Can "Ultrasupercritical" Technology Save Coal Power?

January 14, 2014

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It's hard to find many people who don’t think coal-fired power plants’ days in the U.S. are numbered. Coal power is under pressure from a bevy of forces that includes ever-tightening emission restrictions from the U.S. Environmental Protection Agency, encroachment by both renewable energy and natural gas power, and interest groups whose goals include debunking clean coal.

Annual coal consumption from the electric power sector has not topped 1 billion tons since 2008, according to the U.S. Energy Information Administration (EIA), and the number of domestic coal-fired power plants has fallen every year since 2002 except in 2011. The country’s total coal power infrastructure and plants controlled by electric utilities both fell precipitously in 2012. As the natural gas boom continues, the EIA forecasts this energy source to take over as the country’s primary fuel for electric power generation by 2035 in its latest Annual Energy Outlook.

Although there are little signs of a coal power resurgence, a new kind of coal power plant has been operating in Fulton, Ark., since December 2012, after surmounting years of regulatory delays, lawsuits, and other obstacles. The 600-megawatt John W. Turk Jr. Power Plant employs 109 people to run the first facility in the nation that uses ultrasupercritical (USC) coal combustion technology, a method that experts say is cleaner and more efficient than normal pulverized coal plants.

POWER magazine, a power industry publication, recently named the Turk facility its Plant of the Year for 2013, lauding it for its USC boiler technology and “overcoming numerous legal and regulatory obstacles.”

Columbus, Ohio-based utility American Electric Power (AEP), through its subsidiary, Southwestern Electric Power Co. (SWEPCO), opened the plant at a cost of $1.8 billion, which makes it the most expensive project ever built in Arkansas.

As explained by POWER, the main steam pressure at the plant is above the thermodynamic critical point of water (3,208 psi), where water ceases to boil but changes directly from liquid to superheated steam. The plant becomes classified as USC when the main and reheat steam temperature exceeds 600°C (1,112°F), which is much higher than temperatures in conventional subcritical steam plants.

Construction of the plant began in November 2008. The plant was vigorously fought in court by organizations like the Natural Resources Defense Council (NRDC), the Sierra Club, and the National Audubon Society, as well as other local environmental organizations in Arkansas. SWEPCO reached a settlement with the organizations in December 2011.

Is the USC plant better environmentally than traditional coal-fueled plants, and will it impact coal power in the U.S.? There is no definitive answer as of yet, but viewpoints around the debate are heated. AEP declined to comment, with a company spokesperson saying through email that the company has "just been overwhelmed with requests for interviews, plant visits, and other information."

Revis James, director of generation research and development at the Electric Power Research Institute (EPRI), a Palo Alto, Calif.-based nonprofit that studies and researches energy issues, however, said about USC, "This has been worked on for a couple of decades, and it's always promising to look at new technologies and new ways to operate plants." James, an engineer with M.S. and B.S. degrees from the University of California, Berkeley, added, "It's definitely better from an economic standpoint, and from a standpoint of pollution, than traditional coal plants.”

A diagram of ultrasupercritical coal combustion technology. Credit: cenvironment.blogspot.com

A diagram of ultrasupercritical coal combustion technology. Click to enlarge. Credit: cenvironment.blogspot.com

He said USC isn't a rigorously defined term, as it refers more generally to coal plants that operate at higher pressures and temperatures. "The challenge for USC plants is that a lot of the materials used at the high temperatures might not be able to last as long, and the damage of exposure would happen more quickly," James said.

How much of an improvement in efficiency does the USC plant yield? The Turk plant's steam cycle efficiency is 39 to 40 percent, compared with 35 percent for a boiler operating at subcritical steam conditions. Carbon dioxide emissions are also lower, POWER stated: USC technology produces approximately 0.97 tons per megawatt-hour compared with emissions from subcritical plants that average around 1.06 tons/MWh.

"It's economically good (for AEP) because for each ton of coal you burn, more of that energy will be converted to electricity, and you can then sell more electricity," James said. "The other side of that equation is that…you don't have to produce as much pollution; you can burn less coal and still produce the same (amount of) electricity."

"It sounds impressive, but it's still a coal plant," said Sierra Club’s Glen Hooks, a senior representative for the group’s Beyond Coal campaign. Hooks said that beyond regular concerns about coal plants being dirty and inefficient, he worries that coal continues to restrict clean energy choices for consumers. "The market is only so big, and when you force new coal plants on people, it doesn't allow them to explore other forms (of power)."

"A coal boiler is still a coal boiler,” remarked Ilan Levin, an attorney with the Environmental Integrity Project, based in Washington, D.C. “You'll still creating a great amount of hazardous emissions and emitting them into the air."

Based on the published efficiency numbers, USC technology would lower the amount of coal needed to fuel the Turk plant and thus reduce emission levels of not only CO2 but sulfur dioxide, nitrogen oxide, mercury, PM-10 particulate, and fly ash, a coal combustion waste product. The Arkansas facility, which also serves customers in neighboring Louisisana and Texas, is also said to be using state-of-the-art emission control technologies. It raises the possibility of retrofitting current coal-fueled plants with USC, but EPRI’s James said it’s not that simple.

He explained that for existing plants to become USC plants, they would have to put in redesigned boilers and rebuild much of their existing infrastructure -- a process that would cost millions of dollars. This would include advanced metal alloy components in the boiler, turbine, and piping system that can tolerate prolonged high temperatures.

"There's a lot more engineering that goes into a USC, and these technologies are very wide-ranging in efficiency," Paul Bailey, senior vice president for federal affairs and policy at the American Coalition for Clean Coal Energy, noted. "But what people should understand is that a 5 percent efficiency difference is a very big deal."

Still to be determined, as well, is how the USC plant will hold up to new EPA regulations; the agency last week proposed a new CO2 emission limit of 1,100 lb/MWh for coal power plants. While the Turk plant was reportedly built with future regulations in mind, there's no telling what will happen if greenhouse gas limits continue to tighten in coming years. EPA's wording in the new proposal already seems to stack against USC's favor: "Generation technologies representing enhancements in operational efficiency (e.g., supercritical or ultrasupercritical coal-fired boilers) are clearly technically feasible and present little or no incremental cost compared to the types of technologies that some companies are considering for new coal-fired generation capacity. However, they do not provide meaningful reductions in CO2 emissions from new sources."

The editor of POWER magazine, Gail Reitenbach, said in an email that "given low U.S. natural gas prices and uncertainties regarding pending and anticipated federal environmental regulations — especially concerning carbon emissions — the (power) industry consensus seems to be that no new coal plants will be built in the U.S. in the foreseeable future."

So the AEP plant could end up being a one-off, the only facility of its kind. But its ongoing performance is certainly worth following, as the plant still could be a boost for a coal industry that surely needs it.

Top photo credit: powermag.com 
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