JP3454770B2 - Dioxin removal method and dioxin removal agent - Google Patents

Description

Detailed Description of the Invention

[0001]

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

[0002]

In an incinerator such as a garbage incinerator, organic compounds such as phenol, benzene and acetylene, chlorinated aromatic compounds such as chlorophenol and chlorobenzene, and dioxin precursors such as chlorinated alkyl compounds are burned during combustion. The body develops. These dioxins precursors will be present in the incineration ash and exhaust gas as dioxins due to its catalytic action when fly ash coexists, so conventionally, for the method for removing dioxins in incineration ash and exhaust gas,
Many suggestions have been made.

Further, in a refuse incinerator, etc., a large amount of hydrogen chloride (vinyl chloride plastic mixed in the materials to be incinerated, water-soluble chlorine such as sodium chloride and calcium chloride, and organic chlorine other than vinyl chloride are burned ( HCl) is generated, which causes air pollution and metal corrosion. Therefore, a treatment facility for removing HCl in exhaust gas is provided. As a method of removing this HCl, an alkaline agent (usually slaked lime) is blown into the exhaust gas from the incinerator at the flue,
A dry or semi-dry method in which the neutralization product is collected together with fly ash, and the exhaust gas from the incinerator is led to a wet smoke washing tower, and the exhaust gas is wetted with alkaline water (usually sodium hydroxide) in the wet smoke washing tower. There is a wet method of spraying aqueous solution) to absorb HCl in alkaline water. Compared to the dry method, the wet method has the disadvantage that wastewater treatment is required,
At present, there are few incinerators that employ a wet smoke washing tower, but the gas-liquid reaction is better than the dry method of gas-solid reaction, so the reaction efficiency is good and the fly ash from the dust collector is removed. There is an advantage that the amount of emissions is small and the HCl concentration of exhaust gas can be suppressed to 10 ppm or less, and future expansion is expected.

In many cases, the wet smoke washing tower is provided at the final stage of the 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 influence on the concentration of dioxins in the stack exhaust gas that is subject to regulation. I'm giving. In addition, since dioxins are hydrophobic, they may be adsorbed and desorbed to the rubber or resin running inside the wet smoke washing tower or to the plastic filler through the smoke wash water. It is known to increase.

On the other hand, a case where powdered activated carbon is suspended in the smoke wash water in the wet smoke wash tower to remove dioxins accumulated in the smoke wash tower and reduce the concentration of dioxins in the exhaust gas. Has been reported (Chemosphere 3
2: 159-168 (1996)). This test was planned in MWI-Amsterdam, the Netherlands, and was conducted by carrying out the smoke washing with 1 g / L of activated carbon retained in the circulating water of the wet smoke washing tower. As a result, in the case of no activated carbon, the smoke washing was carried out. Dioxin concentration of tower inlet gas 0.38 to 1.54 ng-TEQ / Nm ³ ,
Dioxin concentration of outlet gas 1.12 to 2.74 ng
-TEQ / Nm ³ and the concentration of dioxins are increased, whereas when activated carbon is applied, the concentration of dioxins in the smoke-washing tower inlet gas is 0.06 to 0.54 ng-TEQ / Nm ³ and the concentration of dioxins in the outlet gas is 0.08. ~ 0.14 ng-T
EQ / Nm ³ and dioxins concentration are reduced.

Further, the adsorption performance of activated carbon used for removing dioxins has also been studied, and it is disclosed in Japanese Patent Laid-Open No.
JP-A No. 1-244658 discloses that the activated carbon used mainly for being sprayed to the flue of an exhaust gas process by a dry system has a pore volume of 10 to 16Å and a pore volume of 0.1 mL / g.
It has been proposed to use powdered activated carbon as described above.

[0007]

When powdered activated carbon is used by suspending it in the smoke washing water of a wet smoke washing tower to remove dioxins in exhaust gas, clogging and wear of pipes and spray nozzles, dead space, etc. Of activated carbon in the wash water due to sedimentation and accumulation in the wash water, malfunction of the wash water circulation pump,
Problems such as leak of activated carbon to chimney exhaust gas become a problem,
The reality is that stable effects cannot be obtained over a long period of time.

This is because the wet smoke washing tower has its original purpose of removing acid gas, and is not designed on the assumption that powdered activated carbon is suspended and sprayed in smoke washing water.

It is an object of the present invention to solve the above conventional problems, and particularly to provide a method for removing dioxins and a dioxins removing agent effective for removing dioxins by activated carbon in a wet smoke washing tower. To do.

[0010]

The method for removing dioxins according to the present invention is 150 to 350 and the average particle size is 20.
SV30 of 5% suspension is 50% or more at μm or less
Powdered activated carbon characterized that you supplied to a wet wash smoke tower.

