Wet Steam Turbine Research Articles

Integrated Studies of Electrophysical Processes in Steam Turbines

The paper deals with comprehensive research in the field of electrization of wet steam flow in a turbine. The experience of the conducted studies on laboratory stands and full-scale objects (CHP and TPP) in Ukraine and the USA is introduced and generalized. It was shown that in the process of steam electrization, the charge density in the flow can reach very high values (an order of magnitude appears to be higher than in a thundercloud), and this phenomenon mainly has a negative effect on the turbine operation. Statistical data on the charge formation of the steam flow in the low-pressure cylinder of the turbine are presented. Results of the research to establish the main electrophysical factors of influence on the surface strength of the blade, such as electric fields, charge density and their polarity, are presented. The research results showed that such factors as the presence of a positively charged steam flow, constant and variable electric fields, which were most often recorded at operating turbines of CHPs and TPPs, significantly (by two or more times) intensify erosion-corrosion processes on the metal surfaces of the blades, thus reducing their working resource. Thermodynamic processes are studied both under conditions of natural electrification of a high-speed flow, which reduce the efficiency by about 0.3–0.35%, and under the influence of artificially created electric charges, which make it possible to increase the efficiency of the steam expansion process in the turbine by 2 or more percent. Various options of local input of electrical energy for steam ionization in the turbine are considered. At the same time, it is noted that for the practical implementation of these approaches, further careful design improvements and tests on model and full-scale installations are required. Water chemistry regimes are also considered in the context of their influence on the flow charge formation process, as well as on reliability and efficiency indicators of the turbine. Experimentally at an 800 MW turbine plant in the USA, it was shown that a change in the pH of the medium affects the intensity and polarity of the charge formation of the steam flow. The paper introduces the physical features of this phenomenon and notes the importance of these processes influence on the strength characteristics of the blades. Information on new methods and technologies that could lead to an increase in the operational efficiency and reliability of wet steam turbines, such as methods for input and removal of electrical energy into the flow; rational choice of water chemistry regimes; space charge neutralization, etc., is provided. These comprehensive electrophysical studies, considered in conjunction with thermal processes, can be characterized as a new scientific direction in the theory of steam turbines – thermal electrophysics.

Effect of Magnetic Field on Optical Density of Distilled Water

Water is considered as the working fluid of wet steam turbine units. The importance of a purposeful change in the thermophysical properties of water used for energy needs is indicated. A reagent-free method (transverse magnetic field of permanent magnets) of influence on water is proposed. Literature data on currently available papers dedicated to the study of water properties is presented. It is shown that the mechanisms of influence of external physical fields on the physicochemical and thermophysical properties of water have not been elucidated as of now. It is emphasized that the properties of distilled water during exposure and after exposure to physical fields are even less studied. The currently existing contradictions between theoretical ideas about the properties of water and experimental results are considered. It was found that currently there are no correct methods and equipment capable of indicating changes in water properties in real time. As a solution, the equipment and method of analyzing the optical density of distilled water is proposed. The shortcomings of most existing experimental works on the study of the influence of physical fields on the optical density of water are analyzed. The requirements for devices intended for measuring the optical density of distilled water are formulated. A stand was made and experimental work on the study of the dependence of the optical density of distilled water on the induction of a magnetic field that affects it was carried out. It is proved that the magnetic field affects the optical density of distilled water in the infrared range of wavelengths both in the direction of increase (4.1%) and in the direction of decrease (1.7%) depending on the induction of the magnetic field and the speed of water flow through the working section of magnetization device. A hypothesis explaining the obtained result is proposed.

