1. A flue gas treatment system comprising: a dust collector provided in a flue through which flue gas flows; a chemical agent supply part that supplies a flue gas-treating chemical agent to a chemical agent supply position that is located between a generation source of said flue gas and said dust collector in said flue; a collected dust transport part that transports collected dust collected by said dust collector along an auxiliary path different from said flue to a collected dust supply position that is located between said generation source and said dust collector in said flue; and a collected dust heating part that is provided in said auxiliary path and heats said collected dust.

2. The flue gas treatment system as claimed in claim 1, wherein said flue gas-treating chemical agent includes a calcium-based agent.

3. The flue gas treatment system as claimed in claim 1 or 2, wherein said collected dust transport part includes a conveyor that has a plurality of retainers provided along said auxiliary path, and said conveyor transports said plurality of retainers that retain said collected dust, along said auxiliary path.

4. The flue gas treatment system as claimed in claim 3, wherein said collected dust transport part further includes a chute part in which said collected dust stored in each retainer is dropped.

5. The flue gas treatment system as claimed in claim 4, wherein said collected dust transport part further includes a pulverizing part in said chute part, the pulverizing part pulverizing said collected dust as a result of colliding with said collected dust that has been dropped.

6. The flue gas treatment system as claimed in any one of claims 1 to 5, wherein said collected dust transport part includes a collected dust reservoir that is provided in said auxiliary path and stores said collected dust, and said collected dust heating part heats said collected dust stored in said collected dust reservoir.

7. The flue gas treatment system as claimed in claim 6, further comprising: a collected dust vibrator that vibrates a vicinity of a portion of said collected dust reservoir that is heated by said collected dust heating part.

8. An incineration plant comprising: a combustion chamber that burns waste; a flue that exhausts flue gas generated in said combustion chamber from said combustion chamber; and the flue gas treatment system as claimed in one of claims 1 to 7, provided in said flue.

TECHNICAL FIELD
The present invention relates to a flue gas treatment system and an incineration plant.
BACKGROUND ART
Non-industrial waste such as municipal solid waste has conventionally been disposed of by incineration in a garbage incineration plant. Flue gas generated by the incineration contains hazardous substances such as particles of soot, hydrogen chloride (HO), sulfur oxides (SOx), nitrogen oxides (NOx), and heavy metals (e.g., Pb, Hg). In view of this, treatment for removing such hazardous substances from flue gas is performed by a flue gas treatment system so as to exhaust treated flue gas to the atmosphere.
For example, Japanese Patent Application Laid-Open No. 59-150525 (Document 1) discloses a technique in which, in the process of removing hazardous acid gas components such as hydrogen chloride from flue gas by blowing hydrated lime powder into the flue gas, part of dust collected by a dust collector is pulverized and blown into a flue with an air blower so as to be recycled for the removal of acid gas. Also, Japanese Patent Application Laid-Open No. 2014-24052 (Document 2) discloses a technique for sending part of collected dust collected by a dust collector back into a flue on the inlet side of the dust collector while using part of treated flue gas as carrier gas.
With the techniques disclosed in Documents 1 and 2, the collected dust is cooled with the carrier gas in a duct through which the collected dust is sent back into the flue, and the collected dust (in particular, calcium chloride or the like) absorbs moisture in the carrier gas and liquefies (i.e., deliquesces). This causes the collected dust to adhere to the inner face of the duct. The diameter of the duct is normally not so large that the adhesion of the collected dust prevents the

