Gas-heat-electricity poly-generation system based on solar-driven supercritical water gasification of waste plastics

Energy shortage and environmental pollution make people aware of the need to recycle waste resources and develop environment-friendly energy. The massive plastic waste and clean solar energy provide new solutions to energy and environment issues. In this study, a solar-driven gas-heat-electricity poly-generation system based on supercritical water gasification of plastics was established. Plastic waste and solar energy were converted into electricity, heat and hydrogen-rich gas. A detailed analysis of mass, energy and exergy flow of the system was analyzed under typical operating conditions. The effects of temperature, pressure, plastics to water ratio, etc., on gasification performance, system efficiency, and energy output distribution were investigated. The results showed that the system exergy loss mainly occurred in cooler, reactor and heat exchanger, and their loss account for more than 85% of the total loss. The increase in temperature significantly increased total gas production and H₂ molar fraction. At 800 °C, the total gas production reached 77.50 kg/h and the H₂ molar fraction was 65.78%. However, increasing temperature had a negative impact on system efficiency. The effect of pressure on the gasification reaction and system efficiency was not significant. Increasing plastics to water ratio was beneficial in improving system efficiency, while each gas production showed varying degrees of growth. However, H₂ yield and molar fraction decreased dramatically. The increase of turbine feed water led to a slight decrease of energy efficiency, while the exergy efficiency remained basically unchanged. These can provide theoretical guidance for system optimization and promote the industrial application of the technology.