JP3336167B2 - Electric furnace dust treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a vertical melting furnace having a tuyere with two upper and lower stages having a packed bed of a carbon-based solid reducing agent. Is to be recovered.

[0002]

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

[0003] For example, self-generated scrap is iron scrap generated in the process of producing steel. Most of the scrap is consumed in a generating plant because its identity is clear and there is little contamination with impurities.

[0004] On the other hand, secondary processing scraps and waste scraps are separated and recovered during the secondary processing of steel products and in the process up to the final product, and are made of surface-treated steel sheets and special steels. Contains a lot of scrap.

Many of these are usually refined and reused by electric furnace manufacturers, and the electric furnace dust generated at that time contains chromium, cadmium, lead, etc.
When landfilled, it contains several percent of elements that elute and cause environmental pollution, and contains 10-40% of zinc and 25-50% of iron. 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, a vertical smelting reduction furnace having two upper and lower tuyeres is used, and the application of the technique disclosed in Japanese Patent Publication No. Sho 59-18452 in which fine ore is blown from the upper tuyeres of the furnace. Can be considered.

When electric furnace dust is blown from the upper tuyere, zinc oxide contained therein is reduced to Zn vapor, which is discharged from the furnace top through the carbon-based solid reducing agent. Dust collectors such as cyclones and cooling tanks (indirect cooling type cooling tanks in which the cooling target such as cooling water does not come into direct contact with the objects to be cooled by dust and exhaust gas) When a filter or the like is arranged, the following disadvantages cannot be avoided.

1) Jumping out of 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 pipe or the inner wall of the cooling tank, making it difficult to remove and remove the dust. In addition, if the adhered matter grows with the passage of time and becomes aggregated, the dust cannot be discharged smoothly. 2) In the indirect cooling type cooling tank, when a large amount of Zn-containing dust adheres to the cooling water pipes and the cooling tank inner wall arranged inside the cooling tank, the flow path area of the exhaust gas is reduced and the pressure loss in the system increases, resulting in an increase 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 efficiency of cooling the dust and the exhaust gas is greatly reduced, so that the temperature of the exhaust gas rises and troubles such as damage to the bag filter and the discharge device occur.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to propose a novel method capable of treating electric furnace dust without causing the above-mentioned conventional problems.

That is, an object of the present invention is to make it possible to stably transport Zn-based dust discharged from a vertical reduction furnace to the next step without adhering and agglomerating inside the cooling tank. In addition, to prevent damage to the back filter and discharge device due to the increase in pressure loss due to dust adhesion inside the cooling tank and the decrease in cooling efficiency, and to stabilize the operation,
Furthermore, the present invention is to propose a method that enables valuable metals such as Fe and Zn to be recovered and recycled at a high yield.

[0011]

SUMMARY OF THE INVENTION The present invention provides an electric furnace dust using a vertical melting furnace having a bed of a carbon-based solid reducing agent and two upper and lower tuyeres, each of which blows air as hot air. In processing, the powdery electric furnace dust is blown with hot air from the upper tuyere of the vertical melting furnace, and hot air is blown from the lower tuyere to reduce and evaporate the zinc content contained in the electric furnace dust. At the same time, the exhaust gas is subjected to secondary combustion so as to maintain the temperature of the upper portion of the packed bed at 600 ° C. or higher, which is the temperature at which Zn vapor is stabilized, and at the outlet of the vertical melting furnace, first, a cyclone A method for treating electric furnace dust, comprising collecting dust having a low zinc concentration and then spraying water to collect dust having a high zinc concentration as slurry dust. With a pump at the outlet
The slurry dust is transported to the sedimentation tank, and the slurry dust having a high Zn content at the bottom of the sedimentation tank is dehydrated using a dehydrator to reduce the slurry concentration to about 50 to 80%, and is recovered as a dewatered cake. Further, in the present invention, the exhaust gas is preferably subjected to secondary combustion in a duct connected to the furnace top of the vertical melting furnace before water spraying is performed in order to stabilize the Zn vapor.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 shows a configuration of equipment suitable for treating electric furnace dust. The vertical melting furnace 1 is provided with a packed bed 3 which is supplied from a carbon material hopper 2 and maintains a predetermined stock line at the furnace top.

