TECHNICAL FIELD
The present invention relates to a technique for treating flue gas 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. H10-24213 (Document 1) discloses a technique for improving a dechlorination rate by charging powdery hydrated lime into a gas cooler and causing the hydrated lime to absorb moisture and react with acid gas in flue gas.
Incidentally, an excessive rise in HC1 concentration of flue gas may temporarily occur in the case where high chlorine waste is disposed of by incineration. In that case, the system disclosed in Document 1 may not be able to suppress the rise in HC1 concentration within a short time. There is thus demand for techniques that enable providing an efficient dechlorination treatment and taking a proper action under abnormal conditions in which the HC1 concentration is higher than or equal to a predetermined value.
SUMMARY OF INVENTION
The present invention is intended for a flue gas treatment system, and it is an object of the present invention to provide an efficient dechlorination

treatment and to take a proper action under abnormal conditions in which the HCl concentration is higher than or equal to a predetermined value. [0005] The flue gas treatment system according to the present invention includes a dust collector provided in a flue through which flue gas flows, a gas cooler that is provided between a generation source of the flue gas and the dust collector in the flue and sprays water into the flue gas, a first chemical agent supply part that supplies a flue gas-treating chemical agent including a calcium-based agent to a chemical agent supply position that is located between the generation source and the gas cooler in the flue or located within the gas cooler, a second chemical agent supply part that is capable of supplying a flue gas-treating chemical agent including a calcium-based agent to an auxiliary supply position that is located between the generation source and the dust collector in the flue, an HCl concentration measurement part that measures an HCl concentration in the flue gas, and a controller that, in a case where the HCl concentration is higher than or equal to a predetermined value, causes the second chemical agent supply part to increase a supply amount of the flue gas-treating chemical agent that is supplied to the auxiliary supply position in comparison with the supply amount in a case where the HCl concentration is lower than the predetermined value, or that, in a case where the HCl concentration is higher than or equal to a predetermined value, causes the first chemical agent supply part to increase a supply amount of the flue gas-treating chemical agent that is supplied to the chemical agent supply position in comparison with the supply amount in a case where the HCl concentration is lower than the predetermined value, while causing the second chemical agent supply part to supply the flue gas-treating chemical agent to the auxiliary supply position.
[0006] According to the present invention, it is possible to provide an efficient dechlorination treatment and to take a proper action using the first chemical agent

supply part or the second chemical agent supply part under abnormal conditions in which the HCl concentration is higher than or equal to a predetermined value. [0007] In a preferable embodiment of the present invention, the first chemical agent supply part and the second chemical agent supply part share a reservoir that stores the calcium-based agent.
[0008] In another preferable embodiment of the present invention, the second chemical agent supply part supplies collected dust collected by the dust collector as the flue gas-treating chemical agent.
[0009] 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.
[0010] The present invention is also intended for a flue gas treatment method used in a flue gas treatment system. The flue gas treatment system used in the flue gas treatment method according to the present invention includes a dust collector provided in a flue through which flue gas flows, a gas cooler that is provided between a generation source of the flue gas and the dust collector in the flue and sprays water into the flue gas, a first chemical agent supply part that supplies a flue gas-treating chemical agent including a calcium-based agent to a chemical agent supply position that is located between the generation source and the gas cooler in the flue or located within the gas cooler, and a second chemical agent supply part that is capable of supplying a flue gas-treating chemical agent including a calcium-based agent to an auxiliary supply position that is located between the generation source and the dust collector in the flue. The flue gas treatment method includes a) causing the first chemical agent supply part to supply the flue gas-treating chemical agent to a position that is located between

the generation source and the gas cooler in the flue or located within the gas cooler, b) measuring an HCl concentration in the flue gas, and c) in a case where the HCl concentration is higher than or equal to a predetermined value, causing the second chemical agent supply part to increase a supply amount of the flue gas-treating chemical agent that is supplied to the auxiliary supply position in comparison with the supply amount in a case where the HCl concentration is lower than the predetermined value, or in a case where the HCl concentration is higher than or equal to a predetermined value, causing the first chemical agent supply part to increase a supply amount of the flue gas-treating chemical agent that is supplied to the chemical agent supply position in comparison with the supply amount in a case where the HCl concentration is lower than the predetermined value, while causing the second chemical agent supply part to supply the flue gas-treating chemical agent to the auxiliary supply position. [0011] 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 [0012] Fig. 1 illustrates a configuration of an incineration plant according to a first embodiment;
Fig. 2 illustrates a configuration of a flue gas treatment system;
Fig. 3 illustrates a flow of flue gas treatment;
Fig. 4 illustrates a relationship between a dechlorination rate and an equivalence ratio in a flue gas treatment system according to a comparative example;
Fig. 5 illustrates a flue gas treatment system according to a second embodiment;

