JPH046439B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a dust processing device. More specifically, the present invention relates to a processing device that separates and extracts dust generated from a waste incinerator, such as a municipal garbage incinerator, into different components.

Various wastes such as municipal garbage, sewage sludge, and treated wastewater discharged from mines and factories are incinerated in incinerators, and the resulting incinerated ash has conventionally been disposed of in landfills. However, due to problems such as the difficulty in securing land for landfills and the fear that the harmful heavy metals contained in them may leach into the ground and contaminate the area around the landfill site, causing secondary pollution, for example, base metals have been A method of melting and solidifying using an electric arc furnace or a direct current melting furnace has been proposed. When waste is incinerated in the above-mentioned incinerator, the generated dust pollutes the atmosphere, so it is captured by various types of dust collectors such as wet dust collectors, electric dust collectors, bag filters, etc. The dust captured by NaCl,
Water-soluble salts such as KCl, CaO, SiO ₂ , Al ₂
O ₃ , Fe ₂ O ₃ and other oxides that are poorly soluble in water;
It contains heavy metals such as As, Cr, Zn, Cd, Pb, and Hg, which are generally in water-soluble forms such as halides or sulfates. Therefore, if this dust is buried in a landfill as it is, there is a risk that heavy metals will be leached into the ground, so the method of melting and solidifying it, similar to incineration ash, is taken. The present inventors conducted various studies on the melting process of dust generated during the incineration of waste in an incinerator, and found that when dust is melted in a direct current melting furnace, the slag generated has an upper layer and a lower layer. They discovered that they had different compositions, and that by extracting them separately, they could be used effectively according to their characteristics, and that heavy metals could be rendered harmless. 128637;
(Refer to Japanese Patent Application Laid-Open No. 58-30382).

In such fractionated slag, the composition of the upper layer of slag is mainly composed of water-soluble alkali metal salts such as NaCl and KCl, and the composition of the lower layer of slag is CaO, SiO ₂ , Al ₂ It is a component mainly composed of oxides that are poorly soluble in water, such as O ₃ and Fe ₂ O ₃ . However, the main component of the slag component in the upper layer is as described above.
Since it is an alkali metal salt containing halogens such as NaCl and KCl, if a higher temperature than necessary is maintained during slag extraction, it will damage the furnace body and shorten its service life. Furthermore, in the operation of the above-mentioned direct current melting furnace, the melting point of the upper layer of slag is 600°C.
~700℃, above which the viscosity is 1cp
Therefore, it penetrates into the refractory material, for example, refractory bricks constituting the furnace wall of the furnace body, forming a penetration passage. It also flows down the brick joints.
Generally, if the porosity of firebrick is 16%, it is 5 to 10
However, when slag passages made of metal salts soluble in the water in the upper layer are formed in the joints of firebricks, the following problems occur. In other words, the specific conductivity of the water-soluble metal salt in the upper layer is
It is approximately 40 (Ω ^- cm ^- ) at 1300℃, which is approximately 5 × 10 ^-3 times smaller than the 2 × 10 ^-1 of the slag, which is mainly composed of oxides that are poorly soluble in the water in the lower layer. Since this is due to the Joule heat in the direct energized melting furnace, it is easy to leak electricity to other parts, so a heating effect for melting cannot be expected. Furthermore, in the layer where the slag mainly composed of oxides that are poorly soluble in water is melted (above and below the electrode), the slag temperature rises to nearly 1200 to 1400°C. Therefore, in such a layer, if water-soluble slag (salt) is present, it will penetrate into the refractory and form an alkali metal compound, significantly lowering its melting point and reducing the durability of the refractory. exert an effect.

The present invention solves the above-mentioned problems by having a structure that prevents the upper layer slag, which is mainly composed of water-soluble alkali metal salts, from penetrating into the joints of fireproof bricks. The present invention provides an energized melting processing furnace. In other words, the present invention is equipped with two slag discharge ports, upper and lower, and the generated slag is separated into an upper layer of slag that is mainly composed of water-soluble salts and a lower layer that is mainly composed of inorganic oxides that are sparingly soluble in water. In a directly energized melting furnace for dust generated from a waste incinerator that separates the slag from the slag, the furnace body is placed at a level slightly below the boundary level between the upper and lower slag. The gist of the present invention is a dust melting furnace characterized in that a cooling zone is provided in the furnace wall that constitutes the furnace body over the entire circumference.

Hereinafter, the present invention will be explained based on drawings showing one embodiment.

