Mechanical Design of Highly Loaded Large Steam Turbines

2011 ◽  
Author(s):  
N. Lu¨ckemeyer ◽  
H. Almstedt ◽  
T.-U. Kern ◽  
H. Kirchner
Keyword(s):  
Steam Turbine ◽  
Nuclear Power ◽  
Power Plants ◽  
Mechanical Design ◽  
Ductile Failure ◽  
Combined Cycle ◽  
Material Behavior ◽  
Integral Approach ◽  
Steam Turbines ◽  
Creep Fatigue

There are no internationally recognized standards, such as the ASME Boiler and Pressure Vessel Code or European boiler and pipe codes, for the mechanical design of large steam turbine components in combined cycle power plants, steam power plants and nuclear power plants. One reason for this is that the mechanical design of steam turbines is very complex as the steam pressure is only one of many aspects which need to be taken into account. In more than one hundred years of steam turbine history the manufacturers have developed internal mechanical design philosophies based on both experience and research. As the design of steam turbines is pushed to its limits with greater lifetimes, efficiency improvements and higher operating flexibility requested by customers, the validity and accuracy of these design philosophies become more and more important. This paper describes an integral approach for the structural analysis of large steam turbines which combines external design codes, material tests, research on the material behavior in co-operation with universities and experience gained from the existing fleet to derive a substantiated design philosophy. The paper covers the main parameters that need to be taken into account such as pressure, rotational forces and thermal loads and displacements, and identifies the relevant failure mechanisms such as creep fatigue, ductile failure and creep fatigue crack growth. It describes the efforts taken to improve the accuracy for materials already used in power plants today and materials with possible future use such as advanced steels or nickel based alloys.

Repowering and Retrofitting

2002 ◽  
Author(s):  
Andreas Pickard
Keyword(s):  
Steam Turbine ◽  
Power Plants ◽  
Free Market ◽  
Leading Edge ◽  
Project Planning ◽  
Combined Cycle ◽  
Steam Turbines ◽  
Planning Stage ◽  
Reheat Steam ◽  
Plant Optimization

At the start of this new century, environmental regulations and free-market economics are becoming the key drivers for the electricity generating industry. Advances in Gas Turbine (GT) technology, allied with integration and refinement of Heat Recovery Steam Generators (HRSG) and Steam Turbine (ST) plant, have made Combined Cycle installations the most efficient of the new power station types. This potential can also be realized, to equal effect, by adding GT’s and HRSG’s to existing conventional steam power plants in a so-called ‘repowering’ process. This paper presents the economical and environmental considerations of retrofitting the steam turbine within repowering schemes. Changing the thermal cycle parameters of the plant, for example by deletion of the feed heating steambleeds or by modified live and reheat steam conditions to suit the combined cycle process, can result in off-design operation of the existing steam turbine. Retrofitting the steam turbine to match the combined cycle unit can significantly increase the overall cycle efficiency compared to repowering without the ST upgrade. The paper illustrates that repowering, including ST retrofitting, when considered as a whole at the project planning stage, has the potential for greater gain by allowing proper plant optimization. Much of the repowering in the past has been carried out without due regard to the benefits of re-matching the steam turbine. Retrospective ST upgrade of such cases can still give benefit to the plant owner, especially when it is realized that most repowering to date has retained an unmodified steam turbine (that first went into operation some decades before). The old equipment will have suffered deterioration due to aging and the steam path will be to an archaic design of poor efficiency. Retrofitting older generation plant with modern leading-edge steam-path technology has the potential for realizing those substantial advances made over the last 20 to 30 years. Some examples, given in the paper, of successfully retrofitted steam turbines applied in repowered plants will show, by specific solution, the optimization of the economics and benefit to the environment of the converted plant as a whole.

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.

