JPH08260013A - Method for operating electric smelting furnace decreased in electrode consumption - Google Patents

Abstract

PURPOSE: To subjecting various kinds of oxide raw materials, such as dust and sludge, to electric furnace refining while maintaining the voltage between an electrode and a furnace bottom in an adequate range. CONSTITUTION: A tap voltage is increased or decreased in such a manner that the voltage (VT) between the electrode and the furnace bottom is kept in the range of 40 to 55V at the time of operating the electric smelting furnace to recover Ni-, Cr-contg. alloys by dissolving and reducing the oxide raw materials composed mainly of steel making dust and waste acid sludge. The supply rate of externally charged coke is so adjusted that the coke consumption unit attains <=350kg/ton. The compounding of CaO and SiO2 contents is so adjusted as to maintain the basicity (BS) of the slag at 2.4 to 3.0. These controls are executed simultaneously in parallel. As a result, the electric furnace operation which maintains the high productivity and electric power efficiency and is decreased in electric power consumption is made possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric smelting furnace for recovering metal by melting and reducing a raw material mainly composed of an oxide, and an operating method in which consumption of electrodes is reduced while maintaining high production capacity. Regarding

[0002]

2. Description of the Related Art In a smelter using a blast furnace, an electric furnace, a converter or the like, dust containing a metal component is generated during a raw material pretreatment step or during supply of raw material into the smelting furnace or during operation of the smelting furnace. It occurs in large quantities. Further, in a factory equipped with a surface treatment line, a large amount of sludge or the like is generated in a waste acid treatment process, a waste liquid treatment process or a water recycling facility. As one of the methods of treating the generated dust, sludge, etc., a method of manufacturing an alloy by using it as a raw material in a resistance heating type electric furnace with a buried electrode is adopted. In this type of electric furnace, the stability of the raw material composition is an important factor in stabilizing the furnace conditions, but in reality it is possible to avoid fluctuations in the furnace conditions during operation due to raw material circumstances or sudden troubles. I can't. As a result, there is a problem that abnormal consumption of the electrodes and increase in power consumption are caused. Therefore, for example, Japanese Patent Laid-Open No. 62-62
-21342, JP-B-63-5671, etc., the electrode length or the electrode tip position is estimated based on the electrical resistance index such as resistance and reactance from the electrode,
The operating conditions are controlled based on the estimation results.

[0003]

The method of stabilizing the operation to prevent abnormal consumption of the electrode is a situation in which stable resistance heating of slag is difficult due to fluctuations in raw material quality and furnace conditions even under strict raw material control. It is in. In particular, it is difficult to operate in a stable furnace condition in a factory that manufactures special steel or a large variety of small-lot steel types, a steel mill that uses various scraps as raw materials, or a factory that has various surface treatment lines. For this reason, the furnace condition is recovered by increasing the electric power load or by additionally adding a reducing agent in some cases.
However, these actions may rather cause a decrease in power efficiency, an increase in electrode wear, and the like. The present invention has been devised to solve such a problem, paying attention to the amount of electrode wear and the electrical characteristics in the furnace, and avoiding the situation where the amount of electrode wear increases by controlling operating conditions. This aims to operate the electric furnace in a stable furnace condition, reduce the consumption of the electrodes, and prevent the productivity from decreasing.

[0004]

In order to achieve the object, an electric smelting furnace operating method of the present invention is to dissolve and reduce an oxide raw material mainly containing steelmaking dust and waste acid sludge to obtain Ni,
In an electric smelting furnace for recovering a Cr-containing alloy,
It is characterized in that each control of (3) is executed in parallel at the same time. (1) electrode - while managing the voltage between the furnace bottom (V _T), when the voltage the voltage based on the amount of change (V _T) (V _T) drops below 40V increases the tap voltage of the current , Control to reduce the current tap voltage when the voltage (V _T ) rises to 55 V or higher (2) Coke basic unit calculated from the amount of briquette internal coke in the raw material blending process and the amount of external coke cut out during operation ( Based on CT), the coke intensity is 350k
Control for adjusting the amount of exterior coke supplied so as to be g / ton or less (3) The basicity (B _S ) of the slag estimated from the chemical analysis of the slag or the measured value of the electrical conductivity every predetermined time is 2.
Control to adjust the composition of CaO and SiO ₂ contents so as to maintain 4 to 3.0

