Global anthropogenic emissions of CO2 are increasing, and it appears that carbon capture and storage (CCS) has the potential to mitigate CO2 emissions, thereby reducing potential effects of global warming and climate change. The calcium looping cycle is a novel method of CO2 capture, comprising the use of limestone (CaCO3) as a CO2 sorbent within a fluidised bed. An understanding of the hydrodynamics of such a system is important in order to optimise the efficiency of the CO2 capture process. A full-scale 3D cold model of a 25 kW(th) calcium-looping CO2 capture reactor has been designed, constructed and operated in order to investigate the hydrodynamics of the hot system. The system comprises an entrained flow carbonator, and a bubbling fluidised bed calciner, with a lower and upper loop seal to allow control of solids transfer. Investigations into minimum fluidisation velocity, solids flux, gas bypassing between reactors, and pressure profiles of the system have been undertaken, the results of which are presented and discussed. Experimental minimum fluidisation velocity results compare well with the literature and theoretical values calculated from existing models. Gas bypassing results identify that predominant bypassing is from the loop seals to the calciner reactor, but modifications made to the cold model system as a result of the investigations show positive results in terms of reducing gas bypassing to a maximum of 5 %, and also improving the pressure profile of the system. (C) 2012 Elsevier B.V. All rights reserved.