Experimental Investigation Into Thermal Behavior of Steam Turbine Components: Part 3 — Startup and the Impact on LCF Life

2013 ◽  
Author(s):  
Gabriel Marinescu ◽  
Michael Sell ◽  
Andreas Ehrsam ◽  
Philipp B. Brunner
Keyword(s):  
Thermal Behavior ◽  
Steam Turbine ◽  
Low Cycle Fatigue ◽  
Numerical Procedure ◽  
Cyclic Fatigue ◽  
Low Flow ◽  
Steam Turbines ◽  
Early Loading ◽  
Start Up ◽  
The Impact

Steam turbine start-up has a significant impact on the cyclic fatigue life. Modern steam turbines are operated at high temperatures for optimal efficiency, which results in high temperature differences relative to the condition before start-up. To achieve the fastest possible start-up time without reducing the lifetime of the turbine components due to excessive thermal stress, the start-up procedure of cyclic turbines is optimized to follow the specific material low cycle fatigue limit. For such optimization and to ensure reliable operation, it is essential to fully understand the thermal behavior of the components during start-up. This is especially challenging in low flow conditions, i.e. during pre-warming and early loading phase. A two-dimensional numerical procedure is described for the assessment of the thermal regime during start-up. The calculation procedure includes the rotor, casings, valves and main pipes. The concept of the start-up calculation is to replace the convective effect of the steam in the turbine cavity by an equivalent fluid over-conductivity that gives the same thermal effect on metallic parts. This approach allows simulating accurately the effect of steam ingestion during pre-warming phase. The fluid equivalent over-conductivity is calibrated with experimental data. At the end of the paper the impact of ingested steam temperature and mass-flow on the rotor cyclic lifetime is demonstrated. This paper is a continuation of papers [1] and [2].

Experimental Investigation Into Thermal Behavior of Steam Turbine Components: Part 2—Natural Cooling of Steam Turbines and the Impact on LCF Life

2012 ◽  
Author(s):  
Gabriel Marinescu ◽  
Andreas Ehrsam
Keyword(s):  
Steam Turbine ◽  
Numerical Procedure ◽  
Cyclic Fatigue ◽  
Steam Turbines ◽  
Cyclic Operation ◽  
Start Up ◽  
Highly Sensitive ◽  
Higher Temperature ◽  
The Impact ◽  
Fluid Conductivity

Steam turbine cool-down has a significant impact on the cyclic fatigue life. A lower initial metal temperature after standstill results in a higher temperature difference to be overcome during the next start-up. Generally, lower initial metal temperatures result in higher start-up stress. In order to optimize steam turbines for cyclic operation, it is essential to fully understand natural cooling, which is especially challenging for rotors. A two-dimensional numerical procedure is described for the assessment of the thermal regime during natural cooling including the rotors, casings, valves and main pipes. The concept of the cooling calculation is to replace the steam gross buoyancy during the gland steam ingestion phase by an equivalent fluid conductivity, that gives the same thermal effect on the metal parts. The fluid equivalent conductivity is calculated based on measurements. The approach is calibrated with experimental data. Finally, the highly sensitive nature of the cyclic lifetime to the predicted cooling evolution is demonstrated. This paper is complementary with the paper [1].

Experimental Investigation Into Thermal Behavior of Steam Turbine Components—Temperature Measurements With Optical Probes and Natural Cooling Analysis

2013 ◽  
Vol 136 (2) ◽  
Author(s):  
Gabriel Marinescu ◽  
Wolfgang F. Mohr ◽  
Andreas Ehrsam ◽  
Paolo Ruffino ◽  
Michael Sell
Keyword(s):  
Steam Turbine ◽  
Numerical Procedure ◽  
Cyclic Fatigue ◽  
Temperature Measurements ◽  
Steam Turbines ◽  
Equivalent Conductivity ◽  
Cyclic Operation ◽  
Start Up ◽  
Higher Temperature ◽  
Fluid Conductivity

The steam turbine cooldown has a significant impact on the cyclic fatigue life. A lower initial metal temperature after standstill results in a higher temperature difference to be overcome during the next start-up. Generally, lower initial metal temperatures result in higher start-up stress. In order to optimize steam turbines for cyclic operation, it is essential to fully understand natural cooling, which is especially challenging for rotors. This paper presents a first-in-time application of a 2D numerical procedure for the assessment of the thermal regime during natural cooling, including the rotors, casings, valves, and main pipes. The concept of the cooling calculation is to replace the fluid gross buoyancy during natural cooling by an equivalent fluid conductivity that gives the same thermal effect on the metal parts. The fluid equivalent conductivity is calculated based on experimental data. The turbine temperature was measured with pyrometric probes on the rotor and with standard thermocouples on inner and outer casings. The pyrometric probes were calibrated with standard temperature measurements on a thermo well, where the steam transmittance and the rotor metal transmissivity were measured.

