JP6958335B2 - Dry dust collector and how to operate the dry dust collector - Google Patents

Description

The present invention relates to a dry dust collector and a method of operating the dry dust collector. More specifically, the present invention is a technical means for recovering soot (dust) in exhaust gas discharged from an industrial furnace by a dry dust collecting method, and can improve the efficiency of the dust collector as compared with the conventional case. Regarding a dry dust collector that can be used and how to operate it.

As represented by the Waelz process for recovering crude zinc oxide from steel dust, soot dust (hereinafter referred to as "exhaust gas dust") contained in exhaust gas discharged from various industrial furnaces is separated and recovered, and is contained therein. The process of obtaining a valuable metal such as zinc is widely performed (see Patent Document 1).

FIG. 1 schematically shows the configuration of equipment for treating exhaust gas from a reduction furnace in a Waelz process plant. In this facility, exhaust gas G volatilized from steel dust inside the rotary kiln 2 which is a reduction furnace is a series of gooseneck flue 3, dust chamber 1, electrostatic precipitator 4, bag filter 5, exhaust gas fan 6, and stack 7. Exhaust gas dust D containing zinc oxide is discharged from the exhaust gas G in each of the dry dust collectors such as the smoke chamber 1, the electrostatic precipitator 4, and the bag filter 5, while being flowed through the exhaust gas treatment equipment sequentially arranged as a device. Separated and collected.

Here, since the above-mentioned steel dust is mainly dust recovered from the exhaust gas of a smelting furnace for recycling iron waste materials, the properties, composition, etc. of the powder are usually obtained from the supplier (brand). ) Depends on. Further, in the reduction roasting in the rotary kiln, since the treatment is basically performed for each brand, the properties of the exhaust gas dust D, specifically, the angle of repose and the like are greatly varied. Therefore, shelving due to the adhesion of exhaust gas dust often occurs on the surface of the dust collection inclined surface 141 of the smoke dust chamber 1, and it is easy to fall into a situation where the exhaust gas dust D cannot be discharged smoothly.

For example, as a means for removing the adhesion of exhaust gas dust inside a general flue that sends exhaust gas discharged from an industrial furnace, a rod-shaped deposit removing device is used in a manner capable of scraping off the deposits. It has been proposed to have a structure inserted and arranged in the flue (Patent Document 2).

However, such a scraping structure is not a mere flue like the smoke chamber 1 shown in FIG. 2, but is a dry dust collector that collects exhaust gas dust by a dry treatment in a space having a certain volume or more. It is difficult to apply to the device.

In this case, as shown in FIG. 2, it is conceivable to attach an external vibration generator 12 to the smoke chamber 1 to suppress the shelving caused by the adhesion of exhaust gas dust due to the vibration caused by the external vibration generator 12. In fact, a dust collector equipped with such a vibrator has already been put into practical use, and it has been confirmed that this significantly suppresses the above-mentioned shelving.

However, when the vibration generator 12 is constantly and continuously operated, the exhaust gas has a high temperature of about 500 to 700 ° C., so that the life of the vibration generator 12 and the attachment portion of the vibration generator 12 to the dust chamber 1 is long. Will be shortened. In order to avoid this, in the exhaust gas treatment equipment including the smoke chamber 1 in which the vibration generator 12 is installed, the vibration generator 12 is operated as needed while constantly monitoring the shelving condition. It was obliged to perform extremely complicated operation control by repeating the start and stop of. This operation control is extremely complicated work, coupled with the fact that the properties of exhaust gas dust fluctuate greatly depending on the type and composition of steel dust, etc. that are put into the reduction furnace, and it is a heavy work load at the work site of the Waelz process plant. It was.

Japanese Unexamined Patent Publication No. 2005-299979 Japanese Unexamined Patent Publication No. 2004-003761

The present invention has been devised in view of the above-mentioned problems of the prior art, and is an exhaust gas in a dry dust collector by means of an operation control means of a vibration generator having a small work load in a facility for recovering dust from exhaust gas of an industrial furnace. It is an object of the present invention to provide a dry dust collector capable of sufficiently preventing the occurrence of shelving due to dust adhesion, and an operation method of the dry dust collector.

