Sand Fluidized Beds for Wood Waste Gasification: The Pellet Influence on Bed Fluid Dynamics at Ambient-Conditions

Understanding the fluid dynamics of fluidized beds loaded with biomass pellets is of significant value for the design of wood waste gasifiers. In the present study, cylindrical wood pellets are loaded into a lab-scale cold gasifier unit at 2.5 vol% and 7.5 vol% concentrations and studied at superficial air velocities of 0.25, 0.282, and 0.344 m/s (corresponding to 80, 90, and 110 SCFM). Measurements of bubbles, sand particles, and biomass pellets are taken at a 45 cm height from the distributor plate, and at 9, 12, 15, 18, and 21 cm radial positions from the column wall by employing the CREC-GS-Optiprobes, a valuable integrated fiber optic-laser tool system. A new data processing methodology is established using laser signals that are reflected from the outer surface of aluminum-foil-wrapped cylindrical wood pellets. In addition, a new algorithm is implemented to distinguish pellet-reflected signals from those of bubbles and emulsion-phase particles. On this basis, for the first time, a Phenomenological Probabilistic Predictive Model (PPPM), is considered to predict Bubble Axial Chords (BACs) and Bubble Rise Velocities (BRVs), in a sand fluidized bed loaded with biomass pellets. This is accomplished within a set band of values accounting for three standard deviations from their means or including 85.9% of the bubbles measured. Thus, it is demonstrated that the PPPM is adequate to establish the constrained random motion of bubbles in sand fluidized beds, under the influence of uniformly distributed biomass pellets. It is anticipated that the findings of the present study will be of significant value for the design of sand biomass gasifiers of different scales.