Design and commissioning of a flight unloading device

Abstract

Flighted rotary dryers are used extensively to control the temperature and moisture content of granular materials. Despite their extensive use, the solids transport characteristics of flighted rotary dryers are still poorly understood. There are a few studies in the literature that have examined the unloading of small scale flights within pilot dryers using photographic techniques. Further, theoretical considerations and geometric analysis are also reasonably well described in the literature. However, there has been little direct experimental work undertaken on full scale flights. This paper outlines the design and commissioning of an experimental apparatus to study the unloading characteristics of flights similar to those used in industrial sugar dryers. A section of a full-scale dryer flight is unloaded into a collection tray, and four load cells are used to provide continuous measurement of the unloading mass. A range of flight rotational speeds are possible. Facilities are also available for filming the unloading process at the flight tip. The most significant problems associated with directly obtaining mass flow measurements from flights has been the impact forces that occur when falling particles land in the collection tray. Design modifications and modelling techniques to reduce or quantify the impacts are described. Filtering techniques used to reduce signal noise are also described. Preliminary unloading results are given to illustrate that the apparatus provides a means to experimentally measure and compare different flight geometries, and to develop optimal flight designs.