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 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 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.

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.

Rotor Life Prediction and Improvement for Steam Turbines Under Cyclic Operation

2011 ◽  
Author(s):  
Damaso Checcacci ◽  
Lorenzo Cosi ◽  
Sanjay Kumar Sah
Keyword(s):  
Steam Turbine ◽  
Turbine Rotor ◽  
Combined Cycle ◽  
Operating Conditions ◽  
Steam Turbines ◽  
Power Utility ◽  
Simplified Approach ◽  
Cyclic Operation ◽  
Combined Cycle Plant ◽  
The Impact

The evolution of the energy market is leading to a general increase in demand for cyclic operation and rapid startup capability for steam turbines utilized in power utility plants. As a consequence, turbine manufactures must optimize designs to minimize transient stress and make available to plant operators the necessary understanding of the impact of operating conditions on parts life. In addition, if continuous duty operation is not economical for an existing plant, operators considering switching to the cyclic mode need to take into account the cost associated with reduced maintenance intervals and parts replacement. This paper presents the methodologies applied to assess and optimize steam turbine rotor life. The discussion stems from the case analysis of a 60 MW steam turbine that was operated almost uninterrupted for 10 years in a combined cycle plant and was then expected to switch to cyclic operation with approx 250 startups/year. The effects of different rotor geometries on transient thermal stress/strain conditions are presented along with the consequences of startup sequence modifications for rotor life vs. on-line time. The discussion is supported by modeling details and results from transient thermomechanical FEM analyses. The possibility of a simplified approach in the form of approximate models for the analysis of such behavior on a project basis is also addressed.

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.

A discussion on deformation of solids by the impact of liquids, and its relation to rain damage in aircraft and missiles, to blade erosion in steam turbines, and to cavitation erosion - Damage to solids caused by cavitation

1966 ◽  
Vol 260 (1110) ◽  
pp. 245-255 ◽  
Keyword(s):  
Mechanical Properties ◽  
Cavitation Erosion ◽  
Cavitation Resistance ◽  
Steam Turbines ◽  
Single Event ◽  
Cavitation Damage ◽  
Erosion Damage ◽  
Highly Sensitive ◽  
Wide Range ◽  
The Impact

This paper describes the early stages of cavitation damage observed in cavitating venturi tunnels. The cavitating fluids were water and mercury, and a wide range of specimen materials were used. The damage was found to consist of single-event symmetical craters and irregular fatigue-type failures. The degree of damage was highly sensitive to minor flow perturbations, and this is discussed. The effect of stress level in the specimen before testing, and relations between cavitation resistance and the mechanical properties of the materials are considered.

A Simplified Analytical Approach for Calculating the Start-Up Time of Industrial Steam Turbines for Optimal and Fast Start-Up Procedures

2015 ◽  
Author(s):  
Wolfgang Beer ◽  
Lukas Propp ◽  
Lutz Voelker
Keyword(s):  
Steam Turbine ◽  
Analytical Approach ◽  
Three Dimensional ◽  
Steam Turbines ◽  
Time Step ◽  
One Dimensional ◽  
Start Up ◽  
Time Calculation ◽  
Fast Start ◽  
The One

New flexible operational regimes with fast start-ups and fast-changing load cycles for steam turbines require calculation procedures for determining optimal start-up times in order not to exceed the limits of thermal stress for the steam turbine parts. This work presents a start-up time calculation for various kinds of industrial steam turbines. An analytical approach for estimating the optimal thermal load of a turbine from quasi-steady or steady condition is developed. The geometry of the respective turbine components, the changing of the steam parameters and heat transfer effects during the start-up procedure are taken into account while observing the respective material properties and stress limits. The temperature distributions of the respective turbine parts are calculated with a one-dimensional numerical algorithm of Fourier’s heat conduction equation. Three-dimensional influences of the geometry and of the the heat flux are considered analytically by adjusting the numerical solutions of elementary bodies (e.g. one-dimensional plate). The start-up time calculation is performed in small time steps to guarantee the stability of the numerical solution. The unsteady stress analysis for the start-up procedure does not uniquely identify one critical component. The calculation must be repeated for each time step to identify the component which limits the start-up gradient. Other boundary conditions, such as restricted speed ranges of the rotor with minimum transients and time for synchronization with the electrical grid, are considered by the model too and can further limit the start-up gradient and lead to slower start-up procedures. The one-dimensional calculation models were verified with a three-dimensional FEA of the casing and a two axis symmetrical FEA of the rotor. The results for the temperature distribution are presented and compared to the one-dimensional results. The final result of the analytical approach for an optimized start-up time calculation is verified with two typical start-up calculations, one for a generator drive steam turbine and one for a mechanical-drive steam turbine.

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