Rezensionen

Stefan Hamel

On the Packing Properties of Fixed Beds for Thermal Fuel Conversion

Packed beds of fuel wood in the form of chips or pellets are commonly found in thermal conversion processes such as combustion or gasification. This thesis is concerned with the characterization of spatial voidage distribution inside fuel wood chip beds, which is of great importance for flow and reactor modelling. On the basis of a random deposition approach, a packing model was developed in order to transfer geometrical bed structures into CFD software for subsequent flow simulations. In addition, an experimental investigation of voidage distribution by bed solidification, sectioning, and subsequent image analysis of the cuts was carried out for packings of different commercially available wood chips and pellets, in order to derive a mathematical expression correlating radial voidage distribution. The findings of both the experimental results and the simulations are used to interpret fixed-bed wood combustion results from a laboratory-scale combustion tube and a commercial small-scale underfeed stoker. (orig.)

Quelle: 

ETDE - Energy Database-production no.:DE10GE342

Eckehard Tröster

Hochpolige Asynchronmaschine mit Permanentmagnetzwischenläufer als Windkraftgenerator

The multipol asynchronous machine with permanent magnet intermediate rotor (PMASM) is a new electrical machine with characteristics of the synchronous as well as asynchronous machine. In the field of wind energy generators this concept may renounce the gear and the converter. The author of the contribution under consideration reports on theoretical and measuring investigations at the PMASM in order to examine their suitability as wind energy generator. Altogether, the PMASM is especially interesting for an offshore plant, because it is low maintenance and lightweight in comparison to other directly propelled wind energy generators.

Quelle: 

ETDE - Energy Database-production no.: DE10GE318

Rolf Lohse

Einfluss von Beladeeinrichtungen auf die thermische Schichtung in Warmwasserspeichern

In solar thermal plants, the structure and the retention of a thermal stratification in hot water tanks is a basis for the effective use of energy and contributes to the substitution of conventional energy sources. The loading system and unloading system of the storage are a crucial role in carrying out of this task. In the contribution under consideration the flows intensively are examined with priority within and outside of the loading system for storages with a volume of more than 20 cubic metres. Several suction effects are presented in detail resulting in a mixture of a warm fluid and a cold fluid and in a dismantling of the thermal stratification. A multiplicity of CFD computations under variation of geometry parameters as well as operating conditions with the goal of the performance and optimization of the examined loading systems are accomplished. The evaluation of the computed velocity distribution and temperature distribution as well as the mixture procedures is performed under different aspects. By means of the results interpretation guidelines are developed with which a favourable, mixture-poor loading behaviour are reached.

Quelle: 

