Particle breakage in agitated dryers

• Main Author: Hare, Colin Leo
• Published: University of Leeds 2010
• Subjects: 664.0284
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.578680

In agitated dryers the motion of the impeller leads to shear deformation within the bed, which causes attrition. The attrition caused by the prevailing stresses and strains in a particle bed exposed to simple, well defined shear deformation in an annular shear cell has been extensively studied in the literature, however little effort has been made to better understand more complex shearing flows. A method of predicting particle breakage in agitated dryers is introduced here. The method uses models based on the Distinct Element Method (DEM), validated by torque and Positron Emission Particle Tracking (PEPT) measurements, to estimate the stress and strain rate distributions throughout the dryer bed. The attrition of Paracetamol and Aspirin under shear deformation in an annular shear cell is assessed and relationships of attrition to stress and strain developed. These relationships are combined with the stress and strain rate distributions obtained from the DEM to predict the attrition in a small-scale dryer. The attrition of Paracetamol and Aspirin in the small-scale dryer is measured experimentally and compared to the prediction. The relationship of Paracetamol attrition to stress and strain correlates well with the shear cell results; this is not the case for Aspirin. The prediction of Paracetamol attrition in the dryer therefore compares well to that measured experimentally, whereas the prediction of Aspirin attrition is less successful as the attrition resulting from the prevailing stresses and strains is not adequately described. The methodology developed here is generic and can be applied to a wide range of processes, such as dense pneumatic conveying, milling and grinding etc. III