Towards hydrogen self-sufficiency: An innovative integration of coal hydrogasification and biomass-assisted autothermal gasification for synthetic natural gas production

Abstract

The rising demand for natural gas and pursuit for carbon neutrality have intensified research efforts into the production of synthetic natural gas (SNG) from biomass and coal. This study proposed a H₂ self-sufficient process integrating hydrogasification and autothermal gasification (HG-AG) to produce SNG from coal and sawdust. The hydrogasification of coal produces SNG, and the residual char is then co-gasified with biomass to yield H₂. In the hydrogasification subsystem, a moderate hydrogasification temperature favours CH₄ production, with a significant decrease in CH₄ concentration observed above 700 °C under 4 MPa. High hydrogen pressures promote hydrogasification reactions through a shift in the chemical equilibrium towards CH₄ formation. For the autothermal gasification subsystem, increasing temperature and steam to fuel ratio (SFR) enhances H₂ yield. Increasing equivalence ratio (ER) led to higher CO₂ and lower H₂, CO, and CH₄ concentrations. To unveil the synchronized effect of multiple variables, statistical analysis using response surface methodology identified the optimal conditions for maximizing CH₄ and H₂ yields. The optimal conditions for hydrogasification, 613.9 ℃ and 3.7 MPa, resulted in the syngas with 70 mol% CH₄. The optimal ER and SFR for the autothermal gasification are 0.44 and 1.29, respectively, resulting in the syngas with 43 mol% H₂. Compare to traditional two-step system, the studied HG-AG system is energy-efficient and economically feasible. This study illuminates a theoretically compelling pathway for biomass-assisted coal hydrogasification towards SNG production. Future research could focus on the life cycle assessment of HG-AG process to evaluate its environmental impact.