Fly ash circulation device

Abstract

A fly ash circulation device (1) comprises at least: a chemical supply device (3) that supplies a chemical for purifying a dust-containing exhaust gas to a first exhaust gas path (2) through which a dust-containing exhaust gas generated in a combustion furnace plant flows; a dust collection device (4) that has the first exhaust gas path connected to the upstream side and a second exhaust gas path connected to the downstream side, wherein the dust collection device discharges, to the second exhaust gas path (6), dedusted exhaust gas obtained by executing dust removal on the dust-containing exhaust gas in the first exhaust gas path; and a chemical-admixed fly ash supply device (5) that is connected to the lower part of the dust collection device (4) and that supplies, to the first exhaust gas path (2) that passes directly below the former or in the vicinity of directly below the former, a chemical-admixed fly ash provided by the mixing of fly ash and chemical that have descended in the interior of the dust collection device (4) due to dust removal.

Description

Fly ash circulation device

[0001] The present invention relates to a fly ash circulation device that reuses chemicals contained in collected fly ash for purifying exhaust gases.

[0002] In a plant using a combustion furnace such as a waste incinerator (hereinafter referred to as a "furnace plant"), exhaust gas (hereinafter referred to as "exhaust gas") generated by the combustion of fuel such as waste is purified by spraying chemicals such as slaked lime onto the exhaust gas and then removed by a dust collector (e.g., a bag filter or an electrostatic precipitator). The exhaust gas is then released into the atmosphere, i.e., outside the plant, through an exhaust device such as a chimney. The chemicals are generally supplied to a portion of the exhaust gas path from the combustion furnace to the chimney, downstream of the combustion furnace and upstream of the dust collector. The collected dust ash from the dust collector contains fly ash, reaction products of the chemicals, and chemicals that did not fully contribute to the purification of the exhaust gas (unreacted or insufficiently reacted chemicals; hereinafter, these are collectively referred to as "unreacted chemicals" for convenience). To effectively utilize the unreacted chemicals, a so-called "fly ash circulation" technology has been proposed (see Patent Document 1).

[0003] Fly ash circulation technology is a technology that reuses unreacted chemicals that have been supplied to the exhaust gas route without discarding them. Generally, it is a technology that resupplies fly ash mixed with unreacted chemicals collected by a dust collector (hereinafter referred to as "chemical-mixed fly ash") into the exhaust gas route upstream of the dust collector.

[0004] Japanese Patent Application Laid-Open No. 2020-58997

[0005] In combustion furnace plants, especially those equipped with power generation boilers, the boilers are typically large, typically as tall as the third or fourth floor of an office building, i.e., the upper floors. The exhaust gas path carrying the flue gas containing soot and dust (hereinafter referred to as "dust-containing exhaust gas") runs from the high-rise boiler to a dust collector below. However, since the chemical-mixed fly ash stored in the dust collector is discharged from the bottom of the dust collector, the chemical-mixed fly ash is transported to the exhaust gas path by a conveyor or air-transporting device. This can lead to a decrease in the operating rate of the combustion furnace plant depending on the frequency and duration of maintenance of the transport device.

[0006] Therefore, the present invention aims to provide a fly ash circulation device that can circulate chemical-mixed fly ash discharged from a dust collector to an exhaust gas path upstream of the dust collector, without the need to separately install a conveyor-type or air-transporting device to lift the chemical-mixed fly ash, thereby making effective use of unreacted chemicals.

[0007] The fly ash circulation system of the present invention comprises: a chemical supplying device that supplies a chemical for purifying a dust-containing exhaust gas to a first exhaust gas passage through which a dust-containing exhaust gas generated in a combustion furnace plant flows; a dust collector connected to the upstream side of the first exhaust gas passage and the downstream side of a second exhaust gas passage, the dust collector having a hopper below and configured to remove the dust-containing exhaust gas from the first exhaust gas passage and discharge the resulting dust-removed exhaust gas into the second exhaust gas passage; and a dust collector having an inlet connected below the dust collector and configured to discharge the chemical-mixed fly ash, which has fallen into the hopper below the interior of the dust collector as a result of the dust removal, directly or through a pipe into the first exhaust gas passage. and a chemical-mixed fly ash supplying device that supplies the chemical-mixed fly ash to the first exhaust gas path from an outlet that is indirectly connected to the first exhaust gas path by a path and is located below the inlet, and the chemical-mixed fly ash supplying device supplies the chemical-mixed fly ash from the outlet to the first exhaust gas path that passes directly below the outlet or vertically below a position 1 to 5 m horizontally from directly below the outlet, the first exhaust gas path being downstream of the point where the chemical supplying device supplies the chemical, by gravity or by the suction force of gravity and negative pressure of the first exhaust gas path, and the chemical-mixed fly ash supplied to the first exhaust gas path circulates to the hopper.