Repowering Considerations for Converting Existing Power Plants to Combined Cycle Power Plants

2002 ◽  
Author(s):  
Anup Singh ◽  
Don Kopecky
Keyword(s):  
Steam Turbine ◽  
Power Plants ◽  
Combined Cycle ◽  
Current Status ◽  
Entire System ◽  
Steam Turbines ◽  
Good Shape ◽  
The Usa ◽  
Overall Performance ◽  
Cost Studies

Most of the recent combined cycle plants have been designed and constructed as Greenfield Plants. These new plants have been designed mostly as Merchant Plants, owned and operated by Independent Power Producers. There is about 260,000 MW of conventional coal-fired and gas-fired capacity in the USA that is more than 30 years old. About 30,000 MW of conventional gas-fired capacity exists in the area of The Electric Reliability Council of Texas (ERCOT) with relatively poor heat rates in comparison to modern combined cycle plants. These plants are good candidates for HRSG repowering. In addition, there are several coal-fired units in the 200 MW range with steam turbines in relatively good shape or in a condition that can be refurbished and used in repowering. The installed cost of repowered (also called Brownfield) capacity is about 20%–40% less than for comparable Greenfield capacity. There are also other advantages to repowering. Since the site is already existing, it is easier to get the various environmental and construction permits. The efficiency of the repowered units will be significantly higher than the existing units in their current status thus increasing the overall performance of the entire system. The paper will discuss various considerations required for repowering, including steam turbine refurbishment, demolition/relocation of existing equipment, recent cost studies, and various considerations for equipment such as HRSGs.

Stress Corrosion Cracking and Corrosion Fatigue Analysis of Nuclear Steam Turbine Rotor

2014 ◽  
Author(s):  
Gang Chen ◽  
Puning Jiang ◽  
Xingzhu Ye ◽  
Junhui Zhang ◽  
Yifeng Hu ◽  
...  
Keyword(s):  
Stress Corrosion ◽  
Steam Turbine ◽  
Corrosion Fatigue ◽  
Stress Corrosion Cracking ◽  
Nuclear Power ◽  
Power Plants ◽  
Fatigue Cracking ◽  
Corrosion Cracking ◽  
Major Influence ◽  
Steam Turbines

Although stress corrosion cracking (SCC) and corrosion fatigue cracking can occur in many locations of nuclear steam turbines, most of them initiate at low pressure disc rim, rotor groove and keyway of the shrunk-on disc. For nuclear steam turbine components, long life endurance and high availability are very important factors in the operation. Usually nuclear power plants operating more than sixty years are susceptible to this failure mechanism. If SCC or corrosion fatigue happens, especially in rotor groove or keyway, it has a major influence on nuclear steam turbine life. In this paper, established methods for the SCC and corrosion fatigue-controlled life prediction of steam turbine components were applied to evaluating a new shrunk-on disc that had suffered local keyway surface damage during manufacture and loss of residual compressive stress.

Effect of Inlet Steam Temperature on the HP Section Efficiency of a Steam Turbine

2015 ◽  
Author(s):  
Yiping Fu ◽  
Thomas Winterberger
Keyword(s):  
Steam Turbine ◽  
Power Plants ◽  
Pressure Ratio ◽  
Control Valve ◽  
Combined Cycle ◽  
Steam Turbines ◽  
Steam Temperature ◽  
Load Range ◽  
Lp Turbine ◽  
The Relationship

Steam turbines for modern fossil and combined cycle power plants typically utilize a reheat cycle with High Pressure (HP), Intermediate Pressure (IP), and Low Pressure (LP) turbine sections. For an HP turbine section operating entirely in the superheat region, section efficiency can be calculated based on pressure and temperature measurements at the inlet and exhaust. For this case HP section efficiency is normally assumed to be a constant value over a load range if inlet control valve position and section pressure ratio remain constant. It has been observed that changes in inlet steam temperature impact HP section efficiency. K.C. Cotton stated that ‘the effect of throttle temperature on HP turbine efficiency is significant’ in his book ‘Evaluating and Improving Steam Turbine Performance’ (2nd Edition, 1998). The information and conclusions provided by K.C. Cotton are based on test results for large fossil units calculated with 1967 ASME steam tables. Since the time of Mr. Cotton’s observations, turbine configurations have evolved, more accurate 1997 ASME steam tables have been released, and our ability to quickly analyze large quantities of data has greatly increased. This paper studies the relationship between inlet steam temperature and HP section efficiency based on both 1967 and 1997 ASME steam tables and recent test data, which is analyzed computationally to reveal patterns and trends. With the efficiencies of various inlet pressure class HP section turbines being calculated with both 1967 and 1997 ASME steam tables, a comparison reveals different characteristics in the relationship between inlet steam temperature and HP section efficiency. Recommendations are made on how the results may be used to improve accuracy when testing and trending HP section performance.

