JPS5912105A - Starting system of reheat condensing steam turbine - Google Patents

Abstract

PURPOSE:To enable to safely start the intermediate pressure stage turbine by a method wherein low pressure, intermediate temperature steam is poured from a separate auxiliary steam system through a lead-in line of warming steam into the steam inflowing part of the intermediate pressure stage turbine at the starting and during the low speed turning of the turbine. CONSTITUTION:The lead-in line 7 of warming steam, to which steam is supplied from an auxiliary steam source in a steam power plant in lain to the reheat steam inflowing part of the intermediate pressure stage turbine 2 in the steam turbine, in which a high pressure stage turbine 1, the intermediate pressure stage turbine 2, and a low pressure stage turbine 3 are arranged in tandem. By piercing a guide ring 25 which guides the reheat steam radially flowed-in through a reheat steam inflowing passage 27 toward the cascade of stator blades 23, the line 7 is connected so as to open in an auxiliary steam lead-in chamber 26. Furthermore, the line 7 is connected with an extraction pipe 8 for extracting steam from the cooling reheat steam system of the high pressure stage turbine 1 in order to be able to supply rotor cooling steam to the rotor of the turbine 2 during load running.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in the starting method of a large capacity reheat condensing steam turbine comprising a high pressure stage, an intermediate pressure stage and a low pressure stage.

Steam turbines are started by hot, high-pressure steam, and the rotor starts up quickly.

This causes a large thermal υ・strain to occur in the casing, etc., so when starting up, there is a temperature difference at the bottom of the turbine.

It is necessary to start up while suppressing temperature changes and thermal stress to sufficiently low values. Particularly in the case of cold start, the conditions are severe and sufficient consideration must be given to this point. In the alliterative reheat condensing steam turbine, it is the intermediate-pressure turbine that is exposed to the most severe conditions during cold start-up. The reason for this is that prior to starting the turbine, the condenser is vacuumed in order to collect and discharge the condensate remaining in various parts inside the turbine to the condenser, and as a result, this vacuum region extends to the intermediate-pressure turbine. It turns out. If high-temperature reheated steam is introduced into the intermediate-pressure turbine in this state, there is a risk that greater thermal stress will occur in the intermediate-pressure turbine than in the high-pressure and low-pressure turbines. Note that the thermal stress in this case is determined by the temperature increase during the startup process and the rate of temperature increase.

By the way, as is well known, conventional turbine startup has been performed as indicated by the solid line in the startup chart shown in FIG. In the figure, A is the main steam temperature, B is the reheat steam temperature, C is the metal temperature of the intermediate pressure stage turbine rotation speed, N is the turbine rotation speed, and W is the steam driven by the turbine. This is the output of the machine. In other words, prior to startup, p-turning is performed at low speed, then the main steam stop valve and reheat steam stop valve are opened, and while the speed is controlled by the governor, the speed is increased to 1500 rpm and 8 degrees to perform a heat soak. Warm up during the period.

Once the heat sorter is finished, the speed will further increase to the rated speed and the generator'? : After synchronously entering the power system, the load is gradually increased. However, in the conventional startup method described above, even if sufficient time is taken for startup, for the reasons mentioned above, there is a large temperature difference between the metal temperature of the intermediate-pressure turbine and the reheated steam, especially during startup. occurs, and it is inevitable that large thermal stress will be generated due to this. - In the example,
Reheat steam temperature and metal temperature at the time of synchronization in the figure This invention has been made in consideration of the above points, and its purpose is to warm up the intermediate pressure stage turbine, which is exposed to the most severe conditions, and to improve its startup. An object of the present invention is to provide a new starting method for a thermal condensing steam turbine that incorporates a clever warming method that reduces the temperature increase during the process and reduces thermal stress.

According to the present invention, a warming steam introduction line that receives steam from an auxiliary steam system in the plant is piped to the reheated steam inlet of the intermediate-pressure turbine, and when the turbine is cold started, the warming steam is injected into the low-speed casing. This is achieved by injecting low-pressure, medium-temperature steam into the medium-pressure turbine through the introduction line to perform warming.