Experimental Investigation Into Thermal Behavior of Steam Turbine Components: Part 4 — Natural Cooling and Robustness of the Over-Conductivity Function

2014 ◽  
Author(s):  
Gabriel Marinescu ◽  
Peter Stein ◽  
Michael Sell
Keyword(s):  
Steam Turbine ◽  
Fluid Velocity ◽  
Numerical Procedure ◽  
Cyclic Fatigue ◽  
Theoretical Background ◽  
Fluid Temperature ◽  
Steam Turbines ◽  
Main Concept ◽  
Start Up ◽  
Conductivity Function

Steam turbine transient maneuvers have a significant impact on the cyclic fatigue life. Modern steam turbines are operated at high temperatures for optimal efficiency, which results in high time and space temperature gradients. A low initial metal temperature after standstill results in a high temperature difference to be overcome during the next startup and consequently a low lifetime at critical locations. To achieve the fastest possible start-up time without reducing the lifetime of the turbine components, the natural cooling must be captured accurately in calculation and the start-up procedure optimized. At the past two ASME conferences we presented three papers [1], [2], [3], about a 2D numerical procedure for the thermal regime calculation during natural cooling and startup. The analysis included the rotor, casings, valves and pipes. The main concept was to replace the thermal effect of the fluid convectivity by a fluid function K(T) called “over-conductivity”, which is calibrated vs. experimental data. The paper below shows: (a) the theoretical background of the over-conductivity function K(T) and (b) the equation of the correlation function f(T,p) between the fluid velocity and fluid temperature gradient. Both K(T) and f(T,p) are applicable for the flow within the large turbine cavities with negligible pressure gradient. The robustness of the K(T) function is verified on three different turbine configurations. For each machine a separate transient thermal model was built and the calculated temperatures were compared with the corresponding measured temperatures. At the end of the paper conclusions about the natural cooling features are presented.

Utilization of a Thermo-Mechanical Model Coupled With Multi-Objective Optimization to Enhance the Start-Up Process of Solar Steam Turbines

2018 ◽  
Author(s):  
Monika Topel ◽  
Andrea Vitrano ◽  
Björn Laumert
Keyword(s):  
Steam Turbine ◽  
Solar Power ◽  
Low Cycle Fatigue ◽  
Steam Turbines ◽  
Multi Objective Optimization ◽  
Concentrating Solar Power ◽  
Multi Objective ◽  
Start Up ◽  
Turbine Component ◽  
Start Ups

The need to mitigate the climate change has brought in the last years to a fast rise of renewable technologies. The inherent fluctuations of the solar resource make concentrating solar power technologies an application that demands full flexibility of the steam turbine component. A key aspect of this sought steam turbine flexibility is the capability for fast starts, in order to harvest the solar energy as soon as it is available. However, turbine start-up time is constrained by the risk of low cycle fatigue damage due to thermal stress, which may bring the machine to failure. Given that the thermal limitations related to fatigue are temperature dependent, a transient thermal analysis of the steam turbine during start process is thus necessary in order to improve the start-up operation. This work focuses on the calculation of turbine thermo-mechanical properties and the optimization of different start-up cases in order to identify the best solution in terms of guaranteeing reliable and fast start-ups. In order to achieve this, a finite element thermal model of a turbine installed in a concentrating solar power plant was developed and validated against measured data. Results showed relative errors of temperature evolutions below 2%, making valid the assumptions and simplifications made. Since there is trade-off between start-up speed and turbine lifetime consumption, the model was then implemented within a multi-objective optimization scheme in order to test and design faster start-ups while ensuring safe operation of the machine. Significant improvements came up in terms of start-up time reduction up to 30% less than the standard start-up process.

