Euler-Lagrange Modeling of Gas-Solid Flow in a Circulating Fluidized Bed Riser: Evaluation and Comparative Analysis

Introduction: This study presents the development and evaluation of a Computational Fluid Dynamics (CFD) model utilizing the Euler-Lagrange approach to simulate gas-solid flow within a circulating fluidized bed (CFB) riser. The research aims to enhance the understanding of multiphase dynamics in such systems, addressing limitations of prior Euler-Euler models. Using ANSYS CFX, two types of simulations were performed: initial steady-state simulations were conducted to calibrate and evaluate the models' behavior, followed by transient simulations to investigate the system’s time-dependent dynamics. All simulations were isothermal, modeling air as the continuous phase and Nylon-66 particles as the dispersed phase. Key findings indicate that flow movement is concentrated at the riser's inlet, forming a high-intensity jet, with particle velocities aligning with expected values (0.5-2.0 m/s). Pressure distributions exhibited typical patterns for upward two-phase flows, showing significant drops at the inclined solid inlet and stable conditions in the vertical section. While this modeling approach accurately captured turbulent effects in critical inlet regions, the study acknowledges limitations, including computational time constraints and the exclusion of heat transfer effects. This work significantly contributes to the literature by providing a detailed understanding of two-phase flow in risers and offering a robust, comparated Euler-Lagrange computational model that surmounts the inherent practical and informational limitations of purely experimental investigations, laying a solid foundation for future research and optimization in industrial applications like Fluid Catalytic Cracking (FCC) processes. Objective: This study develops and evaluates an Euler-Lagrange CFD model to simulate gas-solid flow in circulating fluidized bed (CFB) risers. It aims to enhance the understanding of multiphase flow dynamics, address the limitations of Euler-Euler models, and compare the model’s performance against existing numerical data from the literature. Theoretical Framework: The theoretical framework outlines key concepts of multiphase flow, emphasizing the use of cold riser pilot units to simulate industrial reactor behavior. It also presents the fundamentals of Computational Fluid Dynamics (CFD), detailing its methodology, relevant modeling approaches, and its complementary role alongside experimental studies in addressing traditional limitations. Method: This computational study employed ANSYS CFX to perform steady-state, isothermal simulations of gas-solid flow in a vertical riser, modeling air as the continuous phase and Nylon-66 particles as the dispersed phase. The SST turbulence model and coupled interphase interactions were implemented to characterize flow behavior and collect key variables. Results and Discussion: The results showed that flow was concentrated near the riser inlet, forming a high-intensity jet. Particle velocities were within expected ranges, and pressure profiles exhibited typical patterns for upward two-phase flow, including significant drops at the solid inlet and stable values along the riser. The discussion also addressed modeling limitations, such as the absence of thermal effects and computational time constraints. Research Implications: This research contributes to the advancement of multiphase flow modeling in chemical engineering by improving the understanding of gas-solid dynamics in risers. Its implications include supporting industrial process design, complementing experimental studies, and offering a foundation for future numerical and hybrid modeling efforts. Originality/Value: The study’s originality lies in developing and evaluating an Euler-Lagrange CFD model that addresses the limitations of Euler-Euler formulations in capturing particle-scale phenomena. It provides an in-depth computational analysis that advances the understanding of multiphase flow behavior in risers.