[0008] According to the fly ash circulation system of the present invention, the first flue gas path upstream of the dust collector passes directly below or below the chemical-mixed fly ash supplying device located below the dust collector. Therefore, the chemical-mixed fly ash that falls below the interior of the dust collector can be easily supplied to the first flue gas path passing below the chemical-mixed fly ash supplying device, and the flue gas in which the chemical-mixed fly ash is dispersed is automatically lifted upward by the flue gas flow and introduced into the dust collector. This eliminates the need for a separate conveyor to lift the chemical-mixed fly ash into the flue gas path, as in the prior art. Therefore, according to the fly ash circulation system of the present invention, the chemical-mixed fly ash discharged from the dust collector can be circulated to the first flue gas path upstream of the dust collector, effectively utilizing the unreacted chemicals, without the need for a separate conveyor-type or pneumatic conveyor to lift the chemical-mixed fly ash.

[0009] Fig. 1 is a schematic configuration diagram of a fly ash circulating apparatus according to an embodiment. Fig. 2 is a schematic configuration diagram of a first modified example of the fly ash circulating apparatus shown in Fig. 1. Fig. 3 is a schematic configuration diagram of a second modified example of the fly ash circulating apparatus shown in Fig. 1. Fig. 4 is a schematic configuration diagram of a third modified example of the fly ash circulating apparatus shown in Fig. 1. Fig. 5 is a schematic configuration diagram of a fourth modified example of the fly ash circulating apparatus shown in Fig. 1.

[0010] Hereinafter, with reference to the drawings (FIGS. 1 to 5), a fly ash circulation system according to an embodiment of the present invention and its modifications (first to fourth modifications) will be described. The embodiment and each modification are merely illustrative and are not intended to exclude various modifications or technical applications not specifically described. The configurations of the embodiment and each modification can be modified in various ways without departing from the spirit of the invention. Furthermore, each configuration, except for those essential to the invention, can be selected and / or removed as needed, or can be appropriately combined between the embodiment and each modification. In FIGS. 1 to 5, an orthogonal coordinate system consisting of an X-axis and a Y-axis will be used for explanation. The X-axis is horizontal, and the Y-axis is vertical. The arrow on the Y-axis points vertically upward.

[0011] [Fly Ash Circulation Apparatus of the Embodiment] A fly ash circulation apparatus 1 of the embodiment will now be described with reference to FIG. 1 . First, a brief overview of the overall configuration of the fly ash circulation apparatus 1 will be described, followed by a detailed description of each component of the fly ash circulation apparatus 1. The fly ash circulation apparatus 1 is connected to a first flue gas passage 2 through which flue gas containing soot and dust such as fly ash (hereinafter referred to as "dust-containing flue gas") flows from a combustion furnace (including an incinerator) in a combustion furnace plant such as a waste incineration plant or a biomass-fired power plant. The flue gas passage 2 is specifically a conduit such as a duct or pipe connected between the combustion furnace and the fly ash circulation apparatus 1. Note that hereinafter, the term "conduit" simply refers to a conduit such as a duct or pipe. The fly ash circulation system 1 includes at least a chemical agent supplying device 3 that supplies a chemical agent, such as slaked lime or activated carbon, to the first flue gas line 2 to purify the dust-containing flue gas flowing through the first flue gas line 2, a dust collector 4 connected to one end of the first flue gas line 2 to remove dust from the dust-containing flue gas, and a chemical agent-mixed fly ash supplying device 5 connected below the dust collector 4. The chemical agent-mixed fly ash supplying device 5 supplies collected dust ash (hereinafter referred to as "chemical agent-mixed fly ash"), which is a mixture of chemical agent and fly ash that has fallen into the lower part of the dust collector 4 due to the removal of the dust-containing flue gas, to the first flue gas line 2 located directly below or near the lower part (in the -Y axis direction) of the chemical agent-mixed fly ash supplying device 5, thereby dispersing and reacting the unreacted chemical agent in the chemical agent-mixed fly ash with the dust-containing flue gas in the first flue gas line 2. Since the fly ash circulation device 1 is configured as described above, the first exhaust gas path 2 passes below the chemical-mixed fly ash supply device 5 (in the -Y-axis direction) and then bends upward (in the +Y-axis direction), and then the above-mentioned one end of the first exhaust gas path 2 is connected to the dust collector 4.

