Investigation of hydrogen-rich syngas production from biomass gasification with CaO and steam based on real-time gas release behaviors

Abstract

Real-time gas release behaviors in biomass gasification using steam and CaO under various operating conditions were investigated by on-line gas analysis to mechanistically understand the enhanced production of hydrogen-rich syngas. Without steam and CaO, the syngas yields increased from 146.6 mL/g at 600 °C to 831.5 mL/g at 850 °C with improved cold gas efficiency (CGE) but corresponding to a low H2/CO ratio of 0.14. By introducing steam with CaO, the syngas yield further increased to > 1000 mL/g with 4 times growth in H2/CO ratio, and the CGE increased to 71.6%. The release of H2 was prolonged and intensified with the synergistic use of steam and CaO, while CH4 and CO almost unchanged. The increase in steam/biomass ratio mainly contributed to the elevated releasing rate of H2 after 6 min, and the growth in CaO dosage led to improved H2 evolutions all through the reaction period where the peak was from 33.1 mL/min∙g without catalyst to ∼100 mL/min∙g under catalyst/biomass = 2. Ternary diagram analysis indicated that CaO and steam with higher addition amount (e.g., CaO/biomass = 1, steam/biomass = 7.5) were more suitable for producing hydrogen-rich syngas with less CO2 emission and the elevated CGE. These synergistic effects were possibly due to that CaO addition in the presence of steam can catalyze the volatiles cracking and absorb CO2 to drive the chemical equilibrium of steam reforming and water gas shift reactions shifting forward, which consequently facilitated H2 formation. The current work will provide fundamentals for efficient conversion of biomass waste to high quality syngas.