Thermodynamic analysis of a solar-assisted supercritical water gasification system for poly-generation of hydrogen-heat-power production from waste plastics

The resource utilization of waste plastics is an effective approach to address the issue of energy shortage. In this study, a comprehensive disposal system for polypropylene plastics was designed by supercritical water gasification coupled with a solar heat collector for poly-generation of power, hydrogen, and heat. The study first demonstrated the transfer behavior and exchange capacity of different streams throughout the entire system. It was found that the disposal system maintained mass conservation by checking the material streams. The thermodynamic results indicated that the largest exergy losses occurred in the oxidizer, accounting for 50.2 % of the total system exergy loss, followed by the heat exchanger at 14.51 %, with other units remaining below 10 %. A sensitivity analysis demonstrated that feedstock concentration significantly impacted exergy efficiency and output steams. Exergy efficiency rose from 49.5 % to 58 % as feedstock concentration increased from 5 wt% to 20 wt%. In contrast, changes in oxidation temperature had a slightly impact, with output power rising slightly from 9089 kW to 9598 kW. The effect of gasification temperature was intermediate between them. Finally, an optimal gasification conditions achieved 58.47 % exergy efficiency at 800 °C gasification, 960 °C oxidation with 5 wt% feed, producing 9496 kW of power, 76.2 kg/h of hydrogen, and 144.7 t/h of hot water.