JPH11152511A - Treatment of steelmaking furnace dust and dust pellet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the dust quantity of a steelmaking furnace, particularly an electric furnace and also, to recover the dust having high zinc content. SOLUTION: A treating method of the dust of the steelmaking furnace is executed, by which carbonaceous material 44 as reducing material is mixed with the steelmaking furnace dust so that the carbon content becomes 6-40 wt.%, and dust pellet is obtd. by pelletizing and this dust pellet is charged into the electric furnace 50 and iron oxide in the dust is reduced and removed in molten iron 51, and zinc oxide in the dust is reduction-vaporized and collected and recovered as the zinc oxide in the collected dust, and the other components in the dust are made to slag to contrive the reducing of the dust quantity. This method can efficiently be applied particularly to electric furnace dust.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the reduction of dust generated from a steelmaking furnace (hereinafter referred to as "steelmaking furnace dust"), and particularly to zinc oxide and oxide in dust generated from an electric furnace (referred to as electric furnace dust). The present invention relates to a method for efficiently reducing iron to reduce the amount of dust and consequently the volume.

[0002]

2. Description of the Related Art In Japan, steelmaking furnace dust, particularly electric furnace dust, reaches about 500,000 tons per year. Approximately 60% of this is taken up by a company specializing in the treatment of dust, and is processed as zinc raw material by dedicated processing equipment such as a rotary kiln and a melting furnace.

[0003] When electric furnace dust is used as a zinc raw material, it is considered that the higher the zinc content in the dust, the better, and preferably at least 50 wt% or more from the viewpoint of processing cost. When the zinc content is less than 50 wt%, the dust discharge side bears the processing cost according to the shortage of the zinc content, and in that sense, it is desired that the zinc content be as high as possible. .

[0004] However, the zinc content of ordinary electric furnace dust is at most about 25 wt%, and the evaluation when it is taken to a specialized company for dust treatment is actually low. Therefore, the entire amount of generated dust has not been processed as a zinc raw material, and about 40% of the dust is directly landfilled.

[0005] In recent years, landfill sites have been reduced, making landfill difficult. In addition, heavy metals such as lead and cadmium contained in dust, and harmful components such as highly toxic dioxins are included. It has been pointed out that there is a danger of causing pollution, and it is expected that landfill disposal will become more and more difficult in the future.

In addition, the cost required for landfilling dust is about ten times as much as the cost for treating slag.
This cost is expected to increase in the future. Therefore, it is extremely important to reduce the amount of dust in steelmaking furnaces, particularly electric furnace dust, and to increase the zinc content in dust as much as possible.

The conventional method of treating electric furnace dust is mainly for recovering valuable metals in dust. For example, a method described in Japanese Patent Application Laid-Open No. 52-53714 is used. (Prior Art 1). In this processing method, carbon powder is mixed with dust collected from a steelmaking furnace such as a converter or an electric furnace at a ratio of carbon powder 1 to 3 with respect to dust 9 to 7 and pelletized, and then other raw materials are mixed. This is a recycling method for collecting dust in a steelmaking furnace, in which only metal oxides (mainly iron oxide) contained in the dust are collected in molten steel.

Japanese Patent Application Laid-Open No. 53-122604 discloses a method (prior art 2) for recovering volatile components such as zinc in iron making dust as shown in FIG. Hereinafter, FIG.
This technique will be described with reference to FIG.

Reducing slag discharged from electric furnace 1
Is received in the reaction vessel 2, the electrode 3 is inserted into this slag,
The slag is heated by passing an electric current to an extent that does not lose fluidity (1450 to 1500 ° C.). The coke powder and dust are previously formed into briquettes by a bunker, and the briquettes are charged into the reaction vessel to reduce volatile components such as zinc. At this time, in order to promote the above reaction, the input power from the electrode is adjusted to secure the flow of the slag.

After completion of the reaction, the slag is discharged from the reaction vessel, crushed so as to be easily used thereafter, magnetically separated, and magnetic materials such as iron and steel are reused. Volatile components such as zinc generated by the above reaction are collected by a dust collecting hood 4 provided at the upper part of the reaction vessel, and collected by a bag filter 5.

