Sustainable Syngas Production From CO₂-Assisted Gasification of Solid Wastes: A Simulation-Based Approach to CO₂ Utilization

CO₂-assisted gasification offers a potential route for waste valorization and CO₂ utilization, yet the suitability of chemically distinct wastes under comparable operating conditions remains insufficiently established. This study compares wood residue (WR), rice straw (RS), poultry litter (PL), and high-density polyethylene (HDPE) using an Aspen Plus equilibrium model. The effects of temperature (500°C-1000°C) and gasifying agent-to-waste (G/W) mass ratio (0.5-3.0) on syngas composition, H₂/CO ratio, gas yield, lower heating value, cold gas efficiency, and net heat duty were evaluated. The feedstocks exhibited distinct thermodynamic responses. Biomass-derived feedstocks generally showed improved gas-phase performance with increasing temperature, whereas HDPE exhibited substantially higher gas yields and a distinct response to CO₂ availability. Contour-based trade-off analysis and constraint-based screening were further applied to identify feedstock-specific feasible operating regions. Within the predefined operating window of 700°C-900°C and G/W = 0.5-2.5, using H₂/CO = 1-2 and CGE ≤ 100% as screening criteria, HDPE exhibited a broad feasible region, WR showed a highly restricted region, and no feasible regions were identified for PL and RS. These findings provide a systematic framework for preliminary feedstock and operating-domain screening for CO₂-assisted waste-to-syngas conversion.