Wet Steam Turbines for Nuclear Power Plants By Alexander S Leyzerovich pdf.
1. The Nuclear Power Industry
at the Turn of the 21st Century
2. The Thermal Process in
Appendix. List of Abbreviations and Symbols
Preface: In 1997, PennWell published my two-volume book Large Power Steam Turbines: Design & Operation. It was conceived as a comprehensive summary of technical insights into the main design concepts and operational problems of large power steam turbines, relying on a totality of the extensive experience accumulated by the end of the 20th century in the power industries of the world’s industrially developed countries: the United States, the former Soviet Union, Japan, Germany, France, the United Kingdom, Denmark, Czechoslovakia, and others. It was the first fundamental monograph on steam turbines in English published in over four decades and the only modern book covering both design and operation of large power steam turbines.
The book differed from its forerunners in the sense that it did not tell readers how turbines should be designed, but rather explained why they were designed the way they were. It was mainly addressed to engineers of power plants and power generation utilities, college professors, and students training for work in the power generation industry. The book was intended to help them comprehend different factors that may impact a turbine’s operating efficiency, reliability, and flexibility, and the book demonstrated main design approaches to improving these characteristics. The book was also intended to provide an adequate comprehension of current concepts and main trends in modern turbomachinery. The second part of the book discussed the operation of steam turbines at power plants. It presented general characteristics of turbine operation and main operating factors affecting turbine performances, described generic types of damages and failures that power plant operators may encounter and methods employed to fix these problems, and considered experimental research on turbine operating conditions. Particular emphasis was given to turbine transients (start-ups, shut-downs, and load changes in the governed range) and methods to improve them, as well as automated control, surveillance, and information support for the operational personnel. The third part of the book commented on and illustrated the notions presented in the first two parts by providing examples of cycling operation of large power steam turbines in various countries, design and operation experience of the largest (1,300 MW) supercritical power units at U.S. power plants, as well as the most advanced modern turbines with elevated ultra-supercritical steam parameters worldwide.
In the next two years, two other books appeared that summarized the current state of knowledge about damages in the turbine steam path and methods for revealing and repairing them: Turbine Steam Path Damage: Theory & Practice by T. H. McCloskey, R. B. Dooley, and W. P. McNaughton (EPRI, 1999) and Turbine Steam Path: Maintenance & Repair by W. P. Sanders (PennWell, 2001). These two books were primarily addressed to power plant maintenance staff, and considered viewpoints of power industry specialists of different backgrounds. A general view on turbomachinery for the power industry as of the end of the 20th century was provided in the book 100 Years of Power Plant Development. Focus on Steam and Gas Turbines as Prime Movers by H. Termuehlen (ASME, 2001).
Although these books were intended to cover steam turbines for both fossil fuel and nuclear power plants, they mainly focused on steam turbines for fossil fuel plants. To a certain extent, this could be attributed to the situation in which the nuclear power industry found itself after the March 1979 accident at Three Mile Island Unit 2 and especially after the April 1986 Chernobyl disaster. Currently, however, the nuclear industry seems to be undergoing a revival stage, attracting the attention of power plant owners and operators in the United States and many other countries.
First of all, this revival can be explained by the excellent operating performances of the nuclear power plants in service that have been demonstrated throughout the world during recent years, with appreciable improvements in safety, availability, and efficiency. In a June 2001 article in Electric Light & Power, K. Davis wrote that “The American Nuclear Society has emphasized that the nuclear industry keeps a safety record “nearly ten times better than that of the total U.S. industrial sector.”* Although the existing nuclear power plants in service have produced very good economic performances, the new, upgraded nuclear power units are expected to be even more economically competitive. It is also assumed that the newly designed advanced nuclear power reactors will be even more safe and reliable. In particular, this applies to the traditional, most widespread types of light-water reactors (pressurized water and boiling water reactors— PWRs and BWRs) and pressurized heavy-water reactors (PHWRs and CANDU) operating with wet-steam turbines.
