Cycle experiments on chemical looping combustion of coal using potassium-improved iron ore as oxygen carrier

The cycle experiments on chemical looping combustion of coal were carried out in a fluidized bed using a K-promoted iron ore as oxygen carrier. The continued effect of the K-promoted iron ore on the gas compositions, fractions of carbonaceous gases was investigated.The results showed that the reaction time was shortened by the K-promoted iron ore,and that the CO₂ concentration was significantly increased.The CO₂ fraction for the K-promoted iron ore was much higher than that for the iron ore whereas,the CO fraction was much lower during 20 cycles.After 11 cycles, the CO₂ fraction slightly decreased with a slight increase in CO fraction for the K-promoted iron ore. The reduced oxygen carriers after different cycles were characterized by SEM-EDS (Scanning Electron Microscope-Energy Dispersive Spectrometer) and XRD (X-ray diffraction).Compared with pure iron ore, the K-promoted iron ore showed serious sinter on the oxygen carrier particles during the first 11 cycles. The oxygen carrier, however, re-obtained the porous structure after 20 cycles due to the loss of potassium.The XRD showed that the KFe₁₁O₁₇ or its derivatives displayed the catalytic effect on coal gasification in the process of chemical looping combustion and the oxygen carrier could be regenerated to Fe₂O₃ after 20 cycles.