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Breaking the Barriers PUBLIC ACCESS

As Gas Turbines are Ever More Widely Used, They are Achieving New Heights of Performance.

[+] Author Notes

Lee S. Langston is an ASME Fellow and professor emeritus of the Mechanical Engineering Department at the University of Connecticut in Storrs. He is a member and a past chair of ASME's International Gas Turbine Institute.

Mechanical Engineering 134(05), 32-37 (May 01, 2012) (6 pages) doi:10.1115/1.2012-MAY-2

Abstract

This article explores the new developments in the field of gas turbines and the recent progress that has been made in the industry. The gas turbine industry has had its ups and downs over the past 20 years, but the production of engines for commercial aircraft has become the source for most of its growth of late. Pratt & Whitney’s recent introduction of its new geared turbofan engine is an example of the primacy of engine technology in aviation. Many advances in commercial aviation gas turbine technology are first developed under military contracts, since jet fighters push their engines to the limit. Distributed generation and cogeneration, where the exhaust heat is used directly, are other frontiers for gas turbines. Work in fluid mechanics, heat transfer, and solid mechanics has led to continued advances in compressor and turbine component performance and life. In addition, gas turbine combustion is constantly being improved through chemical and fluid mechanics research.

Article

The Swedish runner Gunder Hägg set a number of middle-distance running records in the 1940s. In fact, he set the record for the mile run twice in 1942 and once in 1945. During the nine years that Hägg's 1945 record stood, it became something of an obsession for some to see it broken, since, at 4:01.4, it stood tantalizingly close to the four-minute mark.

When finally, in 1954, a 25-year-old medical student named Roger Bannister completed a mile in 3:59.4 at Oxford University's Iffley Road Track, the jubilation was all out of proportion to the two-second improvement. There was worldwide press coverage of the man who broke the four-minute barrier, and Bannister was eventually knighted for his achievement.

We get hung up on round numbers. Auto racing fans cheered in 1977 when Tom Sneva broke the 200-mile-per-hour barrier for a single qualification lap at the Indianapolis Speedway, as did investors when the Dow Industrials blasted through the 10,000 mark in 1999. And 2003. And 2009.

Last year, the gas turbine electric power industry had a consequential barrier broken. For some years, gas turbine combined cycle power plants had been approaching—but never quite reaching—an overall thermal efficiency of 60 percent, which is almost double that of other power plants. On May 19, however, Siemens announced that its new SCC5-8000H gas turbine combined cycle plant at Irsching, Germany, had just reached a thermal efficiency of 60.75 percent with an electrical output of 578 MW. This new record-setting combined cycle power plant, fueled by natural gas, has the world's largest gas turbine, rated at 375 MW (and itself 40 percent efficient), that provides exhaust heat to drive a steam turbine to provide more electrical power.

THE NEW CHAMPION: Siemens's SGT5-8000H, shown during assembly (left), is a 375 MW gas turbine that reached a thermal efficiency of 60.75 percent as part of a combined cycle plant in Irsching, Germany.

Grahic Jump LocationTHE NEW CHAMPION: Siemens's SGT5-8000H, shown during assembly (left), is a 375 MW gas turbine that reached a thermal efficiency of 60.75 percent as part of a combined cycle plant in Irsching, Germany.

To be sure, there was nothing magical about the 60 percent efficiency mark for a heat engine. And it seems likely that manufacturers such as General Electric, Mitsubishi, and Siemens itself will surpass 60.75 percent efficiency as they continue to produce enormous H and J class turbines. But it would have been nice if the record-setting run at Irsching had gotten even a fraction of the hoopla that Bannister received in 1954, especially considering he only ran at about 20 percent efficiency.

The efficiency mark at Irsching wasn’t the only record set this past year in the gas turbine industry. Production values, considered a more accurate benchmark than sales figures, for the industry as a whole were up on an inflation-adjusted measure for the third straight year, and the aviation sector, which accounts for two-thirds of the industry, has never been bigger.

