Technische Universität Bergakademie Freiberg
Recent publications
Microbial enhanced oil recovery (MEOR) is the only method based on the use of living organisms in enhanced oil recovery (EOR) classifications. Ex situ MEOR relies on the performance of the microbial metabolites produced in the industrial facilities and targets one or two major oil recovery mechanisms, such as IFT reduction (biosurfactants) and increase of the water phase viscosity (biopolymers); their operational design and applications differ only slightly from their chemical analogs. In addition to the cost-effective application, in situ MEOR exhibits major differences in impacting oil recovery in the reservoir; the injection of selected nutrients activates specific beneficial microorganisms, which are either injected and/or present in the reservoir in situ. The oil recovery effect of in situ MEOR is due to the multiple mechanisms increasing macroscopic microscopic and displacement efficiencies. This chapter provides an in-depth evaluation of the most applied ex situ and in situ MEOR approaches and covers various aspects of MEOR, including an explanation of basic definitions and concepts and a detailed assessment of the EOR effects involved. Field screening criteria, requirements for MEOR operations, laboratory methods to be employed, numerical modeling of MEOR, and monitoring approaches as well as a comprehensive literature survey of field trials are elaborated and discussed.
This work aims to investigate the mechanical behaviour of medium-grained sandstones under cyclic loading with different loading/unloading rates. This type of cyclic loading is called differential cyclic loading (DCL) and is considered for testing rock behaviour. In the experiments, constant amplitude and multi-level cyclic loadings were performed. Three loading modes were designed to consider different relationships between loading and unloading rates. Axial strain evolution and energy dissipation were analysed for different loading/unloading rates and maximum cyclic load level. The correlations between P-wave velocities and strengths of rocks deduced from this research are compared with existing published data. The relationships between final strength and axial strain at failure under different loading patterns were also discussed and a rough assessment of the remaining fatigue life is introduced using the predicted value by fitting the axial peak strain.
This study presents an example illustrating the role of in situ 3D stress path method in simulating the roof damage development observed in the Mine-by tunnel at Underground Research Laboratory (URL) located in Manitoba, Canada. The 3D stress path, at the point 1 cm in the crown of the Mine-by tunnel, was applied to a cubic Lac du Bonnet (LdB) granite sample to further understand the roof damage process and the associated seismicity. After careful calibrations, a numerical model was used to reproduce the experiment, which produced similar seismicity processes and source mechanisms. Acoustic emission (AE) events obtained from laboratory and numerical modeling were converted to locations in relation to the tunnel face and were compared to the field microseismicity (MS) occurring in the upper notch region of the Mine-by tunnel. The crack development and damage mechanism are carefully illustrated. The difference between tests and field monitoring was discussed. The intermediate principal stress (σ2) unloading process was carried out in numerical simulation to investigate its role in rock damage development. The results clearly showed σ2 could play a significant role both in damage development and failure mode. It should be considered when predicting the damage region in underground excavations. This study highlights the potential role of laboratory and numerical stress path tests to investigate fracture processes and mechanisms occurring during engineering activities such as tunnel excavation.
Biomass ashes are frequently known for their limiting effects in thermochemical conversion processes. Thus, a comprehensive understanding and prediction of the temperature-depending behavior of the ashes is indispensable for practical applications. In the present study, the flow behavior of low-temperature ash (LTA) and high-temperature ash (HTA) of biomass is investigated in detail and monitored by in situ methods. For this purpose, the mineral matter formation and transformation of both ashes are studied by X-ray diffraction (XRD) and X-ray fluorescence (XRF) analysis. A combination of heating-stage microscope and scanning electron microscope equipped with energy-dispersive X-ray spectroscopy (SEM-EDX) has enabled a systematic identification of the microstructures and observations of LTA and HTA. The results have illustrated an associated release of K and Cl and the formation of new mineral phases in the remaining material during ashing at increased temperature. Both ashes have exhibited flow temperatures below 1100 °C and a rarely observed behavior of higher characteristic temperatures for LTA than for HTA is detected. From the heating-stage microscopy, the ashes have given evidence to a significant formation of slag at the characteristic temperatures and a viscosity-driven behavior at the characteristic points of ash fusion. Based on these results, a conclusion can be drawn regarding the usability of this biomass for high-temperature conversion processes on the industrial scale.