Fig. 6 illustrates a flue gas treatment system according to a third embodiment;
Fig. 7 illustrates a flue gas treatment system according to a fourth embodiment; and
Fig. 8 illustrates a flue gas treatment system according to a fifth embodiment.
DESCRIPTION OF EMBODIMENTS [0013] First Embodiment
Fig. 1 illustrates a configuration of an incineration plant 1 according to a first 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 a 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.
[0014] 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 unit

42, a dust collector 43, an HCl concentration measurement part 401, and a controller 40. In the flue 3, the gas cooler 41 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. Other systems such as a denitration system may also be provided between the dust collector 43 and the stack 52.
[0015] 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 unit 42 includes a hydrated lime reservoir 421, a special assistant reservoir 422, a first chemical agent pumping part 423a, a second chemical agent pumping part 423b, a first chemical agent supply line 424a, a second chemical agent supply line 424b, and quantitative supply parts 425 and 426.
[0016] One end of the first chemical agent supply line 424a is connected to the first chemical agent pumping part 423a, and the other end thereof is connected to a position P1 located between the combustion chamber 2 and the gas cooler 41 in the flue 3 (hereinafter, referred to as a “chemical agent supply position P1”). The first chemical agent pumping part 423a is a fan and blows air into the flue 3 in the first chemical agent supply line 424a. One end of the second chemical agent supply line 424b is connected to the second chemical agent pumping part 423b, and the other end thereof is connected to a position P2 located between the gas cooler 41 and the dust collector 43 in the flue 3 (hereinafter, referred to as an “auxiliary supply position P2”). The second chemical agent pumping part 423b is a fan and blows air into the flue 3 in the second chemical agent supply line 424b. [0017] 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 having two exhaust ports, and these two exhaust ports are connected respectively to the first chemical agent supply line 424a and the second chemical agent supply line 424b. At each exhaust port of the quantitative supply part 425, a set amount of hydrated lime is taken out (cut out) from the hydrated lime reservoir 421 per unit time. Thereby, the hydrated lime is supplied into the first chemical agent supply line 424a and the second chemical agent supply line 424b.
[0018] 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. Similarly to the quantitative supply part 425, the quantitative supply part 426 has two exhaust ports, and these two exhaust ports are connected respectively to the first chemical agent supply line 424a and the second chemical agent supply line 424b. At each exhaust port of the quantitative supply part 426, a set amount of special assistant is taken out from the special assistant reservoir 422 per unit time and supplied into the first chemical agent supply line 424a and the second chemical agent supply line 424b. The chemical agent supply unit 42 with the above-described configuration is capable of supplying (blowing) a flue gas-treating chemical agent that includes the hydrated lime and the special assistant into the flue 3 at the chemical agent supply position P1 and the auxiliary supply position P2. 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 (the same applies to the other embodiments).
[0019] If a configuration for supplying the flue gas-treating chemical agent to the chemical agent supply position P1 is referred to as a “first chemical agent supply part 42a,” the first chemical agent supply part 42a includes the hydrated lime reservoir 421, the special assistant reservoir 422, the first chemical agent pumping part 423a, the first chemical agent supply line 424a, and the quantitative supply parts 425 and 426. Similarly, if a configuration for supplying the flue gas-treating chemical agent to the auxiliary supply position P2 is referred to as a “second chemical agent supply part 42b,” the second chemical agent supply part 42b includes the hydrated lime reservoir 421, the special assistant reservoir 422, the second chemical agent pumping part 423b, the second chemical agent supply line 424b, and the quantitative supply parts 425 and 426. The first chemical agent supply part 42a and the second chemical agent supply part 42b share the hydrated lime reservoir 421 that stores the hydrated lime, and also share the special assistant reservoir 422 that stores the special assistant. [0020] 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 unit 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 and the flue gas-treating chemical agent react with each other, and the hazardous substances are removed from the flue gas. The reaction of the flue gas and the flue gas-treating chemical agent also occurs on the upstream side of the dust collector 43 in the flue 3. The chemical agent supply unit 42 may supply other types of chemical agents such as activated carbon, in addition to the hydrated lime. Examples of the hazardous substances removed by the flue gas-treating chemical agent include hydrogen chloride, sulfur oxides, dioxins, and

