JP2001311515A - Exhaust gas treatment method for ash melting furnace and system for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a treatment method for treating incinerated ash by using a melting furnace in which a large amount of harmful materials is not included in exhaust gas. SOLUTION: In the exhaust gas treatment method for the ash melting furnace and an exhaust gas treatment system, when a part of the exhaust gas burnt in an incinerator is supplied to a dust collector through a boiler and a desuperheater, slaked line is sprayed in the pre-stage of the dust collector, and then, the incinerated exhaust gas is separated from fly ash in the dust collector. The fly ash is mixed wit main ash directly exhausted from the incinerator, and then, the melting furnace is charged with the mixed ash. The exhaust gas from the melting furnace is sequentially supplied to a combustion chamber, the desuperheater and a dust remover, and then, supplied to a scrubber. After that, the exhaust gas is mixed with the incinerated exhaust gas and the mixed gas is treated by denitration catalyst.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an exhaust gas treatment method and a treatment system for an ash melting furnace.
The present invention relates to an exhaust gas treatment method for treating incineration ash such as sewage sludge, municipal solid waste, and industrial waste, and incineration ash discharged from a combustion furnace (incinerator) such as a thermal power plant for business use by using a melting furnace.

[0002]

2. Description of the Related Art Conventionally, incinerated ash (powder inorganic material) such as sewage sludge, municipal solid waste and industrial waste has been discharged from an incinerator in order to reduce its resources, reduce its volume and render it harmless. Is melted by a melting furnace and discharged as slag, exhaust gas, and the like. In order to melt incineration ash in the furnace body using such a melting furnace, the incineration ash discharged from the refuse incinerator is pre-treated by a dry ash extraction device using a magnetic separator, incineration ash silo, ash supply conveyor, etc. After passing through the system, the ash is supplied from the ash supply hopper into the furnace body, and the supplied incineration ash is melted. At this time, fly ash similarly discharged from the incinerator is mixed with incinerated ash (main ash) discharged from the incinerator via a fly ash silo or a measuring instrument, and supplied from an ash supply conveyor.

[0003] Molten slag and molten metal generated in the melting furnace are discharged from a slag port through a slag drain to a slag slag discharging apparatus, and guided to a slag discharge system via a slag conveyor.
Provided for various uses. For example, a main electrode and the like are provided in the furnace main body, and nitrogen gas is supplied from a nitrogen gas generator to an upper portion of the furnace main body. The refuse incinerator is connected to the chimney via a bag filter, while the exhaust gas generated in the melting furnace body is guided to an exhaust gas treatment system consisting of a bag filter, a wet smoke washing tower, a chimney, etc. through a slag port. It has become.

[0004] By the way, in the flue gas of an ash melting furnace, high concentrations of dust, hydrogen chloride, sulfur oxides, and harmful organic chlorine compounds such as carbon monoxide, nitrogen oxides, and dioxins are usually present. are doing. Japanese Patent Application Laid-Open No. 9-33027 discloses an incineration melting facility for processing both incineration ash and fly ash in an incinerator in a melting furnace. An exhaust gas treatment device for an incineration ash melting furnace for removing harmful substances such as harmful substances from exhaust gas at low cost is disclosed. However,
These conventional exhaust gas treatment apparatuses only take measures against dust removal or acid gas and nitrogen oxides in addition thereto, and exhaust gas treatment capable of comprehensively treating many harmful substances as described above has not yet been proposed. And, in the conventional exhaust gas treatment on the melting furnace side, there was a problem that it was difficult to treat the smoke washing wastewater, and a serious problem that harmful substances such as dioxins were released.

[0005]

SUMMARY OF THE INVENTION In view of the above problems, the present inventors have constructed a safer and more reliable system for an exhaust gas treatment system including an ash melting furnace, which fully takes environmental issues into consideration. In the case of the whole system, we have studied diligently to develop a more efficient and energy-efficient exhaust gas treatment method. As a result, the present inventors have developed a dust collector (eg, a bag filter, an electric dust collector) for removing dust, a scrubber for removing acid gas, a combustion chamber for decomposing carbon monoxide and dioxin, and a nitrogen oxidizer. It has been found that the above problems can be solved by a method of treating exhaust gas from a melting furnace by comprehensively combining a catalyst device (reaction tower and catalyst carrying bug) for decomposing substances. The present invention has been completed from such a viewpoint.

