JP3332150B2 - How to treat incineration residues - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to hydrothermal treatment of solids such as incineration residues containing organic chlorine compounds.

[0002]

2. Description of the Related Art Dioxins are chemical substances generated unintentionally in the combustion process of wastes and the like.
A wide range of toxic effects have been reported, including acute toxicity, carcinogenicity, teratogenicity, immunotoxicity, and even reproductive toxicity.
Since it is difficult to decompose in the environment, its environmental pollution has attracted attention as a global environmental problem.

[0003] Most of the dioxins generated by refuse incineration are carried along with the combustion gas and are transferred to fly ash collected by a dust collector, so that the fly ash contains a large amount of dioxins. Incinerated ash also contains a small amount of dioxins. For these reasons, fly ash and incineration ash are melt-solidified,
Fly ash is subjected to heat dechlorination.

[0004] In the melt-solidification treatment, fly ash and incinerated ash are reduced to 1500
This is a method in which slag is melt-processed at a high temperature of at least ℃. In addition, heat dechlorination treatment is described in JP-B-6-3886.
For example, as disclosed in No. 3, fly ash is charged into a heating device and heated in a reducing atmosphere (oxygen concentration 1-2%).
This is a method of performing heat treatment at ~ 450 ° C. According to the heat dechlorination treatment, the dioxins in fly ash can be reduced from 0.6 TEQ-ng / g to 0.0
There is a report that it is greatly reduced to 02TEQ-ng / g.

As a method for efficiently decomposing dioxins at a low temperature, JP-A-6-142637 discloses a method.
Hydrothermal treatment of slurry fly ash is disclosed. In this treatment method, 6.7 to 20 parts by weight of water or alkaline water is mixed with 1 part by weight of fly ash to prepare a fly ash slurry, which is subjected to hydrothermal treatment at 100 to 350 ° C. This is a treatment method for decomposing dioxins. According to this method, 80% or more of dioxins contained in fly ash can be decomposed by hydrothermal treatment at 100 ° C. for 10 minutes or more, or 300 ° C. for 2 minutes or more.

[0006]

The melting and solidifying treatment of fly ash and incinerated ash requires a high temperature of 1500 ° C. or more, and requires a large facility because of handling a molten material, resulting in high processing costs.
Also, in the heat dechlorination treatment of fly ash, a large heating device is used to uniformly heat powdery fly ash for a long time, and a rapid cooling device for heated fly ash is used to prevent re-synthesis of dioxins. As in the case of the melt-solidification treatment, the equipment becomes large-scale and the treatment cost is high. As described above, these processing methods have room for improvement in that the processing equipment is large-scale and the equipment cost and operation cost are high.

On the other hand, the hydrothermal treatment of fly ash slurry also requires an expensive pressure vessel. In addition, fly ash slurry after hydrothermal treatment cannot be disposed of as it is, and requires solid-liquid separation. Since the liquid generated by solid-liquid separation contains a high concentration of salts transferred from fly ash, it cannot be discharged into rivers, and requires evaporative drying to dryness. As described above, the treatment process is also complicated in the hydrothermal treatment of the fly ash slurry, and the treatment equipment becomes large-scale, as in the case of the melt-solidification treatment and the heat dechlorination treatment. Slurry transportation is possible with fly ash of uniform powder, but it is difficult to apply it to incinerated ash with a mixture of lumps.

[0008] The present invention provides a method capable of performing low-cost decomposition treatment of dioxins in incineration residues such as fly ash and incineration ash. More specifically, the present invention provides hydrothermal treatment of incineration residues with a smaller pressure than in the past. It is an object of the present invention to provide a method which can be carried out efficiently in a container, eliminates the need for solid-liquid separation and waste liquid treatment, and can provide a processed material having good handling properties for transportation.

[0009]

The present inventors believe that the conventional hydrothermal treatment carried out in a slurry state causes many obstacles, and dioxins in a condition where the water content is further reduced than in the slurry state. The research on the hydrothermal hydrolysis treatment of was carried out in detail. As a result, the water content of the mixture of the incineration residue and water was 10 to 80%, and the heating temperature was 1%.
It was found that hydrothermal hydrolysis of dioxins proceeds at a temperature of 00 to 350 ° C. In addition, the water content is 10 to 50.
% Has been found to be possible.

