JP2003161428A - Exhaust gas processing unit of ash melting furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust gas processing unit of an ash melting furnace which highly efficiently removes a toxic substance such as nitrogen oxides and dioxin and the like. <P>SOLUTION: This device treats exhaust gas exhausted from the ash melting furnace for melting ash generated by combustion of a combustion furnace, and has a boiler 12 for cooling a temperature of the exhaust gas to about 220°C from about 850 to 1,000°C, a front stage side dust collector 13 for performing dust-collecting and denitration from the exhaust gas cooled to about 220°C, and to which a reducing agent and activated charcoal 22 are supplied, and a rear stage side dust collector 14 for collecting dust from the exhaust gas of about 230 to 240°C to which an alkali neutralizer 20 and the activated charcoal are supplied, and simultaneously performing desulfurization, desalting, denitration, and removal of dioxin and the like, and is characterized in that at least one of the dust collectors 13 and 14 is a multilayer bag filter formed by laminating a plurality of filter cloths with a catalyst layer between the filter cloths. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for removing harmful substances contained in exhaust gas discharged from a melting furnace or the like, and more particularly to capturing dust contained in the exhaust gas in an ash melting furnace whose exhaust gas temperature is relatively high. The present invention relates to an exhaust gas treatment device that collects and separates and removes harmful substances such as nitrogen oxides, sulfur oxides, hydrogen chloride and dioxins.

[0002]

2. Description of the Related Art Nitrogen oxides (NOx) and sulfur oxides (S) are contained in exhaust gas discharged from waste incinerators and ash melting furnaces.
Ox), hydrogen chloride (HCl), halogenated aromatic compounds such as dioxins, and harmful substances such as heavy metals are contained, and emission regulations are set because they have serious effects on the human body and the environment. These harmful substances have different component ratios depending on the type of the substance to be treated and the furnace from which they are discharged. For example, when combustible substances such as municipal waste are burned in a fluidized bed incinerator, fly ash, HCl, Exhaust gas containing a large amount of acid gas components such as SOx and dioxins is generated,
In an ash melting furnace that melts and processes incineration ash and fly ash discharged from these incinerators, exhaust gas containing a large amount of nitrogen oxides, dioxins and the like is generated.

As described above, the following treatment methods are generally adopted for treating exhaust gas containing plural kinds of harmful substances. In the exhaust gas treatment method disclosed in Japanese Patent Application Laid-Open No. 2001-17933 shown in FIG. 7, slaked lime 56 which is an alkali neutralizing agent after the exhaust gas 50a introduced into the gas cooling device 51 is cooled by the cooling device 51 and First with activated carbon 57
After being introduced into the bag filter 52, the fly ash in the exhaust gas is collected as dust and the acidic gas components and dioxins are reacted or adsorbed to be removed as dust, and then the first bag filter 5
The exhaust gas 50c from 2 is introduced into the second bag filter 53 together with the activated carbon 58, and the remaining dioxins in the exhaust gas are adsorbed and removed as dust.

In the first bag filter 52, the introduced exhaust gas reacts with the alkali neutralizer to remove sulfur oxides and hydrogen chloride, and the activated carbon 57 adsorbs and removes harmful substances such as dioxins. In the second bag filter, dioxins and the like are removed by the activated carbon 58 charged again. With such a configuration, the load on one bag filter can be reduced, and harmful substances can be removed with high efficiency.

Further, Japanese Patent Laid-Open No. 2001-13 shown in FIG.
7634 is a gas cooling device 62 that cools the exhaust gas discharged from various incinerators 61, and a pre-stage dust remover 63 that removes soot and dust in the exhaust gas and performs desalination and desulfurization.
And a post-stage bag filter 64 which introduces a neutralizing agent 68 to perform desulfurization and desalting treatment by a neutralization reaction, and releases a part of exhaust gas from the incinerator 61 to the post-stage bag filter 68. I am trying. As described above, the soot dust brought into the post-stage bag filter 68 facilitates the formation of a cake layer on the filter surface, and by introducing a neutralizing agent into the post-stage bag filter 68, in addition to the removal of dioxins. Therefore, desulfurization and desalting can be efficiently performed.

