handbook for cogeneration and combined cycle power plants pdf

vi .Handbook for Cogeneration and Combined Cycle Power PlantsIncreasing the Work Output of the Simple Cycle Gas Injection of Compressed Air, Steam, or Water Combination of Evaporative Co

HANDBOOK FOR COGENERATION

AND COMBINED

CYCLE POWER PLANTS

@ 2002 by The American Society of Mechanical Engineers

Three Park Avenue, New York, NY 10016AlI rights reserved Printed in the United States of America Except as permittedunder the United States Copyright Act of 1976, no part of this publication may bereproduced or distributed in any form or by any means, or stored in a database orretrieval system, without the prior written permission of the publisher

INFORMATION CONTAINED IN THIS WORK HAS BEEN OBTAINED BY THEAMERICAN SOCIETY OF MECHANICAL ENGINEERS FROM SOURCES

OF ANY INFORMA TION PUBLISHED IN THIS WORK NEITHER ASME NORITS AUTHORS AND EDITORS SHALL BE RESPONSIBLE FOR ANY ERRORS,

THAT ASME AND ITS AUTHORS AND EDITORS ARE SUPPL YING TION BUT ARE NOT ATTEMPTING TO RENDER ENGINEERING OR OTHER

ASME shall not be responsible (or statements or opinions advanced in papers 9r printed in its publications (B7.1.3) Statement from the Bylaws

For authorization to photocopy material for intemal or personal use under thosecircumstances not falling within the fair use provisions of the Copyright Act,contact the Copyright Clearance Center (CCC), 222 Rosewood Drive, Danvers, MA

This book is dedicated to my

Grandfather Khan Bahdur Jehangir R Colabawala MBE

DEDICATION iii

vi Handbook for Cogeneration and Combined Cycle Power Plants

Increasing the Work Output of the Simple Cycle Gas

Injection of Compressed Air, Steam, or Water

Combination of Evaporative Cooling and Steam

ASME, Performance Test Code on Gas Turbine Heat Recovery

ASME, Performance Test code on Steam Condensing

ASME, Performance Test Code on Atmospheric Water Cooling

TABLE OF CONTENTS vii

117117118118120120

120

121

121121122122

122122

122

ISO, Natural Gas -Calculation of Calorific Value, Density

and RelativeDensity

Table of Physical Constants of Paraffin Hydrocarbons

MechanicalParameters API Std 616, Gas Turbines for the Petroleum, Chemical

andGaslndustryServices

API Std 618, Reciprocating Compressors for Petroleum,

ChemicalandGaslndustryServices

API Std 619, Rotary- Type Positive Displacement Compressors

for Petroleum, Chemical, and Gas Industry Services

API Std 613 Special Purpose Gear Units for Petroleum,

Ch~micalandGaslndustryServices

API Std 677, General-Purpose Gear Units for Petroleum,

ChemicalandGaslndustryServices

API Std 614 , Lubrication, Shaft-Sealing, and Control-Oil

Systems and Auxiliaries for Petroleum, Chemical and

GaslndustryServices

ANSI/API Std 610 Centrifugal Pumps for Petroleum,

Heavy Duty Chemical and Gas Industry Services

API Publication 534, Heat Recovery Steam Generators

API RP 556, Fired Heaters & Steam Generators ' "

ISO 1 0436: 1993 Petroleum and Natural Gas

Industries -General Purpose Steam Turbine for

RefineryService

API Std 67.1, ,Special Purpose Couplings for Petroleum

Chemical and Gas Industry Services '

ANSI/API Std 670 Vibration, Axial-Position, and

Bearing- Temperature Monitoring Systems

API Std 672, packaged, Integrally Geared Centrifugal Air

Compressors for Petroleum, Chemical, and Gas

viii Handbook for Cogeneration and Combined Cycle Power Plants

The Steam Regenerative-Reheat Cycle ".'.""'."' "' ' 223

CI assl Icatlon '1 o f Steam Tur bInes . 227

TABLE OF CONTENTS ix

Back Pressure Considerations (Gas Side) '.'.""""""" 282

x Handbook for Cogeneration and Combined Cycle Power Plants

CoolingTowers Design of Cooling Towers

Chemical Water Treatment

Bearings Rolling Bearings

Journal Bearings

312314319

TABlE OF CONTENTS xi

xii Handbook for Cogeneration and Combined Cycle Power Plants

Steam Turbines

Plant Losses

Nomenclature

487491492

527BIBLlOGRAPRHY

543INDEX

559ABOUTTHEAUTHOR

Handbook for Cogeneration and Conrbined Cycle Power Plants discusses thedesign, fabrication, installation, operation, and rnaintenance of cornbined cyclepower plants The book has been written to provide an overall view for theexperienced engineer working in a specialized aspect of the subject and for fueyoung engineering graduate or undergraduate student who is being exposed tothe field of power plants for the first tirne The book will be very useful as atextbook for undergraduate courses as well as for in-house cornpany trainingprograrns related to power generation.

