Effect of lifter shape and operating parameters on the flow of materials in a pilot rotary kiln: Part II. Experimental hold-up and mean residence time modeling

• The presence of lifters increase significantly the hold-up within the kiln.
• The larger of the two materials used (broken rice) generally have lower residence time.
• We develop a model for the mean residence time by means of a dimensional analysis.

Experiments were carried out on a pilot scale rotary kiln equipped with lifters at room temperature to investigate the effects of the kiln slope, rotational speed, mass flow rate of materials, and exit dam height on the hold-up and the mean residence time (MRT). The MRT was determined from the residence time distribution measurements as detailed in Part I of this work. Two granular solids having different properties were used: sand and broken rice. Furthermore, two shapes of lifters were compared to determine the influence of lifter geometry: straight lifters (SL) and rectangular lifters (RL). A new model to predict the MRT was established by means of a dimensional analysis. The correlation not only gave good agreement with the experimental data from the present study, but also demonstrated good predictive performances when applied to published experimental data of other kilns; the model is applicable for inclined kilns that process materials in cascading (tumbling) motion, whether or not equipped with lifters or fitted with dams at the outlet end.

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