JPS60232477A - Method of controlling position of electrode for electric furnace - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling the electrode position of an electric furnace for manufacturing metals and alloys such as ferroalloys. The present invention relates to an electrode position control method that can be carried out smoothly.

FIG. 1 is a schematic vertical cross-sectional view illustrating a refining operation using an electric furnace. Generally, the upper inner surface of the furnace wall 1 is constructed of chamots refractory bricks, and the lower inner surface is constructed of carbonaceous refractory bricks. It's built with things. The ore in the raw material A (ore and coke) charged through the raw material charging port 4 is transferred to the electrode 2.
(usually three are used) receives resistance heat from electricity and melts, and reduction and refining progresses in the mixed layer H of coke and semi-molten material. Due to the difference in specific gravity, ■Divided into molten metal amount.

In the figure, 3 indicates the furnace lid, 5 indicates the exhaust gas duct, D indicates deposits,
Reference numeral 10 indicates tap holes that are opened periodically.

The amount of heat required for electric furnace operation is the sum of: ■ heat for melting raw materials, ■ heat for reducing oxides such as Fe%Mn%51, and ■ heat for imparting fluidity to molten metal and slag. However, these required amounts of heat are supplied by the resistance heat generated near the electrode tip. When the electrode tip is in the optimal position for the current situation inside the furnace, the heat that contributes to the melting of raw materials, the reduction reaction, and the improvement of product fluidity is distributed in a well-balanced manner, and the power supply is reduced. The human eye can be used effectively and stable furnace operation conditions can be obtained.

From this point of view, the most important issue in increasing the operational efficiency of electric furnaces is how to properly control the electrode tip position (especially the rate of rise) according to the conditions inside the furnace. Various methods have been proposed so far. The typical electrode position control methods currently in use are the following methods (1) and (2), but as explained below, these methods are far from satisfactory.

■A method in which the rising speed of the hot water level is estimated in advance and the electrode is raised at a constant speed according to this speed.

■A method of controlling the rising speed of the electrodes so that the current flowing through each electrode remains constant.

The above method (■) can be said to be the simplest and preferable method as long as the rate of rise of the entire hot water level in the electric furnace is constant.
In most cases, the rising speed of the hot water level during actual operation is not constant, which causes the following problems. In other words, since the position of the hot water level in each electrode arrangement part is not constant as mentioned above, if the height position of each electrode tip is the same, the distance between the tip of each electrode and the hot water level will be slightly different individually. The electric resistance value increases in areas where the distance is long, and the amount of raw material consumed in that area increases.As a result, the amount of electrode consumption increases and the length of the electrode becomes shorter. As the length of the electrode becomes shorter, the electrical resistance value of the electrode becomes higher and the electrode becomes more and more floating above the hot water surface.

On the other hand, in areas where the distance is short, the electrical resistance is low, so the amount of electrode wear is small, and the electrode tends to sink further into the hot water surface.If this vicious cycle occurs, furnace blowing, electrode breakage, and current flow may occur. Troubles such as trips are more likely to occur, making it difficult to maintain stable operating conditions.

On the other hand, in the so-called constant electrode current control method described in (2) above, the electrical resistance value differs for each electrode placement position, and the rate of rise of the molten metal level also varies considerably due to the unevenness of the amount of molten metal produced. As shown in the operation example in the figure, a so-called seesaw phenomenon occurs in which the electrodes individually rise or fall.
Unable to maintain stable dissolution/reduction zone.

The present inventors have focused on these circumstances and have conducted various studies in an attempt to establish an electrode control method that can stably maintain and continue electric furnace operation and make the most effective use of supplied power. The present invention has been completed as a result of such research, and has a configuration in which a predetermined electrical resistance is measured while an electrical resistance index is measured in a method for controlling the height position of an electrode tip during operation of an electric furnace. If the indicator deviates from the upper limit of the optimal range, reduce the rising speed of the electrode,
The gist of this method is to control the electrical resistance index so that it is maintained within a set range by increasing the rising speed of the electrode when the lower limit is exceeded.

In the present invention, the electrical resistance index typically refers to the electrical resistance value itself, but also collectively refers to power factor, impedance, reactance, inductance, etc. that have a correlation with the electrical resistance value.

However, below, the configuration and effects of the present invention will be explained in detail, focusing mainly on the electrical resistance value.

As mentioned above, the resistance heat generated by energizing the electrodes during electric furnace operation is: ■ Heat for melting the raw material, ■ Fe%M
It is consumed as heat to reduce oxides such as n1Si, and heat to give fluidity to molten metal and slag. When resistance heat is consumed in a well-balanced manner as the total heat amount of these The power supplied to the furnace is most effectively utilized and the furnace condition is most stable. The above-mentioned state is also obtained when the tip position of each electrode is at the optimal position with respect to the situation inside the furnace. However, the condition inside the electric furnace at each electrode location is not necessarily constant due to non-uniformity in the packing density of raw materials and unbalanced coke/raw material ratio in each part, and even more so, the amount of molten metal produced during furnace operation is not constant. Since the element of non-uniformity is also added, it is not easy to keep the conditions of each electrode arrangement portion uniform.

Therefore, the inventors of the present invention determined an index that can substantially indicate the optimum tip position of the electrode, regardless of the unevenness of the packing density of the raw materials, and started raising and lowering each electrode based on that index. For example, we thought that it would be possible to maintain stable furnace conditions and make effective use of the supplied power for each electrode, and we proceeded with our research along these lines. As a result, although the absolute value differs depending on the type of furnace contents, etc., if the lifting speed of each electrode is controlled so that the electrical resistance at the electrode placement position is within a certain range, the amount of heat generated at the tip of each electrode is almost constant, and the amount of molten metal produced and the amount of electrode consumption are approximately equal.The objective of effectively utilizing the supplied power is achieved, and unevenness of the electrode length is prevented, which stabilizes the situation inside the furnace. I learned that I can maintain it.

Incidentally, Figure 3 shows an example of electrode control when a simi-air furnace is operated (manufacturing silicomanganese) according to the method of the present invention, and shows changes over time in the electric resistance value in the furnace and the depth of each electrode. It is a graph. In this example, the control range of the electric resistance value in the furnace is set to (3-cut 0-4 to 5-cut 0-4) Ω.
This was determined in advance through preliminary experiments using silicomanganese as the optimum range of electrical resistance values that would allow the most effective use of the supplied power. That is, in this example, when charging each electrode, the depth of each electrode is adjusted so that the in-furnace electrical resistance value at each electrode part is within the above-mentioned preferred range,
As a general rule, the rate of rise of each electrode after the start of dissolution is constant. Then, during the furnace operation period, the electrical resistance value at each electrode section is continuously measured, and when the value deviates from the lower limit of the above-mentioned set electrical resistance value, the rising speed of the relevant electrode is increased, and on the other hand, when the value deviates from the upper limit This is to reduce the rate of rise of the electrode and control so that the in-furnace electrical resistance values at each electrode portion are all within the range of the set electrical resistance values.

That is, in the example of FIG. 3, at the power consumption At after the start of melting, the electrical resistance values of each electrode I, n, I[I are within the set range, and there is no need to change the rising speed of the electrodes. However, when the power consumption amount A was reached, the electrical resistance value of electrode ■ exceeded the lower limit of the set value (3X10-'Ω), so electrode
is increasing its rate of rise.

As a result, the relative amount of heat generated by resistance at the electrode (2) increases, raw material consumption increases, and the amount of wear at the tip of electrode (2) also increases, so that the electrical resistance value tends to rise. Then, when the power consumption amount B is reached, the electrical resistance value returns to within the set range, so the rising speed of the electrode m is returned to the initial speed and operation is continued.

When the power consumption amount C was reached, the electrical resistance value at electrode I exceeded the set value of 1a (5x1o-aΩ), so
Decrease the rising speed of the electrode worker (in the figure, the speed is negative, that is, the electrode is lowered).

As a result, the resistance heat in the electrode part is relatively reduced and the amount of wear at the tip of the electrode 1 is also reduced, so that the electrical resistance value tends to decrease. Then, when the power consumption amount is reached, the electrical resistance value returns to within the set range, so the rising speed of the electrode (2) is returned to the original speed.

As for electrode (3), since it is always within the set electrical resistance value range from the start of melting to the time of tapping, there is no need to change the rising speed.

In this way, the amount of resistance heat generated at the tip of each electrode is controlled within a certain range, and the amount of electrode consumption is also limited to electrodes I~■.
Since both are kept substantially constant, the positions of the tips of each electrode are not adjusted to a substantially constant position, but rise at a substantially uniform speed. As a result, there is no possibility that some of the electrodes will be excessively floating or sinking, and operation can be continued while stably maintaining the dissolution/reduction zone in an appropriate state.

Moreover, the range of the set electrical resistance value is predetermined as the range in which the supplied power can be used most effectively, so by keeping the electrical resistance value of each electrode within this set range, the supplied power can be maximized. Needless to say, it can be put to good use.

As mentioned above, the range of the set electrical resistance value varies depending on the charging raw materials, etc. For example, in the case of high carbon silicomanganese, it is 2X10-' to 10XIO-'Ω (more preferably 4X10-' to 6 In the case of silicomanganese, it is in the range of 2X10-' to 7X10-'Ω (more preferably 3X10-' to 5X10-'Ω),
If you want to show it as a more universal range, 1 cut 0-4~20X
10-'Ω.

As electrode control elements in the present invention, in addition to the electrical resistance value, the control method when employing power factor, impedance, reactance, inductance, etc. that are highly correlated with the resistance value is basically the same, and is preferably set in advance. Set the range and
The rising speed of each electrode may be adjusted so that the value actually measured for each electrode falls within the preferred range. For example, Fig. 4 shows Sf-
This graph shows an example of control when Mn is used as a raw material and power factor is selected as the control element.1. The preferred power factor range is set by considering the period up to the power consumption amount X as the melting period, and the period from X until the start of hot water dispensing as the reduction period. In this example, the power factor for each electrode is within the preferred power factor range from beginning to end, and there is no need to change the electrode depth. However, if the actual power factor deviates from the range, the electrode depth should be changed as in the example in Figure 3. Control is performed so that the power factor always falls within the preferred range by adjusting the rising speed of the power factor.

The present invention is configured as described above, but the point is that an electrical resistance index is adopted as a control element, and the optimum range of the electrical resistance index that can make the most effective use of the supplied power is set in advance, and during operation, By controlling the rising speed of each electrode so that the measured electrical resistance index always falls within the above-mentioned range, the electric furnace can be operated efficiently while maintaining an appropriate and stable furnace condition. Became.

By the way, using an actual machine (transformer capacity 20,0OOKVA), the raw materials were high carbon ferromanganese [setting electrical resistance value range is 3X10' to 7X10-'Ω] and silicomanganese [setting electrical resistance value range is 2X10' to 6X10''
According to a field experiment conducted over a total of 5 months using 1.5-1.5 Ω, the average dissolution power consumption was lower than that without control (the change in electrical resistance was lXl0-' to 20 It was confirmed that high carbon ferromanganese improved by 296, and silicomanganese improved by 1.9.
Comparing the n loss, in the case of high carbon ferromanganese, it is 1.
The results showed that the reduction could be reduced by 4% and 2.5% in the case of silicomanganese. Moreover, the average standard deviation of the raw material consumption ratio around the three electrodes during this period was 4.57'J without control, but it decreased to 3.08% by implementing the control of the present invention. There were no problems such as blowing, electrode breakage, or tripping due to overcurrent.

[Brief explanation of drawings]

Fig. 1 is a schematic vertical cross-sectional explanatory diagram showing the operational status of an electric furnace, Fig. 2 is a graph showing changes in electrode depth over time when constant current control is performed, and Figs. 3 and 4 are examples of electrode control according to the present invention. This is a graph showing. 1... Electric furnace walls 2... Electrodes 3... Furnace lid 4... Raw material charging port 5... Exhaust gas duct A... Raw material C... Coke bed Figure 1 elapsed time u0 ( time) R plate season--this is the jump bag

Claims (1)

[Claims] In a method for controlling the height position of an electrode tip during operation of an electric furnace, an electric resistance index is measured, and if the electric resistance index deviates from the upper limit of a predetermined optimum range, the rising speed of the electrode is reduced, A method for controlling the electrode position of an electric furnace, characterized in that when the lower limit is exceeded, the electric resistance index is controlled to be maintained within a set range by increasing the rising speed of the electrode.