mercury compounds.
[0021] In the dust collector 43, the fly ash and the flue gas-treating chemical agent (including reactants with hazardous substances), which are deposited on the filter cloth, are shaken off every predetermined period of time by back washing using compressed air. The fly ash and the flue gas-treating chemical agent that have been shaken off from the filter cloth are transported to a collected dust treatment part (not shown) and treated with, for example, a chelating agent (heavy metal stabilizer). In practice, part of the fly ash and the flue gas-treating chemical agent is collected by the gas cooler 41 provided between the combustion chamber 2 and the dust collector 43 in the flue 3 and transported to a fly ash treatment part.
[0022] The HCl concentration measurement part 401 is provided between the combustion chamber 2 and the gas cooler 41 (e.g., in the vicinity of an inlet of the gas cooler 41) in the flue 3 and measures the concentration of hydrogen chloride (hereinafter, referred to as an “HCl concentration”) in the flue gas using, for example, laser light. The HCl concentration acquired by the HCl concentration measurement part 401 is output to the controller 40. The controller 40 controls the chemical agent supply unit 42 on the basis of the HCl concentration. The controller 40 also performs overall control of the flue gas treatment system 4. [0023] Fig. 3 illustrates a flow of the flue gas treatment performed by the flue gas treatment system 4. In the flue gas treatment performed by the flue gas treatment system 4, the HCl concentration measurement part 401 measures the HCl concentration in the flue gas (step S11). Also, the first chemical agent supply part 42a supplies the flue gas-treating chemical agent that includes the hydrated lime and the special assistant to the chemical agent supply position P1 (step S12). At this time, the amount of the flue gas-treating chemical agent that is supplied to the chemical agent supply position P1 (supply amount per unit time)

can be controlled by adjusting the outputs of the first chemical agent pumping part 423a and the quantitative supply parts 425 and 426. The controller 40 is preferably designed to increase the amount of the flue gas-treating chemical agent that is supplied to the chemical agent supply position P1 in the case where the HCl concentration acquired by the HCl concentration measurement part 401 is higher than a predetermined set value, and to reduce the amount of the flue gas-treating chemical agent that is supplied to the chemical agent supply position P1 in the case where the HCl concentration is lower than the predetermined set value.
[0024] On the surface of the hydrated lime supplied to the chemical agent supply position P1, a reactant (CaCl2) of the hydrated lime and the hydrogen chloride is formed. Since the hydrated lime flows into the gas cooler 41 along with the flue gas, the moisture concentration at the surface of the hydrated lime increases. Moreover, the reactant on the surface, which has high water solubility, dissolves in and flows with the water sprayed into the gas cooler 41, i.e., removed from the surface of the hydrated lime, and as a result, unreacted hydrated lime appears on the surface. This inhibits the reaction rate from decreasing due to the reactant on the surface of the hydrated lime. Accordingly, the flue gas treatment system 4, in which the hydrated lime is supplied to the chemical agent supply position P1 located between the combustion chamber 2 and the gas cooler 41 in the flue 3, can improve the efficiency of the dechlorination reaction (can reduce the HCl concentration with a small amount of hydrated lime). In the same manner, in the case where the flue gas-treating chemical agent includes other calcium-based agents such as dolomite hydroxide, reactants with 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.

[0025] In parallel with step S12, the second chemical agent supply part 42b supplies the flue gas-treating chemical agent that includes the hydrated lime and the special assistant to the auxiliary supply position P2 (step S13). At this time, the amount of the flue gas-treating chemical agent that is supplied to the auxiliary supply position P2 can be controlled by adjusting the outputs of the second chemical agent pumping part 423b and the quantitative supply parts 425 and 426. The controller 40 increases or reduces the amount of the flue gas-treating chemical agent that is supplied to the auxiliary supply position P2 on the basis of the above-described HCl concentration. That is, in the case where the HCl concentration is higher than or equal to a predetermined value, the second chemical agent supply part 42b increases the amount of the flue gas-treating chemical agent that is supplied to the auxiliary supply position P2 in comparison with that in the case where the HCl concentration is lower than the predetermined value. In particular, in the case where a sudden rise in chlorine concentration of the flue gas occurs during incineration of high chlorine waste and a proper action cannot be taken under the control of only the first chemical agent supply part 42a, the controller 40 causes the second chemical agent supply part 42b to increase the amount of the flue gas-treating chemical agent that is supplied to the auxiliary supply position P2. In step S13, the amount of the flue gas-treating chemical agent that is supplied to the auxiliary supply position P2 by the second chemical agent supply part 42b may be set to zero under normal conditions in which the HCl concentration is lower than the predetermined value, and the supply of the flue gas-treating chemical agent to the auxiliary supply position P2 may be started under abnormal conditions in which the HCl concentration is higher than or equal to the predetermined value.
[0026] In the flue gas treatment system 4 in Fig. 2, the measurement of the HCl concentration (step S11), the supply of the flue gas-treating chemical agent by the

