JPH04260721A - Premixing type gas turbine combustor - Google Patents

Abstract

PURPOSE:To reduce NOx in combustion exhaust has by a method wherein combustion air at the first stage is supplied from a swirl as a non-swirl in a two-stage type combustor. CONSTITUTION:A first stage combustion chamber 1 showing a dispersion type combustion is disposed at an upstream side of a combustor and then the second stage combustion chamber 2 for supplying mixture gas of fuel and air so as to perform a premixing and combustion is disposed at a downstream side. Combustion air for the first stage combustion chamber 1 is supplied by a swirler of which swirlting angle can be varied, wherein a flame holding action is kept in the first stage combustion chamber 1 to keep the flame at the first stage and then ignition is carried out there. At this time, the combustion air for the first stage combustion chamber 1 is supplied as the non-swirl, thereby the flame holding action within the first stage combustion chamber 1 is diminished and the flame is held at the second stage combustion flame in the second stage combustion chamber 2 so as to perform a combustion there. In this way, all fuels can be premixed and ignited and then NOx in the exhaust gas can be reduced.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an industrial gas turbine, and more particularly to a premixed gas turbine combustor with a low NOx concentration in combustion exhaust.

0002

[Prior Art] The main stream of conventional low NOx gas turbine combustors is the combustion zone in the flow direction of the combustor.
This is a so-called two-stage combustion method in which the combustion is separated into the second stage. Here, the generation of NOx is suppressed by lower temperature combustion due to excessive air combustion. Although the first stage combustion is disadvantageous in terms of reducing NOx, diffusion combustion with high flame stability is used, and the second stage uses premix combustion, which is highly effective in reducing NOx. A typical example is U.S. Patent No. 42928.
A No. 01 low NOx combustor is disclosed. This combustor has a plurality of first-stage burners placed upstream of the combustor and a second-stage burner protruding inside the combustion chamber, and the combustion chamber has a throat with a reduced diameter approximately in the middle. It can be divided into upstream combustion and downstream combustion. Fuel is first supplied to the first-stage burner, ignited by a spark plug, and the gas turbine is started and speeded up by combustion in the first-stage burner. Thereafter, fuel is supplied to the second stage burner, and the second stage burner is activated. In this state, both the first stage burner and the second stage burner perform diffusion combustion. After that, while decreasing the fuel in the first stage burner, this fuel is transferred to the second stage burner, and finally, by supplying all the fuel in the first stage burner from the second stage burner, the first stage burner is Extinguish inflammation. After that, by reinjecting fuel into the first-stage burner, the first-stage burner acts as a mere mixing chamber for fuel and air, and the combustible mixture formed here is flame-stabilized by the second-stage burner flame. Achieves mixed combustion and suppresses NOx generation.

[0003] In a conventional low NOx combustor, when transitioning to premix combustion, the entire amount or almost the entire amount of fuel is injected into the second stage burner, so the amount of combustion in the second stage burner becomes excessive. , the combustor wall tends to reach high temperatures, and measures such as enhanced cooling are required to ensure reliability and longevity. Furthermore, in this combustor, even when the first stage burner is in premixed combustion mode, the second stage burner performs diffusion combustion, which generates a large amount of NOx, and it is necessary to effectively suppress the NOx generated here. be.

0004

SUMMARY OF THE INVENTION An object of the present invention is to provide a low NOx combustor suitable for a gas turbine. Another object of the present invention is to provide a fully premixed combustion type low NOx combustor that enables further reduction in NOx.

In order to achieve the above object, the present invention provides a first stage combustion chamber for diffusion combustion on the upstream side of the combustor, and a second stage combustion chamber for premix combustion by supplying a mixture of fuel and air on the downstream side. The formation position and combustion form of the first-stage flame are controlled by arranging the combustion chamber and applying or extinguishing the flame-holding effect of the first-stage combustion chamber. Specifically, combustion air is supplied to the first stage combustion chamber by a swirler that has a variable swirl angle, and by supplying the combustion air to the first stage combustion chamber as a swirling flow, a flame holding effect is achieved within the first stage combustion chamber. By holding the first stage flame here and supplying combustion air to the first stage combustion chamber as a non-swirling flow, the flame holding effect in the first stage combustion chamber is extinguished and the flame here is blown out. It is designed to be burned in a second stage combustion chamber.

