Domestic electric furnace DRI application experience
Source: internal company
The common raw material of EAF (electric arc furnace) is scrap steel because scrap steel is cheap and relatively easy to obtain, but social scrap steel often contains unwanted impurity elements. In order to reduce the harmful impurities in the scrap steel, a certain amount of pig iron or sponge iron must be added to dilute the residual metal elements of the scrap steel, which can help keep the content of residual elements in the final molten iron or molten steel at an acceptable level. The advantages of low-sulphur sponge iron are particularly evident in EAF smelting since desulphurisation is not necessary for the furnace , which can save a lot of time.
The traditional charging method of EAF is to open the whole furnace cover, and load the furnace material into the furnace with a large charging hopper hung into the furnace roof. Using this traditional charging method not only prolongs the charging time but also loses a lot of heat. The sponge iron can be charged into the furnace through small holes, so it is not necessary to open the entire furnace cover again after the initial charge has been melted. Furthermore, it is not required to load a large amount of charge into the furnace at one time, and the sponge iron can be continuously charged into the electric furnace at the same rate as it is melted, so a higher smelting efficiency can be achieved.
Fig. 4 Schematic diagram of the charging system for continuous charging of DRI into an EAF
TPCO is the largest oil casing production base in China at present. It has made long-term systematic test tracking for adding DRI in steelmaking production, and the test data is relatively complete, which provides a reference for other steel mills to use DRI reasonably. TPCO adopts a continuous feeding device with a high silo, and DRI is continuously fed into the furnace with the high silo of the electric furnace through the fifth hole of the furnace cover, which shortens the smelting cycle.
Production Practice of 150t UHP EAF in TPCO: in the case of fixed molten iron (single tank weight ~ 40t), the total load of each furnace is 160-165t, and when adding 30~35t sponge iron, the optimal comprehensive economic and technical indicators can be obtained, and the indicators of smelting power consumption, smelting cycle and "five harmful" elements are in the best state.
For steel mills whose main equipment is EAF, the high proportion of steel scrap and the multiple recycling of self-produced scrap lead to the enrichment of residual elements. In order to dilute the residual elements in scrap steel, purify the burden and ensure the virtuous cycle of returning to the scrap steel, it is necessary to dilute with "clean" iron and steel materials, and DRI can just play this role. The content of other metal elements except for iron in the reduced iron product is low, S and P are generally within 0.03%, so it is a pure steelmaking raw material. Therefore, steel mills with high-quality requirements are willing to use DRI, especially when they have special requirements for products.
Moreover, the addition of reduced iron has little effect on the smelting cycle of electric furnace. In reduced iron smelting, several tons to dozens of tons of molten steel are usually left after the electric furnace is tapped to facilitate the rapid melting of the next furnace of DRI and scrap steel. After adding DRI, it is easy to form foamy slag, which can improve the efficiency of arc heating.
Due to the limitation of raw material conditions, some foreign countries use DRI as the main raw material for electric furnace production, and the actual proportion of DRI used in electric furnace steelmaking can reach 100% (mainly due to the shortage of scrap steel and the price of scrap steel higher than that of reduced iron), while in China, DRI is mostly used as the auxiliary raw material for electric furnace steel production (due to the diversity of domestic raw material supply).