Centennial special: Boilers
Power for the Industrial Age: A brief history of boilers
By Steven E. Kuehn, Senior Editor
To examine the technical history of boilers and steam power is to understand the rise of the industrial revolution. It is hard to imagine another technology more central, more elemental to our present industrial-based culture. Testimony to that fact is everywhere and one need not look any farther than the electric power generating industry for proof that, even after more than 100 years of development, boilers continue to dominate as a power source.
Steam`s recognition as a source of energy stretches well into man`s past. In 200 B.C. Hero, a Greek mathematician and scientist is credited with inventing the first practical application of steam power, the aelopile. Simply a cauldron with a lid, the aelopile had two pipes that channeled steam into a hollow sphere. The sphere, which pivoted on the steam pipes, had two nozzles situated on opposite sides of its axis. Thus, the cauldron was fired, the water in it boiled, the steam was channeled into the sphere, and as the steam escaped through the nozzles, the sphere would spin. Although Hero thought the device only a novelty, the concept remains: use combustion to produce heat, transfer the heat to water, boil the water to generate steam and transfer its energy into a mechanical force.
Fast forward 2,000 years. Steam is emerging as a commercially viable power source and 17th century mining engineers begin to apply it practically using steam-powered pumps. Shell boilers, considered state-of-the-art then, were nothing more than large kettles fired by wood, charcoal and increasingly, from the mines they served, coal. Developments and improvements continued apace and engineer/inventors like Newcomen, Papin, Watt and Trevithick forever placed their mark on the development of boiler and steam technology.
To a certain degree, shell-type boilers had reached their technical zenith by the late 1700s. Boiler capacity was just not keeping up with the demand for power, and boiler-related accidents began to take a terrible toll on lives and equipment. To resolve these and other related issues, great minds began to apply their knowledge to the problems of thermal efficiency, capacity and safety. In the period 1760 through 1825, the historical record credits Msrs. Allen, Blakey, Rumsey, Stevens and Perkins with several important and pivotal developments that preceded the design of the modern water tube boiler or what became known as the steam generator.
In 1856, a man by the name of Stephen Wilcox patented a boiler design that featured improved water circulation, increased heating surface and, above all, safety. By connecting front and rear water spaces with a series of inclined tubes and placing the steam chamber above them (see Figure), Wilcox had designed the first successful water tube boiler. Ten years later, Wilcox became associated with George Babcock, and in 1867 the first Babcock & Wilcox (B&W) boiler was patented.
Powerful and efficient, B&W boilers soon earned a great reputation among industrialists. In 1876, symbolizing a new age of industrial development, a B&W boiler stood adjacent to the massive Corliss steam engine at the Centennial Exhibition in Philadelphia, Pa. In an early company history, the company gave this account: “The 150-horse-power boiler exhibited by Babcock & Wilcox gave good account of itself in the trials. It created much favorable attention, and the Centennial judges gave the partners an award and medal as official recognition of the excellence of their product.”
Age of the cities
B&W boilers continued to win accolades in the ensuing years and that reputation was enough to sell Thomas A. Edison on the merits of using B&W units to make electricity. Granted, there were hundreds of other manufacturers, large and small, producing units, but the historical record suggests that B&W boilers were considered the best engineered at the time.
Heralded as sturdy, safe and reliable, B&W boilers were specified to power two of the earliest electric power generating stations. In 1881, The Brush Electric Light Co. in Philadelphia, Pa., began operations with two B&W boilers and Edison himself threw the switch to open pearl Street Station which employed four B&W units. Ushering in the Age of the Cities, Edison commented later that, “These are the best boilers God has yet permitted man to make.”
Once electricity was recognized as a safe and reliable power source, the demand for boilers took off as generating station after generating station was built to satisfy the needs of industrial and residential customers.
Of course, the increasing demand for power put pressure on boiler manufacturers to improve the output of their products. In the period 1900-1920, great strides were made as utilities and others tried larger boilers and multiple boiler arrangements to achieve greater output. With the help of some key developments, steam pressures and temperatures nearly doubled as manufacturers began to perfect the boiler for electric power generation.
Water-cooled refractory walls, for example, permitted the greater use of pulverized coal and its higher volumetric combustion rates. Water cooling decreased furnace maintenance and convection surface fouling. Water cooling also helped generate more steam. Boiler tube bank surface could then be reduced because additional steam generating surface was available in the furnace. Rising feedwater and steam temperatures and escalating steam pressures led to greater cycle efficiency and further reductions to tube bank size. This meant more room for efficiency-based equipment such as superheaters, economizers and air heaters, essential elements of all steam generators capable of producing steam pressures in excess of 1,200 psi.