Electrode-furnace bottom voltage (V _T ) is 40 to 55 V
After stabilizing within the range of, the voltage (V _T ) between the electrode and the bottom of the furnace is 5
It is preferable to increase the tap voltage within a range not exceeding 5V. The electrode - furnace bottom between the voltage (V _T) 40 to 55
After stabilizing within the range of V, if the power load is less than the target set value, the reduction state is judged from the analysis value during the slag of the previous charge (% Cr ₂ O ₃ ), and when it is judged that the reduction is good, the coke cutout is performed. When the reduction amount is determined to be poor, the desulfurization state is further determined from the actual value of the sulfur distribution ratio (% S) / [% S] of the previous charge, and when it is determined to be good desulfurization, the basicity is lowered. When it is determined that the desulfurization is poor, the current furnace conditions are maintained, and when the tap voltage is increased after the coke cutout amount is reduced or the basicity is decreased, the productivity is improved while suppressing the electrode consumption. Furnace operation becomes possible.

The present invention is an operating method suitable for a blast furnace type electric furnace, a blast furnace type electric furnace and the like as an electric smelting furnace, and particularly for an electric furnace equipped with a Zedaberg type self-baking electrode. In addition, iron oxides generated in smelting / smelting furnaces such as sintering furnaces, blast furnaces, electric furnaces, converters, etc. are used as oxide raw materials mainly of steelmaking dust and waste acid sludge, which are the raw materials of electric smelting furnaces. Dust as the main component is used. In addition, water recycling equipment and waste acid in the factory,
Sludges generated in the waste liquid treatment facility and other oxides containing iron oxides such as abrasive powder and grinding debris are also used as oxide raw materials in the refining method according to the present invention. In particular, the effect of the present invention becomes remarkable when the main raw material is an oxide generated in a factory that produces steel containing Ni, Cr and the like such as stainless steel and special steel.

[0007]

The present inventors investigated the influence of various operating conditions on the recovery of furnace conditions. As a result, increase the power load,
Depending on the case, even if the productivity can be recovered to some extent by adding the reducing agent, when the in-furnace resistance is out of the optimum range, the power efficiency is reduced and the electrode consumption rate is increased, resulting in a comprehensive Found that the negative side becomes large. For example, a decrease in furnace resistance means that the electrical conductivity of slag mainly increases and the residual amount of coke, which is a conductive substance, increases. It becomes easier for current to flow. As a result, the electrodes float in the current-controlled electric furnace. Therefore, the voltage between the bottoms of the furnaces rises, and the consumption of the electrodes increases. In the furnace condition at this time, since the electrode is not deeply immersed in the raw material layer, heat loss to the upper part of the furnace becomes large, and as a result, current efficiency and eventually productivity are lowered. Therefore, the present inventors have found that the voltage between the electrode and the bottom of the furnace (hereinafter referred to as the bottom-bottom voltage).
It was found that an optimal operating condition can be obtained when systematically controlling the power load that directly reflects on slag, the slag composition that reflects indirectly, and the coke supply amount. The power load can usually be controlled by the tap voltage.

Hereinafter, the influence of the electric power load, the coke basic unit, the slag composition and the like on the operating conditions will be described with reference to the flow sheets of FIGS. The first condition for reducing the amount of electrode consumption is the furnace bottom voltage. The bottom-bottom voltage is directly affected by the power load. That is, the power load can be adjusted by switching the tap voltage, and the inter-furnace voltage is determined by the slag composition and the amount of coke added at that time. The bottom-bottom voltage affects the electrode consumption and the productivity index as shown in FIG. That is, when the voltage between the bottoms of the furnaces is suppressed to 55 V or less, the amount of electrode consumption is significantly reduced. On the other hand, the productivity index, when expressed as the ratio of the solubility per tap time to the maximum dissolution rate, drops significantly at a bottom-bottom voltage that does not reach 40 V as seen in FIG.
That is, if the tap voltage is lowered and the current load is lowered, the productivity is low considering the melting capacity of the furnace, which is not preferable. Therefore, in the present invention, as shown in the flow chart of FIG. 1, when the inter-furnace voltage is less than 40 V, the tap voltage is increased to increase the power load, and conversely, the inter-furnace voltage exceeds 55 V. In some cases, the tap voltage is lowered to reduce electrode consumption.

