FG Thermische Energietechnik
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Im Rahmen dieser Arbeit wurde ein Berechnungsmodell zur thermisch-geometrischen Dimensionierung eines kontinuierlich arbeitenden Druck-Wirbelschicht-Verdampfungs-Trockners mit Tauchheizflächen für polydisperse Braunkohle erstellt. Zunächst wurde auf Basis experimenteller Ergebnisse eine strukturell optimierte Grundgleichung zur Beschreibung des zeitlichen Feuchteverlaufes entwickelt. Dabei wurden die Besonderheiten des Trocknungsgutes (z.B. die Polydispersität und die Ausbildung einer Gleichgewichtsfeuchte) berücksichtigt. Mit Hilfe der für den Trockner aufgestellten Energiebilanzen wurde ein Modell zur Beschreibung des zeitlichen Verdampfungstrocknungsverlaufes entwickelt. Dabei wurde auch der Einfluss des Druckes in den Subgleichungen und Stoffwertberechnungen berücksichtigt. (Der Überdruck ist einer der Hauptunterschiede der DDWT zu zahlreichen anderen Trocknungsverfahren). Weiterführend wurde unter Anwendung der Gleichungen zur Beschreibung der wirbelschicht-bedingten asymmetrischen Verweilzeitverteilung ein Gesamtmodell – das Trockner-Auslegungs-Modell (TRAM) – entwickelt und die Modellarchitektur detailliert beschrieben.
In diesem Beitrag wird ein Flammenbewertungsverfahren auf Basis eines Flammenwächtersignals vorgestellt. Mit zunehmender Flexibilisierung der Verbrennungsanlagen und der Absenkung von Emissionsgrenzwerten wird eine unmittelbare Flammenanalyse für die Regelung der Brennersysteme zunehmend erforderlich. Auf Basis eines Flammenwächtersignals wird mittels Frequenzanalyse ein ergänzendes Auswertungsverfahren dargestellt. Anhand der vorgestellten Untersuchungen an einem Erdgas-/Kohle-Kombibrenner wird die Qualifizierung der Prozessmesstechnik für die Flammenbewertung und Brennersteuerung überprüft. Die Ergebnisse im Erdgas- und Kohlebetrieb belegen, dass mit der erweiterten Signalanalyse eine Veränderung des Flammenverhaltens mit dem Flammenwächtersignal in Zusammenhang gebracht werden kann. Dabei konnte einmal das Emissionsverhalten bei verschiedenen Brennereinstellungen beurteilt werden und andererseits ein Zugriff auf das Stabilitätsverhalten der Kohleflamme ermöglicht werden. Durch die Analyse des Strahlungssignals der Chemilumineszenz des OH* bzw. CH*-Radikals ist ein Bezug zur Veränderung in der Reaktionszone hergestellt. Die entwickelte Bewertungsmethodik kann für die Entwicklung und Etablierung von Beobachter- und Regelmodellen von Brennersystemen genutzt werden.
District heating dynamic models arise as an alternative approach to in-situ experimental investigations. The main advantage of dynamic modeling and simulation is the possibility to avoid technical and operational risks that might occur during in-situ experimental investigations (e.g. heat demand is not met, damages in the energy systems etc.). Within this study, the authors present two models for an existing district heating system in Cottbus, Germany. One model is developed using the tool EBSILON Professional, while the other one is developed using the Simscape toolbox for physical modeling in Matlab/Simulink. The models were experimentally validated against measured data from the considered district heating system. The results show that the Simscape model has a better fit and better response than the EBSILON model. Yet, some discrepancies were found between the measured and the simulated data and, therefore, the uncertainties of the models were addressed. A comparative study between both tools is presented. The EBSILON models permit only unidirectional flow, whereas the Simscape toolbox permits reverse flow. Nevertheless, the EBSILON model outperforms the Simscape model in computation time. In addition, this study presents an approach for dynamic thermo-hydraulic modeling of district heating networks. This approach is utilized to examine the role of district heating networks as heat storage as an optimization configuration. The numerical results show less start-ups for additional heat sources. Yet, higher heat losses from the network are observed due to the installation of unburied pipelines.