first chemical agent supply part 42a (step S12), and the supply of the flue gas-treating chemical agent by the second chemical agent supply part 42b (step S13) are, in principle, continuously performed in parallel with one another. Note that the supply of the flue gas-treating chemical agent to the chemical agent supply position P1 or to the auxiliary supply position P2 may be stopped temporarily.
[0027] Here, assume a flue gas treatment system according to a first comparative example in which the flue gas-treating chemical agent is supplied to only the chemical agent supply position P1 located between the combustion chamber 2 and the gas cooler 41 in the flue 3, and a flue gas treatment system according to a second comparative example in which the flue gas-treating chemical agent is supplied to only the auxiliary supply position P2 located between the gas cooler 41 and the dust collector 43. Fig. 4 illustrates a relationship between the dechlorination rate and the equivalence ratio in the flue gas treatment systems according to the first and second comparative examples. Here, the supply amount of the flue gas-treating chemical agent is controlled such that HCl concentration in the stack 52 will be a predetermined value. In Fig. 4, a broken line L21 indicates a relationship between the dechlorination rate and the equivalence ratio in the flue gas treatment system according to the first comparative example, and a solid line 22 indicates a relationship between the dechlorination rate and the equivalence ratio in the flue gas treatment system according to the second comparative example. Note that the equivalence ratio is a value of the ratio between the amount of hydrated lime that is actually supplied and the amount of hydrated lime that is theoretically necessary to completely remove hydrogen chloride and sulfur oxides in the flue gas, i.e., it is an indicator of the degree of oversupply of the hydrated lime. The dechlorination rate is a rate of the amount of hydrogen chloride removed by the flue gas treatment system

to the amount of hydrogen chloride before treatment. For example, the dechlorination rate is determined from (1 - (Amount of Hydrogen Chloride after Dechlorination)/(Amount of Hydrogen Chloride before Dechlorination)). [0028] In the flue gas treatment system according to the second comparative example, a reactant of powdery hydrated lime and hydrogen chloride is formed on the surface of the hydrated lime, and therefore a new reaction is less likely to occur with hydrogen chloride. Thus, in order to achieve a predetermined dechlorination rate, it is necessary to increase the amount of the hydrated lime that is supplied into the flue 3. In contrast, in the flue gas treatment system according to the first comparative example, the moisture concentration at the surface of the hydrated lime is high, and moreover, the reactant on the surface of the hydrated lime is removed with the water sprayed into the gas cooler 41. Thus, the flue gas treatment system according to the first comparative example can achieve a higher dechlorination rate than the flue gas treatment system according to the second comparative example when they are compared using the same equivalence ratio. In this way, an efficient dechlorination treatment is made possible by supplying the flue gas-treating chemical agent to the chemical agent supply position P1 located between the combustion chamber 2 and the gas cooler 41. [0029] In the flue gas treatment system 4 in Fig. 2, the first chemical agent supply part 42a supplies the flue gas-treating chemical agent including the hydrated lime to the chemical agent supply position P1 located between the combustion chamber 2 and the gas cooler 41. This improves dechlorination performance with efficient use of hydrated lime under normal conditions. As a result, the incineration plant 1 including the flue gas treatment system 4 can cut its running costs with efficient use of hydrated lime (a reduction in the amount of use of hydrated lime). The same also applies to the case where the flue gas-treating chemical agent includes other calcium-based agents.

[0030] Incidentally, municipal solid waste is not uniform, and for example if high chlorine garbage (high chlorine waste) is charged into the combustion chamber 2, the HCl concentration in the flue gas rises suddenly. Even in such a case, the flue gas treatment system 4, which includes the second chemical agent supply part 42b in addition to the first chemical agent supply part 42a, can control both of the first chemical agent supply part 42a and the second chemical agent supply part 42b on the basis of the HCl concentration acquired by the HCl concentration measurement part 401 and can increase the amount of the flue gas-treating chemical agent that is supplied to both of the chemical agent supply position P1 and the auxiliary supply position P2. In other words, the flue gas treatment system 4 increases not only the amount of the flue gas-treating chemical agent supplied by the first chemical agent supply part 42a, but also the amount of the flue gas-treating chemical agent supplied by the second chemical agent supply part 42b under abnormal conditions in which the HCl concentration is higher than or equal to a predetermined value. This enables taking a proper action under abnormal conditions, i.e., suppressing a sudden rise in HCl concentration within a short time, and thereby stabilizing the HCl concentration in the flue gas exhausted from the stack 52.
[0031] Also, the running costs of the flue gas treatment system 4 can be reduced with efficient use of the flue gas-treating chemical agent by controlling the first chemical agent supply part 42a and the second chemical agent supply part 42b on the basis of the HCl concentration. In the flue gas treatment system 4, the first chemical agent supply part 42a and the second chemical agent supply part 42b share the hydrated lime reservoir 421 that stores the hydrated lime. This simplifies the structure of the flue gas treatment system 4 (the same applies to the special assistant reservoir 422). [0032] Second Embodiment

