JPH10169467A - Gas turbine and gas turbine operating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the ignition delay of a diffusion burner by supplying fuel in the flame non-holding quantity of the diffusion burner during premixed combustion in a gas turbine provided with the diffusion burner and a premixed burner and operated only by premixed combusiton at specified load or more. SOLUTION: A goes turbine is operated only by diffusion combustion using a diffusion pilot burner 8 from start to rated rotating speed. Premixed fuel is then charged to ignite a premixed burner 9, and diffusion fuel is reduced by that portion to obtain a diffusionpremixed combusiton mode with load left constant. With a load increase, diffusion fuel flow is reduced, while premixed fuel is increased to obtain 100% premixed combusiton at certain load or more. During this 100% premixed combusiton, a diffusion fuel flow regulating valve 205 is totally closed, and a small quantity of fuel is supplied through a by-pass pipeline 203 with an orifice 208 interposed. Air and combustion gas in a combustor are therefore prevented from infiltrating into a diffusion fuel pipeline to the diffusion burner 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a gas turbine and a method of operating the gas turbine, and more particularly to a gas turbine having a diffusion pilot burner for performing diffusion combustion and a premix combustion burner for performing premix combustion. Also, the present invention relates to a gas turbine which is formed so that combustion is mainly performed only by a premixed combustion burner during a partial load operation, and a method of operating the gas turbine.

[0002]

2. Description of the Related Art In a gas turbine combustor generally used conventionally, it is required to reduce the amount of nitrogen oxide (NOx) generated in the combustor in consideration of environmental problems. NOx is reduced by using premixed combustion in which fuel and air are mixed and burned before combustion, and by burning in a state in which the mixture ratio of fuel and air (fuel-air ratio) is smaller than the stoichiometric mixture ratio. I can do it.

[0003] This is because the flame temperature can be reduced by reducing the local fuel-air ratio on the flame surface. In contrast, in diffusion combustion in which fuel is burned while being mixed with air, since the fuel-air ratio on the flame surface is close to the stoichiometric ratio, the flame temperature increases and the amount of generated NOx increases. Therefore, a premixed 100 without diffusion combustion
% Combustion method is extremely effective in reducing NOx.

[0004] Further, since gas turbines are often operated under rated load conditions, it is possible to design the gas turbine to operate at 100% premixing within a range from a partial load exceeding a certain load to a rated load. However, premixed combustion has a narrower fuel-air ratio range than diffusion combustion. Therefore, it is difficult to maintain a stable combustion state over a wide range of starting, speeding up, partial load, and rated load of the gas turbine.

For this reason, in an actual gas turbine, a combustor combining a diffusion burner and a premix burner is used.
It achieves both low NOx and stability. For example, Japanese Unexamined Patent Publication
In the two-stage combustor having a diffusion combustion burner on the upstream side of the combustor and a premixed combustion burner on the downstream side, the fuel supply device is changed during the operation to increase the upstream side (diffusion combustion side). 3) shows that the combustion chamber of (1) also functions as a premixing chamber to achieve 100% premixed combustion.

[0006]

When a gas turbine is used for power generation, it is required that the gas turbine can withstand a load shedding test. Load shedding is an emergency disconnection between the generator and the gas turbine for some reason. At that time, the gas turbine needs to be immediately put into a state of no-load at the rated speed. Therefore, it is necessary to simultaneously shut off the premixed fuel at the same time as detecting the load shedding signal, and set the flow rate of the diffusion fuel to a flow rate necessary for a state where the rated speed is not loaded.

At the time of rated load, to reduce NOx,
When driving for a long time at 100% premix,
The fuel in the diffusion fuel pipe gradually replaces other gases in the combustor. When a load shedding command is received in this state, it takes time until fuel reaches the diffusion burner after the diffusion fuel control valve is opened, and the diffusion burner does not ignite while the premixed flame is extinguished. In such a case, the gas turbine cannot maintain the rated rotation speed in a normal state, and thus needs to be restarted.

Further, if the quenching of the premix burner is delayed in order to ensure the ignition of the diffusion burner, the rotation speed of the gas turbine increases during that time, and the gas turbine cannot be kept within a certain range. Furthermore, it is conceivable that the premixed burner alone can be set to a state with no load at the rated rotational speed. And may extinguish.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a gas turbine of this kind which does not cause ignition delay of a diffusion burner even when load is cut off or a sudden load drop occurs. And a method for operating a gas turbine.

