JP2006095355A - Method and apparatus for decomposition of dioxins - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for decomposition of dioxins permitting removal of dioxins down to a concentration lower than the standard value of 3-ng-TEQ/g through a relatively simple treatment even in cases of solid materials containing dioxins in a high concentration. <P>SOLUTION: The method comprises mixing and heating the solid materials containing dioxins while adding a dioxin-decomposing agent comprising an alkali metal salt of a 1-3C carboxylic acid to the materials twice or more times at different addition times. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a method and an apparatus for decomposing dioxins in a dioxin-containing substance, and in particular, mixing a dioxin-decomposing agent comprising an alkali metal salt of a carboxylic acid having 1 to 3 carbon atoms with a dioxin-containing substance. The present invention relates to a method and an apparatus for decomposing dioxins by heating while heating.

Dioxins are substances that are unintentionally generated during the synthesis of chemical substances and the combustion process of waste, and their sources are diverse. A wide range of toxic effects such as carcinogenicity, reproductive toxicity, and teratogenicity have been reported. In particular, reproductive toxicity is concerned that even a very low concentration may affect the living body. In addition to the strength of toxicity, it is a hardly decomposable substance, so once produced, it stays in the environment for a long time, and environmental pollution by dioxins has become a major social problem.

Soil and sludge contaminated with dioxins are solidified with cement and contain toxic substances. However, cement solidified products must be managed so that dioxins do not leak to the outside, and the use of cement solidified landfills is also limited. For this,
Methods that can be used effectively by decomposing and detoxifying harmful substances in soil and sludge contaminated with dioxins are being studied. For example, PCB contained in solid substances such as soil
As a method for decomposing aromatic halogen compounds such as dioxins, a method for decomposing aromatic halogen compounds in which sodium formate or potassium formate is added to a contaminated solid substance and heated to 300 to 450 ° C. has been proposed. (Patent Document 1). Further, as a treatment method for removing or detoxifying the organic chlorine compound contained in the object to be treated, a reducing agent addition step for adding a reducing agent containing a salt of formic acid or oxalic acid to the object to be treated, and a reducing agent There has been proposed a method for treating an organic chlorine compound, which includes a heating step of reducing or removing or detoxifying the organic chlorine compound by heating the added object to be treated (Patent Document 2).
JP-A-8-52454 JP 2001-259607 A

In the conventional method, when the fly ash containing dioxin at a high concentration is targeted, the decomposition rate is insufficient. In the “Special Law for Countermeasures against Dioxins” promulgated in 1999, the concentration standard value of dust related to waste incinerators was set to 3 ng-TEQ / g. For example, the concentration of dioxins is 100 ng-TEQ. / G of fly ash is reduced to 3 ng-TEQ / g, a decomposition rate of 97% is required. Even if a normal heat dechlorination apparatus is used, a dioxin-degrading agent such as sodium formate can be used. Even if used, it is not easy to achieve this decomposition rate.

In view of the above circumstances, the present invention removes dioxins to a low concentration of 3 ng-TEQ / g or less, which is a reference value, even for a solid substance containing dioxin at a high concentration by a relatively simple treatment. An object of the present invention is to provide a method and apparatus for decomposing dioxins.

The method for decomposing dioxins of the present invention (Claim 1) comprises heating a solid dioxin-containing substance while stirring, and a dioxin decomposing agent comprising an alkali metal salt of a carboxylic acid having 1 to 3 carbon atoms. The dioxins-containing substance is added a plurality of times at different addition times.

The method for decomposing dioxins according to claim 2 is characterized in that, in claim 1, the alkali metal salt of a carboxylic acid having 1 to 3 carbon atoms is sodium formate.

The method for decomposing dioxins according to claim 3 is characterized in that, in claim 1 or 2, the solid dioxins-containing substance is fly ash.

The apparatus for decomposing dioxins according to the present invention (Claim 4) is an apparatus for decomposing dioxins by heating a solid dioxin-containing substance while stirring, and is an alkali metal of a carboxylic acid having 1 to 3 carbon atoms. A chemical addition means provided at least in one place so that a dioxin-decomposing drug comprising a salt is added to the dioxin-containing substance, and an alkali metal salt of a carboxylic acid having 1 to 3 carbon atoms from the chemical addition means And a control means for controlling the drug addition means so that the dioxin-degrading drug is added to the dioxin-containing substance a plurality of times at different addition times.

The decomposition apparatus for dioxins according to claim 5 is characterized in that, in claim 4, the alkali metal salt of a carboxylic acid having 1 to 3 carbon atoms is sodium formate.