Incorporated in 1900, the Power Specialty Co. replaced the American Water Works Supply Co. which Pell W. Foster and his cousin Earnest H. Foster had founded in 1894. The story really starts with Earnest`s travels in Europe from 1889 to 1900. After returning to the United States, Earnest realized that the United States was many years behind Europe in adopting superheated steam for power generation. Intrigued by this new technology, he was convinced that superheated steam would become the next great development in the U.S. power business. At the May 1901 meeting of the American Society of Mechanical Engineers (ASME), he presented a paper entitled “Superheated Steam,” pointing out the work of European engineers and the several thousand successful installations in Europe. The paper was also presented at the fall 1902 meeting of the Engine Builder`s Association and published soon after in the Dec. 15, 1902, edition of The Engineer. (Editor`s note: The Engineer later became Power Engineering.)
In the paper`s introduction, Foster wrote: “While the subject of superheated steam is of the broadest possible scope, and may be said to penetrate every branch of industry where steam is employed, it should be of special interest to engine builders and rank alongside of such important questions as expansion in the cylinders and condensation in the exhaust. For by this means do we not only increase the amount of work done per expenditure of heat units, but we are enabled to actually simplify construction in many important features.”
Despite an initial reluctance on the part of plant owners to add superheated steam, the adoption of the steam turbine soon made its use a necessity. Thus, the first Foster superheater accompanied the Hartford Electric Co.`s installation of the first Westinghouse Parsons steam turbine in 1902. Now teamed with the turbine, steam for electric generation would never be the same.
In 1903, Foster`s company followed up on earlier successes by installing superheaters in the powerhouse of the Interboro Rapid Transit Co. John Primrose, a Foster engineer, recalled in his memoirs, “These superheaters were important because the boiler pressure was 160 pounds, which seemed too high for the all cast-iron construction. Earnest Foster conceived the idea of covering a steel tube with cast-iron flanged rings, thus utilizing a steel tube to resist pressure, with an outside covering of cast-iron rings, greatly increasing the heating surface. In 1903, Earnest secured a patent which was so effective no one ever attempted to infringe.”
Called gill rings, the new system was quickly recognized by power engineers as superior heat transfer technology. Furthermore, because the design greatly increased heat exchange surface per foot of element, Foster was able to retrofit superheaters into spaces too small for other designs. Power Specialty Co.`s reputation for technical leadership and innovation soon spread to other key boiler efficiency technologies.
The use of economizers, devices which preheated boiler feedwater, began to grow after the turn of the century. But the economizer`s use was initially stifled because of severe internal and external corrosion problems. Boiler engineers were generally unaware that proper feedwater deareation was needed to prevent internal corrosion and that sulfur-bearing coal led to surface corrosion. Power Specialty Co. applied its engineering skills to the basic design concept and incorporated feedwater deareation to prevent internal corrosion and took steps with a proprietary process to protect external surfaces.
Stokers and pulverizers
Two well-known companies also got their start during the first decades of the 20th century, Combustion Engineering and Riley Stoker, now known as DB Riley Inc. More importantly, those companies lead the technical development of fuel handling equipment and pioneered the use of pulverized coal in this country.
Combustion Engineering got its start manufacturing a variety of stoker designs produced from the merger of two companies. One design was a specialized grate capable of burning anthracite coal screenings and the other a screw type suitable for bituminous coal. As the company grew, its repertoire of stokers expanded as well. But soon traveling grate stokers reached their technical limits. A 24-foot-wide, 28-foot-long grate design could generate only about 200,000 pounds of steam per hour.
Similarly, Robert Sanford Riley, working from a reputation started with a good design for an automatic feed stoker, linked up with others and soon was producing large multiple-retort underfeed stokers. By the mid `20s, and with the help of mergers, Riley Stoker Inc. was producing a complete line of stokers for boilers of all sizes.
However, because of the limitations placed on boiler capacity by the size restrictions of stokers, Combustion Engineering decided early on to develop coal pulverization and in doing so, revolutionized coal-fired steam generation. Capitalizing on a pulverized coal firing system design for locomotives, the company adapted this technology to stationary utility boilers at the Oneida Street and Lakeside Stations of the Milwaukee Electric Railway and Light Co. If this scenario seems familiar, it should, considering the current trend of transferring aero engine technology to ground-based industrial gas turbines.
According to Combustion Fossil Power Systems, “This pioneering work, done jointly with Milwaukee Electric`s engineers and the Bureau of Mines, marks the most important single development in the art of solid-fuel combustion in this century.”