[0010]

That is, the present invention relates to a method for operating a gas turbine, comprising a diffusion combustion burner and a premix combustion burner, wherein the operation is performed only by the premix combustion when the gas turbine load exceeds a predetermined load. In the premixed combustion, the diffusion combustion burner is operated while supplying an amount of fuel that does not hold flame to achieve the intended purpose. That is, the fuel supply system of the diffusion combustion burner is provided with fuel supply means for supplying an amount of fuel that does not hold the flame to the diffusion pilot burner during premix combustion.

In this case, the fuel supply means is formed by a bypass provided to bypass the mechanism for adjusting the fuel flow rate of the diffusion burner.
Further, an orifice or a valve for adjusting a fuel flow rate is provided in the bypass passage.

That is, in the gas turbine formed as described above, even during premixed 100% combustion, fuel from the bypass system flows through the diffusion fuel pipe and is replaced by air, combustion gas, and the like in the combustor. Never. Since the bypass fuel flow rate is so small that the diffusion flame cannot be maintained,
Ox is not generated in a large amount. The small amount of bypass fuel flowing into the combustor is oxidized by the high-temperature atmosphere in the process of mixing with the surrounding premixed combustion gas, so that there is no emission of unburned fuel or CO. Therefore, ignition delay of the diffusion burner does not occur at the time of load interruption. Also, NOx reduction is achieved by premixed 100% combustion, and combustion oscillation can be suppressed.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the illustrated embodiments. FIG. 1 shows an enlarged view of a combustor of the gas turbine (gas turbine for power generation). The gas turbine for power generation includes a compressor 1, a combustor 2,
A turbine 3 is provided, and a generator 4 is rotated by an output of the turbine to obtain electric power.

The combustor 2 includes a gas turbine casing 5,
It is stored in the combustor outer cylinder 6 and the combustor cover 7. A diffusion pilot burner 8 for performing diffusion combustion is provided at the center of the upstream end of the combustor 2, and an annular premix burner 9 for performing premix combustion is provided on the outer periphery thereof.

The premix burner 9 includes a plurality of premix burner fuel nozzles 10 and a flame stabilizer 11. Downstream of the premix burner is a combustor liner 12 that separates unburned air from burned combustion gases. Outside the combustor liner, an outer wall (hereinafter referred to as a flow sleeve) 14 for forming an air flow path and controlling the flow is provided.

The high pressure air 100 from the compressor 1 passes through a generally annular space between the flow sleeve 14 and the combustor liner 12 and is used for convective cooling of the combustor liner 12 before the air 101 for the diffusion pilot burner. The premixed burner air 102 is supplied into the combustor and used as combustion air. Burned combustion gas 10
3 is supplied to the turbine 3 through the transition piece 15 through the inside of the combustor liner 12.

The fuel system includes a main fuel system 200, a fuel system 201 for a diffusion pilot burner branched from the main fuel system 200, and a fuel system 202 for a premix burner. The pressure control valve 20 is provided in the fuel system 201 for the diffusion pilot burner.
4. A flow control valve 205 is provided.

The pressure regulating valve 204 also functions as a fuel cutoff valve. The premix burner fuel system 202 includes a pressure regulating valve 2
06, a flow regulating valve 207 is provided. The pressure adjustment valve 206 also functions as a fuel cutoff valve. The diffusion pilot burner fuel system 201 is provided with a pipe 203 so as to bypass the fuel supply means, that is, the flow rate regulating valve. The bypass pipe 203 is provided with an orifice plate 208 for adjusting the fuel flow rate.

As described above, in such a gas turbine combustor, it is required to reduce the amount of nitrogen oxide (NOx) generated in the combustor in consideration of environmental problems. ing. NOx can be reduced by using premixed combustion in which fuel and air are mixed and burned before combustion, and by burning in a state in which the mixture ratio of fuel and air (fuel-air ratio) is smaller than the stoichiometric mixture ratio. . This is because the flame temperature can be reduced by reducing the local fuel-air ratio on the flame surface.

