Development status of smelting electric furnace and application prospect of DC electric furnace

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Development status of smelting electric furnace and application prospect of DC electric furnaceI. Development history of electric furnace ferroalloyThe product

Development status of smelting electric furnace and application prospect of DC electric furnace

I. Development history of electric furnace ferroalloy

The production of ferroalloy by electrothermal method started from the end of the 19th century to the present, which experienced the large-scale development stage from the beginning of the 20th century to the 1960s, and the ferroalloy output of electric furnace surpassed that of blast furnace and occupied an advantage from the 1960s to now.

2. Foreign smelting electric furnace status

From the end of 1970s to 1980s, with the development of the world electronics industry, low-voltage and high-current power rectifier devices appeared, which promoted the application of DIRECT current in the electric furnace metallurgy industry. The application and development of dc arc furnace technology began in Europe.  ASEA of Sweden, BBC-MAN-GHH of Germany and IRSID-Clecim of France are the main companies. Limited by the working current of early high-power silicon rectifier devices, the capacity of DC electric furnace is small. With the development of manufacturing technology of single high-power rectifier devices abroad in the early 21st century,  The average allowable working current of a single rectifier device has exceeded 10 kA. In June 2010, the 420-ton electric arc furnace for steelmaking was successfully put into production in Tahara Plant of Tokyo Steel Co., LTD. At the beginning of the 21st century, 102 kVA AC furnace was successfully put into production. A single DC furnace with capacity of 70MW ~ 120MW has been successfully used abroad.

3. Domestic smelting furnace status quo

At present, the capacity of mainstream ore heat furnaces in China ranges from 12.5mw to 33MW, and few enterprises have adopted 50MW and 63MW giant ore heat furnaces. There are about 360 electric arc furnaces for steelmaking, of which less than half of them have capacity of 50-150t [3,4]. Most of the above-mentioned electric arc furnaces adopt ac power supply, but few adopt dc power supply.  The disadvantages of AC power supply are obvious. With the continuous increase of the capacity of a single electric furnace, the short network AC reactance is a practical problem that we cannot avoid. The short network AC reactance restricts the ability of ac power input to the electric furnace, and it will also reduce the power efficiency due to eddy current loss caused by the surrounding ferromagnetic mechanical components.  In response to the communication of furnace type index of voltage flicker and power factor is low, need to put in the system dynamic compensation device or low voltage reactive power compensation device and other types of reactive power compensation device, adopting ac power of electric arc furnace arc also due to the effect of electrode current magnetic field and molten pool partial arc current magnetic field effect, the partial arc furnace wall hot phenomenon and reduce the service life of the furnace wall,  In the mid - 1980 - s to mid - ninety - s national kair institute cooperation with some domestic ferroalloy plant carried out a research into the essence of the dc -arc furnace and the practical work, and have built 2 MW ~ 6.3 MW single electrode or electrode dc -arc furnace, at the time similar Raw material and production process under the condition of well production smelting index, power consumption reduced by more than 7%,  electrode paste can save more than 40% and increase production more than 10%.

Since the beginning of this century, China's infrastructure construction has promoted the development of metallurgical industry, promoted private enterprises to join the army of iron and steel and ferroalloy industry, also promoted the wide participation and technical support of electric furnace smelting related industries, so that equipment manufacturing technology and smelting operation process has made great progress.  The power consumption per ton of the product, the ore consumption per ton of the product and the capacity of a single electric furnace have been greatly improved.  Several years ago, a plant in Anyang, Henan province smelted 6517 grade silicon-manganese alloy with three-phase AC 16500KVA electric furnace. Under the condition of 34.5° ~ 35.5° manganese in the furnace, the power consumption has been reduced to less than 3500kWh, the manganese recovery rate is ≥ 90%, and the daily output is ≥120 t.  In recent years, with the improvement of the threshold of the industry and the competition between the industries make the emergence of giant electric furnace, AC 25 MW, 33 MW electric furnace has been popular, 51MW and 63MW electric furnace has appeared in succession.  Giant electric furnace has the advantage of high temperature, high single capacity, can effectively promote the optimization of production cost, large electric current index seems to be unsatisfactory, the main reason for the electrode working current is big, the system large eddy current loss and the electrode diameter because do skin effect is very big, increase the difficulty of the production process control, also make relevant corollary equipment cost increases,  The expected smelting index is not achieved in the production, and the smelting work of large electric furnaces without the support of good economic and technical indexes is often due to high operating costs, so the ability of enterprises to resist the risk of market fluctuations is greatly reduced, and they lose their due competitiveness.

Domestic metallurgical industry in the construction of the giant electric furnace, use compared with the foreign counterparts there are still a big gap, core technology of foreign advanced equipment and will not be easily sold us, even if we spend high price to buy foreign counterparts outmoded smelting equipment, but also for foreign equipment operation process control process and we are familiar with the operation of the existing control flow is large,  So that some enterprises have not mastered the introduction of technology when smelting links lead to operating losses difficult.

4.DC electric furnace application prospect

China needs to actively research and develop new smelting equipment suitable for our own national conditions to adapt to the development of the domestic metallurgical industry and enhance the international competitiveness of the industry. Today, when the development of AC electric furnace meets the bottleneck, will we consider using the advantages of DIRECT current to develop our own large DC electric furnace technology?  In recent years, some advantages of direct current used in metallurgical electric furnace are as follows;

(1) DC does not produce alternating electric field and no eddy current loss.

(2) 6 pulse or 12 pulse dc in the short network reactance is small, electric energy can be easily input furnace.

(3) The direct current has no current skin effect in the process of electric energy transmission by the electrode, and the electrode with the same diameter can transmit more electric energy to the load of the electric furnace. Take the smelting of silicon metal in the mineral furnace as an example.

(4) The dc arc is stable, the molten pool burden resistance load is stable to facilitate the reduction reaction or the smelting of the burden, the furnace bottom temperature is high, slag slag flow is good, slag free furnace is not easy to rise the bottom.

(5) The noise reduction of electric furnace is about 7%-15% dB.

(6) The unit consumption per ton of electrode is reduced by 40% ~ 60%.

(7) tons of electricity per unit consumption in the same Raw materials and operating conditions can save electricity 3% ~ 10%.

(8) Open-arc operation furnace has no hot spot phenomenon on the furnace wall, which extends the service life of the furnace wall.

(9) The arc has a good mixing effect on the molten pool and promotes the quality of the product.

(10) The voltage flicker caused by the system to the high voltage network side is small, so there is no need to add dynamic compensation device. The power factor of the system using 6 pulse rectifier device can be ≥0.95, and the power factor of the system using 12 pulse rectifier device can be ≥0.98.