JPH07173549A - Method for recovering metallic zinc and iron from dust containing zinc and iron - Google Patents

Abstract

PURPOSE:To independently and efficiently recover metallic zinc and iron from the dust contg. zinc and iron. CONSTITUTION:Two particle-circulated fluidized-bed reaction furnaces 10 and 20 are used, the dust contg. zinc and iron is introduced into the fluidized bed 10, and the gas discharged from the fluidized bed 20 is heated by a secondary- combustion lance 30. As a result, the zinc in a riser 11 is reduced, vaporized, cooled and recovered by a zinc recovery device 40. The particle collected by a collector 14 is introduced into the fluidized bed 20 to reduce and recover the iron.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering metallic zinc and metallic iron from dust containing iron oxide and zinc oxide in a fluidized bed furnace.

[0002]

2. Description of the Related Art In recent years, social needs for resource recycling and energy saving have increased, and recycling of iron scrap as an iron source has been desired. However, at present, iron scrap is melted and refined in a converter or an electric furnace. In this case, most of zinc is vaporized due to its low boiling point, and fine powder dust mixed with iron oxide is generated.

Since this powdery dust is easily scattered, it is difficult to directly charge and use it in an electric furnace or a converter. For this reason, powdery zinc-containing dust is pelletized and then converted into a converter or an electric furnace. It is processed in a furnace to recover metals such as zinc and iron.
However, when directly agglomerating metallic zinc and metallic iron from dust of iron-based oxides containing zinc oxide such as the dust, without performing a pretreatment step such as pelletization, It is extremely desirable from the viewpoint of saving resources and energy. A process applying a fluidized bed is considered as one of the processes for achieving such an object.

In general, a fluidized bed reactor has a good temperature uniformity in the bed, can carry out a continuous large amount of reaction treatment, and can use fine powder without a pretreatment step.
The application to the dust treatment process as described above is effective. For example, an iron-based dust reduction device using a fluidized bed is disclosed in Japanese Patent Application Laid-Open No. 4-210411. According to the invention, when reducing iron-based dust generated in a steel refining process to metallic iron powder in a fluidized bed reaction vessel, conditions (a) a reaction lower part is a cone type as conditions for preventing sticking in the fluidized bed. Using a fluidized bed reactor, (b) adjusting the particle size of the iron-based dust to 1 to 10 μm, (c) using sand grains of 0.1 to 0.5 mm as the fluidizing medium, (d) reducing temperature Is maintained at 600 to 800 ° C.

However, in this method, since the fluidized bed is a one-stage particle medium fluidized bed of a type that does not circulate particles, (1) when reducing dust containing zinc oxide and iron oxide at the same time, zinc is used. The reduction rates of oxide and iron oxide cannot be increased at the same time. (2) When the flow velocity of the fluidizing gas is increased in order to improve productivity, the residence time of dust in the furnace is shortened, so that the high reduction rate cannot be maintained. There were problems such as.

It has been estimated that the above problem (2) may be solved by a technique before that, for example, the technique disclosed in Japanese Patent Laid-Open No. 3-215621. That is, the fluidized bed of the particulate medium is of a particle circulation type. The invention disclosed in JP-A-3-215621 is such a particle circulation type fluidized bed, and the basic structure thereof is, as schematically shown in FIG. 2, (a) a raw material ore charging port on the side wall. (1) a riser 1 having an inlet 2 for introducing a reducing gas as a fluidizing gas at the bottom, and (b) a particle collecting device for collecting the ore particles that are ejected along with the reducing gas near the top of the riser 1. 4, (c) a downcomer pipe 5 for re-supplying the fly-out ore separated from the reducing gas by the particle collecting device 4 into the riser 1.

However, even if such a particle circulation type fluidized bed is used, the above problem (1) cannot be solved. That is, a method of simultaneously recovering zinc and iron with high efficiency is required.
As a possibility of such a technique, for example, Japanese Patent Laid-Open No. 2-4
Although the technique disclosed in Japanese Patent No. 2887 is also known, the method relates to a method for recovering zinc and iron (as iron carbide) from a mixture containing zinc ferrite. Iron (as iron carbide) treated in the carbonization process of a fluidized bed with carbon feed
Is recovered, and then the zinc residue is recovered by distillation using a tube furnace or the like in which an inert gas is flown.

That is, the two-step process is sequentially performed as another process. However, in such a method, (3) the iron recovery process and the zinc recovery process are separated separately, and the workability is poor, and the productivity of the recovery system is
The efficiency such as energy efficiency was poor.

[0009]

DISCLOSURE OF THE INVENTION The present invention solves the above problems, namely, (1) when recovering metallic zinc and metallic iron from dust containing zinc and iron, in one system at the same time. It is possible to reduce and recover zinc metal and iron (2), and both the zinc reduction rate and the iron reduction rate are
It is an object of the present invention to provide a method capable of simultaneously increasing the productivity and ensuring (3) high productivity.

[0010]

Means for Solving the Problems As a means for solving the above problems, the present invention uses a reactor comprising two particle circulation type fluidized beds, and (a) uses zinc in the first particle circulation type fluidized bed. Dust containing iron is charged, the exhaust gas from the second particle circulation type fluidized bed is secondarily combusted, and the gas is used as the fluidizing gas to reduce and vaporize zinc oxide, and to contain reduced and vaporized zinc. The carryover gas and the carryover dust from the first particle circulation type fluidized bed are separated, the carryover gas is cooled and dust is collected to recover metallic zinc, and (b) the carryover dust is circulated in the second particle. Feeding to the fluidized bed, second
The reducing gas is fed as a fluidizing gas to the particle circulation type fluidized bed of No. 3 to reduce the iron content and recover the iron. A method for recovering metallic zinc and metallic iron from dust containing zinc and iron.

And, preferably in the above method,
The operating temperature of the second particle circulation type fluidized bed is 600 ° C. or higher and 900 ° C. or lower, and the degree of oxidation of the fluidizing gas is 40% or lower,
And, the operating temperature of the first particle circulation type fluidized bed is set to 1200.
It is suitable to set the degree of oxidation of the fluidizing gas to 30 ° C or higher at a temperature of ℃ or higher.

[0012]

In order to solve the above-mentioned problems, the inventors of the present invention arranged the particle circulation type fluidized bed reducing apparatus as disclosed in Japanese Patent Laid-Open No. 3-215621 in two stages in succession. It was proposed to solve the above problems by using the fluidized bed. That is, in order to simultaneously reduce and recover metallic zinc and metallic iron from dust containing zinc and iron, (a) since the boiling point of zinc is lower than the boiling point of iron under normal pressure, zinc is recovered as zinc vapor. It is practical to recover iron as solid metallic iron.

(B) In order to recover zinc as zinc vapor, the temperature in the furnace is set to the boiling point of metallic zinc (1180 at 1 atm).
It is necessary to maintain the temperature higher than (° C). (C) However, when iron oxide in dust is also reduced under such a high temperature condition, the reduced metallic iron easily sinters in the fluidized bed furnace and significantly impairs fluidity in the furnace. Therefore, the operation cannot be continued.

(D) Further, sintering of metallic iron does not occur 8
Since zinc does not vaporize under the conditions of around 00 ° C, zinc cannot be separated and recovered as zinc vapor. From the above, by using at least two fluidized bed furnaces, the temperature in the furnace and the degree of oxidation of the gas in the furnace are independently controlled for each fluidized bed furnace, so that a powdery iron-based oxide containing zinc oxide is obtained. The most preferred method is to recover zinc and metallic iron by separating them from dust.

That is, according to the above method,
(1) By adopting a particle circulation type fluidized bed, the flow velocity of the fluidizing gas can be increased with respect to the particle diameter,
The productivity can be improved, and the amount of the reducible substances scattered as dust can be extremely reduced due to the particle circulation function, and the yield can be expected to be improved. The exhaust gas of the particle circulation type fluidized bed can be effectively used as the first fluidizing gas, and (3) the reduction temperature can be reduced by arranging the particle circulation type fluidized bed in two stages.
It was confirmed that the reduction rate of zinc oxide and the reduction rate of iron oxide can be optimized independently by making the reducing ability of reducing gas different and forming the fluidized bed reducing space separately. It is a thing.

The operation of the present invention will be described more specifically with reference to FIG. FIG. 1 is a diagram schematically showing the basic structure of a particle circulation type fluidized bed reduction furnace consisting of two stages according to the above idea. It is composed of a first fluidized bed 10 and a second fluidized bed 20. The first fluidized bed 10 is a reduction vaporization furnace for reducing and vaporizing zinc oxide in dust. The raw material dust is charged through the raw material charging port 12, and the zinc oxide in the dust is a high-temperature reducing gas introduced through the gas introducing port 13 (this gas is a secondary gas of the exhaust gas of the second fluidized bed 20 as described later). The gas that has been burned) is reduced and vaporized in the riser 11. The dust that has flown out of the riser 11 is separated from the reducing gas by the particle trap 14 and is supplied again into the riser 11 through the downcomer 15. On the other hand, the vaporized zinc vapor is discharged out of the system together with the reducing gas and is recovered by the zinc recovery device 40. On the other hand, the dezinced dust is discharged from the discharge port 16 and sent to the second fluidized bed 20.

The second fluidized bed 20 is a fluidized bed reduction furnace for reducing iron oxide in the dust. The semi-reduced dust dezincified by the first fluidized bed 10 is charged through the raw material charging port 22. This dust is fluidized in the riser 21 by the gas introduced through the reducing gas inlet 23 and reduced until it becomes metallic iron, and is discharged and collected outside the system through the outlet 26.
The ore jumped out from the riser 21 is separated from the reducing gas by the particle collecting device 24, and again passed through the downcomer 25 to the riser 2
Supplied within 1.

Here, the exhaust gas of the second fluidized bed 20 is secondarily burned by the air and oxygen-containing gas supplied from the secondary combustion lance 30, and the degree of oxidation and the temperature are adjusted according to the zinc content of the raw material dust. Is carried out and sent to the first fluidized bed 10. The exhaust gas of the first fluidized bed 10 is a gas containing zinc vapor in which zinc oxide in the raw material dust is reduced and vaporized, and the zinc vapor in the exhaust gas is separated by the zinc recovery device 40 and recovered as metallic zinc. To do. This zinc recovery device is
Any ordinary zinc recovery device such as a bag filter may be used.

That is, in the second fluidized bed 20,
In the first fluidized bed 10, the iron oxide in the dezincified semi-reduced iron-based dust charged from the first fluidized bed 10 is reduced by a reducing gas having a low oxidation degree (high reducing power) as much as possible. Reduces the reduction of iron oxide and performs reduction with a reducing gas having an oxidation degree that actively reduces and vaporizes zinc oxide.

Here, the degree of oxidation of the reducing gas is defined by the degree of oxidation = (% CO ₂ +% H ₂ O) / (% CO +% CO ₂ +% H ₂ +% H ₂ O) (1) To be done. The inventors of the present invention also extensively investigated dust sintering troubles containing zinc and iron during fluidized bed reduction, which are essential for the realistic functioning of this system. As a result, the following (a) to (d) were found.

(A) The sintering trouble in the fluidized bed reduction of zinc-containing dust is caused by the formation of metallic iron on the particle surface, as in the case of the reduction of iron ore. (B) Further, even when metallic iron is produced, if the temperature in the fluidized bed is 900 ° C. or less, the furnace operation can be continued without causing sintering by the produced metallic iron. (C) Furthermore, if the temperature in the fluidized bed is 600 ° C. or lower, the reaction rate becomes extremely slow.

(D) In the above temperature range, SiO is contained in the dust.
₂ and CaO, Al ₂ O ₃ , MgO, MnO, etc. due to the fact that they contain a large amount of oxides that are more difficult to reduce than iron.
When reducing dust that does not contain a large amount of such oxides, sintering is prevented by using unreduced particles such as sand in the fluidized bed as the fluidizing medium even under the same conditions as in (b) to (c) above. can do. In this case, as the non-reduced particles such as sand, those having a particle size of 1 mm or less and 100 mesh or more are preferable.

Next, FIG. 3 shows Zn in consideration of zinc vapor pressure.
The results of the study by the inventors of the present invention regarding (g) and the stable region of ZnO are summarized. That is, in order to reduce zinc oxide in dust to metallic zinc, (a) reduction with a gas having a lower oxidation degree than that of the reducing gas in the reduction reaction of ZnO + CO → Zn + CO ₂ shown in FIG. There is a need to do.

(B) Further, in order to vaporize and recover the reduced metallic zinc as zinc vapor, it is necessary to maintain the temperature of the furnace higher than the boiling point of zinc. The boiling point of zinc is 1 under normal pressure.
It is 180 ° C. As mentioned above, when iron oxide in the dust is reduced and metallic iron is produced at a temperature at which metallic zinc vaporizes, sintering trouble occurs.

That is, in the first fluidized bed 10, it is necessary to positively reduce zinc oxide and suppress the reduction of iron oxide to the reduction to FeO. Since FeO is an oxide, it is extremely difficult to sinter, and if the reduction is limited to the FeO stage, the problem of sintering is solved. In FIG. 3, FeO + CO → Fe +
The CO ₂ reduction reaction line is also shown. In the operating region of the first fluidized bed 10 in which zinc oxide is positively reduced and iron oxide is reduced to reduction to FeO, the partial pressure of zinc vapor is 0.
The case of 1 atm is shown by hatching in FIG. This range is the proper operating condition of the fluidized bed 2.

In this case, it is apparent that the proper operating range changes depending on the partial pressure of zinc vapor. The partial pressure of zinc vapor may be analyzed by chemical analysis by collecting the gas in the first fluidized bed 10 at a high temperature of 1200 ° C. or higher,
Alternatively, the material balance may be calculated for the fluidized bed 10 and estimated from the value. Further, the exhaust gas temperature of the second fluidized bed 20 is about 500 to 850 ° C., and the degree of oxidation is 10 to 50%. Even when this gas is directly introduced to the first fluidized bed 10 and used for reducing zinc-containing dust. Zinc cannot be vaporized.

Therefore, by secondarily burning the exhaust gas of the second fluidized bed 20 with oxygen or air, the temperature of the gas introduced into the first fluidized bed 10 is 1200 ° C. or higher and the degree of oxidation of the introduced gas is 30. % Or more so that the conditions suitable for reduction and vaporization of zinc in zinc-containing dust can be achieved. However, even in this case, SiO in the dust
₂ and CaO, Al ₂ O ₃ , MgO, MnO, and many other oxides that are more difficult to reduce than iron are included. Also, as described below, iron oxides are reduced to FeO as well, so that they do not cause sintering and zinc oxides. Can be reduced and evaporated, but it is more preferable to use non-reduced particles such as sand as a fluid medium in the fluidized bed in order to prolong the residence time of dust in the fluidized bed. As described above, the particle size of this fluid medium is preferably 1 mm or less and 100 mesh or more.

Similarly, the proper operating range in the second fluidized bed 20 can be defined. In the second fluidized bed 20, iron oxide FeO must be reduced to metallic iron. That is, it is necessary to operate below the reduction reaction line of FeO + CO → Fe + CO ₂ in FIG. 3, and at the same time, it is necessary to operate below 900 ° C. to prevent sintering, as described above.

Further, with respect to zinc, it is preferable to stay in ZnO without being reduced to metallic zinc. That is, in the case where the partial pressure of zinc vapor is 0.1 atm, the range indicated by the spotted region in FIG. 3 is the proper operating condition of the fluidized bed 1. Even in this case, it is clear that the proper operating range changes depending on the partial pressure of zinc vapor. Summarizing the above, as preferable operating conditions, the operating temperature of the first particle circulation type fluidized bed is 600 ° C. or more and 900 ° C. or less, the degree of oxidation of the fluidizing gas is 40% or less, and the second particle circulation type fluidized bed is used. Operating temperature of 1200 ℃ or more, the degree of oxidation of fluidized gas is 30%
That is all.

[0030]

EXAMPLE FIG. 1 shows a flow sheet of a fluidized bed reduction apparatus for carrying out the present invention. Table 1 shows the chemical composition of the electric furnace dust used in the test. Table 2 shows the particle size distribution of electric furnace dust. The specifications of the fluidized bed reduction apparatus are as follows.

Note 1) First fluidized bed (zinc oxide reduction furnace) tower diameter: 350
mm Tower height: 2000 mm Dispersion plate: Eye plate (opening ratio 0.2%) 2) Second fluidized bed (iron oxide reduction furnace) Tower diameter: 200
mm Tower height: 1500 mm Dispersion plate: Plate (opening ratio 0.5%) Table 3 shows the test conditions and test results when the electric furnace dust shown in Table 1 was treated by the method of the present invention. As a zinc-containing dust treatment method, a test was conducted under the operating conditions shown by the diagonal lines in FIG. In addition, as Example 2, a test was performed in the case where the degree of oxidation of the reducing gas introduced into the first fluidized bed was lower than that in Examples.

The test method is described below. The test method is the same for both Invention Example 1 and Example 2. 50g of raw material dust
While continuously supplying to the first fluidized bed 10 at a speed of min, semi-reduced dust was continuously discharged from the discharge port 16 at 40 to 55 g / min, and the dust retention amount in the riser 11 was 1.0 kg ( ± 10%). In this case, the average retention time of dust in the riser 11 is about 20 minutes.

The second fluidized bed 20 has a first inlet 22 and a first inlet 22.
Semi-reduced dust from the fluidized bed 10 of 40-55 g / mi
It is continuously fed at a rate of n. In the second fluidized bed 20, the reduced dust was continuously discharged from the discharge port 26 at a rate of 35 to 45 g / min, and the dust retention amount in the riser 21 was maintained at 0.4 kg (± 10%). The average residence time of dust in the riser 21 is about 10 minutes.

The reducing gas was supplied from the reducing gas inlet 23 of the second fluidized bed 20 at 70 Nl / min. The composition of the reducing gas is CO: N ₂ = 40: 60. By supplying oxygen from the secondary combustion lance 30, the second fluidized bed 20
The exhaust gas from the first fluidized bed was secondarily burned to adjust the degree of gas oxidation at the gas inlet 13 of the first fluidized bed 10.

In Example 1, the acid transfer rate was 4 to 5 Nl.
/ Min, and the degree of oxidation of the gas introduced into the first fluidized bed 10 was adjusted to 30%. In Example 2, the acid transfer rate was reduced to 2-3 Nl / min, and the degree of oxidation of the gas introduced into the first fluidized bed 10 was adjusted to 20%. Table 3 shows the test results
It was shown to. In Example 1, the operation could be continued without any sintering trouble. Further, the dust loss from the first fluidized bed 10 could be suppressed to about 3%, and zinc could be recovered with a high efficiency of about 95%.

On the other hand, in Example 2, a sintering trouble occurred in the first fluidized bed 10 and the fluidized state became unstable. Therefore, the dust loss increased to 10 to 20%, and the zinc recovery efficiency was 50 to 65%, which was rather poor.

[0037]

[Table 1]

[0038]

[Table 2]

[0039]

[Table 3]

[0040]

Industrial Applicability According to the present invention, powdery zinc-containing dust can be directly processed without pelletization, and zinc and iron can be independently recovered with high efficiency.

[Brief description of drawings]

FIG. 1 is a flow sheet of a fluidized bed reducing apparatus for carrying out the present invention.

FIG. 2 is a skeleton diagram showing the basic structure of a particle circulation type fluidized bed.

FIG. 3 is a graph showing stable regions of oxides and metals of zinc and iron.

[Explanation of symbols]

 1, 11, 21 Riser 2, 12, 22 Raw material charging port 3, 13, 23 Gas inlet 4, 14, 24 Particle collector 5, 15, 25 Downcomer 10 First fluidized bed 20 Second fluidized bed 30 Secondary combustion lance 40 Zinc recovery device

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shoji Miyagawa 1 Kawasaki-cho, Chuo-ku, Chiba City Kawasaki Steel Co., Ltd. Technical Research Division (72) Inventor Hiroshi Itaya Kawasaki-cho, Chuo-ku, Chiba Kawasaki Steel Co., Ltd. Research headquarters

Claims (2)

[Claims] 1. A reactor comprising two particle circulation type fluidized beds is used, in which dust containing zinc and iron is charged into the first particle circulation type fluidized bed, and the second particle circulation type fluidized bed is used. The secondary combustion gas of the exhaust gas is used as a fluidizing gas to reduce and vaporize zinc oxide, and carry over gas and carry over dust from the first particle circulation type fluidized bed containing the reduced and vaporized zinc. The carrier gas is cooled, the carry-over gas is cooled and dust is collected to recover metallic zinc, the carry-over dust is supplied to the second particle circulation type fluidized bed, and the reducing gas is supplied to the second particle circulation type fluidized bed. A method for recovering metallic zinc and metallic iron from dust containing zinc and iron, which comprises feeding in as a fluidizing gas to reduce iron and recovering iron. 2. The operating temperature of the second particle circulation type fluidized bed is 600 ° C. or more and 900 ° C. or less, and the oxidization degree of the fluidizing gas is 4 or less.
The zinc-containing dust according to claim 1, wherein the operating temperature of the first particle circulation type fluidized bed is 1200 ° C. or higher, and the degree of oxidation of the fluidizing gas is 30% or higher. Recovery method of zinc and iron.