The inventor of the present application controls the operation of the vibration generator installed as a means for suppressing the adhesion of exhaust gas dust in the dry dust collector, with the vibration duration of one cycle of the vibration generator and the vibration stop of one cycle. We have found that the above problems can be solved by determining the time independently and using a vibration control means capable of controlling the vibration cycle, and have completed the present invention.

(1) An operation method of a dry dust collector including a dust collector main body that passes exhaust gas and collects exhaust gas dust in the exhaust gas, and a vibration generator that is in contact with the dust collector main body and vibrates the dust collector main body. The dust collector main body is composed of an upper dust collector and a lower space portion, and the lower space portion is a pair of facing surfaces that focus toward the lowermost center of the lower space portion. The precipitator has a dust collecting inclined surface, and the vibration generator can independently determine one cycle of vibration duration and one cycle of vibration stop time to control the vibration cycle. When it is determined that the accumulated amount of the exhaust gas dust on the surface of the dust collecting inclined surface is equal to or more than a predetermined amount, the vibration control means controls to shorten the vibration stop time, and the exhaust gas dust. A method of operating a dry dust collector, in which the vibration control means controls the vibration duration to be lengthened when it is determined that the viscosity of the dust collector is equal to or higher than a predetermined value.

(2) The dry dust collector is connected to a gas transport pipe that transfers the exhaust gas to the dust collector main body, and the gas transport pipe is bent in a mountain fold at an intermediate portion and faces each other. The degree of viscosity of the exhaust gas dust is determined by observing the accumulated amount of the exhaust gas dust in the inclined portion constituting the goose neck flue, which is a goose neck flue having a portion, according to (1). How to operate the dry dust collector.

(3) The method for operating a dry dust collector according to (1) or (2), wherein the vibration generator is a device that extracts vibration force by rotating unbalanced weights arranged at both shaft ends of a motor.

(4) The method of operating the dry dust collector according to any one of (1) to (3), wherein the dry dust collector is a gravity settling dust collector.

(5) The method for operating a dry dust collector according to any one of (1) to (4), wherein the exhaust gas dust is crude zinc oxide dust.

(6) A dry dust collector including a dust collector main body that allows exhaust gas to pass through and collects exhaust gas dust in the exhaust gas, and a vibration generator that is in contact with the dust collector main body and vibrates the dust collector main body. The dust collector main body is composed of an upper dust collector and a lower space portion, and the lower space portion is a pair of facing surfaces that focus toward the lowermost center of the lower space portion. It has a dust collecting inclined surface, and the vibration generator can control the vibration cycle by independently determining the vibration duration of one cycle and the vibration stop time of one cycle. A dry dust collector equipped with means.

(7) The vibration control means includes a vibration duration indicating unit capable of instructing a plurality of different vibration durations and a vibration stop duration indicating unit capable of instructing a plurality of different vibration stop times. The dry dust collector according to (6).

(8) The dry dust collector according to (6) or (7) and a gas transport pipe for transferring the exhaust gas to the dust collector main body are included, and the gas transport pipe is bent in a mountain fold at an intermediate portion. An exhaust gas treatment facility that is a gooseneck flue with a pair of sloping sections facing each other.

According to the present invention, in a facility that recovers dust from the exhaust gas of an industrial furnace, it is possible to sufficiently prevent the occurrence of shelving due to the adhesion of exhaust gas dust in the dry dust collector by the operation control means of the vibration generator with a small work load. A dry dust collector and a method of operating such a dry dust collector can be provided.

It is a schematic diagram which shows the structural example of the exhaust gas treatment equipment which comprises the dry type dust collector of this invention. It is sectional drawing and side view which show the form of the smoke chamber which is one of the preferable embodiment of the dry type dust collector of this invention. It is a front view which shows an example of the vibration control means which controls the operation of the vibration generator provided in the dry dust collector of this invention.

Hereinafter, preferred embodiments of the dry dust collector of the present invention, an operating method thereof, and an exhaust gas treatment facility including the dry dust collector will be described. Hereinafter, a specific example when the present invention is applied to the production process of zinc oxide ore by the Waelz process will be described. However, the present invention is not limited to the embodiments described in detail below. For example, the dry dust collector in the present invention is not limited to a gravity settling dust collector such as a smoke chamber, but also includes an electric dust collector, a bag filter, and the like, that is, an exhaust gas dust collector from an exhaust gas discharged from an industrial furnace. It refers to all devices that are collected by dry processing, and is a technology that can be widely applied to their structures and operating methods.

