Steam - Its Generation and Use

The Babcock & Wilcox Company

Steam 41iv



Steam 41 v

PrefaceDear Reader:

The founders of our company, George Babcock and Stephen Wilcox, inventedthe safety water tube boiler. This invention resulted in the commercializationof large-scale utility generating stations. Rapid increases in generation of safe,dependable and economic electricity literally fueled the Industrial Revolutionand dramatically increased the standard of living in the United States andindustrialized economies worldwide throughout the twentieth century.

Advancements in technology to improve efficiency and reduce environmen-tal emissions have continued for nearly 140 years, creating a unique and valu-able body of applied engineering that represents the individual and collectivecontributions of several generations of employees. As in other areas of scienceand engineering, our field has continued to evolve, resulting in an extensiveamount of new material that has been incorporated into our 41st edition ofSteam/its generation and use. This edition required an extensive amount ofpersonal time and energy from hundreds of employees and reflects our com-mitment to both our industry and our future.

Today it is clear that the challenge to generate power more efficiently fromfossil fuels, while minimizing impacts to our environment and global climate,will require significant technological advancements. These advances will re-quire creativity, perseverance and ingenuity on the part of our employees andour customers. For inspiration, we can recall the relentless drive and imagi-nation of one of our first customers, Mr. Thomas Alva Edison. For strength,we will continue to embrace our Core Values of Quality, Integrity, Service andPeople which have served us well over our long history as a company.

I thank our shareholders, our employees, our customers, our partners andour suppliers for their continued dedication, cooperation and support as we moveforward into what will prove to be a challenging and rewarding century.

To help guide us all along the way, I am very pleased to present Edition: 41.

David L. KellerPresident and Chief Operating OfficerThe Babcock & Wilcox Company


Steam 41vi

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viii to ixSystem of Units: English and Système International . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xEditors’ Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiIntroduction to Steam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Intro-1 to 17Selected Color Plates, Edition: 41 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Plates 1 to 8

Section I – Steam FundamentalsChapter 1 Steam Generation – An Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1 to 1-17

2 Thermodynamics of Steam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1 to 2-273 Fluid Dynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1 to 3-174 Heat Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1 to 4-335 Boiling Heat Transfer, Two-Phase Flow and Circulation . . . . . . . . . . . . . . 5-1 to 5-216 Numerical Modeling for Fluid Flow, Heat Transfer, and Combustion . . . . 6-1 to 6-257 Metallurgy, Materials and Mechanical Properties . . . . . . . . . . . . . . . . . . . . 7-1 to 7-258 Structural Analysis and Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1 to 8-17

Section II – Steam Generation from Chemical EnergyChapter 9 Sources of Chemical Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-1 to 9-19

10 Principles of Combustion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-1 to 10-3111 Oil and Gas Utilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-1 to 11-1712 Solid Fuel Processing and Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-1 to 12-1913 Coal Pulverization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-1 to 13-1514 Burners and Combustion Systems for Pulverized Coal . . . . . . . . . . . . . . . 14-1 to 14-2115 Cyclone Furnaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-1 to 15-1316 Stokers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-1 to 16-1117 Fluidized-Bed Combustion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-1 to 17-1518 Coal Gasification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-1 to 18-1719 Boilers, Superheaters and Reheaters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-1 to 19-2120 Economizers and Air Heaters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-1 to 20-1721 Fuel Ash Effects on Boiler Design and Operation . . . . . . . . . . . . . . . . . . . . 21-1 to 21-2722 Performance Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-1 to 22-2123 Boiler Enclosures, Casing and Insulation . . . . . . . . . . . . . . . . . . . . . . . . . . 23-1 to 23-924 Boiler Cleaning and Ash Handling Systems . . . . . . . . . . . . . . . . . . . . . . . . 24-1 to 24-2125 Boiler Auxiliaries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-1 to 25-23

Section Ill – Applications of SteamChapter 26 Fossil Fuel Boilers for Electric Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-1 to 26-17

27 Boilers for Industry and Small Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-1 to 27-2128 Chemical and Heat Recovery in the Paper Industry . . . . . . . . . . . . . . . . . 28-1 to 28-2929 Waste-to-Energy Installations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-1 to 29-2330 Wood and Biomass Installations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-1 to 30-1131 Marine Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-1 to 31-13

Table of Contents


Steam 41 vii

Section IV – Environmental ProtectionChapter 32 Environmental Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-1 to 32-17

33 Particulate Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-1 to 33-1334 Nitrogen Oxides Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-1 to 34-1535 Sulfur Dioxide Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-1 to 35-1936 Environmental Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36-1 to 36-15

Section V – Specification, Manufacturing and ConstructionChapter 37 Equipment Specification, Economics and Evaluation . . . . . . . . . . . . . . . . . 37-1 to 37-17

38 Manufacturing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-1 to 38-1339 Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-1 to 39-19

Section VI – OperationsChapter 40 Pressure, Temperature, Quality and Flow Measurement . . . . . . . . . . . . . . 40-1 to 40-25

41 Controls for Fossil Fuel-Fired Steam Generating Plants . . . . . . . . . . . . . . 41-1 to 41-2142 Water and Steam Chemistry, Deposits and Corrosion . . . . . . . . . . . . . . . . . 42-1 to 42-2943 Boiler Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43-1 to 43-17

Section VII – Service and MaintenanceChapter 44 Maintaining Availability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44-1 to 44-21

45 Condition Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45-1 to 45-21

Section VIII – Steam Generation from Nuclear EnergyChapter 46 Steam Generation from Nuclear Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . 46-1 to 46-25

47 Fundamentals of Nuclear Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47-1 to 47-1548 Nuclear Steam Generators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48-1 to 48-1549 Nuclear Services and Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49-1 to 49-2150 Nuclear Equipment Manufacture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50-1 to 50-13

AppendicesAppendix 1 Conversion Factors, SI Steam Properties and Useful Tables . . . . . . . . . . . T-1 to T-16

2 Codes and Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-1 to C-6Symbols, Acronyms and Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S-1 to S-10B&W Trademarks in Edition: 41 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . TM-1Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-1 to I-22


Steam 41

When we completed the 40th edition of Steam in 1992, we had a sense thatperhaps our industry was stabilizing. But activity has again accelerated. To-day, efficiencies are being driven even higher. Emissions are being driven evenlower. Many current technologies are being stretched, and new technologiesare being developed, tested and installed. We have once again changed muchof Steam to reflect our industry’s activity and anticipated developments.

