Hydrogen-rich gas production via fast pyrolysis of biophysical dried sludge: Effect of particle size and moisture content on product yields and syngas composition

After biophysical drying, a novel biophysical dried sludge particle was obtained. This work aims to investigate the function and effects of particle sizes and moisture contents on the fast pyrolysis of biophysical dried sludge particles. The results showed that large particles (>4 mm) favoured the oil generation with a maximum value of 19.0%, and small particles (<0.27 mm) favoured the char yield with a maximum value of 60.6%. Medium particle fractions (between 0.27 mm and 4 mm) benefited syngas production and induced higher H₂ and CO emission, owing to the well-developed microstructure, enrichment of cellulose, and enhanced catalytic effects during the charring process. The introduction of proper moisture content (53.9% to 62.6%) to biophysical dried sludge was found to dramatically enhance syngas yield, hydrogen production, and carbon conversion efficiency. H₂ molar concentration reached a maximum of 46.02% at a moisture content of 53.9%, which was attributed to the steam reforming and steam gasification accompanying the initial biophysical dried sludge pyrolysis.