Numerical analysis method for intra-stage non-equilibrium two-phase condensing flow in wet steam turbine and its application

To improve the numerical calculation performance of the intra-stage wet steam non-equilibrium condensing flow in a wet steam turbine, this paper proposed a numerically modified wet steam non-equilibrium condensation (NEC) model by considering the interphase heat and mass transfer in the Euler/Euler coordinate system. The model was developed based on nucleation kinetics, and the expressions of the critical droplet formation free energy and the nucleation rate were given. First, combining the experimental data, the non-isothermal effect nucleation model was modified by the surface tension coefficient method. Then, the low-pressure modified droplet growth model, which is suitable for describing any range of Knudsen numbers, was employed to calculate the droplet surface heat and mass transfer process, and the steam/liquid two-phase control equations and the turbulence model were presented. Meanwhile, the parameter transfer and coupling problem between the vapor and liquid phases was solved. Subsequently, the modified model and the original model were adopted to solve the wet steam condensing flow at the 1D Moses-Stein nozzle numerically, and the results showed that the modified model could calculate the distribution characteristics of pressure and droplet radius more accurately and fit the experimental results better. Afterward, the characteristicsof the non-equilibrium condensing flow of wet steam in the steam turbine cascade were investigated. Finally, combined with the experimental result on the pressure distribution in the steam turbine plane static cascade, the validity of the proposed numerically modified model was further verified, which provided a theoretical basis for the high-accuracy numerical analysis of the condensing flow in the nuclear power wet steam turbine cascade.

On the issue of creating the optimal last stage of powerful steam turbines of nuclear power plants

THE PURPOSE. To estimate the most effective length of the working blade of the last stage of a powerful wet-steam turbine in terms of obtaining its maximum efficiency and to optimize the parameters of this stage in the design mode. For this stage, perform multi-mode optimization to select the main characteristics of the stage operating with maximum efficiency according to a given model daily load schedule.METHODS. When solving this problem, the method of calculating the axisymmetric flow of steam in the flow part of the turbine stage as an inviscid single-phase working fluid relative to a stationary guide device and rotating with an angular velocity ω of the impeller used, and the losses energy calculated according to the axisymmetric method of the MPEI.RESULTS. The article describes the relevance of the topic, discusses the features of the use of the author's software in solving the tasks. The characteristics of the stages with different lengths of the working blades presented and the results of their calculation in the nominal mode are given. A model daily schedule selected for a nuclear power plant turbine operating in the central region of Russia. The results of calculations of variable modes of the last stage of the turbine operating according to this daily schedule presented.CONCLUSION. The choice of the maximum length of the working blade is limited not only by its strength characteristics, but also by the increase in wave losses in the gratings due to an increase in the optimal available heat drop, or rather the associated increase in supersonic speeds near the meridional contours. So for a high-speed turbine To-1200-6,8/50 the maximum efficiency of the last stage is achieved at a length of 1400 mm, both when the turbine is configured with both three two-flow LPC and four. Selection of the main characteristics of these stages, such as the available heat drop, the degree of reactivity, etc. it should be made taking into account the variable operating modes of the turbine on the basis of the forecast of daily schedules of loads of turbine units. When using a typical daily load schedule, the average internal relative efficiency in the range of operating modes according to this schedule is higher by 0.6 % when choosing a 10% increased available heat drop compared to the optimal one in the design mode.

Online estimation approach of the steam specific enthalpy for wet steam turbines in nuclear power plants

Wet steam turbines are widely used in pressurized water reactor nuclear power plants. The specific enthalpy of the wet saturated steam is an indispensable variable for the thermodynamic balance and performance monitoring of the wet steam turbines, but it is rarely online measured in practice. In this study, a model-based online estimation approach of the steam specific enthalpy for the wet steam turbine in nuclear power plants is proposed. The wet steam turbine is divided into several stage groups. In each stage group, the steam expansion process, the moisture separation process, and the steam extraction process are captured in mechanism modeling at first. Then, by solving the model, the specific enthalpy and the dryness fraction of the wet saturated steam are obtained. Using the historical operation data of a 1000 MW pressurized water reactor unit, the model-based pseudo-online simulations and the measured data are compared which suggests a high accuracy of the proposed approach.

