Activity Of Oxygen Carrier Research Articles

Chemical-looping gasification of biomass in a 10 kWth interconnected fluidized bed reactor using Fe2O3/Al2O3 oxygen carrier

The aim of this research is to design and operate a 10 kW hot chemical-looping gasification (CLG) unit using Fe2O3/Al2O3 as an oxygen carrier and saw dust as a fuel. The effect of the operation temperature on gas composition in the air reactor and the fuel reactor, and the carbon conversion of biomass to CO2 and CO in the fuel reactor have been experimentally studied. A total 60 h run has been obtained with the same batch of oxygen carrier of iron oxide supported with alumina. The results show that CO and H2 concentrations are increased with increasing temperature in the fuel reactor. It is also found that with increasing fuel reactor temperature, both the amount of residual char in the fuel reactor and CO2 concentration of the exit gas from the air reactor are degreased. Carbon conversion rate and gasification efficiency are increased by increasing temperature and H2 production at 870°C reaches the highest rate. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and BET-surface area tests have been used to characterize fresh and reacted oxygen carrier particles. The results display that the oxygen carrier activity is not declined and the specific surface area of the oxygen carrier particles is not decreased significantly.

Investigation of perovskite supported composite oxides for chemical looping conversion of syngas

In typical chemical looping processes, a transition metal oxide based oxygen carrier is used to indirectly convert carbonaceous fuels into concentrated CO2 and carbon free products through cyclic redox reactions. Among the various oxygen carrier candidates, iron oxide represents a promising option due to its abundance, low cost, and unique thermodynamic properties. A key challenge for ferrite based oxygen carriers resides in their low redox activity. In the current study, composite iron oxides with three types of mixed ionic–electronic conductive (MIEC) supports, i.e. lanthanum strontium ferrite (Sr-substituted lanthanum ferrite or LSF), barium cerium ferrite (Ce-substituted barium ferrite, BCF) and calcium titanate ferrite (Fe-substituted calcium titanate, CTF), are synthesized using solid state reaction (SSR) and sol–gel methods. Among the three MIEC materials, CTF support is found to possess superior structural stability. MIEC supported oxygen carriers are found to be significantly more active than a reference, yttrium-stabilized zirconia (YSZ) supported oxygen carrier. Higher support conductivity and smaller iron oxide precursor sizes generally lead to enhanced oxygen carrier activity. In contrast, surface area of the oxygen carrier is weakly correlated with its redox activity. CTF, although less conductive compared to BCF and LSF, is stable and sufficiently effective in shuttling active O2− and electrons for syngas oxidation and iron oxide regeneration. Therefore, CTF supported ferrites can potentially be a cost-effective oxygen carrier candidate for chemical looping processes. Further improvements in redox activity of the oxygen carriers can be achieved through iron oxide particle size reduction and support conductivity enhancement.

The Preparation Methods of Fe<sub>2</sub>O<sub>3</sub>/Al<sub>2</sub>O<sub>3</sub> Oxygen Carriers and their Chemical Looping Combustion Performance

60wt%Fe2O3/Al2O3 oxygen carriers were prepared by different methods and characterized by means of XRD, H2-TPR, infrared gas analyzer. The effects of preparation methods on the structure and activity of Fe2O3/Al2O3 oxygen carriers for chemical looping combustion of methane were also investigated. The factors on the selectivity of CO2 in the chemical looping combustion process at different reaction temperatures were discussed. Methane can be quickly converted to CO2 and H2O with high selectivity at 850°C for 15 min. After redox cycling in alternant methane/air atmosphere for 30 times, the formation of CO2 was enhanced, indicating higher activity of oxygen carrier after the redox experiment.