[0012] The flue gas from which dust has been removed by the dust collector 4 (hereinafter referred to as "dust-removed flue gas") is drawn by a blower (first blower) 7 installed in a second flue gas passage 6 connected between the dust collector 4 and an exhaust device such as a chimney. The blower 7 is appropriately selected from, for example, a fan, a blower, or a compressor depending on the design. Note that, like the first flue gas passage 2, the second flue gas passage 6 is a conduit such as a duct or pipe. In terms of the flow of exhaust gas, the first flue gas passage 2 is connected upstream of the dust collector 4, and the second flue gas passage 6 is connected downstream of the dust collector 4. Then, as a result of the above-mentioned drawing by the blower 7, the dust-containing flue gas in the first flue gas passage 2 flows from the combustion furnace toward the dust collector 4. Furthermore, as a result of the above-mentioned drawing by the blower 7, the dust-removed flue gas in the second flue gas passage 6 flows from the dust collector 4 toward an exhaust device such as a chimney and is discharged into the atmosphere.

[0013] Next, each component of the fly ash circulation system 1 will be described in detail. First, as described above, the chemical supply device 3 is a device that supplies a chemical to the first flue gas path 2. The chemical can be sprayed into the first flue gas path 2 by a blower (not shown), such as a high-pressure blower. The positional relationship between a specific location (hereinafter referred to as "location A") in the first flue gas path 2 to which the chemical-mixed fly ash supply device 5 supplies the chemical-mixed fly ash and a specific location (hereinafter referred to as "location B") in the first flue gas path 2 to which the chemical supply device 3 supplies the chemical may be such that location B is either upstream of location A or downstream of location A. However, this example illustrates a case in which location B is upstream of location A so that the reaction time of the new chemical can be longer than the reaction time of the unreacted chemical in the chemical-mixed fly ash. The chemical supply device 3 may spray the chemical into the first exhaust gas path 2 using compressed air from a compressed air supply device (not shown) instead of the above-mentioned blower, or may cut out the chemical using a rotary valve or table feeder (not shown) and distribute it by free fall due to gravity into the first exhaust gas path 2. Even in the case of free fall, the inside of the first exhaust gas path 2 is under negative pressure due to the blower 7, and therefore, in addition to gravity, a suction force due to the negative pressure is applied to the first exhaust gas path 2, and the chemical supplied from the chemical supply device 3 is introduced into the first exhaust gas path 2 and dispersed in the dust-containing exhaust gas.

[0014] Next, the dust collector 4 may be a bag filter device or an electrostatic precipitator. Here, as an example, a bag filter device including multiple bag filters 4a made of cylindrical, bag-shaped filter cloth will be described. In the dust collector 4, the dust-containing exhaust gas flowing through the first exhaust gas path 2, the chemical-mixed fly ash supplied at point A, and the chemical supplied at point B are removed from the outside of the bag-shaped filter cloth of the bag filter 4a, and the post-dust removal exhaust gas flows upward (in the +Y-axis direction) inside the filter cloth. Therefore, the second exhaust gas path 6 is connected to the dust collector 4 above the inlet (inlet of the bag-shaped filter cloth) of the bag filter 4a in the Y-axis direction. The bottom of the dust collector 4 is a hopper 4b with a sloping wall that is larger at the top and smaller at the bottom, such as an inverted pyramid, ship's bottom, or inverted cone. The bottom may also be a flat bottom without a sloping wall.

[0015] The dust collector 4 may include a feeder 4c disposed inside or below the hopper 4b (in the -Y-axis direction) for feeding the chemical-mixed fly ash stored in the hopper 4b to the chemical-mixed fly ash supply device 5. A conveying device such as a screw conveyor may be disposed at the bottom of the hopper 4b for transporting the stored chemical-mixed fly ash toward the feeder 4c. The feeder 4c may be, for example, a rotary valve or a table feeder. While FIG. 1 illustrates an example in which the feeder 4c is directly connected to the bottom of the hopper 4b, the feeder 4c may also be indirectly connected to the bottom via a pipe. The amount and timing of the feeder 4c feeding the chemical-mixed fly ash are controlled by a control device (not shown) depending on the design.

