Chemical absorption using potassium-based sorbents is an effective method of low-temperature CO2 capture during the post-combustion process. In this work, a three-dimensional simulation is carried out to investigate the CO2 capture process with potassium-based sorbents in a fluidized bed absorber. The Dense Discrete Phase Model (DDPM) is employed to account for the effect of sorbent size distribution. The model prediction can give a good agreement with experimental data. The effects of sorbent size distribution on the temperature field and CO2 concentration are evaluated. Meanwhile, the influence of operating velocity on sorbent size distribution and bed expansion is also examined. The result reveals that the mean diameter of particles at the bed bottom will be weakened as operating velocity increases. (C) 2019 Elsevier B.V. All rights reserved.