On the other hand, in diffusion combustion in which fuel is burned while being mixed with air, since the fuel-air ratio on the flame surface is close to the mixture ratio, the flame temperature increases and the amount of generated NOx increases. Therefore, a premixed 100 without diffusion combustion
% Combustion method is extremely effective in reducing NOx. Further, since the gas turbine is often operated under the rated load condition, it is possible to design such that the gas turbine is operated at 100% premixing in a range from a partial load of a certain load or more to a rated load.

However, premixed combustion has a narrower fuel-air ratio range than diffusion combustion. Therefore, it is difficult to maintain a stable combustion state over a wide range of starting, speeding up, partial load, and rated load of the gas turbine. Therefore, in an actual gas turbine, as shown in the present embodiment, both low NOx and stability are achieved by a combustor combining a diffusion burner and a premix burner.

Here, FIGS. 2 and 4 show the fuel control from start-up, speed-up, partial load to rated operation of the gas turbine shown in this embodiment, and the combustion mode at that time.
A description will be given based on (a) to (d).

First, as for the operation method, when the gas turbine load is small from the start to the rated rotation speed, the operation is performed only by diffusion combustion (FIG. 4A). Thereafter, the premixed fuel is supplied, the premixed burner is ignited, and the diffusion fuel is reduced by that amount, thereby setting the diffusion-premixed combustion mode with the load kept constant (FIG. 4B). When the load increases, the flow rate of the diffusion fuel is reduced as the load increases, and the premixed fuel is increased. Then, premixed 100% combustion is performed at a certain load or more (FIG. 4C).

Conventionally, as described above, at the time of rated load, the premix 100
%, The fuel in the diffusion fuel pipe gradually replaces the other gas in the combustor due to diffusion, and the diffusion burner may not ignite even if the diffusion fuel control valve opens when the load is cut off. However, in the present embodiment, during premixed 100% combustion, the flow control valve for the diffusion fuel is fully closed, but the pressure control valve is open. Flows (FIG. 4C).

As described above, the flow of the bypass fuel in the diffusion fuel pipe prevents the diffusion of air and combustion gas in the combustor from the fuel injection port of the diffusion burner into the diffusion fuel pipe. In this case, the flow rate of the bypass fuel is set so small that the diffusion flame cannot be maintained at the tip of the diffusion burner by the orifice provided in the bypass pipe.
This flow rate depends on the flow rate of the air for diffusion combustion, but is preferably 1% or less of the total fuel flow rate. At this time, since no diffusion flame is formed, the generation of NOx is suppressed. When the premixing is 100%, the load of the gas turbine is high, so that the inside of the combustor has a high temperature atmosphere due to the premixed combustion gas.

Therefore, the bypass fuel flowing into the combustor is mixed with the surrounding high-temperature combustion gas and oxidized while passing through the combustor liner.
Is also suppressed (FIG. 4C). When trying to control such a small amount of fuel with the original diffusion fuel flow rate adjustment valve, a valve capable of controlling the flow rate from a small flow rate to a large flow rate,
It needs to be a control system and is actually difficult. In this regard, the method according to the present invention requires relatively simple addition of piping.

Next, a description will be given with reference to FIG. 3 showing a state of fuel flow control at the time of load shedding. When a load shedding signal is detected, the flow control valve of the diffusion fuel system is opened to a preset opening degree. Diffusion fuel begins to flow immediately. After a certain period of time τ, the shutoff valve
Fully close both flow control valves. The premixed fuel gradually decreases with a certain delay, and the premixed flame extinguishes.

The time difference τ between the opening of the diffusion valve and the closing of the premixing valve is 0.
The diffusion flame can be ignited before the premixed fuel is reduced and the premixed flame is extinguished. After that, the process shifts to the normal control of the diffusion fuel system, and the fuel flow rate and the pressure are automatically adjusted so that the gas turbine is in a no-load condition at the rated speed (FIG. 4D). When there are multiple premixed fuel systems, such as when there are multiple premixed combustors, partly shut off,
Part may be left. In this case, it is necessary that the total of the diffusion fuel and the remaining premixed fuel have an appropriate fuel flow rate in a state where the rated rotational speed is not loaded, but the ignition reliability of the diffusion flame is further improved.