[0006]

[Operation] By supplying the first stage combustion air as a swirling air flow using a swirler with a variable swirl angle installed at the upstream end of the first stage combustion chamber, a backflow region is created in the center of the first stage combustion chamber. It is formed. A portion of the fuel supplied from the first-stage fuel nozzle is drawn into this backflow region, and the flame is held in this region for stable combustion, which is used as a spark to form a first-stage combustion flame in the first-stage combustion chamber. On the other hand, if the first stage combustion air is supplied as a substantially non-swirling air flow by reducing the installation angle of the swirl vanes of the swirler or making it zero, the flow inside the first stage combustion chamber becomes a forward flow field with no backflow. becomes. In this flow field, there is no backflow region that has a flame-holding effect, so the first-stage combustion flame cannot remain in the first-stage combustion chamber and flows away downstream. At this time, if a premixed combustion flame is formed in the second stage combustion chamber, the first stage combustion flame is flame held by the second stage combustion flame and combustion continues. In this case, since mixing of the first stage fuel and first stage combustion air progresses in the first stage combustion chamber, premix combustion of both the first stage fuel and the second stage fuel occurs in the second stage combustion chamber. vice versa,
In this state, if the installation angle of the swirl vanes is increased, the first stage combustion air will be supplied as a swirling air flow, so a backflow region will be formed in the center of the first stage combustion chamber.
The flame travels upstream through this part and forms a first-stage combustion flame within the first-stage combustion chamber. In other words, by changing the flow pattern of the first-stage combustion air supplied into the first-stage combustion chamber, the presence or absence of a flame-holding effect in the first-stage combustion chamber can be controlled, and the combustion pattern can be changed from diffuse combustion to predetermined combustion without switching the fuel supply method. It is possible to switch to mixed combustion, or vice versa, from premixed combustion to diffusion combustion.

[0007]

[Embodiments] Hereinafter, embodiments of the present invention will be explained with reference to the drawings. FIG. 1 shows an embodiment of the present invention. The gas turbine combustor is cylindrical, and the turbine casing 2
The downstream end of the transition piece 25 consists of the first stage combustion chamber 1, the second stage combustion chamber 2, and the transition piece 25, which are housed by the combustor outer cylinders 22, 22' and the combustor outer cylinder cover 23 attached to the combustion chamber 6. It is connected to the turbine stationary blade 27. Projected air 100 from the compressor is guided to each combustion chamber 1, 2, and burns the fuel supplied from the first stage fuel system 200 and second stage fuel system 201 to generate high temperature combustion gas 106, which is then Supply to the turbine. The first-stage combustion chamber on the upstream side has a first-stage combustion tube 3 with a narrowed diameter, and its upstream end is connected to a pair of air introduction members 4, 4' that smoothly expand toward the outer circumference. The air introduction members 4 and 4' have a predetermined interval and form a first stage combustion air passage 5 whose upstream end is open to the combustor outer circumferential side and whose downstream end is open into the first stage combustion chamber. Road 5
Inside, a plurality of swirling vanes 6 are attached to the wall of the first stage combustion air passage by a rotating shaft 7 having gears, and the gears of the rotating shaft extend from the rotating device 8 via the combustor outer cylinder cover 23. A rotation control gear 10 driven by a rotation link 9 allows the mounting angle of the swirl vane to be freely adjusted. The first stage fuel nozzle 1 is located in the center of the head of the first stage combustion chamber.
1 is attached so as to be in contact with the air introduction member 4, and the first stage fuel 200' is injected into the first stage combustion chamber 1 from the fuel injection hole 12.