[0016] Here, since the dust collector 4 is a bag filter device, by periodically performing so-called "backwashing," chemical-mixed fly ash adhering to the outer surface of the bag filter 4a can be sifted into the hopper 4b. When the first exhaust gas passage 2 is connected to the dust collector 4, the one end of the first exhaust gas passage 2 may be connected to the dust collector 4 above the hopper 4b, or the one end may be connected to the hopper 4b. When the one end is connected to the hopper 4b, the pressure caused by the flow of dust-containing exhaust gas ejected from the one end into the dust collector 4 causes the chemical-mixed fly ash that has fallen into and accumulated in the hopper 4b to be stirred up within the dust collector 4, allowing unreacted chemicals in the chemical-mixed fly ash to be more effectively used to purify the dust-containing exhaust gas.

[0017] Next, the chemical-mixed fly ash supplying device 5 will be described. The inlet of the chemical-mixed fly ash supplying device 5, into which the chemical-mixed fly ash supplied from the dust collector 4 is introduced, is connected below the dust collector 4 (in the -Y-axis direction). Therefore, the chemical-mixed fly ash can be easily supplied from the dust collector 4 to the inlet of the chemical-mixed fly ash supplying device 5 by free fall due to gravity. The chemical-mixed fly ash supplying device 5 has two outlets: a first outlet connected directly or indirectly via a pipeline to point A of the first flue gas path 2, and a second outlet that discharges a portion of the chemical-mixed fly ash to the outside of the fly ash circulation device 1 for dust ash treatment, such as heavy metal elution prevention treatment. The first flue gas path 2 is located directly below or adjacent to the first outlet. Here, "vicinity" refers to a position a predetermined horizontal distance away from "directly below" the first outlet, such that the chemical-mixed fly ash discharged from the first outlet is appropriately introduced into point A of the first exhaust gas path 2 by gravity or by the suction force of gravity and negative pressure on the first exhaust gas path 2. Therefore, "nearby and below" corresponds to a position vertically below the first outlet a predetermined horizontal distance. This predetermined distance may vary depending on the design, but can be considered to be approximately 1 to 5 meters. The chemical-mixed fly ash supply device 5 includes at least a distributor 5a, and a sealing device 5b may also be added as appropriate depending on the design. These components will be described in detail below.

[0018] The distributor 5a distributes the chemical-mixed fly ash introduced from the inlet of the chemical-mixed fly ash supply device 5 to a first path 5aA connected to the first outlet by a pipeline and a second path 5aB connected to the second outlet by a pipeline. The first path 5aA and the second path 5aB are, for example, ducts, pipes, or other conduits. One end of the first path 5aA may serve as the first outlet. Alternatively, one end of the second path 5aB may serve as the second outlet. The distributor 5a may be, for example, a screw conveyor with a rotation axis aligned in the X-axis direction. When the distributor 5a is a screw conveyor, for example, the rotation direction of the rotation axis may be rotated forward to transport the chemical-mixed fly ash toward the first outlet via the first path 5aA, and when the rotation direction is reversed, the chemical-mixed fly ash may be transported toward the second outlet via the second path 5aB. That is, the distributor 5a selectively selects either the first path 5aA or the second path 5aB to distribute the chemical-mixed fly ash.

[0019] In addition to the screw conveyor described above, the distributor 5a may also be configured with a bifurcated chute branching into two paths, a first path 5aA inclined diagonally downward and a second path 5aB inclined diagonally downward, and a damper (e.g., a double-flap damper) disposed at the branching point of the chute. The damper closes one of the paths of the bifurcated chute, selectively selecting either the first path 5aA or the second path 5aB, and distributing the chemical-mixed fly ash toward the first or second outlet. Furthermore, in this case, by adjusting the opening of the damper, the chemical-mixed fly ash can be simultaneously distributed at a predetermined ratio to both the first path 5aA and the second path 5aB. Here, the distributor 5a may be provided with a device equivalent to the sealing device 5b described below, such as a rotary valve, a table feeder, or a double-flap damper, at each outlet of the bifurcated chute.

[0020] In addition to the above-mentioned example, the distributor 5a may be configured such that an inlet dedicated to the first path 5aA and an inlet dedicated to the second path 5aB are separately connected to the bottom of the dust collector 4, and the chemical-mixed fly ash is introduced into each inlet independently from openings in the bottom. Note that the distributor 5a, such as the control of the rotation direction of the screw conveyor, the control of the operation of the damper, and the control of the operation of the rotary valve, etc. (the rotation speed in the case of a rotary valve or table feeder), is performed by the above-mentioned control device according to the design or according to the operation of the operator.