In the present invention, a self-baking electrode is preferably used. For example, a Zedaberg type self-baking electrode is smelted while charging an electrode raw material 3 into an electrode case 2 equipped with a water-cooled cylinder 1 as shown in FIG. The electrode raw material 3 charged in the electrode case 2 becomes a paste 4 by heating and is baked in the holder 5. After the firing process, the electrode raw material becomes a sufficiently dense structure from the paste 6 during the firing process. The portion having this dense structure is called a firing point 7. When the firing of the raw material is not completed in the holder 5, that is, when the firing point 7 is not in the holder 5, the firing portion 8 coming out of the holder 5 is not sufficiently densified and reacts with oxygen in the air. The structure becomes coarse and brittle. The electrode composed of the firing part 8 having such a structure is extremely inferior in wear resistance, and becomes the red heating part 9 to form the slag 10 and the metal 1.
When it contacts 1, it is quickly consumed.

In an electric smelting furnace using this self-baking electrode,
When the voltage between the furnace bottoms becomes high, the whole including the electrode case 2 is controlled so as to rise. Therefore, when the electrode immersion depth becomes shallow, as a result, the temperature inside the holder 5 decreases, and a raw material having a structure that is not sufficiently densified is sent to the metal 11. Such a state appears when the voltage between the bottoms of the furnaces exceeds 55 V, and the amount of electrode consumption is sharply increased. The in-furnace resistance is influenced by the slag composition as described later, but depends on the coke addition amount. It is considered that the coke bed suspended in the slag layer has the optimum coke bed generation condition. In the present invention, by optimizing the coke intensity as the index, it is possible to stabilize the immersion depth of the electrode at an optimum level and to stabilize the inter-bottom voltage.

The basic unit of coke is set to 350 kg / ton-metal or less. Coke basic unit is 35
When it exceeds 0 kg / ton-metal, the electrode resistance is remarkably increased due to the decrease in the furnace resistance as shown in FIG. 6, and the distance between the furnace bottoms becomes large. As a result, the voltage across the furnace bottom rises, and the amount of electrode wear increases. Further, as a secondary phenomenon, the reduction of SiO _{2 in} the slag becomes active, and the electrode consumption increases due to the composition change of the slag, that is, the increase in basicity. Therefore, as shown in the flow chart of FIG. 2, by controlling the supply amount of the internal coke and the external coke,
Coke intensity below kg / ton-metal is maintained.
At this time, the lower limit value of the basic unit of coke is determined by the amount of oxide contained in the raw material used at that time, that is, the amount of carbon required for reduction. 3 units of coke
When the amount exceeds 50 kg / ton-metal, the cut-out amount of the exterior coke is reduced. Coke basic unit is 350 kg
In the case of / ton-metal or less, control is performed at least at the supply pitch interval of the exterior coke after a certain time has elapsed.

When the electrical conductivity of the slag is stabilized at a low level, the resistance heating efficiency is improved, melting with less electric power is possible, and as a result, electrode consumption is reduced. Further, the electrode during operation becomes difficult to float, and the distance between the bottoms of the furnaces does not increase, so that the voltage between the bottoms of the furnaces can be kept low. In order to reduce the electric conductivity, it is preferable that the slag has a low basicity [(CaO + MgO) / SiO ₂ ], and [(CaO + MgO) / SiO ₂ ] = 2.4 to
3.0 is the optimum range. As shown in FIG. 7, the basicity of the slag affects the relationship between the electric power load and the distance between the bottoms of the furnaces. When the basicity increases within a certain power load range, the distance between the bottoms of the furnaces tends to increase. Target furnace bottom voltage 40-55
In order to secure V, depending on the coke conditions, when the distance from the bottom of the furnace to the upper surface of the raw material, that is, the depth of the furnace is H, the distance between the bottoms of the furnace is 0 as an average value during operation from FIG. ．
It is necessary to set it to 4 to 0.6H. Also, in order to make the distance between the bottoms of this range, considering productivity,
The basicity is set to 2.5 to 3. under an electric power load of 75 to 90%.
It can be seen from FIG. 7 that the range should be set to 0.