collected dust from being properly sent back into the flue.
SUMMARY OF INVENTION [0005] The present invention is intended for a flue gas treatment system, and it is an object of the present invention to suppress adhesion of collected dust to a path through which the collected dust is sent back into a flue. [0006] The flue gas treatment system according to the present invention includes a dust collector provided in a flue through which flue gas flows, a chemical agent supply part that supplies a flue gas-treating chemical agent to a chemical agent supply position that is located between a generation source of the flue gas and the dust collector in the flue, a collected dust transport part that transports collected dust collected by the dust collector along an auxiliary path different from the flue to a collected dust supply position that is located between the generation source and the dust collector in the flue, and a collected dust heating part that is provided in the auxiliary path and heats the collected dust.
[0007] According to the present invention, it is possible to suppress the adhesion of the collected dust to the auxiliary path through which the collected dust is sent back into the flue.
[0008] In a preferable embodiment of the present invention, the flue gas-treating chemical agent includes a calcium-based agent.
[0009] In another preferable embodiment of the present invention, the collected dust transport part includes a conveyor that has a plurality of retainers provided along the auxiliary path, and the conveyor transports the plurality of retainers that retain the collected dust, along the auxiliary path.
[0010] In this case, preferably, the collected dust transport part further includes a chute part in which the collected dust stored in each retainer is dropped. [0011] More preferably, the collected dust transport part further includes a

pulverizing part in the chute part, the pulverizing part pulverizing the collected
dust as a result of colliding with the collected dust that has been dropped.
[0012] In yet another preferable embodiment of the present invention, the
collected dust transport part includes a collected dust reservoir that is provided in
the auxiliary path and stores the collected dust, and the collected dust heating part
heats the collected dust stored in the collected dust reservoir.
[0013] In this case, preferably, the flue gas treatment system further includes a
collected dust vibrator that vibrates a vicinity of a portion of the collected dust
reservoir that is heated by the collected dust heating part.
[0014] The present invention is also intended for an incineration plant. The
incineration plant according to the present invention includes a combustion
chamber that burns waste, a flue that exhausts flue gas generated in the
combustion chamber from the combustion chamber, and the above-described flue
gas treatment system provided in the flue.
[0015] These and other objects, features, aspects and advantages of the present
invention will become more apparent from the following detailed description of
the present invention when taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF DRAWINGS [0016] Fig. 1 illustrates a configuration of an incineration plant;
Fig. 2 illustrates a configuration of a flue gas treatment system; Fig. 3 illustrates a lower portion of a collected dust reservoir; Fig. 4 is a sectional view illustrating a supply conveyor; Fig. 5 illustrates deliquescence conditions for calcium chloride; and Fig. 6 illustrates another example of the flue gas treatment system.

DESCRIPTION OF EMBODIMENTS [0017] Fig. 1 illustrates a configuration of an incineration plant 1 according to an embodiment of the present invention. The incineration plant 1 is a plant that disposes of waste such as municipal solid waste by incineration. The incineration plant 1 includes a combustion chamber 2, a flue 3, a flue gas treatment system 4, an induced draft fan 51, and a stack 52. In the combustion chamber 2, garbage and combustible gas generated from the garbage are burned. The flue 3 connects the combustion chamber 2 and the stack 52. The flue gas treatment system 4 and the induced draft fan 51 are provided in the flue 3. The induced draft fan 51 exhausts flue gas (combustion gas) generated in the combustion chamber 2 to the flue 3 and guides the flue gas via the flue gas treatment system 4 to the stack 52. That is, the flue gas generated in the combustion chamber 2, which serves as a generation source, flows through the flue 3 from the combustion chamber 2 toward the stack 52, and the flue gas treatment system 4 gives predetermined treatment to the flue gas. The stack 52 exhausts the flue gas to the atmosphere. In Fig. 1, the flue 3 is indicated by a thick solid line.
[0018] Fig. 2 illustrates a configuration of the flue gas treatment system 4. The flue gas treatment system 4 includes a gas cooler 41, a chemical agent supply part 42, a dust collector 43, and a collected dust transport part 44. In the flue 3, the gas cooler 41, the chemical agent supply part 42, and the dust collector 43 are provided in order from the combustion chamber 2 toward the stack 52, i.e., from the upstream side to the downstream side in the flow direction of the flue gas. In practice, a denitration system or other systems may also be provided between the dust collector 43 and the stack 52.
[0019] The gas cooler 41 sprays water into the flue gas entering from the combustion chamber 2 to drop the temperature of the flue gas. The temperature