<Zinc oxide ore manufacturing process>
The process for producing zinc oxide ore by the Waelz process to which the present invention can be preferably applied is a process in which at least each step of reduction roasting step, exhaust gas dust recovery step, wet step, and drying heating step is sequentially performed.

[Whole process]
The reduction roasting step is a step of reducing and roasting zinc-containing ore such as steel dust to generate zinc-containing exhaust gas. The exhaust gas dust recovery step is a step of separating and recovering crude zinc oxide dust from the zinc-containing exhaust gas generated in the reduction roasting step, and it is assumed that the dry dust collector of the present invention and its operating method are carried out in this step. There is. The wet step is a step of separating and removing fluorine and cadmium from the crude zinc oxide dust obtained in the exhaust gas dust recovery step to obtain a crude zinc oxide cake. The drying and heating step is a step of drying and heating the crude zinc oxide cake obtained in the wet step to obtain zinc oxide ore (burnt ore).

By using the dry dust collector of the present invention or its operating method in the exhaust gas treatment equipment that performs the above-mentioned exhaust gas dust recovery process, it is possible to avoid operation stoppage due to a trouble in the same process, and to improve the operating efficiency and maintainability of the equipment. Can also be improved.

[Reduction roasting process]
In the reduction roasting step, reduction roasting treatment of zinc-containing ore such as steel dust is performed. The reduction roasting treatment is usually carried out by roasting a zinc-containing ore and a reducing agent using a reduction roasting rotary kiln (RRK) 2. The metallic zinc volatilized by reduction roasting in the furnace of RRK2 is reoxidized in the furnace of RRK2 to become powdery zinc oxide, which is discharged to the outside of the furnace of RRK2 as exhaust gas dust D together with the exhaust gas G discharged from RRK2. Will be done. The exhaust gas G including the exhaust gas dust D is sucked by the exhaust gas fan 6 and sent to the exhaust gas treatment facility 10.

[Exhaust gas dust recovery process]
In the exhaust gas dust recovery step, a process is performed in which the exhaust gas dust D containing zinc oxide is captured from the exhaust gas G containing the exhaust gas dust D discharged from RRK2, and the exhaust gas dust D is separated and recovered. The separation and recovery of the exhaust gas dust D is performed in the process in which the exhaust gas G including the exhaust gas dust D is sent through the exhaust gas treatment facility 10.

(Exhaust gas treatment equipment)
Exhaust gas treatment equipment of the present invention, a dry dust collector of the present invention at least arranged one or more, other, and are connected as necessary by each device required to implement exhaust gas dust collection step. The exhaust gas treatment facility 10 shown in FIG. 1 is a facility in which a gooseneck flue 3, a dust chamber 1, which is a dry dust collector of the present invention, an electrostatic precipitator 4, a bag filter 5, an exhaust gas fan 6, and a stack 7 are connected to each other. The exhaust gas G passes through each of these devices in sequence and is flowed, and the exhaust gas dust D is separated and recovered at any time in the smoke chamber 1, the electrostatic precipitator 4, or the bag filter 5 in this process.

As described above, the dry dust collector of the present invention is a technique that can be widely applied not only to the smoke chamber 1 but also to various dry dust collectors such as the electric dust collector 4 and the bag filter 5 described above. Therefore, not limited to the configuration shown in FIG. 1, as long as any of the dry dust collectors in the exhaust gas treatment facility satisfies the constituent requirements of the present invention, all such facilities are included in the technical scope of the present invention.

In the exhaust gas treatment equipment 10, the gas transport pipe for transferring the exhaust gas to the dust collector main body 11 is preferably a gooseneck flue 3 as shown in FIG. As shown in the figure, a gooseneck flue is a flue composed of pipes that are bent in a mountain fold at the middle and have a pair of inclined portions facing each other. When the gas transport pipe that transfers the exhaust gas to the dust collector main body 11 is the gooseneck flue 3, the rest angle of the exhaust gas dust is estimated from the inclination angle of the inclined portion, the accumulated amount of the exhaust gas dust in the inclined portion, and the accumulated state. It is possible to do. Thereby, the information necessary for controlling the operation of the dry dust collector (smoke chamber) 1 can be obtained more quickly and easily. Details of the operation method of the dry dust collector will be described later.

