Boiler under-hopper arching removal system

Abstract

To safely remove arching without damaging a hopper below a boiler during operation of a combustion plant equipped with a boiler. [Solution] The removal system 1 has a bullet ejection device 22 that ejects bullets toward an arching formed by fly ash 21 that has fallen from a flue 5 into the boiler lower hopper 16 through an opening 23 formed in the wall of the boiler lower hopper 16, a temperature sensor 26 that measures the temperature of the outer or inner surface of the boiler lower hopper 16 below the arching and near the hopper discharge port 17, or the outer or inner surface of the falling fly ash transfer device 18 near the hopper discharge port 17, or the outer or inner surface of a piping 28, and / or a pressure sensor 25 that measures the air pressure in the falling fly ash transfer device 18. A control device 29 causes the bullet ejection device 22 to eject bullets during operation of the combustion plant 2 based on the temperature information measured by the temperature sensor 26 or the air pressure information measured by the pressure sensor 25.

Description

[Technical field]

[0001] The present invention relates to an arching removal system for a hopper below a boiler in a combustion plant having a boiler. [Background technology]

[0002] In facilities such as waste incineration plants that generate electricity while incinerating waste and power plants that burn fuels such as coal, i.e., combustion plants equipped with boilers, in order to prevent fly ash from the exhaust gas from adhering to the heat transfer tubes arranged in the flue and reducing the heat conversion efficiency, the fly ash that has adhered to the heat transfer tubes is removed by an ash removal device that uses steam or pressure waves. The removed fly ash (hereinafter referred to as "falling fly ash") falls into a hopper arranged below the boiler (hereinafter referred to as "boiler below hopper"), is discharged from a hopper discharge port formed below the boiler below hopper, and is transported from the boiler below hopper to the outside of the combustion plant.

[0003] On the other hand, fly ash adheres to not only heat transfer tubes but also flue gas ducts, and if it grows, it may affect exhaust gas emissions. Therefore, in order to remove fly ash adhered to not only heat transfer tubes but also flue gas ducts, an ejection device that ejects bullets made of non-metallic materials such as fly ash at the adhered fly ash has been developed as a type of ash removal device. Examples of such ejection devices include an ejection device that ejects bullets from between two rotating bodies like a pitching machine (Patent Document 1) and an ejection device that ejects bullets using high-pressure gas such as compressed air (Patent Document 2 and Patent Document 3). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2004-116909 A [Patent Document 2] JP 2014-031941 A [Patent Document 3] JP 2022-115482 A Summary of the Invention [Problem to be solved by the invention]

[0005] Falling fly ash has a wide range of sizes, from fine fly ash to clumped fly ash. If multiple clumped fly ash fall from the flue into the boiler lower hopper, arching may occur. If arching occurs in the boiler lower hopper and blocks the hopper discharge port, the falling fly ash cannot be transported from the boiler lower hopper. As a result, the flue narrows, which may affect the discharge of exhaust gas. Therefore, in order to eliminate arching and facilitate the discharge of the falling fly ash from the hopper discharge port, it is considered to use the above-mentioned injection device during the operation of the combustion plant.

[0006] The location where arching occurs is near the hopper discharge port, and the location is specified. On the other hand, exhaust gas is toxic to the human body. Therefore, it is preferable to apply a technology that starts the injection device during the operation of the combustion plant without opening the door, rather than the technology of Patent Documents 1 and 2 that opens a door such as a manhole connecting the inside and outside of the flue when starting the injection device.

[0007] However, if the injection device is started when no arching exists, even non-metallic bullets may damage the boiler lower hopper. Therefore, before starting the injection device, it is necessary to check that an arching has already been formed and that the shape is being maintained before starting the injection device.

[0008] However, since the boiler lower hopper becomes an enclosed space through which high-temperature exhaust gas flows during operation of the combustion plant, it is not easy to place an imaging device inside the boiler lower hopper to check the state of arching. Therefore, there has been a demand for a system that can appropriately detect the state of arching inside the boiler lower hopper during operation of the combustion plant by other means and start the injection device.

[0009] The present invention has been made in consideration of the above-mentioned problems, and aims to provide an arching removal system for a boiler below hopper that can safely remove arching that occurs in a boiler below hopper without damaging the boiler below hopper during operation of a combustion plant equipped with a boiler. [Means for solving the problem]

[0010] The boiler under hopper arching removal system of the present invention comprises: a boiler below hopper in which flue gas containing fly ash from a combustion plant equipped with a boiler is drawn by an induced draft fan and flows through a flue, the fly ash adheres to a heat transfer tube arranged in the flue, and the fly ash falls through the flue and is discharged from a hopper discharge port as fallen fly ash; a bullet ejection device that ejects a bullet made mainly of a non-metallic material toward an arching formed by the falling fly ash in the vicinity of the hopper discharge port through an opening formed in a wall surface of the boiler lower hopper; A falling fly ash transport device, in which a falling fly ash inlet is connected to the hopper outlet directly or indirectly through a pipe, and the falling fly ash introduced from the falling fly ash inlet is discharged from a falling fly ash outlet; a temperature sensor for measuring the temperature of the outer or inner surface of the boiler lower hopper below the arching and in the vicinity of the hopper discharge port, or the outer or inner surface of the falling fly ash transfer device in the vicinity of the hopper discharge port, or the outer or inner surface of the piping, and a pressure sensor for measuring the air pressure in the boiler lower hopper below the arching and in the vicinity of the hopper discharge port, or in the falling fly ash transfer device in the vicinity of the hopper discharge port, or in the piping; or and a control device that receives temperature information measured by the temperature sensor or air pressure information measured by the pressure sensor, and ejects the bullet from the bullet ejection device based on the temperature information or the air pressure information during operation of the combustion plant. The path of the bullet from the bullet ejection device to the opening is kept airtight.

[0011] When the temperature sensor is not installed and the pressure sensor is installed, the control device causes the bullet ejection device to eject the bullet if the air pressure information indicates that the air pressure increased from a negative pressure lower than atmospheric pressure toward atmospheric pressure and that the increased air pressure was maintained for a first predetermined period of time; when the pressure sensor is not installed and the temperature sensor is installed, the control device causes the bullet ejection device to eject the bullet if the temperature information indicates that the air pressure changed from a high temperature to a low temperature that was reduced by more than a predetermined temperature range and that the low temperature was maintained for a second predetermined period of time; and when both the pressure sensor and the temperature sensor are installed, the control device causes the bullet ejection device to eject the bullet if the air pressure information indicates that the air pressure increased from negative pressure toward atmospheric pressure and the temperature information changed from the high temperature to the low temperature. Effect of the Invention

[0012] The boiler below hopper arching removal system of the present invention fires bullets toward the arching when arching occurs and is maintained based on temperature information from a temperature sensor or air pressure information from a pressure sensor installed in either or both of them. In other words, bullets are not fired when arching is not occurring, or when arching occurs but is quickly eliminated by natural collapse or the like. In addition, the bullets are formed mainly from nonmetallic materials. Therefore, the bullets fired to remove arching are unlikely to damage the boiler below hopper. In addition, the boiler under-hopper arching removal system of the present invention automatically shoots bullets through an opening formed in advance in the wall of the boiler under-hopper while the combustion plant is in operation. In other words, there is no need to open a door such as a manhole when shooting bullets. The bullet path from the bullet shooting device to the opening is kept airtight, so there is no risk of adverse effects on the human body.