Forecast International in Newtown, Conn., uses computer models and an extensive database to record value of production for both the aviation and non-aviation gas turbine markets. According to analyst Bill Schmalzer of FI, the value of production for all gas turbines was $47.9 billion in 2011, up 10.2 percent from 2010. Currently then, the gas turbine market represents about a $50 billion global business, and FI projects that in 2012 the global industry will surpass the inflation-adjusted peak of $50.47 billion set in 2001, during a short-lived spike in sales of gas turbine generating sets driven by electricity deregulation.

Projecting out to 2016, FI predicts the global market will reach almost $65 billion.

The gas turbine industry has had its ups and downs over the past 20 years, but the production of engines for commercial aircraft has become the source for most of its growth of late. By 2016, commercial aviation is projected to account for nearly $48 billion of the $65 billion in global gas turbine production.

Grahic Jump LocationThe gas turbine industry has had its ups and downs over the past 20 years, but the production of engines for commercial aircraft has become the source for most of its growth of late. By 2016, commercial aviation is projected to account for nearly $48 billion of the $65 billion in global gas turbine production.

The value of production for aviation gas turbines—the jet engines that are the major source of propulsion for military and commercial aircraft—was $32.0 billion, up 16.7 percent from 2010. The largest segment of this market was engines for commercial airliners, of which $26.6 billion worth of gas turbines were produced in 2011.

Forecast International projects that by 2016, the entire aviation market will see a value of production of $47.7 billion, nearly the value of all worldwide gas turbines in 2011. That's a huge jump, but it's not hard to see where they are getting their bullishness. Boeing, in a 2011 forecast of the total commercial airplane market to 2030, estimated that the number of airplanes (currently 19,400) in the worldwide air transport fleet will grow at an annual rate of 3.6 percent over the next 20 years. Such growth would add nearly 20,000 airplanes to the worldwide fleet, and the company's outlook predicts that airplane deliveries, for fleet growth and replacement of aging airplanes, will total 33,500 over the 20-year period with a value of about $4 trillion.

Consider that one rule of thumb is that a quarter of the cost of a commercial airplane goes to its engines, and one can see that this would represent a bonanza to the manufacturers of aviation gas turbines.

The most lucrative market for engine manufacturers is the single-aisle, narrow-body jet airplane. These SANBs (as they are known) are the workhorses of the world's airlines; with a nominal seating capacity from 100 to 210 seats, they are more versatile than their wide-body, jumbo cousins. According to Airbus, for aircraft above 100 seats, 87 percent of all routes flown and 78 percent of all seats offered globally are in singleaisle, narrow-body airplanes.

SANBs such as Boeing's 737 and Airbus's A320 families, powered by twin 30,000-pound-thrust engines from CFM International (a collaboration of General Electric and Snecma) or from International Aero Engines (a collaboration of Pratt & Whitney, Rolls-Royce, MTU, and Japanese Aero Engines Corp.), are ubiquitous. About 7,000 Boeing 737s, introduced in 1969, and about 5,000 Airbus A320s (first produced in 1988) have been delivered.

Now, because of the size of the SANB market and its forecast growth, three other airframe companies are challenging the Boeing/Airbus duopoly. Canada's Bombardier CSeries, China's Comac C919, and Russia's Irkut MS-21 are all new SANB aircraft under development and scheduled for first delivery in or before 2016.

To fend off these challenges, Airbus has begun offering an A320 with a new engine option that promises a 15 percent reduction in fuel consumption and an 8 percent reduction in operating costs. This A320neo will be delivered beginning in 2015, and already there are more than 1,200 on order. Boeing was reluctant at first to follow suit, but last August it launched its own re-engined SANB airplane, the 737 MAX, with first deliveries scheduled for 2017.

This re-engining is happening now because of a combination of high fuel prices and new technology that promises greater efficiency.