[Wet process]
In the wet process, the crude zinc oxide dust recovered through the exhaust gas dust recovery step is repulped with a treatment liquid to form a crude zinc oxide slurry, and impurities such as cadmium, chlorine, and fluorine contained in the crude zinc oxide are treated. Distribute in liquid. Then, the crude zinc oxide slurry that has undergone the above treatment is dehydrated and put into a drying and heating step of the next step as a zinc oxide cake.

[Drying and heating process]
In the drying and heating step, the crude zinc oxide cake obtained in the wet step is charged into a drying and heating device such as a drying and heating rotary kiln (DRK) and fired. By this step, zinc oxide ore (burnt ore) having a further reduced concentration of cadmium or the like can be obtained.

<Dry dust collector and its operation method>
The details of the dry dust collector of the present invention and the operation method thereof will be described. As described above, the present invention can be applied to various dry dust collectors used in the exhaust gas treatment equipment 10 that separates and recovers the exhaust gas dust D from the exhaust gas G. Here, as a specific example of the preferred embodiment, the smoke chamber 1 which is one of the dry dust collectors constituting the exhaust gas treatment facility 10 for performing the exhaust gas dust recovery step in the production process of zinc oxide ore by the Waelz process is configured. And the details of the driving method will be explained.

[Smoke room (dry dust collector)]
In the process of passing the zinc-containing exhaust gas G discharged from the RRK through the expansion portion inside the smoke chamber 1, the exhaust gas contained in the exhaust gas G due to gravity sedimentation due to a sudden decrease in flow velocity and the collision effect with the inner wall. It is a kind of dry dust collector that captures dust D and separates and collects it. As shown in FIG. 2, the dust chamber 1 includes a hollow dust collector main body 11 that allows exhaust gas to pass in the horizontal direction, and a vibration generator 12 that is installed in the dust collector main body 11 and vibrates the dust collector main body 11.

The dust collector main body 11, which is also a gas flow path for passing exhaust gas in the horizontal direction by a predetermined distance, has an upper dust collector 13 that constitutes an upper portion in a cross section perpendicular to the flow direction of the exhaust gas and a lower portion that constitutes a lower portion. It is composed of a side space portion 14. The lower space portion 14 has a pair of facing dust collecting inclined surfaces 141 that focus toward the center of the lowermost portion thereof. A discharge port 142 for discharging the separated and recovered exhaust gas dust D is formed at a position where the dust collection inclined surface 141 at the lowermost portion of the lower space portion 14 is focused.

As described above, the exhaust gas dust D separated from the exhaust gas G by the gravity settling and the collision effect is collected in the lower space portion 14 in the dust collector main body 11, mainly in the upper dust collecting portion 13. It falls along the inclined surface 141 and is discharged from the discharge port 142. The exhaust gas dust D discharged from the smoke dust chamber 1 is collected by a flow conveyor 8 arranged adjacently below the discharge port 142, and is conveyed to a facility for performing a wet process, which is the next process.

A vibration generator 12 that vibrates the dust collector main body 11 is attached to the smoke chamber 1. The vibration generator 12 is installed inside the dust collector main body 11 to drop the exhaust gas dust deposit d adhering to the surface of the dust collection inclined surface 141 by vibration. The exhaust gas dust D that has slid off the surface of the dust collection inclined surface 141 due to this vibration is smoothly discharged from the discharge port 142.

Further, the vibration generator 12 is provided with a vibration control means 15 capable of controlling the vibration cycle by independently determining the vibration duration of one cycle and the vibration stop time of one cycle.

The vibration generator 12 can control the vibration cycle of the above aspect, and generates sufficient vibration to drop the exhaust gas dust adhering to the inside of the dust collector main body 11 along the dust collection inclined surface 141 by gravity. It is not limited to a specific device as long as it can be made to do so. However, as shown in FIG. 2, it is preferable that the vibration generator 12 has a configuration in which a plurality of small vibration generators that can be easily installed and replaced are attached to the outer surface of the dust collector main body 11. A preferred example of such a small vibration generator is a device that extracts vibration force by rotating unbalanced weights arranged at both shaft ends of a motor. As the vibration generator, in addition to the above-mentioned device that extracts the vibration force by rotating the unbalanced weights arranged at both shaft ends of the motor, a turbine type, a piston type, a knocker type vibrator, etc. are widely and industrially implemented. The equipment that has been used can be applied. In addition, regardless of which vibration generator is adopted, the mounting position of the vibration generator is the outer surface of the dust collection inclined surface 141 in order to efficiently transmit the vibration to the exhaust gas dust deposit d. Is preferable.

