Thermodynamics-CFD-DPM modeling of dross formation and diffusion in a Zn-0.3Al galvanizing bath

In order to further reduce the production cost and enhance product of steel strip marketing competitiveness, industrial enterprises will choose to increase production rate, leading to the more dross generation. This paper proposes a numerical simulation based on thermodynamics, computational fluid dynamics (CFD) and discrete particle method (DPM) to simulate the η-Fe2Al5 dross formation distribution, and to track the trajectories of different sized dross particles in a Zn-0.3Al galvanizing bath. An optimized modeling of interfacial reactions involving the instantaneous rate of iron dissolution and aluminum uptake is firstly set up and validated with the previous experimental results and theoretical calculation. On the basis of the analysis on interfacial reaction, a potential influence factor (strip velocity) is discussed. The results show that higher strip velocity will result in much more η-Fe2Al5 dross around the strip entry side and the average dross formation within the V-typed region increases with the increase of the strip velocity due to the higher dissolved Fe concentration in molten zinc. Additionally, the trajectories of dross particles are discussed by injecting particles in the specific generation area. It can be concluded that the η-Fe2Al5 is likely to adhere to the steel-strip and roll surface. Furthermore, the trajectories of the dross particles are affected significantly by the flow of zinc and the particle size, thus the trajectories of particles resemble the streamlines. The average residence time of the suspended dross particles in the outer area of steel strip exit is longest. It is illustrative that the dross build-up region is the front wall area of the zinc pot.