Combustion engineering also engineered modern water-cooling techniques that led to the first installation of watertubes on furnace sidewalls at Consolidated Edison`s Hell Gate Station followed by the first boiler to have bottom, rear and sidewall watertubing. In 1929, Combustion Engineering erected the first steam generator unit to produce steam at 1 million pounds per hour for New York Edison`s East River Station.
Between the wars, both Combustion Engineering and Riley Stoker acquired companies and assets that put them in the forefront of steam generator technology. By the 1930s both companies were manufacturing all the essentials, boilers, burners, economizers, superheaters, pulverizers, waterwalls, etc.
Pulverized firing develops
According to Combustion Engineering, the company`s pioneering work on pulverized-coal firing at Milwaukee was followed in 1927 by the introduction of tangential firing, progenator of systems engineered by the company today. Commercially installed for the first time at a Detroit, Mich., rubber company, the tangentially fired system permitted optimum combustion conditions because fuel and air were introduced into the furnace from its four corners. In 1940, a major modification to the basic tangential firing concept was applied to a boiler at Duke Power Co.`s Buck Station; the fuel and air nozzles were made vertically tiltable. The new design allowed operators to move the flame envelope within the furnace and thus provide more control over steam temperatures.
Fusion-welded boiler drum
While the development and application of superheaters, economizers, air preheaters and other elements contributed a great deal to modern steam generator design, a variety of physical limitations, primarily having to do with fabrication techniques, held boiler capacity in check. Until the late 1920s, heavy pressure vessels were manufactured by riveting together plates of steel and then caulking the joints to prevent leaks. However, the thermal and mechanical stresses from firing would cause these crevices to leak. Furthermore, at high pressures the crevices created a place for corrosion concentration. These conditions posed serious safety issues and engineers realized other construction methods had to be explored. Forgings were one possibility, but they were very expensive and welding was still an experimental exercise in need of further research and development.
It was about this time that a subsidiary of Combustion Engineering began to apply its resources to the problems associated with welding pressure vessels. From 1927 through 1929, engineers at Combustion Engineering`s Chattanooga Works began welding and testing boiler plate material coupons and developing welding techniques and technology to construct welded pressure vessels. Because elements such as coated electrodes for electric arc fusion welding and accompanying production apparatus were not mature technologies, the importance of this research and development activity to the industry cannot be understated.
Combustion Engineering continued its work and on May 2, 1930, the first of the company`s welded boiler drums was hydrostatically tested to destruction. The first welded pressure vessel was fabricated from rolled 1-inch-thick shell plate purchased to American Society of Testing and Materials standards of 55,000 psi tensile strength for firebox boiler plate. Two dish-shaped heads were formed from 1-1/2-inch-thick plate material made to the same specifications as the cylindrical shell. One of the heads was blank, and the other had an opening fitted with a standard manway cover. A single longitudinal seam weld joined the edges of the rolled shell and two girth welds joined the heads to the end of the shell. With an overall length of 98 inches and a 34-inch inside diameter, the first all welded boiler drum was a small but historic start.
By 1931, Combustion Engineering had installed the first boiler to operate at 1,800 psi, and through improved materials, ultimate steam temperatures began to climb as well. In 1939, Combustion Engineering constructed a unit for Ford Motor Co. capable of steam temperatures of 925 F. Ten years later, the first unit to exceed 1,000 F was sold to Public Service Electric and Gas of New Jersey`s Sewaren Station.
The `50s and beyond
Throughout the war years and into the cold war, there was a tremendous push from both government and private concerns to advance numerous technologies deemed important to the war effort. Great strides were made in all areas of manufacturing, materials and related disciplines. This developmental aegis applied to steam generator technology as well; during and after the war a variety of technologies contributed to a fast-advancing state-of-the-art.
So, in the pursuit of capacity and efficiency, manufactures turned to the reheat cycle and improved boiler circulation properties for more power. Further strides were also made in the area of combustion and burner technology, a facet of steam generator design that remains on a fast development track for a number of companies.
The net effect on boiler development was that steam temperatures and pressures continued to climb and by 1959, Philadelphia Electric Co. was operating the highest pressure and temperature unit ever, the 5,300 psi, 1,210 F supercritical Eddystone Unit 1. By the middle of the next decade, Tennessee Valley Authority`s (TVA) Bull Run Station was operating with a 3,650 psi superheater outlet pressure at 1,003 F superheater and 1,003 F reheater outlet temperatures.
It was also during this time that men devised what might be termed the “ultimate” boiler, the light water reactor. Old-line boiler makers like B&W and Combustion Engineering became deeply involved in the development of nuclear power and, along with the likes of Westinghouse and General Electric, launched this country into the nuclear age.