[0006]

That is, the present invention is directed to a method in which a part of the exhaust gas burned in an incinerator is passed through a boiler and a cooling tower to a dust collecting apparatus, and is provided at a stage upstream of the dust collecting apparatus. After spraying slaked lime in the above, the exhaust gas is separated into incineration exhaust gas and fly ash by the dust collector, and the fly ash is mixed with incineration ash (main ash) discharged directly from the incinerator, and then melted. A treatment method, wherein the exhaust gas from the melting furnace is a combustion chamber, a cooling tower,
It is an object of the present invention to provide an exhaust gas treatment method for an ash melting furnace, wherein the exhaust gas is sequentially passed through a scrubber, mixed with the incineration exhaust gas, and treated by a denitration catalyst. Further, the present invention, when a part of the exhaust gas burned in the incinerator, to reach the dust collector through a boiler and a cooling tower, after spraying slaked lime in the preceding stage of the dust collector, A processing method in which the incinerator exhaust gas and fly ash are separated by the dust collector, and the fly ash is mixed with incineration ash (main ash) directly discharged from the incinerator, and then charged into a melting furnace, An exhaust gas treatment method for an ash melting furnace, wherein the exhaust gas from the melting furnace is sequentially passed through a combustion chamber, a cooling tower, and a dust removing device, mixed with the incineration exhaust gas, and then treated with a scrubber and a denitration catalyst. To provide. Here, in the exhaust gas treatment method of the present invention,
A mode in which the smoke washing wastewater discharged from the scrubber is sprayed to any one of the cooling towers, or the smoke washing wastewater discharged from the scrubber is passed through a reverse osmosis membrane, A mode of spraying to any one of them is preferably exemplified.

According to the treatment method of the present invention, the emission of dioxins can be effectively prevented by providing a combustion chamber at an effective position after the melting furnace. Further, as an effect of the combustion chamber, the inside of the melting furnace can be kept in a reducing atmosphere, whereby the inside of the furnace becomes a low oxygen gas atmosphere, and the heavy metals can be easily discharged to the outside. In this case, the concentration of carbon monoxide in the gas discharged from the melting furnace increases, but the concentration of carbon monoxide can be suppressed to a low level by the combustion chamber in the subsequent stage. Further, according to the present invention, the running cost required for treating exhaust gas from an incinerator can be kept low.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on illustrated embodiments. Embodiment (No. 1) FIG. 1 is a diagram showing an example of a processing system suitable for performing an exhaust gas processing method according to the present invention. In the present embodiment, a part of the exhaust gas burned in the incinerator 1 is guided to the waste heat boiler 3 and the cooling temperature reducing tower 4. Similarly, the main ash discharged from the incinerator 1 is supplied to the melting furnace 2 as it is. The exhaust gas cooled in the cooling tower 4 is supplied to a bag filter 5 which is a dust collector.
Slaked lime is sprayed and supplied. At this time, activated carbon can be further added. The exhaust gas sprayed with such slaked lime is separated by the bag filter 5 into incineration exhaust gas and fly ash. Here, besides the bag filter,
An electric dust collector, a cyclone, or the like can be used. Then, the separated fly ash component is mixed with the main ash directly discharged from the incinerator 1 and then charged into the melting furnace 2.

In the melting furnace 2, main ash produced by incineration in a normal incinerator and fly ash such as dust remaining in exhaust gas are mixed and usually fed from an ash supply hopper. A screw is provided at the lower part of the hopper, from which it is supplied to the melting furnace through the ash inlet, and the furnace is in a nitrogen atmosphere. In the furnace, there is a molten slag layer in which main ash and fly ash are melted, and the supplied ash is also deposited thereon. The temperature of the molten slag is usually about 1600 ° C. The slag, which is the molten ash, is discharged from the slag port. Specific examples of the melting furnace include an electric melting furnace such as a plasma arc type, an arc type, an electric resistance type and a high frequency type, and a fuel type melting furnace such as a burner type and a coke bed type. The melting furnace usually has a furnace main body formed in a cylindrical shape with a bottom, and a slag port for extracting molten slag and exhaust gas is provided on a lower side surface of the furnace main body. In general, the inside of the melting furnace is surrounded by a brick or the like, which is a standard refractory, and a water cooling jacket is provided outside the inside to cool the inside.

