JP2001219032A - Dioxin removal method and dioxin removal agent - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To efficiently remove dioxins contained in exhaust gas discharged from a wet smoke tower. SOLUTION: The molasses number is 350 or less,
The wear resistance of SUS-304 by blast test is 0.01
Dioxins in exhaust gas are removed by supplying powdered activated carbon having a g / cm ² or less, an average particle diameter of 20 μm or less, and a 5% suspension having an SV30 of 50% or more to a wet smoke washing tower.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an agent for removing dioxins, and more particularly, to polychlorinated-p-dibenzodioxins (PCDD) and polychlorinated dioxins in exhaust gas generated in an exhaust gas treatment step by a wet smoke washing method. The present invention relates to a method and an agent for efficiently removing organic chlorine compounds such as dibenzofurans (PCDF) and polychlorinated biphenyls (PCB) (hereinafter, these are collectively referred to as “dioxins”).

[0002]

BACKGROUND OF THE INVENTION In incinerators such as refuse incinerators, during combustion, organic compounds such as phenol, benzene, and acetylene; chlorinated aromatic compounds such as chlorophenol and chlorobenzene; and dioxin precursors such as chlorinated alkyl compounds. The body develops. These dioxin precursors, when fly ash coexists, becomes a dioxin due to its catalytic action and is present in incinerated ash and exhaust gas.Conventionally, regarding the method of removing dioxin in incinerated ash and exhaust gas,
Many suggestions have been made.

Further, in a refuse incinerator or the like, a large amount of hydrogen chloride is produced by burning vinyl chloride plastics, water-soluble chlorine such as sodium chloride and calcium chloride, and organic chlorines other than vinyl chloride mixed in the incineration material. HCl) is generated and causes air pollution and metal corrosion. Therefore, a treatment facility for removing HCl in exhaust gas is provided. As a method for removing HCl, an alkaline agent (usually slaked lime) is blown into the exhaust gas from the incinerator through a flue,
Dry or semi-dry method for collecting the neutralized product together with fly ash, and exhaust gas from the incinerator into a wet smoke tower, where the alkaline gas (usually sodium hydroxide) Aqueous solution) to absorb HCl in alkaline water. The wet method has the disadvantage of requiring wastewater treatment compared to the dry method,
At present, there are few incinerators that use wet smoke washing towers, but because of the gas-liquid reaction compared to the dry method of gas-solid reaction, the reaction efficiency is good, and fly ash from the dust collector is good. There is an advantage that the emission amount is small and the HCl concentration of the exhaust gas can be suppressed to 10 ppm or less, and further expansion is expected.

[0004] Wet smoke washing towers are often provided at the final stage of an exhaust gas treatment process, and the concentration of dioxins in the exhaust gas at the outlet of the wet smoke washing tower has a great effect on the concentration of dioxins in the chimney exhaust gas to be regulated. Have given. In addition, since dioxins are hydrophobic, they may be adsorbed and desorbed to the rubber or resin running or plastic filler inside the wet-type smoke cleaning tower through the smoke-washing water. It is known to increase.

[0005] On the other hand, a case in which dioxins accumulated in a smoke-washing tower are removed by suspending powdered activated carbon in smoke-washing water in a wet-type smoke washing tower to reduce the concentration of dioxins in exhaust gas. (Chemosphere 3
2: 159-168 (1996)). This test is planned at MWI-Amsterdam, The Netherlands, and 1 g / L in the circulating water of wet smoke tower.
The activated carbon was held to perform smoke washing. As a result, in the case of no activated carbon, the concentration of dioxins in the gas at the inlet of the smoke washing tower was 0.38 to 1.54 ng-TEQ / N
m ³ , outlet gas dioxin concentration 1.12 to 2.7
While the concentration of dioxins increases to 4 ng-TEQ / Nm ³ , when activated carbon is used, the concentration of dioxins in the gas at the inlet of the smoke washing tower is 0.06 to 0.54 ng-TEQ / N.
m ³ , concentration of dioxins in outlet gas from 0.08 to 0.1
4 ng-TEQ / Nm ³ and dioxin concentration are reduced.

