• Energy Research

Abstract This work aimed at deeply investigating the effects of H2O and CO2 on NO formation under volatile-N combustion. The characteristics and mechanism of NO formation during volatile-N model compounds (pyridine and pyrrole) combustion in H2O/CO2 atmosphere were systematically investigated via experiments and numerical simulations. The results both showed NO formation significantly decreased with addition of H2O and CO2 during combustion of pyridine and pyrrole. Under O2/H2O atmosphere, H2O can significantly promote the reaction H + O2(+M) ↔ HO2(+M) which consumed H and O2 in reaction system. As a result, the chain reaction of H + O2 ↔ OH + O was inhibited and O radical decreased, thus NO formation was inhibited. Under O2/CO2 atmosphere, addition of CO2 inhibited CO + HO ↔ CO2 + H and NCO + O2 ↔ NO + CO2. As a result, NO reduction was promoted via 2CO + 2NO ↔ N2 + 2CO2 and oxidation of NCO to form NO was inhibited. Under O2/H2O/CO2 atmosphere, NO formation was further inhibited due to inhibitions of HCN + OH ↔ CN + H2O and NCO + O2 ↔ NO + CO2. The mechanism of nitrogen conversion was found: Nitrogen in pyridine and pyrrole was firstly pyrolyzed into NH3 and HCN, then oxidized by O and OH groups to be nitrogen-containing intermediate phases such as NH, HNO, N, NCO, etc. HNO and NCO will continue to be oxidized to generate NO. NCO, NH and NH2 would react with the generated NO to form N2, and NCO dominated.

Sludge pyrolysis and biomass gasification integrated process (SPBG) is an attractive route for the comprehensive utilization of the two materials but more tar is produced in this process compared to traditional biomass steam gasification. Nitrogen-containing compounds in the tar bring threatens to the environment and heavy components in the tar contributes to undesired coke formation. In current study, the evolution of heavy tar, especially the nitrogen-rich components, during SPBG is revealed for the first time. It was found that heavy components were mainly distributed in the mass range of 150-450 Da, where aromatics consisted of carbon, hydrogen and nitrogen atoms were the most abundant. Deamination (NH3) and the combination of quinoline accompanied with the generation of the heavy components. Organics from sludge could react with biomass to form heavier oxygen-containing molecules. Meanwhile, steam from sludge promoted heavy components to crack by tar reforming reactions and consumed radicals in bio-char to inhibit the catalytic cracking of tar. Under the combination of above reactions, more heavy molecules were generated at low sludge volatile/biomass ratio and the aromatic content in the heavy tar decreased at high sludge volatile/biomass ratio.

Abstract Fe-modified Ni/Al2O3 catalysts with Fe/Ni molar ratios of 0, 0.5, 1 and 2 were prepared to promote the co-production of H2 and carbon nanotubes (CNTs) during steam reforming of toluene as a tar model compound. After the addition of Fe, toluene conversion increased from 55.1% of Ni/Al2O3 to 73.6% of F1N1A (Fe/Ni ratio of 1), and H2 yield over F1N1A reached the maximum of more than 2000 mmol/(g-cata). Multi-walled carbon nanotubes with average diameter of 10–30 nm were generated and follow tip-growth mechanism. Compared with Ni/Al2O3, the addition of Fe remarkably increased the amount and quality of CNTs which had longer length and less tortuosity. These dual promoting effects on H2 and CNTs after the addition of Fe were attributed to the strong interaction between Ni and Fe in Fe-Ni alloy. Fe-Ni alloy had the high activity for the decomposition performance of toluene and H2O to generate more H2 and intermediates for improving the reforming reaction. Meanwhile, the high catalytic decomposition activity supplied more carbon species and the formation of Fe-Ni alloy enhanced the generation of metal carbide for promoting CNTs growth. Besides, the deposition of amorphous carbon was suppressed and the interaction between Ni particle and catalyst support was weakened after the addition of Fe, which kept the activity of catalyst and promoted the tip-growth of CNTs.