Thermodynamic, Economic and Environmental Assessment of Renewable Natural Gas Production Systems

One of the options to reduce the dependence on fossil fuels is to produce gas with the quality of natural gas but based on renewable energy sources. It can encompass, among other, biogas generation from various types of biomass and its subsequent upgrading. The main aim of this study is to analyze under a combined technical, economic and environmental perspective three of the most representative technologies for the production of biomethane (bio-based natural gas): (i) manure fermentation and its subsequent upgrading by CO₂ removal, (ii) manure fermentation and biogas methanation using renewable hydrogen from electrolysis, and (iii) biomass gasification in the atmosphere of oxygen and methanation of the resulted gas. Thermodynamic, economic and environmental analyses are conducted to thoroughly compare the three cases. For these purposes, detailed models in Aspen Plus software were built while environmental analysis was performed using the Life Cycle Assessment methodology. The results show that the highest efficiency (66.80%) and the lowest break-even price of biomethane (19.2 €/GJ) are reached for the technology involving fermentation and CO₂ capture. Concerning environmental assessment the system with the best environmental performance varies depending on the impact category analyzed, being the system with biomass gasification and methanation a suitable trade-off solution for biomethane production.