JP2013023719A - Method of reusing wet dust present in material generated in blast furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a simple, practical, and effective method of reusing wet dust present in a material generated in a blast furnace, for effectively using wet dust collected from exhaust gas of an iron-making blast furnace, which method comprises separating the wet dust into three portions, i.e., a portion comprising iron (Fe) as a useful object, a portion comprising carbon (C) as a useful object, and a portion comprising zinc (Zn) as a useful object.SOLUTION: The wet dust is converted into a slurry state, and the resulting slurry is subjected to wet magnetic separation 15, and the magnetically non-attractable portion thereof is subjected to two steps 17, 18 of wet cyclone separation, whereby the wet dust is separated into three portions, i.e., a portion comprising iron (Fe) as a useful object, a portion comprising carbon (C) as a useful object, and a portion comprising zinc (Zn) as a useful object.

Description

The present invention relates to a recycling method for effectively using the products generated in the iron making process again in the iron making process. More specifically, the present invention relates to iron (Fe) and carbon (C ) And zinc (Zn) are separated from each other.

The dust collected from the blast furnace exhaust gas includes a primary dust collection dust (dry dust collection dust) that is collected in a dry manner and a fine secondary dust collection dust (wet dust collection dust, Wet dust). Most of the dry dust collection dust is reused as a sintering raw material for the recovery of Fe.
However, even if wet dust is used as a Fe source in the sintering process, it is fine and therefore has a high moisture content. Even if it is dehydrated, there is an adverse effect on the sintering operation. There are many adverse effects such as damage to furnace materials in the blast furnace and facilitating the generation of deposits on the furnace wall. Recycling as blast furnace raw materials by methods such as using it as a sintering raw material is restricted and discarded There are many things.

In order to utilize the wet dust collected from this blast furnace exhaust gas, it is necessary to perform Zn removal treatment. FIG. 4 shows an example of the entire process for utilizing the wet dust of the conventional method. In many cases, wet dust is treated in a reduction furnace. In the operation of the reduction furnace, although C is used as a reducing agent, the total amount of C is within an appropriate range in relation to the reduction reaction, and excessive C content is the strength of the product reduced pellets (reduced iron). There is a problem of causing deterioration and adversely affecting quality.

However, the blast furnace wet dust contains a large amount of C as shown in Table 1 (cited from the Steel Handbook 4th edition), so it cannot be used in large quantities as a reducing furnace raw material due to the total amount of C charged. As shown in FIG. 4, there is a problem that a part must be discarded.

When the C source is effectively used for combustion, Fe and Zn become obstacles. Fe becomes a combustion residue, Zn volatilizes and causes flue adhesion and the like, which is problematic and practically difficult to use. Therefore, in order to effectively use the three elements of Fe, C, and Zn as resources, it is necessary to separate and concentrate the three elements so that the influence of the content values of the other two elements does not substantially matter. is there. From this viewpoint, several three-way separation techniques of Fe, C, and Zn have been conventionally proposed.

The first is Patent Document 1. This is intended for the recovery of C as activated carbon for both primary ash in blast furnace (dry dust collection dust) and secondary ash (wet dust collection dust). Separation of C as a dissolved residue due to dissolution of metal oxide by acid treatment, while acid is recovered as bengara by heating iron hydroxide and iron carbonate precipitate generated by neutralization with sodium carbonate and further alkalinization. The residual liquid is further concentrated to recover zinc carbonate by adding sodium carbonate. It is also described that magnetic separation is performed before acid dissolution and the magnetic deposit is used as an iron source.
Although the concept of performing the three-part separation to use each is clearly shown, the method is “dissolution of metal oxide by acid treatment, separation of C as a dissolution residue, dissolution thereof” There is no specific method beyond textbook chemical methods, such as neutralization of acid solution with sodium carbonate, etc. Also, since it is necessary to use acid and alkali, equipment costs including wastewater treatment are not shown. , Has the disadvantage of increasing operating costs.

