04 Fakultät Energie-, Verfahrens- und Biotechnik
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/5
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Item Open Access Global potentials and costs of synfuels via Fischer-Tropsch process(2023) Buchenberg, Patrick; Addanki, Thushara; Franzmann, David; Winkler, Christoph; Lippkau, Felix; Hamacher, Thomas; Kuhn, Philipp; Heinrichs, Heidi; Blesl, MarkusThis paper presents the potentials and costs of synthetic fuels (synfuels) produced by renewable energy via PEM water electrolysis and the subsequent Fischer-Tropsch process for the years 2020, 2030, 2040, and 2050 in selected countries across the globe. The renewable energy potential was determined by the open-source tool pyGRETA and includes photovoltaic, onshore wind, and biomass. Carbon dioxide is obtained from biomass and the atmosphere by direct air capture. The potentials and costs were determined by aggregating minimal cost energy systems for each location on a state level. Each linear energy system was modelled and optimised by the optimisation framework urbs. The analysis focused on decentralised and off-grid synthetic fuels’ production. The transportation costs were roughly estimated based on the distance to the nearest maritime port for export. The distribution infrastructure was not considered since the already-existing infrastructure for fossil fuels can be easily adopted. The results showed that large amounts of synthetic fuels are available for EUR 110/MWh (USD 203/bbl) mainly in Africa, Central and South America, as well as Australia for 2050. This corresponds to a cost reduction of more than half compared to EUR 250/MWh (USD 461/bbl) in 2020. The synfuels’ potentials follow the photovoltaic potentials because of the corresponding low levelised cost of electricity. Batteries are in particular used for photovoltaic-dominant locations, and transportation costs are low compared to production costs.Item Open Access A model-based framework for the assessment of energy-efficiency and CO2-mitigation measures in multi-cylinder paper drying(Stuttgart : Universität Stuttgart, Institut für Energiewirtschaft und Rationelle Energieanwendung, 2022) Godin, Hélène; Radgen, Peter (Prof. Dr.-Ing.)Thesis on the effect of energy-efficiency and CO2-mitigation measures in multi-cylinder paper drying.Item Open Access Operational impacts of large-scale wind power generation in the German power system and effects of integration measures : analyses with a stochastic electricity market model(2012) Hasche, Bernhard; Voß, Alfred (Prof.)A strong increase of onshore and offshore wind power capacities is an official political target in Germany and other countries. The wind energy shares therefore rise in many power systems. Wind power generation has other characteristics than the power generation by conventional power plants. The wind is a natural resource that is fluctuating. The meteorological dependency leads to a limited predictability of the available power. A third aspect is the concentration of wind farms at locations with high wind yields as in the North of Germany. From a methodological point of view, the thesis focuses on the analysis of the three aspects with regard to the power system operation and the development of related modelling approaches. This especially refers to the application of a stochastic optimization model for the system analysis and to the simulation of wind power generation and wind power forecasts. The application orientated focus is on a scenario analysis of the German power system in 2020. The analysis aims at the identification of promising system adaptations that lead to an improved wind power integration and a more efficient power system operation. Before the model presentation, the importance of the three aspects above is discussed giving the basics for the latter modelling. It is shown that the residual load fluctuations are increased by the wind power generation, especially if they are related to the residual load levels. The flexibility of thermal power plants is also regarded here. An analysis of operational uncertainties shows the importance of wind power forecast errors in relation to load forecast errors. The DC load flow model and characteristics of the transmission grid are explained. A stochastic market model is presented that allows an integrative analysis of the wind power integration. One characteristic of the optimization model is the application of a rolling planning so that forecast errors can be specifically considered. A main modification of the model compared to earlier model versions is given by the representation of grid constraints. A grid reduction approach is developed that reduces the transmission grid to a simplified structure that is applied in the market model. The grid reduction approach is based on a comparison of DC load flow solutions in the reduced and unreduced grid. Additionally, an approach for the calculation of tertiary reserves is given. The approach considers the wind forecast quality and combines