Comparison of Steam Turbine Pre-Warming and Warm-Keeping Strategies Using Hot Air for Fast Turbine Start-Up

2020 ◽  
Author(s):  
Lukas Pehle ◽  
Piotr Łuczyński ◽  
Taejun Jeon ◽  
Manfred Wirsum ◽  
Wolfgang F. D. Mohr ◽  
...  
Keyword(s):  
Steam Turbine ◽  
Energy Demand ◽  
Energy Use ◽  
Renewable Energy Sources ◽  
Mechanical Analysis ◽  
Temperature Fields ◽  
Transient Temperature ◽  
Steam Turbines ◽  
Hot Air ◽  
Start Up

Abstract Adaptability of coal-based power generating units to accommodate renewable energy sources is becoming increasingly important. In order to improve flexibility, reduce start-up time and extend the life cycle, General Electric has developed solutions to pre-warm/warm-keep steam turbines using hot air. In this paper two main contributions to optimize the warming arrangements are presented. Firstly, the calibrated model of a 19-stage IP steam turbine is analyzed regarding time-dependent mass flow rates in a pre-warming mode. The influences on the duration time of the process and the thermally induced stress are investigated. This investigation utilizes a detailed 3D hybrid (HFEM-numerical FEM and analytical) model of the turbine including the rotor, inner casing and blading for computationally-efficient determination of transient temperature fields in individual components. The thermal boundary conditions are calculated by means of heat transfer correlations developed for this purpose. Moreover, a separate FEM model allows for the implementation of a structural mechanical analysis. As a result of this investigation, the pre-warming time can be further reduced while simultaneously lowering the thermal load in the components. Secondly, selected pre-warming strategies are compared with the warm-keeping scenarios. This analysis is aimed at a minimum thermal energy use required for a reheating of air in a warming arrangement. Hence, the pre-warming and warm-keeping operating strategies are evaluated with regard to their energy demand before start-up. Thus, based on the duration of standstill, the most energy-efficient turbine warming strategy can be chosen to ensure hot start-up conditions.

Thermo-Structural Analysis of Steam Turbine Start-Up with and Without Integrated Pre-Warming System Using Hot Air

2021 ◽  
Author(s):  
Piotr Luczynski ◽  
Lukas Pehle ◽  
Manfred Wirsum ◽  
Wolfgang F. D. Mohr ◽  
Jan Vogt ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Steam Turbine ◽  
Thermal Contact ◽  
Temperature Fields ◽  
Transient Temperature ◽  
Operating Modes ◽  
Hot Air ◽  
Start Up ◽  
Simulation Strategy ◽  
Transient Thermal

Abstract In this paper, the transient thermal and structural analyses of a 19-stage IP steam turbine in various start-up operating modes are discussed. The research utilises a hybrid (HFEM - numerical FEM and analytical) approach to efficiently determine the time-dependent temperature distribution in the components of the steam turbine. The simulation strategy of the HFEM model applies analytical correlations to describe heat transfer in the turbine channel. These are developed by means of unsteady multistage conjugate heat transfer simulations for both start-up turbine operation with steam and pre-warming operation with hot air. Moreover, the numerical setup of the HFEM model considers the thermal contact resistance (TCR) on the surfaces between vane and casing as well as blades and rotor. Prior to the analysis of other turbine start-up operating modes, the typical start-up turbine process is calculated and validated against an experimental data as a benchmark for subsequent analysis. In addition to heat transfer correlations, the simulation of a turbine start-up from cold state uses an analytic pressure model to allow for a consideration of condensation effects during first phase of start-up procedure. Finally, the presented thermal investigation focuses on the comparison of transient temperature fields in the turbine for different start-up scenarios after pre-warming with hot air and provides the subsequent structural investigation with boundary conditions. As a result, the values of the highest stress are numerically determined and compared to the values obtained by means of cold start-up simulation.

Thermostructural Analysis of Steam Turbine in Prewarming Operation With Hot Air

2019 ◽  
Vol 141 (11) ◽  
Author(s):  
Piotr Łuczyński ◽  
Dennis Toebben ◽  
Lukas Pehle ◽  
Manfred Wirsum ◽  
Wolfgang F. D. Mohr ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Finite Element Method ◽  
Finite Element ◽  
Steam Turbine ◽  
Thermal Contact ◽  
Temperature Fields ◽  
Cooling Curve ◽  
Steam Turbines ◽  
Hot Air ◽  
Element Method