of the flue gas exhausted from the gas cooler 41 is, for example, approximately 170°C. The chemical agent supply part 42 includes a hydrated lime reservoir 421, a special assistant reservoir 422, a chemical agent pumping part 423, a chemical agent supply line 424, and quantitative supply parts 425 and 426. One end of the chemical agent supply line 424 is connected to the chemical agent pumping part 423, and the other end thereof is connected to a position P1 that is located between the gas cooler 41 and the dust collector 43 in the flue 3 (hereinafter, referred to as a “chemical agent supply position P1”). The chemical agent pumping part 423 is a fan and blows air into the flue 3 in the chemical agent supply line 424. The hydrated lime reservoir 421 stores powdery hydrated lime (calcium hydroxide (Ca(OH)2)) as a calcium (Ca)-based agent. The hydrated lime is a chemical agent for dechlorination and desulfurization. The quantitative supply part 425 is mounted on the lower portion of the hydrated lime reservoir 421. The quantitative supply part 425 is, for example, a table feeder and takes out (cuts out) a set amount of hydrated lime from the hydrated lime reservoir 421 per unit time. The quantitative supply part 425 is connected to the chemical agent supply line 424, and the hydrated lime taken out from the hydrated lime reservoir 421 is supplied into the chemical agent supply line 424. [0020] The special assistant reservoir 422 stores a powdery chemical agent (e.g., Bag-Ace (registered trademark) produced by Hitachi Zosen Corporation or activated carbon, and hereinafter referred to as a “special assistant”). The quantitative supply part 426 is mounted on the lower portion of the special assistant reservoir 422 and takes out a set amount of special assistant from the special assistant reservoir 422 per unit time. The quantitative supply part 426 is connected to the chemical agent supply line 424, and the special assistant taken out from the special assistant reservoir 422 is supplied into the chemical agent supply line 424. The chemical agent supply part 42 with such a configuration

allows the hydrated lime and the special assistant (which are hereinafter collectively referred to as a “flue gas-treating chemical agent”) to be supplied (blown) into the flue 3 at the chemical agent supply position P1. The flue gas-treating chemical agent may contain other calcium-based agents (calcium-containing agents) such as dolomite hydroxide [Ca(OH)2•Mg(OH)2], instead of or in addition to the hydrated lime.
[0021] The dust collector 43 is of, for example, a filter type and removes fly ash contained in the flue gas with a filter cloth. The dust collector 43 is also called a bag filter. The flue gas-treating chemical agent supplied by the chemical agent supply part 42 is deposited on the filter cloth. Inside the dust collector 43, when the flue gas passes through the filter cloth, hazardous substances contained in the flue gas react with the flue gas-treating chemical agent, and accordingly the hazardous substances are removed. The reaction of the flue gas and the flue gas-treating chemical agent also occurs in the flue 3. Examples of the hazardous substances removed by the flue gas-treating chemical agent include hydrogen chloride, sulfur oxides, dioxins, and mercury compounds. The dust collector 43 shakes off the fly ash and the flue gas-treating chemical agent (including reactants with hazardous substances), which are deposited on the filter cloth, every predetermined period of time by back washing using compressed air. In the following description, the fly ash and the flue gas-treating chemical agent that are shaken off from the filter cloth are collectively referred to as “collected dust.” The collected dust is a collection collected by the dust collector 43. The chemical agent supply part 42 may supply other types of chemical agents such as baking soda (NaHCO3) or activated carbon, and in this case, the collected dust also includes those other types of chemical agents.
[0022] The collected dust transport part 44 includes an auxiliary path 441, a collected dust distribution part 45, a collected dust reservoir 442, a quantitative

