DEM-CFD modeling of limestone flowing-down in a combustion field in a rotary kiln

Abstract

A new efficient numerical approach for Reynold-averaged Navier–Stokes (RANS) simulation coupled with the discrete element method (DEM) is developed for the calcination of limestone flowing down in a real kiln, considering the combustion reaction of practical fuel. The validity of the method is assessed by comparison with experiments. In addition, the calcination process in a real kiln is investigated in detail by injecting the limestone with a particle size distribution that reflects actual conditions, while also considering chemical reactions occurring inside the kiln, including the combustion flow field formed by two spray burners and surface reactions on limestone particles. The results show that the calcination of limestone in a real kiln is successfully reproduced by the RANS/DEM, which is developed under the assumption that air turbulence does not significantly affect the movement of limestone, and therefore enables the analysis of the long residence time in the real kiln. The limestone with a small diameter of 5 mm is fully calcinated more than 10 m upstream from the kiln outlet, while larger limestones with a diameter of 35 mm are discharged without complete calcination, even upon reaching the outlet. This suggests that the proper control of the limestone size leads to the optimal design of real kilns.