The second stage combustion chamber has a second stage combustion cylinder 13,
The first stage combustion cylinder 3 and the second stage combustion premixer 20 are assembled so as to be joined to each other. In the second-stage combustion premixer 20 , a second-stage fuel nozzle 21 is installed in a second-stage combustion air passage 17 defined by an inner circumferential passage 15 and an outer circumferential passage 16 . , and the combustion tube 1 corresponding to the downstream position of the second-stage combustion premixer 20.
A flame stabilizer 14 is attached to the inner surface of the combustion chamber 3, and a dilution air port 28 for controlling combustion gas temperature is further provided on the downstream side of the second stage combustion tube 13. Although not shown, each combustion cylinder is provided with a cooling air port for cooling the wall surface. Air 100 discharged from the compressor flows along the outer periphery of the combustion tube and enters the combustion chamber as dilution air 101, second stage combustion air 102, and first stage combustion air 104, respectively.
and flows in as cooling air.

Next, a method of operating such a combustor will be described. FIG. 2 illustrates the fuel supply method, with the horizontal axis representing time and the vertical axis representing the flow rate ratio of the first-stage fuel 200 and the second-stage fuel 201 to the total fuel flow rate, respectively. First, the gas turbine is supplied with only the first-stage fuel 200 at the start-up ignition at time ■, which is ignited by the ignition plug 24 to form a first-stage combustion flame in the first-stage combustion chamber, and operates in this state until the rated rotation speed condition is reached. be done. Note that at this time, the first stage combustion air is supplied as a swirling flow. During the fuel change at time ■, the first stage fuel 201 is injected while the second stage fuel 201 is injected.
By subtracting 0, the second stage combustion is activated, and a diffusion combustion flame and a premix combustion flame are formed in the first stage combustion chamber and the second stage combustion chamber, respectively. The switching of the combustion mode at time ■ involves supplying the first stage combustion air from a swirling flow to a non-swirling flow to allow the first stage combustion flame to flow downstream, and the second stage combustion flame ignites the first stage fuel, holds the flame, and then the second stage combustion air is supplied as a non-swirling flow. This is achieved by combustion in a combustion chamber. After that, increase the first stage fuel by 200 and the second stage fuel by 201 for a time
The rated output operation will be achieved. 3 and 4 respectively explain the operation and effect before and after switching the combustion mode at time (3). FIG. 3(a) shows the installed state of the swirl vane before switching the combustion mode, and FIG. 3(b) shows the flow pattern in the first stage combustion chamber. The swirl vanes are installed so as to have a swirl angle A as shown in FIG. will be introduced in Therefore, in the first stage combustion chamber, a swirling flow 107 as shown in FIG.
is formed. Because the pressure at the center of the swirling flow 107 is lower than that at the outer periphery due to the centrifugal force caused by the swirling motion, a backflow 108 from the downstream to the upstream of the combustor as shown by the dotted line is caused. When fuel is injected into such a flow field and ignited by the igniter, a portion of the high-temperature flame, including a portion of the second-stage combustion flame, is drawn into this reverse flow and transports the high-temperature combustion gas to the upstream side of the combustor. As a result, combustion is promoted by this high-temperature gas, and the flame is maintained in a low-velocity region with reverse flow, making it possible to sustain combustion even in high-speed airflow such as in a gas turbine combustor. A flame is formed stably. In addition,
This combustion is so-called diffusion combustion in which the fuel and air are mixed and burned in the combustion chamber, and although the amount of NOx generated is relatively large, the combustion stability is high. Figure 5 shows the flame formation state at this time. A first combustion flame 300 is formed in the first combustion chamber, and a second combustion flame 301 is formed in the second combustion chamber. Next, as a combustion switching operation, when the mounting angle A of the swirl vane is set close to zero as shown in FIG. It is introduced into the first stage combustion chamber with a chisel. Therefore, in the first-stage combustion chamber, a forward flow 109 is formed in which most of the flow flows from upstream to downstream of the combustor, as shown in FIG. 3(b). In such a flow field, there is no low-velocity region to hold the flame, so unless the airflow velocity inside the combustor is extremely slow, the flame will flow downstream of the combustor and will not be able to remain in the first stage combustion chamber. . At this time, by forming a second-stage combustion flame in the second-stage combustion chamber located downstream of the first-stage combustion chamber, the combustible mixture of fuel and air from the first-stage combustion is transferred to the second-stage combustion chamber. The heating effect of the combustion flame ignites, holds the flame, and burns. The state of flame formation at this time is shown in FIG. A first stage combustion flame 300 is also formed in the second stage combustion chamber, being flame stabilized by a second stage combustion flame 301 of the second stage combustion chamber. This switching of combustion results in so-called premixed combustion, in which the first stage fuel and second stage fuel are mixed with their respective combustion air before combustion, resulting in so-called premixed combustion, so the flame temperature does not change to diffuse combustion. By supplying fuel at a lean mixture ratio and performing low-temperature combustion, it is possible to suppress the generation of NOx.