In the last two decades, a rapid expansion of photovoltaic (PV) power plants of different sizes has taken place. Along with this, the interest from science and industry is growing, exploring the strengths and weaknesses of this technology as well as further developing the efficiency in its production and operation. For planning and operating of PV power plants, valid energy yield forecasts are desirable. These forecasts are also important to draw conclusions for the monitoring of future PV technologies. The analysis, evaluation and processing of meteorological and technical measurement datasets play an essential role.
In this article, high-resolution measurement data sets of a mobile, autarkic test system are analyzed firstly. The measured data are checked for plausibility and validity with the corresponding methods. After this observations and phenomena with meteorological cause are described. In a second step, a practicable procedure for the preparation of the measurement data is presented, in order to make it suitable for further calculations, e.g. identification of photovoltaic module parameters for energy yield calculations. The focus is particularly on the flexibility, adaptability and code performance of the processing procedure. Results, evaluations and outlooks on the methods used, measurement data and selected software packages are made.
PEM water electrolysis is a clean and efficient conversion technology for hydrogen production and energy storage, especially when coupled with renewable energy sources. In spite of its many advantages, the high component and cell manufacturing costs of the conventional PEM electrolysis cell makes the PEM water electrolysis technology commercially less competitive vis-à-vis its peers. An alternative and cost effective cell design has been proposed which has up to a 25 % costs advantage over the conventional cell. In this alternative cell design, the flow channel plate which bears the most material costs in the conventional cell design has been replaced with a 3-D Porous Transport Layer (PTL) structure. While both designs perform comparably the same at low to mid current density (0 – 2 A/cm²), it has been observed that the conventional cell by far out performs the low cost cell at high current density operations, due to increased mass transport limitation in the cell without flow channels. Since industrial and commercial hydrogen production efforts are focused towards high current density operation (> 3 A/cm²), it thus becomes obvious that, in order for the cost effective alternative cell design to establish itself over the conventional cell design, the mass transport issues at high current densities have to be well understood and described.
This research work seeks to understand the source of, and to eliminate the mass transport losses in the cost effective alternative cell design in order to get it performing at least as good as the conventional cell design at current densities up to 5 A/cm². To meet this objective, 2-D non-isothermal semi-empirical fully-coupled models of both cell designs have been developed and experimentally validated. The developed validated models were then used as tools to simulate and predict the best operating conditions, design parameters and micro-structural properties of the PTL at which the mass transport issues in the design without flow channels will be at its minimum, so that both cells can exhibit comparable performance even at high current densities.
The models developed in this work are based on a multi-physics approach in which thermodynamic, electrochemical, thermal and mass transport sub-models are coupled and solved numerically, to predict the cell polarization and individual overpotentials, as well as address heat and water management issues. The most unique aspect of this work however, is the development of own semi-empirical equations for predicting the mass transport overpotential imposed by the gas phase (bubbles) at high current densities. Also, for the very first time, calculated PEM water electrolysis polarization curves up to 5 A/cm² have been validated by own experimental data.
The results show that, the operating temperature and pressure, inlet water flowrate and thickness of the PTL are the critical parameters for mitigating mass transport limitation at high current densities. In fact, it was found that, for the size of the cells studied (25 cm² active area each), when both cells are operating at the same temperature of 60 °C, the low cost cell design will have a comparable performance to the conventional designed cell even at 5 A/cm² current density when; the operating pressure is ≥ 5 bar, the feed water flowrate is ≥ 0.024l/min∙cm², PTL porosity is 50 %, PTL pore size is ≥ 11 µm and PTL thickness is 0.5 mm. At these operating, design and micro-structural conditions, the predicted difference between the polarizations of both cells will be only ~10 mV at 5 A/cm² operating current density.
As power generation from variable renewable energy sources such as wind and solar power continues to increase in the future, fewer baseload power plants will be needed. As a result, high operational flexibility is becoming a vital requirement for conventional power plants to allow for the smooth integration of the variable renewable energy sources (v-RES) into the grid. To understand the impact of high operational flexibility (increased cycling) for coal-fired power plant materials, five commercial coal boiler superheater and reheater materials were investigated under isothermal and cyclic conditions for 1000 h each. The candidate alloys investigated were: T91, VM12-SHC, TP347-HFG, DMV304 HCu and DMV310 N. The results (weight change kinetics and metallographic analysis) after exposure at a metal surface temperature of 650 °C clearly showed the impact of increased flexibility on the corrosion and oxidation of the materials. Oxide growth (weight gain), metal loss, oxide spallation, and grain boundary attack were found to be more severe under cyclic conditions than under isothermal conditions.
From its foundation of the chair of power plant
technology at Brandenburg University of Technology
Cottbus – Senftenberg, the combustion
research has engaged with current issues of conventional
power plant technology. The focus of
his research activity was starting from development
of technology to maximize the efficiency,
switched to the new research field of oxyfuel
technologies and working currently on questions
about operational flexibility as reaction of
changes in the current energy sector. There are
many concepts for increasing plant flexibility,
but without optimization of flame monitoring
and re-evaluation of existing limits, this potential
for optimization can’t be sufficiently used.
The current research project to increasing thermal
plant flexibility of existing coal-fired power
plants is implementing the necessity for analysis
and optimization research. Therefore, one
goal is a significant progress in the evaluation
of cyclic operation with higher load transients
and load cycles of coal-fired power plants. Furthermore,
a research evaluation about the effects
on the components life of components of
the water-steam cycle is possible.
At first I was wondering what the structure of an article about pressurized steam fluidized bed drying could look like. After some thought, I knew that it should be divided into two parts. In order to highlight the creative and inventive spirit of former engineers, as well as their struggle to increase the efficiency of drying machines, a historical outline of the drying technology in general and the concept of steam fluidized bed drying in particular will form the first part of the article. The second part will present the practical and research contribution of Prof. Krautz and his colleagues to the advancement of this field. The article as a whole will be able to provide an overview of the coal/lignite drying, with focus on the pressurized steam fluidized bed drying principle implemented in the Lusatian mining area.
Mit der steigenden Erzeugung volatilen Stroms aus erneuerbaren Energien werden die Anforderungen an die Flexibilität der konventionellen Kraftwerke erhöht. Der Einsatz von Stützfeuerungssystemen auf Basis von Trockenbraunkohle (TBK) ermöglicht die Erweiterung des Lastbereiches und der Lastgradienten am Dampferzeuger. Untersuchungen zum Teillastverhalten von TBK-Brennern wurden an der BTU Cottbus – Senftenberg an einem 400 kWth Verbrennungsversuchstand und an dem industriellen 30 MWth TBK-Staubbrenner der Firma BBS (Babcock Borsig Steinmüller GmbH) durchgeführt. Der verfügbare Einsatzbereich des Brenners ist maßgeblich von der Intensität den brennernahen Mischungsvorgang abhängig. Mit der Absenkung der Brennerleistung ist beispielsweise eine signifikante Steigerung der NOx-Emission verbunden. Dieser Effekt ist auf die Veränderung des brennernahen Strömungsprofiles zurückzuführen. Mit Maßnahmen wie der Erhöhung der Drallzahl, Verteilung der Luftimpulsströme und Veränderung des Primärimpulses konnte eine Stabilisierung und Intensivierung der Reaktionszone und somit eine Verbesserte des Teillastverhaltens nachgewiesen werden.
1.
