Performance of a bauxite waste as oxygen-carrier for chemical-looping combustion using coal as fuel

In the Chemical-Looping Combustion (CLC) technology, the oxygen needed for the oxidation of the fuel is provided by an oxygen-carrier. Today, there is an increasing interest on CLC application to coal. One of the possibilities is the in situ gasification and subsequent combustion of the product gases (iG-CLC). Potential CLC oxygen-carriers should be as inexpensive as possible, as some losses are expected accompanying the ashes. In the present work, a residue from alumina production mainly constituted by Fe2O3 has been tested as oxygen-carrier. Batch experiments were carried out in a fluidized-bed reactor using a bituminous coal as fuel. The effect of operating conditions, such as temperature and gasification agent on the char conversion and combustion efficiency of gasification products were evaluated. After 50 hours of cycling operation in a batch fluidized bed, no defluidization or agglomeration problems were observed. A gain in the reactivity of the bauxite waste was observed with the number of redox cycles. The carrier showed high combustion efficiencies at all temperatures. The percentage of CO2 in the feeding should be limited in order to maintain high gasification rates and combustion efficiencies. Results indicate that this bauxite waste is a promising oxygen-carrier for the iG-CLC of coal.

► The iG-CLC was evaluated using an abundant waste material as the oxygen carrier
► Bauxite waste (BW) reactivity increased after several cycles using char as fuel
► BW has high reactivity to gasification products and high combustion efficiencies
► H2O:CO2 molar ratio of 70:30 gives combustion efficiencies higher than 0.95
► Combustion and carbon capture efficiencies of 0.99 and 0.95 obtained for 812 kg/MWth