02.Introduction to Steam_Steam, Its Generation & Use, 41_Ed

The Babcock & Wilcox Company

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 todays 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 Herosaeolipile. 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 Heros aeolipile.


Intro-2 Steam 41 / Introduction to Steam

Todays steam plants are a complex and highly so-phisticated combination of engineered elements. Heatis obtained either from primary fossil fuels like coal,oil or natural gas, or from nuclear fuel in the form ofuranium. Other sources of heat-producing energy in-clude waste heat and exhaust gases, bagasse and bio-mass, spent chemicals and municipal waste, and geo-thermal and solar energy.

Each fuel contains potential energy, or a heatingvalue measured in Btu/lb (J/kg). The goal is to releasethis energy, most often by a controlled combustionprocess or, with uranium, through fission. The heat isthen transferred to water through tube walls and othercomponents or liquids. The heated water then changesform, turning into steam. The steam is normally heatedfurther to specific temperatures and pressures.

Steam is also a vital resource in industry. It drivespumps and valves, helps produce paper and woodproducts, prepares foods, and heats and cools largebuildings and institutions. Steam also propels muchof the worlds naval fleets and a high percentage ofcommercial marine transport. In some countries, steamplays a continuing role in railway transportation.

Steam generators, commonly referred to as boilers,range in size from those needed to heat a small build-ing to those used individually to produce 1300 mega-watts of electricity in a power generating station enough power for more than one million people. Theselarger units deliver more than ten million pounds ofsuperheated steam per hour (1260 kg/s) with steamtemperatures exceeding 1000F (538C) and pressuresexceeding 3800 psi (26.2 MPa).

Todays steam generating systems owe their de-pendability and safety to the design, fabrication andoperation of safe water tube boilers, first patented byGeorge Babcock and Stephen Wilcox in 1867 (Fig. 3).

Because the production of steam power is a tremen-dous resource, it is our challenge and responsibility tofurther develop and use this resource safely, efficiently,dependably, and in an environmentally-friendly manner.

The early use of steamSteam generation as an industry began almost two

thousand years after Heros invention, in the seven-teenth century. Many conditions began to stimulatethe development of steam use in a power cycle. Min-ing for ores and minerals had expanded greatly andlarge quantities of fuel were needed for ore refining.

Fuels were needed for space heating and cooking andfor general industrial and military growth. Forests werebeing stripped and coal was becoming an importantfuel. Coal mining was emerging as a major industry.

As mines became deeper, they were often floodedwith underground water. The English in particularwere faced with a very serious curtailment of theirindustrial growth if they could not find some economi-cal way to pump water from the mines. Many peoplebegan working on the problem and numerous patentswere issued for machines to pump water from themines using the expansive power of steam. The earlymachines used wood and charcoal for fuel, but coaleventually became the dominant fuel.

The most common source of steam at the time wasa shell boiler, little more than a large kettle filled withwater and heated at the bottom (Fig. 4).

Not all early developments in steam were directedtoward pumps and engines. In 1680, Dr. Denis Papin,a Frenchman, invented a steam digester for food pro-

Fig. 3 First Babcock & Wilcox boiler, patented in 1867.

Fig. 4 Haycock shell boiler, 1720.Fig. 2 Brancas steam turbine.



cessing, using a boiler under heavy pressure. To avoidexplosion, Papin added a device which is the first safetyvalve on record. Papin also invented a boiler with aninternal firebox, the earliest record of such construction.

Many experiments concentrated on using steampressure or atmospheric pressure combined with avacuum. The result was the first commercially suc-cessful steam engine, patented by Thomas Savery in1698, to pump water by direct displacement (Fig. 5).The patent credits Savery with an engine for raisingwater by the impellant force of fire, meaning steam.The mining industry needed the invention, but theengine had a limited pumping height set by the pres-sure the boiler and other vessels could withstand.Before its replacement by Thomas Newcomens engine(described below), John Desaguliers improved theSavery engine, adding the Papin safety valve and us-ing an internal jet for the condensing part of the cycle.

Steam engine developments continued and the ear-liest cylinder-and-piston unit was based on Papinssuggestion, in 1690, that the condensation of steamshould be used to make a vacuum beneath a piston,after the piston had been raised by expanding steam.Newcomens atmospheric pressure engine made prac-tical use of this principle.

While Papin neglected his own ideas of a steam en-gine to develop Saverys invention, ThomasNewcomen and his assistant John Cawley adaptedPapins suggestions in a practical engine. Years of ex-perimentation ended with success in 1711 (Fig. 6).Steam admitted from the boiler to a cylinder raised apiston by expansion and assistance from a counter-weight on the other end of a beam, actuated by thepiston. The steam valve was then closed and the steamin the cylinder was condensed by a spray of cold wa-ter. The vacuum which formed caused the piston tobe forced downward by atmospheric pressure, doingwork on a pump. Condensed water in the cylinder wasexpelled through a valve by the entry of steam whichwas at a pressure slightly above atmospheric. A 25 ft(7.6 m) oak beam, used to transmit power from thecylinder to the water pump, was a dominant feature

of what came to be called the beam engine. The boilerused by Newcomen, a plain copper brewers kettle,was known as the Haycock type. (See Fig. 4.)

The key technical challenge remained the need forhigher pressures, which meant a more reliable andstronger boiler. Basically, evolution of the steam boilerparalleled evolution of the steam engine.

During the late 1700s, the inventor James Wattpursued developments of the steam engine, nowphysically separated from the boiler. Evidence indi-cates that he helped introduce the first waggon boiler,so named because of its shape (Fig. 7). Watt concen-trated on the engine and developed the separate steamcondenser to create the vacuum and also replacedatmospheric pressure with steam pressure, improvingthe engines efficiency. He also established the mea-surement of horsepower, calculating that one horsecould raise 550 lb (249 kg) of weight a distance of 1 ft(0.3 m) in one second, the equivalent of 33,000 lb(14,969 kg) a distance of one foot in one minute.