supply part 443, a supply conveyor 46, and a chute part 444. The auxiliary path 441 connects the lower portion of the dust collector 43 and a position that is located between the gas cooler 41 and the dust collector 43 in the flue 3 (hereinafter, referred to as a “collected dust supply position P2”). In Fig. 1, the auxiliary path 441 is indicated by a thin solid line. The auxiliary path 441 is different from the flue 3. In the auxiliary path 441, the collected dust distribution part 45, the collected dust reservoir 442, the quantitative supply part 443, the supply conveyor 46, and the chute part 444 are provided in order from the dust collector 43 toward the collected dust supply position P2. [0023] The collected dust distribution part 45 distributes and supplies the collected dust that has been shaken off from the filter cloth in the dust collector 43 into the collected dust reservoir 442 and the collected dust treatment part 49. To be more specific, the collected dust distribution part 45 includes a conveyor 451 and a gate 452. The conveyor 451 is, for example, a flight conveyor and has the same structure as the supply conveyor 46, which will be described later. The gate 452 is provided in a transport path through which the conveyor 451 transports the collected dust. In the case where the amount of collected dust storage acquired by a level meter (not shown) of the collected dust reservoir 442 is less than a predetermined amount, the gate 452 is opened and the collected dust is supplied to the collected dust reservoir 442. In the case where the amount of collected dust storage in the collected dust reservoir 442 is greater than or equal to the predetermined amount, the gate 452 is closed and the collected dust is supplied to the collected dust treatment part 49. In this way, the collected dust distribution part 45 distributes the collected dust received from the dust collector 43 into the collected dust reservoir 442 and the collected dust treatment part 49 by opening or closing the gate 452 so as to make the amount of collected dust storage in the collected dust reservoir 442 approximately constant. The collected dust

supplied to the collected dust treatment part 49 is treated with, for example, a chelating agent (heavy metal stabilizer). Alternatively, another conveyor or other equipment may be provided between the gate 452 and the collected dust reservoir 442.
[0024] Fig. 3 illustrates the lower portion of the collected dust reservoir 442. The flue gas treatment system 4 further includes a collected dust heating part 47 and a collected dust vibrator 48. The collected dust heating part 47 includes a plurality of heaters 471. The plurality of heaters 471 is mounted on the outer face of the lower portion of the collected dust reservoir 442. Each heater 471 uses electricity to heat the outer face of the collected dust reservoir 442. In the present example of treatment, the collected dust heating part 47 heats the collected dust stored in the collected dust reservoir 442 to, for example, 60°C or higher. The temperature to which the collected dust would have to be heated is preferably higher than or equal to 70°C and more preferably higher than or equal to 120°C. Typically, the temperature to which the collected dust would have to be heated is less than or equal to the temperature (e.g., 170°C) of the flue gas in the dust collector 43. Alternatively, the collected dust heating part 47 may use, for example, steam flowing from a boiler provided above the combustion chamber 2 to heat the collected dust.
[0025] Similarly to the collected dust heating part 47, the collected dust vibrator 48 is mounted on the lower portion of the collected dust reservoir 442. The collected dust vibrator 48 intermittently or continuously vibrates the vicinity of the portion of the collected dust reservoir 442 that is heated by the collected dust heating part 47. This enables changing the collected dust positioned in the vicinity of the inner face of the lower portion of the collected dust reservoir 442 and helps improving the efficiency of heating of the collected dust in the collected dust reservoir 442.

