JP2000328130A - Method for decomposing dioxin group compounds in steel dust - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decompose dioxin group compounds and to reduce the total exhaust quantity of the dioxin group compounds occupying in the whole steel dust by directly blowing the steel dust containing the dioxin group compounds collected together with the exhaust gas emitted from a melting furnace or a refining furnace into molten steel or slag covering the molten steel surface with a blowing device at steel melting and refining. SOLUTION: The steel dust containing the dioxin group compounds collected from the exhaust gas emitted from the melting furnace for melting steel or the refining furnace for refining molten steel is directly blown into the molten steel or the slag covering the molten steel surface with the blowing device at steel melting and refining. The dioxin group compounds in the steel dust can be decomposed and only dioxins emitted by the melting of newly charged scrap is emitted. The total exhaust quantity of the dioxin group compounds in the whole steel dust seen from the treating quantity of the whole scraps can be reduced by applying the blowing treatment of the produced steel dust.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for decomposing dioxins existing in dust by directly blowing steel dust into molten steel and slag during melting and refining of steel.
The present invention relates to a processing method for reducing the content.

[0002]

2. Description of the Related Art In the industry where scrap is used as a raw material in the production of steel, the separation and recovery of scrap are particularly advanced, which contributes to the upgrading of steel. However, on the other hand, even in the case of scrap containing a large amount of impurities such as steel plates and cords coated with a resin such as chloride, the quality of the steel has been improved and its quality has been improved by improving the operation method. On the other hand, the amount of generated steel dust and the like tends to increase, and at present, the waste is mainly disposed of by various approaches other than the treatment method of landfill as industrial waste. (FIG. 6)

[0003] The method of treating steel dust and the like generally involves a neutralization treatment by adjusting pH using sulfuric acid or the like, and then burying the landfill. In recent years, however, the generation of dioxins and the inclusion of dioxins in particular have been reduced. On the other hand, its existence and processing method are becoming problems.

As a method of treating the dioxin-containing steel dust, for example, Japanese Patent Application Laid-Open No. 2-9643 proposes an iron making / steel making method using aluminum dross. The steelmaking and steelmaking method using this aluminum dross is a method of manufacturing steel dust, steel scale, steel refining, iron or powder containing one or more irons of two or more kinds of raw material oxides for steelmaking and steelmaking, and aluminum consisting of aluminum dross. The mixture with the contained powder is simultaneously poured into the ladle when the molten iron or molten steel in the melting furnace or the refining furnace is taken out of the ladle, and the oxide and aluminum in the mixture are heated by the heat of the molten iron and molten steel. A method for causing an oxidation reaction between the two is disclosed.

According to the iron making and steel making method, it is proposed that steel dust and the like and aluminum dross can be effectively reused as metal resources, the amount of industrial waste can be reduced, and energy can be improved by reaction heat. are doing.

In Japanese Patent Application Laid-Open No. 9-67610,
As an iron and steel making method using aluminum dross,
In addition to the technique disclosed in JP-A-2-9643, an iron-containing powder and an aluminum-containing powder in a mixture are adhered to each other via a substance serving as a binder, and the mixture is adsorbed to a magnet and transported.・ A method characterized by being introduced into molten steel is proposed.

[0007]

SUMMARY OF THE INVENTION In the case of producing iron or steel from raw materials generally called scrap, including steel plates and cords coated with a resin such as chloride, etc., in the steel melting and refining process. The disclosure of the above-mentioned publication is no exception that the steel dust is discharged together with the gas discharged from the furnace. Steel dust discharged from the furnace is collected by a dust collector, although various heavy metals and the like in the steel dust are recovered, but synthesized dioxins are present in the steel dust, and ultimately Many of them are being reclaimed and are starting to be problematic.

