Simultaneous tribo-charging of the wall and particles during pneumatic transport of powders in dilute phase is modelled. The concepts of "simple-condenser model" and ''effective work function" are used to Lake into account the local charge transfer between the two materials during particle wall collisions. Exact analytical solutions are provided for the model, It is shown that, the tribo-charging process is mainly governed by the ratio between the charge transfer constants of the wall and particles. The results show that for high tribo-charging conditions of wall with respect to particles, the accumulated charge of the particles tends to an asymptotic limit imposed by the charge saturation of the wall. For low charging walls, the particle charge is no more limited by the charge of the wall and increases continuously. Quantitative analyses show that the predominant regime (i.e particles or wall limited) could be fairly predicted using a dimensionless group (3 beta D/2d(p)) based on the volume fraction of the powder, beta, the pipe diameter, D, and the particles mean diameter, d(p). Furthermore, a dimensionless criterion is established allowing the prediction of tribo-charging regimes and the trend of space evolution of particles charges. A comparison between the experimental and calculated data was carried out and permitted the validation of the model. (C) 2013 Elsevier Ltd. All rights reserved.