The flow and dispersion behaviors of the fine particle injection in a gas-solid fluidized bed were studied numerically based on the two-dimensional multi-fluid model. The injection path and flow pattern of the flotsam solids were investigated. A distinct pair of counter-rotating vortices of flotsam particles appeared in the middle and upper parts of the fluidized bed. Higher injection rate was preferred for faster flotsam dispersion. The effects of flotsam injection on bed hydrodynamics were investigated with regard to the velocity distribution and volume fraction of bulk materials and the bubble size. Consequently, the mixing properties of the flotsam particles and bulk solids were quantified by the fluid-free flotsam fraction profile and the standard deviation. The fluidized bed was mixed acceptably with modest local segregation for all the conditions simulated. Lower injection velocity made contributions to better mixing especially for the duration of injection. (C) 2019 Elsevier B.V. All rights reserved.