|The 625-MW L.V. Sutton combined-cycle natural gas plant began commercial operation in November 2013.|
|By Justin Martino, J.D., Associate editor|
As utilities aim to modernize their generation fleet to cut emissions and increase efficiency, one method is to replace older assets with modern assets. Duke Energy chose to do this with its $600 million L.V. Sutton combined-cycle natural gas plant, a 625-MW facility that replaces a retired 575-MW coal-fired plant at the same site.
The natural gas-fired turbines at the site began commercial operation in November 2013.
The first coal-fired unit at the Sutton site began operating in 1954, with additional units added in 1955 and 1972. The three coal-fired units were retired in 2013 as their generation was replaced by the new natural gas-fired units.
Replacing older facilities with new assets has been a major aspect of Duke’s efforts recently.
|The coal units at the site were retired in 2013, and their generation has been more than replaced by the capacity of the new gas-fired units.|
Inside the plant
The plant was built by Kiewit Power Engineers and The Industrial Co. It uses two dual-fuel Siemens combustion turbines. The exhausted heat from the turbines is captured by two Vogt triple-pressure reheat heat recovery steam generators, which heat water inside a series of tubes to produce steam. Gas burners increase the steam temperature.
The plant uses a selective catalytic reduction (SCR) system, which reduces NOx from the combustion process, while an oxidation catalyst removes most of the CO and volatile organic compounds produced.
Each gas turbine has a common exhaust stack and a bypass stack that is only used when the HRSG is not in use. After going through the SCR system, the remaining flue gas is channeled through one of two 195-foot exhaust stacks. Plant workers monitor emissions to ensure air quality regulations are being met.
The steam produced by the plant turns a Toshiba steam turbine that produces an additional 265 MW. This turbine generator uses steam from the HRSGs to produce electricity, which increases plant efficiency.
The plant can go from cold shutdown to full capacity in about four hours, and can ramp up and down or run 24 hours a day.
Building the plant involved almost 35,000 cubic yards of concrete, more than 295 miles of electrical cable, more than 1,800 tons of structural steel and more than 180,000 linear feet of underground and aboveground pipe.
|The Sutton gas-fired plant uses two dual-fuel Siemens combustion turbines, which send heat to two Vogt triple pressure heat recovery steam generators. Photo courtesy of Siemens.|
The plant’s SCR system to remove NOx from the combustion process, and a oxidation catalyst removes most of the CO and volatile organic compounds produced by the plant.
The technology and firing natural gas has resulted in significantly lower emissions than the coal plant it replaced while increasing overall generation capacity by 50 MW. Compared to the coal-fired units on the site, the gas-fired units reduce SO2 by 99 percent, NOx by 97 percent and CO2 by 41 percent.
“We continue to transform our power plant fleet while maintaining our focus on generating electricity that is both reliable and affordable,” Sutton Plant Manager Allen Clare said when the facility went online. “Our new natural gas plant is another stride forward in meeting customer needs using highly efficient, increasingly clean energy sources.”
Challenges in building the Sutton plant
One of the challenges facing the construction of the Sutton plant was placing it on the same site as the coal-fired units that are replaced.
“The Sutton site presents one specific unique challenge – a small footprint,” said Catherine Butler, associate communications consultant for Duke..
The coal and natural gas plant sit in close proximity to each other, which presented challenges during the construction phase of the plant. The challenge presented by the small footprint at the site will continue as the company moves forward.
“As we begin the decommissioning and demolition of the retired coal units, we will face similar challenges due to the limited space at the site,” Butler said.
A trend of clean energy
The construction of the Sutton plant continues a long-term Duke strategy of reducing emissions and modernizing its fleet.
“Duke Energy invested $9 billion in the last decade in building some of the cleanest natural gas and coal plants possible today, with high efficiency and start of the art emissions controls,” Butler said. “This allows the company to retire nearly 6,800 MW of older coal and large oil-fired units. Nearly 6,300 MW of the capacity we’ll retire is coal, which represents 25 percent of our coal fleet. By the end of 2013, Duke Energy retired more than 3,800 MW of this older coal capacity, including the Sutton plant.”
The company added five natural gas-fired plants within a two-year period, replacing some of its coal-fired generation with 2,760 MW of new generation through moderinzation projects.
Other recent projects that reduce emissions in the Duke generation fleet while maintaining generation capacity include the Cliffside modernization project, which retired several older units while equipping another unit with modern emissions control technology and building a new supercritical unit; the 618-MW Edwardsport Integrated Gasification Combined Cycle plant; replacing the 276-MW coal-fired Dan River Steam Station with the 620-MW Dan River Combined Cycle Station and the construction of the 920-MW H.F. Lee Plant.
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