JPH0297816A - Disposing method for heavy metal-contained dust - Google Patents

Abstract

PURPOSE:To prevent volatilization of a noxious heavy metal from a molten slug surface by a method wherein the upper surface temperature of a covering layer is held at a value lower than a specified temperature. CONSTITUTION:In a direct energization type melting disposing furnace in which heavy metal-contained dust generated from a waste incinerator is disposed, a covering layer 12 formed, in order, from below with a molten slug layer 9, a molten salt layer 10, and a unmolten dust is formed. The covering layer 12 forms and approximately conical layer with a lower end 2a of a charge port 2 serving as an apex and a is formed in a manner to be accumulated on the molten slug 9. The portion, having a temperature of 650-1,000 deg.C or higher, of the lower part of the covering layer forms a molten salt layer 10. The thickness of the covering layer 12 can be variably regulated through vertical movement of the charge port 2, and a surface temperature is regulated to 100 deg.C or lower. Namely, when a molten slug level 9a is raised and the thickness of the covering layer 12 is decreased, regulation is made so that the thickness of the covering layer 12 is adjusted to a value higher than a given value through rising of the charge port 2, and this method regulates a surface temperature to 100 deg.C or lower. This method enables prevention of volatilization of a heavy metal.

Description

DETAILED DESCRIPTION OF THE INVENTION OBJECTS OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for detoxifying heavy metal-containing dust generated from waste incinerators such as municipal waste in a direct current melting furnace.

[Prior Art] Waste such as municipal waste is generally incinerated in an incinerator. The dust generated at this time is captured by an electrostatic precipitator or the like. The captured dust contains Pb, Cr, Zn, C
It contains toxic heavy metals such as d, Hg, and As, and if it is disposed of as is in a landfill, these toxic heavy metals may leach into the ground and cause secondary pollution.

Therefore, methods have been invented to melt these dusts in an arc type melting furnace or a direct current type melting furnace to confine harmful heavy metals in the molten slag.
A method described in Japanese Patent No. 30382 is known.

[Problem to be solved by the invention] However, Pb and Zn contained in the above dust.

Since Hg, Cd + As, etc. volatilize at a relatively low temperature of about 300 to 1000°C, there is a problem that these harmful heavy metals leak out of the furnace.

As described in the above publication, it is known that in the method of melting dust in a direct current melting furnace, a covering layer is formed on the surface of the molten slag by unmelted dust supplied into the furnace. ing. however,
The covering layer is formed transiently during the processing process, and its surface temperature is not regulated. Therefore,
Heavy metals are directly volatilized from the surface of the covering layer, or
There was a problem in that heavy metals volatilized from the molten slag penetrated the covering layer and leaked out of the furnace.

Therefore, as a result of intensive studies, the inventor of the present application has developed a method comprising the following structure, which prevents harmful heavy metals from volatilizing from the surface of molten slag by forming the above-mentioned covering layer under predetermined conditions. He invented it.

[Means for Solving the Problems] That is, the gist of the present invention is to provide a method for treating heavy metal-containing dust generated from a waste incinerator in a direct energized melting furnace. In the method for treating heavy metal-containing dust, which forms a covering layer of unmelted dust, there is provided a treatment blade for heavy metal-containing dust, characterized in that the temperature of the upper surface of the covering layer is maintained at 100° C. or less.

The method of the present invention is applied, for example, when processing heavy metal-containing dust in a direct current melting furnace as shown in FIG.

Figure 1 is a schematic cross-sectional view of a direct current melting furnace, where 1 is, for example, 5i.
n2 Al2O3ZrO2 series and 5iO2-A1203-
The furnace body is hermetically constructed using a Cr203-based refractory material, such as refractory bricks, and includes an inlet 2 for dust generated when extinguishing waste, an exhaust pipe 3, an electrode 5.5 that can be retracted in the horizontal direction, and an upper stage. A slag discharge port 6, a lower slag discharge lower, etc. are provided. The inlet 2 slides up and down as shown by the arrow in the figure, and the dust inlet height is variable. Also, 2
The two slag discharge ports 6.7 are provided with a head difference as much as possible within the allowable range of the furnace structure. An alternating current is passed through the electrode 5.5 through the voltage regulating power transformer 8, and the dust introduced from the inlet 2 is melted, and the generated molten slag layer 9 itself becomes a conductor, which generates Joule heat. , which functions to maintain a molten state by internal heating. A typical example of the material is a molybdenum electrode, and other examples include graphite, iron, tin oxide, and a tungsten electrode. When processing dust generated in a waste incinerator using the direct energization type melting furnace shown in FIG. The temperature of the molten slag layer 9 in this case varies depending on the type of dust introduced, but is in the range of about 1000 to 1400°C. At that time, the electrode 5.5 attached to the furnace body 1 is immersed in the slag in advance and an alternating current is passed through it, and the molten state is maintained by the Joule heat generated using this as a conductor.

