JP2001179052A - Method and device for treating exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a device for treating exhaust gas, in which dioxins are surely removed from exhaust gas containing dioxins of high concentration and also post-treatment after removal is made easy. SOLUTION: Alkali chemicals sent from an alkali chemicals feeder 40 are added to exhaust gas and acidic gas starting with hydrogen chloride is solidified and removed by a dust collector 10. Thereafter, a powdery carbonaceous adsorbent is introduced from a carbonaceous adsorbent feeder 23 and granular dioxins contained in exhaust gas are adsorbed. Both the powdery carbonaceous adsorbent and gaseous dioxins are adsorbed or stuck to the granular carbonaceous adsorbent filled in a moving bed type adsorption reactor 20 and removed. The carbonaceous adsorbent of the adsorption reactor 20 is regenerated in a desorption regenerator 21 and thereafter sorted by particle diameter in a separator 22 and respectively returned to the adsorption reactor 20 and the carbonaceous adsorbent feeder 23.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method and an apparatus for treating exhaust gas, and more particularly to a method and an apparatus for treating exhaust gas containing harmful chlorine compounds such as dioxins.

[0002]

2. Description of the Related Art Exhaust gas from incinerators, particularly from general waste incinerators, contains dioxins and their precursors, such as hydrogen chloride. As a method for removing such a harmful chlorine compound, JP-A-9-234333 and JP-A-11-234333 are known.
Slaked lime and activated carbon powder as disclosed in Japanese Patent No. 114374 are injected into a flue, and calcium chloride is formed and solidified by the reaction of slaked lime and hydrogen chloride, and dioxins are adsorbed by activated carbon. A method of removing an object with a dust collector such as a bag filter is known.

[0003]

However, according to these methods, when the concentration of dioxin in the exhaust gas is high, a large amount of activated carbon powder needs to be injected, so that the running cost increases. . at the same time,
Post-treatment of a large amount of activated carbon powder adsorbing dioxin is also a problem.

[0004] In view of the above problems, the present invention provides an exhaust gas treatment method and apparatus which can surely remove dioxins from exhaust gas containing high concentrations of dioxins and also facilitate post-treatment after removal. As an issue.

[0005]

In order to solve the above problems, the exhaust gas treatment method according to the present invention comprises the steps of (1) adding an alkali agent to exhaust gas and reacting with an acidic component in the exhaust gas to form a solid. A step of obtaining a reaction product; and (2) a step of removing solids containing the reaction product by a dust collector;
(3) a step of injecting a powdery carbonaceous adsorbent into the exhaust gas passing through the dust collector to adsorb particulate organic chlorine compounds onto the carbonaceous adsorbent; and (4) adsorbing the powdery carbonaceous substance. The exhaust gas containing the adsorbent is passed through a moving bed type adsorption tower filled with a granular carbonaceous adsorbent to remove the powdery carbonaceous adsorbent and gaseous organic chlorine compounds in the exhaust gas. And (5) a step of desorbing and regenerating the carbonaceous adsorbent taken out of the adsorption tower, and (6) a step of returning the desorbed and regenerated particulate carbonaceous adsorbent to the adsorption tower. It is characterized by having.

On the other hand, an exhaust gas treatment apparatus according to the present invention
(1) an alkali agent adding means for adding an alkali agent to the exhaust gas; (2) a dust collector to which the exhaust gas after the addition of the alkali agent is guided; and (3) a powdery carbon in the exhaust gas passing through the dust collector. Carbonaceous adsorbent injection means for injecting the porous adsorbent,
(4) a moving bed type adsorption tower which is filled with a granular carbonaceous adsorbent and into which exhaust gas after injection of a powdery carbonaceous adsorbent is introduced; and (5) a carbonaceous adsorbent taken out of the adsorption tower A desorber / regenerator for desorbing / regenerating carbon, (6) first returning means for returning the desorbed / regenerated granular carbonaceous adsorbent to the adsorption tower,
It is characterized by having.

