JP3537280B2 - Waste molten slag treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for producing slag by directly melting waste such as municipal waste, industrial waste, and sludge, and a method for once incinerating waste to form ash and then melting the slag. And a method for producing the same.

[0002]

2. Description of the Related Art At present, most waste is treated by an incineration method. However, the incineration method has a drawback that a disposal site for incinerated ash is required. In particular, in the metropolitan area, it is difficult to secure a disposal site for incinerated ash.
There is an increasing need to dissolve incinerated ash from waste in a manner that allows volume reduction and further recycling. Moreover,
In order to recycle slag from molten waste, it is necessary to have physical properties (strength, particle size distribution) comparable to natural sand and crushed stone, and to have chemical properties .
In particular, as for chemical properties, it is necessary from the viewpoint of safety that heavy metals in the slag are not eluted.

[0003] To improve the properties of slag, Japanese Patent Publication No. 8-29312 discloses a method of melting refuse and then adding ± 10 ° C in a range of 2 to 50 ° C lower than the boiling temperature of the atmosphere pressure in the melting furnace after melting the waste. , And pH 8.0-1
A slag production method is disclosed in which a slag is obtained by flowing and cooling a melt in hot water adjusted to 3.0.

[0004]

Problems to be Solved by the Invention
The method disclosed in Japanese Patent No. 312 provides a method for producing slag capable of obtaining stable slag of high quality, which is as strong as natural sand, has irregularities on the surface, and has an appropriate particle size distribution as a material for civil engineering and construction. It is intended to be. That is, the purpose is to obtain a slag having a physical property close to that of natural sand, and there is no description about chemical properties such as elution characteristics of heavy metals. Slags intended for recycling require strict control over chemical properties such as the elution characteristics of heavy metals rather than incineration ash, which is the main disposal method for landfills and ocean dumping. An object of the present invention is to provide a method for producing slag that can obtain chemically stable slag equivalent to natural sand from which heavy metals do not elute.

[0005]

In the current melting method, no heavy metal is eluted from the slag produced during normal operation, and a stable product can be obtained. During normal operation, trace amounts may be detected within the standards of the Environmental Agency Notification No. 25 of 1994. The characteristic means of the present invention for solving the problem is that, after melting the waste, the slag cooled and solidified is periodically stirred or blasted for 30 days or more in the elution prevention pit to perform slag blasting. It is an object of the present invention to prevent heavy metals from being eluted from slag by making the heavy metals therein hardly soluble lead oxide and lead carbonate and incorporating them into a three-dimensional network structure of silicate SiO ₂ in slag.

Normally, the slag after the melting treatment is stored in a storage hopper for a short period of about 3 days to 1 week, and then shipped or discarded collectively. The present invention provides an elution prevention pit instead of a storage hopper and exposes the slag to the air for a certain period of time,
The heavy metal in the slag is converted into a hardly soluble substance to prevent the elution of the heavy metal. For example, lead compounds are oxidized and carbonated in the air, and lead oxide PbO and lead carbonate P are hardly soluble.
It becomes bCO ₃ and is further incorporated into the three-dimensional network structure of silicate SiO _{2 in} the slag, thereby preventing elution. Therefore, when the slag produced by the method of the present invention is used for civil engineering materials and the like, heavy metals can be safely used without elution of heavy metals.

[0007]

【Example】

(Example 1) As an example in which waste is melted, FIG. 1 shows a case in which waste is directly melted using coke. In FIG. 1, waste and coke and limestone as auxiliary materials are charged into the melting furnace 1 from the furnace upper part of the melting furnace 1. Municipal waste was disposed of as waste. Air and oxygen are supplied from a tuyere 2 provided around the lower part of the melting furnace 1. Waste treatment amount is 560 kg / h, coke and limestone are about 6% of waste, and air is 520 Nm ³
/ H and oxygen are 30 Nm ³ / h. The waste, coke, and the like charged into the melting furnace form a packed bed in the furnace, and the air and oxygen blown from the tuyere 2 at the lower part of the furnace form
Some of the coke and waste will burn. The combustion gas rises in the melting furnace from the bottom of the furnace, and the waste is preheated, dried and thermally decomposed by the sensible heat of the combustion gas. Steam, pyrolysis gas and fine dust generated in the process of drying and pyrolysis of waste are discharged from the gas discharge pipe 4.

On the other hand, ash and non-combustible waste, coke and lime of waste are heated to a high temperature and descend to the furnace bottom, where coke burns with air and oxygen blown from tuyeres, and ash and non-combustible Is heated from 1300 ° C. to 1450 ° C. to be in a molten state and discharged from the slag discharge hole 3 to the outside of the furnace. Limestone slag basicity, namely the lime CaO and the ratio of the silicic acid content of SiO ₂ in the slag is 0.5 or more, is added in order to adjust the fluidity of the slag in the molten state. The molten slag discharged from the slag discharge port is charged into the granulation equipment 5 and becomes fine sand-like particles. Also,
Slag in the molten state contains molten metal,
Metal also becomes fine particles like slag.

