Gas-fired combustor upgrades offer flexible counterpart to high renewable output

In a world where solar and wind energy are commanding a bigger piece of the global power generation puzzle, some renewable purists certainly think of natural gas as a piece of the retreating past.

In reality, the growing need for flexible and responsive generation to intemittencies might make it a sustainable fit.

Perfect, that is, if you have the right technologies to make utility-scale gas-fired generation behave more like on-site power in the big picture. The key question in many renewable-happy locales is not how much capacity can gas gen-sets give me, but how fast can they ramp up and how low can they go down without shutting off?

“Regardless of the energy mix, we are seeing inevitable trends of decarbonization and renewables causing increased volatility across the world,” Alexander Pistner, senior product manager for GE Power, said in an interview with Power Engineering. “We’re seeing people ask for flexibility.”

These people are utilities and independent system operators (ISO). Early next year, GE is installing a combustor solution for its 7F gas turbine in the Southern California Public Power Authority territory. The DLN2.6+Flex upgrade solution will go into SCPPA’s Magnolia Power Plant operated  by Burbank Water and Power.

These type of combustor upgrades are not new to GE and the industry, but Pistner believes this is ideal to the type of challenges faced by California utilities, working in a state which is embracing rooftop and utiltiy-scale and, thus, is at the mercy of the dreaded “duck curve” in which demand and supply often contradict each other.

“Essentially they always have to be on,” Pistner said of generation units such as at Magnolia.

They have to support demand increases in the evening, when customers come home and begin using appliances even though the sun is waning. At the same time, even in the solar-intense daytime simply shutting down and then turning on a conventional power plant is expensive and wasteful from an emissions and fuel-burn perspective.

Traditionally, these units are at “between 25 and 40 percent at minimum load,” Pistner noted. “By being able to go 20 points lower in load, they can save fuel and emissions in the equivalent of thousands of cars per year.”

Flexible gas-fired generation may be the complementary solution to renewable fluctuations as much or more than energy storage, gen-set supporters say. Natural gas does emit, but it’s offers nearly baseload-type security and about half of the carbon output of coal.

“I do see renewables and gas as complementary technologies,” Pistner said. “I don’t see them as competitors.”

He would not speak to the specific characteristics of the Burbank Maginolia plant, but the typical GE 7F fleet may run at 280 MW full load in a 1-on-1 combined-cycle plant with a current minmum load of about 150 MW. If a combustor upgrade can help that minimum down to 100 MW, it can save a plant like Magnolia about $1 million in annual fuel costs.

Power plants in Europe began embracing the flexible conventional solutions years ago. And this is not GE’s first Flex combustor solution, having rolled out products for the 7HA and three other turbine models. Newer models already have the DLN (for dry low NOx) solution built in.

The technology injects fuel further downteam in the combustion chamber and allows it to run effectively at a lower level. The DLN2.6+ combustor will be combined with Axial Fuel Staging technology on the 7F at Magnolia, according to GE.

Many on-site power gen-set manufacturers are also using large-scale gas-fired gen-sets in strategic locations to balance out areas of high wind and/or solar market penetration. Different ISOs have different needs and requirements, but GE’s Pistner sees that variability as a positive.

“We’re at an exciting point, where some assumptions about power generation are being challenged,” he said.

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Gas-fired Turbines and Plants, On-site Power and Optimizing Plant Performance are all unique content tracks offering sessions at POWERGEN International happening Nov. 19-21 in New Orleans. Registration is open and discounts are available for power generators such as utilities.



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