Analysis of the residence time distribution in rotary kilns and the effect of particle sizes

In this study, a mathematical model based on the segregation-induced ring-core structure was developed to predict the residence time and axial velocity of particles of different sizes within a rotary kiln. Validation experiments were conducted using a pilot-scale rotary kiln with bidisperse particle systems comprising particle sizes of 0.7 mm, 2 mm, and 4 mm. The entire process was recorded using video analysis, which enabled the tracking of tracer particle movement from the inlet to the outlet. Based on the recorded data, the average axial velocity for each particle size across different kiln regions was determined. At the outlet, the tracer particles were analyzed using statistical methods and diffusion theory, allowing for the calculation of the residence time distribution (RTD), mean residence time (MRT), variance, axial dispersion coefficient ( D z ), and Peclet number (Pe). The experimentally obtained MRT exhibited strong agreement with the predictions of the mathematical ring-core structure model, confirming its accuracy and reliability. Additionally, the influence of particle size and mixing behavior was systematically evaluated by varying particle size ratios and mass concentrations. • Developed a model for predicting residence time and velocity of bidisperse particles in rotary kilns. • Validated the model using pilot-scale tests with various size ratios and mass concentrations. • Measured RTD, MRT, D z , and Pe via tracer tracking and statistical methods. • Achieved high model accuracy by comparing predictions with experimental data. • Evaluated size and mixing effects by changing size ratios and mass concentrations.