Identification of flow regime in a co-current upflow packed bed reactor (U-PBR) using gamma-ray densitometry (GRD)

Owing to their significant impact on the reaction rate, the comprehensive understanding of the hydrodynamics in any novel design of the Upflow Packed Bed Reactor (U-PBR) is essential for the optimization of its throughput. In this regard, the identification of the flow regime is of paramount importance. Therefore, in this work, we use the photon counts time-series data obtained using the non-invasive Gamma-ray densitometry (GRD) to identify, for the first time, the flow regimes and their transition velocities at two axial locations ($Z/D=0.8,1.56$$Z/D=0.8,1.56$) and five radial locations ($r/R=0,\pm 0.5,\pm 0.9$$r/R=0,\pm 0.5,\pm 0.9$) within the packed catalysts’ bed of U-PBR with a novel plenum design consisting of five deflectors. The photon counts, which were obtained for a wide range of superficial inlet gas velocities ($0.06-9.6cm/s$$0.06-9.6cm/s$) and superficial inlet liquid velocities ($0.003-0.021cm/s$$0.003-0.021cm/s$), were analyzed using the Kolmogorov Entropy (KE) method and the Standard Deviation method. Using these two methods, three flow regimes (bubble, pulse, and spray) as well as transient phases were identified at the center of the reactor (r/R = 0) at varying superficial inlet gas and liquid velocities depending on the axial location. At most other radial location, owing to more significant pressure drop, only two flow regimes are identified. Furthermore, the transition velocities were more distinctly identified using the KE method, compared to the standard deviation. These transition velocities were also found to vary significantly depending on the void fraction which substantially affects the liquid and gas distribution and mixing, as well as the local gas and liquid velocities.