JPH1176755A - Decomposing method of dioxin derived from incineration furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To safely and completely decompose dioxin generated from an incineration furnace by adsorbing dioxin discharged from the incineration furnace on an activated carbon and oxidizing and decomposing a waste activated carbon, on which dioxin is adsorbed, in a supercritical water having equal to or above the critical temp. and critical pressure of water. SOLUTION: At the time of charging a refuse in the incineration furnace and combusting, dioxin is generated by incompletely combusting a chlorine-containing compound. Dioxin in a waste combustion gas is adsorbed on the activated carbon, the waste activated carbon and a fly ash are collected in a bag filter, in which water is added to form a slurry. The slurry is charged in a supercritical water oxidation device 9 to be treated by supercritical water oxidation. That is, the pressure of the device is elevated to the supercritical pressure of water by a high pressure compressor 11. Next, the slurry is forcibly charged in the reactor 12 by a high pressure pump 10 and simultaneously air is elevated in pressure by the high pressure compressor 11 to be forcibly fed to the reactor 12. The forcibly fed slurry is heated to the supercritical temp. of water by a heater 13 and the oxidation reaction proceeds in the reactor 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for decomposing dioxin from incinerators, which has recently become a social problem.

[0002]

2. Description of the Related Art Non-combustible refuse among household refuse and municipal refuse is landfilled, and combustible refuse is incinerated by an incinerator. FIG. 4 shows a flow chart of a conventional incinerator combustible waste combustion disposal method. Combustible waste is incinerated in incinerator 1,
The combustion residue is collected as incineration ash, and the high-temperature combustion exhaust gas containing fly ash is cooled in the temperature reducing tower 2, and then the fly ash contained in the combustion exhaust gas is collected by the bag filter 3. Slaked lime is added to remove sulfur contained in the exhaust gas discharged from the bag filter 3, slaked lime that has been treated by the filter 4 is removed, and the exhaust gas is smoke-cleaned by the smoke-cleaning equipment 5, and then the catalyst is denitrated by the catalytic denitration equipment 6. The NOx contained in the exhaust gas is removed and released into the atmosphere from the chimney 7.

[0003] Plastics mixed into combustible waste, especially substances containing chlorine atoms such as vinyl chloride resin are 800.
It has been reported that dioxin is generated when incomplete combustion is performed below ℃. Dioxin generated by incomplete combustion of the vinyl chloride resin is diffused into the atmosphere from the chimney together with the combustion exhaust gas, so that a wide area around the incineration plant is contaminated with dioxin.

As a method for solving the problem of dioxin contamination from incinerators, combustible waste is treated by a new type incinerator capable of burning at a high temperature of 800 ° C. or higher, or the combustion exhaust gas discharged from an existing incinerator is used. There is a method for removing dioxin. The method using the new incinerator, which can burn at high temperature, requires the disposal of existing incinerators and the construction of new incinerators, which increases disposal costs.

[0005] The method of removing dioxin in the combustion exhaust gas has the advantage that it can be treated at low cost because it is not necessary to dispose of the existing incinerator. As such a method, a method of installing an apparatus filled with an adsorbent such as activated carbon in an incinerator to prevent the release of dioxin into the atmosphere (Japanese Patent Laid-Open No.
No. 763), a method of reacting activated carbon to which dioxin has been adsorbed at 350 ° C. or higher in an inert atmosphere to decompose the adsorbed dioxin and regenerate and reuse activated carbon. 30102
Various methods have been proposed, for example, a method of incineration of used waste activated carbon in an incinerator (JP-A-8-86425).

[0006]

The method of Japanese Patent Application Laid-Open No. 7-763 discloses a method of treating activated carbon adsorbing dioxin.
Although not particularly described, the method disclosed in JP-A-5-301022 is intended to remove the finally used activated carbon from JP-A-8-86.
Like 425, it must be disposed of by incineration.
In order to decompose dioxin by combustion, 80
Since a combustion temperature of 0 ° C. or higher is required, a large amount of fuel must be used. Exhaust gas is generated by the amount of the fuel. Furthermore, if a substance containing a chlorine atom is mixed in the incineration, dioxin may be generated again, and NOx and SOx may be generated, which may cause air pollution. In addition, incineration ash remains, causing the problem of disposal.

