Metallurgical Knowledge
Energy saving measures for steelmaking arc furnace

2017-04-12 hit:

Electric arc furnace power consumption

The energy saving work of EAF steelmaking should not only focus on reducing the consumption of electricity and other energy, but also pay attention to the energy consumption of various materials. In addition to energy consumption power consumption of smelting, including oxygen lance, oxygen burner, scrap charge preheating the energy consumption, the energy consumption of the total energy consumption is about the proportion of scrap preheating accounted for 9.5%, 57.1%, and power consumption of smelting burner 9.5%, blowing ladle refining accounted for 9.5%, accounting for 9.5%, accounting for 4.8% of the other.

In recent years, with the continuous development of steelmaking arc furnace steelmaking technology, arc furnace energy saving technology has made significant progress. In the world, the EAF steelmaking furnace has been explored to reduce the heat loss, improve the thermal efficiency, shorten the melting cycle, reduce the power consumption and the consumption of graphite electrodes. At the same time, through the use of oxygen and oxygen - fuel injection nozzle, powder chemical energy flux method, as far as possible to improve power and comprehensive effective heating auxiliary energy efficiency, reduce loading times, shorten the charging time and the operation of the outage time, greatly reduces the power consumption of smelting electric arc furnace steelmaking. At present, with the continuous development of EAF technology in the world, the power consumption of steel smelting arc furnace is decreasing, the average power consumption is 300 kW - h/t, and the minimum power consumption has been reduced to kW h/t. China's key enterprises all scrap smelting, the average smelting power consumption of 435 kW • h/t. Large electric arc furnace more than 50 t in China have adopted the basic production process of hot metal charging, the electric power consumption was significantly lower in the hot metal charging case, the electric power consumption of electric furnace steelmaking plant can reach 250 kW - h/t, the minimum can reach 100 kW - h/t, the power consumption to reach international advanced level. Of course, there is still a certain gap between the total scrap smelting power consumption and the world advanced level.

In this paper, the energy saving technology of steelmaking furnace is introduced briefly.

Energy saving measures for steelmaking arc furnace

1, AC arc furnace

(1) the development of EAF technology

In the birth date of the electric arc furnace for about 100 years, small arc furnace smelting special alloy steel from the beginning, and later developed into the large-scale electric arc furnace and smelting alloy steel and carbon steel in recent years, until the ultra high power large scale. With the problem of excess scrap is becoming more and more prominent, so it is necessary to take part in the process of smelting alloy steel in the arc furnace. Therefore, the development direction of how to improve the productivity and reduce the production cost is proposed. In 1964, the United States carbide company schwaber and northwest steel Line Material Company Robinson jointly put forward the concept of ultra high power electric arc furnace. Soon the countries around the world to promote UHP operation, smelting time greatly reduced, from 3-4 hours to 2 hours. From the beginning of 70s, in order to maximize the use of the working efficiency of the transformer, around how to further improve the power efficiency and time utilization, many countries have developed a series of related technologies, such as furnace wall, water-cooled furnace cover, long arc foaming slag operation, eccentric bottom tapping, bottom blowing, therefore, the power level the transformer reached 800 ~ 1100 kVA/t, smelting time is further reduced to less than 1 hours, power consumption dropped to 400 kW - h/t, and gradually in the process of popularization and operation mode of steel "- arc furnace refining continuous casting hot rolling mill or send", the electric arc furnace has evolved into a fast simple scrap melting equipment.

(2) energy saving technology of AC arc furnace

1) the adoption of ultra high power technology

1971, the United States northwest steel Line Material Company put into operation 400 t ultra-high power electric arc furnace, productivity increased by 100%, power consumption up to 460 kW • h/t, electrode consumption of 5 kg/t, the effect is significant. Usually, the level of power transformer with rated power transformer (kVA) and the rated capacity of the furnace (T) in 1981 is that, the international iron and Steel Association (IISI) classification proposed by power level arc furnace transformer, electric arc furnace for more than 50 t, regulations:

Common power electric arc furnace 300 ~ 500 kVA/t

High power electric arc furnace 500 ~ 800 kVA/t

Ultra high power electric arc furnace > 800 kVA/t

Main technical features of ultra high power arc furnace:

* power utilization and time utilization ratio of arc furnace transformer;

* high electrical efficiency and thermal efficiency, the average thermal efficiency should not be less than 0.9, the average electrical efficiency should not be less than 0.92.

