By Russell Ray, Chief Editor
|The SGT-8000H gas turbine rotor shown here is being transported to the assembly stand at the Lausward combined cycle power plant in Düsseldorf, Germany. Photo courtesy: Siemens|
In the U.S., coal-fired power plants are being converted to burn natural gas; peaking plants are being retrofitted with gas-fired combined cycle systems; and a meaningful share of new power projects in the U.S. are being fueled with cleaner-burning natural gas.
Nearly one third of all electricity in the U.S. is now generated by natural gas. In 2016, natural gas is expected to overtake coal as the nation’s leading source of power generation. as natural gas prices are projected to remain at or below $5 per million British thermal units (Btu) for the next 24 years, according to data from the U.S. Energy Information Administration (EIA).
“Natural gas use for power generation reached a record high in 2015 and is expected to be high in 2016 as well, likely surpassing coal on an annual average basis,” EIA said.
Nearly 19,000 MW of power generation fueled with natural gas is expected to be built and commissioned between 2016 and 2018 in the U.S. Not surprisingly, more than half of that capacity (52 percent) is being built near shale formations containing prolific amounts of low-priced natural gas.
The transition to more gas-fired generation stems from abundant supplies of low-priced gas, stricter emission standards for coal-fired power plants, and the rapid growth of generation produced with intermittent renewable resources such as wind and solar.
Last year, renewable resources accounted for almost two thirds (63.85 percent) of new generation placed into service in the U.S. This means gas-fired plants must be faster and more flexible to effectively offset the inherent fluctuations of renewable power. In addition to speed and flexibility, superb fuel efficiency is essential of any new or modified gas-fired plant, as power producers face flat or declining demand for electricity for the foreseeable future.
To meet these needs, the industry’s three major gas turbine manufacturers – GE Power, Siemens, and Mitsubishi Hitachi Power Systems – have launched some innovative gas turbine designs that are faster, more efficient, more flexible, and more durable than the designs of a decade ago, when combined cycle efficiencies hovered below 50 percent.
Today’s heavy-duty gas turbines, in combined-cycle mode, are more than 60-percent fuel efficient, thanks to better materials capable of withstanding higher firing temperatures, improved blade designs and advanced cooling technologies, among other things.
“Based on the fundamental laws of thermodynamics, increasing the temperature of the cycle is the primary way to increase the cycle effeciency,” said David McDeed, gas turbines product manager at Mitsubishi Hitachi Power Systems Americas. “This is possible thanks to enhanced cooling schemes and application of thermal barrier coatings, among others. There is room for improvement, but the rate of efficiency increase is trending asymptotically toward a hard limit.”
Meanwhile, the global market for gas turbines used in power generation is expected to grow 3 percent a year until 2020, according to a report released last month by research firm Technavio. If the U.S. Clean Power Plan survives opposition and is implemented, the amount of U.S. generation produced with natural gas should rise from 27 percent in 2015 to 33 percent in 2020, the report showed.
This year, revenues from gas turbine sales are projected to be around $18 billion, according to a report from research firm GlobalData. In 2017, that number is expected to drop to less than $17 billion, and by 2020, the market will stabilize at around $5.6 billion, the company said.
“Although China will still heavily rely on coal, many countries are decommissioning coal-fired power plants and encouraging the use of cleaner and more efficient fuels for power generation, such as natural gas, in order to reduce carbon emissions and achieve climate targets,” said Siddhartha Raina, GlobalData’s senior analyst covering the power sector.
Barry Nicholls, president of Power & Gas for Siemens USA, said the industry will continue to improve upon the efficiencies of today’s gas turbines, although it will be challenging. “The real challenge is: How do we improve efficiency without trading off other benefits like robustness and flexibility?” Nicholls said.
Equipped with Siemens’ SGT-8000H gas turbine, the Lausward combined cycle power plant in Düsseldorf, Germany, achieved a net energy conversion efficiency of 61.5 percent earlier this year. The higher efficiency reduces carbon dioxide emissions by a theoretical 2.5 million tons annually, Siemens said. In addition, the unit achieved a net output of 603.8 MW. Siemens has sold 76 H-class gas turbines worldwide.
“The SGT-8000H achieves a very high degree of efficiency and is marked by short startup times and fast load-changing capabilities,” said Theo Maas, head of Large Gas Turbines and Generators in Siemens’ Power and Gas Division. “The turbines have proven themselves extensively in daily power plant operation after more than 200,000 hours of operation: The reliability of the SGT-8000H fleet is over 99 percent, and availability is over 96 percent.”
Siemens’ H-class turbine was introduced to the market in 2010. It has a gross power output of 296 MW. Twenty-four of these turbines are being installed in the Beni Suef, Burullus and New Capital power plants in Egypt.
