Scrap steel is the main raw material for electric arc furnace smelting. What are its alternatives?

  Scrap steel is the main raw material for electric arc furnace smelting. What are its alternatives?

 

   Scrap steel is the main raw material for electric arc furnace smelting. Lack of scrap steel resources is one of the main reasons affecting the development of EAF steelmaking. There are generally three sources of scrap steel, that is, iron and steel enterprises' self-produced steel during the production process, industrial and mining enterprises processing scrap in the production process, and social (production, living, national defense, etc.) waste iron and steel materials (including demolition of scrap steel such as scrapped automobiles) , Ships, steel bridges and construction steel, etc.). Due to technological progress, the amount of scrap produced by the first two reasons has decreased, and the amount of social scrap has continued to increase. Due to the repeated use of social scrap steel or containing a large amount of harmful elements such as Cu, Sn, As, and Pb, which are not easily removed, some harmful elements are enriched in the steel, and the quality of the scrap steel is reduced. In order to solve the problem of scrap shortage and quality degradation, it is necessary to develop scrap substitutes. At present, the main scrap steel substitutes are: molten iron (pig iron), direct reduced iron (DRI), decarburized granular iron, iron carbide, composite metal materials, etc.

  1 hot metal (pig iron)

   Modern arc furnaces widely use carbon-oxygen guns, secondary combustion, oxygen burner technology, furnace gas secondary combustion technology, etc., and absorb and integrate converter to strengthen the smelting technology, especially the oxygen supply intensity is greatly improved, and the oxygen consumption is up to about 30Nm3 / t. Some even exceed 40Nm3 / t, which is close to the oxygen consumption of the converter. Correspondingly, the amount of carbon is increased, and molten iron (pig iron) is the most effective method of carbon. When the molten iron is added in a large amount, due to the oxidation of elements (mainly carbon) in the molten steel, a large amount of chemical heat is generated. There may be a period of time when power is not supplied during smelting, that is, electric furnace converter smelting. Chemical smelting method. Long-flow iron and steel enterprises basically use the hot metal process with electric arc furnaces, and some electric arc furnace process steel mills newly build blast furnaces to provide hot metal to solve the shortage of scrap steel resources and the high production cost of electric furnace processes. The method of supplying molten iron to an electric arc furnace in a newly constructed blast furnace is not preferable from the current and future development.

   Electric arc furnace steelmaking and hot metal technology has the following advantages:

1) For non-flat smelting furnace smelting furnace type, power supply can be optimized, forming a molten pool in advance, increasing the time for high-power power supply, and shortening the smelting cycle;

2) Increase physical and chemical heat and improve thermal efficiency;

3) It can dilute the content of harmful metal impurities in the molten steel.

    It is not better to add more molten iron, and it is more appropriate to control the ratio of molten iron to 30% -50%. When the oxygen supply intensity is low, the optimal molten iron ratio is about 30%; when the oxygen supply intensity is large, the molten iron ratio can reach 50%. In order to obtain sufficient preheating benefits, the Quantum electric arc furnace developed by Primetals of Germany proposes that scrap steel should be used at least 50%. The converter smelting method of the all-metal hot water electric furnace has caused the electric arc furnace to lose its superiority in sustainable development.

Pig iron is mainly cast from molten iron (liquid iron) into ingots. The average global use of pig iron in electric arc furnaces is 5% -10% of the total metal.

02 Direct reduced iron

    Currently, 95% of DRI is used in electric arc furnace production. Direct reduction refers to the ironmaking process in which iron ore and iron-containing oxides are reduced to metal products below the melting temperature, and is generally carried out in a shaft furnace or a rotary kiln. According to different products, it is divided into three categories: sponge iron, metalized pellets and hot briquetted iron. Production methods include gas-based direct reduction and coal-based direct reduction. Table 1 shows the data of a domestic electric furnace plant using DRI. From the data in Table 1, the advantages of using direct reduced iron in EAF steelmaking can be derived:

1) Stable chemical composition, less harmful impurities, especially P, S, N content, which is conducive to the production of high value-added products

2) Stable quality and low residual elements (such as copper is less than 0.002%), which can well dilute the harmful elements in scrap steel and increase the choice of scrap supply;

3) Sponge iron and hot briquette iron can be continuously loaded into the furnace, with less power-off time and small heat loss, which is conducive to saving electricity, and also shortening the smelting time of the electric furnace and increasing output;

4) It is beneficial to make foam slag and prolong the service life of refractory and electrodes in the furnace.

At present, the amount of DRI used in electric arc furnaces in foreign countries has basically exceeded 50%, and some even use 100% DRI.