According to a sixth aspect of the present invention, there is provided the apparatus for decomposing dioxins according to the fourth or fifth aspect, wherein the solid dioxin-containing substance is fly ash.

According to the present invention, when heating while mixing a solid dioxin-containing substance, the dioxin-decomposing agent comprising an alkali metal salt of a carboxylic acid having 1 to 3 carbon atoms is added to the dioxin-containing substance. By adding different times, dioxins can be decomposed more effectively than adding a dioxin-degrading agent all at once.

The dioxins decomposition action by the dioxins decomposing agent comprising an alkali metal salt of a carboxylic acid having 1 to 3 carbon atoms is considered to be mainly caused by the thermal decomposition of the dioxin decomposing agent itself. To happen. If a chemical is added all at once, thermal decomposition products are generated all at once, and the portion that is wasted without contributing to the decomposition of dioxins increases, so even if a certain amount of chemical is added at a time, An improvement in decomposition rate cannot be expected. Moreover, since there is no supply of thermal decomposition products from new chemicals thereafter, it is considered that the thermal decomposition reaction is not significantly accelerated even if the heating time is extended. On the other hand, when a chemical is added several times at different addition times, the thermal decomposition product can be brought into contact with the dioxin-containing substance a plurality of times, so that it is considered that the decomposition of the dioxins preferably proceeds.

Hereinafter, embodiments of the method for decomposing dioxins and the apparatus for decomposing dioxins of the present invention will be described in detail.

In the present invention, “dioxins” means polychlorinated p-dibenzodioxins (P
CDD) and dioxins such as polychlorinated dibenzofurans (PCDF), organic compounds such as phenol, benzene and acetylene, dioxin precursors such as chlorinated aromatic compounds and chlorinated alkyl compounds such as chlorophenol and chlorobenzene, Alternatively, dioxin-related substances such as brominated dioxin and brominated diphenyl ether are also included.

Solid dioxin-containing substances include powdered activated carbon and dioxins added to adsorb fly ash and incineration ash and dioxins discharged from various incinerators such as garbage incinerators containing dioxins. Examples include contaminated soil.

Examples of the alkali metal salt of a carboxylic acid having 1 to 3 carbon atoms include sodium formate, potassium formate, sodium acetate, potassium acetate, sodium propionate, and potassium propionate. Among these, sodium formate is particularly preferable. is there.

Dioxins are efficiently decomposed by contacting with thermal decomposition products of alkali metal salts of carboxylic acids having 1 to 3 carbon atoms, so alkali metal salts of carboxylic acids having 1 to 3 carbon atoms are decomposed by dioxins. Those that cause thermal decomposition at temperature are preferred.

Since the alkali metal salt of a carboxylic acid having 1 to 3 carbon atoms is solid at room temperature, it is preferably mixed with a dioxin-containing substance in a powder state. However, the alkali metal salt of a carboxylic acid having 1 to 3 carbon atoms is highly hygroscopic, and when left in an air environment for a long time in a powder state with a large surface area, it absorbs moisture and the powder particles stick together and solidify. Cheap. Accordingly, it is preferable to mix a dehydrating agent such as zeolite, quicklime, silica gel, and magnesium carbonate or a fluidizing agent such as fats and oils with an alkali metal salt of a carboxylic acid having 1 to 3 carbon atoms to prevent caking.

Moreover, the particle size of the powder particle | grains of the dioxin decomposition | disassembly chemical | medical agent which consists of a C1-C3 carboxylic acid alkali metal salt becomes hygroscopic when it is too small, and it becomes easy to solidify, and a particle size is too large. And the mixing property with the object to be processed deteriorates. Specifically, it is preferable to contain 90% by weight or more of particles having a particle size of 20 μm to 5 mm, and more preferably 95% by weight or more of particles having a particle size of 20 μm to 5 mm.

In the method and apparatus for decomposing dioxins of the present invention, a solid object to be treated containing dioxins is mixed and heated, and the object to be treated is composed of an alkali metal salt of a carboxylic acid having 1 to 3 carbon atoms. Add the degradation agent in several batches. At that time, the heating temperature is preferably 300 to 450 ° C. If the heating temperature is less than 300 ° C., the thermal decomposition of the dioxins-decomposing agent becomes insufficient, and there is a possibility that the detoxification of the dioxins does not proceed completely. When the heating temperature exceeds 450 ° C., the organic matter in the object to be treated may be carbonized to cause a failure in the heating apparatus, and the heat energy may be wasted.

