JP2000000545A - Resource recovery method for incineration ash - Google Patents

Abstract

PROBLEM TO BE SOLVED: To carry out the resource recover, particularly the resource recovery, for a cement raw material, by turning the incineration ash harmless. SOLUTION: Carbon is mixed into incineration ash and then a mixture thus formed is introduced into a plasma ash melting furnace 6. The mixture formed of incineration ash mixed with carbon is melted and turned into slug in a plasma ash melting furnace 6 to form a molten metal layer 8 and a molten slug layer 9 coating the molten metal layer 8 on a furnace bottom section, and chromium oxide contained in the incineration ash is reduced to metallic chromium, which is made to migrate to the molten metal layer 8. Then molten slug is extracted from the ash melting furnace 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is to detoxify incineration ash generated from refuse incinerators for incinerating municipal solid waste and industrial waste, and from pyrolysis gasifiers, and to be used as cement raw materials, asphalt mixtures, backfill materials, roadbed materials. And so on.

[0002] In this specification, the term "incinerated ash" includes fly ash.

[0003]

2. Description of the Related Art In recent years, municipal solid waste incineration ash has been melted into a molten slag by, for example, a plasma type ash melting furnace for the purpose of reducing the volume, eliminating pollution and recycling resources. Thereafter, the molten slag extracted from the ash melting furnace is solidified and recovered as slag, and is used as a cement raw material, an asphalt mixture, a backfill material, a roadbed material, and the like.

By the way, among cement raw materials, asphalt mixtures, backfill materials, and roadbed materials, those which can be used most constantly are cement raw materials. However, in this case, there are the following problems. That is, slag obtained from incinerated ash usually contains about 400 ppm of chromium oxide, and when this is used as a cement raw material, a compound of hexavalent chromium, which is a harmful substance, is generated in the firing step of cement production. there's a possibility that. Therefore, the chromium oxide in the slag needs to be 80 ppm or less, which is equivalent to that of the current cement raw material specified in JIS.

[0005] In addition, since slag of incinerated ash usually contains about 1000 ppm of chlorine, there is a problem that it cannot be used as a raw material of cement for a structure containing a reinforcing bar from the viewpoint of corrosion resistance. Therefore, chlorine in slag can be reduced to 20% as much as the current cement raw material specified in JIS.
It must be 0 ppm or less.

[0006] An object of the present invention is to solve the above problems and to provide a method suitable for detoxifying incinerated ash and recycling it into resources, particularly as a raw material for cement.

[0007]

According to a first aspect of the present invention, there is provided a method for recycling incinerated ash, comprising mixing carbon into incinerated ash, charging the mixture into a plasma type ash melting furnace, and then using a plasma type ash melting furnace. In the ash melting furnace, the above mixture is melted into slag to form a molten metal layer and a molten slag layer covering the molten metal layer at the bottom of the furnace, and the chromium oxide contained in the incinerated ash is converted into metal by carbon. It is characterized in that it is reduced to chromium and transferred to a molten metal layer, and thereafter, molten slag is extracted from an ash melting furnace.

[0008] In the resource recycling method according to the first aspect of the present invention, the carbon may be, for example, unburned carbon having a carbon content of 95 wt% or more, activated carbon, activated carbon powder, carbon black,
It is mixed with incineration ash in the form of graphite and carbon fiber. The content of unburned carbon, activated carbon, activated carbon powder, carbon black, graphite and carbon fibers in the mixture with the incineration ash is preferably at least 5 wt%.

According to the resource recycling method of the first aspect of the present invention, after mixing carbon with incineration ash, this mixture is charged into a plasma type ash melting furnace, and then the mixture is converted into a molten slag in the plasma type ash melting furnace. By forming a molten metal layer and a molten slag layer covering the molten metal layer at the bottom of the furnace, the chromium oxide contained in the incinerated ash is reduced to metallic chromium by carbon, and this is converted to a molten metal layer. After the transfer, the molten slag is extracted from the ash melting furnace, so that the amount of chromium oxide in the slag obtained from the molten slag extracted from the ash melting furnace can be reduced. Therefore, even when this slag is used as a cement raw material, the possibility of generating a compound of hexavalent chromium, which is a harmful substance, in the firing step of cement production is reduced.

According to a second aspect of the present invention, there is provided a method for recycling incinerated ash, wherein incinerated ash containing unburned carbon is charged into a plasma type ash melting furnace, and the incinerated ash is converted into a molten slag in the plasma type ash melting furnace. By forming a molten metal layer and a molten slag layer covering the molten metal layer at the bottom of the furnace, the chromium oxide contained in the incineration ash is reduced to metallic chromium by the unburned carbon in the incineration ash. This is transferred to a molten metal layer, and thereafter, molten slag is extracted from the ash melting furnace.