[0011]

According to the study of the present inventors, electric furnace dust is composed of slag composed of 20 to 30% by weight of iron oxide, 15 to 25% by weight of zinc oxide, and balance of silica, alumina, calcium oxide and the like. Contains. If iron oxide and zinc oxide are recovered as valuable metals, it is theoretically possible to reduce the weight by about 50 wt%.

At the same time, the slag component in the dust is melted,
If slag is reformed, further reduction can be expected. This method is also effective from the viewpoint of recycling valuable metals, and it is considered that the cost of landfill treatment can be significantly reduced.

However, the above-mentioned prior art has the following problems from the viewpoint of reducing the amount of dust and reforming into slag. That is, in the prior art 1, although it is possible to recover iron from iron oxide, since reduction of zinc oxide and slagging of other components are insufficient, it is expected to reduce dust. has no effect. In addition, zinc in dust is not recovered.

In the prior art 2, in order to recover the iron oxide, it is necessary to process a predetermined amount of dust, discharge the slag from the reaction vessel, and perform a process of cooling → crushing → magnetic separation. For this reason, there are problems that heat energy is lost, equipment costs for recovering iron are required, and processing time is long.

The present invention has been made in order to solve the above-mentioned problems, and it is intended to easily reduce and recover zinc oxide and iron oxide in dust, and to make steelmaking furnace dust, particularly electric furnace dust. The aim is to promote slagging and significantly reduce dust.

[0016]

SUMMARY OF THE INVENTION The present invention relates to an electric furnace dust by mixing a reducing carbon material with a steelmaking furnace dust, particularly an electric furnace dust, to form an agglomerate, returning it to an electric furnace, and reducing it in molten iron. In the method for reducing the amount of carbon, (1) the amount of the carbon material for reduction, (2) the particle size of the carbon material for reduction, (3) the particle size of the dust pellet, (4) the timing of charging the dust pellet to the electric furnace, etc. By properly adjusting the value, zinc oxide and iron oxide can be reduced more efficiently. In addition, by promoting the slagging of components other than zinc oxide and iron oxide, it is possible to achieve a significant reduction in electric furnace dust, and at the same time, to significantly increase the zinc content in the reduced dust. With the knowledge described above, the following invention has been attained.

According to a first aspect of the present invention, a carbon material as a reducing agent is mixed with a steelmaking furnace dust so as to have a carbon content of 6 to 40% by weight, and agglomerated to obtain dust pellets. Charged into a furnace, reduce the iron oxide in the dust and recover it in the hot metal, and reduce and vaporize the zinc oxide in the dust, collect and collect it in dust collected dust as zinc oxide, A method for treating steelmaking furnace dust, characterized in that other components in the dust are converted into slag to reduce the amount of the dust.

A second invention is a method for treating steelmaking furnace dust, wherein the steelmaking furnace dust is electric furnace dust.

A third invention is a method for treating steelmaking furnace dust, wherein the dust pellets are charged into an electric furnace between the end of the scrap iron melting period and the early stage of the refining period of the electric furnace operation.

According to a fourth aspect of the present invention, as a carbon material, any one of coke and coal having a particle size of 5 mm or less is added to steelmaking furnace dust.
This is a dust pellet characterized by adding a seed or a mixture thereof, adjusting the carbon content to 6 to 40 wt%, and agglomerating this.

According to a fifth aspect of the present invention, the steelmaking furnace dust is an electric furnace dust, and the particle size of the dust pellet is 2 to 15 m.
m is a dust pellet.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION The basic structure of the present invention is to use a carbon material as a reducing agent in steelmaking furnace dust with a carbon content of 6 to 40 wt.
% And agglomerate to obtain dust pellets. The dust pellets are charged into an electric furnace, and the iron oxide in the dust is reduced and collected in hot metal. This is a method for treating steelmaking furnace dust in which zinc oxide is reduced and vaporized, collected and collected as dust, and collected as dust, and the other components in the dust are converted into slag to reduce the volume and volume of the dust. .

