JP7202271B2 - Combustion exhaust gas treatment method and device - Google Patents

Description

The present invention relates to a combustion exhaust gas treatment method and apparatus, and in particular, by using activated carbon that hardly adsorbs dioxins, the content of dioxins in the collected fly ash is reduced, and a subsequent dioxin decomposition device is used to reduce the content of dioxins. The present invention relates to a combustion exhaust gas treatment method and apparatus that reliably decomposes dioxins in the exhaust gas.

In general, the exhaust gas after incineration in a waste incineration facility contains dust derived from ash, chlorine, sulfur, etc., and hazardous substances such as mercury and dioxins. It is discharged to the atmosphere after being removed by dusting or decomposition equipment.
In the dust collector and the decomposer, dioxins are removed by detoxification by reacting with an alkaline agent or acid gas, or by blowing activated carbon into the dust collector.
In addition, the fly ash collected by this dust collector contains a large amount of harmful substances such as mercury and dioxins, so it is prevented from being eluted by melting and solidifying, cement solidification, chemical treatment, acid or other solvent methods, etc. processing is taking place.
Techniques of Patent Documents 1 and 2 are known as techniques related to exhaust gas treatment in such waste incineration facilities.

JP 2014-213304 A JP 2013-107023 A

However, in the techniques of Patent Documents 1 and 2, the fly ash collected by the dust collector contains a large amount of dioxins, and a standard value is set for the content of dioxins. The problem is what to do when this standard value is exceeded.
The present invention has been made in order to solve such conventional problems, and the object thereof is to use activated carbon that does not easily adsorb dioxins, so that the collected fly ash contains dioxins. The object of the present invention is to provide a flue gas treatment method and apparatus capable of reducing the dioxin rate and reliably decomposing dioxins in the flue gas by a subsequent dioxin decomposing device.

As a means for achieving the above object, the combustion exhaust gas treatment method according to claim 1 uses as an adsorbent activated carbon having pores of 2 nm or less to which dioxins are less likely to be adsorbed, to capture mercury and dust in the exhaust gas. a collection step of collecting, a decomposition step of reheating the exhaust gas that has passed through the collection step to decompose dioxins, and in the collection step, introducing the activated carbon together with the exhaust gas into the bag filter of the filtration type dust collector. and a step of recovering activated carbon that has collected mercury and dust in the exhaust gas.

In the method for treating combustion exhaust gas according to claim 2 , activated carbon containing a pore volume of 2 nm or less in which dioxins are difficult to adsorb is at a ratio of 1/3 or more of the entire pores as an adsorbent. A collection step of collecting mercury and dust in the collection step, a decomposition step of reheating the exhaust gas that has passed through the collection step to decompose dioxins, and a bag filter of a filtration type dust collector in the collection step It is characterized by having a step of introducing the activated carbon together with the exhaust gas and recovering the activated carbon that has collected mercury and dust in the exhaust gas.

The combustion exhaust gas treatment apparatus according to claim 3 is an apparatus used in the treatment method according to claim 1 or 2 , which includes a filtration type dust collector using an adsorbent and a heating device for heating the exhaust gas after the collection process. and a dioxin decomposing device for decomposing dioxins.

In the method for treating combustion exhaust gas according to claim 1, there is provided a collection step of collecting dust mainly composed of mercury in the exhaust gas using an adsorbent that hardly adsorbs dioxins, and exhaust gas that has passed through the collection step. and a decomposition step for decomposing the dioxins in the fly ash, the content of dioxins in the fly ash recovered in the collection step is reduced.
Therefore, the concentration of dioxins in the collected fly ash is suppressed to a predetermined reference value, and the environmental load is reduced during its treatment.

In the method for treating combustion exhaust gas according to claim 1 , since activated carbon having pores of 2 nm or less is used in the collecting step, dioxins having a large molecular size are not or hardly adsorbed by the activated carbon. Therefore, the content of dioxins in the collected fly ash is reduced.

In the method for treating combustion exhaust gas according to claim 2 , in the collection step, activated carbon containing pore volume of 2 nm or less is used at a ratio of 1/3 or more of the total pores, so mesopores and macropores are used. Even when activated carbon containing some pores is used, the effect of reducing dioxins in collected fly ash is achieved.

