Wladimir Linzer

Flow reversal in natural circulation systems

Boiling flow in natural circulation systems can be susceptible to thermohydrodynamic instabilities which can be the cause of mechanical damage. This paper presents an analysis of a circulation system where two unequal heated riser circuits are connected to a common downcomer. It can be shown that for such systems a critical heat absorption ratio exists which is dependent on the geometry and the overall heating conditions. Based on computer simulations, the static and dynamic behaviour of the riser systems with emphasis on the lower heat absorption circuit is discussed. Criteria to avoid flow reversal are presented.

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.

Flow Stability of Heat Recovery Steam Generators

This paper presents the results of theoretical flow stability analyses of two different types of natural circulation heat recovery steam generators (HRSG)-a two-drum steam generator-and a HRSG with a horizontal tube bank. The investigation shows the influence of the boiler geometry on the flow stability of the steam generators. For the two-drum boiler, the steady-state instability, namely, a reversed flow, is analyzed. Initial results of the investigation for the HRSG with a horizontal tube bank are also presented. In this case, the dynamic flow instability of density wave oscillations is analyzed.

Flow Reversal in a Horizontal Type Natural Circulation Heat Recovery Steam Generator

Natural circulation heat recovery steam generators (HRSG) are used in many applications for the thermal recycling of the waste flue gas. Many of these boilers are designed as a horizontal type HRSG (see fig. 1). The evaporator of such a steam generator is characterized by an array of parallel tubes with different heat input. The paper presents the results of a theoretical stability analysis for a HRSG with a vertical tube bank. For the horizontal type HRSG the static instability, namely the reverse flow was analysed. The study was done at low system pressures and under hot start-up conditions for the boiler. The investigations show the influence of the geometry, the system pressure and the heat absorption of the individual tubes in the evaporator on the stability of the boiler. The aim of the study was to find design criteria to avoid reverse flow in the tubes of the evaporator. Addition of flow resistance at certain locations of the evaporator can improve the stability. A higher stability will be also achieved by the homogenization of the heat absorption in the individual layers of the bundle heating surface.Copyright

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.

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.

Density Wave Oscillation in a Vertical Type Natural Circulation Heat Recovery Steam Generator: A Numerical Study

The dynamic flow instability, namely density wave oscillation (DWO), was investigated theoretically. The analysis was done for different design configurations of the evaporator of a vertical type natural circulation heat recovery steam generator (HRSG) at low operation pressure under hot start-up conditions. The study was done for co-current and counter flow designs of the HRSG evaporator, different drum heights and different heat flux distributions over the heating surface of the evaporator. The investigations for the HRSG show that the heat flux distribution to the evaporator tubes has an important influence on the flow stability. The simulation results indicate that a lower amplitude of the mass flow oscillation of the working medium is given by a more uniform heat flux to the single tubes of the evaporator. This leads the two-phase flow system to a more stable condition. This study has also shown that changes in the drum height of the boiler have no significant influence on the oscillation amplitude of the DWO. The simulation results have shown that the counter flow design is much more stable under the investigated conditions compared to the co-current design.Copyright

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