JPS60145407A - Reheating type steam turbine plant - Google Patents

Abstract

PURPOSE:To prevent consumption of a turbine life, by setting a temperature detector with which the temperature of steam exhausted from a high pressure turbine is detected, and operating a low pressure turbine bypass valve as it opens at the specific time. CONSTITUTION:In a reheating type steam turbine plant, a high pressure bypass system and a low pressure bypass system are set. In the way-out of a high pressure turbine 5, a temperature transmitter 26, with which the temperature of exhaust steam is detected, is set. When the temperature of steam exhausted from the high pressure turbine 5 becomes higher, output of the temperature transmitter 26 increases, and output of an adder 27 decreases. This output is compared with a hot reheated steam pressure signal 23, through a high value gate 22, and a low pressure bypass valve 17 is operated as it operated as it opens by an adder 24 and an actuator 25. In this way, the temperature of steam exhausted from the high pressure turbine 5 becomes lower, and consumption of the turbine life can be prevented.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] [Technical Background of the Invention and Problems Therewith] The configuration of a conventional reheat steam turbine facility will be explained with reference to FIG. Main steam leaving the boiler 1 enters the high pressure turbine 15 via the main steam pipe 2, main stop valve 3, and steam control valve 4, and after doing work, passes through the low temperature reheat check valve 7 and the low temperature reheat steam pipe. After being reheated, it enters the low pressure turbine 12 via the high temperature reheat steam pipe 9, reheat steam stop valve 10 and intercept valve 11, and after doing work, it enters the condenser 13. is discharged.

A recent trend in such steam turbine equipment is to install a turbine bypass device to ensure stable boiler combustion and reduce turbine thermal stress during startup. In other words, in Figure 1, at startup, the main steam generated from the boiler is
After passing through the high-pressure turbine bypass pipe 14 and being depressurized and temperature-reduced at the high-pressure turbine bypass valve 15, it enters the high-temperature reheat steam pipe 9, further depressurized and temperature-reduced by the low-pressure bypass pipe 16 and low-pressure bypass valve 17, and then returned to the high-pressure turbine bypass pipe 14. It is discharged into the water container 13.

At this time, the internal pressure of the reheat steam pipe is usually maintained at about 8 kg/an2 in consideration of the diameter of the low-pressure bypass valve and economic efficiency. That is, the reheat steam pressure is controlled by a low pressure bypass valve, and the method will be explained with reference to FIG. Since the high pressure turbine first stage outlet pressure is proportional to the turbine load in normal operation, this is detected by the pressure transmitter 20 and the adder 21 uses the low pressure bypass valve 17 to detect the high pressure turbine first stage outlet pressure.
The set pressure is set to be slightly higher than the reheat pressure during normal operation, that is, the pressure is higher by P in FIG.

This controls the reheating pressure during load fluctuations, but when the load is low, for example when the boiler load is high during turbine 2 trip, there is a large amount of surplus steam, and it is necessary to flow this to the condenser 13 using the low pressure bypass valve 17. . At this time, low pressure bypass valve 1
In order to set the 70mm diameter to an appropriate size, the minimum pressure of the reheater during bypass operation (Pm1n in Figure 3) is set and input to the high value gate 22, resulting in a low pressure bypass as shown in Figure 3. Set the valve setting pressure. This set pressure is compared with the high temperature reheat pipe pressure, and the output signal of the adder 24 is used as the bypass valve set pressure to operate the actuator 25 of the low pressure bypass valve.

The minimum pressure Pmin of the reheater is determined by considering the following equation. That is, the higher the minimum pressure Pm1n is, the smaller the diameter of the low-pressure bypass valve 17 is, which is more economical, but there is a reason why Pm1n cannot be made unnecessarily high, considering the high-pressure turbine exhaust temperature at the time of turbine startup.

Normally, when starting the turbine without using the high pressure bypass valve 15 or the low pressure bypass valve 17, the reheat steam pressure valve 10,
Since the intercept valve 11 is fully open, the inside of the turbine unit after the main blocking valve 3 is in a vacuum like the condenser 13. When starting the turbine in this state, the main stop valve 3
A built-in width valve is used to control the steam flow rate, but when the turbine is under no load or low load, the pressure inside the turbine remains in a clean air area, and the turbine blades rotate in a vacuum.

On the other hand, when starting the turbine while using the high pressure bypass gt5 or the low pressure bypass valve 17, the reheat pressure is the lowest pressure Pm1n.
Therefore, the sub valve and reheat valve 10 built into the main city valve 3
Alternatively, the steam flow rate is controlled using the sub-valve built in 11.

