Non-invasive and non-intrusive diagnostic techniques for gas-solid fluidized beds – A review

Gas-solid fluidized-bed systems offer great advantages in terms of chemical reaction efficiency and temperature control where other chemical reactor designs fall short. For this reason, they have been widely employed in a range of industrial applications where these properties are essential. Nonetheless, the knowledge of such systems and the corresponding design choices, in most cases, rely on heuristic expertise rather than a deep physical understanding of the phenomena taking place in fluidized beds. This limitation hinders the design, scale-up, and optimization of these complex units. Fortunately, a wide array of diagnostic techniques has enabled researchers to strive in this direction, with non-invasive and non-intrusive techniques particularly standing out for their ability to avoid affecting the flow field while not making direct contact with the medium under study. This work provides an overview of the most commonly applied non-invasive and non-intrusive diagnostic techniques to fluidized-bed systems, highlighting their measurement capabilities, advantages, and limitations. The latest developments and future trends are also examined, revealing that no single methodology represents an optimal solution on all fronts.