Mass transfer phenomena in fluidized beds with horizontally immersed membranes

Abstract

Mass transfer phenomena in fluidized bed reactors with horizontally immersed membranes have been investigated using a verified and validated Two-Fluid Model. A binary hydrogen-nitrogen mixture was injected into the fluidized bed which was operated in the bubbling fluidization regime, and hydrogen was extracted via horizontally immersed membranes. The hydrogen flux is lowest on top of the membranes and highest at the bottom of the membranes. The main causes for the low flux on top of the membranes are densified zones and insufficient hydrogen replenishment due to the flow pattern of the gas. Gas pockets do not have a negative effect on the mass transfer towards the membranes. In systems with membrane tube banks, the membranes located at the walls perform worst, because solids mostly flow downwards near the walls of a fluidized bed, which causes gas back-mixing, which hinders hydrogen replenishment and thereby decreases the driving force for hydrogen transport. Removing the membranes closest to the wall increases the overall efficiency of the system. Replacing wall membranes with inactive tubes has no significant effect on the system. The membrane tube banks also have a significant effect on the hydrodynamics.