JPH08128636A - Gas combustion apparatus - Google Patents

Abstract

PURPOSE: To obtain a gas combustion apparatus which enables stable combustion especially at a lower fuel ratio (lower load) in a type which enables a low NOx combustion by supplying a premixed gas in two stages. CONSTITUTION: In a two-stage premixed gas combustion apparatus, a jetting hole 2 of a premixed gas for primary combustion with a mixing ratio between air and a fuel gas fixed or variable according to the need is arranged in the perimeter of a pilot gas nozzle 50 comprising a pilot gas passage 51 at the central part thereof and an air passage 52 in the perimeter thereof and moreover, a jetting hole 3 of a premixed gas for secondary combustion with the mixing ratio between the air and the fuel gas varied by varying the amount of a fuel gas is arranged in the perimeter thereof. This enables the obtaining of a stable combustion of a pilot fuel gas at a low load, eventually expanding a load range of the combustion apparatus.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas combustor, and more particularly to a gas combustor capable of low NOx combustion by supplying premixed gas in two stages, which is stable at a low fuel ratio (low load). The present invention relates to a gas combustion device that enables combustion.

[0002]

2. Description of the Related Art The release of NOx generated by combustion into the atmosphere has become a serious problem, and the reduction of so-called thermal NOx discharged from a gas combustion apparatus has also become an issue. Considering a gas turbine combustor as an example of a gas combustor, when diffusion combustion that provides stable combustion is used, combustion of a fuel-air mixture has an adiabatic flame temperature of around 2000 ° C. Combustion gas is mixed with air in order to lower the combustion gas temperature below the heat resistant temperature of the metallic turbine blade installed downstream of the combustor. However, due to the high temperature of the diffusion flame surface, N
The generation of Ox cannot be avoided entirely. As an effective combustion method for lowering the temperature of the combustion flame to reduce the production of NOx, a premixed combustion method is used in which fuel and combustion air are mixed before combustion and burned as a lean premixed gas. .

The applicant of the present invention has already proposed and developed a premixed gas combustion apparatus as shown in FIGS. 8 and 9 as an improved gas combustion apparatus using the premixed combustion method (Japanese Patent Laid-Open No. Hei. -296412 reference). This premixed gas combustion device is provided with an ignition fuel gas injection hole in the center, and a primary combustion premixed gas injection hole having a constant mixing ratio of air and fuel gas around the injection hole, and further on the outer periphery thereof. The injection holes for the premixed gas for secondary combustion in which the mixing ratio of air and fuel gas is made variable by making the amount of fuel gas variable are concentrically provided.

The ignition fuel gas injection hole 1 is supplied with the ignition fuel gas G via a conduit 11, and the primary combustion premixed gas injection hole 2 is supplied with the primary fuel gas G ₁ via a conduit 12. In addition, a conduit 1 is provided in the premixed gas ejection hole 3 for secondary combustion.
The secondary fuel gas G ₂ is supplied via 3 and is ejected from the tip side (ejection end). On the other hand, an air inlet 100a is formed on the downstream side (right side in the figure) of the tubular body 100, and the combustion air A is supplied from this. In addition, the premixed gas injection holes 2 for primary and secondary combustion
And 3 are swirlers 14 and 1 at the end opposite to the ejection end.
It communicates with the inside of the cylindrical body 100 via 5, and the air for premixing is introduced.

In the premixed gas combustion apparatus according to the above-mentioned proposal, at the time of startup, the ignition fuel gas is ejected from the ignition fuel gas ejection hole 1 to diffuse and burn, and the primary combustion premixed gas ejection hole 2 is supplied with air. A premixed gas having a constant mixing ratio with the primary fuel gas is jetted and burned, and after starting, the mixture of air and the secondary fuel gas having a mixing ratio corresponding to the load is preliminarily discharged from the premixed gas injection holes 3 for secondary combustion. The mixed gas is ejected and burned, and then the fuel gas for ignition is narrowed down. In this combustion system, the premixed gas for primary combustion was supplied in a fixed amount to continue combustion, so diffusion combustion with a large amount of NOx components in the exhaust gas is only at start-up, and thereafter the unburned gas content is wide in a wide air ratio. The NOx emission can be suppressed while keeping the NOx emission at a low value, and the NOx emission can be significantly reduced as compared with the conventional premixed gas combustion device. Further, since the supply amount of the combustion air A is fixed regardless of the load fluctuation, there is no need for a variable mechanism for controlling the flow rate of the combustion air, which simplifies the structure of the combustor and has the advantage of downsizing. is there.