Cogeneration and cornbined cycle power plants are not new but with fueirnprovernent of fue gas turbine technology; efficiencies in the rnid-SOs arecornrnon, and with a little bit of ingenuity, efficiencies in the low 60s will bepossible These high efficiencies have totally revolutionized the industry, rnakingthe old stearn plants a thing of the pasto

The use of cogeneration and cornbined cycle power plants in all industries, and

in fue power generation field, has rnushroorned in the past few yea"rs It is to theseusers and rnanufacturers of cornbined cycle power plants that this book is directed.The book will give the rnanufacturer a glirnpse of sorne of the problerns associatedwith bis equiprnent in the field and help the user to achieve rnaxirnurnperformance efficiency and high availability for bis planto

I have been involved in the research, design, operation, and rnaintenance ofvarious types of cornbined cycle power plants since the early 1960s I have alsotaught courses at the graduate and undergraduate levels at the University ofOklahorna and Texas A&M University, and now, in general, to the industry for thepast 30 years I have taught over 3000 students frorn over 400 corporations aroundthe world The enthusiasrn of the students associated with these courses gave rnethe inspiration to undertake this endeavor The rnany courses I have taught over thepast 37 years have been an educational experience for rne, as well as for thestudents The Texas A&M University Turbornachinery Syrnposiurn, which I had theprivilege to organize and chair for 7 years, is a great contributor to the operationaland rnaintenance sections of this book The discussions and consultations thatresulted frorn rny association with highly professional individuals have been arnajor contribution to both rny personal and professionallife as well as to this book

In this book, I have tried to assirnilate the subject rnatter of various papers, andsornetirnes diverse views, into a cornprehensive, unified treatrnent of cornbinedcycle power plants Many illustrations, curves, and tables are ernployed to broadenthe understanding of the descriptive texto Mathernatical treatrnents are deliber-

xiv PREFACE

ately held to a mínimum so that the reader can identify and resolve any problemsbefore he is ready to execute a specific designo In addition, the references direct thereader to sources of infonnation that will help him to investigate and salve bisspecific problems It is hoped that this book will serve as a reference text after it hasaccomplished its primary objective of introducing the reader to the broad subject

of combined cycle power plants

I wish to thank the many engineers whose published work and discussions havebeen a comerstone to this work

Lastly, I wish to acknowledge and give special thanks to my wife, Zarine, for herreadiness to help and her constant encouragement throughout this project

I sincerely hope that this book will be as interesting to read as it was for me towrite and that it will be a useful reference to the fast-growing field of combinedcycle power plants

MEHERW AN P BOYCE

2001

Energy costs in the past decade have rigen dramaticaIly With this large increase

in energy costs, the acceptability of inefficient engine systems is very limited.Turbine and diesel engine efficiencies range from the 30% to 45% range (withsome even lower), which implies that between 55% and 70% of the energysupplied is wasted The privatization of large central energy corporations mn bylarge govemment bureaucracies throughout the world has been a majar incentive

in the search for more efficient techniques of generation of power The UnitedKingdom spearheaded the privatization schemes in the 1980s and 1990s; othercountries, small and large, have foIlowed The United States of Arnerica isopening up its large power market, and by the year 2010, a very open market wiIl

The energy market place of the first quarter of the new century (2000 to' 2025)wiIl be very different from the last quarter of the 1900s Competition for the energymarket will be very fierce and non-traditional, with many new and efficient energyconversion systems in the market place The traditional utilities of the 1900s wiIlnot exist in the 2000s The traditional utilities, which were generating power,transmitting power and then distributing the power wiIl be broken up into threeseparate companies in these areas These companies wiIl be autonomous and wiIlhave no relationship with each other than what the market place wiIl exert onthem The transmitting companies wiIl be transmitting power purchased by thedistributing companies from various power generation companies Power will be acommodity, like grain, and will be traded freely, aIlowing Consumers to buy fromvarious power sources

The total production capacity of electric power in the world exceeds 3000 GW,with the power in the U S in 1998 being 891 GW, and the component ofcombined cycle is about 300 GW, which amounts to about 10% of the existingcapacity Figure 1-1 shows the various power systems which make up the overaIlcapacity Steam plants account for about 56% of fue capacity, nuclear plantsaccount for about 12%, hydro plants about 20%, combined cycle and gas turbinepower plants about 10%, diesel plants about 2%, renewable energies amount toabout a tenth of 1 % Some predict that the expected power by 2050 would beabout 10,000 GW This wouId mean that there would have to be an addition of

140 GW/year at an investment of US$100 to $150 billion/year A moreconservative estimate wouId be that in the next 20 years, through 2020, the

An Overview of Power Generation 3

new additional power in the world would arnount to about 400 GW, frorn which

it is expected that the cornbined cycle cornponent could be as high 100 GW.Throughout the world, there are over 300 GW of gas turbine and cornbined cyclepower plants, which have been brought on line rnostly in the 1990s in electricalutility service

The growth of the power industry over a 10-year period indicates that therewould be about 642 GW of additional power, an increase of about 20% on theexisting world capacity Figure 1-2 shows the type of power that is expected 10rnake up the new power The industry has seen and will see sorne very largehydroelectric projects, such as Arnerica's Grand Coulee (6480 MW) In Egypt,20,000 MW ofpower is supplied by the Aswan Darn and the Aswan High Darn onthe Nile The Guri hydroelectric plant; with over 10,000 MW of installed capacity(the world's fourth largest capacity), becarne Venezuela's largest single source ofelectricity upon its cornpletion in 1986 The Guri Darn, located on the Río Caroní,saved the country the equivalent of 300,000 barreIs of oil ayear The next rnajorhydroelectric project corning on line is China's Three Gorges Darn, an 18,000-MWproject scheduled for operation in the year 2009 The Three Gorges Darn, which islocated on the Yangtze River, the third longest river in the world, rneasuresapproxirnately 6390 km frorn its headwaters at the Gelandandong Glacier in Tibet

to its rnouth near Shanghai on China's eastem seaboard

In rnany countries, where there is an abundance of coal, stearn plants willgrow China, India and the U S are three rnajor countries that have vast coal

