JPH0238851B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a gas turbine combustor, and particularly relates to the structure of a natural gas-fired low NOx combustor for the purpose of reducing nitrogen oxides (hereinafter referred to as NOx). .

[Background of the invention]

Methods for reducing NOx in gas turbine combustors can be roughly divided into wet methods that use water, steam, etc., and dry methods that are based on improving combustion performance. The former method uses other media (water, steam, etc.), which causes a decrease in turbine efficiency, while the latter combustion suppression method
Although it is superior to other methods, since the objective is uniform low-temperature lean combustion, its combustion form is subject to extremely severe conditions such as increasing CO generation in the direction of reducing NOx.

In general, NOx generation during combustion is dominated by the combustion gas in the local high-temperature area (above 1800℃) in the combustion area, and is mainly caused by the nitrogen content of unburned fuel exhaust and the oxidation of nitrogen in the combustion air. Occurs. These are
Thermal No. is called Fuel No., and Thermal No. in particular is highly dependent on nitrogen concentration and reaction time, and these phenomena are considerably influenced by gas temperature. Therefore, if a uniform low temperature (approximately 1500°C or less) is achieved in which no localized high temperature regions are formed during the combustion process, effective low NOx combustion will be possible.

Conventional combustion technology aimed at reducing NOx in gas turbines has a relatively large air flow rate compared to the fuel flow rate, and the air amount distribution within the combustion chamber can be selected with some degree of freedom. Lean diffusion combustion is the most advantageous. In particular, during combustion, the main objective is to achieve uniform low-temperature combustion by lowering the combustion temperature, promoting mixing, and shortening the NOx generation time.

As a means for realizing the above-mentioned combustion mode, a specific example of the prior art is as shown in Japanese Patent Publication No. 55-20122, in which a plurality of fuel nozzles are arranged in an annular shape in an annular combustion chamber, and the combustion chamber is It is constructed so that air, steam, etc. are introduced from the tip of an inner cylindrical cone provided at the center. The combustion mode of this combustor employs a combustion method in which fuel is distributed and supplied in the cross-sectional direction within the combustion chamber to equalize the combustion temperature and to lower the gas temperature in the downstream region of the combustion chamber. In addition, a flame stabilizer that mainly uses air swirling flow is installed around the fuel nozzle, and its flame stabilization mechanism is maintained by the circulating flow region formed by the air swirling flow from the flame stabilizer. It is known that it catches fire (Japanese Unexamined Patent Publication No. 57-202431). However, during combustion, relatively high temperature gas is involved in the circulating flow region to maintain the flame near the fuel nozzle and stabilize it, which is quite disadvantageous in low NOx combustion.
In particular, a flame stabilizer with air swirling vanes requires a relatively high-speed air jet (V>30 m/s) due to its functional form (applicable range: Reynolds number Re>10 ⁵ ). Rapid combustion is likely to occur near the fuel nozzle as a result of the shortened flame. Furthermore, the strength of the flame holding mechanism in the locally high temperature area within the circulating flow region, which is 1 to 2 times the diameter of the flame holding device, is a factor in the NOx generation mechanism. Therefore, even if we attempt to use multiple fuel nozzles with conventional flame holders, the
It is not possible to achieve NOx reduction. Especially low NOx
In combustion aimed at reducing NOx, the flame holding mechanism that is advantageous for reducing NOx is not reliable, and the combustion form is greatly influenced by the flame holding characteristics. The present invention relates to a more effective low NOx combustor that compensates for the above-mentioned drawbacks.

[Purpose of the invention]

The object of the present invention is to provide, in a combustor head combustion chamber,
An object of the present invention is to provide a gas turbine combustor that enables effective flame holding and combustion with lower NOx.