[0026] As illustrated in Fig. 2, the quantitative supply part 443 is mounted on the lower portion of the collected dust reservoir 442. The quantitative supply part 443 is, for example, a table feeder and takes out a set amount of collected dust from the collected dust reservoir 442 per unit time. The quantitative supply part 443 is connected to the supply conveyor 46, and the collected dust taken out from the collected dust reservoir 442 is supplied into the supply conveyor 46. [0027] Fig. 4 is a sectional view of the supply conveyor 46. The supply conveyor 46 is, for example, a flight conveyor (also referred to as a “scraper conveyor”) and transports the collected dust along a conveyor transport path from below the collected dust reservoir 442 to above the collected dust supply position P2 in the flue 3. The conveyor transport path is part of the auxiliary path 441 described previously. The supply conveyor 46 includes a housing 461, a pair of endless chains 462, a plurality of flights (scrapers) 463, and a plurality of sprockets 464 (see Fig. 2). The housing 461 is provided along the conveyor transport path. The pair of endless chains 462 is arranged at a predetermined distance from each other in a direction perpendicular to the plane of Fig. 4 (hereinafter, referred to as a “width direction”). Each endless chain 462 engages with a sprocket 464 arranged below the collected dust reservoir 442 and a sprocket 464 arranged above and in the vicinity of the collected dust supply position P2 in the housing 461. Due to rotation of the sprockets 464 caused by a driver (not shown), the pair of endless chains 462 rotates (cyclically moves) continuously in the housing 461. In practice, sprockets are also provided at such positions that the conveyor transport path changes its direction. [0028] The plurality of flights 463 is fixed to the pair of endless chains 462 at a predetermined interval. Each flight 463 is a substantially rectangular plate member, and its one side along the width direction is fixed at its opposite ends to the pair of endless chains 462. On an outward travel from below the collected

dust reservoir 442 to above the collected dust supply position P2, an edge of each flight 463 (one side on the side opposite the one side fixed to the endless chains 462) slides over the bottom surface portion of the housing 461. The remaining two sides of the flight 463 are in close proximity to the opposite side surface portions of the housing 461 (side surface portions perpendicular to the width direction). Accordingly, a space in the supply conveyor 46 between each pair of flights 463 that are adjacent to each other in the conveyor transport path forms a retainer 465 that can store the collected dust. In this way, the supply conveyor 46 includes a plurality of retainers 465 provided along the auxiliary path 441. [0029] The upper surface portion of the housing 461 has an inlet opening at a position facing the quantitative supply part 443, and the collected dust dropped from the quantitative supply part 443 is supplied through the inlet opening into the supply conveyor 46. The collected dust is stored in clusters 9 in the retainers 465 and transported to above the collected dust supply position P2 in the flue 3. The bottom surface portion of the housing 461 has an outlet opening at a position facing the collected dust supply position P2, and the collected dust is discharged through the outlet opening to the outside of the supply conveyor 46. The chute part 444 is provided above the collected dust supply position P2 in the flue 3 and connected to the outlet opening. Thus, the collected dust stored in each retainer 465 is dropped into the chute part 444 that extends vertically downward from the outlet opening.
[0030] As illustrated in Fig. 2, the chute part 444 preferably includes a gate 446 and a pulverizing part 445. The pulverizing part 445 is, for example, a metal mesh or a grid-like metal member and pulverizes the collected dust as a result of colliding with the collected dust that has been dropped from the supply conveyor 46. The chute part 444 is open to the collected dust supply position P2 in the flue 3, and the pulverized collected dust is dispersed at the collected dust supply

position P2 into the flue gas flowing through the flue 3. The gate 446 is, as a general rule, open while the collected dust is being transported along the auxiliary path 441. The pressure in the housing 461 is higher than the pressure in the flue 3, which prevents the flue gas from flowing into the housing 461. Note that the gate 446 may be closed in such cases as where the transport of the collected dust is stopped.
[0031] In the collected dust transport part 44, the quantitative supply part 443 connected to the lower portion of the collected dust reservoir 442 has an enclosed structure. A connection part that connects the quantitative supply part 443 and the inlet opening of the housing 461 also has an enclosed structure. The housing 461 is enclosed except at the inlet opening and the outlet opening, and the chute part 444 that connects the outlet opening of the housing 461 and the flue 3 also has an enclosed structure. In this way, a portion of the auxiliary path 441 that is located between the collected dust reservoir 442 and the flue 3 is an enclosed space into which outside air hardly flows.
[0032] Also, a connection part that connects the collected dust reservoir 442 and the collected dust distribution part 45 has an enclosed structure, and the same applies to the collected dust distribution part 45 connected to the lower portion of the dust collector 43. Thus, a portion of the auxiliary path 441 that is located between the dust collector 43 and the collected dust reservoir 442 is also an enclosed space into which outside air hardly flows. Note that depending on the structure of the collected dust transport part 44, the pressure in the collected dust reservoir 442 to which the collected dust is sequentially supplied may become a positive pressure higher than the atmospheric pressure. In this case, a mechanism for exhausting gas in the collected dust reservoir 442 to the outside via a predetermined filter may be provided. In this case as well, outside air hardly flows into the collected dust reservoir 442 because the collected dust