[0013] Therefore, according to the boiler below-hopper arching removal system of the present invention, arching that has occurred in the boiler below-hopper can be safely removed without damaging the boiler below-hopper during operation of a combustion plant equipped with a boiler. [Brief description of the drawings]

[0014] [Figure 1] 1 is a schematic configuration diagram of an arching removal system for a boiler lower hopper according to an embodiment. FIG. [Diagram 2] 2 is a partially enlarged view showing a portion of a boiler lower hopper surrounded by a dashed-dotted circle in FIG. 1. [Diagram 3] 4 is an explanatory diagram showing a wall surface 16A in which an opening is provided in a boiler lower hopper. FIG. [Figure 4] FIG. 13 is a schematic diagram of a modified example of the arching removal system for the boiler lower hopper. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an embodiment and a modified example of the arching removal system 1, 1' (hereinafter referred to as "removal system 1, 1'") for a boiler under hopper according to the present invention will be described with reference to Fig. 1 to Fig. 4. For ease of explanation, an orthogonal coordinate system with X-axis, Y-axis, and Z-axis will be used in the drawings. The embodiments and modifications are merely illustrative and are not intended to exclude the application of various modifications or techniques not specifically described. Except for the essential configurations of the present invention, the configurations of the embodiments and modifications can be selected and / or modified as necessary.

[0016] First, a combustion plant 2 to which a removal system 1 of an embodiment is applied will be described, and then each component of the removal system 1 and its control will be described in order.

[0017] Next, a combustion plant 2 to which the removal system 1 is applied will be described. The removal system 1 is applied to a combustion plant 2 equipped with a boiler. The combustion plant 2 generally includes at least a combustion device that combusts fuel (such as waste material or coal), a boiler that exchanges heat generated by the combustion (which may include, for example, a heat transfer tube or an economizer disposed in a flue as a component), a dust removal device such as a bag filter that removes dust from exhaust gas containing fly ash generated by the combustion, and a chimney that releases the cleaned and purified exhaust gas into the atmosphere. Here, as an example, the combustion plant 2 will be described as a waste incinerator plant equipped with a boiler for generating electricity, but the combustion plant 2 may be another type of combustion plant, such as a thermal power plant or a chemical plant.

[0018] The components of a waste incineration plant, which is a combustion plant 2, will be described in order with reference to FIG. A waste incineration plant is generally equipped with an incinerator 3 (which includes at least a hopper 10 in which waste is stored, a feeder 11 that pushes out the waste stored in the hopper 10 from below the hopper 10, a stoker 12 that incinerates the waste pushed out to the feeder 11 while transporting it, and a bottom ash chute 13 that discharges the bottom ash that is the residue of the incineration in the stoker 12), a flue 5 through which the exhaust gas generated by the incineration of the waste in the incinerator 3 flows, a temperature reducing tower 8 that reduces the temperature of the exhaust gas, a bag filter 9 that removes fly ash contained in the exhaust gas that has been reduced in temperature by the temperature reducing tower 8, a chimney 4 that releases the exhaust gas that has been removed by the bag filter 9 into the atmosphere, and an induced draft fan 6 that draws the exhaust gas in the flue 5 into the chimney 4. Some waste incineration plants do not include a temperature reducing tower 8. The induced draft fan 6 is installed in the flue 5 between the bag filter 9 and the chimney 4. The flue 5 is a transport path that transports the exhaust gas generated in the incinerator 3 to the chimney 4 in a substantially airtight manner, and is composed of a rectangular cylindrical duct or the like. When the combustion plant 2 is in operation, the induced draft fan 6 operates, so that the inside of the incinerator 3 and the inside of the flue 5 are pressurized by the induced draft fan 6 to a negative pressure lower than atmospheric pressure.

[0019] Then, in the flue 5 between the stoker 12 and the cooling tower 8, a heat transfer tube 7 and an economizer 14 are installed as described below. Note that, like the heat transfer tube 7, the economizer 14 is a device for exchanging heat with the exhaust gas, and is installed in the flue 5 between a third flue 5C and the cooling tower 8 as described below. The flue 5 is disposed between the incinerator 3 and the economizer 14 and includes, in this order from the upstream side in terms of the flow of the exhaust gas, at least a first flue 5A, a second flue 5B, and a third flue 5C. The first flue 5A (in FIG. 1, it is indicated as "1 path" and may also be referred to as "1 cavity") extends upward in the Z-axis direction (i.e., vertical direction) from directly above the stoker 12 of the incinerator 3. Then, at the upper end of the first flue 5A, it bends in the +X-axis direction (i.e., horizontal direction). The second flue 5B (shown as "2-path" in FIG. 1, or sometimes as "2-cavity") is connected to the bent portion of the first flue 5A and extends downward in the Z-axis direction adjacent to the first flue 5A. Then, the second flue 5B is bent in the +X-axis direction at the lower end thereof. The third flue 5C (shown as "3 path" in FIG. 1, and sometimes called "3 cavity") is connected to the bent portion of the second flue 5B and extends upward in the Z-axis direction adjacent to the second flue 5B. Therefore, as shown by the black arrows in FIG. 1, the exhaust gas flows from the stoker 12 upward through the first flue 5A, downward through the second flue 5B, and upward through the third flue 5C.

[0020] Here, the "pass" in "1 pass", "2 pass", and "3 pass" for the first flue 5A, the second flue 5B, and the third flue 5C means "pass" in English. Similarly, the "cavity" in "1 cavity", "2 cavity", and "3 cavity" means "cavity" in English. In FIG. 1, the first flue 5A, the second flue 5B, and the third flue 5C are arranged between the incinerator 3 and the economizer 14, but a similar configuration may be repeated, for example, a fourth flue having a similar configuration to the second flue 5B may be arranged between the third flue 5C and the economizer 14.