Fig. 6 Newcomens beam engine, 1711.

Fig. 7 Waggon boiler, 1769.Fig. 5 Saverys engine, circa 1700.



Fire tube boilersThe next outstanding inventor and builder was Ri-

chard Trevithick, who had observed many pumpingstations at his fathers mines. He realized that theproblem with many pumping systems was the boilercapacity. Whereas copper was the only material previ-ously available, hammered wrought iron plates couldnow be used, although the maximum length was 2 ft(0.6 m). Rolled iron plates became available in 1875.

In 1804, Trevithick designed a higher pressure en-gine, made possible by the successful construction of ahigh pressure boiler (Fig. 8). Trevithicks boiler designfeatured a cast iron cylindrical shell and dished end.

As demand grew further, it became necessary to ei-ther build larger boilers with more capacity or put upwith the inconveniences of operating many smallerunits. Engineers knew that the longer the hot gases werein contact with the shell and the greater the exposed sur-face area, the greater the capacity and efficiency.

While a significant advance, Newcomens engineand boiler were so thermally inefficient that they werefrequently only practical at coal mine sites. To makethe system more widely applicable, developers of steamengines began to think in terms of fuel economy. Not-ing that nearly half the heat from the fire was lostbecause of short contact time between the hot gasesand the boiler heating surface, Dr. John Allen mayhave made the first calculation of boiler efficiency in1730. To reduce heat loss, Allen developed an inter-nal furnace with a smoke flue winding through thewater, like a coil in a still. To prevent a deficiency ofcombustion air, he suggested the use of bellows to forcethe gases through the flue. This probably representsthe first use of forced draft.

Later developments saw the single pipe flue replacedby many gas tubes, which increased the amount of

heating surface. These fire tube boilers were essen-tially the design of about 1870. However, they werelimited in capacity and pressure and could not meetthe needs that were developing for higher pressuresand larger unit sizes. Also, there was the ominousrecord of explosions and personal injury because ofdirect heating of the pressure shell, which containedlarge volumes of water and steam at high tempera-ture and pressure.

The following appeared in the 1898 edition ofSteam: That the ordinary forms of boilers (fire tubeboilers) are liable to explode with disastrous effect isconceded. That they do so explode is witnessed by thesad list of casualties from this cause every year, andalmost every day. In the year 1880, there were 170explosions reported in the United States, with a lossof 259 lives, and 555 persons injured. In 1887 thenumber of explosions recorded was 198, with 652 per-sons either killed or badly wounded. The average re-ported for ten years past has been about the same as thetwo years given, while doubtless many occur which arenot recorded.

Inventors recognized the need for a new design, onethat could increase capacity and limit the conse-quences of pressure part rupture at high pressure andtemperature. Water tube boiler development began.

Early water tube designA patent granted to William Blakey in 1766, cover-

ing an improvement in Saverys steam engine, includesa form of steam generator (Fig. 9). This probably wasthe first step in the development of the water tubeboiler. However, the first successful use of a watertube design was by James Rumsey, an American in-ventor who patented several types of boilers in 1788.Some of these boilers used water tube designs.

At about this time John Stevens, also an American,invented a water tube boiler consisting of a group ofsmall tubes closed at one end and connected at the

Fig. 8 Trevithick boiler, 1804. Fig. 9 William Blakey boiler, 1766.



other to a central reservoir (Fig. 10). Patented in theUnited States (U.S.) in 1803, this boiler was used ona Hudson River steam boat. The design was shortlived, however, due to basic engineering problems inconstruction and operation.

Blakey had gone to England to obtain his patents,as there were no similar laws in North America.Stevens, a lawyer, petitioned the U.S. Congress for apatent law to protect his invention and such a law wasenacted in 1790. It may be said that part of the basisof present U.S. patent laws grew out of the need toprotect a water tube boiler design. Fig. 11 shows an-other form of water tube boiler, this one patented byJohn Cox Stevens in 1805.

In 1822, Jacob Perkins built a water tube boiler thatis the predecessor of the once-through steam genera-tor. A number of cast iron bars with longitudinal holeswere arranged over the fire in three tiers by connect-ing the ends outside of the furnace with a series ofbent pipes. Water was fed to the top tier by a feedpump and superheated steam was discharged from thelower tier to a collecting chamber.

The Babcock & Wilcox CompanyIt was not until 1856, however, that a truly success-

ful water tube boiler emerged. In that year, StephenWilcox, Jr. introduced his version of the water tubedesign with improved water circulation and increasedheating surface (Fig. 12). Wilcox had designed a boiler

with inclined water tubes that connected water spacesat the front and rear, with a steam chamber above.Most important, as a water tube boiler, his unit was in-herently safe. His design revolutionized the boiler in-dustry.

In 1866, Wilcox partnered with his long-time friend,George H. Babcock. The following year, U.S. PatentNo. 65,042 was granted to George H. Babcock andSteven Wilcox, Jr., and the partnership of Babcock,Wilcox and Company was formed. In 1870 or 1871,Babcock and Wilcox became the sole proprietors, drop-ping Company from the name, and the firm wasknown as Babcock & Wilcox until its incorporation in1881, when it changed its name to The Babcock &Wilcox Company (B&W). (see Fig. 3).

Industrial progress continued. In 1876, a giant-sized Corliss steam engine, a device invented in RhodeIsland in 1849, went on display at the Centennial Ex-

Fig. 10 John Stevens water tube boiler, 1803.

Fig. 11 Water tube boiler with tubes connecting water chamberbelow and steam chamber above. John Cox Stevens, 1805.

Fig. 12 Inclined water tubes connecting front and rear waterspaces, complete with steam space above. Stephen Wilcox, 1856.