Pratt & Whitney's recent introduction of its new geared turbofan engine is an example of the primacy of engine technology in aviation. P&W has been developing this new engine, the PW1000G, since the 1980s. As I detailed in these pages in May 2008, the PW1000G has a hub-mounted planetary gearing system that drives the fan at lower speeds, permitting up to 16 percent fuel savings, higher bypass ratios, and much lower fan noise. Pratt & Whitney's new engine has been adopted on the Bombardier CSeries airplane, one factor that prompted Airbus to introduce the A320neo. It's also featured on the Irkut MS-21 and the new Mitsubishi MRJ regional jet.

In answer to the P&W geared fan engine, CFM International has introduced the LEAP-X (an acronym for Leading Edge Aviation Propulsion) as a successor to its best-selling CFM56 for single-aisle narrow-body jets. The LEAP-X will have a high bypass ratio of 12:1, a higher compression ratio of 22, and significant weight savings, all to yield fuel savings in the 15 to 16 percent range, along with lower noise.

READY FOR CLOSER INSPECTION: Pratt & Whitney's PW1000G promises both fuel savings and less noise.

Grahic Jump LocationREADY FOR CLOSER INSPECTION: Pratt & Whitney's PW1000G promises both fuel savings and less noise.

The LEAP-X will be powering the 737 MAX and the Comac C919. The A320neo will come with either the LEAP-X or the PW1000G.

Many advances in commercial aviation gas turbine technology are first developed under military contracts, since jet fighters push their engines to the limit. But military engines, while profitable, are a small portion of the industry. In 2011 the value of production of military engines was $5.3 billion, down 6.1 percent from the year before.

The biggest story in military aviation last year was the engine for the supersonic Joint Strike Fighter, now known as the F-35 Lightning II. Nine countries are involved with the development of the Pratt & Whitney F135, the most advanced military gas turbine, capable of 40,000 pounds of thrust. Development started more than ten years ago. There are three variations: F-35A for conventional air force operation, the F-35B for short takeoff and vertical landing, and the F-35C for naval carrier operation.

In October, two F-35B aircraft were flown on and off the LMD-class amphibious assault ship Wasp in Hampton Roads sea trials. Videos available on the Internet show the truly impressive F-35B vertical landings on the deck of the assault ship and the gazelle-like takeoffs—all made possible by the F135's separately clutched lift fan and vectored engine exhaust nozzle. During vertical flight, the Rolls-Royce lift fan generates about 20,000 lbt, half of the output of the F135.

An alternative engine for the F-35, the F136, had been developed by General Electric and Rolls-Royce, but faced with calls from budget cutters in Washington for economizing the JSF program, the companies ended their joint program in December.

The other segment of the gas turbine market meets demand in non-aviation uses: Marine power and propulsion for naval and cruise ships, mechanical drive gas turbines that are found driving compressors for natural gas pipelines and for liquefying natural gas, and turbines for generating electricity. That last use is the largest, accounting for some 83 percent of the non-aviation market, but overall that segment was flat with the value of production for nonaviation turbines coming in at $16 billion.

Gas turbines used to generate electricity come in all sizes, from the 2.6 kW IHI Dynajet portable generator to the record-breaking Siemens 340 MW H class machine. The turbine at Irsching weighs 489 tons, more than a fully fueled Airbus A380.

It's hard to know exactly what accounts for Siemens's breakthrough this year, or why in 2003 General Electric's similarly large combined-cycle plant at Baglan Bay, Wales, never broke 60 percent efficiency. (Companies tend not to detail their failures or give away too many secrets of their successes.) But in general, many gas turbine improvements can be chalked up to advanced materials and heat transfer research, which has yielded long-lived film-cooled superalloy turbine blades and vanes. They can operate for tens of thousands of hours in gas path flows at temperatures greatly exceeding alloy melting points. Work in fluid mechanics, heat transfer, and solid mechanics has led to continued advances in compressor and turbine component performance and life. And gas turbine combustion is constantly being improved through chemical and fluid mechanics research.