The present invention will be explained below based on the illustrated embodiments.

In FIG. 1, 1 is a high-pressure turbine, 2 is an intermediate-pressure turbine, 3 is a low-pressure turbine, 4 is a condenser, and 5 is a reheater. In this steam system, a warming steam introduction line 7 that receives steam from an auxiliary steam source 6 in a steam power station is installed at the reheated steam inlet of the intermediate-pressure turbine 2. The detailed structure of the steam introduction part is as shown in Fig. 2.

In the figure, 21 is the casing of the intermediate-pressure turbine 2, 22 is the casing of the intermediate-pressure turbine 2, 22 is the stator blade, 2 is the rotor blade, and 25 is the casing of the intermediate-pressure turbine 2 through the reheat steam inlet passage 27 as shown by the dotted arrow. The piping of the warming steam introduction line 7 passes through the rectifying ring 25 and connects to the p-tube 22 on the back side of the rectifying ring 25. Auxiliary steam introduction chamber 26 defined between
It is opened to

The rectifier 25 itself is well known and has been conventionally employed in many turbines. This prevents high-temperature reheated steam of 538° C. to 560° C. from being directly blown onto the rotor 22, and suppresses generation of excessive thermal stress in the rotor and creep based on this. Further, the auxiliary steam introduction chamber 26 is defined as a nearly closed space, and communicates with the steam passage in the blade row through a small gap on both sides of the rectifying ring 250. Returning to the first @, an on-off valve 71 and a check valve 72 are inserted in the warming steam introduction line 7. With the configuration so far, the auxiliary steam source 6 is supplied through the warming steam introduction line 7 at a pressure of lO~30ψ-・g and a temperature of 250~40.
When low-pressure, medium-temperature steam of about 0°C is injected into the intermediate-pressure turbine 2, this steam is discharged into the auxiliary steam introduction chamber 26 as shown by the solid arrow in Fig. 2, warms the rotor 22, and then rectifies it. ] / It flows out from the left and right side of the blade 25 to the blade cascade passage through a minute gear knob. In this process, the auxiliary steam introduction chamber 2
Since the space 6 is almost closed and the pressure of the injected steam is maintained sufficiently inside the room, efficient heat transfer to the tank 22 can be performed.

Now, according to the present invention, when starting up the turbine, warming is performed by injecting the warming steam through the above-mentioned warming steam introduction line 7 during low-speed turning at a stage before reheating steam is supplied. Therefore, the metal temperature of the intermediate-pressure turbine 2 is increased compared to the metal temperature C according to the conventional startup method, as indicated by the dotted line curve C' in FIG.

In particular, the temperature difference between the reheated steam temperature t at the same time and the metal temperature t3 at the same time is 1, -1 compared to the conventional temperature difference.
This is greatly reduced compared to No. 2, and the thermal stress applied to some parts is reduced accordingly, and the rate of change in temperature rise is also reduced because the temperature rise during the subsequent temperature rise up to the rated operation is also small. Note that the warming steam also flows out of the auxiliary steam introduction chamber 26 and flows to the blade row, and does a small amount of work on the blade row. For this reason, the turbine rotational speed during turning is reduced by the dotted line N' in FIG.
Since the speed increases to some extent as shown in FIG. This flow rate restriction can be implemented by appropriately providing a flow rate regulating mechanism such as a throttle in the line 7.

