Particle Residence Time and Particle Mixing in a Scaled Internal Circulating Fluidized Bed

Abstract

A process is under development for the steam gasification of biomass to produce a hydrogen-rich gas for use with a fuel cell to generate electricity on a local scale. A pilot plant is currently under construction in southern Italy operated with a circulating fluidized bed, and to predict the fluid dynamic conditions within the plant, a cold laboratory rig was built according to existing scaling laws, and experimental studies were carried out. In this paper, we present the experimental results concerning the solids residence time of particles introduced into the system and the particle mixing in the “gasifier” section of the model. Both parameters are of fundamental importance for the operation of the pilot plant as they determine the performance of the gasification process. It is shown that the biomass particles spend sufficient time in the gasifier to be fully gasified, and an equation is derived to predict the mean residence time of the biomass particles as a function of the dimensionless mass turnover of the circulating bed material. In addition, it is shown that the biomass particles are well mixed within the circulating bed material. One reason for this is a result of the geometric design of the apparatus.