The smoke chamber 1 of the present invention is not only provided with the vibration generator 12 as described above, but also has a technical feature in that the mode of operation control of the vibration generator 12 is specially devised. As described above, the vibration control means 15 that controls the operation of the vibration generator 12 independently determines the vibration duration of one cycle and the vibration stop time of one cycle of the operation of the vibration generator 12. Any technical means that can be used. Conventionally known control devices such as electric devices or control systems can be appropriately adopted.

As described above, the vibration control means 15 that controls the operation of the vibration generator 12 is not limited to the specific technical means, but the mode of the operation unit, the so-called user interface, is shown in FIG. 3, for example. As shown, a vibration duration indicator 151 capable of instructing a plurality of different vibration durations (operation time) and a vibration stop duration indication capable of instructing a plurality of different vibration stop times (cycle pause times). It is preferable that the unit 152 and the like are provided. By making the vibration generator 12 have such a user interface, it is possible to control the operation of the vibration generator 12 extremely easily.

Further, regarding the arrangement position of the vibration control means 15, at least the above-mentioned operation unit is preferably installed in the vicinity of the smoke chamber 1. As a result, the operating time of the vibration generator 12 can be set more quickly after confirming the status of the exhaust gas dust.

[How to operate the dust chamber (dry dust collector)]
Regarding the operation of the vibration generator 12 in the smoke chamber 1, specifically, when it is determined that the amount of the exhaust gas dust deposit d on the surface of the dust collection inclined surface 141 is equal to or more than a predetermined amount, the vibration control means 15 Therefore, control is performed to shorten the vibration stop time. Further, as an independent determination, when it is determined that the viscosity of the exhaust gas dust is equal to or higher than a predetermined value, the vibration control means 15 controls to lengthen the vibration duration.

Regarding the amount of exhaust gas dust deposit d in the smoke chamber 1, which is the control information for determining the vibration stop time of the vibration generator 12, the inside of the smoke chamber 1 can be visually confirmed directly through an inspection port or the like. It is good, but it can also be estimated from the fluctuation of the amount of dust discharged to the flow conveyor 8 per unit time. This amount can also be indirectly estimated by measuring the current value of the drive motor of the flow conveyor. It is also possible to estimate the amount of the exhaust gas deposit d in the smoke chamber 1 from the accumulated state of the exhaust gas dust in the gooseneck flue 3.

The viscosity of the exhaust gas dust, which is the control information for determining the vibration duration of the vibration generator 12, may be measured by collecting a test sample for each lot in advance and measuring the angle of repose, for example. As described above, the degree of viscosity can be determined by estimating the angle of repose of the exhaust gas dust from the inclination angle of the goose neck flue 3 inclined portion, the accumulated amount of the exhaust gas dust in the inclined portion, and the accumulated state. preferable.

Regarding the vibration generator 12, for example, as shown in FIG. 3, the vibration duration (operating time) of the vibration generator 12 is selected from 5 seconds, 7 seconds, and 10 seconds, and the pause time is 30 seconds and 45 seconds. If it is set so that it can be selected from one of 60 seconds, 9 ways (3 × 3) of control patterns (see Table 1) can be easily selected and executed. As a matter of fact at the time of filing, there are about 20 to 30 domestic suppliers of raw material ores such as steel dust to zinc oxide ore production plants by the Waelz process. It is possible to set an intermittent operation cycle of the vibration generator 12 that matches the properties of exhaust gas dust (crude zinc oxide) derived from any steel dust. In addition to directly observing the state of exhaust gas dust and the like to obtain control information, this is automatically performed by a combination of a detection means such as a CCD camera, a level sensor, a thermometer, and an information processing terminal. , It is also possible to automate the operation control of the vibration generator 12.

