The calculation accuracy of solid friction factor (f(p)) is important for the prediction of pressure drop, gas-solid drag force and particle velocity in a horizontal dilute phase pneumatic conveying system. In this study, some modifications were applied to the commonly-used f(p) correlation developed by Yang. First, the data processing to implicitly correlate fp was improved. Unlike the method used Yang's derivation, the solid volumetric concentration. the ratio of the particle's radial velocity to axial velocity and the ratio of inertial force to gravity force of the fluid were separately used instead of combining together. In addition, the sphericity of the particles was considered such that the correlation can be valid for the non-spherical particles. Experiments were also conducted to validate the correction of the modified correlation. Compared with the experimental data, the modified correlation has remarkably better accuracy on fp prediction than the existing correlation. Moreover, the correlations of solid velocity and pressure drop based on the newly proposed fp correlation were derived. The predictions of the derived correlations agree well with the present and literature experimental data. (C) 2011 Elsevier B.V. All rights reserved.