The present invention is based on the finding that dioxins in incineration residues can be decomposed almost in the same manner as in a slurry even in a kneaded state.

[0011] By changing the form of the incineration residue to be subjected to hydrothermal treatment to a kneaded state having a low fluidity instead of a slurry state, the volume of the whole treated material containing water can be reduced, and the pressure vessel used for performing hydrothermal treatment Can be reduced in size.
Further, since the processed material is in a kneaded state, there is no need for solid-liquid separation and waste liquid treatment. By setting the moisture content of the kneaded material to the condition described below, it is possible to obtain handleability necessary for transporting the processed material. Hydrothermal treatment can be performed even when a lump of material such as incineration ash is mixed.

The bulk density of the kneaded material is the highest when all voids are filled with water and free of moisture (capillary state). In this state, the volume of the incineration residue is small, and the volume of the pressure vessel used for hydrothermal treatment can be reduced. Also,
At this time, the mechanical strength of the kneaded material is high, there is no sticking to the transporter during loading into the pressure vessel, generation of floating water, etc.,
Handling becomes easy. Since the stirring torque of the kneaded material becomes highest in the capillary state, the water content in the capillary state can be easily determined by measuring the stirring torque while gradually adding water during kneading. Moisture content of refuse incineration fly ash is about 20-3
There is a moisture content in a range of 0% to be in a capillary state.

[0013] In order to obtain good handling properties in which a kneaded material and a processed material are not adhered to a transporting device during transport,
It is necessary that the kneaded material and the processed material do not show liquidity. In particular, since the processed material is carried out to the final disposal site by a truck or the like, it is important to obtain good handling of the processed material. The state that does not show liquidity is, for example, JIS-A-
Judgment can be made by a liquid limit / plastic limit test of soil 1205, and an appropriate moisture content range of the kneaded material and the processed material can be determined. In other words, at the time when the kneaded material discharged from the pressure vessel ends the water evaporation by sensible heat after the completion of the hydrothermal treatment, the water content at the time of kneading is set by setting the water content at the time of kneading so that the processed material is below the liquid limit. Good handleability can be obtained. The kneaded material of refuse incineration fly ash exhibits liquidity when the moisture content exceeds about 30%. Therefore, in order to reduce the water content of the processed product to approximately 30% or less, it is desirable that the moisture content of the kneaded material to be charged into the pressure vessel be approximately 50% or less in consideration of evaporation of water. However, since the moisture content of the mixture of the incineration residue and water that exhibits liquidity varies depending on the particle size and components, even if the moisture content of the kneaded product exceeds 50%, the treated product does not exhibit liquidity. The moisture content at the time of kneading may be set. When a water-soluble organic solvent such as methanol is added, water and the water-soluble organic solvent are treated as moisture.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Incineration residue and water, aqueous alkali solution,
After mixing with any of the alkaline aqueous solutions containing a water-soluble organic solvent, loading the mixture into a pressure vessel, sealing it,
Heat to 100-350 ° C. When a predetermined time according to the heating temperature has elapsed, the pressure vessel is opened and the mixture is discharged. The moisture of the mixture evaporates by sensible heat when the pressure vessel is opened, so that the mixture becomes a kneaded material having good handleability for conveyance, and is discharged by an unloading device such as a belt conveyor.

The water content of a mixture of the incineration residue and water, an aqueous alkaline solution, or an aqueous alkaline solution containing a water-soluble organic solvent is 1%.
0 to 80% is appropriate, but the moisture percentage may be 10 to 50%. If the water content is less than 10%, the effect of the hydrothermal treatment is reduced. If the water content is more than 80%, the volume of the mixture of the incineration residue and water, an alkaline aqueous solution, or an alkaline aqueous solution containing a water-soluble organic solvent becomes extremely large, and The pressure vessel to be provided becomes large. If the water content exceeds 50%, an obstacle such as adhesion occurs in the transport of the processed product. In addition, the water content is 50 to
For 80% of the treated material, good handling properties can be obtained by adding and kneading cement or the like after the hydrothermal treatment.

FIG. 1 shows the relationship between the volume ratio and the water content of a mixture of the incineration residue and water, an aqueous alkaline solution, and an aqueous alkaline solution containing a water-soluble organic solvent. It can be seen that the volume of the mixture rapidly increases when the water content is 80% or more.

