Steam Turbine Stage Research Articles

AN ANALYSIS OF THE LIQUID FILMS BREAK-UP USING THE COMPUTER VISION TECHNIQUE

The aim of this paper is to introduce a novel approach for analysing the droplet formation in a transonic flow. The method suggested in this work is based on the combination of the measured data from the wind tunnel by an optical measurement and image processing. A new wind tunnel was developed for the study of the liquid film atomization at high speed flows similar to ones that can be found in steam turbines. The coarse droplets in steam turbines are formed from the liquid films on the blades and inner casings. The coarse droplets formed on the stator blades don´t follow the bulk flow and collide with the following moving blades. These collisions cause erosion and corrosion processes, which have an unfavourable effect on the reliability and the efficiency of the low pressure stages of steam turbines. The tunnel is equipped with a standard instrumentation for the measurement of the flow properties and for the analysis of the size distribution of the droplets. Two measurement methods were used for the measurement of the size of the droplets, photogrammetry and light scattering. In this paper, the image processing of the captured images is discussed. The images were taken by a camera with a telecentric lens. The paper contains an assessment of three image processing methods used for the measurement of the droplet distribution by the light extinction. Moreover, the formation of the droplets is captured on the trailing edge of the profile in the flow. The results bring a new view on the formation of droplets at high speeds.

Natural Frequency Evaluation of Last Stage Steam Turbine Blade Power Plant Using Finite Element Method

The possibility of a power plant trip can disrupt the stability of the network frequency settings. Load shedding is done at the frequency level. In case of frequency under nominal setting, the load shedding or trip generator decision must pay attention to the generator equipment factor, especially the last stage turbine blade and lacing wire. In this study analysis modal using ANSYS 2019 R2 was carried out to determine natural frequency of the last stage blade LP (low pressure) Steam Turbine Tanjung Awar Awar Indonesia power plant when operating at low frequencies, which is below the nominal operating frequency of 50 HZ or at a rotation of 3000 rpm. The finite element method analysis is applied to the 1 blade and 5 blade systems. The result for a natural frequency of 1 blade system occurs at 2639.6, 2783 and 2915 rpm. For the 5 blades system, natural frequency occurs at 2648 and 2563 rpm, so it can be concluded that the setting under frequency is not in the range of natural frequency last stage LP turbine blade, and lacing wire damage is not triggered by the natural frequency steam turbine blade.

Numerical and Analytical Investigation of Heat Transfer Mechanisms and Flow Phenomena in an Intermediate Pressure Steam Turbine Blading During Startup

Abstract As a result of an ever-increasing share of volatile renewable energies on the worldwide power generation, conventional thermal power plants face high technical challenges in terms of operational flexibility. Consequently, the number of startups and shutdowns grows, causing high thermal stresses in the thick-walled components and thus reduces lifetime and increases product costs. To fulfill the lifetime requirements, an accurate prediction and determination of the metal temperature distribution inside these components is crucial. Therefore, boundary conditions in terms of local fluid temperatures as well as heat transfer coefficients (HTCs) with sufficient accuracy are required. As modern numerical modeling approaches, like 3D-conjugate-heat-transfer (CHT), provide these thermal conditions with a huge calculation expense for multistage turbines, simplified methods are inevitable. Analytical heat transfer correlations are thus the state-of-the-art approach to capture the heat transport phenomena and to optimize and design high efficient startup curves for flexible power market. The objective of this paper is to understand the predominant basic heat transfer mechanisms such as conduction, convection, and radiation during a startup of an intermediate pressure (IP) steam turbine stage. Convective heat transport is described by means of heat transfer coefficients as a function of the most relevant dimensionless, aero-thermal operating parameters, considering predominant flow structures. Based on steady-state and transient CHT simulations, the heat transfer coefficients are derived during startup procedure and compared to analytical correlations from the literature, which allow the calculation of the heat exchange for a whole multistage in an economic and timesaving way. The simulations point out that the local convective heat transfer coefficient generally increases with increasing axial and circumferential Reynolds' number and is mostly influenced by vortex systems such as passage and horseshoe vortices. The heat transfer coefficients at vane, blade, hub, and labyrinth-sealing surfaces can be modeled with a high accuracy using a linear relation with respect to the total Reynolds' number. The comparison illustrates that the analytical correlations underestimate the convective heat transfer by approximately 40% on average. Results show that special correlation-based approaches from the literature are a particularly suitable and efficient procedure to predict the heat transfer within steam turbines in the thermal design process. Overall, the computational effort can be significantly reduced by applying analytical correlations while maintaining a satisfactory accuracy.