[0006]

In the process of further continuing the combustion experiment for the above-mentioned premixed gas combustion apparatus, the present inventor has achieved combustion in which both NOx emission and unburned component emission are suppressed at the rated load of the combustion apparatus. If the load is reduced (the amount of secondary fuel gas is reduced to dilute the premixed gas for secondary combustion), a large amount of unburned components (CO) are discharged below a certain load factor. Therefore, it was found that the combustion efficiency was lowered. By conducting further research, the most effective means for obtaining combustion that suppresses both NOx emissions and unburned component emissions even at a low load is to use the primary combustion premixed gas as opposed to the secondary combustion premixed gas. I found it necessary to increase the ratio sufficiently. This is because the premixed gas for primary combustion carries out normal combustion with a flame, whereas the premixed gas for secondary combustion carries out gas phase combustion due to the heat when the premixed gas for primary combustion burns. In addition, it is necessary to provide the primary combustion premixed gas sufficient to give sufficient heat to the secondary combustion premixed gas.

However, in the above-mentioned premixed gas combustion apparatus, the premixed gas for primary combustion is supplied in a constant amount regardless of the load. Therefore, increasing the amount of the primary fuel gas relatively corresponds to the load. It means reducing the amount of secondary fuel gas in the premixed premixed gas, which means that the load range during operation of the combustion device is narrowed. If the supply ratio of the secondary fuel gas is increased to expand the load range, the ratio of the primary fuel gas becomes smaller, and as described above, the calorific value can be obtained by giving sufficient heat to the secondary combustion premixed gas. As a result, unburned components are generated in the secondary fuel gas, and the range in which high combustion efficiency can be obtained is similarly narrowed.

As a method of expanding the load range of the combustion device, it is possible to change the mixing ratio of the fuel gas of the primary combustion premixed gas and air, but the fuel gas concentration of the primary combustion premixed gas is NOx production. It is considered to be a practical solution because it is made sufficiently dilute to reduce the above, and further diluting may cause misfire. FIG. 7 shows an example of a fuel supply schedule when a combustion test is performed on the above combustion apparatus under substantially the same conditions as a gas turbine combustor. According to the experiments conducted by the present inventors, a fuel ratio of 100% to 85% is obtained. Combustion with low NOx and high combustion efficiency is possible in the range, but in order to maintain high combustion efficiency in this range, it is necessary to supply about 60% of the rated fuel gas as the primary fuel gas, The load fluctuation will be adjusted by adjusting the secondary fuel gas of about 40% of the rated fuel gas.
The operating load range of the combustion device at this time is 60% in terms of fuel ratio.
Limited to ~ 100% range. To expand the load range,
If the supply ratio of the secondary fuel gas is increased and the ratio of the primary fuel gas is decreased, as described above, a sufficient calorific value cannot be obtained, and unburned components are generated in the secondary fuel gas so that a range in which high combustion efficiency is obtained can be obtained. Narrowed.

As described above, in the already proposed combustion apparatus, it is not possible to achieve the expansion of the load range with low NOx and high combustion efficiency only by adjusting the primary fuel gas and / or the secondary fuel gas. From a different point of view, an attempt was made to supply fuel gas only from the combustion gas ejection holes for ignition and burn it, but in that case, NOx generation increased due to an increase in the diffusion combustion ratio, and at the time of rated fuel gas supply The amount of fuel gas was about 30% of the amount, and the fire broke out, and a satisfactory result was not obtained. This is about 60% of the rated value
In the setting to supply the fuel gas as the primary fuel gas, about 50% of the combustion air is supplied to the primary premixed gas ejection holes,
The fuel gas supplied from the ignition fuel gas ejection hole diffuses and burns with a relatively large amount of combustion air supplied to the primary premixed gas ejection hole, so to maintain the ignition state, the primary premixed gas ejection hole It is understood that the reason is that a relatively large amount of gas commensurate with the amount of combustion air supplied to is required.

An object of the present invention is to eliminate the above-mentioned disadvantages of the premixed gas combustion apparatus of the type shown in FIGS. 8 and 9 which the present applicant has already proposed. More specifically, Improves combustion conditions at low loads, which results in low NO
It is to provide a gas combustion device in which the combustion range of high combustion efficiency is expanded to a low load range.

[0011]

A gas combustion apparatus according to the present invention for solving the above problems and achieving the object basically comprises a pilot gas flow passage in a central portion and an air flow passage around the pilot gas passage. Pilot gas nozzle, an injection hole for the primary combustion premixed gas around the pilot gas nozzle, in which the mixing ratio of air and fuel gas is constant or variable as necessary, and the primary combustion premixed gas injection hole Around,
It has a structure in which an injection hole of a premixed gas for secondary combustion is arranged in which the mixing ratio of air and fuel gas is made variable by making the amount of fuel gas variable.

In a preferred aspect of the gas combustion apparatus of the present invention, a swirler is arranged in the air passage around the pilot gas passage. In another preferred aspect, a plurality of gas ejection holes of the pilot gas flow passage are arranged in the air flow passage around the pilot gas flow passage and at different radial positions downstream of the swirler. Further, the gas ejection hole of the pilot gas passage may be at the same axial position as the axial position of the ejection hole for the primary combustion premixed gas, and the axial upstream side of the ejection hole for the primary combustion premixed gas. The position may be deviated to.

[0013]

[Operation] In the gas combustion apparatus according to the present invention having the above-described structure, the pilot fuel gas is supplied from the pilot gas flow path, and at the same time, the combustion air is supplied from the air flow path located around the pilot fuel gas. . That is, in the previously proposed combustion apparatus, the ignition fuel gas ejected from the ignition fuel gas ejection hole is the air in the primary combustion premixed gas ejected from the surrounding primary combustion premixed gas ejection hole. However, in the combustion apparatus according to the present invention, the pilot fuel gas mainly mixes with the air supplied from the air passage and burns.

As a result, the combustion of the pilot fuel gas becomes stable, and it becomes possible to achieve stable combustion even at a low fuel ratio without misfiring. The heat also causes stable combustion of the premixed gas for primary combustion, so that stable combustion with low NOx at low load and high combustion efficiency is achieved. According to the experiments by the inventors, the amount of air supplied to the air passage around the pilot gas passage is made smaller than the amount of premixed gas for primary combustion (for example, the amount of premixed gas for primary combustion is By designing the air flow path so that it is about 50%), more stable combustion can be obtained, and thus the load range can be further expanded.

In the gas combustion apparatus of the present invention, the pilot fuel gas is supplied at the time of ignition and at the time of low load as in the fuel supply schedule shown in FIG. 6, and if necessary, at all loads up to the rated load. Supply in range.
According to the experiments by the inventors, the concentration of the mixed gas ejected from the pilot gas nozzle (hereinafter referred to as the pilot mixed gas) is equal to the concentration of the primary combustion premixed gas at a high load or is lower than the concentration of the primary combustion premixed gas. As shown in FIG. 5, it has become possible to simultaneously achieve high combustion efficiency and almost the same amount of NOx production as the conventional combustion device, by making it somewhat lean.

When a swirler is provided in the air flow passage around the pilot gas flow passage, swirling can be caused in the pilot fuel gas air flow or the pilot mixed gas, whereby the pilot mixing at low load is performed. The stability of the gas flame is further improved. The position of the gas injection hole in the pilot gas flow passage is located at the same position as the axial position of the injection hole for the primary combustion premixed gas, or at a position offset axially upstream thereof, but the pilot gas injection If the holes are arranged axially upstream of the injection holes for the primary combustion premixed gas, the effect of the primary combustion premixed gas on the pilot fuel gas can be reduced, and a smaller amount of gas can be stabilized. Combustion is obtained and the combustor load range is further expanded.

In the combustion apparatus of the present invention, when the gas ejection hole of the pilot gas passage is located at the central position and the air passage is arranged around it, the mixing of the pilot fuel gas and the air is not actively promoted. In this state, since the pilot mixed gas is supplied to the combustion field on the downstream side, diffusion combustion is the main combustion, and stable combustion can be promoted. However, in this case, some increase in NOx is unavoidable. When it is particularly necessary to reduce the NOx emission amount, the gas is ejected at different positions in the radial direction in the air flow passage around the pilot gas flow passage and at the downstream position of the swirler. Arrange a plurality of holes. As a result, the pilot fuel gas and the air are mixed more rapidly than in the above conditions, so that the combustion state becomes closer to premixed combustion, and low NOx combustion can be achieved.

FIG. 4 shows the combustion performance when only the ignition fuel gas is supplied in the previously proposed combustion apparatus according to the present application and the combustion performance when only the pilot fuel gas is supplied in the combustion apparatus according to the present invention. ing. In addition,
In the combustion apparatus of the present invention, when the position of the jet nozzle of the pilot fuel gas is set to the same position as the axial position of the jet hole of the primary combustion premixed gas (the same position arrangement), the axis of the bilot gas nozzle is about the same as the flow path diameter. Two modes are shown in the case of being displaced to the upstream side in the direction (arrangement on the upstream side).

As can be seen from the graph, in the combustion apparatus proposed above, there was a misfire at a combustion rate of about 30% of the rated fuel supply amount, and the combustion range was about 30% or more. In the combustion device by the above, even if the ejection holes are at the same position, there is an improvement of several%, and if the ejection holes are offset to the upstream side in the axial direction by the flow path diameter of the bilot gas nozzle, the fuel at the rated The combustion range was expanded to the range of about 7% or more of the supplied amount. Generally, the lower limit of the combustion range required for a gas turbine combustor is generally about 20% to 40% of the fuel supply amount at the time of rating, and the combustion apparatus according to the present invention sufficiently satisfies this. It is proved that the risk of misfire at low load can be further reduced when mounted on a gas turbine.

Further, the NOx generation amount at a low load is higher when the pilot fuel gas is supplied by the combustion device of the present invention than when the ignition fuel gas is supplied by the previously proposed combustion device. It is reduced regardless of the hole position. This means that when the ignition fuel gas is supplied to the previously proposed combustion device, all of them undergo diffusion combustion, whereas when the pilot fuel gas is supplied to the combustion device according to the present invention, the pilot fuel gas is generated as described above. NO in order to take a combustion mode intermediate between diffusion combustion and premix combustion in which the fuel gas and the air supplied from the air flow channel are burned while being rapidly mixed.
It seems that x can be reduced.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A gas combustion apparatus according to the present invention will be described in more detail below with reference to the accompanying drawings. In addition, in the gas combustion apparatus according to the present invention, except for the configuration related to the pilot gas nozzle, other configurations are similar to those shown in FIGS.
This is basically the same as the combustion device previously proposed by the applicant of the present invention. Therefore, members having the same functions as the members of the combustion apparatus shown in FIGS. 8 and 9 are designated by the same reference numerals in the drawings, and detailed description thereof will be omitted. In addition,
At the time of combustion, in the combustion device proposed above,
As shown in FIG. 7, a fixed amount of primary fuel gas is supplied, and a combustion method is adopted in which the amount of secondary fuel gas is changed to correspond to the load. In the combustion apparatus according to the present invention, the pilot gas and the primary fuel gas are almost In addition to the constant supply combustion method, a constant amount of pilot gas and primary fuel gas is supplied at high load, but there are also cases where a pilot gas and / or primary fuel gas is made variable at low load. Figure 6
Shows an example of a fuel supply schedule of the combustion apparatus according to the present invention.

In FIGS. 1 and 2, reference numeral 50 is a pilot gas nozzle, which is arranged in the central portion on the upstream side of the combustion apparatus. Around the pilot gas nozzle 50, a primary combustion premixed gas ejection hole 2 is located, and further, a secondary combustion premixed gas ejection hole 3 is located on the outer periphery thereof. The pilot gas nozzle 50 has a central pilot gas flow channel 51 and an air flow channel 52 around the pilot gas flow channel 51, and the air flow channel 52 communicates with the inside of the cylindrical body 100 through an opening 53. The area of the opening 53 is not particularly limited, but according to the experiments conducted by the present inventors, it is desirable to design the air so as to introduce about 50% of the amount of the primary combustion premixed gas.

In this embodiment, the tip end side of the pilot gas flow passage 51 is closed, and the axial position of the tip end thereof is substantially the same as the axial position of the primary combustion premixed gas ejection hole 2. ing. Further, a plurality of (six in the figure) nozzle tubes 55 are provided in the radial direction from the vicinity of the closed end.
Extend to the air flow path 52, and each nozzle pipe 5
The tip of 5 is also blocked. And the nozzle tube 5
A plurality of gas ejection holes 56 (four in the drawing) are formed in a portion where 5 is located in the air flow path 52.

Further, in this embodiment, a swirler 57 is attached to the air passage 52 upstream of the position of the nozzle pipe 55. In the gas combustion apparatus according to this embodiment, the pilot combustion gas G _p is fed to the pilot gas flow passage 51 through a pipe line (not shown), and the pilot gas flow passage 51 is supplied from the gas ejection holes 56 formed in the nozzle pipe 55. It is jetted into the air flow path 52 located in the surroundings.
Air is introduced into the air passage 52 through the opening 53, and the introduced air is swirled by passing through the swirler 57. The pilot fuel gas G _p burns intermediately between diffusion combustion and premixed combustion in which the pilot fuel gas G _p is burned while being rapidly mixed with the introduced air that has become a swirling flow.

The combustion air of the pilot fuel gas is the air mainly introduced from the air flow path 52, and is greatly affected by the primary combustion premixed gas ejected from the primary combustion premixed gas ejection holes 2. Can be burned without. As a result, the combustion can be maintained in a more stable state than the ignition fuel gas in the combustion device shown in FIGS. 8 and 9, and as described above with reference to FIG. 4, stable combustion is maintained up to a low combustion ratio. It becomes possible to do. Further, since the pilot mixed gas is in a stable and lean combustion state close to premixed combustion, low NOx combustion is also maintained.

FIG. 3 shows another embodiment of the gas combustion apparatus of the present invention. In this embodiment, the pilot gas passage 5 is used.
1 is the axial position of the closed front end portion of the nozzle 1, i.e., the front end position of the pilot gas nozzle 50
It is in a state of being displaced by a predetermined distance to the upstream side of the axial position. In this example, the pilot mixed gas ejected from the pilot gas nozzle 50 is less affected by the premixed premixed gas as compared with that shown in FIG. 1, and the combustion of the pilot mixed gas is further stabilized. Therefore, as shown in FIG. 4, it becomes possible to continue combustion stably up to a very low fuel ratio, and the load range is further expanded.

The above description is only a description of some embodiments of the gas combustion device according to the invention, and many variants exist. For example, it is not essential that the tip of the pilot gas flow channel 51 is closed, and the flow channel may have an open tip. In that case, the air that flows in from the air flow path 52 and the pilot fuel gas are moved to the combustion field on the downstream side in a state where they are not positively mixed, and combustion close to diffusion combustion is performed. A stable combustion state can be obtained. Thereby, the load range is further expanded.

Further, the swirler 57 provided in the air flow path is not always essential and may be omitted. In that case, the degree of mixing of air and pilot fuel gas decreases, which is effective for expanding the load range, but on the other hand, diffusion combustion increases and low NOx combustion becomes somewhat difficult.

[0029]

As described above, in the present invention, by providing the air flow passage around the pilot gas flow passage, it becomes possible to improve the combustion condition under a low load, and it has been previously proposed. It is possible to expand the combustion load range in a premixed gas combustor of the type that enables low NOx combustion by supplying the premixed gas described above in two stages (see Japanese Patent Application Laid-Open No. 5-296412). .

[Brief description of drawings]

FIG. 1 is an axial sectional view showing an example of a gas combustion apparatus according to the present invention.

FIG. 2 is an end view of the gas combustion device shown in FIG.

FIG. 3 is an axial sectional view showing another example of the gas combustion apparatus according to the present invention.

FIG. 4 is a graph showing a comparison of combustion performance.

FIG. 5 is a graph showing NOx emission amount and combustion efficiency at a high fuel ratio.

FIG. 6 is a graph showing an example of a fuel schedule of the gas combustion device according to the present invention.

FIG. 7 is a graph showing an example of a fuel schedule of the premixed gas combustion device according to the above proposal.

FIG. 8 is an axial sectional view showing a premixed gas combustion device according to the above proposal.

9 is an end view of the premixed gas combustion device shown in FIG.

[Explanation of symbols]

50 ... pilot gas nozzle, 51 ... pilot gas passage, 52 ... air flow channel, 53 ... air introducing hole, 55 ... nozzle pipe, 56 ... gas ejection hole, 57 ... swirler, G _p ... pilot gas, G ₁ ... Primary fuel gas, G ₂ ... Secondary fuel gas, 2 ... Premixed gas injection hole for primary combustion, 3 ... Premixed gas injection hole for secondary combustion

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display area F23R 3/34

Claims (4)

[Claims] 1. A pilot gas nozzle comprising a central pilot gas flow passage and an air flow passage around it, and a mixing ratio of air and fuel gas around the pilot gas nozzle is constant or variable as necessary. A certain primary combustion premixed gas injection hole and secondary combustion around the primary combustion premixed gas injection hole in which the amount of fuel gas is made variable so that the mixing ratio of air and fuel gas is made variable. A gas combustion device, characterized in that it is provided with a premixed gas ejection hole. 2. The gas combustion apparatus according to claim 1, wherein a swirler is arranged in an air flow path of the pilot gas nozzle. 3. The plurality of gas ejection holes of the pilot gas flow passage are arranged in different positions in the radial direction in the surrounding air flow passage and downstream of the swirler. The gas combustion device described. 4. The gas ejection hole of the pilot gas passage is located at a position displaced upstream of the axial position of the ejection hole for the primary combustion premixed gas. 4. The gas combustion device according to any one of 3 to 3.