By Lee S. Langston

Charles Dickens's beginning to A Tale of Two Cities, "It was the best of times, it was the worst of times," provides a good characterization of events in the gas turbine industry during the year 2000.

On the one hand, the gas turbine industry has never had it so good. Jet engine production continues to be substantial as more of the public flies. This first year of the new millennium has seen the largest sales of electric power gas turbines in the industry's 60-year history, with order books filled to 2004.

On the other hand, the gas turbine combustion humming problem hasn't been solved and continues to plague users and manufacturers of electric power gas turbines, as they attempt to meet environmental regulations. The new dominance of the gas turbine in power markets has helped natural gas prices more than triple in 2000, raised the price of new and used gas turbines, and caused a shortage of qualified engineering firms to manage new power plant projects.

Double-Digit Gains

The value of production of gas turbines in 2000 totaled $36.5 billion worldwide, up 5.8 percent from $34.5 billion in 1999.

The value-of-production estimates, which are provided by Forecast International of Newtown, Conn., are more timely indicators than original equipment manufacturers' sales.

The value of production of jet engines was $18.3 billion, down about 2 percent from 1999.

Following trends of the past few years, the civil aviation market for gas turbines continued to be strong, reflecting the healthy economics of the world's airlines. Value of production remained steady at $15.9 billion.

Among manufacturers, General Electric has the greatest share of the large turbofan market, followed by Rolls-Royce and Pratt & Whitney.

Continuing the trend of past years, the nonaviation segment of the gas turbine market has had the faster rate of growth. The value of production for 2000 in this market segment is estimated to be $18.2 billion, up approximately 15 percent from 1999. It represents 50 percent of the total gas turbine market, up from 46 percent in 1999.

The electric power gas turbine value of production for 2000 was $17.4 billion, up 18 percent from $14.8 billion in 1999. By itself, the segment represented 48 percent of the total value of gas turbine production last year.

Marine gas turbines, unchanged at $300 million, are mostly for propulsion and electrical power generation in surface ships in navies, but can be expected to grow in the civilian market in the near future. FastShips, a company formed to transport perishables and cars between Philadelphia and France, is building four gas turbine-powered, high-speed cargo ships, with more to follow. The cruise industry is in a growth mode, with about 54 ships on order (about $17.5 billion worth) between 2000 and 2005. Due mainly to environmental restrictions being placed on vessels making Alaskan cruises, many of the new ships will have at least some gas turbine power, both for propulsion and hotel electrical load.

Gas as Prime Mover

Deregulation of the huge U.S. electric power market, and of markets in other parts of the world, is helping to drive the increased use of gas turbines. Also, because of the uncertainties brought about by the prospect of the deregulation, U.S. electric utilities have lagged in replacing old equipment and buying new, so electric power reserve margins have gotten dangerously low, especially in the Midwest, the Northeast, and California.

High operating efficiencies (40 percent for simple cycle and up to 60 percent for combined-cycle operations), low capital and operating costs, and combustion of clean natural gas all combine to make the gas turbine the prime mover of choice to satisfy the needs brought about by deregulation.

U.S. spot markets for electrical power experienced wide price swings in 2000 and in the past few years. During a heat wave last summer, utility companies in California say they lost $6 billion because of spikes in wholesale prices, the loss resulting from the difference between their cost of buying wholesale power and what they are allowed to charge their customers.

Gas turbine power plants can be designed to have about the shortest startup time of any large power output prime mover, so they are uniquely suited for the spot market as well as for providing base load capability. This has helped to fill gas turbine order books in 2000, with some production lines booked to 2004.

Last year marked the largest sales of electric power gas turbines in the industry's 60-year history. This time of plenty is giving rise to other consequences, some of them unintended.

During 2000, the wellhead price of natural gas more than tripled. Much of the increase may be attributed to the rise of oil prices, but some must be due to increased demand caused by new gas turbine power plants coming on line. The market for used and refurbished gas turbines has increased greatly.

The humming problem continues to be a major concern. The degree of this difficulty varies considerably from one manufacturer to another. In order to meet new environmental regulations and to lower NO_x emissions, gas turbine manufacturers are using lean premixed combustion systems. These systems have proven to be subject to induced pressure oscillations that can cause a hum.

