Experimental Investigation on Motion Characteristics and Thermal Behaviour of Lumps in Gas-Solid Fluidized-Bed Reactors

Gas-solid fluidized-bed reactors are characterized by excellent mixing. This led to their widespread use in waste pyrolysis and gasification processes. Although undesirable, the formation of lumps in such applications cannot always be prevented. If these lumps form, they may hinder the temperature homogeneity that usually characterizes fluidized-bed reactors. This work aims to investigate the motion characteristics and thermal behaviour of such lumps as these can help determine how lumps impact the reactor operation. A particular focus is placed on the segregation behaviour, the dispersion coefficients and the heat transfer coefficient between lumps and fluidized beds. The fluidization velocity, the particle size of the bed material and the density ratio between the lump and the bed material are varied to study their effects on the lump’s motion characteristics and thermal behaviour. A down-scaled pseudo-2D fluidized bed operated at ambient temperature is used. X-ray imaging is used to track the lump’s position, and infrared imaging allows to determine its temperature evolution over time. Dispersion coefficients were found not to be affected by the lump density, while they increased with the bed material particle size and the fluidization velocity. The segregation behaviour was mostly influenced by the fluidization velocity. An optimal value of gas superficial velocity guaranteeing proper mixing, regardless of the lump density, was found. The heat transfer coefficient was found to be strongly related both to the fluidization velocity and to the particle size of the bed material, with an increase in the particle size causing a deterioration of the heat transfer. Values of fluidization velocities guaranteeing maximum heat transfer coefficients were also identified.