The preliminary analysis of a package-scale circulating fluidized bed (CFB) combustor through modeling and experimentation was performed to help determine particle trajectories and carbon burnout efficiency. The CFB consisted of a primary fast fluidizing bed and two bubbling beds. The fluidized bed models found in literature and a freeboard model utilizing a commercial code, FLUENT, were used in simulations. Primary gas velocity of the fast fluidizing bed was varied between 4.9 and 12.2 m/s and gas temperatures were varied between 800 and 1200 K. For comparison with computations of hydrodynamics, a scaled down version of the combustor was run using granulated plastic particles at 300 K.
The results of computations showed that the freeboard has a very complex flow with many recirculation zones that usually become larger and move away from the walls with increasing primary velocity. There was less particle movement in the experiments than in the simulations due to the differences in particle diameters, the type of particles, the gas temperature, and the scaling geometry.