An object of the present invention is to provide a method for safely and completely decomposing dioxin generated from an incinerator.

[0008]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that the above-mentioned problems can be solved by performing supercritical hydroxylation treatment on waste activated carbon adsorbing dioxin, and complete the present invention. Reached.

That is, the present invention is characterized in that (1) dioxin discharged from an incinerator is adsorbed on activated carbon, and waste activated carbon having adsorbed dioxin is oxidatively decomposed in supercritical water at or above the critical temperature and pressure of water. (2) Waste activated carbon adsorbed with dioxin is supplied directly to the supercritical water oxidation reactor as slurry without performing pretreatment such as drying without supercritical water oxidation. (3) The method for decomposing dioxin derived from an incinerator according to the above item (1), wherein the fly ash discharged from the incinerator is supercritically hydroxylated together with waste activated carbon adsorbed with dioxin. (4) The method for decomposing dioxin derived from an incinerator according to the above item (1) or (2), wherein (4) wastewater discharged from a smoke washing facility of the incinerator is supercritical. The present invention relates to the method for decomposing incinerator-derived dioxin according to any one of the above items (1) to (3), which is used for a hydroxylation reaction.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The refuse to be treated by the method of the present invention is refuse that has been conventionally incinerated. For example, combustible materials such as paper, kitchen waste, fiber, wood / bamboo, plastic, and non-combustible Metal, glass, ceramics, and the like, and naturally contains 30 to 60% of water.

In the present invention, dioxin generated by incineration must first be adsorbed on activated carbon. The method of causing the activated carbon to be adsorbed is not particularly limited.For example, a method in which the combustion exhaust gas discharged from the incinerator is cooled and the activated carbon is directly added from the flue, or the combustion exhaust gas is passed through a packed tower filled with the activated carbon And the like. The method of adding the activated carbon directly from the flue is preferable because fly ash can be easily and inexpensively collected together with the activated carbon by a bag filter without installing a packed tower.

Waste activated carbon that has been brought into contact with incineration exhaust gas usually contains 1 to 10% by weight of water, but the method of the present invention oxidizes and decomposes waste activated carbon in supercritical water, so that a pretreatment step such as drying is not required. It is. Water may be added to the recovered waste activated carbon to form a slurry, which is then injected into a reactor for supercritical water oxidation.

In the method of adding activated carbon directly into a flue,
Since fly ash is also collected by the bag filter, the fly ash may be injected into the reactor together with the waste activated carbon.

Further, in the combustion furnace equipment, a smoke cleaning equipment for washing the combustion exhaust gas with water is provided before the combustion exhaust gas is released from the chimney to the atmosphere. It can be used for critical hydroxylation treatment. The method of using the wastewater from the smoke washer for the supercritical water oxidation treatment is the method of using the waste activated carbon slurry or the slurry of the mixture of the waste activated carbon and the fly ash as a solvent, or directly pressing it into the reactor to produce supercritical water. There is a way to use it. In addition, even when the wastewater generated from the smoke washer contains chemical substances such as dioxin, these substances can be decomposed by the supercritical water oxidation.

The supercritical water oxidation reaction is a reaction in which a treated product is oxidatively decomposed in a pressure-resistant reactor in the presence of supercritical water at a temperature not lower than the critical temperature and critical pressure of water. The supercritical water oxidation reactor is a high-pressure gas target facility, but may be a pipe type or a vessel type, and a pipe type is preferable in that a mixed state of the decomposition target, supercritical water, and an oxidizing agent is improved. The reaction temperature of supercritical water oxidation is generally 400 ° C. or higher,
Preferably around 600 to 650 ° C., the reaction pressure is:
It is 22 to 50 MPa, preferably 22 to 25 MPa. The reaction time is as short as 1 to 10 minutes, preferably 1 to 2 minutes. As the oxidizing agent, a liquid phase oxidizing agent such as hydrogen peroxide as well as air and oxygen gas can be used. The waste activated carbon may be injected as an aqueous or oily slurry into the reactor for supercritical water oxidation at a predetermined temperature and pressure.