In the present invention, the dioxin-degrading agent is added to the object to be treated in several batches,
Although the quantity of the chemical | medical agent added at once changes also with the dioxin density | concentration in a to-be-processed object, it is preferable that it is 0.1-10 wt% with respect to a to-be-processed object, and it is 1-5 wt%. More preferred. Moreover, it is preferable that the addition frequency of the chemical | medical agent with respect to a to-be-processed object is 2-5 times, and it is more preferable that it is 2-3 times.

Moreover, although the heating time after adding a dioxin decomposition | disassembly chemical | medical agent to a to-be-processed object changes also with heating temperature, it is preferable that it is 1 to 30 minutes for every addition of chemical | medical agent once, and is 2 to 10 minutes. More preferably. If it is too short, decomposition will be insufficient, and if it is too long, the processing cost will become unnecessarily large.

The ash or soil treated according to the present invention is subjected to, for example, solidification treatment, packing in a drum can or storage, or landfill as it is or after performing the above-described heavy metal immobilization treatment.

A preferred embodiment of the dioxin decomposition apparatus of the present invention will be described with reference to FIGS. The dioxins decomposition apparatus in FIG. 1 is for batch processing of solid dioxins-containing substances. Although not shown, the reactor 1 is provided with stirring means such as a stirring blade and a fluidizing air blowing nozzle.

The solid dioxin-containing substance is charged into the reactor 1 from the workpiece supply unit 2 through the gate valve 6. After the required amount of dioxin-containing material is introduced into the reactor 1, the gate valve 6 is closed, and the dioxin-decomposing agent in the drug storage container 3 is added into the reactor 1 while stirring the dioxin-containing material. . The addition of the dioxin-decomposing agent is performed a plurality of times at intervals by the control means 9. The dioxins-decomposing agent is not only added in the apparatus, but the dioxins-decomposing agent may be mixed before putting the object to be processed into the apparatus.

After adding the dioxin-decomposing agent a required number of times, the discharge valve 7 at the bottom of the reactor 1 is opened, and the processed product is discharged. It is preferable that the gas discharged from the exhaust gas path at the top of the reactor 1 is returned to the flue before the dust collector, or the powder in the gas is recovered by a dust collecting means provided separately. The powder recovered by the dust collecting means is preferably returned to the workpiece supply unit 2 of the reactor 1. Reactor 1
Is heated to 300 to 450 ° C. by a heater or an air heater (not shown).

The dioxin decomposition apparatus in FIG. 2 is an apparatus for continuously treating a solid dioxin-containing substance.

Transfer means (not shown) such as a screw conveyor or an air slide is installed in a reactor 11 having a required length such as a cylindrical shape, and is supplied from the workpiece supply unit 12 into the harm reactor 11. The supplied solid dioxin-containing substance continuously moves in the reactor 1 toward the right in the figure, and is eventually discharged from the treatment product outlet 15 at the other end of the reactor 11. An exhaust gas passage 14 is also provided on the other end side. Although not shown, the reactor 11 is provided with a heater, 300
Heat to ~ 450 ° C. When the transfer means is an air slide, an air heater may be used as the heater.

In a portion between one end side and the other end side of the reactor 11, a plurality of (three in this embodiment) drug addition portions 16 a, 16 b, and 16 c are provided at intervals in the longitudinal direction of the reactor 11. is set up. The dioxins-decomposing drug in the drug storage container 13 is supplied to the adding units 16a, 16b, and 16c by the control means 19a, 19b, and 19c.

In addition, you may add a dioxin decomposition | disassembly chemical | medical agent before adding in the reactor 11. FIG.
In this case, it is preferable to provide a mixing means such as a kneader or a stirrer for mixing the solid dioxin-containing substance and the dioxin-decomposing agent. The reactor 11 may also be a casing of a pulverizer such as a ball mill or a rod mill. In this case, the dioxin decomposition agent is added while the solid content is pulverized. The reactor 11 may be a kiln wall.

