JP2001310113A - Process and device for decomposing organic matter in exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process and a device for efficiently decomposing organic matters contained in exhaust gas when the exhaust gas from an incinerator, or the like, is cooled. SOLUTION: When the exhaust gas exhausted from the incinerator, or the like, is cooled while preventing the re-synthesizing of dioxins, or the like, hydrogen peroxide is atomized in exhaust gas under the presence of ferrous ions, and the exhaust gas is cooled while oxidative destruction of composing heat-to- decompose organic matters such as dioxin precursors, and the like, contained in the exhaust gas is carried out.

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 apparatus for chemically decomposing hardly decomposable organic substances such as dioxin contained in exhaust gas from an incinerator or the like.

[0002]

2. Description of the Related Art Exhaust gas treatment in an incinerator will be described with reference to FIG.

[0003] Garbage and the like are burned in a fluidized bed incinerator 30 and the heat of the exhaust gas is recovered in a boiler 31. The gas is cooled at a high speed by a cooling water from a cooling water injection nozzle 33 in a gas cooler 32, and is cooled downstream. The desulfurizing agent is supplied from a desulfurizing agent supply device 35 such as slaked lime to the duct 34 of
The x is adsorbed and removed, and the dioxins in the exhaust gas are adsorbed by the supply of activated carbon from the activated carbon supply device 36.
After that, the exhaust gas from which the desulfurizing agent after desulfurization and the activated carbon which adsorbs the dioxins are removed by the bag filter 37 is exhausted from the stack 41 via the gas heater 38, the catalyst layer 39, and the attraction fan 40.

[0004] In this exhaust gas treatment, the incinerator 30 is burned at 850 ° C or higher, and hardly decomposable organic substances (for example, dioxins) are little generated, but the exhaust gas contains a large amount of a dioxin precursor. The exhaust gas is cooled to 280 ° C. in the boiler 31 and
When the temperature is cooled to 0 ° C. or lower, the resynthesis temperature of dioxins is 400 ° C. or lower. Therefore, dioxins are resynthesized, and it is necessary to perform adsorption removal using activated carbon or the like on the downstream side.

In order to prevent the resynthesis of dioxins, the exhaust gas at 600 ° C. is instantaneously (0.5 sec) rapidly cooled to 160 ° C. or less by water spray to lower the temperature of the exhaust gas. Recombination temperature (3
(400-400 ° C.) to prevent instantaneous resynthesis.

[0006]

However, since it is difficult to quickly and uniformly instantaneously lower the temperature of the exhaust gas in a large-volume gas cooler by water spray, resynthesis is inevitable.

Therefore, powdered activated carbon is sprayed in the subsequent stage to adsorb the resynthesized dioxins, and the activated carbon is collected by a bag filter to remove the dioxins. However, the load on the bag filter is increased. However, there is a problem that post-treatment (such as ash melting) of the adsorbed activated carbon is required.

Accordingly, an object of the present invention is to solve the above-mentioned problems and provide a method and an apparatus for decomposing organic substances in exhaust gas which can efficiently decompose organic substances contained in the exhaust gas when cooling the exhaust gas from an incinerator or the like. To provide.

[0009]

Means for Solving the Problems In order to achieve the above object, the invention according to claim 1 is characterized in that when exhaust gas discharged from an incinerator or the like is cooled while preventing resynthesis of dioxin or the like, the exhaust gas is contained in the exhaust gas. A method for decomposing organic matter in exhaust gas, wherein hydrogen peroxide is sprayed in the presence of ferrous ions to cool while oxidatively decomposing hardly decomposable organic substances contained in the exhaust gas such as dioxin precursors in the exhaust gas.

[0010] According to a second aspect of the present invention, the exhaust gas discharged from the incinerator is sprayed with ferrous ion-containing water such as ferrous sulfate, and then hydrogen peroxide water is sprayed. It is an organic matter decomposition method.

According to a third aspect of the present invention, the hydrogen peroxide solution is sprayed while maintaining the pH of the exhaust gas in an acidic atmosphere of about 3.
Or the method for decomposing organic substances in exhaust gas according to 2.

According to a fourth aspect of the present invention, the exhaust gas is introduced into a gas cooler, and hydrogen peroxide solution is sprayed as cooling water into the gas cooler. Is the way.

