CFD-DEM study of geometry changes in an AnFMBR towards particle momentum

An anaerobic fluidized bed membrane bioreactor (AnFMBR) with granular activated carbon (GAC) particles as a scouring material was numerically investigated with the use of a CFD-DEM approach. After validation of the numerical solver, two different shapes of impediments, i.e., linear decreasing of the gap and linear de-/increasing of the gap, with variable impediment lengths were introduced to the geometry. The effects of built-in impediments, different fluid inlet velocities and particle sizes on the hydrodynamics, resulting particle momentum and required power input were evaluated and compared to the reactor geometry without an impediment. The disadvantage of reactor geometry without an impediment, i.e., the non-uniform distribution of particle momentum across the height, can be compensated with the use of built-in impediments depending on the fluid inlet velocity, particle diameter and impediment lengths. Furthermore, with the introduction of impediments the maximum achievable particle momentum can be increased or the optimum of particle momentum in regards to the power input can be shifted towards lower power inputs. The latter case is especially important for collisional- and scouring-sensitive membranes. The most promising effect towards particle momentum in terms of uniform distribution and magnitude was observed with small scouring particles (1.25 and 1.55 mm) for both impediments.