passes through the reheat steam turbine 42 and then flows into the low pressure turbine 43. A generator 44 is connected to the shaft end of the low pressure turbine 43 .

Steam exhausted from the low-pressure turbine 43 flows into the condenser 45, where it becomes condensed water. The condensate flows into a deaerator 49 through a condensate line 48 in which a condensate pump 46 and a low-pressure heater 47 are provided. Deaerator 4
The water supply that has passed through 9 further flows into the boiler 31 again through a water supply line 51 in which a water supply pump 50 and a high-pressure heater 52 are disposed.

A high-pressure bypass line 53 connected to a low-temperature reheat pipe 36 branches off from the main steam pipe 32, and a high-pressure bypass valve 54 and a temperature reducing device 55 are disposed on this high-pressure bypass line 53. Further, in order to adjust the supply of hot water to the temperature reducing device 55, a high pressure spray line 56 and a high pressure bypass spray valve 57 are provided branching off from the water supply line 51.

Furthermore, a low-pressure bypass line 58 that bypasses reheated steam to the condenser 45 branches off from the high-temperature reheat pipe 39 . Low pressure bypass line 58 for adjusting the flow rate and pressure of this low pressure bypass line 58
A low-pressure bypass valve 59 is disposed at.

Furthermore, a temperature reducing device 60 for reducing the temperature of the bypass steam, a low pressure bypass spray valve 61, and a low pressure bypass spray line 62 branching from the condenser 45 are provided.

When steam is not passed through the high-pressure turbine 35, that is, when the steam control valve 34 is fully closed, the space between the low-temperature reheat pipe 36 at the outlet of the high-pressure turbine 35 and the condenser 45 is maintained in order to maintain a vacuum inside the high-pressure turbine 35. A steam dump line 64 equipped with a steam dump valve 63 is disposed at.

An embodiment of the method of operating a reheat steam turbine plant of the present invention using the reheat steam turbine plant configured as described above is carried out as described below.

That is, in the present invention, the steam supply to the high-pressure turbine 35 is cut off when the turbine is started, and the steam of the high-pressure turbine 35 is guided to the condenser 45 through the steam dump line 64 and the high-pressure turbine 35 is
Reheat steam is supplied to the reheat steam turbine 42 to drive the turbine, and then, when the high pressure turbine 35 takes a load, the opening degree of the steam dump valve 63 is adjusted to that of the steam control valve 34. The operation is performed in the opposite direction to the opening direction, and is gradually closed according to the opening degree of the steam control valve 34.

That is, as shown in FIG. 3, in which time is plotted on the horizontal axis and valve opening degree is plotted on the vertical axis, the steam control valve 34 begins to open at time _T0 , and at the same time the steam dump valve 63 moves as shown by straight line a. , start of closing time T ₂
It becomes fully closed.

The outlet pressure characteristics of the high-pressure turbine 35 when the steam dump valve 63 is fully closed is represented by curve b in FIG. 4, where the horizontal axis represents time and the vertical axis represents steam pressure.
As shown, although the rate of pressure rise is somewhat slow, the pressure suddenly rises just before time _T2 when the steam dump valve 63 is fully closed, and reaches the low-temperature reheat steam pipe pressure C.

Such a rapid pressure increase does not cause chattering when viewed from the perspective of the pressure relationship between the front and back of the check valve 37, which is a very desirable characteristic.

On the other hand, the amount of steam flowing in from the steam control valve 34 at time _T2 is already a sufficient flow rate, as is clear from the straight line d in FIG. flows inside the high-pressure turbine 35, and the temperature does not become abnormally high.

Here, the time T ₂ for the steam dump valve 63 to be fully closed
As long as the steam dump valve 63 is open, the condenser 4
It is desirable that the time is as short as possible, as steam will be wasted in the high-pressure turbine 35.
It is generally determined based on the relationship with the amount of cooling steam in the passenger compartment and the opening speed of the normal steam control valve 34.

However, as mentioned above, in order to minimize wasteful disposal of steam from the steam dump valve 63,
By using a temperature detector (not shown) or the like and a drive control device (not shown) of the steam dump valve 63, the casing temperature and the steam temperature at the exhaust port of the high-pressure turbine 35 are constantly monitored during startup of the turbine.
If the temperature is below the allowable value, the steam dump valve 63
Even if the steam dump valve 63 is in the closing operation, when these temperatures fall below the allowable value, the valve open signal is output again.
It is also possible to operate and operate the steam dump valve 63 so as to open it.

