Investigation of Chemical Looping Combustion of Coal with CuFe2O4 Oxygen Carrier

Chemical looping combustion (CLC) has great advantages to obtain pure CO 2 from coal combustion flue gas at a manageable cost. CuFe 2 O 4 was put forward as a novel oxygen carrier, which integrated Cu and Fe metals into one oxide matrix with superior characteristics over single metal oxide of either CuO or Fe 2 O 3 and had a high potential to be used in CLC. In this study, the reaction of CuFe 2 O 4 with two Chinese coals of different ranks [Liu Pan Shui (LPS) sub-bituminous coal and Yang Quang (YQ) anthracite] was performed in a thermogravimetric analyzer (TGA). Fourier transform infrared (FTIR) spectroscopy was used to detect in situ the emitted gases from the TGA. Field scanning electron microscopy/energy-dispersive X-ray spectrometry (FSEM/EDX) was used to study the morphology and elemental compositions present in the solid residues, and the related phases were further identified by X-ray diffraction (XRD). Meanwhile, to explore the reaction mechanisms involved for the reaction of CuFe 2 O 4 with coal, a more realistic simulation system with 376 species was designed for thermodynamic analysis. Through all of these measures, it was found that the reaction of LPS lean coal with CuFe 2 O 4 underwent two distinct reaction stages at 300–600 and 600–850 °C, respectively. At these two reaction stages, CuFe 2 O 4 was dominantly reduced into Cu and Fe 3 O 4 by transfer of the lattice oxygen [O] in CuFe 2 O 4, and then the formed Fe 3 O 4 was further reduced into Fe 2.962 O 4 . However, above 800 °C, CuFeO 2 and Cu 2 O were produced through direct decomposition of CuFe 2 O 4 into CuFeO 2 and then further partial decomposition of CuFeO 2 into Cu 2 O. Especially, O 2 generated was greatly beneficial to the full conversion of the remaining coal. Different from LPS, the reaction of YQ with CuFe 2 O 4 presented only one discernible reaction stage above 600 °C. Besides Cu and CuFeO 2, Fe 2.957 O 4 was also generated. Furthermore, four cycles of reduction of CuFe 2 O 4 with H 2 and then oxidation with air displayed a good reaction stability of synthesized CuFe 2 O 4 . However, if coal was used, iron silicates were formed from the interaction of the reduced CuFe 2 O 4 with ash and resulted in the insufficient reoxidation of reduced CuFe 2 O 4 . As such, effective separation of coal ash should be included in the CLC process to ensure the full regeneration of reduced CuFe 2 O 4 .