Modeling the pyrolysis of wet wood using FireFOAM

Abstract

A wet wood pyrolysis model was developed involving the combined influence of moisture, char oxidation, flame radiation and chemical reaction kinetics. Especially instead of multiple parallel reactions, a simple one-step nth-order Arrhenius expression for dry wood pyrolysis was combined with moisture drying reaction, which aimed at reducing the difficulty of obtaining kinetic and thermophysical parameters of intermediate solids. Code validation shows that the predicted surface temperature and total solid conversion ratio agree well with Shen et al.’s measured values in cone calorimeter under air atmosphere. The mass fluxes of water vapor and pyrolysate are analyzed as a function of wet wood thickness under various external radiation heat fluxes. The thickness has no effect on the maximum mass flux of vapor. The thickness of 8mm is found to be the critical value with two peaks appearing simultaneously at pyrolysate mass flux profiles under 40kWm−2. For the cases with two peaks of pyrolysate mass flux, the thickness has little effect on the time and value at the first peak of pyrolysate. However, those at second peak vary obviously with thickness. The fitting correlations of vapor duration and second pyrolysate flux peak time were also obtained.