Recognizing the rich history of this publication, we previously drew wordsfrom an 1883 edition’s preface to say that “we have revised the whole, andadded much new and valuable matter.” For this new 41st edition we can drawfrom the 1885 edition to say “Having again revised Steam, and enlarged it bythe addition of new and useful information, not published heretofore, we shallfeel repaid for the labor if it shall prove of value to our customers.”

We hope this new edition is of equal value to our partners and suppliers,government personnel, students and educators, and all present and future em-ployees of The Babcock & Wilcox Company.

Editors’ Foreword

xi


Steam 41 / Introduction to Steam Intro-1

Introduction to Steam

Throughout history, mankind has reached beyondthe acceptable to pursue a challenge, achieving sig-nificant accomplishments and developing new tech-nology. This process is both scientific and creative. En-tire civilizations, organizations, and most notably, in-dividuals have succeeded by simply doing what hasnever been done before. A prime example is the safeand efficient use of steam.

One of the most significant series of events shap-ing today’s world is the industrial revolution that be-gan in the late seventeenth century. The desire to gen-erate steam on demand sparked this revolution, andtechnical advances in steam generation allowed it tocontinue. Without these developments, the industrialrevolution as we know it would not have taken place.

It is therefore appropriate to say that few technolo-gies developed through human ingenuity have doneso much to advance mankind as the safe and depend-able generation of steam.

Steam as a resourceIn 200 B.C., a Greek named Hero designed a simple

machine that used steam as a power source (Fig. 1).He began with a cauldron of water, placed above anopen fire. As the fire heated the cauldron, the caul-dron shell transferred the heat to the water. When thewater reached the boiling point of 212F (100C), itchanged form and turned into steam. The steampassed through two pipes into a hollow sphere, whichwas pivoted at both sides. As the steam escapedthrough two tubes attached to the sphere, each bentat an angle, the sphere moved, rotating on its axis.

Hero, a mathematician and scientist, labeled thedevice aeolipile, meaning rotary steam engine. Al-though the invention was only a novelty, and Heromade no suggestion for its use, the idea of generatingsteam to do useful work was born. Even today, the basicidea has remained the same – generate heat, trans-fer the heat to water, and produce steam.

Intimately related to steam generation is the steamturbine, a device that changes the energy of steaminto mechanical work. In the early 1600s, an Italiannamed Giovanni Branca produced a unique invention(Fig. 2). He first produced steam, based on Hero’saeolipile. By channeling the steam to a wheel thatrotated, the steam pressure caused the wheel to turn.Thus began the development of the steam turbine.

The primary use of steam turbines today is for elec-tric power production. In one of the most complex sys-tems ever designed by mankind, superheated high-pressure steam is produced in a boiler and channeledto turbine-generators to produce electricity.

Fig. 1 Hero’s aeolipile.


Intro-8 Steam 41 / Introduction to Steam

Fig. 15 Thomas Edison’s endorsement, 1888.


Steam 41 / Selected Color Plates Plate 1

Low NOXBurners

OverfireAir Ports

Primary AirFan

TrisectorAir Heater

Axial ForcedDraft Fan

VerticalSteam Separators

Primary Superheater

Primary Reheater

IntermediateSuperheater

Furnace

SCR

Economizer

PlatenSuperheater

FinalSuperheater

FinalReheater

CirculationPump

B&W Roll Wheel Pulverizers

B&W supercritical boiler with spiral wound Universal Pressure (SWUP™) furnace.


Steam 41 / Numerical Modeling for Fluid Flow, Heat Transfer, and Combustion 6-1

Chapter 6Numerical Modeling for Fluid Flow,

Heat Transfer, and Combustion

Numerical modeling – an overviewContinuous and steady advances in computer tech-

nology have changed the way engineering design andanalyses are performed. These advances allow engi-neers to deal with larger-scale problems and more com-plex systems, or to look in more detail at a specificprocess. Indeed, through the use of advanced com-puter technology to perform engineering analysis, nu-merical modeling has emerged as an important fieldin engineering. While this chapter focuses on fluidflow and heat transfer, Chapter 8 provides a brief dis-cussion of numerical modeling for structural analysis.

In general, the term numerical method describessolving a mathematical description of a physical pro-cess using a numerical rather than an analytical ap-proach. This may be done for a number of reasons,including the following:

1. An analytical means of solving the equations thatdescribe the system may not exist.

2. Even though an analytical method is available, itmay be necessary to repeat the calculation manytimes, and a numerical method can be used to ac-celerate the overall process.

A small-scale replica of an apparatus is considereda physical model because it describes the full-size ap-paratus on a smaller scale. This model can incorpo-rate varying levels of detail depending on need andcircumstances. A mathematical description of a physi-cal system (referred to as a mathematical model) canalso incorporate varying levels of detail. Similar to aphysical model, the amount of detail is often deter-mined by the accuracy required and the resourcesavailable to use the model. This creates a need tostrike a balance between accuracy, complexity andefficiency.

