Significance of the gas release on the mixing of larger particles in bubbling fluidized beds.

Paper in proceeding, 2024

The mixing of larger particles (e.g. fuel particles) in dense fluidized bed units is governed by the interplay between buoyancy forces and the drag from the surrounding solids, whose movement is induced by the bubble flow. The contribution of the gas released from the converting particles (from e.g. drying or devolatilization) to their own mixing is often overseen. This experimental study aims to evaluate the influence of the gas release from larger particles on their mixing with the bed solids.
In this work, experiments are performed in a fluid-dynamically scaled cold flow model resembling typical conditions for the thermochemical conversion of solid fuels (more specifically, the pyrolysis of biomass at 700°C in a bed of sand fluidized by flue gas). Magnetic particle tracking is used to obtain the trajectory of a large particle resembling biomass properties, while freely moving in the bed. The work uses tracer particles loaded with dry ice to yield a gas release that mimics that of a biomass particle during drying and devolatilization, and compares them with particles of similar physical properties but without the ability to release gas. Different fluidization velocities are examined, revealing that the gas-releasing tracers tend to a deeper immersion within the dense bed at low fluidization velocities, whereas higher fluidization velocities render the gas-releasing tracers more buoyant.