Experimental study on the vaporization characteristics of wood chips under airflow bed conditions

High-temperature gasification experiments of wood chips were conducted on a drop-tube furnace experimental platform to study the effects of temperature and steam-to-biomass ratio (S/B) on the gaseous and solid-phase products under entrained flow reactor conditions. Gaseous products were analyzed using a gas analyzer, and the results revealed that increasing the temperature significantly promoted the production of effective gases, specifically H₂ and CO, in the syngas. When the temperature reached 1300 ℃, the yield of effective gases in the syngas reached its maximum value of 814.88 g/kg. As the temperature increased, both the gas yield and carbon conversion efficiency increased. At 1300 ℃, the gas yield was 1.98 m³/kg, and the carbon conversion efficiency reached 90.65%. The H₂/CO ratio exhibited a trend of increasing first and then decreasing with temperature; it peaked at 2.18 at 1100 ℃, indicating that while temperature promoted H₂ production, it also influenced the balance between H₂ and CO. The introduction of steam into the gasification process enhanced the generation of H₂ but reduced the overall yield of effective gases in the syngas. As the S/B ratio increased, the gas yield and carbon conversion efficiency showed a pattern of first increasing and then decreasing. At an S/B ratio of 2.0, both gas yield and carbon conversion efficiency reached their maximum values of 1.78 m³/kg and 86.90%, respectively. This suggests that while higher S/B ratios can boost H₂ production, they may also have an inhibitive effect on the overall gasification efficiency by reducing the yield of other gases. Under high-temperature conditions, the C and H elements in the wood chips tended to transfer to the gas phase rather than to remain in the liquid or solid phases. The introduction of steam encouraged the transfer of C elements, which would otherwise remain in the liquid phase, into the gas phase, while some of the C elements also remained in the solid phase. Furthermore, a large influx of steam caused most of the hydrogen to exist in the liquid phase in the form of H₂O. This process suggests that steam plays a dual role in enhancing H₂ production while also altering the distribution of carbon and hydrogen in the different phases. Scanning electron microscope (SEM) analysis of the solid-phase products showed that, as both temperature and S/B ratio increased, spherical particles gradually formed on the surface of the gasification char. Initially, these particles were hypothesized to result from the melting of inorganic elements. However, further X-ray diffraction (XRD) analysis indicated that these spherical particles were likely the result of the aggregation of inorganic elements through solid-phase reactions at high temperatures, rather than being formed through a melting process. X-ray photoelectron spectroscopy (XPS) analysis of the carbon-containing functional groups in the solid-phase products revealed that as the temperature increased, the C−C and C−H bonds in the gasification char were broken down, leading to the formation of oxygen-containing functional groups such as hydroxyl (−OH) and ether (C−O) bonds. However, the increase in the S/B ratio did not significantly affect the C−C/C−H bonds, suggesting that the effects of steam on the chemical structure of the gasification char are limited compared to temperature.