When the basicity is less than 2.5, the electrode can move to a low position, but the resistance value of the slag itself is so high that the voltage between the bottoms of the furnace cannot be lowered so much that blowing up or the like occurs during operation. There is a strong tendency that the yield increases and the melting yield decreases. On the other hand, if the basicity exceeds 3.0, the electric conductivity is too high, so that the distance between the bottoms of the furnaces increases and the amount of electrode consumption increases. At this time, in order to reduce the amount of consumption, the power load must be significantly reduced. However, depending on the raw material circumstances, it is often the case that the ideal slab component cannot always be maintained. Therefore, it is important to finely adjust the basicity of the slag. Therefore, as shown in the flow chart of FIG. 3, the basicity [(CaO + M
When gO) / SiO ₂ ] is less than 2.4, CaO content is increased or SiO ₂ content is decreased. On the other hand,
When the basicity [(CaO + MgO) / SiO ₂ ] exceeds 3.0, the SiO ₂ component is increased or CaO is increased.
Reduce the ingredients. As a result, the basicity [(CaO + M
The slag composition is adjusted so that gO) / SiO ₂ ] is maintained in the range of 2.4 to 3.0. At this time, a CaO, SiO ₂ containing raw material is supplied as the adjusting material, and a flux of these components is supplied in some cases. In this case as well, this control is similarly performed after a certain time has elapsed.

The slag basicity during operation can be controlled by chemical analysis of slag samples. In addition, when the method of estimating the slag composition by measuring the specific electric conductivity, which the present inventors previously applied for, is adopted, it is possible to quickly respond. That is, basicity [(CaO + MgO) / SiO
₂ ] is reflected in an increase in electric conductivity, and conversely, a decrease in basicity [(CaO + MgO) / SiO ₂ ] is reflected in a decrease in electric conductivity of slag. Based on the result, the raw material supply for adjustment is determined. Here, in order to maximize the productivity, in the present invention, as shown in the flow chart of FIG. 1, the inter-furnace voltage (V _T ) is stabilized within the range of 40 to 55 V,
It is preferable to increase the tap voltage within a range in which the inter-furnace voltage (V _T ) does not exceed 55 V after a certain time has elapsed. That is, even when the voltage between the bottoms of the furnaces is stabilized within the range of 40 to 55V, the composition of the raw materials is different from the target, so that the voltage between the bottoms of the furnaces reaches the upper limit even within the range of 40 to 55V. Moreover, it is effective to constantly increase the tap voltage in order to improve productivity.

Further, the furnace bottom voltage (V _T ) is 40 to 55 V.
When the power load is below the target set value when stabilized within the range of, the reduction status of the previous charge is slagging (% Cr ₂ O
₃ ) Decrease the amount of coke cut out if it is not judged to be poor reduction from the analysis value. On the contrary, when it is determined that the return is defective,
In addition, the desulfurization status of the pre-charge was determined by the sulfur distribution ratio
[% S]) is used for the determination. Then, when it is not determined that the desulfurization is defective, the basicity is reduced. When it is judged that the desulfurization is poor, the current operating conditions are maintained. For example, it is assumed that the productivity required from the factory production situation at that time, that is, a tap voltage of 130 V or higher is required as judged by the power load. Here, the actual tap voltage is 13
If it is less than 0V, the slag (% Cr
_{If 2} O ₃ ) is less than 2.0%, it is determined that the reduction is good, and the coke supply amount is reduced. Further, if the sulfur distribution ratio ((% S) / [% S]) of the precharge is 30 or more, it is determined that the desulfurization is good, and the basicity of the slag is reduced.

As a result, it is possible to maintain the in-furnace resistance that constantly corrects the tap voltage upward while maintaining the target reduction and desulfurization refining reactions. Therefore, it is possible to reduce the amount of electrode wear while maintaining the refining ability above a certain level and the maximum productivity. Coke is supplied both internally and externally. As the exterior method, the raw material is supplied in a normal operation, and the raw material is added according to the decrease in the level of the charged raw material. Coke can be charged in various forms such as powder, granules, and lumps, but it is charged in the optimum form according to the characteristics of the electric furnace used and the particle sizes of the main and auxiliary raw materials. . As an interior method, a coke having an optimum amount and particle size is mixed with a binder in an oxide raw material, kneaded, and then formed into briquettes, pellets, etc., and subjected to heat treatment such as drying and sintering as necessary. To use. Alternatively, a material having a certain degree of strength after a curing period of several days is used as a charging raw material.