Simulation of the Erosion-Corrosion Destruction Process of Steam Turbine Low-Pressure Cylinder Blades

This paper is devoted to the important problem of creating a method for predicting the intensity of erosion-corrosion destruction of the working blades material of low-pressure stages of powerful steam turbines, considering the complex physical processes that accompany the emergence, transformation of erosion-hazardous droplets and their interaction with elements of the flow path. The features of the construction of some existing erosion models are considered. The model that is developed at the Institute of Mechanical Engineering Problems of the National Academy of Sciences of Ukraine and based on a deterministic-statistical approach to its creation is analyzed in detail. The calculations performed during the research showed a satisfactory coincidence with the results of experimental tests by various authors, obtained on droplet impact stands, which contributed to the successful use of the model in creating a comprehensive method of predicting the wear of working blades. To do this, it was supplemented by the method of determining the parameters of the erosive environment based on the droplet movement equation, taking into account the size distribution law. Along with that, it is shown that the considered model, although it allows to carry out fairly accurate prediction of the development of erosive wear at the modern level, has difficulties in its construction due to the need to identify it from the data of full-scale experiments, the number of which is limited. It has been established that one of the important reasons for the discrepancies that arise is the failure to include of the electrophysical component of the processes occurring in a two-phase flow. In this regard, the results of comprehensive studies of steam electrization and its influence on the working processes of wet steam turbines are considered. It is shown that the change in the properties of the working medium as a functional erosive medium as a result of electrification causes a significant increase (relative to neutral wet steam) of electrochemical processes. At the same time, the kinetics of the damage accumulation to the metal surface layer changes due to the joint occurrence of several negative processes: droplet impact influence; electrochemical processes caused by mechanical and structural and chemical heterogeneity of the surface; hydrogen absorption; changes in mechanical properties under the electric field influence. It was noted that the contribution of hydrogen absorption to changes in mechanical properties is the greatest. According to a preliminary assessment, the complex negative droplet impact and electrophysical influence on the metal surface reduces the incubation period and intensifies the erosion-corrosion process by approximately 2 times

Experimental Evaluation of the Wet Steam Flow Electrification Effect on Its Dielectric Properties

It has been established that in order to study thermo- and electrophysical phenomena in wet steam turbines, studies of the wet steam flow volume charge effect on its dielectric and thermophysical properties have recently been carried out at A. Pidhornyi Institute of Mechanical Engineering Problems of the National Academy of Sciences of Ukraine. According to their results, it was established that the most representative electrophysical parameter, which allows to evaluate changes in the thermophysical properties of steam, which occur under the action of its own volume charge, is its dielectric constant. It is assumed that the value of the dielectric constant of an electrified steam can be significantly different from the value for a neutral steam, and a mathematical assessment of its possible change is made. It has been confirmed that the influence of electrophysical phenomena caused by the wet steam flow electrification is significant, but is not taken into account in the existing physical and mathematical thermodynamic models of the steam expansion process. It is proved that in order to clarify the main thermodynamic parameters and calculated characteristics of the electrified wet steam flow, it is necessary to determine how its dielectric constant changes. On the basis of the analysis, the relevance of experimental determination of the dielectric constant of a wet steam flow with a volume charge in order to obtain the dependence of its change on the temperature and pressure of the flow, as well as the density of the volume charge, is substantiated. To perform the research, a gas dynamic laboratory plant, which allows to obtain a wet steam flow with a volume charge, was used. The internal space of the flow part of a real wet steam turbine has a significant size and allows the formation of a flow with a volume charge of a complex spatial configuration and structure. It is emphasized that in the flow part of the plant of a small volume, in contrast to the turbine flow part, significant technical difficulties arise when organizing the conditions for the occurrence of a wet steam flow with a volume charge. Taking this into account, at the first stage, it was decided to conduct a study of a steam flow with a volume charge flowing into the atmosphere in a laboratory room with a sufficient volume to form its spatial structure. To estimate the value of its dielectric constant, the inductive method (L-method) of determining dielectric properties, in which the substance under study is introduced into the inductive solenoid cell, was chosen. Experiments were conducted and, according to the obtained data, it is possible to make a preliminary assessment of the change in dielectric constant in the presence of a volume electric charge in the steam flow

