Investigation on the Fluid Flow and Decarburization Process in the RH Process
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THE Ruhrstahl–Heraeus (RH) degasser plays an extremely important role in secondary refining processes. The RH process is designed to perform various metallurgical operations such as decarburization, deoxidization, desulfurization, temperature control, inclusion removal, and composition homogenization. These operations above are mainly dependent on the gas–liquid flow behavior in the RH degasser. Due to the limitations of high temperature, multiphase system, and vacuum conditions, the numerical simulation is widely used to investigate the fundamental phenomenon in the RH degasser.[1–3] Relevant modeling procedures include the Eulerian–Lagrangian approach,[4] the Eulerian–Eulerian models[5–10] and the quasi-single phase model.[2,3] However, in these approaches, the top gas phase and slag phase above the liquid are ignored, and the free surface is assumed to be flat. The interfacial
HAITAO LING is with the School of Metallurgical Engineering, Anhui University of Technology, Ma’anshan, Anhui, 243002, China. Contact e-mail: [email protected] LIFENG ZHANG is with the Beijing Key Laboratory of Green Recycling and Extraction of Metals (GREM) and the School of Metallurgical and Ecological Engineering of University of Science and Technology Beijing (USTB), Beijing 100083, China. Manuscript submitted February 13, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS B
behavior between the liquid steel, slag phase, and gas phase can hardly be captured. Recently, a coupled model combining the volume of fraction (VOF) method and the discrete particle model (DPM) is developed to describe the multiphase flow. The free surface and motion of gas bubbles can be simultaneously simulated and tracked. The predicted results using the coupled model are well validated against the experimental measurements.[11–15] The recirculation rate and mixing time are regarded as the dominant factors influencing the decarburization rate. It is well known that the recirculation rate increases, and the mixing time decreases with a higher gas flow rate,[1–4,7,16,17] lower vacuum pressure,[3] larger immersion depth,[3,4,18] larger snorkel diameter,[3,18,19] multi-snorkels instead of two snorkels,[1,4] an appropriate number of nozzles.[3,16,20–23] Furthermore, the decarburization process is extensively studied in the literature,[8,20,24–29] which involves different reaction sites, such as the free surface, inner sites in the vacuum chamber, and the bubble surface. Although there are many investigations focusing on the gas–liquid flow behavior and the decarburization process, the following issues are still unresolved. First, the expansion of gas bubbles in the molten steel caused by the temperature change, and the static pressure drop is seldom considered. Li[1] and Chen et al.[15] reported that the bubble volume near the steel surface in the vacuum chamber could expand to be eight to ten times of its initial value at the nozzle exit. As a result, the recirculation rate is greatly increased.
Second, according to the assumption of a flat free surface, the decarburization r
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