[0006]

As described above, exhaust gas properties such as components of harmful substances contained in exhaust gas, exhaust gas temperature, and exhaust gas amount are different depending on various factors such as combustion equipment and burned material. There is. The ash melting furnace exhaust gas treated in the present invention is characterized by a small amount of gas at high temperature and a relatively low sulfur oxide content and a large amount of nitrogen oxides as compared with exhaust gas discharged from various incinerators. Have. Therefore,
Introducing an alkali neutralizing agent on the upstream side of the treatment apparatus in the exhaust gas treatment apparatus of an ash melting furnace, as in the above-mentioned Japanese Patent Laid-Open No. 2001-17933, causes deterioration of treatment efficiency. This is because when an alkali neutralizing agent is used, the removal rate decreases as the temperature rises.

Dioxins are about 250 to 280.
Since it is easy to re-synthesize in the temperature range of ℃, when the exhaust gas temperature is high as in the ash melting furnace exhaust gas, it is only necessary to introduce an adsorbent or a catalyst in the front and rear stages as described in the above-mentioned prior art. Efficient removal of substances is very poor. Also,
Even if these conventional techniques are applied to the ash melting furnace exhaust gas, the removal of nitrogen oxides is not sufficient, and there is a possibility that the emission control value will be exceeded. The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to provide an exhaust gas treatment apparatus capable of removing harmful substances such as nitrogen oxides and dioxins with high efficiency.

[0008]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a flue gas discharged from an ash melting furnace for melting ash produced by combustion in a combustion furnace. In the device for treating the exhaust gas, means for cooling the temperature of the exhaust gas from about 850 to 1200 ° C. to 350 ° C. or less, and means for sequentially removing harmful substances from the exhaust gas cooled to 350 ° C. or less by a plurality of types of dust collecting functions. It is characterized by having. According to this invention, since a plurality of types of dust collecting functions are provided to sequentially remove harmful substances, the removal rate of harmful substances is improved. Furthermore, it is possible to increase or decrease the type and the number of stages of the dust collecting function according to the properties of exhaust gas to be treated, the emission amount, and the content of each harmful substance, to provide an exhaust gas treatment device having high treatment efficiency and a wide range of application. You can

Further, in the invention according to claim 2, the harmful substance removing means is composed of a plurality of dust collectors arranged in series, and an alkaline neutralizing agent is added to the inlet side of the latter-stage dust collector. Desulfurization and desalting are performed, and at the same time, a reducing agent is supplied to at least one of the pre-stage side dust collector and the post-stage side dust collector to perform denitration. As described above, the exhaust gas from the ash melting furnace has a high temperature, and the removal efficiency is low when the alkali neutralizer is added to the pre-stage side dust collector. Therefore, the treatment efficiency is improved by adding an alkali neutralizing agent to the latter stage side, and further, by supplying a reducing agent for removing nitrogen oxides contained in a large amount in the exhaust gas, it is suitable for the exhaust gas properties of the ash melting furnace. The purification process can be performed. Since nitrogen oxide has a higher removal efficiency when it is at a higher temperature, it is preferable to supply the reducing agent by a high temperature pre-stage dust collector.
When the nitrogen oxide concentration is high, it is better to supply both.

The invention according to claim 3 is characterized in that the temperature of the latter-stage dust collector is set to about 250 ° C. or lower and a catalyst is supplied to the dust collector to remove dioxins. This is because the dioxins are 250 to 280
Since it is re-synthesized at around ℃, by removing dioxins in the above temperature range, re-synthesis is prevented and the treatment rate is improved. Here, the catalyst is, for example, Ti, Si, Al,
At least one of oxides of V, W, Mo, Nb, and Ta is added to a carrier composed of at least one selected from Zr, P, and B or a carrier composed of a composite oxide containing two or more of these elements. Examples thereof include catalysts such as those supporting an active component composed of an oxide, and known dioxin decomposition catalysts, but are not particularly limited. Note that these catalysts include those that exert a catalytic action even during denitration.

Furthermore, in the invention according to claim 4, the temperature of the exhaust gas introduced into the pre-stage side dust collector for performing the denitration is about 220.
The temperature of the exhaust gas supplied to the latter-stage dust collector for desulfurization and desalting is set to about 110 to 250 ° C. As described above, a high temperature range is suitable for efficient denitration, and when a catalyst is used as a denitration promoter as a reducing agent, the lower the temperature, the more catalyst is required and the cost increases. On the other hand, if the temperature is about 350 ° C. or higher, the reducing agent may be oxidatively decomposed and the performance may deteriorate. Therefore, it is possible to maintain the highest removal rate by performing denitration within the above temperature range. Further, in desulfurization and desalting, when the temperature is high, the reaction of the alkali neutralizing agent used is lowered and the removal rate is lowered.