4 COGENERATION ANO COMBINEO CYCLE POWER PLANTS

reserves Conventional steam turbine plants are base-Ioad operated and use coal

as fuel The choice between conventional steam plants and combined cycle plants

is fuel If natural gas is available, the combined cycle plant will be the plant ofchoice It is estimated that 43% of the power in the years from 1997 to 2006 will

be from steam plants mainly operating on coal The development of newabatement techniques make steam plants environmentally friendly, as comparedwith their predecessors

The shape of this market place will be very dependent of the availability andcost of fossil fuel In the majority of the 1900s, coal was the preferred fuel Today,natural gas is by far the preferred fuel; that is not to say that coal and oil will not

be used, rather than natural gas, for its minimum pollution and very lowmaintenance cost, will be the preferred fuel as long as it is available and the price

is affordable

Natural gas is the fuel of choice wherever it is available because of its cleanbuming and its competitive pricing as seen in Figure 1-3 Prices for uranium,the fuel of nuclear power stations, and coal, the fuel of the steam power plants,have been stable ayer the years and have been the lowest Environmental, safetyconcems, high initial cost, and the long time from planning to production havehurt the nuclear and steam power industries Whenever oil or natural gas is thefuel of choice, gas turbines and combined cycle plants are fue power plants ofchoice, as they convert the fuel into electricity very efficiently and costeffectively It is estimated that from 1997 to 2006, 23% of the plants will becombined cycle power plants, and that 7% will be gas turbines It should benoted that about 40% of gas turbines are not operated on natural gas

The use of natural gas has increased and in the year 2000, has reached prices ashigh as $4.50 in certain parts of the V.S This will bring other fuels anta the n:tarket

to compete with natural gas as the fuel source Figure 1-4 shows the growth'of thenatural gas as the fuel of choice in fue V.S., especially for power generation This

Figure 1-3 Typical Fuel Costs per Million BTUs

6 COGENERATION ANO COMBINEO CYClE POWER PLANTS

GW

ASIA

MIDDLE EAST SOUn-IEASTASIA

REGIONS

NORTHAMERCA

Figure 1-5 Technology Trends Indicate That Natural Gas is the Fuel of Choice

growth is based on completion of a good d~stribution system This signifies thegrowth of combined cycle power plants in ihe U S

Figure 1-5 shows the preference of natural gas throughout the world This isespecially true in Europe, where 71 % of the new power is expected to be fueled

by natural gas, Latin America, where 73% of the new power is expected to _b~fueled by -natural gas, and North America, where 84% of the new power- Isexpected to be fueled by natural gas This means a substantial growth ofcombined cycle power plants

Figure 1-6 shows the growth of the power industry in the U S, through 2020

In the year 2000, there is about 14% of the power in the U.S generated bycombined cycle power plants and gas turbines This is expected to rise to about43% by the year 2020 This is dependent on the use of natural gas as the mainfuel It will require new pipelines to bring competitive-priced natural gas to allparts of the U S

The last two decades, the 1980s and 1990s, have seen the growth ofcogeneration systems and combined cycle power plants throughout the world

In the next 20 years, wherever natural gas or oil is available, combined cycle powerplants and high-efficiency gas turbine plants will be the plants of choice

Cogeneration is the production of two or more forms of energy from a singleplanto The most common application of the term is for the production of electricalpower and steam for use in process applications This does not mean that othertypes of cogeneration plants are not being designed and used Cogeneration plantsare used to produce power, and use the direct exhaust gases from the prime moversfor preheating air in fumaces, or for the use in absorption cooling systems, or forheating various types of fluids in different process applications Between 1996 and

2006, cogeneration plants will account for 3% of the new power being generatedworldwide, this amounts to 19.6 GW of power Cogeneration systems are also used

An Overview of Power Generation 7

Figure 1-6 projected U.S Generating Capacity 2000-2020

in petrochemical plants, where the prime-mover drives are used to drivecompressors to compress process gasses, and then the heat is used to eitherproduce steam for process use, or for use direct in processes

Figure 1-7 A Typical Combined Cycle Facility (Courtesy of Enron Corp.)

8 COGENERATION AND COMBINED CYCLE POWER PLANTS

.c ~

~ c

-'" ~ '":) -

t-~ o

"¡:: ra

>

-o'"

Q)

+"'

ra

~ +"'

ra

Q)

:J:rov

U-10 COGENERATION ANO COMBINEO CYClE POWER PLANTS

Combined cycle power plant is a term usually associated with electrical powerplants, which uses the waste heat from the prime mover for the production ofsteam and, consequently, the steam is used in a steam turbine for the production ofadditional power This is usually a combination ofthe Brayton Cycle (Gas Turbine)

as the topping cycle , and the Rankine Cycle (Steam Turbine) as the bottomingcycle However, technically, the term can be used for any combination of cycles.Many small plants use the Diesel Cycle as the topping cycle, with the Rankine Cycle

as the bottoming cycle Plants are also using the Brayton Cycle as both the toppingand the bottoming cycles

The fossil power plants of the 1990s and into the early part of the newmillennium will be the combined cycle power plants It is estimated that between

