Gas Turbine Combined Cycle Power Plants

S. Gülen

• Publisher: CRC Press
• Year: 2019
• ISBN:
  9780429534577
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Energy

This book covers the design, analysis, and optimization of the cleanest, most efficient fossil fuel-fired electric power generation technology at present and in the foreseeable future.

The book contains a wealth of first principles-based calculation methods comprising key formulae, charts, rules of thumb, and other tools developed by the author over the course of 25+ years spent in the power generation industry. It is focused exclusively on actual power plant systems and actual field and/or rating data providing a comprehensive picture of the gas turbine combined cycle technology from performance and cost perspectives.

Material presented in this book is applicable for research and development studies in academia and government/industry laboratories, as well as practical, day-to-day problems encountered in the industry (including OEMs, consulting engineers and plant operators).

1 Introduction

Neither the gas turbine nor the steam turbine is the most efficient heat engine burning fossil fuels. At the time of writing, the crème-de-la-crème of either prime mover is at low 40s in thermal efficiency (as a percentage). That distinction belongs to the reciprocating, i.e., piston-and-cylinder, internal combustion engines burning natural gas. Presently, best-in-class representatives of that group can claim close to 50% in brake thermal efficiency. However, when combined through a heat recovery boiler, a gas and steam turbine power plant is by far the most efficient and cleanest technology to generate electric power from burning a fossil fuel, i.e., the natural gas. Field-proven performance of the best of the bunch is above 60%. Why this is so is going to become clear when we look at the thermodynamic principles governing the respective cycles of the two prime movers.

Using a system approach, there are four major subsystems in a combined cycle power plant system:

1. Gas turbine generator (operating in Brayton cycle)
2. Steam turbine generator (operating in Rankine cycle)
3. Heat recovery boiler or, using the more common terminology, heat recovery steam generator (HRSG)
4. Heat rejection system comprising either
   1. A water-cooled condenser (with or without a cooling tower) or
   2. An air-cooled condenser (ACC).

In addition to these four major subsystems, there is a maze of condensate, cooling water and steam piping with a large number of valves along with pumps (condensate, boiler feedwater and circulating cooling water pumps) and myriad heat exchangers, which are lumped under the term “balance of plant” (BOP). (In some sources, the BOP includes some or all of the equipment in the heat rejection system as well – not in this book.)

Each major subsystem can be and is the subject of a separate book in and of itself. Therefore, no attempt will be made herein to go into the nitty-gritty details of any of them. For such information, the reader’s best source should be the original equipment manufacturer’s (OEM) user manuals, technical information letters (TILs), white papers (such as General Electric’s GER series freely available on its website) and information documents (such as GE’s GEK series available to its customers). Another good source of pertinent technical information is OEM papers presented in technical conferences. Quite a few of them are available on OEM websites. Internally published technical journals such as The Brown Boveri Review are unfortunately a thing of the past. The only OEM continuing that tradition is Mitsubishi Hitachi Power Systems (MHPS); MHI (Mitsubishi Heavy Industries, the old name of the company) Technical Review articles are available online and provide in-depth information on MHI/MHPS steam and gas turbine technology.

The focus herein will be on the salient aspects of design and off-design performance and operability of each major subsystem within the combined cycle system. Furthermore, this is primarily a book of numerical/quantitative analysis. Aspects of performance and operability, which are amenable to numerical calculations, will be covered in detail; others will be mentioned in passing. High-level, physics-based but reasonably accurate calculation procedures will be described with two goals in mind:

1. Familiarize the reader with the “ghost in the machine”, i.e., the basic fundamental principles of thermodynamics (by far, the most important discipline of mechanical engineering – at least in this author’s opinion) governing the operation of the prime movers and heat exchange devices in the gas turbine combined cycle power plant.
2. Provide tools to do high-level analysis at different stages of design (conceptual, detailed, etc.) and operation (performance test, root cause analysis, etc.) and check the results of sophisticated computer simulation tools with steep learning curves and “black box” inner details.

This book is not intended for laypersons or dilettantes. There are books out there serving that segment quite adequately. This book is intended for serious practitioners and researchers in the field, who need practical “tools” to help them in their day-to-day activities. As such, no ink will be wasted on generalized information and textbook examples or esoteric variants, which have zero chance to see the daylight in the field in commercial operation. All information in this book, including charts, equations, examples and rules-of-thumb, is directly related to actual, state-of-the-art hardware in commercial operation. This is as close as you can get to the “real stuff” – one step removed from proprietary information – unless you are the employee of an OEM.

In the next chapter, the reader will be introduced to vital references (textbooks, industry codes and standards, etc.) and software tools requisite for the “job” because, to stress it once more, this book is intended for those who need to get the “job done” and do it properly. This requires access to commercial or in-house simulation software such as “cycle decks” and flowsheet simulators. Nowadays, complex cycle calculations are done using such tools, which are extremely expensive (e.g., commercial software) and proprietary (e.g., in-house software) so that only those employed by large organizations have access to them. All rigorous examples in the book are done with such specialized software so that the readers can familiarize themselves with their usage. It is an unavoidable fact that a lone engineer lacking specialty software knowledge cannot go too far in power generation industry (just like an amateur investor who, no matter how well he or she is versed in finance and economics, cannot hope to compete with institutional investors armed with millions of dollars’ worth of computer software and hardware). It is hoped that this book will help inspire the reader in that direction (except those who already have hands-on experience in those tools).

1.1 Note on Units

The entire professional career of the author was spent in US companies. While thoroughly conversant in SI units, his technical experience is primarily based on research studies, commercial projects and myriad assignments dealing with every conceivable aspect of gas and steam turbine combined cycle power plant technology where the US customary system (USCS), i.e., British units, was the standard unit system.¹ Therefore, this book primarily uses the USCS. Not doing so would require conversion of an immense body of work into SI units, which would introduce unnecessary errors into the treatise.

Despite this caveat, in many places in the text, SI units are provided in parentheses for convenience. Otherwise, the reader is asked to do his or her unit conversions. Note that the US companies still play a big role in power generation industry, and many of them still use the “archaic” pounds and degrees Fahrenheit and so on and so forth. Anyone who is serious on building a career in this particular industry would be well advised to be conversant in either unit system.

Ordinarily, no space and ink would be wasted to provide unit conversions herein. In this day and age when everybody is armed with a smartphone, even the most obscure units are one “click” away – one can simply google them. Nevertheless, in case your electronic arsenal is out of reach or your battery is dead or the power system is down because of Hurricane Zelda, below is a list of the most common unit conversions and some important caveats.

¹ The US customary system was developed from English units which were in use in the British Empire before the United States became an independent country. In the United Kingdom, the system of measures was overhauled in 1824 to create the imperial system, changing the definitions of some units. Nevertheless, as far as the most commonly used units in power generation calculations, both are the same.

Temperature

• ° C = (° F − 32)/1.8
• K = ° C + 273.15 (degrees Kelvin)
• R = ° F + 459.67 (degrees Rankine).

Unless a particular equation is an empirical curve-fit and the author specifically identifies which temperature units to use, one has to make sure that absolute temperatures (in degrees Kelvin or Rankine) are used in scientific formulae.

Pressure

• 1 psi = 0...