Quantitative characterization of mixing processes in rotary calciners

Experiments were conducted to determine the effects of rotational speed, feed rate, and angle of inclination on the mean residence time, hold-up, and axial dispersion coefficient of cylindrical zeolite catalytic pellets in a rotary calciner (kiln). Nonintrusive sampling and analysis techniques were employed to measure the residence time distribution (RTD) of tracer pellets (injected at the feed entrance) both along and at the exit of the calciner. A single-parameter continuum model was applied to the residence time distribution (RTD) data to compute the dispersion coefficient as a function of distance. It was observed that the mean residence time is strongly dependent on axial velocity, hence, inversely related to rotational speed and angle of inclination, and is not a function of feed rate up to 10% fill. Material holdup was observed to be directly related to feed rate, inversely related to rotational speed, and slightly inversely proportional to angle of inclination. The dispersion coefficient was found to be strongly dependent on rotational speed and angle of inclination, but weakly dependent on flow rate.