Further, Patent Document 2 proposes a method for enriching and separating Fe, Zn, and C for wet dust collecting dust of steelmaking and steelmaking. The first step is separation of iron rich dust (lower discharge) and zinc and C rich dust (upper discharge) by magnet cyclone treatment. In the second step, contact with C and flotation treatment by adding and dispersing an organic solvent such as n-hexane to the upper effluent of the previous step (in the precipitation layer; zinc-rich component, in the flotation layer; C main component dust) ).

Although a specific method of three-way separation is provided, the results presented in the examples show that the C distribution ratio to the Fe recovery side mainly composed of Fe is as high as 39 to 63%, which is not necessarily Fe— The separability of C is not good. In addition, there is a disadvantage that the cost is increased by using an organic solvent. Furthermore, disaster prevention, safety and hygiene considerations are also necessary when using organic solvents. For example, the hexane described is a flammable substance with a flash point of −22 ° C. and has a low explosive limit concentration in the air. Strict countermeasures are required.

Many proposals have been made for the purpose of separating two of the three elements of Fe, Zn, and C, or a method for separating one component of the three from the other two. Among them, Patent Documents 3 to 7 are examples of proposals aimed at separating Zn and Fe from blast furnace dust or separating Zn from components other than Fe using a wet cyclone.
Patent Document 3 discloses a method for separating C, Fe, Zn, and Pb by a two-stage treatment of a wet cyclone.
Patent Document 4 discloses a method for separating Fe and Zn by an electromagnetic cyclone having a positive magnetic field gradient.
Patent Document 5 discloses a method of separating Fe and Zn by a special wet cyclone using ultrasonic treatment and negative pressure using a dispersant.
Patent Document 6 discloses separation of Fe and Zn by ultrasonic treatment and hydrocyclone treatment.
Patent Document 7 discloses a method for separating Fe and C and Zn and Pb by two-stage treatment of a hydrocyclone, but wet magnetic separation is not performed, and Fe and C are further reduced from reduced waste to Fe. It is not disclosed that C and C are separated and used independently as raw materials.

JP-A-48-052616 Japanese Patent Laid-Open No. 53-025201 Japanese Patent Laid-Open No. 51-120466 Japanese Patent Application Laid-Open No. 53-039907 Japanese Patent Laid-Open No. 53-081479 JP 58-034051 Japanese National Patent Publication No. 8-507577

Chemical Engineering Association; Chemical Engineering Handbook 4th Edition, 1964, Maruzen

However, these are proposals of an optimum method for the purpose of separating the three parts into two, but combining the different proposals does not mean that the three-way separation of Fe, C, and Zn can be performed optimally. That is, combining these does not provide a part of the optimum three-way separation method for efficiently separating Fe, C, and Zn.
The present invention has been made in view of such circumstances, and in order to separate the three of iron (Fe), Zn, and carbon (C) from each other in order to effectively reuse each of the wet dust of blast furnace exhaust gas. An object of the present invention is to provide a simple, practical and effective method for reusing wet dust in blast furnace products.

The method for reusing wet dust in the blast furnace product according to the present invention in accordance with the above object is to slurry wet dust (blast furnace wet dust) collected when the exhaust gas generated from a blast furnace for iron making is collected by wet dust. A first step,
A second step of dividing into "part a using iron for the purpose" and "part b using carbon and zinc for the purpose" by performing wet magnetic separation of the wet dust in the slurry state;
A third step of performing a first wet cyclone treatment on the “part b utilizing carbon and zinc for the purpose”;
A fourth step of further performing a second wet cyclone treatment on the lower discharge of the first wet cyclone treatment,
A combination of the upper discharge from the first wet cyclone treatment and the upper discharge from the second wet cyclone treatment is referred to as “part c using zinc for the purpose”, and the second wet cyclone treatment. By setting the lower discharge to be “part d that uses carbon for the purpose”, the “part a that uses iron for the purpose of iron” and the “part d that uses carbon for the purpose” and It is separated into three parts, “the part c that uses zinc for the purpose”.

In the method for reusing wet dust in blast furnace products according to the present invention, it is preferable that ultrasonic treatment is applied to the wet dust in the form of slurry before the wet magnetic separation in the second step.

Here, the ultrasonic treatment parameter is expressed as the product of “ultrasonic intensity expressed in kW per 1 m ^{3 of} slurry” and “ultrasonic irradiation time expressed in minutes”, and the ultrasonic treatment parameter is 20 kW · min / It is preferably m ³ or more.