0010

Effects of the Invention According to the present invention, by supplying the first stage combustion air from a swirling air flow to a non-swirling air flow in a two-stage combustor, diffusion combustion is achieved in the first stage and premix combustion is achieved in the second stage. Since it is possible to transition from this state to a combustion state in which all the fuel is premixed and combusted in the second stage combustion chamber, NOx can be effectively reduced. Furthermore, since the combustion mode can be switched without changing the fuel supply method, the combustion mode can be switched without changing the fuel supply method, while maintaining smooth operation of the gas turbine and without causing excessive thermal stress to the combustor hardware. It can be replaced and the combustor control equipment can be simplified.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a premix combustion type gas turbine combustor of the present invention.

FIG. 2 is a characteristic diagram showing the fuel supply method of the present invention.

FIG. 3 is an explanatory diagram of air flow conditions with different flame conditions in the first stage combustion chamber depending on the mounting angle of the swirl vanes.

FIG. 4 is an explanatory diagram of air flow conditions with different flame conditions in the first stage combustion chamber depending on the mounting angle of the swirl vanes.

FIG. 5 is a cross-sectional view showing the state of flame formation before and after combustion switching.

FIG. 6 is a cross-sectional view showing different flame formation states before and after combustion switching.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1...1st stage combustion chamber, 2...2nd stage combustion chamber, 3...1st stage combustion tube, 5...1st stage combustion air flow path, 6...Swirling vane, 11...1st stage fuel nozzle, 13...2nd stage combustion tube , 21...Second stage fuel nozzle.

Claims (1)

[Claims] Claim 1: A first-stage combustion chamber in which fuel and air for first-stage combustion are supplied to the upstream side of the combustor for combustion, and a combustible mixture is supplied by pre-mixing fuel and air to the downstream side thereof. This gas turbine combustor is composed of a second-stage combustion chamber that performs combustion, and an air swirler for first-stage combustion that can change the swirling angle is located on the outer circumferential side of the combustor at the head end of the first-stage combustion chamber. Further, a first-stage fuel nozzle is provided on the inner circumferential side of the head end of the first-stage combustion chamber, and the second-stage combustion chamber is connected to the downstream end of the first-stage combustion chamber, and the connection part thereof is connected to the downstream end of the first-stage combustion chamber. A premix burner for supplying and combusting a combustible mixture of fuel and air is provided on the outer peripheral side of the combustor near the combustor, and the gas turbine combustor is operated by supplying air for first-stage combustion as a swirl flow. A first stage combustion flame is formed in the first stage combustion chamber,
In addition, the first stage combustion flame is moved downstream by supplying air for the first stage combustion as a non-swirling flow, held by the second stage combustion flame, and combusted in the second stage combustion chamber. Mixed combustion gas turbine combustor.