reservoir 442 has a positive pressure.
[0033] Here, the collected dust contains calcium chloride that is a reaction product of the hydrogen chloride in the flue gas and the hydrated lime contained in the flue gas-treating chemical agent. The collected dust contains calcium chloride also in the case where the flue gas-treating chemical agent contains other calcium-based agents such as dolomite hydroxide. Fig. 5 illustrates deliquescence conditions for the calcium chloride in the flue gas. In Fig. 5, the area above a line L1 is a dry area where deliquescence does not occur, the area between two lines L1 and L2 is a partial deliquescent area where deliquescence partially occurs, and the area below the line L2 is a deliquescent area where deliquescence occurs almost wholly. It can be seen from Fig. 5 that the calcium chloride is more likely to deliquesce as the temperature decreases. [0034] Next description is given regarding a flue gas treatment system according to a comparative example, which uses outside air or treated flue gas to send the collected dust back into the flue 3. In the flue gas treatment system according to the comparative example, the collected dust is cooled with the outside air or carrier gas that is treated flue gas, and calcium chloride contained in the collected dust deliquesces. This causes the collected dust to adhere to the inner face of a duct through which the collected dust is sent back into the flue 3. As a result, in the case where the duct has a small diameter, the collected dust cannot be sent back properly into the flue 3.
[0035] In contrast, the flue gas treatment system 4 in Fig. 2 includes the collected dust transport part 44 and the collected dust heating part 47 in the auxiliary path 441 through which the collected dust is sent back into the flue 3. The collected dust transport part 44 transports the collected dust collected by the dust collector 43 along the auxiliary path 441 to the collected dust supply position P2 in the flue 3 without using, for example, either outside air or treated flue gas.

Also, the collected dust heating part 47 heats the collected dust in the auxiliary path 441. This suppresses the deliquescence of the calcium chloride contained in the collected dust and suppresses the adhesion of the collected dust to the auxiliary path 441. In addition, it is possible to omit a blower for carrier gas or other equipment required in the flue gas treatment system according to the comparative example. Since the blower is expensive, the omission of the blower helps reducing the manufacturing cost of the flue gas treatment system 4. The incineration plant 1 including the flue gas treatment system 4 can stabilize operations while reducing running costs by recycling the flue gas-treating chemical agent contained in the collected dust.
[0036] Also, the collected dust is supplied to the collected dust supply position P2 by the supply conveyor 46 of the collected dust transport part 44 transporting the plurality of retainers 465, which stores the collected dust, along the auxiliary path 441. As compared with other conveyors such as a screw conveyor that transports the collected dust while stirring the collected dust, the supply conveyor 46 that stores the collected dust in the retainers 465 can suppress a reduction in the temperature of the collected dust during transport. As a result, the adhesion of the collected dust to the auxiliary path 441 can be further suppressed. Since the auxiliary path 441 has a structure into which outside air hardly flows, the collected dust transport part 44 can further suppress a reduction in the temperature of the collected dust during transport, can prevent an increase in moisture concentration in surrounding gas, and can further suppress the adhesion of the collected dust to the auxiliary path 441. As the supply conveyor 46, the collected dust transport part 44 may use other types of conveyors that do not stir the collected dust. Depending on conditions such as the temperature to which the collected dust heating part 47 would heat the collected dust, a screw conveyor or other conveyors that stir the collected dust may be used as the supply conveyor