Furthermore, in the invention according to claim 5, the temperature of the exhaust gas introduced into the pre-stage side dust collector for performing the denitration is about 2
The temperature of the exhaust gas is set to 20 to 350 ° C., and a cooler is provided between the pre-stage side dust collector and the post-stage side dust collector, and the exhaust gas temperature introduced into the post-stage dust collector for desulfurization and desalination is about 110.
The feature is that the temperature is set to ˜170 ° C. As described above, the present invention is the most preferable temperature range for using the reducing agent and the denitration catalyst in the pre-stage side dust collector, and by interposing the cooler, the post-stage dust collector is most desulfurized and desalted. It is possible to provide an exhaust gas treatment apparatus having a highly efficient temperature range, suppressing the cost of additives such as a reducing agent, a catalyst, and a neutralizing agent to be introduced, and having a high removal efficiency.

According to a sixth aspect of the present invention, at least one means of the harmful substance removing means is a bag filter, the filter cloth of the bag filter is formed in a multi-layer structure, and the filter cloth space is By sandwiching the catalyst layer having a function of removing harmful substances, the device can be made compact. Further, in the invention according to claim 7, a cake layer carrying at least one of a chemical agent such as an alkali neutralizing agent and activated carbon is formed on the surface of the filter cloth, and harmful substances are removed by the cake layer. It is characterized by

With such a constitution, the dust removal rate can be improved, and further, depending on the substance to be treated, the catalyst layer or the cake layer may contain a catalyst, a chemical agent such as an alkali neutralizing agent, activated carbon or the like. At the same time as removing dust, harmful substances in the exhaust gas can be removed. The type of filter cloth to be used and the number of laminated layers may be appropriately adjusted depending on the type of exhaust gas. Further, since the ash melting furnace exhaust gas, which is the exhaust gas to be treated in the present invention, has a small discharge amount, the dust removal rate hardly decreases due to the pressure loss, but a fan or a blower may be appropriately provided.

Further, as described in claim 8, it is preferable that the gap of the filter cloth located on the exhaust gas discharge side is smaller than the gap of the filter cloth located on the exhaust gas introduction side. With such a configuration, it is possible to remove soot dust having a large particle size by the filter cloth located on the exhaust gas introduction side, and further removing soot dust having a small particle size by the filter cloth located on the exhaust gas discharge side. Therefore, it is possible to reduce the load on each filter cloth, improve the durability, and improve the dust removal rate.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be exemplarily described in detail below with reference to the drawings. However, the dimensions, materials, shapes, relative positions, etc. of the components described in this embodiment are not intended to limit the scope of the present invention thereto unless specifically stated otherwise, and are merely illustrative examples. Not too much. FIG. 1 is a schematic cross-sectional view of a filter cloth of a bag filter used in the present invention, FIG. 2 is a schematic configuration diagram of an exhaust gas treating apparatus according to a first embodiment of the present invention, and FIGS. FIG. 6 is a schematic configuration diagram of exhaust gas treatment according to second to fifth embodiments which are the embodiments of the present invention.

The exhaust gas targeted in this embodiment is an exhaust gas discharged from an ash melting furnace, which emits a smaller amount of gas than exhaust gas discharged from various incinerators, has a relatively high temperature, and contains nitrogen oxides. It also has the feature of containing a large amount of dioxins. As shown in FIG. 2, the exhaust gas treating apparatus according to the first embodiment includes an ash melting furnace 10 for burning incinerated ash and fly ash, and a high temperature of about 850 to 1000 ° C. discharged from the ash melting furnace 10. A boiler 12 that cools exhaust gas by heat exchange, a pre-stage side dust collector 13 that collects and separates soot dust in the exhaust gas that has been cooled to approximately 250 ° C. or less in the boiler 12, and a front-stage side dust collector 13 that are arranged in series, About 23
Rear stage dust collector 14 into which exhaust gas of 0 to 240 ° C is introduced
And a post-processing device 15 for processing the soot dust collected by the post-stage dust collector 14.