According to a fifth aspect of the present invention, a gas cooler for cooling exhaust gas discharged from the incinerator is connected to the incinerator,
This is an apparatus for decomposing organic matter in exhaust gas, wherein a ferrous ion-containing water spray means is connected to an exhaust gas duct between the incinerator and the gas cooler, and a hydrogen peroxide water spray means is provided for the gas cooler.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

In FIG. 1, reference numeral 10 denotes an incinerator,
It burns incineration materials 12 such as garbage supplied to 0, and includes, for example, a fluidized bed incinerator and a stoker incinerator.

The exhaust gas generated in the incinerator 10 is supplied to the boiler 1
Heat is recovered in the exhaust gas duct 14 and the gas cooler 15
At the top, where it is cooled at high speed and
Is more exhausted.

In the present invention, the exhaust gas duct 14 connecting the incinerator 10 and the gas cooler 15 is provided with ferrous ion-containing water spray means 18 for spraying ferrous ion-containing water. A hydrogen oxide water spray means 20 is provided.

The spray nozzle 22 used for the spray means 18 and 20 comprises, for example, a pressurized two-fluid nozzle.
As shown in FIG. 2, an air nozzle 25 is provided so as to cover the liquid nozzle 24 for injecting ferrous ion-containing water or hydrogen peroxide water at the center, and is directed from the liquid nozzle 24 toward the center as indicated by an arrow. To form a donut-shaped liquid film, and a high-speed air flow is sprayed from the air nozzle 25 on the outer periphery of the swirling blade 26 as shown by an arrow to atomize the liquid film from the liquid nozzle 24. It is sprayed and can be atomized with a lower liquid pressure than before, and the liquid diameter can be adjusted by adjusting the air flow rate.

In the above, ferrous sulfate (FeS) is used as the ferrous ion (Fe ²⁺ ) -containing water in the exhaust gas duct 14 by the ferrous ion-containing water spray means 18.
O ₄ ) aqueous solution, the concentration of hydrogen peroxide solution (H ₂ O ₂ ) from the hydrogen peroxide solution spraying means 20 is 10 to 3
Use 5 wt%.

When hydrogen peroxide is sprayed into the exhaust gas in the presence of ferrous ions, hydroxyl free radicals (.OH) are generated by the following Fenton reaction.

H ₂ O ₂ + Fe ²⁺ → Fe ³⁺ + HO ⁻ + .OH The OH radical reacts with the dioxin precursor when the dioxin precursor is re-synthesized into dioxins by the gas cooler 15. Thus, the precursors are oxidatively decomposed to prevent resynthesis of dioxins, and oxidatively decompose dioxins that have already been formed.

Here, dioxins will be described.

Dioxins have many isomers, and are typically PCDD (polychlorinated dibenzoparaoxin) and PCDF (polychlorinated dibenzofuran).
It is classified variously according to the number of substitution of 1 (chlorine).

Although the mechanism of dioxin formation has not been completely elucidated yet, the mechanism of the generation in incinerators is that unburned organic matter accompanying the thermal decomposition of garbage and the like and incomplete combustion causes the emission in the exhaust gas. On the ash surface, polycyclic carbon soot (a large number of naphthalene, anthracene, chrysene, pyrene, phenanthrene, etc.) produced by catalysis such as copper chloride or produced by combustion was decomposed by catalysis or produced by thermal decomposition It is presumed that the combustible gas reacts with chlorine by a catalytic action to form a precursor such as chlorophenol (C ₆ H ₃ Cl ₃ O), which generates a dioxin such as PCDD by a condensation reaction.

However, chlorophenol, which is a precursor, is considered to have been produced by the reaction of Cl with phenol which had originally reacted with OH on the benzene nucleus, and polycyclic carbon soot was also a substance obtained by polymerizing a large number of aromatic rings. And is basically in the benzene nucleus.

Therefore, the present invention assumes that the precursor of dioxins is a benzene nucleus, and this benzene nucleus is decomposed by the Fenton reaction to a simple substance (hydrocarbon or CO ₂ , which cannot be dioxin). Decompose.

Therefore, the oxidative decomposition route of benzene will be described by a reaction formula.

Regarding the Fenton reaction: ferrous ion (Fe ²⁺ ), hydrogen peroxide (H ₂ O ₂ ), and (H ⁺ ) for forming an acidic atmosphere of about pH 3 In the presence, .OH radicals are generated.

