How does an electric arc furnace work? eaf melting process and operation

By:Win Oct 27, 2020
How does an electric arc furnace work? eaf melting process and operation
The work of arc furnace is to melt scrap steel through electric heating of electrodes. It is mainly divided into direct heating, indirect heating and resistance heating.

How does an electric arc furnace work?

1. An arc will be generated between the graphite electrode and the furnace burden to melt the waste steel. The charge is directly melted by electric arc, mainly used for steelmaking, smelting iron, copper and refined steelmaking liquid.
2. An arc is generated between the three graphite electrodes, and the charge is melted by the radiant heat of the arc for the smelting of copper and copper alloy. Indirect heating is gradually replaced by low melting quality due to high noise.
3. Take the ore with high resistivity as raw material, the graphite electrodes are buried in the furnace burden. When the current passes through the furnace burden, the heat will be generated by the resistance, and the arc heat will be generated between the electrode and the furnace burden.

Eaf melting process

The smelting process of EAF is divided into melting period and refining period. During the melting period, many solid blocks in the charge path will be inserted into the molten metal, and a short circuit of gold properties will be formed between the electrodes. Therefore, it is necessary to rely on the eAF transformer and the reactor in the series to limit short circuit current.
Three characteristics of arc furnace smelting:
1. At the initial melting stage, the solid charge melts and the energy requirement is the greatest. At the beginning of melting, the arc is frequently truncated and reignited. Prone to collapse resulting in short circuit
2. In the full melting and primary refining heating stages, electric arc fluctuation occurs in the full melting stage, which leads to sharp change of current
3. Refining phase, in which the input energy only needs to balance the heat
The smelting cycle of ordinary AC arc furnace is about 3~8h, depending on the power supply circuit parameters, furnace capacity and smelting process. The melting period is about 0.5~2h, which is an asymmetric three-phase impact load. The current is extremely unstable and consumes a large amount of electric energy, accounting for about 60%~70% of the total power consumption. The voltage fluctuation and power consumption decreased significantly during the refining period of oxidation and reduction.

Operation of electric arc furnace

1. Preparation before smelting:
Check whether the mechanical, electrical, water cooling, hydraulic, feeding and other equipment and systems are normal, and prepare all kinds of tools and materials before opening the furnace.
2. Plug the steel outlet: first clean the slag steel stuck on the inside and outside of the steel outlet, close the tray of the steel outlet, and then fill the steel outlet with the steel outlet filler, and require the steel outlet to be filled and compacting.
3. Furnace repair: Furnace repair requires quick repair, thin repair, temperature drop fast repair first.
4. Charging: After the steel outlet is filled and sealed, the back support of the furnace body is put in place, the furnace body is lifted, the electrode is lifted, the lock of the rotating frame is lifted, the furnace cap and the rotating furnace cap are lifted in place, and the prepared steel and iron materials are added into the furnace. Special personnel should be assigned to direct the rest of the train to stay away from the furnace. When feeding, the bottom of the basket should be within 200mm from the edge of the furnace wall. The material basket is located in the middle of the furnace body slightly away from the position of the transformer.
5. Press: after adding the material, when the material exceeds the upper edge of the furnace body, press the material. It is required to use a heavy hammer to press the burden lower than the upper edge of the body, and it is required to remove the material supported on the upper edge of the body.
6. Close the furnace cover: after the material is pressed, turn the furnace cover back. After it is in place, close the furnace cover to ensure that the furnace cover is inside the plug and the lock pin of the rotating big frame is properly locked.
7. Power transmission: Assign an electrician to ring the bell three times after receiving the power transmission instruction and carefully observe the situation on and around the furnace body to make sure that there is no one on the furnace and turn off the power transmission.
8. Power supply system: The sixth voltage (760V) is used in the melting period, and the current is 35 ~ 45KA. The specific power supply system is determined by mastering the equipment performance and smelting conditions.
10. Oxygen combustion-supporting melting: oxygen combustion-supporting melting starts immediately when electricity is sent. Operate in strict accordance with the operating procedures required by the oxygen combustion aid equipment.
11. Oxygen blowing assisted melting: after power transmission, switch to oxygen blowing assisted melting when oxygen burning assisted melting reaches a certain degree. It is required that oxygen flow should be converted gradually from low oxygen to medium oxygen to high oxygen when oxygen blowing for melting. It is strictly prohibited to directly open to medium oxygen and high oxygen operation.
12. Hot metal mixing: at the same time, the electric furnace can send electricity and add hot metal into the furnace through the hot metal mixing device. The molten iron should be mixed evenly and stably with moderate speed.
13. Secondary feeding: When the first feeding is melted by about 85%, the second feeding can be arranged. First, the power is cut off, the oxygen gun gas of the furnace wall is switched to the protective state, the horizontal support is well done, the electrode is lifted to the limit position, the revolving frame is unlocked, the furnace cap is lifted, the furnace cap is unscrewed to the maximum position, and the second batch of material is loaded. When the charge is higher than the furnace edge, the material is pressed as required. Press the material to cover the furnace.
14. The requirements of the second batch of materials, such as electricity transmission, oxygen-combustion-assisted melting, oxygen-blown melting and power supply system, are the same as those of the first batch of materials.
15. Advance slagging and dephosphorization: when the charge melts more than 90%, lime is added into the furnace. The amount of lime is controlled by 3% of the total weight of the charge and added in 2 to 3 times to realize the fast material, fast slag, fast temperature rise and low temperature dephosphorization.
16. Toner spray: when the furnace slag can't bury arc effectively, toner is sprayed into the furnace. The amount of toner sprayed into the furnace is controlled at about 15Kg/min, subject to the stable burying arc of furnace slag and good fluidity of furnace slag.
17. Oxidation refining: When the temperature is greater than 1520 ° C, sampling analysis will be carried out at 1560 ~ 1580 ° C to remove most of the molten slag, and the amount of slag added, oxygen supply intensity and oxygen supply will be determined according to the composition analysis results and target control composition. When adding slag, stop spraying toner into the furnace to ensure the rapid melting of slag. After the slagging is opened, spray toner into the furnace and take samples for analysis.
18. Steel outlet operation:
1) Open the horizontal support after the furnace and push the tilting furnace operation button to the operation position behind the furnace.
2) Open the outlet. When the outlet packing fails to flow spontaneously, burn oxygen and drain immediately.
3) After the steel flows down, control the speed of tilting furnace according to the speed of discharging steel. It is strictly prohibited that the speed of tilting furnace is too fast, resulting in eccentric cap burning and leakage or more serious accidents.
4) Realize the operation of retaining steel and slag. Ensure that the amount of steel remaining in each furnace is controlled within 10 ~ 15T.
5) When returning to the furnace after the discharge of steel, start slowly, go fast in the middle, and turn to the slow gear when no slag is left, so as to avoid shaking off the electrode and slag during the process of returning to the furnace after the discharge of steel. It is forbidden to drop a lot of slag in the process of steel production.
6) Stirring in the process of steel discharging: argon gas is switched on before steel discharging, and the pressure of argon gas is 0.4 ~ 0.6mpa. The pressure of argon gas is adjusted according to the effect of steel liquid stirring to ensure good mixing of steel liquid.