Alternatively, the quenching of a portion of the premixed flame is delayed, during which a diffusion flame is applied and then the premixed flame is extinguished. However, in order to control the rotational speed, the premixed quenching delay time (τ) is preferably as short as possible, and purging of the diffusion system according to the present invention is effective. Also, the closer the burner and the premix burner are in the axial direction, the better the ignitability. However, as in the embodiment, in a combustor having a large premix ratio,
The diffusion burner must use the premixed air at the time of acceleration and low load. Therefore, the diffusion burner and the premix burner are necessarily designed to be close to the axial direction, and the diffusion flame has a structure that is easy to ignite.

Embodiments of adjusting the flow rate of the bypass piping system according to the present invention are shown in FIGS. 5 to 8 and will be described below. FIG.
(A) is the same as FIG. 1 except that the flow control valve of the diffusion fuel system is bypassed and an orifice is provided. Premix 10
In the 0% mode, the pressure control valve 204 of the diffusion fuel system is
Since the opening degree is constant, the flow rate is set according to the differential pressure between the fuel supply pressure (primary pressure) and the internal pressure of the combustor, and the orifice area. To change the flow rate in this case, the orifice plate must be replaced.

In order to avoid this exchange, FIG.
The flow rate may be adjusted by attaching a manual valve 209 as shown in FIG. This facilitates the adjustment of the degree of opening of the bypass system during test operation. Further, a remotely operable valve 210 may be attached to improve operability or automatically control.

FIGS. 6A to 6C show a configuration in which the orifice 208, the manual valve 209, and the control valve 210 are provided bypassing the pressure regulating valve of the diffusion fuel system.
In this case, the opening degree of the flow control valve 205 of the diffusion fuel system is constant during the premixing 100% mode.

FIGS. 7 (a) to 7 (c) show a configuration in which an orifice 208, a manual valve 209, and a control valve 210 are provided, bypassing both the pressure regulating valve 204 and the flow regulating valve 205 of the diffusion fuel system. Upstream of the orifice, manual valve, and control valve, a pressure reducing valve or pressure regulating valve 211 is provided.
By controlling the fuel secondary pressure (pressure downstream of the pressure regulating valve), more accurate bypass flow rate control becomes possible. In the case of FIG. 7 (c), a single control valve may serve as both a pressure regulating valve and a flow regulating valve.

FIGS. 8A to 8C show a bypass pipe 203 provided from the downstream of the premixed fuel pressure regulating valve 206 to the downstream of the diffusion fuel flow regulating valve 205. In the premixed 100% mode, the bypass fuel flows by utilizing the differential pressure between the secondary pressure of the premixed fuel system and the internal pressure of the combustor. In this case, since the bypass system can be made independent of the diffusion and premixed fuel control system, the control system is simplified.

By the method as described above, in the premixed 100% mode, the flow rate of the bypass fuel is controlled so that the diffusion flame does not hold and the flow in the diffusion fuel system does not stagnate. Becomes possible. Therefore, even during the premixed 100% combustion, it is possible to prevent the fuel from the bypass system from flowing through the diffusion fuel pipe and replacing the fuel in the pipe with air, combustion gas, or the like in the combustor.

At this time, the bypass fuel flow rate is so small that the diffusion flame cannot be maintained, so that a large amount of NOx is not generated. The small amount of bypass fuel flowing into the combustor is oxidized by the high-temperature atmosphere in the process of mixing with the surrounding premixed combustion gas, so that there is no emission of unburned fuel or CO. In this way, it is possible to perform 100% premixed combustion, and it is possible to suppress the generation of NOx.

Further, by setting the premix to 100%, it is possible to suppress the occurrence of combustion oscillation. In the combustion oscillation, pressure fluctuations due to instability in the combustor are transmitted to the fuel or air supply system, and are converted into fluctuations in the fuel-air ratio, resulting in heat generation fluctuations and pressure fluctuations in the combustion field. It is a phenomenon that forms and self-oscillates. In premixed combustion, since a sharply exothermic reaction occurs locally in the combustor as compared with diffusion combustion, the reaction and the flow of air or fuel resonate, and combustion oscillation is likely to occur. In particular, when the combustion frequency matches the natural frequency of the combustor, the combustor may cause a resonance phenomenon and be instantaneously damaged.

In this case, the combustor components scatter,
It can cause enormous damage to downstream gas turbine components, which has a significant impact on the life of the entire gas turbine plant, not just the combustor. When the gas-to-air ratio of the diffusion burner is reduced to reduce NOx at the time of high load of the gas turbine, diffusion combustion becomes unstable and premix combustion also oscillates, so that combustion oscillation is likely to occur. Condition. However, in the case of premixing of 100%, combustion oscillation is less likely to occur because the instability of the diffusion flame does not cause oscillation. Thus, eliminating diffusion combustion and operating at 100% premixing is desirable from both aspects of NOx reduction and combustion vibration suppression.

