New coal-fired generating plants are not showing up in the U.S. Elderly plants are retiring in large numbers. But other parts of the world continue to develop coal generation. Advances in combustion and emissions cleanup are part of the reason.
Battered in the U.S., coal is holding its own in the rest of the world. That’s the finding in the latest BP Statistical Review of World Energy, a highly-regarded annual assessment of global energy. BP analyst Spencer Dale said, “Coal consumption increased by 25 million tonnes of oil equivalent (mtoe) since 2013. Consumption growth was driven largely by India (18 mtoe), with China consumption also up slightly (4 mtoe) following three successive annual declines during 2014–2016.”
While burning coal to generate power has well-known environmental issues—conventional pollutants such as sulfur dioxide, oxides of nitrogen, and mercury, as well as new concerns about carbon dioxide and global warming—advanced coal technologies, both on the combustion side and with emissions controls, suggest that coal-fired generation is far from doomed.
Ultrasupercritical and CFB Technology
In much of the world, including most of Asia, advanced coal technologies—ultrasupercritical combustion, circulating fluidized bed (CFB) combustion, and coal gasification—have been the focus. In the U.S. and much of the developed world, the target for advanced coal has been removing CO 2 from flue gas, either from conventional technology or coal gasification.
Ultrasupercritical and CFB technologies also play a role in reducing CO2 emissions. They increase the efficiency of the plant, meaning more power for a given amount of coal. The U.S. focus on carbon capture (and storage either for use in enhanced oil recovery, or sequestered in geologic repositories on land or deep under the sea) targets CO2 directly.
A paper from the Department of Energy’s (DOE’s) National Energy Technology Laboratory lays out the advantages of ultrasupercritical coal plants. “Increasing the temperature and pressure of steam improves the efficiency of boilers and turbines that use steam as a working fluid. These higher efficiency boilers and turbines require less coal and produce less greenhouse gases.” Ultrasupercritical boilers produce steam in the 1,200F to 1,400F range, compared to about 1,100F in supercritical plants.
The National Coal Council, a DOE advisory group, says, “As steam pressure and temperature are increased above 3,208 psi and 706F, the steam becomes supercritical; the water and steam form a single-phase mixture,” producing significantly increased efficiency. A typical subcritical coal-fired steam electric plant in the U.S. operates at about 32% efficiency, according to the coal council.
Two years ago, the Power Technology website reported, “General Electric (GE) is pioneering ultrasupercritical technology at the RDK 8 coal-fired power plant in Karlsruhe, Germany, with considerable success. Operated by German utility EnBW, the plant achieves 47.5% net thermal efficiency while producing 912 MW of electricity, making it one of the world’s most efficient hard coal-fired steam power plants.”
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