WO2017014204A1 - Method and apparatus for recovering zinc and iron from electric furnace dust - Google Patents

Abstract

With attention directed at the reduction treatment gas that contains metallic zinc vapor generated when reduced iron is manufactured from electric furnace dust that contains iron oxides and zinc oxide, the present invention addresses the problem of providing a method and apparatus for manufacturing reduced iron that allows zinc to be recovered efficiently with respect to process and energy efficiency perspectives as well. In view of the foregoing problem, the present invention is characterized in comprising: a carbon-containing molded article manufacturing step for admixing a binder with a charcoal material and electric furnace dust that contains zinc oxide and iron oxides, and molding the resulting mixture to manufacture a carbon-containing molded article; a preheating step for heating the carbon-containing molded article in an internally heated rotary kiln; a reduction treatment step in which the carbon-containing molded article heated in the preheating step is further heated in a hermetically sealed externally heated rotary kiln to manufacture reduced iron; and a zinc recovery step for recovering zinc from the reduction treatment gas generated in the reduction treatment step

Description

Method and apparatus for recovering iron and zinc from electric furnace dust

The present invention produces iron (reduced iron) from electric furnace dust containing iron oxide and zinc oxide (dust generated in the electric furnace steelmaking process), and in the gas generated by the reduction treatment (reduction treatment gas) The present invention relates to a method and apparatus for recovering iron and zinc from electric furnace dust, which recovers contained metallic zinc.

In recent years, due to the rising price of zinc, effective use of zinc has been demanded, and recovery from iron-making dust containing a large amount of zinc has attracted attention. The basic unit of iron dust, especially dust (electric furnace dust) generated in the electric furnace steelmaking process is about 1.8% of the amount of crude steel produced in the electric furnace, and the amount of electric furnace dust generated in Japan was about 1999. It is estimated to be about 520,000 tons and about 440,000 tons in 2013.

Usually, the electric furnace (electric furnace) steelmaking process uses iron scrap as a raw material, and a large amount of galvanized steel sheet scrap is input. Therefore, the electric furnace dust contains about 25% zinc on average. Various efforts have been made to recover this zinc. In 2013, about 80% of the amount generated was intermediately processed in the zinc recovery industry, and the remaining 20% was landfilled at managed and closed disposal sites after detoxification such as chemical injection. Yes.

As a method for recovering metallic zinc from electric furnace dust, a method combining a Wertz method and an ISP (Imperial Melting Process) method has been proposed (Non-patent Documents 1 and 2). For example, Non-Patent Document 1 describes a method for producing crude zinc oxide (ZnO), which is a raw material for zinc, from steelmaking ash by the Wertz method. Non-Patent Document 2 describes a method in which crude zinc oxide (ZnO) recovered by the Wertz method is finally treated by the ISP method and recovered as metallic zinc. Briefly explaining the process (Weltz method) disclosed in Non-Patent Document 1, powder coke is mixed with electric furnace dust, charged into a rotary kiln (internally heated rotary kiln in Non-Patent Document 1), and 1200 in the rotary kiln. Heat to ° C. As a result, the charge moves while rolling in the rotary kiln, and during this movement, zinc oxide and iron oxide in the electric furnace dust are reduced by carbon. Zinc volatilizes as metallic zinc and is then reoxidized by oxygen in the exhaust gas to form crude zinc oxide (ZnO) powder. The crude zinc oxide powder is collected and collected by a dust chamber, an electrostatic precipitator or the like. On the other hand, iron oxide is discharged from the downstream side of the rotary kiln and collected as a clinker (lumps) containing metallic iron.

The crude zinc oxide recovered by the Welts method has a zinc quality of about 60%. The dezincification rate (zinc recovery rate) from electric furnace dust is only about 60% to 70%, and the remaining 30 to 40% of zinc is contained in the clinker.
Recently, there has been an example in which electric furnace dust is reduced by the rotary hearth method (RHF method). Since RHF is processed by briquette, the recovery rate is slightly higher than the Welts method.

The obtained crude zinc oxide (ZnO) is recovered as zinc by the ISP method. Zinc refining by the ISP method is roughly divided into a sintering process, a smelting process, and a refining process.
In the sintering process, zinc and lead concentrate (sulfide ore), the main raw material, and crude zinc oxide recovered by the Welts method are mixed and granulated together with a solvent at a predetermined ratio, and desulfurized and sintered with a sintering machine for sintering. Mines.

The obtained sintered ore is charged into a blast furnace in a layered manner with lump coke preheated to 800 ° C., and hot air at 950 ° C. is blown from the tuyere. Zinc in the sinter is reduced and evaporated in the furnace, and is discharged from the top of the blast furnace together with CO and CO ₂ gas at a zinc concentration of about 8%. Exhaust gas containing zinc enters the lead splash condenser. In the condenser, the blast furnace exhaust gas is rapidly cooled to 550 ° C. by the lead droplets stirred and scattered by the rotor immersed in the lead bath, and the zinc vapor is condensed and dissolved in the lead droplets.
The lead in which zinc is dissolved is cooled to 440 ° C. with a cooling rod, and zinc is floated and separated using the difference in solubility depending on temperature. This is so-called blast furnace zinc, and the lead from which zinc has been separated is returned to the capacitor again.

In the refining process, the zinc in the blast furnace is sent to the casting furnace in a continuous furnace, where it is deleaded and deironed by temperature refining, and commercialized as distilled zinc having a zinc purity of 98.5% or more.

The combination of the Welts method and the ISP method has the following drawbacks as a method for recovering metallic zinc while producing reduced iron from electric furnace dust. That is, in the Wertz method, a large amount (300 kg / per ton of electric furnace dust) of carbonaceous material is added to reduce iron oxide and zinc oxide. At this time, despite being evaporated as metal zinc vapor, the metal zinc is reoxidized by the oxygen in the combustion exhaust gas present in the internal heat kiln to become crude zinc oxide. As a result, about 25% of crude zinc oxide in terms of zinc in the electric furnace dust is simply concentrated to about 60%.

In addition to the blast furnace, the ISP method requires not only large equipment such as a sintering machine and a hot air furnace, but also has an economic problem that an expensive lump coke must be used. Further, in the current combination of the Welts method and the ISP method, the process is complicated because zinc oxide is reduced twice, so that energy is wasted and facilities are also complicated. For this reason, instead of these methods, when producing reduced iron from electric furnace dust, a method capable of recovering zinc with reduced process, energy saving, and high efficiency is required.

Therefore, the present invention pays attention to a reduction treatment gas containing metallic zinc vapor generated when producing reduced iron from electric furnace dust containing iron oxide and zinc oxide, and from the viewpoint of process efficiency and energy efficiency. Another object of the present invention is to propose a method for producing reduced iron, a method for recovering zinc, and an apparatus therefor that can efficiently recover zinc.

As a result of intensive studies to solve the above problems, the present inventors have found the following matters.
(A) By performing the reduction treatment in a closed space where the atmosphere is shut off, the reduction treatment can be performed in an oxygen-free atmosphere, and the reduction treatment gas containing mainly metal zinc vapor (mainly CO , CO ₂ and metal zinc vapor) and found that solid reduced iron can be obtained. In order to reduce iron oxide with carbon, a temperature of 950 ° C. or higher is necessary, and if it is 1000 ° C. or higher, stable reduction treatment can be performed. On the other hand, since the boiling point of zinc under atmospheric pressure is 907 ° C., both iron oxide and zinc oxide can be reduced at 950 ° C. or higher. As an apparatus having a closed space capable of performing such a high temperature treatment, for example, there is an external heating type rotary kiln.

(B) Electric furnace dust contains moisture and chlorine, and these must be removed in advance. For this reason, it has been found that preheating and drying should be performed before the electric furnace dust is reduced. The preheating / drying and the reduction treatment may be performed in separate processes so that chlorides and moisture generated during the preheating / drying are not mixed into the reduction treatment gas. Preheating / drying is desirably performed at a temperature lower than the temperature (907 ° C.) at which the reduction reaction occurs.
For example, an internally heated rotary kiln currently used in the Welts method can be used for preheating and drying of electric furnace dust.
When heating with an internal heat type rotary kiln, heating is performed only up to about 900 ° C., so that a dam ring (a deposit on the inner surface of the kiln due to a gangue component in the raw material) is not formed. For this reason, the problem resulting from the dam ring which has been a problem in the conventional Welts method can be solved.

