Influence of solids moisture content on the average residence time in a rotary dryer

The solids mean residence time in a rotary dryer is influenced by several v ariables such as dryer dimensions and solids characteristics. One of these characteristics, usually not taken into account in correlations proposed to estimate the mean residence time, is the solids feed moisture content. Alt hough it is well known that the solids moisture content has a major impact on the ability of the solids to move along the rotary dryer, it does not en ter as a parameter in available correlations. In this investigation, numero us experiments were performed in a pilot-scale rotary dryer to study the in fluence of solids moisture content and drying gas temperature on the mean r esidence time. Sand employed in cement makeup was used to perform these exp eriments. Results show that the mean residence time for a moisture content in the range of 8% to 12% is four times higher than for dry solids. The moi sture content and the drying gas temperature influence significantly the sh ape of the residence time distribution curve.