By hydrothermal treatment, the dioxins C-C
The l-bond is hydrolyzed to form a C-OH bond and HCl, and this reaction is promoted by an alkali neutralization reaction. The addition of methanol facilitates the dissolution of dioxins and lowers the surface tension of the solution. Regarding the fact that the solvent easily penetrates into the pores of the ash to increase the reaction efficiency, see Chemical Apparatus, July 1995, p. 55-59
It is shown in "Decomposition of dioxins by hydrothermal reaction".

In the present invention, it is expected that the hydrothermal hydrolysis reaction of dioxins proceeds in the water film on the particle surface of the incineration residue. It is assumed that even in the presence of a small amount of water, evaporation and condensation of water are repeated in the pressure vessel, and water is constantly supplied to the particle surface of the kneaded material. Moreover, since the dioxins generated in the incineration process are adsorbed on the particle surfaces of the incineration residue, and the dioxins are present at a low concentration, it should be possible to obtain a practical level of decomposition characteristics as shown in the examples. Seem.

[0019]

<Example 1> 100 g of refuse incineration fly ash and 1 g of sodium hydroxide were mixed with water so that the mixture had a water content of 5 to 87%, and the mixture was filled in an autoclave.
Heated to 250 ° C. and held for 1 hour. Next, the autoclave was cooled and the processed product was taken out. Dioxins contained in the test fly ash and the treated fly ash were analyzed. Table 1 shows the TCDD equivalent equivalent concentration (TEQ) per dry ash and the decomposition rate of dioxins. At a water content of 10% or more, the decomposition rate of dioxins was 90% or more, and a decomposition rate almost equal to the water content of 87% (slurry state) of the comparative example could be obtained.

[0020]

[Table 1] <Example 2> 100 g of refuse incineration fly ash, 1 g of sodium hydroxide and 30 g of water were mixed and mixed, and the mixture was filled in an autoclave, heated to 100 to 350 ° C and held for 1 hour. Next, the autoclave was cooled and the processed product was taken out. Dioxins contained in the test fly ash and the treated fly ash were analyzed. Table 2 shows the TCDD equivalent equivalent concentration (TEQ) per dry ash and the decomposition rate of tyoxins.
At 100 ° C. or higher, the decomposition rate of dioxins was 80% or higher, confirming the effect of hydrothermal treatment.

At this time, the kneaded material was not muddy but had good handleability. The moisture content of the kneaded product was 23%.
FIG. 1 shows the results of measuring the water content of the kneaded material and the motor torque of the kneader. When the water content was 23%, the motor torque became maximum, and at this time, the kneaded material was in a capillary state.
The processed material was not muddy and had good handling properties. The water content of the processed product was 20%. In addition, water was added to the test fly ash, and a test in accordance with JIS-A-1205 soil liquid limit / plastic limit test was performed, and the test results shown in FIGS. 2 and 3 were obtained. It was found that when the water content was 30% or more, the kneaded material showed liquidity and became muddy.

[0022]

[Table 2] Example 3 100 g of refuse incineration fly ash and 30 g of an aqueous solution containing 1 g of the following alkaline agent were mixed and kneaded. The mixed alkaline agents were calcium hydroxide, potassium hydroxide, magnesium hydroxide, ammonia, and urea. Further, 100 g of refuse incineration fly ash and 30 g of purified water were mixed and kneaded.
After filling these kneaded materials in an autoclave, 250
C. and kept for 1 hour. Next, the autoclave was cooled and the processed product was taken out. Dioxins contained in the test fly ash and the treated fly ash were analyzed. T per dry ash
Table 3 shows the equivalent concentration of CDD toxicity (TEQ) and the decomposition rate of dioxins. When an alkaline agent was used, the decomposition rate of dioxins was higher than that of purified water. Both the kneaded material and the processed material were not muddy and could withstand transportation.

[0023]

[Table 3] <Example 4> Waste incineration fly ash 2 kg, sodium hydroxide 2
After mixing and kneading 0 g and 1000 g of water, the mixture was filled in an autoclave, and then heated to 230 ° C. and held for 1 hour.
Next, the autoclave was cooled and the processed product was taken out. Dioxins contained in the test fly ash and the treated fly ash were analyzed. TCDD toxicity equivalent concentration per dry ash (T
Table 4 shows the decomposition rates of EQ) and dioxins. The water content of the kneaded material was 33%, which was in a greasy state. However, the processed material taken out was not muddy and could withstand transportation. The water content of the processed product was 29%.