[0017]

【Example】

Example 1 (Charge No. 100) Electric furnace dust generated in a steelmaking plant producing various stainless steels, wet-collected converter dust, scales and the like were dehydrated by a filter press and dried by an internal combustion kiln. Further, the scale generated by annealing pickling of the stainless steel strip and the hydroxides recovered by precipitation aggregation in the waste acid treatment step were similarly dehydrated and dried. These oxide raw materials are
Mix with coke and binder and knead into briquettes
It was formed. The briquettes were cured for several days and then fed into a Zedaberg submerged electric furnace. As shown in Fig. 8, changes in tap voltage and hearth voltage during operation are judged from the hearth voltage at that time every 10 minutes, and if necessary, the voltage is switched, and the hearth voltage is set as a target. It was controlled so as to be in the range of 40 to 55V. On the other hand, the slag was sampled and analyzed every 20 minutes. Basicity based on the analysis result ((% CaO + MgO) / SiO 2) is 2.4 to 3.0
As the range of was adjusted with CaO and SiO ₂ containing feedstock. Further, the coke supply amount was adjusted so that the coke consumption rate was 350 kg / ton-metal with the external supply amount. The adjustment situation at this time is shown in FIG. FIG.
As can be seen from Fig. 3, the furnace condition was relatively stable, and the amount of electrode consumed by this charge until the final tapping was 7.1 kg / MWH per electric power.

Example 2 (Charge No. 101) The same raw materials as in Example 1 were used and the same operation was performed. In this case, it was judged from the inter-furnace voltage at that time every 10 minutes, the tap voltage was switched if necessary, and the inter-furnace voltage was controlled to fall within the target range of 40 to 55V. On the other hand, the slag was sampled and analyzed every 20 minutes.
Basicity ((% CaO + MgO) / Si based on analysis results
O ₂₎ is to be in the range of 2.4 to 3.0, was adjusted using CaO and SiO ₂ containing feedstock. In addition, the coke supply rate is 350 kg /
Adjusted to become ton-metal. Then, after stabilizing the inter-furnace voltage (V _T ) within the range of 40 to 55 V, the tap voltage was increased within a range where the inter-furnace voltage V _T did not exceed 55 V after a lapse of a certain time. . The adjustment status at this time is shown in FIG. In this case, the tap voltage was changed 140 minutes and 220 minutes after the start of energization. Even if the tap voltage is increased by 10 V at 140 minutes, the inter-furnace voltage (V _T ) is 5
It never exceeded 5V. However, at the 220th minute, the voltage between the bottoms (V _T ) was 5 due to the tap voltage rising by 10V.
It was expected to exceed 5V, so tap voltage should be 5V
Only raised. As a result, the inter-furnace voltage from the start to the end of energization changed from 47V to 55V as the electrode was raised. The amount of electrode consumed by this charge until the final tapping was 7.2 kg / MWH per electric power, which was only 0.1 kg / MWH higher than that in Example 1. On the other hand, the amount of tapped metal was 0.2 tons higher than that in Example 1.

Example 3 (charge Nos. 102 to 104) The same raw materials as in Example 1 were used and the same operation was performed. In this case, the inter-furnace voltage (V _T ) is stabilized within the range of 40 to 55 V, and after a certain time has elapsed, the inter-furnace voltage is 55 V.
The tap voltage was raised within the range not exceeding. here,
The target setting value of the power load was set at the tap voltage of 130 V by the current value control. When the voltage between the bottoms (V _T ) is stabilized and the power load is below the target set value, the pre-charge (10
Since the reduction status of 1) was judged to be good from the analysis value of 2.0% in the slag (% Cr ₂ O ₃ ), the amount of coke cut out was reduced. Furthermore, sulfur distribution ratio ((% S) / [% S])
Since the actual value of No. was 45 and the desulfurization status of the precharge was not determined to be poor, the basicity of the slag was lowered, and the tap voltage was increased within a range where the inter-furnace voltage did not exceed 55V.

