JPH11156328A - Treatment of zinc-containing dust and zinc-containing dust pellet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To finally recover dust high in zinc content by producing a dust pellet from the zinc-containing dust contained in the exhaust gas of an electric furnace or the exhaust gas of the scrap iron preheating apparatus arranged on the way of the exhaust gas treatment system of the electric furnace. SOLUTION: Zinc-containing dust is treated by a method wherein an adsorbing material containing a carbon material is blown into the exhaust gas of an electric furnace for melting and refining scrap iron or the exhaust gas of a scrap iron preheating apparatus for preheating scrap iron by the exhaust gas of the electric furnace in the front stage of a dust collector and a carbon material with a particle size of 5 mm or less is added to the dust collected by the dust collector to agglomerate the dust to form pellets with a carbon content of 6-40 wt.% and these pellets are charged in the electric furnace during the period from the terminal stage of the scrap iron melting period of the electric furnace to the front stage of the refining period thereof to be melted and refined along with scrap iron.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an electric furnace exhaust gas,
Alternatively, the present invention relates to a method for treating zinc-containing dust contained in exhaust gas of a scrap iron preheating device provided in the middle of an electric furnace exhaust gas treatment system and zinc-containing dust pellets used in this treatment method.

[0002]

2. Description of the Related Art In Japan, dust generated from electric furnaces reaches about 500,000 tons per year. Of these, about 6
0% is reduced to zinc raw material by specialized processing equipment such as rotary kilns and melting furnaces at a dust processing company. When electric furnace dust is used as a zinc raw material, the dust is evaluated according to the zinc content, and the zinc oxide content needs to be 50 wt% or more.

[0003] However, the zinc oxide content in dust generated from an electric furnace or the like is generally as low as about 15 to 25 wt%.
The fact is that the evaluation when it is taken from an electric furnace manufacturer to a company specializing in dust treatment is low. Therefore, electric furnace manufacturers need to increase the content of zinc oxide (hereinafter simply referred to as zinc) in dust as much as possible.

On the other hand, harmful substances such as dioxin contained in exhaust gas of an electric furnace or in exhaust gas of a scrap iron preheating apparatus for preheating scrap iron, which is a raw material of an electric furnace, with the exhaust gas of an electric furnace have been regarded as a problem in recent years. As a method for removing harmful substances such as dioxin, see, for example,
There is a method disclosed in US Pat.

According to this method, an adsorbent is sprayed into exhaust gas at a stage preceding a dust collector attached to an electric furnace, and then the adsorbent and dust are collected by the dust collector, and the collected dust mixed with the adsorbent is agglomerated. And then return it to the electric furnace again. According to this method, harmful substances such as dioxin adsorbed by the adsorbent in the dust can be decomposed at a high temperature of the electric furnace.

In this conventional technique, when dust collected in a dust collector containing an adsorbent is further agglomerated and returned to an electric furnace to be melted again, zinc contained in the dust and collected is re-formed as zinc vapor during refining. Adsorbed to dust collection. By repeating this step, the zinc content in the dust gradually increases.

FIG. 3 is a view for explaining the detailed steps of the method disclosed in Japanese Patent Laid-Open No. 6-47237. In the scrap iron dissolving step shown in the figure, in step 2, scrap iron is put into an electric furnace, power is supplied in step 4, additional raw materials are charged in step 6, and scrap iron is dissolved in step 8. Next, in step 10, the components are adjusted, and in step 12, the steel is tapped.

On the other hand, in the dust treatment step, the dust collector is operated in step 20 to suck the electric furnace exhaust gas containing dust.
In step 22, an adsorbent is charged, and in step 24, dust is collected by a dust collector. Charcoal powder or reduced slag powder is used as the adsorbent introduced in step 22. The introduced adsorbent adsorbs organic substances such as oil and dioxin and moisture in the exhaust gas, thereby improving the dust collection efficiency of the bag filter as a dust collector.

