Local hydrodynamics and phase distribution in large-scale trickle bed reactors using multi-detector γ-ray densitometry

This study presents a new approach of using gamma ray computed tomography (CT) in a form of arc multi-detector gamma-Ray Densitometry (Arc MD-GRD) Technique where it measures the line averaged holdups of the phases which are projected on the diameter of the column to obtain their diameter profiles. This technique then was used to investigate the diameter profiles of the phases' holdups in a 12-inch diameter trickle bed reactor (TBR) using sulfur hexafluoride (SF6) as the gas phase to represent to a certain extent the industrial higher density of the used gas phase due to either the type of the gases or higher pressure and water with 8 g/l of Sodium Dodecyl Sulfate (SDS) to obtain a surface tension of 31.6 mN/m that is of interest to industrial applications as the liquid phase. The study provides the diameter profiles of dynamic liquid holdup, void fraction that includes the bed void and the void of the porosity of the catalyst, dynamic liquid holdup and the solid materials holdup (the catalyst solid materials without the porosity of the catalyst) under various gas and liquid flow rates, addressing the lack of engineering knowledge, need experimental data for models and computation validation for large-scale two phase flow packed beds. Experimental conditions included gas mass fluxes ranging from 0.13 to 0.28 kg/ m2 center dot s and liquid mass fluxes from 6.3 to 12.7 kg/m2 center dot s. The results reveal that the diameter profiles of the dynamic liquid holdup (or total) increase with increasing liquid mass fluxes and decreases with increasing gas mass fluxes. However, gas holdup increases with increasing mass fluxes and decreases with increasing liquid mass fluxes. The void fraction (void holdup) that includes the bed void and the porosity of the catalyst have had localized variations along the reactor height which is higher at the wall region. Solid material holdup profiles demonstrated negligible variation along the bed height and during the flow conditions used. Two different porous spherical packings were tested in the column. The two packings were made of alumina and had different diameters, corresponding to 1/16 in. (0.159 cm) and 1/8 in. (0.318 cm) with the latter approaching structured bed of packing. Liquid holdup and gas holdup measurements demonstrate that phase equilibrium is strongly dependent on packing geometry, where Case II exhibits a more homogeneous gas-liquid distribution, reducing maldistribution effects. A key novelty of this study is the use of Arc MD-GRD technique that can provide high resolution and also real-time hydrodynamic analysis, allowing for the detection of transient fluctuations in phase content. The findings validate the Arc MD-GRD technique as a fast-response and reliable tool for obtaining high-resolution, real-time phase distribution profiles in large-scale TBRs, thus supporting its application for optimizing industrial reactor design and operation.