Process optimisation and enviro-economic assessment of carbon-negative hydrogen production from biomass co-gasification

Biomass wastes are abundantly available, yet leveraging these resources for large-scale green energy production requires a comprehensive and strategic evaluation. In this study, an environmentally sustainable and economically viable gasification process for generating pure hydrogen gas from waste biomass was developed. Switchgrass was combined with two co-feeds: low-density polyethylene (LDPE) and high ash coal to improve hydrogen production efficiency. Two process configurations for biomass gasification/co-gasification were investigated: (1) baseline scenario without addition of key units towards sustainability, including carbon-capture (CC), waste heat recovery (WHR) and in-plant power & steam generation (PSG), and (2) integrated scenario with the addition of CC, WHR and PSG. The integrated gasification scenario achieved over 99 % hydrogen purity and high carbon capture efficiency, leading to negative carbon emissions of –323.55, −465.84, and −68.28 kg CO₂ eq. for biomass, biomass-LDPE and biomass-coal gasification, respectively. Besides this, integrated scenarios also displayed negative emissions in most of the other impact categories like ecotoxicity, acidification, eutrophication and many more. The corresponding net present value (NPV) for biomass, biomass-LDPE and biomass-coal gasification integrated scenario was $69.7 million, $108 million, and $76.4 million, respectively. The results indicate that biomass co-fed with LDPE in integrated gasification scenario represents the most environmentally and economically sustainable case with the highest hydrogen production, lowest environmental emissions and highest economic returns. It was also shown that process energy requirements were the key driver of environmental emissions and production costs. This research provides a comprehensive evaluation framework for waste-to-hydrogen technologies by identifying critical process hotspots and necessary policy measures for large-scale implementation of sustainable hydrogen.