1997 and 2006, there will be an addition of 147.7 GW ofpower These plants havereplaced the large steam turbine plants, which were the main fossil power plantsthrough the 1980s Figure 1-7 shows a large combined cycle power planto Thecombined cycle power plant is not new in concept, since some have been inoperation since the mid-1950s These plants carne into their own with the newhigh-capacity and high-efficiency gas turbines

The new market place of energy conversion will have many new and novelconcepts in combined cycle power plants Figure 1-8 shows the heat rates of theplants of the present and future, and Figure 1-9 shows the efficiencies of the sameplants The plants referenced are the simple cycle gas turbine (SCGT), with firingtemperatures of 2400°F (1315°C), recuperative gas turbine (RGT), the steamturbine plant (ST), the combined cycle power plant (CCPP), and the advancedcombined cycle power plants (ACCP), such as combined cycle power plants usingadvanced gas turbine cycles, and, finally, the hybrid power plants (HPP)

T.Qe demographics, both local and worldwide, will determine the capitalavailable for investment Countries, such as India, startíng the new century with apower capacity of about 95,000 MW, will require another 100,000 MW through theyear 2050 The world population will continue to increase for the next three to fourgenerations, reaching a peak of about 11 to 12 billion people in the year 2150 as perWorld Bank figures

Distributed Generation

The very large fossil plants ranging upwards of 1500 MW will be fewer, ando plantsbetween 150 and 300 MW will dot the landscape and will reduce transmissionlosses, which can reach as high as 20% to 30% due to electricallosses, as well astheft and other parasite losses In fact, there has been a growth in the late 1990s atthe very low end of the power spectrum with the advent of the micra-gas turbine, aturbine that produces power in the 50 to 100 kW range, leading to theconcept ofdistributed generation Distributed generation (DG) is the integrated or stand-alone use of small, modular electricity generation resources by utilities, industryand retail centers, in applications that benefit the entire electric system

The growth of centralized power plants in the 1950s and 1960s was due to agingequipment, plus the growth of the U.S Rural Electrification Agency (REA), andabundant supply of low casi fuels A growth of distributed generation is expected in

An Overview of Power Generation 11

the next 20 to 30 years Historically, the distributed power plants were the "nonn"

in the 1920s, 1930s, and 1940s Cities, especially in Europe, have both large andsmall municipal plants with district heating from the waste energy

Distributed energy would find the best expectance in the following areas:

.Ernergency generation

.Peak shaving

.Special base load application

There are many baIriers to distributed generation that have to be overcome toenable distributed generation to be widely used:

1 Technical Requirernents for Interconnection

1.1 The adoption of uniforrn standards for interconnecting distributed

power to the grid "Plug and play" standards are key to opening

rnarkets for distributed generation

1.2 Adoption of IEEE standards for interconnection equiprnent,

irnplernentation, testing, and certification would assure utilities

1.3 The technology of various distributed power technologies rnust

be irnproved

1.3.1 Reduce installed cost frorn about $1400 to about

$400/kW1.3.2 Reduce NOx output to less than 9 pprn

1.3.3 Irnprove plant efficiency to about 39% to 45%

2 Business Practices and Contractual Requirerne~ts

2.1 Standard cornrnercial practices will have to be adopted in dealing

with utilities to review interconnection

2.2 Establish standard business plan for interconnection agreernents

2.3 Help utilities to assess the value irnpact of distributed power at

any point on the grid

3 Regulatory Barners

3.1 New regulatory principIes will have to be adopted favorable to

distributed generation in both competitive and utility markets

3.2 Conditions for a right to interconnect must be spelled out

3.3 Expedited dispute resolutions processes

3.4 New tariffs must be established in the following traditional

tariff areas

3.4.1 Demand charges

3.4.2 Backup tariffs

Distributed generation provides benefits for both the user and the utility Thebenefits to the user would be:

.Power reliability -reduced power outages, and thus the minimization

of fue cost associated with power outages in many chemical processes

12 COGENERATION AND COMBINED CYClE POWER PLANTS

Finally, the safety and loss of production associated with power los sfrom the grid

.Improved power quality -voltage fluctuations are minimized, whichnegatively effect many machinery, increasing maintenance costs

.Reduced total energy costs -these systems can produce hot or cold waterfor heating or cooling Steam for other processes in the planto Efficienciescould reach 80% with combined heat and power (CHP)

.Barrier against price volatility -the price of electric supply in manycountries varies significantly from year to year

.Source of revenue -the ability to sell any excess power to otherneighboring plants, as well as in so me cases to the utility itself

.Environmental -reduction of NOx can be reduced, as most of fuesesmaller plants run at lower firing temperatures

There are algo many benefits for the utility to consider in the area of distributedpower generation:

.Reduced transmission and distribution losses -these loses can run ashigh as 30%, continuous losses are between 12% and 15%

.Avoid or defer increase in capacity -since this gives an increase in powersolloce, the need for large capital investment is greatly reduced

.Deferral of transmission and distribution upgrades -use of DG reducesthe need, or defers the need." for upgrnding existing transmission ordistribution lines Grid extensÍon can cost anywhere from $8000 to

$18,000/km depending on the terrain Distribution capacity can beestimated to cost in majar metropolitan areas as much as $400 to $500/kW V AR suppórt -provide reactive power (V AR) that helps utilities maintainsystem voltage

.Peaking power -the DG power can reduce the need for peaking plants,which are expensive to operate and maintain

.Improved power quality -DG plants can eliminate the demand thatnegatively impacts the power quality of the grid system

