SEGREGATION OF FUEL-PARTICLES AND VOLATILE MATTER DURING DEVOLATILIZATION IN A FLUIDIZED-BED REACTOR .1. MODEL DEVELOPMENT

The phenomenology of fuel particles segregation at the surface of flui dized beds during devolatilization is modeled. The beds are assumed to be at incipient fluidization in order to focus the attention on the s egregation mechanism caused by the formation of endogenous bubbles of volatiles. These are generated during fuel particle devolatilization i mmediately after its underbed feeding to a fluidized-bed reactor, and are distinct from exogenous bubbles, which are always present in the b ed under aggregative fluidization conditions. Submodels describing the volatile flow pattern, the volatile bubble formation, the vertical mo tion of the volatile bubble and of the fuel particle are developed and combined in a coherent framework. Results of extensive model computat ions are presented and discussed. Qualitative and quantitative feature s of the fuel particle and of the volatile matter segregation processe s are assessed by looking at the time required for the fuel particle t o become segregated, at the frequency of volatile bubble formation, at the amount of volatiles emitted in the bed prior to particle segregat ion on the top of it. The proposed framework should complement previou s studies on the segregation of fuel particles in freely bubbling flui dized beds based on the effects of exogenous bubbles only. (C) 1997 El sevier Science Ltd.