Under supercritical conditions, oxygen is arbitrarily dissolved in supercritical water, so that the oxidative decomposition reaction proceeds very quickly. Therefore, not only dioxin but also activated carbon is easily decomposed. In the supercritical water oxidation reaction of the present invention, carbon atoms in the treated product are decomposed into carbon dioxide, hydrogen atoms are decomposed into water, and chlorine atoms in dioxin molecules are discharged as chloride ions, so that dioxin is adsorbed. The waste activated carbon thus obtained can be harmlessly decomposed. Further, in the supercritical water reaction, the NOx component N ₂ gas, since SOx components are discharged as SO ^3- ₄ ions, can cause air pollution without providing a removal system for NOx and SOx Absent.

According to the method of the present invention, the supercritical water oxidation reaction can be sustained by the calorific value of the activated carbon, so that it is not necessary to add an additional fuel, and the fuel cost can be reduced as compared with the incineration method. Exhaust gas due to fuel combustion can be reduced.

FIG. 1 is a flowchart for explaining the present invention. In FIG. 1, the same devices as those of the conventional refuse combustion facility are denoted by the same reference numerals, and description thereof will be omitted.

The general waste to be treated is put into an existing incinerator 1 and burned and disposed. Non-combustible materials such as metals and glass contained in general garbage are collected as incinerated ash, and combustible materials such as paper, kitchen waste, fiber, wood and bamboo, and plastic are burned and emitted as combustion exhaust gas. Is done. When a chlorine-containing compound such as a vinyl chloride resin incompletely burns, dioxin is generated. The combustion exhaust gas at 200 to 400 ° C is cooled to 100 to 200 ° C by the cooling tower. Activated carbon is sprayed in the flue to the cooled combustion exhaust gas to adsorb dioxin contained in the combustion exhaust gas to the activated carbon.
The waste activated carbon and fly ash to which dioxin has been adsorbed are collected by the bag filter 3. The collected ash activated carbon and fly ash are temporarily stored in the slurry storage tank 8 as slurry by adding water without any pretreatment. As the water of the solvent of the slurry, wastewater discharged from the smoke cleaning facility 5 may be used. The slurry of the ash activated carbon and the fly ash is sent from the slurry storage tank 8 to the supercritical water oxidation device 9 where the slurry is subjected to a supercritical water oxidation treatment.

FIG. 2 shows the details of the supercritical water oxidation apparatus 9.

First, the pressure inside the apparatus is raised to the supercritical pressure of water by the high-pressure compressor 10. Next, the slurry of waste activated carbon and fly ash sent from the slurry storage tank 8 is pressed into the tube reactor 12 by the high-pressure pump 10. At the same time, air as an oxidizing agent is pressurized by a high-pressure pump 11 and injected into a tube reactor 12. The slurry pressed into the tube reactor 12 is heated by the heater 13 to the supercritical temperature of water, and the oxidation reaction proceeds in the tube reactor 12 under the supercritical state of water. Because supercritical water is a solvent with excellent solubility, air dissolves well in supercritical water, and waste activated carbon with adsorbed dioxin is oxidatively decomposed into carbon dioxide, water, and chlorine compounds by oxygen in the air. Is done. The oxidation reaction is completed in a very short time. The processing fluid decomposed by supercritical hydroxylation is decompressed to normal pressure by the pressure reducing valve 15,
Discharge outside the system.

The heat source used for the heater 13 is a supercritical water oxidation device 9 using the heat of the combustion exhaust gas of the incinerator 1 shown in FIG.
Can reduce the heat cost for operating the.

