Energy and techno-economic analysis of integrated supercritical water gasification of sewage sludge and fast pyrolysis of wood for power, heat, and hydrogen production
Richard Ochieng, Shiplu Sarker
Abstract
• Integrated wet and dry biomass conversion into electricity, heat, and hydrogen. • Aspen Plus modeling of integrated supercritical water gasification and fast pyrolysis. • Supercritical water gasification of pyrolysis oil and sewage sludge. • Assessment of energy, exergy, and techno-economics in integrated waste biorefineries. This paper uses Aspen Plus process modeling to investigate the integration of supercritical water gasification (SCWG) of sewage sludge with fast pyrolysis of wood residue to produce hydrogen, power, and heat. A sensitivity analysis was investigated, including the effect of co-gasifying pyrolysis oil with sewage sludge. Energy and techno-economic analyses were conducted to assess the thermodynamic efficiency and feasibility of the integrated concept. Under the study conditions, the system produced 23.1 mol of hydrogen per kilogram of total biomass, 684 kW of power, and 3400 kW of excess heat. The integrated process had an energy efficiency of 61.2 % and an exergy efficiency of 44.9 %. The techno-economic evaluation revealed a minimum hydrogen selling price of 3.04 $/kg, which was lower than standalone SCWG but higher than pyrolysis. The findings demonstrate that coupling SCWG and fast pyrolysis is feasible and enables the conversion of wet organic and dry biomass wastes into bioenergy.