.Reduced reserve margin -by lowering the overall power demand, reservemargins can be reduced

.Transmission congestion -by generating the power near the point ofconsumption, the effectiveness of the transmission and distributionsystem for all customers "

.Increased the system that are overloaded power reliability -reduction of power outages in certain part of..Environmental impact -societal concems of transmission lines isgrowing, thus DG reduces the necessity of new lines to be constructed

The most common type of distributed generation in the near future can beclassified into four majar categories:

.Emergency generation

.Hospitals

.Nursing homes

An Overview of Power Generation 13

.Special base-Ioad application

.Colleges and schools

There are rnany sources of energy available for fue production of electric powerfor a distributed network of energy generation systerns A nurnber of thetechnologies that will rnake DG a very viable altemative will depend on the newtechnologies, such as fuel cells and rnicro-turbines, proving thernselves Distribu-tion systern stability and safety, as well as interconnection standards, have yet to besettled The following is a list of sorne of the cornrnon power generationtechnologies available today and will be available in the next 20 years, whichcan be used, and ~~ being used, for distributed generation throughout the world:

1 Diesel and gasoline engines

2 Natural gas reciprocating engines

3 Gas turbines

4 Micro-turbines

5 Fuel cell technology

6 Solar energy-photovoltaic cells

MicroTurbines(lb/MW.h)

Diesel Engines

(lb/MW.h)

GasEngines(lb/MW.h)

Combined

Cycle

(lb/MW.h)

Large GasTurbines(lb/MW.h)

SmallTurbines(lb/MW.h)

0.4

An Overview of Power Generation 15

values of these initial cost have to be greatly reduced before sorne of thesetechnologies becorne cornpetitive

Diesel and Gasoline Engines

The diesel and gasoline engine has be en providing power frorn the early 1900s,especially for the rural areas, through the 1950s The diesel engines have be enrelatively robust and have efficiencies which vary frorn 30% to 37% Diesel enginescan be classified into three groups: low-speed dieseIs (200 to 400 rprn), rnediurn-speed dieseIs (800 to 1200 rprn), and high-speed dieseIs diesel (1500 to 3600 rprn).The low-speed diesel engines can be very large units, ranging in size to 100 MW Thernediurn-speed diesel engines range frorn 600 to 7000 kW, while the high-speeddiesel is between 200 and 1800 kW Mediurn-speed dieseIs are generally used in thepower generation in distributed generation systerns Diesel fuel is easily availableand is, thus, still the rnajor source of independent and back-up power used aroundthe world 1t is not uncornrnon to see these engines being used as the power sourcefor hotels, hospital s and shopping centers

Natural Gas Reciprocating Engines

The natural gas reciprocating engine is getting more and m~re popular and, inmany areas, is replacing the diesel engine Natural gas is a cleaner burning fueliban diesel oil, and these engines have slightly higher efficiencies, as well as lowermaintenance costs iban the ~~.esel engines

Gas Turbines

The simple cycle gas turbine is classified into three groups: industrial type,aeroderivative gas turbines, trame type The industrial-type gas turbine varies inrange from about 500 to 15,000 kW This type of turbine has been usedextensively in many petrochemical plants, and is the source of remote power Theefficiencies of fuese units is the low 30s Aeroderivative, as the llame indicates,are power generation units, which have origin in the aerospace industry as theprime mover of aircraft These units have be en adapted to the electricalgeneration industry by removing the by-pass fans and adding a power turbine

at their exhausto These units range in power from 2.5 to about 50 MW Theefficiencies of fuese units can range from 35% to 42% The trame units are thelarge power generation units ranging from 3 to 350 MW in a simple cycleconfiguration, with efficiencies ranging from 30% to 43%

Micro-Turbines

These

TheyMicro-turbines are usually referred to units of less iban 350 kW

units are usually powered by either diesel fuel or natural gas

16 COGENERATION AND COMBINED CYClE POWER PLANTS

utilize technology already developed The micro-turbines can be eitheraxial flow or centrifugal-radial inflow units The initial cost, efficiency,and emissions will be the three most important criteria in the design ofthese units

The micro-turbines, to be successful, must be compact in size, have manufacturing cost, high efficiencies, quiet operation, quick startups and minimalemissions These characteristics, if achieved, would make micro-turbines excellentcandidates for providing base load and cogeneration power to a range ofcornmercial customers The micro-turbines are largely going to be a collection

low-of technologies that have already been developed The challenges are ineconomically.packaging these technologies

The micro-turbines on the market today range from about 20 to 350 kW.Today's micro-turbines are using radial-flow turbines and compressors, as seen inFigure 1-11 To improve the overall thennal efficiency, regenerators are used in thernicro-turbine design, and in combination with absorption coolers or otherthennal loads, very high efficiencies can be obtained Figure 1-12 shows a

Figure 1-11 A Compact Micro-Turbine Schematic

(Courtesy of Capstone Corporation)