Fig. 5 illustrates a flue gas treatment system 4 according to a second embodiment of the present invention. In the flue gas treatment system 4 in Fig. 5, the first chemical agent supply part 42a and the second chemical agent supply part 42b individually include hydrated lime reservoirs 421a and 421b that store the hydrated lime, and also individually include special assistant reservoirs 422a and 422b that store the special assistant. Also, the chemical agent supply position P1 is set within the gas cooler 41, and the first chemical agent supply part 42a supplies the flue gas-treating chemical agent into the gas cooler 41. The other configuration is similar to that in Fig. 2, and the same constituent elements are given the same reference signs.
[0033] In the flue gas treatment system 4, the first chemical agent supply part 42a includes the hydrated lime reservoir 421a, the special assistant reservoir 422a, the first chemical agent pumping part 423a, the first chemical agent supply line 424a, and quantitative supply parts 425a and 426a. One end of the first chemical agent supply line 424a is connected to the first chemical agent pumping part 423a, and the other end thereof is connected to the chemical agent supply position P1. The hydrated lime stored in the hydrated lime reservoir 421a is supplied via the quantitative supply part 425a into the first chemical agent supply line 424a, and the special assistant stored in the special assistant reservoir 422a is supplied via the quantitative supply part 426a into the first chemical agent supply line 424a. Thereby, the flue gas-treating chemical agent including the hydrated lime and the special assistant is supplied to the chemical agent supply position P1 located within the gas cooler 41.
[0034] The second chemical agent supply part 42b includes the hydrated lime reservoir 421b, the special assistant reservoir 422b, the second chemical agent pumping part 423b, the second chemical agent supply line 424b, and quantitative supply parts 425b and 426b. One end of the second chemical agent supply line

424b is connected to the second chemical agent pumping part 423b, and the other end thereof is connected to the auxiliary supply position P2. The hydrated lime stored in the hydrated lime reservoir 421b is supplied via the quantitative supply part 425b into the second chemical agent supply line 424b, and the special assistant stored in the special assistant reservoir 422b is supplied via the quantitative supply part 426b into the second chemical agent supply line 424b. Thereby, the flue gas-treating chemical agent including the hydrated lime and the special assistant is supplied to the auxiliary supply position P2 in the flue 3. [0035] The flue gas treatment system 4, in which the first and second chemical agent supply parts 42a and 42b individually include the hydrated lime reservoirs 421a and 421b, can change the amount of hydrated lime that is supplied to the chemical agent supply position P1 and the amount of hydrated lime that is supplied to the auxiliary supply position P2 with a higher degree of flexibility than the flue gas treatment system 4 in Fig. 2 (the same applies to the amounts of special assistant). In a preferable flue gas treatment system 4, the amount of hydrated lime supplied by the first chemical agent supply part 42a is greater than the amount of hydrated lime supplied by the second chemical agent supply part 42b under normal conditions. Note that the chemical agent supply position P1 in the flue gas treatment system 4 in Fig. 5 may be set on the upstream side of the gas cooler 41 in the flue 3, as in the flue gas treatment system 4 in Fig. 2. Alternatively, the chemical agent supply position P1 in the flue gas treatment system 4 in Fig. 2 may be set within the gas cooler 41.
[0036] The flue gas treatment system 4 in Fig. 5 can also take a proper action under abnormal conditions in which the HCl concentration is higher than or equal to a predetermined value, by controlling both of the first chemical agent supply part 42a and the second chemical agent supply part 42b on the basis of the HCl concentration acquired by the HCl concentration measurement part 401.

