JPH01137117A - Premixing pilot nozzle for dry type low nox combustion apparatus - Google Patents

Abstract

PURPOSE: To provide a sufficient safety heat source for firing a premixed flow in which NOx is reduced significantly by sustaining a diffusion pilot using a diffusion-premix nozzle and a relatively small quantity of fuel and supplying an extra fuel from the premix section of an auxiliary nozzle in order to fire a main fuel being supplied into a combustion chamber from a main nozzle in the upstream. CONSTITUTION: A main nozzle 36 is arranged annularly around a central auxiliary nozzle 38 and serves as a main premix chamber for main fuel flow being supplied thereto. A diffusion-premix nozzle 100 has a diffusion pilot section 62 equipped with a fuel supply pipe 64 comprising an axial fuel supply pipe 66 and a radial fuel distribution pipe 68 being set to supply a desired percentage of fuel flow into a premix chamber. According to the structure, diffusion flame is supported by only 2% of the total fuel flow of combustor and production of NOx is reduced significantly and heat input sufficient for furing main premix flow can be attained by increasing fuel flow through the auxiliary nozzle 38.

Description

DETAILED DESCRIPTION OF THE INVENTION BACKGROUND OF THE INVENTION The present invention relates to a combustor for a gas turbine, and more particularly, to a combustor for a gas turbine that reduces the amount of atmospheric pollutants such as nitrogen oxides (No,).

Two-stage, two-mode combustors have been developed to reduce the amount of NOx in gas turbine exhaust gases.

This two-stage, two-mode combustor is described in U.S. Patent No. 4,292.8.
It is disclosed in No. 01. In this U.S. patent, the upstream combustion chamber functions as a premixing chamber under normal operating load conditions;
It has been shown that when two combustion chambers are provided, such that the actual combustion occurs in the downstream combustion chamber, NOx emissions are significantly reduced compared to a conventional single-stage, single-fuel nozzle combustor. Ta. In the "double operation state", since there is no flame in the first-stream combustion chamber, the amount of NOl produced is reduced, and the central nozzle, which corresponds to the auxiliary nozzle, becomes the flame source for the operation of the combustor. According to a particular aspect of the invention in the above-mentioned U.S. patent, a plurality of annularly arranged main nozzles for injecting fuel into an upstream combustion chamber, a central nozzle for injecting fuel into a downstream combustion chamber; is provided. These main nozzles and central nozzles are all considered diffusion nozzles. This is because the nozzle has an axial fuel delivery tube, the discharge end of which is surrounded by an air swirler. The air swirler supplies combustion air to the fuel discharged from the fuel nozzle.

The inventors have discovered that the production of NO,c can be further reduced by changing the design of the central or auxiliary nozzle to what can be described as a diffusion-premixing nozzle. In operation, a relatively small amount of fuel is used to maintain the diffusion pilot while the premixing section of the auxiliary nozzle adds additional fuel to ignite the main fuel that is delivered upstream into the combustion chamber from the main nozzle. supply fuel.

OBJECTS OF THE INVENTION It is an object of the invention to provide a stable and sufficient heat source to ignite the main premix stream over the entire range of operating conditions.

Another object of the invention is to minimize the influence of the flame source on NOl emissions.

Another object of the invention is to minimize the amount of fuel used to create the pilot diffusion flame.

The features of the invention believed to be novel are set forth in the claims. However, the invention itself, as well as other objects and advantages thereof, may be best understood by reference to the following description and drawings.

SUMMARY OF THE INVENTION The present invention is particularly applicable to gas turbine combustors of the type having two combustion chambers separated by a venturi throat region. A plurality of annularly arranged main nozzles inject fuel into the upstream or first combustion chamber. In contrast, one auxiliary or central nozzle injects fuel downstream or into the second combustion chamber. According to the operating method, under base load, one central nozzle sustains combustion of the premixed fuel injected from the main nozzle while the gold main nozzle is extinguished.

According to the invention, the diffusion nozzle conventionally used in the central nozzle is replaced by a diffusion-premix nozzle, which accounts for approximately 20% of the total fuel flow rate throughout the combustor.
% to about 2% of the total fuel flow. To achieve this, air delivery pipes are provided surrounding the minimum quantity fuel delivery pipe to support diffusion flame combustion, while the maximum quantity of fuel delivery in the central nozzle is directed towards the radial fuel delivery pipe. Performed by a distribution pipe. Each fuel distribution tube injects fuel into a premixing chamber surrounding a diffusion pilot section. The diffusion pilot section is composed of an axial fuel feed tube and an air feed tube surrounding the axial fuel feed tube. In this way, a relatively small amount of fuel can be used as a diffusion flame to ignite the stream exiting the premixing chamber of the central nozzle. However, the amount required is considerably less than that required to ignite the main premix stream exiting the remaining main nozzles.