Parametric and economic analysis of high-temperature cascade organic Rankine cycle with a biphenyl and diphenyl oxide mixture

High-temperature organic Rankine cycle (ORC) systems have the potential to improve the heat-to-power conversion efficiency and expand the temperature range for heat recovery, heat battery and solar power generation. Restricted by the critical temperature of the commonly used organic working fluids, the current ORC technology has a maximum working temperature of around 300 °C. This paper proposes a high-temperature cascade organic Rankine cycle (CORC) system using a biphenyl and diphenyl oxide (BDO) mixture as the top cycle fluid and conventional organic fluids for the bottom cycle. The BDO mixture has excellent heat stability over a wide operation condition from 12 °C to 400 °C in single-phase and binary-phase states. However, at present a detailed study on the ORC using the mixture is lacking. In this paper, a parametric analysis of the high-temperature CORC system is conducted. A mathematical model based on the equivalent hot side temperature is built to simulate the ORC efficiency. The thermodynamic and exergetic performances of the novel CORC system under different bottom ORC working fluids, mixing chamber temperatures, evaporation temperatures, and condensation temperatures are investigated. The results show the maximum thermal efficiency of the CORC system is 38.74 % and 40.26 % at top ORC evaporation temperatures of 360 °C and 400 °C. The largest exergy destruction takes place in the heat exchanger between the top and bottom ORCs. Besides, the heat regenerators have a significant impact on the thermodynamic performance and can elevate the CORC efficiency by about 4 %. The proposed system has a higher efficiency and a lower equipment cost than conventional steam Rankine cycle at 400 °C while eliminating the challenges of wet steam turbines.

Analysis of the Influence of Steam Electrification on the Working Processes of a Wet Steam Turbine

The effect of steam electrification on the operation of a wet steam turbine, as well as the main processes sensitive to the electrification of the working fluid are considered in the paper. The types of additional losses caused by electrification are indicated. It is noted that these losses are not counted in the currently existing physical and mathematical models, since data on electrification are not taken into account and there is no possibility to make a clear theoretical description of the electrophysical model of a neutral steam even. In this regard, a simplified qualitative physical model of the electrophysical processes that occur during the electrification of the steam flow in the turbine was studied. Based on this, an assumption regarding the properties of the space charge in the steam flow, which is the source of the electric field and determines its intensity and spatial distribution in the flow part, is made. A qualitative analysis of the effect of the space charge field on the physical and thermodynamic properties of the steam flow was carried out with the set assumptions. It is proposed to perceive the process of steam polarization in the space charge field as the main result of its influence, and the dielectric constant of the steam – as the most representative parameter characterizing the thermodynamic state, including with the field influence. The thermodynamic relations of the operation of the dielectric in an electric field are given. The relation between the dielectric constant of steam and the change in the internal energy of the working fluid, its entropy and free energy is shown. It is theoretically substantiated that the influence of the electric field also leads to a change in the isobaric heat capacity and enthalpy. It is concluded that the process of expansion of the wet steam flow of charged steam in the turbine unit can be accompanied by a change in the main thermodynamic parameters of the working fluid, and therefore, its design characteristics can change, including the losses that occur in the process of expansion. On the basis of previously obtained experimental data on real turbines, a numerical assessment of the change in the thermodynamic parameters of the working fluid under the influence of an electric field is carried out. The performed numerical studies unequivocally indicate the need to take into account the phenomena caused by the electrification of the wet steam flow in the low-pressure cylinder in the existing physical and mathematical thermodynamic models of the wet steam expansion process, as well as to clarify the main thermodynamic parameters and calculated characteristics of the flow of electrified wet steam depending on the change in its dielectric constant.