Improvement in the Rapid Startup Performance for the Solar Steam Turbine

2018 ◽  
Author(s):  
Peng Wang ◽  
Gang Chen ◽  
WenFu Li
Keyword(s):  
Steam Turbine ◽  
Cyclic Fatigue ◽  
Steam Turbines ◽  
Load Variations ◽  
Start Up ◽  
Reheat Steam ◽  
Startup Performance ◽  
Transient Thermal ◽  
Life Consumption ◽  
Operation Flexibility

In the latest several years, concentrated solar plants (CSP) have been rapidly developed. Steam turbines employed in these plants are subjected to daily start up and continuous load variations. There is a general increase in demand for operation flexibility and rapid start up capability for solar steam turbines. Accordingly, how to decrease the low cyclic fatigue life consumption during the daily start up process is a hot researched topic at present, and this greatly depends on the transient thermal stress. A number of studies show that the startup schemes and the unit’s structural form decide the LCF life consumption directly. In this paper, a 50MW double cylinder (HP and ILP Section) reheat solar steam turbine is studied, and it is operated continuously with inlet steam conditions of 540[°C], 140[bar], reheat steam conditions of 540[°C], 24[bar] and exhaust conditions of 41.5[°C], 0.08[bar]. A number of comparisons are made with the FEM numerical simulation, and some optimal designs which are applied to improve the rapid start up performance and decrease the LCF life consumption during the startup are presented.

Investigation Into the Thermal Limitations of Steam Turbines During Start-Up Operation

2017 ◽  
Author(s):  
Monika Topel ◽  
Björn Laumert ◽  
Åsa Nilsson ◽  
Markus Jöcker
Keyword(s):  
Electricity Market ◽  
Low Cycle Fatigue ◽  
Operating Conditions ◽  
Limiting Factor ◽  
Steam Turbines ◽  
Expansion Behavior ◽  
Start Up ◽  
Schedule Design ◽  
Turbine Component ◽  
Differential Expansion

Liberalized electricity market conditions and concentrating solar power technologies call for increased power plant operational flexibility. Concerning the steam turbine component, one key aspect of its flexibility is the capability for fast starts. In current practice, turbine start-up limitations are set by consideration of thermal stress and low cycle fatigue. However, the pursuit of faster starts raises the question whether other thermal phenomena can become a limiting factor to the start-up process. Differential expansion is one of such thermal properties, especially since the design of axial clearances is not included as part of start-up schedule design and because its measurement during operation is often limited or not a possibility at all. The aim of this work is to understand differential expansion behavior with respect to transient operation and to quantify the effect that such operation would have in the design and operation of axial clearances. This was accomplished through the use of a validated thermo-mechanical model that was used to compare differential expansion behavior for different operating conditions of the machine. These comparisons showed that faster starts do not necessarily imply that wider axial clearances are needed, which means that the thermal flexibility of the studied turbine is not limited by differential expansion. However, for particular locations it was also obtained that axial rubbing can indeed become a limiting factor in direct relation to start-up operation. The resulting approach presented in this work serves to avoid over-conservative limitations in both design and operation concerning axial clearances.

Modeling Partial Admission in Control Stages of Small Steam Turbines With CFD

2018 ◽  
Author(s):  
Juri Bellucci ◽  
Filippo Rubechini ◽  
Andrea Arnone
Keyword(s):  
Steam Turbine ◽  
Three Dimensional ◽  
Admission Rate ◽  
Point Of View ◽  
Test Case ◽  
Steam Turbines ◽  
Turbine Stage ◽  
Performance Curves ◽  
Partial Admission ◽  
The Impact

This work aims at investigating the impact of partial admission on a steam turbine stage, focusing on the aerodynamic performance and the mechanical behavior. The partialized stage of a small steam turbine was chosen as test case. A block of nozzles was glued in a single “thick nozzle” in order to mimic the effect of a partial admission arc. Numerical analyses in full and in partial admission cases were carried out by means of three-dimensional, viscous, unsteady simulations. Several cases were tested by varying the admission rate, that is the length of the partial arc, and the number of active sectors of the wheel. The goal was to study the effect of partial admission conditions on the stage operation, and, in particular on the shape of stage performance curves as well as on the forces acting on bucket row. First of all, a comparison between the flow field of the full and the partial admission case is presented, in order to point out the main aspects related to the presence of a partial arc. Then, from an aerodynamic point of view, a detailed discussion of the modifications of unsteady rows interaction (potential, shock/wake), and how these ones propagate downstream, is provided. The attention is focused on the phenomena experienced in the filling/emptying region, which represent an important source of aerodynamic losses. The results try to deepen the understanding in the loss mechanisms involved in this type of stage. Finally, some mechanical aspects are addressed, and the effects on bucket loading and on aeromechanical forcing are investigated.