Therefore, this design minimizes the percentage of total fuel flow in the combustor that burns as a diffusion flame (high NO, (low) to provide sufficient heat input to ignite the main premix stream.

DETAILED DESCRIPTION OF THE INVENTION As shown in FIG. 1, gas turbine 12 includes compressor 14, combustion 316, and turbine 18, represented by a single blade. Although not shown, the turbine 1
8 is connected to and drives the compressor 14 by a common shaft, as is well known. Compressor 14 pressurizes inlet air, and this pressurized air is redirected (i.e., flows in the opposite direction) toward combustor 16 and is used within combustor 16 to cool the combustor. It is also used as combustion air. Gas turbine 12 has a plurality of combustors 16 (only one is shown in the figure), and these combustors are arranged around the outer periphery of gas turbine 12 . In one model of gas turbine, 14 combustors such as those described above are arranged around the outer circumference of the gas turbine. A transition duct 20 connects the outlet end of its corresponding combustor 16 to the inlet end of the turbine 18 and delivers the hot products of combustion to the turbine 18 .

The present invention is particularly applicable to U.S. Pat. 292. It is useful in two-stage, two-mode, low NO, C combustors of the type described in No. 801. As described in this U.S. patent and as shown in FIG. 2 of this application, each combustor 1
6 is a ml combustion chamber, that is, an upstream combustion chamber 24, and a second
or downstream combustion chamber 26 and a venturi throat region 28 between the upstream and downstream combustion chambers 24 and 26. Combustor 16 is surrounded by a combustor airflow sleeve 30 that provides a flow path for directing the flow of air discharged from compressor 14 to combustor 16 . The combustor 16 is further surrounded by an outer casing 31 . The outer casing 31 is bolted to the turbine casing 32.

A plurality of main nozzles 36 are arranged annularly around a central auxiliary nozzle 38 for respectively delivering fuel to the upstream combustion chamber 24 . In one model of gas turbine,
Each combustor may have six main nozzles and one auxiliary nozzle. In further discussion of combustor 1G, the fuel is as described in the above-referenced U.S. Pat.
2,801, via piping 42 to the main nozzle 36 and the central auxiliary nozzle 38. Ignition within the combustor is provided by a spark plug 48 (not shown in FIG. 2). Ignition of adjacent combustors is also provided by crossfire tubes 50, which are well known to those skilled in the art.

U.S. Patent Box 4,292. No. 801 points out that all fuel nozzles (both main and auxiliary nozzles) are the same, ie all fuel nozzles are of the diffusive type. As shown in FIG. 2, the main diffuser nozzle 36 has a fuel delivery nozzle 54 and an annular swirler 56. As shown in FIG. The fuel feed nozzle 54 feeds only fuel.

This fuel is then mixed with air from swirler 5B for combustion. According to US Pat. No. 4,292,801, the auxiliary nozzle is also a diffusion nozzle.

This will be explained below.

During base load operation, the two-stage two-mode combustor is designed to operate in premix mode.

In this premix mode, all main nozzles only mix fuel and air, and this mixture is ignited by a diffusion flame supported by an auxiliary or central diffusion nozzle. This premixing by the main nozzle and the ignition by the auxiliary diffusion nozzle reduce the amount of NO, c produced in the combustor. However, the system described above has at least one
There were two fundamental flaws. For example, laboratory tests have shown that NOx emissions are minimized under operating conditions consisting of using the lowest possible percentage of fuel for the auxiliary diffusion nozzle, but that at other operating conditions the same % fuel was found to not provide sufficient heat input to satisfactorily combust the main premix stream. The inventor has discovered that by using a minimum diffusion pilot in combination with the premix chamber of the central nozzle, a satisfactory pilot flame can be maintained for the main premix flow discharged from the upstream premix nozzle (main nozzle). I found it. Therefore, the present invention minimizes the percentage of total fuel to the combustor that is combusted as a diffusion flame (with high NO,c production) while at the same time using an auxiliary premix or pilot flow to Ensure sufficient heat input is available to ignite the premix stream.

