Electrically Charged

mechanical engineering power 2002

electrically charged

Demand from new power plants drives gas turbines into another record year.

By Lee Langston

Gas turbine history was made during the calendar year 2001. The value of gas turbines produced worldwide during the year—both aviation and non-aviation combined—reached an all-time high, just short of $50 billion. This figure exceeds the annual sales of all but the top 35 businesses in the world, and the value of the manufacturing output of many countries. The gas turbine industry has come a long way since its beginnings in 1939.

Gas turbines produced in 2001 spanned a wide range of capacities. For instance, microturbines weighing little more than 100 pounds, or about 45 kg, were produced in the 25-kW range to provide electrical power and heat for fast-food restaurants. At the other extreme, base load electric power gas turbines with power ratings to 250 megawatts and weighing as much as 300 metric tons, were shipped and installed in 2001. Many will drive electric generators and, at the same time, supply heat for steam turbines in combined-cycle operations with thermal efficiencies that will approach 60 percent.

As the engineer's most versatile energy converters, gas turbines producing thrust power continued in 2001 to propel most of the world's aircraft, both military and commercial. The largest commercial jet engines today can produce as much as 120,000 pounds thrust, or some 534,000 newtons.

Lockheed Martin's concept demonstrator for the Joint Strike Fighter in hover flight.

The 2001 value of gas turbines produced for shaft power applications—for electrical power, ship propulsion, and natural gas pipeline compression—exceeded that of aviation applications, and by an unprecedentedly wide margin.

Robert Post, a technology historian, has pointed out that "invention is the mother of necessity"—not the other way around. No one foresaw the impact or the utility of telephones, cars, or television when they were invented.

Once people began to make use of them, they came to believe the products were invented for important reasons, whereas in reality the necessities arose from the use of
the invented device. The same can be said of the gas turbine, as its applications become wider and more prevalent in our society.

Gas Turbine Production Values

According to a market analysis firm, Forecast International Inc. of Newtown, Conn., the value of production of all gas turbines in 2001 totaled $47.9 billion worldwide. The total is an 18 percent increase from $40.6 billion in 2000 (which, in turn, was up 18 percent from 1999).

Forecast International considers the value of production figures for gas turbines more accurate and timely indicators of demand than estimates of gas turbine original equipment manufacturers' sales.

Until recently, jet engines had dominated the gas turbine marketplace ever since the technology was developed, in 1939. As has been pointed out in previous articles over the past few years, gas turbines for non-aviation work have been gaining market share.

In 2001, the value of electric power turbines surged ahead of the aviation sector for the first time. The two areas were about equal in 2000, but last year electric power turbines exceeded jet engines by $7 billion.

The value of production for non-aviation gas turbines, the fastest growing segment of the industry, was $28.0 billion in 2001, up 34 percent from $20.9 billion in 2000, and represented 59 percent of the total gas turbine market (up from 52 percent in 2000).

Electric power gas turbines are the big players in the category. They represent 96 percent of the non-aviation market and 56 percent of the total 2001 gas turbine market. Their value of production totaled $26.9 billion last year, an increase of 34 percent from $20.1 billion in 2000.

This tremendous growth has been aided by the deregulation (also called privatization and liberalization) of electricity markets around the world, but particularly in the United States. Almost all of the new electric power plants being constructed to serve the new deregulated electricity markets are gas turbine-powered, fueled largely by natural gas.

During 2001, new electric power gas turbines with lean premixed combustion systems continued to experience serious system pressure oscillations in operation. The degree of difficulty caused by this problem varies considerably from one manufacturer to another, as all strive to meet lower NO_x emission regulations.

These system pressure oscillations, brought about by combustion mechanisms not yet fully understood, have been given descriptive names ranging from humming to hooting, screech, chub, buzz, and rumble. Last year, manufacturers took a number of paths to deal with these combustion-induced pressure oscillations, such as the use of catalysis, resonators, fuel schedule tuning, active control, and simply cutting back on power output levels. Work will continue through the coming year to solve this widespread problem.

An article discussing what is understood about the phenomenon and questions that still remain to be answered is also in this issue ("That Elusive Hum").

The value of mechanical drive gas turbines in 2001 was $700 million, up from $500 million in 2000, for an increase of about 40 percent. Increases in the value of production can be expected in the future, coming from natural gas pipeline compression and vehicular applications.

Gas-driven Plants Surge

More natural gas pipeline capacity will be added to feed the surge in gas-driven electric power plants that have been coming online in the United States and other parts of the world. Also, a new General Electric/Honeywell gas turbine, rated at 1,118 kW, will be produced in the coming years to power the U.S. Army's M1A2 Abrams main battle tank and the Crusader next-generation armored and supply vehicles.

Marine gas turbines showed about a 33 percent increase, to $400 million last year, from $300 million in 2000. Part of this growth comes from the cruise ship industry, which has some 50 ships on order (worth about $17 billion to $18 billion).

Many of them will be fully or partly powered by gas turbines.
In 2001, Celebrity Cruises' gas turbine-powered ship Millennium went into service. In the near future, several gas turbine-powered cruise ships will enter service. They include four Vesta class ships for Holland America Line, four others for Princess Cruises, and the Queen Mary 2 for Cunard Line.

Rolls-Royce announced last year that it will supply
recuperated, intercooled gas turbines to power Type 45 destroyers for the British Royal Navy.

