JP2000185216A - Treatment of exhaust gas from incinerator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform a treatment for making fly ash or the like harmless in a simple way and at a low cost by first bringing an exhaust gas from an incinerator into contact with a hydrochloric acid acidic absorbing solution in a gas/liquid contact mode and thereby, migrating an acidic gas and the fly ash contained in the exhaust gas into the absorbing solution and further retaining the absorbing solution under such conditions that a reaction catalyst is dissolved to dissolve and make dioxins harmless. SOLUTION: An exhaust gas discharged from an incinerator is guided to a gas/liquid contact device which performs a smoke washing step 1 and fly ash and an acidic gas contained in the exhaust gas are supplementally absorbed by an absorbing. solution. The exhaust gas after treatment has its relative humidity lowered by a dehumidifier 2 and is made to pass through a dust collector which performs a dust collection step 3. Right before the dust collection step 3, active carbon powder is blown into the exhaust gas to remove dioxins contained in the exhaust gas. Further, in the gas/liquid contact device for the smoke washing step 1, a part of the absorbing solution is extracted into a dioxin decomposition step 4 and is treated as the product of the fly ash and the acidic gas is accumulated in the absorbing solution. The absorbing solution is maintained under such conditions that the solution remain hydrochloric acid acidic and a reaction catalyst be contained, in a molten state, in the solution and thus the decomposition reaction is promoted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for treating exhaust gas. More specifically, the present invention treats waste incinerator exhaust gas containing at least an acidic gas such as hydrogen chloride or sulfurous acid gas, fly ash, and dioxins mainly present in the form included in the fly ash. On how to do it.

[0002]

2. Description of the Related Art The emission of organic chlorine compounds, particularly dioxins, into the environment accompanying the combustion of municipal waste and industrial waste has been regarded as a problem. In the past, Japan did not regulate the emission of dioxins from incineration facilities for municipal solid waste or industrial waste, but the danger of dioxin emission was pointed out and this became a major social problem. Published “Guidelines on Prevention of Dioxins Generation in Waste Disposal” in January 2010, and set the concentration of dioxins in exhaust gas discharged from the newly installed continuous furnace at 0.1 ng-
They are instructed to make TEQ / Nm ³ or less. Also,
With the revision of the Air Pollution Control Law in December 1997, the Environment Agency has specified dioxins as designated hazardous substances and has regulated the concentration of dioxins in exhaust gas generated not only from general waste but also from industrial waste incineration. We decided to set a value.

[0003] In general, organic chlorine compounds include DDT and PCB.
There are many things that have a harmful effect on the human body and environmental ecosystems when released into the environment like dioxins, but dioxins, which have recently become a problem from waste treatment facilities, The most toxic 2,3
7,8-tetrachlorodibenzo-p-dioxin (2,
7,3,8-TCDD) is said to be a very toxic substance far exceeding the above-mentioned DDT and PCB. Generally, dioxins refer to the above 2,3,7,8-TCDD and its analogous compounds, and 1 to 8 are added to the dibenzo-p-dioxin nucleus.
Polychlorinated dibenzo-p-dioxins (PCDDs) substituted with two chlorine atoms, and 1 to the dibenzofuran nucleus
It is a general term for polychlorodibenzofurans (PCDFs) in which eight chlorine atoms are substituted. Note that coplanar PCBs, which are a part of PCB homologs, are also PCDDs and PCDFs.
Since it exhibits toxicity very similar to s, it may be referred to as dioxins including this, but since regulation of dioxins currently assumed does not include this, when it is referred to as `` dioxins '' in this specification Coplanar PC
B is not included. However, the method of the present invention
It is not intended to decompose and decompose only PCDDs and PCDFs, but treats a wide range of organochlorine compounds including PCDDs, analogous compounds of PCDFs, and coplanar PCBs.