I also suspect that for this combined-cycle application, Siemens paid special attention to the steam cycle half of the combination.

It's likely that the 60.75 mark set at Irsching won’t be the last word. Mitsubishi Heavy Industries, for instance, is aiming for 64 percent efficiency in its J series turbine, under development, using higher turbine inlet temperatures. A simple calculation shows that if the Brayton (gas) cycle efficiency could be raised to 50 percent—highest now is 46 percent— and a Rankine (steam) cycle to 40 percent, a CCGT could reach 70 percent efficiency.

Whether that would be practical remains to be seen. The gas surging into the American market from shale gas plays has raised the importance of natural gas in the electricity market; already it fuels 22 percent of electricity generated in the United States (and 46 percent in the United Kingdom). The superstar gas turbine combined cycle plants are in the 100 to 600 MW range. But many electric power gas turbines are derived from aviation engines. Called aeroderivatives, they are noted for their ability to start and go to full load quickly, so they can provide backup power in minutes, rather than for their use for baseload power.

A recent addition to this gas turbine family is General Electric's LMS100, derived from the company's CF6 jet engine. (The low compressor is from their 6FA heavy frame gas turbine, making it a hybrid rather than a pure aeroderivative.) That machine has an intercooler between the low and high compressor, the net effect of which results in a 46 percent thermal efficiency (the highest for a simple cycle gas turbine) at an output of 100 MW.

At the Power-Gen trade show in December, Pratt & Whitney announced development of its latest aeroderivative, the FT4000, derived from the PW4000 used on the Airbus A330 and Boeing 777. It will have an output of 60 MW and a thermal efficiency of 41 percent, with a high enough exit temperature to be used in combined cycle configurations.

Distributed generation and cogeneration, where the exhaust heat is used directly, are other frontiers for gas turbines. Microturbines can be found in such places as wastewater treatment plants, hospitals, breweries, and data centers. And they are now being used extensively at gas pipeline compression stations for station electrical power and pipe cathodic protection, and for shale oil and gas drilling rigs, turning flare gas into electricity.

Capstone Turbines, a major player in the microturbine field, has produced close to 7,000 units in the 30 kW to 200 kW range. Turbines such as these have thermal efficiencies of between 26 percent and 33 percent; using the available exhaust heat for thermal applications raises the efficiency calculation even higher. A cleverly designed co-gen plant, such as the 25 MW one we have at the University of Connecticut in Storrs, can use almost every unit of available energy from the supplied natural gas.

Distributed power has another advantage: during two storms in 2011, the campus had full power when much of the state was black. The State of Connecticut is now looking into the possibility of having more independent cogeneration plants scattered across the state to abate the effects of future grid blackouts.

Unlike records for athletic achievements, which are pursued for their own sake, efficiency improvements have the added benefit of providing something of value to the rest of humankind. No matter how much gas can be extracted from the shale plays found under various parts of the world, it makes sense to use this energy source as wisely as possible. And the surest way to conserve valuable energy resources is to increase the thermal efficiency of energy converters.

READY TO JUMP: One variant of the F-35 is capable of gazelle-like takeoffs and vertical landings, thanks to its engine's separately clutched lift fan and vectored exhaust nozzle.

Grahic Jump LocationREADY TO JUMP: One variant of the F-35 is capable of gazelle-like takeoffs and vertical landings, thanks to its engine's separately clutched lift fan and vectored exhaust nozzle.

Since their beginnings in 1939 as the youngest of prime movers, the gas turbines on aircraft, in power plants, and elsewhere have gone from efficiencies of 18 percent to the 40 to 60 percent levels now achieved. Maybe raising those levels even higher won’t provide cause for general hoopla, but it will provide the means by which we can do more and use less.

Copyright © 2012 by ASME
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