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.

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.

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.

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.

Numerical Investigation of the Heat Transfer and Flow Phenomena in an IP Steam Turbine in Warm-Keeping Operation With Hot Air

2017 ◽  
Author(s):  
Dennis Toebben ◽  
Piotr Łuczyński ◽  
Mathias Diefenthal ◽  
Manfred Wirsum ◽  
Stefan Reitschmidt ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Steam Turbine ◽  
Flow Structure ◽  
Conjugate Heat Transfer ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Hot Air ◽  
Start Up ◽  
Flow Phenomena

Nowadays, steam turbines in conventional power plants deal with an increasing number of startups due to the high share of fluctuating power input of renewable generation. Thus, the development of new methods for flexibility improvements, such as reduction of the start-up time and its costs, have become more and more important. At the same time, fast start-up and flexible steam turbine operation increase the lifetime consumption and reduce the inspection intervals. One possible option to prevent these negative impacts of a flexible operation is to keep the steam turbine warm during a shut down and a startup. In order to do so, General Electric has developed a concept for warm-keeping respectively pre-warming of a high-pressure (HP) / intermediate-pressure (IP) steam turbine with hot air: After a certain cool-down phase, air is passed through the turbine while the turbine is rotated by the turning engine. The flow and the rotational direction can be inverted to optimize the warming operation. In order to fulfill the requirements of high flexibility in combination with reduced costs and thermal stresses during the start-up, a detailed investigation of the dominant heat transfer effects and the corresponding flow structure is necessary: Complex numerical approaches, such as Conjugate Heat Transfer (CHT), can provide this corresponding information and help to understand the physical impact of the flow phenomena. The aim of the present work is thus to understand the predominant heat transport phenomena in warm-keeping operation and to gain detailed heat transfer coefficients within the flow channel for blade, vane and shrouds. A multitude of steady-state simulations were performed to investigate the different warm-keeping operation points. Data from literature was recomputed in good agreement to qualitatively validate the numerical model in windage operation. Furthermore, the steady-state simulations were compared with transient Computational Fluid Dynamics (CFD) simulations to verify that the flow in warming operation can be simulated with a steady-state case. The transient calculations confirm the steady-state results. A variation of the mass flow rate and the rotational speed was conducted to calculate a characteristic map of heat transfer coefficients. The Conjugate Heat Transfer simulations provide an insight into the flow structure and offer a comparison with the flow phenomena in conventional operation. In addition, the impact of the flow phenomena on the local heat transfer was investigated.

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.

scholarly journals SOLVING TRANSIENT INVERSE HEAT TRANSFER PROBLEMS IN COMPLEX GEOMETRIES USING PHYSICS-GUIDED NEURAL NETWORKS (PGNN)

2021 ◽  
Vol 2021 (3) ◽  
pp. 4540-4547
Author(s):  
D. Emonts ◽  
◽  
J. Yang ◽  
R. H. Schmitt ◽  
◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flow ◽  
Input Parameter ◽  
Temperature Fields ◽  
Elastic Behavior ◽  
Transient Temperature ◽  
Complex Geometries ◽  
Inverse Heat Transfer ◽  
Geometric Inspection ◽  
Transfer Problems

Temporally and spatially unstable thermal conditions lead to transient or inhomogeneous thermo-elastic behavior of workpieces during manufacturing or geometric inspection. Temperature monitoring by means of sensors consign transient temperature fields, but do not yield information about the heat flow acting as thermal boundary condition, which is a relevant input parameter for nearly any thermal simulation. Addressing the need for efficient methods, the authors propose an approach to solve inverse heat transfer problems in complex geometries. In the presented study, locally acting heat loads are experimentally investigated based on virtual demonstrators running in FEM. The conducted method shows high potential for transient heat flow modelling in terms of accuracy and computational efficiency.

Steam Turbine Hot Standby: Electrical Pre-Heating Solution

2019 ◽  
Author(s):  
Y. Kostenko ◽  
D. Veltmann ◽  
S. Hecker
Keyword(s):  
Heat Transfer ◽  
Power Plant ◽  
Steam Turbine ◽  
Power Plants ◽  
Heating System ◽  
Heating Process ◽  
Steam Turbines ◽  
Start Up ◽  
New Apparatus ◽  
General Aspects