Further, in such a device, the alkali neutralizer 20 is provided between the front side dust collector 13 and the rear stage dust collector 14.
And a reducing agent 21 such as ammonia are added to remove harmful substances such as nitrogen oxides, sulfur oxides and hydrogen chloride in the exhaust gas. At this time, a catalyst is added to accelerate the reduction of sulfur oxides. Examples of the alkaline neutralizer 20 supplied for the purpose of desulfurization and desalination include slaked lime (Ca (OH) ₂ ), Mg (OH) ₂ , CaO, M
gO, NaCO ₃ or the like is used in the form of powder or slurry. On the other hand, examples of the reducing agent 21 used for denitration include ammonia (NH ₃ ) and urea (CO (NH ₂ ) ₂ ).

As the denitration catalyst, Al is used as a carrier.
₂ O ₃ , TiO _2, etc. as active metals Pt, V
₂ O ₅ , Fe ₂ O ₃ , CuO, Mn ₂ O ₃ , Cr
₂ O _{3, MoO 3,} CoO and the like. further,
If SOx is contained at a high concentration due to the properties of the exhaust gas, S
V ₂ O ₅ which has the highest activity in the presence of Ox is used as an active metal, and TiO ₂ which is difficult to react with SOx is used as a carrier.
It is preferable to select it appropriately according to the properties of the exhaust gas. still,
Since the catalyst includes the same catalyst as that used when decomposing dioxins, it is possible to remove dioxins at the same time by using these in an appropriate combination.

Further, since dioxin, nitrogen oxides and the like remain in the soot dust collected by the pre-stage side dust collector 13, as shown in FIG. Return to the melting furnace together with ash discharged from the furnace or post-process it so that it will not be discharged to the outside. The dust collectors 13 and 14 used in such an apparatus are not particularly limited, but, for example, an electric dust collector, a bag filter, a multi cyclone, or the like can be used. In this way, a plurality of devices having a dust collecting function are provided, and the temperature is about 230 to 240 ° C.
Dust collection by using an alkaline neutralizer in the temperature range of
The desulfurization and desalination treatment efficiency is improved.

FIG. 3 shows a second embodiment of the present invention. Like the first embodiment, the high temperature exhaust gas discharged from the melting furnace 10 is introduced into the boiler 12 and cooled to around 220.degree. . Then, the reducing agent 2 is added to the cooled exhaust gas.
1 is supplied and introduced into the pre-stage side dust collector 13, then activated carbon 2
2 is supplied to adsorb and remove harmful substances such as dioxins, and the alkaline neutralizer 20 is added to the exhaust gas at about 200 ° C. discharged from the pre-stage side dust collector 13 to perform desulfurization and desalting, and the latter-stage dust collector Introduced in 14. The rear side dust collector 1
In 4, the activated carbon 22 is supplied again to further reduce dioxins. In this way, the exhaust gas introduced into the pre-stage side dust collector 13 is cooled to 250 ° C. or lower,
By supplying activated carbon to both 14, dioxins can be removed without causing resynthesis.

In the third embodiment shown in FIG. 4, the exhaust gas temperature in the boiler 12 is cooled to about 250 ° C., the reducing agent 21 and the catalyst (not shown) are supplied to the exhaust gas, and then the pre-stage side dust collector 13 is provided. To introduce. And 240 ℃
Exhaust gas exhausted at a level of about 150 to 1 in the cooler 16
After cooling to 70 ° C., it is introduced into the latter stage dust collector 14.
In addition, the cooler 16 and the cooler 16 and the rear side dust collector 1
4, an alkali neutralizer is added, and activated carbon 22 is further supplied by the latter-stage dust collector 14. Like this, 25
Denitration is performed at a relatively high temperature of about 0 ° C, and 150 to 170
By performing desulfurization and desalting in a low temperature atmosphere of about ℃, the treatment efficiency is maintained at the highest level.

FIG. 5 shows a fourth embodiment of the present invention, in which a cooler 16 is added to the first embodiment as in the third embodiment. In this embodiment, the pre-stage side dust collector 13 is installed mainly for dust collection,
250-350 of relatively high temperature discharged from the boiler 12
After collecting and separating soot dust from the exhaust gas at about ℃, the exhaust gas at about 240 ℃ discharged from the pre-stage side dust collector 14 is cooled by the cooler 1.
Introduce to 6. After being cooled to a low temperature exhaust gas of about 150 to 170 ° C. by the cooler 16, the alkali neutralizing agent 20 and the reducing agent 21 are supplied and introduced into the post-stage side dust collector 14. The latter-stage dust collector 14 supplies the catalyst 23 to decompose and remove dioxins and the like.

