Modelling of Devolatilization in Fluidized Bed Combustion

A mathematical model is developed to describe the devolatilization process in a circulating fluidized bed combustor. The model is a combination of two submodels: single particle devolatilization and fluid dynamics. The single particle model includes the influence of both chemical kinetics and heat transfer on the rate of devolatilization.The results show a good agreement with literature data.

The fluid dynamic model describes the main characteristics of a CFB: A dense zone in the bottom, followed by a splash zone and a dilute zone with a core-annulus structure. Each zone is modelled as a number of CSTR's and the size and number of CSTR's has been estimated from tracer experiments in an 80 MWth CFB boiler.

It was not possible to evaluate the model against experimental data, but the dependence of particle size on the degree of devolatilization in the dense bed agrees qualitative with the expected behavior. The model shows that the devolatilization mainly occurs in the dense bed.