[0011] The removal agent of dioxins of the present invention, 15
0 to 350 , with an average particle size of 20 μm or less, 5%
The suspension is characterized by comprising powdered activated carbon having an SV30 of 50% or more .

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 iodine adsorption amount, methylene blue adsorption amount, specific surface area, and pore volume. In the above-mentioned JP-A No. 11-244658, the pore volume is taken up among them. It is used as an adsorption index.

However, since dioxins are medium-sized molecules having a molecular weight of about 300 to 450, the adsorption performance cannot be accurately evaluated by the above-mentioned general adsorption index of activated carbon. For example, diameters of 10 to 16 Å Dioxins cannot be adsorbed efficiently even with activated carbon having a pore volume of 0.1 mL / g or more.

As a result of intensive studies on the adsorption mechanism of activated carbon for dioxins, the present inventors have found that the sites where such medium-molecule dioxins are adsorbed are mainly intermediate pores (macropores) having a pore diameter of 20 to 200Å. And mesopores (pore diameter of 200Å or more) that are the introduction part to such intermediate pores
That is, the pore volume of the mesopores and mesopores is evaluated, and what is appropriate as an index showing the adsorption performance of activated carbon for dioxins is the molasses number that measures the decolorizing power of special molasses. The present invention has been completed by finding that there is a correlation between the number and the ability to adsorb and remove dioxins, and that an activated carbon having a molasses number of 150 to 350 has an excellent effect of adsorbing and removing dioxins. .

[0015] The present invention is particularly suitable for the removal of dioxins in the exhaust gas in the wet washing smoke column, in this case, additional
In addition, the abrasion resistance of SUS-304 by the blast test is 0.
01g / cm ² Oh Rukoto is preferable below.

Thus, the molasses number is 150 to 3
5 0 pores or intermediate pores developed in, by the addition of activated carbon suitable for adsorption and removal of dioxins Araikemuri circulating water can be removed efficiently dioxins in the wet wash smoke tower. Also, SUS by blast test
-304 has a low wear resistance of 0.01 g / cm ² or less, and an average particle size of 20 μm or less, and S of 5% suspension.
By applying activated carbon having a V30 of 50% or more, which is difficult to settle, problems such as clogging and wear of pipes and nozzles, failure of a circulation pump, and accumulation of activated carbon can be avoided, and stable treatment can be performed for a long time.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the method for removing dioxins and the removing agent of the present invention will be described in detail below.

The molasses number is a measured value of the decolorizing power of special molasses, and a large value means that the molecular weight is 200.
Adhesive power for medium to high molecular weight compounds of about 10,000 to 10000 is low, and conversely, low adsorbent power for medium to high molecular weight compounds is high.

The molasses number is 150 to 3.
If the activated carbon is 50, good dioxin adsorption performance can be obtained. The molasses number of activated carbon is particularly preferably in the range of 150 to 250.

Molasses number is molasses decolorizing test method N
It is a numerical value measured by STM 2.19, and shows the number of mg of sample activated carbon required to decolorize a certain amount of molasses which can be decolorized with 350 mg of A8100 activated carbon serving as a standard. 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 Kratzina Fern
t Klaienaveen).

Molasses number range of 150-350
And a 5% suspension with an average particle size of 20 μm or less
The powdered activated carbon according to the present invention having SV30 of 50% or more may be injected into a flue in a dry exhaust gas treatment process, and is not limited to removal of dioxins in exhaust gas. However, it can be effectively applied to the removal of dioxins from wastewater, sludge, and other substances containing dioxins, but is particularly effective for the removal of dioxins from the exhaust gas in the exhaust gas treatment process of the wet smoke washing method. , in this case, activated carbon, the molasses number is good Mashiku 150
In the range of up to 250, and further SU by blast test
Abrasive S-304 is 0.01 g / cm ² or less der Rukoto is preferred.

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

When powdered activated carbon is applied to the wet smoke washing tower, it is not sufficiently dispersed or suspended in the circulating water depending on the activated carbon, and it is accumulated in the dead space in the wet smoke washing tower or the activated carbon slurry preparation tank and circulated. The activated carbon concentration in water may not be maintained stably. Usually, the activated carbon concentration in the smoke wash circulation water is 50 to 2000 ppm, preferably 500 to 1000.
It is desirable to maintain the concentration in ppm, but a large amount of such deposits requires a larger amount of activated carbon to maintain a predetermined suspended concentration, which increases the processing cost and also periodic deposit removal. Is required. In order to maintain an appropriate concentration in the smoke wash circulating water, it is necessary to use activated carbon that does not easily settle. Therefore, the SV30 of the 5% suspension is 50% or more, preferably 60% or more, and the average particle diameter 20μm or less, preferably using those which are 5 to 15 [mu] m.

