Modelling Solid Mixing in a Rotating Drum
Dennis Van Puyvelde
Department of Chemistry, Materials and Forensic Science
University of Technology, Sydney
Monday, June 7, 1999 3:30 pm
Ben Bandy Conference Center
Center for Applied Energy Research
Rotary kilns are commonly used in the mineral industry but in the past their applications have been mostly limited to drying or calcining of granular materials. The AOSTRA-Taciuk rotary kiln processor is being used in a new process in Australia to decompose kerogen from oil shale. The retort zone of this processor is unique in that it requires the mixing of two separate solids, one of which is the preheated shale and the other which is the combusted recycled material. The mixing of this hot recycled material with the preheated shale results in the decomposition of the oil shale kerogen.
Previous rotary kiln research has mainly focussed on the steady state configuration of the solid bed, especially with respect to segregation as this has important energy efficiency implications. Limited research has been published to date on the mixing dynamics of solids in a rotating kiln. The previously published research does not allow the mixing in a rotating kiln to be determined. It is the purpose of the current research to build a model which will allow the mixing rate to be determined. This model may then be combined with granular heat transfer mechanisms so that the volatile evolution rate in the retort of the AOSTRA-Taciuk processor can be determined.
This seminar will describe the novel method used to determine the mixing dynamics of solids in a rotating drum. The method involves analyzing images of the rolling bed at different times in order to measure the change in contact between the different solids as time progresses.
Typical mixing dynamics followed constant mixing rate kinetics until a fully mixed bed was obtained. Slight fluctuations in contact occurred after the bed was fully mixed. The results from numerous experiments were collected and modelled, the experimental variable were rotational velocity, particle size, drum loading and material ratio. This model allows the mixing rate of solids in a rotating drum to be predicted and has been tested against independent experiments with success.