04 Fakultät Energie-, Verfahrens- und Biotechnik
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Item Open Access Behavior of sulfur oxides in air and oxy-fuel combustion(2019) Spörl, Reinhold; Scheffknecht, Günter (Univ.-Prof. Dr. techn.)This thesis evaluates the behavior of sulfur oxides in pulverized fuel (PF) fired air and oxy-fuel systems. Sulfur oxides are responsible for certain operational problems and considerable gas cleaning requirements in air as well as oxy-fuel firing. A better understanding of the related issues will allow for a technical and economical optimization of the oxy-fuel combustion technology. A range of experimental investigations studying the stability and retention of sulfur oxides in ashes and deposits, acid gas (SO2, SO3, and HCl) control in air and oxy-fuel combustion by dry sorbent injection, and SO3 formation were conducted. The experimental work is in parts supported by theoretical considerations and thermodynamic equilibrium simulation. Studies for different coals and lignites showed that in practically relevant oxy-fuel configurations the exclusion of airborne N2 from combustion leads to an increase of the SO2 concentrations in oxy-fuel, compared to air firing, by a factor of about 3.4 to 4.2, referring to dry, and of about 2.9 to 3.5, when referring to wet flue gas conditions. The increased SO2 levels in oxy-fuel combustion are responsible for an increased stability of sulfates in oxy-fuel power boiler systems so that for example the decomposition temperature CaSO4 rises by about 50 to 80 °C, depending on flue gas atmospheres. The enhanced stability of sulfates in deposits at high temperatures when operating with increased SO2 levels was experimentally demonstrated. Compared to air firing, a considerable increase of the sulfur retention in the ash by 10 to 12 percentage points has been observed for oxy-fuel recycle combustion of Lusatian lignites. This leads to lower SO2 emissions and higher SO3 levels in process ashes and deposits. The results indicate that for fuels, such as the used lignites, the temperature level at which fouling by sulfatic deposits is problematic may be shifted to higher temperatures in oxy-fuel combustion and that the sintering of deposits by sulfation may be more pronounced. In contrast, in air and oxy-fuel combustion experiments with a hard coal with a low sulfur retention potential differences in the SO3 contents and degrees of sulfation of ashes and deposits were small. Besides higher SO3 contents and sulfation degrees, no other significant changes between the deposit samples from air and oxy-fuel combustion were identified. Experiments on dry sorbent injection in air and oxy-fuel mode showed that an increase of the average flue gas residence time in the furnace by flue gas recirculation and, to a lesser extent, the higher sulfate stability enhance the desulfurization efficiency in oxy-fuel recycle combustion considerably. SO2 capture efficiencies in oxy-fuel recycle combustion of 50 % to more than 80 % at moderate molar sulfur to calcium ratios between 1.7 and 2.9 were reached, when injecting CaCO3 and Ca(OH)2 together with the fuel or directly to the furnace. Under comparable injection conditions, the oxy-fuel performance was by as much as 29 percentage points higher than in air firing. Also an efficient SO3 and HCl control by DSI could be demonstrated. Experiments on formation of SO3 show that higher SO2 levels in oxy-fuel firing are the most important parameter responsible for the observed increase of the SO3 concentrations.Item Open Access Insights into the structural and functional properties of the eukaryotic porin Tom40(2012) Gessmann, Dennis; Nußberger, Stephan (Prof. Dr.)Tom40 forms the preprotein conducting channel in the outer membrane of mitochondria enabling transport of up to 1500 different preproteins through an optimized pore environment. Moreover, Tom40 exhibits a voltage-dependent gating mechanism in terms of an ‘electrical switch’ making this eukaryotic beta-barrel a promising target for nanopore based applications. In this work, new bioinformatics methods were developed and verified through practical approaches to shed light on the structural elements of Tom40 facilitating its particular function in mitochondria. Based on these results, Tom40 proteins were designed with modified and optimized structural properties. TmSIP, a physical interaction model developed for TM beta-barrel proteins, was used to identify weakly stable regions