JP3333618B2 - Incineration ash treatment system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system for treating incinerated ash generated during incineration of municipal waste, sewage sludge, and other general waste.

[0002]

2. Description of the Related Art Incineration ash generated during incineration of municipal garbage, sewage sludge, and other general waste is partially melted from cement filler, aggregates such as blocks, and even incineration ash. Later, most of them have been used as roadbed materials, but most of them have been used for landfill.

[0003]

However, in recent years,
It is becoming increasingly difficult to secure landfills, and incinerated ash usually contains heavy metals such as cadmium, lead, mercury, and chromium. Severe, as a result, there is a problem that high-cost managed landfills are becoming difficult to use. Therefore, today, the effective use of the incinerated ash is a very important issue.

[0004] As an effective use of incinerated ash, it is conceivable to use it as a cement raw material. However, incinerated ash includes CaO, SiO ₂ , Al ₂ O ₃ , Fe ₂ O
Although it contains an active ingredient as cement, such as ₃ ,
On the other hand, it contains a large amount of alkali components such as K ₂ O and Na ₂ O and chlorine components such as Cl, and it is not preferable to use these as raw materials for cement. That is, in a modernized cement production plant, not only the alkali and chlorine components adhere to the suspension preheater and block it, but also a stable firing operation becomes impossible, but also the produced cement has an alkali-aggregate reaction. There is a problem in using steel as it is as it causes corrosion of reinforcing steel by chlorine and chlorine. i

[0005] In view of the above circumstances, it is an object of the present invention to simply and efficiently treat incinerated ash and to make effective use of it.

[0006]

The alkali and chlorine components in the incineration ash can be used as a cement raw material by washing and removing them with water. However, heavy metals such as cadmium (Cd) and lead (Pb) in the incineration ash dissolve in the washing water, and cannot be directly discarded.

[0007] As in cadmium (Cd) contained in the incineration ash, the solubility generally decreases as the PH (pH) increases. However, lead (Pb) contained in incinerated ash does not conform to this principle, and the relationship between solubility (g / l) and PH is as shown in FIG. That is, for Pb, the solubility becomes minimum at PH9, and conversely, the solubility increases as the PH increases further.

According to the present invention, the pH is adjusted so as to minimize the solubility of each heavy metal substance contained in the incineration ash, and by precipitating the same, this is effectively used as a cement raw material or the like, and the wastewater is rendered harmless. Thereby, the above object is achieved.

That is, in order to achieve the above object,
According to the incineration ash treatment system of the present invention, a step of adding a first pH adjuster to the incineration ash to form a primary slurry having a pH optimum for precipitation of the first obstacle substance in the incineration ash; Removing the first obstacle substance precipitated in the slurry;
Adding a second pH adjuster to the primary slurry from which the precipitate has been removed to form a secondary slurry having a pH optimal for the precipitation of the second obstacle substance (claim 1). The optimum pH for precipitation is the pH of the minimum solubility of the obstacle.
(Claim 2), the first PH regulator is at least one of water, carbon dioxide, combustion exhaust gas, and acid (claim 3), and the second PH regulator is water, carbon dioxide , Combustion exhaust gas, or acid (claim 4).

[0010]

[Function] A first PH adjuster, for example, water is added to incineration ash,
One of PH12 which is most suitable for precipitation of the first obstacle substance, for example, Cd
Next slurry. Cd in the primary slurry is removed after precipitation and used as a raw material for cement and the like. Next , 1
A second pH adjuster, for example, a combustion exhaust gas, is added to the next slurry, and a pH which is the minimum solubility of the second obstacle substance, for example, Pb is added.
9 to make a secondary slurry. And P in the secondary slurry
b is removed after precipitation and used as a raw material for cement.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. Incineration ash (fly ash) collected by a dust collector at a garbage incineration plant
1 is sent to a water tank 2, to which a first pH adjuster 3, for example, water is added, and stirred by a stirrer 4 to form a primary slurry of about PH12. The incineration ash 1 usually shows a high pH, and the pH of the primary slurry can be adjusted by adding water, but it can also be adjusted with carbon dioxide, combustion exhaust gas, or an acid such as HCl. In this embodiment, the incineration ash becomes about PH12 at about 100 kg / hr with respect to 1 m ³ / hr of water, and the solubility of Cd becomes the minimum at about PH12,
According to the metal analysis value in water, although Pb was 200 mg / l, Cd was ND, that is, not detected, and Cd in the primary slurry precipitated.

The solid containing precipitated Cd is discharged from the water tank 2 and sent to the centrifuge 5. In addition, 1 in water tank 2
The next slurry is sent to the water tank 7 while the solid matter is further removed by the filter 6. The solid matter containing Cd removed by the filter 6 is sent to the centrifugal separator 5.

The solid matter containing Cd put into the centrifugal separator 5 is separated from water, sent to a heater 8 and further removed of water to be recovered as a cement raw material 9 or the like.
The separated water is sent to the water tank 7.

A second pH adjuster 10, for example, carbon dioxide (CO ₂ ) is added to the water tank 7 and stirred by a stirrer 11 to form a secondary slurry having a pH of about 9. In this embodiment, C
By introducing O2 at about 4 m ³ / hr, PH becomes 9
At PH9, the solubility of Pb is minimal, and the metal analysis in water is 0.2 mg / l for Pb and ND for Cd, and Pb in the secondary slurry precipitates most. The solid matter containing the precipitated Pb is discharged from the water tank 7, and the above-described C
Like the solid containing d, it is recovered as a cement raw material 9 or the like.

Since the heavy metal substance is removed from the water 12 after the Pb is removed by precipitation in the secondary slurry, the water 12 can be properly adjusted and discarded as it is. Can be used to recover the alkali, which can be used effectively.

As the second pH adjuster 10, one or more of water, combustion exhaust gas, and acid may be added instead of or together with the carbon dioxide gas. In the above example, the PH was adjusted to 9 by adding about 53 m ³ / hr of flue gas and about 40 kg / hr of acid (H ₂ SO ₄ ) to the water tank 7. In adjusting the pH, the carbon dioxide, combustion exhaust gas, sulfuric acid, etc.
May be adjusted to PH9 by adding water.

Next, Cd and Pb in the slurry can be positively precipitated by adding a precipitation accelerator without adjusting the pH. As the precipitation accelerator, a sulfide having a small solubility product, for example, Na ₂ S is preferably used. For example, Na ₂ S is added to the first slurry in the water tank 2.
By adding about 0.1 kg / hr of P
Both b and Cd were not detected and precipitated. The precipitated solid can be used as a cement raw material or the like as described above.

Although the treatment of Pb and Cd has been mainly described above, the present invention is not limited to the above-described embodiment, and the same can be achieved by adjusting the PH to obtain the optimum solubility even in the treatment of chromium, arsenic, copper, zinc, and the like. Can be processed.
For example, chromium has a minimum solubility at a pH of about 7.5, and the pH of the slurry from which the Pb has been removed is adjusted with an acid such as carbon dioxide or sulfuric acid as a third pH adjuster, and precipitated and recovered. Can be.

[0019]

As described above, according to the present invention, incineration ash can be treated very effectively, and this can be effectively used as a cement raw material or the like. Further, since the water generated during the treatment does not contain any heavy metal substances, it can be discarded as wastewater after pH adjustment without causing any pollution problem.

[Brief description of the drawings]

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

FIG. 2 is a graph showing the relationship between solubility of heavy metals and PH.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Incineration ash 2 Water tank 3 1st pH adjuster 4 Stirrer 5 Centrifuge 6 Filter 7 Water tank 8 Heater 9 Cement raw material 10 2nd PH adjuster 11 Stirrer 12 Water

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B09B 3/00-5/00 A62D 3/00 C02F 11/00-11/20

Claims (4)

(57) [Claims] 1. A step of adding a first pH adjuster to incinerated ash to form a primary slurry having a pH optimal for precipitation of a first obstacle substance in the incinerated ash, and a first slurry precipitated in the primary slurry. A step of removing an obstacle and a step of adding a second pH adjuster to the primary slurry after removing the precipitate to form a secondary slurry having a pH optimum for precipitation of the second obstacle. A special incineration ash treatment system. 2. The incineration ash treatment system according to claim 1, wherein the optimum pH for precipitation of the obstacle substance is the minimum solubility PH of the obstacle substance. 3. The incineration ash treatment system according to claim 1, wherein the first PH adjuster is at least one of water, carbon dioxide, combustion exhaust gas, and acid. 4. The incineration ash treatment system according to claim 1, wherein the second PH adjuster is at least one of water, carbon dioxide, combustion exhaust gas, and acid.