Last month, GE Power said its H-class gas turbines are expected to generate more than $100 billion in revenue over time. The new air-cooled turbines can reach full capacity in less than 30 minutes, and can deliver 61.4 percent net fuel efficiency in combined cycle operation.
“Our plan around the H is to take this from 61 to 65 percent efficiency,” said Joe Mastrangelo, president and chief executive officer of Gas Power Systems at GE Power.
|GE Power’s 9HA gas turbine. Photo courtesy: GE Power|
In addition to higher firing temperatures and bigger turbines, the use of additive manufacturing, or 3D printing, will play an important role in achieving further improvements in net fuel efficiency, Mastrangelo said.
Gas turbine components manufactured in 3D printers “allow us to put tighter and more complex geometries into the fuel flow and the air flow of these parts, which allows you to increase efficiency,” he said. “We’re seeing more opportunities to bring that into our combustion technology.”
GE’s H-class turbines can be turned down to less than 40 percent output and still operate in low-emissions mode. The turbines’ turndown capabilities and rapid response times translate to significant savings for power producers. But the fuel conversion rate of 61.4 percent, in combined cycle mode, is perhaps the most impressive feature.
The high levels of fuel efficiency and flexibility have captured the industry’s attention. In addition, construction time of the 7HA turbine is greatly reduced because of the machine’s modular structure, and the removal and replacement of turbine blades are easier thanks to a removable turbine roof.
Exelon Corp. was the first U.S. power producer to buy the new air-cooled turbines for two combined-cycle power projects in Texas. Each plant will feature two 7HA.02 gas turbines, which will accommodate the state’s growing supply of renewable power by maintaining better balance between supply and demand.
Mastrangelo said GE Power has received 39 orders for its new HA air-cooled gas turbines. What’s more, the HA turbine has been “technically selected” for more than 90 new gas-fired units worldwide, he said. A tech-selection means the unit will use GE’s technology if it is commissioned and constructed. GE expects the vast majority of those tech-selections will lead to real contracts with power producers.
While GE’s 9HA.01 and 9HA.02 gas turbines cover the 50 Hz market, the company’s 7HA.01 and 7HA.02 turbines serve the 60 Hz market. The 9HA.01 is rated at 397 MW and the 9HA.02 is rated at 510 MW in a simple-cycle configuration, with each offering more than 41 percent efficiency.
In a 1-on-1 combined-cycle configuration, the 9HA.01 is rated at 592 MW and the 9HA.02 is rated at 755 MW, with each offering more than 61 percent efficiency. The 7HA.01 is rated 275 MW and the 7HA.02 is rated 337 MW in a simple-cycle configuration, with each offering more than 41 percent efficiency. In a 1-on-1 combined-cycle configuration, the 7HA.01 is rated 405 MW and the 7HA.02 is rated 486 MW, with each offering more than 61 percent efficiency. Together, the 9HA and 7HA turbines can cover a wide power range of 275 MW to 510 MW in simple-cycle configuration.
Mitsubishi Hitachi Power Systems
In April, Mitsubishi Hitachi Power Systems Americas (MHPSA) said it had received orders for two M501J gas turbines from Nebraska-based Tenaska. The two 327-MW turbines and associated generators will be used at the Westmoreland Generating Station in South Huntington Township, Pennsylvania.
Mitsubishi Hitachi Power Systems’ M501J gas turbine. Photo courtesy: MHPS
The J-Series gas turbine is also being used at a new combined cycle plant under construction at the Grand River Energy Center in Chouteau, Oklahoma. The turbine arrived in Oklahoma in February and is the first such turbine in the Western Hemisphere.
In commercial operation since 2011, J-series turbines approach 62-percent efficiency in combined-cycle operation, and maintain greater than 99-percent reliability.
“The M501J is the most advanced gas turbine currently in operation,” said David McDeed, product manager for gas turbines at MHPSA. “This level of reliability is better than the well-established F-class technology that has been around for the past three decades.”
McDeed said the company has received 45 orders for J-series gas turbines worldwide. Nineteen of these units are in commercial operation with collective actual operating hours exceeding 240,000.
The M501J turbine has an ISO base rating of 327 MW in simple-cycle operation, and a rated rotor speed of 3,600 RPM. Weighing in at about 320 tons, the 60-Hz machine has a ramp rate of 40 MW per minute, and a startup time of about 30 minutes. In a 1-on-1 combined-cycle configuration, the turbine delivers 470 MW, with efficiency approaching 62 percent. The new J-Series technology fires at an inlet temperature of 2,912 degrees F, about 100 degrees hotter than its G-Series predecessor.