Abstract Growing renewable energy generation share causes more irregular and more flexible operational regimes of conventional power plants than in the past. It leads to long periods without dispatch for several days or even weeks. As a consequence, the required pre-heating of the steam turbine leads to an extended power plant start-up time [1]. The current steam turbine Hot Standby Mode (HSM) contributes to a more flexible steam turbine operation and is a part of the Flex-Power Services™ portfolio [2]. HSM prevents the turbine components from cooling via heat supply using an electrical Trace Heating System (THS) after shutdowns [3]. The aim of the HSM is to enable faster start-up time after moderate standstills. HSM functionality can be extended to include the pre-heating option after longer standstills. This paper investigates pre-heating of the steam turbine with an electrical THS. At the beginning, it covers general aspects of flexible fossil power plant operation and point out the advantages of HSM. Afterwards the technology of the trace heating system and its application on steam turbines will be explained. In the next step the transient pre-heating process is analyzed and optimized using FEA, CFD and analytic calculations including validation considerations. Therefor a heat transfer correlation for flexible transient operation of the HSM was developed. A typical large steam turbine with an output of up to 300MW was investigated. Finally the results are summarized and an outlook is given. The results of heat transfer and conduction between and within turbine components are used to enable fast start-ups after long standstills or even outages with the benefit of minimal energy consumption. The solution is available for new apparatus as well as for the modernization of existing installations.

Investigation and Thermal Modeling of the Thermal Contact Resistance at a Steam Turbine Blade Root

2019 ◽  
Author(s):  
Dennis Toebben ◽  
Alexander Goerner ◽  
Piotr Luczynski ◽  
Manfred Wirsum ◽  
Wolfgang F. D. Mohr ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Steam Turbine ◽  
Ambient Pressure ◽  
Thermal Contact ◽  
Measurement Data ◽  
Life Cycles ◽  
Heat Fluxes ◽  
Fe Model ◽  
Heat Transfer Correlations ◽  
Start Ups

Abstract Increasing load ramps and temperature gradients in steam turbines, especially during start-ups, have a high impact on the component lifetime. Calculation models are commonly used to predict the lifetime consumption during such start-up procedures. However, the changing energy landscape requires innovative solutions to increase the power plant flexibility. In order to accelerate the start-ups with a simultaneously reduced lifetime consumption, hot air can be used to keep the steam turbine warm during shut downs. The calculation of heat fluxes within the steam turbine is crucial for the accurate prediction of the thermal state and the resulting lifetime consumption. Improved models enable the determination of life cycles as exact as possible. During warm-keeping and pre-warming operations, the steam turbine rotates slowly. Thus, low centrifugal forces lead to high thermal contact resistances (TCR) at the blade roots, which influence the temperature distribution at the lifetime limiting locations, e.g. blade grooves. The paper presents heat transfer correlations, which describe the TCR depending on the rotational speed of the rotor. For this purpose, an experimental setup is designed in order to investigate the influence of contact pressure, ambient pressure and surface properties. For the detailed investigation of the complex heat fluxes at the T-root, a 3D Finite-Elements (FE) model is developed. This model calculates the TCR and specific heat fluxes based on measurement data. On the basis of the detailed evaluation, different analytical heat transfer correlation approaches with respect to the application in an overall steam turbine model are developed. These heat transfer correlations are integrated into the FE model and validated with additional measurements.

scholarly journals A Comprehensive Thermal and Structural Transient Analysis of a Boiler’s Steam Outlet Header by Means of a Dedicated Algorithm and FEM Simulation

Energies ◽  
2019 ◽  
Vol 13 (1) ◽  
pp. 111 ◽  
Author(s):  
Marcin Pilarczyk ◽  
Bohdan Węglowski ◽  
Lars O. Nord
Keyword(s):  
Finite Element ◽  
Power Unit ◽  
Thermal Power ◽  
High Capacity ◽  
Fem Simulation ◽  
Temperature Fields ◽  
Transient Temperature ◽  
Element Analysis ◽  
Start Up

Increasing the share of renewables in energy markets influences the daily operation of thermal power units. High capacity power units are more frequently operated to balance power grids and, thus, steam boilers are exposed to unfavorable transient states. The aim of this work was to perform thermal and structural analyses of a boiler’s outlet steam header, with a capacity of 650∙103 kg/h (180 kg/s) of live steam. Based on the measured steam pressure and temperatures on the outer surface of the component, transient temperature fields were determined by means of an algorithm that allows determination of transient stress distributions on the internal and external surfaces, as well as at stress concentration regions. In parallel, a finite element method simulation was performed. A comparison of the obtained results to a finite element analysis showed satisfactory agreement. The analyses showed that the start-up time could be reduced because the total stress did not exceed the allowed values during the regular start-up of the analyzed power unit. The algorithm was efficient and easy to implement in the real control systems of the power units. The numerical approach employed in the presented algorithm also allowed for determination of the time- and place-dependent heating rate value, which can be used as input data for the control system of the power unit.

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