Enameling large-scale process vessels presents significant thermal challenges due to their high thermal mass and complex geometries. In particular, the use of half-pipe jackets for cooling, commonly welded around the outer wall of reactors, significantly affects heat transfer during firing. While furnace setpoints often suggest sufficient thermal exposure, the actual internal temperatures of such vessels may lag behind, risking underfiring or, conversely, overfiring if overcompensated.
This work presents a simplified but effective thermal model to simulate heating behavior of enamelled vessels in closed industrial furnaces. The approach distinguishes between areas shielded by half-pipe jackets and exposed surfaces such as bottom zones or openings. Heat transfer is modeled using separate heat transfer coefficients (h-values) for each surface segment, taking into account reduced radiation and convection in shielded areas.
The simulation is based on fundamental thermal processes: heat conduction, heat transfer via convection and radiation, and the thermal capacity of the vessel. It models the transient temperature response of the system without invoking thermodynamic equilibrium assumptions.
Based on typical vessel and furnace parameters, temperature profiles are calculated over time, revealing a pronounced delay in the internal temperature rise compared to furnace air temperature. The model also allows evaluation of furnace control strategies, such as elevated setpoint temperatures during ramp-up and controlled cooling phases, to ensure full-through heating without exceeding critical enamel temperatures.
The simulation results show that this physically intuitive and easy-to-implement model can predict the thermal behavior of large enamelled vessels with good accuracy. It provides valuable guidance for optimizing enamel firing schedules and avoiding thermal defects in large, slow-to-heat components.