Thermoanalysis of the combined Fe3O4-reduction and CH4-reforming processes
The chemical equilibrium composition of the system Fe3O4 + 4CH4, at 1300 K and 1 atm consists of solid Fe and a 2:1 gas mixture of H2 and CO. Thermogravimetric (TG) analysis combined with gas Chromatographic measurements was conducted on the reduction of Fe3O4 (powder, 2-µm mean particle size) with 2.3, 5, 10, and 20 pct CH4 in Ar, at 1273, 1373, 1473, and 1573 K. The reduction proceeded in two stages, from Fe3O4 to FeO, and finally to Fe. CR, conversion and H2 yield increased with temperature, while the overall reaction rate increased with temperature and CH4 concentration. C (gr) deposition, due to the cracking of CR,, was observed. By applying a topochemical model for spherical particles of unchanging size, the reaction mechanism was found to be mostly controlled by gas boundary layer diffusion. The apparent activation energy reached a maximum at 30 pct reduction extent and decreased monotonically until completion. When compared with the results using instead either H2 or CO as reducing gas, the reduction achieved completion faster using CH4, at temperatures above 1373 K.
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