By the method for reusing wet dust in the blast furnace product according to the present invention, the blast furnace wet dust can be separated into three parts that are used for the purposes of Fe, Zn, and C, respectively. As a result, the adverse effects of Zn and C when recycling the main part of Fe are reduced, and the adverse effects of Fe and Zn when recycling the main part of C are reduced. Make the main parts easier to recycle. Thereby, the quantity which can utilize blast furnace wet dust effectively can be increased. In other words, there is an effect that the amount of blast furnace wet dust discarded without being used can be reduced and resources can be effectively used.

It is a flowchart which shows the process of the reuse method of the wet dust in the blast furnace product which concerns on one embodiment of this invention. It is a figure explaining the processing flow of the reuse method of the wet dust in the blast furnace product which concerns on 1st Example of this invention. It is a figure explaining the processing flow of the reuse method of the wet dust in the blast furnace product which concerns on 2nd Example of this invention. It is a flowchart which shows an example of the processing process of the wet dust in the blast furnace generated product which concerns on a prior art example.

Next, a method for reusing wet dust in blast furnace products according to an embodiment of the present invention will be described with reference to the accompanying drawings.
(Slurry conditions)
As shown in FIG. 1, the dust (exhaust gas) generated in the blast furnace 10 for iron making is a dilute slurry immediately after being collected by the dust catcher 11 and the wet venturi scrubber 12. In order to facilitate handling, the thickener 13 is subjected to sedimentation and concentration and then dehydrated with a dehydrator (not shown).

In order to apply the present invention, the wet dust needs to be in a slurry state. As a method for the wet dust, the slurry collected by the wet venturi scrubber 12 may be used as it is, or a slurry that is sedimented and concentrated by the thickener 13 may be used. . A slurry concentrated or diluted by any method based on these slurries may be used.
Further, for convenience of transportation and storage, water may be added to the blast furnace wet dust that has been dewatered by a dehydrator and turned into sludge to form a slurry.

In the present invention, although not essential, it is more preferable to maintain the pH of the slurry at about 8.5 to 10. This is because, in this pH range, there is less elution of metal elements such as Fe and Zn into the liquid compared to other pH values, and the drainage treatment after the final solid-liquid separation is easy.

(Each meaning of wet magnetic separation and wet cyclone treatment)
A significant portion of the Fe content contained in the blast furnace wet dust is a ferromagnetic material. On the other hand, the C or Zn content contained in the blast furnace wet dust is hardly magnetized by magnetic separation with a normal magnetic flux density gradient of 1 Tesla or less. Therefore, it is preferable to apply wet magnetic separation in order to separate the Fe content from the C content and the Zn content.
The size of particles mainly composed of Zn is 60 to 80% in terms of the mass ratio of sizes of 8 to 10 μm or less, and 60 to 80% of particles mainly composed of Fe and particles mainly composed of C exceed 15 μm. Has a diameter. Therefore, if a wet cyclone designed to have a calculated 50% classified particle size of 8 to 15 μm is used, particles mainly composed of Zn, particles mainly composed of Fe, and particles mainly composed of C can be classified and separated.

As shown in FIG. 1, the process of the method for reusing wet dust in blast furnace products according to an embodiment of the present invention is a slurry blast furnace moisture after or without sonication 14. Wet magnetic separation (wet magnetic separation) 15 is performed on the dust, and the wet cyclone treatment is applied twice to the non-magnetization side (part b used for the purpose of carbon and zinc) (that is, the first The first wet cyclone treatment 17 and the second wet cyclone treatment 18 are performed. Hereinafter, it may be simply referred to as “wet cyclone treatment”), Fe content, Zn content, and C content are used for each purpose. Collected material (part that uses iron for the purpose) a "," carbon-based recovered product (part that uses carbon for the purpose) d "," zinc-based recovered product (part that uses zinc for the purpose) c " Isolated on Is shall.

(Conditions for wet magnetic separation)
Any wet magnetic separation method such as drum-type wet magnetic separation or filter-type wet magnetic separation can be applied as long as it is a method capable of macroscopically separating a slurry containing a large amount of Fe. Moreover, as long as it can be industrially separated, the specific conditions such as the wet magnetic separation and the magnetic flux density may be any conditions.

