Clausthal University of Technology
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Quecksilber im Zementherstellungsprozess: Ursprung, Verbleib und Minderungspotenziale
Full text linkQuecksilber als hochtoxischer und umweltpersistenter Schadstoff ist mittlerweile im Fokus nationaler und internationaler Bestrebungen einer dauerhaften Minderung der Emission aus allen anthropogenen Quellen. Auf globaler Ebene wird über das Minamata-Abkommen als international verbindlichem Vertrag zukünftig ein vollständiger Verzicht auf quecksilberhaltige Produkte und eine größtmögliche Minimierung der Quecksilberemission aus industriellen Prozessen angestrebt, was mittelfristig über die europäische Gesetzgebung in nationalen Gesetzgebungen umgesetzt wird. Aus Sicht der Zementindustrie ist es im Sinne einer nachhaltigen Produktion daher wichtig, diesen kommenden Anforderungen gewachsen zu sein und Umweltbelastungen auf ein kleinstmögliches Maß zu vermindern. Dafür wurden mit den in dieser Arbeit vorgestellten Ergebnissen die Pfade des Quecksilbers vom Ursprung in den Brenn- und Rohstoffen bis hin zum Verbleib in den Produkten und der Emission in die Luft für das Referenzjahr 2017 quantifiziert und es wurde mit der sorbensunterstützten Staubausschleusung im Direktbetrieb eine mögliche Maßnahme zur weiteren Minderung der Emission in die Luft untersucht. Eine umfangreiche Datenerhebung auf Basis von Quecksilberanalysenwerten in Verbindung mit Materialeinsatzmengen und Emissionsdaten zeigt, dass rund 60 % des Quecksilbers über Rohstoffe und 40 % über Brennstoffe in den Produktionsprozess gelangen. Etwa 40 % des Quecksilbers werden in die Luft emittiert, während 60 % in den Produkten verbleiben. Der Bilanzfehler beträgt für die betrachtete Variante einer mittleren Emission in die Luft bei mittleren Gehalten in Brenn- und Rohstoffen 10,5 % Hierbei bestehen Unsicherheiten aufgrund der äußerts großen Materialmassenströme in Verbindung mit gleichzeitig sehr geringen Quecksilberkonzentrationen vor allem in den Rohstoffen Kalkstein, Mergel und Kreide unterhalb der analytischen Bestimmungsgrenzen. Werden diese begrenzt, verringert sich der Fehlbetrag auf 0,6 % und die Bilanz kann als vollständig geschlossen angesehen werden. Die Eindüsung von Sorbenzien, wie Aktivkoks und bromierter Aktivkohle in den Abgasstrang von Drehrohrofenanlagen der Zementindustrie wurde in Labor- und Betriebsversuchen hinsichtlich ihrer Eignung zur Quecksilberminderung und möglicher Produktauswirkungen untersucht. Die Abscheideleistung der getesteten Sorbenzien ist vornehmlich vom Gehalt an koks-/kohlehaltigem Sorbens und damit von der zur Verfügung stehenden Oberfläche abhängig. Darüber hinaus ist die Temperatur weiterhin ein maßgeblicher Einflussfaktor. In den Betriebsversuchen wurde bei Filtertemperaturen von unter 140 °C die Quecksilber-Abscheidung bezogen auf die Rohgaskonzentration durch die Eindüsung eines Sorbens von etwa 92 % auf bis zu 97 % erhöht. Hierbei ist zu berücksichtigen, dass ein nachhaltiger Effekt in Form eines Abbaus des Quecksilberkreislaufs nur bei einer Ausschleusung des Sorbens- und Quecksilberhaltigen Filterstaubs im Direktbetrieb erreicht werden kann. Die Produktuntersuchungen zeigen, dass die Eigenschaften der Produkte durch sorbenshaltigen Filterstaub nicht signifikant beeinflusst werden. Leichte Verfärbungen könnten jedoch in bestimmten Anwendungen relevant sein. Hinsichtlich der Minderungspotenziale werden zwei Ansätze identifiziert, die zu einer Verringerung der Quecksilberemissionen der Zementindustrie führen können. Der Quecksilbereintrag in den Zementherstellungsprozess erfolgt hauptsächlich über nicht ersetzbare Rohstoffe. Bei den alternativen Brennstoffen besteht zwar ein Minderungspotenzial von etwa 12 % über eine Minimierung des Eintrags. Eine damit Verbundene Rückkehr zu fossilen Regelbrennstoffen widerspricht jedoch den Nachhaltigkeitsbestrebungen der Politik und der deutschen Zementindustrie. Durch eine breitere Anwendung der sorbensgestützten Staubausschleusung könnte die Quecksilberemission in der deutschen Zementindustrie um etwa 25 % reduziert werden. Eine Pauschale Übertragung auf alle Drehofenanlagen ist jedoch aufgrund der individuellen Eintragssituation und Anlagengestaltung nicht möglich. Sie müssen bei einer Umsetzung differenziert berücksichtigt werden.Mercury, a highly toxic and environmentally persistent pollutant, has become the focus of national and international efforts to permanently reduce emissions from all anthropogenic sources. Globally, the Minamata Convention, as a binding international treaty, aims to eliminate mercury-containing products entirely and to minimise mercury emissions from industrial processes to the greatest extent possible. In the medium term, this objective will be incorporated through European legislation into national legislation. It is therefore imperative for the cement industry to address these imminent requirements and to mitigate environmental degradation in pursuit of sustainable production. In order to achieve this objective, the findings presented in this study quantify the paths of mercury from its origin in the fuel and raw materials to its fate in the products and its emission into the air in the German cement