To this end, in accordance with the present invention, a diffusion-premixing nozzle 100 is provided, as shown in FIGS. 2 and 3. Diffusion-
Premix nozzle 100 has a diffusion pilot section 62 with a fuel delivery tube 64 .

The fuel delivery tube 64 includes an axial fuel delivery tube 66 and a number of radial fuel distribution tubes 68 extending radially outwardly from the tube 66 and closed at their ends. In the preferred embodiment, six fuel distribution lines are provided. As best shown in FIG. 3, each fuel distribution pipe 68 serves a plurality of fuel discharge holes 70. As best seen in FIG. The fuel discharge holes 70 are oriented downstream toward the discharge end of the diffusion-premix nozzle 100 .

The dimensions of the fuel discharge holes 70 are set to deliver a desired percentage of fuel flow into the premix chamber, which will be described below.

The diffusion pilot section 62 further includes an air supply pipe 74. Air delivery tube 74 is coaxial with and surrounds axial fuel delivery tube 66. Air input to the air supply pipe 74 is as follows:
This is air discharged from the compressor 14. This discharge air has its flow direction reversed and flows through the combustor airflow sleeve 30.
and a combustor liner 78 .

Diffusion pilot section 62 has a first annular swirler or diffusion pilot swirler 82 at its discharge end. This diffusion pilot swirler 82 is for sending air discharged from the air supply pipe 74 toward the diffusion pilot flame.

A premixing chamber 84 is defined by a sleeve-like frustoconical tube 85 . Premixing chamber 84 surrounds diffusion pilot section 62 and has a discharge end proximate to the discharge end of diffusion pilot section 62 . The discharge air from the compressor 14 has its flow direction reversed and flows into the premixing chamber 84 from the space 76 as well as from the air feed tube 74 . A plurality of fuel distribution pipes 68 extend through the air supply pipe 74 into the annular premixing chamber 84 . Fuel and air are mixed in this premixing chamber and fed to a second swirler or premixing chamber, swirler 86 . The premixing chamber swirler 86 is connected to the diffusion pilot section 62
and the truncated conical cylinder 85 of the premixing chamber 84.

A third swirler or central nozzle swirler 90 is located downstream of the discharge end of the diffusion premix nozzle 100. A central nozzle swirler 90 is positioned between an extension or cup 92 of frustoconical tube 85 and a centerbody wall 95 of upstream combustion chamber 24 . Discharge air from compressor 14 has its flow direction reversed and flows from space 76 surrounding combustor liner 78 to central nozzle swirler 90 . The purpose of the central nozzle swirler 90 is to stabilize the flame of the diffusion-premix nozzle 100 when combined with the main premix flow from the first combustion chamber.

The required design of the diffusion pilot swirler 82, premix chamber swirler 86, and central nozzle swirler 90 is well known to those skilled in the art and will not be described further.

The frustoconical tube 85 of the premixing chamber 84 is made of a metal suitable for use within a gas turbine environment.

To explain the operation, at the time of starting, fuel is introduced into the first combustion chamber and combustion is started. When a predetermined intermediate range of loads is reached, the fuel flow is split between the main nozzle and the auxiliary nozzle to reach the desired load, and the auxiliary nozzle is ignited. Thereafter, fuel flow to the main nozzle is shut off, stopping combustion within the first combustion chamber.

The fuel flow is then set to the main nozzle again, this time
The main nozzle acts as the main premixing chamber for the main fuel stream fed to it, while the central nozzle is kept lit to form a pilot flame for the main premix stream.

In this respect, according to the prior art, approximately 20% of the total combustor fuel flow
Diffusion flame using % produces relatively large amounts of NO and X.

With the present invention using a diffusion-premix nozzle, only about 2% of the total combustor fuel flow is used to support the diffusion flame, resulting in significantly lower NO, C production. The remaining fuel in the pilot or auxiliary nozzle is premixed in the premixing chamber, thus emitting considerably reduced levels of NO8. In summary, as described above, according to the present invention, the amount of NO gas produced is reduced, and this reduction makes it possible to increase the flow rate of fuel passed through the auxiliary nozzle. By relying on the premixed flow of the diffusion pilot rather than the total premixed flow from the main nozzle, the turndown ratio or ability to operate under varying conditions is greatly expanded.

Although the invention has been illustrated and described with respect to specific embodiments, those skilled in the art will readily recognize that various modifications may be made within the scope of the appended claims. Therefore, the scope of the claims of the present application includes such modifications.

