Development and validation of an enhanced filtered drag model for simulating gas-solid fluidization of Geldart A particles in all flow regimes

State-of-the-Art Review of Fluid Catalytic Cracking (FCC) Catalyst Regeneration Intensification Technologies

Fluid catalytic cracking (FCC) is the workhorse of modern crude oil refinery. Its regenerator plays a critical role in optimizing the overall profitability by efficiently restoring the catalyst activity and enhancing the heat balance in the riser reactor. Improvement in the device metallurgy and process operations have enabled industrial regenerators to operate at high temperatures with a better coke burning rate and longer operating cycle. Today, the carbon content of regenerated catalyst has drastically reduced to less than 0.1 wt.%. However, the unit is still plagued with operational complexities and insufficient understanding of the underlying dynamic, multiscale intricacies. Recent process-intensification strategies provide insights into regenerator performance improvement potentials. In this review, the importance of the uniform distribution of spent catalysts through structural modification and operational manipulations of the catalyst distributor is discussed. The knowledge of the role of baffles in enhancing excellent gas–solid interaction has been increasing, but skepticism due to its complex hydrodynamic effects on gas–solid flows fends off operators from its application, a critical evaluation of its implication in the regenerators is covered. The understanding of the contribution of air/steam distributor design and feed gas injection techniques for even contact with spent catalyst leading to the improvement in FCC performance is also investigated. The reliability of FCC components is equally a big concern, as unplanned shutdown and enormous economic losses are being witnessed due to device failure. To this end, mitigation approaches to damaging afterburn and high-temperature erosion problems with respect to process control and geometric adjustment in the bed, freeboard, cyclone separators and collection ducts are explored. Emission limits for fluid catalytic cracking unit (FCCU) and products are consistently ratcheting downward; the commingled turnkey solutions to reducing pollutants generation are also reviewed.

Hydrodynamics of Irregular-Shaped Graphite Particles in Coaxial Two-Phase Jet Flow

Expanded graphite particle is characterized by the low density in comparison with those of bead glass and copper particles. Hydrodynamics of the irregular-shaped graphite particle swirling flows in a coaxial chamber are investigated via an improved kinetic frictional stress model. A drag force coefficient considering the effects of irregular shapes based on the artificial neural network algorithm is adopted to describe the momentum transfer between nonspherical particles and gas phases. The proposed model, algorithm, and source code for modeling and simulation are validated by measurement using spherical glass beads, and acceptable agreement is obtained. Lower sphericity particles enhance the anisotropic particle dispersions and induces the redistributions of the Reynolds stresses of the two-phase flow. Irregular-shaped particles are more sensitive to the gas followability instead of own inertia, whereas spherical particles are easier to be affected by the inlet effects. The interlock force between nonspherical particles takes great effect on particle flow than the spherical particle. The axial-axial normal stresses of sphericities of 0.63 and 0.72 are approximately 3.4 times larger than those of shear stress of spherical particle, and their axial velocities locating at near central regions are 3.0 times larger than those of sphericities.

On the drag force closures for multiphase flow modeling

Drag force models are one of the most important factors that can affect TFM and CFD-DEM simulation results of two-phase systems. This article investigates the accuracies, implementation issues and limitations of the majority of the drag models for spherical, non-spherical and systems with size distribution and evaluates their performance in various simulations. Around 1888 data points were collected from 19 different sources to evaluate the drag force closures on mono-dispersed spherical particles. The Reynolds number and fluid volume fraction ranges were between 0.01 and 10,000 and between 0.33 and 1, respectively. In addition, 776 data points were collected from seven different sources to evaluate the drag force closures on poly-dispersed spherical particles. The Reynolds numbers were between 0.01 and 500, fluid volume fractions between 0.33 and 0.9, and diameter ratios up to 10. A comprehensive discussion on the accuracy and application of these models is given in the article.