On the other hand, as a method of treating the above-mentioned steel dust, it is also conceivable to put it in a furnace together with scrap as a raw material, dissolve it at a high temperature, and decompose dioxins. White smoke is generated due to the evaporation and volatilization of zinc oxide and oil at the initial temperature rise of melting, and it is difficult to confirm the operation status. 2. In the early stage of dissolution, an oxygen-enriched operation is performed to promote dissolution, so that a rapid oxidation-reduction reaction occurs with the introduced reducing agent, and a flame is generated to make the operation difficult. There is a problem.

[0009] From the viewpoint of the generation of dioxins, Decompression operation is performed in the oxygen-enriched state to promote dissolution in the initial stage of dissolution, but the mixture of steel dust and aluminum dross introduced together with scrap is scattered due to decompression,
It is sucked and collected by the dust collector together with the generated gas. 4. Since the exhaust gas temperature at the initial stage of dissolution is low, decomposition of dioxins is not sufficient, and a cooling rate between 250 ° C. and 500 ° C. in a temperature range where dioxins are synthesized cannot be sufficiently obtained to suppress generation of dioxins. I'm not expecting to. 5. Further, it is easily presumed that the dioxins newly generated from the scrap and the dioxins contained in the steel dust are added, and the concentration of dioxins in the finally discharged steel dust is increased.

As described above, in the conventional method, if the steel dust is charged together with the scrap and the melting treatment is performed, many problems remain, and dioxins in the steel dust cannot be suppressed. On the other hand, a method using a powder blowing device is generally widely known as a method for charging powder such as aluminum dross, carbon, lime, etc., respectively. It has not been disclosed or suggested as a method for reducing the decomposition of dioxins.

[0011]

DISCLOSURE OF THE INVENTION An object of the present invention is to decompose dioxins contained in steel dust by directly blowing steel dust into molten steel and slag during melting and refining using a blowing device. It is intended to reduce the total emission of dioxins in the total steel dust from the viewpoint of the total scrap throughput.

The gist of the present invention is a technology for reducing the decomposition of dioxins in steel dust generated during the melting and refining of steel, by using a melting furnace for melting steel and a refining furnace for refining the molten steel. This is to blow steel dust containing dioxins collected from gas directly into molten steel during smelting and refining of steel or slag covering the surface of molten steel by a blowing device. As a result, the dioxins in the steel dust can be decomposed, and the amount of dioxins generated as the newly introduced scrap is dissolved can be reduced. That is, by blowing the generated steel dust, it is possible to reduce the total emission of dioxins in the total steel dust as viewed from the total scrap processing amount.

According to a second aspect of the present invention, the blowing device blows steel dust and a reducing agent into molten steel or slag at the time of melting and refining the steel and heats the molten steel or slag into the steel dust. An oxidation-reduction reaction occurs between the oxide of the compound and the reducing agent to decompose dioxins. Thereby, it is possible to further prevent the generation of white smoke due to the evaporation and volatilization of zinc oxide and the like, so that it is easy to secure the visibility during operation.

According to a third aspect of the present invention, when the steel dust and the reducing agent are directly blown into molten steel or slag by a blowing device, the steel dust and the reducing agent are blown into the molten steel or slag with a mixture of the steel dust and the reducing agent. It is. This further prevents the mixture from being scattered by the reduced pressure and being discharged together with the generated gas during the decompression operation performed in the oxygen-enriched state for promoting the dissolution at the initial stage of dissolution.

As described above, the heat of the molten steel in the furnace causes an oxidation-reduction reaction between the oxide in the steel dust and the reducing agent, thereby promoting complete decomposition of dioxins.
It is also effective in preventing the scattering and discharge of steel dust.

According to a fourth aspect of the present invention, the steel dust and the reducing agent are in the form of powder or granules. Thereby, it becomes easy to melt into molten steel or slag having a high temperature, and it is possible to further promote the decomposition of dioxins. Further, even when the effective molten steel depth or the effective slag thickness is small due to the limitation of the furnace shape, scattering can be easily prevented by selecting the shapes and blowing speeds of the steel dust and the reducing agent.

