Electric Arc Furnace: 2020

2020年5月12日星期二

Clean Production Technology for Electric Arc Furnace Steelmaking

Development of Clean Production Technology for Electric Arc Furnace Steelmaking

Cleaning technology includes both internal and external aspects of improving the cleanliness of steel and reducing the load on the external environment. It is a production technology that consumes waste steel materials from society and recycles. It does not consume non-renewable resources and uses the cleanest energy-electrical energy. The development of electric arc furnace steelmaking itself is the development of clean production. In addition, the clean development of EAF steelmaking technology is as follows.

(1) Clean steel production.
① Increase the proportion of pure iron source in raw materials (such as direct reduction iron and molten iron);
② Low-oxygen smelting, control the end molten steel Wr0≤450 × 10;
③ Slag modification;
④ Clean steel refining process;
⑤ Molten steel protection pouring;
⑥ Electromagnetic brake and large inclusion control technology.

(2) Reduce the environmental load.
① Use clean energy in electric arc furnace steelmaking;
② Use desi process to reduce the amount of slag;
③ Promote gas recovery process technology;
④ Develop electric arc furnace scrap preheating technology;
⑤ Refining slag steel-making return utilization technology;
⑥ Dust recovery and treatment technology.

Major Technological Progress in Recent Years

Electric arc furnace steelmaking production technology has made great progress in recent years. Following the ups and downs of compact small steel mills in the 1960s in the 20th century, it changed the unique situation of the joint venture. In recent years, some short-flow steel mills using cutting-edge technology integrated arc furnaces have emerged.

(1) Cremona ESP Headless Rolling Strip Plant of Alvedi, Italy. The company built the world's first Arvedi ESP headless rolling strip steel plant, including one 250t electric arc furnace, two 250t ladle refining furnaces and ESP headless rolled strip production line. The designed annual production capacity is 2 million tons, which can produce strip steel with a thickness of 0.8 ～ 12.0mm and a width of 1590mm.

(2) Crawfordsville Plant of Nucor Corporation, USA. After the transformation of the company's electric arc furnace steelmaking workshop, there is no heating device between the casting machine and the hot rolling stand. The strip passes through the hot rolling stand, that is, the thickness of the finished product is 0.7-2.0mm and the width is 2000mm. The designed annual output capacity is about 50 million tons. Using the Castrip process, due to the high cooling rate, short solidification time, and high pulling speed (generally 8O ~ 1500m / min), it has high productivity and can obtain extremely fine microstructure.

(3) MesabiNuggetITmk3 factory of Kobe Steel Corporation of Japan. ITmk3 (IronTeChnologyMarkm) is known as the third-generation ironmaking method. It is a coal-based direct reduction technology that uses a rotary hearth furnace to produce high-quality pig iron jointly developed by Kobe Steel Corporation of Japan and Midland Corporation of the United States. Pulverized coal directly obtains molten iron. Using this technology, iron ore powder can be smelted into slag-free, uniformly sized, and close to pure granulated iron within 10 minutes.

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2020年2月20日星期四

Electric Arc Furnace Reactor

In order to stabilize the arc and limit the short-circuit current, a reactance capacity of about 35% of the transformer capacity is needed to be connected in series into the main circuit of the transformer. For large-scale arc furnace transformers, it has a reactance value that can meet the needs, without an external reactor; for a transformer less than 10MVA, the reactance does not meet the requirements, it needs an external reactor at the primary side. The structural characteristics of the reactor are as follows: even though the short-circuit current is passed, the iron core will not occur magnetic saturation.

The reactor can be installed inside the furnace transformer, which is called an internal type; it can also be made into an independent reactor installed outside the transformer, which is called the external type.

Generally, the furnace transformer should be connected in series with the reactor, so that the sum of short-circuit impedance and reactor reactance of the transformer can reach 0.33 ~ 0.5 standard value (based on the rated capacity of furnace transformer).

For the furnace transformer with a capacity of less than 10MVA, sometimes a series reactor is installed on its high voltage side to reduce short circuit current and stabilize the arc. For large-capacity furnace transformers, its leakage reactance is large enough, and no series reactor is needed.

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2020年2月9日星期日

Influence of Electric Arc Furnace Electric Energy Efficiency

The waste of electric energy in EAF (Electric Arc Furnace) is mainly manifested in two aspects: one is the low power factor; the other is the large amount of flicker and harmonic generated during melting.

Flicker is the main cause of many side effects, such as harmonic distortion, voltage and current phase loss and so on. Transients is a kind of transient distortion of current and voltage in AC sine wave circuit.

Its main manifestations are surge, peak, harmonic and so on. According to Dr. Hershfield, a famous energy theorist in the United States, the main characteristics of this distortion are ultra-high pressure, ultra-high speed and ultra-high frequency. Ultra high voltage: refers to the flicker peak 2-50 times higher than the normal voltage amplitude, up to 500-10000 volts.

Superhigh speed: refers to the flash peak occurring in a very short time, it can complete the process from bursting to disappearing in trillions (one-millionth of the second power) seconds.

UHF frequency: refers to the flicker peak activity is very frequent, it can be said that flicker is everywhere and everywhere, the switch of a lamp, the start of a household appliance, even the click of a computer keyboard or mouse, there are dozens of flickers, the voltage is up to 500-1200 v.

Even so far, the fact that these high-voltage and high-frequency flickers are one of the reasons for the damage to sensitive power equipment is still ignored. On the other hand, we know that electric power is equal to the product of current and voltage, and the instantaneous growth of voltage or current will lead to greater instantaneous consumption of power. Because the heating end of an electric arc furnace is a resistive load, this instantaneous voltage or current can not participate in the arc starting and heating of an electric arc furnace, and can only be distributed in the form of iron loss and line loss through feedback to inductive load in the form of invalid power The inductive load in the EAF system is the transformer, and the consumption of these instantaneous invalid power in the transformer has no contribution to the smelting process, which has not been considered for a long time when the EAF (Electric Arc Furnace) works.

For the time being, the waste of electric energy caused by the low power factor of electric arc furnaces is not considered, only a large amount of flicker produced in the smelting melting period is considered.

As we can know, the electric energy efficiency of the electric arc furnace is also lower than that of the equipment with the same rated power that operates stably (with few flickers).

Restrain or reduce the number and peak value of flicker produced by EAF during the melting period, and change this part of invalid power into effective power, it can not only improve the electric energy efficiency of EAF, save the electric energy, but also eliminate the impact and pollution to the power grid, and protect the sensitive electric equipment.

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