There are two basic approaches to mathematicalmodeling.

1. Model the behavior of a system. Network flow mod-els and heat exchanger heat transfer correlationsare examples of a system model.

2. Model the fundamental physics of a system to de-termine the behavior. Computational fluid dynam-ics (CFD) and chemical reaction models fall intothis category.

The term numerical modeling usually refers to theuse of numerical methods on high-powered computersto solve a complex system of mathematical models basedon the fundamental physics of the system. In this re-spect, it describes the second approach identified above.

As an example, consider analysis of hot air movingthrough a length of duct composed of several differ-ent components all in a cold environment.

The first type of analysis would involve a networkmodel. This model would describe the pressure dropand heat loss along the duct based on the length,shape, number of turns, etc. This model is based onextensive flow measurements taken on the individualcomponents (i.e., straight sections, turns, reductions,etc.) that make up the duct. A set of empirical and fun-damental correlations is used to analyze the flow ratethrough the duct. The computation can be set up quicklyand with minimal effort. Results and multiple variationscan be rapidly obtained. While results are reasonablyaccurate, they are limited to the components for whicha flow correlation already exists. A unique componentdesign that has not been described by a correlation maynot be accurately evaluated with this type of model.

The second type of analysis would involve a CFDmodel of the same duct. The detailed behavior of theflow through the entire duct is modeled. From thisinformation, pressure drop and heat loss along thelength of the duct may be determined. However, un-like the first analysis, this type of model provides ad-ditional details. For example, the first model does notconsider how the flow through a bend differs if it isfollowed by another bend or a straight section; the firstmodel may result in the same pressure drop regard-less of how the components are arranged. The secondanalysis would account for these differences. In addi-tion, variation in heat loss from one side of the duct tothe other can be determined. Most importantly, thismodel is not restricted to duct components where ex-tensive experimental data is available. New conceptscan easily be evaluated.

These two approaches have both benefits and limi-tations. The appropriate use of each is determined bythe information needed and the information available.While both approaches are important engineering tools,the remaining discussion here will focus on the second,specifically on CFD and combustion modeling, and howthey relate to furnaces, boilers and accessory equipment.


6-12 Steam 41 / Numerical Modeling for Fluid Flow, Heat Transfer, and Combustion

through the unit. Fig. 5a shows the case without thetray. The lowest profile shows how non-uniform flowdevelops as the high velocity flue gas is introduced intothe tower, is decelerated, and makes a sharp right-angle turn to flow up the tower. In the absence of atray, the high velocity (red) and low velocity (blue)regions persist as the flue gas moves through themiddle of the tower (middle velocity profile) enteringthe first level of spray headers. Some of the non-uni-formity persists even up to the mist eliminators. Withthe addition of the tray (Fig. 5b), the large high andlow velocity regions are effectively eliminated. The re-sulting more-uniform velocity profile and the gas/re-agent mixing on top of the tray permit higher levelsof SO2 control at reduced slurry recirculation rates.

This model has also been used to explore designchanges to meet site-specific new and retrofit require-ments.25 These have included alternate flue gas exitgeometries, flue gas inlet conditions, tower diametertransitions, header locations, slurry recirculation ratesor other factors while still achieving the desired per-formance. It has also been used to investigate inter-nal design alternatives to boost performance and re-duce pressure drop.

Popcorn ashSituation Popcorn, or large particle, ash forms un-

der certain conditions from the combustion of coal and

is light, porous, irregularly shaped, and often formsin the upper boiler furnace or on the convective heattransfer surface. This ash can plug the top catalystlayer in selective catalyst reduction (SCR) NOx con-trol systems, increasing pressure drop and decreasingcatalyst performance. Modifications to both the econo-mizer outlet hoppers and the ash removal systems canincrease ash capture to address this situation.

Accurately predicting how the popcorn ash behaveswithin the economizer gas outlet requires detailedknowledge of the aerodynamic properties of the ashparticles and sophisticated modeling techniques. Keyash properties include the particle density, drag coef-ficient, coefficients of restitution, and its coefficient offriction with a steel plate. CFD models involve solv-ing the gas flow solution, then calculating the particletrajectories using B&W’s proprietary CFD software.

Analysis Most CFD programs that handle particle-to-wall interactions are not adequate to accuratelypredict the complex behavior seen in the popcorn ashphysical experiments. These deficiencies have beenremedied by adding capabilities to B&W’s proprietaryCFD software. First, the coefficient of restitution isseparated into its normal and tangential components.Next, a particle-to-wall friction model is used for par-ticles sliding along the wall and experiencing a fric-tion force proportional to the coefficient of frictionmeasured in the physical tests. Also, the ability to set

Fig. 5 Effect of B&W’s tray design on gas velocities through a wet flue gas desulfurization system – numerical model results on a 650 MW absorber.


6-24 Steam 41 / Numerical Modeling for Fluid Flow, Heat Transfer, and Combustion

Fig. 23 Detailed numerical model evaluation grid for an advanced coal burner.

Fig. 24 Gas velocity model for the coal burner shown in Fig. 23.


Steam 41 / Fossil Fuel Boilers for Electric Power 26-1

Chapter 26Fossil Fuel Boilers for Electric Power

Most of the electric power generated in the UnitedStates (U.S.) is produced in steam plants using fossilfuels and high speed turbines. These plants deliver akilowatt hour of electricity for each 8500 to 9500 Btu(8968 to 10,023 kJ) supplied from the fuel, for a netthermal efficiency of 36 to 40%. They use steam driventurbine-generators of up to 1300 MW capacity withboilers generating from one million to ten millionpounds of steam per hour. A typical coal-fired facilityis shown on the facing page.

Modern fossil fuel steam plants use reheat cycleswith nominal steam conditions of 3500 psi/1050F/1050F (24.1 MPa/566C/566C) for supercritical pres-sure systems, and 2400 psi (16.5 MPa) with superheatand reheat steam temperatures ranging from 1000 to1050F (538 to 566C) for subcritical pressure systems.For some very small units, lower steam conditions maybe applied. In selected global locations where highercycle efficiencies are required, supercritical pressuresteam conditions on the order of 4300 psi/1075F/1110F(29.6 MPa/579C/599C) and 3626 psi/1112F/1130F(25.0 MPa/600C/610C) have been used.

Most power plants in the U.S. and around the worldare owned and operated by: 1) investor owned elec-tric companies, 2) federal, state or local governments,or 3) finance companies.

These owners, whether public or private, have beengenerally known as utilities. During the 1980s and1990s, there was a trend toward new types of compa-nies supplying significant portions of new generation.However, the fundamental approach to selectingpower generation equipment will remain unchanged.

Selection of steam generating equipmentThe owner has several technologies to choose from

based upon fuel availability, emissions requirements,reliability, and project timing. One of the commonchoices for modern electric power generation is thehigh pressure, high temperature steam cycle with afossil fuel-fired boiler.

Each new electric generating unit must satisfy theuser’s specific needs in the most economical manner.

Achieving this requires close cooperation between theequipment designers and the owner’s engineeringstaff or consultants. The designers, owner and engi-neering group must identify those equipment featuresand characteristics that will reliably produce low costelectricity. The primary costs of electricity include: 1)capital equipment, 2) financing charges, 3) fuel, and4) operation and maintenance. The owner, prior toissuing equipment specifications, reviews and surveysall cost factors. (See Chapter 37.)

The capital cost survey must include all direct costssuch as the boiler, steam turbine and electric genera-tor, emissions control equipment, condenser, feedwaterheaters and pumps, fuel handling facilities, buildings,and real estate. In addition, finance charges, includ-ing interest rates, loan periods, source of funds andtax considerations must be added. Fuel and emissioncontrol reagent costs need to be evaluated based onthe initial costs, plant capacity variations expected dur-ing the life of the plant, and forecasts of cost changesduring plant lifetime. The operation and maintenancecosts should be estimated based on other currentplants with similar equipment, fuels and operatingcharacteristics. Operating and maintenance costs areheavily affected by personnel requirements, and con-sideration should be given to the availability of skilledlabor as well as to the cost of retaining the skilled staffduring the plant lifetime.

Plant efficiency, fuel use and capital cost are criti-cally related. Higher plant thermal efficiency obvi-ously reduces annual fuel costs; however, fuel savingsare partially offset by the associated higher capitalcosts. Therefore, selection of the desired plant effi-ciency should carefully consider the economic tradeoffsbetween capital and operating costs.

Other important criteria are the location of the elec-tric generating plant with respect to fuel supply andthe areas where electricity is used. In some cases, it ismore economical to transport electricity than fuel.Some large steam generating stations have been builtat the coal mine mouth to generate electricity whichis then used several hundred miles away. If the useris a member of a broader grid of interconnected util-


Steam 41 / Boilers for Industry and Small Power 27-1

Chapter 27Boilers for Industry and Small Power

Most manufacturing industries require steam fora variety of uses. Basic plant heating and air condi-tioning, prime movers such as turbine drives for blow-ers and compressors, drying, constant temperature re-action processes, large presses, soaking pits, waterheating, cooking and cleaning are all examples of howsteam is used.

Steam produced by industrial boilers can also beused to generate electricity in a cogeneration modewhich uses a conventional steam turbine for electricpower generation and low pressure extraction steamfor the process. The electricity is then used by the plantor sold to a local electric utility company. As an alter-nate cogenerating system, a gas turbine can be usedfor power generation with a heat recovery steam gen-erator for steam.

Thousands of boilers are installed in industrial andmunicipal plants, providing lower pressure and tem-perature steam than utility boilers dedicated to large,central station electric power generation. In an indus-trial plant, the dependability of steam generatingequipment is critical. Most often, the industrial opera-tion has a single steam plant with one or more boil-ers. If the steam flow is interrupted, production canbe seriously impacted. Accordingly, industrial boilersmust be very reliable because plant productivity reliesso heavily on their availability. Loss of a boiler for a shorttime can stop production for days if, for example, mate-rials cool and solidify in process lines. For this reason,some industries prefer multiple smaller units.

The principles governing the selection of boilers andrelated equipment are discussed in Chapter 37.Proper equipment selection can be accomplished onlyin the framework of a sound technical and cost evalu-ation. This requires a working knowledge and under-standing of the performance of the different steamgenerating unit components under various conditions,including the significance of the many different ar-rangements of heat absorbing surfaces, the charac-teristics of available fuels, combustion methods andash handling. The owner must also establish thepresent and future steam conditions and require-ments. All pertinent environmental regulations mustalso be considered. A brief summary of boiler specifi-cations is provided in Table 1.

Industrial boiler designIndustrial boilers generally have different perfor-

mance characteristics than utility boilers. These aremost apparent in steam pressures and temperaturesas well as the fuel burning equipment.

Industrial units are built in a wide range of sizes,pressures and temperatures – from 2 psig (13.8 kPa)and 218F (103C) saturated steam for heating to 1800psig (12.4 MPa) and 1000F (538C) steam for plantpower production.