(Conditions for wet cyclone treatment)
As described above, from the size distribution of particles using Zn for the purpose and the size distribution of particles using Fe for the purpose and particles using C for the purpose, wet cyclones (first and second wet cyclone treatments 17 In any of (18) and (18), the calculated 50% classified particle size is preferably about 8 to 15 μm.
The calculated 50% classified particle size d50 ^* [μm] of the wet cyclone can be calculated by using the equation (1) described in Non-Patent Document 1, for example.

Symbols in the formula (1) mean the following matters.
Dc: inner diameter [cm] of the body of the cyclone
Di: Inner diameter of cyclone inlet [cm]
De: Inner diameter [cm] of the upper outlet of the cyclone
μ: Viscosity of liquid [kg / m.sec]
ρp: Particle density [kg / m ³ ]
ρ: Density of liquid [kg / m ³ ]
Q: Liquid supply speed to the cyclone [L / sec]

The solid concentration of the slurry supplied to the first and second wet cyclone treatments 17 and 18 is not particularly limited. However, when the solid concentration is high, handling of the slurry may be difficult, and a solid concentration of about 30% or less is preferable in practice. On the other hand, the lean side has the disadvantage that the equipment efficiency is reduced and a larger equipment is required. In the wet cyclone treatment of blast furnace secondary ash, a large amount of solid phase such as C may be discharged on the lower discharge side, resulting in a slurry with a high solid concentration. Therefore, when the lower discharge of the first wet cyclone treatment 17 is subjected to the second wet cyclone treatment 18, it is preferable to dilute to the solid concentration as described above depending on the concentration.

(Meaning of ultrasonic treatment)
As shown in the examples described later, by performing “wet magnetic separation 15 and wet cyclone treatment two stages 17 and 18” on the blast furnace wet dust slurried without ultrasonic treatment of the slurry, Fe content, Zn content, C It is possible to divide into three parts that use each part for the purpose. Furthermore, when the slurry is first subjected to ultrasonic treatment 14 and then “wet magnetic separation 15 and wet cyclone treatment two stages 17 and 18”, the Fe content, Zn content, and C content are compared with the results without the treatment. The degree of separation of the three parts used for each purpose is further improved. In particular, the yield of Zn is improved.

The purpose and function of the ultrasonic treatment 14 is to microscopically separate various types of particles such as Fe, C, and Zn that are physically attached to each other. Here, “micro” means separation of fine particles suspended in the slurry. That is, before performing the macro wet separation such as wet magnetic separation or wet cyclone separation in order to divide the slurry or sludge with high Fe content into the slurry or sludge with high C content and the slurry or sludge with high Zn content, It means to promote the separation of individual particles as much as possible.

(Sonication conditions)
The ultrasonic treatment 14 is sufficient if the slurry can be substantially irradiated with ultrasonic waves. For example, even when ultrasonic irradiation is performed for 2 to 3 minutes at an ultrasonic intensity of 1 kW per 1 m ^{3 of} slurry, separation of Fe from C and Zn is improved as compared with the case without ultrasonic irradiation. More suitable conditions will be described later.
The frequency of the ultrasonic wave to be irradiated is not particularly limited, but a relatively low frequency of 100 kHz or less is more preferable.
Ultrasonic irradiation may be performed in either a batch type container or a continuous flow path.
In both batch processing and continuous processing, sufficient slurry agitation is required by some method. This is because it is impossible to make the slurry uniform and, consequently, uniform ultrasonic irradiation only by the ultrasonic excitation force.

The slurry concentration at the time of ultrasonic irradiation, that is, the ratio of solid substance amount / total mass is not particularly limited. The lower the concentration, the lower the treatment efficiency and the larger the equipment scale for the same wet dust treatment amount on a dry basis, which is economically disadvantageous. Moreover, if it becomes high concentration, processing efficiency will improve, but processing, such as stirring and transfer, will become difficult. Although the effect can be obtained at any slurry concentration, it can be said that about 3 to 25% by mass is a more preferable range from these viewpoints.

