| A one-dimensional, steady state fluidized bed, biomass gasifier model was developed, which consisted of a fuel pyrolysis model, an oxidation model, a gasification model, and a freeboard model. The fuel pyrolysis model predicts gas release from the solid fuel particles. A two-phase fluidization theory facilitates formulation of the system of differential equations in the gasification model which simulates interphase gas conversion in the presence of chemical reactions. The oxidation model sets entrance conditions for the gasification model under the oxygen-depletion assumption. The freeboard model calculates temperature and concentrations of gas and solid at the gasifier outlet. Given the reactor parameters, the fluidized bed temperature, the airflow rate, and other input data, the model predicts the fuel feed required for steady state operation, gas composition and lower heating value of the producer gas, and fuel energy conversion.; Fuel pyrolysis experiments were performed to obtain data for the pyrolysis model. A benchscale fluidized bed system was used. Results were checked for element and energy balances around the reactor and were fitted with quadratic functions of bed temperature which were used in the pyrolysis model. Gasification experiments were conducted to validate the gasifier model. A gasifier-combustor system was used. Data from these experiments were checked on element and energy balances around the system and around the gasifier.; The gasifier model was validated satisfactorily. Major mechanisms (fuel pyrolysis, and the chemical and physical rate processes) were identified for the core of the model. The effect of major input parameters was investigated with application runs of the model. Performance of a gasifier of larger size was also predicted. It is concluded that the model can be used to study gasifier performance and for the design of similar fluidized bed gasifiers especially of larger size.; Recommendations were given for improvement on the fuel pyrolysis and the freeboard models, for further validation experiments, for use of column chromatography for gas analysis, and for the design of the biomass gasifier. |
