Tianju Chen

Integrating oxygen‑enriched decoupled gasification with carbonization pretreatment offers a promising strategy for overcoming the persistent trade‑off between tar suppression and syngas quality during biomass conversion. In this study, oxygen‑enriched decoupled gasification of walnut shell was systematically investigated in a fluidized‑bed reactor. The thermal behavior and tar evolution during pyrolysis were characterized using TG‑FTIR and Py‑GC/MS, while the syngas composition was analyzed by GC. During the pyrolysis stage (Stage I), increasing the temperature from 800 to 900 ºC enhanced secondary cracking and deoxygenation, promoting the formation of stable aromatic tar compounds, including toluene, naphthalene, and pyrene. During the gasification stage (Stage II), oxygen‑enriched gasification at an equivalence ratio of 0.3 produced syngas containing 60.3–69.0 vol% H2+CO at 900 ºC. Increasing the steam addition from 0.14 to 0.23 kg kg-1 shifted the syngas composition toward higher H2 (33.8→44.3 vol%) and lower CO (32.9→16.0 vol%) contents, thereby increasing the H2/CO molar ratio from 1.02 to 2.77. Meanwhile, the H2 yield increased from 0.432 to 0.759 Nm3 kg-1, while carbon conversion efficiency improved from 89.0% to 96.2%. The cold gas efficiency increased from 67.4% to 78.7%. These findings demonstrate that steam addition is an effective parameter for tailoring syngas composition to meet downstream application requirements while maintaining high gasification efficiency, highlighting the potential of oxygen-enriched decoupled gasification for high‑quality syngas production from biomass.

Biomass chemical looping gasification (BCLG) is an emerging and efficient technology for converting biomass into high-quality syngas by employing metal-oxide oxygen carriers (OCs) to indirectly supply oxygen, thereby eliminating the need for air separation units and simplifying downstream gas-cleaning processes. This study proposes a mechanistic framework for active site evolution in a NiO-Fe2O3/Al2O3 OC system to elucidate its role in enhanced syngas production via BCLG. The physicochemical properties of the composite OC were systematically characterized using X-ray diffraction (XRD), H2 temperature-programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS). Both dry biomass (DB) and biomass with inherent moisture (BIM) were investigated as feedstocks to assess the influence of moisture on gasification performance. As the reaction temperature increased from 800 to 900 °C, the tar composition shifted toward more thermally stable aromatic compounds—including toluene, naphthalene, and pyrene—reflecting enhanced secondary cracking of aliphatic chains and accelerated deoxygenation of oxygenated intermediates. Inherent moisture in biomass was found to promote char gasification, improve carbon conversion efficiency, increase H2 yield, and facilitate adjustment of the H2/CO ratio in the syngas. At 900 0C, the DB achieved an effective gas yield of 1.31 m3 kg-1 and a syngas fraction of 94.61%, while the BIM showed values of 1.44 m3 kg-1 dry biomass and 94.64% with an H2/CO ratio of 0.97, confirming that the inherent CO2 and H2O, along with CH4 and tar species, were efficiently reformed into H2 and CO via oxidation-reforming reactions. The NiO-Fe2O3/Al2O3 OC composite demonstrated excellent redox stability over 20 successive cycles, with no significant deterioration in reactivity or structural integrity.

Cocombustion of coal with biomass offers a promising approach for reducing carbon and pollutant emissions, lowering operating costs, and improving combustion efficiency. In this study, the thermal degradation characteristics, gas evolution behavior, ash mineral transformation during the cocombustion and copyrolysis of coal and rice husk (RH) were systematically investigated using thermogravimetric analysis coupled with Fourier-transform infrared spectroscopy (TGFTIR) and a fixedbed reactor. The results showed that biomass addition promoted complete combustion of the blended fuel and further reduced the mass of the solid residue. During combustion, CO2 and H2O were the predominant gaseous products, whereas pyrolysis generated a broader range of volatile species, including CO, CH4, and compounds containing C=C, C–O, and C=O functional groups. The pyrolysis process occurred in two distinct stages: primary pyrolysis and secondary pyrolysis. X-ray diffraction analysis revealed that coal ash was composed mainly of SiO2 and Al2O3, while RH ash consisted predominantly of SiO2 with a minor amount of K₂O. Increasing the RH blending ratio resulted in a gradual increase in ash volume, smoother ash particle edges, and an increased tendency for slagging. However, NO emissions decreased progressively with increasing RH content. Furthermore, synergistic interactions between RH and coal during cocombustion enhanced NO reduction beyond that expected from their individual combustion behaviours. These findings provide valuable insights into the combustion behavior and ash characteristics of coal–biomass blends and offer theoretical guidance for the efficient and lowemission utilization of coal and biomass in co-combustion systems.

Biomass chemical looping gasification (BCLG) is an emerging and efficient technology for converting biomass into high-quality syngas by employing metal-oxide oxygen carriers (OCs) to indirectly supply oxygen, thereby eliminating the need for air separation units and simplifying downstream gas-cleaning processes. This study proposes a mechanistic framework for active site evolution in a NiO-Fe2O3/Al2O3 OC system to elucidate its role in enhanced syngas production via BCLG. The physicochemical properties of the composite OC were systematically characterized using X-ray diffraction (XRD), H2 temperature-programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS). Both dry biomass (DB) and biomass with inherent moisture (BIM) were investigated as feedstocks to assess the influence of moisture on gasification performance. As the reaction temperature increased from 800 to 900 °C, the tar composition shifted toward more thermally stable aromatic compounds—including toluene, naphthalene, and pyrene—reflecting enhanced secondary cracking of aliphatic chains and accelerated deoxygenation of oxygenated intermediates. Inherent moisture in biomass was found to promote char gasification, improve carbon conversion efficiency, increase H2 yield, and facilitate adjustment of the H2/CO ratio in the syngas. At 900 0C, the DB achieved an effective gas yield of 1.31 m3 kg-1 and a syngas fraction of 94.61%, while the BIM showed values of 1.44 m3 kg-1 dry biomass and 94.64% with an H2/CO ratio of 0.97, confirming that the inherent CO2 and H2O, along with CH4 and tar species, were efficiently reformed into H2 and CO via oxidation-reforming reactions. The NiO-Fe2O3/Al2O3 OC composite demonstrated excellent redox stability over 20 successive cycles, with no significant deterioration in reactivity or structural integrity. Furthermore, during 72 hours of stable operation on a pilot-scale chemical looping gasification unit (1,000 tons of biomass per year), with the gasifier temperature maintained between 850 °C and 900 °C, the NiO-Fe2O3/Al2O3 OC produced an effective gas (CO+H2) yield of 1 Nm3 per kilogram of dry biomass, corresponding to an effective gas concentration of 85%.

Oxygen-enriched decoupled gasification of biomass presents an effective approach to mitigating challenges such as high tar yield and low effective gas (CO + H2) production, with carbonization serving as a crucial pretreatment step. In this study, three representative agricultural residues—corn straw (CS), pea straw (PS) and wheat straw (WS)—were carbonized using a thermogravimetric analyzer and a tube furnace at temperatures of 220, 240, 260, 280 and 300 ℃. The evolution of carbon structure and surface morphology of the resulting biochar was systematically characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy. As the carbonization temperature increased from 220 ℃ to 300 ℃, the H/C and O/C ratios of all biochar decreased, while their calorific values increased. The carbonization process for CS, PS, and WS followed a similar transformation pathway dominated by deoxygenation and aromatization. Increasing temperature promoted greater aromatic ring polycondensation and graphitization. The relative content of C=C/C–C bonds, associated with aromatic sp² carbon structures, exhibited a consistent increase across all biomass types. In contrast, thermally liable C–O bonds declined progressively, most notably in PS (from 45.0% to 27.2%), followed by CS (37.4% to 22.7%) and WS (34.3% to 23.0%). This trend reflects the gradual removal of oxygen-containing functional groups, such as hydroxyl and ether groups, through dehydration and bond cleavage reactions. Overall, carbon evolution is temperature-driven and feedstock-dependent: WS favors more ordered carbon structures, whereas PS is better suited for producing highly defective and reactive carbon materials.