Experimental and numerical investigation of flash reduction of magnetite particles using confined H2-air and CH4/H2-air flames

The iron-power cycle emerges as a promising method for clean energy storage and conversion, where iron is oxidized to generate energy and later reduced back to iron. This study focuses on the reduction step, investigating it experimentally and numerically using confined H2-air and CH4/H2-air flames. First, operating regimes are constructed by varying inlet temperatures (300 K≤ Tin ≤800 K) and equivalence ratios (2≤ Φ ≤4.5). The reduction degrees (X) at different regimes are calculated numerically. Then experiments are conducted at one condition<br/>using H2-air flame, in which the inlet velocity (Uin) is twice the laminar flame speed (SL). Furthermore, the particle morphology and composition are analyzed using a combination of scanning electron microscope imaging (SEM) and energy-dispersive X-ray spectroscopy (EDS). Numerical results indicate that the reduction degree (X) increases with inlet temperature due to a rise in product gas temperature. However, X exhibits a non-linear trend with changes in the equivalence ratio(Φ). The results also reveal that CH4/H2-air flames achieve a higher degree of reduction than pure H2-air flames, primarily due to the longer residence time. The experimental results corroborate the numerical study, with SEM images revealing significant morphological changes, including larger and<br/>spherical particles indicative of melting or sintering. EDS analysis confirms the presence of FeO on the surface, verifying the reduction process.