Further, studies have been made on the adsorption performance of activated carbon used for removing dioxins.
Japanese Patent Application Laid-Open No. 1-244658 discloses that activated carbon mainly used for spraying in a flue gas of a flue gas process by a dry method has a pore volume of 0.1 mL / g having a pore diameter of 10 to 16 °.
It has been proposed to use the above powdered activated carbon.

[0007]

In the case where powdered activated carbon is used by suspending it in smoke water of a wet-type smoke tower to remove dioxins in exhaust gas, clogging and abrasion of pipes and spray nozzles, dead space, and the like. Sedimentation, the activated carbon concentration in the smoke wash water has decreased due to sedimentation, malfunction of the smoke wash water circulation pump,
The adverse effects such as leakage of activated carbon into the stack exhaust gas become a problem,
The fact is that stable effects cannot be obtained over a long period of time.

[0008] This is because the wet-type smoke tower is originally intended to remove acidic gas, and is not designed on the assumption that powdered activated carbon is suspended and sprayed in smoke-washing water.

An object of the present invention is to solve the above-mentioned conventional problems, and in particular, to provide a dioxin removal method and a dioxin removal agent which are effective for removing dioxins by activated carbon in a wet smoke tower. I do.

[0010]

The method for removing dioxins of the present invention is characterized by using activated carbon having a molasses number of 350 or less.

The dioxin-removing agent of the present invention is characterized by containing activated carbon having a molasses number of 350 or less.

Activated carbon is used in a wide range of fields as an adsorbent. As a general adsorption index of activated carbon, there are items such as an iodine adsorption amount, a methylene blue adsorption amount, a specific surface area, and a pore volume. In the above-mentioned JP-A-11-244658, the pore volume is taken up. This is used as an adsorption index.

However, since dioxins are medium molecules having a molecular weight of about 300 to 450, the general adsorption index of activated carbon cannot evaluate the adsorption performance correctly. Activated carbon having a pore volume of 0.1 mL / g or more cannot always adsorb dioxins efficiently.

The inventors of the present invention have conducted intensive studies on the mechanism of adsorption of activated carbon on dioxins. As a result, the sites where such medium-molecular dioxins are adsorbed are mainly intermediate pores (macropores) having a pore diameter of 20 to 200 °. And a meso-hole (a hole diameter of 200 mm or more) which is an introduction portion to such an intermediate hole.
That is, the pore volume of the intermediate pores and the mesopores was evaluated, and an appropriate index indicating the adsorption performance of activated carbon to dioxins is a molasses number obtained by measuring the decolorizing power of special molasses. There is a correlation between the number and the adsorption removal ability of dioxins, and if the molasses number is 350 or less activated carbon,
It is found that it has an excellent effect of adsorbing and removing dioxins,
The present invention has been completed.

The present invention is particularly suitable for removing dioxins from exhaust gas in a wet smoke tower, in which case the molasses number is 350 or less and the abrasion of SUS-304 by blast test is 0.01 g / g. cm ² or less, an average particle diameter of 20μm or less, SV30 5% suspension it is preferred to supply the powdered activated carbon is 50% or more in a wet wash smoke tower.

As described above, pores having a molasses number of 350 or less and intermediate pores or more develop, and by adding activated carbon suitable for adsorbing and removing dioxins to the smoke washing circulating water, dioxin can be efficiently produced in a wet smoke washing tower. Can be removed. In addition, SUS-
304 has a low abrasion of 0.01 g / cm ² or less and an average particle diameter of 20 μm or less, and a 5% suspension SV
By applying activated carbon which hardly settles to 50% or more, problems such as clogging and abrasion of pipes and nozzles, failure of a circulation pump, accumulation of activated carbon, and the like can be avoided, and stable treatment can be performed for a long period of time.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of a method for removing dioxins and a remover according to the present invention will be described in detail.

The molasses number is a measured value of the decolorizing power of special molasses.
A low adsorption power for medium to high molecular compounds of about 10000 to about 10000 indicates a high adsorption power for medium to high molecular compounds.

Thus, if the activated carbon has a molasses number of 350 or less, a good dioxin adsorption performance can be obtained. The molasses number of activated carbon is especially 1
It is preferably in the range of 50 to 250.