An innovative concentrated solar power system driven by high-temperature cascade organic Rankine cycle

Direct steam generation (DSG) solar power systems eliminate synthetic oils and molten salts in the solar field and enable efficient heat collection. Commercial DSG solar plants usually have a steam generation temperature of 250–285 °C to reduce the technical challenges of wet steam turbines and the costs of high-pressure water storage tanks. The power conversion efficiency is relatively low due to the limited steam generation temperature. This paper proposes a high-temperature solar power system driven by the cascade organic Rankine cycle (CORC). It has three features: water/steam for solar heat transfer, water and phase change material (PCM) for heat storage, and CORC for power conversion. It is the first time that the storage tank temperature is independent of the steam generation temperature in a DSG. Steam can be generated in the solar field at a temperature of 310 °C or even 370 °C. The fundamental of the innovative system is illustrated. The thermodynamic performances during the normal operation and discharge processes are investigated. The results show the maximum thermal efficiency of the CORC system in the normal operation mode is 32.85% at a steam temperature of 311 °C, while the top and bottom cycle efficiencies are 15.38% and 20.86%, respectively. The efficiency increases to more than 37% at 370 °C. Combining the two-tank storage and the PCM unit can overcome the problems of decreasing the heat release rate from PCM during heat discharge while maintaining the CORC system's power output and prolonging the heat storage time. The proposed system is potentially more cost-effective than the existing DSG solar plants.

Optimization of the Trailing Edge Inclination of Wet Steam Turbine Stator Blade Towards the Losses Reduction

Optimization of the Trailing Edge Inclination of Wet Steam Turbine Stator Blade Towards the Losses Reduction

Design and analysis of an innovative concentrated solar power system using cascade organic Rankine cycle and two-tank water/steam storage

Direct steam generation (DSG) solar power systems have the potential to improve heat collection performance and reduce capital cost. One challenge of the DSG solar thermal power technology is the unsteadiness of steam generation and power conversion under fluctuating solar radiation. A novel concentrated solar power generation system is proposed. It has three features: two-phase water/steam as heat transfer fluid, two-tank water storage, and cascade organic Rankine cycle (CORC) with a mixing chamber as power block. Steam is produced in the solar field and condensed in a high temperature tank, while an organic fluid replaces water for power conversion. The system enables smooth cycle operation by resilient control strategy and can tackle the challenge associated with wet steam turbines. It can tolerate lower purity of water/steam that only serves as the heat transfer fluid, thereby reducing the technical requirement. Thermodynamic performance in the normal operation condition and heat discharge process are assessed. The influences of ORC working fluid and storage tank size are examined. Results indicate that the mixing chamber temperature plays a crucial role in thermal efficiencies of both charge and discharge processes, storage capacity, and overall performance. A CORC efficiency of about 27.4% is achievable. The equivalent heat-to-power efficiency ranges from 13.35% to 18.81%, depending on the ORC fluid and volume of the storage tank. The novel system has an efficiency comparable to a conventional DSG system while a lower technical requirement in heat collection and power generation.

Electrochemical and Chemical Mechanisms of the Erosion-Corrosion Process of Wet-Steam Turbine Rotor Blades Destruction Under the Influence of Electrified Moisture

This paper is devoted to the electrochemical and chemical aspects of the erosion-corrosion destruction of the surface layer of a wet-steam turbine rotor blade under the influence of an electrified working fluid. It considers a hypothesis about a complex mechanochemical-electrochemical mechanism of chromium and iron wash-out from the surface layer of the rotor blade metal during the destruction of the oxide film under the influence of a high-speed wet steam flow. Various versions of this process are analyzed for positive, negative, quasi-neutral, and neutral electrifications of wet steam. The possibility to hydrogenate the surfaces of rotor blades under the influence of negatively-charged droplets is shown theoretically. The damage to the blades in this case is similar to that from anodic etching. It is also shown that the process of blade surface hydrogenation takes place in any case both for electrically-charged droplets and for neutral ones. However, in the case of neutral droplets, the intensity of the process is insignificant. An experimental study was carried out for the erosion-damaged surface of a last-stage rotor blade from of the BK-50 LMP turbine that had exhausted its lifetime. The quantitative content of chromium was determined in the steel sample cut out from the blade. A decrease in chromium content in the erosion-damaged blade surface layer was found. To test the hypothesis about the similarity between the process of anodic electro-etching and the process of surface destruction under the influence of negatively-charged droplets, an electrochemical experiment was carried out on a model sample of 20X13 chromium steel. The reliefs of the damaged areas on the model sample after anodic etching and on the observable blade in the zone of exposure to negatively-charged droplets are shown to be similar. The experimental studies have confirmed the presence of a complex mechanochemical-electrochemical process of blade destruction. On the basis of the data obtained, recommendations for extending the useful life of turbine blades are formulated.