At present, converters and electric furnaces are mainly used as steelmaking furnaces, and it is necessary to treat these dusts. However, since the dust from the converter has a low zinc content, iron oxide is mainly recovered. Be the purpose. Since the dust from the electric furnace has a high zinc content as described later, the main purpose is to recover zinc and iron in iron oxide and to reduce the amount.

In normal electric furnace operation, for example, the amount of dust generated when melting 100 tons of scrap per charge is about 1.4 tons. In the present invention, this dust is reduced by about 0.5 t. The amount of newly generated slag is desired to be about 0.2 t.

An embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic diagram of an electric furnace dust treatment apparatus according to the present invention. This device can also be applied to converter dust. The exhaust gas from the arc type 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 to become high-temperature exhaust gas. This exhaust gas is passed through a gas cooler 56
Then, the dust in the exhaust gas is collected by the dust collecting device 58.

The dust collected by the dust collector 42 is stored in a dust hopper 41, and together with a reducing coke powder 44, which is a carbon material stored in a carbon material hopper 43, a mixer 45.
And mixed well. The mixture is agglomerated 46
To agglomerate into dust pellets to a size of about 2 to 15 mm in diameter.

The dust pellets are dried and preheated by a preheating device 4.
In 7, after being dried and preheated, it is quantitatively fed into an electric furnace 50 by a quantitative feeder 49 via an intermediate hopper 48. The electric furnace 50 is provided with an electrode device 63 at its center, from which an arc is generated, the heat of which melts the scrap, produces steel and is used for dust reduction.

The dust pellets are charged into the electric furnace from the end of the scrap melting period to the early refining period in which the molten iron 51 exists in the electric furnace 50. In addition, in the case where the scrap is charged into the electric furnace in a plurality of times, the scrap can be additionally loaded and even after 3 minutes from the start of energization.

The electric furnace 50 contains molten iron 51 in which scrap is melted, and the dust pellets 52 have a specific gravity of 1.2 to 2.5.
Because it is smaller than 1, it floats on the surface of molten iron. The iron oxide in the dust is mainly reduced by the carbon material in the dust pellet and is recovered as iron in the molten iron.

The zinc oxide is reduced by the carbon material in the dust pellets, evaporates, and is oxidized by the oxygen in the air introduced from the air introduction port 54 installed in the exhaust gas duct 53. It becomes zinc particles.

On the other hand, part of the dust pellets
, And is discharged out of the system as unreacted. Further, during the melting period of the scrap in the electric furnace 50, dust containing zinc oxide is generated from the scrap.

The exhaust gas from the electric furnace 50 is attracted by an exhaust fan 57, and the combustion tower 55 burns unburned components in the exhaust gas.
Collects unreacted dust and dust generated during scrap melting. Part of the collected dust is stored in a product hopper 59 and delivered to a smelting maker as a raw material for zinc material.

The remaining collected dust is returned to the dust hopper 41 via the dust recycling line 60. This recirculated dust is again mixed with the raw material dust in the
Agglomerated by 8 and recharged into the electric furnace,
It is reduced.

The converter and electric furnace, which are steelmaking furnaces, are provided with an electric dust collector or a bag filter as a dust collector, and dust is collected by the dust collector. Since this dust is a powdery substance and is inconvenient for subsequent processing, it is agglomerated and pelletized. In producing pellets, a carbon material such as coke powder is included as a reducing agent for reducing iron oxide and zinc oxide.

According to the result of studying the carbon content required as a reducing agent, zinc oxide in dust is 15 to 25%.
It is contained by about wt%. Therefore, ZnO + C = Zn
The stoichiometric amount of carbon required for the reduction of zinc oxide in dust, calculated based on the reaction formula of + CO, is 1 t of dust.
The weight is 22 to 37 kg. However, in order to reduce the amount of dust, not only zinc oxide but also 20-
It is also necessary to promote the reduction of iron oxide present at 30 wt%.

Considering the reduction of iron oxide, the stoichiometric amount of carbon involved in the reduction of zinc oxide is three times as large.
However, considering the efficiency of the carbon in the dust pellets actually contributing to the reduction reaction, a carbon amount that is 10 times the stoichiometric amount of carbon involved in the reduction of zinc oxide is required.