(Suitable conditions for ultrasonic treatment)
The ultrasonic treatment conditions are as follows. The ultrasonic treatment parameter represented by the product of the ultrasonic intensity expressed in kW per 1 m ^{3 of} slurry and the ultrasonic irradiation time expressed in minutes is particularly less than 20 kW · min / m ^3. As the value of the sonication parameter increases, the separation result of each component is greatly improved. When the value of the sonication parameter is in the region of 20 kW · min / m ³ or more, the separation state of each component does not change much even if the value of the sonication parameter is further increased.

In the region where the value of the sonication parameter is less than 20 kW · min / m ³ , micro mutual separation of Fe-based particles, C-based particles, and Zn-based particles by sonication is still insufficient. It shows that separation progresses rapidly with increasing sonication intensity. On the other hand, if it is 20 kW · min / m ³ or more, the separation progresses somewhat as the ultrasonic treatment intensity increases, but the degree of improvement becomes small.
For this reason, it can be said that it is particularly preferable to satisfy the condition that the value of the ultrasonic treatment parameter is 20 kW · min / m ³ or more industrially in consideration of the efficiency balance between the equipment cost and the effect.

Moreover, the combination of ultrasonic intensity and irradiation time is not particularly limited. As long as the condition of 20 kW · min / m ³ or more is satisfied, a long-time irradiation with a low intensity such as 4 kW / m ³ and a long-time irradiation with a high intensity such as 35 kW / m ³ There is no clear difference between and any combination can be selected.

Example 1
According to the process shown in FIG. 2, the wet magnetic separation 15 is performed after the ultrasonic treatment 14 and the non-magnetized material is treated twice by the first wet cyclone treatment 17 and the second wet cyclone treatment 18, 18a. Separation treatment was performed.
Blast furnace wet dust having the composition shown in Table 2 was used.

Incidentally, the slurry containing the blast furnace wet dust having the composition shown in Table 2 was a concentrated slurry extracted from the thickener, and its mass concentration was 12%. The pH of the slurry was adjusted to 9-10. The slurry was sonicated for 25 minutes at a sonication intensity of 4 kW / m ³ . The ultrasonic treatment was performed by irradiating ultrasonic waves with a predetermined intensity for a predetermined time while impeller stirring in order to prevent the particles from settling and separating in a storage tank.
Thereafter, wet magnetic separation 15 was performed. The wet magnetic separation 15 was performed with a drum type magnetic separator having a surface magnetic flux density of 0.24 Tesla.

Although the cyclone treatment of the non-magnetized material of the wet magnetic separation 15 was performed twice, the cyclone treatment (second wet cyclone treatment 18 of the second wet cyclone treatment 18) was again performed on the lower discharge slurry (lower discharge 20) of the first wet cyclone treatment 17. ), The mass concentration was diluted to about 12%. In the cyclone treatment, a normal type cyclone that does not use a negative pressure was used, and the classification was performed by adjusting the flow rate so that the calculated 50% classified particle size d50 ^{* was} approximately 10 μm using the above-described equation (1). .
As shown in the flow in FIG. 2, each of the magnetic deposits of wet magnetic separation 15 and the four types of separations by the cyclone two-stages were individually analyzed. The results are shown in Table 3.

The magnetized product of wet magnetic separation 15 (see No. 1 in Table 3) had a high Fe value of 50% by mass and a low component value of C and Zn, so it was judged that it would become a Fe recovery part as a part for directly using Fe for the purpose.
The non-magnetized material of the wet magnetic separation 15 was subjected to a cyclone two-stage treatment.
In the second stage treatment of the cyclone first stage upper waste (upper and lower emissions when treated in the second stage of the cyclone, see No. 2 and 3 in Table 3) and the cyclone first stage lower waste. The upper discharge (refer to No. 4 in Table 3) was found to have a Zn concentration significantly enriched from the raw blast furnace wet dust, and was determined to be a Zn recovery part as a part utilizing Zn for the purpose. When the amount distribution is calculated, 2/3 of the total amount of Zn brought in from the raw blast furnace wet dust is included in this Zn recovery portion.

