Steam gasification of plastic and woody biomass for hydrogen-rich syngas production with CO₂ reduction, emission and energy analysis

This study investigates the steam gasification of high-density polyethylene (HDPE), wood waste, and their blend into H₂-rich syngas using a simulation model under varying temperatures (650°C-950 °C) and steam/feed (S/F) ratios (0.5–2). Results show temperature enhances H₂ and CO and reduction of CO₂ and CH₄. The S/F ratio exhibits varying effects: H₂ decreases for plastic (69–63.6 mol%) but increases for wood (53.2–63.2 mol%), remaining stable for the 50:50 blend. Lower heating value and higher heating value of syngas at optimal conditions were 10.87/12.83 MJ/m³ for plastic, 9.26/10.35 MJ/m³ for wood, and 10.13/11.46 MJ/m³ for the blend. The study also investigate CO₂ capture with CaO which enhances syngas composition. For plastic, H₂ increases by 8 % (72.7 mol%) and CO₂ decreases by 5 % (2.4 mol%); for wood, H₂ rises by 17 % (78.4 mol%) and CO₂ reductions of 9 % (10.9 %); and for blend, H₂ increases to 75.8 % while CO₂ drops to 6.5 %. CO₂ emissions are highest for plastic (5.545 kg/h), lowest for wood (1.350 kg/h), and intermediate for blend (3.464 kg/h), highlighting the environmental benefits of co-gasification. The utility analysis shows energy-saving potentials: 37.6 % (plastic), 14.9 % (wood), and 31.8 % for the blend, with process heat integration identified as a key strategy for optimizing energy use.