According to the present invention, by adding an alkaline agent to exhaust gas, first, an acidic component such as hydrogen chloride reacts with the alkaline agent to produce a solid reaction product, which is removed by the dust collector. You. Since the solids collected by this dust collector hardly contain dioxins, post-treatment is easy. By injecting the powdery carbonaceous adsorbent into the exhaust gas after the treatment, among the dioxins in the exhaust gas, mainly particulate dioxins are adsorbed by the powdery carbonaceous adsorbent. Subsequently, by guiding this exhaust gas to a moving bed type adsorption tower, the remaining gaseous dioxins of the dioxins in the exhaust gas are adsorbed by the particulate carbonaceous adsorbent in the adsorption tower, The powdery carbonaceous adsorbent that adsorbs dioxins in the form of particles is also adsorbed and removed. By heating the carbonaceous adsorbent having adsorbed dioxins in the desorption / regeneration tower, the dioxins are thermally decomposed and the carbonaceous adsorbent is also regenerated. Since it is not necessary to adsorb all of the dioxins with the powdery carbonaceous adsorbent, even when the concentration of dioxins is high, the amount of the powdery carbonaceous adsorbent to be used is small. Also, solid matter after removal from exhaust gas,
Post-treatment of the carbonaceous adsorbent becomes easy.

[0008] The present invention further comprises a step of separating the desorbed and regenerated carbonaceous adsorbent according to the particle size, and injecting the separated powdery carbonaceous adsorbent into the exhaust gas passing through the dust collector. A treatment method, separation means for separating the desorbed / regenerated carbonaceous adsorbent by particle size, and second return means for guiding the separated powdery carbonaceous adsorbent to the carbonaceous adsorbent injection means, An exhaust gas treatment device further provided may be used. By reusing the powdery carbonaceous adsorbent after desorption and regeneration,
Further, running costs can be reduced.

An exhaust gas treatment method for additionally injecting a new powdery carbonaceous adsorbent having high activity into exhaust gas passing through a dust collector, and injecting a new powdery carbonaceous adsorbent having high activity into carbonaceous adsorbent The exhaust gas treatment apparatus may further include a carbonaceous adsorbent supply unit for leading the unit. The adsorptive performance of the regenerated carbonaceous adsorbent decreases with regeneration, but by additionally introducing a highly active carbonaceous adsorbent, the overall adsorptive performance can be maintained.

[0010]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG.
It is a schematic diagram showing a preferred embodiment of an exhaust gas treatment device according to the present invention.

The apparatus comprises a dust collector 10 and an adsorption reactor 20.
And the chimney 30 are connected in series by lines L11 and L12. Exhaust gas to be treated is introduced into the dust collector 10 via a line L10, and is, for example, a dry dust collector such as a bag filter or an electric dust collector. The line L30 is connected to a line L30 for introducing an alkaline drug from the alkaline drug supply device 40. For example, slaked lime (Ca (OH)
₂ ) is used. On the other hand, a line L25 for introducing a powdery carbonaceous adsorbent, for example, activated carbon having an average particle diameter of 1 mm or less, from the carbonaceous adsorbent supply device 23 is connected to the line L11. And this carbonaceous adsorbent supply device 23
Is connected to the carbonaceous adsorbent storage tank 24 by a line L24.

The adsorption reactor 20 contains therein a particulate carbonaceous adsorbent, for example, having an average particle diameter of 4 mm or more, preferably 8 to 9 m.
This is a cross-flow moving bed type adsorption reactor in which m activated carbons are filled, and the activated carbon is brought into contact with the exhaust gas while being moved in a direction orthogonal to the introduced exhaust gas. The lower part of the adsorption reactor 20 is connected to a desorption / regeneration unit 21 via a line L20. The desorption / regeneration unit 21 has a structure in which the introduced activated carbon is moved and heated in an inert gas atmosphere.
The desorber / regenerator 21 is connected to a separator 22 via a line L21. The separator 22 separates the introduced activated carbon into granular activated carbon and powdered activated carbon in accordance with the particle size. A line L22 for returning the granular activated carbon to the adsorption reactor 22 and a powder L L23 leading to the adsorbent supply device. Further, the gas line L40 extending from the desorption / regeneration unit 21 is a line L40.
They are connected upstream from the connection with the ten lines L30.

Next, the operation of this embodiment, that is, the exhaust gas treatment method according to the present invention will be described. Line L
Slaked lime is introduced into the exhaust gas flowing through the line 10 from the alkaline chemical supply device 40 via the line L30. This allows
The acid gas in the exhaust gas, particularly hydrogen chloride, reacts with slaked lime to produce insoluble calcium chloride and other calcium salts, which are solidified in the gas. The exhaust gas thus treated is guided to the dust collector 10 and passed therethrough, thereby removing dust and solidified acidic gas components in the exhaust gas. The removed dust and calcium salt are treated separately. At this time, since dioxins are hardly contained in the dust and calcium salt, the subsequent treatment is easy.