The molasses number is determined by the molasses bleaching power test method N
It is a value measured by STM 2.19 and indicates the number of mg of sample activated carbon required to decolorize a certain amount of molasses that can be decolorized with 350 mg of standard A8100 activated carbon. The activated carbon used in the present invention is this standard activated carbon A810
It has molasses decolorizing power equal to or higher than 0. This standard activated carbon A
8100 is Norit Krazina Fern (Nori
t Klaienaveen).

The activated carbon according to the present invention may be injected into a flue in a dry exhaust gas treatment process.
It can be effectively applied not only to the removal of dioxins in exhaust gas, but also to the removal of dioxins in wastewater, sludge, and other dioxin-containing substances. In this case, the activated carbon has a molasses number of 350 or less, preferably 150 to 250.
SUS-30 by blast test
4 has an abrasion of 0.01 g / cm ² or less and an average particle size of 2
It is preferable that the SV30 of a 5% suspension of 0 μm or less is 50% or more.

That is, since activated carbon is generally hard particles, as described above, clogging and abrasion of pipes and nozzles of smoke washing water,
This may cause troubles for the smoke water circulation pump, etc. When such a trouble occurs, it is necessary to stop the incineration and cope with it, which is a serious problem for the incinerator. For this reason, the hardness of the activated carbon used in a wet smoke washing tower must be low, and specifically, 500 g /
In a blast test in which the weight change of the metal was measured by spraying the metal surface at a rate of hr for 4 hours, the wear amount of SUS-304 was 0.01 g / cm ² or less, particularly 0.002 g /
It is desired that the material has a relatively low hardness such as cm ² or less.

Further, when powdered activated carbon is applied to a wet smoke washing tower, some activated carbon is not sufficiently dispersed and suspended in circulating water, and is deposited in a dead space in the wet smoke washing tower or an activated carbon slurry preparation tank and circulated. Activated carbon concentration in water may not be maintained stably. Usually, the activated carbon concentration in the smoke washing circulating water is 50 to 2000 ppm, preferably 500 to 1000 ppm.
Although it is desirable to maintain the concentration in ppm, such a large amount of sediment requires a large amount of activated carbon to maintain a predetermined suspended concentration, which increases the treatment cost, and also requires periodic sediment removal. Is required. In order to maintain an appropriate concentration in the circulating smoke water, it is necessary to use activated carbon which is difficult to settle. Therefore, the SV30 of the 5% suspension is 50% or more, especially 60% or more, and the average particle size is 30% or more. Is preferably 20 μm or less, particularly preferably 5 to 15 μm.

In the case of producing activated carbon having a molasses number of 350 or less, that is, activated carbon having many pores of intermediate pores or more, more preferably, activated carbon having the above hardness and suspension characteristics, raw materials are a major factor. Lignite,
Wood is suitable. It is also affected by the activation method, and steam activation of 900 ° C. or more is suitable for activating peat coal and lignite coal, and phosphoric acid or zinc chloride is used for activating wood charcoal. Is suitable for chemical activation.

Commercially available activated carbon suitable for the present invention include:
Norit GLA20 manufactured by Norit Japan Co., Ltd. can be used.

In order to treat dioxins in an incineration plant with such activated carbon, for example, the following method can be adopted. In particular, by using the above method together, the method can be further improved. A reliable dioxin removal effect can be obtained. The activated carbon slurry is injected into a circulation pipe or a storage tank for smoke water in a wet-type smoke tower. Direct dry injection into flue gas from the flue upstream of the wet scrubber.

In any of the above-mentioned methods and in the case of using both of them, the activated carbon concentration in the smoke water of the wet-type smoke tower is 50 to 200.
It is preferable to inject the activated carbon so as to be 0 mg / L, particularly 500 to 1000 mg / L.

The method and the removing agent of the present invention are not limited to incineration facilities for municipal solid waste, industrial waste, medical waste, etc., but are also used in a dioxin discharge process using a wet smoke tower in an exhaust gas treatment process. If you have other sintering furnaces, electric furnaces,
Applicable to zinc recovery process, aluminum refining process, etc.

[0029]

The present invention will be described more specifically below with reference to examples and comparative examples.

