JPH08325646A - Treatment of dust of electric furnace - Google Patents

Abstract

PURPOSE: To efficiently recover valuable metal in a high yield by reducing dust of an electric furnace with carbon base solid reducing agent, recovering molten iron having Fe as the main component, dividing the vaporized Zn into low content dust and high content dust and recovering. CONSTITUTION: The carbonaceous material is charged into a vertical type fusing furnace 1 from a hopper 2 to form a reducing agent packing layer 3. In hear, the dust of the electric furnace is injected from upper step tuyeres 1u and hot blast at about 800-1000 deg.C is blown from lower step tuyeres 1s and reduced. By thus method, the dust containing produced Zn vapor is discharged into a hopper 8 and the molten iron containing Cr, etc., from an iron tap hole 6, and slag fixing harmful Cd, etc., from a slag tapping hole 7, are recovered. Besides, the dust is separated with a cyclone and a part of the low Zn-containing dust is returned back to the fused furnace 1 and the other part is recovered through a hopper 12. Further, the high Zn-containing dust is formed to slurry 16 by a water spraying means 15 in a cooling vessel 14 and shifted to a dehydrator 20 through a precipitator 23 to obtain a dehydro-cake having 50-80% Zn, desirably about 60-80%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a vertical melting furnace having two upper and lower tuyeres having a packed bed of a carbon-based solid reducing agent to efficiently produce effective resources, especially zinc, from electric furnace dust. It is about to be collected.

[0002]

2. Description of the Related Art In recent years, it has been desired to recycle iron scrap from the viewpoint of resource recycling and energy saving, but the quality of iron scrap varies greatly depending on its source.

[0003] For example, self-generated scrap is iron scrap generated in the steel manufacturing process, and most of it is consumed in the generation plant because its identity is clear and impurities are little mixed.

On the other hand, the secondary processing scrap and the abolished scrap are those which are separated and collected during the secondary processing of the steel product and in the process of reaching the final product, and include the surface treated steel plate and the special steel. It contains a lot of scraps.

Most of these are usually refined and reused by electric furnace manufacturers, but in the electric furnace dust generated at that time, chromium, cadmium, lead, etc.
When it is disposed of in landfill, it contains several% of elements that elute and cause environmental pollution, zinc content of 10-40% and iron content of 25-50%. That is, there has been a strong demand for establishment of a technique for fixing harmful metals such as chromium, cadmium, and lead at low cost and enabling recovery and recycling of valuable metals such as zinc and iron.

In this regard, the technique disclosed in Japanese Examined Patent Publication No. 59-18452 is used, in which a vertical smelting reduction furnace having upper and lower tuyeres is used and powdered ore is blown from the upper tuyeres of the furnace. Can be considered.

When electric furnace dust is blown in from the upper tuyeres, the zinc oxide contained therein is reduced to Zn vapor, which is discharged from the furnace top through the carbon-based solid reducing agent. As a post-stage facility for the vertical smelting reduction furnace, a dust collector such as a cyclone or a cooling tank (an indirect cooling type cooling tank that does not directly contact the object to be cooled such as dust or exhaust gas with a coolant such as cooling water), a bug When a filter or the like is arranged, the following problems cannot be avoided.

1) Jump out from the smelting reduction furnace together with the exhaust gas
When dust mainly composed of Zn is passed through an indirect cooling type cooling tank,
Zn-containing dust adheres to the surface of the cooling water pipes and the inner wall of the cooling tank and is difficult to peel and remove. In addition, when the adhered matter grows over time and becomes clumped, the dust cannot be discharged smoothly. 2) In the indirect cooling type cooling tank, if a large amount of Zn-containing dust adheres to the cooling water pipes placed inside the cooling tank and the inner wall of the cooling tank, the flow passage area of exhaust gas will decrease and the pressure loss in the system will increase, resulting in operation. Becomes unstable. 3) In the indirect cooling type cooling tank,
If a large amount of dust adheres to the cooling water pipe, the cooling efficiency of the dust and the exhaust gas is significantly reduced, and the temperature of the exhaust gas rises, causing problems such as damage to the bag filter and the exhaust device.

[0009]

SUMMARY OF THE INVENTION The present invention proposes a new method for treating electric furnace dust without causing the above-mentioned conventional problems.

That is, the object of the present invention is to make it possible to stably transport the dust mainly containing Zn discharged from the vertical reduction furnace to the next step without adhering to the inside of the cooling tank and agglomerating. In addition, to prevent damage to the vacuum filter and discharge device due to the increase in pressure loss due to the adhesion of dust inside the cooling tank and the decrease in cooling efficiency, and to stabilize the operation,
Furthermore, we are proposing a method that makes it possible to recover and recycle valuable metals such as Fe and Zn with a high yield.

[0011]

The present invention is directed to treating vertical electric furnace dust with a vertical melting furnace having two upper and lower tuyeres equipped with a carbon-based solid reducing agent packed layer. Powdered electric furnace dust is blown from at least the upper tuyeres of the furnace to reduce and evaporate the zinc content contained in the electric furnace dust. At the exit side of the vertical melting furnace, first, a low zinc content is contained. A method for treating electric furnace dust, characterized in that the dust is recovered by a cyclone, and then water spray is applied in the cooling tank to recover the high zinc concentration-containing dust as slurry dust. A pump is placed at the slurry dust outlet inside to transport the slurry dust to the settling tank, and the slurry dust with a high Zn content at the bottom of the settling tank is dehydrated using a dewatering device to a slurry concentration of about 50-80%. age It recovered as dehydrated cake. In addition, in the present invention, in order to stabilize Zn vapor, it is preferable to perform secondary combustion of the exhaust gas before applying water spray, particularly in a duct connected to the top of the vertical melting furnace.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to the drawings. FIG. 1 shows the configuration of equipment suitable for treating electric furnace dust. A vertical melting furnace 1 is provided with a packing layer 3 which is supplied from a carbon material hopper 2 and maintains a predetermined stock line at the furnace top.

In the electric furnace dust, limestone added for the purpose of adjusting the viscosity and melting point of slag and a smelting solvent composed of silica are mixed in a predetermined ratio in advance, and the powder blowing device 4 is used to form a vertical mold. It is blown into the furnace through the upper tuyere 1 _U of the melting furnace 1.

The blown air is heated to about 800 to 1000 ° C.,
The upper tuyeres 1 as hot air through the air duct _UAnd lower tuyeres 1
_SEach is blown into the furnace. At that time, if necessary
Then, an appropriate amount of oxygen is supplied into the hot air,
The carbonaceous material is burned in the air, but the heat of combustion and reducing gas at that time
By upper tuyeres 1_UElectric furnace dust blown from the
Will melt.

Then, Zn oxide in the electric furnace dust is reduced to Zn vapor, which passes through the carbonized material packed layer 3 and is discharged from the furnace top. A secondary combustion lance 5 is arranged above the vertical melting furnace 1 to burn the exhaust gas so as to maintain the temperature of the upper portion of the packed bed 3 at 600 to 1000 ° C. which is the temperature at which Zn vapor is stabilized.

Further, the iron oxide in the electric furnace dust is melted in the tuyere raceway of the upper tuyere 1 _U by the combustion heat of the carbonaceous material together with chromium, cadmium, etc., and the resulting melt forms the carbonaceous material filling layer 3. It descends toward the lower tuyeres 1 _S , and in the process, it is countercurrently contacted with the reducing gas generated at the tuyere tips of the lower tuyeres 1 _S to be reduced, and during contact with the carbonaceous material of the packed bed 3 during the dropping. It is directly reduced and separated into metal and slag.

The molten metal finally accumulated in the hearth is discharged from the tap hole 6 and the slag is discharged from the slag port 7, respectively. At that time, chromium and the like are put into the molten metal and cadmium and the like are put into the slag. It is fixed and rendered harmless.

On the other hand, it was discharged from the upper part of the vertical melting furnace 1.
Dust mainly composed of Zn (including carbon and ash) first passes through the cyclone 8, where dust containing carbon particles of about 10 μm or more, which is relatively coarse and is generated from the carbonaceous material in the furnace, is collected in the dust. Most of the carbon content contained in is separated.

The dust (recovered dust) mainly composed of carbon separated by the cyclone 8 passes through the popper 9, a part of the dust is transferred from the dust transport device 10 to the inside of the furnace through the upper end tuyere 1 _U , and the rest of the dust is valved. 11. Dust is discharged to the outside of the system through the dust discharge popper 12 and the valve 13.

The fine dust that has not been collected by the cyclone 8 is a dust mainly composed of Zn, and is introduced into the cooling tank 14 together with the exhaust gas and cooled by the water spraying means 15 to form cooling water at the bottom of the cooling tank 14. Suspension becomes a slurry liquid 16.

The exhaust gas after dust removal and cooling reaches a temperature of 200 ° C. or less and is discharged to the outside of the system, but the slurry liquid 16 accumulated at the bottom of the cooling tank 14 is leveled by a level meter 17 and a flow control valve 18. Is adjusted and transported to the settling tank 23 by the slurry pump 19a, and then transported to the dehydrator 20 from the bottom of the settling tank 23 by the slurry pump 19b in a concentration range of 50 to 80%, more preferably 60 to 80%. Dehydration, then a slurry transport device 21, and a container 22 as a Zn enriched slurry
Is discharged to.

The waste liquid of the dehydrator 20 is sent to a settling tank 23 to settle solids such as dust contained in the waste liquid, and the treated water 24 from which most solids have been removed is passed through a water spray means 15 by a treated water pump 25. Circulate in the cooling tank 14.

In the present invention, the concentration of the slurry dust collected by the dehydrator 20 is set to 50 to 80% for the following reason.

That is, when the slurry concentration is less than 50%, the amount of dust contained in the waste liquid increases, which is disadvantageous in that the volume of the settling tank 23 increases and the occurrence of troubles such as dust clogging in the water spray means 15 is avoided. On the other hand, if the concentration of the slurry dust exceeds 80%, the load on the slurry transporting device 21 increases and the transport pipe is clogged.

FIG. 2 shows the structure of a conventional electric furnace dust treatment facility. In the equipment shown in FIG. 2, the melting furnace 26 has basically the same configuration as that shown in FIG. 1 above, but after the cyclone 8, a heat exchange type cooling tank 27 and a bag filter 28 are arranged. Cooling tank
27 and a bag filter 28 are provided with valves 30a and 30b for supplying the dust collected there to the transportation device 29.

In such equipment, the exhaust gas containing dust introduced into the cooling tank 27 is cooled to about 200 ° C. or lower here, and the dust contained in the exhaust gas is removed, and then sent to the tap filter 28. However, as described above, there were various problems such as adhesion of Zn-containing dust in the cooling tank 27.

In the present invention, since the high zinc concentration-containing dust contained in the exhaust gas is collected in the cooling tank 14 as slurry dust, the adhesion in the cooling tank 14 and the agglomeration associated therewith are suppressed. It is possible to avoid troubles such as damage to the back filter and the discharging device.

In the present invention, the exhaust gas is secondarily burned before the water spray is applied. The reason for this will be described below.

A large amount of Zn vapor is contained in the exhaust gas in the treatment of electric furnace dust using a vertical melting furnace of the carbon material packed layer type, and Zn is contained in the duct passing through the exhaust gas.
It is feared that a large amount of dust mainly composed of ZnO and ZnO will adhere to it, causing operational troubles such as airflow obstruction frequently and making the operation in the melting furnace unstable.

As a result of various experiments and investigations in order to investigate such a cause, the following has become clear.

1) A large amount of deposits mainly composed of a mixture of ZnO and C are observed on the inner wall of the exhaust gas dust when the ventilation inhibition occurs. 2) Aeration inhibition always occurs when the exhaust gas temperature is low. 3) When the exhaust gas temperature is low, ZnO is more stable than Zn vapor even within the carbonaceous material packed bed, which is estimated to have high reducing properties. 4) Exhaust gas temperature and exhaust gas oxidation degree ((CO ₂ + H ₂ O) / (CO + CO ₂
+ H ₂ + H ₂ O)), the form of Zn present in the exhaust gas (Zn vapor or ZnO
) Is in the situation shown in FIG. 5) The Zn vapor pressure of the furnace top exhaust gas changes according to the Zn content of the electric furnace dust, but in the operating range that can be implemented in the present invention, it was measured by an exhaust gas mass spectrometer or collected by rapid aggregation of the collected gas. It is about 0.01 to 0.1 atm based on the chemical analysis value of aggregates and the value estimated from the collected gas.

From the above, in the operation of a vertical melting furnace (having a two-stage tuyere), in the exhaust gas duct at the top of the furnace
In order to stably operate the vertical melting furnace without causing operational troubles due to aeration of ZnO dust, it is necessary to use Zn vapor as the Zn existence form in the exhaust gas at the furnace top.

Here, in the operation using the equipment having the configuration shown in FIG. 1, even if the exhaust gas temperature at the furnace top is to be maintained under the condition that the Zn vapor is stable, the secondary combustion lance 5 alone is used in the initial operation. It is feared that it will fall below. For this purpose, as shown in FIG. 4, at least one of the exhaust gas ducts 31, 32 is provided with secondary combustion burners 33, 34 for ducts,
Burn exhaust gas.

The adhesion of dust in the exhaust gas ducts 31, 32 is detected by detecting the magnitude of pressure loss in the duct, by detecting the temperature change of a thermometer installed in the duct, or by measuring the outer surface temperature of the duct. It can be detected from the temperature change. Also, if a plurality of pressure gauge or differential pressure gauges p ₁ ~p ₃ in the longitudinal direction of the duct is provided to measure the internal pressure of the duct when it is necessary to specify the position adhering dust,
Alternatively, a plurality of thermometers t _{1 to} t ₄ may be installed and the outer surface temperature of the duct may be measured. With this, the generation state and position of the deposit on the duct can be grasped.

ZnO in the exhaust gas ducts 31 and 32 is adjusted by adjusting the amount of oxygen or the amount of air blown into the ducts 31 and 32 during secondary combustion of the exhaust gas to appropriately maintain the temperature of the exhaust gas and the degree of oxidation of the exhaust gas. However, the exhaust gas temperature that must be achieved by secondary combustion is determined by the exhaust gas temperature before secondary combustion and the partial pressure of Zn vapor in the exhaust gas, as shown in Fig. 3 above. Follow the conditions.

Although FIG. 4 shows the case where one secondary combustion burner is provided in each of the duct 31 and the duct 32, the number of secondary combustion burners installed can be increased or decreased according to the operating condition (Zn adhesion condition). The number of installations is not particularly limited.

When the temperature of the exhaust gas in the exhaust gas ducts 31, 32 before secondary combustion is, for example, 700 ° C., the degree of oxidation of the exhaust gas is 10%, and the partial pressure of Zn vapor in the exhaust gas at that time is 0.1 atm As is clear from FIG. 3, when the effect of increasing the degree of oxidation and the effect of increasing the exhaust gas temperature due to secondary combustion are taken into consideration, the exhaust gas temperature after secondary combustion is 1000 ° C. or higher.

Exhaust gas duct on the outlet side of the vertical melting furnace 1
The dust adhesion state and position are detected at 31, 32, and the exhaust gas temperature and the gas oxidation degree are adjusted so that the Zn vapor is stabilized while adjusting the combustion conditions by the secondary combustion burner based on the detection information. If the Zn in the exhaust gas duct
Adhesion of dust, mainly ZnO and ZnO, is suppressed, operation troubles and damage to refractories in the furnace can be avoided, and zinc in the dust can be recovered in a stable and high concentration for recycling. It will be extremely advantageous. The cooling tank 14 may be either a wet cooling tank or a dry cooling tank.

In the present invention, since the high zinc concentration-containing dust contained in the exhaust gas is collected as the slurry dust in the cooling tank 14, the adhesion in the cooling tank 14 and the agglomeration associated therewith are suppressed. Also, it is possible to avoid troubles such as damage to the air filter and the exhaust device, and further, by secondary combustion of the exhaust gas in the exhaust gas duct, the adhesion of dust mainly composed of Zn and ZnO in the exhaust gas duct is suppressed,
It is possible to avoid operational troubles and damages to the refractory in the furnace. In any case, zinc in dust can be recovered in a stable and high concentration, which is extremely advantageous for recycling.

[0040]

【Example】

Example 1 Using the equipment shown in FIG. 1 equipped with a melting furnace having a furnace diameter of 1.2 m, a height of 8.0 m, and three tuyeres at the top and bottom, the air flow rate was:
1650Nm ³ / hr, blast temperature: 900 ℃, enriched oxygen amount: 50-200N
m ³ / hr, blowing amount of dust: 600 to 800 kg / hr (mixing ratio: electric arc furnace dust 90%, solvent (limestone + Keiseki) 10%) under an electric arc furnace dust (T.Fe: 28.4 %, Zn: 29.9%, C
r: 0.27%, Pb: 2.05%, Cd: 0.04%, SiO ₂ : 2.91%, A
l ₂ O ₃ : 1.55, CaO: 1.23%, MgO: 0.38%, MnO: 2.36
%, Na ₂ O: 1.53, K ₂ O: 0.81%), and the operation status at that time was investigated. The results are shown in Table 1 together with the test conditions.

[0041]

[Table 1]

As is clear from Table 1, when the electric furnace dust was treated in accordance with the present invention, no trouble occurred in the cooling tank and thereafter, and high concentration Zn dust could be recovered.

Incidentally, the composition of the metal obtained in the melting furnace in this test operation was 90 to 93% Fe, 1 to 2% Si,
4.0-4.3% C, 0.8-1.2% Mn, 0.6-0.9%
Pig iron containing Cr, with 24-27% Si for slag
_{O 2, 16~24% Al 2 O} 3, 22~25% of CaO, 2.3 to 2.6 of the Mg
The composition was O 2, 5.7 to 6.8 MnO 2, and 0.01% or less of Cd.

Example 2 Using the vertical melting furnace shown in FIG. 4 having a furnace diameter of 1.2 m, a height of 8.0 m, and three tuyeres in the upper and lower stages, the electric furnace dust of After processing, the operation status at that time was investigated. The survey results are shown in Table 2 together with the test conditions.

[0045] Condition 1) blowing condition air volume: 1650 nm ³ / hr blast temperature: 900 ° C.-enriched oxygen amount: 50~100 Nm ³ / hr 2) Powder blowing conditions blending ratio: electric arc furnace dust 90% (composition embodiment Same as Example 1) Solvent (limestone + silica stone) 10% Injection rate: 650-750 kg / hr

[0046]

[Table 2]

As is clear from Table 2, when the electric furnace dust was treated according to the present invention, no trouble occurred in the exhaust gas duct, and it was possible to recover a high concentration of Zn dust.

The metal composition obtained in this example contains 90 to 93% Fe, 1 to 2% Si, 4.0 to 4.3% C, 0.8 to 1.2 Mn, and 0.6 to 0.9% Cr. Pig iron, for slag 24-27% SiO ₂ , 16-24% Al ₂
O _3, 22~25% of CaO, 2.3 ~2.6% of MgO, 5.7 ~6.8
% MnO 2 and 0.01% or less Cd.

[0049]

As described above, according to the present invention,
The powdery electric furnace dust can be processed as it is, and the separation and recovery of Zn dust and hot metal can be processed in a single vertical melting furnace, so the processing cost can be minimized. Further, Zn can be recovered from the electric furnace dust with high efficiency, and resources can be effectively used.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of equipment suitable for carrying out the present invention.

FIG. 2 is a diagram showing a configuration of a conventional electric furnace dust processing facility.

FIG. 3 is a diagram showing a relationship between exhaust gas temperature and exhaust gas oxidation degree.

FIG. 4 is a diagram showing another configuration of equipment suitable for carrying out the present invention.

[Explanation of symbols]

1 Vertical melting furnace 1u Upper stage tuyeres 1s Lower stage tuyeres 2 Carbon material hopper 3 Packing layer 4 Powder blowing device 5 Secondary combustion lance 6 Tapping port 7 Tapping port 8 Cyclone 9 Hopper 10 Dust transporting device 11 Valve 12 Dust discharge popper 13 Valve 14 Cooling tank 15 Water spraying means 16 Slurry liquid 17 Level meter 18 Flow control valve 19a Slurry pump 19b Slurry pump 20 Dehydrator 21 Slurry transportation device 22 Container 23 Settling tank 24 Treated water 25 Treated water pump 26 Exhaust gas duct 27 exhaust gas duct 28 the secondary combustion burner 29 secondary combustion burner 30 melting furnace 31 cooling bath 32 bag filter 33 transporter 34a valve 34b valve p ₁ ~p ₃ manometer t ₁ ~t ₄ thermometer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Itaya, 1 Kawasaki-cho, Chuo-ku, Chiba, Chiba Prefecture Technical Research Institute, Kawasaki Steel Co., Ltd. (72) Tetsuya Fujii 1 Kawasaki-cho, Chuo-ku, Chiba, Chiba Prefecture Kawasaki Steel Engineering Co., Ltd.

Claims (3)

[Claims] 1. When treating electric furnace dust with a vertical melting furnace having two upper and lower tuyeres equipped with a carbon-based solid reducing agent-packed layer, powder is obtained from at least the upper tuyeres of the vertical melting furnace. -Shaped electric furnace dust is blown in to reduce and evaporate the zinc content contained in the electric furnace dust. At the exit side of the vertical melting furnace, first, the low zinc concentration-containing dust is recovered, and then water spray is applied. A method for treating electric furnace dust, characterized in that the dust containing high zinc concentration is recovered as slurry dust by applying the above. 2. The method according to claim 1, wherein the slurry concentration after dehydration is 50 to 80%. 3. The method according to claim 1 or 2, wherein the exhaust gas is secondarily combusted before the water spray is applied.