Flow behavior of gas and particles in a 2-D riser is simulated using a gas solid two-fluid model with consideration of the effect of particle rotation. The particle particle interactions are simulated from the kinetic theory for flow of dense, slightly inelastic, slightly rough spheres proposed by Lun (Lin, C. K. K. Kinetic theory for granular flow of dense, slightly inelastic, slightly rough sphere. I. Fluid Mech. 1991, 233, 539-559). Inelastic binary collisions of particles with normal and tangential restitution coefficients are considered. The modified expressions for energy dissipation and viscosities of particles are proposed as a function of tangential and normal restitution coefficients of particles. The present model is evaluated by the measured solids concentration and velocities of Miller and Gidaspow (Miller, A.; Gidaspow. D. Dense, vertical gas-solid flow in a pipe. AIChE J. 1992, 38, 1801-1815), and the measured solids concentration, mass flux, and pressure drop of Knowlton et al. (Knowlton, T.; Geldart, D.; Matsen, J.; King, D. Comparison of CFB hydrodynamic models. PSRI challenge problem. Presented at the Eighth International Fluidization Conference, Tours, France, May 1995) in the risers. Computed profiles of particles are in agreement with the experimental measurements. The simulated energy dissipation, granular temperature, viscosity, and thermal conductivity of particles exhibit nonmonotonic tangential restitution coefficient dependences clue to the energy losses resulting from particle collisions.