Discrete Element Simulations of Contact Heat Transfer on a Batch-Operated Single Floor of a Multiple Hearth Furnace

Abstract

The multiple hearth furnace is a common industrial reactor for the thermal treatment of particulate material. The present contribution concentrates on a numerical analysis of contact heat transfer on a batch-operated single floor of a multiple hearth furnace employing the Discrete Element Method (DEM). The particles are agitated on an electrically heated circular floor by a single rotating rabble arm equipped with three flat blades. Blade angles have been varied from 0° to 90°. The DEM simulations (particle mechanics and contact heat transfer) were validated against experimental data. The transient heating of 20 mm diameter polyoxymethylene (POM) spheres was analysed. As the simulations did not consider natural convection inherently leading to time-varying heat losses, an averaged heat loss parameter was determined to represent heat dissipation from the particles to the surrounding gas and incorporated into the DEM simulations. With this approach, a good agreement with measurements was obtained. The DEM simulations and experiments do not show a large influence of the blade angle on the temporal evolution of the mean particle temperatures. However, the frequency distribution of particle temperature is dependent on the blade angle, revealing an increase in the standard deviation of the frequency distribution with an increasing blade angle.