The overall particle motion in bubbling fluidised beds can beconsidered to be the superposition of (1) bubble-induced motiondue to the presence of rising bubbles and (2) particle random walkdue to many consecutive particle–particle collisions (Vanderroostet al., 2012a). In the region near the reactor wall, the local particle motion is also affected by frictional forces between particles andbetween particles and the reactor wall. In this section, the phenomenon of bubble induced particle motion will be discussed inmore detail.