[0021] Finally, the sealing device 5b is installed in the path connecting the first outlet connected to the first path 5aA to the location A of the first exhaust gas path 2. This path is, for example, a conduit such as a duct or pipe. As described below, if the sealing device 5b is not installed, the path may be omitted and the first outlet may be directly connected to the location A. The sealing device 5b separates the first exhaust gas path 2 from the first path 5aA because the internal pressure of the first path 5aA differs from the internal pressure of the first exhaust gas path 2 due to the above-mentioned induction by the blower 7. Furthermore, the sealing device 5b separates the first path 5aA from the first exhaust gas path 2 without interfering with the supply of chemical-mixed fly ash from the first path 5aA to the first exhaust gas path 2 by the distributor 5a. If such separation is not required, the sealing device 5b does not need to be installed. The sealing device 5b can be, for example, a rotary valve, a table feeder, a double flap damper, or the like. When the chemical-mixed fly ash is supplied from the first path 5aA to the first exhaust gas path 2 by the sealing device 5b, the first path 5aA is substantially separated from the first exhaust gas path 2, which has a lower internal pressure than the first path 5aA. The operation of the sealing device 5b, such as the rotary valve, table feeder, and double flap damper, is controlled by the control device described above depending on the design. A vibration device, such as a knocker or vibrator, may be installed in the path connecting the first path 5aA to point A of the first exhaust gas path 2 to prevent blockage due to adhesion of the chemical-mixed fly ash.

[0022] As described above, in the fly ash circulation system 1 according to the embodiment of the present invention, the first flue gas passage 2 upstream of the dust collector 4 passes directly below or below the chemical-mixed fly ash supplying device 5 disposed below the dust collector 4, then flows upward and connects to the dust collector 4. Therefore, the chemical-mixed fly ash supplying device 5 can easily supply the chemical-mixed fly ash that falls downward inside the dust collector 4 to the first flue gas passage 2 passing below the chemical-mixed fly ash supplying device 5 by gravity or by gravity and the suction force of the negative pressure of the first flue gas passage 2. The chemical-mixed fly ash is introduced into the first flue gas passage 2, dispersed, and automatically lifted upward by the flow of dust-containing exhaust gas and reintroduced into the dust collector. In other words, the chemical-mixed fly ash stored in the dust collector 4 can be recirculated by supplying it to the first flue gas passage 2 upstream of the dust collector 4, thereby effectively utilizing the unreacted chemicals in the chemical-mixed fly ash. In this way, the unreacted chemicals in the chemical-mixed fly ash can be effectively utilized, thereby reducing the amount of new chemicals supplied from the chemical supply device 3. This reduces the operating costs of the incineration plant in which the fly ash circulation system 1 is installed. Furthermore, unlike the prior art, a conveyor-type or pneumatic transport device for lifting the chemical-mixed fly ash toward the upper flue gas piping is not required, allowing the fly ash circulation system 1 to be manufactured inexpensively. Furthermore, since the transport device is not required, the maintenance frequency and maintenance period of the fly ash circulation system 1 can be reduced compared to the prior art, resulting in an improved availability of the incineration plant in which the fly ash circulation system 1 is installed.

[0023] Next, fly ash circulating apparatuses 1A, 1B, 1C, and 1D, which are modifications of the embodiment, will be described in order. The same components as those of the fly ash circulating apparatus 1 of the embodiment will be assigned the same numbers and will not be described again.