(C) Since metal zinc vapor is contained in the reducing gas, a method for directly recovering zinc from the reducing gas was examined. As a result, the existing lead splash condenser may be used as the method for recovering zinc, but as mentioned above, the equipment becomes large, and the efficiency is poor and the handling is poor. Therefore, it has been found that the reduction treatment gas may be directly cooled to condense zinc and recover it as molten zinc.

A cooling tube such as a water-cooled tube (pipe) is suitable for direct cooling of the reducing gas, but it cannot be used if it is made of metal (for example, Cu, Al, Fe, etc.) because it reacts with zinc. Thus, it has been found that by applying a ceramic tube (pipe), for example, a ceramic (for example, SiC) tube having good thermal conductivity, zinc can be recovered without reacting. It was also found that SiC is preferable because it is difficult to wet with molten zinc.

The present inventors have made further studies to further increase the zinc recovery rate. As a result, the gas that passes between the cooling tubes and does not come into contact with the tube surface still contains zinc vapor and molten zinc fine particles. Thus, it has been found that a ceramic pellet can be arranged downstream of the cooling tube to condense, aggregate and collect zinc.
That is, when the gas containing zinc vapor or molten zinc fine particles passes through the gaps between the ceramic pellets, it comes into contact with the pellet surface, and the zinc is condensed, aggregated and separated. At this time, the condensed and agglomerated molten zinc becomes droplets and is dropped and recovered.
The material of the ceramic pellet is the same as that of the cooling tube, and silicon carbide (SiC) is preferable.

(D) From the viewpoint of improving the energy efficiency in the reduction treatment, it was found that the reduction treatment gas after zinc recovery can be reused as the fuel for the combustion burner of the externally heated rotary kiln. The reducing gas is mainly composed of CO (carbon monoxide) and CO ₂ (carbon dioxide), and CO can be used as a fuel.

Furthermore, since the combustion gas (mainly CO ₂ ) of the external combustion burner of the external heating rotary kiln has a gas temperature of about 1000 ° C., the combustion gas is introduced into the internal gas of the internal heating rotary kiln for preheating and drying. Thus, the sensible heat of the combustion gas can be used effectively.

Of course, the reducing gas can be introduced not as a combustion burner for an external heating rotary kiln but as a combustion gas for an internal heating rotary kiln in a preheating / drying step.

On the other hand, if CO2 is present in the reducing gas in the process of cooling the reducing gas containing metal zinc vapor, the metal zinc vapor is oxidized with CO2 to become crude zinc oxide (ZnO), and metal zinc cannot be recovered. It turns out that there is a problem. This is because the lower the CO / CO2 ratio, the higher the equilibrium temperature at which zinc can exist as metal vapor.
About 20% of CO2 is contained in the reduction treatment gas of the carbon-containing molded article by the average electric furnace dust. As a result of intensive studies by the inventors, it has been found that if the CO2 concentration in the reducing gas is reduced to 3% or less, oxidation of metal zinc vapor is suppressed and metal zinc can be efficiently recovered. According to the research results of the present inventors, if the CO2 concentration in the reducing gas is 3% or less, the metal zinc recovery rate (the amount of recovered zinc with respect to the amount of zinc contained in the electric furnace dust) can be ensured to be 90% or more. I understood.
Therefore, the present inventors perform reforming to convert CO2 into CO (hereinafter referred to as CO2 reforming in the present specification, and performing the processing is referred to as CO2 reforming processing), and reducing the gas in the reduction processing gas. Worked on reducing CO2 concentration. For example, it has been found that CO2 can be reformed to CO (CO2 + C → 2CO) by charging a powdered carbon material into an external heat rotary kiln, stirring in the rotary kiln and bringing it into contact with CO2 gas.

The present invention has been made on the basis of the above findings, and the gist thereof is as follows.
(1)
A carbon-containing molded body manufacturing step of manufacturing a carbon-containing molded body by mixing and molding an electric furnace dust containing iron oxide and zinc oxide, a carbonaceous material, a binder and water;
A preheating step of heating and drying the carbon-containing molded body;
A reduction treatment step in which the carbon-containing molded body heated and dried in the preheating step is further heated in a closed space to reduce iron oxide to reduced iron, and
A method for recovering iron and zinc from electric furnace dust, comprising a zinc recovery step of recovering zinc from the reduction processing gas generated in the reduction processing step.
(2)
The method for recovering iron and zinc from electric furnace dust according to (1), wherein the heating temperature of the carbon-containing molded body in the preheating step is 740 ° C or higher and 907 ° C or lower.
(3)
The method for recovering iron and zinc from electric furnace dust according to (1) or (2), wherein the heating temperature of the carbon-containing molded body in the reduction treatment step is from 980 ° C to 1150 ° C.
(4)
The preheating step is treated with an internal heating rotary kiln, and the reduction treatment step is treated with an external heating rotary kiln. The iron from the electric furnace dust according to any one of (1) to (3) and Zinc recovery method.
(5)
In the reduction treatment step, the CO2 reforming treatment is performed to reduce the CO2 concentration in the reduction treatment gas to 3% or less from the electric furnace dust according to any one of (1) to (4), Recovery method for iron and zinc.
(6) The method for recovering iron and zinc from electric furnace dust according to (5), wherein the CO2 reforming treatment is performed by charging powdered carbonaceous material into the closed space in the reduction treatment step.
(7)
From the electric furnace dust according to any one of (1) to (6), wherein the reduction treatment gas after the zinc is collected in the zinc collection step is used as a heating fuel in the reduction treatment step. Recovery method of iron and zinc.
(8)
The method for recovering iron and zinc from electric furnace dust according to any one of (1) to (7), wherein the zinc recovery step includes means for recovering zinc with a lead splash condenser.
(9)
The zinc recovery step recovers the iron and zinc from the electric furnace dust according to any one of (1) to (7), wherein the reduction treatment gas is cooled and the zinc is condensed and separated. Collection method.
(10)
The method for recovering iron and zinc from electric furnace dust as set forth in (9), wherein the zinc recovery step comprises bringing a silicon carbide tube whose interior has been cooled into contact with a reduction treatment gas.
(11)
In the zinc recovery step, after bringing the silicon carbide tube into contact with the reduction treatment gas, the silicon carbide pellets and the reduction treatment gas are further brought into contact with each other, and iron and zinc from the electric furnace dust according to (10) Recovery method.
(12)
In an apparatus for recovering iron and zinc from electric furnace dust containing iron oxide and zinc oxide,
A carbon-containing molded body manufacturing means for manufacturing a carbon-containing molded body by mixing and molding an electric furnace dust containing iron oxide and zinc oxide, a carbonaceous material, a binder and water;
Preheating means for heating and drying the carbon-containing molded body,
Reduction treatment means for producing reduced iron by further heating the carbon-containing molded body heated by the preheating equipment,
An apparatus for recovering iron and zinc from electric furnace dust, comprising zinc recovery means for recovering zinc from a reduction treatment gas generated by the reduction treatment means.
(13)
The apparatus for recovering iron and zinc from electric furnace dust according to (12), wherein the preheating means is an internal heating rotary kiln, and the reduction treatment means is an external heating rotary kiln.
(14)
The apparatus for recovering iron and zinc from electric furnace dust according to (13), wherein a powdered carbonaceous material charging device is installed in the externally heated rotary kiln.
(15)
Any one of (12) to (14), characterized in that it has a reduction processing gas reuse means for using the reduction processing gas after recovering zinc in the zinc recovery means as a heating fuel for the reduction processing means. The recovery apparatus of iron and zinc from the electric furnace dust as described in one.
(16)
The apparatus for recovering iron and zinc from electric furnace dust according to any one of (12) to (15), wherein the zinc recovery means has a lead splash capacitor.
(17)
Any one of (12) to (15), wherein the zinc recovery means has a zinc condenser that cools the reducing gas with a silicon carbide tube cooled inside and condenses and separates zinc. For recovery of iron and zinc from electric furnace dust.
(18)
In the zinc condenser, one or more of the silicon carbide tubes are orthogonal to the flow direction of the reducing gas, and the iron and zinc from the electric furnace dust according to (17) Recovery device.
(19)
The apparatus for recovering iron and zinc from electric furnace dust according to (18), wherein the silicon carbide tubes are horizontally disposed.
(20)
In the zinc condenser, a silicon carbide pellet is disposed downstream of the silicon carbide tube, and zinc is further condensed and separated and recovered. An apparatus for recovering iron and zinc from the described electric furnace dust.