The exhaust gas passing through the dust collector 10 is supplied to a line L1.
During the flow through 1, the mixture is mixed with activated carbon powder sent from the carbonaceous adsorbent supply device 23 via the line L25. Thereby, mainly particulate dioxins in the exhaust gas are adsorbed on the activated carbon powder. The exhaust gas after treatment is supplied to the adsorption reactor 20
The activated carbon powder and the gaseous dioxins remaining in the exhaust gas are adhered or adsorbed on the surface of the granular activated carbon in the adsorption reactor 20. As a result, most of the dioxins can be removed. The exhaust gas thus treated is discharged into the atmosphere via the line L12 and the chimney 30.

Activated carbon (including activated carbon powder) having adsorbed dioxins in the adsorption reactor 20 is sent to a desorption / regeneration unit 21 via a line L20 and is heated in an inert gas. Activated carbon itself is regenerated by desorbing and decomposing harmful substances such as adsorbed dioxins. The desorbed gas containing chlorine gas, sulfurous acid gas and the like is sent to the line L10 via the line L40, solidified as a calcium salt by the addition of an alkali agent, and collected and removed by the dust collector 10.

Regenerated activated carbon (including activated carbon powder)
It is sent to the separator 22 and is divided into granular activated carbon and powdered activated carbon. The granular activated carbon is circulated by returning to the upper part of the adsorption reactor 20 via the line L22, and the powdered activated carbon is circulated through the line L23.
This is circulated by returning to 3. Since the adsorption performance of activated carbon decreases with desorption / regeneration, a new high-activity activated carbon powder is supplied from the carbonaceous adsorbent storage tank 24 to the carbonaceous adsorbent supply device via the line L24 in order to compensate for the decrease in performance. 23.

In the present invention, the use of activated carbon powder having a high removal efficiency of particulate dioxins and granular activated carbon having a high removal efficiency of gaseous dioxins is used in combination to obtain granular,
The advantage is that gaseous dioxins can be efficiently removed, and the amount of each used can be reduced compared to the case where activated carbon powder and granular activated carbon are used alone, and the equipment can be compact. There is.

Instead of circulating the activated carbon powder as in this embodiment, the used activated carbon powder may be guided to an incinerator for treatment. If the dioxin concentration is not high, the addition of new activated carbon may be omitted.

As the carbonaceous adsorbent, activated carbon, activated coke, activated char obtained by adding a binder to a carbon-containing substance such as coal, molding, and then heat-treating or activating with steam, air, or the like; Vanadium, iron,
A carbonaceous adsorbent supporting a compound such as copper can be suitably used. In addition, as the alkaline agent, hydroxides of calcium and magnesium, oxides thereof, carbonates thereof, and minerals and dusts containing these compounds such as limestone and dolomite can be used.

[0020]

EXAMPLE The present inventor conducted a comparative experiment to confirm the improvement of dioxin removal efficiency and the effect of reducing the amount of carbonaceous adsorbent of the exhaust gas treatment apparatus and the exhaust gas treatment method according to the present invention. Will be described.

Example 1 Dioxins were 80 ng / m ^{3 in the} apparatus shown in FIG.
(Normal) including an exhaust gas (about 40000m ³ / h) to the slaked lime 0.8~1.6g / m ³ (Normal) was charged activated carbon powder (average particle diameter 15μm) 80~100mg / m ³ (Nor
mal) Input and processed. The adsorption reactor has an average particle size of 4
40000 liters of granular activated carbon having a diameter of 3 mm were filled, and the residence time was 300 to 600 hours. In the desorption / regeneration unit, the treatment was performed at 400 to 450 ° C. for a residence time of 1 to 2 hours.

The dioxin concentration in the dust collected by the dust collector is 0.05 to 0.1 ng / g dust, and the dioxin concentration after passing through the adsorption reactor is 0.016 ng / g, which is the detection limit.
m ³ (Normal) or less, and the decomposition rate in the desorption / regeneration unit was 99.9%.

Comparative Example 1 Slaked lime and activated carbon powder were mixed, introduced into an exhaust gas having the same composition and flow rate as in the example, and recovered by a dust collector. The dioxin concentration in the dust collected by the dust collector is 0.5 ng / g dust, and the dioxin concentration after passing through the dust collector is 3 to 8 ng / m.
³ (Normal). In order to reduce the dioxin concentration in the exhaust gas after the treatment to the same level as in the examples, the required injection amount of activated carbon powder is 300 to 350 mg / m ³ (Normal).
Therefore, it was required to be three to four times as large as in the example.