It is also possible to take measures against aging of the turbine, which will be described below, by using a part of the warming steam introduction line 7. That is, when the rotor 22 is exposed to high-temperature reheated steam for a long period of time during load operation of the turbine and stress is applied, the rotor 22 curves due to the creep phenomenon. As a means to prevent this, a method is conventionally known in which during load operation, steam at a temperature lower than that of the reheated steam is supplied to one rotor at the reheated steam inflow section, which has the strictest conditions, to cool the second rotor. In this method, in the embodiment shown in FIG. 1, an extraction line 8 drawn from the cold reheat steam system of the high-pressure turbine 1 is connected to a point in the middle of the warming steam introduction line 7, particularly at a point downstream from the check valve 72. And in the line 7 there is an on-off valve 81. A circuit is constructed by inserting a check valve 82'af, and by selectively controlling the on-off valves 71 and 81, rewarming steam is supplied from the auxiliary steam source 6 through the warming steam introduction line 7 during turbine startup, and the above-mentioned extraction steam is supplied during load operation. -sl 2 of the previous cold reheated steam extracted from the high pressure stage turbine 1 and introduced into the reheater 5 through the downstream part of the line 8 and the warming steam introduction line 7.
This can be achieved by supplying the auxiliary steam to the auxiliary steam introduction chamber 26 shown above and cooling the steam generator 22. Note that the check valve 82 reliably prevents warming steam from leaking toward the high-pressure turbine through the line 8 during startup, and the check valve 7
2 serves to prevent high pressure steam on the turbine side from leaking to the low pressure auxiliary steam source side during load operation.

As described above, the present invention performs warming by injecting pressure-transfer medium-temperature steam from another auxiliary steam system into the steam inlet of the intermediate-pressure turbine through the warming steam introduction line during low-speed turning when starting the turbine. This is how it was done. 9) Therefore, it is possible to use steam at an appropriate temperature and pressure, which is not limited by the main steam and reheat steam temperatures, as warming steam.
This enables safe startup of intermediate-pressure turbines, which are exposed to the most severe conditions during cold startup.

Moreover, in this case, the warming steam injection point can be freely selected away from the reheating steam introduction path, and in particular, the warming steam injection point can be freely selected between the rectifying ring and the rotor as shown in Fig. 2. By injecting the steam into the heated chamber, the steam pressure in the chamber can be maintained and the efficiency of the rotor can be increased (warming heat can be given to the rotor. Moreover, since the steam is not directly injected into the blade row, the turbine blades can be heated by the warming steam. It is possible to provide a highly practical starting method that meets the conditions required for starting a turbine, such that the amount of work applied to the turbine is small and there is no risk of unduly increasing the rotational speed during turning.

[Brief explanation of the drawing]

Fig. 1 is a steam system diagram of a turbine showing an embodiment of the present invention, Fig. 2 is a sectional view showing the detailed structure of the warming steam introduction part in Fig. 1, and Fig. 3 (10) is a turbine starting point-1.・It is. 1... High pressure stage turbine, 2... Intermediate pressure stage turbine, 3...
...Low pressure stage turbine, 5...Reheater, 6...Auxiliary steam source, 7...Warming steam introduction line, 8...
Cold reheat steam system bleed line, 25... rectifier ring, 2
6...Auxiliary steam introduction room. (11) Age l Figure 20 23 2.5

Claims (1)

[Claims] 1) A warming steam introduction line that receives steam supplied from an auxiliary steam system is piped to the reheated steam inflow part of the intermediate-pressure turbine, and the warming steam is introduced during low-speed turning when starting the turbine cold. A starting method for a reheat condensing steam turbine characterized by performing warming (7) by injecting medium-temperature, low-pressure steam, which has a lower temperature and pressure than reheat steam, into the intermediate-pressure turbine through a line. 2. The starting method according to claim 1, wherein the combining steam introduction line is arranged on the back side of a rectifier ring that is disposed surrounding the rotor at the reheating steam inlet of the intermediate-pressure turbine. 1. A method for starting a reheat condensing steam turbine, characterized in that an opening is connected to an auxiliary steam introduction chamber defined between a side and a rotor. 3) In the startup method described in claim 2, an extraction line of the cold reheat steam system drawn from the high-pressure turbine is connected in the middle of the warming steam introduction line, and the warming steam is supplied through the warming steam introduction line when the turbine is started. 1. A reheat condensing system characterized by being able to selectively supply cooling steam extracted from the cold reheat steam system to the intermediate pressure stage turbine during load operation. Steam turbine starting method.