(513fb) Long-Term Simulation of Gas-Liquid Reactor Using CFD-PBM Integrated Compartmental Model

Gas-liquid reactors are still poorly understood because of the complexity of the flow patterns and their unknown behaviors [1]. Computational fluid dynamics (CFD) is widely used in a gas-liquid reactor to obtain flow information. However, most of the studies are remain in the short-time simulation due to CFD simulation requires an excessive amount of computational time; even when chemical reactions or population balance model (PBM) is added to CFD, large computational load force CFD to simulate only for short-time. To overcome the exorbitant computational time, the CFD-based compartmental model has been widely studied. In the CFD-based compartmental model, the hydrodynamics are computed in CFD, and using the flow information chemical reactions and PBM are calculated in a numerical tool such as MATLAB or PYTHON[3, 4]. This model makes it possible to obtain the long-term dynamics of chemical reactors, but the fact that the model cannot update the flow means that it is inappropriate to be used when physical phenomena such as air aggregation and breakage make significant changes of the flow [5]. For this reason, it is important to improve so that the CFD-based compartmental model can update flow information periodically.

This study proposes a MATLAB-based computational framework for coupling PBM and CFD. The proposed approach is different from the traditional CFD-based compartmental model in that the flow information is updated periodically and the calculations of hydrodynamics and PBM are conducted separately via the compartment model. Hence, this framework enables predictions of the long-term dynamic behaviors of the system by reflecting the interactions between gas and liquid phases over time. In this model, the PBM and interactions between the compartments are solved in each compartment in MATLAB. The flow rate of the gas between two adjacent compartments is assumed homogeneous during the short-time intervals. To reflect the influence of flow change, the hydrodynamics of the gas is updated from CFD simulation using the compartmental model result. Through this cycle, long-term simulation can be performed more accurately. For the validation, the CFD-PBM integrated compartmental model is compared to the built-in CFD-PBM model in FLUENT 18.2. From the validation process, it is confirmed that the proposed model can substantially reduce the computation load simulating long-term dynamics behaviors in a reasonable time and this method can give a better understanding of the complexities of two-phase flows in a gas-liquid reactor.

References

[1] Ekambara, K., Mahesh T. Dhotre, and Jyeshtharaj B. Joshi. "CFD simulations of bubble column reactors: 1D, 2D and 3D approach” Chemical Engineering Science 60.23 (2005): 6733-6746.

[2] Delafosse, Angélique, et al. "CFD-based compartment model for description of mixing in bioreactors." Chemical Engineering Science 106 (2014): 76-85.

[3] Delafosse, Angélique, et al. "CFD-based compartment model for description of mixing in bioreactors." Chemical Engineering Science 106 (2014): 76-85.

[4] Rigopoulos, Stelios, and Alan Jones. "A hybrid CFD—reaction engineering framework for multiphase reactor modelling: basic concept and application to bubble column reactors." Chemical Engineering Science 58.14 (2003): 3077-3089.

[5] Kim, Minjun, et al. "Modeling long-time behaviors of industrial multiphase reactors for CO2 capture using CFD-based compartmental model." Chemical Engineering Journal (2020): 125034.