JPS63179102A - Warming method for steam turbine - Google Patents

Abstract

PURPOSE:To suppress thermal stress occurring in a turbine rotor, by predicting the temperature of steam in the downstream of first stage based on the temperature at the inlet of a steam turbine, and heating a metal in the downstream of the initial stage if the temperature of said metal is lower than said predicted temperature. CONSTITUTION:Steam is fed from a boiler through a steam regulation valve 4 to a high pressure turbine. Here, thermal stress of rotor is most concentrated in the downstream of a first stage. In order to heat said portion near to the temperature at the inlet of steam and to reduce the temperature difference, a steam inlet valve 1 is opened prior to starting so as to lead high temperature steam thus warming the first stage of turbine. Warmed steam is fed through a steam outlet valve 2 to a condenser. Here, a check valve 5 at an exhaust section of the high pressure turbine and a ventilator valve 6 are closed. Control signal for the steam valve in a warming system is set on the basis of a target warming temperature corresponding to a starting pattern which is determined on the basis of measurement of a thermometer 3.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to the reduction of thermal stress during startup of a steam turbine rotor in a commercial thermal power plant.

[Conventional technology]

A well-known example is ``Steam Turbine Warming Method'' (
In Japanese Patent Publication No. 58-17329), due to rapid evaporation of condensate accumulated in the lower part of the high-pressure turbine casing,
In order to prevent ambient heat being taken away and a temperature difference occurring in the casing, causing thermal stress, the pressure during warming is controlled to prevent condensate from stagnation. In this example, the purpose of the present invention is to prevent the casing from cooling properly, and the warm-up temperature target has been revised to 150°C. are different.

[Problem that the invention seeks to solve]

In steam turbines, those with stable operability are:
The combined stresses caused by pressure and heat in the main valves and the casing, as well as the centrifugal force and thermal stress in the rotor, are kept at relatively low values, so the fatigue life of these parts is almost negligible. During transient operating conditions such as stop load changes or emergency operations, large thermal stresses are superimposed on pressure-induced stress for the casing and valves, and centrifugal force-induced stress for the rotor. If such transient operating conditions are extremely severe, high-temperature parts such as the valve number, the casing, and the rotor will yield, resulting in fatigue, which will reduce the life of the valve.

The thermal stress that causes cracks on the rotor surface can be caused by the following three transient states: 1) cold start, 2) warm restart, and 3) large load changes.

However, the warm-up method used for high-pressure turbines is
Set the rotor metal temperature to around 150℃.

By simply raising the temperature, the temperature difference (mismatch) between the steam temperature and metal temperature during turbine ventilation was reduced.

However, in recent years, with the rise of nuclear couplants, the operating method of thermal power plants has been changing from base-load to middle-load. In other words, the operation method such as starting and stopping every day and stopping on weekends depends on the turbine metal temperature and 1. This creates a difference in steam temperature on the boiler side. This is due to the difference between the heat capacity of the boiler and the turbine, so even if the turbine is stopped at the same time, the turbine cools down faster than the boiler, and at the time of primary startup, the turbine metal temperature will exceed 150℃. This is because the turbine metal temperature is lower than the steam temperature from the boiler even when there is no need for warming up. In other words, when starting up and stopping every day or quickly starting up after stopping on weekends, a starting method must be adopted that takes the amount of mismatch into account, and time constraints must be placed on the starting method.

FIG. 2 shows typical main steam, reheat steam temperatures and corresponding post-first stage temperatures in relation to load. A special case is the turbine load.

When changing from 15% to full load (100%).

The temperature of the casing after the first stage changes by about 150°C.

FIG. 3 shows the main steam temperature and the temperature change of the turbine rotor after the first stage for a given load change rate. In the case of cold-slide starting, the temperature of the rotor surface and inner hole is approximately room temperature (if warm-up is performed, the temperature will be the same as when warm-up is completed).The turbine rotates and takes on a load. The temperature of the inner bore of the rotor rises with a delay, resulting in a significant temperature difference between the rotor surface and the inner bore, which generates thermal stress.

The stress on the rotor surface causes compressive stress because the steam temperature is initially higher than the rotor surface temperature. Namely.

The material on the surface of the rotor tends to expand as the temperature rises, but the temperature of the material inside the rotor is low.