AbstractIn pursuit of flexibility improvements and extension of lifetime, a concept to prewarm steam turbines using hot air was developed. In order to further optimize the prewarming operation, an extensive numerical investigation is conducted to determine the time-dependent temperature and stress fields. In this work, the transient thermal and structural analyses of an IP 19-stage steam turbine in prewarming operation with hot air are presented. Based on the previous investigations, a hybrid finite element method (HFEM—numerical finite element method (FEM) and analytical) approach especially developed for this purpose is applied to efficiently calculate the solid body temperatures of a steam turbine in predefined prewarming scenarios. The HFEM model utilizes the Nusselt number correlations to describe the heat transfer between the hot air and the turbine components in the flow channel. These correlations were developed based on unsteady conjugate heat transfer (CHT) simulations of multistage turbine models. In addition, most of the thermal energy in turbine prewarming operation is transferred through vanes and blades. Therefore, the HFEM approach considers the thermal contact resistance (TCR) on the surfaces between vanes/casing and blades/rotor. After the calibration of the HFEM model with experimental data based on measurements of the natural cooling curve, the prewarming processes for different prewarming scenarios are simulated. Subsequently, the obtained temperature fields are imported to an FEM model in order to conduct a structural analysis, which, among other variables, includes the values and locations of highest stresses and displacements.

Thermo-Structural Analysis of Steam Turbine in Pre-Warming Operation With Hot Air

2019 ◽  
Author(s):  
Piotr Łuczyński ◽  
Dennis Toebben ◽  
Lukas Pehle ◽  
Manfred Wirsum ◽  
Wolfgang F. D. Mohr ◽  
...  
Keyword(s):  
Structural Analysis ◽  
Steam Turbine ◽  
Thermal Contact ◽  
Temperature Fields ◽  
Cooling Curve ◽  
Steam Turbines ◽  
Fem Model ◽  
Hot Air ◽  
Multistage Turbine ◽  
Transient Thermal

Abstract In pursuit of flexibility improvements and extension of lifetime, a concept to pre-warm steam turbines using hot air was developed. In order to further optimize the pre-warming operation, an extensive numerical investigation is conducted to determine the time-dependent temperature and stress fields. In this work, the transient thermal and structural analyses of an IP 19-stage steam turbine in pre-warming operation with hot air are presented. Based on the previous investigations, a hybrid (HFEM - numerical FEM and analytical) approach especially developed for this purpose is applied to efficiently calculate the solid body temperatures of a steam turbine in pre-defined pre-warming scenarios. The HFEM model utilizes the Nusselt number correlations to describe the heat transfer between the hot air and the turbine components in the flow channel. These correlations were developed based on unsteady CHT-simulations of multistage turbine models. In addition, most of the thermal energy in turbine pre-warming operation is transferred through vanes and blades. Therefore, the HFEM approach considers the thermal contact resistance (TCR) on the surfaces between vanes/casing and blades/rotor. After the calibration of the HFEM model with experimental data based on measurements of the natural cooling curve, the pre-warming processes for different pre-warming scenarios are simulated. Subsequently, the obtained temperature fields are imported to an FEM model in order to conduct a structural analysis, which, among other variables, includes the values and locations of highest stresses and displacements.

Thermo-Structural Analysis of Steam Turbine Start-Up With and Without Integrated Pre-Warming System Using Hot Air

2020 ◽  
Author(s):  
Piotr Łuczyński ◽  
Lukas Pehle ◽  
Manfred Wirsum ◽  
Wolfgang F. D. Mohr ◽  
Jan Vogt ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Steam Turbine ◽  
Power Plants ◽  
Thermal Contact ◽  
Steam Turbines ◽  
Operating Modes ◽  
Hot Air ◽  
Start Up ◽  
Simulation Strategy ◽  
Transient Thermal

Abstract Motivated by the urgent need for flexibility and start-up capability improvements of conventional power plants in addition to extending their life cycle, General Electric provides its customers with a product to pre-warm steam turbines using hot air. In this paper, the transient thermal and structural analyses of a 19-stage IP steam turbine in various start-up operating modes are discussed in detail. The presented research is based on previous investigations and utilises a hybrid (HFEM - numerical FEM and analytical) approach to efficiently determine the time-dependent temperature distribution in the components of the steam turbine. The simulation strategy of the HFEM model applies various analytical correlations to describe heat transfer in the turbine channel. These are developed by means of extensive unsteady multistage conjugate heat transfer simulations for both start-up turbine operation with steam and pre-warming operation with hot air. Moreover, the complex numerical setup of the HFEM model also considers the thermal contact resistance (TCR) on the surfaces between vane and casing as well as blades and rotor. Prior to the analysis of other turbine start-up operating modes, the typical start-up turbine process is calculated and validated against an experimental data as a benchmark for subsequent analysis. In addition to heat transfer correlations, the simulation of a turbine start-up from cold state uses an innovative analytic pressure model to allow for a consideration of condensation effects during first phase of start-up procedure.