Performance Improvements of Nuclear Power Plants by the Application of Longer LP Last Stage Blades and Advanced Design Techniques

2014 ◽  
Author(s):  
Mike Jones ◽  
Robert Crossland
Keyword(s):  
Steam Turbine ◽  
Nuclear Power ◽  
Power Plants ◽  
Steam Turbines ◽  
Diverse Range ◽  
Performance Improvements ◽  
Shaft Line ◽  
Last Stage ◽  
Water Reactors ◽  
As Stress

Over the last decade, the Author’s company (Alstom Power) has retrofitted the steam turbines in 34 nuclear units on a diverse range of half and full-speed machines, powered by Pressurised and Boiling Water Reactors. Some of those projects have been described in other papers, with an explanation of the novel laser measurement and fast-track installation techniques that have been developed to meet the onerous demands of nuclear plants and authorities. The ageing global nuclear fleet has suffered reduced levels of reliability and performance due to effects such as Stress Corrosion Cracking (SCC), moisture erosion and shaft line torsional faults. Alstom has developed a range of steam turbine retrofit solutions that are resistant to SCC and erosion, have extended maintenance intervals and deliver high levels of efficiency. A portfolio of rear stage blades is available, from which an optimum design can be selected to suit each project. This paper focuses on the improvements in thermal performance and reliability of a number of recent nuclear steam turbine retrofits. It outlines the existing designs and some of the challenges faced by the plants concerning reliability, operation and efficiency and then describes the approach to addressing those issues by retrofitting with modern designs. The paper describes the blading design and the techniques which are used to evaluate exhaust performance. It will also show the methods which have been used to integrate longer Last Stage Blades into existing LP frames. The paper concludes by presenting the experience, in terms of performance and installation, of some of the projects.

A Simplified ASME Acceptance Test Procedure for Steam Turbines

1982 ◽  
Vol 104 (1) ◽  
pp. 224-230 ◽  
Author(s):  
B. Bornstein ◽  
K. C. Cotton
Keyword(s):  
Steam Turbine ◽  
Nuclear Power ◽  
Power Plants ◽  
Test Procedure ◽  
Heat Rate ◽  
Acceptance Testing ◽  
Acceptance Test ◽  
Steam Turbines ◽  
Efficient Operation ◽  
Testing Accuracy

A simplified procedure is proposed, which reduces the cost of steam turbine acceptance testing without significantly affecting testing accuracy. This simplified acceptance test procedure is applicable to both fossil and nuclear power plants. It involves only the measurements required to calculate heat rate and required to compare the test value to guarantee. The object is to simplify the acceptance test and to reduce its cost to the extent that a no-tolerance acceptance test is conducted on every new, large steam turine-generator unit. While maintaining the traditional high level of testing accuracy, this method also facilitates periodic testing. The results of such tests can provide the information required for scheduling plant outages for maintenance or repair thus ensuring efficient operation of the steam turbine/feedwater cycle throughout the life of the turbine.

scholarly journals Ageing Effect on Creep-fatigue Properties of Super-clean 9% CrMoV Steel for Steam Turbine Rotors of Combined Cycle Power Plants

