Reduction and Oxidation Behavior of Ilmenite for Chemical Looping Combustion

To apply chemical looping combustion process, ilmenite was investigated using thermogravimetric analysis (TGA) and fixed-bed reactor to figure out its oxygen transfer capacity. Ilmenite thermally treated at high temperature was used as the oxygen carrier, its oxygen transfer capacity during reduction and oxidation at 850 degrees C was analyzed by TGA analysis and using a fixed-bed reactor system. Air was used as oxidizing gas, and 12 vol% H-2 was used as reducing gas. Non-thermally treated ilmenite had low oxygen transfer capacity of 2.5 wt.% but ilmenite calcined at 1300 degrees C had an oxygen transfer capacity of 4.2 wt.%. The oxygen transfer capacity of ilmenite increased with calcination temperature due an increase in oxidation state. Ten cycles of reduction and oxidation showed ilmenite calcined at 1300 degrees C exhibited consistent reactivity, and that its reactivity was maintained for 10 cycles of reduction-oxidation. As a result of the XPS analysis, it was confirmed that the bonding energy was shifted to the lower binding energy in the tests of the repeated reduction and oxidation reaction. It is considered that ilmenite composed of metal oxide is not completely oxidized during the re-oxidation process after reduction and the sintering of some reduced ilmenite sample occur. Sintering in the metal state of the oxygen carrier may result in a decrease of the oxygen transfer capacity in long-term use.