JP2003334510A - Chlorine removing treatment method for molten fly ash - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a chlorine removing treatment method based on the washing treatment of molten fly ash for removing chlorine in the molten fly ash by a relatively reduced amount of washing water, that is, enhancing the return possibility of a dehydrated cake to the foot of a mountain and capable of reducing not only drain quantity but also the concentration of residual heavy metals in wastewater. <P>SOLUTION: The method for removing chlorine from molten fly ash 1 containing chlorine discharged from waste melting facilities includes two processes, that is, a process (a) for adding washing water to the molten fly ash 1 to elute chlorine in the molten fly ash and dehydrating the molten fly ash to which washing water is added to obtain wastewater 5 and washing residue 6 and a process (b) for adding washing water 8 to the first washing residue 6 obtained in the process (a) to elute residual chlorine in the washing residue and dehydrating the washing residue to which washing water is added to obtain a separated liquid 12 and a desalted cake 11. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chlorine removal treatment method by water washing treatment of molten fly ash discharged together with exhaust gas by melting waste such as municipal waste.

[0002]

2. Description of the Related Art In general, in the fly ash discharged from the refuse incineration ash and the fly incineration fly ash, etc., are dissolved salts such as sodium chloride and potassium chloride. Is contained in high concentration. In addition, harmful heavy metals such as lead and cadmium are also contained in high concentration compared to refuse incineration fly ash, so conventionally they are often landfilled at the final disposal site by cement hardening or chemical chelation.

However, it is becoming difficult to secure the final disposal site year by year, and the amount of disposal for the stabilization treatment by cement solidification increases, which causes a decrease in the life of the final disposal site. On the other hand, solidification of cement or treatment with a chelating agent cannot suppress the elution of soluble salts including the above-mentioned chlorides, and thus there is concern about environmental pollution.

[0004] In addition, there are cases in which the molten fly ash contains several% to several tens of% of zinc and lead, depending on the type, but these heavy metals are recovered from the viewpoint of resource recycling,
It is desired to develop a so-called Yamamoto reduction technology that reuses recovered materials as smelting raw materials.

On the other hand, as one of the conditions for reusing the heavy metals recovered from the molten fly ash as a smelting raw material, in order to avoid corrosion of the smelting equipment and clogging of the flue gas treatment system with chlorides, It is said that it is first necessary to reduce the chlorine content in the recovered material as much as possible.

[0006] One of the methods for recovering heavy metals from molten fly ash is to add a predetermined amount of water to the molten fly ash for washing and dehydration treatment to separate soluble salts from the molten fly ash.
The desalination cake obtained as a result is Yamamoto reduced as a smelting raw material, while the wash water containing separated soluble salts removes trace amounts of heavy metals by wastewater treatment, and the treated water is discharged into the river or the salt is recovered. A method for removing chlorine by washing the molten fly ash with water has been proposed.

[0007]

However, in most of the above-mentioned methods for washing the molten fly ash with water, since some of the soluble salts remain with the residual water in the desalted cake, chlorine removal is insufficient. There was a case. On the other hand, in order to reduce the chlorine concentration in the desalination cake as much as possible, it is necessary to increase the solid-liquid ratio of the molten fly ash and the washing water, but in that case, a large amount of washing water is required, which is a burden of wastewater treatment. There was a problem that became large.

An object of the present invention is to remove chlorine in molten fly ash with a relatively small amount of washing water, that is, to increase the possibility of reducing the hillside of a desalination cake. It is an object of the present invention to provide a chlorine removal treatment method by washing with water of molten fly ash, which can reduce the concentration of residual heavy metals.

[0009]

As a result of intensive studies to solve the above problems, the present inventor has found that the amount of chlorine used can be reduced with a small amount of washing water by washing twice, and has reached the present invention. That is, the present invention provides a chlorine removal treatment method for molten fly ash, which comprises the following two steps when removing chlorine from molten fly ash containing chlorine discharged from a waste melting facility. It is what (A) A step of adding cleaning water to the molten fly ash to dissolve chlorine in the molten fly ash into water and then performing dehydration to obtain drainage and a cleaning residue. (B) Wash water is added again to the wash residue obtained in the above step (a) to elute residual chlorine in the wash residue into water,
A step of performing dehydration to obtain a separated liquid and a desalted cake. Further, in the present invention, preferably, a part or all of the separated liquid obtained in the step (b) is used as washing water used in the step (a), and more preferably (a) In the step) and / or step (b), washing water is added to adjust the pH during stirring and mixing to be in the range of 9 to 12 with an alkaline agent or an acidic agent to insolubilize the water-soluble heavy metals. It is a feature.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
The molten fly ash to which the chlorine removal method of the present invention can be applied is a molten fly ash obtained by an exhaust gas treatment facility by subjecting a refuse incineration ash and a refuse incineration fly ash to a melting treatment. Molten fly ash obtained from equipment that does not require blowing of slaked lime for treatment, and in equipment that uses a two-stage bag filter in the dust collector, molten fly ash trapped in the preceding stage, and treatment of acidic exhaust gas Molten fly ash obtained from equipment in which a sodium hydroxide aqueous solution is sprayed on is preferably used. The properties of such molten fly ash include a relatively high content of soluble salts (50
.About.80%), the content of heavy metals is as high as several%, and 10% slurry pH is 5-8.