Fig. 13 Babcock & Wilcox Centennial boiler, 1876.



hibition in Philadelphia, Pennsylvania, as a symbolof worldwide industrial development. Also on promi-nent display was a 150 horsepower water tube boiler(Fig. 13) by George Babcock and Stephen Wilcox, whowere by then recognized as engineers of unusual abil-ity. Their professional reputation was high and theirnames carried prestige. By 1877, the Babcock & Wilcoxboiler had been modified and improved by the partnersseveral times (Fig. 14).

At the exhibition, the public was awed by the sizeof the Corliss engine. It weighed 600 tons and had cyl-inders 3 ft (0.9 m) in diameter. But this giant size wasto also mark the end of the steam engine, in favor ofmore efficient prime movers, such as the steam tur-bine. This transition would add momentum to furtherdevelopment of the Babcock & Wilcox water tubeboiler. By 1900, the steam turbine gained importanceas the major steam powered source of rotary motion,due primarily to its lower maintenance costs, greater over-loading tolerance, fewer number of moving parts, andsmaller size.

Perhaps the most visible technical accomplishmentsof the time were in Philadelphia and New York City.In 1881 in Philadelphia, the Brush Electric Light Com-pany began operations with four boilers totaling 292horsepower. In New York the following year, ThomasAlva Edison threw the switch to open the Pearl StreetCentral station, ushering in the age of the cities. Theboilers in Philadelphia and the four used by ThomasEdison in New York were built by B&W, now incorpo-rated. The boilers were heralded as sturdy, safe and

reliable. When asked in 1888 to comment on one ofthe units, Edison wrote: It is the best boiler God haspermitted man yet to make. (Fig. 15).

The historic Pearl Street Central station opened with59 customers using about 1300 lamps. The B&W boil-ers consumed 5 tons of coal and 11,500 gal (43,532 l)of water per day.

The B&W boiler of 1881 was a safe and efficientsteam generator, ready for the part it would play inworldwide industrial development.

Water tube marine boilersThe first water tube marine boiler built by B&W

was for the Monroe of the U.S. Armys Quartermaster

Fig. 14 Babcock & Wilcox boiler developed in 1877.

George Herman BabcockGeorge Herman Babcock was born June 17, 1832

near Otsego, New York. His father was a wellknown inventor and mechanic. When George was12 years old, his parents moved to Westerly,Rhode Island, where he met Stephen Wilcox, Jr.

At age 19, Babcock started the Literary Echo,editing the paper and running a printing business.With his father, he invented the first polychro-matic printing press, and he also patented a jobpress which won a prize at the London CrystalPalace International Exposition in 1855.

In the early 1860s, he was made chief draftsmanof the Hope Iron Works at Providence, Rhode Is-land, where he renewed his acquaintance withStephen Wilcox and worked with him in develop-ing the first B&W boiler. In 1886, Babcock becamethe sixth president of the American Society of Me-chanical Engineers.

He was the first president of The Babcock &Wilcox Company, a position he held until hisdeath in 1893.



department. A major step in water tube marine boilerdesign came in 1889, with a unit for the steam yachtReverie. The U.S. Navy then ordered three ships fea-turing a more improved design that saved about 30%in weight from previous designs. This design wasagain improved in 1899, for a unit installed in the U.S.cruiser Alert, establishing the superiority of the wa-ter tube boiler for marine propulsion. In this installa-tion, the firing end of the boiler was reversed, placingthe firing door in what had been the rear wall of theboiler. The furnace was thereby enlarged in the di-rection in which combustion took place, greatly im-proving combustion conditions.

The development of marine boilers for naval andmerchant ship propulsion has paralleled that for landuse (see Fig. 16). Throughout the twentieth centuryand into the twenty-first, dependable water tube ma-rine boilers have contributed greatly to the excellent per-formance of naval and commercial ships worldwide.

Bent tube designThe success and widespread use of the inclined

straight tube B&W boiler stimulated other inventorsto explore new ideas. In 1880, Allan Stirling developeda design connecting the steam generating tubes di-rectly to a steam separating drum and featuring lowheadroom above the furnace. The Stirling Boiler Com-pany was formed to manufacture and market an im-proved Stirling design, essentially the same as shownin Fig. 17.

The merits of bent tubes for certain applications

Stephen Wilcox, Jr.Stephen Wilcox was born February 12, 1830 at

Westerly, Rhode Island.The first definite information concerning his en-

gineering activities locates him in Providence,Rhode Island, about 1849, trying to introduce acaloric engine. In 1853, in association with AmosTaylor of Mystic, Connecticut, he patented a letoffmotion for looms. In 1856, a patent for a steamboiler was issued to Stephen Wilcox and O.M.Stillman. While this boiler differed materiallyfrom later designs, it is notable as his first re-corded step into the field of steam generation.

In 1866 with George Babcock, Wilcox developedthe first B&W boiler, which was patented the fol-lowing year.

In 1869 he went to New York as selling agentfor the Hope Iron Works and took an active partin improving the boiler and the building of thebusiness. He was vice president of The Babcock& Wilcox Company from its incorporation in 1881until his death in 1893.

were soon recognized by George Babcock and StephenWilcox, and what had become the Stirling Consoli-dated Boiler Company in Barberton, Ohio, was pur-chased by B&W in 1906. After the problems of internaltube cleaning were solved, the bent tube boiler replacedthe straight tube design. The continuous and economi-cal production of clean, dry steam, even when using poorquality feedwater, and the ability to meet sudden loadswings were features of the new B&W design.

Electric powerUntil the late 1800s, steam was used primarily for

heat and as a tool for industry. Then, with the adventof practical electric power generation and distribution,utility companies were formed to serve industrial andresidential users across wide areas. The pioneer sta-tions in the U.S. were the Brush Electric Light Com-pany and the Commonwealth Edison Company. Bothused B&W boilers exclusively.