The activity <br/> charcoal molasses number 150-35 0, i.e. the suspension characteristics at the middle hole or holes are often activated carbon
Activated carbon having, more preferably, in the case of producing an activated carbon having the above Hardness raw materials is a major factor, specifically suited peat, lignite, wood is. Also, it is affected by the activation method, and steam activation at 900 ° C. or higher is suitable for activating peat charcoal and lignite charcoal. Phosphoric acid, zinc chloride, etc. are used for activating wood charcoal, and 500 to 6
Chemical activation with treatment at 00 ° C is suitable.

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

In order to treat dioxins in an incineration facility with such activated carbon, for example, the following methods can be adopted. In particular, by using the method and A reliable effect of removing dioxins can be obtained. The activated carbon slurry is poured into the circulation pipe of the washing water of the wet washing tower, the washing water storage tank or the like. Direct dry injection into the exhaust gas of the flue in front of the wet smoke washing tower.

When any of the above methods is adopted, and when and are used together, the concentration of activated carbon in the smoke wash water of the wet smoke wash tower is 50 to 200.
It is preferable to inject activated carbon so that the amount becomes 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 waste, industrial waste, medical waste, etc., but can be used in a dioxin discharge process employing a wet smoke washing tower in the exhaust gas treatment process. Other sintering furnaces, electric furnaces,
It is well applicable to zinc recovery process, aluminum refining process, etc.

[0029]

EXAMPLES The present invention will be described more specifically with reference to Examples and Comparative Examples below.

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

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

[0032]

[Table 1]

Example 3, Comparative Example 3 Molasses number 340, average particle size 12 μm, 5% suspension SV30 52%, SUS by blast test
-304 abrasion resistance (blast test value) is 0.005 g /
cm ² and 0.015 g / cm ² and is activated carbon E, 1000 mg of F to wash the smoke circulating water A industrial waste incinerator / L
It was held, and continuous operation was carried out for one month each.

After the end of the operation, the diameter of the spray nozzle 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 wear, but the activated carbon E did not show a large change.

In each case, the concentration of dioxins in the inlet gas of the wet smoke washing tower was ³ ng-TEQ / Nm ^3, whereas the concentration of dioxins in the outlet gas was 0.8 ng-TE.
A good dioxin removal effect was obtained with Q / Nm ³ .

[0036]

[Table 2]

Example 4, Comparative Example 4 Molasses number 200, blast test value 0.00
2g / cm ² , average particle size 10 μm, SV of 5% suspension
30 is 60% activated carbon G, molasses number and blast test value are equivalent, average particle size is 22 μm, SV30 is 30%
Activated carbon H of 10
The wet smoke washing tower was operated by adding 10 kg to m ³ .

The activated carbon concentration of the smoke wash circulating water after 2 hours was measured, and the results are shown in Table 3. As is clear from Table 3, the theoretical value is 1000 mg / L, whereas the activated carbon G is 980 mg.
/ L and this concentration is maintained, while activated carbon H is 5
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 can be efficiently removed by activated carbon having a pore distribution suitable for adsorptive removal of dioxins. be able to.

In particular, according to the method of claim 2 and the removing agent of claim 4, using activated carbon which is excellent in the adsorptive removal performance of dioxins and has a small hardness and is hard to settle, a serious trouble is caused. In the wet smoke washing tower, stable and efficient treatment can be continued for a long time without causing the above.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI B01J 21/18 B01D 53/34 ZAB C02F 1/28 53/36 G (72) Inventor Nao Tanabe 3chome Nishishinjuku, Shinjuku-ku, Tokyo No. 4-7 Kurita Industry Co., Ltd. (56) Reference JP-A-11-217207 (JP, A) JP-A-11-70320 (JP, A) JP-A-11-199215 (JP, A) JP Sho 59-44089 (JP, B2) (58) Fields investigated (Int.Cl. ⁷ , DB name) B01D 53/34 B01J 20/20

Claims (2)

(57) [Claims] [Claim 1] molasses number is 150-350 Der
SV30 of 5% suspension with an average particle size of 20 μm or less
Method for removing but dioxins characterized that you supply powdered activated carbon is 50% or more in a wet wash smoke tower. 2. The method of claim 1] molasses number is 150-350 Der
SV30 of 5% suspension with an average particle size of 20 μm or less
The agent for removing dioxins in exhaust gas is characterized in that it is made of powdered activated carbon whose content is 50% or more .