industry for the reference year 2017. Furthermore, the present study investigates sorbent-assisted dust shuttling during direct operation as a potential abatement measure for further emission reduction. A comprehensive evaluation of the available data, incorporating mercury analysis values, material input quantities, and emission data, discloses that approximately 60% of mercury enters the production process through raw materials, with the remaining 40% entering via fuels. It has been determined that approximately 40% of the mercury is released into the atmosphere, while the remaining 60% remains within the products. The balance error for an average emission to air with average contents in fuels and raw materials is 10.5%. The presence of substantial material mass flows, in conjunction with concurrently minimal mercury concentrations—particularly in the raw materials limestone, marl, and chalk, which fall below the analytical limits of determination—engenders a state of uncertainty. In the event that these are found to be limited, the shortfall is reduced to 0.6%, and the balance can be regarded as completely closed. The feasibility of injecting sorbents, such as activated coke and brominated activated carbon, into the exhaust gas stream of rotary kiln plants in the cement industry was investigated through a series of laboratory and operational tests. The objective of the present series of tests was twofold: firstly, to assess the sorbents' effectiveness in reducing mercury emissions, and secondly, to determine any potential adverse effects on product quality or performance. The separation efficiency of the sorbents tested is principally dependent on the content of coke/carbon sorbent, and consequently on the available surface area. The temperature is also a significant influencing factor. In the operating tests, at filter temperatures of below 140 °C, the mercury separation in relation to the raw gas concentration was increased from approximately 92% to up to 97% by the injection of a sorbent. It is imperative to acknowledge that achieving a sustainable effect, manifesting as a reduction in the mercury cycle, is contingent upon the discharge of filter dust containing sorbent and mercury during direct operation. The product tests demonstrate that the properties of the products are not significantly affected by filter dust containing sorbents. Notwithstanding, slight discolouration may be pertinent and, in certain applications, must be avoided. With regard to the reduction potential, two approaches are identified that could lead to a reduction in mercury emissions from the cement industry. Mercury is predominantly introduced into the cement production process via non-replaceable raw materials. In the context of alternative fuels, a reduction potential of approximately 12% can be achieved through minimization of input. Nevertheless, a reversion to fossil fuels would contradict sustainability efforts of politics and the German cement industry. A wide-spread implementation of sorbent-assisted dust extraction has the potential to reduce mercury emissions in the German cement industry by approximately 25%. However, given the heterogeneity in raw material inputs and distinct design specifications of individual plants, a universal implementation of this technology across all rotary kiln plants is not possible. Therefore, these factors need to be considered in a nuanced manner during the implementation phase
Investigation of the suitability of underground gas storage facilities for hydrogen storage: an experimental study on mixing processes in porous media
Full text linkThe global transition to renewable energy sources necessitates efficient and large-scale energy storage solutions to balance energy demand and supply. Hydrogen emerges as a promising energy carrier and storage medium for the future. Among various options for storing hydrogen produced from surplus energy, underground hydrogen storage (UHS) in porous reservoirs stands out as particularly promising. Understanding gas mixing processes, which are strongly influenced by molecular diffusion and mechanical dispersion, is critical for optimising these systems to ensure both efficiency and safety. Specialised experimental setups were designed and built to investigate hydrogen diffusion and dispersion properties within geological formations relevant to UHS. Two modified versions of the Wicke-Kallenbach method were employed to assess diffusion in barrier samples (caprock and cement) and reservoir samples (sandstones), while mechanical dispersion was evaluated using a slim tube coil setup. The experiments revealed diffusion coefficients for barrier samples ranging from 1 · 10−11 to 3.1 · 10−10m2/s, confirming their effectiveness as barriers to hydrogen migration. Reservoir rocks exhibited coefficients between 5.00 · 10−9 and 3.71 · 10−7m2/s, indicating dependence on rock porosity and water saturation. Dispersivity values ranged from 0.0042 to 0.06 meters, reflecting variability based on flow conditions. These findings validate the robustness of the measurement approaches and provide essential data for enhancing predictive models and simulation efforts. Using analytical solutions, laboratory measurements