Figure 1-12 A' Cogeneration Micro- Turbine System Package

(Courtesy of Ingersoll Rand Corporation)

typical cogeneration system package using a micro-turbine This compact forrn

of distributed power systems has great potential in the years to come

Fuel Cell Technology

The general concept of a fuel battery, or fuel cell, dates back to the early days ofelectrochemistry A fuel cell is an electrochemical device that combines hydrogenfuel and oxygen from the air to produce electricity, heat, and water Fuel cellsoperate without combustion, so they are virtually pollution-free Since the fuel isconverted directly to electricity, a fuel cell can operate at much higher efficienciesiban most combustion engines, extracting more energy from the same amount offuel The fuel cell itself has no moving parts, making it a quiet and reliable source

of power

The fuel cell is composed of an anode (a negative electrode that repelselectrons), an electrolyte membrane in the center, and a cathode (a positiveelectrode that attracts electrons) As hydrogen flows into the fuel cell anode,platinum coating on the anode helps to separate the gas into protons (hydrogenions) and electrons The electrolyte membrane in the center allows only theprotons to pass through the membrane to the cathode sirle of the fuel cell Theelectrons cannot pass through ibis membrane and flow through an extemal circuit

in the forro of electric current

18 COGENERATION AND COMBINED CYClE POWER PLANTS

As oxygen flows into the fuel cell cathode, another platinum coating helps theoxygen, protons, and electrons combine to produce pure water and heat.Individual fuel cells can be then combined into a fuel cell "stack" The number

of fuel cells in the stack determines the total voltage, and the surface area of eachcell determines the total current Multiplying the voltage by the current yields thetotal electrical power generated

A cell of this sort is built around an ion-conducting membrane such as Nafion(trademark for a perfluorosulfonic acid membrane) The electrodes are catalyzedcarbon, and several construction alignments are feasible Salid polymerelectrolyte cells function well (as attested to by their performance in Geminispacecraft), but cost estimates are high for the total system compared to the typesdescribed a~ove Engineering or electrode design improvements could changethis disadvantage

Fuel cell technology is rapidly growing, and in the early 2000, successfulfactory testing of the first fuel cell/gas turbine has been completed The newhybrid technology combines a pressurized solid oxide fuel cell (SOFC) with amicro-turbine generator as seen in Figure 1-13 The air from the compressor ofthe micro-turbine is pre-heated in a recuperator, from which the pre-heated air

is then sent to a duct bumer, where it is heated to about 1112°F (600°C), andthe gases are then sent to the fuel cell, where they are further heated to about

,

"\

G/

Natural gas = ~

Figure 1-13 Simplified Process Flow Diagram for the SOFC/Micro- Turbine

Hybrid System

An Overview of Power Generation

1562°F (850°C), and if necessary, they are then sent through another duct

bumer where the gases are further reheated to about 1832°F (1000°C) The

gases then enter the gasifier turbine, which drives the micro-turbinecompressor

The gases then enter the power turbine, where the gases arefurther expanded and drive the generator The gases from the power turbine,

which exit at about 1150°F (621°C), enter the recuperatbr to pre-heat the

compressed air

SOFC systems have be en operated at about 100 kW successfully In some'ways,

solid oxide fuel cells are similar to molten carbonate devices Most of the cell

materials, however, are special ceramics with some nickel The electrolyte is an

ion-conducting oxide, such as ziTconia, treated with yttria The fuel for these

experimental cells is hydrogen combined with carbon monoxide, just as for, molten

carbonate cells While intemal reactions would be different in terms of path, the

cell products would be water vapor and carbon dioxide Because of the high

operating temperature, 1500°F to 1850°F (815°C to 1010°C), the electrode

reactions proceed very readily As in the case of the molten carbonate fuel cell,

there are many engineering challenges involved in creating a 10ng-lived

contain-ment system for cells that operate at such a high-temperature range Solid oxide

fuel cells have been designed for use in central power-generation stations, where

temperature variation could be controlled efficiently, and where fossil fuels would

be available The system would, in most cases, be associated with the so-called

bottoming steam (turbine) cycle -i.e., the hot gas product, 1850°F (at 1010°C), of

the fuel cell could be used to generate steam to run a turbine and extract more

power from heat energy The major characteristic of the fuel cell in the final

completed project will be the very high efficiency of over 60% and ext~em.ely low

The direct fuel cell (DFC) application being developed by companies

such as FuelCell Energy, Inc use carbonate fuel cell technology, in which

the reforming action occur within the fuel cell stacks This version of the

carbonate technology is referred to as the direct fuel cell because of the

intemal reforming aspect of the designo The process involves treating

natural gas to remove impurities, after which it is mixed with steam and

sent to the fuel cell stacks The fueVsteam mixture is reformed in the

stacks, providing the hydrogen, which is consumed in the fuel cell anodes

(at a hydrogen utilization rate of up to 80%) The anode reaction also

produces CO2, which is required in the fuel cell cathodes The cathode

feed is produced by taking the anode exhaust, catalytically reacting any

residual fuel with air, and sending the flue gas with excess air to the

cathodes Cathode exit gases are sent to a packaged heat recovery unit to

supply heat for steam generation, fuel pre-heat, and final heating of the

stearn/fuel anode feed gas

A hybrid system which utilizes DFC/gas turbine is shown schematically in

Figure 1-14 The system concept is as follows Fuel and water are sent to

the system heat recovery unit (HRU) unit, where steam is produced and

mixed with heated fuel for use as the fuel cell gas feed As with the

simple-cycle system, residual fuel from the anode exit is consumed in an anode

exhaust oxidizer Air is compressed in an inter-cooled compressor to the

desired turbine pressure, 235 psia (16 bar), in the baseline hybrid system,

20 COGENERATION ANO COMBINEO CYClE POWER PLANTS

Compressed Air is Heated with Fuel Cell

Waste Heat Expanded and then Used as

the Fuel Cell Oxidant

CONDENSER

FUEL

r-GENERATOR l"t~r -'" STEAM

Potential to Significantly Lower $/kW Cost

Power Direct Fuel Ce1185% Gas Turbine 15%

Figure 1-14 Schematic of a Fuel Cell (Courtesy FuelCel1 Energy, Inc.)

