Low Pressure Steam Turbine Research Articles

Shock waves characteristics and losses estimation of non-equilibrium condensation flow in nozzle and steam turbine cascade

The investigation of transonic non-equilibrium condensation is paramount due to its profound influence on the shock patterns and the distribution of losses. This study numerically investigates the shock wave morphology, evolution, and quantitative loss calculation under the influence of non-equilibrium condensation within the Moses-Stein nozzle and Dykas cascade. The results indicate that the vapor near the nozzle wall undergoes phase transition first and forms “X-shaped” condensation shock, which impervious to back pressure variations. Conversely, the “λ-shaped” aerodynamic shock moves towards the throat with increasing back pressure, triggering boundary layer separation. The entropy generation of “λ-shocks” accounts for over 98% and represents the primary source of shock losses. Strong pressure side shock induces shock wave-boundary layer interactions with the blade suction wall, resulting in reflected shocks. However, the latent heat released by non-equilibrium condensation mitigates this effect, increasing the total pressure loss coefficient by 0.188. The decrease in Mach number under high back pressure causes a notable increase in the trailing edge shock angle, with the wave foot shifting upstream. Notably, the proportion of shock losses attributed to the suction side of trailing edge exceeds 80%, significantly surpassing other regions, which progressively increases with rising back pressure. Therefore, it is crucial for cascade optimization. The findings can provide references for the optimization design of low-pressure steam turbine blade profiles. The results can serve as a guide for optimizing the blade profiles of low-pressure steam turbine.

Failure analysis of atmospheric relief diaphragm in the low pressure steam turbine

In this study, the causes of failure and prevention methods for the atmospheric relief diaphragm in a low-pressure steam turbine were evaluated. The atmospheric relief diaphragm is designed to vent and burst at its center when the pressure in the exhaust housing exceeds 0.7 barG due to steam. However, visual inspection revealed that failure occurred along the flange mounting, rather than at the center of the diaphragm. Fatigue failure was identified as the cause, based on SEM analysis. Internal pressure fluctuations in the turbine caused bending along the fixed edge of the diaphragm. To confirm the occurrence of fatigue failure, finite element analysis was performed using a maximum internal pressure of 0.023 barG and a frequency of 60 Hz. The maximum deformation was 18.8 mm, which is less than the distance between the diaphragm and the knife, 30 mm. However, the maximum stress was 23.7 MPa, which exceeded the fatigue strength of A1050, 15 MPa, with stress concentration at the diaphragm edge, confirming edge fatigue failure prior to central knife failure. To identify an alternative material, finite element analysis was conducted using higher fatigue strength than A1050 under the same conditions. While the maximum stress was similar to that of A1050, it was below the fatigue strength of the alternative materials. Consequently, to prevent unexpected failures, it is recommended to use materials with higher fatigue strength than A1050 to enhance fatigue life of the diaphragm.

Boundary conditions in flutter simulations of subsonic, transonic and supersonic blade cascades

Simulations of blade flutter are highly sensitive to undesired wave reflections at inlet and outlet boundaries. A careful treatment of boundary conditions is required to prevent the generation of perturbations. This study is motivated by the need to perform flutter analysis of low-pressure steam turbine blades, for which supersonic inflow conditions may occur in the near-tip region. The exact steady non-reflecting boundary condition (NRBC), the spectral NRBC and a simple isentropic boundary condition are implemented in a time-marching flow solver and applied to turbomachinery flutter simulations covering a wide range of operating conditions. For the first time, the spectral NRBC is applied to a blade flutter simulation with a supersonic inlet and its performance is analysed and compared with other boundary condition formulations. It is shown that an effective non-reflective treatment in the design of the boundary condition is essential for an accurate aeroelastic prediction at all operating conditions, including the subsonic flow regime. The limitation of the exact steady NRBC to spatial modes causes it to perform poorly in some unsteady flow simulations, whereas the spectral NRBC achieves a satisfactory suppression of undesired wave reflections in all investigated cases.