scholarly journals Thermo-mechanical fatigue prediction of a steam turbine shaft

2018 ◽  
Vol 165 ◽  
pp. 22016 ◽  
Author(s):  
Martin Nesládek ◽  
Michal Bartošák ◽  
Josef Jurenka ◽  
Jan Papuga ◽  
Milan Růžička ◽  
...  
Keyword(s):  
Steam Turbine ◽  
Renewable Energy Sources ◽  
Temperature Fields ◽  
Steam Turbines ◽  
Element Analysis ◽  
Operating Cycle ◽  
Elastic Plastic ◽  
Mechanical Fatigue ◽  
Turbine Shaft ◽  
Design Calculations

The increasing demands on the flexibility of steam turbines due to the use of renewable energy sources substantially alters the fatigue strength requirements of components of these devices. This paper presents Thermo-Mechanical Fatigue (TMF) design calculations for the steam turbine shaft. The steam turbine shaft is exposed to complex thermo-mechanical loading conditions during the operating cycle of the turbine. An elastic-plastic structural Finite Element Analysis (FEA) of the turbine shaft is performed for the turbine operating cycle on the basis of calculated temperature fields obtained in a previous transient thermal FEA. The temperature dependent material parameters, which are used in the elastic-plastic FEA, are obtained from the uniaxial tests. Consequently, the TMF is predicted for the steam turbine shaft. Several fatigue criteria are used for the identifications of the critical domain and for the TMF damage assessment of the turbine shaft.

Efficient Multi-Objective Optimization of Labyrinth Seal Leakage in Steam Turbines Based on Hybrid Surrogate Models

2016 ◽  
Author(s):  
Kevin Cremanns ◽  
Dirk Roos ◽  
Simon Hecker ◽  
Peter Dumstorff ◽  
Henning Almstedt ◽  
...  
Keyword(s):  
Steam Turbine ◽  
Surrogate Model ◽  
Power Plants ◽  
Polynomial Regression ◽  
Renewable Energy Sources ◽  
Surrogate Models ◽  
Future Market ◽  
Steam Turbines ◽  
Model Calculations ◽  
Highly Efficient

The demand for energy is increasingly covered through renewable energy sources. As a consequence, conventional power plants need to respond to power fluctuations in the grid much more frequently than in the past. Additionally, steam turbine components are expected to deal with high loads due to this new kind of energy management. Changes in steam temperature caused by rapid load changes or fast starts lead to high levels of thermal stress in the turbine components. Therefore, todays energy market requires highly efficient power plants which can be operated under flexible conditions. In order to meet the current and future market requirements, turbine components are optimized with respect to multi-dimensional target functions. The development of steam turbine components is a complex process involving different engineering disciplines and time-consuming calculations. Currently, optimization is used most frequently for subtasks within the individual discipline. For a holistic approach, highly efficient calculation methods, which are able to deal with high dimensional and multidisciplinary systems, are needed. One approach to solve this problem is the usage of surrogate models using mathematical methods e.g. polynomial regression or the more sophisticated Kriging. With proper training, these methods can deliver results which are nearly as accurate as the full model calculations themselves in a fraction of time. Surrogate models have to face different requirements: the underlying outputs can be, for example, highly non-linear, noisy or discontinuous. In addition, the surrogate models need to be constructed out of a large number of variables, where often only a few parameters are important. In order to achieve good prognosis quality only the most important parameters should be used to create the surrogate models. Unimportant parameters do not improve the prognosis quality but generate additional noise to the approximation result. Another challenge is to achieve good results with as little design information as possible. This is important because in practice the necessary information is usually only obtained by very time-consuming simulations. This paper presents an efficient optimization procedure using a self-developed hybrid surrogate model consisting of moving least squares and anisotropic Kriging. With its maximized prognosis quality, it is capable of handling the challenges mentioned above. This enables time-efficient optimization. Additionally, a preceding sensitivity analysis identifies the most important parameters regarding the objectives. This leads to a fast convergence of the optimization and a more accurate surrogate model. An example of this method is shown for the optimization of a labyrinth shaft seal used in steam turbines. Within the optimization the opposed objectives of minimizing leakage mass flow and decreasing total enthalpy increase due to friction are considered.

The Effect of Stage-Diffuser Interaction on the Aerodynamic Performance and Design of LP Steam Turbine Exhaust Systems

2018 ◽  
Author(s):  
Bowen Ding ◽  
Liping Xu ◽  
Jiandao Yang ◽  
Rui Yang ◽  
Yuejin Dai
Keyword(s):  
Steam Turbine ◽  
Renewable Energy Sources ◽  
Rotor Blades ◽  
Steam Turbines ◽  
Flow Conditions ◽  
Part Load ◽  
Last Stage ◽  
Load Conditions ◽  
Turbine Exhaust ◽  
Exhaust Systems