[Summary of the invention]

Generally, the combustion state within a combustor is controlled by the primary combustion region, and the flame holding mechanism is the basis thereof. That is, in the case of diffusion combustion aimed at low NOx combustion, it is necessary to form the flame structure near the fuel nozzle long and thin to achieve slow combustion that is effective for low NOx combustion. Especially at the beginning of combustion, the combustion form differs depending on the concentration field of fuel and air. Therefore, it is possible to reduce the fuel concentration field conditions during the combustion process by making it possible to separate the flame and burn on the lean side by using a fuel injection method that matches the flow of air.
It is possible to create a combustion form that is advantageous for NOx production.
The inventors have developed a fuel nozzle for the purpose of flame holding and a low
By separating the fuel nozzle that primarily produces NOx, we confirmed that stable lean combustion can be performed in a relatively narrow combustion chamber. First, air is jetted from near the center of the combustor head to form a vortex around the outer periphery of the combustion chamber head. On the other hand, combustion air is jetted toward the center of the combustion chamber from the outer wall of the inner cylinder near the head of the combustion chamber, thereby reinforcing the vortex flow. Fuel is injected into this vortex region for the purpose of flame stabilization. In particular, when fuel is injected into the vortex region, there is a difference in fuel concentration into the vortex region depending on the injection position, and by suppressing this fuel concentration, flame holding on the relatively lean side becomes possible. low
The most effective way to inject fuel into NOx is to inject the fuel at a position after the air jet from the outer wall of the cylinder in the combustion chamber.Since the combustion mode is on the relatively lean side, it is possible to achieve a wide range of low NOx. It is possible to achieve this goal.
Therefore, the above-mentioned fuel injection method for flame holding and low
By effectively combining fuel injection methods for NOx production, it is possible to establish stable and low NOx combustion.

[Embodiments of the invention]

A specific embodiment of the present invention is shown in FIGS. 1 and 2. FIG. In a gas turbine combustor that includes a combustor outer cylinder 1, an end cover 2, a fuel nozzle main body 3, a fuel injection pipe 4, an inner cylinder 5, an inner cylinder cone (small inner cylinder) 6, and a spark plug 7, the inner cylinder 5 An inner cylinder cap 8 is installed on the head of the head, and a tapered inner cylinder cone 6 is protruded concentrically from the upstream end of the head to the downstream end with a gap on the inner circumferential side corresponding to the inner cylinder 5. , an annular combustion chamber 9 is formed near the head of the inner cylinder 5. In addition, a first stage combustion air introduction hole group 1 is provided on the head wall surface side of the inner cylinder 5.
0, a second-stage combustion air introduction hole group 11 and an inner cylinder cooling hole group 12 are provided on the downstream side thereof, and an annular air introduction hole 13 is provided on the wall surface of the inner cylinder cap 8 corresponding to the annular combustion chamber 9. Provide multiple pieces. Furthermore, a group of cooling holes 14 are installed on the wall surface of the inner cylinder cone 6. The fuel nozzle body 3 is fixed to the end cover 2, and the fuel injection pipe 4 extending from the fuel nozzle body 3 passes through an air introduction hole 13 provided in the inner cylinder cap 8 and projects into the annular combustion chamber 9. Near the tip of this fuel injection pipe 4, a nozzle hole 15 for injecting fuel toward the inner cylinder 5 and the inner cylinder cone 6 is provided. Install it larger than the outer wall of item 4 and leave a gap. Moreover, as shown in FIG. 3, in the fuel injection pipe 4,
It is configured by alternately combining long fuel injection pipes 4a and short fuel injection pipes 4b, and changing the position at which fuel is injected into the combustion chamber. For example, when the fuel injection position is based on the first stage combustion air introduction hole group 10, the fuel injection pipe 4a is located in the air introduction hole group 1.
The fuel injection pipe 4b is configured to be able to inject fuel to the same or upstream side of the fuel injection pipe 4b.

Next, we will discuss the operating status of this combustor. First, air 1
6 is introduced into the gap between the combustor outer cylinder 1 and the inner cylinder 5, and air 10a, 11a,
12a, 13a, and 14a are introduced into the combustion chamber. On the other hand, the fuel 17 is guided from the fuel nozzle body 3 to the fuel injection pipes 4a, 4b, etc., and is injected into the inner cylinder head annular combustion chamber 9 from the injection holes 15 provided in each fuel injection pipe, and the ignition plug 7 is actuated. to continue ignition combustion.

The feature of this combustor is that fuel is effectively injected into the vortex and jet stream formed by the air flowing from the combustion head and the annular inner cylinder side in the annular space forming the head combustion chamber. , a combination of flame holding under relatively lean conditions and fuel injection in an even more lean region achieves stability and low NOx.

