JPS60159311A - Starting method for steam turbine - Google Patents

Abstract

PURPOSE:To suppress the thermal stress and thereby prolong the life of a steam turbine by allowing the steam with lower temp. than that of the main steam to flow to the downstream of a steam adjuster valve, in case the high pressure turbine is in cool state after the middle pressure turbine is started, and thereby warming up the high pressure turbine. CONSTITUTION:In this steam turbine, an electric generator 1 is coupled with a low pressure turbine 2, a middle pressure turbine 3 and a high pressure turbine 4. In driving the middle pressure turbine, a steam adjusting valve 9 is held closed when turbine is started, and the speed is raised by supplying the steam only to the middle and low pressure turbines 3, 2. The exhaust side of high pressure turbine 4 is coupled with a condenser 17 through a ventilator valve 18 so as to put inside the high pressure turbine 4 in a vacuum. Here the middle pressure turbine 3 is coupled with the downstream of said steam adjuster valve 9 through a connecting pipe 20 fitted with a warming valve 19. This warming valve 19 is so controlled as to open when the steam adjuster valve 9 is closed in case the high pressure turbine 4 is in cool condition after the start loading has gone out.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for starting a steam turbine applied to a steam turbine power generation plant or the like.

[Technical background of the invention]

In recent years, with the increase in the number of coal-fired boilers and the intermediate load operation of thermal power plants, many steam turbines for power generation plants are equipped with a so-called turbine bypass function that allows main steam to flow through the turbine bypass flow path. There is. In addition, the adoption of such turbine bypasses extends from small-capacity machines to large-capacity machines, and from low-pressure plants to high-pressure plants, and the scope of its application tends to gradually expand.

However, as turbine bypass systems have come to be applied to large-capacity, high-pressure plants, the conventional turbine startup method of simultaneously injecting steam into the high-pressure turbine and medium- and low-pressure turbines has become difficult to operate when switching from turbine bypass operation to turbine startup. The problem arises that the exhaust temperature of the high pressure turbine increases, increasing the thermal stress on the rotor and impairing its service life.

For example, FIG. 1 shows an example of a turbine system to which a conventional startup method is applied. That is, a low pressure turbine 2, an intermediate pressure turbine 3, and a high pressure turbine 4 are connected to a generator 1 as a turbine load.

The zein 5 is provided with a superheater 6 and a reheater 7, and a main steam system 4a to a high pressure turbine 4 having a main steam stop valve 8 and a steam control valve 9 is connected to the superheater 6. Main steam line 4a as well as high pressure bypass valve 10 and desuperheater 1
1 is connected to bypass the high pressure turbine 4. The steam outlet of the high pressure turbine 4 is connected via a check valve 12 to the reheater 7 of the zein 5 together with the high pressure pipe/e gas system. A low pressure reheat steam system 3a is connected from the reheater 7 to an intermediate and low pressure turbine 2.3 via an intercept valve 13 and a reheat stop valve 14, and has a low pressure bypass valve 15 and a desuperheater 16. A condenser 17 is connected via a low-pressure bypass system 15at''. During turbine bypass operation, high-pressure steam from the heater 6 flows into the reheater 7 via the high-pressure bypass valve 10 and the desuperheater 11. It becomes low-pressure steam and is recovered to the condenser 17 via the low-pressure bypass valve 15 and the desuperheater 16. In this case, the high-pressure bypass valve 1o and the low-pressure pipe/e gas valve 15 adjust the primary steam pressure to the design pipe. /e The pressure is controlled to a constant value corresponding to the flow rate of the steam.When starting the turbine from such a turbine bypass operation, the steam control valve 9, reheat stop valve 14, and intercept valve 13 are gradually opened. Steam flows through the high-pressure turbine 4, intermediate-pressure turbine 3, and low-pressure turbine 2 to increase their speed.The high-pressure bypass valve 10. and the low-pressure bypass valve 15 each control the primary pressure to a constant level, so their opening degrees vary depending on the steam flow. It decreases as the control valve 11 or the reheat stop valve 14 opens.

Then, when the turbine rotation speed reaches the rated value, the steam control valve 11 and the intercept valve 13 are opened.
High pressure bypass valve8. The low-pressure bypass valve 15 is fully closed, the turbine pi-seven operation ends, and the rated load is soon reached.

The above-described conventional starting method for starting a high- or intermediate-pressure turbine has the following problem when the turbine is at rated rotation and immediately before merging, when it is in an unloaded state.

