Hydrogen Production via Off-Sun Solar-Thermal Supercritical Water Gasification and Membrane Reforming of Piggery Waste

Abstract

Supercritical water gasification (SCWG) represents an emerging technology for liquid fuel synthesis, offering large potential in significantly improving the efficiency and environmental impact of clean fuel production. Compared to conventional gasification, SCWG proceeds at much lower temperatures, allowing char and tar-free gasification of biomass and for low-quality and high-moisture content biomass to be used. As the thermochemical processes involved in SCWG and steam methane reforming (SMR) are highly endothermic, combining them with concentrated solar power (CSP) and thermal energy storage (TES) could allow the process to be driven solely by renewable energy. As such, this work models an off-sun SCWG/SMR system using novel molten salt, proposed to reach up to 600°C [1], which overcomes the previously limiting molten salt temperature of 550°C. Using an off-sun configuration, it deals with the on-sun configuration’s issues of degraded lifetime and creep-fatigue, allowing for uniform heating and a reduced load on the reactors. The novel technology of an integrated Pd-based membrane reactor, highly selective to H₂, was chosen given its ability to carry out SMR at temperatures in the viable range of new molten salts. The system uses a waste feedstock, piggery waste, to provide the dual benefit of reducing the environmental cost associated with piggery waste’s release of CH4. From the model created in Aspen Plus, a plant output of 7.2 kmolH₂/h (1,135 Nm³/h of H₂), was obtained with a flow rate of 150 kg/h of dry piggery waste, a membrane area of 131.8 m², and a 73% CH4 conversion from the feed.