FIGS. 4 and 5 show an example of the flow pattern of air and fuel near the head of the combustion chamber, which illustrates the key points of the present invention. The solid line in the figure represents air flow, and the chain line represents fuel flow.

Air flowing through the gap formed by the air introduction hole 13 provided in the inner cylinder cap 8 of the head combustion chamber and the fuel injection pipe 4 flows along the fuel injection pipe, and the pressure difference between the jet flow and the space is reduced. This causes a backflow effect in the internal and external directions, and a relatively weak vortex is formed around the upstream side of the fuel injection pipe. This vortex is further strengthened by a backflow component caused by an air jet from the outer wall of the cylinder 5 in the combustion chamber. In the air operating state, when the fuel is injected into the upstream part of the first stage air introduction hole 10 (L _A >L _F ) through the fuel injection pipe 4, a large amount of fuel is drawn into the vortex region A, and the fuel concentration is It gets expensive. In addition, when the fuel injection position is installed after the air jet flowing through the air introduction hole 10 provided on the cylinder outer wall of the combustion chamber (L _A <L _F ), the vortex region A formed on the upstream side of the fuel injection pipe The amount of fuel flowing into the tank becomes extremely small. It has become clear that the difference in fuel concentration in this vortex region has a significant effect on flame holding performance and combustion characteristics.

FIGS. 6 and 7 show experimental results regarding flame holding and combustion characteristics depending on the protruding length L _F of the fuel injection pipe 4 from the inner cylinder cap 8. In terms of flame holding stability,
The shorter the fuel injection pipe L _F is, the better the condition is, but the amount of NOx generated tends to increase. Furthermore, if the fuel injection pipe is lengthened, NOx will be reduced, but unburned emissions such as CO will increase and flame holding stability will also decrease.

On the other hand, in the structure of this combustor, the length of the inner cone constituting the combustion chamber, the position of the air introduction hole, etc. are other factors that greatly affect the combustion characteristics.
First of all, even if multiple air introduction holes are provided in the combustion chamber head inner cylinder cap around the fuel injection pipe, or if they are introduced from positions in the internal and external directions of the combustion chamber, the vortex region that is formed inside the combustion chamber cannot be obstructed. On the contrary, if it is a means of strengthening, it is sufficient to achieve the purpose. In particular, in this configuration, the position of the first stage air introduction hole is a factor that influences the size and strength of the vortex region.
It has a large effect on flame holding performance. Figure 8 shows the flame blowout characteristics when the fuel injection position is constant at the distance L _A from the width L _C of the inner cylinder cap forming the head of the combustion chamber to the air introduction hole of the first stage on the downstream side. Indicated. Applicable range L _A / L _C = 0.6 to 1.7, L _A /
When L _C <0.6, the vortex region that contributes to flame holding is reduced, and combustion becomes unstable due to the dilution of the air-fuel mixture due to air flow from the surroundings and a decrease in combustion temperature, etc. Below 0.5, ignition occurs. It will also be impossible to start up.
Furthermore, when L _A /L _C <1.7, the vortex region is apparently enlarged, but a dead space is formed in part, and this region becomes a local high temperature area, which is disadvantageous in the direction of reducing NOx. In particular, the flame-holding mechanism in main combustion is such that the flame generated near the fuel injection hole of the fuel injection pipe is combusted by combustion products (high-temperature gas) drawn in from downstream to upstream by the flow of air from the surrounding area. continues, and plays an important role in stabilizing the flame.

Next, we will discuss the length of the protrusion of the inner cylinder cone and fuel injection pipe installed in the center of the inner cylinder. The role of the inner cylinder cone is to create a structure that makes it difficult for a high-temperature combustion zone to occur in the center of the combustion chamber than when there is no inner cylinder cone, and to form an annular combustion chamber, which naturally facilitates the dispersed injection of fuel. As a result, the mixture of air and fuel flowing in from the inner cylinder wall is promoted, and by performing combustion on the relatively lean side, it is advantageous for reducing NOx without causing extreme local high temperatures. Slow combustion can be achieved. Figure 9 shows the inner cylinder cone length L _B and the maximum fuel injection pipe protrusion length L _F.
The relationship between NOx generation concentration is shown. As the length L _B of the inner cylinder cone increases, the amount of NOx generated tends to decrease, but if it becomes extremely long, the amount of air inflow toward the head combustion chamber side decreases, and the inner cylinder near the head and the inner cylinder The cooling of the wall surface of the cone portion decreases and the metal temperature increases, which is disadvantageous in terms of reliability. On the other hand, if the inner cylindrical cone L _B is shortened, the fuel and air will not be mixed well, and air will be introduced due to the increase in pressure difference between the inside and outside as the annular combustion chamber expands into the cylindrical combustion chamber during the combustion process. This is because the area has a large amount of fuel, and combustion progresses rapidly near the tip of the inner cylinder cone.
This appears as an increase in NOx production. Therefore,
It is necessary to use the inner cylinder cone part within the applicable range of L _B /L _F =2.0 to 5.0.

