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Abstract Conventional generation units are subject to a changing economic environment and have to adjust their role for modern society's power generation. With substantial amounts of renewable energy production encountering the markets, thermal power plants are facing an increased need for flexible operation and decreasing revenues from selling electricity. Technical adaptations are necessary, though have to be redeemed within very short time spans to secure the plant's profitability. Dynamic simulation in this context serves as a helping tool to evaluate technical improvements and is an established tool in industry as well as in research institutes. This paper focuses on the detailed modelling of a hard coal-fired power plant using the thermohydraulic simulation code Apros. Characteristic of this model is the implementation of the major part of the control system together with the physical model. The comprehensive model enables detailed dynamic simulations with very small error values to process data, as to be seen in the validation. As an application example, the extension of a qualified load jump for secondary control power is realised. The dynamic simulation is thereby used to clarify necessary modifications in the control system and to assess the implications on plant operation.

Abstract Feeding solid oxide fuel cells (SOFCs) with gas from biomass gasification is promising with regard to highly efficient power generation. But it is also intricate since biogenic contaminants are harmful to state-of-the-art anode materials. In this work the influence of phenol as a biogenic model contaminant on the performance of single solid oxide fuel cells was studied under realistic conditions. For this purpose Ni/YSZ anode supported cells were operated with simulated bio-syngas, applying an electrical load of 0.34 A/cm2. Over a duration of several hundreds of hours phenol was periodically added to the fuel gas. The tests showed that for the lowest concentration of phenol no accelerated degradation could be observed regarding cell potential and electrical impedance measurements, but disintegration of the Ni/YSZ support took place. Metal dusting of the anode support was found to be the most important mechanism of degradation.

Models for the analysis of thermoacoustic instabilities are conveniently formulated in the frequency domain. In this case one often faces the difficulty that the response behavior of some elements of the system is only known at real-valued frequencies, although the transfer behavior at complex-valued frequencies is required for the quantification of the growth rates of instabilities. The present paper discusses various methods for extrapolation of frequency response data at real-valued frequencies into the complex plane. Some methods have been used previously in thermoacoustic stability analysis, others are newly proposed. First the pertinent mathematical background is reviewed, then the sensitivity of predicted growth rates on the extrapolation scheme is explored. This is done by applying different methods to a simple thermoacoustic system, i.e. a ducted premixed flame, for which an analytical solution is known. A short analysis determining the region of confidence of the extrapolated transfer function is carried out to link the present study to practical applications. The present study can be seen as a practical guideline for using frequency response data collected for a set of real-valued frequencies in quantitative linear stability analysis.

The transition in the energy market and the growing share of renewable energy sources have been boosting the research in new power cycles. For example, the concept of batch evaporation in the Misselhorn Cycle promises to increase the overall efficiency in low-temperature applications and therefore saves resources. In this paper, a dynamic evaporator model was extended in order to prove the feasibility of the Misselhorn Cycle despite its transient character. In this context, the thermal capacity of the wall material as well as the residence time of the heat source medium were added. The previous, underlying model predicted an improved system efficiency for the Misselhorn Cycle of about 50% compared to an Organic Rankine Cycle (ORC) at 100+C. Initially, the results of the extended model showed a negative influence of the inertial effects on the possible net power output (advantage over ORC only 10%). However, an unheated discharge phase and reduced dimensions of the heat exchanger could compensate these drawbacks and achieved results (about 40% better than ORC) in the same range as the previous, simple model predicted. These findings prove the general practical feasibility of the Misselhorn Cycle.The transition in the energy market and the growing share of renewable energy sources have been boosting the research in new power cycles. For example, the concept of batch evaporation in the Misselhorn Cycle promises to increase the overall efficiency in low-temperature applications and therefore saves resources. In this paper, a dynamic evaporator model was extended in order to prove the feasibility of the Misselhorn Cycle despite its transient character. In this context, the thermal capacity of the wall material as well as the residence time of the heat source medium were added. The previous, underlying model predicted an improved system efficiency for the Misselhorn Cycle of about 50% compared to an Organic Rankine Cycle (ORC) at 100+C. Initially, the results of the extended model showed a negative influence of the inertial effects on the possible net power output (advantage over ORC only 10%). However, an unheated discharge phase and reduced dimensions of the heat exchanger could compensate these drawbacks and achieved results (about 40% better than ORC) in the same range as the previous, simple model predicted. These findings prove the general practical feasibility of the Misselhorn Cycle.

