Bed mixing and heat transfer in a batch loaded rotary kiln

A pilot‐scale rotary kiln simulator has been used to make experimental measurements of the thermal response of solids charged onto a preexisting bed of hot solids material. The measurements clearly show that the bed is not thermally uniform. Time constants for bulk heating and mixing were extracted from the measurements. A simple model is developed that correlates the time constant for mixing to bed turnover rate, allowing the thermal history of a charge of solids to be predicted based on measurable parameters of the kiln and bed. The measured and predicted thermal histories show that mixture greatly augments the initial rate of heat transfer to the fresh charge of solids. This is important because rapid heating of a fresh charge of solids could result in rapid evolution of volatile species.