A Mathematical Model for the Multiphase Transport and Reaction Kinetics in a Ladle with Bottom Powder Injection
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WITH the increase of demands for low-sulfur and ultralow-sulfur steel, high efficiency of desulfurization has become one of the main objectives in the clean steel production process since sulfur in most steel products is detrimental. To produce low-sulfur and ultralow-sulfur steel, a combined flowsheet process, including hot metal pretreatment-basic oxygen furnace (BOF) steelmaking-ladle refining, has been commonly practiced as an effective method in many iron and steel enterprises. However, it is nearly inevitable that this flowsheet is too long, and the metallurgical efficiency is low. The main drawbacks are as follows (1) In the hot metal pretreatment process, multiple times skimming slag are needed before and after desulfurization, which would produce larger iron loss and lower metal yield. Furthermore, the molten
WENTAO LOU and MIAOYONG ZHU are with the School of Metallurgy, Northeastern University, Shenyang 110819, China. Contact email: [email protected] Manuscript submitted March 2, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS B
iron cleanliness is threatened by stirring blades or top lance refractory. (2) In the BOF process, the sulfur content of liquid steel will again increase by 0.004 to 0.012 pct due to the resulfurization from oxidizing slag and steel scrap, which obviously weaken the role of hot metal pretreatment. Therefore, the ladle second desulfurization is necessary to produce low-sulfur and ultralow-sulfur steel. (3) In the ladle second desulfurization process, the top slag desulfurization in the ladle furnace (LF) ladle and top powder injection desulfurization in Ruhrstahl Heraeus (RH) or ladle have been well implemented to reduce the final sulfur content of liquid steel. However, in the LF ladle, the desulfurization efficiency is low due to smaller reaction specific surface area and slower mass-transfer rate at the top slag-liquid steel interface, and the entire desulfurization process needs more than 40 minutes. For the powder injection desulfurization with top lance, the desulfurization rate is fast and the processing cycle become short. However, the liquid steel cleanliness is threatened by top lance refractory, the splash and secondary pollution of liquid steel are serious, and the stability and flexibility of the process are also relatively poor.
Recently, Zhu and his co-workers developed a new technology of bottom powder injection for ladle refining,[1–4] and the fine desulfurization powders are injected into liquid steel through bottom slot plugs in the ladle, as shown in Figure 1. Compared with the traditional desulfurization process, the new technology has many advantages, such as better kinetic conditions, less serious splashing, and higher powder use and desulfurization rate. In addition, there is also no steel cleanliness risk caused by lance refractory. Therefore, this technology has broad application prospects and attracts more and more attention, and it is necessary to reveal clearly the multiphase transport and reaction kinetics in the process of bottom powder injection in the l
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