Numerical simulation analysis of biomass gasification and rich-H₂ production process in a downdraft gasifier

Biomass gasification technology offers a sustainable solution for managing agricultural waste, mitigating environmental pollution, and enhancing living standards. This work deploys Aspen Plus to simulate a downdraft gasifier with an integrated H₂ reforming module. The impact of key factors, including air equivalence ratio (ER), gasification system pressure, water vapor input, gasification agent temperature, and oxygen content, are considered. Specifically, optimal ER initially improved the gasification efficiency, with a peak followed by a decline. Water vapor addition elevated H₂ content, while increased gasifying agent temperature and oxygen concentration enhanced efficiency. However, the increased gasification pressure will lead to a decrease in gasification efficiency. Subsequently, the effect of reforming temperature, CaO, and water vapor input in the hydrogen production model was examined. An appropriate excess of water vapor and calcium oxide were crucial for maximizing H₂ concentration. As the reforming temperature increased from 200 °C to 600 °C, the H₂ concentration showed an initial increase and then stabilizes. However, beyond 600 °C, there was a rapid decline. Under optimal conditions (H₂O/C > 1.3, CaO/C > 1.1, temperature 550–600 °C), the product gas generated during gasification and reforming processes achieved a high H₂ concentration of 98%–99%. These findings affirmed the substantial potential of biomass gasification in high-efficiency H₂ production.