In the present invention, in step (a), first, washing water is added to the molten fly ash. As a result, chlorine in the molten fly ash is eluted in water. The amount of wash water to be added is preferably 200 to 2,000 parts by mass with respect to 100 parts by mass of molten fly ash. When the amount of water is less than 200 parts by mass, the fluidity of a liquid such as a molten fly ash obtained by adding washing water, such as slurry, becomes poor, and the elution rate of chlorine into water tends to decrease. On the other hand, if the amount exceeds 2,000 parts by mass, the amount of liquid may increase and the equipment capacity for treating the liquid may have to be increased. The temperature of the washing water is not particularly limited, but is 40 to 100 ° C. in consideration of the elution efficiency of soluble salts.
Is preferable, and more preferably 70 to 90 ° C. Further, as described below, part or all of the separated liquid obtained in the step (b) may be used as the washing water. It is preferable to use the separated liquid because the amount of washing water used can be reduced.

When the washing water is added, it is usually stirred and mixed. Any means may be used for stirring and mixing, and for example, stirring may be performed for 30 minutes to 6 hours using a rotary stirrer.

At this time, it is preferable to adjust the pH of the mixed solution to 9 to 12 because the water-soluble heavy metals can be insolubilized. For that purpose, an alkaline agent or an acidic agent may be added. As an alkaline drug,
Examples thereof include sodium hydroxide, potassium hydroxide and slaked lime, and examples of acidic agents include hydrochloric acid and sulfuric acid.

In the step (a), dehydration is then performed to separate the waste water and the cleaning residue. Chlorine in the molten fly ash will be transferred to the wastewater. Any method may be used as a means for dehydrating, for example, a centrifugal dehydrator or a belt press is used.

In the present invention, next, wash water is added again to the wash residue obtained in step (a) to elute residual chlorine in the wash residue into water. The amount of wash water is 1
200 to 2,000 parts by mass is preferable per 00 parts by mass. When the amount of water is less than 200 parts by mass, the fluidity of a liquid such as a molten fly ash obtained by adding washing water, such as a slurry, becomes poor, and the elution rate of chlorine into water is likely to decrease. On the other hand, if the amount exceeds 2,000 parts by mass, the amount of liquid may increase and the equipment capacity for treating the liquid may have to be increased.

In step (b), dehydration is then performed to obtain a separated liquid and desalted cake. As the dehydration means, the one used in the step (a) can be similarly used.

In the present invention, part or all of the separated liquid obtained in the step (b) can be used also as washing water in the step (a). This is preferable because the amount of washing water used can be reduced.

Hereinafter, the present invention will be described in more detail with reference to the drawings. FIG. 1 is a schematic flow chart showing an example of the method of the present invention. In FIG. 1, the equipment for treating the molten fly ash includes a first stirring and washing tank 2, a first solid-liquid separation device 4,
It is composed of a second stirring and washing tank 7, a second solid-liquid separation device 10 and a separated liquid storage tank 13. In the step (a), the first
After the molten fly ash 1 is put into the stirring and washing tank 2, a stored liquid 14 which is a separated liquid 12 obtained in the washing water (b) step,
After adding the first pH adjusting chemicals 3 and stirring to dissolve the soluble salts in the molten fly ash, solid-liquid separation is performed by the first solid-liquid separation device 4, and the first cleaning residue 6 and the waste water 5 are separated. obtain.

Next, in the step (b), the first cleaning residue 6
Is transferred to the second stirring and washing tank 7, and water 8 and the second pH adjusting chemical 9
Is added and stirred to dissolve the residual soluble salts remaining in the first washing residue, and then solid-liquid separation is performed in the second solid-liquid separator 10 to obtain a desalination cake 11 and a separated liquid 12. The separated liquid 12 is stored in the separated liquid storage tank 13 and used as washing water.

