In this paper, a multiscale Eulerian-Lagrangian CFD model based on OpenFOAM has been constructed, which takes into account heat and mass transfer, pyrolysis, homogeneous and heterogeneous reactions, radiation, as well as the interactions between the continuous gas phase and discrete particles. The proposed model is validated and applied to a laboratory-scale biomass entrained-flow reactor. The operating temperatures are high (1000-1400 degrees C) and influences of five operating parameters (reactor temperature, steam/carbon molar ratio, excess air ratio, biomass type, and particle size) on the gasification behavior are explored. Results show that an increase in the reactor temperature has a positive effect on both the H-2 and CO productions; increasing the steam/carbon ratio increases the H-2 production but decreases the CO production; increasing the excess air ratio decreases both the H-2 and CO productions; the variations in the gas product for the four biomasses studied are not so significant, because of similar biomass nature and, hence, one type can be replaced by another without any major consequences in the gasification performance; and both the CO and H-2 productions and carbon conversion decrease with an increase in particle size. Moreover, the predicted results follow the same trend as the experimental data available in the literature. Quantitative comparisons are also made, and the agreement is good.