The current at this time is in the range of approximately 700 to 1200 KWH/l (object to be treated), although it depends on the nature of the applied dust. The main component of molten slag N9 is Cab, which is poorly soluble in water.
, A120a, SiO2, Fe203, etc., with a specific gravity of 2.5 to 2.9 and a melting point of 1000 to 14
As high as 00℃, and the viscosity at that temperature is 10'c
The upper part of the molten slag layer 9 contains an unmelted solidified substance having the same composition as the molten slag layer 9, and is mainly composed of water-soluble alkali metal salts such as KCI and NaCl. The molten slag layer 9 has a specific gravity of 1.9 to 2.1, which is lighter than the molten slag layer 9, and a melting point of 650 to 100.
At 0° C., a molten salt layer 10 is formed which has a viscosity of lcp and extremely high fluidity at that temperature. Next, the molten slag layer 9 is discharged from the lower single-hole slag discharge lower of the two slag discharge ports provided in the furnace body 1, and detoxified heavy metals are removed. The molten salt layer 10 is transported and solidified together with the molten salt layer 10, and the molten salt layer 10 is discharged from the upper slag discharge port 6 provided at a high position, and the water is removed by taking advantage of the fact that the salts, which are the main components of the slag, are soluble in water. Filled pit (
(not shown).

Here, in the furnace, a covering layer 12 consisting of a molten slag layer 9, a molten salt layer 10, and unmelted dust is formed in order from the bottom as shown in the figure.

Here, the covering layer 12 becomes a substantially conical layer with the lower end 2a of the input port 2 as the apex, and is deposited on the molten slag 9 at an angle of repose, and the temperature of the lower part thereof is 650°C to 1000°C.
The above portion becomes the molten salt layer 10. The thickness of the covering layer 12 can be variably adjusted by moving the input port 2 up and down, and is adjusted so that the surface temperature is 100° C. or less.

That is, the molten slag level 9a increases and the covering layer 1
When the thickness of the covering layer 2 decreases, the surface temperature is adjusted to 100° C. or less by raising the inlet 2 and adjusting the covering layer 12 to a predetermined thickness or more.

The molten slag level 9a can be determined using a level meter or a microwave detection device (not shown). Alternatively, the molten slag level 9a may be detected by detecting the furnace wall temperature and knowing the 1000° C. level, for example. Furthermore, since the covering layer 12 is formed at an angle of repose with the lower end 2a of the inlet 2 as the apex, its minimum thickness position is at the contact part 12a with the furnace wall as shown in the figure, so the temperature at that position is The height of the lower end 2a of the input port 2 may be adjusted so that the surface temperature can be maintained at 100° C. or less by directly measuring the temperature.

[Function] As described above, by adjusting the thickness of the covering layer 12 to, for example, 300 mm or more in the examples described later, the surface temperature of the covering 112 can be maintained at 100° C. or less, and the molten slag Even if the heavy metals molten in the metal layer 9 try to volatilize, they are cooled and trapped in the covering layer 12 . Furthermore, since a considerable thickness is required to keep the surface temperature below 100° C., the occurrence of drifting due to outgassing is prevented, and the volatilization of heavy metals is suppressed.

[Effects of the Invention] As described above, according to the present invention, by adjusting the thickness of the covering layer to a predetermined thickness or more and keeping the surface temperature below 100°C, dust containing harmful heavy metals can be detoxified. Heavy metals can be prevented from leaking out of the furnace.

[Example] Next, an example of the present invention will be described to clarify its beneficial effects.

As an example, heavy metal-containing dust generated in a municipal waste incinerator and captured by an electrostatic precipitator was used as a sample, and a covering layer with a thickness of 100 mm was prepared in a direct current melting furnace as shown in Fig. 1.
, 250 mm, and 300 mm. The results of three types of tests are shown in FIGS. 2 and 3.

Figure 2 shows the measurement results of the temperature distribution inside the furnace. As shown in the figure, when the covering layer thickness is 300 mm, the surface temperature is 100 °C,
If the same <250mm, 200℃.

In the case of 100 mm, the temperature was 310°C. Note that the covering layer thickness is the minimum thickness above the molten slag level 9a.

The heavy metal capture rates in each case are shown in Figure 3.

As shown in the figure, the covering layer thickness is 300 mm (surface temperature is 10 mm).
0°C), the covering layer thickness is 100mm, 250mm
mm (surface temperature 310℃, 200℃), P
b, Zn, Cd, and Hg all exhibited high capture rates of 2 to 3 times. Further, it is possible to prevent almost the entire amount of Zn from volatilizing.

From this, it is found that the covering layer thickness is 300 mm or more, that is,
It can be seen that by keeping the surface temperature of the covering layer at 100° C. or lower, the effect of preventing volatilization of heavy metals is significantly improved.

It should be noted that the present invention is not limited to the embodiments in any way, and various embodiments can be adopted without departing from the gist thereof.

For example, by cooling the portion along the furnace wall in the cooling zone 11, the molten slag level 9a of the minimum thickness portion of the covering layer 12 is suppressed from rising, and the covering layer 12 is cooled.
It is also possible to prevent the thickness from decreasing.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of the direct current melting furnace used in the example, FIG. 2 is a graph of the temperature distribution measurement results of the example, and FIG. 3 is a graph of the heavy metal capture rate. 1 Furnace body 2 Input port 3 Exhaust pipe 6 Upper discharge port 8 Voltage adjustment power supply 9 Molten slag 2a Lower end 5 Electrode 7 ...lower discharge outlet transformer 9a...molten slag level l 0...molten salt 1...cooling zone 12...covering layer

Claims (1)

[Claims] In a method for processing heavy metal-containing dust generated from a waste incinerator in a direct current melting furnace, the above-mentioned covering method is used to form a covering layer of unmelted dust on the slag in the furnace. A method for treating dust containing heavy metals, characterized by keeping the temperature of the upper surface of the layer below 100°C.