At this time, the pressure inside the turbine, particularly the pressure inside the high-pressure turbine, becomes a pressure higher than the reheat pipe minimum pressure Pm1n, and the blades of the high-pressure turbine rotate in high pressure, that is, high-density steam.

On the other hand, when the turbine is under no load or under low load, the steam flow rate is small, so a phenomenon occurs in which the high pressure turbine exhaust temperature increases due to windage loss of the turbine blades.

The windage loss of a turbine blade increases as the blade height, circumferential speed, radius of rotation, and steam density increase, and decreases as the steam flow rate, that is, the amount of cooling steam increases. Therefore, although the high-pressure turbine exhaust temperature decreases as the turbine load increases, a phenomenon occurs in which, for example, when the turbine is operated continuously without load, the temperature becomes about 100° C. higher than the temperature at the rated maximum load. For this reason, the design temperature of the low-temperature reheat steam pipe and check valve 7 at the exit of the sitapino, which increases the turbine life consumption due to thermal stress, becomes high. Conventionally, the turbine exhaust temperature under such conditions was determined by experience or calculation. As mentioned above, the minimum reheat pressure P min has been set in consideration of the appropriate diameter of the low-pressure bypass valve.

In this conventional method, the minimum reheating pressure P m f n was set based on past experience and calculations, so when the turbine was actually operated, there was still room for the opening degree of the low pressure bypass valve 17. However, since the reheating pressure is too high, the turbine exhaust temperature rises and the turbine life is unnecessarily consumed due to thermal stress, which causes the inconvenience of exceeding the design temperature of the check valve 7.

[Purpose of the invention]

The purpose is to

The system detects the temperature and when the exhaust temperature becomes higher than a predetermined temperature, the low pressure bypass valve is opened in the opening direction to lower the reheat steam pressure and lower the high pressure turbine exhaust temperature. do.

[Embodiments of the invention]

The present invention will be described below with reference to an embodiment shown in FIG.

In FIG. 4, the same parts as those shown in FIG. 2 are designated by the same reference numerals, and their explanation will be omitted. A signal from a temperature transmitter 26 provided at the outlet of the high pressure turbine 15 for detecting temperature is supplied to an adder 27 as a back signal. The adder 27 is also set with a predetermined value T1 of the high pressure exhaust temperature, and the output of the adder 27 is supplied to one of the low value gates 28. The other side of the gate 28 has a reheat minimum pressure P
A signal of min is supplied, and the output of the gate 28 is outputted as P min to one of the high gates 22. The output of this gate 22 is supplied to an adder 24.

When the high pressure turbine exhaust temperature reaches 10,000 yen, the output of the temperature transmitter 26 increases and the output of the adder 27 decreases. When the high pressure exhaust temperature exceeds a predetermined value T, the signal from the adder 27 is lower than the conventionally used minimum reheating pressure Pm1n signal. will begin to produce. This output is passed through a high value gate 22 and compared with a high temperature reheat steam pressure signal 23;
The opening degree of the multi-low pressure bypass valve 17 is operated in the opening direction by the addition@24 and the actuator 25.

By this method, the pressure in the reheat steam pipe is lowered to the pressure P m I n corresponding to the output of the low value gate 28, and the steam density in the high pressure turbine blades is lowered, making it possible to lower the high pressure turbine exhaust temperature.

〔Effect of the invention〕

In view of the above, according to the present invention, the ability of the low pressure bypass valve is effectively utilized to reduce the temperature change at startup.

[Brief explanation of the drawing]

Figure 1 is a piping system diagram of a conventional reheat steam turbine plant, Figure 2 is a configuration diagram showing a conventional low-pressure bypass valve control device, and Figure 3 is a graph showing the set pressure characteristics of a conventional low-pressure bypass valve. FIG. 4 is a configuration diagram showing a low-pressure bypass valve control device for a reheat steam turbine plant according to the present invention, and FIG. 5 is a graph showing the low-pressure bypass valve setting characteristics of the present invention. 1...Boi':) 5...High pressure turbine 8...Reheater 9...High temperature reheat steam pipe 12...Low pressure turbine
13...Condenser 14...High pressure turbine bypass pipe 15...High pressure turbine bypass valve 16...Low pressure turbine bypass pipe 17...Low pressure turbine bypass valve 20...Pressure transmitter 21...Addition Vessel 22
...High price gate 23...Pressure transmitter 24
... Adder 25 ... Actuator (8)

Claims (1)

[Claims] In reheat steam turbine plants equipped with a high-pressure bypass system and a low-pressure bypass system, a temperature detector is installed to detect the exhaust temperature of the high-pressure turbine, and when the high-pressure turbine exhaust temperature exceeds a specified temperature, , a reheat steam turbine plant characterized by operating a low-pressure turbine bypass valve in the opening direction.