JPH04171202A - Steam turbine power generating plant - Google Patents

Abstract

PURPOSE:To increase the internal efficiency of a steam turbine, and also reduce centrifugal stress and thermal stress, by driving a steam turbine into which main steam whose temperature and pressure are higher than normally employed levels is introduced at first, so that the steam turbine drives a power generator on a shaft which is separate and independent from a group of other turbines. CONSTITUTION:A power generator 6a is directly coupled to a super-super-high- pressure turbine 9b, whereas the shafts of turbines from a super-high-pressure turbine 2a through a low-pressure turbine 5 are coupled together in series to form a train, to which a power generator 6b is coupled in series. Since the super-super-high pressure turbine 9b is installed on an independent shaft (to which no other turbine is coupled), its thermal elongation does not affect a high-pressure turbine 3, a medium-pressure turbine 4, and the low-pressure turbine 5, and also axial clearances among the high-pressure turbine 3, the medium- pressure turbine 4, and the low-pressure turbine 5 can be reduced. This allows to reduce leakage loss. Furthermore, thermal stress due to turbine start-up can be reduced by holding the super-super-high pressure turbine, which is apt to produce high thermal stress, always at a high temperature.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a steam turbine power generation plant, and in particular to a power generation plant using an ultra-high temperature and high pressure turbine in which the temperature and pressure of main steam are increased. Regarding plants.

(Prior art) Steam conditions in a conventional steam turbine power plant are as follows:
Main steam pressure 246 kg/cof g, main steam temperature 53
8° C. and reheat steam temperature of 566° C. are common, but by further increasing the steam pressure and temperature, the thermal efficiency of the power plant can be significantly improved. This principle will be explained using the Rankine cycle, which is the simplest steam turbine power generation system.

Figure 6 shows the temperature/entropy diagram of the Rankine cycle (
T-3 diagram) is shown. In the figure, a conventional plant is shown by the line A'BEF'A', and an ultra-high temperature and high pressure plant in which the temperature and pressure are increased is shown by the line ABEFA. Conventional plant effective work is expressed by area A'BEF' and heat loss is expressed by area BCDE. Therefore, the thermal efficiency is the area A
'BEF'/area A'CDF'. In an ultra-high-temperature, high-pressure plant, the effective work increases by the area AA'FF', so the plant thermal efficiency increases by the area AA'FF'/area ACDF.

For example, main steam pressure 316 kg/aig, steam temperature 5
In the case of a two-stage reheat steam turbine at 66/566/566°C (as shown in Figure 8), an approximately 4% increase in thermal efficiency can be expected over conventional plants.

FIG. 7 shows the relationship between main steam temperature and thermal efficiency improvement value.

In the figure, a indicates a conventional plant, and b-d indicate an ultra-high temperature and high pressure plant.

On the other hand, when looking at materials for turbine rotors and casings, levels B and C can be handled using materials improved from the currently used ferritic steel materials for high temperatures.
Up to the level d, austenitic materials are required. FIG. 8 shows a typical steam turbine plant at levels b and c.

In the figure, ultra-high temperature and high pressure steam generated in a boiler 1 works in an ultra-high pressure turbine 2a, then enters the boiler 1 again, is heated to 566° C., and is led to a high pressure turbine 3.

The steam leaving the high-pressure turbine 3 is heated again in the boiler 1, then works in the intermediate-pressure turbine 4° and the low-pressure turbine 5, and is condensed in the condenser 7 to become water. This water is pressurized by the feed water pump 8 and guided to the boiler 1. The work done by the steam in each turbine becomes the rotational energy of the rotor, which generates the generator 6.
is converted into electrical energy.

However, at level d in Figure 7 (main steam temperature 650°C)
In order to ensure the high-temperature strength of the rotor, casing, etc., it becomes necessary to use austenitic stainless steel or nickel-based superalloy containing large amounts of chromium, nickel, etc. as the material for the main parts of the turbine. Since these austenitic materials are expensive, an ultra-super-high pressure turbine 9a is separately installed as shown in FIG. 9 in order to use them only in the ultra-super-high pressure section where both temperature and pressure are high.

In this case, it is not preferable to connect the ultra-super high pressure turbine 9a to the low pressure turbine 5 with a single shaft because the total length of the turbine becomes long and the thermal expansion of the shaft and the size of the building are undesirable. It is common to use separate axes as shown.

(Problem to be solved by the invention) However, although austenitic materials used in steam turbine power plants with main steam temperatures of 650°C class have superior high-temperature strength compared to ferritic steel, they have large thermal elongation and It has characteristics such as poor conductivity.

Normally, when a steam turbine is started, the rotor side (the rotating part) or the casing side (the stationary part) warms up first, and when the steam turbine is stopped, the rotor side or the casing side cools down faster.