Well, it`s 1996 and a lot has happened since TVA`s Bull Run Station lit off its burners in 1966. Utilities faced with the prospect of competition and deregulation for the first time are unsure of which course to take as far as power generating resources are concerned. Most are opting to maintain current plants and ad capacity in increments via gas turbine and combined-cycle units. Nuclear power is relied upon heavily in the industrialized regions of the country but no new plants were built after the 1980s. Nevertheless, coal is still King thanks to the mighty boiler, but its grip on the number one spot is not as sure as it once was.
The heavy hand of regulation has contributed a great deal to the direction that steam generator development has taken over the last 30 years. The Environmental Protection Agency and its Clean Air Act, and legislation such as the Public Utility Regulatory Policies Act have prompted unparalleled research and development in the areas of efficiency and emissions control.
Coal is still an abundant and cheap source of fuel. However, to capture its energy, one has to burn it and that is when all the fun starts. Consider how much a technological tour de force a recent modern boiler/steam generator design is. Every input is tuned to enhance efficiency, influence heat rate and cut emissions. So, to accommodate the growing demand for high-performing and environmentally clean generating sources, boiler technology has broken through to some new ground but not without the help of Uncle Sam and the Department of Energy`s Clean Coal Technology`s (CCT) program.
Designers of advanced coal combustion technologies have been concentrating on the coal-fired combined cycle to meet the environmental regulations and the power industry`s efficiency demands. However, the flow of funds that got its development this far could be trimmed before all planned development work is completed. Nevertheless, progress made in demonstrating pressurized, fluidized-bed combustion (PFBC) could mitigate any loss of research funding might cause. For now, PFBC technology is proving to be environmentally friendly and robust enough for widespread commercial application.
The PFBC power plant burns pulverized coal in a pressurized combustor, providing steam and hot gas for a combined cycle. Heater tubes in the fluidized bed generate steam for a steam turbine while the bed`s hot flue gas is sent to drive a gas turbine. The gas turbine`s compressor is also used to pressurize the boiler. Before expanding through the turbine, the combustion gas is passed through a series of cyclones to remove 98 percent of the ash suspended in the gas. The latest designs incorporate further hot gas cleanup measures to remove even more particulates in an effort to reduce erosion and corrosion in the gas turbine. The turbine`s exhaust gas requires only electrostatic precipitation to make it suitable for release.
PFBC boilers offer high efficiency (up to 39 percent in first generation systems) and lower costs (approximately $300/kW less) than a conventional pulverized-coal boiler with flue-gas desulfurization. These attractive attributes come with the added benefit of meeting or exceeding 1990 Clean Air Act amendments.
With first generation PFBC ready for commercial deployment, any new technology with its roots in PFBC is poised to emerge as a CCT leader. Second generation or advanced PFBC (APFBC) will soon be demonstrated under the CCT program. This process can loosely be described as a combination of first generation PFBC and the integrated coal gasification combined cycle. Research and development programs now being conducted at various companies are producing valuable data and experience for the overall development of APFBC.
The first integrated APFBC site is planned as part of the Power Systems Development Facility in Wilsonville, Ala. The design will emulate a commercial APFBC plant and will be laid out in five modules: an APFBC module, a transport reactor gas source module, a particulate control module, an advanced burner/gas turbine module and an advanced fuel cell module. Foster Wheeler (remember that name?) will be engineering the APFBC module slated for operation sometime this year.
The rich history of boiler technology is still being mined for advancements today, and the crystal ball finds the technology will retain its prominence as a power generating source for many years to come. z
1. Steam/its generation and use. 40th edition. Steven C. Stultz and John B. Kitto. The Babcock & Wilcox Co., Barberton, Ohio.
2. Combustion Fossil Power, A Reference Book on Fuel Burning and Steam Generation. Joseph G. Singer. Combustion Engineering Inc.
3. A Century of Engineering Achievement. An Abridged History. Foster Wheeler Corp.
4. The History Behind the Name. DB Riley Inc.
5. “Gas, coal duke it out over repowering,” Timothy B. DeMoss, Power Engineering, pg. 21. June 1995.
At the turn of the last century, the latest in superheater technology was retrofitted to this boiler in the pursuit of efficiency and capacity. At the turn of this century, plant owners search for the same benefits in the same way, as competition dictates better performing power plants. Photo courtesy of Foster Wheeler.
The first all-fusion welded boiler drum, a national ASME engineering landmark, proved conclusively that welded joints, perfected by Combustion Engineering, were 100-percent efficient.
I would like to gratefully acknowledge the contributions to this article from the following sources: