KR20230045523A - Heat treatment burner for powdery material - Google Patents

Abstract

The present invention provides a heat treatment burner for a powdery material, capable of suppressing the cohesion of a powdery material and heat-treating the powdery material in a dispersion state. The heat treatment burner for a powdery material includes: a powdery material conveying pipe (2) forming a powdery material conveying flow path (2a) in which the powdery material is conveyed by carrier gas; an inner pipe (3) installed by surrounding the periphery of the powdery material conveying pipe and forming a dispersion gas flow path (3a) between the inner pipe (3) and the powdery material conveying pipe (2), in which the dispersion gas for dispersing the powdery material is conveyed in the dispersion gas flow path (3a); a middle pipe (4) installed by surrounding the periphery of the inner pipe (3) and forming a fuel gas flow path (4a) between the middle pipe (4) and the inner pipe (3); an outer pipe (5) installed by surrounding the periphery of the middle pipe (4) and forming a delay gas flow path (5a) between the middle pipe (4) and the outer pipe (5); a nozzle part (6) positioned at a pipe end unit (2b) of the powdery material conveying pipe (2) and having a powdery material spurt hole (6b) for spurting the powdery material from the powdery material conveying pipe (2) through the inner pipe (3), wherein the nozzle part (6) determines an end of the dispersion gas flow path (3a); and a gas spray hole (2c) connecting the dispersion gas flow path (3a) to the powdery material conveying flow path (2a) and spraying the dispersion gas into the powdery material conveying flow path (2a).

Description

Heat treatment burner for powdery material}

The present invention relates to a powder heat treatment burner capable of suppressing aggregation of powder and heat-treating powder in a dispersed state.

BACKGROUND ART Conventionally, Patent Literatures 1 to 4 are known as powder heat treatment burners that pass inorganic powder in a combustion flame to form a fine functional material.

In Patent Document 1, “a burner for producing inorganic spheroidized particles and a burner device thereof” has an inner surface at a tip at a predetermined interval on the outer periphery of a raw material powder supply pipe having an opening in a shape in which the inner surface is wider toward the end, and the inner surface is formed at the tip. A first supply pipe having an opening that widens toward the end is disposed to form a fuel gas flow path between the raw material powder supply pipe and the first supply pipe, and a straight portion is formed at the tip at a predetermined interval on the outer circumference of the first supply pipe. section), and a second supply pipe having a cooling water circulation passage is provided to form a combustion gas passage composed of oxygen or oxygen-enriched air between the first supply pipe and the second supply pipe, and the raw material powder supply pipe The fuel gas flow path and the combustion gas flow path are formed by opening at the bottom of a flame holding portion which is the front end of the second supply pipe and is formed of a concave portion provided to open forward from the combustion gas flow path. .

"A burner for producing inorganic spheroidized particles, an apparatus for producing inorganic spheroidized particles, and a method for producing inorganic spheroidized particles" in Patent Document 2 is a raw material powder that is provided at the center of the tip of the nozzle section and transports the inorganic raw material powder transported by a carrier gas. A ring-shaped groove provided between a transport hole, a groove width changing member disposed in the raw material powder transport hole, and a surface at the tip of the nozzle portion exposed to the raw material powder transport hole and the tip of the groove width changing member, further comprising a carrier gas in a combustion chamber. It has a raw material powder ejection groove for ejecting the inorganic raw material powder transported by the nozzle, and the width of the raw material powder ejection groove exposed on the front end surface of the nozzle section is configured to be changeable.

The "burner for producing inorganic spheroidized particles" in Patent Document 3 is a burner for producing inorganic spheroidized particles, and is provided on the outer periphery of the first raw material supply passage for supplying raw material powder entrained in the carrier gas, and the fuel gas A fuel supply passage, a first oxygen supply passage provided on the outer periphery of the fuel supply passage and supplying an oxygen-containing gas, and a second oxygen supply passage provided on the outer periphery of the first oxygen supply passage and supplying raw material powder entrained in the carrier gas. A raw material supply passage, a second oxygen supply passage provided on the outer periphery of the second raw material supply passage and supplying an oxygen-containing gas, and a powder dispersion plate having a plurality of small holes formed at the tip of the first raw material supply passage A raw material dispersing chamber connected through and a combustion chamber connected to the raw material dispersing chamber and having an enlarged outlet side, and a conical wall surface of the combustion chamber is provided with a fuel supply passage, a first oxygen supply passage, and a second raw material supply passage. The furnace, the tip of the second oxygen supply passage is open, the opening of the fuel supply passage is an ejection hole for ejecting fuel from the wall surface of the combustion chamber in parallel with respect to the central axis of the burner, and the opening of the first oxygen supply passage A first oxygen blowing hole for ejecting an oxygen-containing gas from the wall surface of the combustion chamber in a direction to form a swirling flow within the combustion chamber, and the opening of the second raw material supply passage is from the first oxygen supply hole to the burner tip It is a blowing hole opening to the side, and the opening of the said 2nd oxygen supply path is a blowing hole opening from the 2nd raw material blowing hole toward the tip side of a burner.

The “burner device for producing inorganic spheroidized particles” in Patent Document 4 includes a ring-shaped burner that is formed in a ring shape at the end of a cylindrical member and blows a ring-shaped combustion gas, and is disposed on the inner periphery of the ring-shaped burner, The cylindrical raw material supply pipe opening near the end of the ring is formed of a cylindrical member coaxially arranged on the inner circumference of the ring-shaped burner, and at the end where the raw material supply pipe is opened, from the upstream of the inorganic powder raw material passing through the inside. It is configured by arranging a conical cone that gradually reduces the cross-sectional area of the passage toward the downstream side.

Japanese Patent No. 3001561 Japanese Unexamined Patent Publication No. 2012-193918 Japanese Unexamined Patent Publication No. 2010-36097 Japanese Unexamined Patent Publication No. 2006-76826

Fine powder tends to aggregate, and in the burners of Patent Literatures 1 to 3, the obtained particle diameter becomes large, and the target product may not be obtained.

In Patent Literature 4, a conical cone is provided, and the aggregated powder is collided with and dispersed.

However, there was a problem that it was difficult to sufficiently disperse the aggregated powder only by colliding.

The present invention has been devised in view of the above conventional problems, and an object of the present invention is to provide a powder heat treatment burner capable of suppressing powder aggregation and heat-treating powder in a dispersed state.

The powder heat treatment burner according to the present invention is provided surrounding a powder conveying pipe that forms a powder conveying passage through which powder is conveyed by means of a carrier gas, and surrounds the powder conveying pipe, and disperses the powder between the powder conveying pipe and the powder conveying pipe. An inner tube forming a dispersed gas flow path through which the dispersed gas for use is pumped and provided surrounding the inner tube, and between the inner tube and an inner tube forming a fuel gas flow path, provided surrounding the inner tube and an outer tube forming a delay gas flow path between the core tube and a powder ejection tube for ejecting powder from the powder transfer tube through the inner tube, located at the tube end of the powder transfer tube. A nozzle part having a hole and defining an end of the dispersed gas flow path, and a gas jet for injecting the dispersed gas toward the inside of the powder pressure transfer flow path by communicating the dispersed gas flow path with the powder flow path. It is characterized by having a hole.

In the nozzle parts, it is characterized in that the powder dispersion protrudes into the powder conveying pipe.

It is characterized in that a powder increasing member for increasing the flow rate of powder by narrowing the cross-sectional area of the inner tube is provided in the inner tube.

It is characterized in that the nozzle parts are provided with a tubular portion defining and defining the gas ejection hole between the end of the powder feed pipe and the pipe end.

The nozzle parts are characterized in that they are detachably screwed to the inner circumference of the inner tube.

The core pipe forms the delay gas flow path instead of the fuel gas flow path, and the outer tube forms the fuel gas flow path instead of the delay gas flow path.

In the powder heat treatment burner according to the present invention, powder aggregation can be suppressed and powder can be heat treated in a dispersed state.

1 is a side sectional view showing a first embodiment of a powder heat treatment burner according to the present invention.
FIG. 2 is a cross-sectional view of FIG. 1 viewed along the line AA.
3 is a side sectional view showing a second embodiment of a powder heat treatment burner according to the present invention.
FIG. 4 is a cross-sectional view seen along the line BB in FIG. 1 .
5 is a side sectional view showing a third embodiment of a powder heat treatment burner according to the present invention.
Fig. 6 is a side cross-sectional view showing another example of a powder increasing member provided in the powder heat treatment burner shown in Fig. 5;
7 is a side sectional view showing a fourth embodiment of a powder heat treatment burner according to the present invention.
8 is a side sectional view showing a fifth embodiment of a powder heat treatment burner according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferable embodiments of the powder heat treatment burner according to the present invention will be described in detail below with reference to the accompanying drawings. The powder heat treatment burner according to the present embodiment supplies, for example, inorganic powder such as silica (hereinafter referred to as powder) into a combustion flame to produce a fired body such as spherical silica as a functional material. will be.

As shown in Figs. 1 and 2, the powder heat treatment burner 1 according to the first embodiment includes a powder conveying pipe 2 and an inner pipe 3 provided surrounding the powder conveying pipe 2, A burner nozzle 1a having a multi-tube structure including an inner pipe 4 provided surrounding the inner pipe 3 and an outer pipe 5 provided surrounding the inner pipe 4 is provided.

The powder feed pipe 2 disposed at the center of the burner nozzle 1a forms a powder feed passage 2a through which powder is pressure fed with a carrier gas such as air.

Outside the powder conveying pipe 2, the inner pipe 3, the middle pipe 4, and the outer pipe 5 are arranged coaxially with the tube axis of the powder conveying pipe 2, and the powder conveying pipe 2 and the inner pipe ( 3), the inner tube 3 and the middle tube 4, the middle tube 4 and the outer tube 5 are provided with their outer circumferential surface and inner circumferential surface spaced apart from each other.

Between the inner pipe 3 and the powder feed pipe 2, a dispersed gas passage 3a is formed through which a dispersed gas for dispersing powder is pressure-fed. Between the inner tube 4 and the inner tube 3, a fuel gas flow path 4a through which fuel gas is supplied is formed. Between the outer tube 5 and the middle pipe 4, a delay gas passage 5a is formed through which a delay gas such as air or oxygen for burning fuel gas is supplied.

A delay gas flow path 5a may be provided between the inner tube 4 and the inner tube 3, and a fuel gas flow path 4a may be used between the outer tube 5 and the inner tube 4.

In the following description, terms of upstream or downstream are used based on the flow direction of the gas flowing through the respective flow passages 2a to 5a.

The tube end positions of the inner tube 3, the middle tube 4, and the outer tube 5 disposed in the burner nozzle 1a are arranged substantially aligned.

The position of the end part 2b of the powder conveying pipe 2 is such that the position of the end part 2b of the powder conveying pipe 2 enters the inside of the inner tube 3, the position of the end part of the inner tube 3, the middle tube 4 and the outer tube 5. It is arranged on the upstream side.

A disk-shaped nozzle part 6 is disposed on the pipe end 2b at the tip of the powder feeding pipe 2 so as to come into contact with the pipe end 2b.

A male thread 6a is formed on the outer circumferential surface of the nozzle part 6 . The male thread 6a of the nozzle part 6 is screwed to the female thread 3b formed on the inner circumferential surface of the tube end of the inner tube 3 in a detachable manner.

A powder ejection hole 6b is formed at the center of the nozzle parts 6 to eject powder from the powder conveying pipe 2 through the inner tube 3 to the outside of the burner nozzle 1a.

When the nozzle parts 6 are screwed into the inner pipe 3 and brought into contact with the pipe end 2b of the powder conveying pipe 2, the dispersion gas passage between the inner pipe 3 and the powder conveying pipe 2 (3a) is blocked by the nozzle parts (6). That is, the nozzle parts 6 define the end on the downstream side of the dispersed gas passage 3a.

In the powder feeding pipe 2, the dispersed gas flow passage 3a on the outside of the powder feeding pipe 2 is communicated with the powder feeding flow passage 2a on the inside of the powder feeding pipe 2 to feed the dispersed gas. A gas injection hole 2c for injecting toward the inside of the passage 2a is provided. The gas injection hole 2c is formed through the pipe wall of the powder conveying pipe 2. In the illustrated example, eight gas injection holes 2c are provided at equal intervals in the circumferential direction of the powder feed pipe 2 .

The gas ejection hole 2c is formed in an oblique direction toward the tube axis (center) of the powder feed pipe 2 and from the upstream side toward the downstream powder ejection hole 6b.

The gas injection hole 2c does not necessarily need to be formed at an angle. The gas injection hole 2c has an inclination angle of 0 orthogonal to the pipe axis direction of the powders conveying pipe 2, for example, in order to efficiently disperse the powders to be conveyed in the powders conveying passage 2a in the powders conveying pipe 2. It is preferable to form within the range of an inclination angle of 85 degrees from the direction of ° toward the downstream side.

Referring to the operation of the powder heat treatment burner 1 according to the first embodiment, the burner nozzle 1a is cooled by the fuel gas and the delay gas supplied through the fuel gas passage 4a and the delay gas passage 5a. While a combustion flame is generated, powder is pressurized by a carrier gas through the powder pressure feed passage 2a and ejected from the powder ejection hole 6b into the burner nozzle 1a, thereby supplying the powder into the combustion flame. By heat treatment, fired bodies such as spherical silica are produced.

At this time, the dispersed gas pumped through the dispersed gas passage 3a is injected from the gas injection hole 2c toward the inside of the powder pressure delivery passage 2a.

The dispersed gas injected from the gas ejection hole 2c collides with the carrier gas containing powder in the powder pressure feed passage 2a before reaching the powder ejection hole 6b.

The collision of the dispersed gas with the carrier gas or the air flow of the dispersed gas suppresses the aggregation of the powder in the carrier gas, and the agglomerated powder is disintegrated by the collision of the dispersed gas or the air flow ( ), and thereby, the powder can be ejected from the powder ejection hole 6b in a finely dispersed state and supplied to the combustion flame.

Thus, in the powder heat treatment burner 1 according to the first embodiment, the pulverization action by the dispersed gas injected from the dispersed gas flow path 3a through the gas injection hole 2c into the powder pressure feed flow path 2a, A finely dispersed state of the powder can be secured, and the powder can be appropriately heat treated.

Since the gas ejection hole 2c is inclined toward the powder ejection hole 6b, the dispersion of the powder can be efficiently promoted without the pressure-feeding of the powder being obstructed by the gas flow of the ejected dispersion gas.

3 and 4 show a second embodiment of the powder heat treatment burner according to the present invention. In the powder heat treatment burner 1 according to the second embodiment, the configuration of the nozzle parts 6 is different from that of the first embodiment. Hereinafter, descriptions of the same configurations as those of the first embodiment are omitted.

A powder dispersion body 7 is provided in the nozzle parts 6 so as to protrude toward the inside of the powder conveying pipe 2 . In the illustrated example, the powder dispersion 7 is integrally formed with the nozzle parts 6, but it may be detachable by screwing or the like.

The powder dispersion body 7 is formed in the shape of a cone protruding from the center of the disk-shaped nozzle part 6 toward the upstream side with a tapered end.

In the nozzle parts 6 provided with the powder dispersion 7, the powder ejection hole 6b is in the space between the powder dispersion 7 and the powder conveying pipe 2, A plurality is formed at intervals in the circumferential direction.

In addition to the disintegration by the dispersion gas described in the first embodiment, the powder in the carrier gas that the powder pressure feeding passage 2a is pressurized collides with the powder dispersion 7 together with the carrier gas, thereby aggregating the powder. can be further suppressed, and the aggregated powder can be pulverized by additional mechanical collision by the powder dispersion 7, and the powder is ejected from the powder ejection hole 6b in a finely dispersed state. It can be fed into a combustion flame.

In the illustrated example, the powder dispersion 7 is formed in a conical shape, but it may have any shape as long as it can collide with the powder and mechanically crush it.

In the case of the cone-shaped powder dispersion 7, the cross-sectional area gradually increases from the upstream side toward the downstream side, and the powder feeding passage 2a narrows toward the powder ejection hole 6b, so that the powder is a powder dispersion ( 7), the powder can be smoothly ejected from the powder ejection hole 6b.

Even in such a second embodiment, it is needless to say that the effect achieved by the first embodiment is exhibited.

5 shows a third embodiment of the powder heat treatment burner according to the present invention. In the powder heat treatment burner 1 of the third embodiment, a powder speed increasing member 8 is provided in the inner tube 3 to narrow the cross-sectional area of the inner tube 3 and increase the flow rate of the powder. Hereinafter, descriptions of the same configurations as those of the first embodiment are omitted.

The powder increasing member 8 is provided on the nozzle part 6 so as to be located in the inner tube 3. In the illustrated example, the powder increasing member 8 is provided so as to be attachable or detachable to the nozzle parts 6 by screwing 9, but may be integrally formed.

The powder increasing member 8 is of any form, as long as it can narrow the cross-sectional area of the inner pipe 3 on the downstream side of the nozzle parts 6 having the powder ejection hole 6b and increase the gas flow rate in the inner pipe 3. may be

In the illustrated example, the powder increasing member 8 is formed in a cylindrical shape protruding from the center of the disk-shaped nozzle parts 6 toward the downstream side.

In the nozzle parts 6 provided with the powder increasing member 8, the powder ejection hole 6b is located in the space between the powder increasing member 8 and the powder conveying pipe 2, A plurality is formed at intervals in the circumferential direction.

In the third embodiment, the powder ejected from the powder ejection hole 6b in a finely dispersed state by the dispersed gas from the gas ejection hole 2c is provided by the powder increasing member 8 disposed in the inner tube 3. , can be ejected from the burner nozzle 1a at high speed.

As the powder speed increasing member 8, in FIG. 5, a cylindrical one attached to the center of the nozzle parts 6 was exemplified, but, unlike this, as shown in FIG. 6, the inner diameter of the inner tube 3 is smaller than the inner diameter. A ring-shaped powder increasing member 8 formed with an inner diameter and attached to the inner circumferential surface of the inner tube 3 may be used.

The powder ejection hole 6b in this case is located inside the powder increasing member 8 surrounded by the powder increasing member 8 .

In the drawing, the inner diameter of the powder increasing member 8 is shown larger than the inner diameter of the powder ejection hole 6b, but may be smaller than the inner diameter of the powder ejection hole 6b.

The ring-shaped powder speed increasing member 8 has a male screw 8a screwed into the female screw 3b of the inner tube 3 to which the nozzle parts 6 are screwed, and is screwed from the downstream side of the nozzle parts 6. It is provided to be detachable to the inner tube (3).

Even with such a ring-shaped powder speed increasing member 8, the cross-sectional area of the inner tube 3 can be narrowed to increase the flow speed of the powder.

The powder speed increasing member 8, whether in the cylindrical shape shown in FIG. 5 or in the ring shape shown in FIG. 6, is provided so as to be attachable and detachable to the nozzle parts 6 and the inner tube 3 by screwing, and therefore has a plurality of different dimensions. By preparing the powder increasing member 8 in advance and replacing it with the nozzle parts 6 or the inner tube 3, the powder ejection speed from the burner nozzle 1a can be easily and freely adjusted.

Even in such a third embodiment, it goes without saying that the effect achieved by the first embodiment is exhibited.

7 shows a fourth embodiment of the powder heat treatment burner according to the present invention. The powder heat treatment burner 1 according to the fourth embodiment includes the powder dispersion 7 of the second embodiment and the powder increasing member 8 of the third embodiment, both of which are detachably attached to the nozzle parts 6. it is combined

In such a fourth embodiment, not only the functions and effects achieved by the first embodiment, but also the functions and effects achieved by the second and third embodiments can be exhibited.

8 shows a fifth embodiment according to the present invention. As shown in the figure, in the powder heat treatment burner 1 of the fifth embodiment, at the end of the powder feed pipe 2, the outer diameter of the powder feed pipe 2 is obliquely inclined so that the powder feed pipe 2 is closed toward the downstream side. The 1st taper part 2d is formed over the whole periphery of the powder feed pipe 2, and that part becomes the pipe end part 2b.

On the other hand, the nozzle parts 6 are integrally formed with a tubular portion 6c coaxial with the tube axis of the powder feeding pipe 2 and having the same dimensions as the inner and outer diameters of the powder feeding pipe 2, At the upstream end of the tubular portion 6c facing the first taper portion 2d of the pipe 2, a ridge is formed along the entire circumference of the tubular portion 6c in parallel with the first taper portion 2d. A second tapered portion 6d is formed in a similar manner.

When the nozzle parts 6 are screwed into the inner pipe 3, the second taper part 6d of the tubular part 6c of the nozzle part 6 and the first taper part 2d of the powder conveying pipe 2 Between , a slit-like gas injection hole 2e is formed that is partitioned by these tapered portions 2d and 6d and extends over the entire circumference of the powder feed pipe 2 .

This slit-shaped gas ejection hole 2e is also formed obliquely toward the pipe axis (center) of the powder feed pipe 2 and from the upstream side toward the downstream powder ejection hole 6b, as in the above embodiment. From the slit-shaped gas injection hole 2e, the dispersed gas is injected from the entire circumference of the powder pressure feed pipe 2 toward the powder pressure feed passage 2a.

In 5th Embodiment provided with the slit-shaped gas injection hole 2e, the hole-shaped gas injection hole 2c of the powder conveyance pipe 2 of the said embodiment is abbreviate|omitted.

Also in the fifth embodiment, the dispersed gas pumped through the dispersed gas passage 3a is injected from the slit-shaped gas injection hole 2e toward the inside of the powder pressure delivery passage 2a, and the injected dispersed gas is powder The carrier gas containing

In the fifth embodiment, since the dispersion gas is injected from the entire periphery of the powder pressure feeding passage 2a, the powder in the carrier gas can be uniformly dispersed.

In addition, by adjusting the screwing position of the nozzle parts 6 to the inner tube 3, the distance between the first taper part 2d and the second taper part 6d is increased or decreased, and the slit-shaped gas injection The size of the hole 2e can be adjusted, so that the ejection speed of the dispersed gas can be adjusted.

Further, in the illustrated example, since powder increasing members 8 having a cylindrical shape and an annular shape are provided, the powder ejection speed can be adjusted by both of them.

In such a fifth embodiment, not only the action and effect achieved by the first embodiment, but also the action and effect achieved by the second to fourth embodiments can be exhibited.

The above embodiment is for facilitating understanding of the present invention, and is not intended to limit and interpret the present invention. It goes without saying that the present invention may be modified and improved without departing from the gist thereof, and equivalents thereof are included in the present invention.

1: powder heat treatment burner 1a: burner nozzle
2: powder conveying pipe 2a: powder conveying passage
2b: tube end of powder conveying pipe 2c: gas injection hole
2d: first taper portion 2e: slit-shaped gas injection hole
3: Inner pipe 3a: Dispersion gas flow path
3b: female thread 4: middle pipe
4a: Fuel gas flow path 5: Appearance
5a: delay gas flow path 6: nozzle parts
6a: male screw 6b: powder ejection hole
6c: tubular portion 6d: second tapered portion
7: powder dispersion body 8: powder increasing member
8a: female thread 9: screw coupling

Claims (6)

a powder conveying pipe forming a powder conveying passage through which powder is conveyed by means of a carrier gas;
An inner tube provided to surround the periphery of the powder feeding pipe and forming a dispersion gas flow path between the powder feeding pipe and the dispersed gas passage through which a dispersed gas for dispersing powder is forcefully fed;
a middle tube provided surrounding the inner tube and forming a fuel gas flow path between the inner tube and the inner tube;
an outer cover provided to surround the periphery of the core pipe and forming a delay gas flow path between the outer pipe and the core pipe;
a nozzle part located at a tube end of the powder conveying pipe, having a powder ejection hole for ejecting powder from the powder conveying pipe through the inner pipe, and defining an end of the dispersed gas passage;
A powder heat treatment burner characterized in that the powder heat treatment burner is provided with a gas injection hole through which the dispersed gas flow path communicates with the powder pressure feed flow path and dispersed gas is injected toward the inside of the powder pressure feed flow path. The method of claim 1,
The powder heat treatment burner, characterized in that the powder dispersion protrudes into the powder feed pipe in the nozzle parts. According to claim 1 or claim 2,
A powder heat treatment burner, characterized in that, a powder increasing member for increasing the flow rate of powder by narrowing the cross-sectional area of the inner tube is provided in the inner tube. The method according to any one of claims 1 to 3,
The powder heat treatment burner characterized in that the nozzle parts are provided with a tubular portion defining the gas injection hole between the end portion of the powder feed pipe and the pipe end of the powder feed pipe. The method according to any one of claims 1 to 4,
The powder heat treatment burner, characterized in that the nozzle parts are detachably screwed to the inner circumference of the inner tube. The method according to any one of claims 1 to 5,
The powder heat treatment burner according to claim 1, wherein the core tube forms the delay gas flow path instead of the fuel gas flow path, and the outer tube forms the fuel gas flow path instead of the delay gas flow path.

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