Furthermore, the fifth embodiment shown in FIG.
After the cooler 16 is provided between the pre-stage side dust collector 13 and the post-stage side dust collector 14 as in the fourth embodiment, and after the reducing agent 21 is supplied to the exhaust gas cooled by the cooler 16 to 150 to 170 ° C. The rear side dust collector 14 supplied with the catalyst 23 collects dust and decomposes and removes dioxins. Further, the reducing agent 21 is provided on the upstream side of the pre-stage side dust collector 13.
Is added to perform denitration in the pre-stage side dust collector 13, and a catalyst 23 is supplied to simultaneously remove dioxins.

The catalyst used to promote the decomposition and removal of dioxins is, for example, Ti, Si, Al, Zr,
At least one kind of oxide of V, W, Mo, Nb, and Ta is added to a carrier made of at least one selected from P and B, or a carrier made of a composite oxide containing two or more of these elements. Examples thereof include catalysts such as those carrying an active ingredient consisting of, and known dioxins decomposition catalysts, but are not particularly limited. These catalysts include those that exert a catalytic action even during denitration. At this time, the exhaust gas temperature is set to about 250 ° C. or lower so that re-synthesis of dioxins does not occur.

Further, in this embodiment, the dust collector 13,
The bag filter having the multilayer structure shown in FIG. 1 is used for at least one of the fourteen. The filter cloth of the multilayer bag filter 25 is configured such that the first filter cloth 27 having a coarse gap through which exhaust gas flows and the second filter cloth 29 having a smaller gap than the first filter cloth sandwich the catalyst layer 28. And the first
A cake layer 26 made of soot dust containing an alkali neutralizing agent and activated carbon is formed on the surface of the filter cloth. The catalyst layer 2
The catalyst used in No. 8 is a catalyst used for denitration and removal of dioxins, and the catalysts described in the first to fifth embodiments can be used.

Further, the cake layer 26 is formed so as to contain an alkali neutralizing agent or activated carbon, or both of them, and most of the harmful substances contained in the exhaust gas can be simultaneously removed by the multilayer bag filter 25. The device can be made compact. In addition, the filter cloth is
For example, when used in a high temperature range such as the pre-stage side dust collector 13, glass fiber with high heat resistance, Teflon (trade name)
And the like are preferably used. On the other hand, when it is used in a low temperature range like the latter-stage side dust collector 14, a film-like non-woven cloth or the like can be used, and such a device can be provided at low cost. The multilayer bag filter 2
No. 5 is not limited to the two-layer type shown in the present embodiment, and the number of laminated layers can be appropriately increased or decreased according to the amount of exhaust gas, the properties of exhaust gas, and the like. Also, the reducing agent, catalyst and alkali neutralizing agent are appropriately selected according to these conditions and used so that harmful substances can be removed most efficiently.

[0028]

As described above, according to the present invention, since a plurality of kinds of dust collecting functions are provided to sequentially remove harmful substances, the removal rate of harmful substances is improved. Furthermore, it is possible to provide an exhaust gas treatment apparatus with high treatment efficiency and a wide range of application by increasing or decreasing the type and number of stages of the dust collecting function according to the properties and amount of exhaust gas to be treated and the content of each harmful substance. . Further, the exhaust gas temperature introduced into the pre-stage dust collector for denitration is set to about 220 to 350 ° C., and the exhaust gas temperature supplied to the post-stage dust collector for desulfurization and desalination is set to about 110 to 250 ° C., preferably By setting the temperature to about 110 to 170 ° C. and removing each harmful substance in the temperature range where the removal rate is highest, the treatment can be performed efficiently and at low cost.

Further, a multi-layer bag filter in which a plurality of filter cloths are laminated is used as the dust collecting means, and a reducing agent and a catalyst are sandwiched between the filter cloths to improve the dust removal rate, and depending on the substance to be treated. By holding the catalyst with the catalyst, harmful substances in the exhaust gas can be removed at the same time. Further, by forming a cake layer containing an alkali neutralizing agent or activated carbon on the surface of the multilayer bag filter, desulfurization, desalting and removal of dioxins can be performed simultaneously, and the apparatus can be made compact.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a filter cloth of a bag filter used in the present invention.