Comparative Example 2 Exhaust gas treatment was carried out in the apparatus shown in FIG. 1 without introducing activated carbon powder. Other conditions were set the same as in the example.

The dioxin concentration in the dust collected by the dust collector is 0.05 to 0.1 ng / g dust, and the dioxin concentration after passing through the adsorption reactor is 0.1 ng / m ³ (Normal).
And the decomposition rate in the desorption / regeneration unit was 99.9%.

From the results of the above comparative experiments, it can be seen that the present invention improves the dioxin removal efficiency and activates carbon (carbonaceous adsorbent).
The effect of reducing the amount of used was confirmed.

[0027]

As described above, according to the present invention, powdery carbonaceous material is adsorbed after adding an alkaline agent to exhaust gas to solidify acid gas such as hydrogen chloride and removing it by a dust collector. Adsorbent to adsorb particulate dioxins in exhaust gas, and adsorb powdery carbonaceous adsorbent and gaseous dioxins to particulate carbonaceous adsorbent packed in a moving bed type adsorption reactor Or because it is attached and removed, dioxins can be removed efficiently,
Post-treatment is also easy, and the amount of adsorbent or the like used can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of an exhaust gas treatment apparatus according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Dust collector, 20 ... Adsorption reactor, 21 ... Desorption / regenerator, 22 ... Separator, 23 ... Carbonaceous adsorbent supply apparatus, 30
... Chimney, 40 ... Alkaline chemical supply device.

Claims (6)

[Claims] An exhaust gas treatment method for removing an organic chlorine compound in a combustion exhaust gas, wherein an alkali agent is added to the exhaust gas and reacted with an acidic component in the exhaust gas to obtain a solid reaction product. Removing the solid content containing the reaction product by a dust collector; and injecting a powdery carbonaceous adsorbent into the exhaust gas passing through the dust collector to remove the particulate organic chlorine compound. A step of adsorbing the powdery carbonaceous adsorbent onto the carbonaceous adsorbent, and passing the exhaust gas containing the powdery carbonaceous adsorbent through a moving bed type adsorption tower filled with a granular carbonaceous adsorbent, thereby passing the powdery carbonaceous adsorbent. Removing the carbonaceous adsorbent and the gaseous organochlorine compound in the exhaust gas; desorbing and regenerating the carbonaceous adsorbent taken out of the adsorption tower; Returning the carbonaceous adsorbent to the adsorption tower An exhaust gas treatment method comprising: 2. The method according to claim 1, further comprising the step of separating the desorbed / regenerated carbonaceous adsorbent according to particle diameter, and injecting the separated powdery carbonaceous adsorbent into the exhaust gas passing through the dust collector. Item 7. An exhaust gas treatment method according to Item 1. 3. The exhaust gas treatment method according to claim 1, wherein a powdery carbonaceous adsorbent having high activity is additionally injected into the exhaust gas passing through the dust collector. 4. An exhaust gas treatment device for removing an organic chlorine compound in a combustion exhaust gas, comprising: an alkali agent adding means for adding an alkaline agent to the exhaust gas; and a dust collector to which the exhaust gas after the addition of the alkali agent is guided. A carbonaceous adsorbent injection means for injecting a powdery carbonaceous adsorbent into the exhaust gas passing through the dust collector; and a granular carbonaceous adsorbent filled with the particulate carbonaceous adsorbent, A moving bed type adsorption tower into which exhaust gas after injection is introduced, a desorption / regeneration device for desorbing / regenerating the carbonaceous adsorbent in the adsorption tower, and a granular carbonaceous adsorbent after desorption / regeneration. An exhaust gas treatment device comprising: first return means for returning to the adsorption tower. 5. A separating means for separating the desorbed / regenerated carbonaceous adsorbent according to particle diameter, and a second return for guiding the separated powdery carbonaceous adsorbent to the carbonaceous adsorbent injection means. The exhaust gas treatment device according to claim 4, further comprising: means. 6. The exhaust gas treatment apparatus according to claim 4, further comprising a carbonaceous adsorbent supply unit for guiding a powdery carbonaceous adsorbent having high activity to the carbonaceous adsorbent injection unit.