A blackbox optimization of volumetric heating rate for reducing the wetness of the steam flow through turbine blades

This paper proposes to use a blackbox optimization to obtain the optimal volumetric heating required to reduce the wetness at the last stages of steam turbines. For this purpose, a global multiobjective optimization is utilized through the automatic linking of genetic algorithm and CFD code, where the blackbox function evaluations are performed by CFD runs. The logarithm of number of droplets per volume (LND), the droplet average radius (DAR), and the integral of local entropy (ILE) at the end of the cascade (after the condensation location) are minimized, while the volumetric heating rate is the optimization parameter. The Eulerian–Eulerian approach is implemented to model the two-phase wet steam turbulent flow and the numerical results are validated against well-established experiments. Since higher volumetric heating rates reduce DAR and LND, while increase ILE, according to optimization results, there is an optimum for the volumetric heating rate to reach the best performance of steam turbines. For case studies presented in this work, the optimal volumetric heating rates of 5.21×108 and 4.67×108 W/m2 are obtained for two different cases of supersonic and subsonic outlets, respectively. Particularly, these rates improve DAR by 45.7% and 57.5%, and LND by 6.0% and 7.8% for respective cases.

Control of two-phase heat transfer and condensation loss in turbine blade cascade by injection water droplets

The last few stages of a condensing steam turbine of fossil fuel power units and most stages of steam turbine in nuclear power units operate under wet steam conditions and the condensation phenomena as well as two-phase flow are crucial for efficiency of turbine stages. In this work, the water spray injection ahead of the vanes was used to control the two-phase heat transfer. Five cases of droplets injection with constant radius were considered to study the problem comprehensively. The results show that the injection of the droplets affects flow conditions and two-phase structure. These parameters can also be controlled by increasing or decreasing the number of injected droplets. The conclusions are that with the increase of the number of injected droplets the heat transfer process at the blade cascade inlet increases, whereas at the vicinity of the oblique shock the heat transfer weakens. When the radius and number of injected droplets are 57 nm and 2.5×10151/kg, respectively, the overall heat transfer and the condensation loss are reduced by about 40% and 25%, respectively. The conclusions from this work can provide scientific references for wetness loss control in steam turbine.

Aerodynamic design and computational fluid dynamic analysis of radial outflow turbines for steam Rankine cycle and supercritical carbon dioxide Brayton cycle

The first part of this paper presents the design of a radial outflow steam turbine for a micro steam power pump block of 200 kW capacity based on a unique Ljungstrom turbine design methodology. Computational fluid dynamic (CFD) simulations were carried out for the 18-stage radial outflow steam turbine at design and off-design points, and results proved the validity of the undertaken design methodology. The design point CFD simulation showed a total to total efficiency of 74.4% for the steam turbine. Specific speed and specific diameter values for the radial outflow steam turbine stages were calculated and superimposed on the Balje's specific speed-specific diameter chart, thus identifying a unique radial outflow turbine zone in the chart. The second part of this paper presents a new design methodology based on specific speed and specific diameter values for designing a supercritical carbon dioxide radial outflow turbine for a 1 MW supercritical carbon dioxide (SCO2) Brayton cycle. CFD simulations were carried out at design and off-design points for the SCO2 turbine. The total to total efficiency from the CFD simulation at the design point for the SCO2 turbine is 84.6%.