Wasserstoff – Elektrolyse
(2015)
Druckelektrolyse zur Wasserstoffherstellung- eine Kurzübersicht zu energetischen Vor- und Nachteilen
(2015)
The challenges in maintaining a stable oxy-coal flame have been reported in the open literature. In case of pulverized coal combustion, narrower flammable regimes arise not only of differences in the feed gas composition, but also due to changes in the flow dynamics because of reduced volume flow rate through the burners to match similar temperatures and radiative heat transfer within the furnace. The present work focuses on the study of flame structure and stability of pre-dried lignite fired by a staged feed-gas burner. Experimental runs were carried out in a 0.40 MWth laboratory facility, with the objective of investigating the effects of swirl strength and feed gas distribution in the burner registers. To assess the experimental data, a numerical study of the non-reacting flow in the near burner region is performed. Predicted flow pattern and flame images show that the primary fuel jet penetrates the internal recirculation zone, forming an annular doughnut reverse flow region for both firing conditions and resembling a type-1 flame pattern. Temperature measurements indicate that the feed gas distribution among the burner registers control the flame temperature in parallel with the swirl number in both air-fired and oxy-fired environments. The oxy-fuel cases exhibite markedly reduced temperatures on the flame axis. This difference in the core arises not just from the more pronounced penetration depth of the primary jet, but also due to reaction mechanisms including pyrolysis and gasification reactions at the higher concentrations of CO2 and water vapor. Flame stabilization is shown to be strongly dependent on an appropriate distribution of the feed gas and strength of swirling flow in the burner front. The results correlated in terms of swirl number, secondary/tertiary flow ratio and secondary/primary axial momentum point to similarities in the stability limits between air-firing and oxy-firing.
Heat-transfer from horizontal tube bundles into fluidized beds with Geldart A lignite particles
(2014)
This work investigates the heat transfer mechanism in fluidized beds equipped with horizontal heat exchanger surfaces such as single tubes and especially tube bundles.
Previous works were performed for varying operating conditions and solids' material properties, leading to a heterogeneous and therefore not applicable spectrum of derived correlations for the influence of tube diameter and tube bundle geometry on heat transfer.
Based on a wide range validation of the correlation for the influence of single tube diameter on heat transfer coefficient, tube bundles with different tube diameters and horizontal and vertical spacings and alignments were investigated. Experiments were carried out using electrical heat transfer probes in a 0.15 m2 fluidized bed test facility at ambient conditions. Geldart A lignite and Geldart D solids were used in order to distinguish between predominant particle-convective and gas-convective heat transfer mechanisms.
The tube bundle reduction factor on heat transfer coefficient was derived as a key parameter based on dimensionless geometric numbers. This factor predicts the reduction of the heat transfer coefficient compared to that of the single tube due to the particle and gas flow disturbances caused by the immersed tubes.
Tube diameter as well as tube bundle geometry were successfully implemented into useful correlations for predicting tube bundles' heat transfer of gas–solid fluidized bed systems operating with fine particles.
Numerical simulations using the Two Fluid Model are performed for gas-solid bubbling fluidized beds. The possibility to detect disturbances in the fluidization process is investigated by common analysis of pressure fluctuations and variation of the computational domain. Additionally the influences of different particle sizes and superficial gas velocities are studied. The results are compared with bubble properties obtained from a digital image analysis technique
The German Energiewende is resulting in high grid load changes caused by renewable energies. Therefore flexibility of power plants is getting more and more important. Future CCS power plants are usually equipped with more components than conventional power plants, resulting in a more complex and inert reaction on changes in power output. Additionally, due to the change in price structures and higher fixed and operational costs for CCS power plants, it is harder for them to be economically efficient. This study will show different options to increase the flexibility of CCS power plants and evaluate their benefits.
The present study investigates the fireside corrosion behavior of selected superheater materials, namely: T24, P92,
VM12-SHC, A800HT, and 7RE10 under oxy-coal combustion atmospheres. Data on mass change, scale thickness,
metal loss, surface morphology and micro-structural characteristics of corrosion products were obtained. The alloy
specimens were analyzed by SEM-EDX, light microscopy and X-Ray diffraction techniques. The results after
2000 hours of exposure at a metal surface temperature of 600 °C indicate that metal wastage increased with
decreasing Cr-content under oxy-coal conditions.
Alkalische Druckelektrolyse - Schlüsseltechnologie für zukünftige Energie- und Speicherkonzepte
(2012)
First modeling results of an advanced pressurized alkaline electrolyzer for hydrogen production
(2012)