[0021] In the third flue 5C, a plurality of heat transfer tubes 7 and an ash removal device 15 arranged between the plurality of heat transfer tubes 7 are installed. Each heat transfer tube 7 is one of the components of the boiler, and exchanges heat with the flue gas flowing upward through the third flue 5C. The ash removal device 15 is a device that separates fly ash adhering to the heat transfer tubes 7 by steam, liquid, pressure waves, or the like, and drops it downward to clean the heat transfer tubes 7. As the ash removal device 15, for example, a known soot blower, water spray device, pressure wave generator (for example, a shock pulse generator, a detonation wave generator), etc. can be used.

[0022] When the ash removal device 15 is started, the fly ash 21 that has fallen downward (hereinafter referred to as "falling fly ash") is deposited below the third flue 5C. In order to smoothly discharge the deposited falling fly ash 21 from the flue 5, the portion where the second flue 5B and the third flue 5C are connected is formed into a shape in which the area of ​​the horizontal surface gradually decreases downward, and this is called the boiler lower hopper 16. At the bottom of the boiler lower hopper 16, a hopper discharge port 17 is formed, which is an opening for discharging the accumulated falling fly ash 21 to the outside of the flue 5. The boiler lower hopper 16 is shaped so that the area of ​​the horizontal plane (i.e., the XY plane) gradually decreases toward the bottom, so that the falling fly ash 21 slides down the wall surface of the boiler lower hopper 16 by gravity and is collected in the hopper discharge port 17. The boiler lower hopper 16 may have any shape as long as the area of ​​the horizontal surface gradually decreases as it extends downward. However, when the second flue 5B and the third flue 5C are rectangular cylindrical ducts, the boiler lower hopper 16 can be shaped like an inverted square pyramid that is continuously connected to the wall surfaces of the second flue 5B and the third flue 5C and whose horizontal surface area gradually decreases as it extends downward, thereby enabling the wall surfaces of the second flue 5B and the third flue 5C to be smoothly and continuously connected to the wall surface of the boiler lower hopper 16.

[0023] Therefore, in Fig. 1, the shape of the boiler lower hopper 16 is assumed to be the inverted pyramid shape described above. Of the four wall surfaces of the boiler lower hopper 16 shaped like an inverted pyramid, the most upstream wall surface in terms of the flow of exhaust gas is referred to as the "front surface 16A," the most downstream wall surface is referred to as the "rear surface 16B," and the other two surfaces connecting the front surface 16A and the rear surface 16B are referred to as the "side surfaces" (not specifically numbered in Fig. 1).

[0024] Next, the overall configuration of the removal system 1 will be briefly described with reference to FIGS. 1 to 3, and then each component of the removal system 1 will be described in detail. First, the overall configuration of the removal system 1 will be briefly described. The removal system 1 includes the above-mentioned boiler lower hopper 16, an arching removal bullet ejection device 22 (hereinafter referred to as a "bullet ejection device") that ejects an arching removal bullet (hereinafter referred to as a "bullet") made mainly of a non-metallic material toward the arching formed by the falling fly ash 21 near the hopper discharge port 17 through an opening 23 formed on the wall surface of the boiler lower hopper 16, and a falling fly ash transfer device 18 that has a falling fly ash inlet 18A connected directly or indirectly via a pipe 28 to the hopper discharge port 17 and ejects the falling fly ash 21 introduced from the falling fly ash inlet 18A from the falling fly ash outlet 18B. The removal system 1 also includes a pressure sensor 25 and / or a temperature sensor 26. The pressure sensor 25 measures the air pressure in the boiler lower hopper 16 below the arching and near the hopper discharge port 17, in the falling fly ash transfer device 18 near the hopper discharge port 17, or in the piping 28. The temperature sensor 26 measures the temperature of the outer or inner surface of the boiler lower hopper 16 below the arching and near the hopper discharge port 17, in the falling fly ash transfer device 18 near the hopper discharge port 17, or in the piping 28. Furthermore, the removal system 1 is equipped with a control device 29 that receives temperature information measured by the temperature sensor 26 or air pressure information measured by the pressure sensor 25, and ejects a bullet from the bullet ejection device 22 based on the temperature information or air pressure information while the combustion plant 2 is operating.

[0025] As shown in FIG. 2, the falling fly ash 21 that has fallen into the boiler lower hopper 16 has a wide range of particle sizes, from fine fly ash 21A to lumpy fly ash 21B. When multiple lumpy falling fly ash 21B fall from the third flue 5C into the boiler lower hopper 16, arching may occur near and above the hopper discharge port 17, in which the falling fly ash 21 covers the hopper discharge port 17. When arching occurs, the hopper discharge port 17 is blocked, and the boiler lower hopper 16 cannot discharge the falling fly ash 21. As a result, as shown in FIG. 2, the falling fly ash 21, including the fine falling fly ash 21A and the lumpy falling fly ash 21B, may accumulate without being discharged from the boiler lower hopper 16. The removal system 1, which will now be described in detail, is a system for removing arching that has occurred in the boiler lower hopper 16 without damaging the boiler lower hopper 16.

[0026] The timing when the lump fly ash 21B falls from the heat transfer tube 7 to the boiler lower hopper 16 is mainly when the ash removal device 15 is started periodically. At this time, multiple lump fly ash 21B do not fall at the same time, but often fall separately at different times with a slight time difference. For this reason, in the control of the control device 29 described later, a predetermined time of waiting is set after detecting the occurrence of arching so that bullets are not fired even when arching does not exist.

[0027] Next, each component of the removal system 1 will be described. The bullet ejection device 22 ejects bullets mainly made of non-metallic material through an opening 23 formed in the wall of the boiler lower hopper 16 toward the arching formed by the falling fly ash 21 in the vicinity of the hopper discharge port 17. The bullet ejection device 22 is controlled by a control device 29 described later. This control will be described in detail later. The bullets may be made of non-metallic materials such as fly ash, clinker, concrete, ice, and dry ice. Since the bullets are made of non-metallic materials, there is no risk of damaging the wall surface of the boiler lower hopper 16 even if the bullets hit the wall surface of the boiler lower hopper 16. In addition, even if the bullets are mixed in the falling fly ash 21, they can be directly transported to the outside of the combustion plant 2 and disposed of, so there is an advantage that there is no need to separate the bullets from the falling fly ash 21. However, if there is no problem with the damage or separation, a small amount of metal powder may be mixed into the bullets to increase their hardness. Known technology can be used for the bullet ejection device 22 itself. Therefore, for example, a bullet ejection device that ejects a bullet from between two rotating bodies like a pitching machine (see Patent Document 1) or a bullet ejection device that ejects a bullet using high-pressure gas such as compressed air (see Patent Document 2 or Patent Document 3) can be adopted for the bullet ejection device 22.