Note that a method of fully closing the steam dump valve 63 immediately before taking a load on the high-pressure turbine 35 is also considered, but in this case, the steam dump valve 63 is already fully closed before the steam control valve 34 opens. Because there are
When the steam control valve 34 gradually opens and steam flows into the high-pressure turbine 35, the check valve 37 is also fully closed and the casing of the high-pressure turbine 35 is sealed, so the high-pressure turbine outlet pressure follows the curve e in FIG. As shown, the steam pressure in the low-temperature reheat pipe is reached in a short period of T ₁ and the check valve 37 is fully opened, but the flow rate of steam flowing inside the high-pressure turbine 35 at this time, that is,
The amount of cooling steam is very small as shown by the straight line d in FIG.

Furthermore, a method can be considered in which the opening degree of the steam dump valve 63 is held constant until the exhaust pressure of the high-pressure turbine 35 rises to an arbitrary pressure, but in such a method, the steam dump valve 63 already remains at a constant opening degree. Since the steam control valve 34 is opened while the valve opening degree is maintained, the flow rate of steam flowing inside the high-pressure turbine 35 is sufficient to cool the casing.

In this case, the high pressure turbine outlet pressure characteristic as the flow rate increases from the steam control valve 34 is the curve f in FIG.
As shown in , the rate of increase is very slow, and especially around time T ₃ , the characteristic of being almost close to the reheat steam pipe pressure occurs for a long time. This means that if the outlet pressure of the high-pressure turbine 35 slightly fluctuates, the pressure before and after the check valve 37 will fluctuate, and there is a risk that a chattering phenomenon will occur in the check valve 37. The opening degree of the dump valve 63 is set in advance. Further, the timing for closing the steam dump valve 63 is such that the steam dump valve 63 is closed so that a chattering phenomenon does not occur.

[Effects of the Invention] As described above, in the method of operating a reheat steam turbine plant of the present invention, the reheat steam turbine is ventilated and started when the turbine is started, and then when the high pressure turbine takes a load, the high pressure turbine The opening of the steam dump valve installed between the casing of the high-pressure turbine and the condenser is set to operate in the opposite direction to that of the steam control valve. It is possible to effectively prevent thermal deformation caused by the heat deformation, and to provide a highly reliable reheat steam turbine plant.

[Brief explanation of the drawing]

FIG. 1 is a piping system diagram showing a conventional reheat steam turbine plant, and FIG. 2 is a piping system diagram showing a reheat steam turbine plant to which an embodiment of the reheat steam turbine plant operating method of the present invention is applied. , 3rd
The figure is a graph showing changes in valve opening, FIG. 4 is a graph showing changes in steam pressure, and FIG. 5 is a graph showing changes in flow rate of the steam control valve. 31... Boiler, 32... Main steam pipe, 33...
Main steam stop valve, 34... Steam control valve, 35... High pressure turbine, 36... Low temperature reheat pipe, 38... Reheater, 39... High temperature reheat pipe, 42... Reheat steam turbine, 43... Low pressure turbine, 53... High pressure bypass line, 58... Low pressure bypass line, 63
...Steam dump valve, 64...Steam dump line.

Claims (1)

[Scope of Claims] 1. A boiler having a reheater, a high-pressure turbine driven by main steam led from the boiler through a main steam pipe having a steam control valve, and exhaust gas from the high-pressure turbine to the reheater. a reheat steam turbine driven by reheat steam led from the reheater of the boiler through the high-temperature reheat pipe, and a reheat steam turbine that branches off from the main steam pipe to bypass the high-pressure turbine and A reheat steam turbine comprising: a high-pressure bypass line connected to a reheat pipe; and a steam dump line branching from the high temperature reheat pipe, bypassing the reheat steam turbine, and having a steam dump valve connected to a condenser. In the method of operating the plant, the supply of steam to the high-pressure turbine is cut off when the turbine is started, and the steam of the high-pressure turbine is guided to the condenser through the steam dump line, and the inside of the high-pressure turbine is brought into a vacuum state. When a reheat steam turbine is supplied with reheat steam to drive the reheat steam turbine and then the high pressure turbine takes a load, the valve opening of the steam dump valve is adjusted to prevent the high pressure turbine from overheating. A method of operating a reheat steam turbine plant, characterized in that the plant is closed as a directional operation and a reverse operation.