probabilistic elements with an optimization. The simulation of wind power generation and forecasts combines different analyses and methods. General quantitative relations between the variability of wind power generation and the geographical region size are derived. The equations are applied in the simulation of wind power generation that is based on adapted wind power curves. The adapted power curves consider regional smoothing effects in the transformation of wind speed to wind power. The simulation results reflect the high variability of the concentrated offshore wind power. For the simulation of the wind power forecasts, a scenario generation method based on moment matching is presented that allows simulating non Gaussian distributed forecast errors and their correlations. The results of a statistical analysis of measured forecast errors are used in the simulation. An empirical relation between error correlation and geographical distance is for example given. The German forecast quality that is simulated for 2020 assuming an improvement of forecasting by 20% is, related to the installed capacity, similar to the one of today due to the high spatial concentration of the offshore capacities. For the scenario analysis of the power system in 2020, the power plant portfolios of twelve German regions and other parameters are derived based on different sources. This includes reserve requirement values and reduced grid parameters that are calculated by the methods mentioned above. The results show that, in the regarded scenario, 3% of the yearly wind energy cannot be integrated into the system. They are curtailed nearly exclusively due to transmission constraints. The network congestions also lead to high differences between the regional electricity prices. The yearly costs of wind forecast errors amount to circa 180 million Euros or 1% of the operational system costs. The model results thereby indicate a large cost saving potential by risk management methods. Based on scenario modifications, integration measures related to CAES capacities, demand side management and more flexible power plants as well as infrastructural changes by grid expansions and an adapted geographical allocation of power plants are analysed. The importance of a stochastic modelling approach for the evaluation of flexibility related scenarios is shown. The comparison of the integration measures identifies infrastructural changes as most efficient system improvements whereas the benefits of CAES capacities are small. Assuming a grid without any transmission constraints, the yearly system costs are reduced by one billion Euros. A limited grid upgrade leads to 10% of this cost reduction. Similar cost savings are achieved by adapting the geographical locations of the power plants. Adjusting the generation to the grid is therefore a promising alternative to grid expansions especially considering the long processes that are involved with new transmission lines. A market design with regional electricity prices would give related incentives.Item Open Access Roadmap to neutrality - what foundational questions need answering to determine one’s ideal decarbonisation strategy(2022) Buettner, Stefan M.Considering increasingly ambitious pledges by countries and various forms of pressure from current international constellations, society, investors, and clients further up the supply chain, the question for companies is not so much whether to take decarbonisation action, but what action and by when. However, determining an ideal mix of measures to apply ‘decarbonisation efficiency’ requires more than knowledge of technically feasible measures and how to combine them to achieve the most economic outcome: In this paper, working in a ‘backcasting’ manner, the author describes seven aspects which heavily influence the composition of an ‘ideal mix’ that executive leadership needs to take a (strategic) position on. Contrary to previous studies, these aspects consider underlying motivations and span across (socio-)economic, technical, regulatory, strategic, corporate culture, and environmental factors and further underline the necessity of clarity of definitions. How these decisions influence the determination of the decarbonisation-efficient ideal mix of measures is further explored by providing concrete examples. Insights into the choices taken by German manufacturers regarding several of these aspects stem from about 850 responses to the ‘Energy Efficiency Index of German Industry’. Knowledge of the status quo, and clarity in definitions, objectives, time frames, and scope are key.Item Open Access Lab-scale investigation of palm shell char as tar reforming catalyst(2020) Chen, Yen-Hau; Schmid, Max; Chang, Chia-Chi; Chang, Ching-Yuan; Scheffknecht, GünterThis research investigated the application of palm shell char as a catalyst for the catalytic steam reforming of tar after the sorption enhanced gasification (SEG) process. The catalytic activities of palm shell char and metal-supported palm shell char were