[0028] Here, it is preferable that the opening 23 is formed in the front surface 16A among the four wall surfaces of the boiler lower hopper 16, as shown in Figs. The reason is as follows. That is, since the ash removal device 15 and the heat transfer tube 7 are arranged in the third flue 5C and not in the second flue 5B, the falling fly ash 21 is deposited more on the rear surface 16B arranged below the third flue 5C than on the front surface 16A arranged below the second flue 5B. Therefore, as shown in FIG. 2, when viewed in the XZ plane, the falling fly ash 21 is deposited unevenly on the rear surface 16B. On the other hand, the falling fly ash 21 is hardly deposited on the front surface 16A. Therefore, the front surface 16A, which is least likely to be blocked by the falling fly ash 21, is selected from the four wall surfaces of the boiler lower hopper 16 when the opening 23 is formed. However, as long as the opening 23 is not blocked by the falling fly ash 21, the opening 23 may be formed in either of two side surfaces of the four wall surfaces of the boiler lower hopper 16 depending on the design.

[0029] The bullet ejection device 22 ejects bullets toward the arching through the opening 23, but since the arching occurs near and above the hopper discharge port 17 located at the lowest part of the boiler lower hopper 16 as shown in Fig. 2, it is preferable to eject the bullets from above downward. In other words, colliding the bullets from above against the arching is effective for destroying the arching, i.e., removing the arching. Therefore, as shown in FIG. 2, an injection pipe 24 is installed, which is a curved pipe composed of a straight pipe section 24C and a horizontal section 24D. The straight pipe section 24C is smoothly connected to the horizontal section 24D, and one end 24A of the straight pipe section 24C is connected to the opening 23, and the other end 24B of the horizontal section 24D is connected to the bullet ejection port of the bullet ejection device 22. That is, for both ends of the injection pipe 24, one end 24A is connected to the opening 23, and the other end 24B is connected to the bullet ejection port of the bullet ejection device 22. The connection between the one end 24A and the opening 23 may be by welding. The connection between the other end 24B and the ejection port of the bullet ejection device 22 may be by a fixing method of locking using a bolt and a nut, or by welding.

[0030] In addition, here, the injection pipe 24 is installed so as not to pass through the opening 23, in other words, so that a part of the straight pipe portion 24C does not protrude into the boiler lower hopper 16. If a part of the injection pipe 24 protrudes into the boiler lower hopper 16, the protruding part will corrode and eventually break or fall off because exhaust gas is a corrosive gas, making it difficult to inject bullets toward the arching. However, depending on the design and operation method, such as making the injection pipe 24 out of a material resistant to corrosion or increasing the frequency of maintenance, the part of the injection pipe 24 may protrude into the boiler lower hopper 16.

[0031] The straight pipe section 24C is arranged at an angle so that the extension of its central axis hits the arching, aiming at the position where arching is expected to occur, and so that the further it advances in the +X-axis direction, the further it is positioned in the -Z-axis direction. 2, the straight pipe section 24C is disposed at an inclination diagonally upward to the left. Here, the straight pipe section 24C is disposed at an inclination angle of 30° to 85° upward from the horizontal (in the +Z-axis direction and the -X-axis direction) from the opening 23 toward the extension direction of the ejection pipe 24. Within this angle range, it is easy to accurately hit the arching with a bullet, and the power of the ejected bullet can be increased by gravity, so that the arching can be effectively destroyed. Furthermore, when the removal system 1 is retrofitted to an existing combustion plant 2, there is an advantage that the bullet ejection device 22 can be positioned within the above-mentioned angle range without affecting the positioning of other existing equipment. In addition, if the angle of the front surface 16A with respect to the horizontal (the X-axis direction in Figure 2) is "A" and the angle of the central axis of the straight pipe section 24C with respect to the horizontal is "B", then the following inequality holds between angles A and B. Angle 90° ≧ Angle A > Angle B

[0032] The horizontal section 24D is a straight pipe whose central axis is substantially horizontal (substantially in the X-axis direction in FIG. 2). However, the portion where the horizontal section 24D and the straight pipe section 24C are connected is rounded so that the bullet can move smoothly inside the ejection tube 24. Substantially horizontal means horizontal or may be considered horizontal without being strictly horizontal. Here, the horizontal part 24D is arranged so that the central axis of the horizontal part 24D from the other end 24B toward the straight pipe part 24C is horizontal or at an angle of 2° or less upward from the horizontal. This angle range makes it easy to fix the other end 24B of the horizontal part 24D to the bullet ejection device 22, and has the advantage that when the bullet ejection device 22 is loaded with a bullet, the bullet can be prevented from naturally rolling down toward the opening 23 before it is ejected.

[0033] In the above description, the injection pipe 24 is described as a curved pipe having both the straight pipe section 24C and the horizontal section 24D, but the injection pipe 24 may be composed of only either the straight pipe section 24C or the horizontal section 24D. In this case, one of the two ends of the straight pipe section 24C is one end 24A and the other is the other end 24B, or one of the two ends of the horizontal section 24D is one end 24A and the other is the other end 24B. For example, if the injection pipe 24 is composed of only the horizontal portion 24D, the bullet injection device 22 is installed on the horizontal plane where the hopper discharge port 17 of the boiler lower hopper 16 is located, and the bullet is injected from almost directly to the side of the arching. If the arching can be destroyed, it may be designed to have such a configuration. In addition, the bullet ejection device 22 is disposed outside the boiler lower hopper 16, but the bullet path from the bullet ejection device 22 to the opening 23 via the ejection tube 24 is kept airtight. Therefore, during operation of the combustion plant 2, exhaust gas does not leak out of the flue 5 through this path, so there is no risk of adverse effects on the human body.

[0034] Next, the falling fly ash transporting device 18 will be described. The falling fly ash transporting device 18 is a device installed below the hopper discharge port 17 of the boiler lower hopper 16, and is a device equipped with at least a falling fly ash inlet 18A and a falling fly ash discharge port 18B. The falling fly ash inlet 18A is connected directly to the hopper discharge outlet 17 of the boiler lower hopper 16 or indirectly via a pipe 28. Here, as an example, as shown in FIG. 2, the hopper discharge outlet 17 and the falling fly ash inlet 18A are indirectly and airtightly connected via the pipe 28. The falling fly ash 21 discharged from the hopper discharge outlet 17 by natural gravity or the like is introduced into the falling fly ash transfer device 18 through the falling fly ash inlet 18A, transported to a predetermined location, and discharged to the outside of the falling fly ash transfer device 18 through the falling fly ash outlet 18B. For this transfer, for example, a rotary valve 19 that scrapes off and transfers a predetermined amount of the falling fly ash 21 introduced from the falling fly ash inlet 18A, and a screw conveyor 20 that conveys the falling fly ash 21 scraped off by the rotary valve 19 to the falling fly ash outlet 18B may be used. In this case, the rotary valve 19 and the screw conveyor 20 may be connected by a pipe 27 as shown in Fig. 1, and the falling fly ash 21 may fall by gravity through the inside of the pipe 27 from the rotary valve 19 to the screw conveyor 20. However, the transport path from the falling fly ash inlet 18A to the falling fly ash outlet 18B is configured to be kept substantially airtight in order to obtain air pressure information by a pressure sensor 25, which will be described later.