With the imminent and unavoidable depletion of the world’s gas and oil resources, for the near future, only the nuclear power industry can provide for a large-scale growth in power requirements. For many developed countries, including the United States, nuclear power seems to be the only viable means of making them more independent from gas and oil imports and of providing them with the possibility of sparing their own resources. Of course, growth in nuclear power generation capabilities must be accomplished in parallel with embarking new coal-fired power plants. However, increased large-scale and intensive burning of coal conflicts with the quest for reducing air pollution caused by carbon dioxide and nitric and nitrous oxides (NOx) emissions from power plants. Nuclear power generation is virtually emission free. All of the measures undertaken to decrease emissions from coal-fi red power plants greatly increase the power generation expense, whereas nuclear power production costs are already lower than those of fossil fuel power plants, including coal-fi red plants, not to mention renewables.
Along with launching new power plants with modern power equipment, including nuclear power plants with advanced reactors, and decommissioning old nuclear power units as they age, owners of many old nuclear power plants consider it economically reasonable to renew their operating licenses by refurbishing their equipment, including the steam turbines. Apart from the increase in operating safety and reliability and extending the plant’s lifetime, this provides a noticeable gain in efficiency. After refurbishment of the turbine, the nuclear power unit’s electric output can increase by as much as 5.0% with the same amount of steam production from the reactor (that is, the increase for a 1,000-MW unit can amount to 50 MW).
The vast majority of nuclear power plants operate with wet-steam turbines fed by saturated steam of relatively low pressure—about 6–7 MPa (870–1,015 psi) or less. These steam conditions are much lower than those for superheated-steam turbines of contemporary fossil fuel power plants, and thus wet-steam turbines require much greater steam flow amounts to provide the same electric power outputs. A great portion of a wet-steam turbine’s output is provided by the low-pressure (LP) cylinders. The low initial steam conditions also entail a great steam moisture content in the last stages that could cause intense damage in the turbine steam path and create substantial energy loss. Because of this, special countermeasures are taken for moisture removal within the steam path, and most wet-steam turbines are additionally furnished with external moisture separator and reheaters (MSRs), placed after the high-pressure (HP) cylinder or section and before the LP cylinders or specially separated intermediate-pressure (IP) cylinder or section. Despite these measures, all of the HP sections and a great portion of the LP stages operate using wet steam with relatively high wetness values—up to 12–14%. All the mentioned features determine specific peculiarities of wet-steam turbines, in both their design and operation. In particular, all nuclear wet-steam turbines are designed as single-shaft, or tandem-compound, and a remarkable portion of these turbines, including the largest ones, are low-speed (with a rotation speed of 1,500 or 1,800 rpm for a grid frequency of 50 or 60 Hz, respectively), whereas some of the largest superheated-steam turbines for fossil fuel power plants are of double-shaft, or cross-compound, design.
As the nuclear industry embarks upon a new renaissance, I have found it reasonable to write a new book especially devoted to wetsteam turbines for nuclear power plants, with detailed consideration of special features in their design, operation, and refurbishment. This new book is basically a continuation of the previously mentioned one and to a great degree rests on its contents, not repeating it as far as it concerns general concepts, which are common for both superheatedsteam and wet-steam turbines.
I hope readers will gain from this book a clear understanding of the modern large steam turbines used in the most widespread types of contemporary nuclear power plants and their future analogs, features of their design and operation, main operational problems, and ways these problems can be solved. It seems also advisable to give some knowledge of different design decisions proposed by the world’s main wet-steam turbine manufacturers (ALSTOM, General Electric, Hitachi, LMZ, Mitsubishi Heavy Industries, Siemens Power Generation, Skoda, Toshiba, and Turboatom) to improve the operating performances of aging turbines in service by refurbishing them. The book should also give readers some comprehension of the physical effects that accompany the operating process in wet-steam turbines, the influence of these effects on turbine operating performance, and ways to improve power plant operation with regard to these effects On the other hand, it would hardly be expedient to dig deeply into wet-steam aerodynamics and computational fluid dynamics (CFD), choice of materials, strength assessment, and other details so important for turbine designers and researchers. It is more reasonable to pay more attention to the specific features of operating wet-steam turbines with regard to their peculiarities and the possible information support for operational personnel. This is what differentiates this book to a degree from its predecessors.