tested in a simulated SEG derived syngas with tar model compounds (i.e., toluene and naphthalene) at a concentration of 10 g m-3 NTP. The results indicated that palm shell char had an experimentally excellent catalytic activity for tar reforming with toluene and naphthalene conversions of 0.8 in a short residence time of 0.17 s at 900 °C. A theoretical residence time to reach the complete naphthalene conversion was 1.2 s at 900 °C for palm shell char, demonstrating a promising activity similar to wood char and straw char, but better than CaO. It was also found that potassium and iron-loaded palm shell chars exhibited much better catalytic activity than palm shell char, while the parallel reaction of gasification of K-loaded palm shell char influenced the conversion with its drastic mass loss. Moreover, contrary to CaO, palm shell char presented relatively low selectivity to benzene, and its spontaneous gasification generated extra syngas. In summary, the present study demonstrated that the low-cost material, palm shell char, can successfully be used as the tar-reforming catalyst after SEG process.Item Open Access Steam-oxygen fluidized bed gasification of sewage sludge(2023) Schmid, Max; Scheffknecht, Günter (Univ.-Prof. Dr. techn.)Sewage sludge is a residue that is generated unavoidably by the population. On a first sight, sewage sludge may be a hazardous waste that requires safe disposal. By looking closer, it is recognized as secondary resource. The mineral fraction contains valuable elements such as phosphorous, which can be retrieved as secondary raw material. This thesis focuses on the organic fraction, which is a renewable fuel and carbon source and can be used to substitute fossil carbon in fuels and chemicals. The first step in converting sewage sludge to renewable goods is syngas production via gasification. The experimental work of this thesis demonstrated the feasibility of synthesis gas production from sewage sludge by steam-oxygen fluidized bed gasification. It was shown that the process works reliably in the investigated 20 kW scale and that the syngas contains high H2 and CO concentrations and is thus suitable for synthesis of fuels and chemicals. The impurities NH3, H2S, COS and tar species, including heterocyclic species such as pyridine, were measured in considerable concentrations in the syngas. Small amounts of limestone bed additive enabled cracking of heavy tars and partial capture of H2S and COS. It was further found that the cold gas efficiency increases with rising gasification temperature due to improved tar and char conversion at higher temperatures. The typical operation temperature 850 °C requires an oxygen ratio of 0.33, obtaining a cold gas efficiency of 63 %. Moreover, the H2/CO-ratio could be controlled efficiently by altering the steam to carbon ratio, as steam promotes the water gas shift reaction in the gasifier to achieve the desired stoichiometry for synthesis, however, resulting in higher energy demand for steam provision. The experimental results can be utilized for process design, e.g., for a TRL 7-demonstrator. Furthermore, a gasifier model was developed and an integrated process chain was simulated to assess the conversion of sewage sludge to synthetic natural gas (SNG) with and without inclusion of power-to-gas through electrolysis. The total efficiency of the conversion including own consumption for the case without electrolysis was 51 % with a carbon utilization of 33 %. These values could be enhanced by inclusion of power-to-gas. It was predicted that the produced SNG has a CH4-concentration of between 0.81 m3 m 3 and 0.84 m3 m 3 and nitrogen concentrations of up to 0.16 m3 m 3 originating from fuel-bound nitrogen. The simulations on process integration showed that up to 20% of the sewage sludge feed can be dried by heat integration. This implies that also external heat sources have to be used for drying. Overall, the steam-oxygen gasification proved to be an efficient and technically feasible process for sewage sludge treatment and can be considered as an alternative to fluidized bed incineration for future mono-treatment plants.Item Open Access Analyse der Einsatzpotenziale von Wärmeerzeugungstechniken in industriellen Anwendungen(Stuttgart : Universität Stuttgart, Institut für Energiewirtschaft und Rationelle Energieanwendung, 2016) Ohl, Michael; Voß, Alfred (Prof. Dr.-Ing.)Item Open Access The future role of alternative powertrains and fuels in the German transport sector : a model based scenario analysis with respect to technical, economic and environmental aspects with a focus on road transport(2012) Özdemir, Enver Doruk; Voß, A. (Prof. Dr.