[0004] Usually, dioxins are rarely taken up by taking only specific ones out of them, and various dioxins are often taken up as a problem. However, since the degree of harmfulness of various dioxins differs from one another, a scale for distinguishing and evaluating the harmfulness of different dioxins is required to evaluate the harmfulness of the mixture of various dioxins as a whole. For this reason, based on the short-term toxicity evaluation results of various dioxins, a coefficient (toxic equivalent coefficient) for converting the amount of each dioxin into the amount of 2,3,7,8-TCDD having the same degree of toxicity. The value obtained by adding the value obtained by multiplying the actual amount of each dioxin by this toxic equivalent coefficient is called a toxic equivalent conversion value (TEQ), and represents the emission amount and concentration of dioxins. It is used for

[0005] Unlike DDT and PCB, dioxins are not chemical substances artificially synthesized for a certain purpose of use, but are formed as by-products in the synthesis of useful organic chlorine compounds and the like, and those organic chlorine compounds are not used. It is generated when the compound burns. And it is said that the largest cause of the emission of dioxins into the environment is incineration of municipal solid waste and industrial waste. For this reason, while measures have been sought to control the emission of dioxins during waste incineration, various technologies described below have been developed and the results are being demonstrated.

[0006] First, dioxins are often formed by incomplete combustion of organochlorine compounds.
There is no doubt that thorough combustion or stable combustion is effective in suppressing the production of dioxins. However, this has led to the centralization or enlargement of waste treatment facilities on the one hand, and it cannot be denied that there are factors that may cause new problems in the location of the facilities.

Second, dioxins are generated not only by incomplete combustion but also by the contact of fly ash with precursors such as chlorobenzene and chlorophenol in the exhaust gas during the process of cooling the exhaust gas. This is a process in which dioxins are produced by using metal components in fly ash as a catalyst, and is called de novo synthesis.
It occurs at about 600 ° C., and synthesis at about 300 ° C. is said to be the most active. For this reason, the boiler, where the exhaust gas is cooled, has a structure that prevents fly ash from accumulating, thereby avoiding contact between the exhaust gas and the fly ash in the cooling process, and spraying water directly at the boiler outlet to reduce the temperature of the exhaust gas. Is rapidly cooled to 200 ° C. or less to minimize the chance of de novo synthesis.

Third, as a method of treating exhaust gas containing dioxins, for example, use of a low-temperature bag filter has been proposed (Japanese Patent Laid-Open No. 6-47224). This is 20
It uses a bag filter at an operating temperature of 0 ° C or less,
According to this, the particulate dioxins are captured by the filter, and the dioxins are adsorbed and removed from the exhaust gas by the attached fly ash layer. It is said that a bag filter operated at 150 ° C. can obtain a removal rate of 90 to 95%. It has also been proposed to blow powdered activated carbon into exhaust gas at the inlet duct of the bag filter and collect the powdered activated carbon adsorbing dioxins with a bag filter (for example, Japanese Patent Laid-Open No. Hei 5-2031).
No. 27). According to this, a removal rate of 95% or more is obtained. Another method for removing dioxins in exhaust gas is to oxidize and decompose dioxins in exhaust gas in a temperature range of 200 ° C. or higher using an oxidation catalyst based on a denitration catalyst (Japanese Patent Application Laid-Open No. 4-503772). etc)
Also, there has been proposed a method of performing adsorption removal using a fixed bed or a moving bed filled with activated carbon pellets.

Fourth, dioxins are contained in furnace ash and fly ash more quantitatively than exhaust gas.
It has been said that the effects on the environment are not as great as those contained in exhaust gas if the contents contained in furnace ash and fly ash are properly buried. However, in reality, not all of the furnace ash and fly ash are buried under proper management; they are washed away by rainwater and flow into rivers, and penetrate underground and contaminate groundwater. The situation seems endless. For this reason, it has been attempted to bury the furnace ash or fly ash after performing some processing without burying it as it is. As one example, there is a technique in which furnace ash and fly ash are melted and solidified at a temperature of 1250 to 1450 ° C. or more to form a glassy slag. According to this, the volume can be reduced, the heavy metal can be fixed in the network of glass, and the dioxins are decomposed by the high temperature during melting. As another example for fly ash, fly ash was collected under a low oxygen atmosphere.
A method of heating at 0 to 550 ° C. and detoxifying dioxins by a dechlorination reaction (Japanese Patent Publication No. 6-38863).
No.) or a method of introducing fly ash into supercritical water (374 ° C. or higher and 218 atm or higher) to oxidatively decompose dioxins (Takeshi Sako, Kagaku, Vol. 52, No. 10, 31-34 ( 1997)).

