Continuous Test of Ilmenite-Based Oxygen Carriers for Chemical Looping Combustion in a Dual Fluidized Bed Reactor System

Raw ilmenite was tested as an oxygen carrier for chemical looping combustion (CLC) in a dual fluidized bed reactor for 100 h. After this 100 h test, 21 wt % of the total used raw ilmenite was impregnated with 10 wt % potassium (K). The K-impregnated ilmenite mixed with the remaining used raw ilmenite was tested in the same reactor for 40 h. During the 100 h test, raw ilmenite showed a low reduction reactivity, which only converted 60% CO into CO2 at 900 degrees C with a 4.2 kPa pressure drop in the fuel reactor. By impregnating merely 21% of the used raw ilmenite with 10% K+, the reactivity was promoted and thus the CO conversion was improved to over 78.5% under the same conditions. Although reactivity deterioration of the 10% K+ promoted ilmenite related to K+ volatilization was found, the CO conversion only dropped from 100% to 89% even after 28 h of continuous operation. The effect of different operation parameters on gas conversion behavior was investigated with raw ilmenite; the gas flow rate and temperature of the fuel reactor turned out to be the critical parameters. However, the reduction reactivity of the 10% K+ promoted ilmenite was not affected by temperature as much as that of the raw ilmenite, and therefore, it can be used in a wide temperature range (900-600 degrees C). During use of both the raw and promoted ilmenites, no sintering or agglomeration occurred; the proportions of mass loss caused by fragmentation and attrition to the total solid inventory were low, only 0.87% (100 h) and 0.71% (40 h). Both ilmenite carriers showed good mechanical strength and stability. The 10% K+ promoted ilmenite was proven to be one promising oxygen carrier for chemical looping combustion.