[0024]

[Table 4] <Example 5> Waste incineration fly ash 2kg, sodium hydroxide 2
A mixture obtained by mixing and kneading 0 g, 900 g of water and 100 g of methanol was filled in an autoclave, and then heated to 230 ° C. and held for 1 hour. Then cool the autoclave,
The processed material was removed. Dioxins contained in the test fly ash and the treated fly ash were analyzed. TCDD per dry ash
Table 5 shows the equivalent concentration of toxicity (TEQ) and the decomposition rate of dioxins. The kneaded material and the processed material were not muddy and were able to withstand transportation. The decomposition rate of dioxins was improved as compared with Example 4.

[0025]

[Table 5] <Example 6> Waste incineration ash 2 kg, sodium hydroxide 20
g and 500 g of water were mixed and kneaded, filled in an autoclave, heated to 230 ° C. and held for 1 hour. Next, the autoclave was cooled and the processed product was taken out. Dioxins contained in the test ash and the treated fly ash were analyzed. TCDD toxicity equivalent concentration per dry ash (TE
Table 6 shows the decomposition rates of Q) and dioxins. Kneaded material,
The processed material was not muddy but endured for transportation. The water content of the kneaded product was 20%, and the water content of the processed product was 18%.

[0026]

[Table 6] <Example 7> Waste incineration fly ash 5 kg, sodium hydroxide 5
After filling a mixture of 0 g and 20 kg of water into an autoclave, the mixture was heated to 230 ° C. and held for 1 hour. Next, the autoclave was cooled to take out the processed product, and 25 kg of Portland cement was mixed and kneaded with the processed product. Dioxins contained in the test ash and the treated fly ash were analyzed. Table 7 shows the TCDD equivalent toxicity equivalent concentration (TEQ) per dried product containing cement. Although the mixture was muddy, the treated product obtained by mixing and kneading the cement with the hydrothermally treated product was not muddy but had good handling properties. The water content of the mixture was 80%.

[0027]

[Table 7]

[0028]

According to the present invention, the hydrothermal treatment of the incineration residue can be efficiently carried out in a pressure vessel smaller than before, and furthermore, there is no need for solid-liquid separation or waste liquid treatment, and good handling properties for transportation are achieved. A processed product is obtained. Hydrothermal treatment is possible even for incineration residues containing lumps. in this way,
Hydrothermal treatment of dioxins in incineration residues can be easily performed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a volume ratio of a mixture and a water content.

FIG. 2 is a diagram showing a relationship between a moisture content of a kneaded material and a motor torque (load current value) of a kneader as a test result performed on Example 2.

FIG. 3 is a graph showing the results of a liquid property limit test for Example 2.

FIG. 4 is a view showing a Vicat needle test result for Example 2.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-142637 (JP, A) JP-A-8-66671 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B09B 3/00-5/00

Claims (5)

(57) [Claims] In the hydrothermal treatment of an incineration residue, the moisture content of a mixture of any one of water, an aqueous alkali solution and an aqueous alkaline solution containing a water-soluble organic solvent and the incineration residue is 10%.
A method for treating incineration residues, wherein a mixture of about 80% is heated at 100 to 350 ° C. 2. The method for treating incineration residues according to claim 1, wherein the water content of the mixture is 10 to 50%. 3. The incineration residue according to claim 1, wherein one of water, an aqueous alkaline solution, and an aqueous alkaline solution containing a water-soluble organic solvent is mixed with the incineration residue so that the mixture is in the vicinity of a capillary state. Item 3. A method for treating incineration residues according to Item 2. 4. After the hydrothermal treatment, the discharged hydrothermally treated product is:
At the time when the water evaporation by sensible heat is completed, the incineration residue is mixed with any one of water, an aqueous alkaline solution, and an aqueous alkaline solution containing a water-soluble organic solvent so that the processed material is below the liquid limit point. 3. The method for treating incineration residues according to claim 1 or claim 2. 5. The alkaline aqueous solution is any one of a calcium hydroxide solution, a sodium hydroxide solution, a potassium hydroxide solution, a magnesium hydroxide solution, an ammonia solution, and a urea solution, or a mixture of any one of them. The method for treating incineration residues according to any one of claims 1 to 4, wherein