During the first two decades of the twentieth cen-tury, there was an increase in steam pressures andtemperatures to 275 psi (1.9 MPa) and 560F (293C),with 146F (81C) superheat. In 1921, the North Tessstation of the Newcastle Electric Supply Company innorthern England went into operation with steam at450 psi (3.1 MPa) and a temperature of 650F (343C).The steam was reheated to 500F (260C) and regen-erative feedwater heating was used to attain a boilerfeedwater temperature of 300F (149C). Three yearslater, the Crawford Avenue station of the Common-wealth Edison Company and the Philo and Twin



Fig. 15 Thomas Edisons endorsement, 1888.



Branch stations of the present American ElectricPower system were placed in service with steam at 550psi (38 MPa) and 725F (385C) at the turbine throttle.The steam was reheated to 700F (371C).

A station designed for much higher steam pressure,the Weymouth (later named Edgar) station of the Bos-ton Edison Company in Massachusetts, began opera-tion in 1925. The 3150 kW high pressure unit usedsteam at 1200 psi (8.3 MPa) and 700F (371C), re-heated to 700F (371C) for the main turbines (Fig. 18).

Pulverized coal and water-cooled furnacesOther major changes in boiler design and fabrica-

tion occurred in the 1920s. Previously, as power gen-erating stations increased capacity, they increased thenumber of boilers, but attempts were being made toincrease the size of the boilers as well. Soon the sizerequirement became such that existing furnace de-signs and methods of burning coal, primarily stokers,were no longer adequate.

Pulverized coal was the answer in achieving highervolumetric combustion rates and increased boiler ca-pacity. This could not have been fully exploited with-out the use of water-cooled furnaces. Such furnaceseliminated the problem of rapid deterioration of therefractory walls due to slag (molten ash). Also, thesedesigns lowered the temperature of the gases leavingthe furnace and thereby reduced fouling (accumula-tion of ash) of convection pass heating surfaces tomanageable levels. The first use of pulverized coal infurnaces of stationary steam boilers had been dem-onstrated at the Oneida Street plant in Milwaukee,Wisconsin, in 1918.

Integral Furnace boilerWater cooling was applied to existing boiler designs,

with its circulatory system essentially independent ofthe boiler steam-water circulation. In the early 1930s,however, a new concept was developed that arranged

Fig. 16 Two drum Integral Furnace marine boiler.

Requirements of a Perfect Steam Boiler 1875

the different sections to equalize the water line and pres-sure in all.

7th. A great excess of strength over any legitimatestrain, the boiler being so constructed as to be free fromstrains due to unequal expansion, and, if possible, toavoid joints exposed to the direct action of the fire.

8th. A combustion chamber so arranged that the com-bustion of the gases started in the furnace may be com-pleted before the gases escape to the chimney.

9th. The heating surface as nearly as possible at rightangles to the currents of heated gases, so as to breakup the currents and extract the entire available heatfrom the gases.

10th. All parts readily accessible for cleaning and re-pairs. This is a point of the greatest importance as re-gards safety and economy.

11th. Proportioned for the work to be done, and capableof working to its full rated capacity with the highesteconomy.

12th. Equipped with the very best gauges, safety valvesand other fixtures.

In 1875, George Babcock and Stephen Wilcox pub-lished their conception of the perfect boiler, listing twelveprinciples that even today generally represent good de-sign practice:

1st. Proper workmanship and simple construction, us-ing materials which experience has shown to be best,thus avoiding the necessity of early repairs.

2nd. A mud-drum to receive all impurities depositedfrom the water, and so placed as to be removed fromthe action of the fire.

3rd. A steam and water capacity sufficient to preventany fluctuation in steam pressure or water level.

4th. A water surface for the disengagement of the steamfrom the water, of sufficient extent to prevent foaming.

5th. A constant and thorough circulation of waterthroughout the boiler, so as to maintain all parts at thesame temperature.

6th. The water space divided into sections so arrangedthat, should any section fail, no general explosion canoccur and the destructive effects will be confined to theescape of the contents. Large and free passages between



the furnace water-cooled surface and the boiler surfacetogether, each as an integral part of the unit (Fig. 19).

Shop-assembled water tube boilersIn the late 1940s, the increasing need for industrial

and heating boilers, combined with the increasing costsof field-assembled equipment, led to development ofthe shop-assembled package boiler. These units arenow designed in capacities up to 600,000 lb/h (75.6kg/s) at pressures up to 1800 psi (12.4 MPa) and tem-peratures to 1000F (538C).

Further developmentsIn addition to reducing furnace maintenance and

the fouling of convection heating surfaces, water cool-ing also helped to generate more steam. Boiler tubebank surface was reduced because additional steamgenerating surface was available in the furnace. In-creased feedwater and steam temperatures and in-creased steam pressures, for greater cycle efficiency,further reduced boiler tube bank surface and permit-ted the use of additional superheater surface.

As a result, Radiant boilers for steam pressures above1800 psi (12.4 MPa) generally consist of furnace waterwall tubes, superheaters, and such heat recovery acces-sories as economizers and air heaters (Fig. 20). Units forlower pressures, however, have considerable steam gen-erating surface in tube banks (boiler banks) in additionto the water-cooled furnace (Fig. 21).

Universal Pressure boilersAn important milestone in producing electricity at

the lowest possible cost took place in 1957. The first

Fig. 19 Integral Furnace boiler, 1933.

Fig. 17 Early Stirling boiler arranged for hand firing.

Fig. 18 High pressure reheat boiler, 1925.



boiler with steam pressure above the critical value of3200 psi (22.1 MPa) began commercial operation. This125 MW B&W Universal Pressure (UP) steam gen-erator (Fig. 22), located at Ohio Power Companys Philoplant, delivered 675,000 lb/h (85 kg/s) steam at 4550 psi(31.4 MPa); the steam was superheated to 1150F (621C)with two reheats to 1050 and 1000F (566 and 538C).