Heat pump assisted sorption carbon capture with steam condenser heat recovery in a decarbonised coal-fired power plant

More than 50% energy input of coal-fired power plant is lost in the condensation of steam turbine in a temperature range of 30–35 ℃. Carbon capture technology has a negative influence on power generation efficiency of coal-fired power plant. Thus, it is essential to find an efficient method for waste heat recovery and increase the overall energy efficiency in coal-fired power plant with carbon capture. A novel integrated system including absorption heat pump and adsorption carbon capture based on coal-fired power plant is then presented. Waste heat from steam condenser is recovered by absorption heat pumps driven by steam extracted from low pressure steam turbine. The output hot medium from the absorption heat pumps is further heated to desorption temperature for the regeneration process of adsorbents by the extracted steam. The results show that heat penalty increases with the increase of the desorption temperature, and the heat recovery amount has an opposite trend. Compared with the conventional coal-fired power plant, thermal efficiency of the integrated system increases by 0.854%. The efficiency decrease of the compression work accounts for over a half of the total efficiency decrease due to the compression and the capture process. External heat recovery is applied in flue gas and the multi-compression process, and the thermal efficiency increase can be improved to 1.453% when compared with 0.725% of the system without external heat recovery. It proves that absorption heat pump could play a significant role in the energy saving of adsorption carbon capture system.

An Investigation of Efficiency Issues in a Low-Pressure Steam Turbine Using Neural Modelling.

This study utilizes neural networks to detect and locate thermal anomalies in low-pressure steam turbines, some of which experienced a drop in efficiency. Standard approaches relying on expert knowledge or statistical methods struggled to identify the anomalous steam line due to difficulty in capturing nonlinear and weak relations in the presence of linear and strong ones. In this research, some inputs that linearly relate to outputs have been intentionally neglected. The remaining inputs have been used to train shallow feedforward or long short-term memory neural networks using measured data. The resulting models have been analyzed by Shapley additive explanations, which can determine the impact of individual inputs or model features on outputs. This analysis identified unexpected relations between lines that should not be connected. Subsequently, during periodic plant shutdown, a leak was discovered in the indicated line.

Evaluation of a New Droplet Growth Model for Small Droplets in Condensing Steam Flows

As the condensation phenomenon occurs in the low-pressure stages of steam turbines, an accurate modelling of the condensing flows is very crucial and has a significant impact on the development of highly efficient steam turbines. In order to accurately simulate condensing steam flows, it is essential to choose the right condensation model. Further research to enhance condensation models is of special importance because the outcomes of numerical studies of condensation models in recent years have not been entirely compatible with the experiments and there are still uncertainties in this area. Therefore, the main aim of this paper is to evaluate a proposed droplet growth model for modelling condensation phenomenon in condensing steam flows. The new model is derived to profit from the advantages of models based on the continuum approach for large droplets and those based on the kinetic theorem for small droplets, which results in the model being robust for a wide range of Knudsen numbers. The model is implemented into a commercial CFD tool, ANSYS Fluent 2022 R1, using UDFs. The results of the CFD simulations are validated against experimental data for linear cascades within the rotor and stator blade geometries of low-pressure steam turbine stages. The findings clearly demonstrate the superiority of the new model in capturing droplet growth, particularly for very small droplets immediately following nucleation. In contrast, widely used alternative droplet growth models tend to either underpredict or overpredict the droplet growth rate. This research significantly contributes to the ongoing efforts to enhance condensation modeling, providing a more accurate tool for optimizing the design and operation of low-pressure steam turbines, ultimately leading to a higher energy efficiency and a reduced environmental impact.

Experimental and Numerical Investigations of Steam Expansion Rate in Low Pressure Steam Turbine

Abstract This study focused on the expansion rate of steam; the effect on efficiency was investigated experimentally and numerically by varying the expansion rate of steam in the stage, where condensation occurs by varying the flowrate and inlet temperature using a five-stage model steam turbine. The steam expansion rate of the stator blades in each stage was evaluated from the measured wall pressure and total pressure. In addition, the turbine efficiency was evaluated from the measured torque and mass flowrate, and the effect of flowrate and condensing stage can be taken into account for losses caused by condensation. In addition, numerical calculations to account for the effects of nonequilibrium condensation were performed using ANSYS CFX. The numerical calculations were able to show the details of the nucleation situation and the resulting changes in flow patterns. Numerical evaluation of the subcooling loss showed that there was no difference in subcooling loss between different mass flow rates. The steam expansion rate was evaluated from the measurement results, and it was found that there was no difference in the steam expansion rate due to differences in mass flowrate. This corresponds to the numerical result that the subcooling loss does not vary with flowrate.

