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The Chemical-Looping with Oxygen Uncoupling (CLOU) process is a Chemical-Looping Combustion (CLC) technology that allows the combustion of solid fuels with inherent CO 2 separation using oxygen carriers. This technology has low energy penalty for CO 2 separation and thus low CO 2 capture costs. The CLOU process is a new option, when the direct use of a solid fuel in a CLC technology is considered. The CLOU process uses oxygen carriers based on some metal oxides that have the capability to evolve gaseous oxygen at high temperatures. The oxygen generated by the metal oxide reacts directly with the solid fuel, which is mixed with the oxygen carrier in the fuel reactor. The selection of a suitable oxygen carrier is a key factor for the CLOU technology development. The aim of this work was to produce and characterize oxygen carrier materials based on CuO with high oxygen transfer capability, high oxygen generation rates and good fluidization properties. Several oxygen carriers were prepared with different CuO contents, inert supports and preparation methods (incipient wet impregnation, mechanical mixing following by pelletizing by extrusion, or pelletizing by pressure). The reaction rates for oxygen generation (reduction) and regeneration were determined carrying out successive cycles in a TGA system. In this way, it was determined the chemical suitability of the materials. Selected oxygen carriers were tested by redox cycles in a batch fluidized-bed reactor working at different temperatures and reacting atmospheres. The fluidization behaviour against agglomeration and attrition during a high number of cycles was determined. Oxygen carriers with 60 wt% of CuO on MgAl 2 O 4 and with 40 wt% CuO on ZrO 2 prepared by mechanical mixing following by pelletizing by pressure were identified as suitable materials for CLOU process.

The chemical looping with oxygen uncoupling (CLOU) process is a chemical looping combustion (CLC) technology that allows for the combustion of solid fuels with inherent CO 2 separation. As in CLC technology, in the CLOU process, the oxygen necessary for fuel combustion is supplied by a solid oxygen carrier, which is moving between two reactors: the fuel and air reactors. The CLOU technology uses the property of some metal oxides (CuO, Mn 2 O 3 , and Co 3 O 4 ), which can generate gaseous oxygen at high temperatures. The oxygen generated by the oxygen carrier reacts directly with the solid fuel, which is mixed with the oxygen carrier in the fuel reactor. The reduced oxygen carrier is transported to the air reactor, where it is oxidized by air. In this work, a material prepared by spray drying containing 60 wt % CuO and 40 wt % MgAl 2 O 4 as supporting material was evaluated as an oxygen carrier for the CLOU process using different installations. First, the oxygen release rate and the fluidization behavior, with regard to the agglomeration and attrition rate, were analyzed in a thermogravimetric analyzer (TGA) and in a batch fluidized bed, respectively. Then, the effects of the main operating conditions, such as the temperature, solids flow rate, and gas velocity in the fuel reactor, on the oxygen-carrier capability to release gaseous oxygen were analyzed in a continuous CLOU unit using N 2 and CO 2 as fluidization media. In addition, the effect of the oxygen concentration in the air reactor on the capability of the oxygen carrier to be regenerated was evaluated. The results obtained showed that this oxygen carrier has suitable characteristics for the CLOU process. Nevertheless, after 40 h of continuous operation at high temperatures, the particle integrity decreased significatively, indicating the need to improve the lifetime of this kind of material for use in an industrial CLOU process.

Chemical-Looping with Oxygen Uncoupling (CLOU) process is a Chemical-Looping Combustion (CLC) technology that allows the combustion of solid fuels using oxygen carriers with inherent CO 2 separation The oxygen necessary for the fuel combustion is supplied by a solid oxygen carrier, which contains a metal oxide. The oxygen carrier circulates between two interconnected fluidized reactors: the fuel and the air reactor. In the CLOU process, the oxygen carrier releases gaseous oxygen in the fuel reactor which burns coal as in common combustion with air, so the CO 2 generated is undiluted with N 2. The reduced oxygen carrier is oxidized by air to the initial metal oxide in the air reactor, then being ready to start a new cycle. The aim of this work is to study the performance of the CLOU process using coals of different rank. Experiments were carried out in a continuously operated 1.5 kW th unit. Particles prepared by spray drying containing 60 wt.% CuO were used as oxygen carrier. Four coals of different rank (anthracite, low volatile bituminous, medium volatile bituminous and lignite) were used as fuel. Besides, the temperature in the fuel reactor was varied between 900 and 950 ºC. In all the experiments there was complete combustion of the coal to CO 2 and H 2 O, without any unburnt product. The carbon capture efficiency greatly depends on the coal rank and fuel reactor temperature. High carbon capture efficiencies were obtained for Lignite and Medium Volatile Bituminous coals. The maximum capture efficiency was 99.3% at 950 ºC with Lignite. The analysis of the experimental results was used to evaluate the effect of the coal rank in a CLOU system when a carbon separation system is included. At 925 ºC, the solid inventory needed to reach 95 % of CO 2 capture efficiency with a carbon separation system of 90 % of efficiency is 45 kg/MW th using Lignite, 85 kg/MW th using MV Bituminous, 140 kg/MW th using LV Bituminous and 490 kg/MW th using Anthracite. It must be pointed out the low solid inventories needed in the CLOU process for the different coal rank analyzed in this work.