[0024] [First Modified Fly Ash Circulation Apparatus] A first modified fly ash circulation apparatus 1A will be described with reference to Figure 2. The fly ash circulation apparatus 1A differs significantly from the fly ash circulation apparatus 1 of the embodiment in the chemical supply device 3A and a specific location (hereinafter referred to as "location B'") in the first flue gas path 2 to which the chemical supply device 3A supplies the chemical. The other configurations of the fly ash circulation apparatus 1A are the same as those of the fly ash circulation apparatus 1, and therefore will not be described again. The chemical-mixed fly ash supplied from the chemical-mixed fly ash supply device 5 to location A in the first flue gas path 2 may not be uniformly dispersed in the dust-containing flue gas flowing through the first flue gas path 2. Therefore, in the fly ash circulation system 1A, the chemical supply device 3A includes a blower such as a high-pressure blower or a compressed air supply device that supplies compressed air. The chemical supply device 3A sprays and disperses a chemical toward the chemical-mixed fly ash supplied from point A by the chemical-mixed fly ash supply device 5 using pressurized air (hereinafter referred to as "pressurized air") from point B' of the first exhaust gas path 2, which is upstream of point A in the first exhaust gas path 2 and approximately the same position as point A in the X-axis direction. The chemical supply device 3A may also include a chemical spray nozzle to easily target the chemical toward the chemical-mixed fly ash supplied from point A. With the above configuration, the fly ash circulation system 1A applies pressure to the chemical-mixed fly ash supplied to point A by the chemical supply device 3A to spray new chemicals, thereby crushing relatively large particles and lumps in the chemical-mixed fly ash. This effectively disperses not only the new chemicals but also unreacted chemicals in the chemical-mixed fly ash into the dust-containing flue gas flowing through the first exhaust gas path 2. Therefore, the fly ash circulation system 1A of the first modified example is superior to the fly ash circulation system 1 of the embodiment in that it can more effectively cause the unreacted chemical in the chemical-mixed fly ash to react with the dust-containing flue gas.

[0025] [Second Modification of Fly Ash Circulation Apparatus] A second modification of the fly ash circulation apparatus 1B will be described with reference to Figure 3. The fly ash circulation apparatus 1B differs significantly from the fly ash circulation apparatus 1 of the embodiment in that it includes a pressurized air supply device 8, which includes a high-pressure blower or other fan and a compressed air supply device for supplying compressed air, and injects and supplies pressurized air to a specific location (hereinafter referred to as "location C") in the first flue gas path 2. Other components of the fly ash circulation apparatus 1B are similar to those of the fly ash circulation apparatus 1, and therefore will not be described here. The pressurized air supply device 8 injects pressurized air from location C toward the chemical-mixed fly ash supplied to location A by the chemical-mixed fly ash supply device 5. The pressurized air supply device 8 may also include a nozzle for pressurized air to more easily target the chemical-mixed fly ash supplied from location A. It is desirable that location C be upstream of location A in the first flue gas path 2 and approximately at the same position as location A or adjacent to location A in the X-axis direction. With the above configuration, the fly ash circulation system 1B applies pressure to the chemical-mixed fly ash supplied to location A by injecting pressurized air, thereby crushing relatively large particles and lumps in the chemical-mixed fly ash, thereby effectively dispersing unreacted chemicals in the chemical-mixed fly ash into the dust-containing flue gas flowing through the first flue gas path 2. Therefore, the fly ash circulation system 1B of the second modification is superior to the fly ash circulation system 1 of the embodiment in that it can more effectively cause unreacted chemicals in the chemical-mixed fly ash to react with the dust-containing flue gas. By adding the pressurized air supply device 8 of the fly ash circulation system 1B of the second modification to the fly ash circulation system 1A of the first modification, unreacted chemicals in the chemical-mixed fly ash can be more effectively caused to react with the dust-containing flue gas.

[0026] [Third Modification of Fly Ash Circulation Apparatus] A third modification of the fly ash circulation apparatus 1C will be described with reference to Figure 4. The fly ash circulation apparatus 1C differs significantly from the fly ash circulation apparatus 1 of the embodiment in that a circulating flue gas supply path 9 is connected between point A of the first flue gas path 2 and the second flue gas path 6, and the first outlet of the chemical-mixed fly ash supply apparatus 5 connected to point A is directly connected to the circulating flue gas supply path 9. As a result, the chemical-mixed fly ash supply apparatus 5 indirectly supplies chemical-mixed fly ash to point A of the first flue gas path 2. The circulating flue gas supply path 9 is positioned so as to pass directly below or near the chemical-mixed fly ash supply apparatus 5 (in the -Y-axis direction). Therefore, the chemical-mixed fly ash supply apparatus 5 can easily supply chemical-mixed fly ash to the circulating flue gas supply path 9 by gravity or by a combination of gravity and the suction force of the negative pressure of the circulating flue gas supply path 9. As a result, the chemical-mixed fly ash supplying device 5 can supply the chemical-mixed fly ash to the point A of the first flue gas path 2 by entraining it in the flow of post-dust removal flue gas that branches off from the second flue gas path 6 and flows through the circulating flue gas supply path 9. Like the first flue gas path 2 and the second flue gas path 6, the chemical-mixed fly ash supplying device 5 is a conduit such as a duct or pipe.