The slag and metal in the form of particles are scraped by a scraping device 6
, And is supplied to the wet magnetic separator 7 to be separated into slag and metal. The slag is supplied to the elution preventing pit 8 in a state where water adheres during magnetic separation. In the elution prevention pit 8, the slag was exposed to air while being piled up to a height of 2 to 3 m. In the case of this embodiment, the operation is performed at an ambient temperature of 5 to 15 ° C. in winter, and the treatment period in the elution prevention pit is 3 months. During the treatment period, every 0.5 months so as to uniformly oxidize and carbonate. The slag was stirred. The slag after the treatment is used as an aggregate or a civil engineering material of a secondary concrete product such as an interlocking block.

FIG. 2 shows an embodiment. The properties of the slag 1 in this example were during normal operation, and the lead elution concentration before the treatment was 0.005 mg / liter or less, that is, the lower limit of quantification was less than that, and no lead was eluted. Slag 2 shown in FIG.
Is slag at the time of starting the melting furnace, and the slag before treatment has a lead elution concentration of 0.008 mg / liter.
The lead elution concentration after exposure to air for 3 months at the elution prevention pit was 0.005 mg / liter or less, that is, the determination limit or less, and no lead elution was observed.

When exposing the slag to air, it is necessary to convert heavy metals in the slag into sparingly soluble oxides and carbonates to form a three-dimensional network structure of silicate SiO _{2 in} the slag for a certain period or more. The slag 3 shown in FIG.
This is a slag that has been subjected to the same treatment in a state where the reaction is easily accelerated and the elution was prevented in 30 days. Therefore, the slag must be exposed to air for at least 30 days.

The same effect was obtained as a result of exposing the slag in the elution prevention pit 8 to air without stirring while keeping the slag pile height at 1 m or less. Therefore, the dissolution prevention pit 8 has a limited installation area, and when the pile height of the slag exceeds 1 m, it can be uniformly oxidized and carbonated by exposing it to air while adding a stirring operation, so that the installation area can be widened. When the pile height of the slag can be suppressed to 1 m or less, the elution of heavy metals can be prevented by exposing the slag to air without a stirring operation.

(Embodiment 2) As an example of a method of exposing slag to air, an embodiment in which a ventilation pipe is additionally installed in the elution prevention pit 8 of Embodiment 1 will be described. The slag in this embodiment is:
The same lot of slag as in Example 1 was used. The slag was piled up to a height of 2 to 3 m in the elution prevention pit 8 ′ with a ventilation pipe, and was forced to be exposed to air by blowing at 0.5 Nm ³ / h without stirring. In the case of the present embodiment, the operation was performed in winter at an ambient temperature of 5 to 15 ° C., and the treatment period in the elution prevention pit was set to three months, and the conditions were the same as those in Example 1.

The slag 4 shown in FIG. 2 is slag that has been exposed to air in an elution prevention pit with a ventilation pipe. In the same manner as in Example 1, the slag having an elution concentration of 0.008 mg / liter before treatment has a lead elution concentration of 0.005 mg / liter or less after being exposed to air for 3 months in an elution prevention pit with a ventilation pipe, that is, It was below the lower limit of quantification, and no elution of lead was observed. As in the first embodiment, the slag can be stacked by 1 m or more, and the installation area of the elution prevention pit 8 'can be reduced.

The dissolution test method and analysis method are described in 1994
In accordance with the Notification of the Environment Agency No.25. In addition, arsenic, mercury, cadmium, hexavalent chromium, and selenium were also analyzed as heavy metals other than lead, but before and after the treatment, the quantification was below the lower limit of quantification, and no elution was observed. Furthermore, the physical properties of the slag were compared before and after the treatment, but there was no difference, and there was no problem when the slag was effectively used as an aggregate or a civil engineering material for secondary concrete products.

[0016]

According to the present invention, the following effects can be realized. (1) It is possible to prevent the elution of heavy metals and the like from the slag by exposing the slag obtained by melting the waste to air for a certain period or more. By preventing the elution of heavy metals, slag can be recycled. (2) Also, as shown in the examples, stirring during the treatment period,
If an operation such as air blowing is added, the slag is more uniformly oxidized and carbonated, and the installation area of the equipment exposed to the air can be reduced. (3) The physical properties of slag exposed to air for a long period of time do not deteriorate, and there is no hindrance when slag is effectively used as aggregate or civil engineering material for secondary concrete products. (4) Recycling waste slag not only eliminates the need for a slag disposal site, but also prevents natural destruction due to mining of natural sand.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing an embodiment of the present invention.

[Explanation of symbols]

1 melting furnace 2 tuyere 3 Slag discharge hole 4 Gas exhaust pipe 5 Granulation equipment 6 Raising device 7 Magnetic separator 8 Elution prevention pit Elution prevention pit with 8 'blower

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B09B 3/00 B09B 5/00 C04B 5/02 C04B 18/04

Claims (1)

(57) [Claims] 1. After melting the waste, the solidified slag that has cooled and solidified is subjected to regular stirring or forced air blowing for 30 days or more in a dissolution prevention pit to hardly dissolve heavy metals in the slag. /> Silicated silicate in slag as lead oxide and lead carbonate
A method for treating waste molten slag, wherein the metal is incorporated into a three-dimensional network structure of O ₂ to prevent the elution of heavy metals from the slag.