In the method according to the present invention, the amount of unburned carbon in the incinerated ash containing unburned carbon is 5 wt%.
It is preferable that it is above. Incineration ash containing 5% by weight or more of unburned carbon can be obtained in a refuse incinerator by suppressing the amount of combustion air or shortening the residence time in the furnace. Further, incineration ash containing 5% by weight or more of unburned carbon is obtained as incineration ash of a pyrolysis gasifier for incinerating municipal solid waste and the like.

According to the method of the present invention, incinerated ash containing unburned carbon is charged into a plasma type ash melting furnace,
Next, the incinerated ash is converted into molten slag in the plasma type ash melting furnace to form a molten metal layer and a molten slag layer covering the molten metal layer at the bottom of the furnace, and the chromium oxide contained in the incinerated ash is formed. Is reduced to metallic chromium by the unburned carbon in the incinerated ash and transferred to the molten metal layer, and then the molten slag is extracted from the ash melting furnace, so the slag obtained from the molten slag extracted from the ash melting furnace The amount of chromium oxide therein can be reduced. Therefore, even when this slag is used as a cement raw material, the possibility of generating a compound of hexavalent chromium, which is a harmful substance, in the firing step of cement production is reduced.

According to a third aspect of the present invention, there is provided a method for recycling incinerated ash according to the first or second aspect, wherein steam is used as a working gas of the plasma type ash melting furnace, and the chlorine contained in the incinerated ash is used. Is reacted with hydrogen gas or water vapor generated by water vapor plasma, thereby generating hydrogen chloride gas.

According to the method of the third aspect of the present invention, steam is used as a working gas of the plasma type ash melting furnace, and chlorine contained in the incinerated ash is replaced with hydrogen gas generated by the steam plasma. Since it reacts with steam to generate hydrogen chloride gas, the amount of chlorine in the slag obtained from the molten slag extracted from the ash melting furnace can be reduced. Therefore, it can be used as a raw material of cement for a structure into which a reinforcing bar enters. The generated hydrogen chloride gas is processed by an appropriate method.

In the method according to the first, second or third aspect of the present invention, the molten slag extracted from the plasma type ash melting furnace is granulated with water, and further crushed as necessary, and is used as a cement raw material, an asphalt mixture, and filling. It is used as a return material and a roadbed material. When used as a cement raw material, it is mixed with gypsum to form blast furnace cement.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, one embodiment of the present invention will be described.
This will be described with reference to the drawings.

In FIG. 1, incineration ash is stored in an incineration ash storage hopper (1) after being subjected to iron removal processing using a magnet and the like. Activated carbon is stored in an activated carbon storage hopper (2) arranged alongside the incineration ash storage hopper (1). Then, the incinerated ash and activated carbon are sent out from the hoppers (1) and (2) by a predetermined amount, and a mixture of the incinerated ash and activated carbon is put into the mixture storage hopper (4) by the transport device (3). Next, the mixture in the mixture storage hopper (4) is put into the plasma type ash melting furnace (6) by the pusher (5). The plasma ash melting furnace (6) has two graphite electrodes (7). The graphite electrode (7) has a hollow shape with upper and lower ends open, and the working gas is blown from the lower end opening through the inside.

Next, a plasma is generated between the graphite electrode (7) and the mixture put into the ash melting furnace (6) while the working gas is blown out from the lower end opening of the graphite electrode (7). Is melted to form a molten slag. Then, the molten metal layer (8) and the molten metal layer (8) are placed at the bottom of the ash melting furnace (6).
And a molten slag layer (9) covering the slag. At this time, the chromium oxide contained in the incineration ash is reduced by the carbon to metal chromium by the reaction of the formula, and this is transferred to the molten metal layer.

3C + 2Cr ₂ O ₃ → Cr + 3CO ₂ ... Then, the molten slag is withdrawn from the ash melting furnace (6), put into water in a granulating tank (10), and rapidly cooled to obtain granulated slag. The granulated slag is further finely crushed by the crusher (11) and then stored in the slag storage tank (12). The crushed slag stored in the slag storage tank (12) is used as a cement raw material, and gypsum is mixed with the slag to form blast furnace cement.

When steam is used as the working gas of the ash melting furnace (6), the following reaction occurs in the ash melting furnace (6).

H ₂ O → H ₂ + 1 / 2O ₂ ... MCl ₂ + H ₂ + 1 / 2O ₂ → MO + 2HCl... MCl ₂ + H ₂ → M + 2HCl... Where M is a divalent metal. .

As a result, the amount of chlorine in the obtained granulated slag is reduced. The HCl gas passes through a secondary combustion chamber (6a) provided at the upper part of the ash melting furnace (6), and is treated with an exhaust gas by an appropriate method.

In the method shown in FIG. 1, instead of charging the mixture of incinerated ash and activated carbon into the ash melting furnace (6),
Ash melting furnace for incineration ash containing 5% by weight or more of unburned carbon
You may put it in (6). In this case, the amount of chromium oxide and the amount of chlorine are reduced as in the method shown in FIG.

Next, specific examples of the present invention will be described together with comparative examples.

Examples 1 to 4 In the method shown in FIG. 1, nitrogen gas was used as a working gas for a plasma type ash melting furnace (6), and the amount of activated carbon in a mixture of incinerated ash and activated carbon was 2 wt% (implemented). Example 1) 5 wt%
(Example 2), 7 wt% (Example 3) and 10 wt%
In Example 4, a mixture of incinerated ash and activated carbon was kept at 1450 to 1500 ° C. for 30 minutes in an ash melting furnace (6) to obtain crushed slag.

Comparative Example 1 The above Example 1 was repeated except that activated carbon was not mixed with the incinerated ash.
Crushed slag was obtained in the same manner as in No.4.

Evaluation Test The chromium oxide content in the crushed slag obtained in Examples 1 to 4 and Comparative Example was measured. The result is shown in FIG.

As is apparent from FIG. 2, the content of chromium oxide in the crushed slag obtained when incinerated ash and activated carbon were mixed was lower than when not mixed. In particular, the amount of activated carbon in the mixture of incinerated ash and activated carbon is 5w.
It can be seen that when the content exceeds t%, the chromium oxide content in the obtained crushed slag is significantly reduced.

Example 5 In the method shown in FIG.
The incinerated ash was charged into a plasma type ash melting furnace (6) without mixing with activated carbon. Then, steam is used as the working gas, and the incinerated ash is
It was kept at １1500 ° C. for 30 minutes to obtain a crushed slag. When the amount of chlorine in the obtained crushed slag was measured, it was 180
ppm.

Comparative Example 2 A crushed slag was obtained in the same manner as in Example 4 except that nitrogen gas was used as a working gas for the plasma type ash melting furnace (6). It was 900 ppm when the chlorine amount in the obtained crushed slag was measured.

Incidentally, for reference, chlorine is added to 1.
Incinerated ash containing 5 wt% is converted into molten slag in a resistance melting furnace, and the slag obtained from the molten slag has a chlorine content of 2500 p.
pm.

[Brief description of the drawings]

FIG. 1 is a flow sheet showing an embodiment of a method for recycling incinerated ash of the present invention.

FIG. 2 is a graph showing the results of Examples 1 to 4 and Comparative Example 1, showing the relationship between the amount of activated carbon in the mixture and the amount of chromium oxide in the obtained slag.

[Explanation of symbols]

 (6): Plasma type ash melting furnace (8): Molten metal layer (9): Molten slag layer

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kazunori Nakamura 1-7-89 Minami Kohoku, Suminoe-ku, Osaka F-term in Tachibai Shipbuilding Co., Ltd. 4G012 JB03 JC05

Claims (3)

[Claims] After mixing carbon into the incinerated ash, the mixture is put into a plasma type ash melting furnace, and then the mixture is melted into slag in the plasma type ash melting furnace to form a molten metal layer on the furnace bottom. While forming a molten slag layer covering the molten metal layer, the chromium oxide contained in the incinerated ash is reduced to metallic chromium by carbon and transferred to the molten metal layer, and then the molten slag is removed from the ash melting furnace. A method for recycling incinerated ash, characterized by extracting. 2. An incinerated ash containing unburned carbon is put into a plasma type ash melting furnace, and then the incinerated ash is converted into a molten slag in the plasma type ash melting furnace to form a molten metal layer at the bottom of the furnace. While forming a molten slag layer covering the metal layer, the chromium oxide contained in the incineration ash is reduced to metallic chromium by the unburned carbon in the incineration ash, and this is transferred to the molten metal layer, and then the ash melting A method for recycling incinerated ash, comprising extracting molten slag from a furnace. 3. Use of steam as a working gas in a plasma type ash melting furnace, wherein chlorine in chloride contained in incinerated ash is reacted with hydrogen gas or steam generated by steam plasma, thereby producing hydrogen chloride. 3. The method for recycling incinerated ash according to claim 1, wherein gas is generated.