FeSO ₄ → Fe ²⁺ + SO ₄ ²⁻ H ₂ O ₂ + Fe ²⁺ + H ⁺ → H ₂ O + .OH + Fe ^{3+ When} not acidic (no H ⁺ ), Fe ²⁺ + H ₂ O ₂ → Fe ^{3 + + OH - + · OH Fe} 3+ + H 2 O 2 → Fe 2+ + HO 2 · + H + eventually, in the presence of iron _{salt, 2H 2 O 2 → H 2} O + O 2 and radicals by redox reaction is not generated.

In order to generate the .OH radical, Fe
Not only ²⁺ but also Cu ⁺ may be used.

Fly ash in the exhaust gas contains heavy metals such as Fe and Zn, which serve as a catalyst to produce various organic chlorine compounds and phenols.

For example, when benzene reacts with Cl _{2, it} becomes chlorobenzene, and when there is a metal oxide (eg, FeO), it becomes phenol.

Benzene is known to be produced by polymerization of hydrocarbons such as acetylene at high temperatures, and acetylene is known to be produced by dry distillation of organic substances. Accordingly, benzene is produced as a result of thermal decomposition of aromatic compounds such as plastics contained in garbage, but is also produced by decomposition of unburned polycyclic carbon soot components.

Estimation of dioxin production route; once formed phenol can be converted to dimer diphenyl ether by the following chemical formula 1.

[0035]

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If this phenol is 1-chlorophenol, it is represented by Chemical Formula 2.

[0037]

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It is also considered that resorcinol having two OH groups is present. If Cl is attached to resorcinol, dimerization occurs, for example, the reaction of formula 3 occurs, and 3,7 dichlorodibenzoparadioxin (PCDD) is formed. No wonder it is created.

[0039]

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It is sufficiently presumed that benzene reacts with the coexisting substance in the exhaust gas to produce the dioxin PCDD of Chemical formula 4.

[0041]

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Oxidative decomposition of benzene by the Fenton reaction; first, benzene is oxidized to maleic acid as shown in Chemical formula 5, in which case it is said that benzene first becomes quinone and then maleic acid.

[0043]

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As described above, benzene is oxidized to maleic acid, and after maleic acid, C is obtained by simple oxidation.
Decomposes into O ₂ and H ₂ O.

Thus, the oxidative decomposition of benzene is considered as decomposition by the Fenton reaction, that is, oxidation by .OH radicals. The reaction A in which maleic acid and glyoxal are generated from benzene by oxidation by .OH radicals,
There are two types of reaction B, in which benzene turns into quinone and quinone turns into maleic acid. In addition, there are other reactions A and B, but there is no limit.
The oxidative decomposition pathway by OH radical will be described.

FIGS. 3 and 4 show the oxidative decomposition pathways by the .OH radicals in Reaction A.

In FIG. 4, the oxidative decomposition of glyoxal is omitted because it is simply CO ₂ and H ₂ O.

The oxidative decomposition pathways shown in FIGS. 3 and 4 are represented by Chemical Formula 6 in total.

[0049]

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Next, the oxidative decomposition route by the .OH radical in the reaction B will be described.

In order for benzene to become quinone,
Becomes

[0052]

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[0053]

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That is, the total is as follows.

[0055]

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Next, the decomposition of quinone to maleic acid will be described. The formation of HO ₂ by the reaction of Fe ³⁺ + H ₂ O ₂ → Fe ²⁺ + HO _2. + H ⁺ (4HO ₂ .fwdarw.4.OH +
4 [O]) If it is explained by the OH and the oxygen [O] in the active period, the following formulas are obtained.

[0057]

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[0058]

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The total is as shown in FIG.

[0060]

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Although it has been described above that benzene can be oxidatively decomposed by OH radicals, the combustion gas temperature in an incinerator is 800 ° C. or higher, usually 850 ° C., for the reaction time.
Although the residence time is set to 2 seconds or more at a temperature of not less than ° C, the benzene as a precursor can be sufficiently decomposed in the gas cooler 15 because the Fenton reaction occurs instantaneously.

In FIG. 1, the boiler 13 is provided to recover the heat. However, the temperature after the heat recovery by the boiler 13 is usually 280 ° C., and the boiler 13 passes through the temperature range for recombining dioxins. The temperature of the exhaust gas after the boiler 13 is set to be equal to or higher than the resynthesis temperature (for example, 350 ° C.), and the gas cooler 15
The solution is instantaneously cooled to 160 ° C. at a high speed with a hydrogen peroxide solution, and at the same time, the precursor is decomposed by the Fenton reaction.

