Numerical modeling of combustion and pyrolysis of cellulosic biomass in thermogravimetric systems

A two-dimensional axisymmetrical numerical model for pyrolysis and combusti on of cellulosic biomass in a thermogravimetric system is presented. Both c hemical reactions and physical phenomena are considered, using fundamental principles. This mathematical model has combined the transient mass, specie s and energy conservation equation, Darcy momentum equation and a global Ar rhenius decomposition for a porous reacting biomass. It can predict weight loss rate, ignition temperature and gas composition. The results show that the biomass ignition is preceded by pyrolysis and subsequent release of vol atiles. The secondary ignition of char occurs after pyrolysis is complete. The volatile and char ignition temperature increases with the increase in t he heating rate and biomass volume, and decrease in biomass porosity. A com parison of weight loss calculations with experimental data indicates accept able agreement at different operating conditions. The model can be used for expanding limitations of thermogravimetric furnaces. The sensitivity analy sis, carried out for selected combustion parameters, was useful for setting up a pilot-scale combustor. (C) 2000 Elsevier Science Ltd. All rights rese rved.