Impact of granular segregation on heat transfer in horizontal drums

Abstract

In the production of biofuel from scrap tire pieces by pyrolysis in a rotary kiln, particle size segregation is believed to affect the temperature evolution and control within the reactor. To study the impact of granular segregation on heat transfer in rotary kilns, a thermal discrete element method-based model incorporating a thermal resistance network was developed for bidisperse particulate blends. It was validated using a system of glass and aluminum beads differing in size. The harmonic mean radius was found to best represent bidisperse contacts. Heat transfer in six different segregated bed structures in a wall-heated drum for two particle size ratios was studied. Granular segregation significantly influenced the temperature profiles in the beds, dragging down the temperature of the center of the bed, where a core of smaller particles had formed. This resulted in an inverse relationship between the effective heat transfer coefficient of the bed and the intensity of segregation. Within the segregated cases investigated, the temperature difference between the large and small particles could be up to 30 times higher than that of a well-mixed configuration.