ETDE - Energy Database-production no.:DE10GE340

Mohammed N. Anany

Numerical Modelling of Combustion Processes at Elevated Pressures

As more and more CO{sub 2} quantities are discharged into the atmosphere from flue gases due to fossil fuel combustion, increasing concerns over greenhouse gas emissions have caused extensive research to be directed to the field of new power generation cycles that enable CO{sub 2} capture and storage. Raising the pressure of the coal conversion enables economic separation of CO{sub 2}. Two technologies working at elevated pressures are, for example, the Integrated Gasification Combines Cycle (IGCC) technology and the pressurised oxy-fuel combustion power cycles. Both Technologies rely on conversion of coal at elevated pressures, and hence enabling the CO{sub 2} separation process. For the numerical simulation of such processes, it has been proven that global models of atmospheric char conversion are neither directly applicable nor extrapolatable for elevated-pressure atmospheres. Therefore, abandoning these global models of char conversion and developing more reliable mechanistic char gasification/combustion models is a key point in being able to successfully predict the char gasification/combustion processes taking place at elevated pressures for these new clean-coal technologies. Since oxygen is, by far, the most efficient oxidising agent, the principal aim of this work is to develop a mechanistic model for Char Burn-Out (CBO) that is capable of providing correct predictions of char oxidation rates for wide ranges of temperature and pressure. Hence, this work also contributes to the work being conducted on the char conversion modelling at elevated pressures. In order to validate the predictions of the model, the finite volume (FV) CFD combustion simulation code AIOLOS has been used. During the course of development of the coal conversion model, a non-dissipative SIMPLEC algorithm (Semi Implicit Method for Pressure Linked Equations Consistent) for non-staggered (collocated) grids has been developed, since its robustness has been proven to be higher than their SIMPLE counterpart. Furthermore, the applicability of the Allspeed methods to reactive flows has been tested showing the need of double-precision declaration of variables when working with Mach numbers approaching the limit of zero. The Allspeed method has proven to predict similar results as is its SIMPLE algorithm equivalent for low-speed flows. The method has not been tested (in this work) for combustion applications of high-speed flows, i.e. Mach numbers exceeding 0.3. Moreover, an implicit under-relaxation approach has been developed to stabilise the solution of the pressure-correction equations. This approach has proven to be successful at the initial stage of the iterative solution of the problem as it has shown a reduction of one order of magnitude in the pressure-correction residuals. The development of the elevated-pressure coal conversion model necessitated the introduction of an elevated pressure pyrolysis model. A single first order reaction kinetic rate has been adopted to predict devolatilisation of raw coal. The total volatile yield has been made achievable by creating a data base of 14 coals, on the van Krevelen (coalification) diagram, which range from anthracite to lignite coals, and whose total volatile yields are fixed by experiment. An interpolation technique was adopted afterwards to predict the total volatile yield of coals which are not directly obtainable from the data base. For tar yield predictions a correlational model was incorporated within the CFD code. The model correlates the tar yield to the elemental composition of the parent coal and to the system pressure applied. The mechanistic char burn-out model relies on a three-step char oxidation process in contrast to the well-known two-step chemisorption-desorption mechanism (Langmuir-Hinshelwood kinetics). The third reaction step represents a reaction between oxygen molecules and the already formed carbon-oxide complexes. The specific reaction rate of char oxidation has been modelled by means of the Extended Resistance Equation (ERE) which accounts for Boundary Layer Diffusion (BLD) effects as well as pore diffusion effects by using a reaction penetration factor that accounts for the contribution of the interior surface of the coal particle to the oxidation process. The predictions of the two-step extended resistance equation and the three-step one have been compared against the results of experiments conducted on a pressurised Entrained Flow Reactor (p-EFR). The comparison has reflected the successfulness of the three-step char oxidation mechanism of predicting a combustion rate enhancement as partial pressures of oxygen are increased. However, the two-step mechanism has predicted the wrong trend as pressure was increased for the pressure range reported by the experiment. (orig.)

Quelle: 

ETDE - Energy Database-production no.: DE10GE336

Hannes Weckmann

Aspekte industrieller Fertigung von Festelektrolyt-Brennstoffzellen (SOFC) mittels thermischer Beschichtungsverfahren

The present thesis deals with measures to optimize the large-volume production of Solid Oxide Fuel Cells (SOFC) based on thermal spraying technology. Based on the well-established Vacuum Plasma Spraying (VPS) at DLR the potential of alternative thermal spraying techniques as well as alternative base materials was investigated in order to deposit SOFC-anode, electrolyte and insulating layers. Production costs, reproducibility and long-term stability of the production process as well as the fuel cell performance were major target criteria. Depending on the parameter set applied when using the cost efficient Atmospheric Plasma Spraying (APS) in combination with Nickel-Graphite as base material a significant improvement of gas permeability and electrical conductivity was achieved in comparison to the VPS sprayed reference anode. The power density of a fuel cell with an APS-Nickel-Graphite anode (184 mW/cm{sup 2}) was slightly better than the performance with a VPS reference anode (159 mW/cm{sup 2}). In comparison to the VPS process, ceramic electrolyte layers of fully stabilized Zirconia (YSZ) with significantly higher gas tightness could be demonstrated when high energy processes such as Low Pressure Plasma Spraying (LPPS). Thin-film Low Pressure Plasma Spraying (LPPS-Thin-film) and High Velocity Oxy Fuel Spraying (HVOF) were applied. The power density of a fuel cell equipped with an HVOF electrolyte was significantly improved to 234 mW/cm{sup 2} as compared to 187 mW/cm{sup 2} with the VPS sprayed reference cell. Further improvement of the power density was achieved with an LPPS-electrolyte (273 mW/cm{sup 2}). HVOF and VPS sprayed layers of pure Spinel in composite with metallic active braze (equivalent to the sealing between individual layers in the fuel cell stack) could exceed the demanded charge transfer resistance of >1 k{omega}cm{sup 2} at 800 C operating temperature only in few cases. When blended base powder of Spinel and Magnesia in combination with the VPS was applied significantly higher charge transfer resistance of up to 1,7 M{omega}cm{sup 2} could be demonstrated at layer thicknesses between 20 {mu}m and 117 {mu}m. In the further course of the thesis an online controller was developed for the VPS process based on insitu process diagnostic systems in order to reproducibly produce thermal sprayed functional layers. In pretests the process diagnostic system Accuraspray appeared to be cable of identifying changes in the process by detecting particle properties in the spray torch. In order to serve as a knowledge base for the controller the plasma spraying process was successfully modelled as correlation between machine parameters, spray torch- und layer properties by using artificial neural networks (ANN). The ability for the generalization as well as the accuracy of the model was improved further by measures such as active learning (additional experiments at poorly represented regions) and the combination of several models with different network architectures as an ensemble (mixture of experts). Based on the artificial neural network model, an online process controller was developed, which manipulates major process parameters in case of a deviation in order to get back to the initial state. The ability of the prototype controller could be demonstrated successfully in most cases. (orig.)