In addition, industrial units often supply steam formore than one application. For some applications, steamdemand may be cyclic or fluctuating, thereby complicat-ing unit operation and control of the equipment.

The Babcock & Wilcox Company (B&W) industrialboilers, such as the unit shown in Fig. 1, are watertube design and generally rely upon natural circula-tion for steam-water circulation.

Most utility boilers are designed to burn pulverizedor crushed coal, oil, gas, or a combination of oil or gaswith a solid fuel. Industrial boilers can be designed forthe above fuels as well as coarsely crushed coal for stokerfiring and a wide range of biomass or byproduct fuels.

Table 1Typical Industrial Boiler Specification Factors

1. Steam pressure 2. Steam temperature and control range 3. Steam flow Peak Minimum Load patterns 4. Feedwater temperature and quality 5. Standby capacity and number of units 6. Fuels and their properties 7. Ash properties 8. Firing method preferences 9. Environmental emission limitations sulfur dioxide (SO2), nitrogen oxides (NOx), particulate, other compounds 10. Site space and access limitations 11. Auxiliaries 12. Operator requirements 13. Evaluation basis


Steam 41 / Chemical and Heat Recovery in the Paper Industry 28-1

Chapter 28Chemical and Heat Recovery

in the Paper Industry

In the United States (U.S.), the forest products in-dustry is the third largest industrial consumer of en-ergy, accounting for more than 11% of the total U.S.manufacturing energy expenditures. In 2002, 57% ofthe pulp and paper industry relied on cogenerationfor their electric power requirements.

Approximately one-half of the steam and power con-sumed by this industry is generated from fuels thatare byproducts of the pulping process. The mainsource of self-generated fuel is the spent pulping li-quor, followed by wood and bark. The energy requiredto produce pulp and paper products has been signifi-cantly reduced. Process improvements have allowed U.S.pulp and paper manufacturers to reduce energy con-sumption to 2.66 × 1012 Btu (2806.5 × 1012 J), a signifi-cant reduction.

Pulp and paper mill electric power requirementshave increased disproportionately to process steamrequirements. This factor, coupled with steadily ris-ing fuel costs, has led to the greater cycle efficienciesafforded by higher steam pressures and temperaturesin paper mill boilers. The increased value of steam hasproduced a demand for more reliable and efficient heatand chemical recovery boilers.

The heat value of the spent pulping liquor solids isa reliable fuel source for producing steam for powergeneration and process use. A large portion of thesteam required for the pulp mills is produced in highlyspecialized heat and chemical recovery boilers. Thebalance of the steam demand is supplied by boilersdesigned to burn coal, oil, natural gas and biomass.

Major pulping processesThe U.S. and Canada have the highest combined

consumption of paper and paperboard in the world(Fig. 1), consuming 105.6 million tons each year. Witha base of more than 800 pulp, paper and paperboardmills, the U.S. and Canada are also the leader in theproduction of paper and paperboard. North Americaaccounts for 32% of the total world output; pulp pro-duction is nearly 43%.

Total pulp production in the U.S. is divided amongthe following principal processes: 85% chemical,groundwood and thermomechanical; 6% semi-chemi-cal; and 9% mechanical pulping. The dominant NorthAmerica pulping process is the sulfate process, deriv-

ing its name from the use of sodium sulfate (Na2SO4)as the makeup chemical. The paper produced from thisprocess was originally so strong in comparison withalternative processes that it was given the name kraft,which is the Swedish and German translation forstrong. Kraft is an alkaline pulping process, as is thesoda process which derives its name from the use ofsodium carbonate, Na2CO3 (soda ash), as the makeupchemical. The soda process has limited use in the U.S.and is more prominent in countries pulping nonwoodfiber. Recovery of chemicals and the production ofsteam from waste liquor are well established in thekraft and soda processes. The soda process accountsfor less than 1% of alkaline pulp production and itsimportance is now largely historic.

Kraft pulping and recovery process

Kraft processThe kraft process flow diagram (Fig. 2) shows the

typical relationship of the recovery boiler to the over-all pulp and paper mill.1 The kraft process starts withfeeding wood chips, or alternatively a nonwood fi-brous material, to the digester. Chips are cooked un-der pressure in a steam heated aqueous solution of

Fig. 1 World paper and board consumption by country, 2000.

USA31%

All OtherCountries

30%

Germany6%

Canada2%

Italy3%

France3%

United Kingdom 4%Japan10%

Peoples Republicof China

11%

Steam 41 / Environmental Considerations 32-1


Chapter 32Environmental Considerations

Since the early 1960s, there has been an increas-ing worldwide awareness that industrial growth andenergy production from fossil fuels are accompaniedby the release of potentially harmful pollutants intothe environment. Studies to characterize emissions,sources and effects of various pollutants on humanhealth and the environment have led to increasinglystringent legislation to control air emissions, waterwaydischarges and solids disposal.

Comparable concern for environmental quality hasbeen manifest worldwide. Since the 1970s, countriesof the Organization for Economic Cooperation andDevelopment have reduced sulfur dioxide (SO2) andnitrogen oxides (NOx) emissions from power plants inrelation to energy consumption. In at least the fore-seeable future, emission trends are expected to con-tinue downward due to a combination of factors: changein fuel mix to less polluting fuels, use of advanced tech-nologies, and new and more strict regulations. In Japan,the reductions in SO2 emissions were particularly pro-nounced due to strong environmental measures takenin the 1970s. As an example, in the United States (U.S.)between 1980 and 2001, electricity generation increasedby 56%, while SO2 emissions declined 38%.