[0035] The falling fly ash transporting device 18 may be configured as a falling fly ash transporting device 18' in a modified example described later, simply consisting of piping such as a duct or a chute having a falling fly ash inlet 18A at one upper end and a falling fly ash outlet 18B at the other lower end, so that the falling fly ash 21 slides down inside the falling fly ash transporting device 18 by gravity. Additionally, the piping may be circular or angular (eg, square) in cross section, depending on the design.

[0036] Next, the pressure sensor 25 and the temperature sensor 26 will be described. The pressure sensor 25 is installed below the position where arching is expected, and measures the air pressure in the boiler lower hopper 16 near the hopper discharge outlet 17, or in the falling fly ash transport device 18 near the hopper discharge outlet 17, or in the piping 28 constantly or periodically (for example, intermittently at short intervals of about 10 seconds), and transmits the air pressure information resulting from the measurement in chronological order and continuously to the control device 29 described below. 1 shows, as an example, a configuration in which the pressure sensor 25 is installed in the pipe 27 inside the falling fly ash transferring device 18 to obtain air pressure information. However, the pressure sensor 25 may be installed at any position inside the falling fly ash transferring device 18 as long as it is not near the falling fly ash discharge port 18B of the falling fly ash transferring device 18. The temperature sensor 26 is installed below the position where arching is expected, and measures the temperature of the outer or inner surface of the boiler lower hopper 16 in the vicinity of the hopper discharge outlet 17, or the outer or inner surface of the falling fly ash transport device 18 in the vicinity of the hopper discharge outlet 17, or the outer or inner surface of the piping 28 constantly or periodically (for example, intermittently at short intervals of about 10 seconds), and transmits the temperature information resulting from the measurement in chronological order and continuously to the control device 29 described later. FIG. 1 shows, as an example, a configuration in which a temperature sensor 26 is installed on the outer surface of a pipe 28 connecting the hopper discharge port 17 and the falling fly ash inlet 18A, and temperature information on the outer surface is obtained.

[0037] The "temperature of the inner surface" is not limited to the inside of the wall surface where the temperature sensor 26 is installed, i.e., the surface temperature of the inner wall surface itself, but may be the temperature of air or gas passing through the inside. The "temperature of the outer surface" is the surface temperature of the outer wall surface where the temperature sensor 26 is installed, i.e., the temperature of the iron shell. When the temperature sensor 26 measures the "internal temperature", the response speed of the temperature measurement is fast, but there is a risk that the temperature measurement may be inaccurate due to the influence of falling fly ash, etc., whereas when the temperature sensor 26 measures the "external temperature", the response speed is slow but the temperature can be measured accurately. The temperature sensor 26 may measure either the "internal temperature" or the "external temperature" depending on the design, but in the following explanation, it is assumed that the temperature sensor 26 measures the "external temperature".

[0038] Finally, the control device 29 and its control will be described. The control device 29 receives air pressure information measured by the pressure sensor 25 or temperature information measured by the temperature sensor 26, and based on the air pressure information or temperature information, controls the bullet ejection device 22 to automatically eject a bullet from the bullet ejection device 22 while the combustion plant 2 is operating. 1 illustrates the removal system 1 equipped with both the pressure sensor 25 and the temperature sensor 26. However, the removal system 1 may be equipped with both the pressure sensor 25 and the temperature sensor 26, or may be equipped with only one of the pressure sensor 25 or the temperature sensor 26. Therefore, the control of the bullet ejection device 22 by the control device 29 will be explained below by dividing it into three cases (1), (2), and (3).

[0039] (1) When the temperature sensor 26 is not installed and only the pressure sensor 25 is installed (1-1) When the air pressure information received by the control device 29 indicates that the air pressure has increased from a negative pressure lower than atmospheric pressure toward atmospheric pressure and then that the increased air pressure has been maintained for a first predetermined time (for example, about one minute), the control device 29 activates the bullet ejection device 22 to eject a bullet. This is because in this case, it can be determined that arching has occurred that is unlikely to resolve naturally.

[0040] The reason for this will be explained below. When arching is not occurring in the boiler lower hopper 16, the inside of the flue 5 is at negative pressure, so that the inside of the falling fly ash transporting device 18, specifically the air in the above-mentioned transport path, flows from the falling fly ash discharge port 18B through the falling fly ash inlet 18A and the hopper discharge port 17 in this order to the boiler lower hopper 16. In other words, air flows from the falling fly ash discharge port 18B toward the inside of the flue 5. At this time, the air pressure measured by the pressure sensor 25 becomes a negative pressure lower than atmospheric pressure. On the other hand, when arching occurs, the air path is blocked and air no longer flows from the falling fly ash discharge outlet 18B into the flue 5, so that the air pressure measured by the pressure sensor 25 increases from a constant negative pressure toward atmospheric pressure and eventually reaches atmospheric pressure, which is the same as the air pressure at the falling fly ash discharge outlet 18B. Therefore, if the air pressure information received by the control device 29 indicates that the air pressure has increased from a negative pressure lower than atmospheric pressure toward atmospheric pressure, it can be determined that arching has occurred, and if it further indicates that the increased air pressure, e.g., atmospheric pressure, is then maintained for a first predetermined period of time (e.g., one minute), it can be determined that arching has occurred that is not likely to resolve naturally. Here, if there is a small through hole in the generated arching, the increased air pressure does not necessarily reach atmospheric pressure, and therefore the increased air pressure is greater than the above-mentioned constant negative pressure and less than atmospheric pressure.