[Brief explanation of the drawing]

FIG. 1 is a side view of a gas turbine engine, partially shown in section. FIG. 2 is an enlarged side sectional view of the combustor portion of the gas turbine engine. FIG. 3 is a schematic side sectional view of a diffusion-premixing nozzle according to the invention. [Explanation of main symbols] 36: Main nozzle, 38: Center nozzle, 100: Diffusion-premixing nozzle, 62: Diffusion pilot section, 64: Fuel feed pipe, 66: Axial fuel feed pipe, 68: Radius direction fuel distribution pipe, 70: fuel discharge hole, 74: air supply pipe, 82,8
6.90: swirler, 84: premixing chamber, 85: truncated conical cylinder.

Claims (6)

[Claims] (1) a fuel delivery pipe having an axial pipe having an inlet end and a discharge end; an air delivery pipe coaxial with the axial pipe and surrounding the axial pipe; and a first annular swirler provided between the fuel supply pipe and the discharge end of the axial pipe, the fuel supply pipe further comprising: a diffusion pilot section including a plurality of radial fuel distribution tubes extending outwardly from the tube beyond the outer circumference of the air delivery tube and disposed proximate the inlet end of the axial tube; a premixing chamber surrounding the diffusion pilot section and having an inlet end and a discharge end, the radial fuel distribution tube extending into the premixing chamber; at least one fuel discharge hole provided in a radial fuel distribution pipe and directed towards the discharge end of the premixing chamber; and provided between the air delivery pipe and the wall of the premixing chamber. and a second swirler located at the discharge end of the premixing chamber. (2) first and second combustion chambers, and the first and second combustion chambers;
has a smaller volume than the combustion chamber of the first and second combustion chambers.
a plurality of diffusion-type main fuel nozzles arranged annularly upstream of the first combustion chamber to introduce fuel into the first combustion chamber; 1. A combustor for a gas turbine that includes a plurality of diffusion-type main fuel nozzles each having an annular swirler that introduces pressurized air into the combustion chamber to produce a combustible mixture of fuel and air. , disposed upstream of the second combustion chamber, and
A combustor for a gas turbine having a diffusion-premixing nozzle with a discharge end directed toward a combustion chamber. (3) In the combustor according to claim (2), the diffusion-premixing nozzle includes: an axial fuel feed pipe; an air feed pipe surrounding the axial fuel feed pipe; a diffusion pilot section having an annular diffusion pilot swirler disposed between a fuel supply pipe and the air supply pipe; a premixing chamber surrounding the diffusion pilot section; and a radial direction from the fuel supply pipe. a plurality of radial fuel distribution tubes extending outwardly through the air delivery tube into the premix chamber, at least one radial fuel distribution tube containing at least one fuel a plurality of radial fuel distribution pipes with discharge holes facing toward the discharge end of the premixing chamber, thereby distributing fuel into the premixing chamber; the air supply pipe and the premixing chamber; a premixing chamber swirler disposed adjacent the discharge end of the diffusion-premixing nozzle between the wall of the combustor. (4) The combustor according to claim (3), wherein the wall of the premixing chamber is a truncated conical cylinder. (5) In the combustor according to claim (2), the diffusion-premixing nozzle is disposed at the center of the annular arrangement of the plurality of main nozzles, and the diffusion-premixing nozzle A combustor in which a third swirler is disposed between the nozzle and a central body wall surrounding the nozzle. (6) In a central fuel nozzle used in a two-stage two-mode low NO_x combustor, a fuel delivery pipe including an axial pipe having an inlet end and a discharge end, and a fuel delivery pipe coaxial with the axial pipe and the axial pipe and a first annular swirler disposed between the axial pipe and the air feed pipe and located at the discharge end of the axial pipe. The fuel feed tube further includes a plurality of tubes extending outward from the axial tube beyond an outer periphery of the air feed tube and disposed near an inlet end of the axial tube. a diffusion pilot section including a radial fuel distribution tube; and a premixing chamber surrounding the diffusion pilot section and having an inlet end and a discharge end, the radial fuel distribution tube including a premixing chamber. a premixing chamber extending into the premixing chamber; at least one fuel discharge hole in at least one of said radial fuel distribution pipes and directed toward a discharge end of said premixing chamber; and said air supply. a second annular swirler disposed between a tube and a wall of the premixing chamber and located at the discharge end of the premixing chamber; a cup located downstream of the discharge end of the central fuel nozzle; a third annular swirler disposed between the cup and a center body wall surrounding the central fuel nozzle.