The present paper considers the numerical simulation of horizontal pneumatic conveying in a 2-d channels. The gas-phase is calculated by the time time-averaged Navier-Stokes equations, and the well known k-ε model of turbulence is used to close these equations. The particle-phase is treated with the Lagrangian approach, and the PSI-IN-CELL method is used for coupling the phases. A detailed model for the particle-wall interaction including the effect of wall roughness has been considered in the numerical calculation. The roughness of the walls and slight non-sphericities in the particle shape was simulated by changing the local wall inclination by a stochastic process. Inter-particle collisions were modelled using a stochastic approach in which for every particle in every time step the collision probability was calculated and the particle velocity was modified accordingly. The numerical results agree reasonably with the experimental results.