Further, without providing the boiler 13, water containing ferrous ions is injected into the exhaust gas so that, for example, the exhaust gas temperature is reduced to 60 ° C.
After the temperature is reduced to about 0 ° C., the mixture may be introduced into the gas cooler 15 and hydrogen peroxide solution may be injected to cool to 160 ° C. and cause the Fenton reaction.

As the ferrous ion-containing water, the ferrous sulfate (FeSO ₄ ) aqueous solution is 0.1 to 0.5 times the hydrogen peroxide solution (H ₂ O ₂ ) in terms of Fe molar ratio, or
80 ml / l.

The optimum value of the addition amount is obtained by sampling and analyzing exhaust gas components in advance and performing a decomposition test by the Fenton reaction. In this case, if the exhaust gas is passed through water and the correlation with the oxidation-reduction potential of the water is determined, it is possible to easily monitor at the site of various incineration facilities.

After the gas cooler 15, the desulfurizing agent described in the conventional example of FIG. 5 is charged, but the activated carbon need not be charged. Further, a scrubber for spraying hydrogen peroxide solution may be provided after the bag filter, and residual dust, HCl, SOx components, etc. in the exhaust gas may be washed and removed by the hydrogen peroxide solution scrubber.

[0067]

In summary, according to the present invention, the following excellent effects are exhibited.

(1) The dioxin precursor in the exhaust gas can be decomposed without adding a special device.

(2) Decomposition of Hydrogen Peroxide Aqueous ferrous ions indispensable for the OH radical component may be elemental iron when the dust component in the exhaust gas contains a large amount of iron.

(3) The administration of powdered activated carbon for adsorbing and removing dioxins can be completely eliminated or greatly reduced, the load on the bag filter can be reduced, and all or most of the activated carbon treatment becomes unnecessary.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a sectional view of a main part showing details of a two-fluid pressurizing nozzle used for a spray unit in FIG.

FIG. 3 is a view for explaining the oxidative decomposition route of benzene as a dioxin precursor in the present invention by using OH radicals.

FIG. 4 is a diagram illustrating a continuation of the oxidative decomposition route in FIG. 3;

FIG. 5 is a diagram showing a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Incinerator 15 Gas cooler 14 Exhaust gas duct 18 Ferrous ion containing water spray means 20 Hydrogen peroxide water spray means

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Junya Nishino 1st Shin-Nakahara-cho, Isogo-ku, Yokohama-shi, Kanagawa Ishikawashima-Harima Heavy Industries, Ltd. Machinery and Plant Development Center F term (reference) 3K065 AA18 AC01 BA01 HA02 4D002 AA21 AC04 BA04 BA05 BA13 CA01 CA13 DA14 DA22 DA52 EA02 GA01 GB09 4H006 AA04 AA05 AC13 AC26 BA19 BA36 BB31 BC10 BC34 BD80 BE32

Claims (5)

[Claims] When cooling exhaust gas discharged from an incinerator or the like while preventing resynthesis of dioxin or the like, hydrogen peroxide is sprayed into the exhaust gas in the presence of ferrous ions,
A method for decomposing organic substances in exhaust gas, comprising cooling while performing oxidative decomposition of hardly decomposable organic substances contained in the exhaust gas such as dioxin precursors in the exhaust gas. 2. The method for decomposing organic matters in exhaust gas according to claim 1, wherein ferrous ion-containing water such as ferrous sulfate is sprayed onto the exhaust gas discharged from the incinerator, and then hydrogen peroxide water is sprayed. 3. The method for decomposing organic matter in exhaust gas according to claim 1, wherein the hydrogen peroxide is sprayed while maintaining the pH of the exhaust gas in an acidic atmosphere of about 3. 4. The method for decomposing organic matter in exhaust gas according to claim 1, wherein the exhaust gas is introduced into a gas cooler, and a hydrogen peroxide solution is sprayed as cooling water into the gas cooler. 5. An incinerator is connected to a gas cooler for cooling exhaust gas discharged from the incinerator, and a ferrous ion-containing water spray means is connected to an exhaust gas duct between the incinerator and the gas cooler. An apparatus for decomposing organic substances in exhaust gas, wherein a hydrogen peroxide water spray means is provided in the gas cooler.