Rotary hearth furnace for steel solid waste recycling: Mathematical modeling and surrogate-based optimization using industrial-scale yearly operational data

The presence of zinc in byproduct dust produced during steel production poses a challenge to resource man-agement and can have adverse environmental effects. This study investigates the dezincification behavior of a commercial-scale rotary hearth furnace used to recycle the byproduct dust. A mathematical model of iron-ore/ carbon-composite pellets was developed, incorporating a one-dimensional dynamic model to examine the non -uniform distribution of temperature and solid weight fraction. The Arrhenius kinetics of the ZnO reduction re-action (ZnO + CO -> Zn + CO2) was fitted using operational data yielding estimated parameters of 163.6 kJ mol-1 and 868.6 m s- 1. The simulation results of our study showed good agreement with the operational data from the furnace, with a relative error of 10%. Six factors were identified as having an impact on the dezinci-fication ratio, with the most significant being operational time, particle size, temperature, C/O ratio, porosity, and emissivity in descending order. The mathematical model was used to examine two scenarios of environ-mental problems and derive optimal solutions for each. Our results show that extreme gradient boosting using operating temperature, operating duration, and C/O ratio as trained variables was the most accurate in pre-dicting dezincification and metallization, resulting in a 33% increase in waste recycling through surrogate-based optimization. The Pareto front analysis highlights the importance of considering the net impact of carbon emissions, total production cost, and solid waste penalties together.