Understanding the fracture behavior and fracture-morphology evolution of granite after coupled thermo-hydro-mechanical (THM) environment is important for many geotechnical projects. Previous studies mostly focused on the fracture-response mechanism of rocks after a thermal treatment, whereas only a few studies were conducted on the fracture toughness, fracture-process-zone (FPZ) size, and fracture-morphology evolution of granite after the THM multifield coupling. Therefore, a coupled THM damage treatment (i.e., THM-induced damage) of granite was carried out using a self-developed, high-temperature, and high-pressure multifield coupling triaxial universal tester. Subsequently, a series of test methods was employed, which included the full-field 3D digital-image correlation technique (real-time tracking of the strain/displacement field on the specimen surface), X-ray computed tomography scanning technique (to obtain the microdamage structure inside the specimen), and 3D laser scanner (to obtain the section morphology of the specimen). These methods were employed to study the response mechanism of mode-I fracture of a granite specimen (fracture toughness, fracture trajectory, FPZ size, and fractal dimension of the section topography). Furthermore, to elucidate the correlation between the coupled THM induced damage and fracture characteristics of granite, the same experimental test was also carried out on the granite using a thermal treatment. The result show that the evolution pattern of the fracture and morphological parameters of granite after the coupled THM treatment was different from that using only the thermal treatment, and the value of these physical parameters fluctuated at approximately 400 °C–500 °C. This is due to the limitation of the triaxial stress on the thermal expansion (25 °C–300 °C), competitive effect of “opening” and “closing” of micropores/microcracks (400 °C–500 °C), and deterioration of the coupled THM field (600 °C–650 °C). The results provide insights and theoretical guidance for high-temperature underground rock-mass engineering such as deep nuclear-waste reservoir.
Stiffness loss and catastrophic failure frequently occur in natural stone masonry subject to freeze-thaw action and cyclic stress, which may incur serious engineering disasters and casualties. This work strives to experimentally unveil the mechanical responses of a medium-grained building sandstone exposed to dual effects of freeze-thaw and cyclic stress. Testing results are presented from the insights of volumetric deformation, secant modulus evolution. A drop in secant modulus of the first cycle is observed in the failure cyclic loading stage, whereas all former stages exhibit a modulus increase. This precursor well applies to all samples which is freeze-thaw and stress level independent. The development of Poisson's ratio as well as stress level at onset of volume reversal are also presented. A theoretical modelling is put forward to characterize the axial and circumferential strains exposed to variable cyclic stress. The model shows decent effectiveness calibrated by testing results, the way to determine constants in models is introduced in detail, which can be used by readers in a broader range of construction materials.
The usage of artificial intelligence (AI) is increasing in many fields of research, since complex physical problems can be ‘learned’ and reproduced by AI methods. Thus, instead of numerically solving partial differential equations, describing the physical processes in detail, appropriate AI methods can be used to decrease the calculation time significantly. In the present study, artificial neural networks (ANNs) were used to predict temperature and species concentrations in a laminar counter-flow diffusion flame. To improve the accuracy of the ANNs, a support vector machine (SVM) was used to subdivide the wide range of operating conditions (air–fuel ratio, strain rate, fuel mixture) into ‘flame’ and ‘no flame’ cases. Due to classification with the SVM the prediction performance of the ANNs was optimized and an average error to the reference values (GRI3.0) below 10 K for all cases was detected, whereas the calculation time was decreased by a factor of about 4,800 (solving the transport equations with GRI3.0).
An edge-coloured graph G is called properly k-connected if any two vertices are connected by at least k internally vertex-disjoint paths whose edges are properly coloured. The proper k-connection number of a k-connected graph G, denoted by pck(G), is the minimum number of colours that are needed in order to make it properly k-connected. Let fk(n,r) be the minimum integer such that every k-connected graph of order n and size at least fk(n,r) has proper k-connection number at most r. Our main results are as follows: (1) Let G be a 2-connected graph of order n≥19. If |E(G)|≥n−32+7, then pc2(G)=2. (2) Let G be a hamiltonian graph G of order n≥50 and size |E(G)|>n24. Then pc2(G)=2. We also determine lower and upper bounds for f2(n,r).