Optimization of operating conditions in the steam turbine blade cascade using the black-box method

Water droplets cause corrosion and erosion, condensation loss, and thermal efficiency reduction in low-pressure steam turbines. In this study, multi-objective optimization was carried out using the black-box method through the automatic linking of a genetic algorithm (GA) and a computational fluid dynamics (CFD) code to find the optimal values of two design variables (inlet stagnation temperature and cascade pressure ratio) to reduce wetness in the last stages of turbines. The wet steam flow numerical model was used to calculate the optimization parameters, including wetness fraction rate, mean droplet radius, erosion rate, condensation loss rate, kinetic energy rate, and mass flow rate. Examining the validation results showed a good agreement between the experimental data and the numerical outcomes. According to the optimization results, the inlet stagnation temperature and the cascade pressure ratio were proposed to be 388.67 (K) and 0.55 (−), respectively. In particular, the suggested optimal temperature and pressure ratio improved the liquid mass fraction and mean droplet radius by about 32% and 29%, respectively. Also, in the identified optimal operating state, the ratios of erosion, condensation loss, and kinetic energy fell by 76%, 32.7%, and 15.85%, respectively, while the mass flow rate ratio rose by 0.68%.

Enhancing low-pressure stage steam turbine using the TDLD criterion and the TOPSIS analysis

The liquid phase in the wet steam flow causes thermodynamics losses and affects steam turbine blade durability. The main objective of the present research is the design of the rotor stagger angle and different operating conditions in the low-pressure stage of the steam turbine. A two-phase Eulerian-Eulerian model and the SST k − ω model are used to simulate the viscous wet steam flow inside the steam turbine stage. Frozen rotor methodology is employed for modeling the stator-rotor interaction. The effects of different rotor stagger angles and different outlet pressure levels on the wet steam flow parameters are studied to introduce an improved case. The turbine stage efficiency, droplet average radius, liquid mass fraction, and degree of reaction (TDLD) are considered as design criteria. The search for the improved value of pressure ratio and rotor stagger angle is performed using the TDLD criterion by TOPSIS (Technique for Order of Preference by Similarity to Ideal Solution). The improved case is selected with a rotor stagger angle of 64 degrees and outlet pressure of 6.5 kPa, at which the turbine stage efficiency (TSE) is increased by 21.3% compared to [Formula: see text]. Also, the liquid mass fraction (LMF) and the degree of reaction (DOR) reduced by 39.53 and 26% relative to [Formula: see text], and [Formula: see text], respectively. In addition, droplet average radius (DAR) increases by 26.14% compared to [Formula: see text].

Fatigue life prediction of mistuned steam turbine blades subjected to deviations in blade geometry

The blades of the steam turbine are subjected to bending of the steam flow, centrifugal loading, vibration response, and structural mistuning. These factors mentioned contribute significantly to the fatigue failure of steam turbine blades. Low pressure (LP) steam turbines experience premature blade and disk failures due to the stress concentrations in the root location of the blade of its bladed disk. This study of mistuned steam turbine blades subjected to variation in blade geometry will be of great significance to the electricity generation industry. A simplified, mistuned, scaled-down steam turbine bladed disk model was developed using ABAQUS finite element analysis (FEA) software. The acquisition of the vibration characteristics and steady-state stress response of the disk models was carried out through FEA. Such studies are very limited. Subsequently, numerical stress distributions were acquired and the model was subsequently exported to Fe-Safe software for fatigue life calculations based on centrifugal and harmonic sinusoidal pressure loading. Vibration characteristics and response of the variation of the geometric blade of the steam turbine were investigated. Natural FEA frequencies compared well with the published literature of real steam turbines, indicating the reliability of the developed FEA model. The study found that fatigue life is most sensitive to changes in blade length, followed by width and then thickness, in this order. Analytical life cycles and Fe-Safe software show a percentage difference of less than 4.86%. This concludes that the numerical methodology developed can be used for real-life mistuned steam turbine blades subjected to variations in blade geometry.

SEM and EDX analysis of erosion products formed on steam turbine blade

ABSTRACT Water droplet erosion (WDE), which is brought on by the high-energy impact of liquid water droplets, is a serious problem for steam turbine blades. Nevertheless, rather than addressing the WDE of actual steam turbine blades, the majority of the published research on this issue uses laboratory test rigs. In this study, scanning electron microscopy and energy-dispersive X-ray analysis are used to examine how the surface of low-pressure steam turbine blades that had been in service eroded over time. The results of this study provide valuable insights into the microstructural features and elemental composition of X20Cr13 steel in steam turbine blades, as well as the factors that can contribute to damage and failure.

