Time-dependent behavior of the ash particle size distribution in a circulating fluidized bed system

Abstract

In the present work, a particle population balance for a circulating fluidized bed combustor (CFBC) is developed that allows a description of the fate of individual particles in terms of attrition and transport effects. In the modeling of abrasion and shrinkage of particles, we consider besides operating conditions and particle size distribution also the residence time of particles in the system. The model takes account of the fact that fresh particles have a higher attrition rate than particles that have stayed for some time already in the system. The model aims at the description of the dynamic adjustment of the particle size distribution in a given system. The model is validated with experimental data from a pilot plant scale combustor, i.e., a CFBC with an inner diameter of 0.1 m and height of 15 m. A comparison between experimental and calculated data shows the suitability of the model. The model gives furthermore the opportunity for studying the effects of changes in operating conditions on the steady state solids particle size distribution and solids mass fluxes. The results of modeling a load change of the CFBC are presented and discussed in this work.