  The exhaust gas and powder discharged from the exhaust gas passage 14 are processed in the same manner as in the case of FIG.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.
Example 1
35 g of municipal waste incineration fly ash with a dioxin concentration of 193 ng-TEQ / g and sodium formate [Kanto Chemical Co., Ltd., special grade, white powder, purity 98.0 wt% or more, average particle size 200 μm] 1
. 75 g (5 wt%) was thoroughly mixed in a mortar, and then placed in a three-necked flask heated to 350 ° C., and the fly ash temperature was maintained at 350 ° C. for 10 minutes after the temperature of the fly ash reached 350 ° C. Thereafter, 1.75 g of sodium formate was further added to the fly ash, and the temperature of the fly ash was similarly maintained at 350 ° C. for 10 minutes after the fly ash temperature reached 350 ° C. Table 1 shows the result of measuring the dioxin concentration in the obtained processed product.
Comparative Example 1
35g of municipal waste incineration fly ash with the same dioxin concentration 193ng-TEQ / g as Example 1.
And 3.5 g (10 wt%) of sodium formate were sufficiently mixed in a mortar, and then placed in a three-necked flask heated to 350 ° C., and maintained at 350 ° C. for 10 minutes after the fly ash temperature reached 350 ° C. Table 1 shows the result of measuring the dioxin concentration in the obtained processed product.
Comparative Example 2
The treatment was performed under the same conditions as in Comparative Example 2 except that the holding time at 350 ° C. was 20 minutes. Table 1 shows the result of measuring the dioxin concentration in the obtained processed product.
Example 2
The treatment was performed under the same conditions as in Example 1 except that the concentration of dioxins in the municipal waste incineration fly ash as the object to be treated was 25.8 ng-TEQ / g. Table 1 shows the result of measuring the dioxin concentration in the obtained processed product.
Comparative Example 3
Municipal waste incineration fly ash 35 with the same dioxin concentration of 25.8 ng-TEQ / g as in Example 2.
g and 3.5 g (10 wt%) of sodium formate were sufficiently mixed in a mortar, and then placed in a three-necked flask heated to 350 ° C., and maintained at 350 ° C. for 10 minutes after the fly ash temperature reached 350 ° C. Table 1 shows the result of measuring the dioxin concentration in the obtained processed product.
Comparative Example 4
The treatment was performed under the same conditions as in Comparative Example 3 except that the holding time at 350 ° C. was 20 minutes. Table 1 shows the result of measuring the dioxin concentration in the obtained processed product.

According to Table 1, in Example 1 and Example 2 in which sodium formate was added in two portions, the dioxins concentration of the treated fly ash was 1.8 ng-TEQ / g and 0.27 ng-TEQ, respectively.
The decomposition rate of dioxins has reached 99.1% and 98.9%, respectively, and the reduction of the concentration of dioxins that sufficiently satisfies the target value of 3.0 ng-TEQ / g has been achieved. I understand that. On the other hand, in Comparative Example 1 and Comparative Example 3 in which sodium formate was added all together, the dioxins concentration of the treated fly ash was 12.7 ng-TEQ / g, 7.0 n, respectively.
The decomposition rates of g-TEQ / g and dioxins are 93.4% and 72.9%, respectively, which is far from the target value of 3.0 ng-TEQ / g, and is incomplete or insufficient as a decomposition treatment. It was a result. Also in Comparative Example 2 and Comparative Example 4 in which the heating time was doubled compared to Comparative Example 1 and Comparative Example 3 and the same treatment for 20 minutes as in Example 1 and Example 2 was performed, the target value was 3.0 ng- TE
It can be seen that the decomposition rate is not far from Q, and the decomposition rate cannot be greatly improved by simply extending the heating time.

It is the schematic which shows an example of the decomposition | disassembly apparatus of the dioxins of this invention. It is the schematic which shows another example of the decomposition | disassembly apparatus of the dioxins of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,11 Reactor 2,12 Processed object supply part 3,13 Chemical storage container 4,14 Exhaust gas path 5,15 Processed object outlet 6,7,8 Valve 9,19a, 19b, 19c Control means 16a, 16b, 16c medicine addition part

Claims (6)

A solid dioxin-containing substance is heated with stirring, and a dioxin-decomposing agent composed of an alkali metal salt of a carboxylic acid having 1 to 3 carbon atoms is added to the dioxin-containing substance several times at different times. A method for decomposing dioxins, comprising: The method for decomposing dioxins according to claim 1, wherein the alkali metal salt of a carboxylic acid having 1 to 3 carbon atoms is sodium formate. The method for decomposing dioxins according to claim 1 or 2, wherein the solid dioxin-containing substance is fly ash. A device for decomposing dioxins by heating solid dioxins-containing substances with stirring, and a dioxin-decomposing agent comprising an alkali metal salt of a carboxylic acid having 1 to 3 carbon atoms is added to the dioxins-containing substances In such a case, the drug addition means provided at least in one place and the dioxin decomposition agent comprising an alkali metal salt of a carboxylic acid having 1 to 3 carbon atoms added to the dioxin-containing substance from the drug addition means at different times. And a control means for controlling the drug addition means so that it is added a plurality of times. The apparatus for decomposing dioxins according to claim 4, wherein the alkali metal salt of a carboxylic acid having 1 to 3 carbon atoms is sodium formate. 6. The apparatus for decomposing dioxins according to claim 4, wherein the solid dioxin-containing substance is fly ash.

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