A Novel Energetically Self-Sufficient Process for the Hydrogen Production from Waste Biomasses

Abstract

A conceptual design with Aspen Plus simulations of an integrated Supercritical Water Gasification and Oxidation (SCWG‑coOx) is presented in this work. Global municipal solid waste already exceeds 2 billion tonnes per year and could reach about 3.4 billion tonnes by 2050, underscoring the need for advanced waste-to-energy routes. Supercritical water gasification (SCWG) converts wet organic residues into a hydrogen- and methane-rich gas at conditions above the critical point of water, but its strong energy demand hampers standalone deployment. Supercritical water oxidation (SCWO) is an exothermic aqueous oxidation process that avoids energy-intensive drying and can achieve near-complete mineralization of organics with very low emissions of NOx, SOx and particulates. Coupling SCWG and SCWO into an integrated SCWG-coOx system allows energetic self-sufficiency while treating aqueous waste streams that are poorly suited to conventional thermal or biological processes. In this study, the oxidation step is modelled as a Gibbs reactor and the gasification step as a plug-flow reactor with reaction-specific kinetics, with thermal integration assessed for different feed splits and organic loadings. For an 8 t/h sludge feed split equally between SCWG and SCWO, the process is predicted to be energy self-sufficient and to deliver more than 3 MW of fuel-gas thermal power, highlighting SCWG-coOx as a promising low-impact route for sewage-sludge valorization.