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Lessons From Lodi

New turbine technologies offer unprecedented flexibility.

Fortnightly Magazine - April 2010

9 ppm. With the installation of SCR and CO 2 catalysts, stack emissions compliance can be reached in about 30 minutes.

“You can get 10 to 30 MW a minute from a large industrial gas turbine,” Wilson says. “With the more traditional combined-cycle plants, the HRSG/steam turbine cycle limits the gas turbine to a much slower rate. So with the Lodi project, we’ve designed the steam cycle with enough flexibility to accommodate the gas turbine.”

Though the GT24 has been around for more than a decade, Alstom’s Meier says its dual combustor design always has been ideally suited to cycling duty. For example, he says, the turbine can maintain low load operations on only one of the two combustor stages. The turbine still delivers enough heat to keep the water-steam cycle, including the HRSG and steam turbine operating, allowing the combined cycle to be turned down as low as 20 percent, while still meeting emissions requirements.

“In today’s energy markets customers need a plant that can react quickly to take advantage of the most profitable hours in the market,” he says. “With our integrated combined-cycle concept, we can reach full system output in less than 50 minutes, compared to the traditional 60 to 90 minutes.”

If necessary, he adds, the system’s HRSG can be fitted with additional gas burners to quickly provide additional output, if and when it’s necessary. “If you need more power, you ignite the supplementary burners. In that case, the overall system efficiency declines, but you can boost the output,” he says.

O&M Squeeze

OEMs are adding such flexibility to their plant designs because they expect natural gas to play an increasing role across various load profiles, from peaking to base load operations. This reliance on gas is driven, in part, by the expansion of unconventional gas sources ( See “ Gas Market Outlook ). According to a report released last year by the Colorado School of Mines, the country’s natural gas reserves estimates rose to 2,074 trillion cubic feet in 2008, up from 1,532 trillion cubic feet in 2006. With this supply increase due in particular to new domestic shale gas opportunities, the availability of natural gas appears stable.

At the same time, however, OEMs understand uncertainties affecting gas sources—including imported liquefied natural gas (LNG)—and they’ve taken steps also to address potential fuel composition issues, should they arise. Each company says its machines will adjust automatically to changes in chemical composition—as opposed to shutting the unit down to address burner components and settings—if a large amount of regasified LNG enters the system, for example.

OEMs also have applied newer, more protective coatings to extend the operating life of key internals, particularly those exposed to the higher operating temperatures in the hot gas path; such high temperatures are needed to increase unit output and efficiency. Further, they have established remote, 24-7 diagnostics phone centers with trained technicians using Web-enabled technology to help resolve operations issues if or when they arise.

In a somewhat novel approach, Alstom has begun offering a GT24 MXL upgrade package that allows plant operators to