46.
[0037] The collected dust can easily be dispersed in the flue 3 by providing the pulverizing part 445, which pulverizes the collected dust as a result of colliding with the collected dust, in the chute part 444 in which the collected dust is dropped from the supply conveyor 46. This improves the capability of flue gas treatment.
[0038] The collected dust can efficiently be heated by the collected dust heating part 47 heating the collected dust reservoir 442 in which the collected dust is stored. Also, by the collected dust vibrator 48 vibrating the vicinity of the portion of the collected dust reservoir 442 that is heated by the collected dust heating part 47, it is possible to suppress the adhesion of the collected dust to the inside of the collected dust reservoir 442 and efficiently heat the collected dust in a wide range of the collected dust reservoir 442. Depending on the design of the flue gas treatment system 4, the collected dust heating part 47 may be provided at a position other than on the collected dust reservoir 442 in the auxiliary path 441. [0039] Fig. 6 illustrates another example of the flue gas treatment system. A flue gas treatment system 4a in Fig. 6 is configured by adding another supply conveyor 46a to the flue gas treatment system 4 in Fig. 2 and is capable of supplying collected dust to a position P2a that is located between the combustion chamber 2 and the gas cooler 41 in the flue 3 (hereinafter, referred to as a “second collected dust supply position P2a”). The supply conveyor 46a has a similar structure to that of the supply conveyor 46. The other configuration is the same as that in Fig. 2, and the same constituent elements are given the same reference signs.
[0040] In the flue gas treatment system 4a, the bottom surface portion of the housing 461 has a second outlet opening on the way of the transport path of the supply conveyor 46 that extends in the horizontal direction. The second outlet

opening has a connection part that includes a gate 469. When the gate 469 is open, the collected dust in the retainers 465 (see Fig. 4) is discharged through the connection part to the outside of the supply conveyor 46. The upper surface portion of a housing 461 of the supply conveyor 46a has an inlet opening at a position facing the aforementioned connection part, and the collected dust discharged from the supply conveyor 46 is supplied through the inlet opening into the supply conveyor 46a.
[0041] The collected dust is transported to above the second collected dust supply position P2a in the flue 3 while being stored in retainers 465 (see Fig. 4) of the supply conveyor 46a. The bottom surface portion of the housing 461 has an outlet opening at a position facing the second collected dust supply position P2a, and the collected dust is discharged through the outlet opening to the outside of the supply conveyor 46a. The outlet opening is connected to a chute part 444 that extends vertically downward, and the collected dust is supplied via the chute part 444 to the second collected dust supply position P2a in the flue 3. [0042] As described above, the flue gas treatment system 4a is capable of supplying the collected dust to the second collected dust supply position P2a, in addition to supplying it to the collected dust supply position P2. Here, a reactant of the hydrated lime and the hydrogen chloride formed on the surface of the hydrated lime has high water solubility, and in the case where the hydrated lime is supplied into the gas cooler 41, this reactant is dissolved in the water sprayed into the gas cooler 41 and carried away, i.e., the reactant is removed from the surface of the hydrated lime. As a result, unreacted hydrated lime appears on the surface, and this suppresses a reduction in the reaction rate of the hydrated lime caused by the reactant. Accordingly, the flue gas treatment system 4a that supplies the collected dust to the position located between the combustion chamber 2 and the gas cooler 41 in the flue 3 (second collected dust supply position P2a) can