[0041] Incidentally, when the air pressure information received by the control device 29 indicates that the pressure has increased from a negative pressure lower than atmospheric pressure toward atmospheric pressure, the control device 29 does not immediately start the bullet ejection device 22 because, as described above, multiple lumps of fly ash 21B often fall at different times with a slight time difference between them, and therefore, once arching has occurred, the arching may be destroyed by further falling lumps of fly ash 21B, causing the arching to naturally disappear. If the bullet ejection device 22 ejects a bullet after the arching has naturally disappeared, there is a risk of adverse effects such as damage to the boiler below hopper 16. Therefore, when the air pressure information received by the control device 29 indicates that the increased air pressure has been maintained for a first predetermined time (e.g., one minute) after increasing from a negative pressure lower than atmospheric pressure toward atmospheric pressure, the control device 29 determines that the arching is unlikely to naturally disappear, and starts the bullet ejection device 22 to eject a bullet.

[0042] If there is no change in the air pressure information received by the control device 29 after the bullet is fired under the control of (1-1) and the increased air pressure is maintained, the control device 29 again measures the first predetermined time or a shorter predetermined time (for example, about 30 seconds) from the firing of the bullet, and repeats the control of (1-1). This is because it can be determined that the arching was not destroyed by the bullet fired under the control of (1-1), i.e., the arching was not removed. Even in this case, the control device 29 judges whether the arching is maintained or not based on the air pressure information received by the control device 29 for the first predetermined time or a predetermined time shorter than that. In other words, the state of the arching is observed for the first predetermined time or a predetermined time shorter than that. This is because the arching may not be destroyed immediately due to the impact of the bullet fired previously, but may collapse after a short time lag.

[0043] (1-2) If the air pressure information received by the control device 29 indicates that the constant negative pressure is maintained, or indicates that the negative pressure has increased from the constant negative pressure toward atmospheric pressure and then decreased back to the constant negative pressure within a first predetermined time, the control device 29 does not cause the bullet ejection device 22 to eject a bullet. In this case, it can be determined that arching has not occurred, or that arching has formed temporarily but then naturally disappeared, so there is no need to have the bullet ejection device 22 eject a bullet.

[0044] (2) When the pressure sensor 25 is not installed and only the temperature sensor 26 is installed (2-1) When the temperature information received by the control device 29 indicates that the temperature has changed from a high temperature (e.g., 350°C) measured when no arching is occurring to a low temperature (e.g., 150°C) that is lowered by more than a predetermined temperature range (e.g., 200°C), and that the low temperature has been maintained for a second predetermined time (e.g., about 10 seconds), the control device 29 starts the bullet ejection device 22 to eject a bullet. This is because in this case, it can be determined that arching has occurred that is unlikely to resolve naturally.

[0045] The reason for this will be explained below. The temperature of the exhaust gas flowing below the second flue 5B of the flue 5 is generally high, at 700°C or more. When arching does not occur in the boiler lower hopper 16, the inside of the flue 5 is under negative pressure, so air flows from the falling fly ash discharge port 18B toward the inside of the flue 5. The heat of the exhaust gas is transferred along the wall surface surrounding this air flow. The transferred heat is greatly reduced in temperature by the refractory material installed on the wall surface of the boiler lower hopper 16, and is transferred to the falling fly ash transfer device 18. As described above, an example in which the temperature sensor 26 measures the iron shell temperature is described here. Therefore, although the temperature measured by the temperature sensor 26 has decreased below the temperature of the exhaust gas flowing below the second flue 5B, it is still a high temperature (for example, 350° C.) that is high as before. On the other hand, when arching occurs in the boiler lower hopper 16, the air flow is blocked, making it difficult for the heat of the exhaust gas to be transmitted to the surrounding wall surfaces. As a result, a large temperature difference of several hundred degrees or more occurs between the boiler lower hopper 16 side and the falling fly ash transport device 18 side, with the arching as the boundary. Therefore, if the temperature information received by the control device 29 indicates that the temperature has changed from a high temperature (e.g., 350°C) to a low temperature (e.g., 150°C) that is reduced by more than a predetermined temperature range (e.g., a temperature range of 200°C), it can be determined that arching has occurred, and if it further indicates that the low temperature is then maintained for a second predetermined time period (e.g., approximately 10 seconds), it can be determined that arching has occurred that is not expected to resolve naturally.

[0046] In addition, when the temperature information received by the control device 29 changes from a high temperature to a low temperature that is reduced by more than a predetermined temperature range, the control device 29 does not immediately start the bullet ejection device 22 because, as described above, multiple lumps of fly ash 21B often fall at different times with some time difference between them, and therefore, after arching occurs, the arching may be destroyed by further falling lumps of fly ash 21B, causing the arching to naturally disappear. For this reason, similarly to the control (1-1), the state of arching is observed for a second predetermined time (for example, about 10 seconds). Then, when the temperature information received by the control device 29 changes from a high temperature to a low temperature that is reduced by more than a predetermined temperature range and then confirms that the low temperature is maintained for a second predetermined time (e.g., 10 seconds), the control device 29 determines that the arching is unlikely to resolve naturally, and starts the bullet ejection device 22 to eject a bullet.

[0047] As described above, the first predetermined time in the control of (1) and the second predetermined time in the control of (2) are appropriately set according to the design of the combustion plant 2, but the second predetermined time may be smaller than the first predetermined time, i.e., "first predetermined time" > "second predetermined time". When arching occurs, the air pressure information changes immediately, but the temperature information changes more slowly than the air pressure information. Therefore, at the time when the temperature information becomes low, it is considered that arching has been maintained for a considerably longer period of time than in the case of the air pressure information.

[0048] If there is no change in the temperature information received by the control device 29 and the temperature remains low even though the bullet is ejected under the control of (2-1), the control device 29 measures a third predetermined time (e.g., about 30 seconds) longer than the second predetermined time (e.g., about 10 seconds) from the ejection of the bullet, and repeats the control of (2-1). This is because it can be determined that the arching was not destroyed by the bullet ejected under the control of (2-1), that is, the arching was not eliminated. Even in this case, the control device 29 judges whether the arching is maintained for the third predetermined time based on the temperature information received by the control device 29. In other words, the state of the arching is observed for the third predetermined time. This is because the arching may not be destroyed immediately due to the impact of the bullet fired previously, but may collapse after a short time lag.

[0049] However, the third predetermined time is set to be longer than the second predetermined time. That is, the first predetermined time may be set to be greater than or equal to the third predetermined time > the second predetermined time. Since a temperature change takes longer to transmit than a change in air pressure, even if the arching is eliminated by the impact of a bullet, it takes time for the temperature measured by the temperature sensor 26 to rise from the low temperature. For this reason, by setting the third specified time longer than the second specified time, it is possible to avoid the bullet being fired when the arching has been eliminated.