After the collected dust is pelletized in step 30, the dust is charged into the electric furnace in step 34 when scrap iron is charged into the electric furnace (step 2) or when melting (step 8). The dust charged in the electric furnace is dissolved at a high temperature of 1600 ° C or higher, so that dioxin is decomposed and made harmless, zinc oxide in the dust is reduced, zinc is vaporized, and collected as dust collector dust. Is done. By repeatedly returning the dust to the electric furnace, the zinc content in the dust increases, and the dust having the increased zinc content is discharged in step 38 as a zinc raw material.

[0010]

The above-mentioned prior arts are:
Efficient in adsorbing harmful substances such as dioxin contained in the exhaust gas of electric furnaces into dust efficiently, charging the dust containing dioxin etc. collected by the dust collector into the electric furnace again, and exposing it to high temperatures to decompose dioxin. It is a target. However, the need to maximize the zinc content in the dust collected by the dust collector is disadvantageous because components other than zinc increase by the amount of the adsorbent added.

Further, even if the operation of returning the dust to the electric furnace is repeatedly performed, it is difficult to increase the zinc content in the total dust to 25 wt% or more because newly generated dust having a low zinc content is mixed. And could not be used directly as a raw material for zinc refining.

[0012]

Means for Solving the Problems The inventors of the present invention have studied the reason why the concentration of zinc in dust does not proceed in the prior art. As a result, the amount of adsorbent (carbon powder) introduced into exhaust gas in the above technology is small. Therefore, it is because zinc oxide in dust is not reduced quickly enough, and in order to increase the content of zinc oxide in dust, volume reduction of dust itself is indispensable, and added to dust pellets The present inventors have found that there are appropriate conditions for the particle size of the carbon material and the timing of charging the dust pellets into the electric furnace, and have led to the invention described below.

A first aspect of the present invention is a method for treating zinc-containing dust, comprising the following steps. (a) blowing an adsorbent containing a carbon material into the exhaust gas of an electric furnace for melting and refining scrap iron or exhaust gas of a scrap iron preheating device for preheating scrap iron with the exhaust gas of the electric furnace at a stage preceding the dust collector; and (b) the dust collector. Particle size is 5m
m or less, and agglomerate to form a carbon content of 6 to
(C) charging the dust pellets into the electric furnace and melting and refining the dust pellets together with the scrap iron during the period from the end of the scrap iron melting period to the early refining period of the electric furnace. A method for treating zinc-containing dust.

According to a second aspect of the present invention, an adsorbent containing a carbon material is blown into an exhaust gas of an electric furnace or an exhaust gas of a scrap iron preheating device for preheating scrap iron with the exhaust gas of an electric furnace in a stage preceding a dust collector, and a human body in the exhaust gas is blown. Harmful organic matter is absorbed, dust containing the carbon material is collected by a dust collector, and the collected dust is further added with a carbon material to form an agglomerate, and the carbon content is 6 to 40 wt%.
It is a dust pellet characterized by having been adjusted to become.

In the third invention, when agglomerating the collected dust, any one of coke, coal, and activated carbon having a particle size of 5 mm or less, or a mixture thereof is added, and the carbon content is reduced. Is adjusted to be 6 to 40 wt%.

According to a fourth aspect of the present invention, there is provided a dust pellet wherein the particle size of the dust pellet obtained by agglomerating the collected dust is 2 to 30 mm.

[0017]

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a bag filter or an electric precipitator installed at a subsequent stage by blowing an adsorbent containing a carbon material into exhaust gas generated from an electric furnace to adsorb harmful substances such as dioxin. Dust containing adsorbent containing carbon material is collected. Then, to the collected dust,
An appropriate amount of carbon material is added to agglomerate to produce pellets.
The pellets are again charged into an electric furnace and melted together with the scrap iron. By repeating this operation, zinc oxide in dust is concentrated, and harmful substances such as dioxin are decomposed.

