A coupled thermal-granular model in flights rotary kiln: Industrial validation and process design

The advancement on the physical heat transfer model in granular system is crucial for the energy process efficiency development such as flights rotary kiln encountered in many industrial areas. The present paper is devoted to a coupled thermal-granular model development applied to that process. Based on the exchange surfaces estimation governing the heat transfer phenomena, the granular motion distribution is calculated in the kiln cross-section. The granular volume fraction is accurately obtained in a dilute regime characterized by one active phase (curtain area) and a granular dense regime characterized by two passive phases (within a bed and the loaded flights). A suitable energy balance, where the fully heat transfer phenomena are considered, is established in an elementary volume and integrated along the kiln. The numerical results are compared to a set of experiments performed in an industrial flights rotary kiln applied to the hot-mix asphalt materials manufacture. The relative errors reach less than 5% on the gases and materials temperature. Finally, a set of simulations is carried out in order to analyze the role played by the rotational speed and flights in the frame of a suitable energy diagnostics for future process design.