Segregation of Fuel Particles and Volatile Matter During Devolatilization in a Fluidized Bed Reactor. I: Model Development

The phenomenology of fuel particles segregation at the surface of fluidized beds during devolatilization is modeled. The beds are assumed to be at incipient fluidization in order to focus the attention on the segregation mechanism caused by the formation of endogenous bubbles of volatiles. These are generated during fuel particle devolatilization immediately after its underbed feeding to a fluidized-bed reactor, and are distinct from exogenous bubbles, which are always present in the bed under aggregative fluidization conditions. Submodels describing the volatile flow pattern, the volatile bubble formation, the vertical motion of the volatile bubble and of the fuel particle are developed and combined in a coherent framework. Results of extensive model computations are presented and discussed. Qualitative and quantitative features of the fuel particle and of the volatile matter segregation processes are assessed by looking at the time required for the fuel particle to become segregated, at the frequency of volatile bubble formation, at the amount of volatiles emitted in the bed prior to particle segregation on the top of it. The proposed framework should complement previous studies on the segregation of fuel particles in freely bubbling fluidized beds based on the effects of exogenous bubbles only.