Aerodynamic design and computational fluid dynamic analysis of radial outflow turbines for steam Rankine cycle and supercritical carbon dioxide Brayton cycle

The first part of this paper presents the design of a radial outflow steam turbine for a micro steam power pump block of 200 kW capacity based on a unique Ljungstrom turbine design methodology. Computational fluid dynamic (CFD) simulations were carried out for the 18-stage radial outflow steam turbine at design and off-design points, and results proved the validity of the undertaken design methodology. The design point CFD simulation showed a total to total efficiency of 74.4% for the steam turbine. Specific speed and specific diameter values for the radial outflow steam turbine stages were calculated and superimposed on the Balje's specific speed-specific diameter chart, thus identifying a unique radial outflow turbine zone in the chart. The second part of this paper presents a new design methodology based on specific speed and specific diameter values for designing a supercritical carbon dioxide radial outflow turbine for a 1 MW supercritical carbon dioxide (SCO2) Brayton cycle. CFD simulations were carried out at design and off-design points for the SCO2 turbine. The total to total efficiency from the CFD simulation at the design point for the SCO2 turbine is 84.6%.

Determination of the Idle Mode of the Stage of Axial Turbine during Operation at Partial Loads

On the basis of the one-dimensional theory of calculating the operation of steam turbine stages the method for determining the idle mode, the initial data for which are the geometric characteristics of the blade rows is proposed. Formulas have been obtained that make it possible to calculate the efficiency in the proximity of Rotor Blades (RB) at operating modes from nominal to the idle mode, depending on the flow rate of the stage and taking into account the use of kinetic energy with the runaway velocity and losses arising at off-design angles of flow on the Rotor Blade (RB). The results of possible computational studies and their comparison for an incompressible working fluid with the results of experimental studies showed the good possibilities of the proposed method for determining the idle mode in a wide range of the characteristics of stages.

Numerical simulation of the liquid film suction process through the slots of various geometry in the last stages of steam turbines

The liquid film suction process through the slot is considered. The stator blade row of the last stage of the steam turbine was used as an object of study. Based on the CFD modelling of two-phase flow in blades cascade the boundary conditions for slots modelling have been obtained. The numerical analyses of film removal were conducted in a domain including only a flow zone near the studied slot. The multi-phase VOF model was used to calculate the interaction between liquid and steam phases and model the interface evolution during the water removal process. Four different geometries of the slots were considered. For each of them, the unsteady calculations at two different operating regimes have been performed. The numerical results provide information about film suction details in a space of the slot. The behaviour of the film flow was analysed for each slot shape. The conditions of the film separation and its further breakup have been considered. For the studied slot designs efficiency analysis was performed. The results have shown how the way the liquid film moves in the slot effects on the removed water and steam mass flow rates.

Application of numerical modelling for determining the optimal position of the suction slot in the steam turbine vane cascade

The numerical investigations of liquid film development in the last stages of steam turbines were performed. This data was used to suggest the position of the suction slot used to evacuate the liquid phase from the turbine flow path. The object of study is a periphery 2D section of vanes cascade. The movement of coarse droplets in the blade passage was simulated. Their collision with the blade surfaces results in the appearance of additional sources of mass and momentum for liquid film. The influence of theoretical Mach number on the features of liquid film formation was studied. The distributions of main characteristics, reflecting the formation of the film, have been obtained. They were used to analyse the liquid phase flow along the surfaces and to point out base recommendations about the location of the suction slot.

Distribution of condensation droplets in the last stage of steam turbine under small flow rate condition

The parameter variation, condensation and distribution of wet steam are very complicated when the steam turbine works under small flow rate condition. In this paper, the two-phase fluid model, the homogeneous nucleation model and the droplet growth model are combined to study the parameter variation in the last stage flow field, the condensation and distribution rule of wet steam and the interaction among them under small flow rate condition. The results show that the condensation location of wet steam, the number and size of droplets are influenced greatly by the location of vortex and the parameters of flow field. The droplet is mainly distributed on the side of pressure surface and the downstream of trailing edge of rotor blade. And the distribution of droplet corresponds to the distribution of the vortex. At 5%THA condition, the flow angle fluctuates violently, and the velocity triangle presents a distribution of “X“ shape. Besides, the vortex at corresponding locations is obvious, which corresponds to the distribution of droplets. The larger the droplet number, the larger the droplet size is.

