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 Abschaltung von dezentralen Erzeugungsanlagen infolge von Unterspannungen im Kontext von LFSM-O(2022) Schöll, Christian; Lehner, Joachim; Weidner, Johannes; Lens, HendrikBei einer Überfrequenz jenseits von 50,2 Hz müssen sämtliche Erzeugungsanlagen ihre in das Netz eingespeiste Wirkleistung reduzieren. In den zumeist resistiv geprägten Verteilungsnetzen der Mittel- und Niederspannung führt diese überfrequenzbedingte Leistungsreduktion zu einer lokalen Absenkung des Spannungsprofils. Unterschreiten die Spannungen die Vorgaben aus den Netzanschlussbedingungen, unter denen dezentrale Erzeugungsanlagen die Verbindung zum Netz aufrechterhalten müssen, kann es zu unterspannungsbedingten Schutzabschaltungen kommen. Theoretisch könnten diese bei großflächigem Auftreten zu einer Umkehr des ursprünglichen Überfrequenzereignisses in ein Unterfrequenzereignis führen. Anhand von simulationsbasierten Untersuchungen wird in diesem Beitrag jedoch aufgezeigt, dass unter realitätsnahen Annahmen und unter Berücksichtigung der nationalen Richtlinien sowie der zugehörigen netzplanerischen Leitplanken kein besonderes Risiko hinsichtlich der Anregung der beschriebenen Wirkungskette vorliegt.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 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.Item Open Access Heterogeneously catalyzed reactions over newly developed SCR DeNOx catalysts(2022) Schwämmle, Tobias; Scheffknecht, Günter (Prof. Dr. techn.)Catalysts for selective catalytic reduction (SCR) can, in addition to the reduction of NOx, also contribute to the oxidation of elemental mercury (Hg0) as well as to the undesired conversion of SO2 to SO3. By placing the catalysts in the high-dust configuration, oxidized mercury (Hg2+) can then be separated in downstream wet flue gas desulfurization units, allowing mercury to be removed efficiently from the flue gas. The aim of this work is to show how mercury oxidation can be increased by newly developed SCR catalysts, which influences there are on Hg oxidation, and which mechanisms lie behind the three reactions over the SCR catalysts. The research with parameters derived from the experiences and conditions in power plant operation is carried out in synthetic flue gas in laboratory micro-reactors as well as in a lab-scale firing system under real flue gas conditions. The research forms a comprehensive examination of all reactions relevant in power plant operation with conventional as well as newly developed SCR catalysts. As a benchmark of the catalysts regarding all reactions, the performance indicator P3 is introduced. The research is mainly conducted with standard SCR catalysts as reference and newly developed, modified honeycomb SCR catalysts, and supplemented by tests on plate-type SCR catalysts. In this research, modifications in the active component (V, Cu, Fe, Mn, Ce), of the promoters (W, Mo) as well as modifications of the base materials are studied. Through the dedicated application of the promoter molybdenum and modifications of the base material, a significant and clear increase in catalyst performance (high values of P3) can be achieved. An increased wall thickness of the catalyst also leads to an increase in Hg oxidation; however, the SO2/SO3 conversion is increased in parallel. Examinations on the influences of the flue gas on the oxidation of Hg show a strong effect of the halogen content (HCl, HBr) in the flue gas. Likewise, the sulfation of the catalysts has a positive effect on the reactions over the catalysts. A parallel DeNOx reaction in the catalyst with the addition of NH3 and the presence of CO in flue gas inhibits Hg oxidation as well as SO2/SO3 conversion. The oxidation of Hg over SCR catalysts seems to proceed according to an Eley-Rideal or Mars-Maessen mechanism: mercury adsorbs on the SCR catalyst and reacts with weakly adsorbed hydrogen halide or hydrogen halide species from the gas phase. The Hg adsorption and release can be correlated with the catalyst composition. The Deacon reaction might bring an additional contribution, but does not seem to be exclusively responsible for the measured effects.Item Open Access Dynamic monitoring of Frequency Containment Reserve activation(2021) Maucher, Philipp; Lens, HendrikFrequency Containment Reserve (FCR), also known as primary control reserve, is the fastest active power reserve (APR) used for system balancing. In the past, FCR was provided by a limited number of large units and the technical requirements on FCR activation could be monitored by a manual procedure. Due to the fact that FCR increasingly is provided by a large number of smaller units, manual procedures are no viable option for the future. For this reason, this article describes an automated concept for monitoring the quality of the activation of FCR during operation. Before FCR monitoring can be carried out, however, the measured active power has to be apportioned among the scheduled power and the different APR products, as they may be provided simultaneously. This article presents a method for the separation of different APR products based on dynamic models. In the proposed monitoring concept, a tolerance channel is created based on the FCR setpoint, defining the admissible range for FCR activation. This tolerance channel is established by means of a dynamic model corresponding to the slowest reserve provider (RP) whose FCR activation is still considered to be compliant. For the purpose of evaluation for longer time periods, the actual FCR activation is normalized relative to the tolerance channel. Finally, the article discusses results obtained with the proposed monitoring concept for different kinds of non-compliant FCR activation such as limited or delayed activation.Item Open Access Leaching of fly ash particulate matter in MEA solutions and its relevance to the CO2 capture process with flue gas of coal-fired power plants(2020) Schallert, Bernd; Scheffknecht, Günter (Prof. Dr.)This study underlines the relevance of leaching of fly ash particulate matter to carbon capture plants and strives for a better understanding of the solubility of various elements and heavy metals, especially Fe, in MEA solutions and of relevant leaching parameters.Item Open Access Parametric study on the adjustability of the syngas composition by sorption-enhanced gasification in a dual-fluidized bed pilot plant(2021) Hafner, Selina; Schmid, Max; Scheffknecht, GünterFinding a way for mitigating climate change is one of the main challenges of our generation. Sorption-enhanced gasification (SEG) is a process by which syngas as an important intermediate for the synthesis of e.g., dimethyl ether (DME), bio-synthetic natural gas (SNG) and Fischer-Tropsch (FT) products or hydrogen can be produced by using biomass as feedstock. It can, therefore, contribute to a replacement for fossil fuels to reduce greenhouse gas (GHG) emissions. SEG is an indirect gasification process that is operated in a dual-fluidized bed (DFB) reactor. By the use of a CO2-active sorbent as bed material, CO2 that is produced during gasification is directly captured. The resulting enhancement of the water-gas shift reaction enables the production of a syngas with high hydrogen content and adjustable H2/CO/CO2-ratio. Tests were conducted in a 200 kW DFB pilot-scale facility under industrially relevant conditions to analyze the influence of gasification temperature, steam to carbon (S/C) ratio and weight hourly space velocity (WHSV) on the syngas production, using wood pellets as feedstock and limestone as bed material. Results revealed a strong dependency of the syngas composition on the gasification temperature in terms of permanent gases, light hydrocarbons and tars. Also, S/C ratio and WHSV are parameters that can contribute to adjusting the syngas properties in such a way that it is optimized for a specific downstream synthesis process.Item Open Access Design- and simulation-based comparison of grid-forming converter control concepts(2021) Schöll, Christian; Lens, HendrikUntil now, the textbook example of voltage source behavior along with the provision of inertia is the behavior of the synchronous generator (SG). This can be explained by the historical success of large scale electrification with AC power systems, which is closely linked to the SG. Therefore, previously SG-based electrical power systems face significant challenges due to the shift towards renewable energy sources (RES). Being generally converter-based, these do not provide essential stabilizing properties as SG do. Consequently, beyond a certain share of this kind of generation, interconnected power system stability is at stake. If, on the other hand, the previous paradigm of converter control is changed, then system operation without any SG is possible. To this end, the converters have to exhibit essential voltage source properties as SG do. Such converters are then referred to as grid-forming converters (GFC). However, the dynamic behavior of GFC is not defined by physical properties as in the case of SG. It is defined by the grid-forming control concept only, providing a high degree of freedom for possible implementations. Taking advantage of this freedom, a wide range of different, but partly also similar or even equivalent grid-forming control concepts have been developed in recent years. Therefore, in this paper, ten of today's most discussed control concepts are compared. In this comparison, unique features, similarities and equivalences of the control concepts are shown. The focus is on the instantaneous and stationary behavior of the control concepts, which is analysed by means of a system-theoretical and simulative analysis. The insights gained from this comparison can be helpful for the functional specification, development and improvement of GFC, as the variety of control concepts can be better understood.Item Open Access Developing a cloud-based air quality monitoring platform using low-cost sensors(2024) Samad, Abdul; Kieser, Joschka; Chourdakis, Ioannis; Vogt, UlrichConventional air quality monitoring has been traditionally carried out in a few fixed places with expensive measuring equipment. This results in sparse spatial air quality data, which do not represent the real air quality of an entire area, e.g., when hot spots are missing. To obtain air quality data with higher spatial and temporal resolution, this research focused on developing a low-cost network of cloud-based air quality measurement platforms. These platforms should be able to measure air quality parameters including particulate matter (PM10, PM2.5, PM1) as well as gases like NO, NO2, O3, and CO, air temperature, and relative humidity. These parameters were measured every second and transmitted to a cloud server every minute on average. The platform developed during this research used one main computer to read the sensor data, process it, and store it in the cloud. Three prototypes were tested in the field: two of them at a busy traffic site in Stuttgart, Marienplatz and one at a remote site, Ötisheim, where measurements were performed near busy railroad tracks. The developed platform had around 1500 € in materials costs for one Air Quality Sensor Node and proved to be robust during the measurement phase. The notion of employing a Proportional-Integral-Derivative (PID) controller for the efficient working of a dryer that is used to reduce the negative effect of meteorological parameters such as air temperature and relative humidity on the measurement results was also pursued. This is seen as one way to improve the quality of data captured by low-cost sensors.