According to the present invention, not only high-quality reduced iron is produced from electric furnace dust containing iron oxide and zinc oxide, but also high-quality metallic zinc can be efficiently recovered with a compact facility. Furthermore, the energy efficiency can be increased by reusing the exhausted gas. That is, the following effects can be obtained.

(A) The present mainstream technology for recovering metallic zinc from electric furnace dust is a combination of the two steps of the Welts method and the ISP method, which requires only one step according to the present invention. It becomes.

(B) As described above, the two steps can be completed in one step, and the investment of the heavy equipment ISP method can be avoided, so that the present invention can greatly reduce the capital investment.

(C) Since the metallization rate of reduced iron (DRI) produced in the present invention is higher than conventional RHF and is as high as 95% if conditions are adjusted, it can be used as an iron scrap substitute in electric furnace manufacturers. Complete recycling to electric furnace manufacturers is possible.

(D) Since the generation of dam rings, which is one of the problems of the Welts method, can be avoided, stable operation is possible.

(E) According to the present invention, a method for producing reduced iron from electric furnace dust and a method for recovering metallic zinc can be provided as an integrated system.
(F) Further, by performing the CO2 reforming treatment on the reducing gas, metallic zinc can be efficiently recovered.

It is a conceptual diagram of the recovery method and equipment of iron and zinc from electric furnace dust according to the present invention. It is a conceptual diagram of the carbon-containing molded object manufacturing step which concerns on this invention. 1 is a conceptual diagram of a test apparatus according to the present invention. It is a conceptual diagram of the zinc collection | recovery apparatus which concerns on this invention. FIG. 4A shows an example in which a cooling tube is arranged. FIG. 4B shows an example in which a ceramic pellet packed layer is further arranged on the cooling tube. It is a figure which shows the relationship between the reduction process temperature of a carbon-containing molded object, and residence time (reduction process time).

Hereinafter, the details of the present invention will be described using the conceptual diagram shown in FIG. 1 as an example. In addition, the embodiment shown below is an example, and the embodiment of the present invention is not limited to this.

[Carbon-containing molded body manufacturing step]
In the carbon-containing molded product manufacturing step, the electric furnace dust 10 containing iron oxide and zinc oxide is mixed with a carbon material (carbon material) that serves as a reducing agent, a binder material that serves to connect the particles, and water. Thus, a carbon-containing molded body is manufactured (FIG. 2).

As the raw material for reduced iron in the present invention, electric furnace dust, which is dust generated in an electric furnace type steelmaking process at a steel mill or the like, is used. Electric furnace dust has a high content of iron oxide, and there is a strong need for reuse.

Also, since scrap is used in the electric furnace, the electric furnace dust contains not only iron oxide but also a lot of zinc oxide. The present invention may be of any type as long as it is an electric furnace dust containing not only such iron oxide but also zinc oxide.

These electric furnace dusts are fine and difficult to handle. However, since it is a fine powder, its specific surface area (surface area per unit weight) is widened, the reduction reaction easily proceeds, and the dezincing property is improved.

Therefore, the present inventors conceived of using the electric furnace dust as fine powder in order to improve the reduction reactivity while keeping the specific surface area of the electric furnace dust particles large, and intensively studied the usage method. As a result, practically sufficient reduction reactivity can be obtained if the average particle size (D50: particle size corresponding to 50% cumulative frequency from fine particles in the cumulative particle size distribution) of the electric furnace dust is 3.0 μm or less. I found that I can do it.

* Existing electric furnace dust is collected by a bag filter. The collected electric furnace dust may be converted into pseudo particles (pellets) to prevent dust generation. Since the pellet diameter is about 8 mm, the pellet may be pulverized with a ball mill or the like to obtain a particle size of 3.0 μm or less before forming a carbon-containing molded body.

In addition to the electric furnace dust, the converter dust generated in the converter at the steel works also contains iron oxide and zinc oxide, and is therefore a target material of the present invention. In that case, since the moisture of the converter dust is as high as about 25%, the moisture content may be adjusted by blending quick lime or the like, and then the carbon-containing molded body may be obtained.

The carbonaceous material is a reducing agent for reducing iron oxide to metallic iron, and is added so that the C equivalent is in the range of 0.7 to 1.3. Here, the C equivalent is a ratio to the theoretical carbon amount based on the following formulas 1 and 2. If the total amount of iron oxide in the electric furnace dust is Fe ₂ O ₃ and the total amount of zinc oxide is ZnO, in order to reduce 1 mol of Fe ₂ O ₃ to obtain 2 mol of metallic iron, 3 mol of C (carbon ) And 1 mol of C is required to reduce 1 mol of ZnO to obtain 1 mol of zinc. This is the theoretical carbon content. This means that 0.7 to 1.3 times the theoretical amount of carbon is added.

Fe ₂ O ₃ + 3C + ΔH (1) → 2Fe + 3CO (Formula 1)
ZnO + C + ΔH (2) → Zn + CO (Formula 2)
The chemical reactions of the above formulas 1 and 2 are endothermic reactions, and the endothermic amount is ΔH (1) = 966 × 10 ³ kcal / t (Fe),
ΔH (2) = 882 × 10 ³ kcal / t (Zn).
In order to cause these reactions, it is necessary to add a heat amount corresponding to the endothermic amount from the outside.

The binder is, for example, corn starch. It is added so that the crushing strength after drying of the carbon-containing molded product is 20 kg / cm ² or more. The dried crush strength of less than 20 kg / cm ² of the molded body, the molded body by tumbling in a handling and rotary kiln is because being partly destroyed.

The water of the molded body can be adjusted by adding water as necessary so that the water content is around 10%.

こ れ ら Put these raw materials into the mixer and mix the raw materials. As the mixer, a rotary batch type is usually used, but the method is not particularly limited as long as the raw materials can be mixed uniformly. The blended raw material after mixing passes through a relay tank and is molded by an extrusion molding machine or a roll molding machine. The mixed raw material body subjected to the molding process is referred to as a carbon-containing molded body 20.

For example, electric furnace dust, carbonaceous material and binder are mixed with water and kneaded and granulated. At this time, when the kneaded material is pushed into a die having a hole and molded by applying pressure, a high strength carbon-containing molded body can be obtained. By adjusting the properties of the electric furnace dust and charcoal, the amount of water to be added, and the hole diameter, depth, indentation pressure, and the like of the die, conditions for producing a carbon-containing molded article suitable for the raw material powder can be obtained.

The shape of the carbon-containing molded body is generally spherical or cylindrical, but the shape is not limited to a cube, a rectangular parallelepiped, a triangular prism, or a briquette. The size of the carbon-containing molded article is preferably a spherical shape having a diameter of about 10 to 30 mm or a cylindrical shape having a diameter of 10 to 30 mm and a length of 10 to 30 mm in consideration of the subsequent reduction treatment. If the diameter or length is smaller than 10 mm, the reduced iron after the reduction treatment becomes small. On the other hand, if it is smaller than 10 mm, the powdering rate accompanying rolling in the rotary kiln increases as the surface area increases, and in addition, the size of reduced iron (DRI) is reduced because it shrinks by about 40% with reduction. It becomes too much, and the handling problem at the time of recycling arises. Moreover, if it is larger than 30 mm, the powdering rate decreases, but the reduction required time increases. Therefore, if the residence time in the reduction furnace is constant, the metalization rate and the dezincification rate are reduced. This is because. The diameter and length are preferably 10 to 30 mm, and more preferably 15 to 25 mm.

