The production of synthetic natural gas (SNG) from renewable sources in cases requires a dynamic and intermitted operation of the methanation reactors. This may lead to catalyst damage. Therefore, the present work is aiming at identifying restrictions and optimization approaches of the start‐and‐stop operation of fixed‐bed methanation reactors. 2D modeling and simulation work is conducted and the warm‐start behavior of a fixed‐bed reactor after one to four hours operation intermittence is analyzed. The result reveals the possibility for an operation interruption of up to four hours without high adaptation effort to restart the reactor. After approximately four hours, the catalyst bed at the inlet part of the reactor reaches a temperature that provokes problems for a subsequent warm start.
Biogas, with its high carbon dioxide content (30–50 vol%), is an attractive feed for catalytic methanation with green hydrogen, and is suitable for establishing a closed carbon cycle with methane as energy carrier. The most important questions for direct biogas methanation are how the high methane content influences the methanation reaction and overall efficiency on one hand, and to what extent the methanation catalysts can be made more resistant to various sulfur-containing compounds in biogas on the other hand. Ni-based catalysts are the most favored for economic reasons. The interplay of active compounds, supports, and promoters is discussed regarding the potential for improving sulfur resistance. Several strategies are addressed and experimental studies are evaluated, to identify catalysts which might be suitable for these challenges. As several catalyst functionalities must be combined, materials with two active metals and binary oxide support seem to be the best approach to technically applicable solutions. The high methane content in biogas appears to have a measurable impact on equilibrium and therefore CO2 conversion. Depending on the initial CH4/CO2 ratio, this might lead to a product with higher methane content, and, after work-up, to a drop in-option for existing natural gas grids.
Limited alternative fuels for a CO2-neutral aviation sector have already been ASTM certified; synthetic paraffinic kerosene from hydrotreated esters and fatty acids (HEFA-SPK) is one of these—a sustainable aviation fuel. With the hypothesis to improve the greenhouse gas (GHG) balance of a HEFA plant by realizing the required hydrogen supply via electrolysis—power to gas (PTG)—an exemplary SynBioPTx approach is investigated in a comprehensive feasibility study, which is, regarding this comparatively new approach, a novelty in its extent. About 10 scenarios are analysed by technical, environmental, and economic aspects. Within the alternative scenarios on feedstocks, electricity supply, necessary hydrogen supply, and different main products are analysed. For different plant designs of the hybrid refinery, mass and energy balances are elaborated, along with the results of the technical assessment. As a result of this environmental assessment, the attainment of at least 50% GHG mitigation might be possible. GHG highly depends on the renewability grade of the hydrogen provision as well as on the used feedstock. One important conclusion of this economic assessment is that total fuel production costs of 1295 to 1800 EUR t−1 are much higher than current market prices for jet fuel. The scenario in which hydrogen is produced by steam reforming of internally produced naphtha proves to be the best combination of highly reduced GHG emissions and low HEFA-SPK production costs.
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