ECA controls the chemical composition in a ladle metalurgy plant. This involves reducing the amount of carbon in the molten iron as well a lowering the overall sulfur concentration. ECA can also be used to improve the quality of steel by reducing the iron oxide. The process utilizes a combination of rapid chemical heating, exact alloying and capped stirring as well as a slag conditioning additive which acts as a desulfurizing agent.
ECA is generally added to the steel ladle after the steel molten from the electric melting furnace (EAF) has been tapped into it. It can be formulated using various raw materials including but not limited to: recycled ladle metallurgy furnace slag; soda ash; fluorspar; borax; aluminum; an alumina source consisting of bauxite, calcined dolomitic limestone or synthetic slags from rotary kilns; and calcium carbide.
As the slag conditioner is injected into the steel, it begins deoxidizing and removing sulfur from the slag layer in the ladle. It provides also atmospheric coverage for metallic alloys which are added to the molten to achieve specified levels of aluminium and silicon. Without such coverage, the elements could be oxidized back into the slag during subsequent mixing, thus forcing costly re-alloying procedures.
According to this invention, slag conditioning additive consists of a mix of particulate aluminum and limestone that is poured onto the molten iron ladle for deoxidization and desulfurization. The slag can contain additional components depending on the ladle's metallurgy.
The slag is mixed into the molten metal in the ladle using the slag injection, which looks like a teapot's spout. The alloy slag melts and lowers temperature as it mixes in with the molten iron. The slag can also act as a slag-blanket to keep the molten material from coming into direct contact with the electric current during heating.
CFD models that simulate turbulent multiphase flow have provided accurate simulation data used to monitor the mixing and dissolution of different alloys. It is possible to evaluate the optimal slag and injection conditions. A series of experiments was performed using the three main alloys of copper, columbium, and vanadium.
In this study, it was found that the ECA formulations for the three alloys were significantly influenced by the number of plugs and the argon gas flow rate for stirring. In addition, the study found that combinations of factors had an impact on the mixing time in the ladle. Specifically, the single-plug ladle required the longest gas stirring time while the dual-plug ladle exhibited the shortest mix time. The study concluded that a slag-conditioning additive, which is a mix of solid recycling ladle metallurgy slags, aluminum soda ash fluorspar borax alumina calcium oxide and metallic deoxidizers, such as silicon, aluminum and desulfurizing agent, manganese, and niobium and/or metallic deoxidizers, such as manganese, requires the shortest mixing time in order to achieve a desired homogeneity.
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