B&W built and tested its first once-through steam gen-erator for 600 psi (4.1 MPa) in 1916, and built an experi-mental 5000 psi (34.5 MPa) unit in the late 1920s.

The UP boiler, so named because it can be designedfor subcritical or supercritical operation, is capable ofrapid load pickup. Increases in load rates up to 5% perminute can be attained.

Fig. 23 shows a typical 1300 MW UP boiler ratedat 9,775,000 lb/h (1232 kg/s) steam at 3845 psi (26.5MPa) and 1010F (543C) with reheat to 1000F (538C).In 1987, one of these B&W units, located in West Vir-ginia, achieved 607 days of continuous operation.

Most recently, UP boilers with spiral wound fur-naces (SWUP steam generators) have gained wideracceptance for their on/off cycling capabilities andtheir ability to operate at variable pressure withhigher low load power cycle efficiency (see Fig. 24).

Subcritical units, however, remain the dominantdesign in the existing worldwide boiler fleet. Coal hasremained the dominant fuel because of its abundantsupply in many countries.

Other fuels and systemsB&W has continued to develop steam generators

that can produce power from an ever widening arrayof fuels in an increasingly clean and environmentallyacceptable manner. Landmark developments by B&Winclude atmospheric fluidized-bed combustion instal-

Air Heater

Catalyst

Economizer

SCR

PrimarySuperheater

Final ReheatSuperheater

Furnace

SteamDrum

Platen SecondarySuperheater

SecondarySuperheater

PulverizerForced Draft

FanPrimary Air

Fan

PrimaryReheater

Fig. 20 Typical B&W Radiant utility boiler.

lations, both bubbling and circulating bed, for reducedemissions.

Waste-to-energy systems also became a major effortworldwide. B&W has installed both mass burn andrefuse-derived fuel units to meet this growing demandfor waste disposal and electric power generation. B&Winstalled the worlds first waste-to-energy boiler in 1972.In 2000, an acquisition by Babcock & Wilcox expandedthe companys capabilities in design and construction ofwaste-to-energy and biomass boilers and other multi-fuel burning plants.

For the paper industry, B&W installed the firstchemical recovery boiler in the U.S. in 1940. Since thattime, B&W has developed a long tradition of firsts in thisindustry and has installed one of the largest black liquorchemical recovery units operating in the world today.

Modified steam cyclesHigh efficiency cycles involve combinations of gas

turbines and steam power in cogeneration, and directthermal to electrical energy conversion. One directconversion system includes using conventional fuel orchar byproduct from coal gasification or liquefaction.

Despite many complex cycles devised to increaseoverall plant efficiency, the conventional steam cycle

Fig. 21 Lower pressure Stirling boiler design.



remains the most economical. The increasing use ofhigh steam pressures and temperatures, reheat super-heaters, economizers, and air heaters has led to im-proved efficiency in the modern steam power cycle.

Nuclear powerSince 1942, when Enrico Fermi demonstrated a con-

trolled self-sustaining reaction, nuclear fission hasbeen recognized as an important source of heat forproducing steam for power generation. The first sig-nificant application of this new source was the land-based prototype reactor for the U.S.S. Nautilus sub-marine (Fig. 25), operated at the National Reactor

Testing Station in Idaho in the early 1950s. This pro-totype reactor, designed by B&W, was also the basisfor land-based pressurized water reactors now beingused for electric power generation worldwide. B&Wand its affiliates have continued their active involve-ment in both naval and land-based programs.

The first nuclear electric utility installation was the90 MW unit at the Shippingport atomic power stationin Pennsylvania. This plant, built partly by DuquesneLight Company and partly by the U.S. Atomic EnergyCommission, began operations in 1957.

Spurred by the trend toward larger unit capacity,developments in the use of nuclear energy for electricpower reached a milestone in 1967 when, in the U.S.,nuclear units constituted almost 50% of the 54,000MW of new capacity ordered that year. Single unit ca-pacity designs have reached 1300 MW. Activity re-garding nuclear power was also strong outside the

Fig. 22 125 MW B&W Universal Pressure (UP) boiler, 1957.

Fig. 23 1300 MW B&W Universal Pressure (UP) boiler. Fig. 25 U.S.S. Nautilus worlds first nuclear-powered ship.

Fig. 24 Boiler with spiral wound universal pressure (SWUP) furnace.

Low NOXBurners

OverfireAir Ports

FlueGas

Outlet

PrimaryAirFan

AirHeater

Steam CoilAir Heater

ForcedDraftFan

B&WRoll WheelPulverizers

AmmoniaInjection

Grid

SteamSeparator

WaterCollection TankPrimarySuperheater

Economizer

PlatenSuperheater

FinalSuperheater

FinalReheater

CirculationPump

PrimaryReheater

Catalyst

IntermediateSuperheater

SpiralTransitionHeaders

Furnace SCR



U.S., especially in Europe. By 2004, there were 103reactors licensed to operate in the U.S. Fifty of the oper-ating units had net capacities greater than 1000 MW.

Throughout this period, the nuclear power programin Canada continued to develop based on a designcalled the Canada Deuterium Uranium (CANDU)reactor system. This system is rated high in both avail-ability and dependability. By 2003, there were 21units in Canada, all with B&W nuclear steam gen-erators, an additional 11 units operating outside ofCanada, and 18 units operating, under constructionor planned that are based on CANDU technology.

The B&W recirculating steam generators in theseunits have continually held excellent performancerecords and are being ordered to replace aging equip-ment. (See Fig. 26.)

While the use of nuclear power has remained some-what steady in the U.S., the future of nuclear poweris uncertain as issues of plant operating safety and long-term waste disposal are still being resolved. However,nuclear power continues to offer one of the least pollut-ing forms of large-scale power generation available andmay eventually see a resurgence in new construction.

