In this work, an Eulerian/Lagrangian approach has been employed to investigate numerically flow characteristics, heat transfer and combustion processes in a tangentially fired furnace. A new method of cell face velocity interpolation for non-staggered grid system is employed to avoid pressure oscillation. Grid-independence tests have been conducted. To avoid pseudo-diffusion that is significant in modeling tangentially fired furnaces, some attempts have been made at improving the finite-difference scheme. The standard k-epsilon model performs well in predicting Rows without swirling or without sharp change within the calculated region. But for tangentially fired boiler furnaces, where swirling flow is very marked, we must resort to other more valid, more efficient turbulent models to gain accuracy. Tn this paper, we try to use RNG k-epsilon model as an alternative to the standard k-epsilon model. Comparisons have been made between standard k-epsilon and RNG k-epsilon models. Some new developments on turbulent diffusion of particles are taken into account for improving computational accuracy, and probability error is also discussed. Finally, temperature deviation is studied numerically so as to gain deeper insight into tangentially fired furnaces. (C) 2001 Elsevier Science B.V. All rights reserved.