JPH01134030A - Method and device for stopping operation of gas turbine - Google Patents

Abstract

PURPOSE:To enable stoppage of operation without accompanying thermal fatigue by controlling into an intermediate state between a control state where air flow of a gas turbine compressor is fed back to a fuel flow regulating means in order to maintain a constant fuel gas temperature and a control state where air-fuel ratio is maintained constant. CONSTITUTION:A bypass line 3 detouring a fuel pump 2 which is driven through a gas turbine is provided and a bypass valve 4 is arranged in the way thereof. Delivery side of the fuel pump 2 is coupled through a flow divider 5 and a check valve 6 to a fuel nozzle 7. A generator 10 of a signal S2 determined based on the opening of an inlet guide vane, a generator 11 of a signal S3 determined based on the opening of a steam extraction valve for a gas turbine compressor and a generator 15 of a signal S1 determined based on the rotation are provided. Respective signals S1-S3 are added or subtracted through an operating unit 12 then an operation result is applied as a bias signal onto a load demand set signal S fed from a controller 9 at a contact 13 so as to control the opening of the bypass valve 4.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for stopping the operation of a gas turbine so as not to damage the gas turbine, in particular, so as not to cause thermal fatigue to the gas path components of the gas turbine; and a device for stopping its operation.

[Conventional technology]

A gas turbine is a type of internal combustion engine, and is a type of prime mover that burns fuel and air in its combustor to create hot gas, which uses the kinetic energy to rotate a turbine and convert it into mechanical energy. It is.

With current technology, the maximum temperature of hot gas is 1200~14
The temperature of the turbine's moving and stator blade metals reaches a maximum of about 8 degrees Celsius due to forced air cooling.

~850''C is allowed.

When a gas turbine is operated continuously, the metal temperature of the gas path components (rotor blades, stator blades, shroud) that make up the gas turbine does not change significantly, so the stress (thermal Stress) is small, and there is little damage to hot gas pass parts.

However, in recent years, gas turbines have been used particularly in combined power generation facilities combined with steam turbines, and these gas turbines are burdened with so-called intermediate loads in the power system, and are repeatedly started and stopped on a daily basis.

Therefore, for example, in the case of a turbine first-stage stationary blade, when it is stopped,
The metal temperature difference during load operation is approximately 850-
250 = 600"C, and due to the repetition of this heat load, the first stage stator vane will surely undergo thermal fatigue. When the number of repetitions of thermal fatigue exceeds a certain threshold, microcracks will occur in the first stage stator vane, and As the number of times increases, the microcracks gradually grow.

In particular, cracks grow significantly during the gas turbine shutdown process. This is because during startup, the average metal temperature of the first-stage stator vanes increases, and most of the first-stage stator vanes themselves experience compressive stress due to elongation. Therefore, if a crack is present, it tends to be crushed and there is less crack growth.

However, during the stopping process, the average metal temperature of the first-stage stator blades decreases, and most of the first-stage stator blades are subjected to tensile stress due to contraction. Therefore, if a crack exists, the crack will grow from the stress concentration area.

Currently, in order to reduce the occurrence and growth of cracks, when stopping gas turbine operation, the no-load rotation speed is
Operation in which the combustor fire is not extinguished while the rotational speed drops to approximately 40% of that speed (fired shutdown)
The method of doing this is the traditional practice of gas turbines, which is to stop the fuel with no load at the time of shutdown, and suddenly a large amount of cold discharge air from the compressor flows into the first stage stator vanes. Although it is better than the "method of applying thermal shock to the turbine", it lacks the concept of minimizing thermal fatigue, and is the most suitable gas turbine method in terms of minimizing damage to turbine gas path components. There is no driving suspension law. In addition, ASME PA
PER) 79-GT-50, Improvement of Nozzle Life in Gas Turbines (Improvement of Nn
33Qe Life 1nGasturbine) is known.

[Problem that the invention seeks to solve]

The above-mentioned conventional technology has not yet given sufficient consideration to greatly reducing thermal stress when the gas turbine stops operating, and has the problem of cracks occurring and growing on the surface and inside of the gas turbine gas path components. there were.

This problem will be discussed with reference to FIG. FIG. 2 shows the fuel flow rate and air flow rate when the operation of the gas turbine is stopped, with the rotational speed on the horizontal axis.

Although the fuel flow rate is proportional to the rotational speed of the gas turbine, the air flow rate has a downward convex shape due to the characteristics of the gas turbine compressor.

In particular, when the operation is stopped, an inlet guide vane (IGV) at the air inlet of the compressor moves in the closing direction to reduce the air flow rate in order to avoid a stall in the latter stage of the compressor. In Figure 2, I
This indicates that the GV set angle has changed. Therefore, the fuel-air ratio determined by the ratio of fuel and air flow rate is
% (and no load), for example, it is approximately twice as large at 50% rotation speed.

FIG. 3 shows the combustion temperature of the gas turbine, with the horizontal axis representing the rotational speed when the gas turbine is stopped.

In particular, curve A drawn with a chain line indicates the combustion temperature when a fired shutdown is performed. Its feature is that due to the above-mentioned fuel-air ratio characteristics, the combustion temperature is higher in the low rotational speed range than in the case of 100% rotational speed (no load).

Fired shutdown is maintained up to about 45% of one revolution.

Below this speed, the fire goes out and cold air from the compressor enters.

Therefore, since the amount of gas itself is small and the relative flow velocity with the gas path parts is small, that is, the heat transfer coefficient is small, so the degree of rapid cooling of the gas path parts is reduced, but from the perspective of minimizing thermal fatigue to the first stage stator vane. It's a long way from. In addition, the inner surface of the first stage stator vane is cooled by the compressor discharge air whose temperature decreases as the rotation speed decreases, and the temperature difference between the inner and outer surfaces of the first stage stator vane becomes large. The stress is greater than when the rotation speed is 100% (no load).

In this way, when a gas turbine in operation is stopped, the temperature of the gas path components changes rapidly, causing thermal fatigue and impairing durability.

The present invention has been made in view of the above-mentioned circumstances, and includes a stop operation method that can reduce thermal stress in gas path components and does not cause thermal fatigue when stopping a gas turbine in operation. Another object of the present invention is to provide a stopping device suitable for carrying out the above method.

Means for Solving Problem C] The above purpose is to calculate or actually measure the average temperature of the hot gas of the gas turbine when the gas turbine operation is stopped, or to actually measure the metal temperature of the hot gas path stationary body parts. This is achieved by controlling the fuel-air ratio determined by the fuel flow rate and air flow rate of the gas turbine, and as a result, minimizing the thermal stress that is applied to the gas path components of the gas turbine.

The fuel flow rate of the gas turbine is controlled by a fuel control valve using an external signal. The air flow rate is also a function of the gas turbine rotor rotational speed, atmospheric conditions, and the gas amount/bin compressor bleed valve opening/closing state.

Therefore, by calculating or actually measuring the latter flow rate and controlling the former (fuel flow rate) using an external signal, it is possible to control the fuel-air ratio when stopping the gas turbine operation. Further, since the average temperature of the hot gas flowing from the combustor to the turbine is determined by the fuel-air ratio and the gas turbine compressor discharge temperature, the average temperature of the hot gas can also be controlled.

In particular, the metal temperature of the turbine first-stage stator vane is a representative value of the metal temperature of the hot gas path parts.By feeding this signal back to the fuel flow control, the thermal stress of the hot gas path parts can be calculated with even higher precision. It can be minimized.

[Effect]

In order to prevent the external thermal stress of the first-stage stationary blade of a gas turbine from suddenly changing from the state of 100% rotation speed (no load), it is sufficient to keep the combustion temperature of the gas turbine constant and decrease the rotation speed by one level. be. The inner surface of the first-stage stator vane is impingement-cooled by compressor discharge air, and in order to prevent the thermal stress on the cross-section of the first-stage stator vane from suddenly changing from 100% rotation speed (no load), it is necessary to All you have to do is drive at a constant ratio. However, it is not easy to simultaneously satisfy both the constant thermal stress on the outer surface of the first stage stationary blade and the constant cross-sectional thermal melting force.

In the prior art, when stopping gas turbine operation, the fuel was throttled without being aware of the change in the flow rate of combustion air supplied from the compressor. By detecting this and throttling the fuel while adapting to this, it is possible to stop the operation of the gas turbine without giving a large thermal shock (sudden change in reactive load) to the gas path components.

〔Example〕

FIG. 1 shows an embodiment of a fuel system that performs fuel-air ratio control when the rotational speed decreases.

In this example, fuel oil is directly controlled, but fuel gas can also be handled using the same concept. 1 indicates fuel oil (for example, shaft oil), 2 indicates a fuel pump, and accessories of the gas turbine - gear (not shown)
Driven by.

Since 2 is usually a gear pump, its fuel flow rate is proportional to the rotation speed.

The flow rate Ql of the gas turbine fuel oil 1 is usually expressed by the following formula.

Here, K is the proportionality constant RPM is the % of the rotational speed of the gas turbine. S is the load request signal that varies from 4 to 20. Therefore, when there is no load, if S = 7, the fuel flow rate is as shown in Figure 2. It is proportional to the number of rotations.

3 shown in FIG. 1 is a bypass line of the fuel pump 2, and 4 is a bypass valve. By closing this bypass valve 4, more fuel oil 1 flows to the flow divider 5, and the load on the gas turbine increases. 6 is a check valve, 7 is a fuel nozzle, 8 is a combustion tube, and 14 is a flame in the combustion tube 8.

A first stage stator vane (not shown) is located downstream of the combustion tube 8.

9 is a setting signal S determined by the load request of the gas turbine.
It is a controller that generates a constant value at low rotation speeds below 100% no-load rotation speed. 15 is a generator of a signal s1 determined by the rotation speed, and 1o is a generator of a signal s2 determined by the opening degree of the IGV. 11 is a generator of a signal S8 determined by the bleed valve opening of the gas turbine compressor.