That is, the steam that has flowed into the intermediate pressure turbine 3
．． After sufficient work has been done in the low-pressure turbine 2, it is recovered in the condenser 17, and there is no particular difference from normal operation without turbine bypass operation. However, on the high-pressure turbine 4 side, the low-pressure bypass valve 15 maintains the outlet pressure of the low-temperature reheat line check valve 2 at a pressure equivalent to the designed steam amount, so the high-pressure turbine 4 exhaust pressure This is considerably higher than in normal operation without turbine bypass operation. The high-pressure turbine 4 is rotated at high speed with high exhaust pressure and low flow rate. Under such conditions, the steam cannot expand sufficiently and the windage loss increases, so the temperature of the high-pressure turbine 4, especially the temperature on the exhaust side, rises excessively, causing elongation of each part of the high-pressure turbine 4, an increase in the difference in elongation, and resulting in increased thermal stress. In particular, the surface thermal stress of the rotor in the high-pressure exhaust section adversely affects the life of the rotor.

As turbines become more popular, steam becomes hotter and more pressurized, and bypass capacity increases, the above situation becomes even more severe. Therefore, the high-pressure turbine 4 generated by the conventional high- and intermediate-pressure turbine startup
An intermediate-pressure turbine drive method was devised to reduce the rise in exhaust gas temperature.

FIG. 2 shows the most basic system for implementing this intermediate pressure turbine starting method f. In this system, unlike the above-mentioned high-intermediate-pressure turbine startup, ■When the turbine is started, the steam control valve 9 is closed, no steam flows to the high-pressure turbine 4, and only the intermediate-pressure turbine 3 and low-pressure turbine 2 are used to increase the speed. (1) The exhaust side of the high-pressure turbine 4 and the condenser 17 are connected via a ventilator valve 18.

When starting the turbine, first, when the condenser 17 reaches its rated vacuum, the ventilator valve 18ft is fully opened to create a vacuum inside the high-pressure turbine 4. Next, while keeping the steam control valve 9 fully closed, the reheat stop valve 14 and the intercept valve 13 are
is gradually opened, steam flows into the intermediate pressure turbine 3 and the low pressure turbine 2, and the speed of the turbines is increased. At this time, the opening degree of the high-pressure pipe/gas valve 8 is kept constant, and the opening degree of the low-pressure pipe/gas valve 15 is set to the reheat stop valve 14 in order to perform constant control of the next pressure.
decreases as the opening degree increases.

Eventually, when the turbine reaches its rated speed, it joins in and takes on the initial load. Until this process, the ventilator valve 18 is fully opened and the high pressure turbine 4 is in a substantially vacuum state, so that the temperature of the exhaust gas of the high pressure turbine 4 hardly increases due to windage damage or the like.

Next, the ventilator valve 18 is closed, the steam control valve 9 is quickly opened to prevent the exhaust temperature of the high-pressure turbine 4 from rising excessively, and the high-pressure bypass valve 10 is closed to complete the switching of the high-pressure pinosu system. When the bypass operation is completed, the steam control valve 9 is further opened to increase the load and take the rated load.

As described above, by starting the intermediate-pressure turbine, the rise in exhaust gas temperature of the high-pressure turbine 4 is reduced, the life consumption of the rotor can be reduced, and the system can be easily adapted to large-capacity, high-pressure turbines.

[Problems with background technology]

However, in such an intermediate-pressure startup method, steam is not allowed to flow into the high-pressure turbine 4 during startup, so the turbine may be in a cold state when steam is introduced into the high-pressure turbine 4 after the initial load. Second, the temperature rise due to the introduction of high-temperature main steam becomes excessive, resulting in a problem of extremely large thermal stress.

[Purpose of the invention]

The present invention has been made in view of these circumstances, and in an intermediate pressure turbine startup method, it is possible to properly warm up the high pressure turbine when the high pressure turbine is in a cold state, suppress thermal stress, and extend the service life. This provides a method for starting a turbine that allows for a longer period of time.

[Summary of the invention]

In the method for driving a steam turbine according to the present invention, after starting the intermediate pressure turbine, when the feeder pressure turbine is in a cold state, steam at a lower temperature than the main steam is allowed to flow into the downstream side of the steam control valve to warm the high pressure turbine. It is characterized by Preferably, as warming steam at a lower temperature than the main steam,
Bleed air from the medium and low pressure turbine is introduced downstream of the steam control valve.

[Embodiments of the invention]

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

FIG. 3 shows a turbine system for carrying out the turbine driving method according to the present invention. Note that the same parts as those in the turbine system to which the conventional low-pressure turbine drive method is applied are given the same reference numerals as in FIG. 2, and the explanation thereof will be omitted.

In the turbine system shown in FIG. 3, in addition to the configuration shown in FIG. 2, the intermediate pressure turbine 3 and the downstream side of the steam control valve 11 are connected via a warming valve 19 by a separate connecting pipe.

