Bernd Epple

Chemical-Looping Combustion of Hard Coal: Autothermal Operation of a 1 MWth Pilot Plant

Chemical-looping combustion (CLC) is an emerging carbon capture technology that is characterized by a low energy penalty, low carbon dioxide capture costs, and low environmental impact. To prevent the contact between fuel and air, an oxygen carrier is used to transport the oxygen needed for fuel conversion. In comparison to a classic oxyfuel process, no air separation unit is required to provide the oxygen needed to burn the fuel. The solid fuel, such as coal, is gasified in the fuel reactor (FR), and the products from gasification are oxidized by the oxygen carrier. There are promising results from the electrically heated 100 kWth unit at Chalmers University of Technology (Sweden) or the 1 MWth pilot at Technische Universitat Darmstadt (Germany) with partial chemical-looping conditions. The 1 MWth CLC pilot consists of two interconnected circulating fluidized bed reactors. It is possible to investigate this process without electrically heating due to refractory-lined reactors and coupling elements. This work presents the first results of autothermal operation of a metal oxide CLC unit worldwide using ilmenite as oxygen carrier and coarse hard coal as fuel. The FR was fluidized with steam. The results show that the oxygen demand of the FR required for a complete conversion of unconverted gases was in the range of 25%. At the same time, the carbon dioxide capture efficiency was low in the present configuration of the 1 MWth pilot. This means that unconverted char left the FR and burned in the air reactor (AR). The reason for this is that no carbon stripper unit was used during these investigations. A carbon stripper could significantly enhance the carbon dioxide capture efficiency.

Simulation von Kraftwerken und Feuerungen

Dieses Lehrbuch beinhaltet neben den Grundlagen der Stromungssimulation auch die Modellbildung von Komponenten und Gesamtanlagen der Kraftwerkstechnik. Die Grundgleichungen fur den Warme- und Stoffaustausch werden fur die Anwendung in der numerischen Simulation aufbereitet. Ausgewahlte numerische Methoden werden ausfuhrlich diskutiert. Inhalt des Buches ist die Simulation von Feuerungen und Gasstromungen als auch die der Wasser/Dampfstromung. Regelung und Steuerung, vereinfachte Modelle und Hybridmodelle sowie die Validierung von Messwerten werden ebenfalls behandelt. Zahlreiche ausgearbeitet Beispiele und Illustrationen sollen dem Leser das Verstandnis der Zusammenhange von Theorie und Praxis erleichtern. Einfache Plausibilitatskontrollen sollen dem Studierenden zeigen, wie er seine numerischen Ergebnisse einer ersten Uberprufung unterziehen kann. In der 2., korrigierten und erweiterten Auflage wird die noch relativ neue Discrete Element Method in Theorie und Praxis aufgenommen. Einzelne Kapitel wurden erganzt, wie zum Beispiel die Simulation und das Monitoring von Speisewasserpumpen. Das Lehrbuch wendet sich an Studierende und Forscher sowie an in der Industrie tatige Praktiker, die hier Anregungen fur ihre berufliche Tatigkeit finden konnen.

Technical and Economical Assessment of the Indirectly Heated Carbonate Looping Process

Carbonate looping promises low energy penalties for postcombustion CO2-capture and is particularly suited for retrofitting existing power plants. To further improve the process, a new concept with an indirectly heated calciner using heat pipes was developed, offering even higher plant efficiencies and lower CO2 avoidance costs than the oxy-fired standard carbonate looping process. The concept of the indirectly heated carbonate looping (IHCL) process was tested at sufficient scale in a 300 kWth pilot plant at Technische Universitat Darmstadt. The paper presents a technical overview of the process and shows first test results of the pilot plant. Furthermore, the concept is economically evaluated and compared to other carbon capture processes.

Validation of a Detailed Reaction Mechanism for Sulfur Species in Coal Combustion

The understanding of the kinetics leading to the formation of gaseous sulfur species is of great importance because of their corrosive nature in coal-fired energy systems. In this study, reaction kinetics of important gaseous sulfur species in coal combustion are investigated using a detailed reaction mechanism with 10 sulfur species and 49 sulfur-related elementary reactions in combination with GRI-Mech 2.11 for hydrocarbon related reactions and a global two-step reaction mechanism for coal devolatilization and char oxidation. The reaction mechanism was applied to numerical simulations of an entrained-flow reactor, where lignite was burned with varying air ratio. The results of numerical simulations showed that H2S released during devolatilization is fast oxidized and is formed again under reducing conditions as coal conversion proceeds. Calculated concentrations of CO2, CO, and H2S show very good agreement with experimental data. SO2 concentrations under sub-stoichiometric conditions are overpredicted, most likely because not all sulfur is released or because part of the sulfur is bound by minerals in the fly ash in the experiments, which is not taken into account by the simulations.

Numerical Simulation of Power Plants and Firing Systems

The book comprises the fundamentals of the numerical simulation of fluid flows as well as the modelling of a power plant and plant components. The fundamental equations for heat and mass transfer will be prepared for the application in the numerical simulation. Selected numerical methods will be discussed in detail. The book will deal with the gas as well as with the water/steam flow. Regulation and controller, simplified models and hybrid models as well as the validation of measurement data are also included in the book.

Checking Results, Accuracy, and Assessment

In the final chapter of this book, we have put together a few suggestions and thoughts regarding the issue of checking results, accuracy, and assessment.

Simulation of Firing and Gas Flow

Gaseous, liquid, and solid fuels are generally (and understandably) burned in very different furnaces—but there are of course furnaces that can be fueled with gaseous, liquid, and solid fuels.

Conversion and Transport of Mass, Energy, Momentum, and Materials

Before we go into the mathematical description of the balance equations for the conservation of mass, energy and momentum in more detail, a brief explanation concerning three types of time derivatives is given by way of introduction. A simple example is used, namely, the problem of determining the concentration of fish in a river (Bird et al. 2002). Clear descriptions of balance equations can be found in (Muller 2001), (Bird et al. 2002), (Baehr and Stephan 2008) and in many others.

Ergebniskontrolle, Genauigkeit und Auswertung

Im abschliesenden Kapitel dieses Buches sollen noch einige Anregungen und Gedanken zur Problematik der Ergebniskontrolle, Genauigkeit und Auswertung gemacht werden.

Simulation der Feuerung und Gasströmung

Gasformige, flussige und feste Brennstoffe werden verstandlicherweise i. Allg. in sehr unterschiedlichen Feuerungen verbrannt. Naturlich gibt es auch Feuerungen, die sowohl mit gasformigen als auch mit flussigen und festen Brennstoffen befeuert werden konnen.