As described above, in the gas turbine formed as described above, in the premixed 100% mode, the flow rate is such that the diffusion flame does not hold flame and the flow in the diffusion fuel system does not stagnate. In addition, it is possible to control the bypass fuel flow rate. Therefore, even at the time of premixed 100% combustion, it is possible to prevent the fuel from the bypass system from flowing through the diffusion fuel pipe and replacing the fuel in the pipe with air, combustion gas or the like in the combustor. It is possible to prevent the ignition delay of the diffusion burner when the load is cut off. Since the bypass fuel flow rate is so small that the diffusion flame cannot be maintained, a large amount of NOx is not generated. The small amount of bypass fuel that has flowed into the combustor is oxidized by the high-temperature atmosphere in the process of mixing with the surrounding premixed combustion gas.
There is no emission of O. Further, since it becomes possible to perform 100% premixed combustion, it is possible to suppress the generation of NOx. Further, combustion oscillation can be suppressed.

[0040]

As described above, according to the present invention, it is possible to obtain a gas turbine of this kind which does not cause ignition delay of the diffusion burner even when the load is cut off or a sudden load drop occurs. it can.

[Brief description of the drawings]

FIG. 1 is a system diagram showing one embodiment of a fuel system of a gas turbine of the present invention.

FIG. 2 is a diagram showing an example of fuel flow control of the gas turbine combustor of the present invention.

FIG. 3 is a diagram showing a fuel flow rate at the time of load interruption.

FIG. 4 is a vertical sectional side view showing an example of a combustion mode of the gas turbine of the present invention.

FIG. 5 is a system diagram showing an example of a fuel supply system of the gas turbine of the present invention.

FIG. 6 is a system diagram showing another example of the fuel supply system of the gas turbine of the present invention.

FIG. 7 is a system diagram showing another example of the fuel supply system of the gas turbine of the present invention.

FIG. 8 is a system diagram showing another example of the fuel supply system of the gas turbine of the present invention.

[Explanation of symbols]

2 burner, 8 diffusion pilot burner, 9 premix combustion burner, 201 diffusion pilot burner fuel system, 2
02: premix burner fuel system, 203: bypass piping system, 208: bypass piping orifice, 209: bypass piping manual valve, 210: bypass piping control valve,
211: bypass pipe pressure regulating valve or pressure reducing valve.

Claims (6)

[Claims] 1. A method for operating a gas turbine, comprising: a diffusion combustion burner and a premix combustion burner, wherein operation is performed only by premix combustion at a predetermined load or more of the gas turbine. A method for operating a gas turbine, wherein the operation is performed while supplying an amount of fuel that does not maintain flame. 2. A method for operating a gas turbine having a diffusion combustion burner and a premix combustion burner, wherein when the gas turbine is operated at a rated load or a partial load, combustion is mainly performed only by the premix combustion burner and the diffusion fuel system is used. Is a method for operating a gas turbine, characterized in that an amount of fuel is supplied so that the diffusion flame does not hold flame and the flow in the diffusion fuel system does not stagnate. 3. A gas turbine comprising a diffusion combustion burner and a premix combustion burner, wherein the gas turbine is operated only by premix combustion at a predetermined load or more of the gas turbine. A gas turbine characterized by comprising a fuel supply means for supplying an amount of fuel that does not hold a flame to the diffusion combustion burner. 4. A gas turbine comprising a diffusion combustion burner and a premix combustion burner, wherein the gas turbine is operated only by a premix combustion at a predetermined load or more of the gas turbine, wherein the diffusion combustion burner has a fuel supply system. And a fuel distribution means for flowing an amount of fuel in which the diffusion flame is not maintained and the flow in the diffusion fuel system does not stagnate. 5. The gas turbine according to claim 4, wherein said fuel distribution means is formed by a bypass provided by a mechanism for adjusting a fuel flow rate of said diffusion combustion burner. 6. The gas turbine according to claim 5, wherein an orifice or a valve for adjusting a fuel flow rate is provided in the bypass passage.