A water-cooled dual-channel capacitance probe system was developed for in-furnace measurements of solids concentration and solids velocity in a 1 MWth dual fluidized bed pilot plant. Measurements were conducted in both reactors of the pilot plant during carbonate looping and combustion test campaigns. Solids velocities were derived by cross correlating the signals of the two channels of the capacitance probe. Thus, horizontal profiles of solids concentration and velocity were simultaneously determined in the reactors. These profiles show a strong core annulus flow structure in both reactors of the pilot plant. The influence of bed material characteristics, operating conditions as well as riser geometries on the particle flow structure is evaluated. (C) 2018 Elsevier Ltd. All rights reserved.