[0050] (2-2) If the temperature information received by the control device 29 indicates that the high temperature is maintained, or that the temperature has changed from a high temperature to a low temperature by decreasing by more than a predetermined temperature range and then changed from a low temperature to a high temperature again within a second predetermined time, the control device 29 does not cause the bullet ejection device 22 to eject a bullet. In this case, it can be determined that arching has not occurred, or that arching has formed temporarily but then naturally disappeared, so there is no need to have the bullet ejection device 22 eject a bullet.

[0051] (3) When both the pressure sensor 25 and the temperature sensor 26 are installed (3-1) When the air pressure information received by the control device 29 increases from a negative pressure lower than atmospheric pressure to atmospheric pressure, and the temperature information received by the control device 29 changes from a high temperature (e.g., 350°C) measured when no arching is occurring to a low temperature (e.g., 150°C) that is lowered by more than a predetermined temperature range (e.g., 200°C), the control device 29 starts the bullet ejection device 22 to eject a bullet. This is because in this case, it can be determined that arching has occurred that is unlikely to resolve naturally.

[0052] The reason for this will be explained below. As mentioned above, pressure changes are transmitted faster than temperature changes. Therefore, after the air pressure information received by the control device 29 changes from negative pressure toward atmospheric pressure, the temperature information received by the control device 29 changes from high to low. From a time perspective, it can be considered that arching occurs at the point when the air pressure information changes toward atmospheric pressure, and that the arching is maintained thereafter until the temperature information changes to a low temperature. Therefore, unlike the case of control (1) or control (2), there is no need to wait and see whether the arching is maintained for a further predetermined time. Therefore, when both the air pressure information and temperature information received by the control device 29 satisfy the above-mentioned specified conditions, the control device 29 determines that the arching is unlikely to resolve naturally, and immediately causes the bullet ejection device 22 to eject a bullet.

[0053] If there is no subsequent change in the air pressure information and temperature information received by the control device 29 even though a bullet has been fired under the control of (3-1), the control device 29 will measure a fourth predetermined time (e.g., about one minute) from the firing of the bullet, and repeat the control of (3-1). This is because the arching may not be destroyed immediately due to the previous impact of the bullet, but may collapse after a short time lag. The fourth predetermined time may be set to be equal to or less than the first predetermined time and equal to or greater than the second predetermined time, i.e., "first predetermined time" ≧ "fourth predetermined time" ≧ "second predetermined time".

[0054] (3-2) If the air pressure information and temperature information received by the control device 29 do not satisfy the predetermined conditions described in (3-1), the control device 29 does not cause the bullet ejection device 22 to eject a bullet. In other words, the control device 29 does not start up the bullet ejection device 22. In this case, it can be determined that arching has not occurred, or that arching has formed temporarily but then naturally disappeared, so there is no need to have the bullet ejection device 22 eject a bullet.

[0055] According to the above-mentioned removal system 1, even if arching occurs, if the arching naturally disappears within a predetermined time, the bullets are not shot. Therefore, since the bullets mainly composed of non-metallic materials can be shot against the existing arching and the arching can be removed, there is no risk of damaging the boiler below hopper 16. In addition, the bullet path from the bullet ejection device 22 to the opening 23 is kept airtight, and the bullet is automatically ejected from the opening 23 toward the arching to remove the arching while the combustion plant 2 is in operation, so there is no need to open a door such as a manhole connecting the inside and outside of the flue 5. Therefore, the removal system 1 can be operated safely for the human body.

[0056] Next, a modified removal system 1' will be described with reference to FIG. Except for the fact that the falling fly ash transport device 18' of the removal system 1' has a different configuration from the falling fly ash transport device 18 of the removal system 1 of the embodiment, and that the removal system 1' does not have a temperature sensor 26 but only a pressure sensor 25, the removal system 1' has the same configuration as the removal system 1. Therefore, a description of the same configuration and the same effects as those of the removal system 1 will be omitted. In addition, FIG. 4 shows an example in which the pressure sensor 25 is installed in the boiler lower hopper 16 below the arching and near the hopper discharge port 17.

[0057] The falling fly ash transfer device 18' is a device that is installed below the hopper discharge port 17 of the boiler lower hopper 16, similar to the falling fly ash transfer device 18, and is equipped with at least a falling fly ash inlet 18A' and a falling fly ash outlet 18B'. However, unlike the falling fly ash transfer device 18, the falling fly ash transfer device 18' is not equipped with an active transport device such as a rotary feeder or a screw conveyor, but is simply a pipe such as a duct or a chute. The falling fly ash inlet 18A' is connected directly or indirectly via a pipe to the hopper discharge port 17 of the boiler lower hopper 16. Fig. 4 shows an example in which the falling fly ash inlet 18A' is directly connected to the hopper discharge port 17. The falling fly ash discharge port 18B' is connected to an opening formed in the outer wall of the main ash chute 13. Therefore, in the falling fly ash transport device 18', the falling fly ash 21 discharged by gravity from the hopper discharge outlet 17 slides down due to gravity and is transported to the falling fly ash discharge outlet 18B', and is discharged from the falling fly ash discharge outlet 18B' into the main ash chute 13 with the same momentum as the sliding down. Then, below the bottom ash chute 13, the bottom ash and the falling fly ash 21 are mixed together and discharged outside the combustion plant 2. That is, the removal system 1' can automatically mix the main ash and the fly ash and carry them out. Therefore, in cases where the main ash and the fly ash can be mixed for disposal, the removal system 1' is superior to the removal system 1. In addition, the removal system 1' has a simpler configuration than the removal system 1, and therefore has the advantage of being cheaper to manufacture.

[0058] Here, since the incinerator 3 and the bottom ash chute 13 are sealed spaces airtightly connected to the flue 5, they are under negative pressure like the flue 5 during operation of the combustion plant 2. However, when comparing the air pressure in the boiler lower hopper 16 (here, referred to as "air pressure A") with the air pressure in the incinerator 3 and the bottom ash chute 13 (here, referred to as "air pressure B"), the air pressure A in the boiler lower hopper 16 is more negative than the air pressure B in the incinerator 3 and the bottom ash chute 13 because it is closer to the induced draft fan 6. In other words, although air pressure A and air pressure B are the same in that they are both negative pressures, the relationship is atmospheric pressure > air pressure B > air pressure A.

[0059] The control by the control device 29 in the removal system 1' is the same as that described in "(1) Case where the temperature sensor 26 is not provided, and only the pressure sensor 25 is provided" in the removal system 1, and so a description thereof will be omitted. In the removal system 1', for example, in the control of (1)(1-1), if the air pressure information received by the control device 29 indicates that the air pressure has increased from air pressure A, which is a negative pressure lower than atmospheric pressure, toward atmospheric pressure, and then indicates that the increased air pressure, air pressure B, has been maintained for a first predetermined time (for example, about one minute), the control device 29 activates the bullet ejection device 22 to eject a bullet. Although the falling fly ash transporting device 18' has been described as being merely a pipe, a conveyor or other transporting device may be provided inside the pipe in order to facilitate the transport of the falling fly ash 21 to the main ash chute 13.

