Browsing by Subject "Power-to-Gas"

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    Assessment of stakeholder perception of implementing power-to-gas in the biogas sector : implications for risk governance
    (2019) Pestalozzi, Johanny Arilexis; Bieling, Claudia
    The connection of power-to-gas (PtG) with biogas facilities to convert excess renewable electricity into biomethane represents an innovation in the biogas industry. This concept could play a role in stabilizing the German renewable energy system and make the biogas value chain and derived products more competitive and environmentally friendly. With increasing interest in this technology, potential risks, uncertainties and challenges associated with the implementation of PtG in the biogas industry need to be assessed. The biogas sector is controversial in German society mainly due to its environmental and economic impacts and its critical safety deficiencies. Against this background, this thesis aims at analyzing how the German biogas chain could be transformed with the emergence of a PtG concept and at identifying approaches to efficiently tackle potential risks, uncertainties and challenges accompanying this renewable energy concept. The investigation draws on notions of risk perception and risk governance as a theoretical framework to identify and assess influential factors determining risk management for the implementation of PtG in the biogas sector and characterize essential requirements in the process of diffusion of the technology, its acceptance and legitimation. Following a random as well as a purposive sampling strategy, 27 experts representing key interest groups of the German biogas sector, i.e., industry, politics, research and associations, were interviewed face-to-face. Their perspectives on potential environmental, safety, sociopolitical and techno-economic risks and challenges that could hinder the implementation of PtG in the biogas value chain were systematically examined with the method of qualitative content analysis. With this technique, conclusions were derived based on a thorough scrutiny of the data collected. Overall, the participants of this study perceived a low risk of accidents, such as fires, explosions and environmental pollution, from biogas installations running with a PtG concept. They identified a lack of business models, missing political incentives as well as stigmatization of the sector as the main challenges in the adoption of PtG in the biogas sector. The stakeholders emphasized a knowledge gap in the general public to explain the low popularity of the biogas sector and its biobased products. In a successful deployment of this technological concept, the interviewees envisioned a replacement of farm-based biogas plants with fully industrialized facilities. The interviewed experts strongly emphasized the existence of regulations as the principal means to avoid potential technological risks. The perception of the stakeholders corresponds with hierarchists as in the Cultural Theory of Risk. This mindset influences the way the experts recognize, manage and communicate risks. The participants prominently identified politicians as the primary accountable actors to handle risks, challenges and uncertainties of biogas associated with PtG. Although the media was broadly seen as a knowledge broker, the interviewees did not consider it as an instrument for effective risk communication to deal with distrust and stigmatization in the public and the controversies influencing the biogas sector, which could potentially affect the diffusion of PtG in the industry. The present study delivers key insights for the governance of the adoption of this technological concept in German society. In order to create a joint understanding among relevant stakeholders, facilitate informed decision-making and ultimately promote legitimacy for this technology, it is recommended to increase risk awareness among actors dealing with biogas and PtG. It is essential to foster deliberate communication among the multiple interest groups on diverging perceptions of risk and corresponding management options, so that an effective, accountable and participatory strategy to risk governance can be developed.
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    Biologische Wasserstoffmethanisierung in Hochdruck-Rieselbettreaktoren für Power-to-Gas-Konzepte
    (2018) Ullrich, Timo; Jungbluth, Thomas
    In order to achieve climate protection targets, intermittent and decentralised energy sources such as wind power and photovoltaics will be expanded in the future. However, the power grids are not designed for the large-scale expansion and connection of different decentralised and fluctuating generation plants. This represents a major challenge for grid stability and requires an increasing expansion of energy storage. Power-to-Gas technology, a process for converting electrical energy into chemical energy, will play a central role in this process. In this two-stage process, hydrogen is first produced by electrolysis, which then reacts with carbon dioxide to form methane. It can be stored and transported in the natural gas grid almost indefinitely and can be used flexibly in a wide variety of applications. In addition to the chemical-catalytic methanation of hydrogen, there is also the biological methanation process. Characteristic features are a flexible load change behaviour and a marked robustness regarding the educt gas composition. Compared to chemical-catalytic methanation, however, the gas flow rates are significantly lower, which is the greatest challenge of this process. For this reason, the aim of this work was to optimize the performance of trickle-bed reactors for biological hydrogen methanation. The focus was on improving the gas-liquid-mass-transfer as described in the literature, but not yet which has not yet been investigated in the context of this promising concept. In an automated and continuous test plant, the operating pressure was initially varied in stages of 1.5, 5 and 9 bar in the first publication. With increasing pressure, conversion rates were improved and gas quality increased by 34%. Furthermore, the circulation of the process liquid to the trickling bed of the reactors was paused for periods up to 1440 min in the second publication. As the circulation pause rose, there was a noticeable increase in all performance parameters with maximum methane contents > 97 Vol.-%. Finally, different temperature levels of 40 - 55 °C were also examined. In spite of the continuous increase in gas volumes in the three publications, the performance parameters increased again. Overall, the combined optimization measures more than doubled the output with an MFR of 4.28 ± 0.26 m3 m-3 d-1 to 8.85 ± 0.43 m3 m-3 d-1, while simultaneously increasing the methane content in the product gas. Periodical analyses of the process liquid, especially the acid concentrations, as well as the stable conversion rates indicated a stable biological process in all experiments. The tests were done with three identical reactors, underlining the high degree of reproducibility. It was noticeable that the microorganisms quickly adapted to the changing operating parameters within a maximum of 24 hours. The performance increases could thus be related to the successful increase in the gas-liquid-substance exchange rate and not to a changed microorganism concentration or selection. The studies have also revealed further optimisation potential. In particular, the properties of the process liquid with regard to pH and nutrient composition should be the subject of further investigations. Thus, the present study not only successfully demonstrated the goal of increasing performance; with stable and uncomplicated operation over several months and a wide range of operating parameters, it also demonstrated that trickle bed reactors for the biological methanation of hydrogen are a reliable, flexible and thus promising concept in the context of power-to-gas applications.