Slag fuming (SF) is a critical process for recycling zinc-containing slags, but the corrosive nature of
molten slag poses challenges to the reactor durability. The freeze-lining (FL) technique offers a
solution by forming a protective layer on the reactor wall. It requires intensive cooling using water-
cooled jackets, which can stabilise the FL while compromising the energy efficiency of the process.
This study presents a computational fluid dynamic (CFD)-based model to optimise the SF process
by considering FL formation and its impact on heat transfer and reactor wall temperature. A volume-
of-fluid (VOF) model is coupled with a mixture continuum (MC) solidification model to capture the
intricate multiphase flow dynamics within the SF furnace. Two FL types are considered: FL solidifying
on the reactor wall in the slag bath region; and FL solidifying on the reactor wall in the freeboard
region. The FL of the first type forms when the slag temperature drops below liquidus temperature.
The FL of the second type only forms when a splash-induced slag droplet collides with the freeboard
wall and solidifies. A series of splashing events are necessary to coat the freeboard wall.
The simulation was run until a global energy balance was reached. This means that the heat losses
from the water-cooled jacket, bottom wall, outlet and fuming balance the heat gains from the hot gas
injected through the submerged plasma torches. The increase in FL thickness, due to its low thermal
conductivity, reduces the heat losses through the reactor walls. The calculated FL thickness and
heat fluxes were in good agreement with industrial data, validating the model’s credibility.
The simulation results provided valuable insights into the fuming process, including slag bath
temperature evolution, slag splashing dynamics, FL formation patterns, local heat fluxes through the
reactor wall and overall energy balance. These findings can inform process optimisation strategies
to enhance the energy efficiency and sustainability of SF operations.
The authors have built a prior version of the model framework and applied it to simulate FL formation
in an electric smelting furnace (ESF). The results from both the ESF and the current SF highlight the
applicability of such model framework to a range of industrial processes involving FL formation. This
model framework can ultimately contribute to more energy-efficient and sustainable industrial
operations.