improve the efficiency of the dechlorination reaction. In the same manner, in the
case where the flue gas-treating chemical agent includes other calcium-based
agents such as dolomite hydroxide, reactants of the other calcium-based agents
and the hydrogen chloride formed on the surface of the other calcium-based
agents are removed with the water sprayed into the gas cooler 41, and this
suppresses a reduction in the reaction rates of the other calcium-based agents.
Note that the same also applies to the case where the collected dust supply
position P2 is set to a position located between the combustion chamber 2 and the
gas cooler 41 in the flue 3 in the flue gas treatment system 4 illustrated in Fig. 2.
[0043] The incineration plant 1 and the flue gas treatment systems 4 and 4a
described above can be modified in various ways.
[0044] In the flue gas treatment systems 4 and 4a, both of the supply of the flue
gas-treating chemical agent to the chemical agent supply position P1 and the
supply of the collected dust to the collected dust supply position P2 or P2a do not
necessarily have to be performed constantly, and either of them may be stopped
temporarily.
[0045] The chemical agent supply position P1 may be set to, for example, a
position located between the combustion chamber 2 and the gas cooler 41. That
is, the chemical agent supply position P1 may be set to any position between the
combustion chamber 2 and the dust collector 43 in the flue 3.
[0046] The flue gas treatment systems 4 and 4a may be used in plants other than
the incineration plant 1.
[0047] The configurations of the above-described preferred embodiments and
variations may be appropriately combined as long as there are no mutual
inconsistencies.
[0048] While the invention has been shown and described in detail, the
foregoing description is in all aspects illustrative and not restrictive. It is

therefore to be understood that numerous modifications and variations can b devised without departing from the scope of the invention.
REFERENCE SIGNS LIST
[0049] 1 Incineration plant
2 Combustion chamber
3 Flue
4, 4a Flue gas treatment system
42 Chemical agent supply part
43 Dust collector
44 Collected dust transport part 46, 46a Supply conveyor

47 Collected dust heating part
48 Collected dust vibrator

441 Auxiliary path
442 Collected dust reservoir

444 Chute part
445 Pulverizing part 465 Retainer
P1 Chemical agent supply position P2, P2a Collected dust supply position

I/We Claim:
1. A flue gas treatment system comprising:
a dust collector provided in a flue through which flue gas flows;
a chemical agent supply part that supplies a flue gas-treating chemical agent to a chemical agent supply position that is located between a generation source of said flue gas and said dust collector in said flue;
a collected dust transport part that transports collected dust collected by said dust collector along an auxiliary path different from said flue to a collected dust supply position that is located between said generation source and said dust collector in said flue; and
a collected dust heating part that is provided in said auxiliary path and heats said collected dust.
2. The flue gas treatment system as claimed in claim 1, wherein
said flue gas-treating chemical agent includes a calcium-based agent.
3. The flue gas treatment system as claimed in claim 1 or 2, wherein
said collected dust transport part includes a conveyor that has a plurality of retainers provided along said auxiliary path, and
said conveyor transports said plurality of retainers that retain said collected dust, along said auxiliary path.
4. The flue gas treatment system as claimed in claim 3, wherein
said collected dust transport part further includes a chute part in which said collected dust stored in each retainer is dropped.
5. The flue gas treatment system as claimed in claim 4, wherein

said collected dust transport part further includes a pulverizing part in said chute part, the pulverizing part pulverizing said collected dust as a result of colliding with said collected dust that has been dropped.
6. The flue gas treatment system as claimed in any one of claims 1 to 5,
wherein
said collected dust transport part includes a collected dust reservoir that is provided in said auxiliary path and stores said collected dust, and
said collected dust heating part heats said collected dust stored in said collected dust reservoir.
7. The flue gas treatment system as claimed in claim 6, further comprising:
a collected dust vibrator that vibrates a vicinity of a portion of said
collected dust reservoir that is heated by said collected dust heating part.
8. An incineration plant comprising:
a combustion chamber that burns waste;
a flue that exhausts flue gas generated in said combustion chamber from said combustion chamber; and
the flue gas treatment system as claimed in one of claims 1 to 7, provided in said flue.