Therefore, if the difference in thermal elongation between the rotor and the casing is large, it becomes necessary to increase the axial clearance between each part of the turbine, which causes steam leakage and a reduction in turbine internal efficiency.
There is a risk of an accident occurring due to contact between the rotating part and the stationary part.

In addition, if the thermal conductivity is poor, only the steam passage side of the rotor, casing, etc. becomes hot when the turbine is started, and the temperature difference between the inner and outer surfaces increases, resulting in large thermal stress on the steam passage side. Therefore, it takes a long time to warm up the turbine, and rapid startup and shutdown are not possible.

Furthermore, since the pressure of the steam passing through the ultra-super high pressure turbine is high, the volumetric flow rate is small, so the turbine blade length is also short, and the turbine internal efficiency is also low.

Therefore, the purpose of the present invention is to eliminate defects caused by thermal elongation and thermal stress in turbine power generation plants using austenitic materials, and to achieve high efficiency.

Our objective is to provide a steam turbine power generation plant with high reliability and high operability.

[Structure of the Invention (Means for Solving the Problems) The present invention provides a system in which the temperature and pressure of main steam initially supplied from a boiler to a steam turbine are at higher levels than conventional ones, and the turbine is connected to a plurality of steam turbines. In a steam turbine power plant that consists of a steam turbine group in which turbines are connected in series or a steam turbine group in which multiple steam turbines are connected in series in parallel, only the steam turbine into which main steam is first introduced is separated from the shaft. It is designed to independently drive a generator.

(Function) The steam turbine into which the main steam generated in the boiler at a temperature and pressure higher than conventional levels is first introduced is designed to drive a generator independently on a separate shaft from the other steam turbines. As a result, operating conditions can be selected without being influenced by other steam turbine groups, making it easy to configure configurations compatible with the materials used, improving internal efficiency, and reducing centrifugal stress, effects of thermal elongation, thermal stress in high-temperature parts, etc. can do.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram showing an embodiment of the present invention.

In the figure, 1 is a boiler, 2a is an ultra-high pressure turbine, and 3
4 is a high-pressure turbine, 4 is an intermediate-pressure turbine, 5 is a low-pressure turbine, and 9b is an extremely high-pressure turbine.

A generator 6a is directly connected to this ultra-super high pressure turbine 9b, a shaft is connected from the ultra high pressure turbine 2a to the low pressure turbine 5, and the generator 6b is directly connected to this shaft.

Steam generated in the boiler 1 flows from the ultra-high pressure turbine 9b to the ultra-high pressure turbine 2a, is reheated by the boiler 1, and is guided to the high-pressure turbine 3. Steam leaving the high-pressure turbine 3 is reheated in the boiler 1 and guided to the intermediate-pressure turbine 4, flows from the intermediate-pressure turbine 4 to the low-pressure turbine 5, and is condensed in the condenser 7 to become water.

This water is pressurized by a water supply pump 8 and supplied to the boiler 1.

Therefore, the ultra-high-pressure turbine 9b uses an austenitic material in order to cope with high temperature and severe changes, and the ultra-high-pressure turbine 2
Operates at approximately 1/2 rotation speed of a etc. and generates power to generator 6.
Convert it to electrical energy at a. Note that ferritic steel is used for the ultra-high pressure turbine 2a and the high pressure turbine 3 because their pressure and temperature are relatively low.

As mentioned above, the ultra-high pressure turbine 9b is operated at half the rotation speed of the ultra-high pressure turbine 2a, etc., but the blades are designed so that the axial velocity of steam inside the turbine is proportional to the rotation speed of the turbine. Therefore, in order to reduce the axial velocity of steam to match the rotational speed, the blade length must be approximately doubled.

Here, the relationship between the blade length of the turbine and the stage efficiency is shown in FIG. As is clear from the same figure, when the blade length becomes 5 (1 mm or less), the stage efficiency decreases rapidly.This is because the secondary flow l
Since the range l affected by O is approximately constant regardless of the blade length, the secondary flow 10 is relatively constant as the blade length becomes shorter.
This is thought to be because the range of

Therefore, the blade length of the ultra-super high pressure turbine 9b is 20 to 3
If the length increases from 0 mm to about 50 mm, which is about twice the length, the turbine internal efficiency will also increase.

In addition, the centrifugal force of the ultra-high pressure turbine 9b set at a low rotation speed will be compared with that of a conventional rotation speed. The centrifugal force of the rotating body is expressed as mrω2, and since the blade mass m is twice the length, it is approximately doubled, the rotation radius r, and the rotational angular velocity ω are approximately 1/2.

Therefore, the ultra-high pressure turbine 9b with a rotational speed of approximately 1/2 and a blade length approximately twice as large has a centrifugal force approximately 1/2 that of a conventional rotational speed, and therefore reliability is greatly improved.