2003 ◽  
Vol 89 (7) ◽  
pp. 796-802 ◽  
Author(s):  
Li-Bin NIU ◽  
Masato OKADO ◽  
Tsukasa AZUMA ◽  
Yoshihiro SAKAI ◽  
Mitsuyuki KOBAYASHI ◽  
...  
Keyword(s):  
Steam Turbine ◽  
Power Plants ◽  
Combined Cycle ◽  
Fatigue Properties ◽  
Ageing Effect ◽  
Creep Fatigue ◽  
Turbine Rotors

Development of Steam Turbines for State of the Art Combined Cycle Power Plants (CCPP)

2012 ◽  
Author(s):  
Rainer Quinkertz ◽  
Simon Hecker
Keyword(s):  
Steam Turbine ◽  
Gas Turbines ◽  
Power Plants ◽  
Three Dimensional ◽  
Plant Evolution ◽  
Combined Cycle ◽  
Steam Turbines ◽  
Electricity Grid ◽  
Capital Costs ◽  
Intermediate Pressure

In order to reduce CO2 emissions, reduce capital costs and increase the percentage of renewable energy in the electricity grid, common drivers of fossil power plant evolution continue to be efficiency, increased electricity output and operating flexibility. For CCPP, the efficiency level has reached more than 60%. Besides new and updated gas turbine frames, an improved bottoming cycle also contributes to this achievement. Without increasing steam temperatures above 565°C, improving steam turbine inner efficiency and enhancing the cold end, the overall efficiency of >60% would not be feasible. Extensive thermodynamic optimization is required to determine steam temperatures and condenser pressures. In addition, from a design standpoint, an optimum product strategy has to be developed. In order to minimize risks with future designs, both the practical and theoretical experiences from both ultra super critical applications at coal-fired steam power plants as well as from the CCPP steam turbine fleet have to be incorporated. For advanced technologies and components appropriate validation programs have to be defined. This paper presents the approach being taking to develop steam turbines for CCPP with modern gas turbines and it also displays the operating results of the first unit. Operational validation included the thermal behaviour of the high and intermediate pressure parts, a new last stage blade for the low pressure turbine and a patented start-up procedure. In particular, the paper focuses on the validation of three dimensional CFD calculations of the high and intermediate pressure turbine.

Aerodynamic Design and Prototype Testing of a New Line of High Efficiency, High Pressure, 50% Reaction Steam Turbines

2007 ◽  
Author(s):  
Joseph A. Cotroneo ◽  
Tara A. Cole ◽  
Douglas C. Hofer
Keyword(s):  
High Pressure ◽  
Steam Turbine ◽  
Power Plants ◽  
High Efficiency ◽  
Combined Cycle ◽  
Volume Flow ◽  
Steam Turbines ◽  
Aerodynamic Design ◽  
Flow Paths ◽  
Low Volume

The aerodynamic design and prototype performance testing of a new line of high efficiency, high pressure (HP), 50% reaction steam turbines is described in some detail. Three designs were carried out that can be used in a repeating stage fashion to form high efficiency steam paths. The designs were performed employing a blade master concept. The masters can be aerodynamically scaled and cut to cover a wide range of applications while maintaining vector diagram integrity. Three equivalent prototype flow paths, one each for Gen 0, 1 and 2, masters were designed and tested in a Steam Turbine Test Vehicle (STTV). These prototype designs are representative of high pressure steam turbines for combined cycle power plants. Design of experiments is used to optimize the flow path, stage counts and diameters for production designs taking into account multidisciplinary design constraints. Four such Gen 1 steam path designs have been executed to date as part of a structured series of combined cycle power plants. [1-5] There are two A14 HEAT* (High Efficiency Advanced Technology) steam turbine HP flow paths for GE’s 107FA combined cycle power plants and two A15 HEAT HP flow paths for the 109FB. The larger of the A14 HEAT steam turbine HP’s has recently been performance tested at a customer site demonstrating world class efficiency levels of over 90% for this low volume flow combined cycle turbine [1]. HP volume flows are likely to drop even lower in the future with the need to go to higher steam inlet pressure for combined cycle efficiency improvements so steam path designs with high efficiency at low volume flow will be increasingly important.

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