Figure 1 is a schematic cross-sectional view of a direct current melting furnace.
For example, SiO ₂ −Al ₂ O ₃ −Zr ₂ with a high content of Zr ₂ O ₃
The furnace body is hermetically constructed of O3 _- based refractory material, such as firebrick, and includes an inlet 2 for dust generated during waste incineration, an exhaust pipe 3, and a heating device for initial melting of the input dust. For example, a fuel gas injection nozzle 4, horizontally retractable electrodes 5, 5, an upper slag discharge port 6, a lower slag discharge port 7, etc. are provided. The two slag discharge ports 6 and 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 voltage regulating power transformer 8 to the electrodes 5, 5, and the dust introduced from the dust inlet 2 is melted by gas heating from the fuel gas injection nozzle 4.
The generated molten slag 9 itself becomes a conductor, generates Joule heat therein, and functions to maintain the 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. With the direct current melting furnace shown in Figure 1,
When processing dust generated in a waste incinerator, the dust is put into the furnace body 1 through the dust inlet 2, heated with gas through the fuel gas injection nozzle 4 for initial melting, and melted into a molten slag. The temperature of the slag 9 in this case varies depending on the type of dust introduced, but is in the range of approximately 1000 to 1400°C. At that time, the electrodes 5, 5 attached to the furnace body 1 are immersed in the slag in advance, and an alternating current is passed through them.
This is maintained in a molten state by the Joule heat generated as a conductor. The current at this time is approximately 700 to 1,200 KW, depending on the nature of the injected dust.
t (workpiece). In the generation of the slag described above, the slag 9 in which the electrodes 5 and 5 are buried mainly consists of oxides such as CaO, Al ₂ O ₃ , SiO ₂ and Fe ₂ O ₃ that are poorly soluble in water, and has a specific gravity of 2.5. ~2.9, melting point ~1000
The temperature is as high as 1400℃, and the viscosity at that temperature is
¹⁰⁴ cp, and the upper part of the slag 9 contains an unmelted solidified material having the same composition as the slag 9, and is mainly composed of water-soluble alkali metal salts such as KCl and NaCl. Thus, a molten slag 11 is formed, which has a specific gravity of 1.9 to 2.1, which is lighter than the slag 9 described above, a melting point of 600 to 800°C, and a viscosity of 1 cp at that temperature, which is extremely fluid. Next, the slag 9 is removed from one of the two slag discharge ports provided in the furnace body 1.
The slag 11 is discharged from the slag discharge port 7 of the lower single-hole body installed at a low position, and transported and solidified together with detoxified heavy metals, while the slag 11 is discharged from the slag discharge port 7 of the upper stage installed at a high position. The slag is discharged from the outlet 6 and is discharged and dissolved into a water-filled pit (not shown), taking advantage of the fact that salts, which are the main components, are soluble in water.

In the above-mentioned separated slag, as mentioned above, the molten slag 11
Inside, unmelted solidified substances having the same composition as the slag 9 are mixed, and the temperature of the alkali metal salts (halides) such as NaCl and KCl is lower than the melting point due to heat transfer from the slag 9. is much higher. Therefore, it is necessary to prevent the alkali metal salts in the slag 11 from penetrating into the refractory material, such as refractory bricks, constituting the furnace wall to form a penetration passage or flowing down through the joints. . Reference numeral 10 denotes a cooling zone made of a refractory material such as refractory bricks that constitutes the furnace body 1, and is buried inside the furnace wall around the entire circumference of the furnace body, such as a lintel or conduit that can circulate water inside. (not shown). Thus, the cooling zone 10 is located at a level slightly below the boundary level between the molten slag 9 and the molten slag 11 formed above it. That is, as shown in the enlarged view of FIG.
For example, molten slag 11b that has been cooled and solidified is generated in contact with the lintel wall, preventing the formation of a penetration path and flowing down below the boundary level 11a, while on the lower furnace wall near the boundary level 11a, slag is Solidified slag 9a of slag 9 having a higher melting point than slag 11 is formed. That is, this prevents the penetration of the slag 11, which is mainly composed of alkali metal salts, into the furnace wall in the portion of the furnace body 1 where the electrodes 5, 5 are provided, which causes attenuation of the generation of Joule heat. In addition, the level of the molten slag 9 moved significantly in the area where the solidified slag 9a was formed, and the refractories were severely worn out, but by providing a cooling zone, the solidified slag 9a was formed. As a result, the durability of the refractories near the solidified slag is improved. Note that 12 is slag 11
This is a covering layer formed on top, and is made of unmelted dust input from the input port 2.

As described above, the present invention is directed to the treatment of dust containing water-soluble alkali metal salts and insoluble oxides generated from a waste treatment furnace by combining the upper layer slag and the lower layer slag in a direct energization type melting treatment furnace. A direct dust energization type with a cooling zone installed around the entire inside of the furnace wall of the furnace body at a level slightly below the boundary level, and a structure that allows heating and energization by Joule heat to occur without any hindrance and improves the durability of the refractory. It is a melting processing furnace and has great industrial utility value.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view of a dust melting furnace showing an example of the present invention, and FIG. 2 is an enlarged sectional view showing a part thereof. 1...furnace body, 2...inlet, 3...exhaust pipe,
4... Fuel gas injection nozzle, 5... Electrode, 6...
Upper stage discharge port, 7...Lower stage discharge port, 8...Power transformer for voltage adjustment, 9...Slag, 10...Cooling zone,
11... Slag, 12... Covering tank.

Claims (1)

[Scope of Claims] 1. A slag discharge port is provided in two upper and lower stages, and the generated slag is transferred to an upper layer containing slag mainly composed of water-soluble salts,
In a directly energized melting furnace for dust generated from a waste incinerator, the slag in the upper layer and the slag in the lower layer are separated into the slag in the lower layer, which mainly consists of inorganic oxides that are poorly soluble in water. A dust melting furnace characterized in that a cooling zone is provided in the furnace wall constituting the furnace body, extending around the entire circumference of the furnace body at a height slightly below the boundary level. 2. The dust melting furnace according to claim 1, wherein the cooling zone is made of a lintel or piping through which cooling water can flow. 3 The upper layer slag is composed mainly of water-soluble alkali metal salts such as NaCl or KCl, and the lower layer slag is water-soluble such as CaO, Al ₂ O ₃ , Fe ₂ O ₃ , and SiO ₂ 3. The dust melting furnace according to claim 1 or 2, which comprises a component mainly consisting of an oxide that is hardly soluble in water.