[0010]

Among the various countermeasures described above, the first and second ones attempt to suppress the production of dioxins themselves, while the third and fourth ones attempt to suppress the production of dioxins themselves. It can be said that those which try to remove the generated dioxins. By the way, harmful substances contained in exhaust gas are dioxins (or fly ash containing it)
In addition, as is well known, acid gases such as hydrogen chloride and sulfur dioxide are often included. Facilities for removing acidic gases in exhaust gas are already widely provided, and dust collectors (eg, bag filters and electric dust collectors) for removing fly ash in exhaust gas are generally used. If it is possible to remove dioxins using the equipment described above, it is extremely advantageous in terms of cost. Among the methods described as the third method, the method of blowing powdered activated carbon into the inlet of the bag filter has a common viewpoint in that an existing bag filter can be used. There is a demand that the development of economical means for decomposing dioxins in such solid waste is indispensable in order to generate a large amount of activated carbon waste. In other words, there is a need for an economical method for treating waste gas from waste incinerators that can effectively use conventional equipment and suppress generation of hazardous wastes including dioxins.

[0011]

The present invention relates to a method for detoxifying incinerator exhaust gas containing an acid gas and fly ash and further containing dioxins, wherein the exhaust gas is brought into gas-liquid contact with a hydrochloric acid acidic absorbing solution. A smoke washing step of transferring acid gas and fly ash in the exhaust gas into the absorbing solution, a hydrochloric acid absorbing solution containing the fly ash obtained in the smoke washing step, under conditions containing a reaction catalyst in a dissolved state. By maintaining the temperature at a temperature lower than 100 ° C., the dioxins in the fly ash are decomposed and made harmless, the exhaust gas passing through the smoke cleaning step is passed through a dust collector, and the dust is collected in the dust collecting step. A circulation method for returning the collected fly ash to the decomposition step, and a method comprising the above steps are provided, thereby solving the above-mentioned problems.

The inventors of the present invention have found that dioxins contained in solids such as fly ash cause the solids to reach 100 ° C.
They have been found to be decomposed by treating in the following acidic aqueous hydrochloric acid solution in the presence of a reaction catalyst. In this case, it is sufficiently possible to reduce the decomposition rate of dioxins to at least 60% under practically acceptable processing conditions. The present invention, based on this finding, the step of capturing and absorbing fly ash in the exhaust gas together with the acid gas in the absorbent, and the step of decomposing the dioxins contained in the fly ash by subjecting the absorbent to the above treatment A system in which the amount of dioxins finally discharged can be significantly reduced by removing the fly ash remaining in the exhaust gas that has undergone the combination and capture and absorption treatment by a dust collector and returning it to the dioxin decomposition process. It is.

Most of the dioxins in the exhaust gas from the incinerator are present mainly in the form contained in fly ash, and a part is present in the gas phase as gas or mist. Generally, the exhaust gas contains an acidic gas such as hydrogen chloride or sulfurous acid gas. Therefore, first, by contacting the exhaust gas with a predetermined absorbing liquid, the fly ash and the acidic gas are captured and absorbed by the absorbing liquid and removed (smoke washing step). By removing fly ash from the exhaust gas, most of the dioxins contained in the exhaust gas are removed. At the same time, some of the dioxins contained in the gas phase are absorbed by the liquid and removed.

In the smoke washing step, since the absorbing solution absorbs the acidic gas in the exhaust gas to lower the pH, an alkaline agent is added to the absorbing solution. Limestone, slaked lime,
Caustic soda, soda ash, magnesium hydroxide and the like are generally used. When the acidic gas contained in the exhaust gas is mainly sulfurous acid gas, it is preferable to use a calcium compound such as limestone or slaked lime. This is because the calcium compound reacts with sulfate ions generated when sulfurous acid gas is absorbed and oxidized by the liquid to form gypsum precipitate, which can be easily separated from the liquid. On the other hand, when the acidic gas contained in the exhaust gas is mainly hydrogen chloride, there is no such advantage even if a calcium compound is used, so that an appropriate one may be selected in consideration of handling and cost. .

