(204c) Comparison of Coarse-Grained CFD-DEM and KTGF Simulation for Industry Scale Fluidized Beds

Since its introduction [1], the Discrete Element Method (DEM) has proven to be a valuable method for the analyzing and understanding particulate flows. Supported by the continuously increasing computational power, CFD-DEM simulations have found their way into the chemical and process industry for various applications like solid suspension in mixing vessels, fluidized and spouted beds, granular transport and coating applications in rotary drums [2,3]. The major shortcoming of DEM, however, is its computational cost that increases with the amount of particles involved, their material properties (stiffness) and size. This hinders the application of CFD-DEM simulation to large-scale systems of industrial size. To overcome this shortcoming a coarse grain (CG) model has been described [4]. Using straightforward scaling rules, a group of particles gets replaced by a representative coarse parcel. This effectively reduces the number of particles that need to be processed and subsequently shortens the computational time. On the other hand, they introduce a modeling error into the simulation. In a previous study we were investigating different coarse graining models and quantify the effect on different parameters and their fluctuation like pressure drop and expansion height in a fluidized and spouted bed and we were comparing the simulation with experimental results. In general, it can be stated that bed expansion and pressure drop are well predicted for all investigated CG methods but depending on the CG factor the dynamic of the system cannot be captured. [5]

An alternative approach is the kinetic theory of granular flow based on the eulerian multiphase model. The different phases are treated as interpenetrating continua, but additionally the intraphase interaction of the dispersed solid phase is considered. A validation of different KTGF-models and the influencing model parameters was recently presented. [5]

In this work we are comparing coarse-grained CFD-DEM, EMP-KTGF and experimental results for an industrial scale fluidized bed in terms of averaged as well as dynamic data. Results of different modeling aspects are quantified and discussed with a focus on model modifications to capture the mesoscale effects. Finally, the effect on runtime and ways to reduce it ate discussed.

References:

1. Cundall, O.D.L. Strack, Geotechnique, 29 (1979), 47
2. Eppinger, O. Baran, R. Aglave, S. Lo, Simulating Solid Suspension in Stirred Vessels with a Fully Coupled CFD-DEM Algorithm (161d), AIChE Annual Meeting 2017, Minneapolis
3. Baran, R. Aglave, M. Tandon, A. Karnik, S. Lo, Numerical Simulation of Dense Gas-Solid Fluidized Beds: Comparison Between Eulerian Multiphase and Discrete Element Methods, AIChE Annual Meeting 2015, Salt Lake City, UT.
4. Sakai, Y. Yamada, Y. Shigeto, K. Shibata, V.M. Kawasaki, S. Koshizuka, Numerical Methods in Fluids 64 (2010), 1319
5. Eppinger, T., Tourani, C., Aglave, R., Quantifying Effects of Coarse-Grain Model Parameter in CFD-DEM Simulations of Fluidized and Spouted Beds and Comparison Against Eulerian Multiphase Simulation Results, AIChE Spring Meeting 2019, New Orleans