Quelle: 

ETDE - Energy Database-production no.:DE10GD688

Torsten Schwarz

Das Wasserstoffsubsystem und sein Einfluss auf die Kenngrößen des Brennstoffzellenantriebes

The objective of this work is to investigate how the hydrogen subsystem can influence the characteristics of a fuel cell power train. In the main focus are the aspects safety, emissions, efficiency, and durability. At the beginning fundamentals of hydrogen safety and degradation mechanisms of fuel cells are investigated. Afterwards the necessary development of a non-invasive online measuring system that is based on ultrasound is described. Starting from the experiences with the VW HyMotion2 fuel cell engine a completely new concept has been developed and tested. Due to the use of an active recirculation the complexity can be reduced and there is the possibility for the implementation of several new operating strategies. Therefore the occurrence of conditions which cause degradation can be reduced considerably. Operating the anode recirculation with 30 % nitrogen allows a significant reduction of the hydrogen losses and therefore increases the fuel cell engine efficiency in the New European Driving Cycle to approx. 48 %. Thus the HyMotion3 drive train has a tank to wheel efficiency of approx. 33 %. Additionally hydrogen emissions can almost completely be avoided by catalytic combustion at the cathode. The maximum exhaust concentration is less than 0,2 %. (orig.)

Quelle: 

ETDE - Energy Database-production no.:DE10GD754

Ernst Christian Hengstenberg, Gerhard Meighörner, Claus Rasmus

Ganzheitliche Architektur-Wahrnehmung

Münchner Bauten – ihr Körper, ihre Seele, ihr Geist

Das Buch eröffnet Möglichkeiten sich Bauten ganz neu zu nähern, um zu erfahren, was bewirkt, dass ich mich symphatisch oder antiphatisch, ja, gleichgültig und uninteressiert gegenüber einem Bauwerk verhalte. Herr Meighörner bemüht sich im ersten Teil dieses Buches den Interessierten aufzuschließen für Beurteilungskriterien, die jedem helfen können, sich einem Gebäudecharakter zu nähern. Er legt die Grundlagen, auf denen dann im zweiten Bildteil auf bestimmte Bauten im Münchner Raum die Beurteilung von Herrn Hengstenberg und Herrn Rasmus erfolgt. Diese Beurteilung ist natürlich keine bindende, sonder soll jeden dazu auffordern, diesen Gang durch München und Umgebung anzutreten, um nun selbst nach den sehr hilfreichen Beurteilungskriterien eine Zuordnung zu treffen. Die Bauten sind in 8 Gruppen gegliedert und nach den Gesichtpunkten von Körper, Seele und Geist beschrieben und dann im Bereich des Doppeldreiecks klassifiziert. Ein weiteres Doppeldreieck daneben ist für die Beurteilung des Lesers vorgesehen. Die Blätter lassen auch viel Raum, um Vermerke einzutragen. Die Abbildungen sind bewusst so klein gewählt, um den Leser zu informieren, ihm aber keine richtige Handhabe für eine sinnvolle Beurteilung zu geben. Man sollte hier auch eher von einer Charakterisierung als von einer Beurteilung sprechen. Eine ungeheuere Arbeit steckt in dem kleinen Buch. Es entstand durch Erfahrungen von Gerhard Meighörner bei Stadtführungen durch München und sollte einem wirklichen Bedürfnis vieler entsprechen. Die Tendenz von Claus Rasmus war es, Kriterien auch für eine organische Architektur aufzunehmen, was jedoch eine Zukunftsaufgabe bleibt. Eine Fortsetzung in dieser Richtung wäre sicherlich ein Gewinn. Wilhelm Oberhuber