Among the processing fluids subjected to the supercritical water oxidation treatment,
Carbon dioxide is released to the atmosphere, and water is released as wastewater. In addition, since the inorganic substance in the fly ash remains as a solid residue, it is filtered by a filter 16 as shown in FIG.

[0024]

【Example】

Reference Example 1 First, an experiment was performed to confirm whether activated carbon could be decomposed by the supercritical water oxidation method.

New activated carbon (trade name "Diasorb B4")
-8 "(manufactured by Mitsubishi Chemical Corporation) and 0.5 ml of pure water in an autoclave (300 ml in volume, Inconel 625)
The air in the autoclave was replaced with oxygen. The autoclave was then heated in an electric furnace. The time when the temperature in the autoclave reached 650 ° C. was defined as the start time of the supercritical water oxidation reaction, and the temperature was maintained for 1 minute to carry out the supercritical water oxidation reaction. After the completion of the reaction, the power supply to the electric furnace was stopped, and the sample was collected after cooling to room temperature. Here, the temperature in the autoclave was measured using a K thermocouple, and the pressure was measured using a pressure sensor.

The collected sample was first filtered through a 0.1 μm membrane filter, and the membrane filter was dried at about 110 ° C. all day and night. From the weight change before and after drying at this time, the residue weight and the weight loss rate were determined by the following formulas.

[0027]

(Equation 1)

Further, a TOC analyzer ("T" manufactured by Shimadzu Corporation)
OC-5000 ") was used to measure the TOC concentration of the filtrate. Table 1 shows the measurement results.

[0029]

[Table 1]

As is clear from the results shown in Table 1, the activated carbon itself is almost completely decomposed by supercritical water oxidation.

REFERENCE EXAMPLE 2 Using a tube reactor of Inconel 625 having an inner diameter of 6.8 mm and a length of 6 m as shown in FIG. 3, activated carbon was continuously subjected to supercritical water oxidation treatment. A 1 wt% slurry of activated carbon (trade name “Diasorb B4-8”, manufactured by Mitsubishi Kasei Corporation) was treated with hydrogen peroxide (30%) at 650 ° C. and 25 MPa.
(wt% solution) as an oxidizing agent. The experiment was performed four times while changing the flow rates of the activated carbon and the hydrogen peroxide solution. Table 2 shows the reaction conditions at this time.

[0032]

[Table 2]

The reaction was performed according to the following procedure. First, water is supplied by the plunger pump 24, and the inside of the reactor 26 is set to a predetermined pressure by the pressure regulating valve. The heater 25 is started to heat the inside of the reactor 26 to a predetermined temperature. Reactor 2
When the temperature in the chamber 6 reaches a predetermined temperature, the hydrogen peroxide solution is supplied under pressure by a plunger pump 24. Further, a predetermined amount of the activated carbon slurry 21 is supplied by a syringe pump 22 to cause a supercritical hydroxylation reaction in a reactor 26. After the reaction is completed, the processing fluid is cooled by the cooler 27, depressurized by the pressure adjusting valve 28, and separated into the exhaust gas and the processing liquid by the gas-liquid separator 29. The exhaust gas was a gas pack, and the processing liquid was collected in a sample bottle, respectively, and was subjected to analysis.

The exhaust gas was analyzed by gas chromatography with a TCD detector, using carbon dioxide (CO ₂ ), oxygen (O ₂ ),
Carbon monoxide (CO), was measured methane (CH _4). The treatment liquid was filtered through a 0.1 μm membrane filter, and the residue weight was measured. Further, the TOC concentration was measured with a TOC analyzer (“TOC-5000” manufactured by Shimadzu Corporation).

Table 3 shows the measurement results of the residue weight, the TOC concentration and the exhaust gas concentration in the processing solution.

[0036]

[Table 3]

From the results shown in Table 3, the residue weight was 1 mg.
Hereinafter, since the TOC concentration is 1 mg / L or less and the carbon monoxide and methane concentrations are 0.01% or less, it can be seen that the activated carbon is almost completely decomposed continuously by supercritical water oxidation.

Example 1 Using the supercritical water oxidation apparatus used in Reference Example 2, waste activated carbon (used for removing harmful substances such as dioxin installed in the chimney) used in the incinerator A was supercritical water. It was oxidized. The treatment was performed according to Reference Example 2.

1 g of waste activated carbon is mixed with 1 L of water to obtain 1 wt.
% Slurry and 26 ml / mi with a syringe pump.
n and fed to the tube reactor. The reaction conditions are temperature 6
The reaction was carried out at 50 ° C. and a pressure of 25 MPa.
min (reaction conditions: Run No. 4 in Table 2).
Is the same as). The oxygen ratio at this time was 2.2.

Table 4 shows the measurement results of the residue weight, TOC concentration and exhaust gas concentration in the treatment liquid, and Table 5 shows the analysis results of the dioxin concentration in the treatment water.

[0041]

[Table 4]

[0042]

[Table 5]

From the results shown in Tables 4 and 5, it was confirmed that activated carbon and dioxins adsorbed on activated carbon were almost completely decomposed by the supercritical water oxidation treatment.

[0044]

According to the method of the present invention, dioxin generated from an existing incinerator can be almost completely decomposed, and dioxin contamination from the incinerator can be prevented.

According to the present invention, the waste activated carbon having adsorbed dioxin can be subjected to a supercritical hydroxylation decomposition treatment without performing a pretreatment such as drying.

According to the third aspect of the present invention, fly ash containing dioxin can be treated at the same time as waste activated carbon, so that there is no need to install a separate treatment system and equipment costs can be reduced.

According to the present invention, the wastewater discharged from the smoke washing facility can be used as a slurry solution of a mixture of waste activated carbon and fly ash as it is, and also the chemical substances in the wastewater can be treated.

[Brief description of the drawings]

FIG. 1 is a flowchart for explaining the outline of the method of the present invention.

FIG. 2 is a flowchart for explaining the supercritical water oxidation treatment of the method of the present invention in detail.

FIG. 3 is a flowchart for explaining a supercritical water oxidation treatment apparatus used in Reference Example 2 and Example 1.

FIG. 4 is a flowchart for explaining a conventional refuse incineration method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Incinerator 2 Cooling tower 3 Bag filter 4 Bag filter 5 Smoke washing equipment 6 Catalytic denitration equipment 7 Chimney 8 Waste activated carbon slurry storage tank 9 Supercritical oxidation treatment device 10 High pressure pump 11 High pressure compressor 12 Tube type reactor 13 Heater 14 Cooler 15 Pressure reducing valve 16 Filter 21 Spent activated carbon slurry tank 22 Syringe pump 23 Hydrogen peroxide water tank 24 Plunger pump 25 Heater 26 Tube reactor 27 Cooler 28 Pressure control valve 29 Gas-liquid separator

Claims (4)

[Claims] 1. An incinerator-derived method comprising: adsorbing dioxin discharged from an incinerator onto activated carbon; and oxidatively decomposing the waste activated carbon having adsorbed dioxin in supercritical water at a critical temperature and pressure of water or higher. Dioxin decomposition method. 2. A supercritical water oxidation treatment in which waste activated carbon adsorbing dioxin is directly supplied to a supercritical water oxidation reactor in a slurry state without performing pretreatment such as drying. 2. The method for decomposing dioxin derived from the incinerator according to 1. 3. A process for decomposing dioxin derived from an incinerator according to claim 1, wherein the fly ash discharged from the incinerator is subjected to a supercritical water oxidation treatment together with waste activated carbon adsorbing dioxin. Method. 4. The dioxin derived from an incinerator according to claim 1, wherein waste water discharged from a smoke washing facility of the incinerator is used for a supercritical water oxidation reaction. Decomposition method.