The impact of physical and process parameters on flow of gas and particles in a vertical duct has been examined. Steady-state solutions were sought to equations of continuity and motion with closures from kinetic theory and the variations of the solutions with changes in parameters were computed using a bifurcation/continuation approach. When the particles are assumed elastic, we find that the segregation of particles transits from the center to the walls with an increase in the bed width or solids load. The origin of this transition arises from the contribution of the gas-particle slip term on the pseudothermal energy transport. When the particles are inelastic, we find particles always segregate to the center of the channel, irrespective of the bed width or solids load. As we track the variation of the average solids fraction with a number of parameters, multiple steady-state solutions can be observed. Recent interest in using fluidized beds on Mars or the Moon for local production of oxygen has prompted us to examine the effect of gravity on steady fully developed flows in gas-particle fluidized beds. When the average gas velocity is held constant, the flow profiles are found to be insensitive to the magnitude of gravity if the gas flow rate is high and particles always move upward in the bed. The physical mechanism leading to this insensitivity can be traced to the automatic compensation of the gas-particle drag force to the body force. However, when the gas flow rate is low, particles move downward in the region close to the walls with high gravity, whereas this downflow is not observed under low gravity. Finally, the effects of two dimensionless numbers are investigated. It is found that the flow behaviors are not sensitive to the variation of the Reynolds number when this number is high because of a relatively small value of the gas viscous term. With an increase in the Froude number, the gas and particle velocities decrease as well as the granular temperature. (c) 2005 American Institute of Chemical Engineers.