Materials and fabricationPressure parts for water tube boilers were originally

made of iron and later of steel. Now, steam drums andnuclear pressure vessels are fabricated from heavysteel plates and steel forgings joined by welding. Thedevelopment of the steam boiler has been necessarilyconcurrent with advances in metallurgy and progres-sive improvements in the fabrication and welding ofsteel and steel alloys.

The cast iron generating tubes used in the first B&Wboilers were later superseded by steel tubes. Shortlyafter 1900, B&W developed a commercial process forthe manufacture of hot finished seamless steel boilertubes, combining strength and reliability with reason-able cost. In the midst of World War II, B&W completeda mill to manufacture tubes by the electric resistancewelding (ERW) process. This tubing has now been usedin thousands of steam generating units throughout theworld.

The cast iron tubes used for steam and water stor-age in the original B&W boilers were soon replacedby drums. By 1888, drum construction was improvedby changing from wrought iron to steel plates rolledinto cylinders.

Before 1930, riveting was the standard method ofjoining boiler drum plates. Drum plate thickness waslimited to about 2.75 in. (70 mm) because no satisfac-tory method was known to secure a tight joint inthicker plates. The only alternative available was toforge and machine a solid ingot of steel into a drum,which was an extremely expensive process. Thismethod was only used on boilers operating at what wasthen considered high pressure, above 700 psi (4.8 MPa).

The story behind the development of fusion weld-ing was one of intensive research activity beginningin 1926. Welding techniques had to be improved inmany respects. Equally, if not more important, an ac-ceptable test procedure had to be found and institutedthat would examine the drum without destroying it

in the test. After extensive investigation of varioustesting methods, the medical radiography (x-ray) ma-chine was adapted in 1929 to production examinationof welds. By utilizing both x-ray examination andphysical tests of samples of the weld material, thesoundness of the welds could be determined withoutaffecting the drum.

In 1930, the U.S. Navy adopted a specification forconstruction of welded boiler drums for naval vessels.In that same year, the first welded drums ever ac-cepted by an engineering authority were part of theB&W boilers installed in several naval cruisers. Alsoin 1930, the Boiler Code Committee of the AmericanSociety of Mechanical Engineers (ASME) issued com-plete rules and specifications for the fusion weldingof drums for power boilers. In 1931, B&W shipped thefirst welded power boiler drum built under this code.

The x-ray examination of welded drums, the rulesdeclared for the qualification of welders, and the con-trol of welding operations were major first steps in thedevelopment of modern methods of quality control inthe boiler industry. Quality assurance has receivedadditional stimulus from the naval nuclear propulsionprogram and from the U.S. Nuclear Regulatory Com-mission in connection with the licensing of nuclearplants for power generation.

Research and developmentSince the founding of the partnership of Babcock,

Wilcox and Company in 1867 and continuing to thepresent day, research and development have played im-portant roles in B&Ws continuing service to the powerindustry. From the initial improvements of Wilcoxs origi-nal safety water tube boiler to the first supercritical pres-sure boilers, and from the first privately operatednuclear research reactor to todays advanced environ-mental systems, innovation and the new ideas of its em-ployees have placed B&W at the forefront of safe, effi-cient and clean steam generation and energy conver-sion technology. Today, research and development activi-ties remain an integral part of B&Ws focus on tomorrowsproduct and process requirements.

Fig. 26 B&W replacement recirculating steam generators.



A key to the continued success of B&W is the abil-ity to bring together cross-disciplinary research teamsof experts from the many technical specialties in thesteam generation field. These are combined with state-of-the-art test facilities and computer systems.

Expert scientists and engineers use equipment de-signed specifically for research programs in all aspectsof fossil power development, nuclear steam systems,materials development and evaluation, and manufac-turing technology. Research focuses upon areas of cen-tral importance to B&W and steam power generation.However, partners in these research programs havegrown to include the U.S. Departments of Energy andDefense, the Environmental Protection Agency, pub-lic and private research institutes, state governments,and electric utilities.

Key areas of current research include environmen-tal protection, fuels and combustion technology, heattransfer and fluid mechanics, materials and manufac-turing technologies, structural analysis and design,fuels and water chemistry, and measurement andmonitoring technology.

Environmental protectionEnvironmental protection is a key element in all

modern steam producing systems where low coststeam and electricity must be produced with minimumimpact on the environment. Air pollution control is akey issue for all combustion processes, and B&W hasbeen a leader in this area. Several generations of lownitrogen oxides (NOx) burners and combustion tech-nology for coal-, oil- and gas-fired systems have beendeveloped, tested and patented by B&W. Post-combus-tion NOx reduction has focused on both selective cata-lytic and non-catalytic reduction systems. Combinedwith low NOx burners, these technologies have reducedNOx levels by up to 95% from historical uncontrolledlevels. Ongoing research and testing are being com-bined with fundamental studies and computer numeri-cal modeling to produce the ultra-low NOx steam gen-erating systems of tomorrow.

Since the early 1970s, extensive research effortshave been underway to reduce sulfur dioxide (SO2)emissions. These efforts have included combustionmodifications and post-combustion removal. Researchduring this time aided in the development of B&Wswet SO2 scrubbing system. This system has helped con-trol emissions from more than 32,000 MW of boiler ca-pacity. Current research focuses on improved removaland operational efficiency, and multi-pollution controltechnology. B&W has installed more than 9000 MWof boiler capacity using various dry scrubbing tech-nologies. Major pilot facilities have permitted the test-ing of in-furnace injection, in-duct injection, and dryscrubber systems, as well as atomization, gas condi-tioning and combined SO2, NOx and particulate con-trol. (See Fig. 27.)