FIG. 2 shows the calculated value of the average zinc content of the collected dust, with the zinc content of the dust pellet after the reduction process as a parameter, with respect to the dust pellet input amount to the electric furnace. The zinc content of the collected dust in FIG. 2 is determined by comparing the zinc content of the dust pellets fed into the electric furnace after the reduction treatment and the zinc content (25
wt%).

As shown in FIG. 2, when the zinc content in the dust pellet after the reduction treatment is set to 50% wt, one charge and one scrap iron
When this dust pellet is put into a 1-t electric furnace with respect to 00 t, the zinc content in the collected dust is calculated to be about 31 wt%. The zinc content is thus enriched according to the invention. Further, when the concentrated collected dust is further recycled as dust pellets, the zinc content of the collected dust gradually increases.

Next, the carbon material added during agglomeration will be described. The carbon material may be any of coke and coal effective as a reducing agent for zinc oxide and iron oxide in dust, or a mixture thereof, but preferably has a particle size of 5 mm or less. If the particle size is 5 mm or more, agglomeration becomes difficult.

Further, after adjusting the carbon content, the dust is agglomerated to a size having an outer diameter of 2 to 15 mm and an average particle size of 4 to 10 mm, and the agglomerated dust pellets are again placed in an electric furnace. Charge into the retained molten iron.

The outer diameter of 2 mm is the lower limit of the particle size that is not conveyed together with the exhaust gas.
If it exceeds mm, it is not carried out together with the gas outside the system, but on the contrary, the particle size is too large, and it takes too much time to complete the reduction reaction.

The optimal charging time when the agglomerated dust pellets are charged into the electric furnace is determined from the viewpoint of ensuring a sufficient reaction time and high temperature for the reduction reaction to proceed sufficiently.
It is necessary that molten iron be present in the electric furnace, and it should be from the end of the melting period of scrap iron to the beginning of refining.

FIG. 3 shows the calculation result of the reduction of the amount of collected dust with respect to the amount of dust pellets charged into the electric furnace, with the zinc content after reduction of the dust pellets as a parameter. In the calculation, the content of zinc from dust generated from newly charged scrap is assumed to be 25 wt%, and reduction in the zinc content of the charged dust pellets is shown.
For example, the zinc content of the dust pellet after the reduction treatment is 30
wt%, the reduction rate of this dust pellet is about 2
5/30 (= 0.83).

Therefore, when the amount of the dust pellets charged into the electric furnace is 1 ton, the amount is reduced by 0.17 ton.
In addition, as shown in FIG. 3, the higher the zinc content of the dust pellet after the reduction treatment, the greater the dust reduction. In addition, when the charged amount of the dust pellets is constant, as the iron oxide ratio in the charged dust pellets increases, the iron oxide in the dust is reduced, so that the zinc content in the collected dust increases.

In the present invention, as a result of the stable reduction of zinc, the zinc content of the dust pellet after the reduction treatment can be ensured to be 50 wt% or more from an experiment described later.
Therefore, in this case, it is calculated that, for example, when the dust pellets are charged into a 100-t electric furnace at 1 t / ch, the weight can be reduced by about 0.5 t. In addition, if the amount of the dust pellet charged into the electric furnace is increased, the amount of reduction is also increased.

Further, according to the present invention, dioxin adhering to dust, whose toxicity has been regarded as a problem in recent years, can be removed at a high efficiency of 99% or more because it is treated at a high temperature.
The present invention is not intended only for dust in exhaust gas directly discharged from an electric furnace, and is applicable without any problem to dust in exhaust gas from a scrap iron preheating device inserted in an exhaust gas treatment system of an electric furnace. it can. Needless to say, this method can be applied to converter dust.

[0047]

EXAMPLE Into 200 kg of molten iron held in a high-frequency induction furnace, 15 kg of dust pellets (dust amount: 11.25 kg) whose carbon content was adjusted to 25 wt% were charged, and the molten iron temperature was set to 1500 ° C. and maintained for 5 minutes. Then, the weight and iron content of the generated dust and slag were analyzed. The result is shown in FIG.

