Modeling of flow conditions in down draft gasifiers using tin film models

In order to examine how an inhomogeneous char bed affects the gas flow through the bed, a dynamic model have been developed to describe the flow distribution in a down draft gasifier. The gas flow distribution through the bed was determined using a thin film model approach. The temperatures in the bed were determined from a thermodynamic model of the gasification process. Model calculations showed that a relatively small fraction of the gas was flowing through a part of the bed that was fuelled with smaller particles compared to a part of the bed that was fuelled with larger particles. The calculations also show that if the height of the two different parts of the bed were not evened out the bed would not be stable. However, if transport of particles from one part of the bed to the other occurred the bed would be stable.