were scaled to assess the potential impacts of hydrogen mixing in larger scenarios. These analyses of the scaled laboratory measurements indicated that caprock leakage is negligible, with an annual diffusion loss of only 0.005 % of the total storage volume, highlighting the caprock’s effectiveness as a barrier for hydrogen. Within the reservoir, the mixing zone for molecular diffusion is limited to a few meters, while mechanical dispersion expands it to approximately 30 meters, providing valuable insights for storage strategy optimisation. The monitoring of UHS requires specialised techniques distinct from natural gas storage due to hydrogen’s unique characteristics and the potential for microbial activity. Key methods include continuous pressure and temperature monitoring using advanced sensors placed strategically at wellheads and reservoirs, ensuring real-time data collection for early anomaly detection. Gas chromatography and mass spectrometry are employed to assess gas composition continuously, safeguarding purity. Unlike natural gas, UHS demands additional microbial monitoring to prevent potential storage integrity issues due to biochemical interactions. The UHS monitoring program integrates continuous and periodic assessments aligned with international guidelines, focusing on maintaining both engineering and geological integrity. Preventive measures are strategically implemented to detect and address potential issues early, minimising risks and ensuring the facility’s safety and efficiency
Literaturverwaltung mit Zotero
Full text linkIm Rahmen der Veranstaltungsreihe TUpdate Compressed fand am 13. Mai 2025 ein Vortrag zum Thema Zotero statt. Die Vortragsfolien sind hier zu finden. TUpdate Compressed ist eine Online Veranstaltung, die an jedem zweiten Dienstag im Monat um 13:00 Uhr innerhalb von 15 Minuten Neuigkeiten aus der TU vorstellt
Konstruktion und Validierung einer Vorrichtung zur Gasaufbereitung für die sauerstofffreie Produktion
Full text linkDurch die Verwendung des Gasgemisches Argon/Silan innerhalb einer Handschuhbox können sauerstofffreie Atmosphären geschaffen werden. Dies eröffnet der Industrie weitreichende Möglichkeiten, Bauteile mit innovativen Materialeigenschaften herzustellen, indem die Oxidbildung auf Metalloberflächen verhindert wird. Solch eine Atmosphäre kann besonders beim Walzplattieren oder beim Lichtbogenspritzverfahren für eine bessere Anbindung der Metalle sorgen. Es hat sich jedoch gezeigt, dass die Reaktion von Silan mit Wasser kinetisch gehemmt ist und die verbleibende Restfeuchtigkeit in der Atmosphäre zur Oxidbildung führen kann. Zusätzlich kann sich der entstandene SiO2-Staub durch die Reaktion von Silan mit Sauerstoff an den Oberflächen ablagern und somit die Materialeigenschaften negativ beeinflussen. Daher ist eine Vorrichtung zur Gasaufbereitung erforderlich, die sowohl die SiO2-Partikel als auch die verbleibende Restfeuchtigkeit herausfiltert und gleichzeitig die Konzentrationen der Gase Sauerstoff, Wasserstoff und Restwasser überwacht. In diesem Zusammenhang wird die Adsorptionseffizienz des Molekuarsiebs für Wasser untersucht. Zusätzlich werden verschiedene Filterbauelemente verwendet, welche den SiO2-Staub aus der Atmosphäre filtern und die empfindlichen Sensoren schützen. Das Projekt zur sauerstofffreien Produktion wird in einem interdisziplinären Sonderforschungsbereich (SFB) in Kooperation mit der Leibniz Universität Hannover und dem Laser-Zentrum Hannover e.V. durchgeführt
Simulation of hydrogen distribution in submerged arc welded heavy plates as tool for evaluating cold cracking sensitivity for offshore structures
Full text linkFoundation structures for offshore wind turbines are typically made of heavy plate structural steels, such as S420ML, welded by submerged arc welding. Due to the welding process conditions, higher amounts of hydrogen can be introduced. In this context, large plate thicknesses result in long diffusion paths and a prolonged diffusion time for hydrogen at ambient temperature and possible delayed hydrogen-assisted cold cracking. As a result, hydrogen can accumulate in areas of high mechanical stress and strain. Due to the delayed diffusion, a minimum waiting time of up to 48 h must be observed before nondestructive testing can be performed. In addition, the assessment of possible cold crack locations is very complex. For this reason, a numerical model of a component-like weld test was developed to simulate the temperature field during welding and subsequent cooling. A hydrogen diffusion model based on the temporal-local temperature distribution was established. It was applied to simulate the change of hydrogen distribution as a function of temperature cycle during multi-layer welding and further for the entire waiting time interval ≤ 48 h. As a result, crack critical areas could be evaluated in terms of accumulated hydrogen. An advantage of the diffusion model is the simulation of a normalized concentration, i.e. between "0" (no hydrogen) and "1" (max. concentration), which can be scaled to experimentally determined hydrogen concentrations. Finally, selected results for increased real hydrogen ingress are presented, which confirm the relatively high crack resistance of the S420 submerged arc welded joint