The electric furnace dust is prepared by mixing limestone and a smelting solvent made of silica stone at a predetermined ratio in advance to adjust the viscosity and melting point of the slag. It is blown into the furnace through the upper tuyeres 1 _U of the melting furnace 1.

The blowing air is heated to about 800 to 1000 ° C.
Upper tuyere 1 as hot air through blower tube _UAnd lower tuyere 1
_SFrom the furnace. At that time, if necessary
In the meantime, an appropriate amount of oxygen is supplied into the hot air,
Combustion of carbonaceous material, the combustion heat and reducing gas
By the upper tuyere 1_UElectric furnace dust blown from
Will melt.

[0015] Then, the Zn oxide in the electric furnace dust is reduced and becomes Zn vapor, passes through the carbon material packed bed 3, and is discharged from the furnace top. A secondary combustion lance 5 is disposed above the vertical melting furnace 1 and burns exhaust gas so as to maintain the temperature of the upper portion of the packed bed 3 at 600 ° C. or higher, which is the temperature at which Zn vapor is stabilized.

Further, the iron oxide in the electric furnace dust is melted in the tuyere tip raceway of the upper tuyere 1 _U by the heat of combustion of the carbon material together with chromium, cadmium, etc., and the resulting melt forms the carbon material packed layer 3. while being reduced down toward the lower tuyere 1 _S contacts the lower tuyeres 1 _S reducing gas countercurrently generated in tuyere in the process, in contact with the carbonaceous material filled layer 3 in the middle dropwise It is directly reduced and separated into metal and slag.

The molten metal finally collected in the hearth is discharged from the tap hole 6, and the slag is discharged from the slag port 7, in which case chromium and the like are contained in the molten metal and cadmium and the like are contained in the slag. Fixed and detoxified.

On the other hand, the water discharged from the upper part of the vertical melting furnace 1
Dust mainly composed of Zn (including carbon and ash) is introduced into the cooling tank 14 together with the exhaust gas, cooled by the water spray means 15 and suspended in the cooling water at the bottom of the cooling tank 14 to form a slurry liquid 16. However, when passing through the cyclone 8, dust containing relatively coarse carbon of about 10 μm or more generated from the carbon material in the furnace is collected, and most of the carbon contained in the dust is separated. You.

The dust mainly composed of carbon (recovered dust) separated by the cyclone 8 passes through the hopper 9, a part of which is transferred from the dust transport device 10 into the furnace through the upper tuyere 1 _U , and the remaining dust is supplied to the valve. 11. Can be discharged outside the system via dust discharge hopper 12 and valve 13.

The fine dust not collected by the cyclone 8 is mainly composed of Zn, and the fine dust mainly containing Zn is introduced into the cooling tank 14 together with the exhaust gas in the same manner as described above.
The slurry is cooled by 15 and suspended in the cooling water at the bottom of the cooling tank 14 to form a slurry liquid 16.

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

The waste liquid from the dehydrator 20 is sent to a sedimentation tank 23 to settle solids such as dust contained in the waste liquid, and treated water 24 from which most of the solids have been removed is passed through a water spray means 15 by a treated water pump 25. Circulate through 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, if the slurry concentration is less than 50%, the amount of dust contained in the waste liquid is increased, so that the volume of the sedimentation tank 23 is disadvantageously increased, and troubles such as dust clogging in the water spray means 15 are avoided. On the other hand, when the concentration of the slurry dust exceeds 80%, the load on the slurry transport device 21 increases, and there is a disadvantage that 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, but a cooling tank 27 and a bag filter 28 of a heat exchange type are arranged after the cyclone 8. Cooling tank
The bag filter 28 is provided with valves 30a and 30b for supplying the dust collected there to the transport device 29, respectively.

