Karl Ponweiser

Dynamic simulation of a solar power plant steam generation system

Abstract An innovative steam generation system for a solar power plant has been designed in Germany by Balcke-Duerr. In order to assist its construction, a dynamic simulation of the thermal oil heated boiler has been developed by the Vienna University of Technology. Aim of this work is to assess how critical is the boiler behavior for the plant operation during a start-up phase, and especially to check if the natural water circulation starts correctly. After a description of the heat exchanger design, the different stages of the simulation build-up with the software APROS are described. As a result of the model validation, the improvement of the model discretization is outlined along with the calibration of the heat transfer coefficients. Further on, the observation of relevant parameters of the system (water circulation rate, steam mass fraction and critical heat flux) during the simulated start-up, allow characterizing the boiler. Thus, the natural circulation start can be described with a good fidelity. Findings about the economizer behavior and the occurrence of boiling crisis are also exposed. Eventually, a design optimization can be carried out through the applied method.

Interdisciplinary Strategies for Simulation-Based Optimization of Energy Efficiency in Production Facilities

This paper presents an approach for interdisciplinary optimization of energy efficiency in production plants. Domain-specific areas of action are discussed as well as the integration into a dynamic co-simulation that helps predicting the impact and financial benefit of selected energy saving measures by comparing and quantifying different scenarios. This should help giving incentives and creating impulses for strategic investment decisions. In a comprehensive methodological approach, optimization potential of both the production process itself as well as the production infrastructure is combined. The technical implementation involves several simulation environments and a framework for synchronization and data exchange in terms of co-simulation. The paper concludes with a discussion of some exemplary simulation results.

Assessment of Catalysts for Hydrogen-Peroxide-Based Thrusters in a Flow Reactor

Hydrogen peroxide is a candidate propellant for rocket-propulsion applications with the potential to replace highly toxic propellants currently used. Decomposition of hydrogen peroxide yields a high-temperature oxygen-steam mixture, which can be used as monopropellant or as oxidizer in a bipropellant configuration. This work examines different types of cellular ceramic-based catalysts for hydrogen-peroxide decomposition at miniature scale of nominal mass flows of 0.3  g s−1. An exhaustive investigation of different catalysts in a flow reactor configuration similar to a propulsion application is conducted. The test matrix includes honeycomb monoliths with different channel geometries, densities, lengths, different carrier materials, and wash-coating procedures, as well as different types of catalysts such as pellets and foams. Thirty nine catalyst configurations with a total of 121 catalysts have been experimentally investigated based on their transient and stationary performance at design mass-flow levels...

Hydrogen Peroxide Decomposition for Micro Propulsion: Simulation and Experimental Verification

Hydrogen peroxide is under investigation with regard to its potential to replace the presently used highly toxic oxidizers such as NTO or MON-3. Catalytically decomposed hydrogen peroxide results in a steam-oxygen mixture at elevated temperature and can be used either as a monopropellant or as an oxidizer in a bipropellant system. In order to achieve high decomposition efficiencies it is essential to understand and to be able to control the decomposition processes in detail. In particular, the choice of catalyst is one of the most essential issue in designing a propulsion system based on hydrogen peroxide. However a catalyst is defined by a multidimensional parameter matrix including the catalyst nature, diameter, length, inner and outer shape, heat capacity and conductivity of the carrier material, and, manufacturing method and many others. Reliable experimental investigation of a catalyst is a time consuming effort. To guide the experimental assessment, Fotec (formerly Austrian Institute of Technology – AIT) has developed an analytical model of the decomposition implemented into a numerical thermal model. The one dimensional decomposition model coupled to a finite element structural domain of the decomposition chamber is used to investigate the impact of the catalyst and, in addition, of the chamber structure on the decomposition behavior. Special focus is laid on the transitional behavior of hydrogen peroxide conversion to facilitate immediate start-up of the thruster system. The numerical results have been validated with experimental values. The comparison shows high accuracy of the predictions not only in the general decomposition behavior but also in intrinsic details such as the transitional behavior. Major findings of the model such as the existence of a radial temperature gradient across the catalyst have been experimentally validated. These findings point to an overestimation of experimentally determined decomposition performances, in the case of temperature measurements just downstream of the catalysts cental line. Another major finding is the identification of an mass flow overload threshold by the simulation, yielding a sudden decrease in decomposition performance after surpassing the threshold. This sudden decrease in decomposition performance has been experimentally verified.

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.

Optimization of Load Flows in Urban Hybrid Networks

A sustainable supply of energy in urban regions requires an adequate infrastructure and operation. At present, the different energy sources (i.e., electricity, gas, district heating) are used separately without any connection to each other. To increase the flexibility of energy supply, the usage of energy hubs is a possible way. Energy hubs are connection points between the energy sources that comprise the key elements of so-called hybrid networks. Using the energy/hub approach, surpluses and power shortages from a specific energy network can be avoided. The hubs offer various technologies of energy conversion and can include electrical and thermal storage. Thus it is possible to convert electrical into thermal energy (heat pump, electric heating), chemical (gas) into thermal (furnace), or electrical energy (micro gas turbine) into, respectively, thermal and electrical energy (combined heat and power) depending on the used technology. The correct operating strategy for these energy hubs is an essential factor in order to minimize CO2 emissions of urban energy systems. Therefore, a simulation model was developed in MATLAB®. The minimization of CO2 emissions is based on a mixed-integer linear optimization of the overall system, consisting of the supplying infrastructure, energy hubs, and thermal/electric loads. First results have been obtained by a case study for an urban region supplied by three different energy carriers (gas, electricity, and district heating).

