JP2013001938A - Method for operating electric furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for operating an electric furnace with which an effective operation can be applied by adjusting a fluidity of slag with a simpler method than the conventional one.SOLUTION: In the method for operating the electric furnace 10 energized by applying three-phase alternating current into three electrodes 11, suspended in the electric furnace 10, the compositions of the slag 13 produced in the electric furnace 10 are periodically measured, and according to the measured compositions of the slag, the electrodes 11 are risen or lowered to control the current applied to the slag 13.

Description

  The present invention relates to a method for operating an electric furnace, and more particularly, an electric furnace that enables efficient operation by adjusting the fluidity of slag in ferronickel smelting, in which the composition of the slag has a large influence on the furnace condition. Related to the operation method.

  Conventionally, in electric furnaces used for the smelting of steel and non-ferrous metals, it has been a very important issue in terms of production efficiency and safety to adjust the fluidity of the slag produced as the raw material ore melts. It was.

  As a specific example, a general operation method of an electric furnace used for ferronickel smelting will be described using a three-phase AC electrode type electric furnace. First, in an electric furnace, a metal layer is present at the bottom, and a slag layer is present thereon. In this electric furnace, ore is charged on the slag layer in the electric furnace, and by using three electrodes that can be suspended in the electric furnace, the electric furnace is heated to reduce and melt the ore.

Here, the following two operation methods have been used in the reductive melting of ore with a conventional three-phase AC electrode type electric furnace.
(1) A method in which an electrode is immersed in a slag layer, a metal and slag are directly energized from the electrode, and ore is melted indirectly through slag by resistance heat generation (high current low voltage operation method).
(2) A method in which a certain distance is provided between the slag layer and the electrode, an arc is generated from the electrode, and the ore is melted directly by the heat of the arc (low current high voltage operation method).

  However, in the operation method (1), the temperature of the slag near the furnace wall also rises due to the heat convection of the slag to which heat is applied, and as a result, the fluidity of the slag near the slag hole becomes excessive. There is also a problem of melting the furnace wall bricks. On the other hand, in the operation method (2), since the ore is directly melted by the heat of the arc, the slag temperature near the furnace wall is difficult to rise, but the coating on the side wall of the electric furnace may become thick. There is a problem of causing trouble.

  In ferronickel smelting, the slag composition resulting from the raw material composition has a great influence on the furnace condition. On the other hand, the raw material composition may not be controlled due to the influence of raw material conditions and economic market conditions. The slag is usually extracted at 1500 to 1600 ° C. However, the slag composition resulting from the raw material composition cannot be optimized, and when the melting point of the slag rises, it becomes difficult to extract the slag. In this case, there is a possibility that the operating rate must be reduced due to the deterioration of the furnace condition. On the other hand, if the slag fluidity is excessive, the slag slag overflows in the extraction route, and there is a great risk in terms of safety including a steam explosion.

  In the operation of such an electric furnace, for example, Patent Document 1 discloses an operation method in which the current is adjusted by the slag bath resistance, and the arc resistance is controlled to be constant and stable operation is possible even if the slag composition varies. Proposed. However, in the technique described in Patent Document 1, it is necessary to measure the thickness of the slag layer necessary for calculating the slag bath resistance by powering off the electric furnace. Therefore, it cannot measure frequently and a response | compatibility of operation may be overdue with respect to a slag composition. Moreover, it is an indirect method of adjusting the current by calculating the furnace resistance from the slag composition, which takes a lot of work.

  Similarly, Patent Document 2 proposes an operation method in which the slag bath resistance is calculated from an approximate expression, the current is adjusted, the coating thickness is kept constant, and the refractory in the electric furnace is protected. . However, even the technique described in Patent Document 2 is an indirect method of adjusting the current by calculating the furnace resistance from the slag composition, which is very troublesome. Since the extraction of slag from the electric furnace is performed at any time, a simpler and more efficient method is required to reduce field work.

