Numerical and experimental study of gas–particle radiative heat exchange in a fluidized-bed reactor for steam-gasification of coal

A heat transfer numerical model is developed for the steam-gasification of coal in a fluidized bed contained in a quartz tubular reactor that is directly exposed to concentrated thermal radiation. The Monte Carlo method is applied for solving the radiative exchange within the reactor quartz walls, the bed particles, and the gas phase. The reaction kinetics are described by Langmuir–Hinshelwood type rate laws. Steady-state mass and energy conservation equations that link heat transfer to the chemical kinetics are formulated and solved iteratively by the finite volume method and Newton algorithm. Numerically computed temperature profiles, product gas composition, and conversions are compared to experimentally measured values in a directly irradiated tubular quartz reactor, tested in a high-flux solar simulator. At above 1450 K, the gas composition consists of a nearly equimolar mixture of H2 and CO, with less than 5% of CO2. Heat is transferred to the particles predominantly by thermal radiation and to the gas by particle–gas convection, since radiation absorption by particles is three orders of magnitude higher than that of the gas phase.