The exhaust gas that has passed through the smoke washing step is further passed through a dust collector to remove residual fly ash (dust collection step).
As the dust collector, a wet dust collector or a dry dust collector can be used. In the case of a dry dust collector, since the exhaust gas that has passed through the smoke washing process has a relative humidity of almost 100%, moisture is often condensed in the dust collector in the subsequent dust collection process. To prevent this, the exhaust gas that has passed through the smoke washing step may be dehumidified or heated. Further, when the removal of dioxins in the gas phase in the above-mentioned smoke washing step is not sufficient, the dioxin in the gas phase is blown by blowing activated carbon powder into the exhaust gas before passing the exhaust gas having passed through the smoke washing step through the dust collector. Can be removed more effectively. The blowing amount of activated carbon powder is generally 1 Nm ^{3 of} exhaust gas (based on dry gas containing 12% by volume of oxygen).
It is good to be about 100-300 mg per. As a means for blowing the activated carbon powder, a commonly used means such as an air spray nozzle can be used.

On the other hand, the absorbing liquid which has captured and absorbed fly ash and acidic gas in the above-mentioned smoke washing step is maintained at a temperature lower than 100 ° C. under conditions of being acidic with hydrochloric acid and containing the reaction catalyst in a dissolved state,
This decomposes the dioxins contained in the fly ash (decomposition step). Practically, it is preferable to carry out the treatment at 80 ° C. or lower. Since the absorption liquid contains the reaction catalyst in a dissolved state and is under acidic conditions of hydrochloric acid, the decomposition reaction of dioxins proceeds even under such low temperature conditions. However, the lower limit temperature is about 30 ° C. At this time, the fly ash (and activated carbon powder) collected in the dust collection step is put into the absorbing solution in the decomposition step and processed together (circulation step).

[0017] In the present invention, the hydrochloric acid absorbing liquid chlorine ions - refers to an acidic aqueous solution containing ^(Cl).
The chloride ion concentration of the liquid is preferably 10 mmol / L or more, and more preferably 100 mmol / L or more. Chloride ion and sulfate ion (SO
Preferably the molar ratio is 5 or more ₄ ^2-), and more preferably is 20 or more. Since the solution is acidic, the pH is naturally 7 or less, but is preferably 6 or less. However, if the pH is too low, problems such as corrosion tend to occur, so it is not advisable to lower the pH below 2. The absorption liquid is generally adjusted to a pH range of 2 to 6 by absorption of an acidic gas and addition of an alkali agent, but if necessary, the pH may be adjusted in the decomposition step. The acid or alkali for adjusting the pH of the solution is not particularly limited, but hydrochloric acid is more preferably used than sulfuric acid because the ratio of chloride ions to sulfate ions in the solution is preferably larger.

In the decomposition step, the hydrochloric acid acidic absorbing solution must contain a reaction catalyst for promoting the decomposition of dioxins in a dissolved state. Such reaction catalysts are generally metal ions and include iron, manganese, copper, zinc, nickel, cobalt, molybdenum, chromium, vanadium, tungsten, cadmium, aluminum and the like. The metal ions need not be one kind, and two or more kinds of metal ions may be mixed. Many metal ions can have different valences, but such different valences of the same metal ion may be mixed in the liquid. The valence of the metal ion may change during the reaction and may form a complex. The most preferred metal ion is a copper ion. For copper ions,
The concentration in the liquid is preferably about 20 to 10000 mg Cu / liter, more preferably 100 to 5000 mg Cu / liter. 10,000mgCu
Even if it exceeds / liter, an increase in the catalytic effect cannot be expected.
In general, fly ash contains catalytic metal ions, which are eluted into the absorbing solution. Therefore, a necessary and sufficient amount of catalytic metal ions may be present in the absorbing solution. In this case, there is no need to separately add a catalytic metal ion.

In the liquid in the decomposition step, a substance that promotes contact between the liquid and fly ash or activated carbon powder (contact promoter)
Is preferably included. Such contact promoters include surfactants and alcohols. The type of surfactant is not particularly limited, and various surfactants such as anionic, cationic, nonionic and amphoteric surfactants can be used. The surfactant is preferably contained in the liquid in an amount of 0.005 to 1% by weight,
More preferably, the content is 0.01 to 0.5% by weight. As the alcohols, lower alcohols are preferably used, and specific examples thereof include methanol, ethanol, and propanol. Alcohols are preferably contained in the liquid in an amount of 0.5 to 10% by weight, more preferably 1 to 10% by weight.