heated with system exhaust in the HRU, heated further with exhaust fromthe anode exhaust oxidizer, and expanded in a turbine to produce additionalelectricity The expanded, low-pressure air leaving the turbine is used as theoxidant in the anode exhaust oxidizer Flue gas leaving the oxidizer is firstcooled by the turbine air, and then sent as the cathode feed gas to the fuelcells The cathode exhaust gas is sent through the HRU to provide therequired pre-heat and water vaporization A typical 20-MW system wouldhave an efficiency of 71 % based on the lower heating value (LHV) of thefuel, the direct fuel cell power is 17 MW, the gas turbine power is 3.44 MW,and the parasitic los s is 0.03 MW

lnstalled costs for fuel cells in the year 2000 are still very expensive, averagingover $1500/kW For the fuel cell to be competitive, costs will have to be reduced toaround $400 to $600/kW

Solar Energy-Photovoltaic CelIs

Photovoltaic process is a process in which two dissimilar material s in clase contactact as an electric cell when stnlck by light or other radiant energy Light strikingsuch crystals as silicon or gernlanium, in which electrons are usually not free tomove from atoro to atoro within the crystal, provides the energy needed to freesome electrons from their bound condition Free electrons cross the junctionbetween two dissimilar crystals more easily in one direction than in the other,giving one sirle of the junction a negative charge and, therefore, a negative voltage

An Overview of Power Generation 21

with respect to the other sirle, just as one electrode of a battery has a negativevoltage with respect to the other The photovoltaic battery can continue to providevoltage and current as long as light continues to fall on the two materials Thiscurrent can be a source of power in an electrical circuit, as in the modem solarbattery Tropical islands like Hawaii may favor rooftop photovoltaics, whichcompete economically with fossil fuels for power generation in those more isolatedregions Presently, the cost ofthese systems is prohibitive, but in the next 10 to 20years, the costs will be more competitive Hybrid systems using this technologyhave a very bright future

Wind Energy

Wind energy is also an area of remóte power, and large wind energy farrns havebeen growing throughout the woilcl In 1999, there were more than 3600 MW ofnew wind generating capacity, bringing total worldwide installed capacity to a13,400-MW range This an increase of 36% over the 1998 figures Wind turbinesgenerating 2.5 MW/turbine are being presently designed with a rotor diameter of

262 ft (80 m); the prototype turbines are to be installed by early 2000

River Hydro- Turbines

Small-scale hydroelectric systems capture the energy in flowing water, and convert

it to electric power The potential for these systems depends on the availability ofsuitable water flow; where the resource is available, it provides cheap and reliablepower Norway is one of the leading countries in the technology of river hydroprojects These systems blend with their surroundings and have minimal negativeenvironmental impacto

Table 1-2 gives an economic comparison of distributed generation technologiesfrom the initial cost of such systems to the operating costs of these systems.Because distributed generation is very site-specific, the cost will vary and thejustification of installation of these type of systems will algo vary Sites fordistributed generation vary from large metropolitan areas to the slopes of theHimalayan mountain range The economics of power generation depend on thefuel cost, running efficiencies, maintenance cost, and first cost, in that order Site

An Overview of Power Generation 23

selection depends on environmental concerns such as emissions aIld noise, fuelavailability, and size and weight

Cogeneratlon

An ideal cogeneration situation exists when there is an equality between power andthermal demands In several cases, the heat demand mayvarywith seasonal changes(greater heat loads during the winter and less during the summer) ~rhe choice ofequipment (type, size, etc.) is strongly influenced by the load demand pattem

The following data is required to evaluate cogeneration feasibilit:V:

.Power demand with variations (seasonal and daily)

.Required heat loads (heat content and mass flow)

.Peak requirements for heat and power

.Special plant requirements -heaters, chillers, plant air requirements, etc Fuel availability

.Environmental impact

.Reliability, availability, and maintainability considerations

The recovery of waste heat has become economically feasible and is beingaddressed today on a very large scale Industrial plants throughout the world areconsidering cogeneration and combined cycle power plants Bottoming cycles forgas turbine drives are being investigated with many working fluids, such as steam,freon, arnmonia, butane, ethylene, to llame just a few The use of heavy crude andother dirty fuels, such as pulverized coal and waste products, such as sawdust,support fue use of externally fired gas turbines to overcome the reduced hot gaspath life caused by contaminants in the fuel The use of waste heat in plants fromvarious processes, whether they be in the petrochemical, iron/steel, or the paperindustry, require the design of modified power generation units, which can directlyconvert waste energy into useful energy

Cogeneration, or the combined generation of both power and heat, has beenutilized for ayer a hundred years and has be en given a number of llames (totalenergy or combined heating and power) As a result of the energy awarenessthat started around 1973, United States industry has shown an increasinginterest in the cogeneration concepto Early cogeneration systems did not tie intothe electric utilities This created problems in steadily maintaining the demandfor electricity and beato Because of this, some of the early cogener:ation systemswere not totally successful