Environmental control is primarily driven by gov-ernment legislation and the resulting regulations atthe local, national and international levels. These haveevolved out of a public consensus that the real costsof environmental protection are worth the tangibleand intangible benefits now and in the future. Toaddress this growing awareness, the design philoso-phy of energy conversion systems such as steam gen-erators has evolved from providing the lowest costenergy to providing low cost energy with an accept-able impact on the environment. Air pollution controlwith emphasis on particulate, NOx, SO2, and mercuryemissions is perhaps the most significant environmen-tal concern for fired systems and is the subject of Chap-ters 33 through 36. However, minimizing aqueous dis-charges and safely disposing of solid byproducts arealso key issues for modern power systems.

Sources of plant emissionsand discharges

Fig. 1 identifies most of the significant wastestreams from a modern coal-fired power plant. Typi-cal discharge rates for the primary emissions from anew, modern 615 MW coal-fired supercritical pressureboiler are summarized in Table 1.

Atmospheric emissions arise primarily from the

byproducts of the combustion process (SO2, NOx, par-ticulate flyash, and some trace quantities of othermaterials) and are exhausted from the stack. A sec-ond source of particulate is fugitive dust from coal pilesand related fuel handling equipment. This is especiallysignificant for highly dusting western U.S. subbitu-minous coals. Some low temperature devolatilizationof the coal can also emit other organic compounds. Afinal source of air emissions is the cooling tower andthe associated thermal rise plume which containswater vapor.

Solid wastes arise primarily from collection of thecoal ash from the bottom of the boiler, economizer andair heater hoppers, as well as from the electrostatic pre-cipitators and fabric filters. Pyrite collected in the pul-verizers (see Chapter 13) is usually also included. Mostof the ash is either transported wet to an ash settlingpond where it settles out or is transported dry to silosfrom which it is taken by truck for beneficial use (e.g.,cement additive). The chemical composition and char-acteristics of various ashes are discussed in Chapter 21.

The second major source of solids is the byproduct fromthe flue gas desulfurization (FGD) scrubbing process.Most frequently, this is a mixture containing primarilycalcium sulfate for wet systems and calcium sulfite fordry systems. After dewatering, the wet system byproductmay be sold as gypsum or landfilled. Additional sourcesof solids include the sludge from cooling tower basins,wastes from the water treatment system and wastes fromperiodic boiler chemical cleaning.

Aqueous discharges arise from a number of sources.These include once-through cooling water (if used),cooling tower blowdown (if used), sluice water from theash handling system (via the settling pond), FGD wastewater (frequently minimal), coal pile runoff from rain-fall, boiler chemical cleaning solutions, gas-side waterwashing waste solutions, as well as a variety of low vol-ume wastes including ion exchange regeneration ef-fluent, evaporator blowdown (if used), boiler blowdownand power plant floor drains. Many of these streamsare chemically characterized in Chapter 42. Additionaldiscussions of these systems as well as the controllingregulations are provided in References 1 and 2.

Air pollution control

U.S. legislation – Clean Air ActThe Federal Clean Air Act (CAA) is the core driv-

ing force for all air pollution control legislation in theUnited States (U.S.). The original CAA was first en-

32-2 Steam 41 / Environmental Considerations


acted in 1963, and since that time the Act has evolvedthrough five significant amendment cycles in 1965,1967, 1970, 1977, and 1990.

The primary objective of the CAA is to protect andenhance the quality of the nation’s air resources topromote the public health and welfare and the pro-ductive capacity of its population.3 The legislation gen-erally provides for the U.S. Environmental ProtectionAgency (EPA) to set national air quality standards andother minimum regulatory requirements through fed-eral regulations and guidance to state and local regu-latory agencies. The individual states are required todevelop state implementation plans (SIPs) to define howthey will meet the minimum federal requirements. How-ever, state and local government agencies may also de-velop and implement more stringent air pollution con-trol requirements. The CAA as amended prior to 1990included the following regulatory elements of potentialinterest to boiler owners and operators.

National Ambient Air Quality Standards (NAAQS) Fed-eral standards were developed to define acceptable airquality levels necessary to protect public health andwelfare. The EPA promulgated National Ambient AirQuality Standards for six Criteria Pollutants: sulfurdioxide (SO2), nitrogen dioxide (NO2), carbon monox-ide (CO), ozone (O3), particulate matter and lead. Twolevels of standards have been established: primarystandards aimed at prevention of adverse impacts onhuman health and secondary standards to preventdamage to property and the environment. All geo-graphic areas of the country are divided into a num-ber of identifiable areas known as air quality controlregions which are classified according to their air qual-ity. Air quality control regions that meet or better theNAAQS for a designated pollutant are classified as

attainment areas for that pollutant, and regions that failto meet the NAAQS are classified as nonattainment ar-eas for that pollutant.

New Source Performance Standards (NSPS) FederalNew Source Performance Standards were establishedfor more than 70 categories of industrial processes and/or stationary sources. The NSPS rules set source-spe-cific emission limitations and corresponding monitor-ing, recordkeeping and reporting requirements thatmust be met by new sources constructed on or afterthe effective date of an applicable standard. Sourcesconstructed prior to the promulgation of an applicableNSPS are generally grandfathered and are not sub-ject to the standards until such time that the sourceundergoes major modification or reconstruction. TheEPA’s NSPS regulations are published under Title 40,Part 60 of the Code of Federal Regulations.4 Table 2provides reference to select Subparts of 40 CFR 60applicable to a variety of industrial and utility boil-ers. The various NSPS rules governing fossil fuel-firedboilers include emission limitations for NOx, SO2, par-ticulate and opacity. The NSPS emission limits arebased on the EPA’s evaluation of best demonstratedtechnology, and these limits are subject to periodicreview and revision. Finally, the NSPS rules gener-ally establish the least stringent emission limitation anew source would have to meet. Typically, more strin-gent emission limitations are necessary to meet otherfederal, state or local permitting requirements. Forexample, any significant new source or major modifi-cation to an existing source of emissions may be subjectto the federal New Source Review rules discussed below.