in the TM domain of Tom40 from mammals and fungi. Three unfavorable beta-strands were determined for human Tom40A. Via CD and Trp-fluorescence spectroscopy it was shown that substitution of key amino acid residues in theses strands resulted in an improved resistance of the protein to chemical and thermal perturbations. Further, the mutated form of hTom40A was strictly found in its monomeric state. Equal improvements were gained for the apparent stability of Tom40 from Aspergillus fumigatus. Tom40 was isolated and purified in its native state from Neurospora crassa mitochondria. Time-limited proteolysis of native NcTom40 coupled to mass spectrometry revealed comparable protease-accessibility to VDAC isoform 1 from mammals suggesting a similar fold. Thus, a homology model of NcTom40 was developed on the basis of the solved mouse VDAC-1 crystal structure. It was found that Tom40 forms a 19-stranded beta-barrel with an N-terminal alpha-helix inside the pore. Further, a conserved ‘polar slide’ in the pore interior is possibly involved in preprotein translocation and a second conserved domain, termed ‘helix anchor region’, in arresting the helix inside the Tom40 pore. Based on the homology model of NcTom40, the structure and function of the N-terminal domain of Tom40 was addressed. Examination of the model structure revealed two different domains for the N-terminus, the inner-barrel and outer-barrel N-terminus. In vivo investigations showed that both parts prevent a heat-induced dysfunction of Tom40 in N. crassa mitochondria independently. By applying CD spectroscopy the predicted N-terminal alpha-helix could be allocated to the inner-barrel N-terminus. Further, in combination with Trp-fluorescence spectroscopy it was found that the N-terminal alpha-helix unfolds independently from the Tom40 beta-barrel, but is not necessary for pore stability or integrity. However, a conserved amino acid residue, Ile47 of NcTom40, in the inner-barrel N-terminus is essential for the structural integrity of the N-terminal alpha-helix. In conclusion, these results may offer a basis for future works on TM beta-barrel proteins with the aim to alter the structural properties in the absence of a high atomic resolution structure or an established knowledge of the biochemical and biophysical properties.Item Open Access Construction of a super-competent Bacillus subtilis 168 using the PmtlA-comKS inducible cassette(2015) Rahmer, Regine; Morabbi Heravi, Kambiz; Altenbuchner, JosefCompetence is a physiological state that enables Bacillus subtilis 168 to take up and internalize extracellular DNA. In practice, only a small subpopulation of B. subtilis 168 cells becomes competent when they enter stationary phase. In this study, we developed a new transformation method to improve the transformation efficiency of B. subtilis 168, specially in rich media. At first, different competence genes, namely comK, comS, and dprA, were alone or together integrated into the chromosome of B. subtilis 168 under control of mannitol-inducible PmtlA promoter. Overexpression of both comK and comS increased the transformation efficiency of B. subtilis REG19 with plasmid DNA by 6.7-fold compared to the wild type strain 168. This transformation efficiency reached its maximal level after 1.5 h of induction by mannitol. Besides, transformability of the REG19 cells was saturated in the presence of 100 ng dimeric plasmid or 3000 ng chromosomal DNA. Studying the influence of global regulators on the development of competence pointed out that important competence development factors, such as Spo0A, ComQXPA, and DegU, could be removed in REG19. On the other hand, efficient REG19 transformation remained highly dependent on the original copies of comK and comS regardless of the presence of PmtlA-comKS. Finally, novel plasmid-free strategies were used for transformation of REG19 based on Gibson assembly.Item Open Access Effiziente und konsistente Strukturen - Rahmenbedingungen für die Nutzung von Wärmeenergie in Privathaushalten(2010) Koch, Andreas (Hrsg.); Jenssen, Till (Hrsg.)Der vorliegende Bericht fasst die Arbeiten zur Strukturanalyse des vom Bundesministerium für Bildung und Forschung (BMBF) im Rahmen der Sozialökologischen Forschung (SÖF) geförderten Projektes „Energie nachhaltig konsumieren – nachhaltige Energie konsumieren: Wärmeenergie im Spannungsfeld von sozialen Bestimmungsfaktoren, ökonomischen Bedingungen und ökologischem Bewusstsein“ zusammen. Im Fokus dieses Projektes steht