(22d) Simulating Radiation and Conduction in an Aggregate Dryer Using Coupled CFD-DEM

Granular heat transfer is an important mechanism in many industrial applications. While convective heat transfer in multiphase systems is common in some industrial applications radiation and conduction are dominant modes and must be considered. An application in which all modes are critical is an aggregate dryer in a hot mix asphalt plant. For efficient mixing, the aggregate material must be completely dried in order to be coated by the liquid asphalt cement binder. This process is accomplished in a counter flow drum heated by a direct fire burner with internal metal slats (flighting) to facilitate heat transfer. In the region immediately surrounding the flame, special flights are designed to shield the drum from radiation. Direct observation of the dryer is impossible and thus simulation gives the ability not only to monitor the behaviour of the material, but also to optimize the flight design for increased drying efficiency and mitigate to thermal damage to the drum from the heat of the burner flame. In this study coupled CFD-DEM was used to investigate different flight designs in order to optimize both heat transfer to the aggregate particles and thermal shielding of the drum shell. Radiation from the flame to the particles and drum and flights was included as well as conduction between particles and geometry. The results of the simulation have been corroborated by field observations.