Prediction of fatigue life of mistuned steam turbine blades subjected to variations in blade geometry

There is a large number of power stations suffering from fatigue failures of the steam turbine blades. The steam turbine blades are also subjected to steam flow bending, centrifugal loading, vibration response, and structural mistuning. These mentioned factors significantly contribute to the fatigue failure of the steam turbine blades. Low-Pressure (LP) steam turbines experience premature blade and disk failures due to the stress concentrations at the blade root area of its bladed disk. Driven by the problems encountered by the steam power plant electricity generating utilities with regards to steam turbine blades fatigue failure, this study of the mistuned steam turbine blades subjected to variation in blade geometry will be of great significance to the electricity generation industry. A simplified, scaled-down mistuned steam turbine bladed disk model was developed using ABAQUS finite element analysis (FEA) software. Acquisition of the vibration characteristics and steady-state stress response of the disk models was performed through FEA. Thereafter, numerical stress distributions were acquired, and the model was subsequently exported to Fe-Safe software for fatigue life calculations based on centrifugal and harmonic sinusoidal pressure loading. The vibration characteristics and the response of the variation steam turbine geometric blade was conducted. The FEA natural frequencies compared well with published literature of the real steam turbines indicating reliability of the developed FEA model. The study found that the fatigue life is most sensitive to changes in blade length, followed by the width, and then the thickness, in this order. The analytical life cycles and Fe-Safe software shows the percentage difference of less than 4.86%. This concludes that the developed numerical methodology can be used for real-life mistuned steam turbine blades subjected to variations in blade geometry.

Failure investigations of last stage low-pressure steam turbine blade

Failure investigations of last stage low-pressure steam turbine blade

Multimode Tip-Timing Analysis of Steam Turbine Rotor Blades

Presented in this paper is a multimode tip-timing analysis of steam turbine rotor blades using the Least Squares Technique. The rotor blade velocity obtained from the measured time of rotor blade arrival is used in the functional of the Least Square Technique, which is a novelty. The approach requires only two sensors in the casing for the algorithm to find blade multi-mode vibration components. For comparison, three and four sensors have also been used. An additional technique has been devised to determine the frequencies of blade vibration coupled modes, which is also a novelty. Verification of the algorithm is based on experimental and numerical analyses of steam turbine Low Pressure last stage rotor blades vibrating during run-down in a vacuum spin chamber, for synchronous vibrations, and during nominal work at 3000 rpm in a real working turbine for asynchronous vibrations. A multimode analysis is carried out for blade vibration at a nominal rotation speed of 3000 rpm. The considered steam turbine rotor blade is found to vibrate with two-mode shapes. This article considers the use of this method in BTT measurement uncertainties in the form of noise uniform distribution and noise normal distribution.

Thermo-economic and environmental assessment of a combined cycle fueled by MSW and geothermal hybrid energies

The hybrid renewable energy-based power generation systems offer a reliable solution to mitigate the drawbacks of individual energy source. In this respect the biomass and geothermal energies have some well-known advantages (such as continuous provision) over the solar and wind energies. In the present paper, two integration modes are proposed for hybridization of geothermal heat with a biomass-driven gas turbine based combined power cycle. The Mode 1 configuration employs geothermal heat to increase the temperature of feedwater before the deaerator, whereas the Mode 2 structure applies the geothermal energy to generate more steam for the low pressure steam turbine. Detailed exergetic, environmental and economic appraisals are carried out to examine the hybrid systems performances. In order to represent an accurate comparison of the suggested hybridization modes, the systems are optimized to achieve minimum levelized electricity cost. The results have indicated better performance for Mode 2 hybridization scenario over the Mode 1. The former system yields 10.0% greater exergy efficiency with 20.1% less electricity cost compared to Mode 1, while it can generate 22.5% more electricity. Also, it brings about 22.5% lower CO2 emission. However, the Mode 2 configuration possess one drawback compared to Mode 1, which is its higher overall system cost rate by 17.9%. The results show that, the higher cost rate of Mode 2 configuration is mainly due to larger pressure ratio of the air compressor which causes more costs for the compressor and gas turbine components.