Since 1975, B&W has been a leader in fluidized-bed combustion (FBC) technology which offers theability to simultaneously control SO2 and NOx forma-tion as an integral part of the combustion process, aswell as burn a variety of waste and other difficult tocombust fuels. This work led to the first large scale (20

MW) bubbling-bed system installation in the U.S.B&Ws research and development work has focusedon process optimization, limestone utilization, and per-formance characteristics of various fuels and sorbents.

Additional areas of ongoing environmental researchinclude air toxic emissions characterization, efficientremoval of mercury, multi-pollutant emissions control,and sulfur trioxide (SO3) capture, among others (Fig.28). B&W also continues to review and evaluate pro-cesses to characterize, reuse, and if needed, safelydispose of solid waste products.

Fuels and combustion technologyA large number of fuels have been used to gener-

ate steam. This is even true today as an ever-widen-ing and varied supply of waste and byproduct fuelssuch as municipal refuse, coal mine tailings and bio-mass wastes, join coal, oil and natural gas to meetsteam production needs. These fuels must be burnedand their combustion products successfully handledwhile addressing two key trends: 1) declining fuelquality (lower heating value and poorer combustion),and 2) more restrictive emissions limits.

Major strengths of B&W and its work in researchand development have been: 1) the characterizationof fuels and their ashes, 2) combustion of difficult fu-els, and 3) effective heat recovery from the productsof combustion. (See Fig. 29.) B&W has earned inter-

Fig. 27 B&W boiler with SO2, NOx, and particulate control systems.



national recognition for its fuels analysis capabilitiesthat are based upon generally accepted procedures,as well as specialized B&W procedures. Detailedanalyses include, but are not limited to: heating value,chemical constituents, grindability, abrasion resis-tance, erosiveness, ignition, combustion characteris-tics, ash composition/viscosity/fusion temperature, andparticle size. The results of these tests assist in pul-verizer specification and design, internal boiler dimen-sion selection, efficiency calculations, predicted unitavailability, ash removal system design, sootblowerplacement, and precipitator performance evaluation.Thousands of coal and ash samples have been ana-lyzed and catalogued, forming part of the basis forB&Ws design methods.

Combustion and fuel preparation facilities aremaintained that can test a broad range of fuels atlarge scale. The 6 106 Btu/h (1.8 MWt) small boiler

simulator (Fig. 30) permits a simulation of the time-temperature history of the entire combustion process.The subsystems include a vertical test furnace; fuelsubsystem for pulverizing, collecting and firing solidfuels; fuel storage and feeding; emission control mod-ules; gas and stack particulate analyzers for O2, CO,CO2 and NOx; and instrumentation for solids grind-ing characterization.

Research continues in the areas of gas-side corro-sion, boiler fouling and cleaning characteristics, ad-vanced pulp and paper black liquor combustion, oxy-gen and oxygen enhanced firing systems, and coal gas-ification, among others.

Heat transfer and fluid dynamicsHeat transfer is a critical technology in the design

of steam generation equipment. For many years, B&Whas been conducting heat transfer research from hotgases to tube walls and from the tube walls to enclosedwater, steam and air. Early in the 1950s, research inheat transfer and fluid mechanics was initiated in thesupercritical pressure region above 3200 psi (22.1MPa). This work was the technical foundation for thelarge number of supercritical pressure once-throughsteam generators currently in service in the electricpower industry.

A key advancement in steam-water flow was theinvention of the ribbed tube, patented by B&W in1960. By preventing deterioration of heat transferunder many flow conditions (called critical heat fluxor departure from nucleate boiling), the internallyribbed tube made possible the use of natural circula-tion boilers at virtually all pressures up to the criticalpoint. Extensive experimental studies have providedthe critical heat flux data necessary for the design ofboilers with both ribbed and smooth bore tubes.

Fig. 28 Tests for multi-pollutant emissions control.

Fig. 29 Atomic absorption test for ash composition. Fig. 30 B&Ws small boiler simulator.



Closely related to heat transfer, and of equal im-portance in steam generating equipment, is fluid me-chanics. Both low pressure fluids (air and gas in ductsand flues) and high pressure fluids (water, steam-water mixtures, steam and fuel oil) must be investi-gated. The theories of single-phase fluid flow are wellunderstood, but the application of theory to the com-plex, irregular and multiple parallel path geometry ofpractical situations is often difficult and sometimesimpossible. In these cases, analytical procedures mustbe supplemented or replaced by experimental meth-ods. If reliable extrapolations are possible, economi-cal modeling techniques can be used. Where extrapo-lation is not feasible, large-scale testing at full pres-sure, temperature and flow rate is needed.

Advances in numerical modeling technology havemade possible the evaluation of the complex three-di-mensional flow, heat transfer and combustion pro-cesses in coal-fired boiler furnaces. B&W is a leaderin the development of numerical computational mod-els to evaluate the combustion of coal, biomass, blackliquor and other fuels that have a discrete phase, andthe application of these models to full boiler and sys-tem analysis (Fig. 31). Continuing development andvalidation of these models will enhance new boilerdesigns and expand applications. These models arealso valuable tools in the design and evaluation of com-bustion processes, pollutant formation, and environ-mental control equipment.

Research, analytical and field test studies in boil-ing heat transfer, two-phase flow, and stability, amongother key areas, continue today by B&W alone andin cooperation with a range of world class organizations.

Materials and manufacturing technologiesBecause advanced steam producing and energy

conversion systems require the application and fabri-cation of a wide variety of carbon, alloy and stainlesssteels, nonferrous metals, and nonmetallic materials,it is essential that experienced metallurgical and ma-terials science personnel are equipped with the finestinvestigative tools. Areas of primary interest in themetallurgical field are fabrication processes such aswelding, room temperature and high temperature ma-terial properties, resistance to corrosion properties,wear resistance properties, robotic welding, andchanges in such material properties under variousoperating conditions. Development of oxidation-resis-tant alloys that retain strength at high temperature,and determination of short-term and long-term hightemperature properties permitted the increase insteam temperature that has been and continues to beof critical importance in increasing power plant effi-ciency and reducing the cost of producing electricity.