In the late 1970s and 1980s, the first period of proliferation in the nuclear power industry preceding the Three Mile Island accident and Chernobyl catastrophe, there appeared some valuable and highly profi – cient books devoted especially to steam turbines for nuclear power plants, including a few monographs in Russian, such as: Steam-Turbine Installations for Nuclear Power Plants edited by Y. F. Kosyak (1978); Turbines for Nuclear Power Plants by B. M. Troyanovsky (2d ed., 1978);Operation of Turbines at Nuclear Power Plants by Y. F. Kosyak, V. N. Galatsan, and V. A. Paley (1983); Steam and Gas Turbines for Nuclear Power Plants by B. M. Troyanovsky, G. A. Filippov, and A. E. Bulkin (1985); Operating Conditions of Turbosets for Nuclear Power Plants by B. A. Arkad’ev (1986); and Two-Phase Flows in Elements of Thermal Power Equipment by M. E. Deich and G. A. Filippov (1987). Highly appraising these books and taking into consideration that they have not been accessible for most professionals in the United States and many other countries, I have used their contents in this book as broadly as possible.
During the same period, there appeared a renowned monograph that became a handbook for all those who have been engaged in wet-steam turbine development: Two-Phase Steam Flow in Turbines and Separators (1976), edited by M. J. Moore and C. H. Sieverding and composed with participation of the best specialists from the United States, Germany, the United Kingdom, and Switzerland, including R. L. Coit of Westinghouse, W. Engelke of KWU, G. Gyarmathy of Brown Boveri, and A. Smith of C. A. Parsons.
All of the above-mentioned books were written by scientists and engineers mainly involved in the design of wet-steam turbines and developments for them, and include investigations into problems related to them. These books presented the accumulated and generalized experiences of these experts and mainly appealed to specialists of the same profi le. Even when the authors wrote about turbine operation, they approached the emerging problems as if from an external point of view. It makes sense to look at the same subjects from another side. In addition, all of those books are now somewhat out-of-date and do not cover some of the more recent trends and achievements in the turbomachinery and power industry. This book attempts to provide the best information from those books, generalizing, updating, and supplementing their contents, but mainly from the viewpoint of a turbine operator rather than a turbine designer. So many problems that are very topical and important for turbine designers and researchers, but perhaps are only of abstract interest for power plant engineers, are mentioned in this book only casually or skipped altogether. This book contains substantial reference and bibliography sections to provide readers with the opportunity of fi nding more detailed information.
I have tried to take into consideration diverse materials pertaining to wet-steam turbines and nuclear power plants published during the last decades in leading U.S., European, Russian, and Japanese power engineering journals and presented at international power generation conferences. In addition to published materials of other authors, this book includes some results of my own experimental and computational investigations as applied to wet-steam turbines, and depicts some of the developments that I completed and implemented at various nuclear power plants. Working for over 30 years as a leading specialist at the All-Russian Thermal Engineering Research Institute in Moscow (VTI by Russian abbreviation), since 1971 I had been deeply involved in experimental investigations, calculational research, and several projects for nuclear power plants until the Chernobyl disaster. My main fields of interest included transient operating conditions of wet-steam turbines and their automated operating control, monitoring, and diagnostics, as well as information support for power plant personnel. I participated in field tests of wet-steam turbines with individual capacities of 220, 500, and 1,000 MW, conceptualized the development of special devices and systems for their automated control and surveillance, and participated in their implementation. I have also participated in inspections of wet-steam turbines at various nuclear power plants. Some results of these works were presented in my previous books (in Russian): Start-Ups of Power Units’ Steam Turbines (in co-authorship with E. R. Plotkin, 1980; translated into Chinese, 1985) and Technological Fundamentals of Power Steam Turbine Start-Up Automation (1985), as well as in many papers published in various power engineering periodicals, in both Russian and English.
Dr. Alexander S. Leyzerovich
⏩Author: Alexander S. Leyzerovich
⏩Publisher: PennWell Corp.; American ed. edition
⏩Puplication Date: June 10, 2005
⏩Size: 22.7 MB
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