New Source Review (NSR) New Source Review regu-lations were established to: 1) preserve existing airquality in areas of the U.S. that are in compliance with

Fig. 1 Typical bituminous coal-fired power plant effluents and emissions.

Heat-Thermal Rise

Plume

Fugitive Dust

Coal PileWater Runoff

SCR

AirHeaterHopper

Ash

BottomAsh

Noise SaleableAsh

Coal Pile

Turbine

CondenserCoolingTower

CoolingTower

Blowdown

Sludge / Landfill BlowdownWater

Chemical CleaningWaste Liquid

Gas Side WashingWaste Water

FGD ByproductGypsum or

Landfill Sludge

FGD WasteTreatment

andDewatering

FGDWasteWater

FGD

WESP

Stack

Fabric Filteror

Precipitator

Boiler

Note: SCR-Selective Catalytic Reduction System

FGD-Flue Gas Desulfurization System

WESP-Wet Electrostatic Precipitator

Flue Gas

SO2NOX

ParticulateVOCCOCO2

Other

Steam 41 / Maintaining Availability 44-1


Chapter 44Maintaining Availability

The design of boiler systems involves the balanc-ing of near-term and long-term capital costs to maxi-mize the availability and useful life of the equipment.Fossil fuel-fired boilers operate in a very aggressiveenvironment where: 1) materials and technology arepushed to their economic limits to optimize efficiencyand availability, and 2) the erosive and corrosive na-ture of the fuels and combustion products result incontinuous and expected degradation of the boiler andfuel handling components over time. As a result, theoriginal boiler design is optimized to balance the ini-tial customer capital requirement and the long-termexpected maintenance, component replacement, andservice costs for a possible operating life of many decades.

When a new power plant is started up, there is arelatively short learning period when the operatorsand maintenance crews learn to work with the newsystem and resolve minor issues. This period may bemarked by a high forced outage rate, but this quicklydeclines as the system is broken in and operating pro-cedures are refined.

As the plant matures, the personnel adapt to thenew system, and any limitations in the plant designare either overcome or better understood. During thisphase, the forced outage rate remains low, availabil-ity is high, and the operating and maintenance costsare minimal. The power plant is usually operated nearrated capacity with high availability.

As the plant continues to operate, a number of themajor boiler pressure part components reach the pointwhere they are expected to be replaced because of ero-sion, corrosion, creep, and fatigue. Without thisplanned replacement, increasingly frequent compo-nent failures occur resulting in reduced availability.In some instances such as waste-to-energy systems,this period can be as short as one to three years forsuperheaters because of the very corrosive flue gas com-position. However, for most fossil fuel-fired utility boil-ers operating on their design fuels, major pressure partcomponents are economically designed for more than twodecades of operation before economic replacement. Fail-ures of major components such as steam lines, steam

headers and drums can cause major, prolonged forcedoutages. Significant capital expenditures are normallyrequired to replace such components.

A strategic availability improvement program thatincludes capital expenditures to replace or repair thisequipment before major forced outages occur cansmooth out and raise the availability curve. Higheravailabilities usually require higher maintenance,higher capital expenditures, and better strategic plan-ning. The large expenditures needed for high avail-ability in older plants require a strategic plan to yieldthe best balance of expenditures and availability.

Strategic plan for high availabilityMature boilers represent important resources in

meeting energy production needs. A systematic stra-tegic approach is required to assure that these unitsremain a viable and productive resource. The moreefficient, but older boilers in the system can be thebackbone of the commercially available power for autility.

Emphasis on high availabilityToday, the need for high commercial availability is

of prime importance to the financial livelihood of apower supplier. This means that the low- cost unitsin a system must be available for full capacity powerproduction during critical peak periods, such as hotsummer days. Competition in the electrical supply in-dustry requires that low-cost units be available so thatthe system can supply power to the grid at low over-all costs. Usually, the large fossil powered units arethe lowest cost units in the system. Lost revenue as-sociated with having a large, low-cost unit out of ser-vice for repairs can be in excess of one million U.S.dollars per day. Owners are attempting to maintainavailability levels of 90% or more on these large work-horses in the system.

The emphasis on maintaining or even improvingavailability means that a strategic plan must be putin place. Times between planned outages have been


Steam 41 / Steam Generation from Nuclear Energy 46-1

Chapter 46Steam Generation from

Nuclear Energy

Since the early 1950s, nuclear fission technologyhas been explored on a large scale for electric powergeneration and has evolved into the modern nuclearpower plants. (See frontispiece and Fig. 1.) Many ad-vantages of nuclear energy are not well understoodby the general public, but this safe, environmentallybenign source of electricity is still likely to play a ma-jor role in the future world energy picture. Nuclearelectric power generation is ideally suited to providelarge amounts of power while minimizing the overallenvironmental impact.