The underlying concept involving cogeneration is that current day primemovers have low efficiencies, which implies that a greater part of fue fuel energy

is being converted to heat rather than shaft horsepower Cogeneration wouldthen involve the sequential utilization of the waste heat for some process-relatedneeds such as drying, steam production, absorption cooling, and auxiliary heat

to furnaces

In 1983, about 5% of the power in the United States was cogenerated; in theyear 2010, ayer 20% of the power will be cogenerated In Europe, where

24 COGENERATION AND COMBINED CYCLE POWER PLANTS

energy costs have been historically higher, cogeneration has been wellestablished For example, in Gerrnany, about 25% to 35% of the powerconsumed is cogenerated In the fall of 1978, the United States Congressenacted the Public Utility Regulatory Policies Act, commonJy known as PURPA.Part of PURPA required that the Federal Energy Regulatory Commission(FERC) develop rules to encourage cogeneration This resulted in t:he February

1980 ruling that qualified cogeneration facilities may parallel utility grids andshould be paid rates for electricity that are equal to the cost that the utilityavoids by not having to generate or obtain power from another source, i.e., theutilities avoided cost Utilities algo had to provide standby power at non-discriminatory rates and were obligated to interconnect Statt~ regulatorycommissions were then ';'equired to implement FERC's rules By March 1981,most states (and unregulated utilities) had some rules in place Several statessimply rubber-stamped the ideas and adopted FERC rules, while other statesdeveloped very detailed specific documents, including methods for measure-ment of avoided costs, setting rate levels and defining contract terms Therubber-stamp approach left it to the utilities to determine how avoided costswere to be measured and how rates were to be structured Initially, the utilitieswere very much against this law, however, most utilities have now their owncogeneration divisions, and are now some of the largest independent powerproducers (IPP) in the world

There are several unresolved legal, environmental, interconnection andregulatory problems that make implementation of cogeneration difficult Thebest advice for any potential cogenerator is to get expert help in dealing andnegotiating with the state agencies and utilities, and to keep informed of changesoccurring in the laws There are severa! firms that specialize in the legGlI, regulatoryand procedural steps of initiating a cogeneration project, and these consultantsshould be utilized There are several cases in which obstacle~; will seeminsurmountable, and professional help is the best way to salve this problem

The term avoided cost is deceptively simple to define, but it is very difficult tofind much agreement on the termo Several legal battles have occurred, andprobably millions of dollars have been spent in legal fees on this issu(~ As utilitiesutilize economic dispatch programs, they use their most efficient units first, andtheir least efficient plants last Therefore, as a cogenerator comes on-line, theutility would shut clown the least efficient unit The avoided cost would thus relate

to this unit, which explains why avoided costs are high (typically $0.05 to $0.07/

kW.h).

Gas turbine cogeneration is far more efficient iban the typical steam utilitycentral plant's of the 1970s About 75% heat utilization can be realized for powerand heat, with about 25% leaving in the exhaust gases In a fossil steam plants, only35% of the fuel energy is obtained as power with condenser losses and boiler lossesaccounting for 48% and 15%, respectively

Over 19.6 GW in cogeneration capacity is estimated by 2010 Gas turbine-basedcogeneration and combined cycles will dominate this market Some interestingprojections regarding gas turbine cogeneration predict that about 70% ofcogeneration market growth will take place in the developing nations of the world,with about half of the sales occurring in the petrochemical industry Most of thesystems will be for units with steam capabilities exceeding 100 million Btulhr

An Overview of Power (jeneration 25

Cogeneration systerns are so varied that classification is not an easy task Oneway of classifying the systerns is as follows:

.Utility cogeneration -these are funded and operated by a rnunicipality,

usualIy involving large units with district heating and cooling 'This concepthas been and is still being widely used in Europe In fue U.S , new sportscomplexes, as welI as downtown areas of large cities, are looking intosimilar heating and cooling complexes with power generation utilities

.Industrial cogeneration -this is operated for a private sector j.ndustry, i.e.,

a petrochemical plant, paper mill, glass factories, textile milIs, and manyother industrial complexes The popularity of the "inside the fence" powerplants especially in the developing world will be large, as not only does itprovide cheap energy, but very importantly, it produces reliable energy

.Desalination plants -desalting costs are reduced by using c:ogenerationand hybrid processes Cogeneration desalination plants are large-scalefacilities that produce both electric power and desalted seawater.Distillation methods, in particular, are suitable for cogeneration Thehigh-pressure steam that runs electric generators can be rec:ycled in thedistillation unit's brille heater This significantly reduces fuel consump-tion compared with what is required if separate faciliti~~s are built.Cogeneration desalination plants using gas turbines are very common inthe Middle East and North Africa, wh.ere they have been in clperation forthe past 30 years

Cogeneration Qualifications

Cogeneration qualifications in the U S were designed to promote meaningfulenergy conservation and to ensure that the cogeneration concept is not abused bythe creation of facilities that produce power and a trivial amount of beato Toqualify as a cogenerator, the system designed (utilizing fuel oil or natural gas) musthave a "PURPA efficiency" of at least 42.5% on an annual basis If the therrnalenergy output is less than 15% of the total energy output, the PURJP A efficiency to

O/P = output power

For example, as sume the cogeneration system as shown in :Figure 1-15 Inthis system, the exhaust gas from the gas turbine enters the duc1: bumer, wherethe exhaust gas is further heated The heated gas then enters tht~ HRSG, wheresteam is created This steam is sent to an extracting condensing steam turbine,where the steam is extracted for the process purpose, and the remainder steam

is sent through the steam turbine to generate additional powt~r if needed Asimpler system would have no steam turbine, and all the steam produced