A simple control-oriented model of an indirect-fired strip annealing furnace

A simple mathematical model of an indirect-fired strip annealing furnace for real-time control and optimization purposes is developed. The considered furnace is part of a hot-dip galvanizing line and is used for continuous heat treatment of steel strips. The heat that is released during the combustion process inside the radiant tubes is calculated by means of steady-state mass and enthalpy balances. For discretizing the heat conduction problem of the radiant tube wall and the furnace wall, Galerkin’s method is used. Furthermore, simple heat balances are employed to model the temperature evolution of the guiding rolls and the strip. To facilitate an accurate representation of the strip temperature, the strip motion is described by Lagrangian coordinates. Heat transfer by conduction and radiation interconnects the individual dynamic submodels. Measurements from the real plant demonstrate the accuracy of the derived model, which is computationally rather inexpensive and thus suitable for model-based control and optimization.