According to a fifth aspect of the present invention, the blowing time of the steel dust and the reducing agent by the blowing device is the last stage of the acid during melting and refining. The term “acid end stage” as used herein refers to a state in which scrap as a raw material is melted and slag covers the surface of molten steel. Thereby, since the operation of the furnace is more stable, the influence of disturbance is small and the reproducibility can be easily maintained.

According to a sixth aspect of the present invention, the reducing agent is:
The main component of the present invention is to contain at least one of C, Fe, Mg, and Al, which oxidizes and reduces oxides in the steel dust. As a result, it is possible to impart the value of the industrial waste, such as aluminum dross, to the present, and to reduce the waste as a whole industry.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 is an overall view showing a method for treating steel dust according to Embodiment 1 of the present invention, FIG. 2 is an enlarged explanatory view of a blowing device, and FIG. 3 is a steel pipe and molten steel in the blowing device. And a diagram for explaining the relationship with the slag.

The scrap as the main raw material is melted by the electric furnace 50, and the high-temperature exhaust gas 51 generated when the steel is melted is discharged from the exhaust port 52. The exhaust gas 51 is cooled by a cooling tower 54 via a combustion tower 53, and a steel dust 60 contained in the exhaust gas is collected by a dust collector 56 via an intermediate duct 55, and is conveyed to conveyors 57 and 58. Collected by The steel dust 60 contains dioxins, and is kneaded with the aluminum dross 61 generated and collected in a step (not shown), or granulated and sent to the blowing device 10.

The blowing device 10 is provided with the steel dust 6.
0 and aluminum dross 61 are stored in powder or granular form and blown into molten steel in the electric furnace 50 or slag covering the surface of the molten steel at a predetermined flow rate.

FIG. 2 shows the blowing device 10 in detail. The material receiving hopper 1 stores steel dust,
The iron and steel dust charged therein is pressurized in a blow tank 2, weighed by a load cell 3, and fed in a predetermined amount. Then, while finely adjusting the feed amount and the feed speed of the steel dust by the cutting feeder 4, any one of Ar, N2, and air supplied from the carrier gas supply pipe 5 is blown at 10 to 90 kg / min together with the carrier gas. At a speed, it is configured to be blown from a steel pipe 5 having a refractory applied to the outer periphery thereof through a hose 6 to an arbitrary depth in molten steel or slag in a melting furnace or a smelting furnace.
(Fig. 3)

The content of dioxins in steel dust was compared between the above-described structure of Example 1 of the present invention and the conventional method for comparison. The measurement results are shown in Table 1, and the steel dust at this time was compared. Tables 2 and 3 show components of the reducing agent.

[0024]

[Table 1]

[0025]

[Table 2]

[0026]

[Table 3]

From Table 1, it can be seen from the results of the conventional method that the iron dust (Table 2) alone and the iron dust + aluminum dross as a reducing agent (Table 3) show that the amount of dioxins contained in the secondary iron dust varies. It is extremely large even when considered. On the other hand, in the case of Example 1 in which the steel dust alone of the present invention was blown by the spraying device, the amount of dioxins contained in the secondary steel dust was detected by as much as two orders of magnitude. Here, the secondary steel dust refers to steel dust generated from scrap as a raw material of a target molten steel when the steel dust is blown.

Embodiment 2 Next, Embodiment 2 will be described with reference to Table 4. This is an example for observing the influence of the shape of the steel dust at the time of blowing by the blowing device in the first embodiment. This is the result of estimating the distribution ratio of secondary steel dust and molten steel by replacing the content in steel dust newly generated due to the shape of steel dust and the content dissolved in molten steel with Ni, which is an impurity. It is. Table 4 shows the results.

[0029]

[Table 4]

Table 2 shows that the steel dust is not retained in the secondary steel dust and is absorbed into the molten steel as compared with the case where the steel dust is supplied together with the scrap. Thus, powder or granular steel dust by the blowing device,
It can be determined that the blowing efficiency into molten steel is superior.

Example 3 Next, as Example 3, Table 5 shows the results of white smoke when the steel dust is blown into the powder as in the present invention and when the dust is simultaneously injected with the conventional scrap.