[0060] As described above, according to the boiler below hopper arching removal system of the present invention, arching that has occurred in the boiler below hopper 16 can be safely removed without damaging the boiler below hopper 16 during operation of a combustion plant 2 equipped with a boiler. The above-mentioned first to fourth predetermined times can be set appropriately depending on the design of the combustion plant 2. In addition, the control device 29 may also appropriately control the start-up and driving of devices provided in the combustion plant 2, such as the stoker 12, the feeder 11, the induced draft blower 6, the ash removal device 15, the rotary valve 19, and the screw conveyor 20. Furthermore, in the case of a combustion plant in which the above-mentioned fourth flue is connected to the third flue 5C, a boiler below hopper other than the boiler below hopper 16 may also be formed below the fourth flue. In this case, similar to the case of the boiler below hopper 16, the control device 29 may control the bullet ejection device arranged corresponding to the other boiler below hopper. [Explanation of symbols]

[0061] 1, 1′ Boiler lower hopper arching removal system (removal system) 2. Combustion plant 3. Incinerator 4. Chimney 5 flue 5A First flue (1 pass) 5B Second flue (2 passes) 5C Third flue (3 passes) 6. Induced draft fan 7 Heat transfer tube 8. Cooling Tower 9. Bag filter 10 Hopper 11 Feeder 12 Stalker 13. Main Ash Shoot 14 Economizer 15 Ash removal equipment 16 Boiler lower hopper 16A Front (wall) 16B Rear (wall) 17 Hopper discharge port 18, 18′ Falling fly ash transfer device 18A, 18A′ Falling fly ash inlet 18B, 18B′ Falling fly ash outlet 19 Rotary Valve 20 Screw Conveyor 21 Fallen fly ash 21A Fine fly ash 21B Lumpy fly ash 22 Arching removal bullet ejection device (bullet ejection device) 23 Aperture 24 Injection tube 24A one end 24B other end 24C straight pipe section 24D horizontal section 25 Pressure Sensor 26 Temperature Sensor 27 Piping 28 Piping 29 Control device

Claims

1. a boiler below hopper in which flue gas containing fly ash from a combustion plant equipped with a boiler is drawn by an induced draft fan and flows through a flue, the fly ash adheres to a heat transfer tube arranged in the flue, and the fly ash falls through the flue and is discharged from a hopper discharge port as fallen fly ash; a bullet ejection device that ejects a bullet made mainly of a non-metallic material toward an arching formed by the falling fly ash in the vicinity of the hopper discharge port through an opening formed in a wall surface of the boiler lower hopper; A falling fly ash transport device, in which a falling fly ash inlet is connected to the hopper outlet directly or indirectly through a pipe, and the falling fly ash introduced from the falling fly ash inlet is discharged from a falling fly ash outlet; a temperature sensor for measuring the temperature of the outer or inner surface of the boiler lower hopper below the arching and in the vicinity of the hopper discharge port, or the outer or inner surface of the falling fly ash transfer device in the vicinity of the hopper discharge port, or the outer or inner surface of the piping, and a pressure sensor for measuring the air pressure in the boiler lower hopper below the arching and in the vicinity of the hopper discharge port, or in the falling fly ash transfer device in the vicinity of the hopper discharge port, or in the piping; or a control device that receives temperature information measured by the temperature sensor or air pressure information measured by the pressure sensor, and causes the bullet ejection device to eject the bullet based on the temperature information or the air pressure information during operation of the combustion plant; having The path of the bullet from the bullet ejection device to the opening is kept airtight, The control device includes: In the case where the temperature sensor is not installed and the pressure sensor is installed, when the air pressure information indicates that the air pressure has increased from a negative pressure lower than atmospheric pressure toward atmospheric pressure and then the increased air pressure has been maintained for a first predetermined time, causing the bullet ejection device to eject the bullet; In the case where the pressure sensor is not installed and the temperature sensor is installed, when the temperature information indicates that the low temperature has been maintained for a second predetermined time after the high temperature has changed to a low temperature that is lowered by a predetermined temperature range or more, the bullet ejection device is caused to eject the bullet; When both the pressure sensor and the temperature sensor are installed, When the air pressure information indicates that the air pressure is increasing from the negative pressure toward atmospheric pressure and the temperature information indicates that the temperature has changed from the high temperature to the low temperature, the bullet ejection device is caused to eject the bullet. Boiler under-hopper arching removal system.

2. The bullet further includes an ejection tube through which the bullet travels. The injection tube has a straight tube portion that is inclined upward from the horizontal at an angle of 30 degrees to 85 degrees from the opening toward the extension direction of the injection tube. The boiler under hopper arching removal system of claim 1.

3. The injection pipe is a straight or curved pipe that does not protrude into the boiler lower hopper, has one end connected to the opening, and the other end connected to the bullet injection device. The boiler under hopper arching removal system according to claim 2.

4. The wall surface of the boiler lower hopper has an inverted quadrangular pyramid shape including a front surface on the upstream side, a rear surface on the downstream side, and two side surfaces connected to the front surface and the rear surface, respectively, as viewed in the flow of the exhaust gas, The opening is disposed on the front surface. The boiler under hopper arching removal system according to claim 3.

5. The bullets are mainly composed of fly ash, clinker, concrete, ice, or dry ice. The boiler under hopper arching removal system according to claim 4.

6. The flue includes at least a first flue extending vertically upward, a second flue connected to the first flue and extending vertically downward, and a third flue connected to the second flue and extending vertically upward, The third flue includes the heat transfer tube, The boiler lower hopper is located at a location where the second flue and the third flue are connected, The falling fly ash transport device includes at least a rotary valve or a screw conveyor. The boiler under hopper arching removal system according to any one of claims 1 to 5.

7. The combustion plant is a plant equipped with a waste incinerator, Further comprising a bottom ash chute for discharging bottom ash from the waste incinerator; The flue includes at least a first flue extending vertically upward, a second flue connected to the first flue and extending vertically downward, and a third flue connected to the second flue and extending vertically upward, The third flue includes the heat transfer tube, The boiler lower hopper is located at a location where the second flue and the third flue are connected, The falling fly ash transporting device connects the hopper discharge port of the boiler lower hopper to the bottom ash chute, and transports the falling fly ash from the hopper discharge port to the bottom ash chute; The pressure sensor is installed The boiler under hopper arching removal system according to any one of claims 1 to 5.

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