The Importance of Viscous and Interfacial Forces in the Hydrodynamics of the Top-Submerged-Lance Furnace

Abstract

The purpose of this work is to focus on the hydrodynamics of a Top-Submerged-Lance (TSL) smelting furnace, understanding how liquid properties and operational parameters act on key factors of a TSL process, such as splashing, mixing, mass transfer area, and bubble development. A deep knowledge of all those aspects is needed since they all influence the smelting reaction rates; hence the efficiency of the reactor. The characterization and scaling of the TSL gas injection are commonly based on the modified Froude number, the ratio of dynamic and gravitational forces. Detailed literature research reveals a potential weakness of this approach, since it does not consider the effects of viscosity and surface tension. To investigate this question an extensive parametric study was performed applying computational fluid dynamics to cold and non-reactive flows, which provided a broad overview of the physics of the flow. The analysis was performed on fluid dynamic properties (liquid density, liquid viscosity, surface tension) and operational variables (gas volume flow, lance immersion depth). The coupled Level Set-Volume of Fluid model, available in the commercial solver ANSYS Fluent Ò , was used to resolve the gas-liquid interface in the multiphase flow. The results of the work underscore the significance of the viscous and interfacial forces for gas injection in smelting slags, confirming the incompleteness of applying only the Froude number to describe such flows.

Modelling of gas injection into a viscous liquid through a top-submerged lance

“…Since the gas velocity is much larger than the liquid velocity, the volume-averaged velocity in the simulation is significantly overestimated in the high void fraction region. To obtain an averaged velocity of the liquid phase for a further model validation, the gas velocity is filtered out of the final averaged velocity by adopting the post-processing method proposed by Obiso et al (2019). The liquid velocity contour profiles are shown in Fig.…”

“…Due to difficulties of high temperature experiments (e.g., opacity of a slag pot, hazardous operating environment, lack of velocity measuring techniques at high temperature), physical modelling (Igwe et al, 1973;Mazumdar and Guthrie, 1985;Iguchi et al, 1994;Morsi et al, 2000;Zhao et al, 2016Zhao et al, , 2017Pan and Langberg, 2010) and numerical simulation (Mazumdar and Guthrie, 1985;Liovic et al, 2002;Huda et al, 2010Huda et al, , 2012Wang et al, 2018;Sattar et al, 2014;Obiso et al, 2019) have been performed on a top injection two-phase flow in a metallurgical vessel. Iguchi et al (1994) performed some cold model experiments to analyze the fluid flow initiated by the top submerged gas injection in a cylindrical bath.…”

“…This limits the reliability of the combined numerical model, because the submerged lance depth plays a significant role in the flow Nomenclature a average radius of the slag pot, m A cross-section area of lance, m 2 C 1e ; C 2e model constants, 1.42, 1.68, respectively (Morsi et al, 2000;Huda et al, 2010). Obiso et al (2019) studied the effect of liquid properties on the hydrodynamics of a smelting process by using the coupled Level Set-VOF model. The results highlighted the importance of the viscous and interfacial forces on gas injection in smelting slags.…”

“…Only normalized numerical data were presented in their work, making it difficult to compare with other studies. Based on the above literature study, it can be concluded that (1) compared to low viscosity liquids (such as water, mercury and Wood's metal), viscous liquids have been much less employed in physical modelling (Pan and Langberg, 2010;Huda et al, 2012;Wang et al, 2018;Sattar et al, 2014;Obiso et al, 2019); (2) the standard k-e turbulence model is normally applied to the simulations, and a full validation of different turbulence model is necessary for the case with a large lance submerged depth; (3) the flow characteristics of a top gas injection in metallurgical processes have not been comprehensively investigated yet under industrially relevant conditions, for which simply the phenomenal descriptions of surface sloshing and splashing are available in literature, and a quantitative prediction of the phenomena is needed for process optimization.…”

Dynamics of Rising Bubbles in a Quiescent Slag Bath with Varying Thermo-Physical Properties

“…A few numerical investigations have been performed with CFD analysis. Cold models have been applied to study the hydrodynamics of gas injection in iso-thermal liquid slag, [36][37][38] while simulations of hot and reactive systems were conducted by Huda et al [39,40] They studied the process of zinc fuming using CFD for a Tuyere-Blown and a TSL furnace, solving the heat transfer and the multiphase chemical interactions. Although the application of an Euler-Euler framework does not allow the interface between the phases to be reconstructed, or offer a detailed insight into the bubbly flow, the physical behaviors of the system were reproduced, and the fuming rate trends obtained were similar to experimental campaigns.…”