Effect of Sulfur on the Reduction of Ilmenite by Syngas in Chemical Looping Combustion

The reactivity of ilmenite as an oxygen carrier (OC) in the presence of H₂S was studied. A simulated syngas (66% CO, 34% H₂) was used as the fuel. H₂S concentrations were set to 4700 and 6580 ppm. The effect of the presence of CO₂ was also investigated. The experiments were carried out using a thermogravimetric analyzer (TGA) at atmospheric pressure, with temperatures varying from 1073 to 1223 K. The results showed that the presence of H₂S had no effect on the reduction kinetics of ilmenite. With the presence of only CO₂ in the syngas, deposition on ilmenite samples was not observed. In the presence of H₂S, deposition was observed regardless of the presence of CO₂. Higher H₂S concentration led to more pronounced deposition. It was shown that deposition only occurred after the ilmenite sample was sufficiently reduced. For ilmenite oxidation, the mass change curves display a distinct peak followed by a valley when the sample was previously reduced in the presence of H₂S, indicating reactions between the sulfur deposit and air. The amount of the sulfur deposit could be calculated using the oxidation curves. Scanning electron microscope-energy dispersive X-ray (SEM-EDX) and X-ray diffraction (XRD) analyses were conducted to examine the surface of the reduced samples and the results from these analyses confirmed the presence of the sulfur deposit on the surface of the samples that were reduced in H₂S-containing atmospheres.