Performance of iron sand as an oxygen carrier at high reduction degrees and its potential use for chemical looping gasification

Iron sand as an industrial by-product has a reasonable iron content (35 wt% Fe) and low economical cost. The reactivity of iron sand as an oxygen carrier was examined in a bubbling fluidized bed reactor using both gaseous and solid fuels at 850-975 degrees C. Pre-reductions of iron sand were performed prior to fuel conversion to adapt the less-oxygen-requiring environment in chemical looping gasification (CLG). Based on the investigations using CO and CH4, iron sand has an oxygen transfer capacity of around 1 wt%, which is lower than that of ilmenite. The conversion of pine forest residue char to CO and H2 was higher when using iron sand compared to ilmenite. Depending on the mass conversion degree of iron sand, the activation energy of pine forest residue char conversion using iron sand was between 187 and 234 kJ/mol, which is slightly lower than that of ilmenite. Neither agglomeration nor defluidization of an iron sand bed occurred even at high reduction degrees. These suggests that iron sand can be utilized as an oxygen carrier in CLG. Furthermore, this study presents novel findings in the crystalline phase transformation of iron sand at various degrees of oxidation, altogether with relevant thermodynamic stable phases.

Automated summary

Iron sand, a by-product of the industry, has a reasonable iron content and low cost. It has been found that iron sand can be used as an oxygen carrier in chemical looping gasification (CLG), with an oxygen transfer capacity lower than ilmenite. Utilizing iron sand leads to higher conversion rates of pine forest residue char to CO and H2 compared to ilmenite. The study also presents novel findings on the crystalline phase transformation of iron sand at different oxidation levels.