Advancements in manufacturing have included aprocess to manufacture large pressure componentsentirely from weld wire, designing a unique manu-

facturing process for bi-metallic tubing, using pressureforming to produce metallic heat exchangers, devel-oping air blown ultra-high temperature fibrous insu-lation, and combining sensor and control capabilitiesto improve quality and productivity of manufactur-ing processes.

Research and development activities also includethe study of materials processing, joining processes,process metallurgy, analytical and physical metallur-gical examination, and mechanical testing. The resultsare subsequently applied to product improvement.

Structural analysis and designThe complex geometries and high stresses under

which metals must serve in many products requirecareful study to allow prediction of stress distributionand intensity. Applied mechanics, a discipline withhighly sophisticated analytical and experimental tech-niques, can provide designers with calculation meth-ods and other information to assure the safety of struc-tures and reduce costs by eliminating unnecessarilyconservative design practices. The analytical techniquesinvolve advanced mathematical procedures and compu-tational tools as well as the use of advanced computers.An array of experimental tools and techniques are usedto supplement these powerful analytical techniques.

Computational finite element analysis has largelydisplaced experimental measurement for establishingdetailed local stress relationships. B&W has developedand applied some of the most advanced computer pro-grams in the design of components for the power in-dustry. Advanced techniques permit the evaluation ofstresses resulting from component response to ther-mal and mechanical (including vibratory) loading.

Fracture mechanics, the evaluation of crack forma-tion and growth, is an important area where analyti-cal techniques and new experimental methods permita better understanding of failure modes and the pre-

Fig. 31 B&W has developed advanced computational numerical modelsto evaluate complex flow, heat transfer and combustion processes.



diction of remaining component life. This branch oftechnology has contributed to the feasibility and safetyof advanced designs in many types of equipment.

To provide part of the basis for these models, exten-sive computer-controlled experimental facilities allow theassessment of mechanical properties for materials un-der environments similar to those in which they willoperate. Some of the evaluations include tensile andimpact testing, fatigue and corrosion fatigue, fracturetoughness, as well as environmentally assisted cracking.

Fuel and water chemistryChemistry plays an important role in supporting the

effective operation of steam generating systems.Therefore, diversified chemistry capabilities are essen-tial to support research, development and engineer-ing. The design and operation of fuel burning equip-ment must be supported by expert analysis of a widevariety of solid, liquid and gaseous fuels and theirproducts of combustion, and characterization of theirbehavior under various conditions. Long-term opera-tion of steam generating equipment requires exten-sive water programs including high purity wateranalysis, water treatment and water purification.Equipment must also be chemically cleaned at inter-vals to remove water-side deposits.

To develop customized programs to meet specificneeds, B&W maintains a leadership position in theseareas through an expert staff for fuels characteriza-tion, water chemistry and chemical cleaning. Studiesfocus on water treatment, production and measurementof ultra-high purity water (parts per billion), water-sidedeposit analysis, and corrosion product transport.

B&W was involved in the introduction of oxygenwater treatment for U.S. utility applications. Special-ized chemical cleaning evaluations are conducted toprepare cleaning programs for utility boilers, indus-trial boilers and nuclear steam generators. Specialanalyses are frequently required to develop boiler-spe-cific cleaning solvent solutions that will remove thedesired deposits without damaging the equipment.

Measurements and monitoring technologyDevelopment, evaluation and accurate assessment

of modern power systems require increasingly precisemeasurements in difficult to reach locations, often inhostile environments. To meet these demandingneeds, B&W continues the investigation of specializedsensors, measurement and nondestructive examina-tion. B&W continues to develop diagnostic methodsthat lead to advanced systems for burner and combus-tion systems as well as boiler condition assessment.

These techniques have been used to aid in labora-tory research such as void fraction measurements forsteam-water flows. They have also been applied tooperating steam generating systems. New methodshave been introduced by B&W to nondestructivelymeasure oxide thicknesses on the inside of boilertubes, detect hydrogen damage, and detect and mea-sure corrosion fatigue cracks. Acoustic pyrometry sys-tems have been introduced by B&W to nonintrusivelymeasure high temperature gases in boiler furnaces.

Steam/its generation and useThis updated and expanded edition provides a broad,

in-depth look at steam generating technology and equip-ment, including related auxiliaries that are of interest toengineers and students in the steam power industry. Thereader will find discussions of the fundamental technolo-gies such as thermodynamics, fluid mechanics, heat trans-fer, solid mechanics, numerical and computational meth-ods, materials science and fuels science. The various com-ponents of the steam generating equipment, plus theirintegration and performance evaluation, are covered indepth. Extensive additions and updates have been madeto the chapters covering environmental control technolo-gies and numerical modeling. Key elements of the bal-ance of the steam generating system life including opera-tion, condition assessment, maintenance, and retrofits arealso discussed.



Introduction to SteamSteam as a resourceThe early use of steamFire tube boilersEarly water tube design

The Babcock & Wilcox CompanyGeorge Herman BabcockStephen Wilcox, Jr.Water tube marine boilersBent tube designElectric powerPulverized coal and water-cooled furnacesIntegral Furnace boilerRequirements of a Perfect Steam Boiler 1875Shop-assembled water tube boilersFurther developmentsUniversal Pressure boilersOther fuels and systemsModified steam cyclesNuclear powerMaterials and fabrication

Research and developmentEnvironmental protectionFuels and combustion technologyHeat transfer and fluid dynamicsMaterials and manufacturing technologiesStructural analysis and designFuel and water chemistryMeasurements and monitoring technology

Steam/its generation and use

Documents

02.Introduction to Steam_Steam, Its Generation & Use, 41_Ed