In this work, the mathematical frame to obtain burnoff distributions of char particles in a model bubbling fluidized bed reactor (BFBR) is presented. The developed equations are functions of the kinetic rate and attrition constants of the char particles, which can be determined by batch combustion experiments in a lab-scale fluidized bed reactor. Following this method, the burnoff distributions in a model BFBR of char particles obtained from four different materials (a metallurgical coke, a medium-ash anthracite, a medium-ash lignite and a graphite) were calculated. From these distributions, the combustion efficiencies of these materials were estimated.