Pyrolysis of the waste organic fraction is expected to be a central element to meet the primary energy demand in future: it increases the impact of renewable energy sources on the power generation sector and allows the amount of waste to be reduced, putting an end to landfills. In the present study, kinetic studies on the pyrolysis of biomass wastes are carried out. Two kinds of industrial organic waste are investigated: brewery spent grain (BSG) and medium-density fiberboard (MDF). The main target of this work is to provide a global equation for the one-step pyrolysis reaction of the investigated materials in an argon atmosphere using isoconversional methods. The conducted analysis allowed to estimate the activation energy as 225.4–253.6 kJ/mol for BSG and 197.9–216.7 kJ/mol for MDF. For both materials nth order reaction was proposed with reaction order of 7.69–8.70 for BSG and 6.32–6.55 for MDF. The developed equation allowed to simulate the theoretical curves of thermal conversion. These curves indicated the highest conversion at the temperature of the degradation of dominant component, which was experimentally verified. By this method, a one-step kinetic model is derived, which can be applied for the reaction kinetics in the CFD modelling of, e.g., pyrolysis and gasification processes.
The Digermulen Peninsula in northeastern Finnmark, Arctic Norway, comprises one of the most complete Ediacaran–Cambrian transitions worldwide with a nearly continuous record of micro- and macrofossils from the interval of the diversification of complex life. Here, we report on the provenance and post-depositional alteration of argillaceous mudstones from the Digermulen Peninsula using rare earth elements and Sm–Nd and Rb–Sr isotopic systematics to provide an environmental context and better understand this important transition in Earth’s history. The studied sections comprise a mid-Ediacaran glacial–interglacial cycle, including the Nyborg Formation (ca. 590 Ma) and Mortensnes Formation (related to the ca. 580 Ma-old Gaskiers glaciation), and the Stáhpogieddi Formation (ca. 560–537 Ma), which yields Ediacara-type fossils in the Indreelva Member and contains the Ediacaran–Cambrian boundary interval in the Manndrapselva Member and basal part of the informal Lower Breidvika member (ca. 537–530 Ma). Three sample groups, (1) Nyborg and Mortensnes formations, (2) the lowermost five samples from the Indreelva Member and (3) the remaining samples from the Indreelva as well as from the Manndrapselva and Lower Breidvika members, can be distinguished, belonging to distinct depositional units. All samples have negative εNd(T) values (−6.00 to − 21.04) indicating a dominant input of terrigenous detritus with an old continental crust affinity. Significant shifts in Sm–Nd isotope values are related to changes in the sediment source, i.e. Svecofennian province vs Karelian province vs Svecofennian province plus in addition likely some juvenile (late Neoproterozoic volcanic) material, and probably reflect palaeotectonic reorganisation along the Iapetus-facing margin of Baltica. The combined Rb–Sr isotopic data of all samples yield an errorchron age of about 430 Ma reflecting the resetting of the Rb–Sr whole-rock isotope systems of the mudstones during the Scandian tectono-metamorphic event in the Gaissa Nappe Complex of Finnmark. Preservation of palaeopascichnids coincides with the sedimentation regimes of sample groups 2 and 3 while other Ediacara-type fossils, e.g. Aspidella-type and frondose forms, are limited to the sample group 3. Our results are similar to those of earlier studies from the East European Platform in suggesting oxic seafloor conditions during the late Ediacaran.
Ambitious decarbonization pathways to limit the global temperature rise to well below 2 °C will require large-scale CO2 removal from the atmosphere. One promising avenue for achieving this goal is hydrogen production from biomass with CO2 capture. The present study investigates the techno-economic prospects of a novel biomass-to-hydrogen process configuration based on the gas switching integrated gasification (GSIG) concept. GSIG applies the gas switching combustion principle to indirectly combust off-gas fuel from the pressure swing adsorption unit in tubular reactors integrated into the gasifier to improve efficiency and CO2 capture. In this study, these efficiency gains facilitated a 5% reduction in the levelized cost of hydrogen (LCOH) relative to conventional O2-blown fluidized bed gasification with pre-combustion CO2 capture, even though the larger and more complex gasifier cancelled out the capital cost savings from avoiding the air separation and CO2 capture units. The economic assessment also demonstrated that advanced gas treatment using a tar cracker instead of a direct water wash can further reduce the LCOH by 12% and that the CO2 prices in excess of 100 €/ton, consistent with ambitious decarbonization pathways, will make this negative-emission technology economically highly attractive. Based on these results, further research into the GSIG concept to facilitate more efficient utilization of limited biomass resources can be recommended.