These signals are subjected to addition, subtraction, and multiplication in the arithmetic unit 12, and are added as a bias signal to the load request setting signal S at the contact point 13 to control the opening degree of the bypass valve 4. The characteristics of the gas turbine air flow rate Q2 are approximately expressed as a quadratic function of the rotation speed, including the rotation speed, the IGV opening degree, and the bleed valve opening degree, as shown below.

Here, Ko, Kip Kl Ka is the constant of proportionality (IGV)
The signal (AB) that changes from 0 to 1 for open O2 closed 1 is a signal that changes from 0 to 1 for open O2 closed 1.

Therefore, in equation (1), gas turbine operation stop 5z=
Kx (IGV), 5a=Kz (AB). That is, the load request bias signal S4 is proportional to the rotation speed, and its coefficient is a function of the IGV opening and the bleed valve opening. This calculation result is fed back to the opening degree of the bypass valve 46. In other words, since the compressor air flow rate changes depending on the number of revolutions, the opening degree of the IGV, and the opening degree of the bleed valve, this influence is fed back to the fuel flow rate. This shows a method for performing constant fuel/air ratio control.

Although this embodiment shows a method of constant fuel/air ratio control, it is also possible to perform constant combustion temperature control and control in between. During load operation, the rotation speed IGV opening is constant and the bleed valve is closed, so the bypass valve 4 is
It is driven only by changes in the load request signal S.

If the fuel pump 2 is installed separately from the gas turbine and driven by a motor, the rotation speed of the motor is controlled by an inverter, and the output signal (81, S
If I Sa) is fed back to the inverter, the same effect as described above can be obtained.

In the above embodiments, the fuel was controlled by feeding back the rotational speed, IGV, and the position of the bleed valve when the gas turbine was stopped, which indirectly determined the air flow rate.

As an embodiment other than the above, it is also possible to detect the combustion temperature as shown in FIG. 3 and feed it back to the fuel flow rate control means. In this case, combustion temperature detection is performed at the combustor outlet (
The gas temperature at the first stage inlet) may be directly measured, or the gas turbine exhaust temperature may be measured and calculated.

Furthermore, the metal temperature of the hot gas pass component may be detected based on the same technical idea.

In this case, it is recommended to detect the metal temperature of stationary components in hot gas bath components.

〔Effect of the invention〕

According to the method of the present invention, it is possible to significantly reduce thermal fatigue of hot gas path components when stopping gas turbine operation, and to practically completely prevent the occurrence and growth of cracks due to thermal fatigue. I can do it.

Therefore, the durability of the hot gas pass component is significantly improved.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing one embodiment of the device of the present invention. FIG. 2 is a chart showing the relationship between the fuel and air flow rates and the rotational speed when stopping the operation of the gas turbine. FIG. 3 is a chart showing the relationship between combustion temperature and rotational speed when stopping the operation of the gas turbine. l...Fuel oil, 2...Fuel pump, 4...Bypass valve. 8... Combustion cylinder.

Claims (1)

[Claims] 1. A method for stopping an operating gas turbine,
A control state in which the air flow rate of the gas turbine compressor is detected and the detected signal output is fed back to the fuel flow rate adjustment means of the gas turbine combustor to keep the combustion gas temperature of the gas turbine combustor constant, and the fuel-air ratio A method for stopping operation of a gas turbine, the method comprising: controlling the gas turbine to an intermediate state between a control state that makes the gas turbine constant; 2. The air flow rate is detected by detecting at least one of the rotational speed of the gas turbine compressor and the operating state of the inlet guide vane. Method of stopping gas turbine operation described in . 3. According to claim 1, the air flow rate is detected by detecting at least one of the rotational speed of the gas turbine compressor and the operating state of the bleed valve. Method of stopping the operation of the gas turbine described. 4. In a method for stopping a gas turbine in operation,
The gas temperature of the gas turbine is detected and the detection signal output is fed back to the fuel flow rate adjustment means of the gas turbine combustor to keep the combustion gas temperature of the gas turbine combustor constant and the fuel-air ratio constant. A method for stopping operation of a gas turbine, characterized by controlling the operation to an intermediate state between a closed control state and a closed control state. 5. The method for stopping operation of a gas turbine according to claim 4, wherein the gas temperature is detected at an outlet of a gas turbine combustor. 6. The method for stopping operation of a gas turbine according to claim 4, wherein the gas temperature is detected at a gas turbine exhaust outlet. 7. (a) An automatic control valve is provided for controlling the flow rate of fuel supplied to the combustor of the gas turbine, and (b) a controller (9) is provided for generating a setting signal S determined by the load request of the gas turbine. and (c_1) a signal generator (15) for generating a signal S_1 determined by the gas turbine rotational speed, and (c_2) generating a setting signal S_2 determined by the air flow rate of the gas turbine compressor. a signal generator (10); and (c_3) a signal generator (11) that generates a setting signal S_3 determined by the bleed valve opening of the gas turbine compressor.
and (d) adding at least one of the setting signals S_1, S_2, and S_3 to the setting signal S and providing the result to the automatic control valve. characterized by being provided with an addition calculation means,
A device that stops gas turbine operation.