Multi-objective optimization and exergoeconomic analysis of solar and geothermal-based power and cooling system using zeotropic mixtures as the working fluid

The current paper proposes a double-flash geothermal system with a dual-pressure organic Rankine cycle binary system. To improve the system’s performance, the inlet geofluid is preheated via an indirect mode of a solar system, and an Ejector Refrigeration Cycle system is installed to the geofluid’s brine line to produce cooling capacity. Comprehensive investigations are performed to select the Dual-pressure Organic Rankine Cycle s working fluid among various pure substances and zeotropic mixtures that refer to choosing the R245ca/R142b. The system presents 12.12 MW net power at the base mode with a 1.87 MW cooling load and 4.88 years payback period. Some main parameters’ change effect on the system is studied. The low-pressure steam turbine’s exit pressure influences the cooling load and energetic efficiency. The high-pressure turbine’s input pressure affects the total exergy destruction and net power higher than the other. The optimum state of the system is obtained through two energy-economic and exergy-economic assessments. The energy-economic assessment provides a higher cooling load of about 5.7 MW and a lower net power of about 10.8 MW with 4.59 years payback period. The exergy-economic assessment represents 12.22 MW net power and a cooling load of about 1.97 MW with 4.77 years payback period.

Vibration analysis and parametric identification of low-pressure steam turbine blade with crack using ANN

Vibration analysis and parametric identification of low-pressure steam turbine blade with crack using ANN

Second law evaluation and environmental analysis of biomass-fired power plant hybridized with geothermal energy

Two novel configurations for hybridization of geothermal and biomass energies are proposed and analyzed in this paper. In the first system (named Configuration 1) geothermal heat is employed for feed water heating, while in second one (named Configuration 2) the geothermal energy is employed for steam generation to be entered into the low pressure steam turbine stage. The method of hybridization of geothermal and biomass resources in this paper is quite different than the schemes proposed in previous researches. Another unique feature of the proposed hybrid configurations is the ability of utilizing geothermal resources with various temperature level. In order to assess the feasibility of proposed systems and to compare their performance, detailed simulation models are made based on the first and second laws. Also, the systems’ performances are evaluated from the environmental perspective using three exergo-environmental factors. In addition, the optimal operating conditions of the systems are determined with respect to the maximum exergy efficiency. For a wide range of practical operating conditions it is found that, the proposed Configuration 2 outperforms the Configuration 1 due to the direct steam injection into the law-pressure turbine in the former. Under the optimal operation, it yields 8.65 % higher exergy efficiency as well as 12.5% lower environmental damage effectiveness compared to Configuration 1. Also it is concluded that, the gasification and combustion processes own more than 55% of overall exergy destruction in both systems.

복합화력 중압 및 저압 증기터빈의 최적 입구압력 선정

본 연구 목적은 초초임계압 관류형 HRSG를 적용한 증기터빈의 중압 및 저압터빈의 입구 압력에 대한 시뮬레이션을 수행하여 최적 설계점을 도출하는데 있다. 증기터빈 입구압력 조건 마다 HRSG 설계, 증기터빈 출력 및 건설비가 다르다. 그리고 출력이 높으면 건설비가 증가되고, 출력이 낮으면 건설비가 감소된다. 따라서 30년 설계수명을 고려하여 경제성 평가 계수를 적용한 경제성 분석을 통하여 그 상관관계를 도출하고 고성능의 경제적인 최적 설계점을 선정하였다.

Failure analysis of a low-pressure stage steam turbine blade

ABSTRACT Steam turbine blades are regularly damaged because of their harsh working conditions, which include elevated temperatures and fluctuating loads. Most investigations of blade failures end with a metallurgical analysis, which does not provide sufficient positive identification of the mechanisms involved. Hence, in the current research work a mechanical analysis is performed in conjunction with the metallurgical analysis for competent analysis of blade failure. For the purpose of evaluating the damage, non-destructive testing (NDT) was carried out. The purpose of this examination is to qualitatively examine the blade of a 210 MW low-pressure steam turbine after 1,52, 241 h of working to identify the critical locations of damage and the reason behind it. Visual examination, chemical analysis, dye penetration testing, and metallurgical testing are all part of this examination. In addition, mechanical properties were evaluated using hardness and tensile testing. The findings revealed that water droplet erosion accelerated blade failure, preferentially attacking the blade’s edges. These erosion pits act as stress concentrators and serve as a potential crack propagator if neglected, which can lead to catastrophic failure of the system. Hence, to increase reliability and to avoid such failures in future, this type of failure analysis is highly recommended.