In the combustion exhaust gas treatment method of the present application, the exhaust gas is reheated to decompose the dioxins in the decomposition process. It can be returned to the normal temperature and can be reliably decomposed in the subsequent dioxin decomposing unit.

The apparatus for treating combustion exhaust gas according to claim 3 is equipped with a filter-type dust collector using an adsorbent, a heating device for heating the exhaust gas after the collection process, and a dioxin decomposition device for decomposing dioxins. The content of dioxins in the ash can be kept low, and the dioxins in the exhaust gas can be reliably decomposed.

1 is a block diagram showing a schematic configuration of a combustion exhaust gas treatment apparatus according to an embodiment; FIG. 4 is a graph showing cumulative pore volume distribution of activated carbon. It is an explanatory view of a waste disposal facility.

As shown in FIG. 3, the flue gas treatment apparatus of this embodiment is installed in a waste treatment facility equipped with a stoker furnace and operated.
The stoker furnace 1 puts the waste stored in the waste pit 2 into the waste hopper 3, supplies air from the lower part of the combustion device, dries and heats it on the fire grate 4 (stoker), stirs and moves it, and burns it. It is configured.

The flue gas generated by combustion in the stoker furnace 1 passes through a boiler 5 and a temperature reducing device 6, is treated by a filtration type dust collector 8 after introducing activated carbon from an activated carbon storage silo 7, and is recycled by an induced draft fan 9. After being sent to a heater 10 and passing through a dioxin decomposition device 11 (catalytic reaction tower), it is finally discharged from a chimney 12 as a clean gas to the outside air.

As shown in FIG. 1, the combustion exhaust gas treatment apparatus according to the present embodiment includes a filtration type dust collector 8 using activated carbon, a reheater 10 for reheating the exhaust gas that has passed through the filtration type dust collector, and after reheating A dioxin decomposing device 11 for decomposing dioxins is provided.
Exhaust gas after burning the waste is reduced in temperature to 200° C. or less and introduced into the filtration type dust collector.
A filter-type dust collector is provided with a bag filter, into which activated carbon is introduced together with exhaust gas.
In the bag filter, the exhaust gas and the activated carbon come into contact with each other, and the pores of the activated carbon adsorb mercury, harmful substances, and dust.
Mercury, harmful substances, and activated carbon that has adsorbed dust in the collection process using these filter-type dust collectors are recovered as fly ash.

また、ダイオキシン類とは、ポリ塩化ジベンゾパラジオキシン（PCDD）、ポリ塩化ジベンゾフラン（PCDF）、ダイオキシン様ポリ塩化ビフェニル（DL-PCB）の総称であり、これらは塩素で置換された２つのベンゼン環という共通の構造を持っている。そして、このダイオキシン類は分子サイズが大きいため、活性炭のミクロ孔には吸着されにくい性質を有している。 Here, activated carbon has micropores, and the micropores possessed by activated carbon are classified as follows according to their size.

Dioxins are a general term for polychlorinated dibenzoparadioxin (PCDD), polychlorinated dibenzofuran (PCDF), and dioxin-like polychlorinated biphenyl (DL-PCB), which are two benzene rings substituted with chlorine. have a common structure. Since dioxins have a large molecular size, they have the property of being difficult to be adsorbed by the micropores of activated carbon.

In this embodiment, in the step of collecting dust by a filtration type dust collector, only activated carbon having pores with a diameter of 2 nm (nanometers) or less is used, and dioxins having a large molecular size are not adsorbed by the activated carbon.
Since activated carbon having pores with a diameter of 2 nm or less is used as described above, dioxins are not adsorbed, and the content of dioxins in the fly ash collected by the filter type dust collector is kept low.

After passing through the filter type dust collector, the exhaust gas is heated by a reheater to 180° C. or higher, which is suitable for decomposing dioxins, and introduced into the dioxin decomposing device.
Reheating is based on a heat source such as steam generated with waste incineration.
In a dioxin decomposition apparatus, exhaust gas is introduced into a honeycomb-shaped treatment tank, and dioxins are decomposed by contact with a catalyst while passing through this treatment tank over several meters.
Exhaust gas from which dioxins are decomposed is discharged into the atmosphere through a chimney as clean gas.
In this embodiment, since dioxins are not collected by the filtration type dust collector, the content of dioxins in the fly ash is low and can be recovered without exceeding the standard value set by local governments.

