Movement and mixing behavior of a single biomass particle during combustion in a hot fluidized bed combustor

Abstract

The characteristic motion of fuel particles in a fluidized bed (FB) reactor has an important impact on combustion behaviors. Therefore, monitoring the characteristic motion of fuel particles is of great significance for understanding the process of fuel conversion in fluidized bed. In this work, the characteristic motion of a single fuel particle (lignite and rice hull) in the different locations (including the dense phase, bed surface, and splash zone) was investigated in a two-dimensional visualized fluidized bed combustor. The movement behaviors of the fuel particle in the combustion process were recorded using a color video camera. The results showed that the particle was likely to be found in the dense phase during drying and devolatilization processes. As the combustion continued, the particle density decreased and the char was likely to be found floating on the bed surface. It was observed that the different fuel particles exhibited significantly different characteristic motion. To be specific, the lignite particle preferred to be observed in the dense phase, while the biomass particle tended to be found floating on the bed surface. Additionally, increasing the oxygen concentration significantly improved the probability of the particle to be found floating on the bed surface, while increasing the fluidization velocity exerted the opposite effect. At a high fluidization velocity, the probabilities of finding a particle in the dense phase and splash zone were increased as a result of the high bed voidage and bubble fraction. Replacing N2 by CO2 did not affect the probability that a particle would be found in a different location.