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

2006 ◽  
Author(s):  
Heimo Walter ◽  
Wladimir Linzer
Keyword(s):  
Steam Generator ◽  
Heat Recovery ◽  
Reverse Flow ◽  
Natural Circulation ◽  
Heating Surface ◽  
Heat Absorption ◽  
System Pressure ◽  
Horizontal Type ◽  
The Stability ◽  
The Individual

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.

Flow Stability of Heat Recovery Steam Generators

2004 ◽  
Author(s):  
Heimo Walter ◽  
Wladimir Linzer
Keyword(s):  
Heat Recovery ◽  
Flow Instability ◽  
Reverse Flow ◽  
Natural Circulation ◽  
Density Wave ◽  
Horizontal Tube ◽  
Steam Generators ◽  
Tube Bank ◽  
First Results ◽  
The Stability

In this paper the results of a theoretical stability analysis are presented. The investigation was done for 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 stability of the steam generators. For the two-drum boiler the static instability, namely the reverse flow is analysed. First results of the investigations for the HRSG with a horizontal tube bank are also presented. In this case the dynamic flow instability of density wave oscillations is analysed.

scholarly journals Gas Turbine Heat Recovery Steam Generators for Combined Cycles Natural or Forced Circulation Considerations

1988 ◽  
Author(s):  
Akber Pasha
Keyword(s):  
Gas Turbine ◽  
Steam Generator ◽  
Heat Recovery ◽  
Power Plants ◽  
Natural Circulation ◽  
Combined Cycle ◽  
Heat Recovery Steam Generator ◽  
Steam Generators ◽  
Forced Circulation ◽  
Gas Turbine Exhaust

In recent years the combined cycle has become a very attractive power plant arrangement because of its high cycle efficiency, short order-to-on-line time and flexibility in the sizing when compared to conventional steam power plants. However, optimization of the cycle and selection of combined cycle equipment has become more complex because the three major components, Gas Turbine, Heat Recovery Steam Generator and Steam Turbine, are often designed and built by different manufacturers. Heat Recovery Steam Generators are classified into two major categories — 1) Natural Circulation and 2) Forced Circulation. Both circulation designs have certain advantages, disadvantages and limitations. This paper analyzes various factors including; availability, start-up, gas turbine exhaust conditions, reliability, space requirements, etc., which are affected by the type of circulation and which in turn affect the design, price and performance of the Heat Recovery Steam Generator. Modern trends around the world are discussed and conclusions are drawn as to the best type of circulation for a Heat Recovery Steam Generator for combined cycle application.

scholarly journals Russian and foreign steam generators for NPP power units with wet steam turbines

2020 ◽  
Vol 178 ◽  
pp. 01007
Author(s):  
Mikle Egorov ◽  
Ivan Kasatkin ◽  
Ivan Kovalenko ◽  
Irina Krectunova ◽  
Nataliya Lavrovskaya ◽  
...  
Keyword(s):  
Steam Generator ◽  
Nuclear Power ◽  
Temperature Drop ◽  
Heating Surface ◽  
Vessel Diameter ◽  
Absorption Efficiency ◽  
Steam Turbines ◽  
Steam Generators ◽  
Horizontal Type ◽  
Generator Design

The main aim of the current study is to analyze advantages and shortcomings of horizontal and vertical types of steam generator design. Design solutions and experience of operation of steam generators of horizontal type accepted in Russia and of vertical type applied by Westinghouse, Combustion Engineering, Siemens, Mitsubishi, Doosan were analyzed within the framework of the present study. It was established that steam generator equipment of horizontal type is characterized by disadvantages of design, technological and operational nature. Thus, horizontal steam generators with dimensions permissible for railroad transportation and, for VVER-1200 with reactor vessel diameter equal to 5 m, by water transport as well, have exhausted the possibilities for further significant increase of the per unit electric power. The demonstrated advantages of vertical-type steam generators are as follows: 1) absence of stagnant zones within the second cooling circuit; 2) uniformity of heat absorption efficiency of the heating surface that ensures improved conditions for moisture separation; 3) increased temperature drop with parameters of generated steam elevated by 0.3 – 0.4 MPa. Conclusion was made on the advisability of introduction of steam generators with vertical-type layout in the Russian nuclear power generation.