[0020]

EXAMPLES The present invention will be specifically described below with reference to examples. Example 1 Processing was performed according to the flow chart shown in FIG. Molten fly ash 1
As the chemical composition is soluble salt concentration 77.7 dry%, Cl 34.
60 dry%, F 0.07 dry%, Na 20.80 dry%, K 12.70 dry
%, Zn 6.11 dry%, Pb 2.82 dry%, Cd 0.06 dry%, Cu 3.
Using 41 g of dry fly ash generated from a mixing and melting furnace for municipal waste incineration ash and incineration fly ash, which is spraying an aqueous sodium hydroxide solution for acidic exhaust gas treatment of 41 dry% and Ca 0.69 dry%, Add 900 mL of the stored liquid 14 from the separated liquid storage tank 13,
After stirring for 3 hours in the first stirring and washing tank 2 to dissolve the soluble salts in the molten fly ash, solid-liquid separation is performed by the first solid-liquid separation device 4, and the first washing residue 6 is obtained. Chemical composition soluble salts 23.80 dry%, Cl 7.29 dry%, F 0.15 dry%, Na
6.50 dry%, K 3.38 dry%, Zn 23.47 dry%, Pb 14.08dry
%, Cd 0.21 dry%, Cu 0.98 dry%, Ca 2.25 dry% 1st
36.7 g (dry weight) of the washing residue and 870 mL of drainage 5 were obtained.

Next, the first washing residue is mixed with the second stirring washing tank 7
After adding 900 mL of water 8 and stirring for 3 hours to dissolve the residual soluble salts remaining in the first washing residue, solid-liquid separation is performed in the second solid-liquid separator 10 to remove the desalted cake. 11, the chemical composition is soluble salts 6.79 dry%, Cl
2.31 dry%, F 0.21 dry%, Na 0.40 dry%, K 0.35 dry
%, Zn 37.38 dry%, Pb 16.23 dry%, Cd 0.15 dry%, Cu
22.5 g (dry amount) of desalted cake of 3.77 dry% and Ca 1.67 dry% and 860 mL of the separated liquid 12 were obtained.

Example 2 100 g of the same molten fly ash 1 as used in Example 1 was added, 900 mL of the stored liquid 14 from the separated liquid storage tank 13 was added, and 10% sodium hydroxide was added as the first pH adjusting agent 3. 13 mL was added, and stirring was performed for 3 hours while adjusting the pH at the time of stirring and mixing to 11 to dissolve the soluble salts in the molten fly ash. Next, solid-liquid separation is performed by the first solid-liquid separation device 4, and as the first cleaning residue 6, the chemical composition is soluble salts 19.2 dry%, Cl
5.96 dry%, F 0.15 dry%, Na 5.22 dry%, K 2.34 dry
%, Zn 19.74 dry%, Pb 13.54 dry%, Cd 0.20 dry%, Cu
35.2 g (dry amount) of the first washing residue of 1.00 dry% and Ca 1.73 dry% and 880 mL of drainage 5 were obtained.

Thereafter, the first washing residue 6 was transferred to the second stirring and washing tank 7, 900 mL of water 8 was added, and 1 mL of 10% sodium hydroxide was further added as the second pH adjusting agent 9, and the pH at the time of stirring and mixing was 11. The mixture was stirred for 3 hours while adjusting to. Next, solid-liquid separation is performed in the second solid-liquid separator 10, and the desalination cake 11 has a chemical composition of 5.97 dry salts.
%, Cl 2.09 dry%, F 0.19 dry%, Na 1.16 dry%, K 0.4
7 dry%, Zn 37.46 dry%, Pb 11.41 dry%, Cd 0.25 dry
%, Cu 3.71 dry%, Ca 1.73 dry% desalted cake 22.5 g (dry amount), and 880 mL of the separated liquid 12 were obtained.

Comparative Example 1 100 g of the same molten fly ash 1 as in Example 1 was added with 1,900 mL of water (20-fold dilution), and after mixing and stirring, the washing residue had a chemical composition of soluble salts of 21.95 dry% and Cl 3.14. dry%, F 0.17 dry
%, Na 2.64 dry%, K 1.21 dry%, Zn 11.05 dry%, Pb 9.
33.5 g (dry amount) of 53 dry%, Cd 0.12 dry%, Cu 0.46 dry%, Ca 1.93 dry% washing residue, and 1,860 mL of waste water were obtained.