Towards non-destructive machine learning-based acoustic resonance testing of aluminium 2024 riveted joints
Full text linkIn the aerospace industry, non-destructive testing is commonly used to ensure structural integrity. Methods such as eddy current, ultrasonic and radiographic testing are applied, but often require relatively expensive equipment and experienced operators for scanning and data interpretation. Acoustic resonance testing is an objective and cost-effective method that can test entire structures. This study investigated a machine learning-based acoustic resonance testing method for predicting relative stiffness loss as an indicator of progressive damage in riveted joints. Fatigue tests were performed in which the specimens were excited by a hammer impulse and acoustic emissions were measured at intervals. Two feature extraction approaches were applied to the frequency response function and different machine learning models for the prediction. The best results were obtained using a Convolutional Neural Network. It achieved an R² of 0.98 for predicting the loss of the joint stiffness and a classification accuracy of 100 % for defect detection based on these predictions
In-situ observation of the wetting behavior during pw-cw-laser beam brazing
Full text linkIn flux-free laser beam brazing, the surface oxides of the base material and the filler wire have a significant influence on the wetting behavior. In order to achieve optimal wetting results, the surface oxides must be removed. One approach is to use a ns-pulsed laser beam source to remove them prior to the cw-laser beam brazing process. To further improve wetting, the oxides on the filler wire also need to be removed. Therefore, the pw-beam source is now also used to remove the wire oxides during brazing in a combined pw-cw-laser beam brazing process. The ns-pulsed laser beam is applied in a line and a circle across the filler wire. The novel brazing process is observed using a high-speed camera. The camera's built-in illumination laser enables it to see through the bright process light, allowing in-situ observations of the wetting process. The experiments are conducted using a bead-on-plate brazing technique with aluminum AlSi12 filler wire and a copper Cu-OF base material. The position of the ns-pulsed laser beam is adjusted throughout the process zone, with the pulse energy varying from 120 μJ to 300 μJ. It can be observed that the ns-pulsed laser beam ablates the surface of the molten filler wire and exerts a pressure on the surface of the melt, thereby inducing a forced wetting behavior. The aim of the study is to understand the differences in wetting behavior and to obtain suitable parameters for future flux-free brazing experiments using this novel method
Thermodynamic modeling of carbon diffusion in manganese steels
No full textDecarburization of steels is a diffusion-controlled thermochemical process that is largely dependent on the process conditions, such as the process atmosphere and the reaction temperature, as well as the composition of the steel alloy. When modeling such diffusion processes, Fick´s law is commonly used that is based on a concentration gradient as the driving force for diffusion. However, this approach holds only for “ideal mixtures”. Steel alloys are far away from ideal mixtures, for which complete mutual solubility of all components without formation of intermetallic phases are necessary requirements. In order to overcome this problem, a thermodynamic approach for describing the diffusion is proposed, which takes into account the real mixing behavior of steels. Especially, the thermodynamic modeling of carbon diffusion in the martensitic hardenable tool steel 22MnB5 compared to a binary Fe-C steel is presented. Results are discussed with regard to the necessary process conditions for successful edge area decarburization of this steel grades
Synthesis and Application of Bio-Based Polyesters and Poly(ester amide)s
Full text linkThis cumulative habilitation deals with the utilization of bio-based building blocks as monomers for polymer applications. A focus is placed on the development of novel polymeric materials with unprecedented properties that cannot be achieved with building blocks derived from petrochemical resources. As main classes of materials thermoplastic poly(ester amide)s and UV-curing polyesters derived from itaconic acid as alternative to acrylic acid were investigated. In addition, further applicability of these building blocks as monomers for aqueous polyurethane dispersions was investigated. The scientific publications on which this thesis is based are the result of research projects carried out at the Fraunhofer Institute for Wood Research, Wilhelm-Klauditz-Institut WKI over the last 10 years under direction of the author of this thesis. The main motivation behind the research work presented herein, was to develop polymeric materials derived from renewable raw materials with the potential to replace petrochemical materials. Therefore, commercially relevant monomers were chosen and compatible properties were targeted to develop bio-based alternatives that could compete on the mid-term with commercial materials
