In the present study, the fluid dynamic characteristics of the fuel reactor of a novel reactor concept for chemical looping combustion of solid fuels were investigated. In this reactor concept based on two interconnected circulating fluidized beds, flow obstacles are arranged along the height of the fuel reactor to improve gas-solid contact. The experiments have been performed at the scaled cold flow model of a [100]kW pilot plant and were focused on the solids distribution in the fuel reactor and on the limitations of the operating range caused by the flow obstacles. The flow obstacles increase the solids fraction in the upper part of the reactor above the dense zone and cause a more homogenous solids distribution. Both, solids distribution and solids fraction can be influenced by the fluidization rates of the two reactors. Increasing the fluidization rate of one or both reactors shifts the solids distribution towards the upper part of the reactor. Although the global solids distribution of the fuel reactor can be influenced by fluidization parameters, the solids distribution between two constrictions cannot be influenced, i.e. particles are always concentrated directly above the constrictions. The new reactor concept shows operation limits far above standard load. Under such unstable operating conditions, particles start to concentrate in the constriction and the area above the constriction is filled with particles. These effects can be reduced by adapting the design of the constrictions. (C) 2015 Elsevier B.V. All rights reserved.