FIG. 2 is a schematic configuration diagram of an exhaust gas treating apparatus according to the first embodiment of the present invention.

FIG. 3 is a schematic configuration diagram of an exhaust gas treating apparatus according to a second embodiment which is another embodiment of the present invention.

FIG. 4 is a schematic configuration diagram of an exhaust gas treating apparatus according to a third embodiment which is another embodiment of the present invention.

FIG. 5 is a schematic configuration diagram of an exhaust gas treating apparatus according to a fourth embodiment which is another embodiment of the present invention.

FIG. 6 is a schematic configuration diagram of an exhaust gas treating apparatus according to a fifth embodiment which is another embodiment of the present invention.

FIG. 7 is a schematic diagram of an exhaust gas treating apparatus in the prior art.

FIG. 8 is a schematic view of an exhaust gas treating apparatus in the prior art.

[Explanation of symbols]

10 melting furnace 11 ash pit 12 boiler 13 Front stage dust collector 14 Rear stage dust collector 15 Aftertreatment device 16 Cooler 20 Alkaline neutralizer 21 reducing agent 22 Activated carbon 25 multilayer bag filter 26 cake layers 27 First filter cloth 28 Catalyst layer 29 Second filter cloth

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B01D 53/56 F23J 15/00 B 53/68 B01D 53/34 124Z 53/70 ZAB 53/81 134A 53 / 86 134E 53/94 129B F23G 5/44 53/36 101A F23J 15/00 G (72) Inventor Katsuhiko Kobayashi 12 Nishikicho, Naka-ku, Yokohama Mitsubishi Heavy Industries, Ltd. Yokohama Factory F-term (reference) 3K065 AA24 AB03 BA08 HA02 HA03 3K070 DA02 DA03 DA05 DA12 DA25 DA27 DA32. 4D058 JA04 JB39 SA20 TA02 TA03 TA06 UA10

Claims (8)

[Claims] 1. An apparatus for treating exhaust gas discharged from an ash melting furnace for melting ash produced by combustion of a combustion furnace, wherein the temperature of the exhaust gas is about 850 to 1200 ° C. to 350 ° C.
An exhaust gas treatment apparatus for an ash melting furnace, comprising: a cooling means; and a means for sequentially removing harmful substances from the exhaust gas cooled to 350 ° C. or lower by a plurality of types of dust collecting functions. 2. The harmful substance removing means is composed of a plurality of dust collectors arranged in series, and an alkaline neutralizing agent is added to the inlet side of the latter-stage dust collector for desulfurization and desalting, and the former stage. The exhaust gas treatment apparatus of the ash melting furnace according to claim 1, wherein the reducing agent is supplied to at least one of the side dust collector and the rear stage dust collector to perform denitration. 3. The temperature of the latter-stage dust collector is about 250 ° C.
The exhaust gas treatment device for an ash melting furnace according to claim 2, wherein a catalyst is supplied to the dust collector to remove dioxins. 4. The exhaust gas temperature introduced into the pre-stage dust collector for denitration is about 220 to 350 ° C., and the exhaust gas temperature supplied to the post-stage dust collector for desulfurization and desalination is about 11.
The exhaust gas treatment device of the ash melting furnace according to claim 2 or 3, wherein the temperature is set to 0 to 250 ° C. 5. The temperature of the exhaust gas introduced into the pre-stage side dust collector for denitration is set to about 220 to 350 ° C., and a cooler is provided between the front-stage side dust collector and the rear-stage side dust collector. The exhaust gas treatment method for an ash melting furnace according to claim 2 or 3, wherein the exhaust gas temperature introduced into the latter-stage dust collector for desulfurization and desalting is set to about 110 to 170 ° C. 6. At least one means of the harmful substance removing means is a bag filter, the filter cloth of the bag filter is formed in a multi-layer structure, and a catalyst layer having a function of removing harmful substances between the filter cloths. The exhaust gas treatment device according to claim 1, wherein the exhaust gas treatment device is sandwiched between the two. 7. A cake layer supporting at least one of a chemical agent such as an alkali neutralizing agent and activated carbon is formed on the surface of the filter cloth, and harmful substances are removed by the cake layer. The exhaust gas treatment device according to claim 6. 8. The exhaust gas treating apparatus according to claim 6, wherein a gap of the filter cloth located on the exhaust gas discharge side is smaller than a gap of the filter cloth located on the exhaust gas introduction side.