Comparative Example 2 100 g of the same molten fly ash 1 as in Example 1 was added, 2,900 mL of water was added (30-fold dilution), and after mixing and stirring, as a washing residue, the chemical composition was soluble salts 15.51 dry%, Cl 2.72 dry%, F 0.17 dry
%, Na 2.58 dry%, K 1.12 dry%, Zn 10.93 dry%, Pb 9.
33.0 g (dry amount) of 03 dry%, Cd 0.12 dry%, Cu 0.46 dry%, Ca 1.62 dry% washing residue, and drainage 2,880 mL were obtained.

Comparative Example 3 100 g of the same molten fly ash 1 as in Example 1 was added, 4,900 mL of water was added (diluted 50 times), and after mixing and stirring, the washing residue had a chemical composition of soluble salts 12.05 dry% and Cl 2.45. dry%, F 0.16 dry
%, Na 1.99 dry%, K 0.97 dry%, Zn 12.54 dry%, Pb 9.
05 dry%, Cd 0.14 dry%, Cu 0.50 dry%, Ca 1.76 dry%
29.7 g (dry weight) of the washing residue and 4,850 mL of drainage were obtained.

Table 1 shows the chlorine concentrations of the desalted cakes obtained in Examples 1 and 2 and the cleaning residues obtained in Comparative Examples 1 to 3 and the amounts of waste water generated in Examples 1 and 2 and Comparative Examples 1 to 3. Shown in.

[0028]

[Table 1]

Table 2 shows the concentration of each heavy metal contained in the waste water obtained in Examples 1 and 2.

[0030]

[Table 2]

From Table 1, in Comparative Examples 1 to 3, the chlorine concentration in the cleaning residue decreases as the solid-liquid ratio increases, but the concentration is 2.45 to 3.14 dry%, and the amount of drainage is about. Very large amount of 2,000-5,000 mL is generated. On the other hand, the chlorine concentration of the desalted cake obtained in Example 1 is 2.31.
Dry%, the chlorine concentration of the desalted cake obtained in Example 2 is 2.09
It becomes dry% and chlorine is effectively removed. Furthermore, the amount of wastewater per 100 g of molten fly ash is 870 mL and 880, respectively.
Since it is mL, it can be seen that the amount of waste water also decreases.

From Table 2, since the wastewater obtained in Example 1 was not pH-adjusted, the concentration of heavy metals in the wastewater was 1.06 to 2
Although it showed a slightly high value of 5.4 mg / L, it can be obtained by adjusting the pH during stirring and mixing of the first stirring and washing apparatus 2 or the second stirring and washing apparatus 7 to around 11 as in Example 2. It can be seen that the concentration of heavy metals in the wastewater can be reduced to 0.014 to 0.32 mg / L.

[0033]

According to the present invention, since the molten fly ash is washed twice, it is possible to effectively remove chlorine in the resulting desalted cake. In addition, the amount of wastewater generated per molten fly ash is small. Further, the chlorine concentration in the separated liquid obtained in the step (b) is relatively low, and a part or the whole amount of the separated liquid can be reused as the washing water in the step (a). Therefore, the amount of waste water generated per molten fly ash can be reduced. Further, by adjusting the pH in the stirring and washing tank, the heavy metals in the molten fly ash are insolubilized, and most of them are transferred to the desalination cake by solid-liquid separation, so that wastewater with a low concentration of heavy metals can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic flow chart illustrating a chlorine removal treatment method by water washing treatment of molten fly ash according to an embodiment of the present invention.

[Explanation of symbols]

1 molten fly ash 2 First stirring cleaning tank 3 First pH adjusting agent 4 First solid-liquid separator 5 drainage 6 First cleaning residue 7 Second stirring cleaning tank 8 wash water 9 Second pH adjusting agent 10 Second solid-liquid separator 11 desalination cake 12 Separation liquid 13 Separated liquid storage tank 14 Reservoir

Claims (3)

[Claims] 1. A method for removing chlorine from molten fly ash, which comprises the following two steps when removing chlorine from molten fly ash containing chlorine discharged from a waste melting facility. (A) A step of adding cleaning water to the molten fly ash to dissolve chlorine in the molten fly ash into water and then performing dehydration to obtain drainage and a cleaning residue. (B) Wash water is added again to the wash residue obtained in the above step (a) to elute residual chlorine in the wash residue into water,
A step of performing dehydration to obtain a separated liquid and a desalted cake. 2. The method according to claim 1, wherein a part or all of the separated liquid obtained in the step (b) is used as washing water used in the step (a). Processing method. 3. In step (a) and / or step (b), washing water is added to adjust the pH at the time of stirring and mixing with an alkaline chemical or an acidic chemical so as to be in the range of 9 to 12, and The method for removing chlorine from molten fly ash according to claim 1 or 2, wherein heavy metals are insolubilized.