Effect of water spray in exhaust passage of steam turbine on flow field of the last stage during windage

Under the windage condition, the steam in the last stage of steam turbine absorbs energy from rotor blade, which leads to overtemperature of the exhaust steam. Water spray is an effective way to lower the temperature in exhaust passage. The Euler-Lagrange particle tracking method is used to study the heat and mass transfer of the water spray in exhaust passage. The quantity of water spray under different conditions is predicted and the effect of water spray on the last stage flow field is analyzed. The results show that there is a small temperature difference between steam and liquid in the exhaust passage and a minimum evaporation of droplets for high steam velocity. The water spray quantity has a negative correlation with the inlet steam mass flow rate under different conditions and the ratio of water spray quantity to the inlet mass flow rate (water/steam ratio) has a quadratic relationship with the operating conditions. From 20%THA (Turbine Heat Acceptance) to 7%THA, the ratio of steam evaporated by water to mixture-vapor (H2O/mixture-vapor ratio) increases from 0.05% to 0.95%, and the water/steam ratio increases from 22% to 300%. The water spray has little effect on the rotor-stator clearance vortex and the separation vortex, but the height and velocity of the back flow vortex are increased. Meanwhile, the pressure of the last stage and the pressure ratio of the rotor blade increase, which result in the dissipating shaft power of the rotor blade reduces. Water spray has an effect on the flow field of the last stage, which is of great significance to correctly predict the windage conditions and study the dynamic characteristics of the rotor blade.

The operation of the last stage of steam turbine at low-flow rate modes

At the present time, thermal power plants and combined heat and power plants operate in highly manoeuvrable modes with almost daily deep unloading, shutdowns on weekends and holidays followed by launches from various thermal conditions. During start-ups, the operation at partial modes and shutdowns, the turbine flow path operates at low-flow rate modes and, as a result, varying tear-off phenomena appear — depending on a relative volumetric flow rate of steam Gv2 in the low-pressure cylinder starting from the last stage. This is especially true for the operation of the low-pressure path for cogeneration turbines. Under low-flow rate modes a change in the flow structure occurs accompanied by the appearance of the bushing tear-off, the rotating vortex in the gap between stator blades and rotor blades, and an increase in pressure in the main flow when switching to the operation at the compressor mode. The formation of the tear-off area is accompanied by a significant increase in the temperature of steam during its overheating due to ventilation losses created by vortex structures in the areas of tear-off. The temperature change along the working blade length is considered, the characteristic points of this change depending on the relative volumetric flow rate of steam are highlighted. The boundaries of transition from the wet steam to the su— perheated steam with decreasing Gv2 are determined. The power consumption for the operation of the stage with a decrease in the flow rate of steam and a change in the flow structure is considered.

Research on Method of the Flow Passage Condition Monitoring and Diagnosis for Steam Turbine

Monitoring and diagnosis of the steam turbine flow passage is the most important premise to achieve the power plant condition maintenance. The existing characteristic flow area of steam turbine changes with main steam flow and can not accurately reflect the flow passage state of steam turbine. In order to reflect the state change in turbine passage accurately, the characteristic flow area of steam turbine stage should be investigated in the same main steam flow. Because main steam flow on-line measuring method accuracy is deficient, a new method based on the exhaust pressure of IP cylinder as character parameter of main steam flow is proposed, and a correction method which takes the impact of the heat regenerative system on main steam flow into consideration is presented. Meanwhile, in the diagnostic process, the measuring result is strongly influenced by the system inevitable measuring error which directly affects the deviation between the characteristic flow area and its standard. Thus confidence intervals of characteristic flow area is given to eliminate the system errors. Finally, the actual diagnostic example in the article indicates the practicability of the method. It can be used to diagnose the flow passage of steam turbine and provide reliable basis to find out the steam turbine potential.