The exhaust gas discharged from the melting furnace 2 first passes through a combustion chamber 6 and then is sent to a cooling tower 7. Combustion chamber 6
In this method, air is supplied from a combustion air fan and a method of introducing high-temperature air is usually used, but a combustion burner may be provided. By the action of this combustion chamber,
Among the exhaust gas generated from the melting furnace 2, carbon monoxide CO,
Substances such as dioxins are burned and decomposed. Then, in the cooling tower 7, cooling is performed so that the exhaust gas can be further sent downstream for processing. As the cooling tower 7 (cooling tower), an apparatus of an air cooling type by blowing cooling air or a water cooling type by spraying cooling water can be used.

The exhaust gas that has passed through the cooling tower 7 is guided to a bag filter 8, which is a dust remover, and slaked lime or activated carbon may be added immediately before. In the bag filter 8, dust is removed and separated into exhaust gas and molten fly ash, and the molten fly ash is sent to a connected molten fly ash processing device or the like. As the dust removing device, besides the bag filter, a dust removing cyclone or the like can be used.

In the present embodiment, the exhaust gas that has passed through the bag filter 8 is supplied to a scrubber 9, and the acid gas is absorbed and removed by the scrubber 9, resulting in a clean exhaust gas. From the scrubber 9, smoke cleaning wastewater is discharged during purification. The purified exhaust gas is mixed with the incineration exhaust gas discharged from the bag filter 5 disposed downstream of the cooling tower 4. The mixed exhaust gas is discharged out of the system after being subjected to a denitration treatment by the denitration catalyst 10. As described above, according to the present embodiment, harmful substances such as CO and dioxins can be burned and decomposed at extremely effective timing from the exhaust gas generated from the melting furnace 2, so that the exhaust gas is released as safer. It becomes possible.

Embodiment (No. 2) FIG. 2 is a diagram showing an example of another processing system suitable for carrying out the exhaust gas processing method according to the present invention. In the present embodiment, similarly to the above-described embodiment (part 1), a part of the exhaust gas burned in the incinerator 1 is passed through the boiler 3 and the cooling tower 4 to a dust collecting device (such as a bag filter 5). Is sprayed with slaked lime before the bag filter 5. Then, it is separated into incineration exhaust gas and fly ash by the bag filter 5,
This fly ash is mixed with the main ash discharged directly from the incinerator 1 and is put into the melting furnace 2. Exhaust gas from the melting furnace 2 sequentially passes through the combustion chamber 6, the cooling tower 7, and a dust removing device (eg, a bag filter 8). The operation of these devices is the same as that of the first embodiment.

In the present embodiment, the exhaust gas from the bag filter 8 which is a dust removing device is mixed with the incineration exhaust gas discharged from the dust collecting device (the bag filter 5) and then sent to the scrubber 11. In the scrubber 11, the acidic gas is absorbed and removed, and becomes a clean exhaust gas, while the smoke washing wastewater at the time of purification is discharged. This purified exhaust gas is treated by a denitration catalyst for decomposing nitrogen oxides.
As a catalyst device having a denitration catalyst, a reaction tower, a catalyst-carrying bug, or the like can be used. According to the present embodiment,
The scrubber can also be used for treating incineration exhaust gas from an incinerator, and can be treated efficiently.

Embodiment (Part 3) FIGS. 3 and 4 are diagrams showing examples of another processing system suitable for carrying out the exhaust gas processing method according to the present invention.
In the embodiment of FIGS. 3 and 4, a part of the exhaust gas burned in the incinerator 1 is similar to the first embodiment.
When the dust is collected through the boiler 3 and the cooling tower 4 to the dust collector (eg, the bag filter 5), slaked lime is sprayed before the dust collector, and then the incineration exhaust gas and fly ash are removed by the dust collector. This fly ash is mixed with the main ash discharged directly from the incinerator 1 and then put into a melting furnace. Exhaust gas from the melting furnace 2 passes through a combustion chamber 6, a cooling tower 7, a dust removing device (eg, a bag filter 8) sequentially, passes through a scrubber 9, is mixed with the incineration exhaust gas, and is treated by a denitration catalyst. Here, in the present embodiment, the smoke washing drainage discharged from the scrubber 9 is sprayed to the cooling tower 4 or 7 in the preceding stage and used as cooling water.
That is, the discharged smoke washing drainage is not used as it is, but is used for spraying water or air with a cooling tower or the like. As a result, the amount of wastewater generated when performing exhaust gas treatment can be reduced, and the system can be made to have no drainage.

On the other hand, in this embodiment, since there is a possibility that mercury (Hg) may be concentrated in the system, means for discharging mercury to the outside of the system in the exhaust gas treatment of the melting furnace (activated charcoal spraying, Mercury removal) is required. Generally, unlike lead and cadmium, mercury cannot be collected by a bag filter or the like, but is scattered in a melting furnace. Since such mercury has a low boiling point and an extremely low adsorption ability to molten fly ash, it is difficult to substantially recover the mercury unless, for example, activated carbon or the like is used in the middle. Therefore, when using the smoke-washing wastewater in addition to the system of the first embodiment (part 1), the mercury is added to the system so that mercury does not accumulate (concentrate) inside the system as the operation continues. It is necessary to remove it outside.
Therefore, when returning the smoke washing wastewater as in the embodiment of FIG. 3, it is necessary to add the activated carbon before the dust remover (eg, the bag filter 8). Slaked lime can be added as needed.

The system shown in FIG. 3 uses the smoke washing wastewater as a coolant as it is. However, as in the system shown in FIG. 4, the smoke washing wastewater passes through the reverse osmosis membrane 12 and is used as a coolant. In some embodiments, In the embodiment of FIG. 4, the mercury is removed outside the system by the reverse osmosis membrane 12.
Activated carbon is different from the form of
Etc.) need not be added in the preceding stage. However, if necessary, activated carbon can be added in the same manner as slaked lime.

Embodiment (Part 4) FIGS. 5 and 6 are diagrams showing examples of another processing system suitable for carrying out the exhaust gas processing method according to the present invention.
In the embodiment of FIG. 5 and FIG. 6, as in the embodiment (2), a part of the exhaust gas burned in the incinerator 1
The slaked lime is sprayed before the dust collector (eg, the bag filter 5), and then separated into incineration exhaust gas and fly ash.
After being mixed with the main ash discharged directly from the furnace, it is charged into the melting furnace 2. The exhaust gas from the melting furnace 2 passes through the combustion chamber 6, the cooling tower 7, and the dust removing device 8 in that order, is mixed with the incineration exhaust gas, and then treated by the scrubber 11 and the denitration catalyst 10. Here, in the present embodiment, similarly to the above-described embodiment (No. 3), the smoke washing drainage discharged from the scrubber 11 is sprayed to the cooling tower 4 or 7 in the preceding stage and used as cooling water.

The system shown in FIG. 5 is an embodiment in which the wastewater of smoke cleaning is used as it is as a coolant.
In a stage after the melting furnace 2 and in a stage before the dust removing device 8, addition of activated carbon is essential. Slaked lime is added as needed. In addition, as in the system shown in FIG. 6, there is also an embodiment in which the smoke washing wastewater is passed through the reverse osmosis membrane 12 and then used as a coolant. Need not be added before the dust remover (eg, the bag filter 8). Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications and changes can be made without departing from the spirit of the present invention. is there.

[0020]

According to the present invention, the emission of dioxins can be effectively prevented by arranging each device effectively, such as providing a combustion chamber at the latter stage of the melting furnace. Further, the inside of the melting furnace can be kept in a reducing atmosphere, whereby the atmosphere becomes a low oxygen gas atmosphere and the heavy metals can be easily discharged outside. In this case, for the gas discharged from the melting furnace,
Although the concentration of carbon monoxide increases, the concentration of carbon monoxide can be suppressed to a low level by the combustion chamber in the subsequent stage. Further, according to the present invention, the running cost required for treating exhaust gas from an incinerator can be kept low. And it becomes possible to perform the exhaust gas treatment by the ash melting furnace continuously and safely for a long period of time.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a system for implementing an exhaust gas treatment method according to the present invention.