As for the operating condition at this time, as shown in FIG. 10, the coke was reduced at 150 minutes and 250 minutes, and the tap voltage was changed after the supply of SiO ₂ . The voltage across the furnace bottom changed from 40V to 55V during this charge.
Moreover, the amount of the electrode finally consumed is 7.0 k per electric power.
It was g / MWH. In the next charge (103), when the voltage (V _T ) between the bottoms of the furnaces is changed within the range of 40 to 55V, if the power load similarly falls below the target set value of the tap voltage 130V, the previous charge (102). The reduction status of was judged to be defective from the analysis value of 2.5% or more in the slag (% Cr ₂ O ₃ ). Therefore, the desulfurization status of the pre-charge (102) is determined by the sulfur distribution ratio ((%
S) / [% S]). Since the actual value of the sulfur distribution ratio ((% S) / [% S]) was 40, it was not determined that the desulfurization was poor, so the basicity of the slag was reduced, and The tap voltage was raised within a range not exceeding 55V. Figure 11 shows the operating status at this time.
As shown in, the tap voltage was changed after supplying SiO ₂ at the 150th and 260th minutes. The voltage across the furnace bottom changed from 45V to 55V during this charge. The finally consumed amount of the electrode was 7.1 kg / MWH per electric power.

In the next charge (104), the inter-furnace voltage (V _T ) was stabilized within the range of 40 to 55V. At this time, similarly, when the power load falls below the target set value of the tap voltage of 135 V, the pre-charge (103) is slagging (%).
The analysis value of Cr ₂ O ₃ ) was 1.8% and the reduction was good, but the sulfur distribution ratio ((% S) / [% S]) was 23, and the desulfurization ability was slightly lowered. Therefore, the control to lower the basicity was not performed. As shown in FIG. 12, the operation status in this case was that the tap voltage was changed after the coke supply amount was reduced at the 190th minute and the 250th minute. The voltage between the bottom of the furnace changed between 40V and 55V during this charge. Also,
The final amount of electrode consumed was 7.2 kg / M per power.
It was WH. As described above, in the third embodiment, when the power load is lower, the coke supply amount and the basicity are adjusted based on the result of the precharge. By this control, it can be seen that the rise in the voltage between the bottoms of the furnaces is suppressed even when the electric load (tap voltage) is subsequently switched upward. Therefore, it was confirmed that the electrode consumption was suppressed and the high productivity was maintained even when operating in a high power load state.

Comparative Example 1 (Charge No. 120) Electric furnace dust generated in a steelmaking plant producing various stainless steels, wet-collected converter dust, scales, etc. were dehydrated by a filter press and dried by an internal combustion kiln. . Further, the scale generated by annealing and pickling the stainless steel strip and the hydroxides recovered by precipitation aggregation in the waste acid treatment step were similarly dehydrated and dried. These oxide raw materials were blended so that the slag composition was CaO / SiO ₂ = 2.8, kneaded with a coke and a binder, and formed into a briquette. The obtained briquette was cured for several days and supplied to a Zedaberg type electric furnace. The operating condition was that the electric load was set higher than in the examples, and the coke was supplied by the exterior method so that the basic unit of coke was 300 kg / ton-metal on average. The voltage between the bottoms of the furnace varied widely in the range of 40V to 59V with the rise of the electrode during the period from the start to the end of energization. In Comparative Example 1, the power load was not adjusted. The final amount of electrode consumed by this charge (120) was 9.2 kg / MWH.

Comparative Example 2 (Charge No. 121) The same oxide raw material as in Comparative Example 1 was used and the slag composition was CaO / Si.
It was blended so that O ₂ = 3.1, kneaded with a coke and a binder, and formed into a briquette. The obtained briquette was cured for several days and supplied to a Zedaberg type electric furnace. The average coke consumption during operation is 360 kg
A predetermined amount of coke was supplied by the exterior method so as to obtain / ton-metal. Then, the power load was controlled in the same manner as in the example, but the furnace bottom voltage was 51% from the start to the end of energization.
The voltage changed from V to 62 V, and the furnace bottom voltage could not be within the target range. Finally this charge (121)
The amount of electrode consumed in 13.0 kg was 13.0 kg / MWH, which was a large amount as compared with the examples. Table 1 shows the operation results in each of the above examples. As can be seen from Table 1, the operating method according to the present invention makes it possible to reduce the amount of electrode wear and to produce metal with high productivity.

