JPS599801B2 - Once-through boiler steam temperature control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a temperature control device for steam supplied from a boiler to a steam turbine in a steam turbine plant using a once-through boiler, particularly when the steam turbine is started.

Conventional once-through boilers tend to have a tendency for the steam temperature to rise too much, especially when starting cold, and the matching characteristics between the turbine metal part temperature and the steam temperature at the time of steam turbine startup are poor, causing excessive thermal stress in the turbine metal parts. This could lead to excessive turbine life consumption.

The purpose of the present invention is to increase the temperature of main steam or reheated steam by mixing low-temperature steam generated in a flash tank provided in the startup bypass system of a once-through boiler with main steam or reheated steam when starting a steam turbine. An object of the present invention is to provide a steam temperature control device for a once-through boiler, which lowers the temperature and supplies steam suitable for the temperature of a steam turbine metal part.

A feature of the present invention is that the low-temperature steam generated in the flash tank at the time of plant startup is mixed with the high-temperature steam that has passed through the boiler superheater or reheater, and the amount of low-temperature steam is adjusted. The goal is to create a suitable steam temperature.

An embodiment of the present invention will be described with reference to the drawings.

In the once-through boiler plant to which the present invention is applied, the boiler is operated by performing pre-ignition recirculation, then igniting the boiler, and
Circulating the steam generated in the secondary superheater 2 and the flash tank 9 to warm up the equipment of the power generation plant,
At the same time, the pressure in the flash tank 9 is increased.

The flow of steam and water at this time is as follows.

'The steam that has passed through the primary superheater 2 passes through the pipe 21 to the 2
It then passes through the superheater bypass valve 11 and enters the flash tank 9.

At the same time, a portion of the heated water sent to the primary superheater 2 through the water wall 1 enters the flash tank 9 through the primary superheater bypass valve 10 through the piping 22.

These steam and superheated water are mixed in the flash tank 9 to become low-temperature steam, which is then passed through the condenser 15 through the piping 23.
The condensed water is sent to the deaerator 16 and the high-pressure feedwater heater 17, and is sent to the water wall 1 again through the water supply pipe 8.

(The condenser, deaerator, and high-pressure feedwater heater are not shown.) When the pressure in the flash tank 9 reaches 7 atg, the low-temperature steam generated in the flash tank 9 is released to warm up the main steam pipe 4. The steam is guided through the pipe 24, passed through the superheater vent valve 12, heated in the secondary superheater 3, and then passed into the main steam pipe 4.

It is then led to the condenser through the turbine bypass valve 13.

As the main steam pipe 4 warms up, the main steam is gradually vented into the steam turbine 6 through the turbine main blocking valve bypass valve 5 and the turbine control valve 19.

Usually, at this time, the temperature of the main steam is too high compared to the temperature of the metal parts of the steam turbine 6.

For this reason, in the present invention, a pipe 25 is provided that connects the flash tank 9 to the main steam pipe 4 on the downstream side of the superheater 3, and a main steam temperature control valve 18 is installed in the middle of the pipe 25 to control the low-temperature steam generated in the flash tank 9. It is mixed into the main steam in the main steam pipe 4 through this main steam temperature control valve 18 .

By controlling the amount of low-temperature steam mixed into the main steam through the pipe 25 using the main steam temperature control valve 18, it is possible to create a main steam temperature suitable for the temperature of the metal part of the steam turbine 6.

These main steam temperature control devices at startup can produce main steam with a temperature suitable for the steam turbine. By supplying this main steam to the steam turbine, thermal stress in the turbine metal parts can be reduced. This has the effect of significantly improving the life consumption of the steam turbine.

[Brief explanation of drawings]

FIG. 1 is a startup system diagram of a steam turbine plant equipped with a once-through boiler, which is an embodiment of the present invention. Explanation of symbols, 1... water wall, 2, 3...
Superheater, 4... Main steam pipe, 6... Steam turbine, 9... Flash tank, 18...
...Main steam temperature control valve, 24, 25...Piping.

Claims (1)

[Claims] 1 A once-through boiler is equipped with a boiler startup flash tank that introduces a portion of water or steam from the middle of the boiler, and a pipe from the flash tank that introduces steam from the final superheater or reheater of the boiler to the steam turbine is provided. A steam temperature control device for a once-through boiler, characterized in that piping for mixing low-temperature steam is connected to the piping, and a control valve for adjusting the flow rate of the low-temperature steam is provided in the middle of the piping.