As a device for keeping the absorbing solution that has captured and absorbed fly ash and acidic gas at a temperature of 100 ° C. or less under conditions of being acidic with hydrochloric acid and containing the reaction catalyst in a dissolved state, a stirring tank type device is generally used. However, other types can also be used. In addition, ultrasonic waves may be applied to the holding area to promote contact between the solid and the liquid. In addition, air aeration or oxygen-enriched air may be used if necessary,
By performing air aeration while pressurizing the reaction system,
It is also effective to increase the amount of dissolved oxygen in the liquid to increase the oxidation-reduction potential. The concentration of the solid substance in the liquid is not particularly limited as long as effective contact between the liquid and the solid substance is performed, and it is sufficient that a uniform slurry can be sufficiently stirred and mixed. It is on the order of liters. The required processing time varies depending on the operating conditions, so it is difficult to uniquely define it. However, practically, it should be about 1 hour to 100 hours.

In the present invention, the smoke washing step and the decomposition step can be integrally performed as the same step. As a particularly effective apparatus form in this case, there is a jet bubbling reactor having a gas-liquid contact mechanism of a type in which exhaust gas is jetted into an absorbent through a number of sparger pipes. The jet bubbling reactor has a gas-liquid contact section for bringing exhaust gas into contact with the absorbing solution in the same apparatus, and a reaction section for performing processing such as detoxification of components transferred from the exhaust gas into the absorbing solution. Is circulated therebetween. Since the exhaust gas is blown into the absorbing liquid as fine bubbles at the gas-liquid contact portion, the efficiency of absorbing or capturing acidic gas and fly ash in the exhaust gas is good. The acid gas thus transferred to the absorbing solution, dioxins adsorbed on fly ash,
Furthermore, the dioxins contained in gaseous or mist form are rendered harmless by reacting with the absorbing liquid or the oxygen-containing gas blown as required in the reaction section.

Since the present invention is intended to treat incinerator exhaust gas, dioxins contained in the exhaust gas in gaseous or mist form and fly ash containing dioxins are to be treated. It is also included in furnace ash. Furnace ash is not always treated together with the exhaust gas treatment system. However, if furnace ash is introduced into the hydrochloric acid acid absorbing solution in the decomposition step of the present invention, dioxins contained in the furnace ash are also decomposed. In this way, all the emissions from the incinerator are processed for dioxins, which is preferable from the viewpoint of environmental conservation.

[0023]

FIG. 1 shows a preferred process flow for treating incinerator exhaust gas in accordance with the present invention. The exhaust gas discharged from the incinerator is subjected to heat recovery and other pretreatments as required, and is first guided to the gas-liquid contact device 1 that performs a smoke washing process. Here, fly ash and acid gas contained in the exhaust gas are captured and absorbed by the absorbing liquid, and the exhaust gas after the treatment is reduced in the subsequent stage by the dehumidifying device (or the temperature raising device) 2 to such an extent that dew condensation does not occur. , And passes through a dust collector (for example, a bag filter) 3 that performs a dust collecting step. It is a preferred embodiment to remove the dioxins contained in the exhaust gas in the form of gas or mist by blowing activated carbon powder into the exhaust gas before entering the dust collection step. The injected activated carbon is collected by a dust collector together with fly ash. However, most fly ash is removed in the smoke washing process, so that only a small amount of fly ash is collected by the dust collector. Also, since dioxins are not so much contained in the gaseous phase as gaseous or mist, the injected activated carbon powder can be sufficiently reused. Therefore, it is preferable that a part of the activated carbon powder (including a small amount of fly ash) collected by the dust collector is returned to the front of the dust collector again, and is recycled for blowing into the exhaust gas. The exhaust gas that has passed through the dust collection step can be released to the atmosphere. On the other hand, in the gas-liquid contact device in the smoke washing process, fly ash and products from the acidic gas accumulate in the absorbing solution, so that a part of the absorbing solution is extracted into the dioxin decomposition tank 4 and treated. In the dioxin decomposition tank, the absorption liquid is maintained under the condition that it is acidic with hydrochloric acid and the reaction catalyst is contained in a dissolved state, and the decomposition reaction of dioxins proceeds at 100 ° C. or lower. The non-recycled fly ash and activated carbon powder collected by the dust collector are returned to the dioxin decomposition tank for processing. The absorption liquid treated by the dioxin decomposition device is separated into solid matter and filtrate by solid-liquid separation, and the solid matter is disposed of in landfills, etc., and the filtrate is discharged after undergoing wastewater treatment if necessary . FIG.
1 shows a case where the smoke cleaning step and the decomposition step are performed simultaneously in the gas-liquid contact device 1.
Except for this point, it is the same as the process of FIG.