[0032]

[Table 5]

From Table 5, it can be seen that white smoke is generated at the melting stage by simultaneous injection with scrap as in the prior art, but no white smoke was found in the blowing method of the present invention.

Example 4 FIG. 4 shows a flow of a series of operation steps involved in steel production according to Example 4, and FIG. 5 shows the time course of the exhaust gas temperature immediately after the electric furnace at each time.

FIG. 4 (a) is a diagram showing a conventional process, and FIG. 4 (b) is a diagram showing a process flow so as to make it easier to compare the timing of charging and blowing of steel dust in the blowing method of the present invention. Conventionally, steel dust is put into an electric furnace together with scrap as a main raw material, and then melting is started. Then, after the start of melting (after the start of energization of the electric furnace), a new amount of scrap is added again in the melting period to increase the final amount of molten steel (at the first time, scraps and the like are bulky and many gaps are present. Therefore, when melting, the amount is greatly reduced and the efficiency is inefficient), and at the same time, the operation using the heat of the molten steel is performed.

However, as shown in FIG. 5, in the melting period, the temperature inside the melting furnace is rising, and the input scrap and steel dust are not completely melted. Therefore, when new scrap is charged, the temperature in the melting furnace rapidly decreases, and it is not easy to stably dissolve the steel dust and decompose the contained dioxins.

Therefore, as shown in FIG. 4 (b), after the first scrap input and the secondary scrap input,
At the end of the acid period when the scrap as the raw material is molten and the slag covers the surface of the molten steel, the steel duct is blown into the molten steel and / or the slag by a blowing device. Thereby, the steel slag can be melted in the stable temperature condition at the end of acid shown in FIG. 5, and the steel dust is not scattered because it is directly blown into the molten steel or the slag covering the molten steel surface, In addition, dioxins contained in steel dust can be stably and completely decomposed.

In the fourth embodiment according to the present invention, the process of charging the scrap as the raw material twice is employed, but the present invention is not limited to this. However, the same effect can be obtained by blowing steel dust in a state where the furnace temperature is stable (also referred to as acid end stage), as in the fourth embodiment. Therefore, in the electric furnace, 100 times at the end of acid compared to the melting period.
Since the temperature change is stable at 0 ° to 1300 ° C., an effect of preventing generation of dioxins due to a cooling effect up to the intermediate duct can be expected.

Next, Table 6 shows the measurement results of the content of dioxins in the steel dust charged and blown in the melting phase and the acid phase by the conventional method and the method of the present invention.

[0040]

[Table 6]

As shown in Table 6, even with the simultaneous injection of steel dust and scrap (the conventional method) or the method of blowing steel dust (the method of the present invention), the content of dioxins in the steel dust during the melting period is large. Has become. Further, it can be seen from the balance with the total dioxin content that about 80% or more of the dioxins are generated during the dissolution period. Furthermore, the content of dioxins in the last stage of acid shows a low value in both the conventional method and the method of the present invention, but the total dioxin content shows a lower value in the blowing method according to the method of the present invention. .

Therefore, the method of injecting steel dust at the end of the acid period has a considerably lower content of dioxins than the simultaneous injection method of the scraps.
In order to decompose and reduce dioxins, blowing just below high-temperature molten steel at the end of acidity is an effective means. Regarding the shape of the steel dust, although it is formed into a granular shape, the content of the total dioxins is more effective than that of the powder.

[0043]

According to the present invention, the dioxins in the blown steel dust are blown directly into the molten steel or into the slag covering the surface of the molten steel at the end of the acid period when the inside of the furnace is melted at a high temperature. Can be decomposed and reduced.
By blowing a reducing agent together with steel dust,
An oxidation-reduction reaction is caused between the oxide in the steel dust and the reducing agent, and the decomposition of dioxins can be promoted. Further, by forming a mixture of steel dust and a reducing agent, a more active oxidation-reduction reaction is promoted.

