Study on Gas–Solid Flow Characteristics in Fluidized Bed Membrane Reactors with Different Membrane Tube Arrangements Using X-ray Computed Tomography

Abstract

Fluidized bed membrane reactors have been introduced in catalytic reforming hydrogen production recently. The arrangement of membrane tubes is the key factor in the gas–solid distribution in reactors, which decides the production efficiency and wearing characteristics of membrane tubes. Nevertheless, research on optimization of the arrangement of membrane tubes is still inadequate due to a lack of measuring methods which can penetrate solid particles and internal components. In this study, the time-averaged void fraction distributions inside fluidized bed membrane reactors with different fluidization velocities and tube layouts are investigated using X-ray computed tomography. The effects of spacers on the internal gas–solid flow characteristics are studied as well. The results indicate that bubbles first gather toward the bed center axis during rising, then cut by the tube bundle, causing bubbles to split and then aggregate. Increasing the number of bundles makes the distribution of bubbles more uniform. The spacer allows more bubbles to move along the wall, and these bubbles tend to return to the middle of the fluidized bed after passing through the spacer, leading to more particle aggregation around the spacer. Using a multibundle spacer can reduce aggregation. As the bed height increases, the void fraction at the wall of the fluidized bed is less affected by the number of tube bundles, and the use of spacers strengthens the positive impact of the number of tube bundles. As the fluidization velocity increases, bubbles gather toward the bed center. The presence of tube bundles will cause the accumulation of bubbles to be more rapid.