Introducing the Planar Laser-Induced Fluorescence Technique (PLIF) to Measure Mixing Time in Gas-Stirred Ladles
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ED reactors are widely used in the process industries; their performance is usually determined by using the mixing time as a key parameter. The mixing time is defined as the time it takes for a volume of fluid with solute added to fluid without solute in a mixing vessel to blend throughout the whole system to a pre-chosen degree of uniformity,[1] commonly 95 pct of the final concentration in every measurement point. A review reported in the literature regarding the measurement of mixing time by several experimental techniques
LUIS E. JARDO´N-PE´REZ, ADRIAN AMARO-VILLEDA, CARLOS GONZA´LEZ-RIVERA, and MARCO A. RAMI´REZARGA´EZ are with the Metallurgical Engineering Department, Universidad Nacional Auto´noma de Mexico, Edificio D, Circuito de los institutos s/n, Cd. Universitaria, Del. Coyoaca´n, C.P. 04510, Ciudad de Mexico, Mexico. Contact e-mail: [email protected] GERARDO TRA´PAGA is with the CIATEQ, Avenida del Retablo no. 150 col. Constituyentes FOVISSSTE, C.P. 76150 Quere´taro, QRO, Mexico. A.N. CONEJO is with the School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing (USTB), 30 Xueyuan Road, Haidian District, Beijing 100083 P.R. China and also with the Ferrous Metallurgy Research Institute (FeMRI) Morelia Mexico. Manuscript submitted February 26, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS B
for stirred reactors (batch and continuous) under single liquid-phase flows and gas–liquid flows as well as a comparison between these techniques can be found in Reference 2. The measurement techniques revised in Reference 2 include colorimetry, local measurements of conductivity and pH, Planar Laser-Induced Fluorescence (PLIF), among others. In metallurgical ladles stirred by bottom gas injection, the mixing time is influenced by two transport mechanisms: (i) convective flow, that is, macroscopic recirculation of the liquid dragged by the ascending gas plume; and (ii) turbulent diffusion, which is due to dissipation of the turbulent kinetic energy of the system. Even though mixing time is the most popular quantification of mixing efficiency in a batch reactor, it is not the only parameter to consider for proper operation of a gas-stirred ladle system. Additionally, to decrease mixing time there must be promoted multiphase fluid flow structures that enhance slag–metal mass transfer, fast and efficient inclusions removal, and a small as possible slag eye opening area.[3,4] In their review on ladle metallurgy, Liu et al.[5] present a specific section of mixing studies and homogenization in physical models of gas-stirred ladles, summarizing the most important contributions made in the study of mixing time. All the studies presented in that review measured locally the mixing of a solute using conductivity and pH,
although some other mixing studies in ladle have been carried out using colorimetry[6,7] to observe qualitatively the mixing process in the system. Colorimetry is a nonintrusive technique, simple to implement. It reveals flow structures and can be used directly as a qualitative method to
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