Examples 1 and 2 and Comparative Examples 1 and 2 In an A industrial waste incinerator with a treatment amount of 100 t / day, powdered activated carbons A to D having molasses numbers of 200, 340, 700 and 1000 were added to a wet smoke tower (inlet). Exhaust gas dioxin concentration: 2.3 ng-TEQ / Nm ³ ) 100 mg / Nm ³ was sprayed on the flue in front of the exhaust gas for 3 days, and the dioxin concentration in the exhaust gas at the outlet of the wet smoke washing tower was measured on the third day. .
Consideration was given to the operation of the incinerator so that the combustion state during the spraying of activated carbon was almost the same.

As a result, as shown in Table 1, as the molasses number increases, the concentration of dioxins in the exhaust gas at the outlet of the wet-type smoke washing tower increases.
It can be seen that if the activated carbon is 50 or less, a good dioxin removal effect can be obtained.

[0032]

[Table 1]

Example 3, Comparative Example 3 The molasses number was 340, the average particle size was 12 μm, the SV30 of a 5% suspension was 52%, and the SUS was subjected to a blast test.
-304 has a wear property (blast test value) of 0.005 g /
cm ² and 0.015 g / cm ² of activated carbons E and F in the smoke circulating water of an A industrial waste incinerator at 1000 mg / L.
The operation was continued for one month each.

After the operation was completed, the spray nozzle diameter of the smoke washing circulating water was measured, and the results are shown in Table 2. As is clear from Table 2, the activated carbon F showed a remarkable increase in the nozzle diameter due to abrasion, but the activated carbon E did not show a significant change.

In each case, the concentration of dioxins in the gas at the inlet of the wet-type smoke washing tower was ³ ng-TEQ / Nm3, while the concentration of dioxins in the gas at the outlet was 0.8 ng-TE.
Good dioxin removal effect in the Q / Nm ³ was obtained.

[0036]

[Table 2]

Example 4 and Comparative Example 4 A molasses number of 200 and a blast test value of 0.00
2 g / cm ² , average particle size 10 μm, SV of 5% suspension
30 is activated carbon G of 60%, molasses number and blast test value are equivalent, average particle size is 22 μm, SV30 is 30%
Of activated carbon H from A industrial waste incinerators
to m ^3, was carried out the operation of the wet wash smoke tower was 10kg added.

The activated carbon concentration of the circulating smoke washing water after 2 hours was measured, and the results are shown in Table 3. As is clear from Table 3, 980 mg of activated carbon G was used for the theoretical value of 1000 mg / L.
/ L and this concentration, while activated carbon H
Sedimentation was severe at 90 mg / L.

[0039]

[Table 3]

[0040]

As described above in detail, according to the method and agent for removing dioxins of the present invention, dioxins are efficiently removed by activated carbon having a pore distribution suitable for adsorption and removal of dioxins. be able to.

In particular, according to the method of the second aspect and the removing agent of the fourth aspect, the use of activated carbon, which is excellent in dioxin adsorption and removal performance and has low hardness and is unlikely to settle, causes serious troubles. , And stable and efficient processing can be continued for a long time in the wet-type smoke washing tower.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B01J 21/18 B01D 53/34 134E C02F 1/28 53/36 G (72) Inventor: Hisashi Tanabe Shinjuku, Tokyo 3-4-7 Nishi-Shinjuku, Kurita F-term (reference) in Kurita Kogyo Co., Ltd. BB01 CC38 CD02 EA04 4G066 AA05B BA09 BA20 BA38 CA33 DA02 4G069 AA02 BA08A BA08B CA11 CA19 EB18X EB18Y EC14Y EC15Y EC27 ED03

Claims (4)

[Claims] 1. A method for removing dioxins, comprising using activated carbon having a molasses number of 350 or less. 2. A molasses number of 350 or less,
The wear resistance of SUS-304 by blast test is 0.01
g / cm ² or less, an average particle diameter of 20μm or less, 5% suspension SV30 is method for removing dioxins in exhaust gas and supplying the powdered activated carbon is 50% or more in a wet wash smoke tower . 3. A dioxin remover comprising activated carbon having a molasses number of 350 or less. 4. A molasses number of 350 or less,
The wear resistance of SUS-304 by blast test is 0.01
An agent for removing dioxins in exhaust gas, comprising powdered activated carbon having a g / cm ² or less, an average particle diameter of 20 μm or less, and an SV30 of a 5% suspension of 50% or more.