Gas turbines, such as GE's H unit, offer high efficiency, new technology, low cost, and low emissions, making them suitable for a deregulated energy market.

The humming can increase to howling and cause serious damage to the machine unless power output is reduced. The precise mechanisms that lead to combustion-induced pressure oscillations are not fully understood, and most manufacturers are dealing with it (or not dealing with it) by recommending lower power levels, until a better solution is in hand.

David Gillespie, a Duke Energy North America manager of several gas turbine plants in the northeastern states, said that he and other operators have learned to predict the onset of humming, and hence avoid it, but cannot solve it.

On another research front, early in 2000, a U.S. Department of Energy award of $2.25 million was shared by Pratt & Whitney, Rolls-Royce Allison, Siemens-Westinghouse, and General Electric, for early studies of possible "next generation" turbine configurations. The NGT program focuses on an advanced midsize gas turbine design in the 30- to 200-megawatt range. It would be a more efficient simple-cycle machine (40 to 48 percent efficiency) with a lower cost per kilowatt than combined-cycle systems.

The NGT will need to have fast dispatchability (cold start to full power in 10 minutes), be able to take many full-load start-stop cycles without a significant reduction in useful life, and have the capability of repowering existing steam plants to make them more competitive without requiring investment in a full repowering project.

Microturbines, which have been under development for some years, are now coming into the distributed power market in a real way. These gas turbines, in the 50-kW to 500-kW range, are designed for on-site electrical power production, cooling, heating, and mechanical drive applications. In the United States last year, three firms—Capstone, Honeywell Power Systems, and Elliott Energy Systems—offered commercial microturbine units. Capstone led the three with more than 1,000 units shipped last year to customers for applications ranging from oilfield operations to breweries. Ingersoll-Rand has alpha and beta units in the field and DTE Energy (which is teamed with Pratt & Whitney Canada) recently received its first prototype engine.

During 2000, the DOE awarded $40 million for next-generation microturbine systems. Awards were made to Capstone, General Electric, Honeywell, Ingersoll-Rand, Solar, and United Technologies.

Technology in 2000

IGTI's technical committee chairs and other volunteer leaders have highlighted key technical issues and progress for 2000.

Manufacturing and repair: Manufacturing Materials and Metallurgy Committee chair Jeffrey Conner observed that, as the migration of advanced materials and process technologies from aero engines into industrial gas turbines continues, many standard component repair sources for IGT buckets and vanes do not have the experience or processes required to perform repairs, such as welding and brazing on the new directionally solidified and single crystal materials.

What's more, the strong growth of the aviation business continues, with many major purchases being made or planned by airlines around the world. Airbus's A3XX program has now been formally launched along with Boeing's 777-200X/-300X extended range aircraft and 747-400X aircraft. Regional jets are selling at record rates and represent a major growth area for sales and aftermarket service in the coming years.

Ceramics: According to Ceramics Committee chair Stanley Levine, applications of ceramics in gas turbines continue to grow. Fiber-reinforced ceramic matrix composites were put into service in a commercial application at Malden Mills in Lawrence, Mass., in 1999. The component is a low-NO_x combustor liner in the Solar Centaur 50 engine. Successful use of the CMC is enabled by an environmental barrier coating that was developed jointly by NASA, GE, and Pratt & Whitney under the Enabling Propulsion Materials program and optimized on the DOE's Ceramic Stationary Gas Turbine program. Accumulated time on the high time liner is more than 7,000 hours.

NASA also has a program to put CMCs into turbopumps for rocket engines. A CMC blisk was successfully operated in a low-temperature turbopump application at Marshall Space Flight Center.

Interest and progress in the application of monolithic ceramics and, in particular, in si tu toughened silicon nitride, continue to be strong. Honeywell Advanced Ceramic Components has disclosed an AS-950 material superior to AS-900 in its creep resistance. Evaluation of silicon nitride turbine vanes in an auxiliary power unit is continuing on Alaska Airlines Boeing 737s. Silicon nitride development for turbine vanes and blades is continuing at a number of organizations throughout the world.