die Akteursebene mit der Erforschung der Hemmnisse und Anreize für nachhaltiges Konsumverhalten im Bereich der Wärmeenergie. Hierzu werden die auf der Mikroebene angesiedelten individuellen Wahrnehmungen, der Wissensstand sowie die Entscheidungs- und Handlungsstrategien von Akteuren in Bezug auf den Wärmekonsum analysiert. Individuelles Konsumverhalten im Wärmeenergiebereich ist sowohl von strukturellen Rahmenbedingungen, wie Siedlungs- und Gebäudestrukturen, rechtlichen Rahmenbedingungen, Förderinstrumenten und technologischen Systemen geprägt, als auch durch ein breit gestreutes Akteursgeflecht, wie z.B. Architekt/innen, Wohnungsbaugesellschaften, Handwerker/innen oder Wärmetechnologieanbieter im Umfeld der Konsument/innen beeinflusst. Dieses Struktur- und Akteursumfeld der Konsument/innen wurde daher im Vorfeld der eigentlichen Konsumentenanalyse systematisch im Hinblick auf Chancen und Hemmnisse für einen nachhaltigen Wärmeenergiekonsum analysiert und bewertet. Der vorliegende Bericht konzentriert sich darauf, das Strukturgeflecht, in welchem sich der/die Konsument/in bewegt, umfassend zu beschreiben, strukturelle Hemmnisse für nachhaltigen Wärmekonsum zu identifizieren und Ansätze auf der Strukturebene aufzuzeigen, die als Chancen für nachhaltiges Wärmekonsumverhalten zu interpretieren sind. Als strukturelle Rahmenbedingungen des Wärmekonsums werden im Projekt Gebäude- und Siedlungsstrukturen, Versorgungstechnologien sowie rechtliche und förderpolitische Instrumente erörtert. Diese Faktoren geben den Handlungsrahmen vor (bzw. beeinflussen diesen), innerhalb dem sich Konsument/innen nachhaltig verhalten können.Item Open Access Brennstoffzellensysteme auf Basis regenerativer Energieträger(2010) Grüner, Heike; Scheffknecht, G. (Prof. Dr. techn.)Der Einsatz von regenerativen Energieträgern in Brennstoffzellensystemen ermöglicht eine beachtliche Reduzierung von Treibhausgasemissionen im Vergleich zur konventionellen Strom- und Wärmegewinnung. Im Rahmen dieser Arbeit wurde der am besten geeignete, nicht-leitungsgebundene regenerative Energieträger für ein stationäres PEM-Brennstoffzellen-BHKW identifiziert und ein ursprünglich auf Erdgas basierendes Gesamtsystem mit diesem Energieträger charakterisiert. Als leicht speicherbare Energieträger kommen dabei Methanol, Ethanol und Dimethylether (DME) sowie Pflanzenöl, Biodiesel und flüssige synthetische Kohlenwasserstoffe in Frage. Aus diesen wurden Methanol, Ethanol und DME vorselektiert und hinsichtlich der Brennstoffherstellung (Well-to-Tank-Wirkungsgrad) und -reformierung sowie der simulierten Gesamtsystemeffizienz und -komplexität bewertet. Bei vergleichbaren Werten in der Brennstoffherstellung sowie in der Systemeffizienz lässt sich dabei die Aussage treffen, dass grundsätzlich alle drei genannten Brennstoffe für ein stationäres PEM-Brennstoffzellen-BHKW geeignet sind. Die geringe Systemkomplexität sowie die einfache Dampfreformierung von DME führten zu dessen Auswahl als dem am besten geeigneten, nicht-leitungsgebundenen regenerativen Energieträger für ein stationäres Brennstoffzellensystem. Anschließend erfolgten die Charakterisierung des Gesamtsystems im DME-Betrieb sowie der Vergleich des Systems im Betrieb mit Erdgas. Erdgas diente dabei als Ersatz für biogenes Erdgassubstitut (SNG), welches stellvertretend für den Einsatz leitungsgebundener regenerativer Energieträger steht.Item Open Access Transformation von B. subtilis 168 : Optimierung und Regulation des Transkriptionsfaktors ComK(2017) Franzen, Regine; Mattes, Ralf (Prof. Dr. rer. nat.)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 Physical interactions strengthen chemical gelatin methacryloyl gels(2019) Rebers, Lisa; Granse, Tobias; Tovar, Günter E. M.; Southan, Alexander; Borchers, KirstenChemically cross-linkable gelatin methacryloyl (GM) derivatives are getting increasing attention regarding biomedical applications. Thus, thorough investigations are needed to achieve full understanding and control of the physico-chemical behavior of these promising biomaterials. We previously introduced gelatin methacryloyl acetyl (GMA) derivatives, which can be used to control physical network formation (solution viscosity, sol-gel transition) independently from chemical cross-linking by variation of the methacryloyl-to-acetyl ratio. It is known that temperature dependent physical network formation significantly influences the mechanical properties of chemically cross-linked GM hydrogels. We investigated the