FIG. 10 shows a specific example of the state of air flow in the vicinity of the head of a combustion chamber that has the functions of each part of the present invention. The amount of air introduced is set so that it always falls within the flammable range during low-load and high-load combustion during gas turbine operation. The air intake holes provided in the head inner cylinder cap account for 8 to 20% of the total air amount in the primary combustion area of the combustion chamber, and the air intake holes in the first stage combustion air intake account.
10 to 23%, the proportion of combustion air in the primary combustion area of the second and third stages installed downstream.
The optimal allocation is between 57 and 82%. In particular, the head of the main combustion chamber is characterized by the interrelationship between the amount of air from the air introduction hole installed in the inner cylinder cap and the amount of air from the first stage combustion air introduction hole. Since it controls the strength, etc., if it is outside the above lower limit, the flame holding performance will decrease mainly due to a decrease in the vortex strength. Furthermore, the stoichiometric mixing ratio (λ
= 1.0), the fuel shifts toward excess fuel, and at high loads it falls outside the flammable range, making good combustion impossible. On the other hand, when the upper limit is exceeded, there is no problem because the mixture ratio approaches the stoichiometric ratio (λ = 1.0) at high loads, but flame holding becomes unstable at low loads because the combustion is relatively lean. Therefore, during combustion, it is necessary to operate with the air amount distribution described above.

The characteristics of each element of the present invention have been described above, but the fuel supply means, which is the most important in the present combustor configuration, will be explained next. First, to explain the above-mentioned embodiment, the short fuel injection pipe for flame stabilization protrudes to the vicinity of the first stage combustion air introduction hole, and the fuel injection pipe mainly for combustion is connected to the first stage air introduction hole. The length is 1.5 times longer than the position of the hole, and the fuel injection pipes for flame stabilization and combustion are arranged alternately in the annular direction at approximately the same pitch as the length of the protrusion for flame stabilization. The fuel injection direction is configured to be introduced perpendicularly to the axis of the combustion chamber. The combustion form of this combustion method is that the flame in the flame holding section and the combustion flame are formed apart in the axial and annular directions within the combustion chamber, so the flame dispersion effect leads to a uniform low temperature direction for low NOx combustion. Close combustion is possible. As a means of making this combustion form more effective, it is possible to obtain even better performance by spacing the fuel in the axial and annular directions closer together (multi-staged fuel injection pipes), but the size of the combustor etc., are restricted from the shape. In addition, localized temperature increases occur due to flame interference. On the other hand, if the number of fuel injection pipes is reduced, the fuel dispersion effect will be lost, making it impossible to achieve low NOx combustion. Therefore, as shown in the embodiments of the present invention, the introduction is divided into three to four stages in the axial direction within the area corresponding to the amount of air flowing from the head of the combustion chamber and the amount of air from the combustion air introduction hole of the first stage. It is important to have a mechanism and to arrange the flames in an annular direction so that the flames do not interfere with each other.

FIG. 11 shows a structure in which a single fuel injection pipe 4c has fuel injection holes 4d and 4e for flame stabilization and combustion. Figures 12a and 12b show the fuel injection pipe 4.
An application example will be shown in which f, 4g and 4h, 4i protrude from the inner cylinder side or the inner cylinder cone side.

As described above, the present invention was established by clarifying the functions and effects of individual elements, and relates to a low NOx combustor that is the basis of lean, low-temperature combustion.