[0027] Here, as an example, a configuration is shown in which a blower (second blower) 10 is installed in the circulating exhaust gas supply path 9 between the point where the first outlet of the chemical-mixed fly ash supply device 5 is connected and the second exhaust gas path 6. The blower 10 is a device that pressurizes and sends a portion of the post-dust removal flue gas that has been dust-removed by the dust collector 4 and flows through the second exhaust gas path 6 to point A of the first exhaust gas path 2. By providing the blower 10, the post-dust removal flue gas flowing through the circulating exhaust gas supply path 9 can be pressurized and flowed, thereby enabling the chemical-mixed fly ash to be uniformly and effectively dispersed in the post-dust removal flue gas. The blower 10 is appropriately selected from, for example, a fan, blower, or compressor depending on the design. Note that if the circulating exhaust gas supply path 9 is connected between the second exhaust gas path 6 downstream of the first blower 7 and point A of the first exhaust gas path 2, installation of the second blower 10 may not be necessary. The other configurations of the fly ash circulation device 1C are the same as those of the fly ash circulation device 1, and therefore, the description thereof will be omitted.

[0028] The configuration of the fly ash circulation system 1C differs from the fly ash circulation system 1A of the first modification and the fly ash circulation system 1B of the second modification in that pressurized air is not injected into the first flue gas path 2, but instead part of the dust-removed flue gas is used to effectively disperse unreacted chemicals in the chemical-mixed fly ash into the dust-containing flue gas flowing through the first flue gas path 2. Therefore, the fly ash circulation system 1C of the third modification is superior to the fly ash circulation system 1A of the first modification and the fly ash circulation system 1B of the second modification in that it does not increase the total amount of flue gas emitted from the combustion furnace plant.

[0029] In existing combustion furnace plants, such as waste incineration plants, the post-dust removal flue gas is sometimes returned to the incinerator and used for waste combustion to reduce oxides (such as NOx) in the dust-containing flue gas. The technology of returning the post-dust removal flue gas to the incinerator or other combustion furnace is called exhaust gas recirculation (EGR). Therefore, a portion of the post-dust removal flue gas flowing through the circulating flue gas supply path 9 may be branched and injected into the combustion furnace. Furthermore, instead of the pressurized air supply device 8 in the configuration of the fly ash circulation device 1B of the second modification, a circulating flue gas supply path 9 may be disposed between the point C of the first flue gas path 2 and the second flue gas path 6, as in the fly ash circulation device 1C of the third modification. The post-dust removal flue gas may be injected toward the chemical-mixed fly ash directly supplied from the chemical-mixed fly ash supply device 5 to the point A of the first flue gas path 2. In this case, as described in the second modification, relatively large particles and lumps in the chemical-mixed fly ash can be crushed, thereby effectively dispersing unreacted chemicals in the chemical-mixed fly ash into the dust-containing flue gas flowing through the first flue gas path 2. Furthermore, in the fly ash circulation device 1C, the circulating flue gas supply path 9 is directly connected between point A of the first flue gas path 2 and the second flue gas path 6, but in the configurations of the fly ash circulation device 1A of the first modification and the fly ash circulation device 1B of the second modification, the circulating flue gas supply path 9 may be disposed between the second flue gas path 6 and the middle of the path connecting the sealing device 5b and point A. Even in this configuration, unreacted chemicals in the chemical-mixed fly ash can be effectively dispersed by the pressure of the exhaust gas flow after dust removal.

