Abstract
The energy supply in Austria is significantly based on fossil natural gas. Due to the necessary decarbonization of the heat and energy sector, a switch to a green substitute is necessary to limit CO2 emissions. Especially innovative concepts such as power-to-gas establish the connection between the storage of volatile renewable energy and its conversion into green gases. In this paper, different methanation strategies are applied on syngas from biomass gasification. The investigated syngas compositions range from traditional steam gasification, sorption-enhanced reforming to the innovative CO2 gasification. As the producer gases show different compositions regarding the H2/COx ratio, three possible methanation strategies (direct, sub-stoichiometric and over-stoichiometric methanation) are defined and assessed with technological evaluation tools for possible future large-scale set-ups consisting of a gasification, an electrolysis and a methanation unit. Due to its relative high share of hydrogen and the high technical maturity of this gasification mode, syngas from steam gasification represents the most promising gas composition for downstream methanation. Sub-stoichiometric operation of this syngas with limited H2 dosage represents an attractive methanation strategy since the hydrogen utilization is optimized. The overall efficiency of the sub-stoichiometric methanation lies at 59.9%. Determined by laboratory methanation experiments, a share of nearly 17 mol.% of CO2 needs to be separated to make injection into the natural gas grid possible. A technical feasible alternative, avoiding possible carbon formation in the methanation reactor, is the direct methanation of sorption-enhanced reforming syngas, with an overall process efficiency in large-scale applications of 55.9%.
Highlights
To minimize carbon dioxide (CO2 ) emissions and the dependence on energy imports, many European countries see a large potential of biomass gasification for energy or synthetic fuel production
Laboratory experimental and simulation results will be shown for two of three methanation operation strategies, and ideally calculated large-scale power-to-gas set-ups will be assessed based on their technical feasibility for future industrial-scale applications
The focus of this article was on the identification of technological possible methanation routes for a large-scale biomass to SNG set-up, combining biomassbased (b-fuels) and electro-fuels (e-fuels) based on fundamental technical evaluations
Summary
To minimize carbon dioxide (CO2 ) emissions and the dependence on energy imports, many European countries see a large potential of biomass gasification for energy or synthetic fuel production. Biomass is featured with carbon neutrality, which makes clean biomass-based fuel (b-fuel) production through gasification very attractive in future energy systems [2]. Basic considerations of the total process chain of gasification, including up- and downstream process elements, have been discussed in a review by Hofbauer [3], in which the important process principles are explained in detail. For synthetic fuel or electro-fuel (e-fuel) production, a specific gas composition (e.g., H2 /COx ratio) without impurities or catalyst poisons needs to be ensured. Biofuels or e-fuels (especially synthetic natural gas (SNG)) can be stored as green energy carriers in existing infrastructure.
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