In this case, newly generated dust was 4.7 kg and newly generated slag was 2.5 kg per 15 kg of input dust. Dust is about 42
The zinc content in newly collected dust was reduced to about 59 wt%.

When the balance of iron was calculated, 2.6 kg corresponding to 76% of 3.5 kg of iron in the input dust was recovered in the iron bath, and the ratio of no recovery was found in newly generated dust. It turned out to be about 19% and about 5% in newly generated slag.

In the embodiment in the actual operation, one charge 1
The dust generated from the electric furnace of 00t has a zinc content of 25w
t%, and the generation amount was 1.4 t. One ton of the powder was recharged into an electric furnace as dust pellets (containing 25 wt% carbon material), and as a result, the amount of reduction was 0.5 t. Paying attention only to the charged dust pellets, the zinc content in the recovered dust is about 50 wt%, but the zinc content in dust generated from new scrap is 25 wt%.
%, The average zinc content of the recovered dust reached 31 wt%.

As described above, the minimum required dust was recirculated and efficiently treated. As a result, it was possible to reduce the amount of dust and to collect dust having a high zinc content. It is expected that the zinc content of the recovered dust can be gradually increased by sequentially repeating such operations.

[0052]

According to the method of the present invention, dust generated from an electric furnace is mixed with an appropriate amount of a reducing carbon material, agglomerated into dust pellets, and the dust pellets are again charged or loaded into the electric furnace. Depending on the method, electric furnace dust can be reduced. In the method of the present invention, the iron oxide is reduced and recovered in the molten iron, so that it is not necessary to newly separate the recovered iron. Further, since the zinc content in the reduced dust can be increased to 30 wt% or more, the evaluation as a zinc raw material can be enhanced.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an apparatus for implementing the present invention.

FIG. 2 is a diagram showing a calculated value of a zinc content of recovered dust with respect to a charged amount of dust pellets in a 100-t electric furnace.

FIG. 3 is a view showing reduction of dust with respect to the amount of dust pellets charged in a 100-t electric furnace.

FIG. 4 is a diagram showing mass balance in an example of the present invention.

FIG. 5 is a diagram showing an outline of a conventional apparatus for recovering zinc from dust.

[Explanation of symbols]

 41: Dust hopper 42: Dust collection device collected dust 43: Carbon material hopper 44: Carbon material 45: Mixer 46: Agglomeration device (pelletizer) 47: Drying preheating device 48: Intermediate hopper 49: Quantitative feeder 50: Electric furnace 51: Molten steel 52: Pellet 53: Exhaust gas duct 54: Air inlet 55: Gas combustion tower 56: Gas cooler 57: Exhaust gas 58: Dust collector 59: Product hopper 60: Dust recycling line 63: Electrode

Claims (5)

[Claims] 1. A steelmaking furnace dust is mixed with a carbon material as a reducing agent so as to have a carbon content of 6 to 40% by weight, agglomerates to obtain dust pellets, and the dust pellets are charged into an electric furnace. Then, the iron oxide in the dust is reduced and collected in the hot metal, and the zinc oxide in the dust is reduced and vaporized, collected and collected in the dust dust as zinc oxide, and the other in the dust. A method for treating steelmaking furnace dust, comprising reducing the amount of dust by slagging the components. 2. The method according to claim 1, wherein the steelmaking furnace dust is an electric furnace dust. 3. The method for treating dust in a steelmaking furnace according to claim 1, wherein the dust pellets are charged into an electric furnace during the period from the end of scrap metal melting to the early stage of refining during electric furnace operation. 4. Carbon steel having a carbon content of 6 to 40 watts is added to steelmaking furnace dust by adding any one of coke and coal having a particle size of 5 mm or less or a mixture thereof as a carbon material.
Dust pellets characterized by being adjusted to t% and agglomerated. 5. The dust pellet according to claim 4, wherein the steelmaking furnace dust is electric furnace dust, and the particle size of the dust pellet is 2 to 15 mm.