Alternatively, the flue gas treatment system 4 may cause the first chemical agent supply part 42a to supply a fixed amount of the flue gas-treating chemical agent to the chemical agent supply position P1 and may control only the amount of the flue gas-treating chemical agent that is supplied to the auxiliary supply position P2 by the second chemical agent supply part 42b on the basis of the HCl concentration. In this case as well, a proper action can be taken under abnormal conditions in which the HCl concentration is higher than or equal to a predetermined value, by causing the second chemical agent supply part 42b to increase the amount of the flue gas-treating chemical agent that is supplied to the auxiliary supply position P2 in comparison with that in the case where the HCl concentration is lower than the predetermined value.
[0037] As another alternative, the flue gas treatment system 4 may cause the second chemical agent supply part 42b to supply a fixed amount of the flue gas-treating chemical agent to the auxiliary supply position P2 and may control only the amount of the flue gas-treating chemical agent that is supplied to the chemical agent supply position P1 by the first chemical agent supply part 42a on the basis of the HCl concentration. In this case as well, a proper action can be taken under abnormal conditions in which the HCl concentration is higher than or equal to a predetermined value, by causing the first chemical agent supply part 42a to increase the amount of the flue gas-treating chemical agent that is supplied to the chemical agent supply position P1 in comparison with that in the case where the HCl concentration is lower than the predetermined value, while causing the second chemical agent supply part 42b to supply the flue gas-treating chemical agent to the auxiliary supply position P2. Under abnormal conditions in which the HCl concentration is higher than or equal to a predetermined value, the flue gas treatment system 4, in which the first chemical agent supply part 42a and the second chemical agent supply part 42b include chemical agent reservoirs,

increases the sum of the supply amounts of the flue gas-treating chemical agent by both of the first chemical agent supply part 42a and the second chemical agent supply part 42b in comparison with that under normal conditions in which the HCl concentration is lower than the predetermined value, while causing both of the first chemical agent supply part 42a and the second chemical agent supply part 42b to supply the flue gas-treating chemical agent. This helps stabilizing the HCl concentration in the flue gas (the same applies to the flue gas treatment system 4 in Fig. 2). [0038] Third Embodiment
Fig. 6 illustrates a flue gas treatment system 4 according to a third embodiment of the present invention. In the flue gas treatment system 4 in Fig. 6, a collected dust transport part 44 is provided, instead of the second chemical agent supply part 42b, in the flue gas treatment system 4 in Fig. 5, and the chemical agent supply position P1 is set on the upstream side of the gas cooler 41 in the flue 3.
[0039] 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 a position that is located between the gas cooler 41 and the dust collector 43 in the flue 3 (i.e., an auxiliary supply position P2) and the lower portion of the dust collector 43. In Fig. 6, 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 chute part 444 are provided in order from the dust collector 43 toward the auxiliary supply position P2. [0040] The collected dust distribution part 45 distributes and supplies fly ash

and a flue gas-treating chemical agent (hereinafter, collectively referred to as “collected dust”) that have been shaken off from a 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 (also referred to as a “scraper conveyor”). 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.
[0041] 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. The supply conveyor 46 is, for example, a flight conveyor and transports the collected dust along a conveyor transport path from below the collected dust reservoir 442 to above the auxiliary supply position P2 in the flue 3. The conveyor transport path is part of

the auxiliary path 441 previously described. The chute part 444 is provided above the auxiliary supply position P2, and the collected dust transported by the supply conveyor 46 is supplied via the chute part 444 to the auxiliary supply position P2. As described previously, the collected dust includes the flue gas-treating chemical agent. Thus, the collected dust transport part 44 can be considered as a second chemical agent supply part capable of supplying the flue gas-treating chemical agent including the hydrated lime to the auxiliary supply position P2.
[0042] The control of the first chemical agent supply part 42a and the collected dust transport part 44 by the controller 40 is similar to the control of the first chemical agent supply part 42a and the second chemical agent supply part 42b by the flue gas treatment systems 4 in Figs. 2 and 5. Thus, in the case where the HCl concentration is higher than or equal to a predetermined value, the collected dust transport part 44 increases the amount of the collected dust that is supplied to the auxiliary supply position P2 in comparison with that in the case where the HCl concentration is lower than the predetermined value. Alternatively, in the case where the HCl concentration is higher than or equal to a predetermined value, the first chemical agent supply part 42a increases the amount of the flue gas-treating chemical agent that is supplied to the chemical agent supply position P1 in comparison with that in the case where the HCl concentration is lower than the predetermined value, while the collected dust transport part 44 supplies the collected dust to the auxiliary supply position P2.
[0043] As described above, in the flue gas treatment system 4 in Fig. 6, the first chemical agent supply part 42a supplies a virgin flue gas-treating chemical agent to the chemical agent supply position P1 located between the combustion chamber 2 and the gas cooler 41. This improves dechlorination performance with efficient use of hydrated lime under normal conditions. Also, the collected dust