The value of aviation gas turbines produced in 2001 remained fairly constant at $19.9 billion, representing an increase of one percent over the previous year's total of $19.7 billion. Aviation engines accounted for 41 percent of the total market for gas turbines last year.

The civil aviation market, which represents 88 percent of the 2001 aviation total, came to $17.5 billion, a slight increase of 2.3 percent, over the 2000 total of $17.1 billion. Both major airframe companies (Airbus and Boeing) had large backlogs during 2001, but deliveries slowed because of a depressed air travel market, especially after the terrorist attack on the United States on September 11.

Military Contracts

The value of production of military aviation gas turbines was $2.4 billion for 2001, showing a decrease of about 8 percent from $2.6 billion in 2000. This segment of the gas turbine market has remained flat since at least 1998, but can be expected to increase in the future.

In October 2001, the Joint Strike Fighter downselect took place, with Pratt & Whitney selected to supply engines for this unique multirole Mach 1.5-plus Lockheed Martin fighter. JSF is the most significant program of its kind in the foreseeable future. Pratt estimates its contract with Lockheed to be worth more than $4 billion over the coming years.

Another major military engine contract that was in the works during 2001 would bring about the replacement of the current turbofans in the U.S. Air Force's fleet of giant four-engine C-5 Galaxy transport aircraft with new General Electric turbofans.

Gas turbine production and usage topped all records during 2001. For the last 40 years, the gas turbine as a jet engine has dominated aircraft propulsion. The gas turbine is now becoming the prime mover for electric power generation, both in simple cycle and in combined-cycle operation. At the lowest end of the electric power spectrum, the microturbine, if successful, may be creating a niche of its own in the distributed electric power arena.

A reactor's pebble bed holds some 370,000 tennis-ball-size spheres.

The gas turbine may come to be used in a new, commercially promising closed-cycle configuration. A South African company has been working on plans to build and test a prototype of a closed-cycle electric power gas turbine, which uses helium gas as the working fluid and a helium-cooled nuclear reactor to provide heat to power the cycle. The company, Pebble Bed Modular Reactor (Pty) Ltd., is owned by Eskom, the South African state electric utility, together with British Nuclear Fuels, Exelon (a large U.S. electric utility), and the South African government. The gas turbine-nuclear reactor power plant, called PBMR, is to have an output of about 120 MW, with the first test planned for later this year.

In the PBMR unit, after helium gas leaves the turbine compressor, it passes through the nuclear reactor to be heated (as it would in the combustor of an open-cycle gas turbine). The nuclear fuel is contained in 5-cm-diameter graphite spheres—called "pebbles"—each about the size of a rather heavy tennis ball (0.21 kg). The pebbles, some 370,000 of them, are packed into the reactor pressure vessel, and transfer heat to helium flowing through the bed. The heat comes from nuclear reactions going on in 15,000 tiny microspheres (called kernels) of uranium dioxide dispersed in the pebble and individually encased in protective layers of carbon and silicon carbide.

The pebble bed reactor has a negative temperature coefficient of reactivity. Should the coolant flow of helium cease, the reactor core temperature will increase, but as that occurs, reactivity will decrease. As fissioning rate decreases, so does heat generation, causing reactor temperature to fall. Thus, the reactor will not run away, as was the case at Chernobyl.

Design studies and calculations predict that with a recuperator, a precooler, and an intercooler, the thermal efficiency of the PBMR should be about 40 percent, with a capital cost of about $1,300 per kilowatt. A conventional boiling water reactor nuclear power plant costs $2,000/kW or higher, and a simple-cycle gas turbine plant fueled by natural gas is about $400/kW. The PBMR turbine inlet temperature level is modest at 900°C (1,652°F), and the compression ratio is fairly low at about 3:1.

Since the invention of the gas turbine in 1939, closed-
cycle applications have been few, and each presents its own set of design challenges. For example, because the working fluid is not constantly renewed (as occurs with a jet engine operating in the atmosphere) oil leakage from bearing compartments cannot be tolerated, since oil borne in gas path flow will quickly foul critical heat exchange surfaces (for example, the pebbles mentioned above and the regenerator), degrading engine performance. Thus, the use of gas bearings or electromagnetic bearings are a necessary consideration for closed-cycle applications.

If the PBMR power plant proves to be commercially viable, it would have a number of advantages over existing nuclear power plants (which currently provide about 17 percent of the world's electrical power generation) and over hydrocarbon fueled plants. A PBMR power plant is inherently safe because no danger comes about if coolant shutdown occurs. It also has nuclear fuel in a form that is terrorist-proof because it can't be made into a bomb, has no exhaust emissions, and is of a size that would fit distributed generation needs. Typically, conventional nuclear plants (which are centrally located and are in the thousands of megawatts) take a decade or more to construct. A PBMR plant should require only two years (or less), with much lower capital costs.

If the PBMR is successful, the gas turbine may be the key to yet another energy conversion device, as it has been with record-setting numbers of combined-cycle plants installed worldwide.

This article is based on excerpts from IGTI Gas Turbine Industry Overview-2002 Edition, which is available for online purchase in downloadable PDF form from the International Gas Turbine Institute of The American Society of Mechanical Engineers at www.asme.org/igti/.

Lee S. Langston, a professor of mechanical engineering at the University of Connecticut in Storrs, is the editor of ASME's Journal of Engineering for Gas Turbines and Power.