This work strives to experimentally unveil the combining effects of freeze-thaw (FT) action and differential cyclic loading (DCL) on the sandstone masonry. The cylindrical sandstones after different FT actions (0, 20, 40 FT cycles) were cyclically compressed by utilizing two loading modes having distinct loading and unloading rates. The testing results are presented from the perspectives of mass loss, P-wave velocity attenuation, rock deformation, energy dissipation, and stress-strain hysteresis. The results indicate that the stress pattern with a higher loading rate and a lower unloading rate corresponds to a lower fatigue strength as well as a shorter fatigue life. In addition, the stress pattern with rapid loading and slow unloading is more favorable yielding a larger amount of dissipated energy within a cycle. More applied FT cycles impose a more damaging effect on sandstone which is characterized by a lower fatigue life and a higher strain rate. Both FT actions and the stress pattern with rapid loading and slow unloading can lead to an evident elastic aftereffect, a phase lag is clearly visible for axial strain at the peak stress. The phase lag is the fundamental to the more dissipated energy under the stress pattern with rapid loading and slow unloading.
In this work, thermal conductivity and anharmonic properties of chemical vapor transport (CVT) grown pyrite‐FeS2 and mineral single crystals have been investigated and compared. It has been shown that optothermal Raman technique is able to capture the large thermal conductivity difference between the CVT and mineral samples at low temperatures. This difference is attributed to point‐defects such as sulfur vacancies or impurity doping of CVT grown FeS2 crystals. Balkanski‐Klemens model analysis of the samples has shown that three‐phonon scattering of Ag and Eg modes and the lattice thermal expansion are the dominant anharmonic contributors while four‐phonon scattering is negligible in pyrite‐FeS2. Thus, thermal conductivity of materials that is difficult to measure by conventional methods (i.e. flash method), can be measured in their most native form by using optothermal Raman spectroscopy (RS) without rigorous sample preparation.
Recycling is a potential solution to narrow the gap between the supply and demand of raw materials for lithium-ion batteries (LIBs). However, the efficient separation of the active components and their recovery from battery waste remains a challenge. This paper evaluates the influence of three potential routes for the liberation of LIB components (namely mechanical, thermomechanical, and electrohydraulic fragmentation) on the recovery of lithium metal oxides (LMOs) and spheroidized graphite particles using froth flotation. The products of the three liberation routes were characterized using SEM-based automated image analysis. It was found that the mechanical process enabled the delamination of active materials from the foils, which remained intact at coarser sizes along with the casing and separator. However, binder preservation hinders active material liberation, as indicated by their aggregation. The electrohydraulic fragmentation route resulted in liberated active materials with a minor impact on morphology. The coarse fractions thus produced consist of the electrode foils, casing, and separator. Notwithstanding, it has the disadvantage of forming heterogeneous agglomerates containing liberated active particles. This was attributed to the dissolution of the anode binder and its rehardening after drying, capturing previously liberated particles. Finally, the thermomechanical process showed a preferential liberation of individual anode active particles and thus was considered the preferred upstream route for flotation. However, the thermal treatment oxidized Al foils, rendering them brittle and resulting in their distribution in all size fractions. Among the three, the thermomechanical black mass showed the highest flotation selectivity due to the removal of the binder, resulting in a product recovery of 94.4% graphite in the overflow and 89.4% LMOs in the underflow product.
Geothermal heat flow (GHF) data measured directly from boreholes are sparse. Purely physics-based models for geothermal heat flow prediction require various simplifications and are feasible only for few geophysical observables. Thus, data-driven multi-observable approaches need to be explored for continental-scale models. In this study, we generate a geothermal heat flow model over Africa using random forest regression, originally based on sixteen different geophysical and geological quantities. Due to an intrinsic importance ranking of the observables, the number of observables used for the final GHF model has been reduced to eleven (among them are Moho depth, Curie temperature depth, gravity anomalies, topography, and seismic wave velocities). The training of the random forest is based on direct heat flow measurements collected in the compilation of (Lucazeau et al., Geochem. Geophys. Geosyst. 2019, 20, 4001-4024). The final model reveals structures that are consistent with existing regional geothermal heat flow information. It is interpreted with respect to the tectonic setup of Africa, and the influence of the selection of training data and observables is discussed.