Further, it is possible to prevent the generation of white smoke due to the evaporation and volatilization of zinc oxide and the like, which are conventionally generated when steel dust and scrap are simultaneously charged. In addition, by making the shape of the steel dust and the reducing agent into powder or granules, it becomes easy to dissolve into molten steel or slag. In addition, the direct blowing can prevent the steel dust and the reducing agent from being scattered and discharged together with the exhaust gas even when the operation is depressurized. In addition, by setting the blowing timing of the steel dust to the last stage of acidity of melting and refining, dioxins in the steel dust can be decomposed in a stable high temperature state.

By making the reducing agent blown together with the steel dust contain at least one of C, Fe, Mg and Al as a main component, industrial waste such as aluminum dross can be utilized, and the processing cost can be further improved. Can be lowered. As described above, since dioxins contained in steel dust can be decomposed and reduced, the content of dioxins from the viewpoint of the total scrap processing amount can be easily suppressed.

[Brief description of the drawings]

FIG. 1 is an overall view illustrating a method for treating steel dust according to a first embodiment of the present invention.

FIG. 2 is an enlarged view of the blowing device according to the first embodiment of the present invention.

FIG. 3 is an explanatory diagram illustrating a relationship between a steel pipe and molten steel in the blowing device according to the first embodiment of the present invention.

FIG. 4 is a process flowchart according to a fourth embodiment of the present invention.

FIG. 5 is an explanatory diagram showing a time course of exhaust gas temperature immediately after an electric furnace according to Embodiment 4 of the present invention.

FIG. 6 is an overall view showing a conventional steel dust collecting step and a processing method.

[Explanation of symbols]

 1: Material hopper 2: Blow tank 3: Load cell 4: Cut-out feeder 5: Carrier gas supply pipe 6: Hose 7: Steel pipe 10: Blowing device 50: Electric furnace 51: Exhaust port 52: Exhaust gas 53: Combustion tower 54: Cooling Tower 55: Intermediate duct 56: Dust collector 57, 58: Conveyor 60: Steel dust 61: Aluminum dross

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C21C 7/04 B09B 3/00 ZAB 4K056 F27D 17/00 104 303L F-term (Reference) 2E191 BA12 BD11 4D004 AA37 AB07 AC04 CA22 CA36 CA37 CB02 CB31 CC11 4K002 AC10 BA09 4K013 CB03 EA18 EA19 4K014 CB03 CD13 4K056 AA02 AA05 CA02 DB07

Claims (6)

[Claims] 1. A method for decomposing dioxins in dust generated during melting and refining of steel and reducing the content thereof, wherein the dioxin is generated from a melting furnace for melting steel or a refining furnace for refining molten steel. A method for decomposing dioxins in steel dust, characterized by directly injecting steel dust containing dioxins collected together with the discharged exhaust gas into molten steel during smelting and refining of steel or slag covering the surface of molten steel by a blowing device. . 2. The blower according to claim 1, wherein:
The steel dust and the reducing agent are blown into the molten steel or slag at the time of melting and refining the steel, and the heat retained by the molten steel or slag causes an oxidation-reduction reaction between the oxide and the reducing agent in the steel dust to produce dioxin. A method for decomposing dioxins in steel dust, comprising decomposing metals. 3. The method according to claim 2, wherein when the steel dust and the reducing agent are directly blown into the molten steel and the slag by a blowing device, the steel dust and the reducing agent are blown into the molten steel and the slag with a mixture of the steel dust and the reducing agent. Characteristic method for decomposing dioxins in steel dust. 4. The method for decomposing dioxins in steel dust according to claim 1, wherein the steel dust and the reducing agent are in the form of powder or granules. 5. The decomposition of dioxins in steel dust according to any one of claims 1 to 4, wherein the blowing time of the steel dust and the reducing agent by the blowing device is the last stage of the acid during melting and refining. Method. 6. The method according to claim 2, wherein the reducing agent oxidizes and reduces oxides in the steel dust, and the main component contains at least one of C, Fe, Mg, and Al. A method for decomposing dioxins in steel dust, characterized in that: