Distribution of current between electrode shell and electrode paste

Pubdate: 08-05 2022

Distribution of current between electrode shell and electrode paste

On the basis of the above data, it is not difficult to calculate the distribution law of current between the electrode shell and the electrode paste.

The electrode paste is basically non-conductive before 450 ℃, and all current passes through the electrode shell. At 500 ℃, the current through the electrode paste gradually increases. After 800 ℃, more than 50% of the current flows through the electrode paste. As the temperature continues to rise, the resistance increases sharply with the oxidation and ablation of the electrode shell, while the resistance of the electrode paste decreases accordingly, and all the current is borne by the electrode paste. The effect of using electrode paste on the current distribution law at the same temperature is not obvious. For example, when using standard paste at 500 ℃, 0.82% of the current passes through the electrode paste, which is increased to 2.34% with special paste. At 600 ℃, the standard paste is 9.63%, and the special paste is 12%. From this point of view, the low-temperature conductivity of the special paste has not * significantly improved. Its good thermal conductivity can increase the sintering temperature of the electrode, thereby improving its conductivity, which is the main reason why the closed paste is suitable for the use of closed furnaces.

3. Roasting temperature of electrode in submerged arc furnace

It is necessary to find out the actual temperature of the electrode paste at different parts of the electrode in order to finally find out the working characteristics of the electrode. In order to measure the actual baking temperature of electrode paste under industrial production conditions, we installed two nickel chromium nickel aluminum thermocouples in the No. 3 electrode of No. 2 electric furnace in a factory. One is fixed on the * of the electrode, and the other is installed at the position 50m/m away from the edge of the electrode shell. As the electrode is pressed, the thermocouple moves down gradually. According to the data obtained from this measurement, we have a clear concept of the heat source of electrode paste baking.

In terms of the existing electric furnace structure of a factory, the heat source of electrode baking can be analyzed in three stages:

The section is from the paste surface to the sealing ring, and the temperature rises from normal temperature to 270 ℃. The roasting heat source of this section is basically Joule heat generated when current passes through. The temperature of the electrode paste increased by only 25 ℃ from about 235 ℃ at the time of discharging the copper bushing to 270 ℃ at the time of entering the sealing ring. The electrode paste will stay for three and a half days during this period, and the position will be moved down by more than one meter. However, the temperature only rises by 25 ℃, which shows that the effect of other heat sources (such as conduction, radiation, etc.) is negligible. The Joule heat of the electrode * and the heat dissipation to the surrounding space have basically reached a balance. Therefore, the temperature of electrode paste also tends to be stable and no longer rises. Only by continuously increasing the load of the electric furnace and increasing the current intensity, it is possible to make this part of the electrode paste reach a higher temperature, but its potential will not be great (the rated power of the furnace is 16500kVA). This stage is the softening and preheating stage of electrode paste.

The * section is from the upper plane of the sealing ring to 700 mm into the furnace. The temperature of the electrode paste in this section is increased from 270 ℃ to 850 ℃, which is the main sintering stage of the electrode paste, with a large amount of volatiles volatilizing. When the position of the electrode paste is at the same level with the lower surface of the furnace top, the temperature can reach 740 ℃, which is close to the burning state. It has certain conductivity and mechanical strength, and the possibility of accidents is greatly reduced. This part of the heat source mainly depends on the heat conduction of the furnace gas. During normal production, the temperature of furnace gas is 450 ~ 550 ℃, and the electrode is in the high-temperature gas flow. Coupled with its own power on, the Joule heat generated makes the temperature rise rapidly. When the electrode is first put into the furnace, the heat transmitted from the lower part along the burned electrode does not play a major role. From the shape of the 800 ℃ isotherm, it can be seen that the temperature of the electrode * here is about 60 ℃ lower than the edge temperature, indicating that there is not much heat transmitted from the lower part, which is not enough to raise the temperature of the electrode * as high as the edge. At 850 ℃, that is, after entering the furnace 700m/m, about 1200m/m away from the slag surface, the electrode * temperature and edge temperature are equal, which proves that the heat transmitted from the lower part along the electrode in this part has accounted for a considerable proportion.

The third section is from the end of the electrode to 1200m/m above the slag surface, which is the working end of the sintered electrode, with a length of about 1.4 ~ 1.5 meters. Because of the good thermal conductivity of the sintered electrode and its close distance from the high temperature zone of 1500 ℃ ~ 1600 ℃, the heat of the electrode mainly comes from the heat conduction at the lower part, and the temperature of the electrode * is higher than the temperature of the edge of the electrode.

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