FIG. 3 shows the smoke washing step (and the decomposition step).
1 schematically shows the structure and operation of a jet bubbling reactor 11 that can be suitably used as a gas-liquid contact device 1 for performing the above. Exhaust gas containing acid gas and fly ash
Through the inlet plenum 14 partitioned by the lower deck 12 and the upper deck 13, the liquid is blown into the absorbent through a sparger pipe 16 protruding from the lower deck into the absorbent below. Since a large number of holes are provided on the side surface of the sparger pipe, the exhaust gas spouts out of those holes into the absorbing liquid to form fine bubbles. As a result, the exhaust gas and the absorbing liquid have a large gas-liquid contact area, so that the acidic gas in the exhaust gas is quickly dissolved and absorbed in the liquid, and fly ash in the exhaust gas is captured on the gas-liquid contact surface. Is done. The exhaust gas, which has become fine bubbles, rises in the absorbing solution, is separated from the absorbing solution, passes through the gas riser 17, and is discharged through the outlet plenum 18 formed on the upper deck. The dioxins adsorbed on the fly ash that has migrated into the absorbent and the dioxins contained in the form of gas or mist are retained in the hydrochloric acid acidic absorbent containing the reaction catalyst for a predetermined residence time in the reaction unit 15. Detoxification is achieved by doing so. A metal ion as a reaction catalyst is necessary for the decomposition reaction of dioxins, but when the amount of metal ions eluted from fly ash is small, an aqueous solution of a copper salt or the like is converted from the catalyst metal supply pipe 20 into an absorbing solution. Can be added. Further, air is blown into the absorbing liquid in the reaction section from the air blowing nozzle 19 provided near the bottom as needed. This contributes to the decomposition of dioxins by increasing the redox potential of the liquid. Also,
When the acidic gas is mainly composed of sulfurous acid gas, it contributes to oxidizing sulfurous acid ions generated by dissolving the sulfurous acid gas in the absorbing solution into sulfate ions. The absorbing liquid is loosely stirred by the stirring blades 21, and the lower liquid and the upper liquid circulate slowly. From the alkali agent supply pipe 22, an alkali agent such as limestone is supplied into the liquid. When sulfuric acid gas is contained as the acidic gas, the sulfuric acid ion generated by absorption and oxidation of the acid reacts with calcium to form gypsum. Solids such as fly ash and gypsum are converted into slurry by a slurry drawing pipe 2
3 and are continuously extracted and processed. Most of the absorbent separated from the slurry is returned to the reaction section.

[0025]

EXAMPLES The detoxification treatment of dioxins contained in fly ash having the following properties separated and recovered from incinerator exhaust gas was performed as follows. (Properties of fly ash) (I) Carbonaceous substance content: 0.1% by weight (II) Copper content: 0.35% by weight (III) Dioxins content: 3.6 ng-TEQ / g (Experiment Method) 400 g of the fly ash was added to 2 liters of pure water, and hydrochloric acid was added with stirring under heating to 65 ° C., pH
3.5 was maintained for 48 hours. At this time, the Cl concentration in the aqueous solution was 1900 mmol / L, and [Cl] / [SO
4] was 113, and the Cu concentration was 500 mg / liter. After stirring for 48 hours, the slurry was subjected to suction filtration to analyze dioxins contained in the fly ash after the treatment. Dioxin decomposition rate was calculated by the following equation. as a result,
A degradation rate of 92% was obtained.

