Performance Improvement of Downdraft Biomass Gasification Using a Physical Barrier and Low-Cost Catalysts for Syngas Enhancement

Abstract

This study optimized syngas production from Eucalyptus sp. wood chips in a pilot-scale downdraft gasifier through physical modifications (a barrier in the reduction zone) and low-cost catalysts (iron ore and nickel oxide), aiming to enhance gas quality and process efficiency for decentralized bioenergy systems. CFD simulations guided barrier design, increasing gas residence time by 50% (from 4.6 to 6.9 s) and Reynolds number in the reduction zone to > 280, enhancing turbulence. Experimental results showed that the iron ore catalyst boosted hydrogen content to 10.0 vol%, while the nickel catalyst achieved an optimal H₂/CO ratio of 2.3:1 for syngas applications. Combined use of both catalysts with steam further elevated the H₂/CO ratio to 4.19:1. Despite a minor reduction in lower heating value (LHV) from 4.07 to 3.95 MJ/Nm³, the barrier improved operational stability, reducing temperature fluctuations by 100 °C. Cold gas efficiency reached 54.7% for steam-assisted gasification. These results demonstrate the potential of low-cost modifications to enhance gasifier performance.