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

2008 ◽  
Author(s):  
Heimo Walter ◽  
Wladimir Linzer
Keyword(s):  
Heat Flux ◽  
Steam Generator ◽  
Heat Recovery ◽  
Natural Circulation ◽  
Density Wave ◽  
Heat Recovery Steam Generator ◽  
Counter Flow ◽  
Wave Oscillation ◽  
Lower Amplitude ◽  
Simulation Results

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.

scholarly journals Effect of Saturated Steam Carried Downward on the Flow Properties in the Downcomer of Steam Generator

Energies ◽  
2019 ◽  
Vol 12 (19) ◽  
pp. 3650 ◽  
Author(s):  
Yan Liu ◽  
Hui-lie Shi ◽  
Chun Gui ◽  
Xian-yuan Wang ◽  
Rui-feng Tian
Keyword(s):  
Steam Generator ◽  
Water Cycle ◽  
Natural Circulation ◽  
Heat Extraction ◽  
Saturated Steam ◽  
Flow Properties ◽  
Steam Quality ◽  
Pressurize Water Reactor ◽  
The Stability ◽  
Reactor Operating

The saturated water separated by the steam separator in a natural circulation steam generator may carry a small amount of saturated steam into the downcomer. The steam contacts subcooled water and condenses directly in the downcomer causing the variations in the pressure and steam quality and likely affecting the stability of the water cycle in the secondary loop. It is not conducive to core heat extraction and thus affects nuclear safety. The mathematical model of the downcomer was established in this study based on the internal structures of a natural circulation steam generator. The volume-of-fluid (VOF) and large-eddy-simulation (LES) models were used for analysis on FLUENT software (ANSYS, Pittsburgh, PA. USA) platform. The influence of direct contact condensation of top-down flowing steam on the flow properties in the downcomer of the steam generator under high pressure was studied. The trend of the temperature, pressure, and the void fraction were obtained by combining these models with the condensation model. Further, a one-dimensional calculation program based on the differential drop was also developed to assess the flow field in the downcomer. The calculation results are in good agreement with the experimental results which indicated that, when affected by the saturated steam carried downward, the flow temperature close to the exit of the downcomer rises slightly due to the absorption of the heat released by the steam condensation. Furthermore, the density corrected by the pressure-drop is more reliable than that corrected by the temperature. After the velocity in the downcomer has increased to a certain value, the sensitivity of steam quality to the subcooling degree in the downcomer begins to decline. The results in this paper can be used to perform stability analyses and to design steam generators. The results of research are helpful to the stability analysis and the design of a steam generator, and to improve the accuracy of the measurement of the steam generator operating parameters, thus enhancing the safety of Pressurize Water Reactor operating system.

scholarly journals Vertical steam generators for VVER NPPs

2019 ◽  
Vol 5 (1) ◽  
pp. 31-38
Author(s):  
Mikhail Yu. Egorov
Keyword(s):  
Steam Generator ◽  
Nuclear Power ◽  
Temperature Drop ◽  
Heating Surface ◽  
Vessel Diameter ◽  
Absorption Efficiency ◽  
Water Mixture ◽  
Steam Generators ◽  
Loop Design ◽  
Horizontal Type

Steam generators for NPPs are the important large-sized metal consuming equipment of nuclear power installations. Efficiency of steam generator operation determines the overall service life of the whole nuclear facility. The main aim of the current study is to analyze advantages and shortcomings of horizontal and vertical types of steam generator design. This analysis is aimed at the development of recommendations for designing advanced steam generators for future Russian units of NPPs with VVER reactors of increased power. Design solutions and fifty-year experience of operation of 400 steam generators of horizontal type accepted in Russia and of vertical type applied by Westinghouse, Combustion Engineering, Siemens, Mitsubishi, Doosan were analyzed within the framework of the present study. Advantages and drawbacks of both types of equipment determining the development of conditions of the operating processes were also identified and systematized. Currently NPPs equipped with VVER are characterized with extended surface area of containment shells due to the application of four-loop design configuration and horizontal-type steam generators. It was established that steam generator equipment of horizontal type is characterized by such inherent disadvantages of design, technological and operational nature as the following: 1) small height and volume of the vapor space above the evaporation surface reducing separation capabilities and the capacity of the equipment as a whole; 2) impossibility of organizing separate single-phase pre-boiling section. Because of the above, horizontal steam generators with dimensions permissible for railroad transportation and, for VVER-1200 with reactor vessel diameter equal to 5 m, by water transport as well, have exhausted the possibilities for further significant increase of the per unit electric power. The demonstrated advantages of vertical-type steam generators were as follows: 1) absence of stagnant zones within the second cooling circuit, and, consequently, of hold-ups in them; 2) uniformity of heat absorption efficiency of the heating surface ensuring, as well, improved conditions for moisture separation; 3) high degree of moisture removal from steam-water mixture due to the combination of moisture separating elements of chevron and swirl-vane types; 4) increased temperature drop with parameters of generated steam elevated by 0.3 – 0.4 MPa. Conclusion was made on the advisability of introduction of steam generators with vertical-type layout in the Russian nuclear power generation. Practical tasks that need to be addressed in order to ensure introduction of vertical steam generators at NPPs with high-power VVER reactors were formulated.

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