Numerical investigation on the performance of a W-type radiant tube using ammonia/hydrogen/methane blends

Abstract

As crucial equipment in the metallurgical industry, radiant tubes possess significant CO₂ reduction potential. Ammonia/hydrogen/methane blends can mitigate the constraint associated with single-component carbon-free fuel/methane blends, facilitating a higher proportion of methane replacement. Although ammonia/hydrogen/methane blends are promising for the CO₂ reduction of radiant tubes, their effect on the performance of radiant tubes remains unclear. In this study, several cases with different NH₃/H₂/50%CH₄ fuel blend ratios are numerically performed to compare the effect of fuel components on the performance of the W-type radiant tube (WRT). Compared to 100 % CH₄, using NH₃/H₂/50%CH₄ blends in the WRT could enhance temperature uniformity and reduce CO₂ emissions significantly. However, this came with a decreased thermal efficiency and dramatically increased NO_x emissions. As the NH₃ proportion in NH₃/H₂/50%CH₄ blends decreased from 50 % to 25 %, H₂ increased from 0 % to 25 %, the temperature difference increased from 76.2 K to 81.4 K, the non-uniformity coefficient increased from 0.0555 to 0.0591, the thermal efficiency increased from 58.5 % to 59.9 %, the CO₂ emissions increased from 5.10 g/s to 5.28 g/s, and the NO concentration increased from 1725 ppm to 1954 ppm. This indicates that NH₃ in NH₃/H₂/50%CH₄ blends is crucial for enhancing temperature uniformity and reducing emissions, while H₂ importantly boosts thermal efficiency. In addition, although the use of NH₃/H₂/50%CH₄ blends slightly reduced the emissivity of the flue gas, it had no significant effect on the radiative heat transfer between the flue gas and the tube. Moreover, the greenhouse effect caused by N₂O was negligible.