transport part 44 supplies the collected dust including the hydrated lime to the auxiliary supply position P2. By using the collected dust collected by the dust collector 43 as the flue gas-treating chemical agent in this way, it is possible to reduce the amount of use of the flue gas-treating chemical agent in the first chemical agent supply part 42a (i.e., the amount of use of the flue gas-treating chemical agent that is not mixed with fly ash). Moreover, under abnormal conditions in which the HCl concentration is higher than or equal to a predetermined value, both or either of the supply amount of the flue gas-treating chemical agent by the first chemical agent supply part 42a and the supply amount of the collected dust by the collected dust transport part 44 is increased in comparison with that under normal conditions in which the HCl concentration is lower than the predetermined value, while the first chemical agent supply part 42a supplies the flue gas-treating chemical agent and the collected dust transport part 44 supplies the collected dust. Accordingly, a proper action can be taken under abnormal conditions.
[0044] The collected dust transport part 44 may transport the collected dust to the auxiliary supply position P2, using carrier gas such as air. Also, in the flue gas treatment system 4 in Fig. 6, the chemical agent supply position P1 may be set within the gas cooler 41, and the first chemical agent supply part 42a may supply the flue gas-treating chemical agent into the gas cooler 41 (the same applies to flue gas treatment systems 4 in Figs. 7 and 8, which will be described later). [0045] Fourth Embodiment
Fig. 7 illustrates a flue gas treatment system 4 according to a fourth embodiment of the present invention. In the flue gas treatment system 4 in Fig. 7, the auxiliary supply position P2 in the flue gas treatment system 4 in Fig. 6 is set on the upstream side of the gas cooler 41 in the flue 3, i.e., set between the combustion chamber 2 and the gas cooler 41. The other configuration is similar

to that of the flue gas treatment system 4 in Fig. 6, and the same constituent elements are given the same reference signs.
[0046] The flue gas treatment system 4 in Fig. 7 can provide an efficient dechlorination treatment under normal conditions by causing the first chemical agent supply part 42a to supply a virgin flue gas-treating chemical agent to the chemical agent supply position P1 located between the combustion chamber 2 and the gas cooler 41. The system can also reduce the amount of use of the flue gas-treating chemical agent in the first chemical agent supply part 42a by causing the collected dust transport part 44 to serve as a second chemical agent supply part and supply collected dust including hydrated lime into the flue 3. The system can further take a proper action under abnormal conditions in which the HCl concentration is higher than or equal to a predetermined value, by increasing both or either of the amount of the flue gas-treating chemical agent supplied by the first chemical agent supply part 42a and the amount of the collected dust supplied by the collected dust transport part 44 under abnormal conditions in comparison with that under normal conditions in which the HCl concentration is lower than the predetermined value. As described with reference to Figs. 2 and 5 to 7, from the viewpoint of suppressing a sudden rise in HCl concentration under abnormal conditions in which the HCl concentration is higher than or equal to a predetermined value, the auxiliary supply position P2 may be provided at any position between the combustion chamber 2, which is a generation source of the flue gas, and the dust collector 43 in the flue 3. [0047] Fifth Embodiment
Fig. 8 illustrates a flue gas treatment system 4 according to a fifth embodiment of the present invention. In the flue gas treatment system in Fig. 8, two auxiliary supply positions P2 are set in the collected dust transport part 44. One auxiliary supply position P2 is located between the combustion chamber 2

and the gas cooler 41 in the flue 3, and the other auxiliary supply position P2 is located between the gas cooler 41 and the dust collector 43. [0048] The collected dust transport part 44 in Fig. 8 is configured by adding a supply conveyor 47 and a chute part 445 to the collected dust transport part 44 in Fig. 6. The supply conveyor 47 is connected to a predetermined position in the supply conveyor 46 and extends from that position to above the aforementioned one auxiliary supply position P2. This enables supplying the collected dust to the aforementioned one auxiliary supply position P2 by using part of the supply conveyor 46, the supply conveyor 47, and the chute part 445. The collected dust can be supplied to the aforementioned other auxiliary supply position P2 by using the supply conveyor 46 and the chute part 444. The flue gas treatment system 4 in Fig. 8 can reduce the amount of use of the flue gas-treating chemical agent in the first chemical agent supply part 42a by causing the collected dust transport part 44 to serve as a second chemical agent supply part and supply the collected dust including the hydrated lime into the flue 3. The system can also take a proper action under abnormal conditions in which the HCl concentration is higher than or equal to a predetermined value, by increasing both or either of the amount of the flue gas-treating chemical agent supplied by the first chemical agent supply part 42a and the amount of the collected dust supplied by the collected dust transport part 44. [0049] Variations
The above-described embodiments of the flue gas treatment system can be modified in various ways.
[0050] The HCl concentration measurement part 401 may be provided between the gas cooler 41 and the dust collector 43 (e.g., at the inlet of the dust collector 43) in the flue 3, or may be provided between the dust collector 43 and the stack 52. Although the stack 52 is normally provided with another HCl concentration