FIG. 2 is a diagram showing an example of another system for implementing the processing method according to the present invention.

FIG. 3 is a diagram showing an example of another system for implementing the processing method according to the present invention.

FIG. 4 is a diagram showing an example of another system for implementing the processing method according to the present invention.

FIG. 5 is a diagram showing an example of another system for implementing the processing method according to the present invention.

FIG. 6 is a diagram showing an example of another system for implementing the processing method according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Incinerator 2 Melting furnace 3 Waste heat boiler 4 Temperature reduction tower 5 Dust collection device (Bag filter) 6 Combustion chamber 7 Temperature reduction tower 8 Dust removal device (Bag filter) 9 Scrubber 10 Denitration catalyst 11 Scrubber 12 Reverse osmosis membrane

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B01D 53/94 F23J 15/00 E F23G 5/44 ZAB B01D 53/36 ZAB F23J 1/00 101A 15/00 F23J 15/00 H (72) Inventor Susumu Nishikawa 1-8-1 Koura, Kanazawa-ku, Yokohama-shi, Kanagawa Prefecture Inside the Mitsubishi Research Institute of Mitsubishi Heavy Industries, Ltd. F-term in Yokohama, Ltd. F-term (reference)

Claims (6)

[Claims] When a part of the exhaust gas burned in an incinerator is passed through a boiler and a cooling tower to a dust collecting device, slaked lime is sprayed at a preceding stage of the dust collecting device. A method of separating the incineration exhaust gas and fly ash by a dust collector, mixing the fly ash with the incineration ash discharged directly from the incinerator, and then charging the incinerator with a melting furnace. An exhaust gas treatment method for an ash melting furnace, wherein the exhaust gas passes through a combustion chamber, a cooling tower, and a dust removing device, passes through a scrubber, is mixed with the incineration exhaust gas, and is treated by a denitration catalyst. 2. When a part of the exhaust gas burned in the incinerator is passed to a dust collector via a boiler and a cooling tower, slaked lime is sprayed at a stage preceding the dust collector, and A method of separating the incineration exhaust gas and fly ash by a dust collector, mixing the fly ash with the incineration ash discharged directly from the incinerator, and then charging the incinerator with a melting furnace. An exhaust gas treatment method for an ash melting furnace, wherein the exhaust gas sequentially passes through a combustion chamber, a cooling tower, and a dust removal device, is mixed with the incineration exhaust gas, and then is treated by a scrubber and a denitration catalyst. 3. The exhaust gas treatment method for an ash melting furnace according to claim 1, wherein the smoke washing wastewater discharged from the scrubber is sprayed to any one of the cooling towers. 4. The ash melting according to claim 1, wherein the smoke washing wastewater discharged from the scrubber is passed through a reverse osmosis membrane and then sprayed to any one of the cooling towers. Furnace exhaust gas treatment method. 5. When a part of the exhaust gas burned in the incinerator is passed through a boiler and a cooling tower to a dust collecting device, slaked lime is sprayed at a preceding stage of the dust collecting device. A processing system in which the incineration exhaust gas and fly ash are separated by a dust collector, the fly ash is mixed with incineration ash discharged directly from the incinerator, and then charged into a melting furnace. An exhaust gas treatment system for an ash melting furnace, wherein exhaust gas passes through a combustion chamber, a cooling tower, and a dust removing device, passes through a scrubber, is mixed with the incinerated exhaust gas, and is treated by a denitration catalyst device. 6. When a part of the exhaust gas burned in the incinerator is passed through a boiler and a cooling tower to a dust collecting device, slaked lime is sprayed at a stage preceding the dust collecting device. A processing system in which the incineration exhaust gas and fly ash are separated by a dust collector, the fly ash is mixed with incineration ash discharged directly from the incinerator, and then charged into a melting furnace. An exhaust gas treatment system for an ash melting furnace, wherein the exhaust gas sequentially passes through a combustion chamber, a cooling tower, and a dust removal device, is mixed with the incineration exhaust gas, and then is treated by a scrubber and a denitration catalyst device.