For example, in the operation control of the vibration generator 12 of the above aspect in the zinc oxide ore manufacturing plant by the Waelz process, the patrol inspector with the plant controls the gooseneck flue 3 every time the lot of the steel dust as the raw material is updated. By confirming the state of dust accumulation and setting the operation method of the vibration generator 12 on the operation panel of the vibration control means 15 near the smoke chamber 1, exhaust gas dust is continuously and quantitatively discharged from the smoke chamber 1. It will be possible to discharge stably. At the same time, the operating time of the vibration generator 12 can be minimized, so that the dust chamber (dry dust collector) 1, the vibration generator 12, and peripheral members, particularly the outer surface of the dust collecting inclined surface 141 of the vibration generator 12, can be reached. It is possible to prevent cracks and breakage in the mounting portion of the equipment, and it is possible to extend the life of the equipment.

1 Smoke room (dry dust collector)
11 Dust collector body 12 Vibration generator 13 Upper side dust collector 14 Lower side space 141 Dust collection inclined surface 142 Discharge port 15 Vibration control means 151 Vibration duration indicator 152 Vibration stop duration indicator 2 Reduction roasting rotary kiln (RRK) )
3 Gooseneck flue 4 Electrostatic precipitator 5 Bag filter 6 Exhaust gas fan 7 Stack 8 Flow conveyor 10 Exhaust gas treatment equipment G Exhaust gas D Exhaust gas dust

Claims (8)

The main body of the dust collector that allows the exhaust gas to pass through and collects the exhaust gas dust in the exhaust gas.
A vibration generator that is in contact with the dust collector main body and vibrates the dust collector main body,
It is a method of operating a dry dust collector equipped with
The dust collector main body is composed of an upper dust collector and a lower space.
The lower space portion has a pair of opposing dust collecting inclined surfaces that focus toward the lowermost center of the lower space portion.
The vibration generator is provided with a vibration control means capable of controlling the vibration cycle by independently determining the vibration duration of one cycle and the vibration stop time of one cycle.
When it is determined that the accumulated amount of the exhaust gas dust on the surface of the dust collecting inclined surface is equal to or more than a predetermined amount, the vibration control means controls to shorten the vibration stop time.
A method for operating a dry dust collector, in which when it is determined that the viscosity of the exhaust gas dust is equal to or higher than a predetermined value, the vibration control means controls the vibration duration to be lengthened. A gas transport pipe for transferring the exhaust gas to the dust collector main body is connected to the dry dust collector.
The gas transport pipe is a gooseneck flue that is bent in a mountain fold at the middle portion and has a pair of inclined portions facing each other.
The method for operating a dry dust collector according to claim 1, wherein the degree of viscosity of the exhaust gas dust is determined by observing the accumulated amount of the exhaust gas dust on the inclined portion constituting the gooseneck flue. The method for operating a dry dust collector according to claim 1 or 2, wherein the vibration generator is a device that extracts vibration force by rotating unbalanced weights arranged at both shaft ends of a motor. The method for operating a dry dust collector according to any one of claims 1 to 3, wherein the dry dust collector is a gravity settling dust collector. The method for operating a dry dust collector according to any one of claims 1 to 4, wherein the exhaust gas dust is crude zinc oxide dust. The main body of the dust collector that allows the exhaust gas to pass through and collects the exhaust gas dust in the exhaust gas.
A vibration generator that is in contact with the dust collector main body and vibrates the dust collector main body,
It is a dry dust collector equipped with
The dust collector main body is composed of an upper dust collector and a lower space.
The lower space portion has a pair of opposing dust collecting inclined surfaces that focus toward the lowermost center of the lower space portion.
The vibration generator is provided with a vibration control means capable of controlling the vibration cycle by independently determining the vibration duration of one cycle and the vibration stop time of one cycle.
When the vibration control means determines that the accumulated amount of the exhaust gas dust on the surface of the dust collection inclined surface is equal to or more than a predetermined amount, the vibration control means controls to shorten the vibration stop time, and the viscosity of the exhaust gas dust becomes high. A vibration control means that controls to lengthen the vibration duration when it is determined that the value is equal to or higher than a predetermined value.
Dry dust collector. The vibration control means is
A vibration duration indicator that can indicate multiple different vibration durations,
A vibration stop duration indicator that can specify multiple different vibration stop times,
The dry dust collector according to claim 6. The dry dust collector according to claim 6 or 7.
The gas transport pipe for transferring the exhaust gas to the dust collector main body is included.
The gas transport pipe is an exhaust gas treatment facility which is a gooseneck flue which is bent in a mountain fold at an intermediate portion and has a pair of inclined portions facing each other.

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