Furthermore, since the ultra-super high pressure turbine 9b is installed with an independent shaft (to which other turbines are not connected), the effects of thermal expansion will not affect the other high pressure turbines 3, intermediate pressure turbines 4, and low pressure turbines 5. Therefore, the axial clearance between the high pressure turbine 3, intermediate pressure turbine 4, and low pressure turbine 5 can be reduced, and reliability can be improved and leakage loss can be reduced.

On the other hand, as shown in FIG. 4, an auxiliary steam pipe is connected between the main steam stop valve 11, the steam control valve 12, and the ultra-super high pressure turbine 9b via a valve 13, and the exhaust valve 14 of the ultra high pressure turbine 9b is If a branch pipe is connected to the condenser (not shown) via the warming valve 15 on the upstream side, and the main steam stop valve 11 and the exhaust valve 14 are closed while the turbine is stopped, the ultra-super high pressure turbine 9b It is possible to perform a warming operation for only

As a result, the ultra-high pressure turbine 9b, which tends to generate high thermal stress, can be maintained at a high temperature at all times, and the thermal stress caused by starting the turbine can be reduced, and rapid startup and shutdown becomes possible, making it easier to respond to load fluctuations.

In addition, in the embodiment described above, the ultra-high pressure turbine 9b using an austenitic material is set as a separate shaft, but the present invention is not limited to this, and the ultra-high pressure turbine using a ferrite-based material may be set as a separate shaft. A similar effect can be obtained.

FIG. 5 shows another embodiment of the steam turbine power generation plant according to the present invention, in which an ultra-high pressure turbine 2b made of ferrite material is directly connected to a generator 6a through one shaft, a high pressure turbine 3, an intermediate pressure turbine 4. The low pressure turbines 5 connect their shafts to each other and are directly connected to the generator 6b.

Therefore, the ultra-high-pressure turbine 2b has a rotational speed of 172 times the rotational speed of the high-pressure turbine 3, etc., and has a blade length approximately twice that of the high-pressure turbine 3, thereby improving reliability and reducing leakage loss in the same way as in the above-mentioned embodiments. , it is possible to reduce thermal stress due to independent warming of the ultra-high pressure turbine 2b.

This example is based on conventional steam conditions (246 kg/c!Ir
g.

538/566°C) in the above turbine power plant,
A boiler LAS ultra-high pressure turbine 2b equipped with a superheater and a reheater that can meet the main steam conditions described above.

By additionally installing a generator 6a, it has the feature that it can be remodeled into an ultra-high temperature and high pressure power generation plant with high thermal efficiency. Note that 1b indicates a conventional boiler.

[Effects of the Invention] As explained above, according to the present invention, the steam turbine into which main steam with a temperature and pressure higher than the conventional level is first introduced can be used as an independent generator with a separate shaft from the other steam turbines. This makes it possible to improve the internal efficiency of the steam turbine, reduce centrifugal stress in the high-temperature, high-pressure section, and further reduce the effects of thermal elongation and thermal stress in the high-temperature section. plant can be provided.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram showing an embodiment of the present invention, Fig. 2 is a diagram showing the relationship between the turbine blade length and stage efficiency, Fig. 3 is an explanatory diagram showing the flow of steam inside the turbine, and Fig. 4 is a diagram showing the relationship between the blade length of the turbine and the stage efficiency. Figure 5 is a detailed diagram showing a part of Figure 1, Figure 5 is a configuration diagram showing another embodiment of the present invention, Figure 6 is a diagram showing the relationship between temperature and entropy of the Rankine cycle, and Figure 7 is the main An explanatory diagram showing the relationship between steam temperature and thermal efficiency, FIG. 8 is a configuration diagram of a conventional ultra high temperature high pressure turbine power generation plant, and FIG. 9 is a configuration diagram of a conventional ultra high temperature high pressure turbine power generation plant different from FIG. 8. 1, la, lb...Boiler 2a, 2b...Ultra high pressure turbine 3...High pressure turbine 4...Intermediate pressure turbine 5...Low pressure turbine 6a, 6b...Generator 7... Condenser 8...Water pumps 9a, 9b...Ultra-super high pressure turbine (7317) Representative Patent attorney Noriyuki Noriyuki Length (mm) No. 21!1 V Broom 3 Fig. 4 Entrohi. 6th rg! J Donaomarun 11i ('C) Fig. 7 Ta Mu σ

Claims (1)

[Claims] The temperature and pressure of the main steam initially supplied from the boiler to the steam turbine are at higher levels than conventional ones, and the turbine is a steam turbine group in which a plurality of steam turbines are connected in series, or a plurality of steam turbines are connected in series. In a steam turbine power generation plant comprising a group of steam turbines arranged in parallel, only the steam turbine into which the main steam is introduced first has a separate shaft and independently drives a generator. steam turbine power plant.