The generation of fines by attrition in fluidized bed reactors can cause problems. Thus, the objective of this study was to examine the amount of fines generated in the cyclone not only by attrition, but also by detachment of fine attached to surface according to time. Using a circulating fluidized bed (0.076mID x 3.7mheight), variables including cyclone inlet velocity (20.6-30.9 m/s), solid loading ratio (0.5-1 kg-solid/ kg-air), and elapsed time (0.5-13 h) were investigated. The fine generation ratiowas analyzed by dividing it into two components: the surface particle detachment ratio and the attrition ratio. The surface particle detachment ratio decreased rapidly with increasing cyclone inlet velocity and solid loading ratio. The attrition ratio was positively affected by the cyclone inlet velocity but negatively affected by the solid loading ratio, as found in previous studies. As the surface particle detachment ratio decreased with elapsed time, its contribution to the amount of fine particles generated decreased over time (73%-91% at 0.5 h and 41% at 5 h). The mass fraction produced by surface particle detachment was approximately 9% for the iron ore and 0.01% for catalyst particles. (c) 2019 Elsevier B.V. All rights reserved.