Simulations of kinetic theory based two-fluid model for gas-particle flows in vertical riser segments have been performed. In two-dimensional (2D) simulations of flows in a vertical channel segment and in three-dimensional (3D) simulations of flows in a vertical cylindrical riser segment, periodic boundary conditions were employed in the axial direction. These were supplemented by simpler quasi-one-dimensional (1D) simulations of channel flow and quasi-2D simulations in cylindrical geometry, where it was postulated that the flow variables did not change axially. Both 2D and quasi-1D simulations of channel flow were found to manifest in a robust manner quasi-periodic solutions consisting of laterally traveling waves. Similarly, quasi-2D and 3D simulations of cylindrical riser flow manifested spinning flow states, which in the case of high aspect ratios showed signs of transition to swirling flow states. The period of the oscillating/spinning flow could he captured by a rather simple correlation, whose structure suggests a microscopic origin for the flow structure. The centrifugal force associated with the spin appears to be sufficient to impart an influence on the extent of radial segregation of particles. (C) 2013 Elsevier B.V. All rights reserved.