VERTICAL MIXING OF SOLIDS IN BINARY BEDS – ANALYSIS BY MAGNETIC SOLIDS TRACING

Paper in proceeding, 2024

Understanding the dynamics of solids mixing and segregation in fluidized beds is fundamental for the design and improvement of industrial processes that involve several solid phases. In this study, we introduce a novel measurement method for the assessment of solid phases distribution in the vertical direction and their segregation time under bubbling fluidization conditions. This method utilizes the magnetic solid tracing (MST) technique by using small coils mounted along a thin pin to capture the local concentration of one of the solid phases (in this case, the lean solids phase) with a time resolution of 20 Hz. The experimental procedure validates the reliability and efficacy of the MST pin method, highlighting its potential as a useful technique for studying complex solids systems. The measurements are carried out under fluid-dynamically downscaled conditions to resemble the mixing of biomass (lean phase) in a hot large-scale reactor (700⁰C) for thermochemical conversion.

The vertical concentration profiles of the lean phase and the transition times between mixed and segregated states are reported, for different fluidization velocities. The results show a consistent stronger penetration of the lean solids phase (consisting of particles lighter and larger than the bulk solids) into the dense bed as the fluidization velocity is increased. Further, it is shown that at very low fluidization velocity (fluidization number 1.5) segregation occurs much more rapidly than the mixing, while an increase in the fluidization velocity inverses this relation by continuously accelerating the mixing process and slowing down the transition to a segregate state.