heat exchanger tubes in bubbling fluidized bed reactors are necessary to remove the reaction heat of exothermal reactions. Vertical internals that mimic the heat exchanger tubes in cold-flow models, proofed to reduce the bubble size and lead to a more even distribution of the bubbles above the cross-section. Another option is to orientate the internals horizontally inside the column. By means of a measurement campaign at a cold-flow model, differences concerning the hydrodynamic behavior between a column with horizontal and vertical internals were investigated and determined. It turned out that the horizontal internals influence the hydrodynamics in a way which is not beneficial concerning the reactor performance due to an accumulation of bubbles below the horizontal internals and preferential pathways of the bubbles between the horizontal internals.

The design and scale-up of bubbling fluidized bed reactors remain an ongoing challenge, as the bubble size and velocity have to be known to enable a reliable design of this reactor type. Correlations between the average bubble size and rise velocity have been proposed in the literature, however, their distributions are rarely found. Especially the relationship between the distribution is usually unknown. Additionally, in catalytic bubbling fluidized bed reactors used for endothermic/exothermic reactions, bundles of heat exchanger tubes are employed, which are not considered by most correlations. In this work, the results obtained in a previous study and new data obtained using an ultra-fast X-ray apparatus were used to develop both a new type of bubble size and bubble rise velocity correlation, which include the distribution of these values. All of this data can be expressed as a function of the gas velocity and bed height. Two columns, one of laboratory scale and the other of pilot-scale, both with vertical heat exchanger tubes, were investigated.