The Direct Reduction of Iron Ore with Hydrogen

The steel industry represents about 7% of the world’s anthropogenic CO2 emissions due to the high use of fossil fuels. The CO2-lean direct reduction of iron ore with hydrogen is considered to offer a high potential to reduce CO2 emissions, and this direct reduction of Fe2O3 powder is investigated in this research. The H2 reduction reaction kinetics and fluidization characteristics of fine and cohesive Fe2O3 particles were examined in a vibrated fluidized bed reactor. A smooth bubbling fluidization was achieved. An increase in external force due to vibration slightly increased the pressure drop. The minimum fluidization velocity was nearly independent of the operating temperature. The yield of the direct H2-driven reduction was examined and found to exceed 90%, with a maximum of 98% under the vibration of ~47 Hz with an amplitude of 0.6 mm, and operating temperatures close to 500 °C. Towards the future of direct steel ore reduction, cheap and “green” hydrogen sources need to be developed. H2 can be formed through various techniques with the catalytic decomposition of NH3 (and CH4), methanol and ethanol offering an important potential towards production cost, yield and environmental CO2 emission reductions.

Escape and evolution of Titan’s N2 atmosphere constrained by 14N/15N isotope ratios

ABSTRACT We apply a 1D upper atmosphere model to study thermal escape of nitrogen over Titan’s history. Significant thermal escape should have occurred very early for solar extreme ultraviolet (EUV) fluxes 100–400 times higher than today with escape rates as high as ≈1.5 × 1028 s−1 and ≈4.5 × 1029 s−1, respectively, while today it is ≈7.5 × 1017 s−1. Depending on whether the Sun originated as a slow, moderate, or fast rotator, thermal escape was the dominant escape process for the first 100–1000 Myr after the formation of the Solar system. If Titan’s atmosphere originated that early, it could have lost between $\approx0.5\,\, \mathrm{ and}\,\, 16$ times its present atmospheric mass depending on the Sun’s rotational evolution. We also investigated the mass-balance parameter space for an outgassing of Titan’s nitrogen through decomposition of NH3-ices in its deep interior. Our study indicates that, if Titan’s atmosphere originated at the beginning, it could have only survived until today if the Sun was a slow rotator. In other cases, the escape would have been too strong for the degassed nitrogen to survive until present day, implying later outgassing or an additional nitrogen source. An endogenic origin of Titan’s nitrogen partially through NH3-ices is consistent with its initial fractionation of 14N/15N ≈ 166–172, or lower if photochemical removal was relevant for longer than the last ≈ 1000 Myr. Since this ratio is slightly above the ratio of cometary ammonia, some of Titan’s nitrogen might have originated from refractory organics.