Modern large steam turbines for power generation are required to operate much more flexibly than ever before, due to the increasing use of intermittent renewable energy sources such as solar and wind. This has posed great challenges to the design of LP steam turbine exhaust systems, which are critical to recovering the leaving energy that is otherwise lost. In previous studies, the design had been focused on the exhaust diffuser with or without the collector. Although the interaction between the last stage and the exhaust hood has been identified for a long time, little attention has been paid to the last stage blading in the exhaust system’s design process, when the machine frequently operates at part-load conditions. This study focuses on the design of LP exhaust systems considering both the last stage and the exhaust diffuser, over a wide operating range. A 1/10th scale air test rig was built to validate the CFD tool for flow conditions representative of an actual machine at part-load conditions, characterised by highly swirling flows entering the diffuser. A numerical parametric study was performed to investigate the effect of both the diffuser geometry variation and restaggering the last stage rotor blades. Restaggering the rotor blades was found to be an effective way to control the level of leaving energy, as well as the flow conditions at the diffuser inlet, which influence the diffuser’s capability to recover the leaving energy. The benefits from diffuser resizing and rotor blade restaggering were shown to be relatively independent of each other, which suggests the two components can be designed separately. Last, the potentials of performance improvement by considering both the last stage rotor restaggering and the diffuser resizing were demonstrated by an exemplary design, which predicted an increase in the last stage power output of at least 1.5% for a typical 1000MW plant that mostly operates at part-load conditions.

Sequential vs Multidisciplinary Coupled Optimization and Efficient Surrogate Modelling of a Last Stage and the Successive Axial Radial Diffuser in a Low Pressure Steam Turbine

2014 ◽  
Author(s):  
Kevin Cremanns ◽  
Dirk Roos ◽  
Arne Graßmann
Keyword(s):  
Steam Turbine ◽  
Design Process ◽  
Energy Demand ◽  
Three Dimensional ◽  
Flow Simulation ◽  
Low Pressure ◽  
Steam Turbines ◽  
Low Pressure Turbine ◽  
Pressure Steam ◽  
Last Stage

In order to meet the requirements of rising energy demand, one goal in the design process of modern steam turbines is to achieve high efficiencies. A major gain in efficiency is expected from the optimization of the last stage and the subsequent diffuser of a low pressure turbine (LP). The aim of such optimization is to minimize the losses due to separations or inefficient blade or diffuser design. In the usual design process, as is state of the art in the industry, the last stage of the LP and the diffuser is designed and optimized sequentially. The potential physical coupling effects are not considered. Therefore the aim of this paper is to perform both a sequential and coupled optimization of a low pressure steam turbine followed by an axial radial diffuser and subsequently to compare results. In addition to the flow simulation, mechanical and modal analysis is also carried out in order to satisfy the constraints regarding the natural frequencies and stresses. This permits the use of a meta-model, which allows very time efficient three dimensional (3D) calculations to account for all flow field effects.

Model-Based Analysis of the Start-Up Improvement of a CCPP due to Steam Turbine Warm-Keeping With Air

2019 ◽  
Author(s):  
Dennis Toebben ◽  
Tobias Burgard ◽  
Sebastian Berg ◽  
Manfred Wirsum ◽  
Liu Pei ◽  
...  
Keyword(s):  
Power Plant ◽  
Steam Turbine ◽  
Power Plants ◽  
Cold Start ◽  
Nox Emissions ◽  
Data Set ◽  
Water Steam ◽  
Hot Air ◽  
Start Up ◽  
Low Load

Abstract Combined cycle power plants (CCPP) have many advantages compared to other fossil power plants: high efficiency, flexible operation, compact design, high potential for combined heat and power (CHP) applications and fewer emissions. However, fuel costs are relatively high compared to coal. Nevertheless, major qualities such as high operation flexibility and low emissions distinctly increase in relevance in the future, due to rising power generation from renewable energy sources. An accelerated start-up procedure of CCPPs increases the flexibility and reduces the NOx-emissions, which are relatively high in gas turbine low load operation. Such low load operation is required during a cold start of a CCPP in order to heat up the steam turbine. Thus, a warm-keeping of the thermal-limiting steam turbine results in an accelerated start-up times as well as reduced NOx-emissions and lifetime consumption. This paper presents a theoretical analysis of the potential of steam turbine warm-keeping by means of hot air for a typical CCPP, located in China. In this method, the hot air passes through the steam turbine while the power plant is shut off which enables hot start conditions at any time. In order to investigate an improved start-up procedure, a physical based simplified model of the water-steam cycle is developed on the basis of an operation data set. This model is used to simulate an improved power plant start-up, in which the steam turbine remains hot after at least 120 hours outage. The results show a start-up time reduction of approximately two-thirds in comparison to a conventional cold start. Furthermore, the potential of steam turbine warm-keeping is discussed with regards to the power output, NOx-emissions, start-up costs and lifetime consumption.

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.

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