temperature sensitivity of GM derivatives with different degrees of modification (GM2, GM10), or similar degrees of modification but different methacryloyl contents (GM10, GM2A8). Rheological analysis showed that the low modified GM2 forms strong physical gels upon cooling while GM10 and GM2A8 form soft or no gels. Yet, compression testing revealed that all photo cross-linked GM(A) hydrogels were stronger if cooling was applied during hydrogel preparation. We suggest that the hydrophobic methacryloyl and acetyl residues disturb triple helix formation with increasing degree of modification, but additionally form hydrophobic structures, which facilitate chemical cross-linking.Item Open Access Versagensverhalten rissbehafteter Mischschweißnähte - theoretische und experimentelle Untersuchungen(2011) Büttner, Mathias; Roos, Eberhard (Prof. Dr.-Ing habil.)Die Steigerung des Wirkungsgrades und der Wirtschaftlichkeit von chemischen und energietechnischen Anlagen erfordert die optimale Werkstoffauswahl nach den vorherrschenden Betriebsbedingungen. Für das Beispiel des Kraftwerks- und Anlagenbaus stellt die untersuchte Mischschweißverbindung, zwischen einem ferritischen und austenitischen Werkstoff, eine weit verbreitete Kombination in Bezug auf die geforderte Festigkeit und Korrosionsbeständigkeit dar. Durch die deutlich unterschiedlichen mechanischen, thermischen und chemischen Eigenschaften der beiden Werkstoffe ist eine artgleiche Verbindung nicht möglich, weshalb vielfach Nickelbasis-Schweißgüter verwendet werden. Aus dieser Kombination unterschiedlicher Materialen ergibt sich bei Mischnähten eine Abfolge von Bereichen mit teilweise deutlich variierenden mechanischen und thermischen Eigenschaften, woraus ein sehr inhomogener Werkstoff- und Beanspruchungszustand resultiert. Dies kann insbesondere bei Rissen zu deutlich anderen Versagensabläufen, als bei homogenen Werkstoffen oder artgleichen Schweißverbindungen, führen. Aufgrund der fehlenden Detailkenntnis bezüglich des realen Versagensverhaltens angerissener Mischnähte werden nach dem Stand der Technik bruchmechanische Näherungsverfahren zur Bewertung verwendet. Diese Verfahren basieren allerdings auf Methoden, welche für homogene Werkstoffe oder gleichartige Schweißverbindungen entwickelt wurden und liefern bei Mischnähten in der Regel sehr konservative Lösungen. Deshalb liegt der Schwerpunkt der Arbeit auf der Beschreibung des Versagensverhaltens von Mischnähten, unter Verwendung des schädigungsmechanischen Rousselier-Modells. Hierzu wurden umfangreiche experimentelle Untersuchungen zur Charakterisierung der Mischnaht durchgeführt. Im Fokus stand dabei vor allem die Klärung der mikromechanischen Vorgänge während Rissinitiierung und -wachstum durch metallographische und bruchmechanische Untersuchungen. Dadurch konnte der maßgebliche Einfluss der dendritischen Erstarrung auf das Versagensverhalten der Schweißnaht aufgezeigt werden, aus welchem der niedrigste Risswiderstand im Bereich der Verbindungsnaht resultiert. Auf der Basis der durchgeführten experimentellen und fraktographischen Untersuchungen konnte gezeigt werden, dass die Bereiche der Naht, in welchen Risswachstums- und Erstarrungsrichtung parallel verlaufen, als kritisch anzusehen sind. Bei anderen Mischnähten kann sich dadurch je nach Herstellung der Bereich mit niedrigen Bruchzähigkeiten in anderen Nahtbereichen befinden. Die für die schädigungsmechanische Bewertung mit dem Rousselier-Modell notwendigen Parameter wurden anhand der experimentellen Ergebnisse von gekerbten und ungekerbten Zugversuchen bestimmt. Unter Verwendung dieser Parameter konnte im Vergleich zu den bruchmechanischen Untersuchungen gezeigt werden, dass das Berechnungsmodell in der Lage ist, das Last-Verformungsverhalten, den Initiierungszeitpunkt sowie größere Beträge von stabilem Risswachstum in allen Bereichen der Mischnaht zu beschreiben. Mit den in dieser Arbeit durchgeführten schädigungsmechanischen Berechnungen ist eine realistische Vorhersage der real ablaufenden Versagensmechanismen während der Rissinitiierung und -ausbreitung möglich. Es wurden damit die Grundlagen geschaffen, um die Tragfähigkeit sowie den genauen Versagensablauf von integren und rissbehafteten Mischschweißnähten unter komplexen Belastungen zu berechnen.Item Open Access Turbulence flow mechanisms to cause high-cycle thermal fatigue near a horizontal T-junction(Stuttgart : Institut für Kernenergetik und Energiesysteme, 2018) Zhou, Mi; Laurien, Eckart (Prof. Dr.-Ing. habil.)