Résumé -Boucle chimique pour la combustion du charbon avec un transporteur d'oxygène à base d'oxyde de cuivre -Une analyse préliminaire a été conduite pour estimer les performances d'un procédé en boucle chimique découplé (CLOU, chemical looping uncoupling) pour la combustion du charbon avec un transporteur d'oxygène à base d'oxyde de cuivre. Les avantages de ce système sont démontrés en établissant le bilan énergétique, l'inventaire et le débit de circulation du matériau transportant l'oxygène, les taux de conversion du carbone et la pression partielle en oxygène dans le réacteur de combustion. Pour faire cette analyse, des données expérimentales de cyclage CuO/Cu 2 O ont été utilisées afin de déterminer les cinétiques de décomposition et d'oxydation du matériau. Elles ont été obtenues avec un oxyde non supporté. La cinétique de décomposition est très rapide à 950°C dans les conditions du réacteur de combustion. Il est montré que la cinétique d'oxydation est maximale au voisinage de 800°C, la vitesse décroissant ensuite pour des températures plus élevées, à cause de résistances diffusionnelles liées à la formation d'une couche de CuO entourant le Cu 2 O. L'analyse montre que le CLOU permet une combustion rapide du carbone, les temps de combustion du carbone étant plus lents que les temps de décomposition du transporteur d'oxygène. Pour confirmer le potentiel du procédé, des données cinétiques additionnelles sont nécessaires sur des oxydes supportés à haute température (>850°C), dans les conditions du réacteur de combustion permettant la libération d'oxygène par l'oxyde de cuivre.
Abstract -Chemical Looping with Copper Oxide as Carrier and Coal as Fuel -A preliminary analysis has been conducted of the performance of a Chemical Looping system with Oxygen Uncoupling (CLOU) with copper oxide as the oxygen carrier and coal approximated by carbon as the fuel. The advantages of oxygen uncoupling are demonstrated by providing the energy balances
A systematic study on the adsorption of xenon on silver clusters in the gas phase and on the (001) surface of silver-exchanged chabazite is reported. Density functional theory at the B3LYP level with the cluster model was employed. The results indicate that the dominant part of the binding is the σ donation, which is the charge transfer from the 5p orbital of Xe to the 5s orbital of Ag and is not the previously suggested dπ−dπ back-donation. A correlation between the binding energy and the degree of σ donation is found. Xenon was found to bind strongly to silver cluster cations and not to neutral ones. The binding strength decreases as the cluster size increases for both cases, clusters in the gas-phase and on the chabazite surface. The Ag+ cation is the strongest binding site for xenon both in gas phase and on the chabazite surface with the binding energies of 73.9 and 14.5 kJ/mol, respectively. The results also suggest that the smaller silver clusters contribute to the negative chemical shifts observed in the 129Xe NMR spectra in experiments.
An effective copper-based oxygen carrier for use in chemical looping with oxygen uncoupling (CLOU) has been developed, and its physical and reactive properties have been evaluated. The preparation method involves coating β-SiC support material with CuO and then baking the coated material at 980 °C which causes the β-SiC to convert to SiO 2 , thus enveloping the CuO. Variations of the preparation technique, including different forms of SiC, methods of CuO addition, and the order of CuO addition and baking, were tested. It was determined that preparation by rotary evaporation CuO deposition and final sintering produced superior carrier particles. Loadings as high as 60 wt % CuO were achieved. The carrier particles fluidized well, and for loadings to 40 wt % CuO, no agglomeration was observed at temperatures as high as 1000 °C. The particles retained reactivity over many oxidation and reduction cycles. The coat-then-bake preparation method using β-SiC is a viable candidate to be used as oxygen carrying material in CLOU.
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