In this study, filtration of aluminum alloy (Al) with different weight fractions of SiC particles (SiCp) was investigated. Therefore, three different filter materials of 20 pores per inch (ppi) ceramic foam filters (CFF) were tested. A special three-chamber furan mold was used for the casting trials to provide uniform filling and flow conditions for the filtration process. Samples from sections of the gating system, as well as from the filter, were analyzed by optical light microscopy to determine the amount, size, and distribution of SiCp. A scanning electron microscope (SEM) with energy-dispersive X-ray spectroscopy (EDS) was used for obtaining the element distribution in the composite. The filtration efficiency increased by decreasing the weight fraction from 20 to 5% of SiCp and reached a significant particle reduction of over 90%. Investigations of CFFs with a weight fraction of 10% have shown a clogging effect and metal flow interruption through the 20 ppi filter. An oxide layer was detected around the respective SiCp in the EDS. Moreover, a strong accumulation effect was observed, indicated by a steadily flattening curve of the density functions after each additional remelting cycle of the same composite material.
This contribution describes the origins and essential characteristics of the Humboldtian Model of Higher Education. It also shows how this model can be integrated into the European University on Responsible Consumption and Production (EURECA-PRO). Wilhelm von Humboldt and his team developed the innovative Humboldtian Model of Higher Education in Humboldt’s native Prussia between 1809 and 1810 in order to totally reform the education system. After founding the University of Berlin in 1810 and with the support of leading young scientists cum professors, Humboldt intended to implement this new model of tertiary education. The Humboldtian Model requires that universities govern themselves, have academic freedom, and integrate education and research. As a consequence, science is unified and all academic disciplines are present within a given university. This model also calls for university-wide interaction and for all university members to communicate such that students become integrated as researching learners and learning researchers through close co-operation with their teachers. With the emergence of the neoliberal university model in the 1990s, key elements of the Humboldtian Model have been complemented by university obligations to meet expectations from government, the business community, and society at large with regard to the usefulness and benefit of university research and educational outputs. This contribution concludes by discussing the potential of implementing the Humboldtian Model of Higher Education within EURECA-PRO.
The tragic circumstances caused by natural or human-made (unexpected human or technological errors) hazard such as earthquakes, floods, glaciers, fires or industrial explosions causing significant physical damages, loss of lives or destruction of environment as well as economic and social life of people are known as disasters. Planned evacuation is essential to save the maximum number of evacuees in minimum time, which also helps in minimize losses. Due to mass dispatch (movement) of people aftermath of disaster, traffic scenario at the intersection of roads may create the disappointing situation if the vehicles have to wait for hours to cross the intersection. The main reason behind this is the lack of crossing elimination. In this paper, we discuss the partial switching property on an abstract network, in which crossing effect of roads is eliminated to transship optimal flow of evacuees. Due to the switching property, crossing of the flows at the intersections is diverted to non-crossing sides which can be a milestone to smooth the flows during evacuation. We present polynomial time solution procedures to solve abstract maximum static and dynamic flow problems with partial switching of paths. We also introduce the abstract quickest flow and quickest contraflow problems with partial switching and present polynomial time algorithms to solve the problems. For disaster management, maximum, quickest and contraflow problems on partially switched paths play an important role as the flow on a path system without crossing effect is very essential during evacuation process.
The operation of a copper Flash Smelting Furnace (FSF) is often limited by the availability of the downstream Waste Heat Boiler (WHB). Carry-over of concentrate into the boiler leads to accretion formation, which can cause boiler downtime. Hence, the minimization of flue dust and its accretions is an important operational goal. In this study, a Computational Fluid Dynamics (CFD) model is used to investigate how three different baffle plate designs influence accretion formation over a period of 24 hours. The predicted dust accretion patterns were compared for all baffle plate modifications, with differences found both in the resulting sedimentation and accretion of dust particles. While the dispersive design led to large, but evenly coated accretion risk zones, a streamlined design minimized their size but led to locally thick accretion layers. Based on these findings, design recommendations for the baffle plate were derived.
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2,745 members
Nikolaus Klamerth
  • Institute of Geology
Hartmut Stöcker
  • Institute of Experimental Physics
Carsten Felden
  • Institute of Business Computer Science / Information Economy
Oliver Wiche
  • Institute of Biosciences
Edwin Kroke
  • Institute of Inorganic Chemistry
09599, Freiberg, Germany