measurement part, fluctuations in HCl concentration in the flue gas can speedily be dealt with by providing the HCl concentration measurement part 401 on the upstream side of the stack 52. Alternatively, the HCl concentration measurement part provided in the stack 52 (which may be regarded as part of the flue) may be used to control the supply amount of the flue gas-treating chemical agent. [0051] The flue gas treatment system 4 may be used in plants other than the incineration plant 1.
[0052] The configurations of the above-described preferred embodiments and variations may be appropriately combined as long as there are no mutual inconsistencies.
[0053] 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 be devised without departing from the scope of the invention.
REFERENCE SIGNS LIST
[0054] 1 Incineration plant
2 Combustion chamber
3 Flue
4 Flue gas treatment system

40 Controller
41 Gas cooler
42a First chemical agent supply part
42b Second chemical agent supply part
43 Dust collector
44 Collected dust transport part
401 HCl concentration measurement part

421 Hydrated lime reservoir
P1 Chemical agent supply position
P2 Auxiliary supply position
S11 to S13 Step

I/We Claim
1. A flue gas treatment system comprising:
a dust collector provided in a flue through which flue gas flows;
a gas cooler that is provided between a generation source of said flue gas and said dust collector in said flue and sprays water into said flue gas;
a first chemical agent supply part that supplies a flue gas-treating chemical agent including a calcium-based agent to a chemical agent supply position that is located between said generation source and said gas cooler in said flue or located within said gas cooler;
a second chemical agent supply part that is capable of supplying a flue gas-treating chemical agent including a calcium-based agent to an auxiliary supply position that is located between said generation source and said dust collector in said flue;
an HCl concentration measurement part that measures an HCl concentration in said flue gas; and
a controller that, in a case where said HCl concentration is higher than or equal to a predetermined value, causes said second chemical agent supply part to increase a supply amount of said flue gas-treating chemical agent that is supplied to said auxiliary supply position in comparison with the supply amount in a case where said HCl concentration is lower than said predetermined value, or that, in a case where said HCl concentration is higher than or equal to a predetermined value, causes said first chemical agent supply part to increase a supply amount of said flue gas-treating chemical agent that is supplied to said chemical agent supply position in comparison with the supply amount in a case where said HCl concentration is lower than said predetermined value, while causing said second chemical agent supply part to supply said flue gas-treating chemical agent to said

auxiliary supply position.
2. The flue gas treatment system as claimed in claim 1, wherein
said first chemical agent supply part and said second chemical agent supply part share a reservoir that stores the calcium-based agent.
3. The flue gas treatment system as claimed in claim 1 or 2, wherein
said second chemical agent supply part supplies collected dust collected by said dust collector as said flue gas-treating chemical agent.
4. 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 according to any one of claims 1 to 3, provided in said flue.
5. A flue gas treatment method used in a flue gas treatment system,
said flue gas treatment system comprising:
a dust collector provided in a flue through which flue gas flows;
a gas cooler that is provided between a generation source of said flue gas and said dust collector in said flue and sprays water into said flue gas;
a first chemical agent supply part that supplies a flue gas-treating chemical agent including a calcium-based agent to a chemical agent supply position that is located between said generation source and said gas cooler in said flue or located within said gas cooler; and
a second chemical agent supply part that is capable of supplying a flue

gas-treating chemical agent including a calcium-based agent to an auxiliary supply position that is located between said generation source and said dust collector in said flue,
said flue gas treatment method comprising:
a) causing said first chemical agent supply part to supply said flue gas-treating chemical agent to a position that is located between said generation source and said gas cooler in said flue or located within said gas cooler;
b) measuring an HCl concentration in said flue gas; and
c) in a case where said HCl concentration is higher than or equal to a predetermined value, causing said second chemical agent supply part to increase a supply amount of said flue gas-treating chemical agent that is supplied to said auxiliary supply position in comparison with the supply amount in a case where said HCl concentration is lower than said predetermined value, or in a case where said HCl concentration is higher than or equal to a predetermined value, causing said first chemical agent supply part to increase a supply amount of said flue gas-treating chemical agent that is supplied to said chemical agent supply position in comparison with the supply amount in a case where said HCl concentration is lower than said predetermined value, while causing said second chemical agent supply part to supply said flue gas-treating chemical agent to said auxiliary supply position.