When switching from pi-zoos operation to turbine operation, the intermediate pressure turbine is started, and the addition and initial load process are performed in the same manner as shown in FIG. 2 with the warming valve 19 in the closed state.

That is, when the condenser 17 reaches its rated vacuum, the ventilator valve 18 is fully opened to create a vacuum inside the high-pressure turbine 4. Next, while keeping the steam control valve 9 fully open, the reheat stop valve 14 is
Then, the intercept valve 13 is gradually opened to allow steam to flow into the intermediate pressure turbine 3 and the low pressure turbine 2, thereby speeding up the turbines. At this time, the opening degree of the high pressure bypass valve 10 is kept constant,
The opening degree of the low pressure bypass valve 15 decreases as the opening degree of the reheat stop valve 14 increases in order to maintain constant control of the negative pressure.

Eventually, when the turbine reaches its rated speed, it joins in and takes on the initial load. Until this process, the ventilator valve 18 is fully open and the high-pressure turbine 4 is in a substantially vacuum state, so that the temperature of the exhaust gas of the high-pressure turbine 4 hardly increases due to windage damage or the like.

When the high-pressure turbine 4 is in a cold state after the completion of the initial load, the steam control valve 9 is kept closed and the warming valve 17 is opened. As a result, the high-pressure turbine 4 is supplied with steam extracted from the intermediate-pressure turbine at a temperature lower than that of the main steam, and after the high-pressure turbine 4 is warmed up, the warming steam passes through the ventilator valve 18 to the condenser. 17
will be collected.

After the warming of the high pressure turbine 4 is completed, the warming valve 19 and the ventilator valve 18 are closed, then the steam control valve 9 is quickly opened, and the high pressure bypass valve 10 is closed, completing the switching of the high pressure pinose system 10a.

When the bypass operation is completed, the steam control valve 9 is further opened to increase the load and take the rated load.

According to the method for starting a steam turbine according to such an embodiment, first, the turbine is started by supplying steam to the medium and low pressure turbines 2 and 3, and no steam is supplied to the high pressure turbine 4, so when switching from bypass operation However, an excessive heat load on the high pressure turbine 4 is avoided, and
When high-temperature, high-pressure steam is supplied to the high-pressure turbine after the initial load, if the turbine is in a cold state, the main steam will be warmed by the extracted steam from the low-temperature intermediate-pressure turbine 3, so the temperature will rise rapidly. It is also possible to avoid the rise in the pressure, prevent the generation of excessive stress, and effectively prolong the life of the turbine.

In addition, if the high-pressure turbine is warmed using the intermediate-pressure turbine bleed air as in the embodiment, there is no need to prepare a special steam supply system for warming, which simplifies the equipment configuration and improves the effectiveness of heat. It is something that can be put to good use.

However, the present invention is not necessarily limited to such a method, and it goes without saying that warming steam other than intermediate-pressure turbine extraction may be applied in cases where other easily available steam sources are available. be.

〔Effect of the invention〕

As described in detail in the above embodiments, according to the method for starting a steam turbine according to the present invention, if the high-pressure turbine is in a cold state after starting the medium- or low-pressure turbine, the main steam is In addition, the high-pressure turbine is warmed by supplying low-temperature steam, so unlike the method of directly supplying main steam, the temperature rise in the high-pressure turbine does not become excessive, thus suppressing thermal stress. This has the effect of prolonging the useful life.

[Brief explanation of the drawing]

Figure 1 is a system diagram of a turbine implementing the conventional method;
The figure is a system diagram of a conventional intermediate-pressure turbine-started turbine.
The figure is a system diagram showing one embodiment of a turbine system implementing the present invention. 1... Generator, 2... Low pressure turbine, 3... Intermediate pressure turbine, 4... High pressure turbine, 3a... Reheat (low pressure) steam system, 4a... Main steam system, 10a , 15a...
・Bypass system, 17... Condenser. Applicant's agent Hisashi Hatano

Claims (1)

[Scope of Claims] i. A high-pressure innovation system that connects the high-pressure turbine from the main steam system to the high-pressure turbine, and a low-pressure system that connects the high-pressure turbine from the reheat steam system to the medium and low-pressure turbines to the condenser. A bypass system is provided for each, and when starting up from a normal operation, the exhaust part of the high-pressure turbine is connected to the condenser to take in air, and
In a method of starting a steam turbine by flowing steam only through the low-pressure turbine, if the high-pressure turbine is in a cold state after starting the medium or low-pressure turbine, steam at a temperature lower than the main steam is supplied to the high-pressure turbine before main steam is supplied. A method of starting a steam turbine that is characterized by warming the high-pressure turbine. 2. The method for starting a steam turbine according to claim 1, characterized in that air extracted from a medium- and low-pressure turbine is used as warming steam for the high-pressure turbine.