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American Electric Power: Producing Electricity More Efficiently


North America’s first ultra-supercritical (USC) electricity generating unit went into service near Fulton, Arkansas in 2012. The 600 megawatt coal-fired plant was built over a period of four years, in compliance with stringent state and federal environmental standards, at a cost of $1.8 billion.

Operated by Southwestern Electric Power Company, a division of American Electric Power (AEP), the USC plant is more efficient and cleaner than plants with supercritical (SC) generating units. In recognition of these state-of-the-art qualities, POWER magazine named it the Plant of the Year for 2013.

America’s electricity mix is always evolving. Coal currently accounts for about 39% of U.S. electricity, followed by natural gas at 27%, nuclear power at 19%,and hydro power and renewables, at about 6% each, according to the Energy Information Administration. The agency projects that coal will continue to be the country’s leading source of electricity for a period of time, after which it may be surpassed by natural gas. Nonetheless, for the foreseeable future, coal will be a major source, and it will be important to continue to develop affordable, cleaner ways to generate electricity from coal. Clean coal technology is one approach. Getting more electricity per unit of coal is another.

That is where AEP's Arkansas plant comes in. How does it work? The key is the difference between SC and USC modes. The critical point of water, where vapor and liquid are indistinguishable (and added heat or pressure will not cause a change of state), is 705 degrees Fahrenheit. At the AEP plant, the USC unit operates above 1,100 degrees. Since the water is heated to produce superheated steam without boiling, this leads to a more efficient steam cycle, which reduces fuel consumption, reagent consumption, solid wastes, water use, and operating costs. It is more efficient due to the thermodynamics of hotter, higher-pressure steam through the turbine, making USC the most efficient steam-cycle technology available.

Earlier plants were operated in the SC mode, not the USC mode, because of the unavailability of metals that could withstand such temperatures. Now, recently developed chrome and nickel based alloys are used in the components of the steam generator, turbine, and piping systems, and can perform for long periods of time at the higher temperature conditions. The plant is named for former electricity executive John Turk, Jr. Fuel for the plant is low-sulfur coal from the Powder River Basin in Wyoming.