Study on a self-heating disposal system for hydrogen and heat by supercritical water gasification of waste plastics

Plastic pollution is a pressing global issue that demands urgent attention. As a clean and efficient disposal technology, the advent of supercritical water gasification (SCWG) provides a solution for the effective recycling of waste plastics. In this work, the feasibility of SCWG process for waste plastic was investigated by developing a self-heating system for co-generating hydrogen and heat. Through sensitivity analysis, the effects of various process parameters, such as preheated water quantity, gasification temperature, oxidation temperature, and feed concentration, on the thermodynamic efficiency, hydrogen, and steam yields were elucidated. Additionally, a life cycle assessment was employed to evaluate the environmental impacts of the entire disposal process. The results indicated that the system's performance was determined by the exergy losses in each unit, arising from irreversible reaction, heat dissipation and heat transfer. Elevated gasification temperatures and heightened feedstock concentrations were advantageous for both hydrogen production and exergy efficiency. Conversely, increased preheated water quantities and higher oxidation temperatures exerted an adverse effect. The environmental assessment demonstrated that the carbon capture and storage measures could effectively reduce global warming potential (GWP), compared to the alteration of process parameters. Finally, optimization of the disposal process resulted in the attainment of a maximal exergy efficiency of 58.3% for the system.