The description of the fluidization behavior of Group B particles is ambiguous at high velocities in wide vessels like those in commercial solid-fuel converters, such as boiler furnaces and gasifiers. Bubbling, turbulent, and fast-fluidization regimes are analyzed here, especially related to fuel converters. It is claimed that the bottom bed in fluidized-bed boilers is operated in a bubbling regime of fluidization even at high gas velocities accompanied by a tall splash zone, as long as there is sufficient bed material in the system. It is also shown that the upper part of conventional circulating fluidized-bed boilers operates in a dilute-flow mode. In denser flows, a comparison between transport velocity and terminal velocity indicates that clustering flow is much stronger for Group A particles than for Group B, and hence, fast fluidization should be less developed for Group B than for Group A particles. The influence of temperature is also shown. (C) 2016 Elsevier B.V. All rights reserved.