First generation power plantsThe concept of an energy generating plant using

nuclear fission was first considered by nuclear physi-cists in the 1930s. However, peaceful use of the atomwas delayed until after World War II. The UnitedStates (U.S.) had a head start on nuclear technologybecause of its work in the atomic weapons program.The U.S. Atomic Energy Commission (AEC) took thelead in research and development for a controlledchain reaction application to energy generation. Manyconcepts were hypothesized and several promisingpaths were explored, but the real momentum devel-oped when U.S. Navy Captain Hyman G. Rickoverestablished a division in the AEC to develop a nuclearpower plant for a submarine. This program, establishedin 1949, was to become the forerunner of commercialgenerating stations in the U.S. and the world.Rickover’s design succeeded in 1953. Technology andmaterials developed by his team became the corner-stone of future U.S. nuclear plants. Concurrently, theAEC established a large testing site in Arco, Idahowhere, in 1951, the fast neutron reactor produced thefirst electricity (100 kW) generated by controlled fission.

The world’s first civil nuclear power station becameoperational in Obninsk in the former Soviet Union(FSU) in mid-1954, with a generating capability of 5MW. This was about the same energy level producedin the U.S. submarine design.

In 1953, the Navy canceled Captain Rickover’splans to develop a larger nuclear power plant to beused in an aircraft carrier. However, he subsequentlytransformed this project into a design for the first U.S.civilian power stations. Duquesne Light Company ofPittsburgh, Pennsylvania agreed to build and oper-ate the conventional portion of the plant and to buysteam from the nuclear facility to offset its cost of op-eration. On December 2, 1957, the Shippingport,Pennsylvania reactor plant was placed in service witha power output of 60 MW. This event marked the be-ginning of the first generation U.S. commercialnuclear plants.

Several basic concepts were being explored, devel-oped and demonstrated throughout the world duringthis period. The U.S. submarine and Shippingportplants were pressurized water reactors (PWR) thatused subcooled water as the fuel coolant and modera-tor. The FSU developed enriched uranium, graphite-

Fig. 1 Indian Point Station, New York.

Steam 41 / Index I-1


Abrasiveness index, 9-9Absorber (FGD), 35-2Absorption, 35-5Absorptivity

definition, 4-3of gases, 4-12, 4-31

Access doors, 20-6, 23-9Acid mist, 35-18Acid rain, 32-4, 34-2, 35-1Acidity, 36-1Acoustics

electromagnetic, 45-4emissions, 45-5leak detection, 45-16

Adiabatic, 3-4Adiabatic flame temperature, 2-26,

10-11Adipic acid, 35-12Aging (degradation) mechanisms

corrosion, 44-6erosion, 44-6fatigue, 44-6stress, 44-6

Aircombustion, 10-5, 10-16composition, 10-4control, 41-10distributor, fluidized-bed, 17-1, 17-3enthalpy, 10-19flow measurement, 40-20, 41-13infiltration, leakage, 10-16, 10-23,

23-7moisture, 10-5, 10-6properties of, 4-11theoretical, 10-5, 10-7, 10-9, 10-16

Air, quaternary, 28-4Air flow-steam flow control, 41-13Air heater, Chapter 20

applications, 20-15calculations, 22-15cast iron, 20-8cold end minimum metal

temperatures, 20-13

condition assessment of, 45-5, 45-11corrosion, 20-13environmental, 20-15erosion, 20-3, 20-14fires, 20-14industrial, 20-15leakage, 20-12Ljungström, 20-9marine, 31-12operation, 20-13performance, 20-12plate, 20-8plugging, 20-14recuperative, 20-7regenerative, 20-9Rothemühle, 20-10seal(s), 20-10, 20-11steam

coil, 20-9, 29-12, 29-21marine, 31-10

testing, 20-12tubular, 20-7, 29-21

Air pollution, Chapter 32air toxics, 32-5, 32-8carbon dioxide, 32-8carbon monoxide, 32-2, 32-7greenhouse gas, 32-8international regulations, 32-6mercury, 32-8nitrogen oxides (NOx), 32-1, 32-4,

32-7 (see also NOx control)particulate matter, 32-7

(see also Particulate control)sources, 32-1sulfur oxides (SOx), 32-1, 32-4,

32-7 (see also SO2 control)technologies, 32-8U.S. legislation, 32-1

Air swept spout, 16-7, 29-17Air testing, 39-18Albacore hull, 46-24Alkalinity, 35-1, 36-1Allowable stress, 7-20, 8-3, C-4

Allowances, 32-4Alloying elements, 7-5

interstitial, 7-2substitutional, 7-2

Alphaemitters, 47-4particle, 47-3

Alumina ceramics, 13-11, 44-10Aluminizing, 7-15American Boiler Manufacturers

Association (ABMA), 23-6, C-1American Society for Testing and

Materials (ASTM), 9-5, 9-7American Society of Mechanical

Engineers (ASME), 1-14, 2-1Boiler and Pressure Vessel Code,

8-1, 19-8, 20-6, C-1allowable stresses, 7-20, 8-3, C-4calculations, 8-5design criteria, 8-2, 8-14strength theories, 8-2stress classifications, 8-2,

8-9, 8-10Performance Test Code, 10-10,

10-18, 10-21, 40-1Pressure Piping (B31), C-1, C-6

Ammonia, 34-3, 35-2, 35-18anhydrous, 34-6aqueous, 34-7flow control, 34-8, 41-17injection, 34-6reagent systems, 34-6

Ammonia sulfates, 20-15, 34-6Annealing, 7-8Anticipatory reactor trip system

(ARTS), 46-15API gravity, fuel oil, 9-14, 10-20Approach temperature

flue gas desulfurization, 35-14As-received, coal, 9-5, 9-7Ash, black liquor, 28-8 (see also

Recovery boiler, Kraft process)carryover, 28-9

Index

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Steam - Its Generation and Use

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