Comparison of a Discrete Particle Model and a Two-Fluid Model to experiments of a fluidized bed with flat membranes

Fluidized bed membrane reactors gain worldwide increasing interest for various applications. Nevertheless, fundamental understanding of the hydrodynamics of these reactors is required in order to improve the future design of these reactors. This study focuses on a pseudo-2D fluidized bed containing flat vertical membranes, through which gas can be added to – or extracted from – the fluidized suspension. By employing Digital Image Analysis (DIA) in combination with Particle Image Velocimetry (PIV), both solids motion as well as bubble properties were investigated in detail. In addition the experimental results were compared to computational results obtained from a Discrete Particle Model (DPM) and a Two-Fluid Model (TFM).Comparison between results obtained from a 4 cm wide bed and a (previously used) 30 cm bed revealed that the effect of gas addition is qualitatively the same (solids motion inverts and average bubble size decreases). During gas extraction, bubbles (and solids) are forced towards the center, enhancing bubble coalescence compared to the reference condition. Both the DPM and the TFM qualitatively capture these phenomena well. However, these models are not able to predict the experimentally observed solids motion and gas bubbles behavior quantitatively. DPM and TFM simulations for a wider bed reveal that grid dependency and maximum solids fraction play an important role with respect to solids motion. Furthermore, the porosity distribution shows significant differences between the DPM and TFM models.

This paper presents a direct comparison between Particle Image Velocimetry (PIV) experiments in a 4 cm wide fluidized bed with membranes in the left and right wall, a Discrete Particle Model (DPM) and a Two-Fluid Model (TFM). The effect of the membranes on the hydrodynamics, i.e. solids circulation and bubble properties, are investigated.Figure optionsDownload as PowerPoint slideHighlights
► Comparison between PIV in a membrane-assisted fluidized bed, DPM and TFM.
► Qualitatively, both the DPM as well as the TFM agree well with the experiments.
► Quantitatively, both models display some differences compared to experiments.
► The solids distribution shows significant differences between the DPM and the TFM.