In such a facility, the exhaust gas containing dust introduced into the cooling tank 27 is cooled to about 200 ° C. or less, and is sent to the back filter 28 after removing the dust contained in the exhaust gas. As described above, there were various problems such as adhesion of Zn-containing dust in the cooling tank 27.

In the present invention, dust containing a high zinc concentration contained in the exhaust gas is recovered as slurry dust in the cooling tank 14, so that adhesion in the cooling tank 14 and agglomeration associated therewith are suppressed. In addition, damage to the back filter and the discharge device can be avoided.

In the present invention, the exhaust gas is subjected to secondary combustion before water spraying. The reason will be described below.

In the treatment of electric furnace dust using a carbon-filled bed type vertical melting furnace, a large amount of Zn vapor is contained in the exhaust gas, 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 adheres, causing frequent operation troubles such as impeded ventilation and making the operation in the melting furnace unstable.

As a result of repeated experiments and studies in order to find out the cause, the following has been clarified.

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) Inhibition of aeration always occurs when exhaust gas temperature is low. 3) When the exhaust gas temperature is low, ZnO is more stable than Zn vapor even in the carbon bed, which is assumed to be highly reducible. 4) Exhaust gas temperature and exhaust gas oxidation degree ((CO ₂ + H ₂ O) / (CO + CO ₂
+ H ₂ + H ₂ O)), the existence form of Zn in exhaust gas (Zn vapor or ZnO
) Is in the situation as 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 operation range practicable in the present invention, it was collected by measurement with an exhaust gas mass spectrometer or by rapid aggregation of the collected gas. From the chemical analysis value of the aggregate and the value calculated and estimated from the collected gas, it is about 0.01 to 0.1 atm.

In view of the above, in the operation of a vertical melting furnace (having two-stage tuyere), the furnace is operated in the exhaust gas duct at the top of the furnace.
In order to operate the vertical melting furnace stably without causing the operation trouble of obstruction of ventilation due to the adhesion of ZnO dust, it is necessary to use Zn vapor in the exhaust gas at the furnace top as Zn vapor.

Here, in the operation using the equipment having the configuration shown in FIG. 1, even if the temperature of the exhaust gas at the furnace top is to be maintained under the condition that Zn vapor is stable, the secondary combustion lance 5 alone does Is likely to fall below the threshold. To this end, as shown in FIG. 4, at least one of the exhaust gas ducts 31 and 32 is provided with secondary combustion burners 33 and 34 for the ducts.
Burn the exhaust gas.

The adhesion of dust in the exhaust gas ducts 31 and 32 is detected by detecting the magnitude of the pressure loss of 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 provided to measure the outer surface temperature of the duct, and thereby, the generation state and position of the deposit on the duct can be grasped.

During the secondary combustion of the exhaust gas in the exhaust gas ducts 31, 32, the amount of oxygen or the amount of air blown into the ducts 31, 32 is adjusted so that the temperature of the exhaust gas and the degree of oxidation of the exhaust gas are appropriately maintained, so that the ZnO in the duct is reduced. However, the exhaust gas temperature which must be achieved by the secondary combustion is determined by the exhaust gas temperature before the secondary combustion and the partial pressure of Zn vapor in the exhaust gas as shown in FIG. Follow the requirements.

FIG. 4 shows a case where one secondary combustion burner is provided in each of the ducts 31 and 32. However, the number of secondary combustion burners installed can be increased or decreased according to the operating conditions (Zn adhesion status). In particular, the number of installations is not limited.

When the exhaust gas temperature in the exhaust gas ducts 31 and 32 before the 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, the exhaust gas temperature after the secondary combustion is 1000 ° C. or more in consideration of the effect of increasing the degree of oxidation due to the secondary combustion and the effect of increasing the exhaust gas temperature.

Exhaust gas duct on exit side of vertical melting furnace 1
At 31 and 32, the dust adhesion status and position are detected, and the exhaust gas temperature and the degree of oxidation of the gas are adjusted so that Zn vapor is stabilized while adjusting the combustion conditions by the secondary combustion burner based on the detected information. The Zn in the exhaust gas duct
Adhesion of dust mainly composed of ZnO and ZnO is suppressed, and operational troubles and damage to the refractory inside the furnace can be avoided.Also, zinc in dust can be recovered stably and at a high concentration, so it can be recycled. This is extremely advantageous. The cooling tank 14 may be either a wet cooling tank or a dry cooling tank.

In the present invention, dust containing high zinc concentration contained in the exhaust gas is recovered as slurry dust in the cooling tank 14, so that adhesion in the cooling tank 14 and agglomeration accompanying the dust are suppressed. In addition, it is possible to avoid damage to the Baku filter and the discharge device, and furthermore, secondary combustion of the exhaust gas in the exhaust gas duct suppresses the adhesion of dust mainly composed of Zn and ZnO in the exhaust gas duct,
Operational troubles and damage to the refractories in the furnace can be avoided, and 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 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 each having upper and lower tuyeres was used.
1650Nm ³ / hr, blast temperature: 900 ° C, oxygen enrichment: 50-200N
Electric furnace dust (T.Fe: 28.4) under m ³ / hr, dust blowing amount: 600-800 kg / hr (mixing ratio: electric furnace dust 90%, solvent (limestone + silica stone) 10%) %, 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 apparent from Table 1, when the electric furnace dust was treated according to the present invention, no trouble occurred after the cooling tank, and high concentration Zn dust could be recovered.

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

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

Conditions 1) Blowing conditions Blowing amount: 1650 Nm ³ / hr Blowing temperature: 900 ° C. Oxygen enriched amount: 50 to 100 Nm ³ / hr 2) Powder blowing conditions Mixing ratio: electric furnace dust 90% (composition is practiced) Solvent (limestone + silica) 10% Blowing rate: 650 to 750 kg / hr

[0046]

[Table 2]

As is evident from Table 2, when the electric furnace dust was treated according to the present invention, no trouble occurred in the exhaust gas duct, and a high concentration of Zn dust could be recovered.

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

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

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

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

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

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Vertical melting furnace 1u Upper tuyere 1s Lower tuyere 2 Carbon material hopper 3 Packing bed 4 Powder injection device 5 Secondary combustion lance 6 Tap hole 7 Tap hole 8 Cyclone 9 Hopper 10 Dust transport device 11 Valve 12 Dust discharge hopper 13 Valve 14 Cooling tank 15 Water spray means 16 Slurry liquid 17 Level meter 18 Flow control valve 19a Slurry pump 19b Slurry pump 20 Dehydrator 21 Slurry transport 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 Tetsuya Fujii 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Engineering Co., Ltd. (56) References JP-A-5-320779 (JP, A) JP-A Heisei 6-264126 (JP, A) JP-A-62-192513 (JP, A) JP-A-62-182214 (JP, A) JP-A-5-271735 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C22B 1/00-61/00

Claims (3)

(57) [Claims] Claims: 1. A method comprising a packed bed of a carbon-based solid reducing agent ;
In processing electric furnace dust using a vertical melting furnace having two upper and lower tuyeres , each of which blows wind air as hot air, powder electric furnace dust is converted into hot air from the upper tuyere of the vertical melting furnace.
Both blow, the hot air from the lower tuyeres blow, reducing the zinc component contained in the electric arc furnace dust, along with the evaporating
The temperature at the top of the packed bed is the temperature at which Zn vapor stabilizes.
Exhaust gas is subjected to secondary combustion to maintain the temperature above 600 ° C.
On the outlet side of the vertical melting furnace, first, dust having a low zinc concentration is collected by a cyclone , and then water dust is applied to collect the dust having a high zinc concentration as slurry dust. Furnace dust treatment method. 2. The method according to claim 1, wherein the slurry concentration after dehydration is 50 to 80%. 3. The method according to claim 1, wherein the exhaust gas in the exhaust gas duct is subjected to secondary combustion before the step of applying the water spray.