The lower emission (see No. 5 in Table 3) of the cyclone second-stage treatment of the first-stage cyclone emission is concentrated at a component value of 52%. It was judged as a recovery part. In addition, about 60% of the total amount of C brought in from the raw material is distributed to this part.
It was confirmed that the three-part separation of Fe, Zn, and C can be substantially realized by processing as described above and classifying the separated products into the above-mentioned categories.

In other words, if the cyclone treatment is not performed after the wet magnetic separation treatment, it can be said that it is impossible to separate the portion using C for the purpose and the portion using Zn for the purpose. Also, if the lower part of the first stage of the cyclone is a part that uses C for the purpose without performing the second stage treatment of the cyclone, 15% of Zn distribution in the upper discharge of the second stage of the cyclone (No. 4 in Table 3) is obtained. This means that it was not included in the part where Zn was used for the purpose, but was mixed in the part where C was used for the purpose. In other words, the Zn recovery rate decreased from 66% to 51%, and on the other hand, 15% of Zn was mixed and 27% of Zn was distributed to the portion using C for the purpose.

Example 2
Next, the difference in separation behavior with and without sonication was confirmed.
Using the blast furnace wet dust shown in Table 4, processing was performed according to the flow shown in FIG. The conditions for ultrasonic treatment and wet magnetic separation are the same as in the first embodiment. However, the slurry concentration was a dilute slurry of 1% or less.

Table 5 shows the results for the case with sonication, and Table 6 shows the results for the case without sonication.

In the case where the ultrasonic treatment was performed before the wet magnetic separation treatment and the cyclone treatment, in the same manner as in Example 1, about 6% of the total amount of Zn brought in from the raw blast furnace wet dust was used for the portion used for Zn. Percentage is distributed. Further, 80% or more of the total amount of C brought in is allocated to the part that uses C for the purpose.

On the other hand, even in the case where ultrasonic treatment has not been performed in advance, about 70% of the total amount of C brought in is allocated to the part that uses C for the purpose, and the raw material is also used for the part that uses Zn for the purpose. About half of the total amount of Zn brought in from the blast furnace wet dust was distributed.
This means that the three-part separation of Fe, Zn, and C can be realized substantially, although the C recovery rate and Zn recovery rate are slightly reduced by wet magnetic separation and cyclone two-stage treatment without prior ultrasonic treatment. It has been shown that Of course, it is more preferable to perform ultrasonic treatment in advance.

10: Blast furnace, 11: Dust catcher, 12: Venturi scrubber, 13: Thickener, 14: Ultrasonic treatment, 15: Wet magnetic selection, 17: First wet cyclone treatment, 18, 18a: Second wet cyclone treatment , 20: Lower emission

Claims (3)

A first step in which the exhaust gas generated from the blast furnace for iron making is in the form of a slurry of wet dust collected when wet dust is collected;
A second step of dividing into "part a using iron for the purpose" and "part b using carbon and zinc for the purpose" by performing wet magnetic separation of the wet dust in the slurry state;
A third step of performing a first wet cyclone treatment on the “part b used for the purpose of carbon and zinc”;
A fourth step of further performing a second wet cyclone treatment on the lower discharge of the first wet cyclone treatment,
A combination of the upper discharge from the first wet cyclone treatment and the upper discharge from the second wet cyclone treatment is referred to as “part c using zinc for the purpose”, and the second wet cyclone treatment. By setting the lower discharge to be “part d that uses carbon for the purpose”, the “part a that uses iron for the purpose of iron” and the “part d that uses carbon for the purpose” and 3. A method for reusing wet dust in a blast furnace product, characterized in that it is separated into three parts, “part c that uses zinc for the purpose”. 2. The method for reusing wet dust in a blast furnace product according to claim 1, wherein ultrasonic treatment is performed on the wet dust in the form of slurry before the wet magnetic separation in the second step. How to recycle wet dust in the product. 3. The method of reusing wet dust in a blast furnace product according to claim 2, wherein the ultrasonic treatment includes “ultrasonic intensity expressed in kW per 1 m ^{3 of} slurry” and “ultrasonic irradiation time expressed in minutes”. The method for reusing wet dust in a blast furnace product, wherein the ultrasonic treatment parameter represented by the product is 20 kW · min / m ³ or more.

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