A radioactive particle tracking (RPT) technique was used to study the effect of the size and density of an agglomerate on its interactions with internal baffles in a fluidized bed, mimicking the stripper sheds of a Fluid Coker (TM). Dense agglomerates (mimicking Fluid Coker agglomerates with a high liquid concentration) have a lower residence time in the stripper section of the reactor than light agglomerates (mimicking Fluid Coker agglomerates with a low liquid concentration) and small dense agglomerates spend more time in the stripper section than large dense agglomerates. A simple thermal drying model is proposed that uses the particle tracking results to determine the rate of release of hydrocarbons vapors in and below the shed zone, vapors which are responsible for stripper shed fouling. The model predicts that small dense agglomerates dry quickly while large dense agglomerates retain up to 50% of their original liquid when they leave the bed. Up to 18% of the original liquid contained in large dense agglomerates is evaporated and released in and below the shed zone, and thus contributes to shed fouling. (C) 2015 Elsevier B.V. All rights reserved.