Next, a method for treating combustion exhaust gas according to a second embodiment will be described.
In the above example, only activated carbon having pores with a diameter of 2 nm or less was used, but in the present example, activated carbon in which some mesopores and macropores are mixed is used.
In this embodiment, activated carbon containing pores with a diameter of 2 nm or less at a rate of one-third or more of the entire pores is used.
Activated carbon that adsorbs mercury, harmful substances, and dust in the collection process with a filtration dust collector is recovered as fly ash.
Content of dioxins in fly ash collected by a filtration type dust collector even when using activated carbon containing pore volume with a diameter of 2 nm or less at a ratio of 1/3 or more of the total pore volume A rate reduction effect is realized.
FIG. 2 is a graph showing cumulative pore volume distribution of activated carbon used as an example in this embodiment. In this graph, the horizontal axis is the pore diameter, and the vertical axis is the integrated pore volume.

Next, a method for treating combustion exhaust gas according to the third embodiment will be described.
The combustion exhaust gas treatment method of the third embodiment is a method of using zeolite as the adsorbent (activated carbon) described in the above embodiments.
Zeolite has pores inherent to its structure, and is generally a porous body with micropores of 0.2 to 1.0 nm corresponding to the molecular diameter.
By using this zeolite, dioxins having a large molecular size are not adsorbed, and the content of dioxins in the fly ash collected by the filter type dust collector is kept low.
Other configurations and methods are the same as those of the above embodiment.

Although the embodiment of the present invention has been described above, the specific configuration of the present invention is not limited to this embodiment. be
For example, the present invention includes the use of activated carbon containing pores with a diameter of 2 nm or less at a ratio of 40% or more, or a majority of the total pores.
Moreover, the reheater and the dioxin decomposing device described in the above embodiments are not limited to this, and are included in the present invention even if they employ known techniques.
In addition, the exhaust gas temperature described in the above embodiment can be set as appropriate, and the exhaust gas that has been reduced in temperature to 165°C in the temperature reduction tower is further reduced in temperature to 155°C, introduced into the filtration type dust collector, and reheated. The present invention also includes a method of heating to 180° C. with a vessel and introducing it into a dioxin decomposition apparatus.
Furthermore, the exhaust gas, which has been reduced in temperature to 195°C in the temperature reduction tower, is further reduced in temperature to 185°C, introduced into the filtration type dust collector, and introduced directly into the dioxin decomposition unit without passing through the reheater. are included in the present invention.

1 Stoker Furnace 2 Garbage Pit 3 Garbage Hopper 4 Fire Grate 5 Boiler 6 Temperature Reduction Device 7 Activated Carbon Storage Silo 8 Filtration Dust Collector 9 Induced Draft Ventilator 10 Reheater 11 Dioxin Decomposition Device 12 Chimney

Claims (3)

a collection step of collecting mercury and dust in the exhaust gas using activated carbon having pores of 2 nm or less, which hardly adsorbs dioxins, as an adsorbent ;
a decomposition step of reheating the exhaust gas that has passed through the collection step to decompose dioxins;
A method for treating flue gas, characterized in that, in the collecting step, the activated carbon is introduced into a bag filter of a filtration type dust collector together with the flue gas, and the activated carbon that has collected mercury and dust in the flue gas is recovered. . A collection step of collecting mercury and dust in exhaust gas using activated carbon as an adsorbent containing pore volume of 2 nm or less, which hardly adsorbs dioxins, at a ratio of 1/3 or more of the total pores. When,
a decomposition step of reheating the exhaust gas that has passed through the collection step to decompose dioxins;
A method for treating flue gas, characterized in that, in the collecting step, the activated carbon is introduced into a bag filter of a filtration type dust collector together with the flue gas, and the activated carbon that has collected mercury and dust in the flue gas is collected. . An apparatus used in the treatment method according to claim 1 or 2, comprising a filtration type dust collector using an adsorbent, a heating device for heating exhaust gas after the collection process, and a dioxin decomposition device for decomposing dioxins. A flue gas treatment device comprising:

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