Thermo-chemical Fluid Flow Simulation in Hot-Dip Galvanizing: The Evaluation of Dross Build-Up Formation

Abstract

This paper presents a new computational framework to investigate the driving force for the formation of intermetallic dross particles in the zinc bath and dross build-up on the bath hardware. This is a major problem in continuous hot-dip galvanizing lines. The Computational Fluid Dynamics (CFD) model calculates the turbulent thermo-chemical flow conditions within the liquid melt. A detailed modeling of the steel strip-liquid interface enhances this approach, by means of a conjugated heat transfer calculation and a spatially resolved, temperature-and concentration-dependent iron dissolution and aluminum uptake. The heart of the computational framework is a thermodynamic model, which assesses the driving force for the formation or dissolution of dross particles in the bath and dross build-up on stationary and rotating equipment. The simulation results are validated with temperature and species depth profile measurements. The applicability of the CFD model is shown by investigating the locally resolved aluminum uptake and iron dissolution at the steel-strip surface, and the multi-physics conditions in the region near the roll. The novel approach of evaluating the thermodynamic driving force enables the assessment of the formation of dross build-up at the roll surface.

Chemical Recycling of Polyolefins with the Molten Metal Reactor at 460 °C

“…Conversely, the MMR is characterised as having virtually no temperature gradient [16,17] because molten metal has very high thermal conductivity avoiding temperature spikes within the MMR and, as a result, secondary reactions.…”

“…In a molten metal reactor (MMR), the HDPE is in direct contact with molten metal, e.g., tin, zinc or solder. The MMR is thought to have several advantages over other reactors, such as (a) rapid heat transfer to the plastic due to the properties of molten metal 14, resulting in, for example, whole tyre pyrolysis within 20 min 15, (b) minimum temperature gradients 16, 17 and (c) simplicity, i.e., containing no rotating parts 18. Other benefits of the MMR, such as economic viability 19, 20, flexibility to treat other feedstocks such as aluminium‐laminated plastic 20, carbon fibre 21 and recycling tantalum capacitors from printed circuit boards 22, are also noteworthy.…”

“…properties of molten metal [14], resulting in, for example, whole tyre pyrolysis within 20 min [15], (b) minimum temperature gradients [16,17] and (c) simplicity, i.e., containing no rotating parts [18]. Other benefits of the MMR, such as economic viability [19,20], flexibility to treat other feedstocks such as aluminium-laminated plastic [20], carbon fibre [21] and recycling tantalum capacitors from printed circuit boards [22], are also noteworthy.…”

Trajectory of Top-Dross Particles During the Melting of Zinc Ingot in Galvanizing Pot

“…The legacy of the studies already developed and mentioned above make it very clear that the two main sources of dross formation are changes in the chemical composition and/or temperature reduction of the zinc bath, which directly alter the solubility of Fe and Al. These events can be triggered by the temperature difference between the strip and the bath or by the melting of the ingot that is immersed to replace the zinc consumed by the strip in process 9,10 . However, the immersion depth of solid zinc ingot at room temperature and the influence on the formation of top-dross particles as well as their trajectories after they are formed, close to the ingot melting front, have not been widely studied.…”