A model has been developed to predict the flow rates of solids (bottom ash and flyash) out of a circulating fluidized bed (CFB) boiler, using fuel and sorbent properties and the plant solids feed data. Fuel particles were separated by density and size classes, and characterized. The attrition of coarse fuel particles that form flyash after combustion is quantified by means of an attrition coefficient for each particle class. The model was used to calculate attrition coefficients for the heavier (higher mineral content) fuel particles which were obtained by gravity separation (float-sink analysis). Toward this end, solids analyses and operating data from two commercial CFB power plants in Pennsylvania were used. This model can be of use for assessing the ability of the flyash and bottom ash handling systems in a CFB power plant to handle the ash streams produced when a plant changes fuels. (C) 2008 Elsevier Ltd. All rights reserved.