Chemical Looping with Oxygen Uncoupling (CLOU) has been identified as an outstanding option for combustion of solid fuels. CLOU is based on the use of an oxygen carrier with the capability of releasing O2 at temperatures of interest for combustion, which promotes a high conversion of the fuel to CO2 and H2O. This works shows the new operational experience gained in a chemical looping unit at the 20-50 kWth scale at ICB-CSIC (Spain). This unit comprises two interconnected circulating fluidized-beds being the fuel and air reactors, together a carbon stripper between them. A highly reactive oxygen carrier was used in this unit with the capability to be separated from ash by magnetic methods. The oxygen carrier consisted of a highly reactive metal oxide (30 wt.% CuO) supported on a magnetic MnFe mixed oxide with low reactivity. Different fuels were used during 30 h of combustion, including sawdust pine, pelletized pine forest residue, olive stone and coal. The effect of temperature, solids circulation rate and solids inventory in the fuel reactor on the combustion efficiency and CO2 capture was evaluated. In general, high degree of combustion and CO2 capture was achieved. The oxygen carrier showed an excellent behaviour during the first hours of operation. However, its mechanical performance showed a quick degradation after 30 h of combustion with a high amount of fines produced during the operation. The generated fines were separated from ash by magnetic methods and they are being processed to produce new particles.