How is an AC electric arc furnace operated

The working principle of electric arc furnace

The working principle of electric arc furnace is that the electrode forms an arc between itself and the metal surface to be melted.

At the beginning of the operation, the scrap is transported to the scrap workshop at one end of the EAF building. There are many forms of waste, from smashed cars to white appliances, steel and plates used in the kitchen. They are loaded into a scrap container called a basket, which has an open door at the bottom and some pig iron (ingot product of blast furnace), which is needed for steelmaking.

The basket is loaded to ensure that the top layer is light waste, followed by a layer of heavy waste, alternating until the basket contains the correct mix and weight of waste.

On the way to the furnace, a large preheating system can use the industrial waste heat of the electric arc furnace to heat the waste in the form of waste gas, so as to improve the utilization efficiency of waste heat.

Then, the waste basket is transported to the furnace by steel wheel trolley, and the furnace top is recovered for loading.

As I mentioned earlier, I am an engineer in an aluminum smelter. I have an EAF molten iron to fix the rod to the carbon anode block. I found that charging is the worst and most dangerous part of the operation - when the molten metal in the furnace is replaced, it will overflow the top and ignite any oil or grease nearby - it's terrible!

In any case, once the charge is in the furnace, the furnace cover is replaced and the electrode is lowered to the top layer of light waste. The arc is hit, the electrodes begin to sink into the waste, their forward speed and voltage are automatically controlled, the oxygen burner is activated and melting begins.

The molten metal temperature of electric arc furnace is about 2970f, but it is worrying that the temperature of electric arc is in the area of 11000f!

Under normal circumstances, 100 tons of smelting takes more than an hour to complete, and about 400 kwh of electricity is required.

Slag formation is an important part of EAF steelmaking. Slag formation is encouraged due to the following reasons;

1. Molten slag is formed on the top of molten steel and collects impurities in the metal like a sponge.

2. The slag acts as an insulating layer on the metal surface to prevent excessive heat loss.

3. Slag helps to reduce the wear of refractory materials.

Magnesite and dolomite are injected in the form of lime in magnesium oxide and calcium oxide to help form slag. (these fees can also be added to the waste fee.) Now that the melting has reached its final product, another basket of waste can be added and once all the metals are completely melted, the sample can be added and adjusted. The typical impurities burned by the molten steel slag producer and the chemicals injected with oxygen and inclusions are sulfur, manganese, aluminum and phosphorus (their oxygenates are stored in the slag).

This will make the slag produce violent foam and overflow the overflowing slag.

Once more lime is added to the steel and the alloy is preheated, the correct composition of the steel can be determined.