Investigation of a Canadian Ilmenite as an Oxygen Carrier for Chemical Looping Combustion

The use of chemical looping combustion (CLC) for power generation is an advanced energy technology that can capture CO2 inherently, which could prove to be the next electricity generation technology in a carbon-constrained future. For commercial-scale application of the CLC process, the availability of cost-effective oxygen carriers (OCs) with stable performance is imperative. Given the composition of ilmenite, there may be potential for its application as a cost-effective alternative OC for CLC. In this study, the performance of a Canadian ilmenite was investigated and showed promising results. Complete reduction of ilmenite takes a relatively long time; therefore, it is not practical for ilmenite to reach its maximum oxygen transport capacity by counter-balance of capital investment in the fuel reactor. Reduction in the first 30 mm was selected as the effective reaction for the application of CLC, which gave an oxygen transport capacity of about 5.52%. To understand the phase and Fe valence state (Fe3+/Fe2+) transformations of calcined and reacted ilmenite, transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS) were conducted. Using X-ray diffraction (XRD), the effective reaction was identified as Fe3+ reduced to Fe2+ at test conditions. The kinetics of this reaction were studied by doing experiments under different gas concentrations and temperatures based on a shrinking core model. The results showed that the activation energy was 169.6 x 10(3) J mol(-1) with a reaction order of approximately 2.2. The chemical stability of the OC was studied by doing multiple redox cycles. To qualitatively show the difference between ilmenite and a synthetic OC, a freeze-granulated OC with a composition of 50 wt % Fe2O3 and 50 wt % Al2O3 was selected as a reference. The average reaction rate and crushing strength of each sample were compared. The results showed that ilmenite has favorable stability characteristics to be a viable, cost-effective OC for power generation.