〔Effect of the invention〕

According to the present invention, a mechanism for injecting fuel for the purpose of flame stabilization into a vortex region formed by an air jet at the head of the combustion chamber and an air jet from the outer wall of the inner cylinder through a protruding fuel injection pipe, and a combustion Having a function of injecting fuel to the downstream side after introducing air, etc., and arranging the flame holding means and the fuel supply means to the lean side in a ring shape,
This makes it possible to disperse fuel in the circumferential and axial directions of the combustion chamber, preventing the formation of a single high-temperature region within the combustion chamber, making combustion extremely effective for reducing NOx.

FIG. 13 shows an example of combustion test results with the combustor structure of the present invention. Compared to the conventional multi-burner combustion method that uses an air swirl flame stabilizer in an annular combustion chamber, NOx reduction rate is 30% at gas turbine rating.
I got a prospect of improvement. Furthermore, we were able to confirm flame holding stability and stable combustion within the gas turbine load operating range.

Therefore, the present invention can provide a highly reliable low NOx combustor structure that achieves stable combustion as a gas turbine combustor.

[Brief explanation of drawings]

FIG. 1 is a vertical sectional view of the combustor head of the present invention, FIG. 2 is a front view of FIG. 1, FIG. 3 is a three-dimensional view of the combustor head showing the arrangement of fuel injection pipes of the present invention, and FIG. Figure 4,
Figure 5 shows the flow pattern of air and fuel at the head of the combustion chamber, Figure 6 shows the flame holding characteristics depending on the length of the protrusion of the fuel injection pipe, and Figure 7 shows the NOx and CO characteristics depending on the length of the protrusion of the fuel injection pipe. Figures 8, 9, and 10 show the characteristics of each part, Figures 11 and 12 show other application examples, and Figure 13 shows the characteristics of each part.
The figure shows a NOx concentration diagram in the gas turbine operating range. 4... Fuel injection pipe, 4a... Fuel injection pipe, 4b
... Fuel injection pipe, 6 ... Inner cylinder cone, 9 ... Annular combustion chamber, 10 ... First stage combustion air introduction hole,
13...Air introduction hole.

Claims (1)

[Scope of Claims] 1. A combustor outer cylinder with one end closed, and a combustor cylinder arranged approximately concentrically with the combustor outer cylinder inside the combustor outer cylinder, and with combustion air provided in the cylinder wall. an inner cylinder having an introduction hole; a small inner cylinder disposed inside the inner cylinder and forming an annular combustion chamber between the inner cylinder; and closing one end of the annular combustion chamber; and an inner cylinder cap having an air introduction hole for introducing air into the combustion chamber, and an inner cylinder cap that penetrates the wall of the combustion chamber and protrudes into the combustion chamber, and has an injection port upstream of the combustion air introduction hole. a second fuel injection pipe that penetrates the wall of the combustion chamber and protrudes into the combustion chamber, and whose injection port is located downstream of the combustion air introduction hole. A gas turbine combustor, characterized in that the flame is maintained by fuel injection from the first fuel injection pipe. 2. The gas turbine combustor according to claim 1, wherein the first fuel injection pipe passes through an air introduction hole in the inner cylinder cap. 3. In claim 1 or 2, the distance (LA) from the inner cylinder cap to the first stage combustion air introduction hole is defined as the gap length between the inner cylinder and the small inner cylinder. A gas turbine combustor characterized in that the temperature (Lc) is in the range of 0.6 to 1.7 times. 4. In claim 3, the length (LB) of the small inner cylinder with respect to the distance (LF) from the cap to the injection port of the first fuel injection pipe.
A gas turbine combustor characterized in that the range is 2.0 to 5.0 times. 5. In claim 1 or 2, the air amount distribution in the primary combustion region of the combustion chamber is controlled from the air introduction hole provided in the inner cylinder cap to the
~20%, 10~23 from the first stage combustion air introduction hole
%, and the gas turbine combustor is characterized in that combustion is performed in the range of 57 to 82% of the amount of combustion air from the second stage installed on the downstream side. 6. In claim 1 or 2, the injection port provided near the tip of the first fuel injection pipe is installed in a direction substantially perpendicular to the axis of the combustion chamber to inject fuel. A gas turbine combustor characterized in that: 7. The gas turbine combustor according to claim 1 or 2, wherein the first fuel injection pipe and the second fuel injection pipe are arranged alternately in the circumferential direction.