[0024]

[Table 1]

[0025]

As described above, in the present invention, by controlling the operating conditions such as tap voltage, coke supply amount, slag basicity, etc. while maintaining the voltage between the electrode and the bottom of the furnace within an appropriate range. It is possible to reduce the amount of electrode wear and to operate the electric furnace in a stable furnace condition. for that reason,
Valuable metals are highly efficiently recovered from oxide raw materials such as scrap, steelmaking dust, sludge, polishing powder, and grinding dust.

[Brief description of drawings]

FIG. 1 is a flow of adjusting a tap voltage according to the present invention.

[Figure 2] Similarly, the flow for adjusting the coke intensity

[Fig. 3] Similarly, a flow for adjusting the basicity of the slag

FIG. 4 is a graph showing the influence of the bottom-bottom voltage on the electrode consumption and the productivity index.

FIG. 5 is a schematic diagram of a Zedaberg type self-baking electrode.

FIG. 6 is a graph showing the influence of the coke intensity on the fluctuation of the inter-furnace electrode and the bottom-furnace distance.

FIG. 7 is a graph showing the effect of electric power load on the distance between the bottoms of the furnaces.

FIG. 8 is a graph showing changes in tap voltage, coke intensity, and bottom-bottom voltage with time after the start of energization in Example 1.

FIG. 9 is a graph showing variations in tap voltage, slag basicity, coke intensity, and bottom-bottom voltage with time after the start of energization in Example 2.

FIG. 10 is a graph showing variations in tap voltage, slag basicity, coke intensity, and bottom-bottom voltage with time after the start of energization in Example 3.

FIG. 11 is a graph showing changes in tap voltage, slag basicity, coke intensity, and bottom-bottom voltage with time after the start of energization in Example 3 in which the tap voltage was increased.

FIG. 12 is a graph showing changes in tap voltage, slag basicity, coke intensity, and bottom-bottom voltage with time after the start of energization in Example 3 in which the tap voltage was changed after the reduction of coke supply.

[Explanation of symbols]

1: Water cooling case 2: Electrode case 3: Electrode raw material
4: Paste-like electrode raw material 5: Holder 6:
Paste during firing 7: Firing point 8: Firing part
9: Red heat part 10: Slag layer 11: Metal

Claims (3)

[Claims] 1. An electric smelting furnace for recovering an Ni-, Cr-containing alloy by melting and reducing an oxide raw material mainly composed of steelmaking dust and waste acid sludge, and simultaneously controlling each of (1) to (3). A method for operating an electric smelting furnace with reduced electrode consumption, which is characterized in that it is carried out in parallel. (1) electrode - while managing the voltage between the furnace bottom (V _T), when the voltage the voltage based on the amount of change (V _T) (V _T) drops below 40V increases the tap voltage of the current , Control to reduce the current tap voltage when the voltage (V _T ) rises to 55 V or higher (2) Coke basic unit calculated from the amount of briquette internal coke in the raw material blending process and the amount of external coke cut out during operation ( Based on CT), the coke intensity is 350k
Control for adjusting the amount of exterior coke supplied so as to be g / ton or less (3) The basicity (B _S ) of the slag estimated from the chemical analysis of the slag or the measured value of the electrical conductivity every predetermined time is 2.
Control to adjust the composition of CaO and SiO ₂ contents so as to maintain 4 to 3.0 2. The electrode-furnace bottom voltage (V _T ) is 40 to 55.
The method for operating an electric smelting furnace according to claim 1, wherein the tap voltage is raised within a range where the electrode-furnace bottom voltage (V _T ) does not exceed 55 V after stabilizing within the range of V. 3. An electrode-furnace bottom voltage (V _T ) of 40 to 55.
After stabilizing within the range of V, if the power load is less than the target set value, the reduction state is judged from the analysis value during the slag of the previous charge (% Cr ₂ O ₃ ), and when it is judged that the reduction is good, the coke cutout is performed. When the reduction amount is determined to be poor, the desulfurization state is further determined from the actual value of the sulfur distribution ratio (% S) / [% S] of the previous charge, and when it is determined to be good desulfurization, the basicity is lowered. The method for operating an electric smelting furnace according to claim 1, wherein when it is determined that the desulfurization is poor, the current furnace condition is maintained, and the tap voltage is increased after the coke cutting amount is reduced or the basicity is decreased.