R = (ao × co−a × c) / (ao × co) × 100 R: Decomposition rate of dioxins ao: Weight of untreated fly ash (g (dry)) a: Weight of treated fly ash (g) (Dry)) co: concentration of dioxins in untreated fly ash (ng-TE)
Q / g) c: Dioxin concentration in treated fly ash (ng-TEQ)
/ G)

[0026]

According to the present invention, in many factories where exhaust gas treatment equipment has conventionally been installed by a wet method, detoxification of dust fly ash and furnace ash can be performed with a slight modification of equipment. .

[Brief description of the drawings]

FIG. 1 shows a preferred embodiment of the present invention.

FIG. 2 illustrates another preferred embodiment of the present invention.

FIG. 3 schematically shows the structure of a jet bubbling reactor suitably used in the smoke washing step (and the decomposition step) of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Smoke washing process (and decomposition process) 2 Dehumidification (heating) device 3 Dust collection process 4 Decomposition process 11 Jet bubbling reactor 12 Lower deck 13 Upper deck 14 Inlet plenum 15 Reaction unit 16 Sparger pipe 17 Gas riser 18 Outlet plenum 19 Air blowing nozzle 20 Catalyst metal supply pipe 21 Stirring blade 22 Alkaline agent supply pipe 23 Slurry extraction pipe

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazushige Kawamura 2-1-1, Tsurumichuo, Tsurumi-ku, Yokohama-shi, Kanagawa Prefecture Inside Chiyoda Kako Construction Co., Ltd. Chuo 2-chome No. 1 Chiyoda Kako Construction Co., Ltd. F-term (reference) 4D002 AA02 AA19 AA21 AB01 AC04 BA02 BA12 BA14 CA06 DA02 DA05 DA06 DA11 DA12 DA16 DA23 DA35 DA41 DA66 EA12 FA03 GA01 GA02 GB02 GB03 GB09 GB11 4D004 AA46 AB07 AC04 CA10 CA28 CA47 CB34 CC03 CC11 DA01 DA03 DA06 DA08 DA10

Claims (11)

[Claims] 1. A method for detoxifying an incinerator exhaust gas containing an acid gas and fly ash and further containing dioxins, wherein the incinerator exhaust gas is brought into gas-liquid contact with a hydrochloric acid acidic absorbing solution, whereby the exhaust gas is contained in the exhaust gas. A smoke washing step of transferring acid gas and fly ash into the absorbing solution, a hydrochloric acid absorbing solution containing the fly ash obtained in the smoke washing step,
A decomposing step of decomposing and detoxifying the dioxins in the fly ash by maintaining the temperature below 100 ° C. under a condition containing the reaction catalyst in a dissolved state; and a dust collecting step of passing the exhaust gas having passed through the smoke washing step through a dust collector. And a circulating step of returning the fly ash collected in the dust collecting step to the decomposing step. 2. The method according to claim 1, wherein said smoke washing step and said decomposition step are performed as the same step. 3. The method of claim 2, wherein said same steps are performed in a jet bubbling reactor. 4. A dehumidifying step or a temperature increasing step is provided before the dust collecting step, whereby the relative humidity of the exhaust gas having passed through the smoke washing step is reduced to such a degree that water does not condense in the subsequent dust collecting step. The method according to claim 1. 5. The method according to claim 1, wherein in the decomposition step, oxygen or an oxygen-containing gas is brought into contact with the aqueous hydrochloric acid solution.
5. The method according to any one of 4. 6. The method according to claim 1, wherein in the decomposition step, the reaction catalyst comprises copper ions. 7. The method according to claim 1, wherein, in the decomposition step, the pH of the aqueous hydrochloric acid solution is 2.0 to 6.0. 8. The method according to claim 1, wherein in the decomposition step, the chloride ion concentration in the aqueous hydrochloric acid solution is 10 mmol / L or more. 9. The method according to claim 1, wherein the decomposition rate of dioxins in the decomposition step is at least 60%. 10. Activated carbon powder is blown into the exhaust gas that has passed through the smoke washing step, the blown activated carbon powder is collected by a dust collector together with fly ash, and a part of the collected fly ash and activated carbon powder is circulated and supplied. The method according to any of claims 1 to 9, wherein a part is returned to the decomposition step. 11. In the decomposing step, furnace ash generated from an incinerator is charged into the hydrochloric acid aqueous solution.
The method according to any one of claims 10 to 10.