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.@en