-Ing.)The transport sector is facing the challenges of satisfying the ever increasing transport demand on the one hand and achieving greenhouse gas (GHG) emission reduction targets without compromising economic development on the other hand. There are various alternative fuels and powertrains which might play a role in the future of the German transport sector. Amongst these options, biofuels are considered to help lower GHG emissions. However, they are severely criticized to create an additional strain for the energy system and particularly for the transport sector with land area requirement for energy crop production, which may imply a competition with food production. This study aims to assess the future role of alternative fuels and powertrains in the German transport sector in terms of their costs, efficiencies, GHG emissions and land area requirement for energy crops. To fulfill this aim, a techno-economic analysis of all relevant fuels and powertrain options was performed and a model based approach was employed. The utilized model belongs to the TIMES (The Integrated MARKAL EFOM System) family and is a bottom-up linear cost optimization energy system model. A scenario analysis was employed in order to assess the effect of different technological, economic, environmental and political conditions on the overall system. The results of the scenario analysis indicated that the transport system will still be dominated by conventional powertrains in 2030. Alternative powertrains are projected to play only a secondary role until 2030. It is not expected that fuel cell or battery electric passenger cars will be introduced into the market until 2030 in Germany. Nevertheless, hybrid electric powertrains have to be used in the German passenger car sector under ambitious GHG emission reduction targets and high oil prices. The introduction of alternative powertrains (such as hybrid electric and fuel cell powertrain) is much more likely in the bus sector (especially for public buses) than in passenger cars or in the road freight sector. Furthermore conventional fuels are expected to remain an important part of the German transport system until 2030. However, not only conventional fuels will be utilized in the future, but also biofuels and hydrogen are required. It is concluded that the transport sector should not be the first sector to reduce GHG emissions within an overall GHG emission mitigation strategy. However, with the ambitious GHG emission reduction targets (such as self-commitment of the German government) some contributions should also come from the transport sector.Item Open Access Das Kopernikus-Projekt ENavi - Die Transformation des Stromsystems mit Fokus Kohleausstieg(2019) Fahl, Ulrich; Gaschnig, Hannes; Hofer, Claudia; Hufendiek, Kai; Maier, Beatrix; Pahle, Michael; Pietzcker, Robert; Quitzow, Rainer; Rauner, Sebastian; Sehn, Vera; Thier, Pablo; Wiesmeth, Michael; Hufendiek, Kai; Pahle, MichaelIn diesem Bericht wird die Transformation des Stromsystems als zentrale Stellschraube zur Erreichung der Klimaziele analysiert. Dabei wird die Dekarbonisierung, insbesondere der Ausstieg aus der Kohleverstromung, in den Fokus gerückt. Anhand einer systematischen Vorgehensweise werden Transformationsszenarien für das deutsche Energiesystem identifiziert, analysiert und bewertet. Die Analyse erfolgt mithilfe unterschiedlicher computergestützter Modelle, um die Auswirkungen im gesamten System abschätzen zu können. Es werden sowohl Wechselwirkungen im Stromsystem und im Energiesystem, als auch im Wirtschaftssystem und im Bereich Ressourcen und Umwelt untersucht.Item Open Access Measuring circularity in cities : a review of the scholarly and grey literature in search of evidence-based, measurable and actionable indicators(2023) Kapoor, Kartik; Amydala, Nikhil Sayi; Ambooken, Anubhav; Scheinberg, AnneCircularity in cities is key to Earth’s sustainable and resource-efficient future. In contrast to the broad framework of circular economy, circularity is a technical concept associated with avoiding disposal and prolonging the useful life of products and materials, and thereby extracting fewer resources. In search of metrics and indicators to measure the impacts of circular processes in cities in real time, the authors reviewed the literature on the circular economy and circularity, in search of evidence-based circularity indicators suitable for cities to use to benchmark the environmental and climate benefits of six waste prevention cascades. This paper reports on a systematic literature review using the PRISMA protocol to screen, evaluate, and review published and grey literature sources. From more than 15,000 papers screened, after application of criteria, fewer than 25 papers were found that presented evidence-based, measurable, and actionable indicators or indicator sets for benchmarking the performance of circular processes in cities. The authors concluded that the practical commitment to evidence-based tracking of circularity (in cities) is weak. Practical progress towards a circular economy and physical and economic circularity will require stakeholders to strengthen and test the very small number of indicators and indicator sets that are relevant and useful for cities and regions to use for measuring their progress towards becoming more circular, and increase evidence-based monitoring for circularity and the circular economy.