Modelling the hold up of lifters in rotary dryers

Rotary dryers and kilns are commonly used to dry and process granular materials. They have application across a wide range of industries ranging from food production to cement production. Rotary dryers contain lifters to lift the material away from the bottom of the dryer and then to drop it through the gas to promote mass and heat transfer between the granular material and the gaseous phase. Understanding these lifters may result in improved dryer design. This paper describes a model that can be used to predict the hold up of material in lifters during rotation depending on the lifter geometry and the angle of repose of the material. The model is used to evaluate the hold up profile of a range of lifters. According to the model, simple lifters consisting of a single segment do not hold up as much material as lifters containing a number of segments, such as a hook formation. Further, the more complex lifters are able to distribute the material more evenly across the transverse section of the dryer compared to the simple lifters and this may improve the overall heat and mass transfer of the dryer. (C) 2008 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.