[0018] Scrap iron charged as a raw material in an electric furnace has organic substances containing chlorine, such as plastics, attached thereto, and thus dioxin may be generated in exhaust gas. It is more preferable to use activated carbon as an adsorbent containing a carbon material to remove this dioxin, but coke powder or charcoal powder may be used, in which case, in relation to the carbon material added during agglomeration described below, The particle size is desirably 5 mm or less. The adsorbent is preferably mainly a carbon material, but may partially include reducing slag discharged from the electric furnace.

An electric furnace for melting and refining scrap iron is provided with a preheating device for preheating scrap iron to improve thermal efficiency.
Further, a dust collector for collecting dust in the exhaust gas, for example, a bag filter, is provided. In order to agglomerate the electric furnace dust collected by the dust collector, the inventors examined the amount of the carbon material to be further added and the target carbon content.

As a result, the amount of the adsorbent containing the carbon material to be introduced into the exhaust gas before the dust collector is about 0.2 to 0.5 g per m ³ of the exhaust gas. If the amount is less than 0.2 g, the amount of adsorbed dioxin is insufficient, and if it exceeds 0.5 g, the amount of adsorbed dioxin is saturated.

On the other hand, since the amount of dust generated in an electric furnace is about 1.4 t when 100 t of scrap iron is melted in one melting, the carbon material is about 7 to 18 kg in terms of 1 ton of dust. On the other hand, dust contains 15 to 25% by weight of zinc oxide.
It is contained to a degree. Therefore, ZnO + C = Zn + CO
The stoichiometric amount of carbon required for the reduction of zinc oxide in dust is 22 to 37 Kg. That is, stoichiometrically, about 2 to 4 watts per ton of dust
Since a carbon amount of t% is required, a carbon amount of 15 to 19 kg is insufficient.

However, in order to actually perform the reduction of zinc oxide in dust stably and quickly, it is necessary not only to compensate for the above-mentioned carbon deficiency but also to make the stoichiometric carbon content 3 to 10 times the carbon content. There is a need. This means that in order to increase the zinc content in dust, it is essential not only to promote the reduction and vaporization of zinc oxide, but also to reduce the amount of generated dust itself (volume reduction). This is because in order to reduce the volume, it is necessary to promote the reduction of not only zinc oxide but also iron oxide present in the dust in an amount of 20 to 30 wt%.

Considering the reduction of iron oxide (Fe ₂ O _3, etc.), the stoichiometric amount of carbon involved in the reduction of zinc oxide is three times that of zinc oxide. Taking into account the efficiency that contributes to the reduction reaction of iron oxide, about 10 times the stoichiometric amount of carbon involved in the reduction of zinc oxide is required. Therefore, the carbon content of the dust pellet is set to 6 to 40 wt%.

FIG. 2 shows the zinc content of the recovered dust with respect to the charged amount of the dust pellet when the dust pellet adjusted to the above carbon content was charged into the electric furnace using the zinc content after the reduction treatment of the dust pellet as a parameter. Shows the predicted value from the calculation of the quantity. The zinc content of the collected dust in FIG. 2 is determined by the zinc content of the dust pellets charged into the electric furnace,
The amount of dust newly generated when scrap iron was dissolved was 1.4 t, and the zinc content in the generated dust was 25 wt%, and the weighted average was determined.

It is known from experiments in a high frequency induction furnace that the zinc content after the reduction treatment of the dust pellets can be secured to 50 wt% or more. When the dust pellets are put into a 1-t electric furnace, it is estimated from FIG. 2 that the zinc content in the collected dust can be 30 wt% or more.

Next, the carbon material added during agglomeration will be described. The carbon material may be any one of activated carbon, coke, and coal, which are effective as a reducing agent for zinc oxide and iron oxide in dust, or a mixture thereof, but the particle size is 5 m.
m. If the particle size is 5 mm or more, agglomeration becomes difficult. As described above, the amount of the carbon material is required to be 6 to 40 wt%.