Combustion: Clifford Smith, acting chair of the Combustion and Fuels Committee, reported several new government initiatives in the United States to improve engine efficiency and reduce emissions. These include NASA's Ultra Efficient Engine Technology program, the military's Versatile, Affordable Advanced Turbine Engine program, and DOE's Next Generation Turbine for Vision 21 Plants. These programs will develop combustion technology in such areas as smart combustion systems, advanced materials, and alternate fuels. In so doing, future gas turbine engines will be pushed to higher and higher pressure ratios and hotter turbine inlet temperatures.

The NASA program will work to develop and hand off propulsion technologies that will enable future generation vehicles over a wide range of flight speeds. Program goals are sharp reductions in NO_x and CO₂ emissions. New technologies, including lean-burn combustors with advanced controls, will be assessed using new, improved design codes, and tested in sector and full annular rigs.

The DOD focuses on gas turbines with improved performance and cost, including the use of common core architecture in multiple applications to reduce development, production, and maintenance costs. Engine modeling and simulation tools will be developed to significantly reduce development time.

The DOE will produce industrial gas turbines that enhance efficiency and environmental performance of capacities between 30 and 200 MW. With the restructuring of the U.S. electric power industry, an increasing number of power companies are planning units in this midsize range. The DOE's goals are to increase net system efficiency by 15 percent or more while reducing costs by at least 15 percent, compared with similar-size units operating today.

Two programs under the European Union were launched in 2000 to deal with the instability and the modeling of combustors. One, Instability Control of Low Emission Aero Engine Combustors, focuses on the combustion stability of future low-emission aero-engine combustors. The other, Computational Fluid Dynamics for Combustors, aims to improve the quality of the numerical codes used in industry for the calculation of combusting flows.

Additional European programs will deal with advanced computational methods and the demonstration of low-emission combustors with partially or fully premixed stages.

The European Manufacturers of Industrial Gas Turbines and manufacturers of utility gas turbines have initiated their own European programs on the same issues, which will be coordinated with the aero-engine group.

Improvement of high-temperature materials is another high-priority research area. A number of national programs in countries with a developed gas turbine industry complement the European technology development programs.

Natural gas supply: Thomas Robinson predicted for the Oil and Gas Applications Committee that natural gas consumption in North America will increase from the current 24 trillion cubic feet per year to 31 trillion by the end of the decade. This 30 percent increase is due largely to increased use of natural gas for electrical generation and cogeneration.

In North America, two new sources are seen as areas that will contribute to the growth supply. One is Sable gas, off the eastern shore of Canada. Already 400 million cubic feet per day of gas is flowing, with some estimates predicting an increase to 1 billion cubic feet per day by the end of the decade.

The other new source is the Arctic. The Mackenzie Delta, on Canada's Arctic shoreline, has reserves that can produce 2.5 billion cubic feet per day, and the north shore of Alaska can produce up to 4 billion per day.

Proponents are proposing a variety of projects for different pipeline routes and capacities, with gas expected to start flowing in the 2006-07 time frame.

On the Ground, as in the Air

Since the birth of the modern gas turbine in 1939, aviation propulsion has come to be dominated by the gas turbine in the form of the jet engine. Now, through the market forces brought on by industry deregulation and environmental regulations, the gas turbine is becoming the prime mover for electrical power production.

Jet engine reliability has long been a critical concern to ensure that we have safe air travel. Gas turbines, now in a new role as the primary means of electric power generation, will have to meet similar levels of reliability. The cost to a business or a hospital subjected to electric power interruptions or voltage sags or surges can be huge.

Extreme reliability of electrical supply is the new paradigm for our digital economy. Power system reliabilities are now being demanded that are in the "high nines." A "six-nines" system is one with a 99.9999 percent reliability, which means no more than one electrical power interruption for 32 seconds within one year. A nine-nines system would allow for no more than a 0.032-second interruption during a year.

Economic and social forces will increasingly demand high-quality and extremely reliable electric power gas turbines. Thus, research and development activity, which has always been strong for jet engines, will become—and remain—important to the electric power gas turbine industry for years to come.

This article was adapted from another published in the International Gas Turbine Institute's 2001 Technology Report & Product Directory — Land, Sea & Air.

Lee Langston is professor of mechanical engineering at the University of Connecticut in Storrs and editor-elect of the ASME Journal of Engineering for Gas Turbines and Power.

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