Wetness and Losses Control Using Geometry Considerations in Low Pressure Stages of Steam Turbines

Wetness and Losses Control Using Geometry Considerations in Low Pressure Stages of Steam Turbines

Novel post combustion CO2 capture in the coal-fired power plant employing a transcritical CO2 power generation and low temperature steam upgraded by an absorption heat transformer

This paper deals with a double effect heat transformer-aided carbon dioxide capture unit with transcritical carbon dioxide power generation for a coal-fired steam power plant. In the proposed system a double absorption heat transformer is used to upgrade low energy level steam into high-level and drive carbon dioxide capture unit. Also, a transcritical carbon dioxide power generation that is utilized captured carbon dioxide to generate power and compensate a portion of the required electrical energy of the carbon dioxide capture unit. This system avoids extracting high-grade temperature steam extracted from high-pressure stage of steam turbine and hence overall thermal efficiency of power plant increases compared to the reference systems. Comprehensive thermodynamic and economic evaluations are conducted to reveal the feasibility of the presented system. The results show that the evaporator temperature has the highest effect on net power output. An increase of 10 K in the evaporator temperature from 80 °C to 90 °C, leads to a reduction of 4.9% in generated power. However, a 50% increase in carbon dioxide capture rate from 40% to 90%, leads to a rise of 23.4% in the exergy destruction rate. Moreover, the payback period is approximately 4 years and 6 months.

Features of steam turbine stages operation in low-flow modes when modeling hydrodynamic processes in the turbine in steamless and motor modes

Abstract Operating peculiarities of the stage, the group of stages and the flow part of the steam turbine in low-flow modes, in particular, in the steamless and motor modes, and methodological approaches to their registration in the simulation of hydrodynamic processes are considered. Particular attention is paid to determining the power losses for friction and ventilation. The technique and algorithm for calculating the temperature state of the flow part of a steam turbine are given. Based on the conducted studies, the regularities characteristic of the motor regime of most steam turbines are revealed.

Taking into Account the Operating Modes of the Steam Turbine Stage When Modeling Hydrodynamic and Thermal Processes in Non-Steam and Motor Modes

Abstract The modes of operation of the steam turbine stage in non-steam and motor modes are considered. Analytical models of the operation of the stage with and without active power generation are obtained. Calculation expressions are given for quantifying the maximum allowable total power of the turbine stages when the cooling steam flows into the flow part of the turbine from the safety condition of the generator when it is accidentally disconnected from the network. The efficiency of the method using experimental data of the motor mode on the K-200 power unit is shown. Based on the thermal and balance equations, a condition is obtained that excludes the possibility of external steam flows into the intermediate stages of the turbine affecting the parameters of the steam flowing through the flow part.

Computational modeling of non-equilibrium condensing steam flows in low-pressure steam turbines

Abstract Condensation occurring in low pressure stages of steam turbines contributes to many losses in efficiency and damage to the stator blades such as corrosion and pitting. This problem has been observed profusely in power generation industries. The purpose of this study is to properly simulate the condensation and shock wave phenomenon at the last stage of the steam turbine and accordingly understand this phenomenon. Numerical simulation was conducted by using ANSYS Fluent and applying k-omega SST turbulence model. The results agreed with the experimental values.

Distribution characteristics of salt-out particles in steam turbine stage

Exploring the distribution characteristics of salt-out particles on the blade surface is one of the most urgent problems for supercritical steam turbine. To obtain more practical distribution characteristics of salt-out particles in the steam turbine stage, the population balance model is loaded based on Eulerian multiphase model to simulate the real existed microscopic behaviors of salt-out particles such as nucleation, growth, aggregation and breakage. The results show that along the axial direction the number of salt-out particles gradually decreases and a ladder-like distribution is observed both on the stator and rotor blades. For the stator blade, a critical position which is 62.9% of the axial chord length occurs before which the diameter of salt-out particles on the pressure surface is greater than that on the suction surface, while after that the situation is opposite; for the rotor blade, a different critical position which is 81.1% of the axial chord length occurs. Along the axial direction the volume fraction of particles declines in the entrance area, fluctuates in the middle area on the stator blade, and on the pressure surface of rotor blade, a peak position of the volume fraction is consistent with the maximum turbulence intensity and particle diameter.