2) high impedance power supply technology

* high impedance arc furnace operating characteristics

Using the technology of high impedance electric arc furnace, mainly through the installation method of additional series reactor in a side arc furnace transformer, to improve the dynamic behavior of electric arc furnace to reduce current fluctuations, thereby stabilizing voltage, reduce short-circuit current, reduce the power losses in the two circuit, reducing interference of low electric arc furnace on the power network. The installation of series reactor can reduce the current fluctuation of power supply line by about 20 ~ 25%. Typical operating parameters are shown in the following table.

* advantages of high impedance EAF

The main characteristic of the high impedance arc furnace is the high power input, which is attributed to the stable arc starting condition of the high impedance and the high arc voltage. Between the primary side of transformer and power series reactor or non saturable reactor to reduce the impact on the power grid flicker of electric arc furnace, reduce the short-circuit current, thereby reducing the power loss of electrode consumption and two times in the circuit. The technology of long arc foam smelting is adopted in the process, which not only improves the production efficiency, reduces the consumption of electrode and electric energy, but also shortens the smelting cycle.

The main advantages of the high impedance arc furnace are as follows:

High voltage, low current operation, electrode consumption reduced by 15 ~ ~ 20%;

The fluctuation of electrode current reduces the voltage flicker and harmonic interference of electric arc furnace, and the flicker is reduced by about 30%;

Due to the dynamic characteristics of the inductor and the high arc voltage, the arc stability is high, so the input power is high and the power loss is small;

3 long arc foam slag smelting technology

The use of foam slag smelting can play an effective role in saving energy and reducing consumption, so its application has been widely recognized and rapidly spread.

Under the condition of not increasing the slag quantity, the thickness of the slag can be increased, and the submerged arc operation can be realized. Compared with the traditional smelting process, the technology has the advantages of short smelting time, long service life and low power consumption. In the oxidation period of arc furnace smelting furnace to oxygen and injected into the toner, and good control of slag basicity and temperature, so that the formation of foaming slag submerged arc smelting. Electric arc furnace slag foaming process allowed by high voltage and long arc operation mode, so as to improve the power factor of the power supply, the power factor is increased from 0.65 to 0.85, reducing the thermal radiation of electric arc furnace wall and furnace cover, improve service life, improve the thermal efficiency, reduce the power consumption of smelting.

4) eccentric bottom tapping technology

In order to expand the water-cooled furnace wall area, must be reduced when tapping the tilting angle, at the same time in order to adapt to the separation of the oxidation of steel slag, the development of the eccentric bottom tapping, without slag tapping and stay steel slag operation.

The main advantages of EBT (Eccentric Bottom Tapping) approach:

Reduce the temperature drop of the tapping process. Compared with the EBT tapping method of 100 t furnace, the tapping time is reduced from min to 2 min, and the tapping temperature drop is reduced from about 40 DEG C to about 35 DEG C.

* improve productivity. The maximum tilting angle of 20 degrees, short length is shortened, the reactive power is reduced, the improved power factor, increase the input power, reduce the melting time, reduce power consumption, thus improving productivity.

5) electric arc furnace bottom blowing technology

Because the molten pool arc furnace slag interface and internal mixing effect is poor, resulting in mass transfer, heat transfer rate is low, resulting in melting speed is slow, slow oxidation, P removal, S speed is low, uneven liquid steel composition and temperature, industrial high labor intensity, high energy consumption, long smelting and other defects. To this end, in 1933, the Swedish ASEA company put forward the installation of electromagnetic stirring device at the bottom of the arc furnace stirred tank technology, get a lot of attention and application of arc furnace steel. In the mid and late 80s, developed countries began to develop and popularize the technology of electric arc furnace bottom blowing. The bottom blowing gas can greatly improve the mixing condition in the furnace, accelerate the alloy melting and mixing; high desulphurization rate; scrap melting speed: used for steel slag, and the bottom blowing gas, melting period can be shortened to about 10 min; so as to achieve the purpose of increasing productivity and energy saving.