U.S. combined-cycle power plants with duct firing capability ran at a higher average capacity factor (59%) than plants without (47%) in 2020, according to a recent report from the U.S. Energy Information Administration (EIA).

Overall, the combined-cycle fleet ran at a 56% capacity factor, the metric for how often a plant runs at maximum power.

The EIA noted most of the country’s combined-cycle power plants have duct burners that help them make additional use of combustion turbine exhaust gases.

Combined-cycle power plants make up 278 GW of the United States’ electricity generation. About 75% (208 GW) have duct burners located between the combustion and steam turbine components, allowing them to burn additional fuel to heat the combustion turbine’s exhaust gases.

This, in turn, can allow these plants to increase steam production at reduced turbine loads and exhaust gases or in a wider range of conditions, especially in the summer.

Whether a plant makes use of its duct burners depends on a variety of factors such as electricity market price, emissions regulations, and the need for operational optimization and ramping, according to the EIA. Duct firing has associated costs, such as fuel expense, maintenance, increased emissions, and lower fuel efficiency.

Most regions have more capacity from combined-cycle plants with duct burners than without, according to the agency. The mid-Atlantic region, which includes the PJM Interconnection, has the largest amount of combined-cycle capacity, at 52 GW, and 81% of the combined-cycle capacity in that region has duct burners.

In both Florida and New England, a relatively low percentage of combined-cycle capacity has duct burners, the EIA said.

However, those two areas also have larger shares of fuel-switchable combined-cycle capacity, which allow operators to switch fuels based on market conditions, like when one becomes limited or expensive.

The EIA collects duct burner data in its Annual Electric Generator Report and Power Plant Operations Report surveys.

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