Further, after adjusting the carbon content, the dust is agglomerated into particles having a particle size of 2 to 30 mm, preferably 2 to 10 mm, and an average particle size of 4 to 5 mm. Again, it is put into the molten iron held in the electric furnace. If the particle size of the dust is less than 2 mm, the amount of scattering is large,
If it exceeds 30 mm, it takes time to dissolve.

The optimum charging time when the agglomerated dust pellets are charged into an electric furnace is determined from the viewpoint of ensuring a sufficient reaction time and a high temperature for the reduction reaction to proceed sufficiently.
It is necessary for molten iron to be present in the electric furnace, and it is desirable to set the period from the end of the melting period (also referred to as burnout) of the initially charged scrap iron to the early stage of the refining period.

In the present invention, dioxin adhering to dust, whose toxicity has recently been regarded as a problem, is also decomposed during exposure to a high temperature of 1600 ° C. in an electric furnace.
If an electric furnace exhaust gas treatment system is equipped with exhaust gas quenching equipment,
Dioxin in exhaust gas can be removed by 99%.

[0030]

Next, an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic diagram of an apparatus for treating electric furnace generated dust according to the present invention.

The exhaust gas from the electric furnace 50 is attracted by the exhaust fan 57, and the unburned components in the exhaust gas are burned by the air supplied from the air blowing port 54 in the combustion tower 55, and the high temperature of 600 to 800 ° C. It becomes exhaust gas. This exhaust gas is rapidly cooled to 100 ° C. or lower by the gas cooler 56. Activated carbon 64 is blown as an adsorbent between the exhaust fan 57 and the bag filter 58 from the adsorbent blowing device 63 containing a carbon material at a rate of 0.2 g per 1 m3 of exhaust gas, and is collected by the bag filter 58 together with dust generated by the electric furnace. did.

Part of the collected dust is a product hopper 5
9 and handed over to a smelting maker as a zinc raw material. The remaining dust is stored in the dust recycling line 6
After returning to 0, it is returned to the dust hopper 41. The collected dust 42 stored in the dust hopper 41 is mixed with the coke 44 stored in the coke hopper 43 together with the mixer 45.
And mixed well. Coke 44 is added to dust pellets as a reducing agent for zinc oxide.
Had a particle size of 1 mm or less.

The measured dust content of the collected dust is 20 wt%, and the stoichiometric carbon amount required for the reduction of zinc oxide is calculated to be 29 kg / t. 145k of coke breeze per ton of dust
g was added.

Next, the mixture is agglomerated by an agglomeration device 46.
Agglomerated to a size of about 2 to 30 mm in diameter to form dust pellets. Here, when the diameter of the dust pellet is less than 2 mm, it is discharged unreacted by the exhaust gas when put into an electric furnace, and when the diameter exceeds 30 mm, it takes time to dissolve, and the inside of the pellet takes a long time. The above range is desirable because zinc oxide is not sufficiently reduced.

The agglomerated dust pellets are dried and preheated in a drying and preheating device 47, and then charged into an electric furnace 50 by an intermediate hopper 48 by a quantitative feeder 49. The time when the dust pellets are introduced into the electric furnace is after the scrap iron is melted and before the refining is finished. However, when the scrap iron is charged into the electric furnace 50 in a plurality of times, the electric furnace 50 is charged. It is possible even at the time of additional loading of scrap iron in which the molten iron 51 exists.

The electric furnace 50 holds molten iron 51 formed by melting scrap iron therein, and the charged dust pellet 52 has a specific gravity of 1.2 to 2.5 and has a molten iron 51 content. Floats on the surface of molten iron. Iron oxide in the dust is mainly reduced by the carbon material in the dust pellets and recovered in the molten iron.

The zinc oxide is reduced by the carbon material in the dust pellets, evaporates as zinc, and is oxidized by oxygen in the air introduced from the air introduction port 54 installed in the exhaust gas duct 53, and becomes less than 10 μm. It becomes fine zinc oxide particles and is collected as dust by a dust collector. In addition to the dust collected by the dust collector, some of the dust pellets are broken by thermal shock from the molten iron 51 and powdered and discharged from the electric furnace without being reacted, and Occasionally, newly generated zinc-containing dust is also included.

The exhaust gas from the electric furnace 50 is attracted by the exhaust fan 57 together with these zinc oxide particles, unreacted dust and newly generated zinc-containing dust, and
After the unburned components in the exhaust gas are burned in 5, the gas is cooled by the gas cooler 56, and the dust collector bag filter 58 collects zinc oxide particles and dust.

The amount of dust in the recycling system 60 gradually increases because new dust is added each time scrap iron is dissolved. In order to increase the zinc content, dust collected by the dust collector is extracted into the product hopper 59 each time scrap iron is melted, and the entire amount is again put into the electric furnace and collected by the dust collector. The dust collected for the second time is delivered to a company specializing in dust treatment as product dust. The zinc oxide content of this product dust is 34wt
%Met.

[0040]

According to the present invention, zinc oxide contained in dust in the electric furnace exhaust gas or in the exhaust gas of the scrap iron preheating apparatus for preheating scrap iron with the exhaust gas of the electric furnace can be concentrated to 30% or more. At the same time, harmful substances such as dioxin in the collected dust can be decomposed and made harmless.

[Brief description of the drawings]

FIG. 1 is a process chart of an embodiment of a method for recovering zinc oxide from dust according to the present invention.

FIG. 2 is a view showing an average zinc content of recovered dust according to the present invention.

FIG. 3 is a process diagram showing a conventional method for recovering zinc from dust.

[Explanation of symbols]

 41: Dust hopper 42: Raw material dust 43: Coke hopper 44: Coke 44: Mixer 46: Agglomeration device 47: Drying and preheating device 48: Intermediate hopper 49: Quantitative feeder 50: Electric furnace 51: Molten iron 52: Dust Pellet 53: exhaust gas duct 54: air inlet 55: combustion tower 56: gas cooler 57: exhaust fan 58: dust collector 59: product hopper 60: dust recycling line

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI B09B 3/00 303L

Claims (4)

[Claims] 1. A method for treating zinc-containing dust, comprising the following steps. (a) blowing an adsorbent containing a carbon material into the exhaust gas of an electric furnace for melting and refining scrap iron or exhaust gas of a scrap iron preheating device for preheating scrap iron with the exhaust gas of the electric furnace at a stage preceding the dust collector; and (b) the dust collector. Particle size is 5m
m or less, and agglomerate to form a carbon content of 6 to
(C) charging the dust pellets into the electric furnace and melting and refining the dust pellets together with the scrap iron during the period from the end of the scrap iron melting period to the early refining period of the electric furnace. A method for treating zinc-containing dust. 2. An adsorbent containing a carbon material is blown into an exhaust gas of an electric furnace or an exhaust gas of a scrap iron preheating device for preheating scrap iron with the exhaust gas of an electric furnace in a stage preceding a dust collector, and an organic substance harmful to a human body in the exhaust gas. And the dust containing the carbon material is collected by a dust collecting device, and the collected dust collected is further agglomerated by adding a carbon material to adjust the carbon content to 6 to 40 wt%. Dust pellets characterized by being made. 3. When agglomerating the collected dust, any one of coke, coal and activated carbon having a particle size of 5 mm or less is used.
The dust pellet according to claim 2, wherein the carbon content is adjusted to 6 to 40 wt% by adding a seed or a mixture thereof. 4. The dust pellet according to claim 2, wherein a particle diameter of the dust pellet obtained by agglomerating the collected dust is 2 to 30 mm.