Quelle: 

STIL, Goetheanismus in Kunst und Wissenschaft, Michaeli 2010/2011, Heft 3, Seite54

Robert Jüpner, Uwe Müller (Hrsg.)

Tagungsband zur 2. Veranstaltung des Forums der EU-HWRM-RL am 17. Juni 2010 in Kaiserslautern

Die Europäische Hochwasserrisikomanagement-Richtlinie strebt einen einheitlichen europäisch abgestimmten Umgang mit den negativen Auswirkungen von Hochwasserereignissen an. Sie formuliert ehrgeizige Ziele bezüglich der Bewertung von Hochwasserrisiken, der Aufstellung von Hochwassergefahren- und Hochwasserrisikoarten und der Aufstellung von Hochwasserrisikomanagementplänen. In Deutschland wird derzeit - wie in anderen Staaten der Europäischen Union auch - intensiv über die Umsetzung der Europäischen Hochwasserrisikomanagement- Richtlinie diskutiert. Neben der verfahrensrechtlichen Umsetzung steht dabei vor allem die inhaltliche Ausgestaltung der Richtlinie im Vordergrund. Das zweite Forum zur EU-Hochwasserrisikomanagement-Richtlinie fand am 17. Juni 2010 in Kaiserslautern statt. Die dort gehaltenen Vorträge wurden nun in einem Tagungsband zusammengefasst und veröffentlicht.

Quelle: 

Korrespondenz Wasserwirtschaft: Heft 11/10, Seite 625; Korrespondenz Abwasser, Abfall: Heft 11/10, Seite 1159

Jörg Dalhöfer

Komplexitätsbewertung indirekter Geschäftsprozesse

Komplexität im Griff. Die wachsende Komplexität der Produktprogramme hat zu einem Wandel der Kostenstrukturen entlang der Wertschöpfungskette produzierender Unternehmen geführt. Betroffen hiervon sind auch die indirekten Geschäftsprozesse. Diese administrativen Abläufe begleiten und unterstützen die direkte Leistungserstellung der Produktionssysteme und sorgen dafür, dass Geschäftsprozesse der primären Wertschöpfung überhaupt ablaufen können. Auch im administrativen Bereich ist der komplexitätsbezogene Anteil der Kosten überproportional gestiegen. Der Autor entwickelt eine Lösung zur Bewertung der Komplexität indirekter Geschäftsprozesse. Dabei steht die auftragsbezogene Kleinserien- und Einzelproduktion variantenreicher Produkte im Mittelpunkt. Mithilfe der Methode können Entscheider qualitativ abschätzen, ob Modifikationen in Produktions- und Logistikbereichen deren Komplexitätskosten positiv oder negativ verändern. So lassen sich Geschäftsprozesse gestalten.

Quelle: 

Qualität und Zuverlässigkeit, Heft 10/2010, Seite 13

Holger Schüttrumpf

39. IWASA Internationales Wasserbau-Symposium Aachen 2009

Wasserwirtschaft und Klimawandel – Fakten, Folgen, Aufgaben

Der Band 157 der Aachener Wasserbau-Mitteilungen gibt die Beiträge des alljährlichen Symposiums wieder. In diesem Fall lag der Themenschwerpunkt auf den möglichen Auswirkungen des Klimawandels auf die unterschiedlichen Bereiche der Wasserwirtschaft vom Küstenschutz über den Hochwasserschutz bis hin zur Binnenschifffahrt, der von den Referenten aus unterschiedlichen Blickwinkeln beleuchtet wurde.

Quelle: 

Zeitschrift WasserWirtschaft, Heft 10/2010, Seite 41