By using a molded body, reduced iron as a product is slightly contracted, but can be obtained as a molded body and used as an electric furnace raw material as it is. An apparatus required for a series of processes from cutting out the raw material to selecting a carbon-containing molded body having a predetermined size is referred to as a carbon-containing molded body manufacturing apparatus 11. Each individual apparatus forming the carbon-containing molded body manufacturing apparatus 11 is not particularly limited as long as the functions described above can be achieved.

[Carbon-containing molded body production means]
As described above, the electric furnace dust 10 and other carbonaceous materials, binders, and water raw materials are charged into the mixer, and the raw materials are mixed and molded (FIG. 2). A series of devices for cutting out each raw material, mixing, molding, and delivering the molded carbon-containing molded body 20 is a carbon-containing molded body manufacturing means (carbon-containing molded single manufacturing apparatus) 11.

The cutting of each raw material is not limited as long as it can be cut out by metering. For example, a vibration feeder or the like is applied.

The rotary batch type is usually used as the mixer, but the method is not particularly limited as long as the raw materials can be mixed uniformly. The blended raw material after mixing passes through a relay tank and is molded by an extrusion molding machine or a roll molding machine.

The form of the molding machine is not limited as long as it can be molded into a predetermined shape. As described above, the shape of the carbon-containing molded body is generally spherical or cylindrical, but the shape is not limited to a cube, a rectangular parallelepiped, a triangular prism, a briquette, or the like. For example, when a kneaded material is pushed into a die having a hole and molded by applying pressure, a high-strength carbon-containing molded body can be obtained. By adjusting the properties of the electric furnace dust and charcoal, the amount of water to be added, and the hole diameter, depth, indentation pressure, and the like of the die, conditions for producing a carbon-containing molded article suitable for the raw material powder can be obtained.

The form of the carbon-containing molded body dispensing device is not particularly limited. However, it is better to avoid things that destroy the carbon-containing molded body.

[Preheating step]
The preheating step in the present invention refers to heating the carbon-containing molded body 20 manufactured in the carbon-containing molded body manufacturing step 11, thereby evaporating water contained in the carbon-containing molded body and volatilizing chlorine (Cl) or the like. It refers to a series of steps until discharging the carbon-containing molded product from which volatile impurities have been removed. Since the carbon-containing molded product is made of electric furnace dust, various impurities such as chlorine are mixed. In particular, volatile impurities such as chlorine are mixed in the reducing gas after the reduction treatment and cause corrosion of the equipment, and therefore are removed before the reduction treatment. Further, when moisture is mixed in the reducing gas, it is removed to promote reoxidation of vaporized zinc.

The boiling point of zinc is 907 ° C. Therefore, the heating temperature of the carbon-containing molded body in the preheating step is preferably 907 ° C. or lower. If it is 907 ° C. or higher, the possibility that zinc will evaporate increases. When zinc evaporates, it is mixed in exhaust gas, reoxidized, recovered as dust as zinc oxide (crude zinc oxide), and reused. This is not appropriate from the viewpoint of processing efficiency. The heating temperature of the carbon-containing molded body is preferably 890 ° C. or less. Considering temperature variation in actual operation, it is better to set the temperature to 880 ° C. or lower.

If the lower limit of the heating temperature is too low, volatile impurities (particularly chlorine) cannot be removed. In normal electric furnace dust, 10% of zinc is present as zinc chloride (ZnCl2). Since the boiling point of zinc chloride is 732 ° C, the preheating temperature is preferably 740 ° C or higher. This is because if the temperature is lower than 740 ° C., there is a high possibility that zinc chloride is brought into the next reduction treatment step. Considering temperature variation in the carbon-containing molded body, the heating temperature of the carbon-containing molded body in the preheating step is preferably 750 ° C. or higher, more preferably 780 ° C. or higher, and preferably 800 ° C. or higher.
Thus, the carbon-containing molded body 30 from which volatile impurities have been removed, heated and dried is transferred to the next reduction treatment step.

[Preheating means]
In the preheating step, since the purpose is to preheat and dry the carbon-containing molded body 20 for removing volatile impurities and moisture, the atmosphere is not particularly limited. Therefore, the aspect will not be ask | required if it is a means which can heat the carbon-containing molded object 20. FIG. However, since the volatilized zinc chloride is cooled, agglomerated and recovered and used again as a raw material, a structure that does not dissipate the generated gas to the atmosphere is desirable. Furthermore, since it is necessary to avoid the mixing of oxygen (atmosphere) at the time of transfer to the subsequent reduction treatment step, treatment in a closed space is preferable. From this viewpoint, it is preferable to apply an internal heating type rotary kiln as the preheating means 22. Since the internal heat type rotary kiln is also applied in the Wertz method, it has a track record of heating pellet-shaped electric furnace dust such as a carbon-containing molded body. In this invention, it demonstrates as an example preheating a carbon-containing molded object using an internal-heat-type rotary kiln.

In the case of reduction treatment in an internal heat rotary kiln represented by the Welts type, the gangue components (SiO2 and CaO) in the raw material are between Fe ₂ O ₃ that is iron oxide and FeO that is its reduction intermediate. Therefore, it is easy to form a low melting point material as shown below.
Fe ₂ O ₃ · CaO: Melting point 1206 ° C
FeO · SiO ₂ : Melting point 1180 ° C
FeO ・ CaO: Melting point 1105 ° C

If the gangue component content is high, the raw material temperature of the firing zone is too high, the temperature of the combustion flame (burner frame) is too high, the shape of the combustion flame (burner frame) is too wide, and the inner wall surface of the rotary kiln In the case of licking, it produces deposits on the inner surface of the rotary kiln. Since this deposit is formed in a ring shape, it is called a dam ring. The dam ring hinders the movement of the object to be treated (raw material) in the rotary kiln, and the dam ring may fall off in a large amount continuously, which is not preferable from the viewpoint of stable operation. However, since the internal heating type rotary kiln used in the preheating step only heats up to about 900 ° C. as described above, no dam ring is formed.
Further, since the internal heat type rotary kiln sucks and discharges the gas in the kiln from the upstream side, the exhaust gas containing volatile impurities and moisture can be quickly discharged outside the kiln.

The carbon-containing molded body 30 preheated and dried in the internal heat type rotary kiln 22 is discharged from the kiln and transferred to the reduction treatment apparatus in the next process. The discharge device 23 from the internal heat type rotary kiln is preferably considered as an integral part of the charging device 31 to the reduction treatment facility. As will be described later, in the reduction process step, it is necessary to avoid mixing oxygen in the atmosphere as much as possible. Therefore, the discharge device 23 from the preheating means (preheating device) and the charging device 31 for the reduction process are shut off from the atmosphere. It preferably has a function.

[Reduction processing step]
The reduction treatment step in the present invention is to reduce the iron oxide and zinc oxide in the carbon-containing molded body by charging and heating the carbon-containing molded body 30 preheated and dried in the preheating step. It is a series of steps to make iron and zinc (steam). If air (especially oxygen) is mixed during the reduction treatment, the reduced iron or zinc is reoxidized. Therefore, it is important that the treatment be performed in a closed space where air contamination is blocked.

The carbon-containing molded body mixes the electric furnace dust with the carbonaceous material in the form of fine powder. Therefore, the specific surface area of the electric furnace dust is wide, and the reactivity with the carbonaceous material as the reducing agent can be increased, and the reduction treatment temperature can be lowered it can.

The inventors of the present invention have confirmed that the reduction reaction proceeds to an extent that there is no practical problem if the carbon-containing molded body according to the present invention is heated to about 980 ° C. to 1150 ° C. From the experimental results (Table 3), in order to reduce iron oxide with C (carbon) itself, a temperature of 980 ° C. or higher is necessary in practice. Therefore, the lower limit of the reduction treatment temperature is ideally 980 ° C. However, factors such as the contact state between finely divided iron oxide and carbon in the carbon-containing molded body also have an influence, so the reduction treatment temperature is preferably 1000 ° C. or higher.

The upper limit temperature of the reduction treatment depends on the heat resistance of the equipment. For example, in the case of an external heat type rotary kiln, since it is generally made of heat-resistant cast steel, its upper limit temperature of use is 1200 ° C. In consideration of the durability of the equipment, the upper limit temperature of use should be 1150 ° C. The upper limit is preferably 1130 ° C, more preferably 1100 ° C. Since the reduction process proceeds at about 1100 ° C., a lower temperature can be achieved compared to 1250 ° C. in the conventional rotary hearth type reduction method (RHF) and 1200 ° C. in the Welts method. If the facility heat resistance is improved, the reduction treatment temperature can naturally be raised.

The processing time of the reduction process is determined by the relationship with temperature. As a result of experiments in an externally heated rotary kiln, the present inventors have found that the relationship between the reduction treatment temperature (T ° C.) and the reduction treatment time (residence time) (H minutes) defined by the following Equation 3 is conventional. It was confirmed that reduced iron having a quality equivalent to or better than the Welts method and the RHF method can be obtained.

H ≧ 120−0.1T (Formula 3)
However, 980 ≦ T ≦ 1150
T: Reduction treatment temperature (° C) of the carbon-containing molded product,
H: Residence time of carbon-containing molded product (reduction treatment time) (minutes)

In other words, T is the carbon-containing molded body temperature (attainment temperature) inside the external heating rotary kiln, and H is the minimum residence time (residence time at the attainment temperature) in the external heating rotary kiln. The reduction reaction can be processed in a short time because the reaction proceeds faster as the processing temperature is higher. However, the properties of the carbon-containing molded product are not always uniform. However, even if the heat resistance of equipment is improved and a high-temperature treatment at 1150 ° C. or higher can be performed, it is necessary to ensure a certain reaction time. The upper limit of H is not particularly limited, but even if it stays for a long time, there is not much improvement in the reduction rate, so it is sufficient to allow 40 minutes or 10 minutes on the right side of Equation 3. That is, it is preferable that H = 130−0.1T or 40, whichever is smaller.

GLOSS metallization rate was adopted as a quality index of reduced iron, and the RHF method GROSS metallization rate of 60% or more was used as a pass criterion. Details will be described in an embodiment described later.

Further, the gas generated by the reduction treatment of iron oxide is CO (carbon monoxide) gas as can be seen from the equations 1 and 2. Gases generated by the reduction treatment of zinc oxide are zinc vapor (indicated as Zn (gas) for convenience) and CO (Formula 4). Some CO gas also becomes CO ₂ (carbon dioxide).
ZnO + C → Zn (gas) + CO (Formula 4)

From the above, the gas generated in the reduction treatment step in the present invention (reducing process gas 50) is mainly composed of CO, containing zinc vapor and CO _2. The present invention is characterized by having a zinc recovery step of recovering zinc from the reduction treatment gas 50.
In this way, zinc is separated from the carbon-containing molded body, and the reduced iron 40 having a high metallization rate is recovered as a solid. On the other hand, the metallic zinc 60 is recovered from the reduction treatment gas 50 containing zinc vapor in the subsequent zinc recovery step.

[Reduction processing means]
In the reduction treatment step, the reduction treatment must be performed by heating in a closed space where the atmosphere (especially oxygen) is shut off. The aspect is not particularly limited as long as it is a means capable of realizing this restriction. Currently, the externally heated rotary kiln 32 can be applied as a means for realizing this restriction.

As described above, the inventors confirmed that the reduction reaction proceeds to a practically satisfactory level when heated to about 980 ° C. to 1150 ° C. by using a carbon-containing molded body. Compared to 1200 ° C. of the Wertz method, which is an existing reduced iron manufacturing apparatus, and 1250 ° C. of the rotary hearth type reduction method (RHF method), a considerably low temperature can be achieved. This low temperature makes it possible to use an externally heated rotary kiln that could not be used conventionally. The body of the external heat type rotary kiln is generally made of heat-resistant cast steel manufactured by centrifugal casting, and about 1200 ° C. is the upper limit for use. Considering temperature variation, the upper limit temperature is preferably 1150 ° C., preferably 1130 ° C., more preferably 1100 ° C., from the viewpoint of facility maintenance. As a matter of course, if the heat resistance of equipment is improved, the reduction treatment temperature can be naturally increased.

Hereinafter, the reduction processing means (reduction processing apparatus) will be described by taking the external heat type rotary kiln 32 as an example.
Even when the preheated and dried carbon-containing molded body 30 is transferred and charged from the internal heat type rotary kiln 22 to the external heat type rotary kiln 32, it is desirable that air (strictly speaking, oxygen) should not be mixed. Similarly, when discharging reduced iron from the external heat type rotary kiln 32, it is necessary to maintain airtightness so that the atmosphere does not enter the kiln. As described above, the mode of the transfer / loading device 31 (hereinafter simply referred to as “charging device”) and the discharging device 35 are not limited as long as the airtightness can be secured. For example, it can be implemented using a double damper.

The amount of cut of the carbon-containing molded body 30 discharged from the internal heat type rotary kiln 22 is controlled by a rotary valve, and a double damper (for example, two hoppers are installed in series in the vertical direction, and an open / close type damper is installed below each hopper. To the upper hopper. The dampers of the double damper are alternately opened and closed, and the transferred carbon-containing molded body is transferred (dropped) from the upper hopper to the lower hopper. Then, the lower hopper is opened, and the carbon-containing molded body is charged into the external heating type rotary kiln 32. If the carbon-containing molded body is charged by this method, the mixing of air can be suppressed as much as possible.

Similarly, when discharging reduced iron from the external heat type rotary kiln 32, it is possible to prevent air from being mixed into the kiln by applying a double damper. Thus, zinc can be separated, and reduced iron 40 having a high metallization rate can be recovered as a solid.
The reducing gas 50 in the external heat type rotary kiln 32 is guided to the zinc recovery device 51 in the next step through the piping connected to the kiln without being exposed to the atmosphere. By doing so, it is possible to recover zinc without reoxidizing the vaporized zinc.

[CO2 reforming treatment]
If CO2 is present in the reduction gas in the process of cooling the reduction gas containing metal zinc vapor, the metal zinc vapor is oxidized with CO2 to become crude zinc oxide (ZnO), and metal zinc cannot be recovered. This is because the lower the CO / CO2 ratio (the higher the CO2 concentration), the higher the equilibrium temperature at which zinc can exist as metal vapor.
For example, when the CO / CO2 ratio = 4, the equilibrium temperature in the direction of ZnO reduction (ZnO + CO → Zn + CO2) is about 1200 ° C. When this temperature is exceeded, reduction of zinc oxide proceeds. According to the energy / temperature diagram of the oxide (Ellingham diagram), the equilibrium temperature when the CO / CO2 ratio = 10 is 1100 ° C., the equilibrium temperature when the CO / CO 2 ratio = 15 is 1050 ° C., and the CO / CO 2 ratio. The equilibrium temperature when 10 = 20 is 1010 ° C., and the equilibrium temperature when the CO / CO 2 ratio = 100 is 910 ° C.
Since the treatment temperature of the carbon-containing molded article according to the present invention is about 980 ° C. to 1150 ° C., the CO / CO 2 ratio may be about 30 or less in order to promote the reduction of zinc oxide (ZnO). That is, the CO2 concentration may be about 3% or less. According to the study by the present inventors, it is found that if the CO2 concentration in the reducing gas is 3% or less, the metal zinc recovery rate (recovered zinc amount with respect to the zinc amount contained in the electric furnace dust) can be secured 90% or more. It was.

Next, a specific method of CO2 reforming treatment was examined. The CO2 reforming process is for reforming CO2 in the reducing gas into CO. For example, the reducing gas can be brought into contact with carbon (C) by some method, and CO2 can be reformed to CO (CO2 + C → 2CO).
As a specific method of the CO2 reforming treatment with carbon (C), for example, an externally heated rotary kiln 33 is provided with a powdered carbon material charging device (device for charging powdered carbonaceous material) 36 and an externally heated rotary kiln. There is a method in which a powdered carbon material is charged into 33 and brought into contact with a reducing gas. As an example, a protrusion may be attached to the inner surface of the external heat type rotary kiln, and the powdered carbon material may be lifted and dropped onto the protrusion by rotation of the kiln and dropped.
As another example, for example, natural gas (CH 4) may be blown into an externally heated rotary kiln. At this time, natural gas (CH4) reacts with CO2 in the reducing gas and is reformed to CO (CH4 + CO2 → 2CO + 2H2).
The method for the CO2 reforming treatment is not limited to the above method, and any method may be used as long as CO2 in the reducing gas can be reformed to CO.

[Zinc recovery step]
The zinc recovery step in the present invention is a series of steps for recovering zinc from the reduction processing gas 50 generated in the reduction processing step. In order to suppress reoxidation of zinc in the gas, it is necessary to guide the reducing treatment gas so that the atmosphere does not enter.

The method for recovering zinc from a gas containing zinc is not particularly limited. As a method for separating and recovering zinc from the reducing gas, for example, there is a method using a lead splash condenser. However, the equipment becomes large and the recovery efficiency is not good. Accordingly, the inventors have repeatedly studied and found that the reducing gas can be directly cooled to condense zinc and recover it as molten zinc. According to this, compared with a lead splash condenser, the equipment configuration can be made compact, and zinc can be separated and recovered with high efficiency. For example, the gas may be directly cooled by a cooling tube. When the cooling tube is made of metal (for example, steel or copper), it reacts with zinc to produce an alloy. Therefore, the cooling tube material may be other than metal. For example, ceramic is good. Thus, the inventors have confirmed that the reduction treatment gas can be cooled and the zinc can be condensed and recovered by a cooling tube made of silicon carbide (SiC) having good thermal conductivity.

Condensed zinc is collected as droplets. It may be stored as molten zinc in the lower part of the zinc recovery device, or may be recovered as zinc particles by cooling while being dropped as droplets. The collection method is not particularly limited.

[Zinc recovery means]
The aspect of the zinc recovery means (zinc recovery apparatus) is not particularly limited as long as it is a means capable of separating and recovering zinc contained in the reduction treatment gas. For example, a zinc splash capacitor may be applied as described above.
However, it is preferable from the viewpoint of efficiency and zinc quality that the zinc is condensed and recovered by direct cooling of the gas as described above. If it is a means which has this function, the aspect will not be specifically limited. Further, as found by the inventors, a device that directly cools the reducing treatment gas 50 containing zinc and condenses and recovers zinc may be used. In particular, the inventors have found that a zinc condenser (zinc condenser) that condenses zinc in the gas by bringing the cooling tube 56 into direct contact with the gas is efficient. FIG. 4A shows a conceptual diagram thereof. The zinc condensed by the cooling tube 56 falls in a molten state and accumulates in the lower part of the zinc condenser. Of course, after condensation, it can be cooled during the fall and recovered as zinc particles.

It is preferable to install one or a plurality of cooling tubes 56 and to be orthogonal to the gas flow. This is because if it is installed in the gas flow direction, it solidifies and adheres on the pipe. The cooling tube 56 is preferably arranged horizontally. This is because the molten zinc condensed on the cooling tube may move on the cooling tube due to gravity and solidify and be fixed if not horizontal. By arrange | positioning horizontally, it can be dripped before a molten zinc solidifies. When a plurality of cooling tubes 56 are installed, the arrangement of the tubes is not particularly limited. What is necessary is just to set from a viewpoint of cooling efficiency.

The gas that passes between the cooling tubes and does not contact the tube surface still contains zinc vapor and molten zinc fine particles. For this reason, in order to increase the zinc recovery rate, a plurality of pellets made of ceramics or coated with ceramics may be arranged downstream of the cooling tube in the direction of flow of the zinc vapor-containing gas (FIG. 4B). This is because when the gas containing zinc vapor and molten zinc fine particles passes through the gaps between the ceramic pellets, it contacts the pellet surface, and the zinc is condensed, aggregated and separated. At this time, the condensed and agglomerated molten zinc becomes droplets and is dropped and recovered.
The size of the pellet is not particularly limited, but it is easy to handle a cylindrical shape having a diameter of about 5 to 10 mm and a height of about 5 to 10 mm, or a spherical shape having a diameter of about 5 to 10 mm, and an appropriate void can be secured.
The material of the ceramic is not particularly limited, but silicon carbide (SiC) having good thermal conductivity is preferable like the cooling tube. SiC can be easily separated and recovered without getting wet by molten zinc.
The number of pellets to be arranged is not particularly limited as long as it is plural (two or more). However, since it is desirable that the gas uniformly contacts the pellet surface, the gas may be filled so as to fill a cross section through which the gas passes. Further, by overlapping the pellets in multiple layers, the gas and the pellet surface come into contact with each other, and the zinc recovery rate is improved.

The gas introduction pipe from the externally heated rotary kiln 32 to the zinc recovery device 51 needs to be airtight and good in air tightness so that zinc in the reducing gas does not reoxidize. The blower 54 for sucking the reducing treatment gas is preferably installed downstream of the zinc recovery device. This is because zinc is not adhered to the blade (wing) of the blower because zinc is separated. From the viewpoint of protecting the blower equipment, the dust collector 53 may be disposed in front of the blower.

Further, when the zinc-containing gas is cooled, when the zinc-containing gas comes into contact with metallic iron, CO2 (carbon dioxide) is generated by a carbon deposition reaction (2CO → CO2 + C), and the vapor zinc is reoxidized by this CO2. It becomes crude zinc oxide (ZnO). As described above, once crude zinc oxide (ZnO) is obtained, metal zinc cannot be recovered. Therefore, it is desirable to suppress this carbon deposition reaction.
When the zinc recovery device is made of steel, the inner surface thereof may be covered so that the zinc-containing gas does not come into direct contact with the steel. The coating is not particularly limited, but may be painted, for example. The paint is not limited, and examples thereof include heat resistant paint. Further, for example, lining may be performed. For example, there is a lining with ceramic paint or castable.

As mentioned above, although the method and equipment which take out iron (reduced iron) and zinc (reduced zinc) from electric furnace dust were explained, the method and equipment which can be added for effective use of exhaust gas etc. are explained. To do.

[Reduction treatment gas reuse step and means]
The reducing gas after zinc recovery is mainly composed of CO (partially CO ₂ ) because zinc is separated. Of course, it may be emitted into the atmosphere, but it is better to effectively use CO as fuel. For example, you may utilize as a fuel of the heating means (for example, the combustion burner 34 of the external heating type rotary kiln 32) of a reduction process means. Further, for example, it may be reused as fuel for the heating means of the preheating device 22 (for example, combustion gas of an internal heat type rotary kiln). Of course, it may be reused in other facilities.

For that purpose, it is necessary to purify the reducing gas 50. For example, a recuperator 52 that recovers sensible heat of gas and lowers the gas temperature, a dust collector 53 that removes dust in the gas, a blower 54, and a gas holder 55 that stabilizes the gas pressure may be installed. The gas passing through these facilities can be used as fuel for the combustion burner 34 of the externally heated rotary kiln. The refining gas purification method / equipment is not particularly limited to this embodiment, and the refining method and equipment may be appropriately selected according to the use of the gas.

[Other incidental devices]
In the preheating step, the exhaust gas 80 generated after heating and drying the carbon-containing molded body contains dust containing zinc chloride, iron oxide, and zinc oxide as described above. Therefore, it is desirable to separate and recover these components from the exhaust gas generated in the preheating step. Therefore, for example, the exhaust gas 80 generated from the preheating device (for example, the internal heating rotary kiln) 22 is passed through a dust collector (bag filter) 81, and zinc chloride and dust 84 are collected and then released into the atmosphere. Of course, the blower 82 for sucking the exhaust gas may be installed downstream of the dust collector. What is necessary is just to select a gas processing method and installation suitably according to the use of the waste gas in the preheating step.

[Example 1]
Hereinafter, examples of the present invention in a test plant will be described.
Table 1 shows the chemical components of the electric furnace dust used in the test operation and the powder coke as the carbonaceous material. A numerical value shows the mass%. The particle size distribution of the electric furnace dust was measured by a laser diffraction scattering type particle size distribution measuring device (Microtrac), and was D50 = 1.5 μm, and D50 of powder coke was also 36.2 μm. D50 is a particle size corresponding to 50% of cumulative frequency from fine particles in the cumulative particle size distribution.

Table 2 shows the raw material blend ratio and blended raw material moisture of the carbon-containing molded body used in the test operation (almost the same as the carbon-containing molded body moisture). Add powdered coke as charcoal so that the C equivalent is 1.0, add water for water adjustment and corn starch as binder, mix well with a double arm kneader, then use a semi-dry extrusion machine to measure the bottom diameter A carbon-containing molded product 20 having a diameter of 20 mm and a length of 25 mm was produced. The green strength of the carbon-containing molded product (strength immediately after molding) was 8.7 kg / cm ² , and the strength after drying at 150 ° C. for 2 hours was 37.0 kg / cm ² .

<Test plant equipment specifications>
A conceptual diagram of the entire test plant is shown in FIG. The treatment capacity is 50 dkg of carbon-containing molded product (showing the weight (Kg) in the dry state; the same applies hereinafter) / h. Although the basic configuration is close to the actual equipment shown in FIG. 1, the external heating furnace of the external heating type rotary kiln is an electric heating type for simplicity. A hot air generator (a preheater burner) was used to heat the internal heat rotary kiln. The exhaust gas from the external heating rotary kiln was cooled by a zinc recovery device, burned with CO gas by an exhaust gas combustion device, rendered harmless, and then released outdoors.

The main equipment specifications are shown below.
[Internal heat type rotary kiln]
・ Stainless steel: Inner diameter 500mm x Length 4m
・ Heating method: Hot air generator [externally heated rotary kiln]
-Made of heat-resistant cast steel: inner diameter 300mm x length 4m, maximum operating temperature 1150 ° C
・ External heating furnace: Electric heating type, total length 2m
[Carbon-containing molded body supply / discharge device]
・ Supply to internal heat type rotary kiln: Room temperature type double damper ・ Transfer device from internal heat type rotary kiln to external heat type rotary kiln: Two high temperature type water cooled rotary valves in series ・ Discharge device from external heat type rotary kiln: Room temperature type Double damper [Zinc recovery unit]
The zinc recovery device is a vertically long cylindrical container having a square cross section, and has a double structure of an outer wall and an inner wall made of steel plate. Inside the inner wall, a 20 mm thick heat insulating material and an 80 mm thick castable are arranged in this order. Further, the outer wall and the inner wall were separated by 50 mm, and nitrogen was allowed to flow between them so that air was not mixed into the reducing treatment gas. The portion through which the reducing gas flows has a square cross section with a side of 250 mm.
-In the upper part of the zinc recovery unit, 25 SiC pipes (SiC: 99%) having an outer diameter of 30 mm and an inner diameter of 20 mm, which were water-cooled inside, were arranged in a staggered manner as a cooling tube. By placing an SiC triangular prism (25 cm in length) whose bottom was cut so as to be in close contact with the pipe, the deposition of metallic zinc on the pipe was prevented.
-An O-ring was installed at the attachment part of the SiC pipe in order to absorb expansion and contraction accompanying heating and cooling of the SiC pipe and shut off the outside air.
・ Furthermore, heat-resistant paint was applied to the inner surface of the pipe from the externally heated rotary kiln to the zinc recovery unit as a measure against carbon deposition. Also, the inner surface of the inner wall of the zinc recovery unit is lined with a castable, but as a precaution, a heat resistant paint was also applied to the inner surface of the inner wall.

<Test method>
The test was conducted according to the following procedure.
(1) After operating the hot air generator 24 of the internal heat type rotary kiln 22, the carbon-containing molded body manufactured by the above-described method through the charging device (double damper) 21 in the internal heat type rotary kiln 22. 20 was charged at a speed of 50 dkg / h. The fuel combustion amount of the hot air generator 24 and the rotation speed of the internal heating rotary kiln were controlled so that the temperature when the carbon-containing molded body was preheated and dried and discharged from the internal heating rotary kiln 22 was 900 ° C.

(2) The externally heated rotary kiln 32 was heated to an external surface temperature of 1050 ° C. After the carbon-containing molded body heated to 900 ° C. is started to be charged into the external heating rotary kiln 32 via the charging device (two series water-cooled rotary valves) 31, The rotational speed of the external heating rotary kiln was adjusted so that the residence time was 30 minutes, and at the same time, the power input amount of the external heating furnace was controlled so that the external surface temperature of the external heating rotary kiln was maintained at 1050 ° C.

(3) When the reduction is completed, the carbon-containing molded body becomes reduced iron (DRI) 40. The reduced iron at 1050 ° C. was cooled to 200 ° C. or less in a water-cooled box installed at the discharge port of the externally heated rotary kiln 32, and then discharged to the outside via a discharge device (double damper) 35 and collected.

(4) Although the case where the reduction treatment temperature is 1050 ° C. and the reduction treatment time is 30 minutes has been described above, the reduction treatment temperature is between 950 ° C. and 1150 ° C., and the reduction treatment time is between 10 minutes and 40 minutes. Nine levels of tests were carried out with various changes, and the collected DRI analysis results are shown in Table 3.

(5) NET metallization rate is a metallization rate increased by reduction. The GLOSS metallization rate is the total metallization rate of the sample after reduction to which M · Fe (metallic iron (metallic Fe)) originally added in the electric furnace dust is added. The definitions of the metallization ratios of GROSS and NET are shown in Equations 5 and 6. Hereinafter, T · Fe represents total Fe (total iron content), and the weight percent of M · Fe and T · Fe represents the weight percent of the carbon-containing molded body.
GROSS metallization rate = (M · Fe after reduction (% by weight)) / (T · Fe after reduction (% by weight)) (Formula 5)
NET metallization rate = {[(M · Fe (% by weight) after reduction × total weight of the carbon-containing molded product after reduction) − (M · Fe (% by weight) before reduction × carbon-containing molded product before reduction) (Total weight after reduction)] / (total weight after reduction)} / (T · Fe (% by weight) after reduction) (Formula 6)

(6) For comparison, the results when electric furnace dust was treated by the Welts method and the RHF method are also shown in Table 3. The RHF method using a carbon-containing molded product has better results than the Welts method. The metallization rate of DRI reduced with RHF is 60 to 70%, and the entire amount of DRI is recycled in an electric furnace as an iron source, and the dezincification rate is as high as 70 to 90%. Therefore, the test results for obtaining the same GROSS metallization rate and dezincification rate as RHF are indicated by ○, and the test results for the degreasing rate of RHF or less are indicated by Δ for the GLOSS metallization rate as RHF.

(7) From the test results, the relationship between the reduction treatment temperature T ° C. in the external heating rotary kiln and the residence time (reduction treatment time) H is shown in FIG. As can be seen from FIG. 5, it was confirmed that if the relationship between the reduction treatment temperature T ° C. and the reduction treatment time H minutes satisfies the above-described formula 3, a metallization rate comparable to RHF can be obtained. It was also confirmed that a metallization rate and dezincification rate of 95% or more can be obtained by reduction treatment at 1050 ° C. for 30 minutes.

(8) In the internal external heating rotary kiln 32, carbonaceous molded body is reduced, the zinc vapor and CO gas and CO ₂ gas is generated. The exhaust gas 50 was sucked by an exhaust blower 54 and passed through a heat exchanger (zinc recovery device) 51 in which SiC water-cooled pipes were arranged to be rapidly cooled to 500 ° C. By this rapid cooling, the zinc vapor in the exhaust gas was dropped as molten zinc at 500 ° C. and stored in a molten zinc reservoir installed under the zinc recovery device. The stored molten zinc 60 was poured into a mold and collected every hour. Test No. The analytical values of the metal zinc recovered in 6 are shown in Table 4. At this time, the recovered amount of metallic zinc was 4.8 kg / h (hour) on average.

(9) After the exhaust gas 50 of the externally heated rotary kiln 32 is rapidly cooled by the zinc recovery device 51, the exhaust gas at 500 ° C. is burned in the exhaust gas combustion device 57 under excess air, and then diluted with a large amount of air to 200 ° C. After cooling to the following, and further gradually dusting with a dust collector (bag filter) 53, it was diffused into the atmosphere.
As described above, it was confirmed that iron (reduced iron) and zinc (reduced zinc) can be separated and recovered from electric furnace dust containing iron oxide and zinc oxide by a series of tests.

[Example 2]
In the same test apparatus as in Example 1, in order to reform CO2 in the reducing gas into CO, a powdered carbon material charging device 36 was installed in the external heating type rotary kiln 33. Furthermore, a protrusion was installed on the inner surface of the external heat type rotary kiln, and the powdered carbon material was lifted upward by the inner protrusion by the rotation of the kiln, and dropped into the kiln.
First, a carbon-containing molded body not containing zinc was prepared. This was produced by molding fine iron ore, fine coke and binder. The zinc-containing carbon-containing molded body was charged into the modified test apparatus. Thereafter, powder coke having a particle size of 1 mm or less was charged from the powdered carbon material charging device 36 for CO2 reforming. The amount of powder coke charged at this time was 5 d-Kg / h per 50 d-Kg / h of the carbon-containing molded product.
As a result, when CO2 in the reducing gas was compared, CO2 that was 20% before charging the coke breeze was reduced to 3% after charging the coke breeze.

Next, SiC ceramic balls were filled in the downstream side (lower part) of the cooling tube 56 of the zinc recovery device 51 of the test device. The SiC ceramic balls were 8 mm in diameter, and were filled with SiC ceramic balls so that the cross section (250 mm square cross section) of the zinc recovery device had a thickness of about 400 mm. There were about 49000 filled SiC ceramic balls.

Remodeling of CO2 in the reduction gas to reform to CO, and filling the zinc recovery unit with SiC ceramic balls, and subjecting the carbon-containing molded body with electric furnace dust as in Example 1. A reduction test was conducted.
As a result, the recovery amount of metallic zinc was 11.1 kg / h (hour) on average. This indicates that about 90% of zinc contained in the electric furnace dust can be recovered as metallic zinc.

Since the present invention can separate and recover reduced iron and zinc from electric furnace dust generated in an iron making plant using an electric furnace, it can be used in the iron making industry using an electric furnace.

10 Electric furnace dust 11 Carbon-containing molded body production equipment (means)
20 Carbon-containing molded body 21 Charging device 22 Preheating device (internal heat type rotary kiln)
23 Ejector 24 Preheater burner (hot air generator)
30 Preheated and dried carbon-containing molding 31 Charging equipment 32 Reduction processing equipment (external heating rotary kiln)
33 Heating device for reduction treatment device 34 Combustion burner 35 Discharge device 36 Powdered carbon material charging device 40 Reduced iron 50 Reduction treatment gas 51 Zinc recovery device 52 Recuperator 53 Dust collector 54 Blower 55 Gas holder 56 Cooling tube 57 Exhaust gas combustion device 59 Ceramic pellet packed bed 60 Zinc 70 Heater exhaust gas 80 Preheater exhaust gas 81 Dust collector 82 Blower 83 Chimney 84 Dust (recycle)

Claims (20)

1. A carbon-containing molded body manufacturing step of manufacturing a carbon-containing molded body by mixing and molding an electric furnace dust containing iron oxide and zinc oxide, a carbonaceous material, a binder and water;
   A preheating step of heating and drying the carbon-containing molded body;
   A reduction treatment step in which the carbon-containing molded body heated and dried in the preheating step is further heated in a closed space to reduce iron oxide to reduced iron, and
   A method for recovering iron and zinc from electric furnace dust, comprising a zinc recovery step of recovering zinc from the reduction processing gas generated in the reduction processing step.
2. The method for recovering iron and zinc from electric furnace dust according to claim 1, wherein the heating temperature of the carbon-containing molded body in the preheating step is 740 ° C or higher and 907 ° C or lower.
3. The method for recovering iron and zinc from electric furnace dust according to claim 1 or 2, wherein the heating temperature of the carbon-containing molded body in the reduction treatment step is 980 ° C or higher and 1150 ° C or lower.
4. The iron and zinc from electric furnace dust according to any one of claims 1 to 3, wherein the preheating step is treated with an internal heating rotary kiln, and the reduction treatment step is treated with an external heating rotary kiln. Collection method.
5. The iron from the electric furnace dust according to any one of claims 1 to 4, wherein in the reduction treatment step, CO2 reforming treatment is performed to reduce a CO2 concentration in the reduction treatment gas to 3% or less. Zinc recovery method.
6. 6. The method for recovering iron and zinc from electric furnace dust according to claim 5, wherein the CO2 reforming treatment introduces powdered carbonaceous material into the closed space in the reduction treatment step.
7. The iron from electric furnace dust according to any one of claims 1 to 6, wherein the reduction treatment gas after the zinc is collected in the zinc collection step is used as a heating fuel in the reduction treatment step. And zinc recovery method.
8. The method for recovering iron and zinc from electric furnace dust according to any one of claims 1 to 7, wherein the zinc recovery step includes means for recovering zinc with a lead splash condenser.
9. The method for recovering iron and zinc from electric furnace dust according to any one of claims 1 to 7, wherein the zinc recovery step recovers the gas by cooling the reduction treatment gas and condensing and separating the zinc. .
10. 10. The method for recovering iron and zinc from electric furnace dust according to claim 9, wherein the zinc recovery step comprises bringing a silicon carbide tube whose interior is cooled into contact with a reduction treatment gas.
11. 11. The iron and zinc from electric furnace dust according to claim 10, wherein, in the zinc recovery step, after the silicon carbide tube and the reduction treatment gas are brought into contact with each other, the silicon carbide pellet and the reduction treatment gas are further brought into contact with each other. Recovery method.
12. In an apparatus for recovering iron and zinc from electric furnace dust containing iron oxide and zinc oxide,
    A carbon-containing molded body manufacturing means for manufacturing a carbon-containing molded body by mixing and molding an electric furnace dust containing iron oxide and zinc oxide, a carbonaceous material, a binder and water;
    Preheating means for heating and drying the carbon-containing molded body,
    Reduction treatment means for producing reduced iron by further heating the carbon-containing molded body heated by the preheating equipment,
    An apparatus for recovering iron and zinc from electric furnace dust, comprising zinc recovery means for recovering zinc from a reduction treatment gas generated by the reduction treatment means.
13. The apparatus for recovering iron and zinc from electric furnace dust according to claim 12, wherein the preheating means is an internal heating rotary kiln, and the reduction treatment means is an external heating rotary kiln.
14. The apparatus for recovering iron and zinc from electric furnace dust according to claim 13, wherein a powder carbonaceous material charging device is installed in the externally heated rotary kiln.
15. 15. The reduction processing gas reuse means for using the reduction processing gas after recovering zinc in the zinc recovery means as a heating fuel for the reduction processing means. An apparatus for recovering iron and zinc from electric furnace dust described in 1.
16. The apparatus for recovering iron and zinc from electric furnace dust according to any one of claims 12 to 15, wherein the zinc recovery means has a lead splash capacitor.
17. 16. The zinc condenser according to any one of claims 12 to 15, wherein the zinc collecting means includes a zinc condenser that cools the reduction treatment gas using a silicon carbide tube cooled inside and condenses and separates zinc. An apparatus for recovering iron and zinc from the described electric furnace dust.
18. 18. The iron and zinc from the electric furnace dust according to claim 17, wherein one or more of the silicon carbide tubes are orthogonal to the flow direction of the reducing gas in the zinc condenser. Recovery device.
19. The apparatus for recovering iron and zinc from electric furnace dust according to claim 18, wherein the silicon carbide tube is disposed horizontally.
20. The zinc condenser according to any one of claims 17 to 19, wherein a silicon carbide pellet is disposed downstream of the silicon carbide tube, and zinc is further condensed and separated and recovered. Equipment for recovery of iron and zinc from electric furnace dust.

Images