JP 2004-68048 A JP 2011-17032 A

  The present invention has been proposed in view of such circumstances, and the operation of an electric furnace capable of performing efficient operation by adjusting the fluidity of the slag by a simpler method than conventional methods. It aims to provide a method.

  As a result of intensive studies in order to achieve the above-described object, the inventors of the present invention grasped the slag fluidity from the slag composition and controlled the current supplied to the slag by raising and lowering the electrodes to control the slag. The present inventors have found that an efficient operation can be realized by adjusting the fluidity, thereby completing the present invention.

  That is, the electric furnace operating method according to the present invention is an electric furnace operating method in which a three-phase alternating current is applied to three electrodes suspended in the electric furnace to energize the slag generated in the electric furnace. The composition is periodically measured, and the electrode is moved up and down according to the measured composition of the slag, and the current supplied to the slag is controlled.

  According to the present invention, the fluidity of the slag can be adjusted by a simple method, so that the slag can be easily extracted and the safety can be improved, so that efficient operation can be performed.

It is a schematic diagram which shows the state at the time of the high current low voltage operation of a three-phase alternating current electrode type electric furnace. It is a schematic diagram which shows the state at the time of the low current high voltage operation of a three-phase alternating current electrode type electric furnace. It is a graph which shows transition to each value when setting secondary current is increased / decreased according to the slag basicity index | exponent accompanying the time passage of electric furnace operation. It is a graph which shows each transition of the difference (C) from the slag basicity index (A), slag iron quality (B), and slag amount appropriate value with time progress of electric furnace operation.

  Hereinafter, a specific embodiment to which the present invention is applied (hereinafter referred to as “the present embodiment”) will be described in detail with reference to the drawings. In addition, the operating method of the electric furnace which concerns on this invention is not limited to the following embodiment, Unless it changes the summary of this invention, it can change suitably.

  The electric furnace operation method according to the present embodiment is an electric furnace operation method in which a three-phase alternating current is applied to three electrodes suspended in the electric furnace and energized, and the slag composition is measured periodically. And the electric current supplied with respect to slag is controlled according to the composition of the measured slag. In particular, this electric furnace operating method can be suitably used for ferronickel smelting.

  Specifically, as a method of controlling the current to be supplied to the slag, the three electrodes suspended in the electric furnace are moved up and down to operate different currents to be supplied to the slag shown in FIGS. This is done by using different methods. First, the operation methods shown in FIGS. 1 and 2 will be described.

  As shown in FIG. 1 and FIG. 2, the electric furnace 10 is composed of a refractory, and a molten metal 12 layer and a molten slag 13 layer exist in the electric furnace 10, and a slag 13 layer exists. An ore (calcined ore) 14 covers the surface of. The ore 14 is charged into the upper part of the slag 13 layer in the electric furnace 10 from the ore chute. In addition, three electrodes 11 (for example, carbon electrodes) are suspended from the electric furnace 10. In this electric furnace 10, a three-phase alternating current is applied to immerse the three electrodes 11 to the slag 13 layer, and a resistance heat is generated by directly energizing the metal 12 and the slag 13 from the electrodes 11 (high current low voltage operation). Method), or by generating arc 17 from three electrodes 11 and melting ore directly by the heat of arc 17 (low current high voltage operation method), the slag temperature and metal temperature are set to predetermined temperatures, respectively. Thus, the metal 12 and the slag 13 are generated by reducing and melting the ore 14. The generated metal 12 and slag 13 are separated into a metal 12 layer and a slag 13 layer due to a specific gravity difference. The generated metal 12 is extracted through a metal hole 15, and the slag 13 is extracted through a slag hole 16.

  More specifically, the operation method shown in FIG. 1 is a high-current low-voltage operation, and the tips of three electrodes 11 suspended in the electric furnace 10 are immersed in a slag 13 layer so that the slag 13 and the metal are formed from the electrode 11. An electric current is directly passed through 12, and ore 14 is melted indirectly through slag 13 by resistance heating. In the case of this operation method, since the slag 13 is directly energized, the fluidity of the slag 13 can be improved. Therefore, when the fluidity of the slag 13 is deteriorated, the fluidity of the slag can be improved by performing this operation method, and the slag 13 can be satisfactorily extracted through the slag hole 16. In this operation method, the thickness of the coating layer attached to the furnace wall is reduced.

  On the other hand, the operation method shown in FIG. 2 is a low-current high-voltage operation, and the arcs 17 are generated from the electrodes 11 by providing a certain distance from the slag 13 layers at the tips of the three electrodes 11 suspended in the electric furnace 10. And ore 14 is melted directly by arc heat. In the case of this operation method, since the slag 13 is not directly energized, the temperature rise of the slag 13 can be suppressed. Therefore, when the fluidity of the slag 13 is excessive and overflows, the fluidity of the slag 13 can be lowered and the fluidity can be made moderate by performing this operation method. Note that this operation method acts in the direction in which the thickness of the coating layer attached to the furnace wall increases.

  As described above, the operation method shown in FIG. 1 and FIG. 2 has different currents applied to the slag 13, and the current for the slag 13 is controlled by properly using these operation methods. The fluidity can be adjusted. At this time, in the operation method of the electric furnace according to the present embodiment, the proper use of the operation method is determined according to the composition of the slag 13. That is, the composition of the slag 13 is periodically measured, and the above-described operation methods are selectively used by raising and lowering the three electrodes 11 suspended in the electric furnace 10 according to the measured composition of the slag 13. To control the current to be energized (set secondary current).

  In particular, in ferronickel smelting, the influence of the composition of the slag 13 on the furnace condition is great. Therefore, by measuring the slag composition and controlling the current to be supplied to the slag 13 according to the measured slag composition, the fluidity of the slag can be effectively adjusted and efficient operation is performed. be able to.

The composition of the slag 13 is extracted through the slag hole 16 at regular intervals during the operation of the electric furnace, and is periodically analyzed by the extracted slag 13. For example, Ni, Fe, MgO, SiO ₂ , CaO, Al ₂ O ₃ , S, P, Cr (all by mass%) and the like are representative as slag 13 composition analysis targets. The composition analysis of the slag 13 is not particularly limited, but is performed using, for example, a fluorescent X-ray analyzer.

  In the present embodiment, on the basis of the composition analysis result of the slag 13, in particular, elements that greatly affect the melting point of the slag 13 such as slag basicity and Fe quality are calculated, and three elements are calculated according to the calculated value. The electrode 11 is moved up and down to control the current. Moreover, you may make it consider the transition of a long-term ore compounding composition, etc.

Here, the slag basicity is a numerical value obtained by dividing MgO mass% in the slag component by SiO ₂ mass%, and affects the melting point, viscosity, etc. of the slag 13.

Specifically, for example, a state in which slag basicity, Fe (mass%), Al ₂ O ₃ (mass%) is rising or a state in which slag basicity is high due to long-term ore blending is assumed. In this state, the melting point of the slag 13 rises, the fluidity of the slag 13 deteriorates, and it becomes difficult to extract the slag 13 from the slag hole 16.

  Therefore, in such a case, control is performed so as to increase the current supplied to the slag 13 by lowering the three electrodes 11 and immersing the tip of the electrode 11 in the slag 13 layer. That is, the high current low voltage operation shown in FIG. 1 is performed. In this way, by directly passing current from the electrode 11 to the slag 13, the temperature of the slag 13 can be raised and the fluidity of the entire slag 13 can be improved.

On the other hand, in the state where slag basicity, Fe (mass%), Al ₂ O ₃ (mass%) are reduced, or in the state where slag basicity is low due to long-term ore preparation, the melting point of slag 13 is lowered. As a result, the fluidity of the slag 13 becomes excessive. If the fluidity of the slag 13 is excessive, the slag soot provided in the extraction path of the slag 13 overflows and the possibility of a steam explosion occurs.

  Therefore, in such a case, the three electrodes 11 are raised so that the tip of the electrode 11 is not immersed in the slag 13 layer, and the current supplied to the slag 13 is controlled to be low. That is, the low current high voltage operation shown in FIG. 2 is performed. In this operation, although the electrode lower part of the slag 13 is locally hot due to the arc heat, the temperature of the slag 13 in the vicinity of the side wall is unlikely to rise because the tip of the electrode 11 is not immersed in the slag 13. Thereby, the fluidity | liquidity of the whole slag 13 can be made low, a tapping speed can be eased, and extraction with high safety | security can be performed.

  FIG. 3 is a graph showing the relationship between the calculated value of slag basicity with the passage of time from the start of electric furnace operation of ferronickel smelting and the current (set secondary current) controlled according to the calculated value. When the slag basicity increases, the fluidity of the slag 13 deteriorates and it becomes difficult to extract the slag 13, so as shown in FIG. 3, the three electrodes 11 are lowered as the slag basicity increases. Control is performed such that the electrode 11 and the slag 13 layer are brought close to each other, and the current to be supplied to the slag 13 is increased.

  The adjustment of the rising and lowering of the three electrodes 11 is not limited to only two adjustments of whether or not the tip of the electrode 11 is immersed in the layer of the slag 13 as shown in FIG. 1 and FIG. What is necessary is just to make it raise or lower in steps according to a degree etc. That is, since the current supplied to the slag 13 can be controlled by the distance between the tip of the electrode 11 and the slag 13 layer, for example, when the slag basicity increases, By gradually immersing the electrode 11 (in a stepwise manner), control is performed so as to increase the current applied to the slag 13. On the other hand, when the slag basicity becomes low, the distance between the slag 13 layer (the surface of the slag 13) and the electrode 11 is gradually (stepwise) separated accordingly, so that the slag 13 Is controlled so as to reduce the current to be supplied.

  Further, when it is determined that the fluidity of the slag 13 is deteriorated in accordance with the slag composition, in addition to the current control by the lowering of the electrode 11, a reducing agent is added to lower the iron quality contained in the slag 13. You may do it. When the iron grade in the slag 13 is large, the melting point of the slag 13 is increased. Therefore, the melting point of the slag 13 can be lowered by adding a reducing agent to lower the iron quality, and the fluidity of the slag 13 can be more efficiently increased. The reducing agent is not particularly limited, and examples thereof include coal, coke, wood, and the like. Considering the handling at the time of charging, it is preferably used as granular coal, granular coke, wood pellets, and the like. .

  As described above in detail, the operating method of the electric furnace according to the present embodiment is the operating method of the electric furnace 10 in which three-phase alternating current is applied to the three electrodes 11 suspended in the electric furnace 10 and energized. The composition of the slag 13 generated in the electric furnace 10 is periodically measured, and the three electrodes 11 are moved up and down in accordance with the measured composition of the slag 13 to control the current supplied to the slag 13. According to this operation method, even in the ferronickel smelting in which the composition of the slag 13 has a high influence on the furnace condition, the fluidity of the slag can be adjusted easily and effectively. Accordingly, the slag 13 can be easily taken out through the slag hole 16, and the overflow of the slag 13 can be suppressed to optimize the amount of slag output (the output speed). It can be performed.

  1 operates in the direction in which the thickness of the coating layer attached to the furnace wall decreases, while in the operation method in FIG. 2, the thickness of the coating layer attached to the furnace wall increases. Act on. Therefore, by controlling the current passed through the slag 13 according to the slag composition, the thickness of the coating layer formed on the furnace wall can be optimized, and an excessive coating layer is formed on the side wall of the electric furnace 10. On the contrary, since the coating layer melts and becomes thin, it is possible to effectively prevent the furnace wall from being damaged during operation. Thereby, while maintaining the melting processing amount of the ore 14, more efficient operation can be performed, the durability of the electric furnace 10 can be improved, and the economic effect can be enhanced.

  Examples of the present invention will be described below, but the present invention is not limited to the following examples.

Example 1
The diameter of the horizontal cross section of the electric furnace is 17.5m, the height is 6.0m, the daily power is 700-850MWh / day, the number of electrodes is 3, the transformer capacity of the AC power supply is 65MVA, the average metal output is The operation was performed at about 150 to 250 ton / day and the slag tapping amount was about 1000 to 1400 ton / day.

  In Example 1, the slag composition is analyzed periodically using a fluorescent X-ray analyzer (MXF-2400, manufactured by Shimadzu Corporation) at regular intervals during operation of the electric furnace, and electrodes are used according to the composition of the slag. The current was controlled by raising and lowering. Specifically, the current was controlled according to the slag basicity calculated based on the slag composition.

  FIG. 4 shows changes in the secondary current increase / decrease, the slag basicity index, the slag Fe quality index, and the difference from the slag amount suitability value when the electric furnace operation method of the present invention is performed. As shown in FIG. 4A, the basicity of the slag increased (the melting point of the slag increased) with the passage of time, so the three-phase AC electrode was gradually lowered to set the current (set secondary current). ) Was increased. In addition, as shown in FIG. 4B, adjustment was made to lower the iron quality by introducing granular coal as a reducing agent.

  Then, as shown in FIG. 4 (C), the amount of slag slag can be kept within ± 15% from the appropriate value, and the slag fluidity does not deteriorate or become excessive. We were able to operate stably. This is considered to be because the fluidity of the slag can be adjusted by controlling the current to be passed through the slag by raising and lowering the three-phase AC electrode according to the composition of the slag.

(Comparative Example 1)
In Comparative Example 1, when the operation was performed under the same operation conditions as in Example 1, an operation method was performed in which the current was adjusted and controlled by the slag furnace resistance, as in the technique described in Patent Document 1. At that time, the value of the slag layer was measured in order to calculate the slag bath resistance.

  As a result, although it was possible to carry out proper operation in a relatively long range such as a weekly unit, the electric furnace was interrupted in order to obtain the thickness value of the slag layer, and the measuring rod was mounted on the electric furnace from the top of the electric furnace. And the value of the slag layer had to be measured, in which case the operation stop time substantially took 10 minutes / time. Moreover, the measurement frequency of the thickness value of this slag layer required about 3 times / day. For this reason, when the composition and fluidity of slag fluctuate within the same operation day, it was not possible to cope with it sufficiently. Thus, in Comparative Example 1, a lot of labor was required, and an efficient operation was not possible.

10 electric furnace, 11 electrodes, 12 metal, 13 slag, 14 ore (burning), 15 slag hole, 16 metal hole, 17 arc

Claims (4)

In the operation method of the electric furnace in which three-phase alternating current is applied to the three electrodes suspended in the electric furnace and energized,
An electric furnace characterized in that the composition of slag generated in the electric furnace is periodically measured, the electrode is moved up and down in accordance with the measured composition of the slag, and the current supplied to the slag is controlled. Operating method.   The electric furnace according to claim 1, wherein the electrode is moved up and down stepwise according to the composition of the slag, and the tip of the electrode is immersed in the slag or the distance between the tip of the electrode and the slag is separated. Operation method.   The method for operating an electric furnace according to claim 1 or 2, wherein the electrode is raised and lowered according to slag basicity.   When the slag basicity increases, the electrode is lowered to increase the current applied to the slag, and when the slag basicity decreases, the electrode is raised to the slag. The method of operating an electric furnace according to claim 3, wherein the electric current to be energized is controlled to be low.

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