Numerical study on two-phase expansion performance and quantitative analysis of wetness loss in cryogenic turbo-expander

Cryogenic two-phase turbo-expander becomes a prevalent option in process design of high efficiency cryogenic liquefaction system, especially in modern air separation system and helium system. Computational code of turbine off-design performance prediction in overheated expansion and non-equilibrium condensation module are well established in our former works, and the mechanism of nucleation and droplet growth in spontaneous condensation is revealed. However, the analysis between single and two-phase expansion as well as wetness influence on turbine performance is not conducted yet. In this study, we investigate a turbo-expander performance analysis in a wide temperature range (Tin = 118 K ~ 98 K), and present the wetness loss assessment and quantitative calculation in two-phase expansion process. By referring to the previous off-design performance of overheated expansion, the two-phase expansion performance under different pressure ratio and rotational speed is obtained and compared. According to the continuous inlet temperature drop process, the expansion is categorized into three types and their zone boundaries are divided. The transitional feature of unexpected change is frequently figured out on the expansion zone boundary, and the reaction ratio and pressure ratio in diffuser during the continuous inlet temperature drop process are analyzed detailed, which shows the unique and significant role of wetness effect in two-phase expansion. Based on the experimental wetness loss assessment method established by Baumann in wet steam turbine, two numerical assessments by using overheated expansion and equilibrium condensation model as reference expansion are analyzed. To quantitatively analyze the wetness loss influence, the efficiency drop caused by wetness and the relative wetness loss are calculated by eliminating other component losses in turbine, and the relative wetness loss is fitted with outlet liquid mass fraction mathematically to assist future design of cryogenic two-phase turbo-expanders.

Study into the Separation Ability of the New NRU MPEI Peripheral Sealing

Energy losses caused by steam humidity are one of the main components of losses in the steps of nuclear power plants’ wet-steam turbines. The presence of moisture droplets in the flow part of the turbines also poses a serious danger due to erosion wear of their blades. Various separation systems remove part of the erosion-hazardous moisture. However, along with moisture, a certain amount of steam is removed from the flow part of the turbine, which will not take part in performing beneficial work in subsequent stages of this turbine. Other losses are steam leaks through seals, the largest of which occur in seals located above the turbine blades. On the basis of the rectangular-mesh seals developed and studied earlier, the design of a special peripheral seal for NPP turbines was developed at NRU MPEI. The new seal is capable of simultaneously performing two functions: to reduce over-leakage leaks and to ensure the separation of moisture from the flowing part. The results of the studies showed that the presence of special channels in the seal for removing drip moisture hardly worsen the flow characteristics of the new seal. This paper presents the results of experimental studies into the separation ability of new peripheral seals. As a two-phase medium, specially prepared moist air was used. To do this, a plant for the preparation of water and the generation of the droplet phase was designed and manufactured. During the experiments, the ability of the seal structure to remove moisture was investigated. The use of humidified air made it possible to accurately determine the amount of droplet moisture supplied to the seal and separated through it and the separation coefficient of the seal. Studies have shown that the amount of moisture separated through the seal depends on the pressure drop across it, the rotor speed, and the initial degree of humidity of the compressed air supplied to the seal. It is shown that the use of a new seal in the studied range of initial degrees of humidity allows the separation of up to 45% of the moisture passing through the peripheral gap above the working blades. In general, the results of the experiments showed that the use of a rectangular-cell seal from NRU MPEI as a peripheral seal in turbines of nuclear power plants is advisable to remove moisture from the gap above the working blade and to reduce peripheral steam leaks.

