Steam-only Gasification of Hazelnut Shells and Exergy Analysis by ASPEN Plus

Steam-only gasification is an attractive but less studied method despite its potential to manufacture hydrogen-rich gas. Atmospheric-pressure steam-only gasification of lignin-rich hazelnut shells to produce syngas was investigated by ASPEN Plus modeling to simulate small-scale operation where 50 kg/h of raw biomass is gasified in downdraft fixed-bed gasifier. The influence of temperature (700–1000 °C) and steam/biomass ratio (SBR: 0.2-1) on H₂/CO and CO/CO₂ ratios as well as (H₂ + CO) was investigated. It was determined that, the sum of H₂ and CO reached 95.6% of gas product and the concentration of CO is 24.6 times higher than that of CO₂ at 850 °C and 0.2 SBR. Alternatively, gasification can be carried out at 700 °C and with a SBR of 0.6 to yield a syngas that has H₂/CO ratio around two for using in chemical synthesis. The exergy analysis was performed based on both the total exergy of all gas products and only hydrogen. The highest exergy efficiency was calculated as 54.9% for all products, while it varied within 17-31.5% for hydrogen. The results showed that high-lignin content hazelnut shells are highly suitable raw material to produce H₂-rich syngas via steam-only gasification.