This is because expansion is hindered. If the start-up is too severe, the material on the rotor surface will yield due to compression, creating residual tensile stresses when the turbine reaches steady state at full load. Unless yielding of the material in the rotor bore occurs, it will initially be under tension and will reach a steady state and reduce to zero. Repeated harsh cycles exhaust the life of the material and eventually cause it to crack. The faster the rate of change in the rotor surface temperature and the greater the amount of change, the greater the temperature difference between the surface and the inner hole, and the greater the thermal stress. Also, the larger the diameter of the rotor, the greater the thermal stress and the greater the cycle life consumed.

Conventionally, in order to reduce the thermal stress of the rotor,
Warm up the rotor during turning operation.

In other words, steam is guided into the high-pressure turbine from a high heat source such as main steam or auxiliary steam to warm up parts such as the casing, rotor, and diaphragm that make up the high-pressure turbine.
Normally, warming up during turning is done by establishing ground steam,
It starts as soon as the condenser vacuum rises. After the internal pressure of the high-pressure casing reached approximately 4 kg/J and the temperature of the inner wall after the first stage reached 150° C., warm-up was further performed for about a working time.

[Means for solving problems]

In the conventional rotor warm-up, a control method was adopted that aimed for the metal temperature to be 150°C, so warm-up was performed every day when the metal temperature was 150°C or higher, such as during startup after a final stop. Even when this was not done, a mismatch between the steam temperature and metal temperature occurred, and the startup method was regulated.

As shown in Figure 1, a warm-up system is installed in the first stage of the high-pressure turbine to warm up the first stage to a target temperature depending on the startup mode to minimize mismatch, thereby reducing thermal stress on the rotor. By the warm-up method according to the present invention, which makes it possible to heat the first stage portion of the high-pressure turbine to around the ventilation temperature.

[Effect]

In FIG. 1, the warm-up system includes steam inlet valve 1, steam outlet valve 2. It is composed of a thermometer 3.

Prior to startup, open the steam inlet valve 1 to introduce high-temperature steam,
The control signal for the steam valve of the 0-stage machine system that heats the first stage of the high-pressure turbine to the steam turbine inlet temperature is
Based on the measurement results, the warm-up target temperature is determined according to the startup pattern.

〔Example〕

Steam from a boiler is supplied to the high pressure turbine through a steam control valve 4.

Since the part where the rotor thermal stress is the most severe is after the first stage, this part is heated to around the steam inlet temperature.'5. , ! In order to heat the turbine and reduce the temperature difference, the first stage of the turbine is warmed up from a high-temperature steam source through the limit steam inlet valve 1, and the steam after warming up is passed through the steam outlet valve to the condenser.
The check valve 5 and ventilator valve 6 of the high-pressure turbine exhaust section are kept closed.

As shown in FIG. 2, the temperature after the first stage varies significantly depending on the turbine load, varying from about 350° C. at 20% load to about 500° C. at 100% load. The difference is 1
It's 50℃. Therefore, after the first stage, in order to reduce the thermal stress due to the temperature difference between the steam temperature and the temperature of the metal after the first stage immediately after ventilation, the warm-up system is operated before ventilation to raise the metal temperature after the first stage to 350°C. Let it warm up to a certain temperature.

In addition, if rapid startup is required, the metal temperature after the first stage should be set to 35
By operating the warm-up system so that the temperature rises above 0℃, it is possible to rapidly start the turbine until the amount of mismatch turns positive, that is, until the load where the value obtained by subtracting the metal temperature from the steam temperature becomes positive. 0 For example, if the metal temperature after the first stage is warmed up to 400°C, the load will rise rapidly up to 35% [Effects of the Invention] According to the present invention, the difference between the steam temperature and the metal temperature can be reduced. Therefore, the temperature gradient inside the turbine rotor can be made gentler. Therefore, thermal stress generated in the turbine rotor can be minimized.

It also extends from the steam control valve to the turbine inlet. It is also possible to warm up the casing.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of an embodiment of the present invention, FIG. 2 is a temperature characteristic diagram with respect to turbine load, and FIG. 3 is a diagram showing a qualitative relationship between rotor temperature and thermal stress during cold engine startup. 1... Steam population valve, 2... Steam outlet valve, 3... Thermometer. 4... Steam control valve, 5... Check valve, 6... Ventilator valve.

Claims (1)

[Claims] 1. When starting the steam turbine, predict the steam temperature after the first stage of the turbine from the inlet steam temperature of the steam turbine, and compare it with the metal temperature after the first stage, and if the metal temperature after the first stage is low; A method for warming up a steam turbine, comprising heating the metal after the first stage.