MODELING NPP POWER UNIT STEAM TURBINE INSTALLATION STEAM SEPARATOR-SUPERHEATER TEMPERATURE CHARACTERISTICS BY INTERVAL ANALYSIS METHODS

The determination of the temperature characteristics of one of the significant elements of the wet-steam turbines of nuclear power units – the steam separator-superheater is considered: namely the construction of the dependence of the temperature of the heated steam at the outlet of the second stage on the changing load of the power unit. Modeling is carried out taking into account the error limitation without reliable information about its distribution. To evaluate the coefficients of empirical dependence, constructed according to the results of experimental data, it is proposed to use numerical methods of interval analysis. The interval approach allows building a refined tube, guaranteed to contain acceptable dependences of the temperature of the heated steam on the electric power of the power unit. In a situation of data uncertainty and limited errors, numerical methods of interval analysis allow creating models of processes and equipment of NPP units with the maximum possible correspondence to a real object.

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

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.

The new ways to increase the efficiency of thermal hydraulic processes in systems of separation and reheating of NPP wet steam turbines

Systems of moisture separators - reheaters (SMSR) were created simultaneously with the powerful turbines development of nuclear power plants operating on a wet steam from the early 60s of the 20th century. This lengthy experience made the opportunity to identify the moisture separators - reheaters (MSRs) drawbacks, to determine the objectives for their design and computation improvement in order to increase thermodynamic efficiency, MSR devices and MSR systems reliability in general. Based on maintenance experience and results of our and other researchers’ model and field studies this article discusses potential ways of further development and improvement, taking into consideration both SMSR components (separation and reheating) under conditions of their flow in one apparatus.

Steam reheater with helical tube bundle for wet steam turbine

Since steam heat exchangers, used at steam cycle of Russian nuclear power stations, were designed while the knowledge about the separation and the heat exchange processes was limited, deviations between its empirical and theoretical characteristics occur. This limitation also determined application of heating pipes with simple straight shape rather than curved. This study explores a steam heat exchanger with helical heating pipes. It was shown that the model may work stably within the range of parameters, simulating work conditions of the moisture separator and steam reheater at Leningrad nuclear power plant. The experiment included processing of pure water steam as well as mixture of steam and nitrogen. It was obtained a relationship between empirical the heat transfer coefficient and the steam mass flow rate. It was noted that presence of incondensable gas does not affect significantly the heat transfer from the coils, processing high pressure steam.

The Influence of Wet-Steam Flow Electrization on the Surface Strength of Turbine Blade Materials

The phenomenon of droplet impingement erosion of a wet-steam turbine’s last-stage blades is conditionally considered in the aspect of two “opposing” processes: the force impact of droplets on metal and “resistance” of the metal to this impact. The article places its focus on “resistance” of the metal surface layer to the force impact under the influence of electrified steam and concomitant electrophysical phenomena on its mechanical properties. It has been established that the electrophysical phenomena accompanying wet-steam flow electrization facilitate saturation of the metal with hydrogen (6–10 times higher in comparison with a neutral flow) and have a significant effect on its microhardness (the changes toward its decreasing may be as much as 50%). These changes take place in a thin surface layer, and their extent and nature depend on the flow polarity and also on the frequency and polarity of the electric field induced on the turbine blade. The decrease of microhardness observed in the thin surface layer can be attributed to the phenomenon of local microplasticization, which occurs as a result of facilitating the incipience of microshears when hydrogen cations interact with the dislocation nuclei generated in introducing an indenter. Such plasticization at the microlevel facilitates the development of hydrogen brittleness at the macrolevel. It has been established that, as far as the maximal erosion-induced strength degradation of blade materials is concerned, a positively charged wet steam flow is the most dangerous factor, which most frequently takes place in the case of using water chemistry with pH > 9 (ammonia water chemistry). It is shown that it is possible to alter the development kinetics of destruction caused by droplet impingement erosion by changing the physicochemical properties of thin surface layers of metals.