JPS6088804A - Warm-up device for steam turbine - Google Patents

Abstract

PURPOSE:To check an internal thermal stress in time of steam turbine starting and thereby prolong service life in a turbine, by extracting low temperature steam in the middle course of heating from a heating part of a steam generator, while making it mixable in high temperature steam in a main steam pipe. CONSTITUTION:Low temperature steam in the middle course of heating is so constituted as to make it mixable in a main steam pipe 7 leading steam into a high pressure turbine 17 from an evaporator 4 of a steam generator 3 through a low temperature steam pipe 25. In time of turbine starting, a mixed amount of the low temperature steam is controlled by a low temperature main steam control valve 27 whereby main steam is made to drop its temperature to some extent and fed to the turbine 17, thus an internal thermal stress is relieved.

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a warm-up device for a steam turbine, and in particular, the present invention relates to a warm-up device for a steam turbine, and in particular, a low-temperature steam pipe is provided to guide low-temperature steam to a steam turbine from the middle of a heating section of a steam generator. The present invention relates to a warm-up device for a steam turbine that can suitably warm up the inside of a casing of a turbine.

[Technical background of the invention]

Generally, when starting a steam turbine cold, it is important from the viewpoint of safe operation to raise the temperature of the rotor to a temperature higher than the transition temperature of the material to enter the ductile region and to eliminate any risk of brittle fracture. For this reason, for example, a steam turbine in a thermal power plant has conventionally been started according to the operating procedure shown in FIG. First, before starting the turbine, a prewarming device installed in the steam turbine warms up the steam turbine and raises the rotor temperature above the transition temperature. After that, main steam from the steam generator is pumped into the steam turbine. The rotor is caused to flow in at a flow rate, and as shown in diagram I, the rotor rotational speed is increased to a certain rotational speed below the rated rotational speed in a no-load state (la).

After the rotation speed is maintained at that rotation speed for a certain period of time (I'fi), when the turbine internal temperature rises to a certain extent as shown by the diagram (■), the rotor rotation speed is increased to the rated rotation speed (Ic). Further, after maintaining the rated rotational speed for a certain period of time (Id), the load is increased in stages as shown in diagram 1.

[Problems with background technology]

However, in this type of operation, a large temperature difference occurs between the turbine internal temperature (diagram 1), which is warmed up by the prewarming device before the turbine is started, and the main steam temperature (diagram IV). Furthermore, the turbine was to be started with that temperature difference maintained. As a result, large thermal stress is generated in the turbine rotor, turbine row cinder, etc., and the life of the turbine is severely shortened by this thermal stress. Furthermore, Figure 2 shows the relationship between the thermal stress generated inside the turbine (horizontal axis) and the turbine life (vertical axis), and it can be seen from this figure that the turbine life rapidly decreases as the thermal stress increases. .

Furthermore, in this type of operation, the rotation speed (diagram I) of the steam turbine cannot be suddenly increased due to the relationship with internal stress, and as mentioned above, during the increase in rotation, a predetermined holding period (
1b), it takes time for the rotation to increase, and accordingly, the time to start applying a load has to be delayed.

[Purpose of the invention]

The present invention eliminates the drawbacks of the conventional steam turbine warm-up device, reduces the high thermal stress that occurs when starting the steam turbine cold, greatly extends the life of the steam turbine, and shortens the initial load start time. It is an object of the present invention to provide a warm-up device for a steam turbine that can perform the following steps.

[Summary of the invention]

In order to achieve the above object, the steam turbine warm-up device according to the present invention branches a low-temperature steam pipe that leads out the low-temperature steam that is being heated from the heating section of the steam generator to the outside, and The steam turbine is characterized by connecting a main steam pipe that leads high-temperature main steam to the steam turbine so that low-temperature steam can be mixed into the high-temperature main steam, and the steam turbine is connected to a main steam pipe that leads high-temperature main steam to the steam turbine so that low-temperature steam can be mixed into the high-temperature main steam. The temperature of the steam flowing into the turbine is adjusted to decrease.

[Embodiments of the invention]

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Fig. 3 shows an example in which the present invention is applied to a thermal power plant, but the basic cycle is the same as that of the conventional one, and the water is supplied to the steam generator 3 through the water supply pipes by the water supply pump l. The water to be supplied is vaporized by the evaporator D of the steam generator 3, then superheated by the seventh heater 5 and the λ heater B, and then passed through the main steam pipe to the main steam stop valve g and the main steam control valve. It is guided through the valve into the high pressure turbine/7.

The exhaust gas of the high-pressure turbine 1/1 is led into the steam generator 3 again and reheated through the reheat primary heater/co and the reheat co-secondary heater/3, and is then reheated by the reheat main steam pipe/1. It is guided into the intermediate pressure turbine 17 through the reheat main steam stop valve/S and the reheat main steam control valve 16. Furthermore, the intermediate pressure turbine 17
The exhaust gas is led to a low pressure turbine ig to perform final expansion work, then flows into a condenser/9 where it is condensed and is again sent to the steam generator 3 as feed water.

In the evaporator da of the steam generator 3, the seventh
As shown in the figure, the water supply pipe is directly connected to the economizer 2/, and further reaches the final evaporator 23 through the heating evaporation pipe 2,
The outlet of this final evaporator 23 is a primary heater that generates superheated steam through a water separator. and connected to the a-th heater B. This allows the superheated steam to be fed to the high pressure turbine // through the main steam pipe 7.

