A chemical reactor for the steam-gasification of carbonaceous materials (e.g., coal or coke) is modeled by means of a two-phase formulation that couples radiative, convective, and conductive heat transfer to the chemical kinetics. A unique feature of the reactor is that the gas-particle flow is directly exposed to concentrated solar radiation, providing efficient radiative transfer to the reaction site for the high-temperature endothermic process. The governing mass, momentum, and energy conservation equations are solved by applying Monte Carlo, two-flux, and finite-volume techniques. Validation is accomplished by comparing the numerically calculated temperatures, product composition, and chemical conversions with the experimentally measured values obtained from testing a 5 kW prototype reactor in a high-flux solar furnace. (C) 2006 Elsevier B.V. All rights reserved.