Browsing by Person "Holl, Elena"

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Innovative process chain for the resource-efficient production of biomethane-based fuels
(2024) Holl, Elena; Lemmer, Andreas
Biogas is a key component in renewable energy production and holds significant potential for achieving Germany’s climate goals. In the transport sector, where the share of renewa-ble energy was only 6.8% in 2023, greenhouse gas (GHG) emissions must be reduced from 147.9 Mt in 2022 to 84 Mt by 2030. Biomethane-based fuels such as bio-LNG and bio-CNG are promising alternatives that are compatible with existing infrastructure and vehicle technologies, already contributing to emission reductions. This study aims to optimize biomethane production through an innovative process chain for decentralized and resource-efficient provision of methane-based fuels. Biogas production was analyzed using two-stage anaerobic digestion (TSAD) to determine optimal substrate compositions and operating parameters. Biogas upgrading was conducted via biological hydrogen methanation (BHM), a power-to-gas technology that enhances process efficiency and economic viability. The results demonstrate that TSAD achieves high methane content (> 60%) even under high organic loads, while BHM performance can be further improved through pressure and temperature optimization. A life cycle assessment (LCA) confirms the efficiency gains of the new process chain compared to conventional methods. The use of renewable energy in process stages has the greatest impact on reducing GHG emissions. Decentralized bio-LNG production from agricultural residues emerges as a feasible solution for producing CO₂-negative fuels.
Optimization of thermodynamic parameters of the biological hydrogen methanation in a trickle-bed reactor for the conditioning of biogas to biomethane
(2023) Holl, Elena; Oskina, Anastasia; Baier, Urs; Lemmer, Andreas
The increased demand for resources and energy that is developing with rising global consumption represents a key challenge for our generation. Biogas production can contribute to sustainable energy production and closing nutrient cycles using organic residues or as part of a utilization cascade in the case of energy crops. Compared to hydrogen (H2), biogas with a high methane (CH4) content can be fed into the gas grid without restrictions. For this purpose, the CH4 content of the biogas must be increased from 52 to 60% after anaerobic digestion to more than 96%. In this study, biological hydrogen methanation (BHM) in trickling-bed reactors (TBR) is used to upgrade biogas. Design of experiments (DoE) is used to determine the optimal process parameters. The performance of the reactors is stable under all given conditions, reaching a “low” gas grid quality of over 90%. The highest CH4 content of 95.626 ± 0.563% is achieved at 55 °C and 4 bar, with a methane formation rate (MFR) of 5.111 ± 0.167 m3/(m3·d). The process performance is highly dependent on the H2:CO2 ratio in the educts, which should be as close as possible to the stochiometric ratio of 4. In conclusion, BHM is a viable approach to upgrade biogas to biomethane quality and can contribute to a sustainable energy grid.