Dampferzeugersimulation — Simulation der Wasser- und Dampfstrümung

Im Dampferzeugerbau unterscheidet man in Abhangigkeit vom eingesetzten Brennstoff zwischen so genannten konventionellen Anlagen, welche mit fossilen Brennstoffen wie Erdol, Erdgas oder Kohle betrieben werden, und nuklearen Anlagen, bei denen Kernbrennstoffe wie z.B. 235U zur Anwendung kommen. In der nachfolgenden Zusammenfassung der Dampferzeugersysteme wird jedoch nur auf die mit fossilen Brennstoffen befeuerten Anlagen naher eingegangen. Eine kurze Ubersicht zu den Grundzugen zur Reaktortheorie und der Kern- spaltung sowie zum Aufbau von Kernreaktoren geben u.a. (Thomas 1975), (Ziegler 1983), (Ziegler 1984), (Ziegler 1985) oder (Straus 1992).

Umwandlung und Transport von Energie, Impuls und Stoffen

Bevor auf die mathematische Beschreibung der Bilanzgleichungen zur Erhaltung tung von Masse, Energie und Impuls naher eingegangen wird, soll einleitend noch eine kurze Erlauterung hinsichtlich dreier Arten der Ableitungen nach der Zeit angegeben werden. Dies soll anhand eines einfachen Beispiels, namlich des Problems, die Konzentration der Fische in einem Fluss anzugeben, erortert werden (Bird 2002). Ubersichtliche Darstellungen der Bilanzgleichungen finden sich neben (Bird 2002) auch in (Baehr 2008), (Muller 2001) und vielen anderen.

Konzentrierende Solartechnik für Kraft-, Wärme- und Kältekopplung

SummaryDue to Kyoto targets and rising energy prices solar energy is one of the renewable energy sources which encounter high growth rates. Currently, several new power plants of concentrated solar power (CSP) technology are under construction in Spain, the USA and North of Africa. The possible use of CSP technology for combined heat-power-cooling supply has also emerged especially in Mediterranean countries to satisfy the need of energy for air conditioning, space heating and domestic hot water with additional possibility of generating electricity with proper plant configurations. This article presents possible technologies and plant configurations for combined heat-power-cooling supply and gives a technical overview of the most important components.ZusammenfassungDie Solartechnik nimmt infolge der CO2-Problematik und gestiegener Energiekosten aktuell einen starken Aufschwung. Zurzeit findet in Spanien, den USA und auch Nordafrika eine neue Errichtungswelle an Solarkraftwerken statt. Aber nicht nur die zentrale, sondern auch die dezentrale Energieversorgung durch konzentrierende Solarenergiesysteme erfreut sich vor allem in den mediterranen Ländern steigender Beliebtheit. Durch geeignete Anlagenkonfiguration kann der Kältebedarf für Klimatisierungsaufgaben, der Wärmebedarf und zu einem gewissen Teil auch die Erzeugung elektrischer Energie in solchen dezentralen Anlagen gedeckt werden. Der Artikel gibt einen Überblick über mögliche Anlagenkonfigurationen auf Basis der Prozesse ORC, Kalina, Absorptionskälte, Stirling und CPV/T.

Dynamic Behaviour of a Vertical Natural Circulation Two Pressure Stage HRSG Behind a Heavy Duty Gas Turbine

Modern combined cycle gas turbines are highly flexible in their operation, concerning start up, load change and shut down. Heat Recovery Steam Generators (HRSG) arranged downstream of the Gas Turbine (GT) are forced to operate in such a way, that the gas turbine operation is not restricted by them. Therefore, they should be designed for a high cycling capability with typical values in the range of 200 to 250 cold starts, 1000 warm and 2500 hot starts for their typical 25 year life span. Cold starts are defined as a standstill period of over 120 hours, warm starts to a weekend shutdown and hot starts to an overnight shut down.AE Energietechnik GmbH (AE), a Babcock Borsig Power company has specialized in designing, erecting and commissioning vertical natural circulation multiple pressure stage HRSGs. The vertical design combines simplicity and low investment costs with performance reliability and high availability. In order to forecast the dynamic behaviour of such a HRSG, AE has supported the development of a dynamic simulation code at the Institute of Thermal Engineering (ITW) located at the Vienna University of Technology. This finite volume code enables the prediction of velocities, pressures and temperatures for several dynamic processes of the HRSG.In the present paper computational results of starts and load changes will be presented for a vertical natural circulation HRSG. Furthermore, several design optimization changes which where made in order to increase operational reliability and availability will be demonstrated. Finally, practical applications of already constructed HRSG will be discussed and conclusions will be drawn.© 2000 ASME