Calcium looping, CaL, is rapidly developing as a postcombustion CO 2 capture technology because its similarity to existing power plants using circulating fluidized bed combustors, CFBC. In this work we present experimental results from a pilot built to demonstrate the concept at the MW th scale. The pilot plant treats 1/150 of the flue gases of an existing CFBC power plant ("la Pereda") and it has been operated in steady state for hundreds of hours of accumulated experimental time. The pilot includes two 15 m height interconnected circulating fluidized bed reactors: a CO 2 absorber (or carbonator of CaO) and a continuous CaCO 3 calciner operated as an oxy-fuel CFBC. Operating conditions in the reactors are resembling those expected in large CaL CO 2 capture systems in terms of reactor temperatures, gas velocities, solid compositions and circulation rates and reaction atmospheres. The evolution of CO 2 capture efficiencies, solid properties (CO 2 carrying capacity and CaO conversion to CaCO 3 and CaSO 4) have been studied as a function of key operating conditions. It is demonstrated that CO 2 capture efficiencies over 90% are feasible with a supply of active CaO slightly over the molar flow of CO 2 entering the carbonator. Closure of carbon and sulphur balances has been satisfactory during steady state periods. A basic reactor model developed from smaller test facilities seems to provide a reasonable interpretation of the observed trends. This should facilitate the further scale up of this new technology.

This work investigates the kinetics of the reaction of CO 2 with CaO particles partially carbonated that are forced to increase their carbonate content at high temperatures in an atmosphere of rich CO 2. This additional recarbonation reaction, on particles that have already completed their fast carbonation stage, is the basis of a novel process that aims to increase the CO 2 carrying capacity of sorbents in Calcium looping CO 2 capture systems. The CaO reaction rates and the maximum carbonation conversions after the recarbonation step were measured on a thermogravimetric analyzer and the results indicate that they are highly dependent on temperature and CO 2 partial pressure, steam also being a contributing factor. The reaction mechanism governing the reaction rates during the carbonation and recarbonation reactions is explained by the combined control of chemical reaction and CO 2 diffusion through the CaCO 3 product layer. An extension of the Random Pore Model adapted to multi cycled CaO particles was successfully applied to calculate the CaO molar conversion as a function of time and the recarbonation conditions, using kinetic parameters consistent with previous published results on carbonation kinetics under typical flue gas conditions.

This paper reports experimental results from a new 300 kW th calcium looping pilot plant designed to capture CO 2 "in situ" during the combustion of biomass in a fluidized bed. This novel concept relies on the high reactivity of biomass as a fuel, which allows for effective combustion around 700ºC in air at atmospheric pressure. In these conditions, CaO particles fed into the fluidized bed combustor react with the CO 2 generated during biomass combustion, allowing for an effective CO 2 capture. A subsequent step of regeneration of CaCO 3 in an oxy-fired calciner is also needed to release a concentrated stream of CO 2 . This regeneration step is assumed to be integrated in a large scale oxyfired power plant and/or a larger scale post-combustion calcium looping system.The combustor-carbonator is the key reactor in this novel concept, and this work presents experimental results from a 300 kW th pilot to test such a reactor. The pilot involves two 12 m height interconnected circulating fluidized bed reactors. Several series of experiments to investigate the combustor-carbonator reactor have been carried out achieving combustion efficiencies close to 100% and CO 2 capture efficiencies between 70-95% in dynamic and stationary state conditions, using wood pellets as a fuel. Different superficial gas velocities, excess air ratios above stoichiometric requirements, and solid circulating rates between combustorcarbonator and combustor-calciner have been tested during the experiments. Closure of the carbon and oxygen balances during the combustion and carbonation trials has been successful. A simple reactor model for combustion and CO 2 capture in the combustor-carbonator has been applied to aid in the interpretation of results, which should facilitate the future scaling up of this process concept.