scholarly journals Dynamic Response of Rub Caused by a Shedding Annular Component Happening in a Steam Turbine

2015 ◽  
Vol 2015 ◽  
pp. 1-6 ◽  
Author(s):  
J. M. Chen ◽  
D. X. Jiang ◽  
N. F. Wang ◽  
S. P. An
Keyword(s):  
Dynamic Response ◽  
Steam Turbine ◽  
Structural Features ◽  
Frequency Domain Analysis ◽  
Steam Turbines ◽  
Contact Constraint ◽  
Fault Features ◽  
Rotor Bearing ◽  
Main Components ◽  
The Impact

Rub caused by a shedding annular component is a severe fault happening in a steam turbine, which could result in a long-term wearing effect on the shaft. The shafting abrasion defects shortened the service life and damaged the unit. To identify the fault in time, the dynamic response of rub caused by a shedding annular component was studied as follows: (I) a rotor-bearing model was established based on the structural features of certain steam turbines; node-to-node contact constraint and penalty method were utilized to analyze the impact and friction; (II) dynamic response of the rotor-bearing system and the shedding component was simulated with the development of rub after the component was dropping; (III) fault features were extracted from the vibration near the bearing position by time-domain and frequency-domain analysis. The results indicate that the shedding annular component would not only rotate pivoting its axis but also revolve around the shaft after a period of time. Under the excitation of the contact force, the peak-peak vibration fluctuates greatly. The frequency spectrum contains two main components, that is, the working rotating frequency and revolving frequency. The same phenomenon was observed from the historical data in the field.

Coordinated Control of Gas and Steam Turbines for Efficient Fast Start-Up of Combined Cycle Power Plants

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
Yasuhiro Yoshida ◽  
Kazunori Yamanaka ◽  
Atsushi Yamashita ◽  
Norihiro Iyanaga ◽  
Takuya Yoshida
Keyword(s):  
Thermal Stress ◽  
Steam Turbine ◽  
Gas Turbines ◽  
Power Plants ◽  
Thermal Stresses ◽  
Control Method ◽  
Coordinated Control ◽  
Combined Cycle ◽  
Steam Turbines ◽  
Start Up

In the fast start-up for combined cycle power plants (CCPP), the thermal stresses of the steam turbine rotor are generally controlled by the steam temperatures or flow rates by using gas turbines (GTs), steam turbines, and desuperheaters to avoid exceeding the thermal stress limits. However, this thermal stress sensitivity to steam temperatures and flow rates depends on the start-up sequence due to the relatively large time constants of the heat transfer response in the plant components. In this paper, a coordinated control method of gas turbines and steam turbine is proposed for thermal stress control, which takes into account the large time constants of the heat transfer response. The start-up processes are simulated in order to assess the effect of the coordinated control method. The simulation results of the plant start-ups after several different cool-down times show that the thermal stresses are stably controlled without exceeding the limits. In addition, the steam turbine start-up times are reduced by 22–28% compared with those of the cases where only steam turbine control is applied.

Influence of Creep on Low-Cycle Fatigue Life Assessment of Ultra-Supercritical Steam Turbine Rotor

2014 ◽  
Author(s):  
W. Z. Wang ◽  
J. H. Zhang ◽  
H. F. Liu ◽  
Y. Z. Liu
Keyword(s):  
High Temperature ◽  
Steam Turbine ◽  
Fatigue Damage ◽  
Low Cycle Fatigue ◽  
Turbine Rotor ◽  
High Temperature Creep ◽  
Cycle Fatigue ◽  
Term Operation ◽  
Start Up

Linear damage method is widely used to calculate low-cycle fatigue damage of turbine rotor in the long-term operation without fully considering the interaction between creep and low cycle fatigue. However, with the increase of steam turbine pressure and temperature, the influence of high-temperature creep on the strain distribution of turbine rotor becomes significant. Accordingly, the strain for each start-up or shut-down process is different. In the present study, the stress and strain during 21 iterations of continuous start-up, running and shut-down processes was numerically investigated by using the finite element analysis. The influence of high-temperature creep on low cycle fatigue was analyzed in terms of equivalent strain, Mises stress and low cycle fatigue damage. The results demonstrated that the life consumption of turbine rotor due to low cycle fatigue in the long-term operation of startup, running and shutdown should be determined from the full-time coverage of the load of turbine rotor.

Sign in / Sign up

Export Citation Format

Share Document