Spent limestone particles in a circulating fluidized bed combustor (CFBC) may show a bottom-ash-pro (BAP) behavior or a fly-ash-pro (FAP) behavior. In this study, two spent limestone particles showing the BAP behavior and two spent limestone particles showing the FAP behavior in a 125 MW CFBC are characterized based on their total pore volume and specific surface area before and after 800 degrees C calcination. Provided that the limestone primary fragmentation does not significantly affect the particle size distribution immediately after CFBC injection, the limestone particles having a relatively porous structure after 800 degrees C calcination show a BAP behavior in a CFBC. (C) 2013 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.