[0030] [Fourth Modification of Fly Ash Circulation Apparatus] A fourth modification of the fly ash circulation apparatus 1D will be described with reference to FIG. 5 . The fly ash circulation apparatus 1D differs significantly from the first modification of the fly ash circulation apparatus 1A in that a classifier 5c is disposed above the sealing device 5b (in the +Y-axis direction) in the path connecting the first path 5aA and the first exhaust gas path 2. Note that FIG. 5 illustrates an example in which the chemical-mixed fly ash supplying apparatus 5 includes the classifier 5c. The other components of the fly ash circulation apparatus 1D are similar to those of the fly ash circulation apparatus 1A, and therefore will not be described here. The classifier 5c crushes the chemical-mixed fly ash containing relatively large particles or clumps to uniform the size of the particles and clumps overall, and scrapes and removes the layer of reaction product formed on the surface of the chemical in the chemical-mixed fly ash, exposing the unreacted chemical. The classifier 5c can be, for example, a vibrating sieve or a cylindrical trommel with a predetermined number of through-holes. The classifier 5c allows the chemical-mixed fly ash of an appropriate particle size to be supplied to the first flue gas passage 2, and also allows the unreacted chemicals in the chemical-mixed fly ash to be exposed and supplied to the first flue gas passage 2. Therefore, the fly ash circulation apparatus 1D of the fourth modified example is superior to the fly ash circulation apparatus 1A of the first modified example in that it can more effectively disperse and react the unreacted chemicals in the chemical-mixed fly ash with the dust-containing flue gas. The classifier 5c of the fly ash circulation apparatus 1D of the fourth modified example may be installed in the same position as the fly ash circulation apparatus 1D in the fly ash circulation apparatus 1 of the embodiment, the fly ash circulation apparatus 1B of the second modified example, and the fly ash circulation apparatus 1C of the third modified example. That is, the classifier 5c of the fly ash circulation apparatus 1D may be installed above the sealing apparatus 5b (in the +Y-axis direction) in the passage connecting the first passage 5aA of the fly ash circulation apparatus 1, the fly ash circulation apparatus 1B, and the fly ash circulation apparatus 1C to the location A of the first flue gas passage 2. With this configuration, the same effects as those of the fly ash circulation device 1D of the fourth modified example can be obtained in these embodiments and modified examples.

[0031] DESCRIPTION OF SYMBOLS 1, 1A, 1B, 1C, 1D Fly ash circulation device 2 First exhaust gas path 3, 3A Chemical supply device 4 Dust collector (4a Bag filter, 4b Hopper, 4c Feed-out device) 5 Chemical-mixed fly ash supply device (5a Distribution device (5aA First path, 5aB Second path), 5b Sealing device 5c Classifier) ​​6 Second exhaust gas path 7 Blower (First blower) 8 Pressurized air supply device 9 Circulating exhaust gas supply path 10 Blower (Second blower)

Claims

1. A system comprising: a chemical supplying device for supplying a chemical for purifying dust-containing exhaust gas generated in a combustion furnace plant to a first exhaust gas path through which the dust-containing exhaust gas flows; a dust collecting device connected to the upstream side of the first exhaust gas path and to the downstream side of a second exhaust gas path, the dust collecting device having a hopper below and discharging the dust-removed exhaust gas from the first exhaust gas path to the second exhaust gas path; and a chemical-mixed fly ash supplying device having an inlet connected to the bottom of the dust collecting device and supplying chemical-mixed fly ash, which is a mixture of the chemical and fly ash that has fallen into the hopper below the inside of the dust collecting device due to the dust removal, to the first exhaust gas path from an outlet that is directly connected to the first exhaust gas path or indirectly connected via a pipeline and is located below the inlet. The drug-mixed fly ash supplying device supplies the drug-mixed fly ash from the outlet to the first exhaust gas path that passes vertically below the outlet or at a position 1 to 5 m horizontally from directly below the outlet, downstream of the point where the drug supplying device supplies the drug, by gravity or by the suction force of the first exhaust gas path which is a combination of gravity and negative pressure, and the drug-mixed fly ash supplied to the first exhaust gas path is circulated to the hopper by a fly ash circulation device.

2. The fly ash circulation device as described in claim 1, wherein the drug-mixed fly ash supplying device is provided with a dust ash distribution device which selectively distributes the drug-mixed fly ash to either a first path for supplying the drug-mixed fly ash to the first exhaust gas path or a second path for discharging the drug-mixed fly ash for dust ash treatment, or which simultaneously distributes the drug-mixed fly ash to both the first path and the second path.

3. A fly ash circulation device as described in claim 2, further comprising a sealing device connected to the first passage and separating the first passage from the first exhaust gas passage without impeding the supply of the drug-mixed fly ash to the first exhaust gas passage.

4. The fly ash circulating apparatus according to claim 3, further comprising a classifier disposed between said first path and said sealing device for classifying said chemical-mixed fly ash.

5. A fly ash circulation device as described in any one of claims 1 to 4, wherein the chemical supply device disperses the chemical into pressurized air and supplies it to the chemical-mixed fly ash supplied to the first exhaust gas path.

6. A fly ash circulation system as described in any one of claims 1 to 4, further comprising a pressurized air supply device for supplying pressurized air toward the chemical-mixed fly ash supplied to the first exhaust gas path.

7. A fly ash circulation device as described in any one of claims 1 to 4, further comprising a circulating exhaust gas supply path for dispersing the drug-mixed fly ash supplied to the first exhaust gas path with the post-dust removal exhaust gas of the second exhaust gas path.

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