Techno-economic analysis of auto-thermal gasification of municipal solid waste with ash direct melting for hydrogen production

Abstract

Hydrogen is regarded as a promising secondary energy source to tackle the pollutions and carbon emission caused by the usage of fossil fuels. Municipal solid waste (MSW) generated in our daily lives as a potential renewable energy resource can be used for hydrogen production via gasification process. Yet the techno-economic feasibility of the waste-to-H2 process has not been well evaluated. This study proposes a H2 production route from MSW via an auto-thermal steam gasification combined with ash direct melting process. The technical and economic performances of the system are evaluated by process simulation using Aspen Plus. Part of the generated syngas is extracted for combustion with oxygen to provide heat for gasification and achieving ash melting. A net H2 yield of 0.075 kg/kg-MSW was obtained at the gasification temperature of 900 °C and steam/MSW ratio of 0.9. The levelized cost of hydrogen (LCOH) is 18.53 CNY (Chinese Yuan)/kg. Under this condition the energy and exergy efficiency are 47.37% and 40.18%, respectively. Three additional cases were also studied to investigate the effects of external energy supply, ash melting process, and gasification agent on the thermodynamic and economic performances. Using biochar as external supply energy will lead to a higher H2 yield (0.112 kg/kg-MSW), but also a higher LCOH due mainly to the additional biochar cost and CO2 capture cost. If without the ash melting process, the energy efficiency can be improved, yet the generated ash may need further treatment which would otherwise cause environmental pollution. Considering the technical, economical, and environmental perspectives, the gasification and direct melting process as a harmless and resourceful method presents a promising potential for waste-to-H2 conversion.