In addition, a low-temperature main steam pipe is branched from the outlet of the water separator inserted between the final evaporator blade and the primary heater S, and the low-temperature steam before being superheated is transferred to this low-temperature steam pipe. It is designed to be led out of the vessel through the main steam pipe. Furthermore, this low-temperature main steam pipe 8 is connected to the high-pressure turbine inlet portion of the main steam pipe 7, so that the low-temperature steam led by the low-temperature main steam pipe J can mix with the high-temperature steam in the main steam pipe. It has become. Further, a low temperature main steam stop valve roller and a low temperature main steam control valve 27 are provided in the middle of the low temperature steam pipe 2&, and these enable feeding, stopping, and flow rate adjustment of the low temperature steam. .

Furthermore, as shown in Fig. 3 and Fig. S, the low-temperature reheat main steam pipe The low-temperature reheated steam before entering the heater 13 is led out of the vessel. This low-temperature reheat main steam pipe 2g is connected to the reheat main steam pipe/lIO intermediate pressure turbine inlet section, and a low-temperature reheat main steam stop valve 9 and a low-temperature reheat main steam stop valve 9 and a low-temperature reheat main steam stop valve A main steam control valve 3/ is provided.

Further, the opening degrees of the low temperature main steam control valve 27 and the low temperature reheat main steam control valve 3/ are adjusted by the valve control devices 3 and 33. The valve control devices 3 and 33 receive internal temperature signals S from the high pressure turbine// and the intermediate pressure turbine/7, and 8. In response to the temperature signals 8° and S4 in the main steam pipe and reheat main steam pipe, respectively, the main steam control valve 9 and the low temperature main It has a function of issuing valve open signals S, s6, 8f and Ss to the steam control valve 27, the reheat main steam control valve/6 and the low temperature reheat main steam control valve 31, respectively. With this, each valve 9. Ko? , /A, 3/ are opened to an appropriate opening degree, high temperature steam and low temperature steam are mixed, and the turbine inflow temperature can be lowered to an appropriate temperature.

Such a steam turbine warm-up device is operated as shown in Figure 6, for example. Although FIG. 6 is explained using a high-pressure turbine as an example, the same applies to an intermediate-pressure turbine. First, the turbine inflow steam temperature represented by diagram A is determined by the main steam control valve so that #1 is an intermediate temperature between the main steam temperature represented by the broken line and the turbine internal temperature represented by diagram C.
The opening degree of the low temperature steam control valve 27 is adjusted. This intermediate temperature is set so that the thermal stress generated in the turbine rotor and the turbine rotor is equal to or less than a predetermined value. Note that during prewarming, main steam does not flow into the turbine, but each valve mentioned above does not flow into the turbine. and 27 are prepared in advance to have appropriate opening degrees.

As the turbine is started, the temperatures A, C, and C gradually rise, and converge to the same temperature after the rated load. In this case, conventionally, the turbine inlet temperature is the main steam temperature A itself, and the temperature difference between this turbine inlet temperature A and the conventional turbine internal temperature represented by the broken line diagram is very large, and the temperature difference that occurs inside the turbine is very large. The thermal stress also remains large, whereas in the device according to the present invention, the turbine inlet temperature A is always maintained lower than the main steam temperature port, and the difference between the two temperatures remains small. do. Therefore, thermal stress generated inside the turbine can also be suppressed.

Furthermore, since the thermal stress inside the turbine is suppressed to a small level in this way, in the present invention, the rotation speed of the turbine rotor can be increased almost linearly as shown by j in the diagram, and There is no need to provide a period during which the rotational speed is maintained on the way to the secondary (flat part) represented by .

In addition, since the turbine rotor rotational speed can be increased to the rated rotational speed in a short time, the load can be applied earlier as shown in the diagram (T), unlike the conventional method (dotted line (T)). There is no need to delay the initial load start time. [Effects of the Invention] As described above, the steam turbine D warm-up device according to the present invention leads out the low-temperature steam during heating from the heating section of the steam generator. At the same time, the low-temperature steam pipe is connected to the main steam pipe that leads the high-temperature main steam from the outlet of the steam generator to the steam turbine. Since it is possible to lower and adjust the temperature of the steam entering the turbine by mixing Φ, it is possible to reduce the thermal stress when the steam turbine's cold engine starts, and to extend the life of the steam turbine's casing, rotor, etc. Can be extended to nails. In addition, by reducing thermal stress, it is possible to accelerate the initial load start time. Can be shortened.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the start-up operation state of a conventional steam turbine using a warm-up device, Fig. 2 is a diagram showing the relationship between the internal thermal stress of the steam turbine and its service life, and Fig. 3 is a diagram showing the steam turbine according to the present invention. System explanatory diagram showing the warm-up device, Figure 1 and Figure S
The figure is an enlarged system explanatory diagram of the inside of the steam generator, and FIG. 6 is a diagram showing the starting operation state by the steam turbine warm-up device of the present invention. 3...Steam generator, D...Evaporator, S...7th heater, 6...Secondary heater, 7...Main steam pipe, I/...
...High pressure turbine, /co...Reheat primary heater, 13.
... Reheat co-heater, 17... Medium pressure turbine, 23.
...Final evaporator, J...Low temperature main steam pipe, 2g...Low temperature main steam reheat pipe, 32, 3.3...Valve control device. Figure 4, item 65

Claims (1)

[Scope of Claims] /) A main pipe that branches a low-temperature steam pipe that leads out the low-temperature steam that is being heated from the heating section of the steam generator to the outside of the steam generator, and that leads high-temperature main steam from the outlet of the steam generator to the steam turbine. A warm-up device for a steam turbine, characterized in that the low-temperature steam pipe is connected to a steam pipe so that low-temperature steam can be mixed with high-temperature main steam. 2) The low-temperature steam pipe is branched from a pipe line connecting an evaporator that vaporizes feed water and a heater that generates superheated steam, and a pipe line midway through the reheating section. The steam turbine warm-up device according to item 1.