Thermochemical energy storage (TCES) represents one of the most promising energy storage technologies, currently investigated. It uses the heat of reaction of reversible reaction systems and stands out due to the high energy density of its storage materials combined with the possibility of long-term storage with little to no heat losses. Gas–solid reactions, in particular the reaction systems CaCO3/CaO, CaO/Ca(OH)2 and MgO/Mg(OH)2 are of key interest in current research. Until now, fixed bed reactors are the state of the art for TCES systems. However, fluidized bed reactors offer significant advantages for scale-up of the system: the improved heat and mass transfer allows for higher charging/discharging power, whereas the favorable, continuous operation mode enables a decoupling of storage power and capacity. Even though gas–solid fluidized beds are being deployed for wide range of industrial operations, the fluidization of cohesive materials, such as the aforementioned metal oxides/hydroxides, still represents a sparsely investigated field. The consequent lack of knowledge of physical, chemical, and technical parameters of the processes on hand is currently a hindering aspect for a proper design and scale-up of fluidized bed reactors for MW applications of TCES. Therefore, the experimental research at Technical University of Munich (TUM) focuses on a comprehensive approach to address this problem. Preliminary experimental work has been carried out on a fixed bed reactor to cover the topic of chemical cycle stability of storage materials. In order to investigate the fluidization behavior of the bulk material, a fluidized bed cold model containing a heat flux probe and operating at atmospheric conditions has been deployed. The experimental results have identified the heat input and output as the most influential aspect for both the operation and a possible scale-up of such a TCES system. The decisive parameter for the heat input and output is the heat transfer coefficient between immersed heat exchangers and the fluidized bed. This coefficient strongly depends on the quality of fluidization, which in turn is directly related to the geometry of the gas distributor plate. At TUM, a state-of-the-art pilot fluidized bed reactor is being commissioned to further investigate the aforementioned aspects. This reactor possesses an overall volume of 100 L with the expanded bed volume taking up 30 L. Two radiation furnaces (64 kW) are used to heat the reactor. The heat of reaction of the exothermal hydration reaction is removed by water, evaporating in a cooling coil, immersed in the fluidized bed. Fluidization is being achieved with a mixture of steam and nitrogen at operating temperatures of up to 700 °C and operating pressures between −1 and 6 bar(g). The particle size is in the range of d50 = 20 μm. While initial experiments on this reactor focus on optimal operating and material parameters, the long-term goal is to establish correlations for model design and scale-up purposes.

Heat transfer to supercritical water in heated tubes and channels is relevant for steam generators in conventional power plants and future concepts for supercritical nuclear and solar-thermal power plants. A new experimental facility, the high pressure evaporation rig, setup at the Institute for Energy Systems (Technische Universität München) aims to provide heat transfer data to fill the existing knowledge gaps at these conditions. The test rig consists of a closed-loop high pressure cycle, in which de-ionized water is fed to an instrumented test section heated by the application of direct electrical current. It is designed to withstand a maximum pressure of 380 bar at 580 °C in the test section. The maximum power rating of the system is 1 MW. The test section is a vertical tube (material: AISI A213/P91) with a 7000 mm heated length, a 15.7 mm internal diameter, and a wall thickness of 5.6 mm. It is equipped with 70 thermocouples distributed evenly along its length. It enables the determination of heat transfer coefficients in the supercritical region at various steady-state or transient conditions. In a first series of tests, experiments are conducted to investigate normal and deteriorated heat transfer (DHT) under vertical upward flow conditions. The newly generated data and literature data are used to evaluate different correlations available for modeling heat transfer coefficients at supercritical pressures.

Abstract Water electrolysis has the potential to become a key element in coupling the electricity, mobility, heating and chemical sector via Power-to-Liquids (PtL) or Power-to-Gas (PtG) in a future sustainable energy system. Based on an extensive market survey, discussions with manufacturers, project reports and literature, an overview of the current status of alkaline, PEM and solid oxide electrolysis on the way to large-scale flexible energy storage is presented. These main water electrolysis technologies were compared in terms of available capacity, nominal and part-load performance, flexibility (load range, load gradients, start-up time, stand-by losses) lifetime and investment costs. This review provides a basis of the parameters required and the necessary understanding of electrolysis fundamentals and technologies for a techno-economic analysis of water electrolysis-based concepts and an evaluation of PtG and PtL in energy system studies.

The objective of this study is to present a neural observer that estimates changing injection behavior due to wear and aging effects within the nozzle of a common rail diesel injector. Using a dynamic identification system in combination with a modified learning rule, the neural observer is applicable to a wide range of problem sets. A multilayer perceptron (MLP) network with three layers and few neurons in the hidden layer ensures fast computing and high efficiency; network learning is based on quasi-Newton optimization and an additional line search algorithm. Modeling the bottom part of the injector introduces a simulation model, which is validated with experimental data from a solenoid common rail diesel injector. Estimation results conform well with the altered plant and therefore demonstrate the significant benefit of using the proposed neural network observer concept.